Ewing's Sarcoma of the Sacroiliac Joint Presenting as Tubercular Sacroiliitis: A Diagnostic Dilemma.

We report a case of Ewing's sarcoma of the sacroiliac joint in a 21-year-old male mimicking tubercular sacroiliitis, a rare entity not reported in literature. He presented with pain in the lower back radiating to the right lower limb along with constitutional symptoms of 3 months duration. On examination, the right sacroiliac joint was tender. The laboratory investigations showed anaemia, leukocytosis and raised erythrocyte sedimentation rate. On X-ray, features of right sacroiliitis were seen. This was further investigated with magnetic resonance imaging (MRI), which showed features consistent with tubercular sacroiliitis. Patient was then started on antitubercular treatment, but the improvement was not consistent. So, a contrast MRI was done, which indicated features of primary sarcoma. It was then further confirmed by a computed tomography-guided biopsy, which showed features consistent with Ewing's sarcoma of the sacroiliac joint.