Objectives: The individual and socioeconomic burden of sarcopenia in rheumatoid arthritis (RA) is most relevant. However, longitudinal cohort data are scarce. Methods: Prospective, single-center, controlled, observational cohort study of consecutive 124 postmenopausal women, 53 with RA, 71 healthy controls (HC). Low muscle mass and low muscle strengths was defined according to the European working group on sarcopenia in older people 2019 (appendicular lean mass index [ALMI] via dual-energy x-ray absorptiometry < 5.5 Kg/m2; handgrip strength via dynamometer < 16 Kg). Linear regression models were calculated including demographic and anthropometric data, comorbidities, and co-medication as confounders. Results: Median age was 63 (IQR 56, 70), follow-up 2.1 (IQR 2.0, 5.3) years. At baseline, median ALMI was 6.2 (IQR 6.0, 6.5) Kg/m2 in RA patients, 6.3 (IQR 5.6, 6.9) Kg/m2 in HC (p = 0.64) with no difference in rates of low muscle mass (RA 16.2 % vs. HC 15.1 %). In the fully adjusted model, mean change in ALMI per year was -0.05 (95%CI -0.10 to -0.01) Kg/m2 in RA patients and 0.00 (95%CI -0.02 to 0.03) Kg/m2 in HC resulting in a differential loss of -0.06 (95%CI -0.11 to -0.01) Kg/m2 per year (p = 0.027). For RA patients, the adjusted OR of experiencing any loss of muscle mass was 3.98 (95%CI 1.47 to 10.77) compared to HC (p = 0.007). On average, RA patients lost 0.78 % of muscle mass per year. At baseline, low grip strength was seen in 27.3 % of RA patients and in 2.9 % of HC (p = 0.002). In both groups, grip strength did not decline during study period. TNFα inhibitors were associated with less, T-cell inhibition with greater loss of muscle mass. Low mass at baseline, disease duration and disease activity were not associated with loss of muscle mass. Conclusion: Postmenopausal women with RA have a significant risk of accelerated loss of muscle mass over time.

The authors have declared no competing interest.

The study was financially supported by the Alfred and Anneliese Sutter-Stoettner Foundation and by the Novartis Foundation for Medical-Biological Research, P.O. Box CH-4002 Basel.

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The ethics committee of the Canton of Bern gave ethical approval for this work (approval #BE165/13).

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