Gas gangrene

Overview

Gas gangrene (clostridial myonecrosis) is a rapidly lethal soft tissue infection characterised by skeletal muscle necrosis, systemic sepsis, and gas production within tissues. Without prompt surgical intervention it is almost universally fatal.

Aetiology and pathophysiology

•C. perfringens - majority of traumatic cases; obligate anaerobe from soil/GI tract

•C. septicum - spontaneous (non-traumatic) disease; aerotolerant, invades healthy tissue; bacteraemia originates from GI mucosal breach (often colorectal carcinoma)

•Alpha-toxin (phospholipase C) - principal virulence factor; degrades membrane phospholipids causing direct muscle necrosis

•Theta-toxin (perfringolysin O) - pore-forming; causes haemolysis and myocardial depression

•Devitalised/hypoxic tissue provides the permissive anaerobic environment - crush injuries, open fractures, ischaemic muscle

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Spontaneous gas gangrene caused by C. septicum should always prompt investigation for an underlying colorectal carcinoma or other GI malignancy.

Presentation

•Pain - earliest and most prominent; severe and disproportionate to visible wound changes

•Systemic features - fever, tachycardia, diaphoresis early

•Skin changes - pallor and tense oedema → bronze/brown discolouration → dark purple/black necrosis

•Bullae/vesicles - haemorrhagic or serous blisters over affected area

•Crepitus - crackling sensation on palpation due to subcutaneous gas

•Foul-smelling discharge - sweet or 'mousy'; highly characteristic

•Anaesthesia/paralysis - late signs; pain resolution paradoxically signals advanced necrosis (nerve death)

•Septic shock - may be presenting picture in spontaneous disease

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Pain out of proportion to visible wound changes is the earliest and most important warning sign. Do not be falsely reassured by relatively normal-looking skin - muscle destruction occurs beneath it.

Investigations

🥇 First-line

•plain X-ray of affected area - radiolucent gas streaking within soft tissues and muscle planes

•blood cultures - C. septicum bacteraemia warrants GI investigation

•FBC, U&E, LFTs, CRP, lactate, coagulation screen - assess haemolytic anaemia, AKI, DIC, systemic compromise

•wound swab and deep tissue Gram stain - large Gram-positive rods without leucocytes is characteristic

🏆 Gold standard

•CT of affected region - best delineates extent of gas and soft tissue destruction, guides surgical planning; do not delay surgery for CT

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Gas gangrene is largely a clinical and surgical diagnosis - do not delay surgical intervention for investigations if the clinical picture is clear.

Management

🥇 First-line

•emergency surgical debridement - wide excision of all necrotic tissue; amputation frequently required for limb disease; wound left open, re-examined at 24-48 hours

•benzylpenicillin (penicillin G) high-dose IV - first-line antibiotic against Clostridium spp.

•clindamycin IV in combination - inhibits ribosomal protein synthesis, suppressing toxin production at translational level; anti-toxin effect makes it essential adjunct

•immediate HDU/ITU admission with aggressive resuscitation - IV fluids, vasopressors for septic shock, correct haemolytic anaemia, monitor for AKI and DIC

🥈 Second-line

•hyperbaric oxygen (HBO) therapy - raises tissue oxygen tension, inhibits anaerobic metabolism; adjunct only, not a replacement for surgery

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Clindamycin is added alongside benzylpenicillin specifically to suppress toxin production - not just bacterial replication. Antibiotics alone cannot cure established gas gangrene; devascularised muscle has no blood supply through which they can reach the organism.

Complications

Septic shock and multi-organ failure

Acute kidney injury - myoglobinuria and haemoglobinuria

Disseminated intravascular coagulation (DIC)

Haemolytic anaemia - theta-toxin destroys RBC membranes

Amputation - frequently necessary

Death - mortality very high, especially spontaneous disease and truncal involvement

Prognosis

•Prognosis directly related to time-to-surgery and anatomical location - limb disease treated promptly fares better than truncal/perineal disease

•Spontaneous C. septicum disease carries particularly poor prognosis - often diagnosed late, established bacteraemia, truncal involvement, underlying malignancy