Down syndrome‐associated arthritis (DA) is under‐recognized and current therapies used for juvenile idiopathic arthritis (JIA) appear to be poorly tolerated and less effective in patients with DA. This study’s objective was to characterize clinical manifestations and therapeutic preferences in DA compared to JIA, using the new Childhood Arthritis and Rheumatology Research Alliance Registry (nCARRA).

In a case‐control study, between the dates of July 2015 and March 2019, patients diagnosed with JIA and Down syndrome (DS) were identified and matched on age, sex, and JIA subtype to patients with JIA and without DS. Collected data included demographics, disease characteristics, laboratory results, treatment exposure, and outcome measures. Thirty‐six children with DA and 165 with JIA were identified. Most patients had polyarticular RF negative presentations. At entry into the nCARRA, there were minimal differences between groups, and at the last visit, there were significant (p‐value < 0.05) differences for multiple outcome measures. Those with DA and JIA had similar therapeutic exposure to DMARDs and biologics, but those with DA had more DMARD adverse events (93% versus 25%) and biologic therapy ineffectiveness (60% versus 17%).

There was little difference between patients with DA and JIA at baseline, and similar therapy was implemented for those in the nCARRA. However, at the last visit, those with DA had more disease burden. Additionally, there were more DMARD adverse events and biologic ineffectiveness for those with DA. More research is needed to determine differences in pathophysiology and optimal therapeutic approaches.