Ewing’s Sarcoma Presenting as Hip Monoarthritis in a Spondyloarthritis Patient

Seronegative spondyloarthritis (SpA) and Ewing’s sarcoma (ES) are common disorders affecting young males. A great challenge is to diagnose both diseases in the same patient. Here we describe a case of a young male patient having SpA, who developed ES that presented as monoarthritis of left hip which was misdiagnosed twice; first as peripheral manifestation of SpA and second as septic arthritis; before the correct diagnosis was reached. A 17 year-old boy presented with inflammatory low back pain of gradual onset lasting for 4 months and knee arthralgias. Examination revealed the presence of localized tenderness over both SIJs and limited lumbar flexion. Plain x-ray showed bilateral grade 2 sacroiliitis and he was Rheumatoid factor negative. The diagnosis of seronegative SpA was made based on fulfillment of the Association of Spondyloarthritis International Society classification criteria for axial SpA. Nonsteroidal anti-inflammatory drugs (NSAIDs) and sulphasalazine were prescribed resulting in rapid improvement of back pain and knee arthralgia. Four months later, the patient had increased severity of his back pain with pain at the left hip region associated with painful limited internal hip rotation. The diagnosis of left hip arthritis associated with SpA was made without requesting imaging study at that time. The dose of NSAIDs was increased and a low dose steroid was added. Few days later, the general condition of the patient deteriorated with the development of night fever, poor night sleep and poor appetite. On presentation, the patient looked very ill with fever. Hip examination revealed marked painful limited hip movement with flexion deformity. New investigations revealed an ESR of 110 mm/hr, and a CRP of 88 mg/L. There was normochromic normocytic anemia (HB: 9g/dl) and leucocytosis (WBC: 13.300/ L). The diagnosis initially considered was acute septic arthritis. Left hip arthrocentesis failed to aspirate any fluid and ultrasound revealed the absence of joint effusion. A multislice computerized tomography (CT) revealed the presence of a destructive osseous lesion targeting the left pubic bone and the left acetabulum with intra-articular extension into the left hip joint causing bony erosion of the medial aspect of the left femoral head. An MRI showed intra-pelvic extension with enlarged iliac lymph nodes. A biopsy was obtained from the mass. Histopathology revealed a malignant round-cell tumor consistent with ES. The patient was referred for chemotherapy and we knew that he was started on a combination of drugs for a short time before he died. To the best of our knowledge this is the first report in literature of ES in SpA patient and the second report of ES presenting as hip monoarthritis.