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Progressive multifocal leukoencephalopathy is a rare infection of the brain that is caused by the JC virus.

• People with a weakened immune system are most likely to get the disorder.
• People may become clumsy, have trouble speaking, and become partially blind, while mental function declines rapidly.
• Death usually occurs within 9 months.
• Imaging of the head and a spinal tap are done.
• Treating the disorder that weakened the immune system may help.

Progressive multifocal leukoencephalopathy results from infection by the JC virus (which is not related to Creutzfeldt-Jakob disease). The JC virus is often acquired during childhood. Most adults have been infected with the JC virus but do not develop the disorder. The virus appears to remain inactive until something (such as a weakened immune system) allows it to be reactivated and start to multiply. Thus, the disorder affects mainly people whose immune system has been weakened by a disorder, such as leukemia, lymphoma, or acquired immunodeficiency syndrome (AIDS), or by drugs that suppress the immune system (immunosuppressants). Such drugs may be used to prevent rejection of transplanted organs or to treat autoimmune disorders, such as systemic lupus erythematosus (lupus) or multiple sclerosis.

Symptoms

The JC virus appears to cause no symptoms until it is activated.

Symptoms may begin gradually, but they usually worsen rapidly. They vary depending on which part of the brain is infected. In about two of three people, mental function declines rapidly and progressively, causing dementia. Speaking becomes increasingly difficult. People may become partially blind. Walking may become difficult. Rarely, headaches and seizures occur. Death is common within 1 to 9 months of when symptoms start, but a few people survive longer (about 2 years).

Diagnosis

Progressively worsening symptoms in people with a weakened immune system suggest the diagnosis. Magnetic resonance imaging (MRI) of the head is done. It can usually detect abnormalities that suggest the diagnosis.

A spinal tap (lumbar puncture) is done to obtain a sample of cerebrospinal fluid. The polymerase chain reaction (PCR) technique can detect the JC virus in the cerebrospinal fluid. Sometimes the diagnosis is not confirmed until after people have died, when brain tissue can be examined.

Treatment

No treatment has proved effective. However, if the disorder that has weakened the immune system is treated, people survive longer. For example, if the cause is AIDS, highly active antiretroviral therapy is used.

If people are taking immunosuppressants, stopping the drugs may cause progressive multifocal leukoencephalopathy to subside.