Cognitive dysfunctions in mild Parkinson's disease dementia: comparison with patients having mild Alzheimer's disease and normal controls

Although the neuropsychological differences between Alzheimer's disease (AD) and Parkinson's disease dementia (PDD) have been scrutinized in several studies, no study to date has directly compared the cognitive impairment profiles of patients with mild PDD and those with mild AD. In this study, we investigated the cognitive changes of mild PDD patients as compared with age- and education-matched normal controls and matched mild AD patients.

Thirty-one patients with PDD, 24 patients with probable AD (pAD), and 50 controls were recruited prospectively. All the subjects were evaluated with a battery of detailed neuropsychological tests for the assessment of attention, memory, language, and the visuospatial and frontal executive functions.

The PDD and pAD groups demonstrated significant impairments in all cognitive domains compared with the control group. These cognitive declines attributable to dementia were similar in the PDD and pAD patients, but they were not identical. In the subdomain analysis, the pAD group demonstrated more marked changes in delayed memory performance than did the PDD group.

Our result showed that the cognitive changes in mild PDD patients did not differ from those in the mild pAD patients, except for delayed memory items. We concluded that it is difficult to sharply distinguish between mild PDD and mild AD.