Necrotizing fasciitis

Background

• Rapidly progressive, life-threatening infection involving fascia and subcutaneous tissue
• Mortality: 20-40% even with treatment; increases with delayed diagnosis
• Early surgical exploration and debridement are the most important prognostic factors
• Gas formation is NOT required for diagnosis; absence of gas on imaging does NOT rule out NF

Types

• Type I (Polymicrobial): mixed aerobic/anaerobic organisms; most common overall
  • Typically in diabetics, immunocompromised, post-surgical patients
  • Abdominal wall, perineum (Fournier gangrene)
• Type II (Monomicrobial): Group A Streptococcus (most common) or Staphylococcus aureus
  • Can occur in young, healthy patients
  • Extremities most common site
• Type III (Gas gangrene): Clostridium perfringens (myonecrosis)
  • Extremely rapid progression; crepitus common
• Type IV: Fungal (immunocompromised, trauma)

Risk Factors

• Diabetes (most common comorbidity), IV drug use, obesity
• Immunosuppression (HIV, malignancy, chronic steroids)
• Recent surgery or traumatic wounds
• Peripheral vascular disease, chronic renal failure, cirrhosis
• NSAIDs (may mask early symptoms and promote GAS virulence)

Clinical Features

• Pain out of proportion to exam (most important early clinical clue)
  • However: some patients present with "la belle indifference" (painless) — ischemic insensate tissue
• Erythema without sharp margins (unlike erysipelas)
• Rapidly progressive swelling and induration
• Hemorrhagic bullae (violaceous/dusky bullae)
• Skin anesthesia (destruction of superficial cutaneous nerves — late but specific)
• Crepitus (type I infections; absent in many cases)
• Skip lesions (areas of normal-appearing skin between involved areas)
• Lymphangitis and lymphadenopathy are ABSENT (fascia lacks lymphatic drainage)
• Systemic toxicity: fever, tachycardia, shock, DIC

Differential Diagnosis

• Cellulitis (most common misdiagnosis — cellulitis improves with antibiotics; NF does not)
• DVT
• Compartment syndrome
• Pyomyositis
• Gas gangrene without fasciitis
• Erysipelas

Evaluation

Labs

• CBC: leukocytosis (or leukopenia in severe sepsis)
• BMP: creatinine (AKI), sodium <135 (associated with NF)
• CRP: >150 mg/L
• Lactate: elevated (tissue ischemia)
• CK: may be elevated (myonecrosis)
• Blood cultures, wound cultures
• Coagulation studies (DIC screening)

LRINEC Score

• Has NOT been prospectively validated
• Score ≥6: PPV 92% for NF
• 10% of patients with score <6 still had NF — low score does NOT rule out NF
• CRP ≥150 (+4), WBC 15-25 (+1) / >25 (+2), Hgb 11-13.5 (+1) / <11 (+2), Na <135 (+2), Cr >1.6 (+2), Glucose >180 (+1)

HUCLA Criteria

• WBC >15.4 OR Na <135: associated with NF
• PPV 26%, NPV 99% — useful to rule out NF, not confirm it

Imaging

• Should NOT delay surgical exploration if clinical suspicion is high
• CT (study of choice if imaging obtained): soft tissue gas, fascial thickening, fluid collections, fat stranding
• MRI: T2 fascial/subcutaneous edema (very sensitive but time-consuming)
• Bedside US: thickened fascia, subcutaneous fluid, subcutaneous emphysema; limited by gas artifact
• Absence of gas on imaging does NOT exclude NF

Definitive Diagnosis

• Surgical exploration is the ONLY way to definitively diagnose NF
• Findings: grayish necrotic fascia, lack of tissue resistance to blunt dissection, "dishwater" pus, thrombosed vessels

Management

Surgical

• Emergent surgical exploration and debridement — the single most important intervention
• Indicated if: severe pain, systemic toxicity, elevated CK, clinical suspicion with or without imaging findings
• Repeat debridement (planned "second look") typically at 24-48 hours
• Average: 3-4 debridements before wound management
• Delay in surgery increases mortality by approximately 9x

Antibiotics

• Must cover gram-positives (including MRSA), gram-negatives, AND anaerobes
• Empiric regimen:
  • Piperacillin-tazobactam 4.5g IV q6h (or meropenem 1g IV q8h)
  • + Vancomycin 25-30 mg/kg IV loading dose (or linezolid 600 mg IV q12h) — MRSA coverage
  • + Clindamycin 900 mg IV q8h — suppresses toxin production (especially GAS exotoxins)
• Clindamycin should be included in all regimens regardless of other antibiotics

Supportive Care

• Aggressive IV fluid resuscitation
• Vasopressors for septic shock
• Serial lactate monitoring
• Blood products for DIC
• ICU admission

IVIG

• Consider for streptococcal toxic shock syndrome associated with NF (controversial)

Disposition

• ICU admission for all patients
• Surgery consult in ED for any suspected case
• Serial debridements as needed
• Wound management: VAC therapy, skin grafting after infection controlled

Calculators

LRINEC Score

LRINEC Score — Necrotizing Soft Tissue Infection

Lab Value	Select
CRP (mg/L)	1 <150 (0)   ≥150 (+4)
WBC (×10³/μL)	1 <15 (0)   15–25 (+1)   >25 (+2)
Hemoglobin (g/dL)	1 >13.5 (0)   11–13.5 (+1)   <11 (+2)
Sodium (mEq/L)	1 ≥135 (0)   <135 (+2)
Creatinine (mg/dL)	1 ≤1.6 (0)   >1.6 (+2)
Glucose (mg/dL)	1 ≤180 (0)   >180 (+1)
LRINEC Score	/ 13

Interpretation
<6	Low risk — <50% probability of necrotizing fasciitis. Consider other diagnoses but maintain clinical suspicion.
6–7	Moderate risk — 50–75% probability. Consider surgical consultation and advanced imaging.
≥8	High risk — >75% probability of necrotizing fasciitis. Urgent surgical consultation for exploration.

References
Wong CH, Khin LW, Heng KS, et al. The LRINEC (Laboratory Risk Indicator for Necrotizing Fasciitis) score: a tool for distinguishing necrotizing fasciitis from other soft tissue infections. Crit Care Med. 2004;32(7):1535-1541. PMID 15241098. Caution: LRINEC has limited sensitivity (~80%). A low score does NOT rule out necrotizing fasciitis. Clinical suspicion should always guide management.

See Also

• Necrotizing soft tissue infections
• Fournier gangrene
• Cellulitis
• Gas gangrene
• Sepsis

References

• Golger A, et al. Mortality in patients with necrotizing fasciitis. Plast Reconstr Surg. 2007;119(6):1803-7. PMID 17440360
• Puvanendran R et al. Necrotizing fasciitis. Can Fam Physician. 2009;55(10):981-987. PMID 19826154
• Anaya DA, Dellinger EP. Necrotizing soft-tissue infection: diagnosis and management. Clin Infect Dis. 2007;44(5):705-710. PMID 17278065