Necrotizing soft tissue infections

Background

• Includes necrotizing forms of cellulitis, myositis, and fasciitis
• Two types:
  • Type 1: polymicrobial infection
  • Type 2: group A strep
    • May occur in healthy individuals
    • May occur via hematogenous spread from throat to site of blunt trauma

Necrotizing Fasciitis (NF)

Risk Factors

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

Clinical Features

• Skin exam
  • Erythema (without sharp margins)
  • Exquisitely tender (pain out of proportion to exam)
  • Skip lesions
  • Hemorrhagic bullae (violaceous bullae)
    • May be preceded by skin anesthesia (destruction of superficial nerves)
  • Crepitus (in type I infections)
• Swelling/edema may produce compartment syndrome
• Constitutional
  • Fever
  • Tachycardia
  • Systemic toxicity

Work-Up

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

Diagnosis

• 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

HUCLA NF vs Non-NF Criteria (Wall et al)

• 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%
• Good tool to R/O 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

Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) Score (Wong et al)

• May use to risk stratify patients p/w signs of cellulitis to determine likelihood of necrotizing fasciitis
• Useful in context of a diagnosed or strongly suspected severe soft-tissue infxn
• Score based on: CRP, WBC, Hb, Na, Cr, Glucose
• Score > 6 has PPV of 92% and NPV of 96% for necrotizing fasciitis
  • Be aware LRINEC score has not been prospectively validated, index of suspicion is key

1. CRP (mg/L) ≥150: 4 pts
2. WBC count (x10³/mm³):
   1. <15: 0 pts
   2. 15-25: 1 pt
   3. >25: 2 pts
3. Hb (g/dL):
   1. >13.5: 0 pts
   2. 11-13.5: 1 pt
   3. <11: 2 pts
4. Na (mmol/L) <135: 2 pts
5. Cr (mg/dL) >1.6: 2 pts
6. glucose (mg/dL) >180: 1 pt

Treatment

• Surgical exploration and debridement
  • Indicated in setting of severe pain, toxicity, fever, elevated CK (w/ or w/o radiographic evidence)
• Abx
  • Must cover Gram +/- and anaerobes (esp GAS and clostridium)
  • Piperacillin-Tazobactam 3.375-4.5g q6hr AND clindamycin 600-900mg q8hr AND vancomycin 1gm IV q12hr

Necrotizing Myositis

Background

• Much rarer than nec fasc
• May be preceded by skin abrasions, blunt trauma, heavy exercise
• Most patients are otherwise healthy (DM and other underlying conditions do not appear to increase risk)

Clinical Features

• Exquisite pain and swelling of affected muscle with induration
• Overlying skin changes may manifest later in the course of illness (erythema, warmth, petechiae, bullae)
• Hypotension may occur rapidly with development of streptococcal toxic shock syndrome

Management

• Same as necrotizing fasciitis (see above)

Necrotizing Cellulitis

Background

• Pts are often much less toxic compared with nec fasc/nec myo
• Two types:
  • Anaerobic infection (clostridial and nonclostridial)
  • Meleney's synergistic gangrene
    • Rare infection that occurs in postop pts
    • Characterized by slowly expanding indolent ulceration that is confined to superficial fascia
    • Results from synergistic interaction between S. aureus and microaerophilic streptococci

Risk Factors

• Trauma
• Surgical contamination
• Spread of infection from bowel to perineum, abdominal wall, or lower extremities

Clinical Features

• Thin, dark, sometimes foul-smelling wound drainage (often containing fat globules)
• Tissue gas formation (crepitus)

Management

• Same as necrotizing fasciitis (see above)

Source

• UpToDate