Neuropsychological prediction of dementia in Parkinson's disease.
OBJECTIVE: To identify neuropsychological characteristics predictive of later dementia in Parkinson's disease. METHODS: A comprehensive neuropsychological test battery was administered to a cohort of 89 initially non-demented patients with Parkinson's disease consecutively enrolled at a specialised Parkinson's disease clinic. They were reassessed after a mean of 3.5 years for the diagnosis of dementia. The Cox proportional hazards model was used to identify baseline characteristics predictive of dementia. RESULTS: Only four of the baseline clinical characteristics of Parkinson's disease and neuropsychological variables remained independently linked to subsequent development of dementia: the age of onset of Parkinson's disease (>60 years; relative risk (RR) 4.1, 95% confidence interval (95% CI) 1.8-24.0, p<0.03), the picture completion subtest of the Wechsler adult intelligence scale (score<10; RR 4.9, 95% CI 1.0-24.1, p<0.02), the interference section of the Stroop test (score<21; RR 3.8, p=0.08), and a verbal fluency task (score<9; RR 2.7, 95% CI 0.8-9.1, p=0.09). Depressive symptoms and the severity of motor impairment were not predictive of dementia. CONCLUSION: These features are different from the neuropsychological characteristics predictive of Alzheimer's dementia in healthy elderly people (mainly memory and language performance). They are in keeping with the well known specificity of the impairments in Parkinson's disease for visuospatial abilities and difficulties in inhibiting irrelevant stimuli. It is postulated that the composite nature of the picture completion subtest, involving several cognitive abilities impaired in Parkinson's disease, explains its sensitivity.