Atypical progressive multifocal leukoencephalopathy associated with an unusual JC polyomavirus mutation.

Objective: To report the clinical and radiologic features in a patient with myelofibrosis who developed atypical progressive multifocal leukoencephalopathy.

Design: Case report.

Setting: Tertiary referral center. Patient A 72-year-old man with myelofibrosis and mild leukopenia experienced progressive limb weakness and dysarthria.

Results: Imaging revealed almost complete sparing of the white matter with isolated involvement of the brainstem and deep gray matter. Postmortem examination led to definitive diagnosis of progressive multifocal leukoencephalopathy and demonstrated an unusual miliary pattern of disease rather than the typical confluent involvement. Genetic analysis revealed a mutation in the transcription control region of the JC polyomavirus, prompting speculation about the pathogenesis of progressive multifocal leukoencephalopathy.

Conclusions: Leukopenia may render patients effectively immunosuppressed. The differential diagnosis should include progressive multifocal leukoencephalopathy even in patients with atypical clinical and radiologic features.