Insidious Synovial Sarcoma of Bone in a Patient with Rheumatoid Arthritis.

Synovial sarcoma is a rare malignity of mesenchymal origin; the diagnostic approach usually begins by documenting a soft tissue tumor; however, it results in a challenging diagnosis when it is more profound, of small size, or primary from the bone. The present report describes a patient who presented insidious onset hip pain attributed to rheumatoid arthritis, with a fatal outcome due to baseline disease and surgery complications. The underestimation of hip pain, mainly when there is no palpable mass, may delay the diagnosis.