Progressive multifocal leukoencephalopathy (PML)



  • Progressive multifocal leukoencephalopathy, or PML, is a disease that attacks the brain.
  • It is caused by a virus called JC virus (JCV), which is common among the general population and normally harmless.
  • In people with advanced HIV/Aids, JCV attacks the myelin sheaths around the nerve and brain cells, and causes lesions in the white matter of the brain.
  • Symptoms include mental disturbances, muscular dysfunction, speech and vision problems, paralysis and coma.
  • Progress of the disease is usually rapid, leading to death within one to four months.
  • There is currently no standard effective treatment.

What is progressive multifocal leukoencephalopathy?

Progressive multifocal leukoencephalopathy, or PML, is a disease that attacks the white matter of the brain. It is caused by a virus called JC virus (JCV). This is a very common human virus: most people (up to 80% of the general population) are infected with JCV, which is present in their kidneys – most people probably pick up the virus during childhood. In people with healthy immune systems, the virus is harmless.

How can PML affect people with HIV?

It is only in people with suppressed immune systems that the JC virus gives rise to PML – including up to 4% of people with advanced HIV/Aids (CD4 counts below 100). It is a “late stage” disease; it generally only appears once immunity has been greatly compromised.

In a person with a weak immune system, the virus becomes active. In the brain, it destroys the myelin sheaths that cover nerve cells. The myelin sheath is a protective, fatty covering that acts as an insulator. Without it, the nerve cells die, causing lesions in the brain.

Symptoms and diagnosis

Symptoms of PML vary, but can include:

  • muscle weakness and spasms
  • ataxia (inability to co-ordinate movements)
  • difficulty walking
  • difficulty swallowing
  • headaches
  • changes in personality
  • forgetfulness
  • poor concentration
  • confusion
  • loss of speech, or speech problems
  • blurred or double vision
  • loss of vision in one eye
  • paralysis or weakness on one side of the body
  • numbness in one arm or leg
  • seizures (rare)
  • coma

The variety of symptoms is explained by the wide distribution of lesions across different parts of the brain – it is “multifocal”.

How is PML diagnosed?

Symptoms of PML are similar to those of certain other Aids-related diseases (e.g. Aids Dementia and toxoplasmosis). Therefore, tests are necessary to diagnose PML. These may involve:

  • Brain scan: The white matter of the brain can be examined using a CAT scan or MRI scan, which will show lesions or spots.
  • Brain biopsy: This is a risky procedure that is not often performed. It involves surgery to remove a small specimen of brain matter, which is then tested to confirm a diagnosis of PML.

How is PML treated?

There is currently no cure for PML. Although in some cases people have been known to survive with PML for several months or even years, in most cases the disease progresses rapidly, causing death within a few months. Doctors can only provide symptomatic and supportive treatment.

While there is no effective standard treatment for PML at present, research continues into this disease. PML can only be effectively halted or reversed by highly active antiretroviral treatment that leads to immune recovery and prevents further damage to the brain. A drug called cidofovir, which acts against the JC virus, has been used in some cases.

How can I help prevent PML?

PML is not preventable because most people have already been infected by the JC virus. Currently, there are no medicines or treatments that can help to avoid PML.

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