Necrotizing Fasciitis is the Type of Cellulitis That Causes Skin Necrosis
Necrotizing fasciitis is the specific form of deep soft tissue infection that causes skin necrosis, distinguishing it from typical cellulitis which does not produce tissue death. 1
Key Clinical Features Indicating Necrotizing Infection
The following signs suggest necrotizing fasciitis rather than simple cellulitis and indicate tissue necrosis is occurring 1:
- Pain disproportionate to physical findings - often the earliest and most important clue 1
- Skin necrosis or ecchymoses - direct evidence of tissue death 1
- Violaceous bullae - hemorrhagic blisters indicating deeper involvement 1
- Cutaneous hemorrhage 1
- Skin sloughing 1
- Skin anesthesia - from nerve destruction 1
- Rapid progression despite antibiotic therapy 1
- Gas in the tissue (crepitus) 1
- Hard, wooden feel of subcutaneous tissue extending beyond visible skin involvement 1
Bacteriology of Necrotizing Infections
Necrotizing fasciitis occurs in two forms 1:
Monomicrobial (Type II):
- Streptococcus pyogenes (Group A Streptococcus) - most common, with 50-70% mortality when associated with toxic shock 1
- Staphylococcus aureus 1
- Vibrio vulnificus 1
- Aeromonas hydrophila 1
Polymicrobial (Type I):
- Mixed aerobic and anaerobic organisms (average of 5 pathogens per wound) 1
- Typically follows bowel surgery, perianal abscess, injection drug use, or vulvovaginal infections 1
Critical Management Principles
Surgical intervention is the primary therapeutic modality and must not be delayed 1. The diagnosis is primarily clinical, and waiting for imaging studies may delay life-saving treatment 1.
When to Suspect Necrotizing Fasciitis 1:
- Failure of apparently uncomplicated cellulitis to respond to antibiotics after reasonable trial
- Profound toxicity with fever, hypotension, or advancement during antibiotic therapy
- Any of the clinical features listed above
- Systemic toxicity with altered mental status 1
Empiric Antibiotic Coverage 1:
For polymicrobial necrotizing fasciitis, use vancomycin, linezolid, or daptomycin PLUS one of:
- Piperacillin-tazobactam
- Carbapenem (imipenem-cilastatin, meropenem, or ertapenem)
- Ceftriaxone plus metronidazole
- Fluoroquinolone plus metronidazole
For monomicrobial Group A Streptococcal necrotizing fasciitis, use clindamycin PLUS penicillin 1. Clindamycin suppresses toxin production and was superior to penicillin alone in animal models and observational studies 1.
Common Pitfall
These warning signs often appear late in the course of necrotizing infections 1. A high index of suspicion is paramount, as clinical judgment remains the most important diagnostic element 1. When necrotizing fasciitis is suspected, emergent surgical evaluation is mandatory for both diagnosis and treatment 1. Most patients require return to the operating room 24-36 hours after initial debridement and daily thereafter until no further debridement is needed 1.