Neuropsychological differences between the dementias of Alzheimer's and Parkinson's diseases.

The question of whether dementia of the Alzheimer type and dementia associated with Parkinson's disease are clinically separable is controversial. We examined possible neuropsychological differences in these two patient groups matched for overall severity of dementia. Patients with dementia of the Alzheimer type had more severe impairment on measurements of memory, language, and orientation, and, unlike patients with Parkinson's disease, there was evidence of apraxia. Patients with Parkinson's disease had more severe impairment related to speed of information processing, and, unlike patients with dementia of the Alzheimer type, they also had disturbance of mood. The nature of visuospatial abnormalities also differentiated the two groups. The pattern of neuropsychological differences is consistent with the cortical-subcortical hypothesis.