Comorbidities in alopecia areata: A systematic review and meta-analysis.

BACKGROUND: Alopecia areata (AA) may be associated with various systemic diseases according to several studies. OBJECTIVE: To identify prevalent and incident diseases in patients with AA and quantify their prevalence and odds and hazard ratios compared with those in controls without AA. METHODS: A systematic review of the studies published before February 28, 2018, was performed by using the MEDLINE, Embase, Web of Science, and Cochrane Library databases. Observational studies on prevalent or incident diseases in patients with AA were included, whereas studies limited to pediatrics or providing only laboratory results or continuous data were excluded. The inverse variance method with a random-effects model was used for meta-analyses. RESULTS: A total of 87 studies were analyzed. Atopic diseases, metabolic syndrome, Helicobacter pylori infection, lupus erythematosus, iron deficiency anemia, thyroid diseases, psychiatric diseases, vitamin D deficiency, and audiologic and ophthalmic abnormalities were more prevalent in patients with AA. Patients with AA had a higher risk of developing autoimmune diseases. LIMITATIONS: Some diseases were investigated by an insufficient number of studies to be meta-analyzed. Meta-analysis of incident diseases was not performed owing to the limited availability of cohort studies. CONCLUSION: AA is associated with various systemic and psychiatric diseases. Physicians are encouraged to evaluate and manage potential comorbid conditions to achieve better outcomes.