MSTN and rheumatoid arthritis: RA patients with myopenia had a longer disease duration (p = 0.02), worse functional class (II-IV) (p = 0.005), more active disease state (DAS28-ESR ≥3.2, p = 0.003), a higher prevalence of rheumatoid cachexia (p = 0.001), and higher myostatin concentrations (p = 0.02).