IL34 and synovitis: In an attempt to achieve early detection of knee OA synovitis, this study is the first to demonstrate a clinical usefulness of plasma IL-34 as a potential biochemical marker for discriminating knee OA patients with synovitis from those without synovitis, in which ROC curve analysis showed the optimal cutoff value of plasma IL-34 yielding 87.1% sensitivity and 100.0% specificity.