Progressive multifocal leukoencephalopathy.

Progressive multifocal leukoencephalopathy is a rare, opportunistic infection of the central nervous system caused by the John Cunningham virus (JCV). There is no effective antiviral treatment available, and restoring immunocompetence is essential for survival. If this occurs too quickly, however, the inflammatory response may prove fatal. This is an up-to-date review of the disorder, intended for clinicians responsible for immunomodulatory therapy.