leukoencephalopathy

noun

leu·​ko·​en·​ceph·​a·​lop·​a·​thy

variants or chiefly British leucoencephalopathy

-in-ˌsef-ə-ˈläp-ə-thē 

plural leukoencephalopathies

: any of various diseases affecting the brain's white matter

especially : progressive multifocal leukoencephalopathy