AKT · Dermatology/Dermatological emergencies

Necrotising fasciitis

Rapidly spreading infection of fascia (Group A Strep / polymicrobial)

Overview

A life-threatening, rapidly progressive bacterial infection tracking along the fascial planes, causing tissue necrosis. Type 1 is polymicrobial (diabetics, post-surgical — includes Fournier gangrene of the perineum); type 2 is Group A Streptococcus. The hallmark is pain out of proportion to the skin appearance, with systemic toxicity. It is a SURGICAL emergency.

Recognise

Severe PAIN OUT OF PROPORTION to the modest early skin findings — the cardinal clue
Rapidly spreading erythema → dusky/purple discolouration, blistering, then necrosis; crepitus (gas); skin anaesthesia as nerves die
Systemic toxicity (fever, tachycardia, hypotension) progressing to septic shock; risk factors — diabetes, immunosuppression, IV drug use, surgery

Red flags

Pain out of proportion, rapid spread, crepitus, skin necrosis/anaesthesia, or systemic toxicity → immediate surgical referral; do NOT wait on antibiotics alone

Differentials & how to tell them apart

Cellulitispain proportionate to appearance, slower, no crepitus/necrosis, systemically less toxic — necrotising fasciitis has disproportionate pain and rapid progression

Gas gangrene (clostridial myonecrosis)muscle involvement, marked gas, often post-trauma — overlapping emergency

Pyomyositis / deep abscesslocalised collection, less fascial spread

Clinical image

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Necrotising fasciitis — clinical imagesDermNet

Investigations

Clinical and SURGICAL diagnosis — do not delay theatre for imaging. Bloods (raised CRP/WCC/creatinine/lactate; LRINEC score as an adjunct), blood cultures, and urgent surgical exploration (the definitive diagnosis and treatment).

Management

Immediate surgical debridement + broad-spectrum IV antibiotics + resuscitation

1Resuscitate (sepsis pathway) and refer IMMEDIATELY for surgical exploration and debridement; start broad-spectrum IV antibiotics including clindamycin (toxin suppression).Gate: Pain out of proportion to the skin appearance, rapid progression, crepitus or systemic toxicity = necrotising fasciitis → straight to THEATRE; antibiotics alone are not enough and imaging must not delay surgery
2Repeated debridement until clear margins; ICU organ support; reconstructive surgery later. Group A Strep → consider IVIG; notify and screen contacts as advised.

URGENT surgical debridement — the definitive treatment — radical excision of all necrotic tissue, often repeated

Broad-spectrum IV antibiotics — e.g. piperacillin-tazobactam/carbapenem + clindamycin (anti-toxin effect against Group A Strep)

Aggressive resuscitation ± ICU — fluids, vasopressors, organ support

Key points

The cardinal trap is treating it as cellulitis — the disproportionate pain and rapid progression are the discriminators. Fournier gangrene is the perineal/scrotal variant. Surgery saves lives; delay kills.

Monitor & prognosis

Serial surgical review, lactate/organ function, sepsis parameters.

High mortality; outcome depends on the speed of surgical debridement.

Source: UK surgical/sepsis guidance; NICE