Objective: To determine which clinical features best characterize Parkinson disease dementia (PDD), compared with Alzheimer disease (AD) and dementia with Lewy bodies (DLB), and to determine the pathologic basis for PDD.

Methods: We examined 103 participants enrolled in a longitudinal study (nondemented control = 10, PD = 42, DLB = 20, AD = 31) who were followed to autopsy using standardized protocols. We characterized the features of PDD using published criteria for AD and DLB as a framework. Statistical analysis was performed using chi(2) and Fisher exact tests, Kaplan-Meier curves, and logistic regression models.

Results: The sample's mean age was 74.0 years (range 53 to 91 years), and individuals were followed for a mean of 3.4 visits (range 1 to 12 visits). During longitudinal follow-up, 83% of subjects with PD developed dementia, defined as a Clinical Dementia Rating score of >or=0.5. Features that distinguished PDD from AD included cognitive fluctuations (p = 0.001), visual (p < 0.001) and auditory (p = 0.006) hallucinations, depression (p = 0.003), and sleep disturbance (p = 0.003). These PDD features were identical to those observed for DLB. The pathologic substrates for PDD included DLB (38%), AD (32%), and nigral LB alone (24%). Clinical predictors of PDD were visual hallucinations (odds ratio [OR] 21.3; 95% CI: 1.5 to 309.6) and male gender (OR 9.6; 95% CI: 1.3 to 71.4).

Conclusions: Parkinson disease dementia (PDD) shares identical clinical features with dementia with Lewy bodies (DLB); both entities can be distinguished from Alzheimer disease. The presence of PDD/DLB features at any time during the course of PD is highly predictive of dementia and the presence of LB at autopsy; in particular, male gender and visual hallucinations in PD predict dementia.