Necrotizing fasciitis

Background

• A rapidly progressive infection primarily involving the fascia and subcutaneous tissue
• Formerly a rare diagnosis, frequency has risen due to an increase in immunocompromised patients with significant risk factors
• Gas-formation is NOT a requirement for diagnosis, and radiographical lack of the classically taught gas formation should NEVER rule out necrotizing infection
• Most severe form of soft tissue infection and potentially limb and life threatening
• Early recognition and aggressive debridement are major prognostic determinants and delay increases mortality

Categories

• Type I, polymicrobial
• Type II, group A streptococcal
• Type III, gas gangrene or clostridial myonecrosis

Risk Factors

• DM
• Drug use
• Obesity
• Immunosuppression
• Recent surgery
• Traumatic wounds

Clinical Features

Nectrotizing fasciitis

• Skin exam
  • Erythema (without sharp margins)
  • Exquisitely tender (pain out of proportion to exam)
    • Caveat - some patients present with "la belle indifference"
    • May be a result of ischemic, insensate tissue
  • Skip lesions
  • Hemorrhagic bullae (violaceous bullae)
    • May be preceded by skin anesthesia (destruction of superficial nerves)
  • Crepitus (in type I infections)
  • Lymphangitis and lymphadenopathy are absent in necrotizing fasciitis alone
    • Lymphangitis is seen in cellulitis
    • Fascia has no lymph drainage
• Swelling/edema may produce compartment syndrome
• Constitutional or toxic shock-like syndrome
  • Fever
  • Tachycardia
  • Systemic toxicity, sepsis
  • Conjunctivitis

Differential Diagnosis

Skin and Soft Tissue Infection

• Cellulitis
  • Hand cellulitis
  • Facial cellulitis
  • Orbital cellulitis
• Erysipelas
• Lymphangitis
• Folliculitis
• Hidradenitis suppurativa
• Skin abscess
  • Anorectal abscess
  • Bartholin gland abscess
  • Pilonidal abscess
  • Scrotal abscess
• Necrotizing soft tissue infections
  • Necrotizing fasciitis
  • Necrotizing myositis
  • Necrotizing cellulitis
  • Fournier's gangrene
• Mycobacterium marinum

Look-A-Likes

• Sporotrichosis
• Osteomyelitis
• Deep venous thrombosis
• Pyomyositis
• Purple glove syndrome
• Tuberculosis (tuberculous inflammation of the skin)

Necrotizing rashes

• Necrotizing soft tissue infections
  • Necrotizing fasciitis
  • Necrotizing myositis
  • Necrotizing cellulitis
• Purpura fulminans
• Drug rash
• Levamisole toxicity
• Heparin-induced skin necrosis
• Warfarin-induced skin necrosis

Evaluation

CT of necrotizing fasciitis

Work-Up

• CBC
• Chem
• PT/PTT/INR
• CK
• Lactate

Evaluation

• Surgical exploration is the ONLY way to definitively establish the diagnosis of necrotizing infection
• Imaging
  • Should not delay surgical exploration
  • CT is study of choice - soft tissue gas, edema and fluid collections, fascial thickening with fat stranding
  • US may show thickened fascial planes, fluid between fascial planes, irregularity of the fascia, subcutaneous emphysema. The study may be limited by soft tissue gas. Video lecture.
  • MRI - T2 subcutaneous, intramuscular, and fascial edema
• Absence of gas on imaging does not exclude diagnosis, as gas may be occult and/or certain organisms do not classically produce gas (i.e. Group A Strep)

Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) Score

Has not been prospectively validated, index of suspicion is key and 10% of the patients with a score < 6 had Necrotizing Fasciitis. A score > 6 has PPV of 92% and NPV of 96% for necrotizing fasciitis.

1. CRP (mg/L) ≥150: 4 points
2. WBC count (×10³/mm³)
   • <15: 0 points
   • 15–25: 1 point
   • >25: 2 points
3. Hemoglobin (g/dL)
   • >13.5: 0 points
   • 11–13.5: 1 point
   • <11: 2 points
4. Sodium (mmol/L) <135: 2 points
5. Creatinine (umol/L) >141: 2 points
6. Glucose >180 mg/dL (10 mmol/L): 1 point

Grouping by Scores

• Low Risk: score 5 (10% of pts with score < 6 still had nec fasc)
• Moderate Risk: score 6– 7
• High Risk: score >8

Proposed algorithm

HUCLA NF vs Non-NF Criteria:

• Retrospective study discovered:
  • WBC count >15.4(x10³/mm³) OR Na <135(mmol/L)
  • Associated with NF and combo of both increased likelihood of NF
  • PPV 26%/NPV 99%
• Useful tool to rule out NF, not a good tool for confirming presence of NF
  • Helps distinguish NF from non-NF infection, when classic 'hard' signs of NF are absent however clinical judgment should still be used in patient with high suspicion of the disease

Management

• Surgical exploration and debridement is both the definitive diagnostic modality and the definitive treatment
  • Indicated in setting of severe pain, toxicity, fever, elevated CK (with or without radiographic evidence)
• Antibiotics
  • Must cover gram positives, gram negatives, and anaerobes (especially GAS and clostridium)
  • Piperacillin-Tazobactam 3.375-4.5g q6hr AND clindamycin 600-900mg q8hr AND vancomycin 1gm IV q12hr (consider weight base dosing of 20 mg/kg)
  • Piperacillin-Tazobactam 3.375-4.5g q6hr and linezolid 600mg q12hr is an alternative regimen
• In diabetics, maintain strict glycemic control (with IVFs and IV insulin if necessary)

Disposition

• Admit to ICU

See Also

• Necrotizing soft tissue infections
• Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) Score
• EBQ:LRINEC Score

References

📊 LRINEC Score Calculator [show]

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.