see also:

• skin necrosis
• cellulitis

• necrotizing fasciitis is a life or limb threatening, generally rapidly progressive infection of the fascia under the skin which soon results in purpura, cutaneous anaesthesia then skin necrosis due to ischaemia from interruption of the perforating arteries supplying the skin via the fascial layer
• it should be considered as a differential in all patients with cellulitis, and urgent referral to the plastic surgery or general surgery team if suspected

• 70% of cases are said to occur in immunocompromised patients such as diabetics, IVDU patients
• some may follow:
  • minor trauma
  • penetrating or crush injuries
  • post-operative surgery
  • varicella-zoster virus (chickenpox/shingles)
• polymicrobial cases are more likely due to:
  • surgical procedures involving the bowel or penetrating abdominal trauma
  • decubitus ulcers or a perianal abscess
  • the site of injection in intravenous drug users
  • spread from a Bartholin abscess or vulvovaginal infection
  • NB. the term Fournier's gangrene is used for synergistic gangrene of the genitalia, usually following spread from a perianal, retroperitoneal or urinary tract infection, or following genital trauma (eg postpartum).

• monomicrobial cases
  • Streptococcus pyogenes
  • Clostridium perfringens (gas gangrene) and other clostridial species
  • Staphylococcus aureus
  • if water-related:
    • Vibrio vulnificus and other Vibrio species
    • Aeromonas hydrophila
• polymicrobial cases
  • synergistic gangrene caused by mixed aerobe–anaerobe bacterial flora (eg Escherichia coli, Bacteroides fragilis, streptococci and staphylococci)

• inflamed skin with tenderness associated with either:
  • spreading regional purpura
  • blood-filled bullae
  • a wooden-hard feel of the subcutaneous tissue
  • oedema beyond the margin of erythema
  • cutaneous anaesthesia
  • crepitus (from gas forming organisms)
  • rapid spread over hours
  • CRP > 150
  • systemic compromise features such as acutely raised creatinine, or blood sugar levels

• iv access
• FBE, U&E, glucose, lactate
• iv antibiotics (as at 2013 in Australia):
  • if Strept. pyogenes:
    • benzylpenicillin 1.8 g (child: 45 mg/kg up to 1.8 g) IV, 4-hourly, PLUS,
    • clindamycin 600 mg (child: 15 mg/kg up to 600 mg) IV, 8-hourly, PLUS,
    • consider normal immunoglobulin (adult and child) 0.4 to 2 g/kg IV, for 1 or 2 doses during the first 72 hours
  • if Clostridial:
    • benzylpenicillin 2.4 g (child: 60 mg/kg up to 2.4 g) IV, 4-hourly, OR,
    • if penicillin HS, use metronidazole 500 mg (child: 12.5 mg/kg up to 500 mg) IV, 8-hourly
  • if community associated MRSA:
    • vancomycin, PLUS,
    • clindamycin 600 mg (child: 15 mg/kg up to 600 mg) IV, 8-hourly
  • otherwise, use empirical Rx:
    • meropenem 1 g (child: 25 mg/kg up to 1 g) IV, 8-hourly, PLUS,
    • clindamycin 600 mg (child: 15 mg/kg up to 600 mg) IV, 8-hourly, PLUS,
    • consider normal immunoglobulin if suspect Str. pyogenes - (adult and child) 0.4 to 2 g/kg IV, for 1 or 2 doses during the first 72 hours
• immediate referral to a surgical team
  • may require a diagnostic fasciotomy incision in theatre to assess if indeed the fascia layer is inflamed
  • may require laying open the fascial compartment and late reconstructive surgery or limb amputation