Progressive Multifocal Leukoencephalopathy

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Progressive multifocal leukoencephalopathy (PML) is caused by the reactivation of a common virus in the central nervous system of immune-compromised individuals. Polyomavirus JC (often called JC virus) is carried by a majority of people and is harmless except among those with lowered immune defenses. The disease occurs, rarely, in organ transplant patients; people undergoing chronic corticosteroid or immunosuppressive therapy; and individuals with cancer, such as Hodgkin’s disease, lymphoma, and sarcoidosis. PML is most common among individuals with acquired immune deficiency syndrome (AIDS). Studies estimate that prior to effective antiretroviral therapy, as many as 5 percent of people with AIDS eventually developed PML. For them, the disease was most often rapidly fatal.

Currently, the best available therapy is reversal of the immune-deficient state. This can sometimes be accomplished by alteration of chemotherapy or immunosuppression (even if it means losing non-vital transplanted organs). In the case of HIV-associated PML, immediately beginning anti-retroviral therapy will benefit most individuals.

The mortality rates for those with HIV-PML have fallen dramatically from approximately 90 percent to around 50 percent according to most reports. For non-AIDS individuals with PML, the prognosis remains grim; the disease usually lasts for months and 80 percent die within the first 6 months, although spontaneous improvement has been reported. Those who survive PML can be left with severe neurological disabilities.

Prepared by the National Institutes of Health