Increased risk of depression in Bell's palsy: Two longitudinal follow-up studies using a national sample cohort

Background: Recently, a bidirectional association between Bell's palsy and anxiety disorders has been reported. Given the common comorbidity between anxiety and depressive conditions and the typical developmental trajectory of anxiety before depression, we hypothesized that the bidirectional association between Bell's palsy and depression is also reproducible. Methods: Using data from the Korean National Health Insurance Service-National Sample Cohort, data were collected from 3,526 Bell's palsy patients who were 1: 4 matched by age, sex, income, region of residence, and past medical history with 14,104 controls. Additionally, 61,068 depression patients were matched with 244,272 control participants. A Cox proportional hazards model was used to analyze the hazard ratio (HR) of Bell's palsy for depression (study I) and depression for Bell's palsy (study II). Results: In study I, the adjusted HR for depression was 1.41 (95% confidence interval [CI]= 1.20-1.66) in the Bell's palsy group (P < 0.001). In subgroup analyses, an increased risk of depression was more evident, particularly in female participants >= 40 years old. This association was evident in follow-up periods 6 months after the index date. In study II, the adjusted HR for Bell's palsy was 1.08 (95% CI = 0.94-1.25) in the depression group (P = 0.280). Conclusion: A history of Bell's palsy increased the risk of depression. Contrary to our hypotheses, depression did not increase the risk of Bell's palsy.