Clinical Immunology_ Principles and Practice ( PDFDrive )

64









Immunology of Psoriasis



Cristina Albanesi





CLINICAL AND HISTOLOGICAL FEATURES An association with HLA-B13 was first identified and later with
OF PSORIASIS other class I molecules HLA-B17, HLA-B37, HLA-B57, HLA-Cw6,
and HLA-Cw7, and class II molecules HLA-DR4 and HLA-DR7.
Psoriasis is a common chronic, relapsing immune-mediated Among these, the highest and most consistently reported relative
disease involving skin and small joints of genetically predisposed risk is for HLA-Cw6 haplotype. A significantly higher frequency
individuals. It affects approximately 2% of the general population, of HLA-Cw6 is associated with early-onset (type I) psoriasis
with >50% of patients presenting in the first three decades of compared with late-onset psoriasis (type II). Current data suggest
life. There is a wide spectrum of cutaneous manifestations of that HLA-Cw6 is the susceptibility allele within PSORS1, but
psoriasis. Individual lesions vary from pinpoint to large plaques, no disease-specific mutations have been identified, and variants
or even generalized erythroderma. More specifically, the clinical in regulatory sequences potentially affecting several downstream
spectrum of psoriasis includes the plaque, guttate, small plaque, genes cannot be ruled out. HLA-C might be involved in immune
1
inverse, erythrodermic, and pustular variants. The most common responses at the levels of both antigen presentation and natural
and well-recognized morphological presentation of psoriasis is killer (NK)–cell regulation. Recently, compelling evidence has
that of the plaque type (Fig. 64.1). The disease is characterized emerged for an interaction between the HLA-C and ERAP1
by the formation of demarked erythematous plaques with large (involved in major histocompatibility complex (MHC) class I
3
scaling. The scales are a result of a hyperproliferative epidermis peptide processing) loci in psoriasis. 36763ERAP1 variants only
with premature maturation of keratinocytes and incomplete influenced psoriasis susceptibility in individuals carrying the
cornification, with retention of nuclei in the stratum corneum HLA-C risk allele.
(parakeratosis). The mitotic rate of the basal keratinocytes is Other predisposing polygenes were found in the PSORS2
increased compared with that of normal skin. As a result, the region, on chromosome 17q25. Two distinct regions harboring
epidermis is thickened (acanthosis), with elongated rete ridges susceptibility loci have been identified: the first contains the genes
4
that form finger-like protrusions into the dermis. The granular SLC9A3R1 and NAT9 and the second the gene RAPTOR. The
layer of the epidermis (the starting site of terminal keratinocyte SLC9A3R1 gene encodes a PDZ domain-containing phospho-
differentiation) is strongly reduced or missing. The epidermis protein, implicated in several biological processes occurring in T
is infiltrated by neutrophils and activated CD8 T lymphocytes, cells. NAT9 encodes an N-acetyltransferase involved in MHC class
whereas within the dermis there is an inflammatory infiltrate I antigen-presentation and in immunological processes related
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composed mainly of CD3 T cells, dendritic cells (DCs), macro- to autoimmune diseases. Additionally, between SLC9A3R1 and
phages, mast cells, and neutrophils. Elongated and dilated blood NAT9 is a polymorphism for the binding site of a transcription
4
vessels in the dermal papillae represent a further histological factor RUNX1 that may affect regulation of the immune synapse.
hallmark of psoriatic skin lesions (Fig. 64.2). 1 Associations with alleles of interleukin (IL)-12, IL-23 receptor
(IL-23R), IL-19/20, and IRF2 have also been described. Interest-
ingly, IL-12 and IL-23R single nucleotide polymorphisms do
IMMUNE-RELATED GENETIC FACTORS not have interactions with HLA-Cw6. Recently, polymorphisms
4
PREDISPOSING TO PSORIASIS have been found in two genes, IL-36RN and CARD14, and to be
4,5
independently associated with psoriasis. For CARD14 (caspase
The genetic basis of psoriasis has long been recognized, since recruitment domain-containing protein 14) gene, many missense
family members of patients with psoriasis are at greater risk of mutations, leading to elevation of CARD14 mRNA in patients,
developing the disease. The concordance rate of psoriasis is were initially found in pediatric patients with a severe clinical
approximately 70% in monozygotic twins and 20% in dizygotic presentation of psoriasis. CARD14 gene mutation protein, in
2
twins, depending on the study and population. The mode of association with an inflammatory stimulus, may induce aberrant
inheritance is complex. It is thought that there is no single disease activation of nuclear factor (NF)-κb, a transcription factor that
gene, but, rather, a complex set of gene variants, resulting in an controls the expression of many genes, including key chemokines
aberrant response to environmental factors. At least nine chro- upregulated in psoriasis, such as chemokine (C-X-C motif) ligand
mosomal loci with statistically significant linkage to psoriasis (CXCL)8 and CC chemokine ligand (CCL)20. Mutations in
have been identified, termed psoriasis susceptibility loci 1 through IL-36RN gene were described in patients with severe pustular
2
9 (PSORS1 through PSORS9). PSORS1 is the major genetic psoriasis. This gene encodes the antiinflammatory protein IL-36Ra,
determinant of psoriasis and is located within the human leu- antagonist of IL-36γ, a cytokine highly produced in psoriatic
kocyte antigen (HLA) complex on chromosome 6p (Chapter 5). lesions and with important proinflammatory function.

871

872 Part SEVEN Organ-Specific Inflammatory Disease











































FIG 64.1 Clinical Features of Plaque Psoriasis. Scaly, erythematous, sharply demarcated plaques
in different sizes and shapes are hallmarks of psoriasis.


KEY CONCEPtS and the cell types involved in the onset of the disease are still
under debate. Psoriasis is classically responsive to trigger factors
Psoriasis is a common chronic-relapsing immune-mediated skin disease that can induce psoriasis de novo or exacerbate skin lesions.
6
affecting approximately 2% of the general population. Trigger factors range from nonspecific stimuli, such as skin
There is strong evidence that psoriasis is determined by genetic predisposi- trauma (termed the Koebner effect) to more specific triggers,
tion. A complex set of gene variants, rather than a single gene, are
responsible for an aberrant response to environmental factors. such as pathogens (i.e., streptococci) or drugs (i.e., lithium,
Psoriasis is a disease caused by the infiltration of effector immune cells interferon (IFN)-α). All of these factors generate a pathogenic
in both the epidermis and dermis, which determines hyperproliferation cascade culminating in the expansion of lesional and/or circulating
of the epidermis with premature maturation of keratinocytes and T cells in the psoriatic skin (Fig. 64.3). Much effort has been
incomplete cornification. As a result, the epidermis is thickened, with devoted to understanding the link between the trigger stimuli
elongated rete ridges forming protrusions into the dermis.
Primary effector cells are dermal dendritic cells (DCs), in particular and the pathogenic T-cell cascade that leads to psoriasis. Recent
plasmacytoid DCs (pDCs), whose activation can depend on DNA-LL-37 evidence suggests that type-1 IFN may represent the missing link.
or RNA-LL-37 complexes released by injured keratinocytes and leads The prototypical type I IFN, IFN-α, is abundantly produced
to a massive production of interferon (IFN)-α. by plasmacytoid dendritic cells (pDCs) during the early phase
pDC-released IFN-α or RNA-LL-37 complexes released by keratinocytes of psoriasis development (see Fig. 64.3A). In turn, IFN-α
6,7
activate myeloid DCs (mDCs), which in turn induces type-1 and -17 indirectly stimulates the pathogenic T-cell cascade by promoting
T-cell responses. T-helper 22 response is also pathogenetically induced.
Pathological cytokines include T-cell-derived lymphokines, such as IFN-γ, the activation and maturation of myeloid DCs (mDCs) or by
tumor necrosis factor (TNF)-α, IL-17, IL-22, IL-21, and antigen-presenting direct stimulation of IFN-α–sensitive pathogenic T cells (see
cell–derived cytokines, such as IL-12 and IL-23. Fig. 64.3B). The T-cell infiltrate present in active psoriatic skin
Intrinsic alterations of keratinocytes in the activation of signal transduction establishes a cytokine milieu that dictates specific and pathogenic
pathways (i.e., STAT3, IKK-2, AP-1, etc.) are fundamental for the gene signatures in resident skin cells. Thus cytokine-activated
amplification of psoriatic processes.
keratinocytes overexpress a number of inflammatory media-
tors that aberrantly amplify and sustain the psoriasiform tissue
EFFECTOR CELLS AND IMMUNE MECHANISMS reactions (see Fig. 64.3C). Intrinsic defects and/or alterations
OPERATING IN PSORIASIS of keratinocytes in their immune response to proinflamma-
tory cytokines are fundamental to the induction of psoriatic
Even though successful treatment regimens for the therapy of pso- processes, as demonstrated in genetically manipulated mouse
riasis are long established, the primary pathogenetic mechanism systems.

CHaPtEr 64 Immunology of Psoriasis 873


FIG 64.2 Histological Components of a
Mature Psoriatic Plaque. Psoriatic skin lesions
are characterized by a hyperproliferative epi-
dermis showing an increased mitotic rate of
the basal keratinocytes (A, Ki67 immuno-
staining). As a consequence, the epidermis is
thickened, with elongated rete ridges that form
typical finger-like protrusions into the dermis.
The epidermis becomes infiltrated by activated
CD8 T lymphocytes and neutrophils (B and C,
immunostaining for CD8 and CD15, respec-
tively). Within the drmis, an inflammatory
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infiltrate mainly composed of CD3 T cells (D),
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CD11c dendritic cells (E), BDCA-2 plasma-
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cytoid dendritic cells (F), c-kit mast cells (G), A B
and neutrophils (C) is observed. Elongated and
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dilated ICAM-1 (H) blood vessels in the dermis
represent another histological hallmark of
psoriatic skin.











C D



















E F



















G H

874 Part SEVEN Organ-Specific Inflammatory Disease






NF-NB NF-NB
AP1 AP1
STAT1 STAT1
STAT3 STAT3
p38
Trigger factors: p38 Erk 1/2
Pathogens Erk 1/2
Drugs
Stress
PMN
PMN PMN PMN PMN
autoantigens PMN PMN
K17, K13 LL-37 LL-37 growth signals
LL-37/ ?viral antigens? TGF-α, KGF
IL-19, IL-20
DNA
VEGF CD8 amphiregulin
DNA-LL-37 Tc1
DNA-LL-37 Endothelium TNF-α CD8 HLA-DR IL-1
RNA-LL-37 TNF-α Tc1
IFN-α KGF, FGF10
pDC CX3CL1, CCL17 GM-CSF
pDC ICAM-1, VCAM, Th1 INF-γ ICAM-1 IL-36
E-selectin
RNA-LL-37 Th17 Th1 Th22 Tc1 cytokines
RNA-LL-37 Th1 chemokines
pDC mDC Th17 Th17 Th2 CXCL10-9-11, TGF-α, GM-CSF,
Chemerin IFN-α TNF-α, IFN-γ, IL-1, IL-6,
IFN-α IL-17, IL-22 CCL2, CXCL8, IL-19, IL-20, IL-36
CCL20
Fibroblasts TIP-DC CCL5, CCL19
Endothelial cells Th1 Th17
Th17 Th2
PMN Th22
Chemerin Mast cell mDC Th1 Th2
Th17 Fibroblasts
Chemerin Th1 Mast cell Th1
Fibroblasts PMN PMN Th17 Endothelium
NK PMN
Fibroblasts
SlanDC ICAM-1, VCAM,
A B C SlanDC E-selectin
FIG 64.3 Scheme of Pathogenic Mechanisms Operating in Psoriasis. The psoriatic lesion starts to evolve after keratinocytes are
injured, for instance by physical trauma or bacterial products. Thereafter, a cascade of events including the formation of complexes
formed by keratinocyte-derived DNA and the cathelicidin LL-37 leads to the activation of plasmacytoid dendritic cells (pDCs), which
routinely patrol psoriatic skin (A). Other pDCs are recruited in the early phase psoriasis development by the chemokine chemerin,
derived primarily from dermal fibroblasts and, to a lesser extent, from mast cells and endothelial cells, and induced to release high
amounts of IFN-α. IFN-α locally activates keratinocytes and participates in the activation processes affecting myeloid DCs. In turn,
DCs migrate into draining lymph nodes and induce the differentiation of naïve T cells into effector cells, such as type 17 T-helper
(Th) 17 or type 17 T cytotoxic (Tc) cells and type 1 Th1 or Tc1 cells. Effector cells recirculate and proliferate into psoriatic skin and
produce massive amounts of proinflammatory cytokines, such as interferon (IFN)-γ and tumor necrosis factor (TNF)-α (B). The latter
cytokine is also abundantly released by dermal DCs, mainly represented by TNF-α and inducible nitric oxide synthase-producing-DCs
(TIP-DC). SlanDCs also reinforce immunity in psoriasis by interacting with and potentiating the activity of both neutrophils and natural
killer (NK) cells, as well as inducing Th1 and Th17 responses. IFN-γ and TNF-α are responsible for the activation of resident skin
cells, in particular keratinocytes, which respond to cytokines with a stereotypical set of genomic responses leading to synthesis of
inflammatory mediators (C). Keratinocytes are also targets of T cell–derived IL-22, which induces proliferation and de-differentiation
of psoriatic keratinocytes in a signal transducer and activator of transcription 3 (STAT3)-dependent manner. Keratinocyte-derived
chemokines, cytokines, and membrane molecules have a major role in maintaining the recruitment of leukocytes into inflammatory
sites. Because of their intrinsic defects, psoriatic keratinocytes aberrantly respond to cytokines and show altered intracellular signaling
pathways, including STAT3 cascade (C). The uncontrolled hyperproliferation and differentiation observed in psoriatic skin could also
derive from dysregulated production of tissue growth factors and regulators, such as transforming growth factor (TGF)-α, keratinocyte
growth factor (KGF), amphiregulin, granulocyte macrophage–colony-stimulating factor (GM-CSF), fibroblast growth factor-10 (FGF-10),
interleukin (IL)-19, IL-20, IL-36 produced by keratinocytes and fibroblasts. Psoriatic keratinocytes produce autoantigens (i.e., keratin
(K)17, K13, nucleic acid/LL-37 complexes) capable of inducing clonal T-cell responses. Finally, the inflammatory cytokine milieu also
influences the immune functions of fibroblasts and endothelium, with the latter being critical for leukocyte trafficking and extravasation.

CHaPtEr 64 Immunology of Psoriasis 875


Plasmacytoid DCs as Inducers of Primary Immune suggests a fundamental role for LL-37 in alerting resident skin
Responses in Psoriasis pDCs of tissue damage associated with cell death and the release
pDCs are characterized by a plasma cell morphology and a of self-DNA. pDCs are typically absent in unperturbed skin and
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distinctive surface phenotype (CD4 , CD45RA , CD123 , peripheral tissues under homeostatic conditions but can enter
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BDCA-2 , BDCA-4 , CD62L , cutaneous lymphocyte-associated secondary lymphoid organs through the expression of CD62L
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antigen (CLA) , and CD11c ). They are considered as key effector and chemokine receptors (CXCR4, CXCR3, CCR5, and ChemR23).
cells in antiviral defense because of their ability to produce large pDCs can also infiltrate inflamed tissue of immune-mediated
8
amounts of type I IFN. Upon viral stimulation, pDCs differentiate skin diseases, and, in particular, accumulate in the skin of patients
9,10
into a unique type of mature DC and induce an IFN-α–dependent with psoriasis early during disease development. Many studies
activation of bystander mDCs with the ability to induce Th1- have shown an evident IFN-α signature (e.g., increased expression
responses (Chapter 16), thus providing a necessary link between of IRF7 and the presence of MxA, markers for IFN-α activity)
8
innate and adaptive immunity. Several studies have demonstrated in primary psoriatic plaques in the absence of detectable levels
that pDCs infiltrate psoriatic skin, and that pDC-derived IFN-α of the IFN-α cytokine. Indeed, IFN-α expression was detected
initiates the expansion of autoimmune T cells, leading eventually early and transiently during the development of the psoriatic
to the skin lesions of psoriasis. 6,7,9,10 Blocking of type I IFN signal- phenotype, and its effect persisted until lesions became chronic.
+
ing with neutralizing antibodies to IFN-α/β receptors inhibited Paralleling IFN-α expression, BDCA-2 pDCs were detected only
10
the development of psoriasis in symptomless pre-psoriatic skin during the early developmental stages of psoriasis. In fact, pDC
10
engrafted onto immunodeficient AGR129 mice. Moreover, infiltration in psoriatic skin correlates with the expression of
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inhibition of IFN-α release by pDCs through anti–BDCA-2 markers typical of early phases of psoriasis (CD15 neutrophils
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antibody prevented the activation and expansion of pathogenetic and c-kit mast cells localized in the mid- and papillary dermis,
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T cells and the development of a psoriatic phenotype. The detailed and few CD8 T lymphocytes or ICAM-1 keratinocytes), whereas
9
mechanisms responsible for the IFN-α-induced expansion of T they are almost absent in long-lasting lesions. Importantly,
cells in psoriasis are currently unknown, but it appears that pDC recruitment in psoriatic skin is strictly associated with the
IFN-α favors cross-presentation of sequestered tissue-specific expression of the chemokine chemerin, which is temporally
autoantigens by mDCs. pDC-derived IFN-α may also enhance produced by dermal fibroblasts and active during psoriatic plaque
9
the survival of autoreactive T cells through the induction of development. pDC migration toward fibroblast-derived chemerin
IL-15 or by promoting a Th1 cell bias through the induction of is completely dependent on the expression of ChemR23 receptor
T-bet and IL-12Rβ 2 expression. The pathogenetic role of IFN-α on pDC. Compared with other chemokines potentially active
is also suggested by the observations that its signaling signature on pDC (CXCL10 and CXCL12), chemerin is the main, if not
11
is present in resident skin cells of psoriatic plaques and that the only, protein responsible for the pDC chemotactic activity
psoriasis is exacerbated if patients with psoriasis are treated with released by fibroblasts in psoriatic skin. 9
recombinant IFN-α for unrelated conditions (i.e., viral infections
or tumors), or with imiquimod, a Toll-like receptor (TLR) agonist DC Driving of T-Cell Responses in Psoriatic Skin
12
that induces production of IFN-α by pDCs. In addition, excessive Although pDCs are responsible for triggering psoriasis, mDCs
activation of type I IFN signaling in mice deficient for IFN are the main amplifiers of local inflammation. Dermal mDCs are
regulatory factor (IRF)-2, a transcriptional repressor of IFN dramatically increased in psoriasis, and targeted immunotherapy
signaling, causes an inflammatory skin disease resembling reduces their quantity in patients with psoriasis, supporting the
15
psoriasis. Recently, a genome-wide analysis conducted on paired concept that mDCs have a key pathogenetic role. Dermal mDCs
lesional and nonlesional psoriatic skin and on the skin of healthy are found at the dermal–epidermal junction as well as throughout
donors revealed a significant overexpression of many components the whole dermis. mDCs are able to capture extracellular antigens
of the IFN-α pathway in patients with psoriasis, including the for presentation to T cells and also intracellular antigens from
receptor subunits for type I IFN, IFN-AR1, and IFN-AR2, the adjacent cell types via cross-presentation (Chapter 6). In addi-
transcriptional activators of IFN-α-inducible genes, signal tion, mDCs within psoriatic lesions are intrinsically stronger
transducer and activator of transcription (STAT) 1, IRF1, and stimulators of T-cell proliferation compared with DCs derived
11
IRF7. All of these molecules are master regulators of IFN-α- from peripheral blood or from the skin of healthy patients. mDCs
mediated immune responses. uniformly express CD11c, and they can be further subdivided on
The molecular mechanisms leading pDCs to produce type I the basis of expression of CD1c (BDCA-1). Steady-state skin has
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IFN involve the activation of TLR7 and TLR9, intracellular a predominance of CD11c CD1c resident DCs, whereas CD11c
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15
receptors that recognize viral/microbial nucleic acids within CD1c mDCs predominate in psoriatic inflammation. A small
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endosomal compartments. pDCs do not normally respond to fraction of CD11c CD1c DC bears “maturation” markers, such
self-DNA, but this restriction breaks down in some human as DC-LAMP, CD83, and endocytic receptor DEC-205/CD205,
autoimmune diseases. In psoriatic skin, pDCs can be activated suggesting that they could function as conventional DCs and
15
to produce massive amounts of type I IFN in response to extracel- present antigens to T cells to trigger acquired immune responses.
13
lular self-DNA fragments. However, this process requires the These rare, phenotypically mature cells, often aggregating in
coupling of self-DNA to the endogenous antimicrobial peptide dermal clusters, could be required for rapid antigen presentation
LL-37, known to be overexpressed in psoriatic skin. LL-37 breaks to local T cells or for ongoing “micro-” immune responses. During
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innate tolerance to self-DNA by forming aggregated and con- psoriasis development, dermal CD11c DC mature and acquire a
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densed structures that can trigger a robust IFN-α induction via CD1c HLA-DR CD45 CD14 DC-specific ICAM-3–grabbing
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13
15
TLR9 activation. LL-37 can also form complexes with RNA nonintegrin (DC-SIGN) phenotype. These inflammatory mDCs
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and activate pDCs through TLR7. In parallel, LL-37/RNA can are CCR7 and respond to the chemokine CCL19, suggesting
alert myeloid DCs through their TLR8, driving T-cell activation that they may migrate to draining lymph nodes for antigen
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14
and production of cytokines found in psoriasis. This finding presentation. CD11c CD1c inflammatory DC express very

876 Part SEVEN Organ-Specific Inflammatory Disease


high levels of tumor necrosis factor (TNF)-α and the enzyme of T cells shows that these are mainly activated memory T cells
inducible nitric oxide synthase (iNOS) and can be considered expressing HLA-DR, CD25, CD27, and cutaneous lymphocyte
the human equivalent of TIP-DC (TNF-α and iNOS-producing antigen (CLA). Although there is differential T-cell receptor usage
DCs), which have been shown in mice to have effector functions in T cells from psoriatic skin, the causative antigens responsible
15
in clearing some bacterial infections. The proinflammatory for T-cell activation in psoriasis remain unknown. Exposure of
nature of TNF-α in psoriasis and other inflammatory diseases altered autoantigens from keratinocytes could be responsible
is well established, and the receptors TNFR1 and TNFRII are for the activation and expansion of distinct T-cell subpopulations
expressed on a wide range of cells in psoriatic skin, including in psoriatic skin. These autoantigens may include keratin 17
keratinocytes and endothelial cells. TNF-α induces expression of (patients with active psoriasis have an increased frequency of
ICAM-1 on keratinocytes, facilitating the adhesion of circulating circulating Th1 cells reacting to peptides from keratin 17) and
leukocytes. Moreover, TNF-α can stimulate keratinocytes and corneodesmosin, an attractive candidate for psoriasis susceptibility
dermal fibroblasts to produce the potent neutrophil chemoat- based on its putative biological function in keratinocyte adhe-
19
tractant CXCL8, as well as the proinflammatory cytokines IL-6 sion. Keratinocytes could also be responsible for the activation
and IL-1, which help generate and maintain Th17 cells (Chapters of pathogenetic T cells by viral or bacterial products. For example,
10 and 16). The role of TNF-α in psoriasis is underlined by the human papillomavirus 5 (HPV-5) DNA and antibodies to HPV-5
15
therapeutic success of anti–TNF-α therapies in psoriasis. In virus-like particles have been found in psoriasis. Streptococcal
addition, polymorphisms of the TNF-α promoter region have infections are also frequently associated with psoriasis, and
been associated with psoriasis. However, iNOS production by streptococcal superantigens could be presented to T cells by
inflammatory DCs leads to nitric oxide (NO) release, inducing binding to MHC class II molecules expressed by lesional kera-
vasodilation, inflammation, and antimicrobial effects in psori- tinocytes. Putative psoriatic antigens are assumed to be kerati-
atic skin. Interestingly, NO inhibitors (e.g., statins) can have a nocyte proteins that might share structural homology with
beneficial effect on psoriasis, although this has not been studied streptococcal proteins and might thereby induce cross-reactive
20
in a randomized prospective manner. Inflammatory DCs also T-cell responses against skin components. Recently, it has been
produce other cytokines (Chapter 9) (e.g., IL-23 and -12), which found that two-thirds of patients with moderate-to-severe plaque
21
are linked to psoriasis. IL-12 mainly induces IFN-γ production, psoriasis harbor CD4 and/or CD8 T cells specific for LL-37.
whereas IL-23 also stimulates IL-17 and IL-22 release by T cells, LL37-specific T cells produce IFN-γ, and CD4 T cells also produce
16
as shown in mice. Other evidence for a role of IL-23 in psoriasis Th17 cytokines. LL37-specific T cells can infiltrate lesional skin
includes the clinical efficacy of an anti-p40 monoclonal antibody and can be tracked in patients’ blood. The presence of circulating
(mAb) against psoriasis and the association of a single nucleotide LL37-specific T cells correlates significantly with disease activity,
polymorphism in the IL-23R gene in psoriasis patients. mDCs of suggesting a contribution to disease pathogenesis.
psoriatic lesions also release the proinflammatory cytokine IL-15, T-cell migration from the dermis into the epidermis is a key
which induces T-cell proliferation and monocyte activation, as well event in psoriasis. It is controlled by the interaction of α 1 β 1
as skin hyperplasia by protecting keratinocytes from apoptosis. integrin (very late antigen 1) on T cells with collagen IV in the
Another population of inflammatory mDCs, defined by the basement membrane of the epidermis. Blockade of this interaction
selective expression of the 6-sulfo LacNAc residue on the P-selectin inhibits the development of psoriasis in clinically relevant models.
glycoprotein ligand 1 membrane molecule, has been identified Based on the analysis of infiltrating cell types, their secreted
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17
in psoriatic skin. 6-Sulfo LacNAc DCs (slanDCs) have a well- products, and genetic signatures present in lesional skin, psoriasis
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defined phenotype (CD1c , CD11c , CD16 , CD14 ) that clearly has been considered for many years as a type-1 (i.e., Th1)–medi-
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distinguishes them from classic CD1c blood DC (CD1c , CD11c ) ated reaction, with IFN-γ playing a prominent role. Consistent
or pDC (BDCA-2, BDCA-4). SlanDCs produce more TNF-α, with a Th1 pattern of response, CCR10 is preferentially expressed
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IL-23, IL-12, IL-1β, and IL-6 and can thus induce Th1/Th17 by skin homing CLA memory T cells, which secrete TNF-α and
cells. SlanDCs also reinforce innate immunity in psoriasis by IFN-γ, but minimal amounts of IL-10 and IL-4, upon activation.
interacting with and potentiating the activity of neutrophils and However, other cytokines and T-cell subsets have also been
NK cells. 17 identified during inflammatory responses in psoriasis. These
The function of another DC subset, the Langerhans cell, is include Th17 and Th22 cells, which produce large amounts of
still controversial. Langerhans cells are only found in the epidermal IL-17 and IL-22, cytokines that have relevant effects on epithelial
23
compartment where they are similar in number and phenotype cells. Keratinocytes are strongly influenced by IL-17 and
in lesional and nonlesional skin, but they fail to migrate in upregulate chemokines and immunomodulatory molecules in
18
24
response to proinflammatory stimuli (Chapter 19). These response to this cytokine. A functional role of Th17 cells, and
findings and data from Langerhans cell ablation models suggest also Tc17 cells, in psoriasis is suggested by their reduction during
that Langerhans cells may help sustain immune tolerance in successful anti–TNF-α treatment or via blockade with neutralizing
25
psoriasis. In psoriatic skin, the epidermis contains an additional mAb in a clinically relevant xenotransplantation mouse model.
DC subset, known as inflammatory dendritic epidermal cells and IL-22 also acts pathogenetically in psoriatic skin by inducing
are distinguishable from Langerhans cells by the expression of proliferation and de-differentiation of keratinocytes, as well as
the macrophage mannose receptor CD206. promoting their production of antimicrobial peptides and
26
chemokines, including CXCL8 and CXCL1. Binding of IL-22
Activation of T Lymphocytes and Establishment of the to its receptor, whose expression in the skin is confined to
Cytokine Milieu Influencing Keratinocyte Proliferation keratinocytes, mediates epidermal acanthosis through the activa-
tion of STAT3. These observations may explain the increased
and Immune Functions STAT3 expression in the epidermal compartment and the
Psoriasis lesional skin shows many inflammatory T cells in both pathogenicity of STAT3 overexpression in the epidermis of
27
the papillary dermis and the epidermis. Immunophenotyping transgenic mice (see below). The demonstration that T cells

CHaPtEr 64 Immunology of Psoriasis 877


are the primary regulators of keratinocyte proliferation and response in the pathogenesis of psoriasis. Within psoriatic lesions,
differentiation in psoriasis came from studies showing that alterations are observed in the levels of expression of several
supernatants from lesional skin-derived T cells transformed growth factors, such as insulin-like growth factor, keratinocyte
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β-integrin keratin 1/keratin 10 PCNA stem cells of patients growth factor (KGF), transforming growth factor (TGF)-α, and
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with psoriasis, but not stem cells of healthy subjects, into PCNA amphiregulin, all of which stimulate basal cell proliferation in
22
active cycling cells. T cell–derived supernatants contained high an autocrine fashion. Other cytokines aberrantly elevated in
levels of granulocyte macrophage–colony-stimulating factor psoriasis include members of the inhibitory TGF-β family, and
28
(GM-CSF) and IFN-γ, and low levels of IL-3 and TNF-α. cytokines that stimulate keratinocyte proliferation and inflam-
However, among these cytokines, only IFN-γ affects the prolifera- mation, such as IL-19 and IL-20. 22,24 An important pathogenic
tion of psoriatic stem cells. In vivo, IFN-γ injection into prelesional role has also been uncovered for IL-36γ, a cytokine abundantly
psoriatic skin triggers keratinocyte proliferation and plaque induced by IL-17 in keratinocytes, whose overexpression in mouse
development. Considering that IFN-γ is an antiproliferative skin leads to a disease quite similar to human plaque psoriasis,
cytokine and an inducer of squamous differentiation, these latter whereas inhibition in human psoriatic skin ameliorates the
findings are paradoxical. This discrepancy may reflect an intrinsic inflammation. 29
defect in the response of psoriatic keratinocytes to IFN-γ, and/ Finally, two anti-inflammatory molecules, suppressors of
or altered localization and expression of the IFN-γ receptor cytokine signaling (SOCS)1 and SOCS3, are dysregulated in
30
complex in the epidermis of psoriatic skin. psoriatic keratinocytes. These efficiently suppress the IFN-γ– and
Another T cell–derived cytokine that has been shown to TNF-α–dependent molecular cascades in keratinocytes, and it
regulate keratinocyte proliferation in psoriatic skin is IL-21, which has been hypothesized that strengthening of the action of SOCS1
is mainly released by CD4 T cells and natural killer T cells (NKT in keratinocytes could be a valid therapeutic approach for treat-
cells). IL-21 contributes to epidermal hyperplasia, and neutraliza- ment of IFN-γ- and TNF-α-dependent skin diseases, including
tion of IL-21 reduces both skin thickening and expression of psoriasis.
inflammatory molecules. Interestingly, IFN-γ is necessary for
IL-21–induced epidermal hyperplasia, while abrogation of IL-21 ON tHE HOrIZON
signals reduces IFN-γ expression in psoriatic T cells. 22,24
Finally, the importance of T regulatory (Treg) lymphocytes There have been significant advances in therapies for psoriasis during
the past 15 years that strongly reduce both symptoms and relapse
(Chapter 18) in psoriasis has been examined in the peripheral rates. New therapeutic approaches include the targeting of interleukin
blood and the inflamed skin of patients. The number of Treg (IL)-17A.
cells (defined by expression of the transcription factor FOXP3) Personalized therapies based on the employment of antagonists aligned
is increased in the peripheral blood of individuals with psoriasis, with elements of genetic risk of the patients will be likely more
and this increase is positively correlated with the disease activity successful.
+
+
+
index. CD4 CD25 FOXP3 Treg cells are also present in psoriatic Newer strategies will also need to focus on treatments that do not
require continuous, long-term immune suppression (i.e., strategies to
lesions, with more in lesional skin biopsy specimens than those restore immune regulation or tolerance).
from control or uninvolved skin. However, these Treg cells may Future work to identify and clarify risk factors and antigenic triggers for
be less functional in that Treg cells from both the peripheral psoriasis may lead to strategies for preventing the disease.
blood and psoriatic skin lesions showed reduced ability to suppress
effector T cells. This impairment may be dependent on IL-6 as CONCLUSIONS
blockade of IL-6 reversed the impairment in suppression observed
in cocultures of Treg cells and effector T cells from patients with A complex interplay between environmental and genetic factors
psoriasis. triggers a cascade of events that leads to the expression of psoriasis.
Early upstream events occurring in the disease include activation
Intrinsic Defects of Keratinocytes Are Fundamental for of DCs and the generation of effector T cells that migrate into
the psoriatic skin lesions and expand there. Cross-talk between
the Amplification of Psoriatic Processes keratinocytes and immune cells amplifies inflammation and is
Endogenous defects in keratinocytes may be pathogenically responsible for chronicity. Recent research has implicated many
relevant for psoriasis, as shown in mice with engineered epidermal immunological mechanisms in psoriasis progression, and this
phenotypes. Transgenic animals that overexpress the transcription has led to the development of new, pathogenesis-based therapies.
factor STAT3 or that lack the inhibitor of NF-κB kinase-2 (IKK-2) Although this progress is remarkable, much remains unknown,
in their epidermis develop skin lesions that closely resemble especially regarding prevention of the condition and how to
27
human psoriasis. Similarly, the abrogation of JunB in kerati- develop drugs with appropriate risk-benefit and long-term
nocytes triggers a skin phenotype with the histological features profiles. Future work must take into account these aspects to
of psoriasis, including marked hyperplasia of the epidermis and establish therapeutic and preventive approaches that lead to
dense dermal inflammatory cell infiltrates. The hyperplasia improved patient outcomes.
observed in these models may, in part, depend on overexpression
of S100A8 and S100A9, two antimicrobial peptides with che- Please check your eBook at https://expertconsult.inkling.com/
motactic activity and a recognized role in keratinocyte maturation for self-assessment questions. See inside cover for registration
and proliferation. The development of psoriatic lesions in mice details.
with an epidermal deletion of STAT3 depends on the presence
of activated T cells, whereas the inflammatory responses occurring REFERENCES
in the skin of IKK2-transgenic mice are mediated by TNF-α.
This implicates an intrinsically dysregulated interrelation between 1. Griffiths CE, Barker JN. Pathogenesis and clinical features of psoriasis.
keratinocytes and cells of both the innate and acquired immune Lancet 2007;370:263–71.

878 Part SEVEN Organ-Specific Inflammatory Disease


2. Bowcock AM. The genetics of psoriasis and autoimmunity. Annu Rev 18. Cumberbatch M, Singh M, Dearman RJ, et al. Impaired Langerhans cell
Genomics Hum Genet 2005;6:93–122. migration in psoriasis. J Exp Med 2006;203:953–60.
3. Strange A, Capon F, Spencer CC, et al. A genome-wide association study 19. Gudmundsdottir AS, Sigmundsdottir H, Sigurgeirsson B, et al. Is an
identifies new psoriasis susceptibility loci and an interaction between epitope on keratin 17 a major target for autoreactive T lymphocytes in
HLA-C and ERAP1. Nat Genet 2011;42:985–90. psoriasis? Clin Exp Immunol 1999;117:580–6.
4. Tian S, Krueger JG, Li K, et al. Meta-analysis derived (MAD) 20. Prinz JC. Psoriasis vulgaris—a sterile antibacterial skin reaction mediated
transcriptome of psoriasis defines the “core” pathogenesis of disease. by cross-reactive T cells? An immunological view of the pathophysiology
PLoS ONE 2012;7:e44274. of psoriasis. Clin Exp Dermatol 2001;26:326–32.
5. Onoufriadis A, Simpson MA, Pink AE, et al. Mutations in IL36RN/IL1F5 21. Lande R, Botti E, Jandus C, et al. The antimicrobial peptide LL37 is a
are associated with the severe episodic inflammatory skin disease known T-cell autoantigen in psoriasis. Nat Commun 2014;5:5621–36.
as generalized pustular psoriasis. Am J Hum Genet 2011;89:432–7. 22. Albanesi C, Pastore S. Pathobiology of chronic inflammatory skin
6. Nestle FO, Kaplan DH, Barker J. Psoriasis. N Engl J Med 2009;361: diseases: interplay between keratinocytes and immune cells as a target for
496–509. anti-inflammatory drugs. Curr Drug Metab 2010;11:210–27.
7. Albanesi C, Scarponi C, Bosisio D, et al. Immune functions and 23. Eyerich S, Eyerich K, Pennino D, et al. Th22 cells represent a distinct
recruitment of plasmacytoid dendritic cells in psoriasis. Autoimmunity human T cell subset involved in epidermal immunity and remodeling.
2010;43:215–19. J Clin Invest 2009;119:3573–85.
8. Colonna M, Trinchieri G, Liu YJ. Plasmacytoid dendritic cells in 24. Albanesi C, De Pita O, Girolomoni G. Resident skin cells in psoriasis: a
immunity. Nat Immunol 2004;5:1219–26. special look at the pathogenetic functions of keratinocytes. Clin Dermatol
9. Albanesi C, Scarponi C, Pallotta S, et al. Chemerin expression marks early 2007;25:581–8.
psoriatic skin lesions and correlates with plasmacytoid dendritic cell 25. Di Meglio P, Villanova F, Navarini AA, et al. Targeting CD8(+) T cells
recruitment. J Exp Med 2009;206:249–58. prevents psoriasis development. J Allergy Clin Immunol 2016;138:
10. Nestle FO, Conrad C, Tun-Kyi A, et al. Plasmacytoid predendritic cells 274–6.
initiate psoriasis through interferon-alpha production. J Exp Med 26. Sestito R, Madonna S, Scarponi C, et al. STAT3-dependent effects
2005;202:135–43. of IL-22 in human keratinocytes are counterregulated by sirtuin 1
11. Yao Y, Richman L, Morehouse C, et al. Type I interferon: potential through a direct inhibition of STAT3 acetylation. FASEB J 2011;25:
therapeutic target for psoriasis? PLoS ONE 2008;3:e2737. 916–27.
12. Ketikoglou I, Karatapanis S, Elefsiniotis I, et al. Extensive psoriasis 27. Sano S, Chan KS, Carbajal S, et al. Stat3 links activated keratinocytes and
induced by pegylated interferon alpha-2b treatment for chronic hepatitis immunocytes required for development of psoriasis in a novel transgenic
B. Eur J Dermatol 2005;15:107–9. mouse model. Nat Med 2005;11:43–9.
13. Lande R, Gregorio J, Facchinetti V, et al. Plasmacytoid dendritic cells 28. Bata-Csorgo Z, Hammerberg C, Voorhees JJ, et al. Kinetics and regulation
sense self-DNA coupled with antimicrobial peptide. Nature 2007;449: of human keratinocyte stem cell growth in short-term primary ex vivo
564–9. culture. Cooperative growth factors from psoriatic lesional T lymphocytes
14. Ganguly D, Chamilos G, Lande R, et al. Self-RNA-antimicrobial peptide stimulate proliferation among psoriatic uninvolved, but not normal, stem
complexes activate human dendritic cells through TLR7 e TLR8. J Exp keratinocytes. J Clin Invest 1995;95:317–27.
Med 2009;206:1983–94. 29. Gabay C, Towne JE. Regulation and function of interleukin-36 cytokines
15. Nestle FO, Di Meglio P, Qin JZ, et al. Skin immune sentinels in health in homeostasis and pathological conditions. J Leukoc Biol 2015;97:
and disease. Nat Rev Immunol 2009;9:679–91. 645–52.
16. Zheng Y, Danilenko DM, Valdez P, et al. Interleukin-22, a T(H)17 30. Madonna S, Scarponi C, Sestito R, et al. The IFN-gamma-dependent
cytokine, mediates IL-23-induced dermal inflammation and acanthosis. suppressor of cytokine signaling 1 promoter activity is positively
Nature 2007;445:648–51. regulated by IFN regulatory factor-1 and Sp1 but repressed by growth
17. Costantini C, Calzetti F, Perbellini O, et al. Human neutrophils interact factor independence-1b and Kruppel-like factor-4, and it is dysregulated
with both 6-sulfo LacNAc+ DC and NK cells to amplify NK-derived in psoriatic keratinocytes. J Immunol 2010;185:2467–81.
IFN-γ : role of CD18, ICAM-1, and ICAM-3. Blood 2011;117:1677–86.

CHaPtEr 64 Immunology of Psoriasis 878.e1


MUL t IPLE-CHOICE QUES t IONS

1. The age of onset of psoriasis is most commonly: 3. Early pathogenic events of psoriasis includes which one of
A. First three decades of life the following:
B. Before age 7 years A. Signal transducer and activator of transcription 3 (STAT3)
C. Middle age activation in hyperproliferating keratinocytes
D. Fifth and sixth decades of life B. Recruitment of myeloid dendritic cells
C. Targeting of keratinocytes by proinflammatory cytokines
2. Development of psoriatic lesions at sites of skin trauma is
known as: D. A cascade of events including formation of complexes
A. Koebner phenomenon formed by keratinocyte-derived nucleic acid and the
B. Nikolsky sign cathelicidin LL-37
C. Auspitz sign
D. Dennie-Morgan lines
E. Triple response of Lewis

65









Myasthenia Gravis



Arnold I. Levinson







Myasthenia gravis (MG) is a disease characterized by weakness but typically the palatal, pharyngeal, and upper esophageal muscles
of striated muscles. The weakness is caused by impaired neuro- are involved. This results in dysarthria, dysphagia, and difficulty
muscular transmission resulting from a reduction in the number handling secretions. Involvement of the diaphragm and intercostal
of receptors for the neurotransmitter acetylcholine (ACh) at the muscles produces dyspnea and may lead to respiratory failure.
postsynaptic myoneural junction. In most cases, this reduction Involvement of the muscles of the extremities and trunk occurs
is the result of the action of anti–acetylcholine receptor (anti- in 20–30% of patients at initial presentation and causes difficulties
AChR) antibodies. The disease occurs with a reported prevalence with activities of daily living. The hallmark of all muscle involve-
of 0.5–5/100 000 and an incidence of 0.4/100 000/year. Although ment in MG is its variability over time, with weakness usually
MG can occur at any age, it typically presents in the second and exacerbated by repetitive use.
third decades of life, with a later peak occurring after age 50 Furthermore, within the group of patients with generalized
years (late-onset disease). A female preponderance (3:1–4:1) has disease, patients are further subdivided into subtypes on the
been reported in the first 40 years of life; thereafter, the incidence basis of age of onset, for example, early-onset MG (EOMG) and
is comparable between the sexes. late-onset MG (LOMG) with onset before and after age 50 years,
respectively. Moreover, patients can be additionally distinguished
CLASSIFICATION by their profiles of serum autoantibodies (see discussion of serum
autoantibodies) and the presence/absence of thymic pathology
Patients with MG have traditionally been divided into two (see discussion of thymic pathology).
categories: those with generalized disease and those presenting
1
with disease limited to the ocular muscles. Within these two CLINICAL PEARLS
groups, patients can be further subdivided on the basis of age Telltale Signs of Myasthenia Gravis
of onset. Neonatal MG affects 10–20% of offspring born to
mothers with myasthenia. Disease manifestations are those of • Variable muscle weakness
generalized MG (see below) but are transient, dissipating with • Weakness in cranial nerve distribution
the metabolism of maternal anti-AChR antibodies that had been • Normal reflexes and sensation
transmitted across the placenta during the third trimester of
pregnancy. Several congenital myasthenic syndromes have been DIAGNOSIS
described. For the most part, these manifest during the neonatal
period, persist into adulthood, and are not considered to have The differential diagnosis is extremely broad, encompassing
2
an autoimmune basis. Juvenile MG is said to occur in those neuropathies, primary and secondary myopathies, muscular
patients who present with disease between 1 year of age and dystrophy, demyelinating disorders, degenerative diseases,
puberty. Apart from the age of onset, juvenile myasthenia behaves cerebrovascular accidents, mass lesions, and infectious diseases.
like adult MG. The clinical features that point to a diagnosis of MG include
Adult patients may present with ocular involvement or signs the variable nature of the muscle weakness, normal sensation,
of more generalized disease. The ocular involvement is character- and normal deep tendon reflexes. The diagnosis can usually be
ized by impaired ocular muscle motility and lid weakness, confirmed by pharmacological and electrophysiological testing.
manifesting as diplopia and ptosis, respectively. The vast majority A decremental pattern is characteristically seen following repetitive
of patients with MG will experience ocular involvement, with nerve stimulation (Fig. 65.1), and this pattern is normalized
roughly 50% of patients presenting with ocular signs at the time following treatment with the anticholinesterase agent tensilon.
of diagnosis. Those generally at risk of disease progression are Further confirmation rests on detecting anti-AChR antibodies,
(i) patients with evidence of subclinical disease on electrophysi- which are found in 85–90% of patients with generalized disease.
ological testing of limb muscles; and (ii) patients who have In the standard assay, sera are reacted with a nicotinic AChR
markedly elevated titers of anti-AChR antibodies. Typically, preparation labeled with 125 I-α-bungarotoxin, a snake venom
patients with ocular symptoms for >2 years will not progress to polypeptide that binds irreversibly to the receptor. Bound antibod-
a more generalized form of disease. ies are immunoprecipitated by an antiimmunoglobulin reagent
In the generalized disease group, patients can be classified or staphylococcal protein A, and the quantity of antibodies
into those with mild, moderate, or severe disease on the basis detected is expressed in terms of the amount of α-bungarotoxin
of clinical activity. Any skeletal muscle group can be affected, bound.

879

880 PARt SEVEN Organ-Specific Inflammatory Disease


Safety factor of Failure at single Reduced
transmission
Amplitude of EPP Minimum current margin
junctions
safety
for conduction




Muscle action potential






1 2 3s 1 2 3s
Normal response Myasthenic response (decremental)
FIG 65.1 Neuromuscular Transmission in Normal and Myasthenic Subjects. With repetitive
stimulation there is a reduction in the efficiency of acetylcholine (ACh) release, with a subsequent
recovery in efficiency as the train of stimuli continues. Although the endplate potential (EPP)
fluctuates at the normal junction, sufficient current is generated to stimulate an action potential
of constant magnitude. At the myasthenic junction, however, the amplitude of the EPP in response
to a given amount of ACh is reduced. Under conditions of inefficient ACh release, for example,
repetitive stimulation, the minimum current for conduction is not generated, resulting in a
profile of action potentials that shows a progressive decline or “decrement” with subsequent
recovery.

NH 2
δ
β α
ε or γ


α
Main
immunogenic
region


10 nm
C192
C193
Unfolded COOH Acetylcholine-
Carbohydrate binding site
Extracellular
M1
Junctional M2
membrane M3
M4
Cytoplasmic

FIG 65.2 The Acetylcholine Receptor. The subunits of the acetylcholine receptor—α, β, δ, and
γ or ε—are arranged like barrel staves around the central ion pore. Each subunit winds through
the junctional membrane four times (sites M1, M2, M3, and M4). In the unfolded view of the α
subunit, the amino-terminal end of the α subunit is extracellular, where it is accessible to ace-
tylcholine, which binds at the site shown (amino acids 192 and 193). In myasthenia gravis,
autoantibodies may bind to various epitopes of all subunits, but a high proportion of autoantibodies
bind to the main immunogenic region of the α subunit.

ACHR STRUCTURE myoneural junction is composed of four subunits, labeled α, β,
δ, and ε (Fig. 65.2). In fetal muscle and adult denervated muscle
The nicotinic acetylcholine receptor (nAChR) is a member of a or nonjunctional membrane, a γ subunit replaces the ε subunit
larger family of ligand-gated ion channels. The muscle-type found in mature innervated muscle endplates. This form of the
receptor, which is involved in myasthenia, can be subclassified receptor differs from the mature junctional form by its lower
2
further into mature junctional receptors and immature, extra- density (500 receptors/µm ) and its distribution over most of
junctional, or denervated receptors. The nAChR at a mature the surface of the sarcolemma. The immature receptor also has

CHAPtER 65 Myasthenia Gravis 881


a lower conductance, a longer open time, a more rapid turnover,
and a decreased half-life. AChR
The genes for the α, δ, and γ subunits are located on chromo-
some 2 in humans, and subunits β and ε on chromosome 17. ACh vesicle
The subunits of the AChR are homologous to each other and
to their counterparts across species, with the greatest conservation Motor neuron ACh
of sequence being in the α subunit. Two α subunits and one of
each of the other subunits are assembled to form an asymmetrical AChe
hourglass channel spanning the membrane. Each subunit has a
large amino-terminus located extracellularly, four transmembrane Voltage-gated
–
regions, and a short cytoplasmic tail formed by a loop between Ca channel
the third and fourth transmembrane domains. The receptor
appears as a dimer as a result of disulfide bonding between the Rapsyn
δ subunits of two receptors. The two α subunits are not contiguous LPR4
in each receptor but are separated by another subunit. One
ACh-binding site is found on each of the α subunits around the MuSK
pair of cysteines at amino acids 192 and 193. The binding of
ACh to the α subunits is believed to engender a conformational Voltage-gated
change, possibly resulting in rearrangement of charged groups. Na channel
–
The binding of ACh to both α subunits increases the probability
of transition of the channel to an open conformation. Binding
of curare or α-bungarotoxin to the α subunits blocks this channel.
In normal innervated neuromuscular junctions, there are
two forms of the AChR, the predominant form having a long
half-life, and a small subset that is rapidly turned over. The
rapidly turned-over receptors are the precursors of the stable
receptors. It is not clear how these two types differ or how they
are regulated. The receptors are concentrated at the top of the
folds in the muscle endplate, adjacent to the nerve terminus,
2
at a density of 10 000/µm . This localization reflects the action Muscle endplate
of agrin, a nerve-derived synaptic organizing molecule. The
AChRs are organized into clusters by rapsyn, a 43-kilodalton FIG 65.3 Schematic Representation of the Myoneural Junc-
(kDa) cytoplasmic protein. The clustered AChRs are linked to the tion. Vesicles of acetylcholine (ACh) release their contents at
cytoskeleton by connections between rapsyn and a dystrophin– active zones across from acetylcholine receptors (AChRs) in
glycoprotein complex. response to impulses conducted down nerve axons. ACh diffuses
across synaptic cleft and binds to AChRs, with opening of the
NEUROMUSCULAR TRANSMISSION ion channel and the generation of endplate potential. Action
potential is propagated to muscle when sufficient amplitude of
When an impulse is transmitted along an axon terminal, it results summated endplate potentials is attained. MuSK, muscle-specific
in the release of the neurotransmitter ACh across its presynaptic tyrosine kinase.
membrane (Fig. 65.3). ACh diffuses across a 50-nm synaptic
cleft, where it interacts with AChRs, which are displayed in greatest
density at the tops of the junctional folds of the postsynaptic
muscle membrane or endplate. This interaction leads to a local availability of ACh and the reduced number of receptors accounts
depolarization or endplate potential caused by increased mem- for the characteristic decremental nerve conduction pattern seen
brane permeability to sodium and potassium. The endplate on electromyograms of patients with MG following repetitive
potential is terminated by acetylcholinesterases, which are present nerve stimulation (see Fig. 65.1).
in highest concentrations in the synaptic cleft around the
junctional folds. If the summation of endplate potentials attains IMMUNOPATHOGENESIS OF MG
a prescribed threshold, it produces an action potential that
depolarizes the surrounding sarcolemma and causes muscle
contraction. In a healthy individual, the arrival of an impulse KEY CONCEPtS
at the presynaptic membrane of a motor nerve releases consider- Involvement of Anti–Acetylcholine Receptor
ably more ACh than is required to generate an action potential. (AChR) Antibodies in the Pathogenesis of
This reserve, roughly four times the current needed for propaga-
tion of the impulse, is referred to as the safety factor of neuro- Myasthenia Gravis (MG)
muscular transmission. Because of the severe reduction in receptor • AChR antibodies are found in the serum of 85–90% of patients
number in MG, the electrical threshold for propagation of an with MG.
action potential cannot be attained and muscle contraction is • Infants born to mothers with myasthenia sometimes develop MG.
prevented. With a less severe reduction in receptor numbers • Immunoglobulin G (IgG) and complement are deposited at the post-
neuromuscular transmission may proceed normally unless the synaptic junction.
efficiency of presynaptic vesicle release is compromised, as occurs • Transfer of serum IgG from patients with MG to mice induces neu-
romuscular blockade.
with repetitive use of muscles. The combination of decreasing

882 PARt SEVEN Organ-Specific Inflammatory Disease


Anti-AChR antibodies are detected in 85–90% of MG patients decrease in anti-AChR antibody levels often accompanies
3
and are responsible for the impaired neuromuscular transmission. deterioration or improvement, respectively, in clinical activity.
There are several lines of evidence to support this contention. As the quantity of anti-AChR antibodies produced does
Immunoglobulin G (IgG), along with C3 and the terminal attack not fully explain disease severity, studies have also focused
complex (C5–C9), is deposited at AChR-containing areas of the on qualitative differences in these antibodies among different
postsynaptic membrane, and anti-AChR/AChR complexes can patients. These studies, however, have not been able to distin-
be extracted from the muscles of patients with MG. Transfer of guish properties of anti-AChR antibodies that lead to greater
myasthenic serum from mother to fetus, or from human to pathogenicity. Differences in specificity and avidity of binding
mouse, results in symptoms or signs of myasthenia in the recipient. to AChR have not been associated with particular functional
Plasmapheresis, which decreases anti-AChR antibody levels, is effects or disease severity. Anti-AChR antibodies that bind or
associated with clinical improvement. compete for the same region of AChR can have different functional
effects (see anti-AChR blocking antibody discussion). Anti-AChR
Properties of Anti-AChR Antibodies and antibodies show extensive heterogeneity by isoelectric focusing,
but this characteristic also does not correlate with pathogenic
Characterization of B-Cell Epitopes potential.
Anti-AChR antibodies are produced by a small subset of B cells Patients previously classified as seronegative have been found
in affected people. The frequency of IgG-producing AChR-specific to have low-affinity AChR-specific IgG antibodies when their
peripheral blood mononuclear cells is estimated to be 1 in sera were tested with very sensitive assays that rely on tissue
6,7
15 000–70 000. IgG anti-AChR–secreting cells are also found in substrates on which the receptors are aggregated. Antibody
the peripheral blood of healthy volunteers, albeit in much lower binding was facilitated by the high concentrations of AChRs,
numbers. The proportion of immunoglobulin producing AChR- which compensate for the low affinity of the autoantibodies.
specific B cells or plasma cells is greater in the germinal centers Like the anti-AChR antibodies in classic anti-AChR antibody-
of hyperplastic thymuses, but still only 1 in 1000–10 000 antibod- positive MG, these antibodies belong largely to the IgG1 subclass.
ies produced is AChR specific. Anti-AChR antibodies are pre- Like the conventional antibodies, the low-affinity antibodies also
dominantly IgG1 and IgG3, but IgG2 and IgG4 isotypes have bind complement.
also been found. IgA and IgM anti-AChR antibodies are present As noted above, 10–15% of MG patients are persistently
in some patients, but never in the absence of IgG anti-AChR antibody negative. Approximately 50% of these patients have
antibodies. The IgA and IgM anti-AChR antibodies tend to appear been discovered to have serum IgG antibodies specific for muscle-
7,8
in patients whose disease is of longer duration and greater severity specific tyrosine kinase (MuSK). This skeletal muscle receptor
and in association with high IgG anti-AChR titers. tyrosine kinase is activated by agrin and is critical for formation
The pathogenic anti-AChR antibodies in MG are thought to of the neuromuscular junction. Originally, anti-MuSK antibodies
be directed to conformationally dependent structures. Immuniza- were found in patients with marked facial and bulbar weakness,
tion of animals with irreversibly denatured AChR leads to the including tongue weakness and respiratory involvement with
formation of anti-AChR antibodies capable of binding to native relative sparing of upper- and lower-extremity muscles. Oph-
AChR, but the antibodies are not capable of causing disease. thalmoparesis was also seen but was not a first symptom in at
This observation indicates that conformationally dependent least one series of patients. Subsequently, it has become apparent
epitope(s) are important in the induction of disease. Many of that patients with anti-MuSK antibodies can also have a more
the anti-AChR antibodies are directed against the α subunit, traditional clinical phenotype similar to that seen with anti-AChR
particularly to a small region on the extracellular portion referred patients. Patients often respond poorly to anticholinesterase
4
to as the main immunogenic region (see Fig. 65.2). Approximately agents and benefit greatly from plasmapheresis but only modestly
60% of the anti-AChR antibodies are directed against this region, from intravenous immunoglobulin (IVIG). They typically lack
which encompasses a set of overlapping epitopes clustered around thymus pathology and, not surprisingly, thymectomy is not
5
amino acids 67–76 of the α subunit. The reason for the pre- typically beneficial. Most anti-MuSK antibodies are of the
dominant role of the α chain in the antibody response in non–complement-fixing IgG4 isotype. Anti-MuSK antibodies
myasthenia is not known. Not all disease-producing antibodies do not cause destruction of the muscle endplate, as might be
in humans or rats appear to be directed to this region. Many expected because of their inability to activate the classical comple-
patients also have antibodies recognizing the γ-containing ment pathway and reduced capacity to bind activating Fcγ
embryonic form of AChR. This observation has spawned specula- receptors on monocytes and macrophages. However, they have
tion about a nonmuscle source of sensitization. been shown to affect AChR clustering on cultured myotubes.
The clinical relevance of these autoantibodies is underscored by
Anti-AChR Antibody Levels and Relationship to the appearance of a myasthenic illness in animals either immu-
nized with MuSK or infused with serum antibodies from patients
Disease Activity with anti-MuSK antibody–associated MG.
The relationship of anti-AChR antibody and disease activity in IgG antibodies specific for lipoprotein-related protein 4 (LRP4)
MG is complicated. In general, serum levels of anti-AChR antibody have also recently been discovered in the sera of patients with
7,9
or anti-AChR/AChR complexes correlate poorly with disease anti-AChR antibody–negative MG. LRP4 is an important
severity. Among patients within one clinical grade, anti-AChR component of the neuromuscular junction, which serves as a
antibody levels can vary by several orders of magnitude. In receptor for agrin and which is required for agrin-induced
addition, approximately 10–15% of patients with clinical MG activation of MuSK and AChR clustering. The prevalence of
have no anti-AChR antibody by standard assays. Anti-AChR reactivity to LRP4 varied from 2–50% of patients who are negative
antibodies are more likely to be present if the disease is generalized for anti-AChR and MuSK antibodies (double seronegative), with
or severe. In addition, in an individual patient an increase or the differences possibly being related to geography or ethnicity.

CHAPtER 65 Myasthenia Gravis 883


Anti-LRP4 antibodies were found in the sera of 3% of patients Complement-Mediated Damage
with anti-MuSK antibodies in one study but otherwise were The critical problem in MG is the anti-AChR antibody–mediated
−
−
limited to double-seronegative (anti-AChR /anti-MUSK ) patients. reduction in the number of nAChRs at the myoneural junction.
Anti-LRP4 antibodies were not present in the sera of a large There are several possible mechanisms by which the anti-AChR
10
number of patients with other neurological diseases with the antibodies could lead to impaired neuromuscular transmission.
exception of neuromyelitis optica spectrum disorder, where 12.5% Ultramicroscopic studies show marked destructive changes in
of patients had anti-LRP4 antibodies. If larger studies demonstrate some endplates, particularly at the peaks of the postsynaptic
that anti-LRP4 antibodies are found in patients with MG but folds, where AChR is usually present in the greatest concentration.
without anti-AChR or MuSK antibodies and are rare in other The architecture of the muscle endplate is simplified, with loss
neurological disorders, this test could become important in the of junctional folds and widening of the synaptic cleft that contains
diagnosis of MG. membrane debris. C3, C9, and the membrane attack complex
MG sera also contain antibodies reacting with the ryanodine are deposited at the muscle endplate, suggesting a role for
7
11
receptor. These receptors, which are critically involved in muscle complement in membrane destruction. Indeed, in many patients,
2+
contraction, are Ca release channels located in the sarcoplasmic anti-AChR antibodies can fix complement in vitro when bound
reticulum of striated muscles. Antibodies to ryanodine receptors to skeletal muscle and can damage cultured rat myotubes with
are found in 50% of patients with MG who have thymoma, a resultant decrease in AChR content.
and patients with high levels have a worse prognosis than do Although antibody-directed, complement-mediated destruc-
antibody-negative patients with MG who have thymoma. In vitro tion is important in the pathophysiology of MG, it is not the
studies have suggested a pathogenic role for these autoantibodies entire story. The rapid clinical improvement in MG following
in MG. certain therapeutic interventions and the lack of destructive
Antirapsyn antibodies have been detected in a small subset changes in many neuromuscular junctions of symptomatic areas
7
of patients with MG. Seropositive patients with MG are indis- despite prominent immunoglobulin deposition suggest that a
tinguishable from seronegative patients with regard to clinical more readily reversible process is also likely to be involved in
and laboratory features of disease. The presence of antirapsyn the neuromuscular block.
is not specific for MG, having been detected in the sera of an
occasional patient with MS and a majority of the patients with Acceleration of AChR Degradation
lupus tested. In vitro and in vivo studies have shown that anti-AChR antibodies
Antiagrin antibodies have recently been reported, often in can accelerate the rate of degradation of extrajunctional and
12
MG patients with anti-AChR or anti-MuSK antibodies and junctional receptors, respectively. This reaction is complement
occasionally in patients with MG who are “triple seronegative” independent and results from the endocytosis of AChRs via
−
−
−
7
(AChR MuSK LRP4 ). Studies of larger numbers of patients shallow depressions, presumably clathrin-coated pits. Other
will be necessary to determine the prevalence of antiagrin antibod- membrane receptors are not affected. Both stable and rapidly
ies in triple seronegative MG patients and their degree of specific- turned-over receptors appear to be affected, thereby explaining
ity for MG. the greater than expected antibody-mediated loss of AChRs
Patients with MG associated with thymoma show distinct observed at neuromuscular junctions. The reaction requires
patterns of antibody production. Almost all patients with cross-linking of adjacent AChRs, as it can be mediated by
thymoma are anti-AChR antibody positive, and most produce F(ab′) 2 fragments, but not Fab fragments, of anti-AChR anti-
9
antistriational antibodies. These latter antibodies react with titin, bodies. The effect of antibody on the synthesis of new AChR is
a giant filamentous protein of striated muscle. Titin filaments controversial.
are involved in muscle assembly and contribute to the muscle’s
ability to recoil following stimulation. Such antistriational Receptor Blockade
antibodies are also found in approximately 50% of the sera of The inhibition of ACh binding has been assessed by studying
older patients with MG who have thymic atrophy but not the effects of MG serum on the binding of the neurotoxin
thymoma; however, they are not frequently detected in patients α-bungarotoxin to AChRs. Such blocking antibodies are found
with early-onset disease and thymic hyperplasia. The finding of in a variable number of MG sera. Blockade has been generally
antistriational antibodies in a patient with MG who is less than attributed to steric hindrance of the ligand-binding site, rather
13
40 years old strongly suggests the presence of thymoma. There direct binding to the ACh-binding site. The importance of
is no evidence that antistriational antibodies are involved in these antibodies in the pathophysiology of MG remains unclear.
muscle weakness. However, in one study the functional ability of an individual
serum to accelerate degradation and cause blockade of AChRs
Pathogenic Effects of Anti-AChR Antibodies paralleled most closely the clinical status of the patient. The in
vivo significance of such antibodies has also been demonstrated
KEY CONCEPtS by passive transfer of certain rat monoclonal anti-AChR antibodies
into chicks. Complete paralysis was observed within 1 hour of
• Effects of anti–acetylcholine receptor (AChR) antibodies in myasthenia
gravis pathology the transfer, presumably before there was time for complement-
• Reduced number of receptors mediated damage. It has been reasoned that in patients with
• Widening of the synaptic cleft MG, such blocking antibodies could further diminish synaptic
• Distorted geometry of the synaptic membrane function already decreased owing to complement-mediated
• Mechanism of damage damage or accelerated receptor degradation. This could result
• Complement-dependent damage to muscle endplate in acute clinical deterioration or a rapid clinical improvement
• Enhanced rate of AChR degradation
• Block cholinergic binding sites after plasmapheresis, before the repair of damaged membrane
and regeneration of new AChRs.

884 PARt SEVEN Organ-Specific Inflammatory Disease


antibody production requires the integrity of the three-
Role of T Cells dimensional structure of the receptor, as immunization with
An overwhelming body of data indicates that anti-AChR antibody denatured AChR elicits antibody production but not disease, even
production in patients with MG and rodents with experimental in susceptible animals. Anti-AChR antibody levels correlate with
autoimmune myasthenia gravis (EAMG) is dependent on the anti-AChR/AChR complexes and with the AChR content of the
activity of CD4 T cells. Researchers have used freshly isolated muscle, but not with clinical disease severity. No characteristic
CD4 T cells, T-cell lines and T-cell clones stimulated with AChR feature distinguishing disease-producing and nonpathogenic
purified from the electric organs of Torpedo californica (T-AChR), autoantibodies has been defined. Antibodies in rats with and
recombinant human AChR, human AChR concentrated on without disease are predominantly of the same immunoglobulin
immunomagnetic beads, and synthetic AChR peptides. Most of isotope and subclass, express similar clonotypic heterogeneity,
the T cells derived from patients with MG have responded to and show similar avidities. The percentage of antibodies that
the complete AChR or the α subunit, but responses to the δ, ε, recognize the native receptor (as opposed to the foreign eel
14
and γ subunits have also been demonstrated. Unlike EAMG, receptor immunogen) is low (0.2–2%) but similar between the
a T cell–immunodominant epitope has not been found in humans. symptomatic and the asymptomatic mice. The percentage of
However, T cells from most patients recognize a limited number antibody directed against the main immunogenic region of AChR
of AChR sequences. In an individual patient, T cells reactive is also similar. The antibodies that develop in asymptomatic
with a particular AChR epitope can show limited T-cell receptor animals can bind and cause a decrease in receptor half-life, as
Vβ (TCR Vβ) usage, but the same TCR Vβ usage has not been well as those that develop in paralyzed animals. In fact, EMG
observed for different patients. A range of major histocompat- abnormalities can be demonstrated in mice that appear disease
ibility complex (MHC) class II molecules can present AChR free. An analogous situation in humans may be the high frequency
epitopes. This is not surprising, given the degenerate binding of single fiber EMG abnormalities in asymptomatic family
capabilities of MHC molecules needed to present an extremely members of patients with MG. Importantly, antibodies from
large and diverse group of peptides to the immune system. T affected animals will cause disease in resistant strains, indicating
cells from normal controls respond to some of the same epitopes that disease differences between strains is not caused by differences
to which MG patients’ T cells respond, albeit in smaller numbers in the AChR receptor itself.
and less vigorously. Although EAMG is mediated by autoantibodies, it is a T
cell–dependent process. Examination of T-cell responses in rats
EXPERIMENTAL AUTOIMMUNE and mice has shown that EAMG requires the action of CD4 T
MYASTHENIA GRAVIS cells. These cells recognize immunodominant T-cell epitopes
located on the α subunit. The T-cell responses to the immuno-
The serendipitous discovery that rabbits injected with purified dominant epitope in rats involve a variety of TCRVβ and Jβ
AChR developed not only anti-AChR antibodies but signs gene segments (Chapter 4). However, in susceptible C57BL/6
of MG provided the evidence for the pivotal role of antibodies mice, there is a predominant use of the TCRVβ6 family in the
in this disease and paved the way for the development of an CD4 T-cell response. CD4 T cells in susceptible and resistant
15
experimental model of human MG. EAMG has been studied strains recognize different immunodominant AChR α-chain
16
in a number of different animal species. It is generally induced epitopes. 17
by immunizing animals with AChR purified from the electric Early reports suggested that AChR-reactive T-cell clones did
organs of T. californica emulsified in adjuvant. Disease can also not fit neatly into T-helper-1 (Th1) and Th2 subsets. However,
be passively transferred by immunoglobulin from affected animals later studies suggested that interferon-γ production by Th1 cells
or from patients with myasthenia. Animals suffer from fatigue, is essential for the development of disease and that IL-4 may
hypoactivity, weight loss, paralysis, difficulty breathing, and subserve a protective role. 16,18 In addition to interferon-γ, tumor
dysphagia; these signs are reversible with anticholinesterases. necrosis factor (TNF)-α, interleukin (IL)-6, IL-12, IL-18, IL-1,
There is a decremental response to repetitive nerve stimulation IL-5, and IL-10 have been reported to promote the development
on electromyography in EAMG as in MG. Anti-AChR antibodies of EAMG. However, a more recent publication indicated that
are present, and most are directed against the main immunogenic C57BL/6 mice genetically deficient in IL-12/IL-23 and IFN-γ are
region (see Fig. 65.2). They are deposited along with complement susceptible to experimental EAMG, suggesting a pathogenic role
at the muscle endplate. Similar to the pathology in humans, of non-Th1 cells. This result led the authors to suggest that
there is simplification of the muscle endplate and a loss of AChR AChR-specific Th17 cells may also contribute to the pathogenesis
19
content of muscles in the experimental disease. A major difference of this experimental autoimmune disease. Subsequently, Th17
between the induced rodent models of EAMG and spontaneous cells were, indeed, shown to be important in the pathogenesis
human MG is the absence of thymic pathology in the former. of EAMG. 20
In murine models, there are disease-resistant and disease- The roles of a number of costimulatory factors have also been
susceptible strains. The MHC determines this susceptibility, in investigated in EAMG. CD28/B7 and CD40/CD40L appear to
part, with specific H-2 alleles being associated with susceptibility be required for the development of the primary immune response
or resistance. However, even in the high-responder strains, only to AChR. An interaction between ICOS and B7RP-1 may play
50–70% of immunized animals manifest disease. This lack of an important role in the secondary response and/or in the
concordance remains to be fully explained. Differences in the maintenance of the immune response to this autoantigen.
level of complement activation and the physiological safety factor
of neuromuscular transmission may partly account for the THE THYMUS IN MYASTHENIA GRAVIS
variability in disease expression.
Most immunized animals demonstrate anti-AChR antibodies, Several lines of evidence have suggested that the thymus is directly
whether or not they develop EAMG. Induction of pathogenic linked to the pathogenesis of MG.

CHAPtER 65 Myasthenia Gravis 885



KEY CONCEPtS including the α subunit. Additional factors found uniquely in
Pathogenic Roles of the Thymus in hyperplastic MG thymus include increased expression of che-
mokines that attract immigrant CD4 T and B cells (CXCL13,
Myasthenia Gravis (MG) CCL21); the presence of nAChR-reactive B and CD4 T cells;
• Pathological cytokines that can facilitate B-cell activation, differentiation, and
• 65–75% of patients with MG have follicular hyperplasia with germinal survival (IL1β, IL6, APRIL, BAFF); anti-AChR antibody–secreting
+
+
centers plasma cells; and possibly decreased CD4 CD25 T regulatory
• 10% have thymoma cell function. 21-24
• Clinical As yet, it is not known whether or how such perturbations
• Improvement following thymectomy of the thymus lead to a breach in self-tolerance and the induction
• Immunological
• Acetylcholine receptor (AChR) subunits expressed on myoid cells of anti-AChR antibodies, although there is mounting evidence
and thymic epithelial cells that an antecedent inflammatory reaction in the thymic medulla
• AChR-reactive T and B cells localized in the thymus may serve as the initiating trigger. An understanding of this
• Increased thymic AChRα expression enduring mystery likely holds the key to unlocking the immu-
• Anti-AChR antibody secreted by thymic B-lineage cells nopathogenesis of this disease. The reader is referred to other
• Decreased thymic T regulatory cell (Treg) function works for an in-depth discussion of this topic. 22,24,26
• Interleukin (IL)1-β, IL-6, CXCL13, CCL21, and B cell–activating factor
(BAFF) overexpressed in thymus
ETIOLOGICAL FACTORS
Genetic Factors
Thymic Pathology As in most autoimmune diseases, the MHC represents an
Interest in a primary role for the thymus in the pathogenesis of important genetic susceptibility locus for the development of
MG has been fueled by pathological, clinical, and immunological MG. Studies indicate that the extended human leukocyte antigen
lines of evidence, although the nature of its involvement remains (HLA)-A1-B8-DR3 haplotype is associated with EOMG and
to be elucidated. 21-24 The thymus is pathologically abnormal in hyperplastic thymus in Caucasian individuals. This haplotype
80–90% of patients with MG. The majority of patients (65–75%) has been associated with the development of other autoimmune
have thymic follicular hyperplasia with germinal center formation. disorders. An association with HLA-B7-DR2, although weaker,
The architecture of the hyperplastic thymi is generally preserved, has also been described in patients with onset of MG occurring
with well-demarcated cortical and medullary regions. However, after the age of 40 years and associated with atrophic thymic
the medulla is crowded by numerous germinal centers that display histology. However, the strongest association, focused on a
the architectural features and cellular constituents of germinal Norwegian population of patients with late-onset MG, was
centers in the secondary follicles of peripheral lymph nodes from recently shown to be the DRB1*15:01 allele. A recent study found
normal individuals. Although these germinal centers in patients a strong association between the HLA-DQ5 allele and patients
are generally thought to occupy an intraparenchymal position, with anti-MuSK antibody–positive MG. Interestingly, the MuSK-
some observers feel that they may actually lie extraparenchymally positive T-cell repertoire appears to be skewed to the usage of
in the perivascular space. this HLA MHC class II allele. In murine studies, the MHC class
b
k
Thymomas are seen in approximately 10% of patients with II molecules I-A and I-E have been associated with susceptibility
16
MG who tend to be older than those with hyperplastic thymi. 21-24 to EAMG. In EAMG, the permissive MHC class II molecules
The thymomas are characterized by a loss of cortico-medullary are capable of binding AChR peptides that are recognized by
demarcation and consist largely of neoplastic epithelial cells antigen-specific CD4 T cells.
admixed with thymocytes. The affected epithelial cells belong Studies have also addressed the potential genetic contributions
to the cortical epithelial compartment, and the thymocytes have of other immune system–related genes in the pathogenesis of
the immunophenotypic properties of normal immature cortical MG. An association has been reported for a particular IL-1β
thymocytes. allele and MG and increased serum levels of this cytokine have
Further evidence for a pathogenic role of the thymus comes been reported. This was most pronounced in patients who lacked
from the results of empiric trials of thymectomy. Despite the disease-susceptible HLA genes. Several groups have reported an
25
absence of controlled clinical trials until recently, there was association between MG and the presence of particular TNF-α
general agreement in the past that removal of the thymus, polymorphisms. The expression of a high-transcription TNF-α
particularly in young patients with follicular hyperplasia, leads allotype, TNF-α-308 allele 2, correlated with EOMG. In this
to clinical improvement. The underlying basis of this improvement regard, patients with MG demonstrate increased serum levels
remains unknown. of TNF-α and their peripheral blood mononuclear cells display
increased expression of TNF-α messenger RNA (mRNA).
Intrathymic Factors Possibly Contributing to Local Polymorphisms in the IL-10 promoter region have been reported
to be associated with distinct patterns of thymic histology. No
Anti-AChR Antibody Response correlations have been made between IL-4 alleles and MG.
The MG thymus, particularly hyperplastic thymus, is characterized Allotypic markers on IgG and FcγRIIA receptors have been
by several unique features that strongly suggest its primary role associated with the coexistence of MG and thymoma. A single
in the immunopathogenesis of MG. 21-24 The thymus contains nucleotide polymorphism in the gene encoding the intracellular
important constituents necessary for and indicative of an immune tyrosine phosphatase PTPN22, which has been associated with
response directed against nAChRs. There is considerable evidence the risk of developing other autoimmune diseases, has also been
that resident cells in the thymus, including myoid cells and identified in both a subgroup of patients with anti-titin antibody–
medullary epithelial cells, express various subunits of AChR positive nonthymomatous MG and patients with thymomatous

886 PARt SEVEN Organ-Specific Inflammatory Disease


MG. 27,28 The risk of developing MG has also been linked to a and the development of EOMG and human MG. An interesting
polymorphism in the promoter region of CHRNA1, the previously story has emerged concerning miR150-P. Increased levels of this
mentioned gene that encodes the α subunit of AChR and CHRND, miRNA were found in the serum of patients with MG, and
22
the gene that encodes the δ subunit. It has been proposed these levels fell in association with the clinical improvement that
34
that such polymorphisms in genes encoding autoantigens cause followed thymectomy. A decrease in miR320a was observed in
reduced expression of AChRα on thymic medullary epithelial the peripheral blood mononuclear cells of a cohort of Chinese
22
cells, thereby impairing central deletion of autoantigen-specific patients. This finding was associated with increased levels of a
thymocytes. Additional MG-associated risk factors include number of proinflammatory cytokines. Further studies of the role
polymorphisms in CTLA4, type II, IFNII, IL12, CD86, AKAP12, of miRNAs will need to be conducted to elucidate whether they
VAV1, BAFF, TCF19, and TNIP genes. 22,23 contribute to the immunoregulatory abnormalities seen in MG.
Exogenous Factors TREATMENT OF MYASTHENIA GRAVIS
Whether or not sensitization to AChR occurs in the thymus or
the periphery, the stimulus for this autoimmune response remains tHERAPEUtIC PRINCIPLES
a conundrum. Moreover, it remains to be determined whether
the stimulus is a self-antigen (AChR) or a foreign antigen that • Anticholinesterase agents
mimics the receptor’s molecular structure. In this regard, several • Corticosteroids
examples of molecular mimicry between AChRα chain and other • Thymectomy
• Plasmapheresis
molecules have been reported. Studies carried out with certain • Immunosuppressive agents
monoclonal anti-AChR antibodies demonstrated epitope sharing • Intravenous immunoglobulin
between the receptor and several bacteria, including Klebsiella
pneumoniae, Escherichia coli, Proteus vulgaris, and Yersinia Therapeutic intervention in MG usually proceeds in a stepwise
29
35
enterocolitica. However, for the most part, no difference was manner, beginning with anticholinesterase agents. Most of the
observed in the binding of polypeptides from these organisms experience dealing with therapeutic modalities is based on treating
by either sera from patients with MG or control sera. A computer patients with anti-AChR-associated MG.
search of protein banks revealed a sequence homology between
AChRα chain and a short peptide in herpes simplex glycoprotein Anticholinesterases
30
D, although the significance of this finding is unknown. Finally, Anticholinesterases are the mainstay of treatment. These agents
similarities were reported between idiotypic determinants on protect acetylcholine from hydrolysis by cholinesterase, thereby
anti-AChR antibodies and antibodies reactive with α1,3-dextran. increasing the amount of neutrotransmitter and the number of
Interestingly, antidextran antibodies were detected in approxi- contacts with the reduced number of receptors at the postsynaptic
31
mately 13% of patients with MG but rarely in normal controls. junction. This, in turn, raises the probability of attaining the
α1,3-Dextran is found in the cell walls of several common enteric necessary threshold for neuromuscular transmission. In addition,
pathogens and thus represents a potential ubiquitous source of some of the anticholinesterase agents have a direct agonist effect
immunogen. This type of idiotypic network connectivity led at the postsynaptic junction. The three most popular agents in
the investigators to postulate that an unregulated antiidiotypic this group are neostigmine bromide (Prostigmin), pyridostigmine
response to anti-α1,3-dextran antibodies might lead, in certain bromide (Mestinon), and ambenonium chloride (Mytelase).
individuals, to an anti-AChR antibody response. Unfortunately, Although there are only slight differences between these agents,
there has been no follow-up to these observations. Mestinon remains the most commonly used. It has an onset of
A striking association has been reported between the develop- action of 30–60 minutes, peak action at about 2 hours, and loss
ment of MG and treatment with the drug penicillamine, 32,33 of activity after 4 hours. Adverse effects of these agents are caused
particularly in individuals with HLA-DR1. MG developed in by excessive stimulation of nicotinic and muscarinic receptors.
patients with rheumatoid arthritis and patients with Wilson Auxiliary drugs that have been purported to have a salutary
disease treated with this agent. After discontinuation of penicil- effect on neuromuscular transmission are ephedrine and xanthine
lamine, resolution of MG symptoms was reported in some patients derivatives (theophylline), which are thought to increase the
but not others. Penicillamine treatment was associated with the presynaptic release of ACh. The minimal effect of their added
development of anti-AChR antibodies that appeared to have the benefit has not warranted their common usage. As mentioned
same type of specificity profile as found in idiopathic myasthenia. previously, anticholinesterase agents often are not beneficial in
Additional evidence suggests that penicillamine may directly patients with anti-MuSK-antibody–associated MG and may even
interfere with neuromuscular transmission. Although penicil- exacerbate weakness. These agents neither induce sustained
lamine has been shown to have diverse effects on the immune remission of symptoms nor impede disease progression.
response in the normal host and has reactive sulfhydryl groups
capable of modifying self-antigens, its role in the development Thymectomy
of MG remains to be determined. Another mainstay in the therapy of the adult with generalized
Currently, considerable attention is being focused on the role MG is thymectomy. 36,37 The benefit is greatest in younger patients
of epigenetic mechanisms to explain how environmental factors and those with thymic hyperplasia, although many centers include
may promote the development of autoimmune diseases. Although older patients as well. Over many years, despite the absence of
some key epigenomic mechanisms, such as DNA methylation, a controlled study, there was general agreement that removal of
histone acetylation, and microRNAs, have been demonstrated to the thymus leads to clinical improvement, particularly in young
possibly play a pathogenic role in several autoimmune disorders, patients with follicular hyperplasia. In one study, 90% of patients
the analysis of these factors is at a rudimentary stage in MG. To were asymptomatic or in complete remission within a few years
date, there is evidence to support an association between miR155 of thymectomy, and 46% were off all medications. An international

CHAPtER 65 Myasthenia Gravis 887


multicenter controlled trial completed recently compared clinical action most likely involves the removal of the pathogenic
outcome in patients with MG treated with corticosteroid versus autoantibody, as a reduction in titer of anti-AChR antibody
those treated with corticosteroid plus thymectomy and those correlates with clinical improvement. However, it is also possible
receiving thymectomy demonstrated a more favorable clinical that the removal of other phlogistic humoral factors contributes
25
outcome. With improvements in preoperative care, anesthesia, to clinical efficacy.
surgical technique, and postoperative care, thymectomy has
become a safe procedure, but its value and safety in children Intravenous Immunoglobulin
and older patients is less well established. There is still some The efficacy of IVIG in the treatment for MG was suggested by
controversy over what represents the best surgical procedure. several uncontrolled clinical trials. Interest in the use of this
The mechanism responsible for the salutary effect of thymectomy biological grew out of its demonstrated efficacy in other auto-
remains to be elucidated. No obvious effects on immunoregulatory immune diseases, most notably autoimmune thrombocytopenia.
mechanisms have been demonstrated, although anti-AChR titers Subsequent randomized double-blind placebo-controlled trials
tend to fall months after the procedure. Thymectomy is also the provided proof of clinical efficacy. Conventional dosing is infusion
recommended treatment for patients of all ages suspected of of 2 g/kg divided over 5 days, although some practitioners prefer
having thymoma. to administer this dose over 2 days. In a randomized, controlled
trial a total dose of 1 g/kg was found to be as efficacious as a
Corticosteroids dose of 2 g/kg. IVIG therapy is generally associated with rapid
Corticosteroids are used in patients with generalized MG who clinical improvement in responsive patients, independent of
fail to respond to anticholinesterase agents or thymectomy and whether they had undergone thymectomy or were being treated
in patients needing optimization of their clinical condition in concurrently with corticosteroids or immunosuppressive agents.
38
preparation for thymectomy. They are generally not used as In some patients, improvement was sustained over a period of
first-line agents to replace thymectomy but are used in patients several weeks. Improvement has not always been accompanied
with ocular myasthenia who fail to respond to anticholinesterases. by a consistent reduction in anti-AChR antibody titers. In general,
41
Corticosteroids are initially given on a daily basis, with therapy IVIG and plasmapheresis appear to be equivalent in efficacy.
initiated in a hospital. This cautious approach is followed because However, there is a general impression that IVIG is preferable
of the fear of clinical deterioration that may occur in some patients because of better tolerance and less cost. The mechanism(s) of
during the introduction of corticosteroids. This concern resulted this apparent salutary effect is unknown, although there is
in some groups advocating initiation of alternate-day therapy, evidence IVIG contains antibodies directed against the idiotypes
which is not typically associated with clinical deterioration and of anti-AChR antibodies.
can be carried out on an outpatient basis. Daily corticosteroids
are usually started in patients with generalized MG at a dose Immunosuppressive Agents
>1 mg/kg prednisone. Patients should be continued on this dose Immunosuppressive drugs have been tried primarily in patients
until clinical improvement is maintained for several days, then who have failed treatment with anticholinesterases, thymectomy,
42
gradually weaned off, and switched to alternate-day therapy. plasmapheresis, and corticosteroids. Most of the experience
With improvement sustained over several months, an effort has been obtained with azathioprine, which has strong antiinflam-
should be made to reduce the dose (usually in 5-mg decrements) matory effects as well as immunosuppressive activity. The dose
administered on alternate days. Although a Cochrane review of azathioprine has varied between 1 and 3 mg/kg/day, with
underscored the dearth of controlled trials, the improvement improvement seen between 5 and 20 weeks. The drug is usually
39
rate is generally estimated to be 60–90%. Complete remission started at a lower dose and escalated weekly to achieve the
is rare, and most patients will require some dose of steroids maintenance dose. The patient should be followed with complete
indefinitely. The physician should be alert to the possibility that blood counts, particularly during the initiation of therapy, as
anticholinesterase requirements may decrease as the patient azathioprine has a suppressive effect on the bone marrow. A
responds to corticosteroids. white blood cell count below 2500 or a neutrophil count below
1500 should prompt a reduction or termination of the dosage.
Plasmapheresis The results of a randomized double-blind placebo-controlled
Plasmapheresis has enjoyed popularity since its introduction as trial indicated that the addition of azathioprine (2.5 mg/kg) to
an auxiliary treatment modality in patients with generalized MG alternate-day prednisolone was associated with a reduction of
40
in 1976, particularly as a temporizing measure. It appears to the prednisolone dose, fewer treatment failures, longer remissions,
be most beneficial in patients in myasthenic crisis and in those and fewer side effects. 43
experiencing progressive deterioration despite treatment with There is considerably less experience in the treatment of
anticholinesterases and corticosteroids. Plasmapheresis has also steroid-unresponsive patients with cyclophosphamide, another
proved to be useful in preparing patients for thymectomy when powerful immunosuppressive agent. It is associated with more
their course is complicated by involvement of the bulbar and adverse effects and does not appear to offer any significant
respiratory musculature. Such patients may also require short- advantage over azathioprine when used in standard dosing
term plasmapheresis during the postoperative period. Plasma- regimens. High-dose intravenous cyclophosphamide therapy for
pheresis also appears to be particularly efficacious in anti-MuSK patients with MG refractory to conventional immunosuppressive
antibody–associated disease. There is no long-term benefit of agents has been investigated as an approach to immunoablate
plasmapheresis when added to prednisone. bone marrow and allow for subsequent repopulation by endog-
Although there are no hard and fast rules, the average exchange enous stem cells. Although durable responses were seen in some
is 1–2 L/day for 7–14 days. Improvement is usually observed patients in an early trial, this regimen is not readily available
within a few days of concluding the treatment course, although and should only be utilized in refractory patients under treatment
patients in crisis often benefit more quickly. The mechanism of in specialized centers.

888 PARt SEVEN Organ-Specific Inflammatory Disease


Methotrexate has been used in some uncontrolled studies, been used to inhibit pathogenic IgG autoantibody-induced
but there is no information to indicate that it is more efficacious antigenic modulation. Bortezomib, a proteosome inhibitor
or safer than azathioprine and its onset of action may take as approved for usage in multiple myeloma and mantle cell lym-
long as several months. As is true for corticosteroid therapy, it phoma, has been found to reduce anti-AChR antibody titers,
is the rare patient who enjoys a permanent remission following inhibit damage to the postsynaptic muscle membrane, and lead
institution of immunosuppressive therapy, and those who show to clinical improvement. Moreover, this agent was shown to
some improvement often require treatment indefinitely. suppress anti-AChR antibody production and deplete plasma
Cyclosporine, a potent immunosuppressive agent, has been cells from cultures of cell suspensions obtained from thymus
investigated because it interferes with IL-2–mediated T-cell specimens of patients with MG. 34
proliferation and thus would be expected to interfere with the The induction of antigen-specific immune tolerance, the
generation of T cells that would “help” the anti-AChR antibody therapeutic holy grail in autoimmune diseases, has received
response. A retrospective study suggested that cyclosporine considerable attention in EAMG. Early studies utilized extracel-
provided benefit in patients whose disease was refractory to lular domain sequences that form epitopes for pathological
corticosteroids and azathioprine. Serious renal toxicity and autoantibodies to induce tolerance to AChR. However, this
treatment withdrawal, which plagued earlier studies, were reduced approach risks provoking autoimmunity rather than suppressing
by careful selection of patients. In a 12-month European trial, it. To avoid this risk, one group has recently developed a novel
cyclosporine appeared to be as efficacious as azathioprine in vaccine consisting of bacterially expressed human AChR cyto-
46
producing clinical improvement. Tacrolimus has a similar plasmic domains. To date, this group has used this vaccine to
mechanism of action to cyclosporine. When used in low dosage, prevent development of chronic EAMG when administered
it has proved as effective as cyclosporine as a corticosteroid-sparing immediately after the acute phase of EAMG and to rapidly reverse
agent with fewer side effects. Nevertheless, most practitioners established chronic EAMG when started during the chronic phase
reserve these agents for use in patients whose disease is refractory of EAMG. Treatment effects are robust and long-lasting. Although
to the combination of azathioprine and prednisone. the mechanisms of action of this novel approach have yet to be
Mycophenolate mofetil (MMF), another immunosuppressive fully elucidated, they may involve a combination of antibody-
agent that affects both T and B cells, was widely touted following mediated feedback suppression and regulatory T cell–mediated
the completion of early trials as a steroid-sparing agent in patients active suppression.
with MG. That experience suggested that it was effective 70–75% Complement inhibition has shown efficacy in the treatment
of the time, although probably less so in refractory MG. It has of EAMG and represents a target in patients with MG now that
an acceptable safety profile with adverse effects largely related complement inhibitors have demonstrated benefit in the treatment
to gastrointestinal intolerance. Benefit may require many weeks of a number of human disorders. A phase II placebo-controlled
of administration. However, two randomized, placebo-controlled cross-over study with a fully humanized monoclonal anti-C5
trials have challenged the early optimism. In one, the addition antibody was initiated only to be terminated because of inadequate
34
of MMF treatment at the initiation of a 36-week schedule of recruitment. Nevertheless, given the importance of the terminal
prednisone tapering was not found to be superior to placebo in complement pathway in the pathogenesis of cases of MG and
44
maintaining myasthenia control. In the second, the coadministra- the continued development of a number of complement inhibi-
tion of MMF and prednisone provided no better control of tors, it is likely that this strategy will be revisited.
myasthenic weakness than prednisone alone in the initial A B-cell targeting agent that has gotten much attention in
45
management of generalized MG. However, none of the patients patients with MG is rituximab, a mAb specific for CD20, a protein
included in these two studies was known to be steroid resistant. expressed on B lymphocytes. Anecdotal reports and small
Thus whether MMF has long-term benefits with respect to uncontrolled case series using rituximab have shown improvement
myasthenic weakness or steroid-sparing effects in the population of MG. Interestingly, responsive patients do not demonstrate a
of steroid-resistant patients remains an open question. reduction in anti-AChR antibodies, suggesting an effect on
nonantibody functions, such as antigen presentation and pro-
POSSIBLE FUTURE THERAPEUTIC OPTIONS inflammatory cytokine secretion. Although most treated patients
have been anti-AChR antibody positive, benefit has also been
Many possible experimental avenues of investigation that have observed in anti-MuSK-positive/anti-AChR antibody–negative
been opened by studies in EAMG. These are aimed at interrupting patients, in whom longstanding remission has been seen in
the sensitization process of helper CD4 T cells, interrupting their association with reduction of anti-MuSK antibody titers. A
effector function, or interdicting the action of downstream controlled clinical trial of rituximab in anti-AChR–associated
proinflammatory molecules. Studies directed at CD4 T cells MG is currently underway. A number of other mAbs directed
include impeding their activation by inhibitors of the costimula- at CD20, including fully humanized ones, are under study in
tory molecules CD28 and ICOS and the induction of anergy or other autoimmune diseases and will likely attract attention with
34
apoptosis of AChR-reactive T cells. In addition, inhibition of regard to MG.
factors that contribute to AChR antibody production, and against
which monoclonal antibodies (mAbs) are now available for CONCLUSIONS
human use, make this approach possible and, in some cases, are
now under clinical trials. This includes agents that abrogate the MG is a prototypic autoimmune disease in which the autoantigen/s
action of IL-6, IL-17, and BAFF. Additional studies directed at are well defined as are the mechanisms that mediate dysfunction
AChR-specific B cells include the use of AChR/Fcγ fusion proteins of the target tissue, skeletal muscle. EAMG, in which many of
to induce apoptosis of AChR-specific B cells by cross-linking the features of MG are faithfully recapitulated, has provided a
their B-cell AChR receptors and inhibitory FcγRIIb receptors. useful vehicle for elucidating the immunoregulatory abnormalities
In addition, non–cross-linking IgG4 anti-AChR antibodies have that underlie the pathogenesis of the human disease, and the

CHAPtER 65 Myasthenia Gravis 889



ON tHE HORIZON 11. Engel AG, Sahashi K, Fumagalli G. The immunopathology of acquired
myasthenia gravis. Ann NY Acad Sci 1981;377:158.
Development of Immunomodulatory Therapies 12. Drachman DB, Angus CW, Adams RN, et al. Myasthenic antibodies
cross-link acetylcholine receptors to accelerate degradation. N Engl J Med
• Complement inhibitors 1978;298:1116.
• Newly developed B-cell lineage inhibitors, including anti–plasma cell 13. Richman DP, Wollmann RL, Maselli RA, et al. Effector mechanisms of
monoclonal antibodies
• Acetylcholine receptor (AChR)–Fc fusion molecules myasthenic antibodies. Ann NY Acad Sci 1993;681:264.
• Inhibitors that target key immunopathogenic cytokines 14. Conti-Fine B, Navaneetham D, Karachunski PI, et al. T cell recognition
• AChR-specific immunosuppression of the acetylcholine receptor in myasthenia gravis. Ann NY Acad Sci
1998;841:283.
15. Patrick J, Lindstrom J. Autoimmune response to acetylcholine receptor.
Science 1973;180:871.
16. Christadoss P, Poussin M, Deng C. Animal models of myasthenia gravis.
development of novel therapies for use in the humans. MG Clin Immunol 2000;94:75.
occupies a unique position in the pantheon of autoimmune 17. Bellone M, Ostile N, Lei S, et al. Experimental myasthenia gravis in
diseases because of its strong association with thymic pathology. congenic mice. Sequence mapping and H-2 restriction of T helper
epitopes on the α subunits of Torpedo californica and murine
In MG-associated thymic hyperplasia, thymic events, particularly acetylcholine receptors. Eur J Immunol 1991;21:2303.
those leading to antecedent inflammation within the medulla, 18. Karachunski PI, Ostlie NS, Okita DK, et al. Interleukin-4 deficiency
likely serve as a driving force behind the development of the facilitates development of experimental myasthenia gravis and precludes
autoimmune process. Indeed, the overarching idea that tolerance its prevention by nasal administration of CD4+ epitope sequences of the
is breached in the thymus may be viewed as antithetical, given acetylcholine receptor. J Neuroimmunol 1999;95:73.
the established and critical role this organ plays in T-cell central 19. Wang W, Milani F, Ostlie G, et al. C57BL/6 mice genetically deficient in
tolerance. Unravelling the link between the thymus and MG will IL-12/IL-23 and IFN-γ are susceptible to experimental autoimmune
require further study. However, in the meantime, we can expect myasthenia gravis, suggesting a pathogenic role of non-Th1 cells.
that continued exploration of immune perturbations and their J Immunol 2007;178:7072.
underlying molecular mechanisms in animals with EAMG and 20. Schaffert H, Pelz A, Saxena A, et al. IL-17-producing CD4(+) T cells
contribute to the loss of B-cell tolerance in experimental autoimmune
in patients with MG will lead to safer and more robust therapeutic myasthenia gravis. Eur J Immunol 2015;45:1339.
interventions. 21. Levinson AI, Wheatley LM. The thymus and the pathogenesis of
myasthenia gravis. Clin Immunol Immunopathol 1995;78:1.
ACKNOWLEDGMENT 22. Berrih-Aknin S, Lepanse R. Myasthenia gravis: a comprehensive review
of immune dysregulation and etiological mechanisms. J Autoimmun
This work was supported by National Institutes of Health (NIH) 2014;52:90.
grant NS19546. 23. Marx A, Pfister F, Schalke B, et al. The different roles of the thymus in the
pathogenesis of the various myasthenia gravis subtypes. Autoimmunity
Please check your eBook at https://expertconsult.inkling.com/ Rev 2013;12:875.
for self-assessment questions. See inside cover for registration 24. Levinson AI, Zheng Y, Gaulton G, et al. Intrathymic expression of
neuromuscular acetylcholine receptors and the immunopathogenesis of
details. myasthenia gravis. Immunol Res 2003;27:399.
25. Wolfe GI, Kaminski HJ, Aban IB, et al. Randomized trial of thymectomy
REFERENCES in myasthenia gravis. N Engl J Med 2016;375:511–22.
26. Levinson AI. Modeling the intrathymic pathogenesis of myasthenia
1. Lisak RP, Barchi RL. Myasthenia gravis. In: Walton JN, editor. Major gravis. J Neurolog Sci 2013;333:60.
problems in neurology, vol. 11. Philadelphia, PA: WB Saunders; 1982. 27. Chuang WY, Strobel P, Belharazem D, et al. The PTPN22gain-of-
p. 5. function+1858T(+) genotypes correlate with low IL-2 expression in
2. Engel A. The investigation of congenital myasthenic syndromes. Ann NY thymomas and predispose to myasthenia gravis. Genes Immun
Acad Sci 1993;681:425. 2009;10:667.
3. Levinson AI, Zweiman B, Lisak RP. Immunopathogenesis and treatment 28. Greve B, Hoffmann P, Illes Z, et al. The autoimmunity-related
of myasthenia gravis. J Clin Immunol 1987;7:187. polymorphism PTPN22 1858C/T is associated with anti-titin
4. Tindal RSA. Humoral immunity in myasthenia gravis: biochemical antibody-positive myasthenia gravis. Hum Immunol 2009;70:540.
characterization of acquired anti-receptor antibodies and clinical 29. Stefansson K, Dieperink ME, Richman DP, et al. Sharing of epitopes by
correlations. Ann Neurol 1981;10:437. bacteria and the nicotinic acetylcholine receptor: a possible role in the
5. Papadouli I, Sakarellos C, Tzartos SJ. High-resolution epitope mapping pathogenesis of myasthenia gravis. Ann NY Acad Sci 1987;505:451.
and fine antigenic characterization of the main immunogenic region of 30. Schwimmbeck PL, Dyrberg T, Drachman DB, et al. Molecular mimicry
the acetylcholine receptor. Eur J Biochem 1993;211:227. and myasthenia gravis: an autoantigenic site of the acetylcholine receptor
6. Leite MI, Jacob S, Viegas S, et al. IgG1 antibodies to acetylcholine α-subunit that has biologic activity and reacts immunochemically with
receptors in “seronegative” myasthenia gravis. Brain 2008;131:1940. herpes simplex virus. J Clin Invest 1989;84:1174.
7. Levinson AI, Lisak RP. Myasthenia gravis. In: Detrick B, Schmitz J, 31. Dwyer DS, Vakil M, Bradleg RT, et al. A possible cause of myasthenia
Hamilton RG, editors. Manual of molecular and clinical laboratory gravis: idiotypic networks involving bacterial antigens. Ann NY Acad Sci
immunology. 8th ed, ASM Press, 2016. 1987;505:461.
8. Sanders DB, Juel VC. MuSK-antibody positive myasthenia gravis: 32. Bever CT Jr, Chang HW, Penn AS, et al. Chemical alteration of
questions from the clinic. J Neuroimmunol 2008;201-202:85. acetylcholine receptor by penicillamine: a mechanism for induction of
9. Arrli JA, Skeie GO, Mygand A, et al. Muscle striation antibodies in myasthenia gravis. Neurology 1982;32:1077.
myasthenia gravis. Ann NY Acad Sci 1998;841:505. 33. Penn A, Jacques JJ. Cells from mice exposed chronically to
10. Drachman DB, Adams RN, Josifek LF, et al. Antibody-mediated D-penicillamine show proliferative responses to D-penicillamine-treated
mechanisms of ACh receptor loss in myasthenia gravis: clinical relevance. self (macrophage/dendritic cells): a graft-versus-host response? Ann NY
Ann NY Acad Sci 1981;377:175. Acad Sci 1993;681:319.

890 PARt SEVEN Organ-Specific Inflammatory Disease


34. Guptill JT, Soni M, Meriggioli MN. Current treatment, emergent 41. Miller RG, Barohn RJ, Dubinsky R. Expanding the evidence base for
translational therapies, and new therapeutic targets for autoimmune therapeutics in myasthenia gravis. Ann Neurol 2010;68:776.
myasthenia gravis. Neurother 2016;13:118. 42. Sanders DB, Evoli A. Immunosuppressive therapies in myasthenia gravis.
35. Kumar V, Kaminski HJ. Treatment of myasthenia gravis. Curr Neurol Autoimmunity 2010;43:428.
Neurosci Rep 2011;11:89. 43. Palace J, Newsom-Davis J, Lecky B. A randomized double-blind trial of
36. Olanow CW, Wechsler AS, Sirotkin-Roses M, et al. Thymectomy as prednisolone alone or with azathioprine in myasthenia gravis. Myasthenia
primary therapy in myasthenia gravis. Ann NY Acad Sci 1987;505: Gravis Study Group. Neurology 1998;50:1778.
595. 44. Sanders DB, Hart IK, Mantegazza R, et al. An international, phase III,
37. Sonnett JR, Jaretzki A III. Thymectomy for Nonthymomatous Myasthenia randomized trial of mycophenylate mofetil in myasthenia gravis.
gravis: a critical analysis. Ann NY Acad Sci 2008;1132:315. Neurology 2008;71:400.
38. Johns TR. Long-term corticosteroid treatment of myasthenia gravis. Ann 45. The Muscle Study Group. A trial of mycophenylate mofetil with
NY Acad Sci 1987;505:568. prednisone as initial immunotherapy in myasthenia gravis. Neurology
39. Schneider-Gold C, Gadjos P, Toyka K, et al. Corticosteroids for 2008;71:394.
myasthenia gravis. Cochrane Database Syst Rev 2005;(18):CD002828. 46. Luo J, Lindstrom J. AChR-specific immunosuppressive therapy of
40. Seybold M. Plasmapheresis in myasthenia gravis. Ann NY Acad Sci myasthenia gravis. Biochem Pharmacol 2015;97:609.
1987;505:58.

CHAPtER 65 Myasthenia Gravis 890.e1


MUL t IPLE-CHOICE QUES t IONS

1. The most frequent pathogenic autoantibodies found in patients 3. A 35-year-old man presented with diplopia, difficulty swal-
with myasthenia gravis (MG) are specific for a conformational lowing, and weakness in his upper and lower extremities. On
epitope on which subunit of the neuromuscular acetylcholine laboratory testing of his serum, he was found to have elevated
receptor? titers of anti–acetylcholine receptor antibodies and antistria-
A. α tional antibodies. He underwent thymectomy, which very
B. β likely showed which of the following pathologies?
C. δ A. Germinal center hyperplasia
D. ε B. Thymic atrophy
C. Cortical thymoma
2. Patients with MG whose serum is positive for anti- muscle-
specific tyrosine kinase (MuSK) antibodies are most resistant D. Medullary lymphoma
to treatment with which one of the following modalities? 4. An inflammatory process in which of the following anatomical
A. Corticosteroid locales is considered to initiate the development of MG?
B. Intravenous immunoglobulin A. Skeletal muscle
C. Plasmapheresis B. Thymic cortex
D. Pyridostigmine bromide C. Cervical lymph node
D. Thymic medulla

66









Multiple Sclerosis



Benjamin M. Segal







Multiple sclerosis (MS), a chronic inflammatory demyelinating imbalance, tremor, and/or double vision. Serial MRI studies have
disorder of the central nervous system (CNS), is the most frequent demonstrated that the majority of MS lesions are actually clinically
cause of nontraumatic neurological disability among young adults silent. This is not surprising considering the abundance of
in the Western Hemisphere. Although MS is widely considered redundant nerve fiber tracts in the CNS and the commitment
a disease of North America and Europe, there is increasing of large areas of cerebral white matter to subtle personality traits
evidence that it is more common in other regions of the world, and cognitive skills. Consequently, CNS tissue damage may be
including Asia and the Middle East, than previously appreciated. inflicted surreptitiously during clinical remissions, making MRI
The median age at presentation is 28–31 years, which is, in part, a more sensitive indicator of disease activity compared with the
responsible for the disproportionately high social and economic history or the results of neurological examination (see Fig. 66.1).
tolls of the disease. Furthermore, the incidence of MS is increasing Patients with MS often recover function following a clinical
for unknown reasons. Fortunately there have been dramatic relapse, either partially or fully, particularly during the early
advances in the treatment of relapsing forms of MS over the clinical course. However, old symptoms can temporarily reemerge
past 20 years, spurred by the introduction of 14 disease-modifying when the core body temperature is elevated as a result of infection
agents (DMAs); and more are actively under development. These or strenuous exercise. This unmasking of latent deficits, referred
drugs significantly decrease the risk of relapse and lesion forma- to as the Uhthoff phenomenon, is a consequence of the physiologi-
tion. Consequently, the implications of being diagnosed with cal slowing of axon signal propagation that normally occurs at
relapsing-remitting MS have changed considerably in the span high core body temperatures. In healthy individuals, the degree
of a generation. Despite this success, significant challenges persist. of slowing has no clinical consequence, but in MS patients, it
There is a dire need for treatments that slow, or even halt, disability may precipitate the decompensation of white matter tracts already
accumulation in patients with progressive forms of MS, and for compromised by demyelination and axonal drop-out.
interventions that restore lost neurological functions across MS
subsets. Secondary Progressive MS (SPMS)
During the course of RRMS, relapses decrease in frequency
CLINICAL SUBSETS AND PHENOMENOLOGY over time and sometimes disappear completely. However, in
the vast majority of cases, they are replaced by an insidious,
Relapsing-Remitting MS (RRMS) gradual accumulation of disability, referred to as the secondary
In the majority of cases (85–90%), MS presents with a relapsing- progressive (SP) stage. The symptoms and signs that character-
remitting course, characterized by discrete episodes of neurological ize neurological decline during SPMS are diverse. Progressive
dysfunction (relapses or exacerbations) separated by clinically myelopathy, hemiparesis, and/or gait imbalance are common.
quiescent periods (remissions). The frequency of relapses can Subcortical dementia is increasingly recognized as a feature of
vary widely among patients as well as during different periods the disease. Longitudinal natural history studies conducted before
in an individual patient’s disease course. At present no clinical DMAs were widely available found that the majority of patients
features or biomarkers that are predictive of relapse rate have with RRMS transitioned to the SP stage within 10–20 years of
been identified. The signs and symptoms that occur during the initial presentation of disease. An epidemiological study of
relapses are also diverse and unpredictable, since lesions can MS patients in British Columbia, published in 2010, found that
1
form at literally any site in the CNS, spanning the cerebrum, the median time to SPMS onset was 21.4 years. A number of
brainstem, cerebellum, optic nerves, and spinal cord. By definition, factors, including male gender, the presence of motor symptoms
the peripheral nervous system is spared. at clinical onset, and a history of poor recovery from relapses,
MS lesions are readily visualized in CNS white matter via are associated with both a shorter time to, and younger age
magnetic resonance imaging (MRI) (Fig. 66.1). Symptomatic at, evolution to SPMS. It has not been definitively determined
lesions generally occur in locations where nerve fibers converge whether optimal management of RRMS with the use of DMAs can
to subserve a common function. Hence, typical presentations delay, or even prevent, the onset of SPMS. Previous longitudinal
of RRMS include optic neuritis with monocular visual deficits observational and retrospective cohort studies that investigated
(secondary to lesions in the optic nerve), myelitis with weakness whether treatment with first-generation DMAs alters the time
and numbness in the extremities, sometimes accompanied by to reach SPMS yielded conflicting results. However, a recent
incontinence (caused by spinal cord lesions), and brainstem prospective study of 517 actively treated patients found that
syndromes manifesting as slurred speech, swallowing difficulties, rates of worsening and evolution to SPMS were substantially

891

892 Part Seven Organ-Specific Inflammatory Disease


that, analogous to SPMS, acute inflammatory lesions form during
early stages of PPMS, prior to overt clinical progression, but
happen to arise exclusively in clinically silent areas. Conversely,
some investigators have argued that PPMS is a distinct disease
entity driven primarily by neurodegenerative processes from its
3
inception. This viewpoint is supported by the general failure
8
of immunomodulatory agents to attenuate the course of PPMS.
Conversely, in a randomized double-blind placebo-controlled
trial, treatment with a B cell–depleting monoclonal antibody
(mAb) delayed disability progression in a subset of patients with
9
PPMS who were younger and/or had inflammatory lesions.
Collectively, these findings suggest that the pathogenesis of PPMS
is multifaceted and heterogeneous and that the relative contribu-
tion of inflammation and neurodegeneration to clinical outcomes
A B varies among patients.
FIG 66.1 (A) T2-weighted fluid-attenuated inversion recovery
(FLAIR) magnetic resonance imaging (MRI) scan of the brain of CLInICaL PearLS
a patient with multiple sclerosis (MS) showing hyperintense Clinical Features of MS
lesions located in the periventricular and subcortical white matter.
(B) T1-weighted MRI scan showing T1-black holes (arrows), In the majority of cases (80–85%), multiple sclerosis (MS) presents with
indicative of profound axonal loss, and generalized atrophy with a relapsing-remitting course.
enlarged ventricles. • The symptoms and signs experienced by patients with MS are diverse
because lesions can form at any site in the central nervous system
(CNS), including the optic nerves, cerebrum, brainstem, and spinal
cord.
• The rate, severity, and symptoms of relapses are highly variable and
unpredictable.
lower when compared with the findings of earlier natural history • Most MS lesions form silently; magnetic resonance imaging (MRI) is
studies of untreated patients. 2 a more sensitive tool to gauge disease activity compared with history
The cellular and molecular mechanisms underlying the or neurological examination.
conversion from the RR stage to the SP stage are poorly under- • Acute relapses tend to decrease in frequency over time and are typically
stood. Some investigators have questioned the relevance of replaced by a gradual accumulation of disability. This later phase of
neuroinflammation during the SP stage and have posited neu- disease is referred to as secondary progressive MS (SPMS).
rodegeneration as being primarily responsible for the clinical
deterioration that ensues (in the form of neuronal death, DIAGNOSIS
mitochondrial dysfunction in axons, Wallerian degeneration,
3
and gliosis). Conversely, there is evidence of persistent immune The most widely used guideline for diagnosing MS is the
dysregulation in SPMS, although it may differ from RRMS with McDonald criteria, originally proposed by the International Panel
regard to the cytokine networks and leukocyte subsets involved, on Diagnosis of Multiple Sclerosis in 2001 and subsequently
4-6
10
as well as the distribution of infiltrating cells within the CNS. revised in 2005 and 2010 (Table 66.1). RRMS is, by definition,
Nonetheless, DMAs that are therapeutically beneficial in RRMS a dynamic multifocal inflammatory demyelinating disease of the
have generally not been found to be effective in slowing disability CNS. Therefore the demonstration of lesion dissemination in time
7
accumulation in SPMS. At present, the management of SPMS and space is crucial for its diagnosis. The criteria for dissemination
involves alleviation of symptoms, optimization of residual func- in time can be satisfied by ≥2 distinct clinical exacerbations, by
tions, and prevention of complications. one exacerbation followed by the interval appearance of a new
lesion on serial MRI scans, or by the simultaneous presence of
Primary Progressive MS (PPMS) asymptomatic gadolinium-enhancing (i.e., acute inflammatory)
PPMS is distinguished from SPMS by the absence of an antecedent and nonenhancing MRI lesions at any time. Dissemination in
RR phase. Otherwise, the clinical features of SPMS and PPMS space can be demonstrated by objective clinical evidence of
can be indistinguishable. The most common clinical phenotype involvement of ≥2 sites in the CNS (based on the neurologi-
is spastic paraparesis, followed by cerebellar dysfunction and cal examination and/or delayed latencies on evoked potential
hemiplegia. However, there are striking demographic differences testing) or by the presence of T2-weighted MRI lesions in at
between PPMS and RRMS/SPMS. PPMS tends to present at an least two of the following areas: periventricular, juxtacortical,
older age (peaking in the fifth and sixth decades) compared with and infratentorial, cerebral white matter or spinal cord. In the
RRMS (which peaks in the third and fourth decades). Further- latest iteration of the McDonald criteria, an MS exacerbation is
more, RRMS occurs 2–3 times more frequently in females than defined as “patient-reported symptoms or objectively observed
in males, whereas in PPMS the gender ratio is closer to 50 : 50. signs typical of an acute inflammatory demyelinating event
Some investigators have noted that the neuropathological and in the CNS, current or historical, with duration of at least 24
radiological features of PPMS overlap extensively with those of hours, in the absence of fever or infection.” There are no clinical
SPMS, leading them to conclude that PPMS and SPMS belong features or biomarkers that are pathognomonic for MS. Therefore
to the same disease spectrum. In support of that viewpoint, it is essential to rule out competing diagnoses. The presence
familial clusters of MS that include some members with PPMS of unique oligoclonal bands and/or elevated immunoglobulin
and others with RR/SPMS have been described. It is possible G (IgG) index in the cerebrospinal fluid (CSF), indicative of

CHaPter 66 Multiple Sclerosis 893



TABLE 66.1 McDonald 2010 Criteria for (ii) at least two T2 spinal cord lesions; and (iii) positive CSF
the Diagnosis of Multiple Sclerosis findings, defined as the presence of oligoclonal bands or elevated
IgG index.
additional Data needed for an
Clinical Presentation MS Diagnosis RISK FACTORS
≥ 2 attacks; objective clinical None
evidence of ≥ 2 lesions or Genetic Risk Factors
objective clinical evidence A monozygotic twin whose cotwin has MS has a 20–30% risk
of 1 lesion with of developing the disease, whereas the corresponding risk for a
reasonable historical dizygotic twin is 2–5%. In contrast, the incidence of MS in the
11
evidence of a prior attack
≥ 2 attacks; objective clinical Dissemination in space demonstrated general population is approximately 0.1%. Hence, the risk of
evidence of 1 lesion by ≥ 1 T2 lesion in at least 2 or 4 MS drops with increasing genetic distance, suggesting that genes
MS-typical regions (periventricular, play a significant role in determining MS susceptibility. The
juxtacortical, infratentorial, or spinal human leukocyte antigen (HLA) region represents the strongest
cord) MS susceptibility locus, genome wide, and has been implicated
1 attack; objective clinical Simultaneous presence of in all ethnic populations thus far studied. It accounts for up to
evidence of ≥ 2 lesions asymptomatic gadolinium-enhancing 10.5% of genetic variance underlying risk. The primary signal
12
and nonenhancing lesions at any
time; or a new T2 and/or gadolinium- maps to the HLA-DRB1 gene in the class II segment of the locus,
enhancing lesion(s) on follow-up MRI, implicating a role of CD4 T-cell responses in MS pathogenesis.
irrespective of its timing with Genome-wide association studies (GWAS) have revealed over
reference to a baseline scan; or 100 non-HLA susceptibility loci, each of which contributes a
Await a second clinical attack small amount to MS risk. Strikingly, most of these map to regions
1 attack; objective clinical Dissemination in space and time, containing genes implicated in immunological, rather than
evidence of 1 lesion demonstrated by:
(clinically isolated For DIS: neuronal or glial, pathways. Genes involved in T-helper (Th)–cell
syndrome) ≥ 1 T2 lesion in at least 2 of 4 differentiation are overrepresented, including the interleukin-2
MS-typical regions of the CNS (IL-2) receptor α chain and the IL-7 α chain, which modulate
(periventricular, juxtacortical, T-cell proliferation and survival. Over one-third of the MS
infratentorial, or spinal cord); or Await susceptibility loci overlap with regions previously identified in
a second clinical attack implicating a GWAS of other autoimmune diseases, including celiac disease,
different CNS site; and For DIT: type 1 diabetes, rheumatoid arthritis, and/or inflammatory bowel
Simultaneous presence of
asymptomatic gadolinium-enhancing disease. Together these data provide support for a primary
and nonenhancing lesions at any immunological, as opposed to neurodegenerative, etiology of
time; or A new T2 and/or gadolinium- MS. An unresolved question is whether genetic variants affect
enhancing lesion(s) on follow-up MRI, the clinical course of RRMS, including such features as relapse
irrespective of its timing with rate or severity and time to conversion to the SP stage. Genetic
reference to a baseline scan; or variants that are predictive of responsiveness to DMAs have yet
Await a second clinical attack
Insidious neurological 1 year of disease progression to be identified. A growing area of interest that warrants further
progression suggestive of (retrospectively or prospectively investigation is the potential impact of epigenetic modifications
MS (PPMS) determined) plus 2 of 3 of the in different cell types on MS susceptibility, clinical course, and/
following criteria: or therapeutic responsiveness.
1. Evidence for DIS in the brain
based on ≥ 1 T2 lesions in the Environmental Risk Factors
MS-characteristic (periventricular,
juxtacortical, or infratentorial) As mentioned above, twin concordance rates in MS have been
regions used to highlight the importance of heredity in MS susceptibility.
2. Evidence for DIS in the spinal Paradoxically, the same data can be used to argue for the impor-
cord based on ≥ 2 T2 lesions in tance of environmental influences. Hence, over 70% of mono-
the cord zygotic twins of individuals with MS do not develop the disease.
3. Positive CSF (isoelectric focusing Despite arduous attempts, no convincing evidence has been
evidence of oligoclonal bands produced for genetic, epigenetic, or transcriptome differences
and/or elevated IgGindex) 13
that explain MS discordance among monozygotic twin pairs.
From Polman CH, Reingold SC, Banwell B, et al. Diagnostic criteria for multiple The risk of MS appears to be predicated on a complex interplay
sclerosis: 2010 revisions to the McDonald criteria. Ann Neurol 2011; 69(2): 292–302. between genetic and environmental factors.

Geographic Prevalence Patterns
primary antibody production in the CNS, supports a diagnosis One of the most convincing illustrations of the impact of the
of MS, but those findings are observed in a wide range of environment on the development of MS is its geographical
neuroinflammatory conditions, including subacute sclerosing distribution. The prevalence of MS is highest in the Scandinavian
panencephalitis, neurosarcoidosis, Lyme disease, and systemic countries, Canada, and Scotland and lowest in the equatorial
lupus erythematosus (SLE) with CNS involvement. A diagnosis regions. Kurtzke et al. were the first to notice a latitudinal gradient
of PPMS requires 1 year of disease progression plus two of the in the prevalence of MS across the United States, with the disease
three following criteria: (i) at least one T2 lesion in the peri- being most common in the Northern states and gradually declin-
14
ventricular, juxtacortical, or infratentorial cerebral white matter; ing toward the South. Similar latitudinal gradients have been

894 Part Seven Organ-Specific Inflammatory Disease


observed in Europe, Australasia, and Japan. Population migration Although infectious agents, such as EBV, have been implicated
studies indicate that the geographical risk of MS is established in MS pathogenesis, other pathogens may have a therapeutic
prior to adolescence. Prepubescent children who migrate assume effect. It has been suggested that in addition to high levels of
the risk of their adopted country, whereas adults carry forward sunlight exposure, endemic helminth infection is one of the
the risk of the location where they spent their childhood. An factors responsible for the low prevalence of MS in tropical
environmental agent that is encountered in childhood and acts as regions. Infection with helminths, including Heligmosomoides
predisposing factor for the development of MS later in life must polygyrus, Fasciola hepatica, Schistosoma mansoni, and Trichinella,
21
be responsible, but this agent has yet to be definitely identified. has been shown to be protective in animal models of MS.
Several small prospective studies showed that patients with MS
Vitamin D naturally infected with different species of parasitic worms had
The discovery of the protective role of vitamin D in MS may a milder disease course and lower MRI inflammatory activity
22
explain, in part, its geographical distribution. Ultraviolet light compared with uninfected patients. Antiparasite treatment
catalyzes the conversion of vitamin D to its bioactive form, and the was associated with exacerbation of MS. Mechanistic substud-
prevalence of MS is highest in regions with relatively low annual ies have suggested that parasites modulate MS disease activity
sunlight exposure. In a large prospective study, the risk of MS by boosting the frequency of IL-10 and transforming growth
15
decreased with increasing serum levels of 25-hydroxyvitamin D. factor-beta (TGF-β)–producing regulatory T and/or B cells. A
Therefore interventions that raise the level of 25-hydroxyvitamin phase I safety study of orally administered Trichuris suis ova
D levels might have a prophylactic protective effect on healthy (TSO) has been conducted in RRMS, and a number of clinical
individuals who are predisposed to develop MS, such as the trials of TSO or dermally administrated hookworm Necator
first-degree relatives of patients with MS. Indeed, numerous americanus as disease-modifying therapy in MS are planned or
independent prospective studies have found an inverse relationship underway.
between dietary or supplemental vitamin D intake in adults and
future risk of MS. Furthermore, there is accumulating evidence Obesity
that low serum 25-hydroxyvitamin D levels and low dietary Observational studies have found that individuals who are obese
vitamin D intake during pregnancy increase the risk of MS in in early adulthood, as measured by elevated body mass index
16
23
the offspring. Whether vitamin D levels influence the clinical (BMI), have an approximately twofold increased risk of MS.
course of individuals with established MS is more controversial. Obesity in girls is associated with an increased risk of pediatric
24
A randomized controlled trial of vitamin D supplementation in MS or clinically isolated syndrome. Furthermore, higher weight
patients with MS is currently underway in 16 academic centers in adolescence and young adulthood is associated with an earlier
(ClinicalTrials.gov identifier: NCT01490502). The results of that age at onset of MS. A mendelian randomization analysis of large
trial should bring clarity to the issue. GWAS for MS and BMI, respectively, found that one standard
deviation (SD) increase in genetically determined BMI conferred
Infection a 41% increase in the odds of MS. A number of theories have
25
In addition to low levels of vitamin D, another prognostic factor been proposed for a mechanistic link between obesity and MS
for development of MS is primary infection with Epstein-Barr risk. First, obesity is known to cause a systemic proinflamma-
virus (EBV) in adulthood, as indicated by the emergence of tory state, possibly mediated by an adipose-derived hormone
EBV-specific IgM antibodies in serum. Analysis of serial serum that could create a milieu conducive to the differentiation
samples stored in the US Department of Defense Serum Reposi- and/or activation of autoimmune effector cells. Alternatively,
tory revealed that MS risk was extremely low among individuals there is some evidence that genetically elevated BMI decreases
not infected with EBV but increased sharply in the same individu- 25-hydroxyvitamin D levels.
als following seroconversion to positivity for antibodies against
17
EBV. The odds of MS were recently estimated to be >10 times Modifiable Habits
higher among EBV-positive persons than among EBV-negative A substantial body of literature indicates that cigarette smoking
18
persons. One way in which EBV infection could promote MS increases the risk of MS. A recent meta-analysis revealed a dose–
26
pathogenesis is via “molecular mimicry,” which occurs when a response relationship between cigarette pack-years and MS risk.
microbial epitope shares sequence similarities with a self peptide, On the basis of data collected from the Swedish National MS
in this case a myelin peptide (Chapter 50). T-cell receptors Registry, it was estimated that each additional year of smoking
(TCRs) that cross-react with structurally homologous EBV and after diagnosis accelerates the time to conversion to SPMS by
27
myelin antigens have been discovered in the peripheral CD4 4.7%. There is growing evidence that exposure to passive
19
TCR repertoire of individuals with MS. Peripheral CD4 T cells smoking is also a risk factor for MS. Acrolein, a component of
that express such cross-reactive TCRs could be activated during cigarette smoke, was found to exacerbate the clinical course of
EBV infection, enabling them to cross the blood–brain barrier an animal model of MS, in association with enhanced microglial
(BBB), encounter their cognate myelin antigen within CNS white activation. 28
matter, and initiate MS lesion formation. An alternative theory Another behavior that has come under scrutiny in relationship
involves infiltration of the CNS by EBV-infected B cells. B cells to MS is dietary sodium intake. In one study, exacerbation rates
expressing EBV small RNA and proteins have been detected in were found to be 2.75–3.95-fold higher in patients with RRMS
meningeal follicle–like structures and inflamed cortical lesions with medium or high sodium intakes, respectively, compared
29
20
in SPMS brain tissue. EBV-driven expansion and activation of with the low-intake group. In contrast, high salt intake was
meningeal B cells could potentially contribute to the formation not associated with decreased time to relapse in pediatric-onset
30
of the follicle-like structures, which have been associated with MS. High-salt conditions promote the induction of highly
large subpial cortical lesions and a more aggressive clinical pathogenic myelin-reactive T cells in vitro and in animal models
course. 6 in vivo. 31

CHaPter 66 Multiple Sclerosis 895



Sex Hormones
MS relapse rates decline during pregnancy, particularly in the
third trimester, and rebound in the first 3 months post partum
before returning to the prepregnancy rate. This has led to the
hypothesis that certain female sex hormones may play a protective
role in RRMS. Estriol is an estrogen unique to pregnancy. It is
synthesized by the fetoplacental unit and reaches its highest levels
in the last trimester. A randomized, double-blinded, placebo-
controlled phase II trial of estriol in combination with glatiramer
acetate (GA) versus placebo plus GA showed a reduction in the
32
annualized relapse rate at 2 years in the estriol-treated group.
Animal model studies have indicated that estrogens, including
estriol, have antiinflammatory and neuroprotective effects through
engagement of the estrogen receptors expressed on leukocytes
and CNS resident cells, respectively.
Testosterone has neuroprotective effects in animal models of
MS, and decreased testosterone levels in males with MS were
33
reported to be associated with disability. In a small, open-label,
phase II clinical trial, testosterone treatment appeared to arrest
loss of gray matter (and even to reverse atrophy of gray matter
in the right frontal cortex), as quantified by using voxel-based FIG 66.2 A post-gadolinium T1-weighed magnetic resonance
morphology, in 10 male patients with MS. 34
imaging (MRI) scan of the brain showing Dawson fingers (arrows).
KeY COnCePtS
Risk Factors and “chronic silent,” or inactive. Chronic active plaques are
distinguished by a rim of activated microglia and deposits of
The risk of multiple sclerosis (MS) is determined by a combination of complement at the lesion edge, surrounding a hypocellular and
genetic and environmental factors.
• The majority of MS susceptibility loci map to regions containing genes gliotic core. They are slowly expansive as a consequence of active
implicated in immunological pathways, including human leukocyte demyelination at the lesion edge. In contrast, chronic silent plaques
antigen (HLA) class II molecules, the interleukin-2 (IL-2) receptor, and have a sharp border. Other characteristics of silent plaques include
the IL-17 receptor. prominent loss of oligodendrocytes and axons, pronounced
• Relapse rates decline during the third trimester of pregnancy, in astrogliosis, and a paucity of macrophages and activated microglia.
association with high serum levels of estriol. Immunopathological changes in the so-called normal-appearing
• Environmental risk factors include low vitamin D levels, exposure to
the Epstein-Barr virus (EBV) in adulthood, cigarette smoking, and white matter (NAWM), outside of plaques, are pervasive in
childhood obesity. progressive MS but have also been observed in RRMS. These
changes consist of diffuse axonal injury and microglial activation,
as well as scattered lymphocytes.
PATHOLOGICAL FEATURES OF MS MS is widely classified as a demyelinating disorder. The reason
is that a large number of the nerve fiber segments traversing
White Matter Lesions plaques demonstrate myelin loss with relative axonal sparing.
The hallmark of MS pathology is the focal demyelinated lesion, However, it is now recognized that axonopathy also occurs and
or “plaque,” present in the white matter of the optic nerves, is, in fact, an early and prominent feature of acute MS lesions.
brain, and spinal cord. Acute lesions are invariably associated Axonal damage results in dysmorphic mitochondria, focal swell-
with focal breakdown of the BBB and perivascular inflammatory ings, fragmentation, and frank transections with terminal bulbs
infiltrates. MS infiltrates are dominated by T cells (with a relatively at the stumps. Mitochondrial abnormalities and focal swelling
high CD8/CD4 ratio) and myeloid cells (blood-derived monocytes/ have been observed in fully myelinated axons within MS lesions,
35
macrophages and activated microglia). Macrophages/monocytes suggesting that they can occur independent of demyelination.
and activated microglia are spatially associated with disintegrating In animal models of MS, axons with abnormal mitochondria are
myelin sheaths, and they actively take up myelin debris. Apoptosis restricted to areas of immune infiltration, and progressive axonal
35
and loss of oligodendrocytes vary widely among lesions. Frequent changes correlate with the density of infiltrates. Hence, it is likely
sites of lesion formation include subcortical and periventricular that the axonal damage is directly mediated by direct contact with
cerebral white matter, middle cerebellar peduncles, and the inflammatory cells. Although demyelination can be reversed to
posterior columns of the cervicothoracic spinal cord. In the brain, some extent by remyelination, axonal transection is irreversible.
infiltrates frequently follow the course of pericallosal venules, Clinicopathological investigations have found that permanent
resulting in “Dawson fingers,” which are oblong lesions oriented motor disability in MS correlates with loss of corticospinal tract
perpendicular to the long axes of the lateral ventricles (Fig. 66.2). axons more so than with degree of demyelination.
Classic actively demyelinating plaques are primarily seen
during the RR stage of disease and generally decrease in frequency Gray Matter Lesions
with increasing disease duration. Lesions more typical of progres- MS was traditionally considered a white matter disease. It is now
sive forms of MS have been termed “chronic active,” or smoldering, established that the gray matter is affected as well. Three types

896 Part Seven Organ-Specific Inflammatory Disease


of cortical lesions have been described: leukocortical (which span
gray and white matter), intracortical, and subpial. All of these
lesions show demyelination and oligodendrocyte loss, microglial
activation, neuritic transections, neuronal death, and reduced
presynaptic terminals. Subpial lesions are the most common.
They can cover long distances of the cortical ribbon and usually
extend to the cortical layer III or IV. Cortical lesions are not
visible on conventional MRI scans and require special staining
to be appreciated in CNS tissue sections. This explains why they
were not recognized as common features of MS until recently.
In fact, cortical demyelination and gray matter atrophy are evident
from the earliest stages of disease, even before a clinically definite
diagnosis can be made, and continue to advance at an increasing
rate throughout the disease course. Extensive cortical demyelin-
ation is evident in the forebrain and cerebellum during progressive
MS. Gray matter atrophy in individuals with MS correlates
strongly with cognitive deficits and clinical disability. 36

Meningeal Inflammation
White blood cell (WBC) counts tend to be within normal limits
or only slightly elevated in the CSF of most patients with MS.
Nonetheless, there is growing recognition that low-grade diffuse
meningeal inflammation and focal perivascular meningeal
inflammation are common. Meningeal inflammation is most
prominent in progressive forms of MS but is prevalent in early
MS as well. The meningeal infiltrates are topographically associ- FIG 66.3 A mouse with experimental autoimmune encephalitis
ated with cortical lesions. Lymphoid follicle–like structures, (EAE) (arrow) and a healthy littermate. The mouse with EAE has
composed of proliferating B cells, T cells, and follicular dendritic a limp tail and hindlimb weakness.
cells (FDCs), have been observed in the meninges of up to 40%
6
of autopsied brains from individuals with SPMS. In almost
every case, the follicles were found to reside in deep sulci and
abut an underlying subpial lesion, suggesting that toxic factors variety of mammalian species (including nonhuman primates,
are released by inflammatory cells in the follicles and diffuse but most commonly in rodents) by vaccination against major
into the brain parenchyma. The presence of lymphoid follicles histocompatibility complex (MHC) class II–restricted myelin
has been associated with a more severe clinical course, shorter epitopes. EAE can be transferred from myelin-vaccinated mice
disease duration, and younger age at death. to syngeneic naïve hosts with purified CD4 T-cell lines or clones.
These encephalitogenic myelin-specific CD4 T cells invariably
KeY COnCePtS fall within the Th1 or Th17 lineage and produce the proinflam-
matory cytokines interferon-γ (IFN-γ) and IL-17, respectively,
Pathology in response to antigenic stimulation (Chapter 16). Both Th1
37
and Th17 cells produce granulocyte macrophage–colony-
• The hallmark of multiple sclerosis (MS) pathology is the focal demyelin-
ated lesion, or “plaque,” with perivascular inflammatory infiltration stimulating factor (GM-CSF), a monocyte mobilizing and
and focal blood–brain barrier (BBB) breakdown. growth factor that plays a critical role in many models of EAE.
• Axonopathy is an early and prominent feature of acute MS lesions. Upon activation in the periphery, myelin-reactive CD4 T cells
• Central nervous system (CNS) damage includes demyelination, apoptosis upregulate adhesion molecules and chemokine receptors, thereby
and loss of oligodendrocytes, and axonal swellings and transections. acquiring the ability to cross the BBB. Once having infiltrated
• Both gray matter and white matter are affected. the CNS, they are reactivated by local antigen-presenting cells
• The pathological features of MS are heterogeneous and evolve over
time. (APCs), such as perivascular macrophages or microglia, which
constitutively express MHC class II molecules bound to myelin
peptides on their surface. GM-CSF, as well as other Th1 and/or
IMMUNOPATHOGENESIS Th17 cytokines, are subsequently released in situ and initiate an
inflammatory cascade, resulting in the production of chemokines,
Animal Models of MS mobilizing factors and vasoactive substances, upregulation of
According to the current dogma, MS is an autoimmune disease adhesion molecules on the cerebrovascular endothelium, and
mediated by CD4 T cells reactive against myelin antigens. The thus the recruitment of myeloid cells and lymphocytes from
identification of HLA class II, IL-2Rα, and IL-7Rα as MS sus- the circulation to the nascent plaque. GM-CSF may drive the
ceptibility loci is consistent with a role of CD4 T cells in MS differentiation of infiltrating monocytes and CNS-resident
+
pathogenesis. An autoimmune etiology is further supported by microglia into CD11c DCs, which are among the most potent
the animal model experimental autoimmune encephalomyelitis APCs. Adoptive transfer studies with labeled donor T cells have
(EAE). EAE is a multifocal inflammatory demyelinating disease demonstrated that the myelin-specific T cells remain clustered
of the CNS that has striking histological and clinical similarities in the perivascular space throughout lesion development. A
to MS (Fig. 66.3 and Fig. 66.4). It has been induced in a wide secondary wave of myeloid cells infiltrate deep into the CNS

CHaPter 66 Multiple Sclerosis 897




EAE CONTROL
















MBP
DAPI
FIG 66.4 Immunofluorescent histology of spinal cord sections from a mouse with experimental
autoimmune encephalitis (EAE) (left) and a healthy control (right). White matter tracks were
stained with a monoclonal antibody (mAb) specific for myelin basic protein (green). The nuclei
of inflammatory cells are stained with DAPI (4’,6-diamidino-2-phenylindole) (blue). The arrows
point to areas of demyelination.


white matter, associate with nodes of Ranvier, and directly inflict with MS who consistently mounted either IFN-γ– or IL-17–skewed
35
damage to the myelin sheath and axons (see Figs. 66.3 and responses to human MBP over the course of a year were recently
37
Fig. 66.4). identified, while others exhibited mixed or oscillating responses.
Diversity in the immune pathways that drive MS pathology holds
Immune Dysregulation in Patients With MS important implications for the development of a more person-
Studies on the frequency of myelin-reactive T cells in patients alized approach to the management of patients in the future.
with MS have reported conflicting results; some investiga- Indeed, Th1- and Th17-mediated forms of EAE show different
tors found a significantly higher incidence of myelin-specific patterns of responsiveness to the same immunomodulatory
peripheral blood mononuclear cells (PBMCs) in individuals with drug. 42
MS compared with age- and gender-matched healthy controls Perhaps the strongest evidence of an autoimmune basis of
5
(HCs), whereas others found no significant difference. Many inflammatory demyelination in humans comes from clinical
of the earlier studies that found no differences between patients trials of immunomodulatory agents. Patients with RRMS were
and HCs used proliferation as a measure of T-cell reactivity treated with an altered peptide ligand (APL) of MBP with the
and nonhuman myelin proteins for antigenic stimulation. In intention of tolerizing MBP-reactive T cells or deflecting their
contrast, several laboratories have found that untreated patients differentiation toward an immunosuppressive, regulatory, or
with RRMS have increased frequencies of PBMCs that produce innocuous Th2 phenotype. Unexpectedly, administration of the
IFN-γ or IL-17 in response to ex vivo challenge with human APL was temporally associated with expansion of circulating
myelin basic protein (MBP), human proteolipid protein (PLP), MBP-reactive Th1 cells and clinical worsening in a subgroup of
43
or their constituent peptides. 4,38,39 IFN-γ responses to PLP pep- patients. In contrast, as will be discussed in detail below, drugs
38
tides were shown to correlate with level of clinical disability. that impede lymphocyte trafficking to the CNS, 44,45 block growth
46
T cells that coexpress IL-17 and IFN-γ were identified in the factor signaling into T lymphocytes, or deplete lymphocytes
47
brain tissue of patients with MS, and circulating lymphocytes from the periphery suppress MS relapse rates and the accumula-
obtained from patients with MS were found to have an increased tion of MRI lesions.
40
propensity to differentiate into IL-17/IFN-γ double producers.
T cells coexpressing IL-17/IFN-γ, and IL-17–producing T cells DISEASE-MODIFYING THERAPIES
that convert into IFN-γ producers (the so-called ex-Th17 cells),
have been implicated in the pathogenesis of some EAE models. The approval of IFN-β-1b (Betaseron) by the US Food and Drug
In a recent study, untreated patients with RRMS had a higher Administration (FDA) in 1993 for the management of RRMS
frequency of peripheral blood T cells that expressed intracellular marked the beginning of a new era in MS therapeutics. In the
GM-CSF in response to stimulation with phorbol myristate intervening 23 years, an additional 13 disease-modifying therapies
acetate and ionomycin, compared with HCs or IFN-β–treated have been approved, all of which have significantly reduced the
41
RRMS patients. Approximately 15–20% of both CD4 and CD8 annualized relapse rate (in a range from 25% to almost 70%)
T cells in active MS lesions expressed GM-CSF and the majority and the frequency of gadolinium enhancing (acutely inflamed)
coexpressed IL-17 and/or IFN-γ. MRI lesions. Prior to 1993, corticosteroids were the only class
There is an increasing appreciation that the cytokine dysregula- of drugs routinely used to treat MS. Although corticosteroids
tion that occurs during EAE and MS is heterogeneous. Hence, accelerate the rate of recovery from acute exacerbations, there
clinically identical forms of EAE can be induced with stable is little evidence that they alter the ultimate clinical outcome or
42
murine Th1 or Th17 cells independently. Subsets of patients prevent subsequent disease activity. Therefore the introduction

898 Part Seven Organ-Specific Inflammatory Disease


50
of disease-modifying therapies has represented a major advance compared with placebo. In an independent phase III rater-
in the treatment of individuals with RRMS and has had a blinded comparator trial, teriflunomide was found to have a
profound impact by mitigating morbidity and enhancing quality similar efficacy to IFN-β-1a in reducing the proportion of
51
of life. participants with at least one relapse over 1 year. Teriflunomide
is teratogenic in rats and rabbits and is therefore contraindicated
Recombinant IFN-β in pregnant women and women of childbearing potential not
IFN-β is a type I IFN with potent antiviral properties. It has using reliable contraception.
pleiotropic effects on the innate immune system. Recombinant
IFN-β was first tested in MS on the basis of the contemporaneous Dimethyl Fumarate
theory that the disease was caused by an active viral infection Dimethyl fumarate (DMF) is the methyl ester of fumaric acid.
of the CNS. Although MS is now believed to be an autoimmune Prior to being tested as a DMA in MS, DMF was used as a biocide
disease, recombinant IFN-β therapy was serendipitously found in furniture and shoes to prevent the growth of molds during
to significantly reduce annualized MS relapse rates. It is manu- storage or transport. A combination of DMF and three other
factured as four different commercial products, all of which are fumaric acid esters was marketed in Germany as a treatment for
self-administered via either subcutaneous or intramuscular psoriasis. In two phase III trials conducted in 2012, oral DMF
injection. There are two distinct structural forms. IFN-β-1a is was demonstrated to decrease the annualized relapse rate of
produced in mammalian cells and has the same sequence as the adults with RRMS by approximately 34–50% compared with
naturally occurring compound, while IFN-β-1b is produced in placebo. 52,53 An additional cohort of subjects treated with GA
53
modified Escherichia coli and has a Met-1 deletion and a Cys-17 was included as a reference comparator in one of the trials.
to Ser mutation. IFN-β-1a is glycosylated, and IFN-β-1b is There was no significant difference in the effect of twice-daily
nonglycosylated. Studies of the efficacy of IFN-β in RRMS have oral DMF versus daily subcutaneous GA on relapse rate, but
yielded remarkably consistent results across different formulations significantly fewer new or enlarging hyperintense lesions were
of the drug. In multiple randomized, double-blinded placebo- noted on T2-weighted MRI images in participants treated with
controlled trials, IFN-β therapy reduced annual relapse rates by DMF. These results led to FDA approval in 2013. DMF therapy
48
20–35%. However, approximately 30% of patients with MS do is often associated with lymphopenia. Therapeutic efficacy does
not respond to the drug. The mechanism of action of IFN-β in not appear to be inversely related to lymphocyte counts. As with
MS has not been definitively elucidated. Proposed mechanisms IFN-β and GA, the mechanism by which DMF suppresses MS
include induction of the immunosuppressive cytokine IL-10, disease activity remains unclear. The most common side effects
inhibition of pathogenic Th17 cells, and stabilization of the BBB of DMF are flushing and gastrointestinal upset. In the postmarket-
via direct effects on the cerebrovascular endothelium. ing setting, several cases of progressive multifocal leukoencepha-
lopathy (PML), a rare viral infection of the brain, were reported
Glatiramer Acetate in patients who were taking DMF and had persistent lymphopenia.
GA comprises a mixture of polypeptides of different lengths PML has also been reported as a complication of other DMAs,
and sequences, synthesized by the randomized polymerization including fingolimod and, most notably, natalizumab.
of four amino acids, namely, glutamic acid, lysine, alanine, and
tyrosine. These are the most prevalent amino acids in MBP, a Fingolimod
candidate autoantigen in MS. It was originally thought that GA During homeostasis, sphingosine 1 phosphate receptor 1 (S1P1)
would act as a competitive antagonist of MBP peptides for binding signaling into lymphocytes drives their egress from lymph nodes
to MHC class II molecules on APCs. Subsequent mechanistic into the bloodstream. Fingolimod is an orally administered
studies did not support that theory. The mechanism of action S1P1 receptor modulator that effectively traps myelin-specific
of GA in MS is currently unknown, but alternative hypotheses T cells in lymph nodes so that they cannot reenter the circula-
that have been proposed include immune deviation of myelin- tion and gain access to the CNS. In a 24-month randomized,
reactive T cells from a destructive Th1 to an innocuous Th2 double-blinded, placebo-controlled trial, fingolimod was shown
+
54
phenotype, increase in frequency and function of FoxP3 regula- to reduce annualized relapse rates by 50%. Furthermore, the
tory CD4 T cells or regulatory CD8 T cells, and induction of probability of disease progression at the 24-month follow-up
antiinflammatory type II monocytes. A pivotal trial of GA versus was lower in the fingolimod-treated subjects. In an independent
placebo in 1995 demonstrated a mean reduction in the relapse 12-month, double-blind, double-dummy phase III comparator
49
rate of approximately 30%. In contrast, a multinational, study, fingolimod reduced the annualized relapse rate to a range
multicenter, double-blind, placebo-controlled phase III trial of of 0.16–0.20, as compared with 0.33 for IFN-β-1a, corresponding
45
GA in PPMS was stopped after an interim analysis by an inde- to a relative reduction of 38–52%. In 2010, fingolimod became
pendent data safety monitoring board indicated no discernible the first oral DMA approved by the FDA to reduce relapses and
8
treatment effect on the primary outcome measure. GA, admin- delay disability progression in patients with relapsing forms of
istered by subcutaneous injection, was approved by the FDA in MS. However, in a phase III randomized, double-blind, placebo-
1996 for reducing the frequency of relapses, but not for reducing controlled trial, fingolimod did not slow disease progression
the progression of disability. in patients with PPMS. 11,12 Fingolimod does not distinguish
between pathogenic and protective lymphocytes, and a number
Teriflunomide of opportunistic infections have emerged as complications of
Teriflunomide, an oral pyrimidine synthesis inhibitor, was the treatment. Patients taking fingolimod are susceptible herpes
approved by the FDA in 2012 for relapsing forms of MS. It has virus infections, particularly shingles. In the phase III comparator
broad immunosuppressive effects, including a cytostatic effect study with IFN-β-1a, two fatal infections occurred among the
on proliferating T and B lymphocytes. In a pivotal phase III fingolimod-treated subjects: disseminated primary varicella zoster
45
trial, teriflunomide reduced annualized relapse rate by 31% and herpes simplex encephalitis. Consequently, patients are

CHaPter 66 Multiple Sclerosis 899


screened for immunity to varicella zoster before commencing in patients with SPMS, it did not prevent clinical progression
treatment. In the postmarketing setting, there have been at least or progressive cerebral atrophy. 7
three cases of PML in fingolimod-treated patients with no or Despite causing a profound lymphopenia, alemtuzumab
only distant prior exposure to immunosuppressant drugs. Other therapy has only rarely been associated with opportunistic
potential side effects of fingolimod include macular edema, infections and has not been associated an increased incidence
bradycardia, and atrioventricular block. of malignancy. Surprisingly, the principal adverse effect of
alemtuzumab in MS is antibody-mediated autoimmune disease,
Natalizumab most commonly Graves disease. Idiopathic thrombocytopenic
Natalizumab is a humanized mAb reactive against the cell purpura, Goodpasture syndrome, and antiglomerular basement
adhesion molecule α 4 integrin, which is widely expressed on membrane disease have been reported less frequently. The
lymphocytes and monocytes. Natalizumab is believed to mediate underlying mechanism is not fully understood but may be a
its ameliorative effects in RRMS by blocking interactions between consequence of homeostatic T-cell proliferation following
the very late antigen-4 (VLA-4; a heterodimer composed of the lymphoablation, leading to the generation of chronically activated
α 4 and β 1 integrin chains) on leukocytes with its cognate ligand, oligoclonal CD4 and CD8 T cells capable of producing proinflam-
vascular cell adhesion molecule (VCAM)-1, on cerebrovascular matory cytokines. 58
endothelial cells. VLA-4–VCAM-1 interactions are required for the
passage of lymphocytes and monocytes past the BBB. Natalizumab Daclizumab
was approved by the FDA for relapsing MS in 2004 following Daclizumab is a humanized mAb reactive to CD25, the α subunit
a 2-year phase III trial. Natalizumab reduced the relapse rate of the IL-2 receptor. Daclizumab was originally proposed as a
at 1 year by 68% and the number of gadolinium-enhancing treatment for RRMS based on the hypothesis that it would block
MRI lesions at both 1 year and 2 years by over 90%, compared IL-2–dependent expansion of effector T cells. However, mecha-
44
with placebo. Natalizumab also reduced the risk of sustained nistic studies have shown that daclizumab does not inhibit T-cell
progression of disability by 42% over 2 years. In an independent survival, proliferation, or cytokine production. Some patients
placebo-controlled trial, the addition of natalizumab to IFN-β-1a treated with daclizumab exhibit an expansion of circulating
59
suppressed break through disease activity and reduced the risk CD56 bright NK cells, which correlates with treatment response.
of sustained disability in patients who were refractory to IFN-β CD56 bright NK cells have been shown to possess immunoregulatory
55
alone. The effects of natalizumab on leukocyte trafficking are properties and to kill activated autologous T cells in vitro.
not specific to the CNS. In fact, in 2008, the FDA approved Daclizumab might also modulate lymphoid tissue inducer cells
natalizumab for the treatment of refractory Crohn disease. The in patients with MS and thereby suppress the development of
60
most serious complication of natalizumab treatment is PML; meningeal lymphoid follicles. In a phase III randomized placebo-
there have been over 400 reported cases. Factors that increase the controlled clinical trial in RRMS, subcutaneous administration
risk of natalizumab-associated PML include John Cunningham of daclizumab reduced the annualized relapse rate by 45%, the
(JC) virus seropositivity, duration of treatment >2 years, and proportion of patients who relapsed by 41%, and new or newly
prior exposure to immunosuppressant drugs. enlarged T2-weighted MRI lesions by 54%, compared with
61
intramuscular IFN-β-1a over 144 weeks. It was approved by
Alemtuzumab the FDA in 2016 for the treatment of relapsing MS in adults.
Alemtuzumab is a humanized anti-CD52 mAb that globally Side effects include an increased risk of infections, hepatotoxicity,
depletes circulating T and B lymphocytes via antibody-dependent noninfectious colitis, lymphadenopathy, and cutaneous events,
cell-mediated cytotoxicity, complement-dependent cytolysis, and such as rash and eczema. On the basis of its safety profile,
induction of apoptosis. CD52 is primarily expressed on the cell daclizumab is generally reserved for patients who have an
surface of T and B lymphocytes, but it is also expressed at lower inadequate response to ≥2 other disease modifying agents.
levels on macrophages, eosinophils, and natural killer (NK) cells.
The function of CD52 is unknown, although there is some B Cell–Depleting Monoclonal Antibodies
evidence that it is involved in T-cell activation. Hematopoietic A role of B cells in the pathogenesis of MS has been suspected
stem cells (HSCs) do not express CD52, allowing the subsequent since the discovery of unique oligoclonal bands in the CSF of
repopulation of circulating lymphocyte pools following alem- the majority of individuals with MS, indicative of intrathecal
tuzumab treatment, which occurs at variable rates between antibody synthesis. Nonetheless, B cells are not a prominent
lymphocyte subsets. Reconstituted circulating T-cell pools have component of the perivascular infiltrates in MS lesions. This
+
+
low
been found to be enriched in CD4 CD25 high CD127 FOXP3 apparent paradox has been resolved, at least in part, by the
regulatory T cells (Tregs) that might be responsible, in part, for discovery of lymphoid follicle–like structures, composed of
the long-lasting therapeutic effect of alemtuzumab, that has been proliferating B cells, antibody-producing plasma cells, Th cells,
56
6
observed in some individuals. In a 2-year, rater-masked, random- and FDCs, in the meninges of some individuals with MS.
ized controlled phase III trial, previously untreated patients with Although meningeal lymphoid follicles have primarily been
RRMS were randomly allocated to receive intravenous alemtu- detected in autopsy specimens from persons with progressive
57
zumab or subcutaneous IFN-β-1a. Alemtuzumab was given MS, it is possible that nascent immune cell aggregates develop
once per day for 5 days at baseline and once per day for 3 days in the RR stage but are disrupted during the dissection and
at 12 months. Relapse rates were reduced by 54.9% in the processing of CNS tissues. The most direct evidence for a role
alemtuzumab group compared with the IFN-β-1a group. In an of B cells as effector cells in MS pathogenesis comes from trials
independent study, alemtuzumab reduced relapse rates and the of mAbs directed against CD20, a B cell–specific surface molecule.
risk of sustained accumulation of disability in patients with CD20 is expressed on preB cells and mature B cells. It is not
47
RRMS refractory to first-line DMAs. Although alemtuzumab expressed on antibody-secreting plasma cells. Rituximab, a
suppressed new MRI lesion formation and superimposed relapses genetically engineered chimeric anti-CD20 mAb, induces a rapid

900 Part Seven Organ-Specific Inflammatory Disease


depletion of circulating B cells that lasts approximately 6–9 well as pathogenic immune responses may be undermined,
months. In a phase II clinical trial of rituximab in RRMS, subjects increasing the risk of infection. Furthermore, DMAs are generally
in the active treatment arm experienced a significant reduction ineffective in progressive forms of disease. Critical goals of the
in clinical relapses and in the formation of new or enhancing MS research community at present are to better define the cellular
62
MRI lesions compared with subjects in the placebo arm. and molecular mechanisms that link neuroinflammation to
Ocrelizumab is a next-generation fully human recombinant end-organ injury (namely, demyelination and axonopathy) and
anti-CD20 mAb that binds to a different epitope from rituximab to elucidate the pathogenic pathways that underlie clinical
and with higher affinity. In two large phase III studies, ocrelizumab progression. It is also imperative to develop a deeper understand-
reduced the annualized relapse rate in subjects with RRMS by ing of obstacles to endogenous repair pathways in the CNS. This
63
nearly 50% compared with IFN-β-1a over a 2-year period. knowledge could ultimately lead to the discovery of laboratory-
Additionally, ocrelizumab delayed confirmed disability progression based surrogate biomarkers of both acute and chronic disease
by approximately 40% and the total number of gadolinium- activity, as well as drugs that block, or even slow, disability
enhancing lesions by >90% compared with IFNβ-1a. accumulation in progressive MS and promote remyelination and
Interestingly, some patients with progressive MS might also axonal regeneration across clinical subtypes.
+
benefit from the depletion of CD20 cells, particularly if there
is evidence of ongoing activity at the time of treatment initiation.
Hawker et al. found that rituximab significantly delayed the time On tHe HOrIZOn
to confirmed disease progression in a subset of patients with • The introduction of disease-modifying therapies has represented a
primary progressive MS who had gadolinium enhancing lesions major advance in the treatment of individuals with relapsing–remitting
9
on baseline MRI scans of the brain. The benefit was most multiple sclerosis (RRMS). However, these drugs have global effects
dramatic in subjects aged <51 years. In a recently completed on lymphocytes, thereby increasing the risk of infection. A future goal
trial of ocrelizumab in PPMS, the risk of progression of clinical will be to develop drugs that specifically target pathogenic leukocytes
63
disability was reportedly reduced by 24%. As a result, in early and/or autoreactive lymphocytes.
2016, the FDA granted ocrelizumab “breakthrough therapy • Disease-modifying therapy is currently focused on the modulation of
lymphocytes. Drugs that target innate immune cells may enhance
designation” for PPMS. MS therapy in the future.
The mechanism by which B cell–depleting therapy alleviates • Recent studies suggest that B cell–depleting therapy may be beneficial
MS does not appear to be reduction in antibody titers. Rituximab for some patients with primary progressive MS (PPMS). There is a
depletes B cells from the CSF of patients with RRMS with little dire need for drugs that slow, or even halt, disability accumulation in
64
effect on CSF IgG levels. B cells are professional APCs, and progressive forms of MS and that are effective in older patients without
evidence of recent neuroinflammatory activity.
there is some evidence that they are important for sustaining • An increased understanding of the mechanisms by which inflammatory
myelin-specific Th17 responses in MS. The frequency of GM-CSF– cells cause central nervous system (CNS) damage and of the obstacles
65
producing B cells was found to be elevated in RRMS. Hence, to endogenous repair pathways in MS may inform the development
ocrelizumab and rituximab may eliminate an important cellular of neuroprotective and neuroregenerative agents.
source of GM-CSF, a monocyte/macrophage–mobilizing cytokine
that has been implicated in the pathogenesis of autoimmune
demyelinating disease. Disruption of meningeal follicle–like Please check your eBook at https://expertconsult.inkling.com/
structures is yet another putative mechanism of action that might for self-assessment questions. See inside cover for registration
be particularly relevant to progressive forms of MS. details.

tHeraPeUtIC PrInCIPLeS REFERENCES
Pharmaceutical Management of MS 1. Koch M, Kingwell E, Rieckmann P, et al. The natural history of secondary
progressive multiple sclerosis. J Neurol Neurosurg Psychiatry
• Corticosteroids accelerate the rate of recovery from multiple sclerosis
(MS) relapses, but there is little evidence that they impact the ultimate 2010;81(9):1039–43. PubMed PMID: 20639385.
degree of recovery or the future clinical course. 2. Cree B, Gourraud PA, Oksenberg JR, et al. Long-term evolution of
• The US Food and Drug Administration (FDA) has approved 14 disease- multiple sclerosis disability in the treatment era. Ann Neurol 2016 Jul 27.
modifying agents (DMAs) that reduce annualized relapse rates in PubMed PMID: 27464262.
patients with RRMS by approximately 20–70%. 3. Mahad DH, Trapp BD, Lassmann H. Pathological mechanisms in
• Newer generation DMAs either deplete lymphocytes, inhibit their progressive multiple sclerosis. Lancet Neurol 2015;14(2):183–93. PubMed
expansion, or block their migration to the central nervous system PMID: 25772897.
(CNS). 4. Huber AK, Wang L, Han P, et al. Dysregulation of the IL-23/IL-17 axis
• DMAs differ in efficacy and safety profiles. Opportunistic infection, and myeloid factors in secondary progressive MS. Neurology
in particular progressive multifocal leukoencephalopathy, has been 2014;83(17):1500–7. PubMed PMID: 25253754. Pubmed Central PMCID:
observed in association with several DMAs. 4222856.
• The choice of DMAs must be customized on an individual basis, taking 5. Segal BM. Stage-specific immune dysregulation in multiple sclerosis. J
into account disease activity and risk tolerance. Interferon Cytokine Res 2014;34(8):633–40. PubMed PMID: 25084180.
Pubmed Central PMCID: 4128245.
6. Magliozzi R, Howell O, Vora A, et al. Meningeal B-cell follicles in
FUTURE DIRECTIONS secondary progressive multiple sclerosis associate with early onset of
disease and severe cortical pathology. Brain 2007;130(Pt 4):1089–104.
Dramatic advances have been made in the management of RRMS, PubMed PMID: 17438020.
but much remains to be done. The DMAs currently in use have 7. Coles AJ, Cox A, Le Page E, et al. The window of therapeutic opportunity
global effects on lymphocytes, as opposed to specifically targeting in multiple sclerosis: evidence from monoclonal antibody therapy. J
autoreactive Th1 and Th17 cells. Consequently, protective as Neurol 2006;253(1):98–108. PubMed PMID: 16044212.

CHaPter 66 Multiple Sclerosis 901


8. Wolinsky JS, Narayana PA, O’Connor P, et al. Glatiramer acetate in 28. Gao Z, Nissen JC, Ji K, et al. The experimental autoimmune
primary progressive multiple sclerosis: results of a multinational, encephalomyelitis disease course is modulated by nicotine and other
multicenter, double-blind, placebo-controlled trial. Ann Neurol cigarette smoke components. PLoS ONE 2014;9(9):e107979. PubMed
2007;61(1):14–24. PubMed PMID: 17262850. PMID: 25250777. Pubmed Central PMCID: 4176721.
9. Hawker K, O’Connor P, Freedman MS, et al. Rituximab in patients with 29. Farez MF, Fiol MP, Gaitan MI, et al. Sodium intake is associated with
primary progressive multiple sclerosis: results of a randomized increased disease activity in multiple sclerosis. J Neurol Neurosurg
double-blind placebo-controlled multicenter trial. Ann Neurol Psychiatry 2015;86(1):26–31. PubMed PMID: 25168393.
2009;66(4):460–71. PubMed PMID: 19847908. eng. 30. Nourbakhsh B, Graves J, Casper TC, et al. Dietary salt intake and time to
10. Polman CH, Reingold SC, Banwell B, et al. Diagnostic criteria for relapse in paediatric multiple sclerosis. J Neurol Neurosurg Psychiatry
multiple sclerosis: 2010 revisions to the McDonald criteria. Ann Neurol 2016;87:1350–3. PubMed PMID: 27343226.
2011;69(2):292–302. PubMed PMID: 21387374. Pubmed Central PMCID: 31. Kleinewietfeld M, Manzel A, Titze J, et al. Sodium chloride drives
PMC3084507. eng. autoimmune disease by the induction of pathogenic TH17 cells. Nature
11. Willer CJ, Dyment DA, Risch NJ, et al. Twin concordance and sibling 2013;496(7446):518–22. PubMed PMID: 23467095. Pubmed Central
recurrence rates in multiple sclerosis. Proc Natl Acad Sci USA PMCID: 3746493.
2003;100(22):12877–82. PubMed PMID: 14569025. Pubmed Central 32. Voskuhl RR, Wang H, Wu TC, et al. Estriol combined with glatiramer
PMCID: 240712. acetate for women with relapsing-remitting multiple sclerosis: a
12. Hollenbach JA, Oksenberg JR. The immunogenetics of multiple sclerosis: randomised, placebo-controlled, phase 2 trial. Lancet Neurol
A comprehensive review. J Autoimmun 2015;64:13–25. PubMed PMID: 2016;15(1):35–46. PubMed PMID: 26621682.
26142251. Pubmed Central PMCID: 4687745. 33. Bove R, Musallam A, Healy BC, et al. Low testosterone is associated with
13. Baranzini SE, Mudge J, van Velkinburgh JC, et al. Genome, epigenome disability in men with multiple sclerosis. Mult Scler 2014;20(12):1584–92.
and RNA sequences of monozygotic twins discordant for multiple PubMed PMID: 24710799. Pubmed Central PMCID: 4188801.
sclerosis. Nature 2010;464(7293):1351–6. PubMed PMID: 20428171. 34. Kurth F, Luders E, Sicotte NL, et al. Neuroprotective effects of
Pubmed Central PMCID: 2862593. testosterone treatment in men with multiple sclerosis. NeuroImage Clin
14. Kurtzke JF. An epidemiologic approach to multiple sclerosis. Arch Neurol 2014;4:454–60. PubMed PMID: 24634831. Pubmed Central PMCID:
1966;14(2):213–22. PubMed PMID: 4952448. 3952353.
15. Munger KL, Levin LI, Hollis BW, et al. Serum 25-hydroxyvitamin D levels 35. Nikic I, Merkler D, Sorbara C, et al. A reversible form of axon damage in
and risk of multiple sclerosis. JAMA 2006;296(23):2832–8. PubMed experimental autoimmune encephalomyelitis and multiple sclerosis. Nat
PMID: 17179460. Med 2011;17(4):495–9. PubMed PMID: 21441916.
16. Munger KL, Aivo J, Hongell K, et al. Vitamin D Status During Pregnancy 36. Preziosa P, Rocca MA, Pagani E, et al. Structural MRI correlates of
and Risk of Multiple Sclerosis in Offspring of Women in the Finnish cognitive impairment in patients with multiple sclerosis: A Multicenter
Maternity Cohort. JAMA Neurol 2016;73(5):515–19. PubMed PMID: Study. Hum Brain Mapp 2016;37(4):1627–44. PubMed PMID: 26833969.
26953778. Pubmed Central PMCID: 4861670. 37. Carbajal KS, Mironova Y, Ulrich-Lewis JT, et al. Th Cell Diversity in
17. Levin LI, Munger KL, O’Reilly EJ, et al. Primary infection with the Experimental Autoimmune Encephalomyelitis and Multiple Sclerosis. J
Epstein-Barr virus and risk of multiple sclerosis. Ann Neurol Immunol 2015;195(6):2552–9. PubMed PMID: 26238492. Pubmed
2010;67(6):824–30. PubMed PMID: 20517945. Pubmed Central PMCID: Central PMCID: 4561206.
3089959. 38. Moldovan IR, Rudick RA, Cotleur AC, et al. Interferon gamma responses
18. Ascherio A, Munger KL, Lennette ET, et al. Epstein-Barr virus antibodies to myelin peptides in multiple sclerosis correlate with a new clinical
and risk of multiple sclerosis: a prospective study. JAMA measure of disease progression. J Neuroimmunol 2003;141(1-2):132–40.
2001;286(24):3083–8. PubMed PMID: 11754673. PubMed PMID: 12965264. eng.
19. Lang HL, Jacobsen H, Ikemizu S, et al. A functional and structural basis 39. Hedegaard CJ, Krakauer M, Bendtzen K, et al. T helper cell type 1 (Th1),
for TCR cross-reactivity in multiple sclerosis. Nat Immunol Th2 and Th17 responses to myelin basic protein and disease activity in
2002;3(10):940–3. PubMed PMID: 12244309. multiple sclerosis. Immunology 2008;125(2):161–9. PubMed PMID:
20. Magliozzi R, Serafini B, Rosicarelli B, et al. B-cell enrichment and 18397264. Pubmed Central PMCID: PMC2561132. eng.
Epstein-Barr virus infection in inflammatory cortical lesions in secondary 40. Kebir H, Ifergan I, Alvarez JI, et al. Preferential recruitment of
progressive multiple sclerosis. J Neuropathol Exp Neurol interferon-gamma-expressing TH17 cells in multiple sclerosis. Ann
2013;72(1):29–41. PubMed PMID: 23242282. Neurol 2009;66(3):390–402. PubMed PMID: 19810097. eng.
21. Wu Z, Nagano I, Asano K, et al. Infection of non-encapsulated species of 41. Rasouli J, Ciric B, Imitola J, et al. Expression of GM-CSF in T Cells Is
Trichinella ameliorates experimental autoimmune encephalomyelitis Increased in Multiple Sclerosis and Suppressed by IFN-beta Therapy. J
involving suppression of Th17 and Th1 response. Parasitol Res Immunol 2015;194(11):5085–93. PubMed PMID: 25917097. Pubmed
2010;107(5):1173–88. PubMed PMID: 20661746. Central PMCID: 4433790.
22. Correale J. Helminth/Parasite treatment of multiple sclerosis. Curr Treat 42. Kroenke MA, Carlson TJ, Andjelkovic AV, et al. IL-12- and IL-23-
Options Neurol 2014;16(6):296. PubMed PMID: 24744099. modulated T cells induce distinct types of EAE based on histology, CNS
23. Hedstrom AK, Olsson T, Alfredsson L. High body mass index before age chemokine profile, and response to cytokine inhibition. J Exp Med
20 is associated with increased risk for multiple sclerosis in both men and 2008;205(7):1535–41. PubMed PMID: 18573909. Pubmed Central
women. Mult Scler 2012;18(9):1334–6. PubMed PMID: 22328681. PMCID: 2442630. Epub 2008/06/25. eng.
24. Langer-Gould A, Brara SM, Beaber BE, et al. Childhood obesity and risk 43. Bielekova B, Goodwin B, Richert N, et al. Encephalitogenic potential of
of pediatric multiple sclerosis and clinically isolated syndrome. Neurology the myelin basic protein peptide (amino acids 83-99) in multiple
2013;80(6):548–52. PubMed PMID: 23365063. Pubmed Central PMCID: sclerosis: results of a phase II clinical trial with an altered peptide ligand.
3589288. Nat Med 2000;6(10):1167–75. PubMed PMID: 11017150. eng.
25. Mokry LE, Ross S, Timpson NJ, et al. Obesity and Multiple Sclerosis: A 44. Polman CH, O’Connor PW, Havrdova E, et al. A randomized,
Mendelian Randomization Study. PLoS Med 2016;13(6):e1002053. placebo-controlled trial of natalizumab for relapsing multiple sclerosis. N
PubMed PMID: 27351487. Pubmed Central PMCID: 4924848. Engl J Med 2006;354(9):899–910. PubMed PMID: 16510744. Epub
26. Poorolajal J, Bahrami M, Karami M, et al. Effect of smoking on multiple 2006/03/03. eng.
sclerosis: a meta-analysis. J Public Health (Bangkok) 2016 May 8. 45. Cohen JA, Barkhof F, Comi G, et al. Oral fingolimod or intramuscular
PubMed PMID: 27160862. interferon for relapsing multiple sclerosis. N Engl J Med
27. Ramanujam R, Hedstrom AK, Manouchehrinia A, et al. Effect of 2010;362(5):402–15. PubMed PMID: 20089954. eng.
Smoking Cessation on Multiple Sclerosis Prognosis. JAMA Neurol 46. Gold R, Giovannoni G, Selmaj K, et al. Daclizumab high-yield process in
2015;72(10):1117–23. PubMed PMID: 26348720. relapsing-remitting multiple sclerosis (SELECT): a randomised,

902 Part Seven Organ-Specific Inflammatory Disease


double-blind, placebo-controlled trial. Lancet 2013;381(9884):2167–75. Neurol Neuroimmunol Neuroinflamm 2016;3(1):e194. PubMed PMID:
PubMed PMID: 23562009. eng. 26819963. Pubmed Central PMCID: 4723135.
47. Coles AJ, Twyman CL, Arnold DL, et al. Alemtuzumab for patients with 57. Cohen JA, Coles AJ, Arnold DL, et al. Alemtuzumab versus interferon
relapsing multiple sclerosis after disease-modifying therapy: a randomised beta 1a as first-line treatment for patients with relapsing-remitting
controlled phase 3 trial. Lancet 2012;380(9856):1829–39. PubMed PMID: multiple sclerosis: a randomised controlled phase 3 trial. Lancet
23122650. eng. 2012;380(9856):1819–28. PubMed PMID: 23122652.
48. Oliver BJ, Kohli E, Kasper LH. Interferon therapy in relapsing-remitting 58. Jones JL, Thompson SA, Loh P, et al. Human autoimmunity after
multiple sclerosis: a systematic review and meta-analysis of the lymphocyte depletion is caused by homeostatic T-cell proliferation. Proc
comparative trials. J Neurol Sci 2011;302(1-2):96–105. PubMed PMID: Natl Acad Sci USA 2013;110(50):20200–5. PubMed PMID: 24282306.
21167504. Pubmed Central PMCID: 3864306.
49. Johnson KP, Brooks BR, Cohen JA, et al. Copolymer 1 reduces relapse 59. Bielekova B, Catalfamo M, Reichert-Scrivner S, et al. Regulatory
rate and improves disability in relapsing-remitting multiple sclerosis: CD56(bright) natural killer cells mediate immunomodulatory effects of
results of a phase III multicenter, double-blind placebo-controlled trial. IL-2Ralpha-targeted therapy (daclizumab) in multiple sclerosis. Proc Natl
The Copolymer 1 Multiple Sclerosis Study Group. Neurology Acad Sci USA 2006;103(15):5941–6. PubMed PMID: 16585503. Pubmed
1995;45(7):1268–76. PubMed PMID: 7617181. Epub 1995/07/01. eng. Central PMCID: 1458677.
50. O’Connor P, Wolinsky JS, Confavreux C, et al. Randomized trial of oral 60. Perry JS, Han S, Xu Q, et al. Inhibition of LTi cell development by CD25
teriflunomide for relapsing multiple sclerosis. N Engl J Med blockade is associated with decreased intrathecal inflammation in
2011;365(14):1293–303. PubMed PMID: 21991951. eng. multiple sclerosis. Sci Transl Med 2012;4(145):145ra06. PubMed PMID:
51. Vermersch P, Czlonkowska A, Grimaldi LM, et al. Teriflunomide versus 22855463. Pubmed Central PMCID: 3846177.
subcutaneous interferon beta-1a in patients with relapsing multiple 61. Kappos L, Wiendl H, Selmaj K, et al. Daclizumab HYP versus Interferon
sclerosis: a randomised, controlled phase 3 trial. Mult Scler Beta-1a in Relapsing Multiple Sclerosis. N Engl J Med
2014;20(6):705–16. PubMed PMID: 24126064. 2015;373(15):1418–28. PubMed PMID: 26444729.
52. Gold R, Kappos L, Arnold DL, et al. Placebo-controlled phase 3 study of 62. Hauser SL, Waubant E, Arnold DL, et al. B-cell depletion with rituximab
oral BG-12 for relapsing multiple sclerosis. N Engl J Med in relapsing-remitting multiple sclerosis. N Engl J Med
2012;367(12):1098–107. PubMed PMID: 22992073. 2008;358(7):676–88. PubMed PMID: 18272891. eng.
53. Fox RJ, Miller DH, Phillips JT, et al. Placebo-controlled phase 3 study of 63. Sastre-Garriga J, Wiendl H. Highlights from the 31st ECTRIMS
oral BG-12 or glatiramer in multiple sclerosis. N Engl J Med congress - Barcelona 2015. Mult Scler 2016;22(1):7–10. PubMed PMID:
2012;367(12):1087–97. PubMed PMID: 22992072. 26684283.
54. Kappos L, Radue EW, O’Connor P, et al. A placebo-controlled trial of oral 64. Cross AH, Stark JL, Lauber J, et al. Rituximab reduces B cells and T cells
fingolimod in relapsing multiple sclerosis. N Engl J Med in cerebrospinal fluid of multiple sclerosis patients. J Neuroimmunol
2010;362(5):387–401. PubMed PMID: 20089952. Epub 2010/01/22. eng. 2006;180(1-2):63–70. PubMed PMID: 16904756. Pubmed Central
55. Rudick RA, Stuart WH, Calabresi PA, et al. Natalizumab plus interferon PMCID: 1769354.
beta-1a for relapsing multiple sclerosis. N Engl J Med 65. Li R, Rezk A, Miyazaki Y, et al. Proinflammatory GM-CSF-producing B
2006;354(9):911–23. PubMed PMID: 16510745. cells in multiple sclerosis and B cell depletion therapy. Sci Transl Med
56. De Mercanti S, Rolla S, Cucci A, et al. Alemtuzumab long-term 2015;7(310):310ra166. PubMed PMID: 26491076.
immunologic effect: Treg suppressor function increases up to 24 months.

CHaPter 66 Multiple Sclerosis 902.e1


MUL t IPL e -CHOIC e QU e S t IO n S

1. The etiology of multiple sclerosis is believed to be: 3. To make a diagnosis of relapsing remitting MS it is critical
a. a viral infection of the central nervous system to demonstrate:
b. an autoimmune disorder mediated by myelin-reactive a. Dissemination of lesions in time
lymphocytes b. Dissemination of lesions in space
c. a primary neurodegenerative disorder c. Immunoglobulin synthesis in the central nervous system
d. a toxic encephalopathy d. Worsening of symptoms with increases in core body
temperature
2. The mechanism of action of disease modifying therapies
currently used to reduce MS relapse rates is: e. a and b
a. Blockade of lymphocyte trafficking to the central nervous
system
b. Depletion of lymphocytes
c. Inhibition of T cell proliferation
d. Inhibition of pyrimidine synthesis
e. All of the above

67









Autoimmune Peripheral Neuropathies



Marinos C. Dalakas








Autoimmune peripheral neuropathies (APNs) occur when motor or sensory nerve fibers and the myelin sheath or the axon.
1-5
immunological tolerance to peripheral nerve components The GBS subtypes, or GBS variants, include:
(myelin, Schwann cell, axon, and motor or ganglionic neurons) • Acute inflammatory demyelinating polyneuropathy (AIDP),
is lost. In some of these neuropathies, there is direct evidence which accounts for the majority (probably 80%) of patients.
for autoimmune reactivity mediated by specific antibodies or In classic cases, the weakness starts from the legs and spreads
autoreactive T lymphocytes against peripheral nerve. In others, up to the arms, intercostal and diaphragmatic muscles, and
the underlying immune-mediated mechanism is secondary facial or bulbar muscles, causing dysphagia and dysarthria.
or indirect, and an autoimmune cause is suspected when the At times the weakness may be limited to one or two limbs
neuropathy coexists with another systemic autoimmune disease or to cranial nerves. Patients need to be monitored for impend-
or viral infection. ing respiratory failure, hence the need for early admission to
This chapter reviews the most common autoimmune neu- intensive care units (ICUs). Autonomic dysfunction occurs
ropathies (Table 67.1), their clinical features and diagnostic in varying degrees in up to 65% of patients; if severe, it can
criteria, the prevailing autoimmune phenomena that govern each be life-threatening as a result of cardiac arrhythmias or
neuropathy, and the most effective therapeutic approach. hemodynamic changes, such as hypertension, orthostatic
hypotension, and reduced peripheral vascular tone. 1-5
ACUTE INFLAMMATORY POLYNEUROPATHY: • Acute motor axonal neuropathy (AMAN), which exhibits
GUILLAIN-BARRÉ SYNDROME(S) primary axonal damage caused by massive acute demyelination
and inflammation, as occurs in experimental allergic neuritis
Guillain-Barré syndrome (GBS) is an acute demyelinating (EAN) when the animals are immunized with a high dose of
1-5
polyneuropathy characterized by acute (within 1 week) or myelin antigen, or by a primary axonal event mediated by
subacute (within 4 weeks) ascending motor weakness, mild macrophages. These patients have a fulminant course with
or moderate sensory abnormalities, occasional cranial nerve severe paralysis and complete electrical inexcitability of motor
1-5
1-5
involvement, and muscle or radicular pain. Tendon reflexes nerves as early as 3–5 days after onset. In contrast to AIDP,
are reduced but can be normal, especially in axonal GBS. It involvement of cranial nerves is infrequent, and reflexes are
is a disease of all ages, with an incidence of 0.8–1.9 (median normal or increased, especially early in the disease. AMAN is
4
1.1) per 100 000, and occurs sporadically, although occasional common in Asia and Central South America, accounting for
5
outbreaks have been noted. In typical cases, the maximum 30–65% of all GBS cases in these regions. Recovery of motor
deficit is reached by the fourth week, a sign conventionally function is variable; some patients recover within days as a
used to separate GBS from chronic inflammatory demyelinating result of resolution of conduction block, but others have slow
polyneuropathy (CIDP), in which the disease begins slowly and and poor recovery because of excessive axonal degeneration at
1-5
usually reaches a nadir after at least 2 months. There are, however, the root level. Infection with Campylobacter jejuni appears to
1-7
patients with CIDP (perhaps up to 16%) with subacute onset be responsible for many of these cases. A number of patients
and monophasic course and fall between the two time-frames also have high levels of antiganglioside GM1 antibodies. 1-7
and still others with an even more acute onset, reaching a nadir • Acute motor–sensory axonal neuropathy (AMSAN) is similar
1-4
within 6–8 weeks and resembling GBS. Distinguishing GBS to AMAN, but with concurrent involvement of the sensory
from acute-onset CIDP is challenging because the distinction, axons, and has a pathomechanism similar to that of AMAN,
in most cases, becomes evident in retrospect, although pro- including frequent antibodies against GM1 and GD1a gan-
posed criteria may help separate the two early in the disease gliosides following C. jejuni infection.
course. 1-5 • Miller Fisher syndrome (MFS) is characterized by acute onset
After reaching the clinical peak, there is a recovery period of ophthalmoplegia, gait ataxia, normal sensation, and
1-7
that varies from weeks to years according to disease subtype or areflexia. In a third of patients, there is muscle weakness
severity at onset; rapid initial progression over <7 days, severity with pharyngeal, facial, trunk, and respiratory muscle involve-
1-7
at onset requiring mechanical ventilation, age >60 years, and ment; rarely it can present as an isolated ocular nerve palsy.
preceding diarrheal illness are signs associated with incomplete MFS is a variant that is distinct because of the presence of a
recovery or worse outcome. GBS is not one syndrome, but several unique immunoglobulin G (IgG) antibody against GQ1b
syndromes, reflecting the varying degree of involvement of the ganglioside. 1-7
903

904 Part Seven Organ-Specific Inflammatory Disease



TABLE 67.1 Common autoimmune of muscles, such as hypokalemia, inflammatory myopathy
neuropathies (especially the necrotizing autoimmune subtype), acute rhab-
domyolysis, or periodic paralysis; and other rare causes of acute
• Guillain-Barré syndrome(s) (GBS) neuropathy, such as porphyria, toxins, vasculitis, or critical illness
• Chronic inflammatory demyelinating polyneuropathy (CIDP) and its polyneuropathy.
variants
• Polyneuropathy associated with paraproteinemias Antecedent Illnesses or Events
• Immunoglobulin M (IgM) monoclonal gammopathies
• IgG and IgA monoclonal gammopathy Two-thirds of patients with GBS give a history of a flu-like illness
• Polyneuropathy, organomegaly, endocrinopathy, myeloma, and skin or acute dysenteric episodes that precede the development of
changes (POEMS) syndrome GBS by 1–3 weeks. Among the implicated viruses are CMV,
1-5
• Cryoglobulinemic polyneuropathy EBV, herpesvirus, hepatitis A, HIV, and now Zika virus. Among
• Multifocal motor neuropathy with conduction block
• Paraneoplastic neuropathies associated with anti-Hu antibodies bacteria, infection with Mycoplasma pneumoniae and, most
• Autoimmune autonomic neuropathies importantly, C. jejuni may be present in >25% of the patients
1-5
• Vasculitic neuropathies and in some parts of the world up to 50%. Campylobacter
• Infectious neuropathies (human immunodeficiency virus [HIV], is of special interest because it contains glycoconjugates that
cytomegalovirus [CMV], Epstein-Barr virus [EBV], and herpes virus share epitopes with the peripheral myelin, as discussed later. Two
infections; Lyme disease; leprosy; Chagas disease; diphtheria; vaccines—one against rabies and the other against the swine flu
others)
A/New Jersey influenza strain that caused an outbreak of GBS in
1-5
1976 —have been convincingly associated with development
of GBS. Administration of rabies vaccine that contains brain
material is followed by GBS in about 1 in 1000 cases. Apart
• Sensory ataxic GBS results from the involvement of roots and from these vaccines, however, despite anecdotal reports, there is
ganglionic neurons. Some of these patients have antibodies no convincing evidence that the incidence of GBS is increased
to GD1b ganglioside, probably forming a continuum with in association with other vaccines. Presently there is concern
MFS because they share autoantibodies with the same sialic that Zika virus, an arbovirus in the family of Flaviviridae, is
groups. 1-7 emerging in several countries and territories of South America
• Acute pandysautonomic neuropathy, where the target antigen as a cause of microcephaly and GBS. Although the information
is seemingly in the ganglionic neurons, although never identi- is still evolving, compelling data from French Polynesia provide
fied. Autonomic symptoms, however, can coexist in all forms evidence that Zika is associated with GBS in the form of AMAN
of GBS during the acute, stable, or even the recovery phase. 1-5 with rapid disease evolution—within 4–6 days—and antiglycolipid
8
antibodies in 31% of the patients. On the basis of the total
Diagnosis number of 42 reported cases from October 2013 to March 3014,
The diagnosis is often suspected on clinical grounds, but it is the risk of GBS was estimated to be 0.24 per 1000 Zika virus
8
confirmed with elevated levels of cerebrospinal fluid (CSF) protein infections. Although this is clearly alarming, considering that
and abnormal results of electrophysiological studies consistent Zika is a mosquito-borne virus, more data are needed. Surgery
1-4
with active demyelination or nerve inexcitability. can precede the development of GBS in some patients ; surgical
CSF protein may be normal in the early phase of the disease, stress, the release of nerve autoantigens, and infections have been
but it can be as high as 1000 mg/dL by the sixth week. The eleva- proposed as possible explanations for this association. Three
tion of CSF protein levels may result from the involvement of drugs—gold, perhexiline, and suramin at high doses—have been
the roots related to inflammation, but, as the blood–nerve barrier causally associated with acute demyelinating neuropathy. GBS
becomes impaired, serum albumin and IgG may enter freely has occurred in patients who suffer from neoplasms, especially
1-4
into CSF, contributing further to protein elevation. CSF cell count lymphoma, melanoma, and Hodgkin disease. Interestingly,
is normal (or slightly increased <50 cells per microliter); there GBS is rarely seen as part of another connective tissue disorder.
is, however, lymphocytosis when GBS occurs in conjunction
with viral infections, such as human immunodeficiency virus Immunopathology of Guillain-Barré Syndrome
(HIV), cytomegalovirus (CMV), Epstein-Barr virus (EBV), or GBS is an inflammatory demyelinating polyneuropathy in which
Lyme disease. When CSF protein is very high, papilledema can the peripheral myelin, the axon, the node of Ranvier, or the
develop because of impaired reabsorption of CSF and raised Schwann cell are the putative target antigens of an immune
intracranial pressure. Oligoclonal IgG bands can be also seen. attack, possibly triggered by various antecedent events. Both the
Results of nerve conduction studies can be normal early in the cellular and the humoral components of the immune system
disease; they are, however, often helpful to distinguish AIDP have been implicated. 1-5
from AMAN or AMSAN, although sometimes serial studies are
needed in the ensuing weeks. Nerve conduction studies may also Cellular Factors
have prognostic value because features of demyelination suggest Two histopathological features are prominent in typical GBS:
higher chances of needing mechanical ventilation, whereas the perivascular and endoneurial inflammatory infiltrates throughout
1-4
presence of low compound muscle axon potentials from the the nerves, roots, or plexuses and segmental demyelination
4,5
outset (indicative of axonal loss) predicts poor outcome. Dif- in areas associated with the lymphoid infiltrates, especially
ferential diagnosis of GBS should include other forms of acute macrophages. Macrophages, which are the most prominent
flaccid paralysis, such as brainstem stroke; brainstem encephalitis; cells in contact with nerve fibers, break through the basement
acute motor neuron involvement caused by poliomyelitis or West membrane of healthy Schwann cells and make direct contact
Nile virus infection; acute myelopathy; disorders of neuromuscular with the outermost myelin lamellae, leading finally to lysis of the
transmissions, such as myasthenia gravis or botulism; disorders superficial myelin sheath (macrophage-mediated demyelination).

CHaPter 67 Autoimmune Peripheral Neuropathies 905


6
Cytokines and chemokines released by the activated T cells or IgM paraproteinemic polyneuropathies, as discussed later.
complement activation may increase capillary permeability and Anti-GQ1b IgG antibodies are also found in postinfectious
facilitate transmigration of additional macrophages or T cells. ophthalmoplegias as well as in GBS with ophthalmoplegia, but
When the demyelination is extensive or chronic, it is followed not in those without ophthalmoplegia or other autoimmune
1-7
1-5
by axonal degeneration. The degree and effectiveness of remy- conditions. Of interest, anti-GQ1b antibody binds the paranodal
elination and axonal regeneration dictate the degree of clinical regions of oculomotor nerves III, IV, and VI, suggesting that
recovery. damage to these regions blocks impulse propagation at the nodes
The role for a T cell–mediated process in GBS is mostly derived of Ranvier, resulting in a conduction block that is characteristic
by analogy to the animal model of EAN, which resembles GBS in for GBS. Many patients with antibodies to GQ1b also have
1-5
both its pathology and its clinical course. Animals sensitized to antibodies to GD1a.
whole human nerve or to various myelin proteins, such as P0, P2, The reasons for different clinical syndromes in connection
and the neutral glycolipid galactocerebroside, develop segmental with specific gangliosides remains unclear, but distribution,
demyelination with mononuclear cell infiltrates consisting of accessibility, and density or configuration of gangliosides at
macrophages and T cells. In EAN, T cells are sensitized against different sites may be critical factors. For example, there is more
myelin and can passively transfer the disease to healthy animals. GM1 in ventral roots than in dorsal roots, hence the predomi-
Increased levels of interleukin-2 (IL-2) and soluble IL-2 receptors nantly motor neuropathy seen with anti-GM1 antibodies; there
are noted in serum during the acute phase of GBS, suggesting is also more GQ1b in the ocular motor nerves, which may explain
ongoing T-cell activation. Further, lymphocytes from patients the involvement of eyes in MFS. How these antibodies induce
with GBS exert myelinotoxic activity when applied to cultures disease, however, remains unclear. Current evidence suggests
of myelinated axons. that antibodies against different acidic glycolipids or sulfatides
may be related to different viral or bacterial antecedent factors,
Humoral Factors and Antiganglioside Antibodies as discussed below.
There is much stronger evidence that circulating serum factors
are responsible for GBS. On clinical grounds, this is supported Molecular Mimicry: Relationship Between
by the beneficial effect of plasmapheresis, presumably by removing Campylobacter jejuni and Gangliosides in Acute Motor
putative antibodies. On laboratory grounds, it is supported by Axonal Neuropathy
the variety of autoantibodies detected in patients’ sera. Serum Antecedent infection with C. jejuni has been commonly
from the acute phase of GBS can demyelinate rodent dorsal root associated with AMAN. The strain of C. jejuni associated with
ganglionic extracts in a complement-dependent manner. Fur- AMAN (Penner D: 19 serogroup) is, however, different from
thermore, GBS serum injected into rat sciatic nerves causes those causing common enteritis and is more likely to have the
demyelination and conduction block. Complement-fixing IgM genes for enzymes that synthesize sialic acid in the bacterial wall
1-5
antibodies against a human peripheral nerve myelin glycolipid mimicking ganglioside GM1, GD1a, or GQ1b. These patients
that contains carbohydrate epitopes as well as high-titer antibodies have a higher incidence of anti-GM1 antibodies, which suggests
against various sulfated or acidic glycosphingolipids are present cross-reactivity between epitopes in the lipooligosaccharide in
1-5
in several patients with GBS. 1-7 the bacterial wall and the ganglioside. Further, injection of
Gangliosides are present in all tissues but are especially lipooligosaccharides extracted from C. jejuni into rabbits has
abundant in the nervous system. Their lipid portion lies in the been shown to induce acute neuropathy, with development of
1-7
cell membrane, and their signature sugar residues are exposed anti-GM1 antibodies identical to those found in AMAN. In
at the extracellular surface bearing one or more sialic acid addition, immunization of mice with these lipooligosaccharides
molecules, such as one sialic acid ganglioside (GM1), two (GD1a), generates a monoclonal antibody (mAb) that reacts with GM1
1-7
three (GT1a), or four (GQ1b). Although they do not form a and binds to human peripheral nerve. This GM1 mAb as well as
common “GBS antigen,” different gangliosides are involved in the anti-GM1 IgG extracted from patients with GBS block muscle
different GBS subtypes. They are of pathogenic relevance because action potentials in muscle–spinal cord coculture. Carbohydrate
immunization of rabbits with GM1 and GD1b induces acute mimicry between the bacterial lipooligosaccharide and human
1-7
neuropathy with histological features of AMAN. Their patho- GM1 is therefore an important cause of AMAN. Because C.
genicity was also confirmed by an inadvertent experiment in jejuni is a common cause of a diarrheal illness worldwide, and
humans who had received ganglioside injections for various diarrhea has been an antecedent event in up to 50% of patients
maladies and developed AMAN accompanied by anti-GM1 with GBS, Campylobacter appears to trigger the disease in many
1-7
antibodies. Additionally, antibodies to GQ1b or GD1a cause patients, especially in certain parts of the world. Isolation of
conduction block at the motor nerve terminals in a preparation Campylobacter from stools early in acute GBS varies from 44% to
1-7
of mouse phrenic nerve. Similarly, antibodies to GalNAc-Gd1a 88% of patients, and IgG or IgM Campylobacter-specific antibody
from a patient with AMAN blocked neuromuscular transmission titers are seen in a higher percentage (36%) of patients with GBS
in a mouse spinal cord muscle coculture system. than in controls (10%).
IgG antibodies that react with GM1, GD1a, GalNAc-GD1a, Molecular mimicry may not be limited to C. jejuni because
and GM1b are found in 80% of cases with the motor axonal GM1 and GQ1b epitopes are also found in the bacteria wall of
form of GBS (AMAN and AMSAN), but in the most common Hemophilus influenzae, which is also a triggering factor in GBS.
GBS subtype, AIDP, ganglioside-specific antibodies are uncom- GBS triggered by CMV infection has been also associated with
mon. Among gangliosides, the one that clearly correlates with the presence of IgM anti-GM2 antibodies. Another potential
a specific clinical syndrome is the GQ1b, which is specifically factor for molecular mimicry is M. pneumoniae, which precedes
associated with the MFS variant with IgG anti-GQ1b antibodies GBS in 5% of cases and is known to stimulate antibodies against
1-7
present in >90% of these patients In contrast, anti-GQ1b human carbohydrate antigens, including galactocerebroside, the
antibodies of the IgM class can be found in patients with chronic main glycolipid antigen in peripheral nerves. 1-7

906 Part Seven Organ-Specific Inflammatory Disease


Cytokines Barrier (Blood–brain)
(INF-γ, IL-1, IL-2, IL-6 (Blood–nerve)
TNF) APC
Integrins ICAM-1 IL-2 MHC B cell
MAC-1 MHC
TCR MHC-II
LFA-1
T cell MHC-I, II T cell Anti-MAG
INF-γ Autoantigen Anti-GQ1b
Anti-glycolipids
IL-2 IL-1(fever)
TNF-1
CR 1
ICAM-1 Fc
Viruses Mφ
MHC
MHC Mφ
CR 3
Mφ Mφ
TNF O 2
Schwann cell
IL-1 OH
Igs
MHC
CR 3 AG
FIG 67.1 Sequence of events in the mechanisms of immune-mediated demyelinating polyneu-
ropathy. Cytokines lead to increased expression of major histocompatibility complex (MHC) class
I and intercellular adhesion molecules, allowing the sensitized T cells and macrophages to exit
the endothelial cell wall and traffic to the peripheral nerve. There they recognize myelin antigen
and induce a macrophage-mediated demyelination. The antigen-presenting cells (APCs; probably
Schwann cells or macrophages), in concert with MHC class II expression, interact with CD4 T
cells and lead to clonal expansion of B cells, producing antibodies against various peripheral nerve
antigens.








Molecular mimicry may also play a role in the Zika virus– KeY COnCePtS
associated GBS as antiglycolipid antibodies were found in 31%
of these patients. 8 Autoimmunity in Guillain-Barré Syndrome (GBS)
Molecular mimicry between epitopes of viral proteins (which Cellular Factors
trigger the disease) and myelin components may result in sensitiza- • The peripheral myelin or the Schwann cells are targets.
tion of cross-reactive T cells that may stimulate B cells to produce • Activated macrophages are the dominant endoneurial cells and lift
specific antibodies directed against myelin components or may the outermost myelin lamellae, lysing the superficial myelin sheaths.
recruit macrophages as effector cells. A combination of cellular • Peripheral blood lymphocytes exert myelinotoxic activity in vitro.
and humoral factors therefore seems to participate in the cause • Levels of interleukin-2 (IL-2) and soluble IL-2 receptors are increased
1-8
of the disease. Circulating cytokines triggered by the initiating during the acute phase of the disease and decline during recovery.
event (viruses or bacteria) could also upregulate intercellular Humoral Factors
adhesion molecule (ICAM)-1 expression on the endothelial cells • Serum exerts a complement-dependent demyelination in vitro.
and facilitate the entrance of activated T cells or antibodies to • Intraneural injections of serum from patients with acute GBS cause
the endoneurial parenchyma. It is relevant that ICAM-1 is demyelination and conduction block.
1-5
increased in patients with GBS. A scheme summarizing the • Immunoglobulin G (IgG), IgM, and membranolytic attack complex are
immunopathogenic mechanism is shown in Fig. 67.1. detected immunocytochemically on the patients’ nerves.
• High titers of IgG antibodies against peripheral nerve acidic glycolipids
Nodal and Paranodal Alterations and Specific (GM1, GQ1b) are detected in the sera of patients with acute motor
Antinodal Antibodies axonal neuropathy (AMAN) and Miller Fisher syndrome (MFS). The
GQ1b ganglioside is a specific antigen for MFS.
Antibodies to nodal and paranodal antigens seen in CIDP subsets, • There is a high incidence of antibodies to Campylobacter jejuni, and
as discussed later, have been also detected in a small number of GM1, with molecular mimicry between Campylobacter and nerve
patients with GBS in Europe. Antibodies against neurofascin, gangliosides.
ankyrin G, and contactin could potentially explain the acute • Injection of lipooligosaccharides extracted from C. jejuni cause AMAN
conduction block or the paranodal axonal degeneration and the and elicit GM1 antibodies in rabbits.
rapid reversibility or slow and incomplete recovery seen in several • Antiganglioside antibodies extracted from patients with GBS block
muscle action potentials in vitro.
patients with AMAN 1-5,9,10

CHaPter 67 Autoimmune Peripheral Neuropathies 907


CHRONIC INFLAMMATORY DEMYELINATING a relapsing course, with spontaneous remissions necessitating
POLYNEUROPATHY the need to periodically evaluate the usefulness of continuing
immunotherapeutic interventions. Because the demyelination
CIDP is the most common form of chronic APN with prevalence is multifocal, affecting spinal roots, plexuses, and proximal nerve
as high as 9/100 000. 2,3,11,12 It is also the most gratifying chronic trunks, 3,13 the clinicopathological picture may be variable,
autoimmune neuropathy because it is treatable in the majority accounting for the different manifestation of symptoms and
of the cases. It can be considered the chronic counterpart of GBS signs. 2,3,11,12 The most notable CIDP variants include the asym-
because of the various clinical, electrophysiological, histological, metrical, unifocal or multifocal, motor–sensory form (Lewis-
and laboratory similarities. CIDP differs from GBS predominantly Sumner syndrome); the pure motor form; the pure sensory form;
by its tempo, mode of evolution, prognosis, and responsiveness the sensory ataxic form; and the pure distal form.
to steroids. First described as a “steroid-responding relapsing
polyneuropathy,” CIDP shares with GBS a variety of common Diagnosis
autoimmune features. In CIDP, CSF protein is elevated, up to sixfold, without pleocytosis
(except if an infection coexists). Nerve biopsy shows demyelination
Clinical Features and Disease Variants and remyelination, occasional epineurial or endoneurial T cells,
The typical CIDP is characterized by a progressive, symmetrical, and several macrophages that are either scattered or in small
proximal and distal muscle weakness; paresthesias; sensory perivascular clusters in the endoneurium (Fig. 67.2). 2,3,11,12
dysfunction; and impaired balance that evolve slowly over at Electrophysiological testing is fundamental for the diagnosis by
least 2 months. 2,3,11,12 Tendon reflexes are absent or reduced. demonstrating the following typical features of demyelination
Cranial nerves rarely may be affected. The course is often in motor and sensory fibers: (i) slow conduction velocity; (ii)
monophasic, with stepwise progression; at times the disease has prolonged distal motor or sensory latencies; (iii) prolonged F






B cell T cell
Mac
Antibodies
Blood–nerve barrier
Mφ



Mφ

IL-2 TNF-α INF-γ
MMPs
Mφ
Normal conduction


MMPs
TNF-α
Mφ NO TNF-α
Mφ
NO Demyelination and
conduction block






Axonal degeneration

FIG 67.2 Diagrammatic scheme of the main cellular and humoral factors implicated in the
demyelinating process of chronic inflammatory demyelinating polyneuropathy (CIDP) leading to
axonal loss. Activated macrophages (Mϕ) and T cells cross the endothelial cell wall of the blood–nerve
barrier and reach the myelinated fibers. Activated, TNF-α-positive Mϕ invade the myelin sheath,
causing Mϕ-mediated segmental demyelination. Axonal loss secondary to demyelination, probably
enhanced by TNF-α and metalloproteinases, may become prominent in the chronic phases of
the disease. Other cytokines, T cells sensitized to unidentified antigens, and putative antibodies
may participate. IL, interleukin; IFN, interferon; MMP, metalloproteinase; Mϕ, activated macrophage;
TNF, tumor necrosis factor.

908 Part Seven Organ-Specific Inflammatory Disease


waves latencies; and (iv) conduction block with dispersion of transmigration across the blood–nerve barrier. Although T cells
the compound muscle action potentials. An associated axonal are not prominent overall, the few CD8 and CD4 cells found
loss is not unusual in the majority of CIDP cases. A variety of endoneurially have monoclonal or oligoclonal restrictions in
diagnostic criteria have been proposed to capture the most their T-cell receptor (TCR) repertoire, implying an antigen-driven
pertinent of the aforementioned features; the revised European T-cell response. 2,3,12,13
Federation of Neurological Societies/Peripheral Nerve Society Humoral factors seem to play a predominant role, especially
(EFNS/PNS) guidelines seem the most appropriate because they with the recent identification of target antigens at the nodes of
offer 81% sensitivity and 96% specificity to capture patients Ranvier in >10% of patients with CIDP, even though in the
more likely to respond to therapies. 2,3,11,12 Routine CSF testing majority of the patients, the pathogenic antigens remain elusive.
and nerve biopsy are not mandatory for the diagnosis, 2,3,11,12 but The beneficial effect of plasmapheresis provides indirect evidence
they can be helpful when the results of electrophysiological testing that some circulatory factors are pathogenic. The concept that
are not convincing, or there is a need to exclude hereditary and antibodies may be implicated dates back to >30 years when
vasculitic neuropathies. Other diseases causing neuropathy that complement-fixing IgG and IgM were found deposited on a
16
should be excluded include severe diabetes (although CIDP seems patient’s myelin sheath. Antibodies to glycolipids LM1, GM1,
more frequent in patients with diabetes), neoplasms, amyloidosis, or GD1b also have been seen in some patients, but less frequently
IgM paraproteinemia (IgG or IgA monoclonal gammopathy of than in GBS and more frequently than in controls. 2,3,11,12 Over-
undetermined significance (MGUS) can be seen in CIDP), whelming evidence accumulated in the last 5 years indicates that
myelomas, vasculitis, alcoholism, exposures to neurotoxic drugs, molecules associated with saltatory conduction at the nodes of
or family history of neuropathy. Ranvier may be more meaningful targets 3,4,10,17-19 because func-
tional blockade in these regions can best account for the rapid
KeY COnCePtS improvement noticeable within days after plasmapheresis or
Autoimmunity in Chronic Inflammatory intravenous immunoglobulin (IVIG). Likely antigenic targets
include neurofascin-186, moesin, and gliomedin (at the node);
Demyelinating Polyneuropathy (CIDP) neurofascin-155 (NF155), contacting/Caspr 1 (CNTN1), and
• Activated macrophages are the predominant endoneurial cell, displacing connexins (at the paranode); and transient–axonal–glycoprotein-1
the Schwann cell cytoplasm, disrupting myelin, and lysing superficial or potassium channels (at the juxtaparanode). 3,4,10,17-19 Evidence
myelin lamellae. from proteomics, transfected cell lines, teased-nerve fibers,
• Complement-fixing immunoglobulin G (IgG) and IgM antibodies are immunocytochemistry, and enzyme-linked immunosorbent assay
deposited on the myelin sheath. (ELISA) has shown that IgG4 antibodies against paranodal NF155
• IgG antibodies to acidic glycolipids LM1, GM1, or GD1b and against and CNTN1 antigens are the most relevant and seemingly
the 28-kDa P0 myelin proteins are detected in the sera of some
patients. pathogenic antibodies that are currently detected in at least 10%
• There is upregulation of DR and B-7 costimulatory molecules in Schwann of patients. 17-19 Of interest, anti-NF155– and CNTN1-positive
cells and macrophages. patients appear to have a distinct clinical phenotype with more
• Serum IgG can induce conduction block when injected into rat nerves. severe disease, axonal involvement, tremors, sensory ataxia, and
• Up to 25% of patients with CIDP harbor specific antibodies against suboptimal response to IVIG 17-19 ; these patients, however, respond
antigens in the nodes of Ranvier; in 10% of them these antibodies better to anti–B cell therapies, such as rituximab.
have been identified as directed against neurofascin-155 and CASPR
causing conduction block. Overall, the immunopathogenetic scheme proposed for GBS
(see Fig. 67.1) is also appropriately applied to CIDP. Molecular
mimicry can be implicated in rare cases of CIDP associated with
Immunopathogenesis melanoma because the carbohydrate myelin epitopes GM2, GM3,
Because of immunopathological similarities to GBS and the and GD3 are also expressed on melanoma cells, and antibodies
20
relapsing–remitting EAN, in CIDP, activated T cells, macrophages, against melanoma cells react with myelin glycoproteins. The
complement, and autoantibodies seem to work in concert with axonal involvement that accompanies demyelination in both
each other to induce an immune attack against peripheral nerve CIDP and GBS, either acutely or after long-standing demyelin-
antigens 2,3,11,12 (as depicted in Fig. 67.1), but no triggering factors ation, is depicted in Fig. 67.2. The relevant nodal target antigens
have been identified so far. are presented in Fig. 67.3 separately 2,3,10 to highlight their rec-
The predominant endoneurial mononuclear cells in CIDP ognized importance in the field of antibody-mediated peripheral
are the macrophages that constitute the final effector cells associ- demyelination.
ated with demyelination because they express activation markers
probably induced by cytokines released by autoreactive T cells MULTIFOCAL MOTOR NEUROPATHY WITH
in situ or the circulation. These cells sequentially penetrate the CONDUCTION BLOCK
basement membrane of the Schwann cell, displace the cytoplasm,
and split the myelin lamellae, resulting in focal lysis of the myelin MMN is a distinct disease that, although rare with prevalence
sheath. 2,3,11,12 Macrophages as well as Schwann cells may serve of 0.6/100 000, should be recognized early because it is treatable.
as antigen-presenting cells (APCs) because they express human It affects males more than females and is more common in those
leukocyte antigen (HLA)-DR and costimulatory molecules B7-1 <50 years of age. MMN presents with progressive weakness,
(CD80) and B7-2 (CD86), whereas their counterreceptors atrophy, and areflexia that often begins in the hands and is
cytotoxic T lymphocyte antigen-4 (CTLA-4) and CD28 are prominent in distal muscle groups supplied by many individual
expressed on rare endoneurial CD4 T cells. 2,3,14 B7-2–deficient peripheral nerves (multifocal). 2,3,21 It differs from vasculitic
15
mice also develop CIDP. Elevated soluble adhesion molecules, neuropathy because it is slow and is painless because it affects
chemokines, cytokines, and metalloproteinases are detected in only the motor nerve fibers. It also differs from the motor variant
serum and CSF in CIDP, probably facilitating lymphoid-cell of CIDP because it is multifocal and asymmetrical. Because some

CHaPter 67 Autoimmune Peripheral Neuropathies 909


Target antigens at the Node of Ranvier: Explain rapid recovery neuropathy occurs in a setting of myeloma, plasmacytoma, or
Waldenström macroglobulinemia, the majority of patients with
paraproteinemic neuropathies do not have a lymphoproliferative
Axon disease, and the monoclonal gammopathy is of undetermined
JP PN N PN JP significance (MGUS). A benign monoclonal gammopathy may
22
occur in up to 1% of normal people >50 years of age. The
PN: Paranode N: Node JP: Juxtaparanode incidence increases to 1.7% above age 70 years and reaches up
Paranode Juxtaparanode to 6% above age 90 years. Monoclonal gammopathies, however,
ECM Myelin are 10 times more frequent in patients with polyneuropathy
gliomedin than in an age-matched control population, and almost 10% of
23
NF186 Tag1 patients with acquired polyneuropathy have MGUS. If these
NF155 Nav gammopathies are categorized into subclasses, the incidence of
Nav
Kv Kv polyneuropathy among patients with IgM monoclonal proteins
23,24
contactin Caspr2 can be as high as 50%, implying that almost 50% of patients
/Caspr ankyrinG with IgM MGUS may have or will develop polyneuropathy. At
βIVspectrin
Connexin 32, 29, 31.3 present, polyneuropathies with MGUS comprise 10% of patients
Axon with acquired neuropathy, 23-25 and paraproteinemic polyneu-
ropathy is a potentially treatable APN. 25
FIG 67.3 Main proteins in the nodal (N), paranodal (PN), and Patients with demyelinating polyneuropathy associated with
juxtaparanodal (JP) regions in the nodes of Ranvier implicated IgG or IgA MGUS are indistinguishable from those with CIDP; the
as antigens in acquired demyelinating neuropathies (Guillain-Barré paraprotein in such patients is coincidental and causally unrelated
syndrome [GBS] and predominantly chronic inflammatory to neuropathy. In contrast, the demyelinating polyneuropathy
demyelinating polyneuropathy [CIDP]). The two main antigenic associated with IgM MGUS is a distinct clinicopathologic entity,
targets in CIDP are neurofascin-155 and CASPR2 located in the and the IgM is considered pathogenic because it is often directed
paranodal regions; antibodies against these proteins are detected against myelin glycoproteins or glycolipids. 2,3,6,24,25
in the serum of 10% of patients with CIDP, resulting in conduction Some patients with paraprotein may have an associated
block and paranodal axonal changes that probably account for amyloidosis derived from the variable region of the Ig light chain,
resistance to IVIG. 4,13 primarily λ. When amyloidosis is present, the neuropathy is
painful, and the sensorimotor deficits are accompanied by
autonomic symptoms consisting of orthostatic hypotension,
patients with MMN can experience cramps and fasciculations, impotence, impaired gastric motility, or frequent diarrhea.
the disease is often erroneously diagnosed as lower motor neuron Amyloid neuropathy is difficult to treat; apart from symptomatic
disease, and treatment is delayed. In contrast to lower motor therapy (mostly opiates), immunosuppressive therapies, especially
neuron disease, however, MMN progresses very slowly, the with the various anti–B-cell agents, and bone marrow transplanta-
weakness is within distributions of peripheral nerves and not tion are largely applied.
multisegmental, and the cranial musculature is often spared.
CSF protein level is normal, an important finding that distin-
guishes MMN from the motor variant of CIDP. ANTIBODIES TO MYELIN-ASSOCIATED
MMN has a distinct electrophysiological criterion, namely, GLYCOPROTEIN IN PATIENTS WITH IgM M
multifocal conduction block in motor nerves. In contrast to
CIDP, in which sensory conduction block is also present, in MONOCLONAL GAMMOPATHIES OF
MMN the sensory conduction remains normal across the nerve UNDETERMINED SIGNIFICANCE
segments that have motor block. The reason for a selective motor POLYNEUROPATHY (ANTI-MAG NEUROPATHY)
involvement is unclear. Differences in the antigenic specificities
in the myelin components between motor and sensory fibers Most of these patients present with a sensory, large-fiber, demy-
are suspected because the ceramide composition of gangliosides elinating polyneuropathy that manifests as sensory ataxia. 2,3,24,26
differs between sensory and motor fibers. Although the immu- Other patients have a sensorimotor polyneuropathy with mixed
nopathology of the disease remains unclear, patients with MMN features of demyelination and axonal loss. CSF protein is often
respond remarkably well to immunotherapy, as discussed later. elevated. Nerve conduction studies have demonstrated slow
Up to 50% of the patients have high antibody titers to GM1 conduction velocity and a rather characteristic prolonged distal
ganglioside, but the role of these antibodies is uncertain. IgM motor and sensory latency indicative of distal demyelination.
GM1 antibodies can be also seen in other autoimmune neu- Sural nerve biopsy demonstrates a diminished number of myelin-
ropathies and in even up to 25% of patients with amyotrophic ated axons. On electron microscopy, there is splitting of the
lateral sclerosis (ALS) who do not have conduction block. outer myelin lamellae, linked to the presence of IgM deposits
in the same area of the split myelin sheath.
Sera from approximately 50% of these patients react with
POLYNEUROPATHIES ASSOCIATED WITH myelin-associated glycoprotein (MAG), a 100-kilodalton (kDa)
MONOCLONAL GAMMOPATHIES OF glycoprotein of the central and peripheral nerve myelin, as well
UNDETERMINED SIGNIFICANCE as other glycoproteins or glycolipids that share antigenic deter-
minants with MAG. 2,3,24,27,28 The antigenic determinant for the
A distinct subset of acquired polyneuropathies has been associated anti-MAG IgM resides in the carbohydrate component of the
3
with a circulating monoclonal protein (Chapter 80). Although MAG molecule. The anti-MAG IgM paraproteins coreact with

910 Part Seven Organ-Specific Inflammatory Disease


SGPG GM1 GD1a GD1b GT1b GQ1b

Gal Gal Gal Gal NeuAc - Gal
Gal NeuAc - NeuAc - NeuAc -
cUA GlcNAc - GlcNAc GlcNAc GlcNAc
- GlcNAc GlcNAc NeuAc - -
- - - NeuAc - NeuAc -
- Gal NeuAc Gal NeuAc Gal NeuAc Gal NeuAc Gal NeuAc Gal
SO 3
Glc Glc Glc Glc Glc Glc





FIG 67.4 Glycolipids implicated as antigens in immune-mediated neuropathies. Sulfate-3-glucuronyl
paragloboside (SGPG) is the glycolipid sharing a carbohydrate epitope with myelin-associated
glycoprotein (MAG), and the terminal sulfated glucuronic acid is a key part of the epitope. GM1
is the ganglioside implicated in motor nerve disorders, and in most cases the terminal Gal (β1-3)
GalNAc epitope, which is shared with GD1b, is involved. The disialosyl moiety implicated in sensory
neuropathies consists of NeuAca2—8NeuAc—and is present in GD1b and GT1b gangliosides, as
well as the simpler GD2 and GD3 gangliosides (not shown). GQ1b ganglioside, which is the target
antigen in Miller Fisher syndrome (MFS), has two disialosyl moieties. Although GD1a ganglioside
has two sialic acid residues they are not linked to each other, so antibodies to GD1a do not
cross-react with anti-GD1b antibodies. The color-coded sugar moieties represent key aspects
of the various epitopes, but carbohydrate sequences recognized by the antibodies may include
additional sugar residues. GlcUA, glucuronic acid; Gal, galactose; G1cNAc, N-acetylglucosamine;
Glc, glucose; GalNAc, N-acetylgalactosamine; NeuAc, N-acetylneuraminic acid (sialic acid).




an acidic glycolipid in the ganglioside fraction of human periph- C3d, and MAG deposition on the dermal myelinated fibers
eral nerves, identified as a sulfoglucuronyl glycosphingolipid and the concurrent loss of nerve fibers. 29
28
(SGPG). In contrast to MAG, which is mostly present in the 3. Injection of serum from patients with IgM anti-MAG/SGPG
central nervous system, SGPG is found only in the peripheral paraprotein supplemented with fresh complement into feline
nerves. The sera of some patients with IgM-MGUS with sensory peripheral nerve causes complement-dependent demyelination
30
ataxia may not react with MAG, but with various gangliosides, and conduction block within 2–9 days of the injection. The
most commonly those that contain either a disialosyl moiety, IgM injected intraneurally localizes to the outer layer of the
such as GD1b, GQ1b, GT1b, GalNac-GM1b, and GalNAc-GD1a, myelin sheath.
or two gangliosides that share epitopes with GM2, or a combina-
tion of GM2 and GM1, GM1 and GD1b. 2,3,6,24,27,28 More than KeY COnCePtS
half of the IgM paraproteins recognize MAG and SGPG, and Autoimmunity in Polyneuropathy With
75% of the rest recognize ganglioside antigens, indicating that Immunoglobulin G (IgM) Monoclonal
acidic glycolipids are the most common antigenic epitopes. 2,3,6,24,27,28 Gammopathy
The glycolipids implicated as antigens in immune-mediated
neuropathies are depicted in Fig. 67.4. • In more than 50% of patients IgM is an antibody against two antigens,
Human anti-MAG antibodies can be detected readily in sera myelin-associated glycoprotein (MAG) and sulfoglucuronyl glycosphin-
with ELISA or preferably with standard Western blot. Because golipid (SGPG).
anti-MAG–reacting sera always recognize the SGPG glycolipid, • In many patients with non-MAG–reacting monoclonal IgM, the IgM
the assay is often performed by using SGPG as antigen instead recognizes (i) gangliosides containing disialosyl moieties, including
GM1, GM2, GD1b, GD1a, and LM1; (ii) sulfatides; and (iii) rarely,
of purified human MAG. It is preferable, however, to use MAG chondroitin sulfate.
as the target antigen, rather than SGPG, because the IgM binds • Overall, in at least 75% of patients the IgM recognizes gangliosides
to MAG 10–100 times the affinity compared with SGPG—that that appear to be the primary antigenic targets.
is, low-affinity anti-MAG antibodies can be missed if SGPG is • IgM is deposited on the homologous myelin sheath and fixes
used as the antigen. complement.
The following factors suggest that these antibodies are related • IgM, when deposited on the myelin sheath, results in disadhesion
and separation of the myelin lamellae and disruption of normal myelin
to the cause of the neuropathy: function.
1. IgM and complement are deposited on the myelinated fibers • Intraneural injection of anti-MAG–reacting IgM or passive transfusion
2,3
on the patient’s sural nerve biopsy, suggesting that activated into experimental animals causes segmental demyelination, whereas
complement may be needed in the induction of demyelination. complement-fixing IgM is immunolocalized to the myelin sheath,
2. IgM recognizes neural cell adhesion molecules and colocalizes causing myelin separation.
with MAG on the areas of the split myelin lamellae, suggesting • Immunization of cats with purified SGPG causes an ataxic neuropathy,
involvement in myelin disadhesion. Skin biopsies from these similar to the one seen in humans, with involvement of the dorsal
root ganglia.
patients have also confirmed the presence of IgM, complement

CHaPter 67 Autoimmune Peripheral Neuropathies 911


4. Systemic transfusion of anti-MAG IgM paraproteins produces vasculitis, Raynaud phenomenon, renal involvement with pro-
31
segmental demyelination in chickens, with deposition of teinuria, and polyneuropathy. Type II cryoglobulinemia may be
IgM on to the outer lamellae of the myelin along with splitting associated with an underlying lymphoproliferative process. There
of the myelin lamellae, similar to that observed in the human is an increased incidence (up to 90%) of hepatitis C virus infection
neuropathy. in patients with mixed cryoglobulinemia. The nerve biopsy shows
5. Immunization of cats with purified SGPG causes an ataxic perivascular inflammatory cuffing with axonal degeneration.
neuropathy, similar to the one seen in humans, with involve-
ment of the dorsal root ganglia including inflammation within PARANEOPLASTIC PERIPHERAL NEUROPATHIES
the ganglionic neurons. 32 WITH ANTI-HU ANTIBODIES

Peripheral neuropathy is not an uncommon complication of
POLYNEUROPATHY, ORGANOMEGALY, cancer, related either to the systemic effects of the tumor or,
ENDOCRINOPATHY, MYELOMA, AND more often, to various neurotoxic chemotherapeutic agents. It
SKIN CHANGES usually affects the small nerve fibers causing numbness or painful
dysesthesias. The most distinct immune-related neuropathy in
A subset of patients with malignant IgG or IgA monoclonal patients with cancer is paraneoplastic sensory neuronopathy
proteins have polyneuropathy with osteosclerotic myeloma. Most (PSN), often associated with small cell lung cancer, and to a
of them have POEMS syndrome (polyneuropathy, organomegaly, lesser degree with breast cancer or other neoplasms, such as
33
36
endocrinopathy, M protein, and skin changes). Not included lymphoma or thymoma. It might be the presenting symptom
in the acronym are several features, such as sclerotic bone lesions, preceding the discovery of the tumor by months. PSN has a
giant lymph node hyperplasia (Castleman disease), papilledema, unique clinical picture, characterized by burning or aching
34
pleural effusion, edema, ascites, and thrombocytosis. More than paresthesias; sensory loss of the large fibers, causing profound
50% of patients with osteosclerotic myeloma of the IgA or IgG sensory gait ataxia and choreoathetotic movements related to
type have a sensorimotor, symmetric polyneuropathy with mixed loss of proprioception in the feet and hands; normal strength;
demyelinating and axonal features and high (usually 200 mg/ and areflexia. Some patients may have autonomic dysfunction,
dL) CSF protein. Pure axonal neuropathies can be also seen. In encephalopathic symptoms, or cerebellar disturbances. CSF
POEMS, the neuropathy tends to be associated with edema in protein is increased, electrophysiological testing shows an axonal
the legs, with hyperpigmentation, sclerodermatous thickening, sensory neuropathy, and nerve biopsy demonstrates axonal
or papular angiomas of the skin, and hypertrichosis with dark degeneration with rare mononuclear cell infiltrates. PSN is a
hair. Endocrinopathy most often includes gonadal failure, ganglionopathy (sensory neuronopathy) caused by a variable
amenorrhea, impotence, gynecomastia, hypothyroidism, diabetes, degree of inflammation in the dorsal root ganglionic neurons.
or elevated prolactin levels. The IgG class is slightly more common These patients have specific IgG anti-Hu autoantibodies directed
than the IgA class, with λ light chain present in the majority of against a closely spaced group of proteins with a molecular weight
36
34
the patients. Bone lesions can be sclerotic, solitary, or multiple, of 35–40 kDa. The antibodies are found in higher titers in CSF,
sparing the skull and the extremities. Pathological changes in suggesting intrathecal synthesis. The Hu protein is also present
lymph nodes resemble those of Castleman disease, which can in the tumors of patients with PSN. Further, low titers of anti-Hu
34
also be associated with polyneuropathy. In POEMS, there is antibodies can be seen in up to 20% of patients with small cell
an imbalance of proinflammatory cytokines with increased IL-1β, lung cancer, even without neurological symptoms, suggesting
IL-6, and tumor necrosis factor-α (TNF-α). Vascular endothelial that PSN may be the result of an autoimmune reaction against
growth factor (VEGF) may play a major role because it induces antigens shared by both the tumor cells and the dorsal root
a rapid increase in vascular permeability and is a growth factor ganglionic neurons. Although the role of anti-Hu antibodies in
important in angiogenesis and endothelial cells. 34 the causation of PSN is unclear, these antibodies are specific
In some patients, the neuropathy responds to steroids, markers to detect an occult small cell lung cancer in patients
tamoxifen, or alkylating agents. In others, it may respond to the who present with sensory ataxic neuropathy. Some patients may
removal or irradiation of the solitary sclerotic lesion, suggesting have other paraneoplastic antibodies, such as collapsing response
that the tumor may secrete neurotoxic factors. IVIG and plas- mediator protein (CRMP-5) often referred to as anti-CV2. 36
mapheresis are ineffective. The median survival is 165 months. 35
Recently, autologous peripheral blood stem cell transplantation AUTOIMMUNE AUTONOMIC NEUROPATHIES
has been shown to result in significant improvement with reduc-
tion of VEGF, improved nerve conduction velocity, and increased Autoimmune autonomic neuropathy (AAN) is highlighted by
survival. 35 circulating antibodies against the ganglionic nicotinic acetyl-
37
choline receptors (AChRs). These patients present with a
Cryoglobulinemic Neuropathy subacute (within 4 weeks) or chronic (within months) onset of
Cryoglobulins are proteins that precipitate in the cold and neurogenic orthostatic hypotension, defined as a systolic blood
redissolve when heated (Chapter 58). There are three types of pressure reduction of at least 30 mm Hg or mean blood pressure
cryoglobulin: type I, which is monoclonal, often of the IgM and reduction of at least 20 mm Hg that occurs within 3 minutes
IgG class; type II, which is mixed polyclonal, with one monoclonal of head tilting. The subacute onset is often preceded by a viral
(often monoclonal IgM with polyclonal IgG); and type III, which infection. In addition, patients demonstrate three or four
is polyclonal (often IgM and IgG). Polyneuropathy occurs most parasympathetic/enteric symptoms: sicca (dry eyes and dry
often with mixed cryoglobulinemias and presents as distal, sensory, mouth); abnormal pupillary response to light; upper gastro-
symmetrical polyneuropathy or as mononeuropathy multiplex. intestinal symptoms (early satiety, postprandial nausea, and
These patients also have purpura, polyarthralgias, cutaneous vomiting that lead to severe weight loss); and neurogenic bladder.

912 Part Seven Organ-Specific Inflammatory Disease


Patients with more severe cholinergic impairment have higher-titer
antibodies against ganglionic AChRs. Some of these symptoms
can be passively transferred to mice injected with the patient’s
IgG, suggesting that these antibodies may be pathogenic. Further,
rabbits immunized with a fragment of ganglionic AChR protein
37
exhibit autonomic failure, similar to the human disease. Because
ganglionic AChRs have also been found in small cell lung car-
cinoma cell lines, cancer may be a potential initiator of ganglionic
AChR autoimmunity.

A
MONONEUROPATHY MULTIPLEX AND
LOCALIZED, ISOLATED VASCULITIS OF THE
PERIPHERAL NERVES

Polyneuropathy is a common manifestation of systemic vasculitis.
It occurs in patients with polyarteritis nodosa; connective tissue HLA-DR,
diseases, such as rheumatoid arthritis or Sjögren syndrome; Macrophages,
hypersensitivity vasculitis; Churg-Strauss syndrome; temporal CD8 T cells
arteritis; and viral infections, such as those with HIV, human
T-lymphocyte virus (HTLV)-1, and hepatitis B and C viruses.
It classically presents as mononeuritis multiplex affecting several
individual nerves with painful weakness and paresthesias caused B
by ischemia and infarcts caused by inflammation of endoneurial
blood vessels. There is, however, a distinct vasculitic entity local-
ized only to the peripheral nerve, known as isolated peripheral
nerve vasculitis (PNV). PNV involves the small and medium-sized
arteries of the epineurium and perineurium and causes ischemic
changes within the peripheral nerve. The presentation is similar
to the vasculitic neuropathy seen in systemic vasculitis—the only
difference is the lack of systemic organ involvement, slower onset
and progression, and negative serology. The diagnosis is confirmed
with nerve biopsy of the sural, superficial peroneal, or superficial
radial nerve. When nerve biopsy is combined with muscle biopsy, C
the diagnostic yield is higher. PNV has a better prognosis
compared with systemic vasculitides and is a treatable form of FIG 67.5 Serial sections of a nerve biopsy from a patient with
neuropathy. An evaluation for PNV should include all the tests human immunodeficiency virus (HIV)–chronic inflammatory
needed to exclude systemic vasculitis and cryoglobulinemia, as demyelinating polyneuropathy stained for (A) human leukocyte
well as hepatitis B and C infections, which can be associated antigen (HLA)-DR, (B) macrophages, and (C) CD8 T shows that
with PNV. the majority of the endoneurial cells are macrophages. Only rare
CD8 cells are noted.
NEUROPATHY WITH VIRUSES AND HUMAN
IMMUNODEFICIENCY VIRUS

Neuropathy can be seen in a setting of infectious, viral, or bacterial class II molecules on Schwann cells, endothelial cells, and/or
processes. In patients with Lyme disease, various neuropathies, macrophages, but sparse presence of CD8 and CD4 T cells, is
including GBS and mononeuritis (Bell palsy), have been noted. also noted (Fig. 67.5). It is possible that systemic viral infection
Other infections, such as CMV, hepatitis, herpes, leprosy, Chagas or rare HIV-infected endoneurial lymphoid cells may release
disease, and diphtheria, can affect the peripheral nerves, triggering cytokines that expose new nerve antigens against which there is
autoimmune peripheral neuropathy. no self-tolerance, generating a tissue-specific autoimmune attack.
Common neuropathies seen today in a setting of a viral A rare neuropathy seen in later-stage HIV infection is a
infection are those associated with HIV and include GBS, CIDP, lumbosacral polyradiculoneuropathy related to CMV infection
acute ganglioneuritis, or mononeuritis multiplex; they occur that affects roots and sensory ganglia. It presents with lower-
early in the infection, or they are the presenting manifestation extremity muscle weakness, sacral and distal paresthesias, areflexia,
38
of unsuspected HIV infection. HIV has been cultured from the and atrophy, mostly of the legs, associated with sphincteric
peripheral nerves, and HIV viral RNA has been amplified from dysfunction resembling cauda equina syndrome. CMV inclusions
sural nerve biopsies of some patients in the author’s laboratory. can be found within Schwann cells or endothelial cells (Fig.
However, there is no convincing evidence that the neuropathy 67.6). Early recognition is important because anti-CMV therapy
results from direct infection of the peripheral nerves by the with ganciclovir or foscarnet can be helpful.
virus. Immunocytochemical studies have shown that HIV is At present, the most common neuropathy in patients with
present only in rare endoneurial macrophages, but not within acquired immunodeficiency syndrome (AIDS) is a painful sensory
Schwann cells or axons. A strong expression of HLA class I and axonal neuropathy that affects up to 70% of adults with AIDS and

CHaPter 67 Autoimmune Peripheral Neuropathies 913



High-Dose Intravenous Immunoglobulin
1,4
On the basis of the results from two controlled studies, IVIG
(Chapter 84), given at 2 g/kg over 2–5 days, has been shown to be
equally effective as plasmapheresis, with no added benefit when
the two procedures were combined. The decision as to which
treatment to choose is governed by circumstances, availability
of the treatment modality, experience, age of the patient, and
other associated conditions. Early relapses can also occur with
IVIG, as often as with plasmapheresis. IVIG has become the
therapeutic choice worldwide because it is easy to administer
and more readily available and because time to initiate treatment
is of the essence.
Steroids are ineffective in GBS and may even increase the
incidence of future relapses. Combining IVIG with IV methyl-
FIG 67.6 Cross-section of a root from a patient with human prednisolone has shown no significant added benefit.
immunodeficiency virus (HIV)–associated Guillain-Barré syndrome
(GBS) shows cytomegalovirus inclusions within the Schwann Chronic Inflammatory Demyelinating Polyneuropathy
cell. Prednisone
CIDP has been originally described as a classic steroid-responsive
polyneuropathy. The efficacy of steroids was proven in a controlled
study, albeit with inadequate blinding, but reconfirmed in
38
occurs later in the disease. It is caused by a cumulative effect, another. 2,3,11,12,39 A high-dose regimen of 80–100 mg prednisone
on the peripheral nerves, of various endogenous or exogenous daily is preferred, followed by tapering to every-other-day dosing.
neurotoxins related to a multisystem disease and dysfunction of Azathioprine, cyclosporine, or mycophenolate can be used as
many organs along with toxicity from various antiretroviral drugs. steroid-sparing agents, but their efficacy, although not tested in
Clinical findings include distal painful dysesthesias, sensory loss controlled studies, has been disappointing overall. Methotrexate
or hypesthesia, areflexia, and, in advanced cases, distal weakness. in a controlled study was ineffective. 2,3,11,12,39
Despite the relative lack of motor involvement, the severity of
neuropathic pain can be disabling. Intravenous Immunoglobulin
In several controlled studies, 2,3,11,12,39 IVIG has been effective in
TREATMENT the majority of patients with CIDP. The more chronic the disease
and more severe the axonal degeneration that has taken place,
APNs are clinically important because they are potentially treatable the lower are the chances that the recovery will be complete or
with various immunosuppressive, immunomodulating, or significant. IVIG, in the largest-ever controlled study, has been
chemotherapeutic agents. The selection of an effective protocol proven an effective first-line therapy, and maintenance therapy
is based on the results of experimental therapeutic trials, clinical has prevented relapses.
experience, and the risk–benefit ratio of available therapies. The
author’s approach to the treatment of these disorders is described Plasmapheresis
below. Plasmapheresis has been also effective in controlled studies. 2,3,11,12
After a series of six plasma exchanges, maintenance therapy,
Guillain-Barré Syndrome with one exchange at least every 8 weeks, may be required if this
Supportive Care therapy is beneficial. IVIG has now replaced plasmapheresis,
The dramatic reduction in the mortality of GBS is mainly although in the author’s experience, some patients may benefit
attributed to the availability of ICUs, improvement of respiratory more from steroids, others more from IVIG, and still others
support, antibiotic therapy, and control of autonomic cardiac more after plasmapheresis.
dysregulation. A patient with GBS is best monitored in an ICU,
even if respiratory compromise is not evident at the time of Polyneuropathy With Paraproteinemias
admission. When forced vital capacity (FVC) drops or bulbar Patients with benign IgG or IgA demyelinating polyneuropathies
weakness is severe, intubation is necessary. respond in a manner similar to CIDP patients. Patients with
malignant paraproteinemias should be treated with chemotherapy,
Plasmapheresis as needed for the underlying disease. When the neuropathy is
In several double-blind controlled studies, plasmapheresis has axonal, treatments are generally disappointing.
been shown to be effective if performed within the first week For IgM anti-MAG demyelinating polyneuropathies, treatments
from onset of the illness. A series of five or six exchanges, with with prednisone plus chlorambucil, plasmapheresis, and IVIG 2,3,40
one exchange every other day, is sufficient. Early relapses can has shown a variably marginal benefit. Rituximab, an mAb against
41
occur in up to 20% of patients, who may require a second series CD20, is the most promising therapy, providing efficacy in
1-5
of plasma exchanges. Plasmapheresis has been shown to be almost 40% of the patients in a small double-blind study, as
33
effective even in mild cases of GBS; two exchanges are sufficient confirmed later with a larger study, even though both did not
for mild GBS, and four are optimal for moderate cases, but there reach significance. Additional, uncontrolled series with many
is no difference between those who receive four plasma exchanges patients, have confirmed that rituximab is effective in 30–40%
and those who receive six. of these patients.

914 Part Seven Organ-Specific Inflammatory Disease



MULTIFOCAL MOTOR NEUROPATHY Please check your eBook at https://expertconsult.inkling.com/
for self-assessment questions. See inside cover for registration
MMN responds very well only to IVIG, which is the treatment details.
of choice based on controlled trials. In difficult cases, cyclophos-
phamide or rituximab may be promising, but no controlled REFERENCES
studies have been carried out. 2,3,21
1. Yuki N, Hartung H-P. Guillain-Barre syndrome. N Engl J Med
Paraneoplastic Anti-Hu Neuropathy 2012;366:2294–304.
Anecdotally, some of these patients have responded to plasma 2. Dalakas MC. Pathophysiology of autoimmune polyneuropathies. Presse
exchange or IVIG, but overall this neuropathy has not been Med 2013;42(6 Pt 2):e181–92.
consistently responsive to available therapies. 3. Dalakas MC. Pathogenesis of autoimmune neuropathies. Biochim
Biophys Acta 2015;1852:658–66.
Vasculitic Neuropathies 4. Willison HJ, Jacobs BC, van Doorn PA. Guillain-Barré syndrome. Lancet
2016 Feb 29. pii: S0140-6736(16).
For isolated peripheral nerve vasculitis, a combination of pred- 5. Kuwabara S, Yuki N. Axonal Guillain-Barre syndrome: concepts and
nisone 1.5 mg/kg/day with cyclophosphamide 2 mg/kg/day orally, controversies. Lancet Neurol 2013; 12; 1180-8.
2
or 1 g/m intravenously monthly for 6 months, are the treatments 6. Dalakas MC, Quarles RH, editors. Autoimmune ataxic neuropathies
of choice; specific treatment protocol may vary from patient to (sensory ganglionopathies): are glycolipids the responsible autoantigens?
patient. The administration of cyclophosphamide may not be Ann Neurol 1996;39:419–22.
necessary for >6 months, as in systemic vasculitis. Plasmapheresis 7. Illa I, Ortiz N, Gallard E, et al. Acute axonal Guillain–Barré syndrome
has been tried in cryoglobulinemic neuropathies, with variable with IgG antibodies against motor axons following parenteral
results. gangliosides. Ann Neurol 1995;38:218–24.
8. Cao-Lormeau V-M, et al. Guillain-Barre Syndrome outbreak associated
Human Immunodeficiency Virus Neuropathies with Zika virus infection in French Polynesia: a case controlled study.
Lancet 2016;387(10027):1531–9.
The two demyelinating neuropathies, GBS and CIDP, are treated 9. Uncini A, Kuwabara S. Nodopathies of the peripheral nerve: an emerging
with the same immunomodulatory therapies as used in HIV- concept. J Neurol Neurosurg Psychiatry 2015;86:1186–95.
negative patients with IVIG being the preferable choice. Ganci- 10. Stathopoulos P, Alexopoulos H, Dalakas MC. Autoimmune antigenic
clovir may be helpful in CMV-related polyradiculoneuropathy. targets at the node of Ranvier in demyelinating disorders. Nat Rev Neurol
Painful sensory neuropathy can be quite disabling because of 2015;11:143–56.
intractable pain. Tricyclic antidepressants (TCAs), nonsteroidal 11. Dalakas MC. Advances in the diagnosis, pathogenesis and treatment of
antiinflammatory drugs (NSAIDs), anticonvulsants (carbam- CIDP. Nat Rev Neurol 2011;7(9):507–17.
azepine, gabapentin, topiramate), and topical capsaicin in various 12. Koller H, Kieseier BC, Jander S, et al. Chronic inflammatory
combinations provide some relief from neuropathic pain. demyelinating polyneuropathy. N Engl J Med 2005;352:1343–56.
13. Schneider-Hohendorf T, Schwab N, Uceyler K, et al. T cell immunity in
CIDP. Neurology 2012;78:402–8.
14. Murata K, Dalakas MC. Expression of the co-stimulatory molecule BB-1,
the ligands CTLA-4 and CD28 and their mRNAs in chronic inflammatory
On tHe HOrIZOn demyelinating polyneuropathy. Brain 2000;123:1660–6.
15. Salomon B, Rhee L, Bour-Jordan H, et al. Development of spontaneous
• Identification of common causes that break tolerance, either in con-
nection with the gut microbiome or exogenous agents, and expansion autoimmune peripheral polyneuropathy in B7-2-deficient NOD mice.
of the current limited data on molecular mimicry between nerve J Exp Med 2001;194:677–84.
glycoproteins and viral or bacterial antigens 16. Dalakas M, Engel WK. Immunoglobulin deposits in chronic relapsing
• Development of neuroimaging capabilities to image peripheral nerves polyneuropathies. Arch Neurol 1980;37:637–40.
and dorsal roots in vivo and quantify inflammation, demyelination and 17. Devaux JJ, Miura Y, Fukami Y, et al. Neurofascin-155 IgG4 in chronic
axonal degeneration, providing an accessible and reliable tool for inflammatory demyelinating polyneuropathy. Neurology 2016;86:800–7.
diagnosis and monitoring response to therapies, in a model similar to 18. Miura Y, Devaux JJ, Fukami Y, et al. Contactin 1 IgG4 associates to
magnetic resonance imaging (MRI) in multiple sclerosis chronic inflammatory demyelinating polyneuropathy with sensory ataxia.
• Performance of proteome studies aimed to identify biomarkers of Brain 2015;138:1–8.
nerve autoimmunity that may lead to specific therapies 19. Dalakas MC, Gooch C. Close to the node but still far: What antibodies
• Trials with target-specific therapies for acute and chronic demyelinating tell us about CIDP and its therapies. Neurology 2016;86:796–7.
neuropathies, applied in combination with the existing therapies, target- 20. Weiss MD, Luciano CA, Semino-Mora C, et al. Molecular mimicry in
ing early in the disease process complement activation, regulatory T chronic inflammatory demyelinating polyneuropathy and melanoma.
cell (Treg) functions, key proinflammatory cytokines, and B cells Neurology 1998;51:1738–41.
• Identification of agents and trophic factors that could prevent axonal 21. Van Asseldonk JT, Franssen H, Van den Berg-Vos RM, et al. Multifocal
degeneration from the outset, promote remyelination, prevent axonal motor neuropathy. Lancet Neurol 2005;4:309–19.
loss, or trigger axonal regeneration and reverse, early in the disease 22. Kyle RA, Therneau TM, Rajkumar SV, et al. Prevalence of monoclonal
process, a seemingly “permanent” clinical deficit
gammopathy of undetermined significance. N Engl J Med
2006;354:1362–9.
23. Kelly JJ, Kyle RA, O’Brien PC, et al. The prevalence of monoclonal
gammopathy in peripheral neuropathy. Neurology 1981;31:1480–3.
ACKNOWLEDGMENTS 24. Latov N, Hays A, Sherman WH. Peripheral neuropathy and anti-MAG
antibodies. Crit Rev Neurobiol 1988;3:301–32.
The author thanks the various Neurology Fellows who provided 25. Dalakas MC. Pathogenesis and treatment of anti-MAG neuropathy. Curr
excellent care to his patients; and Drs. Amjad Ilyas and Richard Treat Options Neurol 2010;12:71–83.
Quarles for help with immunochemistry of MAG and SGPG 26. Dalakas MC, Engel WK. Polyneuropathy and monoclonal gammopathy:
and gangliosides. studies of 11 patients. Ann Neurol 1981;10:45–52.

CHaPter 67 Autoimmune Peripheral Neuropathies 915


27. Ilyas AA, Quarles RH, McIntosh TD, et al. IgM in a human neuropathy 35. D’Souza A, Lacy M, Gertz M, et al. Long-term outcomes after autologous
related to paraproteinemia binds to a carbohydrate determinant in the stem cell transplantation for patients with POEMS syndrome
myelin-associated glycoprotein and to a ganglioside. Proc Natl Acad Sci (osteosclerotic myeloma): a single-center experience. Blood
USA 1984;81:1225–9. 2012;120:56–62.
28. Ilyas AA, Quarles RH, Dalakas MC, et al. Polyneuropathy with 36. Muppidi S, Vernino S. Paraneoplastic neuropathies. Continuum
monoclonal gammopathy: glycolipids are frequently antigens for IgM (Minneap Minn) 2014;20:1359–72.
paraproteins. Proc Natl Acad Sci USA 1985;82:6697–700. 37. Lennon VA, Ermilov LG, Szurszewski JH, et al. Immunization with
29. Lombardi R, Erne B, Lauria G, et al. IgM deposits on skin nerves in neuronal nicotinic acetylcholine receptor induces neurological
anti-myelin-associated glycoprotein neuropathy. Ann Neurol autoimmune disease. J Clin Invest 2003;111:907–13.
2005;57:180–7. 38. Dalakas MC, Pezeshkpour GH. Neuromuscular diseases associated
30. Willison HJ, Trapp BD, Bacher JD, et al. Demyelination induced by with human immunodeficiency virus infection. Ann Neurol
intraneural injection of human antimyelin associated glycoprotein 1988;23:38–48.
antibodies. Muscle Nerve 1988;11:1169–76. 39. Hughes RA, Donofrio P, Bril V, et al. Intravenous immune globulin (10%
31. Tatum AH. Experimental paraprotein neuropathy; demyelination by caprylate-chromatography purified) for the treatment of chronic
passive transfer of human IgM anti-MAG. Ann Neurol 1993;33:502–6. inflammatory demyelinating polyradiculoneuropathy (ICE study): a
32. Ilyas AA, Gu Y, Dalakas MC, et al. Induction of experimental ataxic randomised placebo-controlled trial. Lancet Neurol 2008;7:136–44.
sensory neuronopathy in cats by immunization with purified SGPG. J 40. Dalakas MC, Quarles RH, Farrer RG, et al. A controlled study of
Neuroimmunol 2008;193:87–93. intravenous immunoglobulin in demyelinating neuropathy with IgM
33. Leger JM, Guimaraes-Costa R, Muntean C. Immunotherapy in peripheral gammopathy. Ann Neurol 1996;40:792–5.
neuropathies. Neurother 2016;13:96–107. 41. Dalakas MC, Rakocevic G, Salajegheh M, et al. Placebo-controlled trial of
34. Dispenzieri A, Kyle RA, Lacy MQ, et al. POEMS syndrome: definitions rituximab in IgM anti-myelin associated glycoprotein antibody
and long-term outcome. Blood 2003;101:2496–506. demyelinating neuropathy. Ann Neurol 2009;65:286–93.

CHaPter 67 Autoimmune Peripheral Neuropathies 915.e1


MUL t IPL e -CHOIC e QU e S t IO n S

1. Which of the following findings predicts an incomplete 3. Which of the following tests is the most useful in establishing
recovery in patients with Guillain-Barré syndrome (GBS)? the diagnosis of GBS?
A. Slow initial progression A. Sural nerve biopsy
B. Absence of bulbar findings B. Cerebrospinal fluid (CSF) protein levels
C. Presentation in the third decade C. Nerve conduction study
D. Requirement of mechanical ventilation D. Brain magnetic resonance imaging (MRI)
2. Which is the most common form of GBS? 4. Which of the following finding is characteristic of chronic
A. Acute inflammatory demyelinating polyneuropathy inflammatory demyelinating polyneuropathy (CIDP)?
B. Acute motor axonal neuropathy A. Asymmetrical weakness
C. Acute motor–sensory neuropathy B. Sensory dysfunction
D. Miller Fisher syndrome C. Normal peripheral reflexes
D. Cranial nerve involvement

68









Immunological Renal Diseases



Meryl Waldman, Howard A. Austin III, James E. Balow







Compelling clinical, pathological, and experimental data indicate Urinary RBCs that result from glomerular or tubulointerstitial
that most forms of glomerular diseases manifest some element of pathology are more likely to appear dysmorphic (abnormal shapes
1
immune-mediated injury. Major advances in our understanding and sizes, fragmented); when these dysmorphic RBCs, called
of the etiology and pathogenesis of the various glomerular diseases acanthocytes, are present, it is usually appropriate to refer the
have occurred in the past decade. However, the primary events patient to nephrology for further evaluation. Erythrocyte and/or
or inciting factors that trigger the host immune responses and leukocyte casts are indicative of glomerulonephritis (or interstitial
secondary pathways that are directly or indirectly pathogenic nephritis). Cellular casts can be formed from erythrocytes and/
to the kidney are still not fully elucidated. In some conditions, or leukocytes that enter the tubular lumen because of glomerular
normal or allergic immune responses to exogenous infectious or tubular inflammation (Fig. 68.1).
agents or drugs can lead to incidental nephropathic injury (e.g.,
postinfectious glomerulonephritis, serum sickness). In the case PROTEINURIA
of autoimmune diseases, nephropathic processes range from loss
of self-tolerance to specific constitutive renal tissues (e.g., anti- Glomerular proteinuria results from a loss of the size-selective
glomerular basement membrane [GBM] disease) or to extrarenal and/or charge-selective properties of the glomerular capillary
tissues and cells (e.g., antineutrophil cytoplasmic autoantibodies wall and disruptions of the glomerular epithelial cells (podocytes),
[ANCAs]). Other mechanisms include excessive and unregulated allowing plasma proteins (especially albumin) to leak into the
polyclonal immune responses that produce nephritogenic immune filtrate. Tubulointerstitial nephropathy often leads to impaired
1,2
complexes (e.g., lupus nephritis). Recent advances have begun tubular absorption of other normally filtered low-molecular-
to uncover candidate antigens involved in the pathogenesis of weight proteins; this so-called tubular proteinuria exhibits a
immune-mediated renal diseases (e.g., some subsets of mem- characteristic pattern on urine protein electrophoresis (low
branous nephropathy [MN]). But it has become increasingly fraction of albumin), rarely exceeds 2 g/day, and is often associated
apparent that the immune system does not operate in isolation with other manifestations of tubular dysfunction.
and that there are extraordinarily complex interactions among Estimates of proteinuria are based on 24-hour urine collections
vast networks involving components of native and adaptive or on the protein/creatinine or albumin/creatinine concentration
immune systems, humoral and cell-mediated immune systems, ratios in random urine samples. Normally, these ratios should
small-molecular-weight mediators derived from lymphoid be <0.1. Filtration of abnormal plasma proteins can be responsible
and other cell types, complement factors and their regulatory for proteinuria (e.g., multiple myeloma or monoclonal immu-
proteins, other inflammatory and coagulation system pathways, noglobulin [Ig] light-chain disease). This type of proteinuria
microvascular biology, and tissue repair, as well as sclerosis and (paraproteinuria) may be undetected by albumin-sensitive dipstick
fibrosis reactions. Underlying this constellation are associated screening. Paraproteinemia may also be undetected or under-
genetic risk factors that modulate these responses and predispose estimated by standard plasma electrophoresis; however, an assay
to a nephritogenic response. Rapidly evolving molecular and for serum free light chains is more sensitive for detection of low
genetic technologies with the tools of modern systems biology levels of circulating light chain paraproteins. Identification of
and bioinformatics will continue to unravel these complex specific Ig-derived paraproteinuria usually requires urine immu-
interactions. 3 nofixation electrophoresis (Fig. 68.2)
Appropriate evaluation of patients with immune-mediated
kidney diseases requires particular attention to the findings of NEPHROTIC SYNDROME
urinalysis, assessment of the type and amount of proteinuria,
tests of renal functions, and renal biopsy. Urine microscopy also Nephrotic syndrome is characterized by substantial degrees of
plays a pivotal role in the assessment of urinary disorders. proteinuria (>3.5 g/day or protein to creatinine ratio >2.5)
resulting in hypoalbuminemia, edema, hyperlipidemia, and
HEMATURIA lipiduria. The degree of proteinuria can offer a helpful diagnostic
clue because some immune-mediated conditions with typically
Red blood cells (RBCs) that emanate from lesions of the calices, diffuse glomerular disease (e.g., MN, systemic lupus erythematosus
ureters, bladder, or urethra tend to maintain their normal mor- [SLE]) are more likely than others with typically focal disease
phology; when nondysmorphic RBCs are present, it is usually (e.g., IgA nephropathy, ANCA-associated glomerulonephritis)
appropriate to refer the patient to urology for further evaluation. to be associated with nephrotic syndrome.

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