Case report: rheumatoid arthritis occurring during observation after surgery for localized pigmented villonodular synovitis.

Abstract In the rare case presented here, arthroscopic resection was performed after a diagnosis of localized pigmented villonodular synovitis (LPVS) of the knee, but the disorder recurred after about 1 year as the diffuse form, and synovectomy was performed through a medial parapatella incision. Subsequently, rheumatoid arthritis (RA) occurred during the postoperative observation period. The course of this case is interesting because of the combination of the two diseases. In cases of PVS, the possibility of RA should always be considered.