Necrotising fasciitis

Classification

• Type I (polymicrobial, ~70%) — mixed aerobic and anaerobic flora; elderly, diabetic, immunosuppressed; Fournier gangrene (perineal) is a subtype.
• Type II (monomicrobial, ~25%) — Group A streptococcus (S. pyogenes) ± Staphylococcus aureus including MRSA; younger; toxic shock syndrome.
• Type III — Gram-negative including marine (Vibrio vulnificus), Aeromonas; cirrhotic / immunosuppressed; rapid systemic toxicity.
• Type IV — fungal (Mucorales, Candida); diabetic / immunosuppressed / post-traumatic.

Clinical features

• Early (high index of suspicion):
  • Pain out of proportion to clinical findings.
  • Erythema with rapidly expanding indurated edge.
  • Systemic features — fever, tachycardia, malaise.
  • Tense oedema beyond visible erythema.
• Late (advanced — surgical emergency now):
  • Dusky / violaceous / mottled skin.
  • Haemorrhagic / serous bullae.
  • Crepitus (subcutaneous gas).
  • Skin anaesthesia from cutaneous nerve necrosis.
  • Sepsis / shock; multi-organ failure.
• Skin-oncology contexts:
  • Ulcerated tumour site (locally advanced cSCC, fungating breast, sarcoma).
  • Post-operative wound, particularly in immunosuppressed.
  • Lymphoedematous limb on chemotherapy / ICI.
  • Fournier gangrene complicating vulval / penile / scrotal SCC.

LRINEC and SIARI scoring

LRINEC score (Laboratory Risk Indicator for Necrotising Fasciitis) — calculated from admission bloods:

• CRP ≥150 (4 points)
• WBC 15-25 (1) / >25 (2)
• Hb 11-13.5 (1) / <11 (2)
• Sodium <135 (2)
• Creatinine >141 (2)
• Glucose >10 (1)

Total 0-13; ≥6 raises suspicion; ≥8 strongly suggests NF. Caveat: low LRINEC does not exclude NF; clinical judgement supersedes.

SIARI: more discriminative recent UK-based score combining Site (perineum / lower limb), Immunosuppression, Age, Renal function, Inflammatory markers.

Investigations

• Do not delay surgery for imaging when clinical suspicion is high.
• Bloods: FBC, U&E, LFT, CRP, glucose, lactate, ABG, coagulation, group & save, blood cultures.
• Imaging only if diagnostic uncertainty and patient stable:
  • Plain radiograph — subcutaneous gas (late, ~25% sensitive).
  • CT — fascial thickening, gas, fluid; better sensitivity.
  • MRI — most sensitive but slow.
• Bedside "finger test": under local anaesthesia, small incision; lack of resistance with dishwater-grey fluid and easy finger-dissection of fascia is pathognomonic — proceed straight to theatre.

Management

• Emergency surgical debridement — the single most important intervention. Delay >12 h dramatically increases mortality. Aggressive radical excision of all non-viable tissue until bleeding healthy tissue; planned second-look in 24-48 h.
• Empirical broad-spectrum IV antibiotics:
  • Meropenem 1 g IV TDS or piperacillin-tazobactam 4.5 g IV QDS.
  • + Clindamycin 900 mg IV TDS / every 8 hours (antitoxin effect against streptococci).
  • + Vancomycin / linezolid for MRSA coverage.
  • + Doxycycline for Vibrio if marine exposure.
  • Antifungal (amphotericin) for type IV.
• Critical care: fluid resuscitation, vasopressors, inotropes, organ support; IVIG considered for Group A strep TSS.
• Reconstruction: large defects — staged with NPWT, dermal substitutes (e.g. Integra), STSG / flap reconstruction; perineal disease may need temporary diversion stoma.
• Multidisciplinary team: emergency general surgery, plastics, ID, ICU, microbiology, nutrition, pain, rehabilitation.
• Hyperbaric oxygen therapy — adjunctive, evidence mixed; consider if accessible.
• Long-term: high morbidity — limb loss, body image, psychological impact, post-traumatic stress; rehabilitation team essential.