Alopecia areata and risk of atopic and autoimmune conditions: population-based cohort study

Background. Alopecia areata (AA) has features of both autoimmune and atopic pathogenesis, but information on the risk of people with AA developing autoimmune and atopic conditions is limited. Objective. To assess the prevalence and incidence of atopic and autoimmune conditions in people with AA. Methods. This was a population-based cohort study of 8051 adults with newly diagnosed AA (AA group) and 32 204 adults in the matched control group, using the UK Oxford-Royal College of General Practitioners (RCGP) Research and Surveillance Centre (RSC) network primary care database, 2009–2018 (trial registration number: NCT04239521). Baseline prevalence of common atopic and autoimmune conditions, and risk of new-onset atopic and autoimmune disease, were estimated. Results. Atopic and autoimmune conditions were more prevalent in the AA group than the control group (atopic 37.2% vs. 26.7%, autoimmune 11.5% vs. 7.9%). The AA group were 43% more likely to develop any new-onset atopic condition [adjusted hazard ratio (aHR) 1.43. 95% confidence interval (CI) 1.28–1.61] and 45% more likely to develop any autoimmune condition (aHR 1.45, 95% CI 1.28–1.66) compared with the control group. When examining individual conditions, the AA group were at increased risk of atopic dermatitis (aHR 1.91, 95% CI 1.67–2.19), allergic rhinitis (aHR 1.32, 95% CI 1.14–1.54), autoimmune hypothyroidism (aHR 1.65, 95% CI 1.35–2.02), systemic lupus erythematosus (aHR 4.51, 95% CI 1.88–10.82) and vitiligo (aHR 2.39, 95% CI 1.49–3.82). There was no evidence for a higher incidence of other conditions examined. Conclusion. People with AA have an increased burden of atopic and autoimmune comorbidity. This supports previous work suggesting that both T helper cell (Th)1 and Th2 immune responses may be implicated in the pathogenesis of AA.