Editing Progressive multifocal leukoencephalopathy (section)

{{Short description|Viral disease affecting human brains}}
{{Infobox medical condition (new)
| name            = Progressive multifocal leukoencephalopathy
| synonyms        =
| image           = Progressive multifocal leukoencephalopathy 002.jpg
| caption         = T2-weighted MRI showing progressive multifocal leukoencephalopathy
| pronounce       =
| field           =
| symptoms        =
| complications   =
| onset           =
| duration        =
| types           =
| causes          =
| risks           =
| diagnosis       =
| differential    =
| prevention      =
| treatment       =
| medication      =
| prognosis       =
| frequency       =
| deaths          =
}}

'''Progressive multifocal leukoencephalopathy''' ('''PML''') is a rare and often fatal [[virus|viral]] disease characterized by progressive damage (''-pathy'') or [[inflammation]] of the [[white matter]] (''leuko-'') of the [[Human brain|brain]] (''-encephalo-'') at multiple locations (''multifocal''). It is caused by the [[JC virus]], which is normally present and kept under control by the immune system. The JC virus is harmless except in cases of weakened immune systems. In general, PML has a mortality rate of 30–50% in the first few months, and those who survive can be left with varying degrees of neurological disabilities.

PML occurs almost exclusively in patients with severe [[immune deficiency]], most commonly among patients with [[acquired immune deficiency syndrome]] (AIDS), but people on chronic [[immunosuppressive]] medications including [[chemotherapy]] are also at increased risk of PML, such as patients with transplants, [[Hodgkin's lymphoma]], [[multiple sclerosis]], [[psoriasis]], [[rheumatoid arthritis]], and other autoimmune diseases.