Nationwide epidemiological survey of juvenile idiopathic arthritis during transition to young adulthood in Japan using the National Database of Designated Incurable Diseases of Japan.

Objectives We aimed to assess the unmet medical needs of young adult patients with juvenile idiopathic arthritis by evaluating real-world treatment data. Methods We analyzed data on juvenile idiopathic arthritis in the 20-29 age group from the National Database of Designated Incurable Diseases of Japan, which records severe cases or those requiring high-cost medical care registered between April 2018 and March 2020. Results Overall, 322 patients with juvenile idiopathic arthritis transitioning to adulthood were included. A high frequency of methotrexate use was observed among all juvenile idiopathic arthritis subtypes. The frequency of methotrexate use at registration was significantly higher in patients with rheumatoid factor-positive polyarthritis and those with oligoarthritis or polyarthritis than in those with systemic arthritis. The historical use percentage of any biological disease-modifying antirheumatic drug was ≥85% for all juvenile idiopathic arthritis subtypes. The proportion of patients with ≥2 biological disease-modifying antirheumatic drug prescriptions was significantly higher in patients with rheumatoid factor-positive polyarthritis than in those with systemic arthritis. Conclusions High-cost drugs were necessary for many patients with juvenile idiopathic arthritis transitioning to young adulthood and registered in the database. Further studies on the medical interventions and support for these patients are needed.