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Progressive Multifocal Leukoencephalopathy (PML)

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Updated January 29, 2008

Definition: A demyelinating disease caused by a type of polyomavirus called the JC virus (JCV). JCV is present in over 80% of the general population, but usually remains latent, causing PML only when the immune system is severely impaired.

In multiple sclerosis (MS), PML has been associated with the use of Tysabri. Three people developed PML while using Tysabri (2 died and one became severely disabled), which caused Tysabri to be temporarily withdrawn from the market. It was reintroduced to the market when several procedures to monitor for new cases of PML were introduced. It is thought that PML was linked to the combination of Tysabri with other immunomodulating or immunosuppressive drugs.

Also Known As: progressive multifocal leukoencephalitis

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