Risk of Depression Following Parkinson’s Disease Diagnosis: A Nationwide Retrospective Cohort Study in South Korea

Background Depression is a common and clinically significant non-motor condition in patients with Parkinson’s disease (PD), but population-level evidence on its temporal risk after PD diagnosis remains limited. Methods We conducted a nationwide retrospective cohort study using Korean National Health Insurance Service data (2012-2023). PD was defined by at least two outpatient diagnoses within 1 month, and incident depression as a new diagnosis after the index date. A 3-year washout period excluded individuals with pre-existing PD or depression. Patients with PD were propensity score–matched 1:5 with controls. Incidence rates and adjusted hazard ratios (aHRs) were estimated using Cox regression with time-stratified analyses. Results The study included 3932 patients with PD and 19 660 matched controls. The incidence rate of depression was higher in the PD group than in controls (43.58 vs 21.83 per 1000 person-years; IRR = 2.00, 95% CI 1.81-2.20). Risk was highest within 0-3 years after PD diagnosis and declined over time. Elevated risks were observed among patients younger than 60 years and among male patients. Conclusions PD was associated with an increased risk of subsequent depression, particularly during the early post-diagnostic period, highlighting the need for early psychiatric assessment and ongoing monitoring.