Health Information

Progressive Multifocal Leukoencephalopathy


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

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PML is caused by a specific 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 suppressed immune systems. The virus damages myelin, the material that wraps around nerves. This impairs nerve function.

Risk Factors

PML is most common in people with supressed immune systems. Supressed immune systems may be the result of:

  • Most commonly, HIV/AIDS
  • Leukemia and lymphoma
  • Organ transplant
  • Cancer
  • Chronic steroid therapy
  • Rare inherited immunodeficiencies
  • Certain medications, such as natalizumab, a medication used to treat multiple sclerosis


Symptoms progress over weeks and may include:

  • Vision problems
  • Speech pronunciation problems
  • Coordination loss
  • Memory loss
  • Weakness in limbs
  • Behavioral changes
  • Changes in thinking
  • Aphasia —a loss of language capability
  • Seizures
  • Sensory loss


Your doctor will ask about your symptoms and medical history. A physical exam will be done. Tests may include:

  • MRI —used to take images of brain structures (key in the diagnosis)
  • Lumbar puncture
  • 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 medications 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.


There are no current guidelines to prevent exposure to the JC virus. If you have a suppressed immune system, get treatment to minimize your risk.

Revision Information

  • AIDS Information, Education, Action, Awareness

  • National Organization for Rare Disorders

  • Canadian AIDS Society

  • Canadian Organization for Rare Disorders

  • AETC National Resource Center. Progressive multifocal leukoencephalopathy. AETC National Resource Center website. Available at: . Accessed July 11, 2013.

  • National Institute of Neurological Disorders and Stroke. Progressive multifocal leukoencephalopathy information page. National Institute of Neurological Disorders and Stroke website. Available at . Updated September 27, 2011. Accessed July 11, 2013.

  • Progressive multifocal leukoencephalopathy. EBSCO DynaMed website. Available at: . Updated May 21, 2013. Accessed July 11, 2013.

  • Warnke C, Menge T, Hartung HP, et al. Natalizumab and progressive multifocal leukoencephalopathy: what are the causal factors and can it be avoided? Arch Neurol . 2010;67(8):923-30.