Subacute encephalopathy in a 5-year-old boy.

A 5-year-old boy presented with an acute ataxia and altered mental status. Although he initially recovered from these symptoms, he presented a second time with myoclonus and seizures and rapidly became vegetative. Cerebrospinal fluid studies, magnetic resonance imaging, and brain biopsy all confirmed the presence of subacute sclerosing panencephalitis. Despite courses of therapy with cimetidine, amantadine, ribavirin, and inosine, no clinical improvement has been seen. Clinicians need to be alert to the possibility of subacute sclerosing panencephalitis even in the vaccinated child in the appropriate clinical setting.