15th Mar 2021

ICRI CASE OF THE WEEK

Contributed by : Dr. G. Ananta Ram, Dr. Mohit Lakhani
KIMS Hospitals, Secunderabad

Copyright of the Case belongs to : Dr G Ananta Ram

Clinical Details

• A 24 years old female patient came with generalized weakness and her serum
sodium levels were 105 mEq/L, but other electrolyte levels were normal.

• Her serum sodium levels normalized (138 mEq/L) in two days, her symptoms
resolved, and she was discharged.

• However, over the next two days, she developed dysarthria, and
incoordination.

• A week later she presented to our institution with complaints of slurring of
speech and weakness in all 4 limbs with dysphagia to liquids.

What should be the normal signal intensity of the basis pontis?

Sparing of lateral corticospinal tract and ventrolateral pons is seen.
No evidence of blooming in the affected region.

• MRI Brain showed T1 hypo, T2 and FLAIR hyperintense signal changes
involving the central aspect of the pons with relative sparing of the
corticospinal tract and ventrolateral pons (Trident shaped).

• Corresponding area shows diffusion restriction with no foci of blooming
on SWI sequence.

Which of the following is true in relation to this syndrome?

a) This condition is irreversible
b) It is caused by the destruction of the layer covering nerve cells in the middle

of the brainstem
c) It occurs on its own
d) Usually contrast enhancement is seen in the affect region

Discussion

• Osmotic demyelination syndrome (ODS) is brain cell dysfunction. It is caused by the
destruction of the layer (myelin sheath) covering nerve cells in the middle of the brainstem
(pons).

• Osmotic myelinolysis affects regions where oligodendroglial cells surround large neurons in
close proximity to the capillary-rich gray matter. Within the pons, pontocerebellar fibers are
the most susceptible, followed by the rostrocaudal tracts; the tegmentum is typically spared,
but is affected in severe cases.

• When the myelin sheath that covers nerve cells is destroyed, signals from one nerve to
another aren't properly transmitted. Although the brainstem is mainly affected, other areas
of the brain can also be involved.

• The most common cause of ODS is a quick change in the body's sodium levels. This most
often occurs when someone is being treated for low blood sodium (hyponatremia) and the
sodium is replaced too fast. Sometimes, it occurs when a high level of sodium in the body
(hypernatremia) is corrected too quickly.

• ODS does not usually occur on its own. Most often, it's a complication of treatment
for other problems, or from the other problems themselves.

• Bilateral and symmetric lesions with restricted diffusion, no or mild mass effect, and
no enhancement are often noted in toxic and metabolic disorders. Inborn errors of
metabolism and hypoxia may have similar imaging features, correlation with clinical
history helps us in arriving at the imaging diagnosis.

• DWI has the capability of detecting lesions undetectable on T2, within 24 hrs.
• 50% of cases -isolated pontine lesions
• 30% of cases -combined pontine and extrapontine(basal ganglia, thalami and white

matter) lesions.
• 20% of cases -only extrapontine lesions

• The main signs or symptoms are seizures and altered mental status, often biphasic,
with altered mental status when hyponatremia has manifested and subsequent
improvement after sodium correction followed by new rapid deterioration after
approximately 1 week.

• Histopathologically, non-inflammatory demyelination (characterized by
intramyelinitic splitting, vacuolization, and myelin sheath rupture) sparing
neurons, axons, and blood vessels, spreads centrifugally from the median
pontine raphe like a “brush fire”.

• CT may demonstrate low attenuation crossing the midline in the lower pons.

• The earliest change is seen on DWI with restriction in the lower pons. The T1
and T2 changes may take up to two weeks to develop. This region has a classic
trident shaped appearance. Occasionally gadolinium enhancement is also
demonstrated, just as in the acute phase of multiple sclerosis (MS) plaque.

• The peripheral fibers (ventrolateral longitudinal fibers), as well as the
periventricular and subpial regions, are typically spared.

• ODS is an emergency disorder that needs to be treated in the hospital though
most people with this condition are already in the hospital for another
problem.

• There is no known cure for central pontine myelinolysis. Treatment is focused
on relieving symptoms.

• Physical therapy may help maintain muscle strength, mobility, and function in
weakened arms and legs.

• The nerve damage caused by central pontine myelinolysis is often long-lasting.
The disorder can cause serious long-term (chronic) disability.

Differential Diagnosis

Many chronic medical disorders greatly increase vulnerability to osmotic insult

1. Chronic ischemic changes from microangiopathic disease: These lesions may
involve a similar location as CPM but typically do not have restricted diffusion
and do not spare the corticospinal tracts. In addition, this entity almost
always has associated supratentorial white matter changes.

2. Acute pontine infarct, acute disseminated encephalomyelitis, and
demyelination: These lesions may have a similar appearance to CPM but
typically are asymmetric and may not spare the peripheral pons and
corticospinal tracts.

Teaching Points

• Acute demyelination is seen in the setting of osmotic changes, typically with
rapid correction of hyponatremia.

• Trident-shaped lesion in the central pons (sparing the pontine tegmentum, and
the peripheral rim of the basis pontis). Sparing of the transverse pontine fibers
is described.

• Inborn errors of metabolism and hypoxia may have similar imaging features,
correlation with clinical history helps us in arriving at the imaging diagnosis.

• DWI has the capability of detecting lesions undetectable on T2, within 24 hrs.

References

• AdamsRD, Victor M, Mancall EL. Central pontine myelinolysis: a hitherto
undescribed disease occurring in alcoholic and malnourished patients. AMA
Arch Neurol Psychiatry1959; 81(2): 154–172.

• MartinRJ. Central pontine and extrapontine myelinolysis: the osmotic
demyelination syndromes. J Neurol Neurosurg Psychiatry2004; 75(suppl 3).

• SternsRH, Riggs JE, Schochet SS Jr. Osmotic demyelination syndrome following
correction of hyponatremia. N Engl J Med1986; 314(24).

• LamplC, Yazdi K. Central pontine myelinolysis. Eur Neurol2002; 47(1).
• LaurenoR, Karp BI. Myelinolysis after correction of hyponatremia. Ann Intern

Med1997; 126(1).