[Progressive multifocal leukoencephalopathy: virological and neuropathological aspects]

Progressive multifocal leukoencephalopathy is a subacute demyelinating disease of the central nervous system due to an opportunistic infection by a polyomavirus, most often JC virus, which predominantly infects oligodendrocytes. Progressive multifocal leukoencephalopathy used to be a rare condition, usually complicating lymphoproliferative diseases. Since the onset of the AIDS epidemic, its incidence has considerably increased and HIV infection has become, by far, the main risk factor for the disease. In AIDS patients, progressive leukoencephalopathy frequently shows atypical clinical and pathological features. The development of malignant glial tumors, within demyelinating regions, in patients with progressive multifocal leukoencephalopathy, has been reported in exceptional cases. The course of progressive multifocal leukoencephalopathy is invariably fatal. The diagnosis can only be made with certainty by histopathological examination of the brain, on cerebral biopsy or at postmortem. However, neuroradiological features may be extremely suggestive in many cases and PCR seems to be a reliable technique for demonstrating viral genome in the CSF. A few antiviral treatments have been proposed, however their efficacy is difficult to assess due to the low prevalence of the disease and the occurrence of rare cases with spontaneously prolonged survival.