Central Pontine Myelinolysis
Central pontine myelinolysis, also called
osmotic demyelination syndrome, is a disorder characterized pathologically by dissolution of
the myelin sheaths of fibers within the central aspect of the basis pontis. In extreme cases
there may be extension to the pontine tegmentum, midbrain, thalamus, internal capsule, and
cerebral cortex. The myelinolysis occurs with relative sparing of the nerve cells and axon
cylinders. Many patients are asymptomatic, and at the other extreme are patients whose
symptoms are masked by coma. Most clinically diagnosed cases present with spastic
quadriparesis, pseudobulbar palsy, and acute changes in mental status, with progression
possible to altered levels of consciousness and death. Survival is possible with varying residual
neurologic deficits. Although initial reports were largely confined to chronic alcoholics,
central pontine myelinolysis has also been seen in patients with electrolyte disturbances,
particularly hyponatremia that has been rapidly corrected, and in liver transplant patients being
immune-suppressed with cyclosporine.
The lesions on MR are seen best as areas of hypointensity on IR images and hyperintensity
on T2-weighted images in the central pons with sparing of the pontine tegmentum and
ventrolateral pons. Lesions have an oval shape on sagittal images, a bat-wing configuration
on coronal images and various shapes on the axial images.
The extrapontine lesions often
resolve completely, leaving some residual pontine abnormality. Enhancement is not a feature
of this disease, but severe cases may show peripheral enhancement of the pontine lesions.
Diffusion techniques usually show increased diffusibility and increased apparent diffusion
coefficient (ADC), but restricted diffusion and decreased ADC can be seen acutely during the
first week.
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