MSTN and rheumatoid arthritis: Taking both serum myostatin and myopenia into consideration, RA patients were then stratified into four subgroups including low myostatin overlapping non-myopenia group (n=87), low myostatin overlapping myopenia group (n=85), high myostatin overlapping non-myopenia group (n=105), and high myostatin overlapping myopenia group (n=67).