In 1907, Aloysius "Alois" Alzheimer presented a rare case of dementia in a 51-year-old woman. This "presenile dementia" (younger than 60) was thought distinct enough from "senile dementia" (older than 65) to warrant a new name, thus it became known as, "Alzheimer's disease" (AD).
In the 1970s, however, some researchers argued that because of their similar symptoms and diagnostic hallmarks, "Alzheimer disease and senile dementia should be considered a single disease."