Necrotizing fasciitis

Revision as of 19:58, 21 March 2026 by Danbot (talk | contribs) (Major update: NF types I-IV, clindamycin toxin suppression rationale, HUCLA criteria, skip lesions, la belle indifference, dishwater pus, repeat debridement timing, IVIG for strep TSS, references with PMIDs)

Background

  • Rapidly progressive, life-threatening infection involving fascia and subcutaneous tissue
  • Mortality: 20-40% even with treatment; increases with delayed diagnosis[1]
  • 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[2]

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[3]
  • 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)[4]
  • Systemic toxicity: fever, tachycardia, shock, DIC

Differential Diagnosis

Template:Skin and soft tissue infection DDX

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[5]

  • 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[6]

  • 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[7]
  • 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)[8]
  • 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

Template:LRINEC Score Calculator

See Also

References

  1. ↑ Hakkarainen TW et al. Necrotizing soft tissue infections: review and current concepts. Curr Probl Surg. 2014;51(8):344-72. PMID 25069713
  2. ↑ Misiakos EP et al. Current concepts in the management of necrotizing fasciitis. Front Surg. 2014;1:36. PMID 25593960
  3. ↑ TheHealthScience. Emergent Management of Necrotizing Soft Tissue Skin Infections. 2013.
  4. ↑ Seal DV. Necrotizing fasciitis. Curr Opin Infect Dis. 2001;14(2):127-32. PMID 11979122
  5. ↑ Wong CH, et al. The LRINEC score: a tool for distinguishing necrotizing fasciitis from other soft tissue infections. Crit Care Med. 2004;32(7):1535-1541. PMID 15241098
  6. ↑ Wall DB et al. A simple model to help distinguish NF from non-NF soft tissue infection. J Am Coll Surg. 2000;191(3):227-31. PMID 10989895
  7. ↑ Core Ultrasound: Soft Tissue. https://www.coreultrasound.com/sti/
  8. ↑ Stevens DL, et al. Practice guidelines for the diagnosis and management of SSTI: 2014 update by IDSA. Clin Infect Dis. 2014;59(2):e10-e52. PMID 24973422
  • 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
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