Progressive Multifocal Leukoencephalopathy — Progress Made and Lessons Relearned

Progressive multifocal leukoencephalopathy is an opportunistic demyelinating infection caused by a ubiquitous, usually nonpathogenic papovavirus known as JC virus. The symptoms and characteristic radiologic findings of progressive multifocal leukoencephalopathy are due to virus-induced lysis of oligodendrocytes, resulting in microscopic foci of myelin breakdown that coalesce to produce increasingly larger lesions.1 The virus also infects astrocytes, in which morphologic features develop that are suggestive of neoplasia, including mitotic figures and multinucleated forms.Progressive multifocal leukoencephalopathy is a disease of immunosuppressed patients. The disease was initially identified by Aström and colleagues as a rare complication of chronic lymphocytic leukemia and Hodgkin's disease. . . .