Population-based case-control study of cognitive function in early Parkinson's disease (NEDICES).

BACKGROUND: Population-based assessments of cognitive function in patients with early Parkinson's disease (PD) are rare. We examined whether patients with early PD have cognitive deficits when compared with matched controls
METHODS: All participants were age 65 years or older (median=76 years) and were enrolled in the Neurological Disorders in Central Spain (NEDICES) study in central Spain. We identified all participants with early PD (<5 years duration) (N=46). These were matched to 138 controls. Neuropsychological test scores were compared in PD patients vs. controls. In logistic regression models, we adjusted for the effects of confounding variables. In these models, the dependent variable was the neuropsychological test score (lowest quartile vs. all other quartiles) and the independent variable was PD vs. control.
RESULTS: Sixteen of 46 patients (34.8%) with early PD were previously undiagnosed. Subjective memory complaint was present in 27 (58.7%) PD patients vs. 51 (37.0%) controls (p=0.010). In logistic regression models that adjusted for gender, education, and depressive symptoms or antidepressant use, PD patients performed less well on the 37-item version of the Mini-Mental State Examination (p=0.04), animal (p<0.001) and fruit fluency (p=0.04) as well as in a delayed free recall memory test (p=0.04) than controls.
CONCLUSIONS: In this population-based sample of older patients with early PD, the rate of subjective and object cognitive impairment was appreciable. Patients with PD of less than five years duration performed relatively poorly on tests of global cognition, verbal fluency and memory. Clinicians should be vigilant to these cognitive difficulties even in the early stages of PD.