Global, regional and national epidemiology of alopecia areata: a systematic review and modelling study.

BACKGROUND: Alopecia areata (AA) is a chronic autoimmune disease that leads to a high psychiatric, economic and systemic disease burden. A comprehensive understanding of AA epidemiology is essential for evaluating healthcare source utilization; however, a systematic approach to summarizing epidemiological data on AA is lacking. OBJECTIVES: To investigate systematically the global, regional and national incidence and prevalence of AA. METHODS: A structured search was conducted using the databases MEDLINE, Embase, Cochrane Library, Web of Science, SciELO and Korean Journal Database from their date of inception to 4 October 2023. Studies that reported the prevalence or incidence of AA were included. We used a Bayesian hierarchical linear mixed model to analyse prevalence estimates. The primary outcomes of our study were the global, regional and national prevalence of physician-diagnosed AA for the overall population, for adults and for children. The incidence data were summarized descriptively. RESULTS: In total, 88 studies from 28 countries were included in the analysis. The reported incidence of AA tended to be higher in adults aged 19-50 years, and this trend was consistent with its estimated prevalence. The reported prevalence in overall populations tended to be higher in men vs. women. The estimated lifetime prevalence rate of AA was 0.10% [95% credible interval (CrI) 0.03-0.39] in the general population worldwide, 0.12% (95% CrI 0.02-0.52) in adults and 0.03% (95% CrI 0.01-0.12) in children. The estimated prevalence of AA was highest in the Asian region and lowest in the African region. CONCLUSIONS: In this study, 48% of the Global Burden of Disease regions had insufficient data on the prevalence or incidence of AA. Further studies are needed to provide epidemiological information on middle- and low-income countries. Our study may serve as a crucial reference in terms of healthcare policy decisions.

Alopecia areata (AA) is a chronic autoimmune disease that can have both a psychological and physical impact on patients. An understanding of in whom, when and where the disease occurs ('epidemiology') is important to evaluate how healthcare resources are used in AA. There is a lack of analysis of epidemiological data in AA. This study investigated the global, regional and national incidence (the number of new cases in a specific time period) and prevalence (the rate of new cases occurring in a specific population over a specific period of time) of AA by reviewing multiple databases. Studies that reported the prevalence or incidence of AA were analysed. The primary outcomes were the global, regional and national prevalence of AA diagnosed by a doctor for the overall population, for adults only and for children only. Altogether, 88 studies from 28 countries were included in the review. The incidence of AA tended to be higher in adults aged 19­50 years, and this trend was consistent with its estimated prevalence. The estimated lifetime prevalence rate (i.e. the proportion of individuals that will be affected) of AA was 0.10% in the general population worldwide, 0.12% in adults and 0.03% in children. The estimated prevalence of AA was highest in the Asian region and lowest in the African region. Overall, we found that 48% of regions did not have enough data on the prevalence or incidence of AA. Further studies are needed to provide epidemiological data on AA, especially in middle- and low-income countries. Our results will help with healthcare policy decisions.

The Alopecia Areata Severity and Morbidity Index (ASAMI) Study: Results From a Global Expert Consensus Exercise on Determinants of Alopecia Areata Severity.

Importance: Current measures of alopecia areata (AA) severity, such as the Severity of Alopecia Tool score, do not adequately capture overall disease impact. Objective: To explore factors associated with AA severity beyond scalp hair loss, and to support the development of the Alopecia Areata Severity and Morbidity Index (ASAMI). Evidence Review: A total of 74 hair and scalp disorder specialists from multiple continents were invited to participate in an eDelphi project consisting of 3 survey rounds. The first 2 sessions took place via a text-based web application following the Delphi study design. The final round took place virtually among participants via video conferencing software on April 30, 2022. Findings: Of all invited experts, 64 completed the first survey round (global representation: Africa [4.7%], Asia [9.4%], Australia [14.1%], Europe [43.8%], North America [23.4%], and South America [4.7%]; health care setting: public [20.3%], private [28.1%], and both [51.6%]). A total of 58 specialists completed the second round, and 42 participated in the final video conference meeting. Overall, consensus was achieved in 96 of 107 questions. Several factors, independent of the Severity of Alopecia Tool score, were identified as potentially worsening AA severity outcomes. These factors included a disease duration of 12 months or more, 3 or more relapses, inadequate response to topical or systemic treatments, rapid disease progression, difficulty in cosmetically concealing hair loss, facial hair involvement (eyebrows, eyelashes, and/or beard), nail involvement, impaired quality of life, and a history of anxiety, depression, or suicidal ideation due to or exacerbated by AA. Consensus was reached that the Alopecia Areata Investigator Global Assessment scale adequately classified the severity of scalp hair loss. Conclusions and Relevance: This eDelphi survey study, with consensus among global experts, identified various determinants of AA severity, encompassing not only scalp hair loss but also other outcomes. These findings are expected to facilitate the development of a multicomponent severity tool that endeavors to competently measure disease impact. The findings are also anticipated to aid in identifying candidates for current and emerging systemic treatments. Future research must incorporate the perspectives of patients and the public to assign weight to the domains recognized in this project as associated with AA severity.