Progressive multifocal leukoencephalopathy

This chapter explores progressive multifocal leukoencephalopathy (PML). Until the advent of the AIDS pandemic, PML remained a vanishingly rare disorder seen almost exclusively in individuals with underlying immunosuppressive disorders. While the introduction of highly active antiretroviral therapy (HAART) led to a decline in AIDS-associated PML, AIDS is currently estimated to be the predisposing disorder for about 80% of all PML cases. However, development of immunosuppressive and immunomodulating therapies has led to a growing incidence of PML in patients with autoimmune disorders. To date, at least 50 drugs have been associated with PML, but the risk of PML with these drugs varies widely.