Cognitive Impairment and Mortality in a Population-Based Parkinson's Disease Cohort

Background: Parkinson's disease (PD) is a heterogeneous disorder with variability in phenotype and progression. Objective: We describe characteristics of PD patients in the largest population-based cohort followed for progression to date, and evaluate clinical risk factors for cognitive impairment and mortality. Methods: We collected longitudinal data using the Unified Parkinson's Disease Rating Scale (UPDRS), Mini-Mental State Exam (MMSE), and Geriatric Depression Scale (GDS) in 242 new-onset PD patients followed for progression. We compared those who developed cognitive impairment (MMSE <= 24) with those who did not, using t-tests, chi-square tests, and Cox proportional hazards regression. Mortality risk factors were assessed in all 360 patients enrolled at baseline. Results: Thirty-four patients developed cognitive impairment during follow-up. Baseline characteristics predictive of faster time to cognitive impairment were older age at diagnosis, fewer years of education, and longer average sleep duration reported. The 197 patients who died were older at diagnosis, reported longer average sleep duration, had lower baseline MMSE scores, higher UPDRS-III scores, and a higher proportion were of the postural instability gait difficulty (PIGD) subtype. Patients with the tremor dominant (TD) subtype at baseline were less likely to develop cognitive impairment or die during follow-up. Progression of cognitive, depressive, and motor symptoms occurred in parallel. Conclusions: Motor symptom severity and subtype influence the incidence of cognitive impairment and mortality in PD, with the TD motor subtype being relatively protective. In addition, we newly found that longer average sleep duration at baseline predicts faster progression to cognitive impairment and mortality.