Difficult-to-treat rheumatoid arthritis with respect to responsiveness to biologic/targeted synthetic DMARDs: a retrospective cohort study from the FIRST registry.

OBJECTIVES Difficult-to-treat rheumatoid arthritis (dt-RA) is an emerging concept defined as persistency of signs and/or symptoms despite prior treatment. However, whether this refractoriness affects effectiveness and tolerance to next treatment is not fully understood. This study aimed to find cut-off values for a definition of dt-RA with respect to responsiveness to newly used biologic and targeted synthetic disease-modifying anti-rheumatic drugs (b/tsDMARDs). METHODS A retrospective cohort study was conducted using the FIRST registry. An inadequate response to current b/tsDMARDs was defined as clinical disease activity index >10 at week 22 or termination of treatment within 22 weeks due to insufficient efficacy. Cut-off values were defined according to the number of past failures to DMARDs and current dose of glucocorticoid. Responsiveness to newly used b/tsDMARDs were compared with respect to above versus below cut-off values. RESULTS Failures to ≥2 conventional synthetic DMARDs (csDMARDs) and ≥4 b/tsDMARDs as well as ≥3mg/day of glucocorticoid were independent cut-off values associated with poor responsiveness to newly used b/tsDMARD treatment. Concomitant use of glucocorticoid was significantly correlated with an increased hazard of infection. Failures to ≥2 csDMARDs was associated with less improvement in inflammatory symptoms, while that to ≥4 b/tsDMARDs was associated with less improvement in health assessment questionnaire and global health as well. CONCLUSIONS We propose cut-off values of ≥2 failures to csDMARDs and/or ≥4 b/tsDMARDs as a definition of dt-RA with respect to responsiveness to use of b/tsDMARDs.