A registry-based, case-control investigation of Parkinson's disease with and without cognitive impairment

In approximately 40% of the patients, Parkinson's disease (PD) is complicated by cognitive impairment. The objective of this study was to evaluate the impact of cognitive impairment on disease severity and motor function in idiopathic PD patients. Forty-one PD patients with cognitive impairment (PD-CI) (Mini-Mental State Examination < or =24) and 41 PD patients without cognitive impairment (PD-Control) matched for age at onset and duration of the disease were examined using the Unified Parkinson's Disease Rating Scale (UPDRS). PD patients with cognitive impairment had overall poorer motor function, worse rigidity (both axial and limb) and bradykinesia, as well as worse performance in activities of daily living compared with matched PD patients without cognitive impairment. This could either be attributed to a direct effect of cognitive impairment on parkinsonian symptoms or to decreased compliance of patients during clinical examination. PD patients should be routinely and carefully screened for dementia and caregivers should be aware of the effect of dementia on PD.