Progressive multifocal leukoencephalopathy.

Abstract

Progressive multifocal leukoencephalopathy (PML) is a subacute demyelinating disease apparently resulting from the selective destruction of oligodendrocytes by papovaviruses. The pathology and pathogenesis of PML are distinct from those of the other slow infections of the human nervous system. Kuru and Creutzfeldt-Jakob disease appear to be caused by obligate “slow viruses” that produce noninflammatory degenerative disease in primate brains and that fail to produce cytopathic infections in cell cultures. Subacute sclerosing panencephalitis (SSPE) results from a defective measles virus infection that causes a diffuse indolent inflammatory disease of the brain in otherwise normal children. In contrast, PML is a noninflammatory demyelinating process, and the pathogenesis appears to be related not to uniqueness or defectiveness of the viruses but to defects in the host immune response. The viruses associated with this disease are not human pathogens in the usual sense but cause disease almost exclusively in patients with disorders affecting their immune response or in patients given immunosuppressive drugs to maintain organ transplants or to treat other illness (41, 42).