Pyomyositis and Infectious Myositis: A Comprehensive, Single-Center Retrospective Study

Abstract

Background: Pyomyositis is a bacterial infection of skeletal muscle that classically leads to abscess formation. A related, but distinct, entity is infectious myositis. The epidemiology of these infections has changed in recent years.

Methods: To better characterize both pyomyositis and infectious myositis, we conducted a retrospective study at our tertiary care institution. We identified 43 cases of pyomyositis and 18 cases of infectious myositis treated between January 2012 and May 2020.

Results: The mean age of patients was 48 years, and 66% were male. Diabetes mellitus affected one third of patients, and 16% had other immunocompromising comorbidities. Staphylococcal species accounted for 46% of all infections, and common symptoms included muscle pain (95%) and subjective fever (49%). Altered mental status was a presenting symptom in 16% of cases. Approximately half of all patients received >1 class of antibiotic, and the median length of antimicrobial therapy was 18 days. Open and percutaneous drainage procedures figured prominently in the management of these infections, with 28% of patients requiring multiple procedures. Pathology specimens were available for 12 of 61 cases. Overall, the treatment success rate was 84%.

Conclusions: Gram-positive bacteria accounted for most infections at our institution, and management commonly involved open or percutaneous drainage procedures. Future studies that prospectively evaluate treatment strategies for pyomyositis and infectious myositis are warranted.

Keywords: Staphylococcus aureus; infectious myositis; muscle; pyomyositis.

Figure 1.

Sites of involvement for pyomyositis and infectious myositis cases. LLE, left lower extremity; LUE, left upper extremity; RLE, right lower extremity; RUE, right upper extremity.

Figure 2.

Influenza A myositis and Actinomyces spp pyomyositis. (A) Photomicrograph of the lower extremity of a 35-year-old female with influenza A infection (×40, hematoxylin and eosin [H&E]; inset: ×1000, H&E). Histologically, the muscle cells are devoid of nuclei, and there is an interstitial infiltrate composed of acute and chronic inflammatory cells. (B) Photomicrograph of the rectus muscle of an 80-year-old male with an intramuscular abscess, the culture of which grew Actinomyces spp (×100, H&E; inset: ×1000, H&E). Histologically, the muscle fibers are infiltrated by acute and chronic inflammatory cells.