Necrotizing Soft Tissue Infection
System: Skin and Soft Tissue Infections · Parent MOC: MOC - Diseases by System
Includes: Necrotizing fasciitis, myonecrosis / gas gangrene spectrum
One-Sentence Definition
Rapidly progressive, life-threatening soft-tissue infection with necrosis along fascial planes or muscle — a surgical emergency where antibiotics alone are insufficient.
Clinical Presentation
- Pain out of proportion, tense edema, bullae, ecchymosis, crepitus, anesthesia of skin
- Systemic toxicity / septic shock early
- Type I: polymicrobial (often after surgery/diabetes perineum — Fournier)
- Type II: monomicrobial Streptococcus pyogenes (± MRSA)
Pathogens
| Type | Organisms | Notes |
|---|---|---|
| Type I | Mixed aerobes/anaerobes ± Enterobacterales | Surgical/perineal |
| Type II | Streptococcus pyogenes | Toxin / superantigen driven |
| Other | Staphylococcus aureus (MRSA), Clostridium (gas gangrene) | Trauma / injection |
Pathogenesis
- Bacterial toxins + thrombosis of perforating vessels → tissue death
- Gas from fermenters in some clostridial disease (Bacterial Endospore ecology)
Diagnosis
| Step | Test | Note |
|---|---|---|
| Clinical | High suspicion | Don’t wait for imaging if obvious |
| OR | Exploration = diagnostic & therapeutic | “Dishwater” fluid, easy plane separation |
| Micro | OR Gram Stain + culture/AST | Blood cultures |
| Imaging | CT gas/fluid — adjunct only | Never delay OR for MRI |
Treatment Principles
- Immediate surgical debridement (repeat often)
- Empiric broad IV therapy including toxin-suppressing agent when GAS suspected (e.g., clindamycin adjunct — practice standard)
- Supportive ICU care; IVIG considered in selected streptococcal toxic shock
- Narrow with cultures
Prevention
- Wound care; early debridement of contaminated wounds; glycemic control
Differential / Pitfalls
- Severe cellulitis without necrosis; compartment syndrome
- Anchoring on “wait for CT” → fatal delay
Learning Aids
Clinical Example
Example
Case: Healthy adult, arm pain extreme after minor abrasion; rapidly hypotensive; skin still looks modestly red.
Question: Working diagnosis and first action?
Answer: Possible type II NSTI (Streptococcus pyogenes). Resuscitate, empiric abx, emergent surgical exploration — do not wait for definitive imaging.
Related
Active Recall
- Why is surgery the definitive diagnostic step?
- Type I vs Type II microbiology?
- Why add protein-synthesis inhibitor in severe GAS disease?