Pyomyositis is usually due to S aureus , common in tropical areas and rare in temperate climates, and often without a known portal entry. Risk factors in nontropical areas include diabetes mellitus, collagen vascular disease, and immunosuppression. Infection remains localized and unless strains produce toxic shock syndrome toxin 1 or certain enterotoxins shock does not occur. Because these infections are deep, there is frequently no cutaneous erythema or warmth, although tenderness and swelling are usually present. In contrast, S pyogenes may induce a primary myositis referred to as streptococcal necrotizing myositis, associated with severe systemic toxicity.
Patients frequently have bacteremia, shock, and organ failure.
Such infections have recently been described as part of the streptococcal toxic shock syndrome. Gas gangrene usually occurs following penetrating injuries severe enough to result in introduction of soil into wounds and an interrupted blood supply. Such cases of traumatic gangrene are usually caused by Clostridium perfringens , Clostridium septicum , or Clostridium histolyticum . Rarely, latent or recurrent gangrene can occur years after penetrating trauma likely due to dormant spores that reside at the previous injury site. Spontaneous nontraumatic gangrene has recently been recognized more frequently among patients with neutropenia, gastrointestinal malignancy, diverticulosis, or following abdominal radiation therapy.