title: Ewing's sarcoma presenting as monoarthritis.
abstract: A 22-year-old woman presented with a monoarthritis which mimicked septic arthritis. Synovial biopsy showed chronic synovitis. The synovial fluid was macroscopically purulent but was subsequently shown to contain malignant cells arising from a Ewing's sarcoma of the distal femur. This case indicates that malignancy should be considered in the differential diagnosis of an unexplained monoarthritis, and documents a monoarthritis as the presenting feature of Ewing's sarcoma.
mesh_terms: D000328:Adult; D001168:Arthritis / Q000209:etiology / Q000473:pathology*; D001853:Bone Marrow / Q000473:pathology; D003937:Diagnosis, Differential; D005260:Female; D005266:Femoral Neoplasms / Q000150:complications / Q000000981:diagnostic imaging / Q000473:pathology*; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging; D011859:Radiography; D012512:Sarcoma, Ewing / Q000150:complications / Q000000981:diagnostic imaging / Q000473:pathology* / Q000556:secondary; D013582:Synovial Fluid / Q000473:pathology