Clinical history

A 34 year old man presented at the hospital because of widespread pain in his left buttock, groin and posterior thigh that had started gradually eight days earlier. He had been diagnosed with human immunodeficiency virus (HIV) disease at the age of 24. Because of a pneumocystis carinii pneumonia he was required to be bedridden for three weeks during the month before admission. On physical examination diffuse pain to palpation on the left groin, buttock, and posterior thigh was noticed. In addition, an excruciating pain was provoked by the movements of left hip, in particular by abduction and external rotation. Moreover, pain did not allow him to put weight on his left hip. However, no other abnormalities were found. At that time he was initially diagnosed as having hip arthritis. Complete blood cell count showed 4400/mm³ white cells (CD4 96/mm³), and 574 000/mm³ platelets. The haemoglobin was 10.6 g/dl. Erythrocyte sedimentation rate was 114 mm 1st h. No abnormality of other laboratory parameters was found. Blood cultures were negative.

Radiological findings

An anteroposterior radiograph of pelvis was normal (fig1).

Sonography of the hip did not show fluid collection.

Computed tomography (CT) showed calcification of the ischiogluteal bursa without synovial fluid and swelling of obturator internus muscle (fig 2). Fine needle aspiration of the obturator internus muscle and the …