Definition | Causes | Risk Factors | Symptoms | Diagnosis | Treatment | Prevention


Progressive Multifocal Leukoencephalopathy (PML) is a rare disease that gets worse over time. It leads to damage of the brain cells.

The Neuron

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PML is caused by an infection by a specific virus. Many people pick up this virus as a child, but do not get sick until later. The virus stays in the body and does not cause problems in most.

If the immune system becomes weak, the virus can begin to cause problems. The virus attacks the coating around the brain cells called myelin. Messages can't be passed between brain cells without myelin.

Risk Factors

PML is most common in people who have problems with their immune system. These problems may be from:

  • HIV/AIDS (most common)
  • Leukemia and lymphoma
  • Organ transplant
  • Cancer
  • Long-term use of steroid medicines
  • Rare, inherited immunodeficiencies
  • Certain medications, such as natalizumab, a medication that treats multiple sclerosis (MS)


Symptoms get worse over time and may include:

  • Vision problems
  • Speech problems
  • Problems with movement
  • Memory loss
  • Weakness in the arms and legs
  • Changes in behavior and thinking
  • A loss of language
  • Seizures
  • Sensory loss


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

An MRI scan will be needed to see any damage to the brain cells. This may help to rule out other causes.

To confirm diagnosis, your doctor may need:

  • Brain biopsy—to check for changes in brain cells
  • Lumbar puncture—to look for the virus in the fluid that surrounds the brain


There is no treatment for the infection or PML. Treatment is aimed at ways to improve the immune system to stop further damage. Options will depend on your specific needs, but examples include:

  • If you have HIV, antiretroviral medicine will be started.
  • If medicine caused PML, your doctor will have you stop taking it.

Damage to the cells cannot be fixed. This can cause severe disability.


The virus that causes PML can’t be avoided. Keep your immune system as healthy as you can. It may help prevent certain infections.