A 25-year-old bodybuilder was hospitalized with a painful left upper arm five days after injecting 1.5 ml of a steroid preparation into the medial aspect of his left biceps brachii muscle. He reported using a sterile needle obtained from a pharmacy, but the source of the steroid vial was unknown. At the injection site, there was a tender, erythematous, palpably fluctuant mass, 10 by 6 cm (Panels A and B). The level of creatine kinase was 18,100 U per liter, and the white-cell count was 20.6x103 per cubic millimeter. Computed tomography revealed a large abscess containing gas in the medial left upper arm (Panels C and D). The abscess was incised and drained, after which extensive débridement was performed. Microscopy of a skeletal-muscle sample showed acute necrotizing myositis, and culture of a swab from the deep wound revealed methicillin-resistant Staphylococcus aureus. Vancomycin was given intravenously, followed by oral trimethoprim–sulfamethoxazole. The wound healed well over the next several days. The patient was discharged home 15 days after the abscess had been drained.
