Cognitive function in early Parkinson's disease: a population-based study

Background and purpose: The study aims to describe the frequency, pattern and determinants of cognitive function in patients with newly diagnosed Parkinson's disease (PD); to compare patients with impaired cognition to patients with intact cognition; and to compare to matched healthy controls. Methods: Patients were identified in a longitudinal population based study of idiopathic non-drug induced parkinsonism. Eighty-eight newly diagnosed patients with PD and no dementia were included during a four year period. The patients and 30 age- and sex-matched healthy control subjects underwent a comprehensive neuropsychological assessment. Results: Patients performed significantly worse than healthy controls in a majority of neuropsychological tests. Test results in attention, psychomotor function, episodic memory (free recall), executive function and category fluency were significantly lower in the patient group. Comparison with normative data revealed that 30% of the patients had deficits in >= 1 cognitive domain (episodic memory, executive function and verbal function). Seventy per cent of the patients had normal performance. Unified Parkinson's Disease Rating Scale (UPDRS) III sub scores; speech, facial expression, rigidity and bradykinesia were significantly higher, and disease duration shorter amongst the cognitively impaired than amongst the cognitively intact patients. Tremor showed no difference. Education level was an independent predictor of dysfunction in patients with >= 2 cognitive domains affected. Conclusion: Cognitive dysfunction is common in untreated patients in early PD, affecting attention, psychomotor function, episodic memory, executive function and category fluency. Education level was an independent predictor of severe cognitive dysfunction.