Necrotizing fasciitis

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Thomas Li

Definition

Necrotizing soft-tissue infection spreading at the level of the fascia, ± overlying erythema and oedema

Commonly affects abdominal wall, extremities and perineum (Fournier’s gangrene)

Introduction of pathogens to subcutaneous tissues by cut, abrasion, burn, injection or surgical incision. Rarely by haematogenous spread

Epidemiology

• Uncommon

• Population-based surveillance in Ontario from 11/91-5/95 noticed increase in annual incidence from 0.085 per 100,000 to 0.40 per 100,000 population

Aetiology

Predisposing injury

Depends on site. In 17% of patients there is no history of injury.

• Limb

  • Animal bites (including insect bites), penetrating trauma (may be trivial eg abrasion), insulin injection, illicit drug injection(increasingly common), decubitus ulcer

• Abdominal

  • Appendicitis, colocutaneous fistula

• Perianal

  • Haemorrhoidal banding, perirectal abscess

• Genitourinary

  • Bartholin’s gland abscess, pundendal nerve block

• Catheter-associated

  • Abscess drainage catheter, PEG

Underlying medical condition

Some medical conditions predispose patients to necrotizing fasciitis:

• Chronic cardiac disease

• Peripheral vascular disease with ischaemic limbs

• Chronic renal failure

• Chronic pulmonary disease

• Diabetes mellitus

• Alcohol abuse

• Intravenous drug abuse

• Immunosuppression

Underlying skin condition

• Psoriasis

• Varicella

Infecting organisms

• Abdominal and perineal NF

  • Polymicrobial enteric pathogens infections: aerobic and anaerobic Gram –ve enteric bacilli, enterococci and less commonly staphylococcal or streptococcal sepcies. Anaerobes include Bacteroides and clostridial species

• Extremity NF

  • Usually monomicrobial: Streptococcus pyogenes

  • In warm costal regions consider marine vibrio: Vibrio vulnificus, parahaemolyticus, damsela, alginolyticus. Risk factors: puncture wound caused by fish, insect bite exposed to sea water, ingestion of raw shellfish

Pathophysiology

• Group A streptococcus secretes exotoxins A, B and M protein (inhibits phagocytosis). These function as superantigens leading to release of cytokines

• Exotoxins cause local vasoconstriction and thrombosis. Tissue ischemia and necrosis support growth of bacteria

Clinical presentation

• Erythema, tender, swollen (looks like cellulitis)

• Early NF is very painful. Later destruction of subcutaneous nerve results in decreased pain

• Local pain out of proportion of physical findings with systemic toxic condition

• Skin then becomes smooth, shiny and intensely swollen with spreading erythema

• No distinct margin with surrounding normal skin

• Later, become dusky blue with blisters and bullae formation

  • Bullae are initially filled with serous fluid, later becomes hemorrhagic

  • In late stages purplish areas of skin become frankly gangrenous and slough off

• Extent of fasciitis is usually more than the overlying skin

• Sepsis syndrome

• Metastatic abscess formation

• Hypocalcemia from extensive fat necrosis has been reported

Investigations

Radiology

• Plain radiography. Rarely may show soft tissue gas.

• Ultrasonography. Uuseful in Fournier’s gangrene to distinguish from other cause of acute scrotum.

• CT scan. More sensitive than plain radiography.

• MRI. Good tissue contrast and soft tissue fluid detection but may be difficult in a critically ill patient.

Finger test

• Infiltrate suspected area with LA

• 2 cm skin incision is made down to deep fascia

• Lack of bleeding: omnious sign

• Look for “murky dishwater” fluid

• Gentle probing maneuver with index finger at the level of deep fascia

  • If the tissue can be dissected with minimal resistance, the finger test is +ve

• Rapid frozen section can also be done in doubtful case

Blood tests

• Leucocytosis

• Hyponatraemia

Treatment

Mainstay of treatment is urgent extensive debridement

Surgery

• Debridement of all necrotic tissue and drainage of fascial planes until healthy fascia is encountered

• Frequent examination for possible need of repeated debridement

• Amputation of extremity (eg PVD, DM)

• Diversion colostomy/ urinary diversion for perineal NF

Antibiotics

Third generation cephalosporin plus quinolone or clindamycin or metronidazole

Miscellaneous

• Hyperbaric oxygen therapy

  • No randomized controlled trials

  • Some retrospective studies suggested decreased mortality

  • Risk of transfer and difficulty in monitoring for unstable patients

Prognosis

• High mortality

• Factors associated with worse prognosis:

• Shock

• Bacteraemia

• Delay in debridement

• Increasing number of organ failures

• Age >60 years

 © Thomas Li March 2003

©Charles Gomersall, October, 2009 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
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