Necrotizing Fasciitis

Overview

Epidemiology

• Incidence: ≤ 1 case per 100,000 individuals per year
• 20%‒40% of affected individuals have diabetes.
• Men to women ratio: 3:1
• Mortality: 20%‒80%

Etiology

Necrotizing fasciitis is divided into microbiologic categories based on the causative organism(s):

• Type I:
  • Polymicrobial infection containing anaerobes and aerobes:
    • Streptococcus pyogenes
    • Bacteroides
    • Peptostreptococcus
    • Escherichia coli
    • Enterobacter
    • Klebsiella
    • Proteus
  • Often seen in older adults with comorbidities, particularly diabetes mellitus
  • Most common type
• Type II:
  • Monomicrobial infection: 
    • Group A Streptococcus (most common)
    • Staphylococcus aureus
  • Occurs in any age group
  • Frequently found in individuals with no significant risk factors
• Type III (the definition or existence of this type varies in the literature):
  • Gas gangrene
    • Most commonly from traumatic inoculation with Clostridium perfringens
    • Clostridium septicum is linked with colon cancer and leukemia.
  • Vibrio vulnificus
    • From aquatic injuries or consumption of raw seafood
    • More often seen in patients with chronic liver disease

Risk factors

• Immunosuppression:
  • Diabetes mellitus 
  • HIV
  • Neutropenia
• Skin damage: 
  • Major penetrating trauma or minor laceration 
  • Intravenous drug abuse 
  • Recent surgery
  • Insect bite
• Malignancy
• Obesity
• Smoking
• Alcoholism 
• Liver cirrhosis

Pathophysiology

• Bacteria extend into the subcutaneous tissue from:
  • Nearby ulcer or superficial infection
  • Trauma
  • Bloodstream (most often S. pyogenes)
• Even in monomicrobial infections, other aerobic and anaerobic pathogens may play a role.
• Infection causes occlusion of subcutaneous vessels → tissue and fascial ischemia → necrosis
  • Damage occurs to superficial nerves → localized anesthesia
  • Hypoxic conditions → ↓ neutrophil function → proliferation of bacteria
• Infection and necrosis can rapidly travel along fascial planes, possibly due to bacterial enzymes and toxins.
• Gangrene may develop:
  • Anaerobic metabolism by facultative organisms → carbon dioxide, hydrogen, and nitrogen production
  • Hydrogen and nitrogen are insoluble and accumulate in the subcutaneous tissues.

Clinical Presentation

Skin and soft tissue findings

Early signs:

• Acute, severe pain out of proportion with physical findings
• Erythema that quickly spreads over hours to days.
• Warmth
• Tense, indurated skin

Late signs:

• Crepitus
• Anesthesia or paresthesia
• Bullae, skin necrosis, or ulceration

Common sites of infection:

• Extremities (most common)
• Fournier gangrene (necrotizing fasciitis of the perineum):
  • Presents as pain, redness, and swelling in the genital area
  • Rapidly spreads to the anterior abdominal wall and gluteal muscles
• Head and neck:
  • Often has a dental or pharyngeal origin from procedures or trauma
  • May spread to the face, lower neck, and mediastinum

Evidence of systemic toxicity

• High fever
• Tachycardia
• Hypotension 
• Altered mentation:
  • Confusion
  • Obtundation

Diagnosis

A definitive diagnosis of necrotizing fasciitis is made by surgical exploration and debridement. These processes should not be delayed to obtain diagnostic information, if the clinical suspicion is high.

However, the following may be helpful:

• Laboratory evaluation:
  • Gram stain and cultures should be obtained from:
    • Blood (preferably before antibiotics are given)
    • Intraoperative specimens 
  • ↑ WBC with left shift
  • ↑ erythrocyte sedimentation rate and c-reactive proteins
  • ↓ HCO3 → metabolic acidosis
  • ↑ lactic acid 
  • ↑ blood urea nitrogen and creatinine → acute renal failure
  • ↑ glucose
  • ↓ Na
• Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) Score:
  • Calculates a score using WBC, c-reactive protein, hemoglobin, creatinine, sodium, and glucose
  • Has a high specificity but low sensitivity
  • Should not be used alone to rule out infection
• Imaging:
  • CT scan is the best imaging modality and may show:
    • Subcutaneous gas 
    • Inflammatory changes along fascial planes
    • Fluid collections
  • Radiographs can reveal gas in the tissues, particularly in the extremities.

Management

Surgery

Surgical debridement is the mainstay of treatment.

• Necrotic tissue is removed.
• Multiple serial debridements are often required to control the infection completely.
• Amputation may be required for severe disease affecting an extremity.
• Tissue samples can be obtained and sent for culture.

Antibiotic therapy

• Early intravenous antibiotics should be given for coverage of gram-positive, gram-negative, and anaerobic bacteria.
• An initial therapy regimen should include each of the following:
  • Carbapenem or piperacillin-tazobactam
  • Vancomycin or daptomycin (MRSA coverage)
  • Clindamycin (for antitoxin effects against toxin-producing streptococci or staphylococci)
• Therapy should eventually be tailored to culture data (when available).

Post-operative care

• The majority of patients will require monitoring in an intensive care unit.
• Hemodynamic support:
  • Aggressive resuscitation with intravenous crystalloid fluids
  • Vasopressor support for septic shock (norepinephrine is first line)
• Monitor hemoglobin and transfuse for blood loss associated with repeated debridements.

Complications

• Septic shock
• Toxic shock syndrome
• Multisystem organ failure
• Limb loss and severe scarring
• Death

Differential Diagnosis

• Cellulitis: a common bacterial skin infection which that affects the deeper layers of the dermis and subcutaneous tissue. This condition is most commonly caused by S. aureus and S. pyogenes. Cellulitis presents as an erythematous, edematous area that is warm and tender to the touch. Crepitus, necrosis, and systemic toxicity are not usually present. Diagnosis is clinical, and management involves antibiotics tailored to the suspected organism.
• Pyoderma gangrenosum: neutrophilic dermatosis that presents with inflammation and ulceration of the skin. Patients present with a painful, inflamed papule that progresses to an ulcer with irregular borders and purulent drainage. Unlike necrotizing fasciitis, there is rarely systemic toxicity, the involvement of the fascial planes, or improvement with antibiotics. This condition will worsen with debridement. Pyoderma gangrenosum is based on the clinical assessment and histologic findings. This is managed with immunosuppressive therapy.
• Gas gangrene: clostridial myonecrosis (gas gangrene) is a life-threatening muscle and soft tissue infection that often develops after traumatic inoculation with Clostridium perfringens. Sudden, severe muscle pain develops shortly after the injury. Skin changes (red/purple to black), tenderness, bullae formation, and crepitus are also present and progress rapidly.  Diagnosis is clinical. Once suspected, intravenous antibiotic therapy should be started, and emergent surgical debridement should be undertaken. 
• Pyomyositis: infection of the skeletal muscle that results from hematogenous spread from a primary infected source. Patients present with localized pain, fevers, and a variable degree of skin findings from minimal erythema to severe tenderness, induration, and edema. The diagnosis is made with imaging and culture data. Management typically consists of percutaneous drainage or, in severe cases, open surgical drainage with antibiotic therapy.