Psychomotor retardation and risk of Parkinson's disease in unipolar depression: A retrospective cohort study.

BACKGROUND: Depression is associated with an increased risk of subsequent Parkinson's disease. Neuroimaging studies suggest a neurobiological overlap in mechanisms underlying Parkinson's disease and psychomotor retardation in depression. Our aim was to investigate whether, among individuals with depression, the presence of psychomotor retardation was associated with the development of subsequent Parkinson's disease. METHODS: In a retrospective cohort study, electronic healthcare records from individuals diagnosed with depression at age 40 or over in a large mental health service in London, UK were examined for the presence of psychomotor retardation. Linkage to general hospital records was used to ascertain diagnoses of Parkinson's disease between 2007 and 2023. A mixed-effects Cox model, incorporating a participant-level random intercept and psychomotor status as a fixed-effects exposure was used to compare the hazard of Parkinson's disease in depression with and without psychomotor retardation. RESULTS: Among 6326 patients with depression, there were 17,998 psychomotor observation intervals and 138 incident Parkinson's disease cases. PMR-positive status was associated with a higher subsequent hazard of Parkinson's disease in the adjusted mixed-effects Cox model (hazard ratio 1.57, 95% CI 1.11-2.22; p = 0.011). Secondary analyses demonstrated a significant difference in psychomotor retardation probability at up to 2.5 years before Parkinson's diagnosis. CONCLUSIONS: Psychomotor retardation in later-life depression is associated with increased risk of subsequent Parkinson's diagnosis over an extended period of time, suggesting that the relationship cannot solely be explained by misdiagnosis. Psychomotor retardation might therefore serve as a marker of prodromal Parkinson's disease.