Definition of Progressive multifocal leukoencephalopathy:

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.

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

Symptoms:

• Headaches
• Loss of coordination, clumsiness
• Loss of language ability (aphasia)
• Memory loss
• Vision problems
• Weakness of the legs and arms that gets worse

Signs and tests:

Tests may include:

• Brain biopsy (rare)
• Cerebrospinal fluid test for the JCV
• CT scan of the brain
• Electroencephalogram (EEG)
• MRI of the brain

Treatment:

In people with AIDS, treatment to strengthen the immune system can lead to recovery from the symptoms of PML. No other treatments have proved effective for PML.

Expectations (prognosis):

PML is a life-threatening condition. Talk to your doctor about care decisions.