Wet gangrene

Overview

Wet gangrene is a life- and limb-threatening condition caused by necrotising bacterial infection destroying soft tissue, fascia, or muscle - rapidly spreading along tissue planes and triggering systemic sepsis. It demands immediate recognition and emergency surgical intervention.

Pathophysiology

•Bacteria release exotoxins/enzymes → local vessel thrombosis → tissue ischaemia → anaerobic environment → bacterial proliferation → further toxin release (self-amplifying loop)

•Gas gangrene - caused by *Clostridium perfringens* (± *C. septicum*); alpha-toxin causes myonecrosis and haemolysis; gas-forming metabolites produce subcutaneous crepitus

•Necrotising fasciitis - rapidly spreading infection along superficial fascia; classified into types by microbiology

•Fournier's gangrene - polymicrobial necrotising fasciitis of external genitalia/perineum; more common in men; high mortality

Presentation

•Poorly demarcated necrosis - key distinction from dry gangrene (which has a sharp demarcation line)

•Pain out of proportion to visible skin findings - classic early warning of necrotising fasciitis; infection tracks along fascial planes beneath intact-looking skin

•Swelling and erythema - may be deceptively mild early

•Haemorrhagic bullae overlying infected tissue

•Subcutaneous crepitus - pathognomonic of gas gangrene or Type I necrotising fasciitis with gas-forming organisms

•Anaesthesia of overlying skin - nerves destroyed by spreading necrosis

•Foul-smelling discharge - anaerobic metabolism

•Systemic: fever, rigors, tachycardia, hypotension (septic shock), confusion

⚠️

Do not be falsely reassured by relatively normal-looking skin - the external appearance grossly underestimates the depth of tissue destruction in necrotising fasciitis.

Investigations

🚨

Do not allow investigations to delay surgical intervention in a clinically obvious case.

🥇 First-line

•FBC (leukocytosis; anaemia from haemolysis in gas gangrene), CRP/ESR, blood cultures (before antibiotics if possible), serum lactate, U&Es/LFTs/coagulation

•First-line imaging: plain X-ray of affected area - may show gas in soft tissues

🥈 Second-line

•CT scan - superior for detecting deep tissue gas and assessing fascial involvement; tissue biopsy/wound swab at time of surgical debridement

•LRINEC score - uses CRP, WBC, haemoglobin, sodium, creatinine, glucose; score ≥6 suggests high risk for necrotising fasciitis; clinical adjunct only - a low score does not rule out the diagnosis

Differential diagnosis

Wet gangrene vs key differentials

Feature	Wet gangrene	Cellulitis	Dry gangrene
Demarcation	Poorly demarcated	No necrosis	Well demarcated
Crepitus	Present (gas-forming)	Absent	Absent
Systemic sepsis	Yes - often severe	Mild/moderate	Absent
Pain	Disproportionate to findings	Proportionate	Minimal - cold, dry tissue
Cause	Infection + ischaemia	Infection	Ischaemia alone

Management

Wet gangrene is a surgical emergency - resuscitation, antimicrobial therapy, and surgical source control must proceed on parallel tracks without delay.

Immediate

1. 1IV fluid resuscitation - treat septic shock
2. 2Empirical broad-spectrum antibiotics: piperacillin-tazobactam + clindamycin (clindamycin inhibits toxin production)
3. 3Critical care referral
4. 4Urgent surgical debridement - remove all necrotic tissue; repeat debridement often required

↓

Debridement achieves clear margins

Continue antibiotics; wound management; reconstruction when appropriate

Unable to achieve clear margins / extent of necrosis

Amputation may be required

Complications and Prognosis

•Septic shock - primary cause of early death

•Toxic shock syndrome - especially Group A Streptococcal Type II necrotising fasciitis

•Multi-organ failure (renal failure, ARDS, hepatic dysfunction)

•DIC - consumption coagulopathy from systemic infection

•Amputation

•Mortality approximately 30% even with optimal management; worse with older age, diabetes/immunocompromise, delayed diagnosis, or toxic shock syndrome

💡

Prognosis is strongly influenced by time to surgery - every hour of delay allows further spread along fascial planes and increases the tissue that will require debridement or amputation.