Risk of incident depression in patients with Parkinson disease in the UK

Background: Non-motor symptoms are not widely recognized in patients with Parkinson disease (PD). We sought to assess the incidence rate as well as the risk of depression in newly diagnosed patients with PD and to compare it to PD-free controls. Methods: We conducted a population-based follow-up study with a nested case-control analysis based on data from the UK-based General Practice Research Database (GPRD). We included PD patients aged 40 years with a first PD diagnosis between 1994 and 2005, and a matched comparison group free of PD. We assessed incidence rates (IRs) and relative risk estimates (odds ratios [ORs] with 95% confidence intervals [CI]). Results: The IR of depression in newly diagnosed PD in the UK community was 26.0 (95% CI 22.9-29.5) per 1000 person-years. The risk of developing depression was increased almost twofold in patients with PD when compared to patients without PD (adj. OR 1.89; 95% CI 1.49-2.40). The increased relative risk was most pronounced in women and in individuals 40-69 years of age. Long-term users of levodopa had an increased depression risk when compared to short-term users. Conclusions: Patients with PD are at an approximately twofold increased risk of being diagnosed with depression compared to the PD-free population.