Pyomyositis (Pyomyositis Tropicans)

Pyomyositis, a disease historically seen in tropical climates, is characterized by primary abscess formation in the skeletal musculature. It is increasing in incidence in temperate climates, especially in immunocompromised hosts. In all cases, Staphylococcus aureus is the most commonly implicated organism. Clinical presentation is nonspecific, with muscle pain, tenderness, and swelling, accompanied by leukocytosis and fever in cases with bacteremia. Computed tomography (CT) and magnetic resonance imaging (MRI) are the diagnostic modalities of choice. Treatment most often involves appropriate antimicrobial therapy coupled with abscess drainage.

A 17-year-old male with no past medical history presents to the emergency department with 1 week of left thigh pain. His pain initially began 24 hours after he had completed a 10-mile run. He went to an urgent care 3 days ago, where he was diagnosed with a muscle strain and instructed to take nonsteroidal antiinflammatory medications, apply ice, and rest the leg. His pain has continued to worsen and he noted that the skin overlying his anterior thigh appears red. He denies any trauma to the thigh, fevers, or recent illnesses. On physical examination, his temperature was 37°C (98.6°F), pulse 105 beats/min, respirations 18/min, and blood pressure 120/70 mmHg. The skin overlying his anterior left thigh was erythematous and tender to palpation. There was no appreciable fluctuance. Point-of-care ultrasound showed a complex fluid collection measuring 5.5 × 4.2 × 2.1 cm in the rectus femoris muscle. He was found to have a slightly elevated white blood cell (WBC) count of 13,500/mm ³ , an elevated ESR of 22, and an elevated C-reactive protein (CRP) of 9. Blood cultures were sent and ultimately returned as negative. A surgical consult was placed and he was started on vancomycin for broad coverage of gram-positive organisms. The surgical team performed an ultrasound-guided aspiration of the collection and were able to obtain 9 mL of purulent fluid which was sent for culture. An MRI demonstrated hyperintensity on T2 in the right rectus femoris. On T1, a small rim enhancing area within the rectus femoris was present, which was concerning for residual abscess. The patient was admitted to the surgical team for observation. On hospital day 2, the patient’s pain had improved and the erythema appeared to be resolving. Aspirate cultures returned as positive for methicillin-sensitive staphylococcus, and the patient was transitioned to oral trimethoprim-sulfamethoxazole and discharged to home with clinic follow-up scheduled in 2 weeks. In the clinic, the patient was doing well with no lingering sequelae. ESR, CRP, and WBC had all returned to normal. Antibiotics were discontinued after a 2 weeks total course.