The diagnosis of Alzheimer's disease.

The diagnosis of Alzheimer's disease is a diagnosis of exclusion. First, dementia must be properly diagnosed using the four-part definition mentioned above and considering the caveat regarding educational levels. Next, the differential diagnosis of dementia must be examined, disease by disease, with clinical and laboratory criteria used to accept or reject each diagnosis. If all other causes of dementia are rejected this way (usually after a thorough history and physical, B-12 and thyroid levels, CT scan, and removal of possibly offending medications), then a diagnosis of probable Alzheimer's disease is made. If at that time the pattern of disease progression, mental status abnormalities, and personality changes is consistent with one of the presentations of Alzheimer's, the diagnosis is made with confidence. If these patterns are not consistent, re-examining the differential diagnosis is indicated.