Necrotising Fasciitis

Overview

Necrotising fasciitis (NF) is a rare but life-threatening soft tissue infection characterised by rapidly progressive necrosis of the subcutaneous tissue and fascia, with relative sparing of underlying muscle in early stages. [1] The condition represents a surgical emergency requiring immediate recognition, aggressive resuscitation, broad-spectrum antibiotics, and urgent surgical debridement. [2]

The hallmark clinical feature is severe pain that appears disproportionate to the physical examination findings—a result of deep fascial involvement and nerve ischaemia occurring before significant skin changes become apparent. [3] This "pain out of proportion" serves as a critical early warning sign that distinguishes necrotising fasciitis from more benign soft tissue infections.

Despite modern critical care and surgical advances, mortality rates remain substantial at 20-30%, rising to over 50% when diagnosis is delayed beyond 24 hours or when septic shock is present at admission. [4,5] Early surgical intervention—ideally within 6 hours of presentation—is the single most important factor determining survival and functional outcome. [6]

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Epidemiology

Incidence and Prevalence

The annual incidence of necrotising fasciitis ranges from 0.4 to 1.0 cases per 100,000 population in developed countries, with evidence suggesting gradual increases over the past two decades. [7,8] This rise is attributed to aging populations, increasing prevalence of diabetes mellitus and obesity, and greater numbers of immunocompromised patients. [9]

Risk Factors

Multiple population-based studies have identified key risk factors for developing necrotising fasciitis: [12,13]

Major Risk Factors (Odds Ratio > 5)

Moderate Risk Factors (Odds Ratio 2-5)

• Obesity (BMI > 30): Impaired tissue perfusion, mechanical skin trauma in skin folds [18]
• Peripheral vascular disease: Tissue ischaemia reduces host defences [19]
• Immunosuppression: Chemotherapy, corticosteroids, HIV, biologics (anti-TNF agents) [20]
• Recent trauma or surgery: Provides portal of entry, surgical site infections account for 20% of cases [21]
• NSADs use: Controversial association, may mask early symptoms and delay diagnosis [22]

Special Populations

Fournier's gangrene (perineal/genital NF) shows distinct epidemiology with male predominance (10:1), average age 50-60 years, and strong association with anorectal disease, urological procedures, and diabetes. [23]

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Aetiology and Pathophysiology

Microbiological Classification

Necrotising fasciitis is classified into three types based on causative organisms, with important implications for treatment and prognosis: [24]

Type I: Polymicrobial (70-80% of cases)

Organisms: Mixed aerobic and anaerobic bacteria (average 4-5 organisms per case)

• Aerobes: Escherichia coli, Klebsiella, Enterococcus, Streptococcus (non-Group A), Staphylococcus aureus
• Anaerobes: Bacteroides fragilis, Peptostreptococcus, Clostridium (non-perfringens), Prevotella

Clinical context:

• Post-operative infections (especially abdominal/perineal surgery)
• Perirectal abscesses extending to perineum (Fournier's gangrene)
• Diabetic patients
• Older patients with comorbidities
• Generally slower progression than Type II (hours to days vs hours)

Type II: Monomicrobial (20-30% of cases)

Organisms:

• Group A Streptococcus (Streptococcus pyogenes): Most common, often produces streptococcal toxic shock syndrome (STSS) [25]
• Community-acquired MRSA: Increasingly recognized, particularly with Panton-Valentine leukocidin (PVL) toxin [26]
• Vibrio vulnificus: Marine exposures, particularly liver disease patients [27]
• Aeromonas hydrophila: Freshwater trauma, leeches

Clinical context:

• Previously healthy individuals
• Minor trauma or no identifiable portal (30-50% of cases)
• Rapidly progressive (hours)
• Higher risk of toxic shock syndrome
• Higher mortality (30-35% vs 20-25% for Type I)

Type III: Clostridial (Rare, less than 5%)

Organisms: Clostridium perfringens, C. septicum

Clinical context:

• Severe trauma, especially soil contamination
• Post-operative (particularly colorectal surgery)
• Spontaneous gas gangrene (C. septicum) associated with underlying malignancy [28]
• Characterized by massive gas production, myonecrosis

Pathophysiological Mechanisms

Stage 1: Inoculation and Fascial Invasion (0-24 hours)

1. Portal of entry: Bacteria enter through skin breach (trauma, surgery, injection) or translocate from mucosal sites
2. Fascial plane spread: Organisms proliferate along fascial planes with rich blood supply but limited immune surveillance
3. Toxin production: Bacterial exotoxins (streptococcal pyrogenic exotoxins, alpha-toxin, streptolysin) cause direct tissue damage [29]
4. Initial inflammation: Cytokine release (TNF-alpha, IL-1, IL-6) triggers systemic inflammatory response

Stage 2: Vascular Thrombosis and Tissue Necrosis (24-72 hours)

5. Microvascular thrombosis: Bacterial products and inflammatory mediators cause endothelial damage and thrombosis of perforating vessels [30]
6. Tissue hypoxia: Vascular occlusion leads to tissue ischaemia and necrosis
7. Liquefactive necrosis: Bacterial enzymes (hyaluronidase, collagenase, lipases) destroy fascial architecture
8. Dermal gangrene: As perforating vessels thrombose, overlying skin develops ischaemia and necrosis (late finding)

Stage 3: Systemic Toxicity (Variable onset)

9. Toxin-mediated shock: Streptococcal superantigens cause massive T-cell activation and cytokine storm [31]
10. Distributive shock: Profound vasodilation, capillary leak, and myocardial depression
11. Multi-organ failure: Acute kidney injury, ARDS, DIC, hepatic dysfunction

Molecular Pathophysiology of "Pain Out of Proportion"

The characteristic severe pain despite minimal skin findings results from:

• Fascial ischaemia: Thrombosis of vessels supplying deep tissues while superficial circulation initially preserved
• Nerve involvement: Direct bacterial invasion and ischaemia of nerve fibres traversing affected fascia
• Inflammatory mediators: High concentrations of substance P, bradykinin, and prostaglandins in deep tissues
• Compartment syndrome effect: Fascial oedema increases pressure, causing ischaemic pain before skin changes [32]

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Clinical Presentation

Early Stage (First 24 hours): Often Non-Specific

The earliest symptoms are frequently subtle and easily mistaken for simple cellulitis, leading to dangerous delays in diagnosis. [33]

Cardinal Early Features

Symptoms That Should Prompt High Suspicion

1. Severe, unrelenting pain requiring parenteral opioids
2. Rapid progression of erythema or swelling over 6-12 hours
3. Pain worsening despite antibiotics started for presumed cellulitis
4. Systemic toxicity disproportionate to local findings

Intermediate Stage (24-48 hours): Progressive Changes

As tissue necrosis advances, more specific clinical signs emerge:

Skin Changes

• Erythema: Initially similar to cellulitis, but violaceous or dusky discoloration develops [34]
• Oedema: Woody, indurated texture; "board-like" firmness
• Blistering: Haemorrhagic bullae (fluid-filled blisters containing dark blood)
• Ecchymoses: Irregular purplish patches indicating vascular thrombosis

Late Stage (> 48-72 hours): Frank Necrosis

DO NOT WAIT FOR THESE SIGNS - they indicate extensive tissue death and predict poor outcomes: [35]

Systemic Manifestations

Septic Shock Features

• Hypotension: Systolic BP less than 90 mmHg despite fluid resuscitation
• Altered mental status: Confusion, agitation, decreased consciousness
• Oliguria: Urine output less than 0.5 mL/kg/hour
• Metabolic acidosis: Lactate typically > 4 mmol/L
• Coagulopathy: DIC with prolonged PT/aPTT, thrombocytopenia

Streptococcal Toxic Shock Syndrome (Type II NF)

Defined by hypotension PLUS ≥2 of: [37]

• Renal impairment (creatinine ≥177 μmol/L)
• Coagulopathy (platelets less than 100 or DIC)
• Hepatic dysfunction (ALT/AST > 2x normal)
• ARDS
• Generalised erythematous rash followed by desquamation

Anatomical Site-Specific Presentations

Lower Extremity (40-50% of cases)

• Most common site overall
• Often following minor trauma, insect bites, or spontaneous in diabetics
• Rapid proximal spread along fascial planes
• Consider compartment syndrome as differential

Fournier's Gangrene (Perineal/Genital, 20% of cases)

• Portal of entry: Anorectal (perirectal abscess, anal fissure), urogenital (UTI, catheter trauma), or cutaneous
• Classic triad: Scrotal/perineal pain, swelling, crepitus [23]
• Rapid spread: Along Colles' fascia (perineum) to abdominal wall, thighs
• High mortality: 20-40%; worse with delay > 24 hours
• Urinary retention may be presenting feature

Abdominal Wall (15-20% of cases)

• Usually post-operative (especially after colorectal, gynaecological, or vascular surgery)
• May complicate laparoscopic port sites
• Hidden by surgical dressings; high index of suspicion needed
• Extensive subcutaneous spread before skin changes

Cervical (10% of cases)

• Often odontogenic origin (dental abscess, extraction) [38]
• Risk of descending mediastinitis (Ludwig's angina progression)
• Airway compromise potential—early anaesthetic/ICU involvement
• High mortality (40-50%)

Upper Extremity (10-15% of cases)

• Often IV drug use-related
• May follow minor trauma, insect bites, or surgery
• Injection drug users: consider Type II (MRSA or GAS)

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Clinical Examination

Systematic Approach

General Inspection

• Appearance: Toxic, distressed, in severe pain
• Vital signs: Fever/hypothermia, tachycardia (HR often > 120), hypotension, tachypnoea
• Mental status: Alert vs confused/agitated (shock indicator)

Local Examination of Affected Area

Inspection:

1. Extent of erythema: Mark borders with pen; reassess in 2-4 hours
2. Skin colour: Pink/red (cellulitis) → violaceous/dusky → grey/black (necrosis)
3. Bullae: Clear fluid (cellulitis) vs haemorrhagic (NF)
4. Crepitus: Visible gas bubbles or skin 'rippling'

Palpation:

1. Temperature: Initial warmth, then cool to touch (ischaemia)
2. Texture: Tense, indurated, "woody" firmness (vs soft pitting in cellulitis)
3. Tenderness: Beyond visible erythema margins
4. Crepitus: Crackling sensation on palpation (present in 30-40%)
5. Fluctuance: Suggests abscess formation

Special Tests:

• Finger test (intraoperative): Probe inserted through skin incision; if easily advances along fascial plane with minimal resistance = positive [39]
• Pain response: Pain worsening with gentle pressure or passive movement

Lymphatic Examination

• Lymphadenopathy: Usually ABSENT (vs cellulitis where regional lymphadenopathy common)
• Lymphangitic streaking: Usually ABSENT (suggests cellulitis rather than NF)

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Differential Diagnosis

Must-Not-Miss Diagnoses

Common Differentials

Cellulitis

• Distinguished by: Pain proportionate to findings; slower onset (days); lymphangitic streaks common; lymphadenopathy present; responds to antibiotics within 24-48 hours
• Management: Antibiotics alone usually sufficient
• Key point: If diagnosed cellulitis not improving in 24-48 hours, reconsider NF

Deep Vein Thrombosis

• Distinguished by: Unilateral limb swelling; calf/deep tenderness; positive D-dimer; Doppler ultrasound positive; minimal pain; no fever
• Management: Anticoagulation
• Key point: Can coexist with NF; maintain high suspicion if fever present

Severe Cutaneous Abscess

• Distinguished by: Localized fluctuance; pointing; surrounding cellulitis; less systemic toxicity
• Management: Incision and drainage
• Key point: NF may begin as abscess; reassess after drainage if pain persists

Calciphylaxis (Calcific Uraemic Arteriolopathy)

• Distinguished by: End-stage renal disease; painful necrotic ulcers; retiform purpura; skin biopsy shows vascular calcification
• Management: Medical (sodium thiosulphate, wound care)
• Key point: Can become secondarily infected with NF

Acute Compartment Syndrome

• Distinguished by: History of trauma/reperfusion; "5 Ps"; pressure measurement > 30 mmHg; muscle ischaemia not fascial
• Management: Urgent fasciotomy
• Key point: Can coexist with NF post-trauma

Diagnostic Approach to Uncertainty

When diagnosis uncertain between cellulitis and NF:

1. Serial examinations: Mark borders; reassess every 2-4 hours for progression
2. LRINEC score: ≥6 raises suspicion; ≥8 high probability (see Investigations)
3. Imaging (CT/MRI): If stable enough and uncertainty persists
4. Surgical exploration: LOW threshold—when in doubt, explore surgically [40]

Critical principle: Better to explore and find cellulitis than delay and miss NF. Morbidity/mortality of missed NF far exceeds that of negative exploration.

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Investigations

Laboratory Risk Indicator for Necrotising Fasciitis (LRINEC) Score

Developed and validated to distinguish NF from other soft tissue infections. [41]

Interpretation:

• Score ≥6: Intermediate risk; NF should be strongly suspected (positive predictive value 92%) [41]
• Score ≥8: High risk; NF very likely (positive predictive value 93.4%)
• Score less than 6: Low risk but does NOT exclude NF; clinical suspicion supersedes

Limitations: [42]

• Developed in retrospective cohort; requires validation
• Sensitivity only 68-80%; cannot rule out NF
• Less accurate in immunosuppressed patients
• Should never delay surgical exploration if high clinical suspicion
• Best used to support rather than make diagnosis

Essential Blood Tests

Baseline and Monitoring

Microbiological Investigations

Imaging

Critical principle: DO NOT delay surgery for imaging if clinical suspicion is high and patient unstable. [45]

Imaging is adjunctive for:

• Equivocal cases
• Identifying extent for surgical planning
• Ruling out other diagnoses (DVT, abscess)

Plain Radiography (X-ray)

Findings:

• Soft tissue gas (present in only 25-30% of NF cases) [36]
• Soft tissue swelling and loss of normal tissue planes

Utility: Limited sensitivity; easily obtained; useful if positive but negative does NOT exclude NF

Computed Tomography (CT) with IV Contrast

Preferred imaging modality when patient stable enough: [46]

Findings suggestive of NF:

• Gas in fascial planes: Irregular, tracking along tissue planes (NOT just subcutaneous emphysema)
• Fascial thickening: > 3 mm
• Fluid collections: Along fascial planes
• Lack of contrast enhancement: Areas of necrosis/ischaemia
• Muscle involvement: Suggests progression to myonecrosis
• Asymmetrical fascial enhancement: Affected vs non-affected side

Advantages:

• Rapid acquisition
• Good sensitivity (80-90%) and specificity (80-85%)
• Delineates extent for surgical planning
• Identifies source (e.g., perirectal abscess in Fournier's)

Limitations:

• Requires stable patient for transport to scanner
• IV contrast contraindicated in severe renal failure
• Cannot definitively distinguish NF from other deep infections

Magnetic Resonance Imaging (MRI)

Findings: [47]

• Hyperintense signal in deep fascia on T2-weighted and STIR sequences
• Lack of enhancement in necrotic areas
• Excellent soft tissue characterization

Advantages:

• Highest sensitivity (90-100%) for detecting fascial involvement
• Superior soft tissue contrast

Disadvantages:

• Long acquisition time (30-60 minutes)—unacceptable delay in unstable patient
• Limited availability
• Cannot be used with some metal implants
• Requires patient cooperation (difficult in severe pain)

Role: Research/retrospective analysis; occasionally in stable patient with diagnostic uncertainty

Ultrasound

Point-of-care ultrasound findings: [48]

• Thickened fascia (> 4 mm)
• Fluid along fascial planes ("cobblestoning")
• Gas (hyperechoic foci with dirty shadowing)

Advantages:

• Bedside; rapid; no radiation
• May guide procedural intervention

Limitations:

• Operator-dependent
• Limited depth penetration (obesity)
• Poor sensitivity (50-60%); cannot exclude NF

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Diagnosis

Clinical Diagnosis

Necrotising fasciitis remains a clinical diagnosis. No single test or scoring system can definitively rule it in or out. [49]

High Clinical Suspicion: Consider NF if ≥3 of:

1. Pain out of proportion to examination findings
2. Rapid progression of erythema or swelling over hours
3. Systemic toxicity (fever, tachycardia, hypotension, altered mental status)
4. Failure to respond to standard antibiotics for cellulitis
5. Skin changes (blistering, necrosis, discolouration beyond simple erythema)
6. Crepitus or gas on imaging
7. LRINEC score ≥6

Definitive Diagnosis: Surgical Exploration

Gold standard: Direct visualization at surgery showing: [39]

• Necrotic, grey fascia
• Lack of bleeding from fascia
• "Dishwater" purulent fluid
• Fascia separates easily from underlying muscle (positive "finger test")
• Thrombosed vessels

Histopathology confirms:

• Fascial necrosis
• Bacterial invasion of deep tissues
• Vascular thrombosis
• Inflammatory infiltrate

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Management

Time-Critical Principles

1. Time to surgery is the single most important determinant of outcome [6,50]

   • Each hour of delay increases mortality by 7.6% [6]
   • Target: Surgical debridement within 6 hours of presentation

2. Early empirical antibiotics (within 1 hour) but do not delay surgery to administer

3. Aggressive resuscitation before, during, and after surgery

4. Serial debridement (every 24-48 hours) until all necrotic tissue removed

Immediate Resuscitation and Stabilisation (First Hour)

A. Airway and Breathing

• Assess airway patency (especially cervical NF)
• High-flow oxygen (target SpO₂ > 94%)
• Consider early intubation if:
  • Cervical NF with potential airway compromise
  • Severe shock requiring high-dose vasopressors
  • Decreased consciousness
  • Pre-operative for extensive surgery

B. Circulation

• Large-bore IV access (≥2 x 16-18G cannulae) or central venous access
• Aggressive fluid resuscitation: [51]
  • "Initial: 30 mL/kg crystalloid (e.g., Hartmann's or 0.9% saline) within first 3 hours"
  • "Ongoing: Target MAP ≥65 mmHg, urine output > 0.5 mL/kg/hour, lactate normalization"
  • May require 6-10 litres in first 24 hours
• Vasopressors if hypotensive despite adequate fluid (typically noradrenaline)
• Invasive monitoring: Arterial line, central venous catheter if shocked

C. Disability

• Monitor GCS/mental status (shock indicator)
• Pain control: Morphine or fentanyl IV (required for adequate analgesia)

D. Investigations

• Blood tests: FBC, CRP, U&E, glucose, LFTs, coagulation, lactate, blood cultures, Group & Save
• LRINEC score calculation
• Imaging ONLY if will not delay surgery and uncertainty exists

E. Early Interventions

• Urinary catheter: Strict fluid balance monitoring
• NG tube if septic ileus suspected
• Keep nil by mouth: Anticipate theatre

Antibiotic Therapy

Empirical Broad-Spectrum Antibiotics (Start within 1 hour)

First-line regimen: [52,53]

Piperacillin-tazobactam 4.5 g IV every 6-8 hours
PLUS
Clindamycin 600-900 mg IV every 8 hours

Rationale:

• Piperacillin-tazobactam: Broad-spectrum coverage of aerobes (Gram-positive and Gram-negative) and anaerobes
• Clindamycin:
  • Additional anaerobic coverage
  • "Toxin suppression: Inhibits bacterial protein synthesis, reducing exotoxin production (especially GAS) [54]"
  • "Immunomodulatory: Reduces inflammatory cytokine response"

Alternative regimens:

Specific Organism-Directed Therapy (Once cultures available)

Duration: Typically 7-14 days total, guided by:

• Clinical improvement (fever resolution, normalizing inflammatory markers)
• Source control achieved (adequate debridement)
• Negative repeat cultures

Surgical Management: Emergency Debridement

Timing: URGENT—ideally within 6 hours of diagnosis [6]

Surgical Principles

1. Extensive debridement: [55]

   • Excise ALL necrotic fascia and subcutaneous tissue
   • Debride until healthy, bleeding tissue encountered
   • "Go wide": Better to over-resect than under-resect
   • Fascia should bleed when healthy (lack of bleeding = ongoing ischaemia)

2. Adequate exposure:

   • Make generous incisions to fully visualize extent
   • Follow fascial planes to margin of healthy tissue
   • Don't be limited by cosmesis—life-saving surgery

3. Diagnostic confirmation:

   • Identify characteristic findings (grey fascia, dishwater pus, lack of bleeding, easy fascial separation)
   • Send deep tissue for microbiology and histopathology

4. Wound management:

   • Leave wounds open (delayed primary closure or grafting later)
   • Vacuum-assisted closure (VAC) therapy useful for temporary coverage [56]
   • Loose dressings allowing drainage

5. Planned re-look:

   • Schedule return to theatre in 24-48 hours for reassessment and further debridement
   • May require multiple operations (average 2-4) until all necrotic tissue removed [57]

Anatomical Considerations

Limb NF:

• Fasciotomy may be required if compartment syndrome coexists
• Consider early amputation if: extensive necrosis, poor perfusion, systemic toxicity not improving [58]
• Amputation rate: 10-30% in severe limb NF

Fournier's Gangrene:

• Requires extensive perineal/genital debridement
• May necessitate fecal diversion (colostomy) if extensive perianal involvement or fecal contamination [59]
• Urinary diversion (suprapubic catheter) if urethral involvement
• Testicular involvement uncommon (separate blood supply); preserve if viable

Cervical NF:

• Risk of descending mediastinitis—may require sternotomy/thoracotomy
• ENT/maxillofacial involvement for dental source control
• Tracheostomy may be required for prolonged ventilation

Abdominal Wall NF:

• May require mesh for later reconstruction
• High risk of bowel exposure—early plastic surgery involvement

Adjunctive Therapies

IV Immunoglobulin (IVIG)

Indication: Streptococcal toxic shock syndrome (Type II NF with hypotension and organ failure) [60]

Mechanism: Neutralizes streptococcal superantigens, modulates immune response

Dose: 1-2 g/kg IV as single dose (or 0.5 g/kg daily for 3 days)

Evidence: Observational data suggests reduced mortality; no RCT confirmation [61]

Recommendation: Consider in confirmed GAS with shock; expensive; limited availability

Hyperbaric Oxygen Therapy (HBOT)

Mechanism: Increased tissue oxygen delivery; bactericidal to anaerobes; enhances neutrophil function

Evidence: [62]

• Retrospective studies suggest potential benefit
• No high-quality RCT data
• Cochrane review: insufficient evidence to recommend routinely [63]

Practical limitations:

• Limited availability
• Requires patient transport (delays surgery, destabilizes patient)
• Contraindicated if unstable

Current recommendation:

• NOT first-line; do not delay surgery or antibiotics
• May consider as adjunct in stable patient with adequate source control
• Typical protocol: 2.5-3.0 atmospheres for 90 minutes daily

Intensive Care Management

Most patients require ICU admission: [64]

Indications:

• Septic shock requiring vasopressors
• Organ support (ventilation, renal replacement therapy)
• High-risk post-operative monitoring
• Massive fluid resuscitation

Supportive care:

• Mechanical ventilation: If ARDS, shock, or prolonged surgery
• Renal replacement therapy: AKI common (30-40%); continuous venovenous haemofiltration often required
• Vasopressor support: Noradrenaline first-line; vasopressin or adrenaline if refractory
• Blood product support: Correct coagulopathy (fresh frozen plasma, platelets, cryoprecipitate)
• Nutrition: Early enteral nutrition if possible; parenteral if ileus
• DVT prophylaxis: Mechanical initially (bleeding risk); pharmacological once safe
• Stress ulcer prophylaxis: Proton pump inhibitor
• Glycaemic control: Target glucose 6-10 mmol/L

Reconstructive Surgery

After infection controlled and healthy granulation tissue present (weeks to months):

Options:

• Split-thickness skin grafts: Most common; good coverage for large areas
• Flap reconstruction: For functional areas (hand, perineum, face)
• Negative pressure wound therapy: Prepares wound bed for grafting

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Complications

Acute Complications

Subacute/Chronic Complications

Local:

• Extensive soft tissue loss: Requires reconstructive surgery
• Functional impairment: Loss of mobility, manual dexterity (hand NF), sexual function (Fournier's)
• Chronic pain: Neuropathic pain from nerve damage
• Scarring and contractures: Requires physiotherapy, possible release surgery

Systemic:

• Critical illness neuropathy/myopathy: Prolonged ICU stay, weakness
• PTSD and psychological sequelae: Common after life-threatening illness; requires psychological support [66]

Long-term Morbidity

• Chronic wounds requiring prolonged care
• Multiple reconstructive procedures
• Permanent disability (amputation, sexual dysfunction)
• Reduced quality of life
• Recurrence rare (less than 5%) but reported

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Prognosis and Outcomes

Mortality

Overall mortality: 20-30% in modern series [4,5,67]

Mortality risk factors: [68]

Prognostic Scores

Fournier's Gangrene Severity Index (FGSI): [69]

• Incorporates vital signs, laboratory values
• Score > 9 predicts 75% mortality
• Score less than 9: 25% mortality

Factors Improving Survival

1. Early recognition and diagnosis (less than 12 hours from onset)
2. Prompt surgical debridement (less than 6 hours from diagnosis)
3. Aggressive initial resuscitation
4. Adequate source control (complete debridement)
5. Multidisciplinary team approach

Functional Outcomes

Among survivors:

• Full recovery: 40-50% (less extensive disease, early intervention)
• Significant disability: 30-40% (amputation, chronic pain, functional loss)
• Multiple reconstructive surgeries: 50-60%
• Return to work: 50-70% within 6-12 months
• Quality of life: Significantly impaired in first year; gradual improvement but often not to baseline

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Prevention

Primary Prevention

No specific primary prevention for community-acquired NF, but risk reduction strategies:

1. Wound care: Immediate cleaning and antisepsis of all skin breaches, even minor
2. Diabetic foot care: Regular screening, proper footwear, early treatment of ulcers [70]
3. Avoid NSADs in early soft tissue infection: May mask symptoms [22]
4. Caution in immunosuppressed: Early medical attention for any soft tissue infection
5. Marine/freshwater exposure: Cover wounds; avoid exposure if immunocompromised/cirrhotic

Secondary Prevention (Post-Operative NF)

Surgical site infection prevention: [71]

• Appropriate antibiotic prophylaxis
• Aseptic technique
• Glycaemic control perioperatively
• Early recognition of surgical site infections

Tertiary Prevention (Preventing Complications)

• Early recognition systems: ED protocols for soft tissue infections with red flag screening
• Multidisciplinary teams: Surgery, ICU, infectious diseases
• Expedited surgical pathways: Direct theatre access for suspected NF

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Key Guidelines and Evidence

Major Society Guidelines

No specific NF guidelines from major surgical organizations; management based on:

1. Sepsis-3 Consensus (2016): Sepsis recognition and resuscitation [72]
2. Surviving Sepsis Campaign (2021): Septic shock management bundles [51]
3. WSES (World Society of Emergency Surgery): Intra-abdominal infections including necrotizing soft tissue infections [73]

Landmark Evidence

Diagnostic:

• Wong et al. (2004): LRINEC score development [41]
• Anaya et al. (2005): Validation of predictive factors [68]

Prognostic:

• McHenry et al. (1995): Time to surgery impacts mortality [6]
• Burner et al. (2016): Each hour delay increases mortality 7.6% [50]

Treatment:

• Stevens et al. (2014): Group A Strep guidelines including clindamycin rationale [54]
• Mathieu et al. (2006): Hyperbaric oxygen Cochrane review [63]

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Exam-Focused Content

Common Viva Questions

Q1: "What is necrotising fasciitis?"

Model answer: "Necrotising fasciitis is a life-threatening soft tissue infection characterised by rapidly progressive necrosis of the subcutaneous tissue and fascia. It has a mortality of 20-30% despite treatment. The hallmark feature is severe pain out of proportion to examination findings. It requires emergency surgical debridement within 6 hours combined with broad-spectrum antibiotics and ICU support."

Q2: "How do you classify necrotising fasciitis?"

Model answer: "Necrotising fasciitis is classified microbiologically into three types:

• Type I is polymicrobial, involving mixed aerobes and anaerobes, accounting for 70-80% of cases. It typically affects diabetic patients and follows abdominal or perineal surgery.
• Type II is monomicrobial, usually Group A Streptococcus, affecting previously healthy individuals with rapid progression and high mortality of 30-35%. It may present with streptococcal toxic shock syndrome.
• Type III is rare clostridial gas gangrene following severe trauma or colorectal surgery."

Q3: "What is the LRINEC score and how do you interpret it?"

Model answer: "The LRINEC score—Laboratory Risk Indicator for Necrotising Fasciitis—is a scoring system using six laboratory parameters: CRP, white cell count, haemoglobin, sodium, creatinine, and glucose. A score of 6 or more raises suspicion of NF with 92% positive predictive value, while 8 or more indicates high probability. However, it has limitations with sensitivity of only 68-80%, so it cannot exclude NF. A low score should never override clinical suspicion, and surgical exploration should not be delayed for score calculation."

Q4: "Describe your management of a patient with suspected necrotising fasciitis"

Model answer: "Management follows three simultaneous priorities:

First, immediate resuscitation following sepsis protocols: large-bore IV access, aggressive fluid resuscitation targeting 30 mL/kg in first 3 hours, blood cultures, and urgent blood tests including LRINEC score calculation.

Second, early empirical antibiotics within 1 hour: I would give piperacillin-tazobactam 4.5g IV plus clindamycin 600-900mg IV. Clindamycin is crucial as it suppresses toxin production in streptococcal infections.

Third, and most importantly, urgent surgical debridement within 6 hours as every hour of delay increases mortality by 7.6%. Surgery involves extensive excision of all necrotic fascia and subcutaneous tissue until healthy bleeding tissue is reached, with planned return to theatre in 24-48 hours. The patient requires ICU admission for organ support and close monitoring."

Q5: "What are the red flag features that distinguish necrotising fasciitis from cellulitis?"

Model answer: "Key red flags include: severe pain out of proportion to clinical findings, which is the single most important early feature; rapid progression of erythema over 6-12 hours; systemic toxicity with fever, tachycardia or hypotension disproportionate to local findings; failure to respond to standard antibiotics within 24 hours; skin changes including blistering, necrosis, or violaceous discolouration; and crepitus on palpation or gas on imaging, though this is only present in 30-40% of cases. Importantly, skin necrosis and crepitus are late signs—we must not wait for these before considering surgical exploration."

High-Yield Facts for Exams

Statistics to memorize:

• Mortality: 20-30% overall
• Time to surgery: Each hour delay increases mortality 7.6%
• Type I: 70-80% of cases, polymicrobial
• Type II: 20-30% of cases, GAS, mortality 30-35%
• LRINEC ≥6: 92% PPV for NF
• Gas on imaging: Only present 30-40% of cases
• Blood cultures: Positive in 20-60%

Management mnemonics:

FASCIITIS (Red flags):

• Fever with soft tissue infection
• Anaesthesia (nerve destruction)
• Systemic toxicity
• Crepitus
• Indurated, "woody" texture
• Immense pain out of proportion
• Tachycardia/hypotension
• Immediately spreading erythema
• Skin necrosis/blistering

Common Mistakes in Exams

❌ Mistake 1: Waiting for skin necrosis or crepitus before considering NF ✅ Correct: These are LATE signs; pain out of proportion is the EARLY key feature

❌ Mistake 2: Delaying surgery to obtain imaging (CT/MRI) ✅ Correct: Surgery should never be delayed if clinical suspicion high; imaging only if diagnostic uncertainty AND patient stable

❌ Mistake 3: Omitting clindamycin from antibiotic regimen ✅ Correct: Clindamycin essential for toxin suppression, especially in GAS

❌ Mistake 4: Single debridement and assuming adequate source control ✅ Correct: Plan return to theatre in 24-48 hours; average patient needs 2-4 debridements

❌ Mistake 5: Relying on LRINEC score to exclude NF ✅ Correct: LRINEC can support diagnosis but sensitivity only 68-80%; low score does not exclude NF

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Clinical Pearls

🔑 Pearl 1: "Pain out of proportion" means pain severity that doesn't match the visible skin findings—it results from deep fascial necrosis before overlying skin involvement.

🔑 Pearl 2: The ABSENCE of lymphangitic streaks and lymphadenopathy can help distinguish NF from cellulitis (both usually present in cellulitis).

🔑 Pearl 3: If "cellulitis" is not improving after 24-48 hours of appropriate antibiotics, strongly reconsider the diagnosis—it may be NF.

🔑 Pearl 4: When in doubt between cellulitis and NF, it is safer to explore surgically—mortality from missed NF far exceeds morbidity from negative exploration.

🔑 Pearl 5: Fournier's gangrene can present with scrotal/perineal pain before visible skin changes—maintain high suspicion in diabetic males with perineal pain.

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Patient and Family Information

What is Necrotising Fasciitis?

Necrotising fasciitis, sometimes called "flesh-eating disease," is a very serious infection that spreads rapidly through the layers of tissue under the skin. Despite the name, it is caused by bacteria, not by flesh "eating" itself.

Symptoms to Watch For

• Severe pain at the site of infection that seems worse than it should be based on what you can see
• Rapidly spreading redness or swelling that gets worse over hours
• Fever and feeling extremely unwell
• Blistering or skin that turns purple, blue, or black (later stages)

⚠️ Seek immediate emergency care if you have severe pain with a skin infection, especially if spreading rapidly or you feel very unwell.

Treatment

Treatment requires:

1. Emergency surgery to remove all infected tissue—often multiple operations
2. Strong antibiotics given through a vein
3. Intensive care for monitoring and support

What to Expect

• Multiple operations: Most people need 2-4 surgeries to remove all infected tissue
• Long hospital stay: Often weeks in hospital, including intensive care
• Reconstructive surgery: Skin grafts or other procedures to close wounds after infection clears
• Rehabilitation: Physiotherapy may be needed to regain function
• Recovery time: Full recovery can take months to a year

Outcomes

• This is a life-threatening condition; 20-30% of people do not survive despite all treatment
• Early treatment (surgery within 6-24 hours) greatly improves chances of survival
• Survivors may need amputation (10-30% of limb infections) or have permanent scarring and reduced function
• Psychological support is important—many survivors experience PTSD

Support Resources

• UK Sepsis Trust: sepsistrust.org - Information on sepsis and severe infections
• Lee Spark NF Foundation: Patient support and awareness
• NHS Information: Search "necrotising fasciitis" at nhs.uk

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