Abstract
Background: Alzheimer's disease (AD) and Parkinson's disease (PD) are associated with severe cognitive decline, but it is still unclear to what extent they become functionally more similar over time. Methods: We compared amnestic mild cognitively impaired (aMCI; n = 29) patients to mild cognitively impaired (MCI) PD patients (n = 25), and patients with AD (n = 34) to patients with PD dementia (PDD; n = 15) with respect to cognitive functioning and mood. Results: aMCI patients were impaired in episodic memory, while MCI PD patients showed deficits in visuoconstruction and attention. AD and PDD patients showed comparable deficits on tests for language, attention and visuoconstruction. However, unlike PDD patients but similar to aMCI patients, AD patients showed a characteristic memory impairment, especially commission errors on recognition tasks, whereas PDD patients scored higher on the depressive mood questionnaire. Conclusions: In advanced stages of both diseases, the pattern of functional deficits associated with parietal and temporal lobe functions (attention, visuoconstruction and language) is similar. However, specific differences, already present in the early stage (recognition errors in AD, associated with mediobasal temporal lobe functioning, and depressed mood in PDD, associated with non-motor basal ganglia loops), are also observed in the late stage.
