Increased risk of alopecia areata among patients with endometriosis: A longitudinal study in Taiwan

Endometriosis has been associated with the risk of several autoimmune diseases; however, its relationship with alopecia areata (AA) remains unknown. This study aimed to investigate the risk of AA in patients with endometriosis. Participants were recruited from the National Health Insurance Research Database in Taiwan. We identified female patients with endometriosis between January 1, 1998 and December 31, 2011. For each patient with endometriosis, four control subjects were included in the control group matched for age, sex, monthly premium, and residence. Patients and control subjects were followed up until AA diagnosis, death, or December 31, 2013, whichever occurred first. The Cox regression model was used for the analyses. Overall, we included 35,123 patients with endometriosis and 140,492 control subjects. Compared with control subjects, patients with endometriosis had an adjusted hazard ratio of 5.60 (95% confidence interval 4.03-7.79) for AA after controlling for age, socioeconomic status, and comorbidities. In conclusion, patients with endometriosis had a significantly increased risk of AA. Further studies are necessary to investigate the pathophysiology underlying the relationship between endometriosis and AA.