JC virus-induced progressive multifocal leukoencephalopathy

Progressive multifocal encephalopathy (PML) is a fatal demyelinating disease of the CNS, caused by the lytic infection of oligodendrocytes by a human polyomavirus, JC virus. PML is rare disease that mostly develops in patients with underlying immunosuppressive conditions, including Hodgkin's lymphoma, lymphoproliferative diseases, AIDS and in those undergoing antineoplastic therapy. However, consistent with the occurrence of PML under immunocompromised conditions, this disease seems to also be steadily increasing among patients with autoimmune diseases (e.g., multiple sclerosis and Crohn's disease) who are treated with antibody-based regimens (natalizumab, efalizumab and rituximab). This unexpected occurrence of the disease among such a patient population reconfirms the existence of a strong link between underlying immunosuppressive conditions and development of PML. These recent observations have generated a new interest among investigators to further examine the unique biology of JC virus.