Prepared by Amarinder S. Bindra, MD, Resident, and Anthony L. Esposito, MD, Chief, Department of Medicine, Saint Vincent Hospital, Worcester, Mass

A 16-year-old Hispanic male presented to the emergency department with a 3-day history of difficulty walking because of pain in the right groin, discomfort in the posterior aspect of the left thigh, and fever up to 104°F. The symptoms were sudden in onset. The patient denied local trauma or intravenous drug use. Physical examination findings included temperature, 102°F; pulse, 136 beats/min. A 10-cm cigar-shaped, firm, tender subcutaneous mass was evident perpendicular and inferior to the right inguinal ligament; the skin was warm and slightly erythematous. A 4- to 5-cm area on the back of the left thigh was tender. Muscle strength and passive range of motion was normal throughout. Laboratory test results included: white blood cell count, 20.4 x 10⁶/μL, with 93% neutrophils; erythrocyte sedimentation rate, 48 mm/h; creatine phosphokinase level, 456 U/L. Computed tomography (CT) (Figure 1) and magnetic resonance imaging (MRI) (Figure 2) scans are shown.

What’s Your Diagnosis?
 Polymyositis

 Pyomyositis

 Dermatomyositis

 Inclusion body myositis