Cutaneous mucinous nodule in a patient with rheumatoid arthritis.

We report a cutaneous mucinous nodule on the inflamed elbow joint in a patient with rheumatoid arthritis (RA). The lesion is clinically characterized by a continuous flow of mucinous exudates from the nodule, and histologically by an extensive mucin deposition and proliferations of the fibroblastic cells and mononuclear cells. The histological findings suggest the histogenesis of this unique nodule is related to extralesional proliferation of synovial lining cells consisting of monocyte-macrophage lineage cells and fibroblast-like cells which potentially produce synovial fluid. Four patients have been hitherto reported in the published work and all of them have been associated with RA. The condition may be one of the characteristic skin manifestations of RA.