Progressive multifocal leukoencephalopathy presenting with an isolated focal movement disorder.

Progressive multifocal leukoencephalopathy (PML) is a rare but fatal papovavirus infection of the central nervous system predominantly affecting immunocompromised patients. Although the basal ganglia circuitry may be involved in the pathology of PML, movement disorders are exceedingly rare as presenting symptoms and have not been described as isolated features in such patients. We report a previously healthy, immunocompetent 24-year-old woman with histologically proven PML who presented with a focal movement disorder of the left arm as an isolated symptom for many months before diagnosis.