Risk of Alzheimer Disease and Other Dementias in Patients With Parkinson Disease

INTRODUCTION: Dementia is a major nonmotor complication of Parkinson disease (PD), yet its subtype-specific and time-dependent risk remains incompletely characterized. METHODS: We conducted a nationwide retrospective cohort study using Korean National Health Insurance claims and health screening data. Newly diagnosed PD patients (ICD-10: G20) and propensity score-matched controls were followed after a 3-year washout period. Dementia outcomes were defined using ICD-10 codes and classified as Alzheimer disease dementia (F00, G30), other dementias (F01-F03), and overall dementia. Incidence rate ratios (IRRs) and adjusted hazard ratios (aHRs) were estimated using Cox models. RESULTS: PD was associated with higher dementia incidence across all subtypes. IRRs were 3.38 (95% CI: 3.12-3.67) for Alzheimer disease dementia, 4.67 (95% CI: 4.16-5.23) for other dementias, and 3.60 (95% CI: 3.33-3.90) for overall dementia. Elevated risks persisted after multivariable adjustment and were more pronounced in younger patients and men, with variation by dementia subtype and time since diagnosis. CONCLUSIONS: PD was associated with an increased risk of dementia in this nationwide cohort. The heterogeneity observed by subtype, age, and follow-up period suggests that dementia risk may emerge early in specific subgroups, supporting early cognitive monitoring without implying causality.