Neuropsychologic features of early- and late-onset Alzheimer's disease.

Forty-one patients with clinically diagnosed Alzheimer's disease were divided into two groups for comparison of neuropsychologic features in those with early- and late-onset disease. Handedness was also assessed in all patients. Twenty-three patients with onset before age 65 had significantly more language impairment, whereas 18 patients with onset at age 65 or older had more difficulty with visuoconstructional function. Memory was severely impaired in all patients. Only one patient in each group was left-handed, and the same results were obtained when these were excluded. These observations support the notion of left hemisphere vulnerability in early-onset Alzheimer's disease and can be interpreted as demonstrating the clinical variability of the illness rather than the necessity of dividing it into two distinct entities.