Psychiatric diseases predated the occurrence of Parkinson disease: a retrospective cohort study.

Purpose: The influence of mental illness early in life on the subsequent risk of Parkinson disease (PD) and its clinical picture remain obscure. This study investigated the effects of psychiatric diseases on a subsequent PD diagnosis.

Methods: We used the Longitudinal Health Insurance Database 2000 of Taiwan to identify 73,597 patients who visited ambulatory care centers or were hospitalized with a first-time diagnosis of anxiety, affective disorders, or schizophrenia between 2001 and 2003 as the study cohort. We also randomly selected 220,791 enrollees matched with the study cohort for comparison. Each patient was individually tracked for 6 years to identify a subsequent PD diagnosis. Stratified Cox proportional hazard regressions were performed for the analysis.

Results: The incidence rate of PD per 1000 person-years was 4.91 (95% confidence interval [CI], 4.71-5.12) and 1.63 (95% CI, 1.56-1.70) for the psychiatric and comparison groups, respectively. Patients with psychiatric illnesses were more vulnerable to developing PD than nonpsychiatric individuals, exhibiting a 2.38-fold increased risk (95% CI, 2.23-2.53) after other covariates were considered. Furthermore, patients with schizophrenia exhibited the highest risk for developing PD.

Conclusions: We suggest effective monitoring of patients with psychiatric disturbances for potential long-term neurodegenerative diseases.