S100A4 and bone disorder: Specifically, we found a moderate correlation of S100A4 serum levels with the MYOACT score (r = 0.34; P = 0.001), constitutional (r = 0.30; P = 0.003), extramuscular (r = 0.36; P = 0.0001) and pulmonary disease activity (r = 0.43; P = 0.0001), but not with skeletal disease activity (r = 0.13; P =0.208).