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PML and MS TherapyA Rare Brain Infection Occurred in Two Patients Taking Natalizumab
Recent reports have linked the occurrence of Progressive Multifocal Leukoencephalopathy with specific treatments for Multiple Sclerosis but this is not the only link.
Progressive multifocal leukoencephalopathy (PML) is a very rare brain disorder that occurs as a result of reactivation of certain viruses known as papovaviruses (or polyoma viruses), most specifically JC or BK viruses. Medical treatments that strongly suppress the activity of the immune system have been associated with its occurrence, as have the presence of other pre-existing illnesses. Recent news reports have linked the use of the multiple sclerosis drug Tysabri (natalizumab) with an increased incidence of PML. What is PMLPML is a disorder of the white matter of the brain. That is the portion of the brain that helps to insulate and protect nerve cells so that they can transmit their signals across the nervous system and out to the rest of the body. The name PML means that there are multiple areas of damage to the white matter of the brain and the damage worsens over time. Presenting symptoms can vary widely dependent upon which areas of white matter are affected. Unfortunately, there are no effective treatments for PML and many patients with this disorder ultimately die. How Do You Get PML?PML occurs as a result of viral infection of the brain with either JC virus or BK virus. Most people actually carry these viruses in a dormant state since they have already been infected with them at an early age. These viruses are widely distributed in the population. The problem arises when these viruses are reactivated in the central nervous system of an immunocompromised person. And while PML is extremely rare, it can occur in people undergoing therapy with a number of compounds including specific anti-neoplastic agents or immune modulating drugs, not just drugs for multiple sclerosis, and it also can occur in people with lymphoma, AIDS or leukemia. The common ground is that something substantially decreases the function of the immune system and for reasons that are not known, the virus re-emerges in an active form in the central nervous system. How Common Is PMLFortunately, PML is not very common. In fact, the occurrence of PML is exceedingly rare. It occurs in fewer than 1 out of every 200,000 people. For many years, it was seen most frequently in people suffering from AIDS. Before the development of effective anti-retroviral regimens for treating AIDS, as many as 5% or more of AIDS patients developed PML. This number is now substantially lower. For more information on PML visit the US National Institute of Neurological Disorders and Stroke.
The copyright of the article PML and MS Therapy in Neurological Illness is owned by Kenneth Rosen. Permission to republish PML and MS Therapy in print or online must be granted by the author in writing.
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