Abstract
BACKGROUND: Juvenile idiopathic arthritis (JIA) is a chronic inflammatory condition that frequently persists into adulthood, posing long-term challenges in disease control and quality of life. However, clinical management during the transitional and young adult phases remains insufficiently characterized, especially in comparison with adult-onset rheumatoid arthritis (RA). This study aimed to compare disease activity, medication use, and treatment practices between patients with oligoarticular/polyarticular JIA and those with RA, focusing on individuals aged 16-30 years. METHODS: Data were derived from two nationwide multicenter databases in Japan-NinJa (National Database of Rheumatic Diseases in Japan) for RA and CoNinJa (a pediatric counterpart of NinJa) for JIA. A total of 176 JIA and 152 RA patients, all aged 16-30 years, were analyzed. Clinical parameters, disease activity indices, and medication profiles were compared using the Mann-Whitney U test and Fisher's exact test. RESULTS: Compared to RA patients, JIA patients demonstrated significantly lower disease activity (median SDAI 0.6 vs. 2.4) and higher remission rates, particularly Boolean remission (70% vs. 44%) (p < 0.001). MTX usage was less frequent in JIA (49% vs. 68%, p < 0.001), whereas biologic use was notably more common (69% vs. 38%, p < 0.001), with 31% involving off-label prescriptions. Among patients in CDAI remission, biologic monotherapy was observed more frequently in JIA (29% vs. 7%, p < 0.001). Discontinuation of MTX was most commonly attributed to disease improvement (58%) or gastrointestinal intolerance (nausea, 29%). Subcutaneous tocilizumab, though unapproved for JIA in Japan, had the lowest discontinuation rate (4%), suggesting favorable tolerability. CONCLUSIONS: Despite an overlap in age, patients with JIA and RA exhibit distinct disease characteristics and therapeutic patterns. These differences underscore the need to expand approved treatment options for JIA, promote equitable access to biologics, and strengthen transitional care frameworks. Further research is warranted to explore long-term outcomes, reproductive health considerations, and socioeconomic barriers that influence treatment continuity in young adults with childhood-onset arthritis.