Tysabri and PML: A Rare But Serious MS Treatment Complication

A small percentage of people taking then drug Tysabri as a treatment medication for multiple sclerosis (MS) may develop progressive multifocal leukoencephalopathy – commonly referred to as PML. PML is a rare but rapidly progressive and often fatal viral infection of the brain.

PML is thought to be caused by the John Cunningham (JC) virus, which many people (a little more than half of people) are exposed to in childhood and carry in a dormant state without ever becoming ill.

PML occurs in other conditions besides MS, but almost exclusively in individuals with suppressed immune systems (such as people with AIDS or those who take immunosuppressant medications to treat cancer or receive an organ transplant). The immune suppression allows the JC virus to become active and cause disease. PML is the result of that process. The symptoms of PML include mental deterioration, vision loss, speech disturbances, loss of coordination, paralysis, and possibly coma and death.

The most recent data (as of January 2012) indicate that of the more than 96,500 people that have been treated with Tysabri, 201 people have developed PML. Of those who developed PML, approximately 20 percent have died.

Among the survivors, the degree of disability ranges widely, from those who have been able to return to work to those who are confined to bed and require extensive assistance with activities of daily living. It appears that the earlier PML is treated, the more likely a person is to survive the infection.

In January 2012, the FDA identified three factors that increase a person’s risk of developing PML while on Tysabri:

  • Antibodies to the JC virus in the person’s blood, which indicate that the person has previously been exposed to the virus. People who have no antibodies to the JC virus aren’t at risk for developing this infection.

    Those who are antibody-positive but have neither of the other two risk factors have less than a 1 in 1000 risk of developing PML. And those individuals who have been exposed to the JC virus and have both of the other risk factors have an 11 in 1000 risk of developing PML.

  • Longer time on treatment (especially more than two years).

  • Prior treatment with an immunosuppressant medication. These include Novantrone, Cytoxan, CellCept, Imuran, Leustatin, and Methotrexate.

The FDA also approved the marketing of a blood test — the Stratify JCV Antibody ELISA test — that detects antibodies to the JC virus in a person’s bloodstream. The FDA recommends that people with MS and their physicians use this test as a way to help evaluate a person’s risk of developing PML.

The blood test to detect JC virus antibodies is only 97 percent accurate, which means that false negative results can occur. And the fact that a person tests negative — indicating that he or she hasn’t been exposed to the JC virus in the past — is no guarantee that the person won’t be exposed today or in the future.

Repeat testing is necessary to demonstrate that a person continues to be free of the antibodies to the JC virus. A person who becomes antibody-positive while taking Tysabri needs to evaluate the potential benefits and risks of staying on treatment.

As you read the information about Tysabri and the risk of PML, some undoubtedly said, “I’d take that risk in a minute for a drug that works so well!” However, others though, “I wouldn’t touch that drug with a ten-foot pole!” This is one of those situations where the right and wrong answers aren’t clearly marked and differ from one person to another.

Fortunately, a blood test is now available to help people assess their risk of PML. In the event that you test positive for the JC virus, you’ll be weighing the risks and benefits of taking Tysabri in order to make the choice that’s right for you. And you’ll face similar complex decisions with the many new, very powerful medications that are expected to emerge over the next few years.

For more information about Tysabri, call 800-456-225 or look online.

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