Long-term dynamic of muscle mass and its effectors in female patients with rheumatoid arthritis: a 5-year prospective cohort study

Background: Rheumatoid arthritis (RA) patients with low muscle mass (myopenia) have a higher risk of physical dysfunction and poor prognosis. However, the evidence of longitudinal changes in muscle mass in female RA patients was scarce. Objectives: This study aimed to explore the long-term muscle dynamics and their potential effectors in female RA patients. Design: A 5-year prospective cohort study. Methods: Female RA patients without a diagnosis of myopenia at baseline were included if they finished the time frame of 5-year follow-up and had at least 2 times of muscle assessments by bioelectric impedance analysis. Linear mixed-effect models (LMEM) were used to analyze the annual progression rates of the appendicular skeletal muscle index (ASMI). Results: There were 210 female RA patients included, with a mean age of 48.4 ± 10.9 years and a median disease duration of 48 (interquartile range (IQR) 19, 95) months. During the median follow-up time of 4.73 (IQR: 2.86–5.15) years, the multivariable-adjusted annual decline rate of ASMI was −0.021 (standard error (SE) 0.007) (95% CI: −0.034 to −0.007, p = 0.002), consistent with a 2.059% decrease of ASMI at 5-year follow-up relative to baseline. Subgroup analyses showed RA patients without sustained remission (−0.031 (SE 0.008) p = 0.0003, p for interaction = 0.022), and those with a total dose of glucocorticoids (equivalent dose of prednisone) >6052 mg (−0.050 (SE 0.017) p = 0.007, p for interaction = 0.049) have a higher annual decline rate of ASMI. There were 15.2% ( n = 32) patients who experienced a transition from non-myopenia to myopenia during the follow-up. The transition proportion of RA patients with sustained remission was significantly lower than that of patients without sustained remission (3.2% vs 20.3%, p = 0.002), and patients with a total dose of glucocorticoids >6052 mg showed a higher transition risk than those without (31.5% vs 11.7%, p = 0.008). Conclusion: Our findings firstly illustrated the annual decline rate of muscle mass in female RA patients from a 5-year longitudinal data, and revealed the potential effect of tight control of disease activity and less glucocorticoid use for delaying the loss of muscle mass.