Necrotizing Fasciitis

Overview:

• Severe bacterial soft tissue infection with edema and necrosis of subcutaneous tissues, affecting adjacent fascia.
• Often starts as cellulitis but progresses rapidly.
• Known as ‘flesh-eating disease’.
• Fournier gangrene: polymicrobial necrotizing fasciitis of the perineal, perianal, or genital areas.

Causative Organisms:

Monomicrobial pathogens:

• Streptococci (especially Streptococcus pyogenes – Group A)
• Clostridium perfringens (gas gangrene) and other Clostridial species
• Staphylococcus aureus
• Vibrio vulnificus
• Aeromonas hydrophila

Polymicrobial pathogens:

• Mixed aerobe-anaerobe bacterial flora (E. coli, Bacteroides fragilis, Streptococcus, Staphylococcus)

Risk Factors:

• Diabetes mellitus (DM)
• Alcohol abuse (ETOH)
• Peripheral vascular disease (PVD)
• Renal failure
• Odontogenic infection
• Malignancy
• Chickenpox
• Local penetrating trauma or animal bite
• Recent surgery (e.g., abdominal or peritoneal)
• Group A Streptococcus has a particular affinity for young, healthy patients.

Clinical Assessment:

History:

• Spreading erythema
• Sepsis (fever, chills, myalgia)
• Severe, constant pain disproportionate to clinical findings
• Cutaneous anesthesia
• Evidence of developing organ failures
• Underlying risk factors
• Commonly affects extremities, but can occur anywhere (e.g., perineum = Fournier gangrene)

Examination:

• Local:
  • Erythematous, tender, swollen skin
  • Smooth, shiny, tense swelling -> darkens, patchy, blisters, bullae -> gangrene
  • Wooden-hard feel of subcutaneous tissue
  • Edema beyond the margin of erythema
  • Crepitus (gas gangrene)
• Systemic:
  • Fever, tachycardia
  • Hemodynamic instability
  • Rapid spread on re-examination

Investigations:

Laboratory:

• Blood cultures
• Full blood count (leucocytosis/leukopenia)
• Elevated C-reactive protein (CRP)
• Coagulation profile (DIC)
• Urea, electrolytes, and creatinine (UEC) (renal failure)
• Elevated creatine kinase (CK)

Imaging:

• X-ray: gas in subcutaneous tissues
• CT: subcutaneous air
• MRI: extent of fascial necrosis, guides limits of debridement

Other:

• Biopsy to differentiate between fasciitis and cellulitis
• Surgery reveals the absence of normally adherent fascia to blunt dissection + watery, thin foul-smelling pus in subcutaneous space

Management:

Resuscitation:

• Aggressive management of septic shock if present

Specific Therapy:

• Extensive urgent surgical debridement (mainstay)
• Antimicrobial therapy:
  • Clindamycin and lincomycin (suppresses toxin production by streptococci)
  • Penicillin often added but not necessary for empiric treatment
  • Vancomycin for nosocomial infections (covers MRSA), plus clindamycin or lincomycin

Empiric Antibiotics:

• Meropenem 1g or 25mg/kg Q8 hrly + Clindamycin 600mg or 15mg/kg Q8h
• Streptococcus pyogenes:
  • Penicillin 1.8g or 45mg/kg Q4 hrly or Cephazolin 2g or 50mg/kg Q6 hrly + Clindamycin 600mg or 15mg/kg Q8 hrly
• Clostridial infection:
  • Benzylpenicillin 2.4g or 60mg/kg Q4 hrly or Metronidazole 500mg or 12.5mg/kg Q8 hrly
• Polymicrobial (e.g., Fournier gangrene):
  • Meropenem 1g or 25mg/kg Q8 hrly

Other Therapies:

• Lincomycin 600mg or 15mg/kg IV Q8 hrly (alternative to clindamycin)
• Hyperbaric oxygen (potentially beneficial in anaerobic gram-negative necrotizing fasciitis, no conclusive evidence)
• Intravenous immunoglobulin (IVIG) 0.4 to 2 g/kg IV, for 1 or 2 doses during the first 72 hours for Group A Strep necrotizing fasciitis (expert advice)

Supportive Care and Monitoring:

• Address underlying causes and complications (e.g., diabetes mellitus)

Consults:

• General surgeon
• ENT (if grommets needed for hyperbaric chamber)
• Infectious diseases

Disposition:

• Urgent transfer to the operating theatre
• ICU admission post-operatively, may need further surgeries and hyperbaric oxygen

Prognosis:

• Mortality 30-40% with appropriate therapy
• Increased mortality in patients with co-morbid conditions
• Mortality directly proportional to delay in diagnosis and treatment