PML is a rare inflammatory disorder that leads to loss of myelin in multiple areas within the white matter of the brain . It is a virus-induced disease seen in people with poor immune function (immunocompromised).
Symptoms and signs include loss of coordination , clumsiness , memory loss, progressively worsening weakness of the legs, and to a lesser extent, arms. Other signs may include loss of language capability ( aphasia ), visual field defects, and headaches . The greatest risk is being immunosuppressed . The causal virus, JC virus, is a common resident in most adults, but it triggers loss of myelin in those whose immune function is deficient. It occurs in 4% of adult individuals with AIDS.