Necrotising Fasciitis

Classification

• Fournier's gangrene - perineal/scrotal involvement
• Meleney's gangrene - abdominal wall; synergistic bacterial gangrene

Microbiology

• Streptococcus pyogenes (group A Streptococcus) - most feared monomicrobial cause
• Staphylococcus aureus (including MRSA)
• Escherichia coli, Pseudomonas, Proteus, Klebsiella
• Anaerobes: Bacteroides, Clostridium (gas-forming)

Pathophysiology

1. Acute inflammatory infiltrate in subcutaneous tissue
2. Thrombosis of microvascular supply → ischaemia
3. Tissue necrosis spreads contiguously along fascial planes (occasionally "skip lesions" that later coalesce)
4. Toxin release + systemic sepsis → septic shock, multiorgan failure

Risk Factors / Predisposing Conditions

• Diabetes mellitus (most common comorbidity)
• Penetrating trauma or recent surgery
• Immunosuppression (steroids, chemotherapy, HIV)
• Intravenous drug use
• Obesity, peripheral vascular disease
• Perineal infection (perianal abscess, Bartholin's cysts)
• Pressure sores, bites, boils, varicella

Clinical Features

Early (may resemble cellulitis)

• Erythema, warmth, swelling, pain
• Fever, tachycardia

Classical signs

• Disproportionate pain relative to visible skin changes (early hallmark)
• Oedema extending beyond the visible erythema
• Woody-hard subcutaneous texture - inability to distinguish fascial planes
• Skin turns dusky-blue/purple-black (progressive thrombosis)
• Skin vesicles and bullae (Figure below) - contain dark purple/haemorrhagic fluid
• Soft-tissue crepitus (gas-forming organisms)
• "Dishwater" (grey/brown) drainage from wound
• Fixed skin staining

Late / severe

• Cutaneous gangrene and frank skin necrosis
• Hypotension, septic shock
• Renal failure (hypovolaemia + cardiovascular collapse)
• Absence of lymphangitis

"Hard" signs (crepitus, skin necrosis, bullae, hypotension, gas on X-ray) are present in less than half of patients at presentation - Tintinalli's Emergency Medicine

Necrotising fasciitis of the anterior abdominal wall - Bailey and Love's Surgery, 28th Ed.

NF at initial presentation - Bailey and Love's Surgery, 28th Ed.

Rapid progression after 24 hours - Bailey and Love's Surgery, 28th Ed.

Typical bullae and induration in NF of the arm - Bailey and Love's Surgery, 28th Ed.

Diagnosis

Investigations

• Score ≥6: PPV 92%, NPV 96% - raise suspicion, carefully evaluate
• Score ≥8: Strongly predictive of NF
• Caution: LRINEC ≥6 misses many cases (especially Vibrio species and neck infections). It should NOT be used in isolation to exclude the diagnosis. - Tintinalli's Emergency Medicine

Imaging

• Plain X-ray: May show gas in soft tissues - do NOT delay surgery for this
• CT: Useful for showing gas tracking along fascial planes, but MRI is preferred
• MRI: Best modality - superior soft-tissue contrast, shows fascial plane involvement without radiation; can map extent for surgical planning
• Ultrasound: Can detect abnormal muscle echo texture; useful in children and resource-limited settings

"Relevant imaging must therefore be performed immediately" - emergency surgical debridement cannot wait - Grainger & Allison's Diagnostic Radiology

Operative diagnosis

• "Finger test": Lack of resistance to blunt finger dissection along fascial planes
• Absence of bleeding (devascularised tissue)
• Grey/necrotic fascia that peels easily from underlying muscle
• "Dishwater" fluid

Management

1. Resuscitation (simultaneous with surgical planning)

• Aggressive IV fluid resuscitation
• Haemodynamic monitoring (ICU admission)
• Oxygen supplementation; intubation if airway compromised
• Correct electrolyte derangements

2. Antibiotics (IV, broad-spectrum, started immediately)

• High-dose penicillin G + third-generation cephalosporins (e.g., cefotaxime) + metronidazole (anaerobic cover)
• Add clindamycin for GAS (inhibits toxin production via ribosomal mechanism - "Eagle effect")
• Cover MRSA if suspected (vancomycin/linezolid)
• Adjust based on wound cultures and sensitivities

3. Surgery (cornerstone of treatment - must not be delayed)

"This is a surgical emergency and the diseased area should be debrided as soon as possible until viable, healthy, bleeding tissue is reached." - Bailey and Love's Surgery

• Radical surgical debridement: Remove all devitalised tissue generously, going beyond the zone of induration
• Wound is lightly packed open with gauze/dressings
• Planned re-look in 24-48 hours - necrosis is prone to spread; multiple debridements are typically required (daily until healthy bleeding tissue is reached)
• Vacuum-assisted closure (VAC) dressings after initial debridement
• Early skin grafting in selected cases to minimise protein/fluid losses

4. Adjuncts

• Hyperbaric oxygen (HBO): Increasingly used; reduces mortality from 30-50% (without HBO) to 9-20% (with HBO). Mechanism: enhances neutrophil killing of anaerobes, promotes wound healing
• IVIG may be considered for streptococcal toxic shock syndrome

Prognosis / Mortality

Key Summary Points

• Surgical emergency - primarily a clinical diagnosis
• Polymicrobial synergistic infection (or monomicrobial with GAS)
• 80% have a history of previous trauma or infection
• Rapid progression to septic shock
• Treat with urgent resuscitation, IV broad-spectrum antibiotics, and radical surgical debridement
• LRINEC score is a useful adjunct but must not replace clinical judgement
• Re-debridement planned at 24-48 hours; multiple procedures are the norm
• Mortality 30-50% even with treatment