Comparative Clinical Practice of Juvenile Idiopathic Arthritis and Rheumatoid Arthritis in Adolescents and Young Adults: A Retrospective Cohort Study Using Japanese Health Insurance Claims Data (2016-2020).

Objectives: This study aims investigates real-world data on the demographics, prescribing practices, and healthcare costs of juvenile idiopathic arthritis (JIA) with polyarthritis or oligoarthritis compared to rheumatoid arthritis (RA) patients in adolescents and young adults.

Methods: Data from the Japan Medical Data Center (JMDC) claims database for fiscal years (FY) 2016-2020 were analyzed. JIA and RA were defined as having at least 2 months of disease-modifying antirheumatic drug (DMARD) prescriptions and corresponding ICD-10 (International Classification of Diseases, 10th Revision) codes for each FY. Therapeutic drug prescriptions and direct medical costs were evaluated.

Results: Among 5,064,539 eligible individuals aged 18-29, 202 were identified with JIA and 2,758 with RA. The prescription rate of b/tsDMARDs (biologic and targeted synthetic DMARDs) for RA remained stable at approximately 40% between FY 2016 and FY 2020. However, from FY 2018 onward, the rate was significantly higher for JIA, reaching approximately 60% (p < 0.05). In FY 2020, biosimilar prescriptions accounted for 15% in RA but only 3% in JIA. Direct medical costs for JIA were 1.6 times higher than those for RA.

Conclusion: Patients with JIA were more frequently prescribed tsDMARDs and less likely to receive biosimilars, contributing to higher healthcare costs compared to RA patients.