Everything You Should Know About Progressive Multifocal Leukoencephalopathy (PML) Virus

Medically reviewed by Alana Biggers, MD, MPH on November 14, 2016Written by Ann Pietrangelo on November 14, 2016

What is the PML virus?

PML stands for progressive multifocal leukoencephalopathy. It’s an aggressive viral disease of the central nervous system. The virus attacks cells that make myelin. Myelin is a fatty substance that coats and protects nerve fibers in the brain, which helps conduct electrical signals. PML can result in symptoms that affect virtually any part of your body.

PML is rare. In the United States and Europe combined, about 4,000 people get PML each year. It’s a life-threatening condition.

Read on to learn more about the symptoms, risk factors, and treatment for this uncommon, but serious viral disease.

What causes PML?

PML is caused by an infection called the John Cunningham (JC) virus. PML may be rare, but the JC virus is quite common. In fact, up to 85 percent of adults in the general population have the virus.

You can get the JC virus at any time in your life, but most of us are infected during childhood. A normal, healthy immune system has no trouble keeping the virus in check. The virus usually remains dormant in the lymph nodes, bone marrow, or kidneys throughout our lifetime.

Most people with the JC virus never get PML.

If the immune system becomes severely compromised for any reason, the virus can be reactivated. Then it makes its way to the brain, where it multiplies and begins its attack on myelin.

As myelin is damaged, scar tissue begins to form. This process is called demyelination. The resulting lesions from the scar tissue interfere with electrical impulses as they travel from the brain to other parts of the body. That communication gap can create a variety of symptoms affecting virtually any part of the body.

Learn more: Demyelination : What is it and why does it happen? »

What are the symptoms?

As long as the JC virus remains dormant, you’ll probably never be aware that you have it.

Once activated, PML can quickly cause a lot of damage to myelin. That makes it hard for the brain to send messages to other parts of the body.

Symptoms depend on where the lesions form. The severity of symptoms depends on the extent of the damage.

Initially, symptoms are similar to those of some pre-existing conditions such as HIV-AIDS or multiple sclerosis. These symptoms include:

  • general weakness that steadily gets worse
  • clumsiness and balance issues
  • sensory loss
  • difficulty using your arms and legs
  • changes to vision
  • loss of language skills
  • facial drooping
  • personality changes
  • memory problems and mental slowness

Symptoms can progress rapidly to include complications such as dementia, seizures, or coma. PML is a life-threatening medical emergency.

Who is at risk of developing PML?

PML is rare in people who have a healthy immune system. It is known as an opportunistic infection because it takes advantage of an immune system already compromised by illness. You’re at increased risk of developing PML if you:

  • have HIV-AIDS
  • have leukemia, Hodgkin’s disease, lymphoma, or other cancers
  • are on long-term corticosteroid or immunosuppressive therapy due to an organ transplant

You also have a slight risk if you have an autoimmune condition such as multiple sclerosis (MS), rheumatoid arthritis, Crohn’s disease, or systemic lupus erythematosis. This risk is higher if your treatment plan includes a drug that suppresses part of the immune system, known as an immunomodulator.

Learn more: The JC virus and risks for MS patients »

PML is a potential side effect of some disease-modifying drugs used to treat MS, including:

The longer you take these medications, the higher the risk of developing PML.

How is PML diagnosed?

Your doctor may suspect PML based on the progressive course of your symptoms, your preexisting conditions, and medications you take. Diagnostic testing may include:

  • Blood test: A sample of blood can reveal that you have JC virus antibodies. A very high level of antibodies could indicate PML.
  • Lumbar puncture (spinal tap): A sample of your spinal fluid may also contain JC virus antibodies, which can aid in the diagnosis.
  • Imaging tests: MRI or CT scans can detect lesions in the white matter in the brain. If you have PML, there will be multiple active lesions.
  • Brain biopsy: a piece of tissue is removed from your brain and examined under a microscope.

Is there any treatment for PML?

There is no specific treatment for PML. Therapy will be tailored to your individual circumstances, such as what caused your PML, as well as other health considerations.

If you take medications that affect your immune system, you’ll have to stop taking them immediately.

Treatment revolves around improving immune system function. One way to do that is via plasma exchange. This is accomplished with a blood transfusion. The procedure helps clear your system of the drugs that caused PML so your immune system can get back to fighting the virus.

If you have PML due to HIV-AIDS, treatment may involve highly active antiretroviral therapy (HAART). This is a combination of antiviral drugs that help reduce viral reproduction.

Treatment may also include supportive and investigational therapies.

What can I expect?

If you are at risk of PML and experience symptoms, seek immediate medical attention. PML can lead to brain damage, severe disabilities, and death.

Within the first few months after diagnosis, the mortality rate for PML is 30-50 percent.

There are also some long-term survivors of PML. Your outlook depends on the severity of the condition, as well as how quickly you receive treatment.

Is there a way to prevent it?

There’s no known way to prevent the JC virus. You can’t completely eliminate your risk of PML, either, but you can make an informed decision about immune suppressing drugs.

If you have an immune system disorder and are thinking about taking an immunomodulator, talk to your doctor about the risks of PML.

You’ll probably take a blood test to see if you have JC virus antibodies. The level of antibodies can help your doctor gauge your risk for developing PML. A spinal tap can also be useful.

If you test negative for JC virus antibodies, you may be advised to repeat the test regularly to reassess your risk. That’s because you can acquire the JC virus at any time.

Your doctor should also consider past usage of immune-suppressing medications.

If you decide to take one of these medications, your doctor will educate you about the signs and symptoms of PML. If you experience any of these symptoms, tell your doctor right away. If PML is suspected, you should stop taking the drug until it can be confirmed.

Continue to monitor your health and see your doctor as advised.

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