Background/Purpose: Adult-onset Still’s disease (AOSD) is a rare systemic autoinflammatory disorder characterised by heterogeneity in clinical course and long-term outcomes. Despite its rarity being recognised globally, population-based epidemiologic studies estimating the incidence, prevalence, and mortality of AOSD remain extremely limited. This study aimed to estimate the national incidence, prevalence, and mortality of AOSD and to describe the demographic and clinical characteristics of affected individuals in South Korea.

Methods: We identified AOSD patients using the Korean National Health Insurance Service (NHIS) database from 2002 to 2022, applying the ICD-10 diagnostic code in conjunction with characteristic patterns of hospital utilisation and medication prescription. To improve diagnostic specificity, individuals with coexisting autoimmune diseases or malignancies diagnosed within three months before or after the first AOSD claim were excluded. Age- and sex-adjusted incidence and prevalence rates per 100,000 population were calculated annually, and temporal trends were assessed. Using operational definitions, disease courses were categorised into monocyclic, polycyclic, and chronic patterns.

Results: A total of 4,825 patients met the criteria for AOSD, and 4,207 patients diagnosed between 2003 and 2020 were included in the final analysis. The overall age- and sex-adjusted incidence and prevalence rates across the study period were 0.49 and 4.25 per 100,000 population, respectively. Annual incidence rates showed a gradually increasing trend from 0.32 in 2003 to 0.50 in 2020, with slight fluctuations across years. The female-to-male ratio was 2.56, and the mean age at diagnosis was 45.5 ± 16.7 years. Based on disease course classification, 1,867 patients (38.7%) had a monocyclic course, 1,197 (24.8%) polycyclic, and 1,761 (36.5%) chronic. During the observation period, 376 patients died, among whom 8 deaths were attributed to macrophage activation syndrome (MAS), the most severe complication of AOSD.

Conclusion: Leveraging 21 years of longitudinal, nationwide claims data, this study provides the first comprehensive national estimates of the incidence, prevalence, and mortality of AOSD in South Korea. Our findings confirm that AOSD remains a rare disease with persistently low incidence and increasing prevalence, mirroring international observations. These data underscore the value of long-term epidemiologic surveillance and may inform future research and health policy planning related to rare systemic autoinflammatory disorders.

Table 1. Baseline demographic and clinical characteristics of South Korean AOSD patients (2003-2020) using 3 year-incidence

Figure1_A flow chart for defining study population.

Figure2_ Annual age-, sex- adjusted incidence and prevalence of AOSD in South Korea 2003-2020

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/epidemiology-of-adult-onset-stills-disease-in-south-korea-a-nationwide-study-using-health-insurance-claims-data/