What is Necrotising Fasciitis?
Necrotising fasciitis is a rare, life-threatening bacterial infection that rapidly destroys the superficial fascia (subcutaneous tissue between skin and muscle), tracking along fascial planes and extending well beyond visible skin changes. 1
Pathophysiology and Tissue Involvement
The term "fasciitis" refers specifically to the superficial fascia—all tissue between the skin and underlying muscles—not the muscular fascia or aponeurosis. 1 The infection is characterized by:
- Rapid spreading necrosis of the fascia, subcutaneous fat, and overlying skin 2, 3
- Fulminant tissue destruction of poorly blood-supplied muscle fascia 4
- Extension along fascial planes that spreads well beyond superficial signs like erythema 1
Microbiological Classification
Necrotising fasciitis is classified into three distinct types based on causative organisms:
Type I (Polymicrobial)
- Caused by multiple aerobic and anaerobic organisms, averaging 5 pathogens per wound (up to 15 different microorganisms) 5
- Associated with: intestinal surgery, penetrating abdominal trauma, decubitus ulcers, perianal abscesses, injection drug use sites, Bartholin gland abscesses 5
Type II (Monomicrobial)
- Caused by single pathogens: Streptococcus pyogenes (most common), Staphylococcus aureus, Vibrio vulnificus, Aeromonas hydrophila, or anaerobic streptococci 1, 5
- Can occur in any age group and in immunologically healthy individuals 5, 6
Type III (Clostridial)
- Caused by Clostridium or Bacillus species 5
- Characterized by gas in tissues and acute infection of healthy tissue 5
Clinical Presentation
Initial Presentation (80% of cases)
Extension from a trivial skin lesion such as minor abrasion, insect bite, injection site, or boil 1 The remaining 20% have no visible skin lesion. 1
Cardinal Clinical Features
Pain disproportionate to physical findings is the hallmark early symptom that distinguishes necrotising fasciitis from simple cellulitis. 7, 8, 5
The "wooden-hard" feel of subcutaneous tissues is the most distinguishing physical finding—unlike cellulitis where tissues remain palpable and yielding, in fasciitis the fascial planes and muscle groups cannot be discerned by palpation. 1, 8
Frequency of Clinical Signs
- Cellulitis/erythema: 90% of cases 1
- Edema: 80% of cases 1, 7
- Skin discoloration or gangrene: 70% of cases 1
- Anesthesia of involved skin: frequent but true incidence unknown 1
- Crepitus (gas in tissues): present but appears in only a minority of early cases 8
Systemic Features
- High fever with systemic toxicity 1
- Altered mental status, disorientation, lethargy 1, 8
- Hypotension and septic shock in advanced cases 7
Late Findings (Often Missed Early)
- Skin necrosis or ecchymoses: present in only 0-5% at initial presentation, increasing to 9-36% by day 4 8
- Bullous lesions accompanying skin necrosis 7
- Broad erythematous tract along the route of infection as it advances 1
Anatomic Distribution and Risk Factors
Approximately two-thirds of cases involve the lower extremities, making leg trauma a high-risk scenario. 7 Most infections are community-acquired. 1
Underlying predisposing conditions include:
- Diabetes mellitus 1
- Arteriosclerotic vascular disease 1
- Venous insufficiency with edema 1
- Chronic vascular ulcers 1
Diagnostic Challenges
Early diagnosis is missed or delayed in 85-100% of cases because the disease lacks specific clinical features in the initial stage and is often confused with cellulitis or abscess. 2 The infection initially presents as cellulitis that can advance rapidly or slowly. 1
A high index of clinical suspicion remains the most important diagnostic tool—more critical than any laboratory test or imaging study. 2, 8
Prognosis
Mortality rates remain high and have shown no tendency to decrease over the past century. 2 In patients who progress to hypotension and multi-organ failure, mortality rates rise to 50-70%. 7
Each hour of delay in surgical intervention is associated with increased mortality, making this a true medical and surgical emergency. 7, 2