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Previous research suggests that lexical and semantic verbal fluency are differentially sensitive to the effects of cortical and subcortical dementias, but little is known about action fluency performance in dementias. The present study compared lexical, semantic, and action fluency in groups of patients with Parkinson's disease (PD) with and without dementia and an elderly control group. Findings revealed an interaction between fluency type and subject group. Although the demented PD (PDD) group performed significantly more poorly than their non-demented counterparts and normal controls on all three fluency tasks, a disproportionate disparity in scores was noted on the action fluency task. The findings suggest that action fluency may be particularly sensitive to PD-associated dementia and may be an early indicator of the conversion from PD to PDD. As reported elsewhere, PD without dementia was not associated with significant impairment on any of the fluency tasks.

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Cognitive deficits are common in Parkinson’s disease (PD), but the pathophysiology and relationship to Alzheimer’s disease (AD) are not understood. We used a case-control format to investigate putative risk factors for the development of dementia in patients with Parkinson’s disease. We compared 52 cognitively intact patients with PD to 43 PD patients with dementia with regard to factors previously suggested as relevant to either AD or PD. Multiple logistic regression yielded the following significant predictors of dementia in PD: lack of education (less than a high school graduate) (OR 21); severity of motor deficit (UPDRS total motor score greater than 20; OR 6.34), and PD onset at greater than 60 years of age (OR 4.12). The predictive probability of dementia in our subjects when all three variables were positive was 97.9%. We conclude that education may modify the risk of cognitive decline in PD. Protective effects of educational attainment, independent of dementia etiology, may be due to greater functional brain reserve.