Primary cerebellopontine progressive multifocal leukoencephalopathy diagnosed premortem by cerebellar biopsy.

A subacute progressive cerebellar brainstem syndrome developed in a patient with systemic lupus erythematosus in remission. Cerebellar biopsy documented the diagnosis of progressive multifocal leukoencephalopathy (PML). Data from this patient and 10 others in the literature emphasize the need to consider this diagnosis when ataxia develops in any patient with underlying malignancy, chronic infection, or other disease that involves immunological incompetence. Although the ataxic form of PML is not of nosological relevance, early diagnosis may eventually have therapeutic importance.