Underlying synovial sarcoma in a patient with a history of complex regional pain syndrome: a case report.

Synovial sarcoma, although commonly found in the lower extremities, is considered a rare neoplasm. One of the distinguishing features of a synovial sarcoma is its initial benign features that can later turn into a more aggressive lesion. Because of the subtle early features, synovial sarcoma can be mistaken for other pathologic entities that present with clinical signs of erythema, warmth, edema, and pain. We present a patient who was originally diagnosed with complex regional pain syndrome. That diagnosis and subsequent treatment of complex regional pain syndrome likely delayed the appropriate evaluation, which led to a 9-month lag in the proper diagnosis. After magnetic resonance imaging and biopsy were performed, synovial sarcoma was diagnosed. The patient was referred to an orthopedic oncologist, who performed a transtibial amputation and chemotherapy. Although rare, neoplasm should always be considered in the differential diagnosis of a clinical presentation of a painful erythematous and edematous mass.