Incidence Trends of Rheumatoid Arthritis in Korea for 11 Years (2006-2017)

Rheumatoid arthritis (RA) is a chronic inflammatory disorder characterized by joint damage. However, no incidence analyses have been conducted on a Korean population since 2013. We aimed to calculate the incidence of RA and examine trends using complete Korean National Health Insurance Service claims data from 2007. We used 16 years of Korean NHIS claims data from 1 January 2002 to 31 December 2017. Patients were defined as having RA when diagnosed with ICD-10 codes M05 and M06. We set the 5-year period prior to 2006 as disease-free. From 2007 to 2017, the incidence rate of RA was 35 to 43 per 100,000 individuals. The female-to-male ratio was approximately 3-3.5 to 1. The sex-standardized incidence rate was highest in the 60-69 age group but gradually declined, resulting in a reversal in 2017, with the highest incidence rate observed in the 50-59 age group. The incidence of elderly onset RA (EORA) in individuals aged >60 years exhibited a decreasing trend during the study period (age 60-69, -6.45, 95% CI = -8.27 to -4.62, < 0.001; age ≥70, -6.09, 95% CI = -7.66 to -4.53, < 0.001). This study is the first to analyze the incidence trend of RA over an 11-year period. In South Korea, the incidence of RA has shown a decreasing trend since 2011; the same trend was observed in the EORA group. Young-onset RA showed the opposite trend, suggesting that RA is diagnosed earlier, due to the new RA classification criteria.