Left-handedness in early and late onset dementia.

Sixty-five men with the diagnosis of dementia of the Alzheimer type were divided into two groups, according to age at onset of dementia before or after 65 years. A handedness questionnaire was then completed for each patient. There was a significantly higher prevalence of left-handedness in the early, as compared with the late, onset group. Taken together with other data, this finding suggests that presenile dementia (Alzheimer's disease) and senile dementia "of the Alzheimer type " may not be biologically identical.