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 with no PMH
    • May occur via hematogenous spread from throat to site of blunt trauma

Necrotizing Fasciitis

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
    • 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

• Labs
  • CBC
  • Chem
  • PT/PTT/INR
  • CK
  • Lactate
• Imaging
  • CT

Diagnosis

• Surgical exploration is the only way to definitively establish the diagnosis of necrotizing infection
• Imaging
  • Should not delay surgical exploration
  • CT

Necrotizing Myositis

• 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

Necrotizing Cellulitis

• 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

• Surgical exploration and debridement required to distinguish between anaerobic cellulitis and fasciitis or myonecrosis

Treatment

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

Source

• UpToDate