The impact of multimorbidity status on treatment response in rheumatoid arthritis patients initiating disease-modifying anti-rheumatic drugs

Objective. When treating RA patients, remission (REM) or at least low disease activity (LDA) is the ultimate therapeutic goal. The aim of this study was to assess the impact of multimorbidity on achieving REM or LDA. Methods. In a prospective RA cohort, we identified patients initiating any DMARD with follow-up data 1 year after. Treatment effects were measured using the clinical disease activity index (CDAI) and the modified health assessment questionnaire (MHAQ); multimorbidity status was assessed using a counted multimorbidity index (cMMI). The proportion of patients reaching REM or LDA 1 year after DMARD commencement with respect to the cMMI was evaluated. In regression models, we calculated the odds ratio of achieving REM or LDA, and predicted CDAI and MHAQ 1 year after DMARD commencement for various levels of cMMI, adjusting for age, sex, disease duration, serostatus, disease activity at DMARD commencement, number of previous DMARDs, and type of DMARD, steroid and NSAID use. Results. A total of 815 patients started DMARDs; 414 were on the same DMARD after 1 year. The proportion of these patients achieving REM or LDA after 1 year was significantly lower in the patients with higher cMMI, following a linear trend (P< 0.01). After accounting for covariates, the odds ratio for REM associated with each additional morbidity in the cMMI was 0.72 (95% CI 0.55, 0.97) and 0.81 (95% CI 0.70, 0.94) for LDA. One year after DMARD initiation, CDAI (+ 0.16 per additional morbidity) and MHAQ scores (+ 0.15 per additional morbidity) were significantly worse (both P< 0.05). Conclusion. Increased multimorbidity negatively affects the therapeutic goal of REM and LDA.