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VIII. Progressive Multifocal Leukoencephalopathy (PML)

A. Clinical features

Onset: occurs in patients with associated immune suppression or chronic disease, e.g. lymphoma, AIDS

Clinical presentation: The major consistent symptom is intellectual deterioration and dementia. Other symptoms include cortical visual symptoms, motor disorders, abnormal movements.

Duration: death usually in 2‑6 months

CSF findings: normal

B. Pathogenesis

Viral encephalitis caused by a polyomavirus. Because the virus preferentially infects oligodendrocytes, demyelination is its principal pathologic effect.