Progressive Multifocal Leukoencephalopathy
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Progressive Multifocal Leukoencephalopathy


Pronounced: LOO-koh-en-sef-ah-LOP-ah-thee

En Español (Spanish Version)


Progressive multifocal leukoencephalopathy is a rare, slowly progressive disease of the nervous system. It is caused by a viral infection of oligodendrocytes, the cells that produce myelin.

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PML is caused by a papovavirus, usually the JC strain. Most people acquire this viral infection in childhood and it produces no illness. It reactivates later in life in immunocompromised patients, most often in the setting of HIV/AIDS , producing progressive multifocal leukoencephalopathy.

Risk Factors

Prior to the onset of HIV and AIDS in the 1980s, PML was extremely rare. The most common risk factor is HIV or AIDS, with up to 4% of AIDS patients developing PML.

Reactivation of the JC virus and development of PML has rarely been associated with leukemia and lymphoma, tuberculosis , sarcoidosis , prolonged immunosuppression (organ transplant or cancer patients), chronic steroid therapy, and rare inherited immunodeficiencies.

Most recently, the use of natalizimab has been reported to increase the risk of developing PML, but this appears to occur when the drug is used in combination with other immunosuppressants.


If you experience any of these symptoms do not assume it is due to PML. These symptoms may be caused by other health 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, and perform a physical exam. Tests may include the following:

  • 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 (rarely done)


While there is no cure for PML, talk with your doctor about the best supportive treatment plan for you.


Exposure to the JC virus is nearly universal in the general population. The virus only becomes problematic in those who are immunocompromised. Patients with HIV/AIDS or other immunosuppressed conditions should be treated to minimize the risk.


National Organization for Rare Disorders (NORD)


Canadian AIDS Society

Canadian Organization for Rare Disorders


NINDS progressive multifocal leukoencephalopathy information page. National Institute of Neurological Disorders and Stroke website. Available at . Accessed September 30, 2005.

Progressive multifocal leukoencephalopathy. EBSCO Publishing Dynamed website. Available from DynaMed: . Updated January 10, 2008. Accessed February 23, 2008.

Progressive multifocal leukoencephalopathy. Medline Plus Medical Encyclopedia website. Available at: . Accessed September 30, 2005.

Last reviewed February 2008 by J. Thomas Megerian, MD, PhD, FAAP

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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