Objectives: Whether treatment response differs across affected joints in rheumatoid arthritis (RA) remains unclear. We sought to determine whether responses to tumour necrosis factor inhibitors (TNFi) and other biologic/targeted synthetic disease-modifying antirheumatic drugs (b/tsDMARDs) vary across individual joints in a large cohort of patients with RA.

Methods: Patients with RA from the Swiss Clinical Quality Management in Rheumatic Diseases registry with ≥1 swollen joint at treatment initiation of a b/tsDMARD (abatacept, interleukin-6 receptor inhibitor (IL-6Ri), Janus kinase inhibitor (JAKi), rituximab and TNFi) were included. Time to resolution of swollen joints was evaluated over a 2-year follow-up using mixed effects models accounting for interval-censored data. The analyses compared the speed of improvement of individual joints within the 28-joint count to that of the wrist. The primary analysis focused on bio-naïve patients initiating TNFi treatment, while secondary analyses included all b/tsDMARD classes, irrespective of treatment line.

Results: A TNFi was initiated in 598 patients with ≥1 swollen joint, while 1942 patients with ≥1 swollen joint started a b/tsDMARD (abatacept: 242, IL-6Ri: 317, JAKi: 333, rituximab: 176, TNFi: 874). Compared with the wrist, all joints demonstrated higher rates of resolution, except for the second and third metacarpophalangeal (MCP2/3) joints and, in some analyses, the knee. This pattern of joint-specific response was consistent across all b/tsDMARDs.

Conclusions: The wrist, MCP2 and MCP3 joints resolve more slowly than other joints following treatment with b/tsDMARDs, indicating that a longer evaluation period of treatment response and/or bridging intra-articular steroid injections may be required when these joints are affected.