Progressive Multifocal Leukoencephalopathy
National Organization for Rare Disorders, Inc.
It is possible that the main title of the report Progressive Multifocal Leukoencephalopathy is not the name you expected.
Progressive multifocal leukoencephalopathy (PML) (1) is a neurological disorder characterized by destruction of cells that produce the myelin, an oily substance that helps protect nerve cells in the brain and spinal cord, also known as central nervous system (CNS) white matter. It is caused by a virus called JC virus (JCV), named after the initials of the patient in whom it was first discovered. The virus is widespread, found in up to 85% of the general adult population. It remains inactive in healthy individuals and causes disease only when the immune system has been severely weakened, such as in people with HIV/AIDS, or hematological malignancies, and in organ transplant recipients who receive immunosuppressant medications to avoid rejection of the transplanted organ. Altogether, PML occurs in approximately one in 200,000 people. Each year, it is estimated that 4000 people develop PML in the United States and Europe combined.
The term "progressive" in PML means that the disease continues to get worse and often leads to serious brain damage. The term "multifocal" means that JCV causes disease in multiple parts of the brain. However, it is possible for an individual with PML to have only one brain lesion instead of several lesions. The term "leukoencephalopathy" means that the disease affects mainly the white matter of the brain or myelin, although there are some rare cases in which the gray matter neurons are also involved.
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Last Updated: 8/18/2015
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