Bipolar Disorder Associated with Another Autoimmune Disease—Pemphigus: A Population-based Study

Objectives: Recent evidence suggests a notable role for inflammation and immune dysregulation in the neuroprogression of bipolar disorders (BD). Several autoimmune comorbidities have been reported in association with BD. However, the epidemiological relationship between pemphigus and BD has not yet been elucidated. We aimed to estimate the association between pemphigus and BD using a large-scale, real-life computerized database. Methods: Data for this study were retrieved from the database of the Clalit Health Services, the largest, state-mandated, health service organization in Israel. This study was designed as a cross-sectional study. The proportion of patients with BD was compared between patients diagnosed with pemphigus and age-, sex-, and ethnicity-matched control subjects. A logistic regression model was performed to estimate how pemphigus and other covariates contributed as risk factors for BD. Results: A total of 1,985 pemphigus cases and 9,874 controls were included in the study. The prevalence of BD was greater in cases with pemphigus than in controls (1.0% v. 0.5%, respectively; P = 0.023). This coexistence was more prominent among patients of Jewish ethnicity. After controlling for confounders, such as age, sex, ethnicity, socioeconomic status, drug abuse, alcohol abuse, smoking, healthcare utilization, and comorbidities, pemphigus demonstrated a substantial independent association with BD (OR, 1.7; 95% CI, 1.0 to 2.9). Conclusions: Pemphigus is significantly associated with BD. Patients with pemphigus should be assessed for comorbid BD. Experimental research is needed to better recognize the biological mechanisms underlying this observation.