The Immunological Association between Alopecia Areata and Respiratory Diseases: A Systematic Review

Background: While alopecia areata (AA) has been associated with atopy, the immunological relationship is unclear, with the association of specific atopic and systemic respiratory diseases not established. The relationship between T-helper (Th) 1-mediated AA and Th2-mediated atopy challenges the conventional Th1/Th2 paradigm of autoimmune disease categorization. Objectives: To determine the association between AA and atopic respiratory diseases in adults and children, and respiratory diseases in general. Method: All primary literature, excluding case reports, were identified within PubMed/MEDLINE, CINAHL, and Web of Science in May 2018 using the following search terms: "(alopecia OR hair loss) AND (respiratory OR pulmonary OR lungs OR asthma OR rhinitis OR bronchitis OR COPD OR atopy OR atopic)." Information from 32 articles meeting the inclusion and exclusion criteria was reviewed. Results: Among the 32 articles identified for inclusion, the prevalence of AA was more strongly associated with allergic rhinitis compared to asthma among pediatric and adult populations. While a significant association was identified between AA, allergic rhinitis, and a late age of onset, the association of AA and asthma remains controversial despite asthma's prevalence among AA patients. No significant difference was identified with regard to the association of AA and non-atopic respiratory diseases between adult and pediatric patients. Conclusions: Adult and pediatric patients with AA warrant further workup for atopic respiratory diseases such as allergic rhinitis. AA may have an underlying Th2-mediated immunological component, which supports its association with atopic respiratory diseases and provides a new avenue for targeted therapies in select cases. (c) 2019 S. Karger AG, Basel