Progressive multifocal leukoencephalopathy

  • Definition

    Progressive multifocal leukoencephalopathy (PML) is a rare disorder that damages the material (myelin) that covers and protects nerves in the white matter of the brain.

    Alternative Names


    Causes, incidence, and risk factors

    The JC virus (JCV) causes PML. By age 10, most people have been infected with this virus, but it hardly ever causes symptoms.

    Anyone with a weakened immune system, however, are at greater risk of developing PML. Causes of a weakened immune system include:

    • AIDS (less common now because of better AIDS treatments)
    • Certain medications used to treat multiple sclerosis, rheumatoid arthritis, and related conditions
    • Leukemia and lymphoma