PML is a rare, slowly progressive disease of the nervous system. It is caused by a viral infection of oligodendrocytes. These are 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 has rarely been associated with:

• Leukemia and lymphoma
• Tuberculosis
• Sarcoidosis
• Prolonged immunosuppression (organ transplant or cancer patients)
• Chronic steroid therapy
• Rare inherited immunodeficiencies
• Natalizumab (medication used to treat multiple sclerosis )—the risk may only occur when also taking other immunosuppressants

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
• Behavioral changes
• Cognitive changes
• Aphasia (loss of language capability)
• Very rarely, seizures and headaches

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

While there is no cure for PML, talk with your doctor about the best treatment plan for you. If you stopped taking HIV medications, taking them again may be helpful. Ask your doctor.