Osmotic demyelination syndromes: central and extrapontine myelinolysis.

Osmotic demyelination syndromes are often progressive disorders, with clinical features ranging from a mild tremor or dysarthria to a progressive quadraparesis. Although rapid correction of serum sodium is known to be a potent causative factor, additional pathogenic factors exist, which appear critical in predisposing pontine and extrapontine glia to osmotic stress. Interestingly, several cases of osmotic demyelination have emerged where serum sodium was found to be within normal limits and minimal or no correction of a hypo or hypernatraemic state was implemented. We describe two cases--one of extra pontine and another of central-pontine myelinolysis, both of which have occurred in the context of relatively normal serum sodium. The first case illustrates the association of extrapontine myelinolysis with the traditional risk factor of alcoholic cirrhosis and intravenous fluid resuscitation, while the second, more unusual case, describes a patient who developed central pontine myelinolysis possibly in association with alpha interferon therapy.