An unusual case of osteoid osteoma clinically mimicking sacroiliitis.

Osteoid osteoma is one of the unusual causes of musculosceletal pain. A case of a 21-year-old man who had low back and hip pain radiating to the posterior thigh for 3 years is presented. Pain was worse at night but reduced with the use of nonsteroidal anti-inflammatory drugs. Straight leg raising test was negative. Patrick-Fabere and sacroiliac compression tests were positive on the right. Neurological examination was normal. Lumbar spinal and pelvic radiographs were normal except for sclerosis at the inferior half of the iliac bone adjacent to the right sacroiliac joint. Sedimentation rate, C-reactive protein, and whole blood counts were normal. Bone scan showed nonspecific increased uptake. Computed tomography revealed the presence of diffuse sclerosis at inferior half of the right iliac bone extending to medial border of sacroiliac joint with subcortical osteolytic region and centrally hyperdense sclerotic nidus inside.