The effects of biologic and targeted synthetic disease-modifying anti-rheumatic drugs (b/tsDMARDs) and conventional synthetic disease-modifying anti-rheumatic drugs (csDMARDs) on body composition and muscle function in rheumatoid arthritis (RA) patients requiring treatment enhancement were compared. This multicenter, prospective, observational study (PRESENT Study) divided RA patients non-randomly into a csDMARD group (n = 100) and a b/tsDMARD group (n = 100). Changes in body composition and muscle function were examined in 80 patients in each group followed for 52 weeks. The percentages of new-onset and improved sarcopenia over 1 year were investigated. Patients in the b/tsDMARD group were divided into three groups by drug type: TNF inhibitors (n = 30), non-TNF inhibitors (n = 23), and JAK inhibitors (n = 27). Baseline median age and disease duration were 70.0 and 4.0 years, respectively. Changes in weight (24 and 52 weeks) and muscle mass (52 weeks) were significantly higher in the b/tsDMARD group (p = .035, p < .001, and p = .002, respectively). On multivariate logistic regression analysis, b/tsDMARD treatment (OR 3.21, p = .002), DAS28-ESR (OR 0.65 p = .011), and muscle mass (OR 0.90, p = .023) were independently associated with increased muscle mass at 52 weeks. The percentages of new-onset and improved sarcopenia were almost equal. There were no significant differences in the time-dependent changes (52 weeks) of clinical status, body composition, muscle function, and status of sarcopenia among TNF inhibitors, non-TNF inhibitors, and JAK inhibitors. Weight and muscle mass increased significantly more with b/tsDMARD than with csDMARD treatment. There were no differences in body composition changes by mode of action with b/tsDMARDs.
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