Key Facts

Necrotising fasciitis is a surgical emergency. Rapid diagnosis and early aggressive debridement are the most important determinants of survival. Antibiotic therapy alone is insufficient.

Epidemiology

• UK incidence: ~500–1,000 cases/year
• Mortality: 20–40% (higher with delayed surgery)
• Mean age: 50–60 years; M:F ~2:1
• Risk factors: diabetes (most common), immunosuppression, peripheral vascular disease, obesity, alcohol excess, IVDU, recent surgery/trauma

Aetiology

• Type I (polymicrobial — 70–80%): mixed aerobes (E. coli, Enterococcus, Klebsiella) + anaerobes (Bacteroides, Clostridium) — abdominal wall, perineum
• Type II (monomicrobial — 20–30%): Group A Streptococcus (most common), S. aureus — limbs; can occur in healthy individuals after minor trauma
• Type III (gas gangrene): Clostridium perfringens — crepitus, rapid gas production
• Portal of entry: often minor (insect bite, skin abrasion, injection site) or post-surgical

Pathophysiology

• Bacteria enter subcutaneous tissue → rapid spread along fascial planes (fascial blood supply is relatively poor)
• Bacterial enzymes and toxins → tissue necrosis, thrombosis of perforating vessels → skin ischaemia
• Streptococcal superantigens → toxic shock syndrome (TSS)
• Positive feedback loop: necrosis → anaerobic environment → further bacterial proliferation → more necrosis
• Overlying skin may initially appear normal despite deep necrosis (iceberg phenomenon)

Early Features

• Pain out of proportion to visible skin changes (most important early sign)
• Erythema, warmth, swelling — may resemble cellulitis initially
• Fever, malaise, tachycardia
• Tenderness extending beyond visible erythema

Progressive Features (hours to days)

• Rapidly spreading erythema/dusky discolouration
• Skin bullae (haemorrhagic or serous)
• Skin necrosis (purple/black discolouration)
• Crepitus (gas in tissues — Type I/III)
• Anaesthesia of overlying skin (cutaneous nerve destruction)
• Systemic toxicity: septic shock, multi-organ failure

Red Flags

• Pain disproportionate to examination findings
• Rapid progression despite antibiotic therapy
• Crepitus on palpation
• Skin necrosis or bullae
• Sepsis with skin/soft tissue focus
• Perineal involvement (Fournier gangrene)

Bedside

• Observations: NEWS2 — will be elevated (sepsis)
• Blood glucose: often elevated (diabetes common)
• Finger test: bedside incision under local — lack of bleeding, dishwater grey necrotic fascia, absence of tissue resistance = diagnostic

Bloods

• LRINEC score: CRP >150 (4 points), WCC >25 (2), Hb <110 (2), Na <135 (2), Cr >141 (2), Glucose >10 (1) — score ≥6 suspicious, ≥8 strongly predictive
• FBC: leucocytosis (may be leucopenic in severe sepsis)
• CRP: markedly elevated (often >300)
• U&Es: AKI
• Lactate: elevated
• CK: elevated if myonecrosis
• Blood cultures: before antibiotics
• Coagulation: DIC screen

Imaging

• CT with contrast: gas in soft tissues (pathognomonic), fascial thickening, fluid tracking along fascial planes
• MRI: more sensitive for fascial involvement but time-consuming — do NOT delay surgery for imaging
• Plain X-ray: may show subcutaneous gas
• USS: can show subcutaneous oedema and fluid along fascia

Special Tests

• Surgical exploration: the definitive diagnostic test — non-bleeding, dishwater grey fascia, lack of tissue resistance
• Tissue samples: intraoperative samples for culture and histology

Non-pharmacological

• URGENT surgical debridement is the definitive treatment — within 6–12 hours of diagnosis
• Radical excision of all necrotic tissue; often requires multiple returns to theatre (planned second look at 24–48 hours)
• ICU admission: almost always required
• Nutritional support: high caloric and protein requirements

Pharmacological

Empirical antibiotics (start immediately — do NOT delay for surgery):

• Meropenem 1g TDS IV (broad Gram-negative and anaerobe cover)
• + Clindamycin 600mg–1.2g QDS IV (inhibits toxin production — essential for streptococcal/staphylococcal superantigens)
• + Flucloxacillin 2g QDS IV (anti-staphylococcal)
• OR: piperacillin-tazobactam + clindamycin ± vancomycin (if MRSA risk)

Supportive care:

• Aggressive IV fluid resuscitation
• Vasopressors for septic shock
• Blood product support (DIC)
• VTE prophylaxis

IV immunoglobulin (IVIG):

• Consider for streptococcal toxic shock syndrome (neutralises superantigens) — evidence limited but used in practice

Surgical/Interventional

• Radical debridement: all necrotic fascia and involved tissue
• Second-look surgery: at 24–48 hours to assess for further necrosis
• Negative-pressure wound therapy (VAC): for large wounds after debridement
• Skin grafting/flap reconstruction: once wound clean and granulating
• Amputation: may be necessary for extremity involvement
• Fournier gangrene: may require diverting colostomy/suprapubic catheter

Referral Criteria

• Immediate surgical referral: any suspicion of necrotising fasciitis
• ICU: all cases
• Plastic surgery: for wound reconstruction
• Microbiology/infectious diseases: antibiotic guidance

• Overall mortality: 20–40%
• Mortality if surgery delayed >24 hours: >70%
• Fournier gangrene: mortality 20–40%
• Type II (GAS): can cause toxic shock syndrome — mortality up to 50%
• Factors associated with worse prognosis: delay in diagnosis, diabetes, immunosuppression, older age, truncal involvement, organ failure at presentation
• Survivors: often require prolonged hospital stay (weeks to months), multiple surgeries, skin grafting
• Long-term: significant morbidity including disfigurement, limb loss, chronic pain, psychological trauma

LRINEC Score (Laboratory Risk Indicator for Necrotising Fasciitis)

Types of Necrotising Fasciitis