Progressive multifocal leukoencephalopathy

Purpose of Review: Progressive multifocal leukoencephalopathy (PML) is an opportunistic viral infection of the human CNS that has gained new importance because of AIDS and newer immunosuppressive therapies. It destroys oligodendrocytes, leading to neurologic deficits associated with demyelination.Recent Findings: PML most commonly occurs in patients who are HIV infected, but increasing numbers of patients are being recognized in the context of immunosuppressive therapies for autoimmune diseases. The precise pathogenesis of infection by JC virus, the etiologic human papovavirus, remains elusive, but much has been learned since the original description of the pathologic entity PML in 1958. Detection and diagnosis of this disorder have become more sophisticated with MRI of the brain and spinal fluid analysis using PCR detection. Immune reconstitution inflammatory syndrome complicates reversal of immunosuppression when PML has established a foothold in the brain.Summary: No effective therapy exists, but there is hope for better management of patients by withdrawing exogenous immunosuppression and reconstituting the immune system, with a projection of better long-term survival.