Increased risk of bipolar disorder in patients with scabies: A nationwide population-based matched-cohort study.

Both scabies and bipolar disorder (BD) are common and troublesome disorders. There are several similarities in both diseases: pruritus, a higher prevalence in crowded environments, and cytokine-mediated inflammatory processes in the pathophysiology. We conducted this nationwide population-based study to investigate the possible relationship between scabies and BD. Based on the National Health Insurance Research Database (NHIRD) of Taiwan, a total of 7096 patients with scabies were identified as a study group and 28,375 matched patients as a control. We tracked the patients in both groups for a 7-year period to identify those newly diagnosed with BD. The demographic characteristics and comorbidities of the patients were analyzed, and Cox proportional hazard regressions were performed to calculate the hazard ratio (HR) of BD. Of the 35,471 patients in this study, 183 (0.5%) patients with newly diagnosed BD were identified, with 58 (0.8%) from the scabies group and 125 (0.4%) from the control group. The patients with scabies had a higher risk of subsequent BD, with a crude hazard ratio of 1.86 and an adjusted hazard ratio of 1.55 (95% confidence interval: 1.12-2.09, P < 0.05). This study shows there is an increased risk for BD among patients with scabies. Immunopathology may contribute to this association.