Historically, diseases of the central nervous system (CNS) have been named after individuals who first described them (eg, Dandy-Walker syndrome, named after Walter Dandy, MD, and Arthur Earl Walker, MD) or initially characterized by histological or clinical features (eg, DeMorsier septo-optic dysplasia, Alzheimer presenile dementia, or Pick frontotemporal dementia [FTD]). If affected patients had variable clinical presentations, the disorder might have been named descriptively, based on timing/onset of symptoms (such as relapsing-remitting multiple sclerosis) or affected parts of the CNS (such as neuromyelitis optica).