Interestingly, in the peripheral compartment, serum VEGF and IL-6 levels increased in proportion to synovitis severity on US, correlating with conventional disease activity markers including ESR, CRP, and DAS28, whereas serum PlGF failed to show such correlation, which is consistent with earlier reports showing that PDUS grade correlates with serum VEGF43,44. Here, CRP is linked to synovitis.