Prevalence and Clinical Determinants of Cognitive Impairment in Diverse Patients with Parkinson's Disease

Importance: The real-world prevalence and the clinical determinants associated with cognitive impairment in diverse patients with Parkinson disease (PD) have been understudied. Objective: To determine the prevalence of cognitive impairment in a diverse PD cohort and explore associations with vascular, motor, and nonmotor factors. Design, setting and participants: Case-only analysis of diverse patients with PD recruited to the East London Parkinson disease project (July 2022 to July 2025) at the Royal London Hospital, a tertiary referral center. Of 237 patients with cognitive status defined by expert, multi-disciplinary, clinical consensus, 223 remained after excluding atypical or secondary parkinsonism, other dementias, and study withdrawal. Exposures: Observational study (no experimental intervention); exposures included vascular risk factors, motor and nonmotor clinical features. Main Outcome(s) and Measure(s): The main outcome was cognitive impairment (PDCI), defined as mild cognitive impairment (PDMCI) or dementia (PDD) by expert clinical consensus based on clinical, imaging, and cognitive screening. Results: Among 223 participants with a median disease duration of 4.0 (1.0-9.0) years, 112 (50.2%) had PDCI, including 62 (27.8%) with PDD and 50 (22.4%) with PDMCI. South Asian ethnicity was associated with PDCI in univariate analysis (OR, 2.30; 95% CI, 1.32-4.00, P = .003) and the association strengthened after adjusting for age, gender, years of education, disease duration and depression scores (OR, 3.60; 95% CI, 1.68-7.69, P < .001). PDCI was associated with increased odds of smoking (OR, 3.62; 95% CI, 1.56-8.41, P = .003) in the adjusted model. Increased odds were also associated with motor severity (Movement Disorders Society Unified Parkinson Disease Rating Scale Part III; OR per point increase 1.07; 95% CI, 1.04-1.10; P < .001), and daytime somnolence score (Epworth Sleepiness Scale; OR per point increase, 1.08; 95% CI, 1.01-1.16; P = .03). Conclusions and Relevance: In this multi-ethnic study of PD using gold-standard expert multidisciplinary consensus, cognitive impairment was common and more prevalent among South Asian individuals. Smoking, greater motor severity, and higher daytime somnolence were associated with increased odds of cognitive impairment.