In 1907, Alois Alzheimer described the case of a 51 year old woman who presented with a relatively rapidly deteriorating memory along with psychiatric disturbances. She died four years later1. While a variety of progressive and fatal neurological conditions were known at that time, including senile dementia, the early age at onset, and a new pathological finding, the neurofibrillary tangle (NFT), made this condition unique. The justification for Alzheimer disease (AD) as a new nosologic entity, and the motivations of the prominent psychiatrist, Emil Kraepelin, for promoting an evidently new condition, continue to be debated. Nevertheless, AD is today, as it was then, a relentless neurologic deterioration accompanied by hallmark pathology.

Over time, AD was split into two clinical conditions depending upon the age of onset. Alzheimer disease, because of its initial description in a relatively young woman, was a term reserved for a type of “presenile” dementia affecting individuals younger than 65 years of age, whereas a similar dementia in the elderly, ie, in individuals over 65 years of age, was referred to as senile dementia of the Alzheimer-type after the pioneering studies of Tomlinson, Roth and Blessed2–4. Of historical note, Alzheimer himself was ambivalent about the possibility that this entity was distinct from “dementia senilis,” 5 and although these age-related classifications are still sometimes used, AD has never been shown to have a bi-modal age of onset. AD is now generally recognized as a single entity with a prevalence that increases sharply after age 65.