Age at onset of Pick's and Alzheimer's dementia: implications for diagnosis and research.

The ages at onset of illness for 39 cases of Pick's and 201 cases of Alzheimer's dementia from two series of unselected cases are presented and analyzed. The frequency of Pick's disease peaks in the sixth decade of life and then decreases, whereas Alzheimer's dementia increases steadily through adult life. At least to age 70 years Pick's and other disorders that cannot reliably be separated from Alzheimer's dementia except by autopsy comprise a significant proportion of dementias. Neuropathological diagnoses are essential for most research in dementing illnesses.