Sacroiliitis and gluteal abscess secondary to Staphylococcus aureus infection.

We present the case of 56-year-old man who came to the emergency department with a 48-h history of fever and pain in left gluteus, radiating to posterior thigh. Three days before the onset of the symptoms, the patient had self-administered a dose of intraurethral alprostadil to treat erectile dysfunction secondary to prostatectomy for adenocarcinoma of the prostate. Physical examination revealed pain in response to pressure on left sacroiliac joint. The responses to the Lasègue test and to pressure applied on left piriformis muscle were positive. Laboratory tests revealed a C-reactive protein level of 251 mg/l (normal level, 0–5 mg/l) and a procalcitonin level of 1.18 ng/ml (<0.25), without leukocytosis or left shift. Abdominopelvic computed tomography (Fig. 1) detected the presence of cortical erosions, predominantly on the lower half of the iliac side of left sacroiliac joint, associated with subchondral sclerosis, all of which is compatible with the radiological diagnosis of left-sided sacroiliitis. Pelvic magnetic resonance imaging (MRI) (Fig. 2) revealed subchondral bone edema on both the sacral and iliac sides of left sacroiliac joint, as well as subtle signal hyperintensity in the articular interosseous space. In addition, myositis was observed in neighboring muscles, in left rotator muscles, as well as in the gluteus maximus, where the area of myositis was greater and was