PML is a rare progressive disease of the nervous system. It is caused by a viral infection of the cells that produce myelin.

PML is caused by a papovavirus, known as JC virus. Most people get this infection in childhood, and it produces no illness. It reactivates later in life in people who have a suppressed immune system (eg, HIV/AIDS ).

The most common risk factor is having HIV/AIDS. PML is rarely associated with:

• Leukemia and lymphoma
• Tuberculosis
• Sarcoidosis
• Prolonged immunosuppression (organ transplant or cancer patients)
• Chronic steroid therapy
• Rare inherited immunodeficiencies
• Natalizumab (medicine used to treat multiple sclerosis )

If you experience any of these symptoms, do not assume it is due to PML. These symptoms may be caused by other conditions. Symptoms progress over weeks and include:

• Vision problems
• Speech pronunciation problems
• Ataxia (loss of coordination)
• Memory loss
• Weakness in limbs
• Behavioral changes
• Cognitive changes
• Aphasia (loss of language capability)
• Seizures and headaches (rare)
• Sensory loss

Your doctor will ask about your symptoms and medical history. She will also do a physical exam. Tests may include:

• MRI scan —a test that uses magnetic waves to make pictures of structures inside the brain (key in the diagnosis)
• Spinal tap —removal of a small amount of cerebrospinal fluid to check for evidence of the JC virus in the brain
• Blood and urine tests
• Brain biopsy

Treatment focuses on strategies to improve the immune system. If you have HIV, your doctor will most likely prescribe antiretroviral medicine to treat this condition. If PML has resulted from the drug natalizumab, your doctor will have you stop taking this drug and may recommend a plasma exchange to remove the drug from your blood system.

Most people have been exposed to this virus. If you have HIV/AIDS, get treatment to minimize your risk.

Last Reviewed March 2013