Suicidal behaviour and suicide mortality in Parkinson's disease: a nationwide register-based cohort study.

Background: Previous population-based studies suggest an increased risk of suicide in Parkinson's disease (PD), but findings have been inconsistent and often limited by residual confounding. We examined the association between incident PD and suicide-related outcomes using extensive confounding control, including both suicidal attempts and suicide. Methods: We conducted a nationwide matched cohort study using Swedish population registers. Individuals with incident PD (n=44 398) were matched 1:5 to population controls (n=2 23 292) by year of birth, sex and municipality. Baseline covariates were assessed during the 3 years before diagnosis and used to estimate propensity scores. Associations with (1) suicide death and (2) suicidal behaviour (suicide attempt or suicide death) were analysed using Cox regression stratified by matching group. Additional confounding was addressed by inverse probability weighting by propensity scores. Analyses were further stratified by sex and age at diagnosis (<65/≥65 years). Results: There were 335 suicide deaths and 1083 suicidal behaviour events during follow-up. In matched analysis, PD was associated with suicide death (HR 1.35 (95% CI 1.03 to 1.76)), but this association attenuated after weighting (HR 1.08 (95% CI 0.81 to 1.45)). PD remained associated with suicidal behaviour after weighting (HR 1.46 (95% CI 1.27 to 1.69)). The association was strongest among individuals diagnosed before age 65 (weighted HR 1.86 (95% CI 1.47 to 2.36)). Conclusions: After extensive confounding adjustment, PD was not independently associated with suicide death overall but remained associated with increased risk of suicidal behaviour. Increased suicide death risk persisted among women and younger-onset PD.