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. Monotherapy with a beta-lactam/beta-lactamase inhibitor:

Piperacillin-tazobactam• 3.375 or 4.5 g IV every six hours Ticarcillin-clavulanate 3.1 g IV every four hours Combination third generation cephalosporin PLUS metronidazole: Ceftriaxone plus 1 g IV every 24 hours or 2 g IV every 12 hours for CNS infections Metronidazole 500 mg IV every eight hours Alternative empiric regimens Combination fluoroquinoloneΔ PLUS metronidazole: Ciprofloxacin or 400 mg IV every 12 hours Levofloxacin plus 500 or 750 mg IV once daily Metronidazole 500 mg IV every eight hours Monotherapy with a carbapenem◊: Imipenem-cilastatin 500 mg IV every six hours Meropenem 1 g IV every eight hours Doripenem 500 mg IV every eight hours Ertapenem§ 1 g once daily

arbapenem or beta-lactam/beta-lactamase inhibitor (table 4), together with clindamycin (dosed at 600 to 900 mg intravenously every eight hours, for its antitoxin effects against toxin-elaborating strains of streptococci and staphylococci) [30,59-64], as well as an agent with activity against methicillin-resistant S. aureus (MRSA) (such as vancomycin, daptomycin, or linezolid) (table 5).

Options for carbapenems include imipenem, meropenem, or ertapenem; options for beta-lactam/beta-lactamase inhibitors include piperacillin/tazobactam, ampicillin/sulbactam, or ticarcillin/clavulanate. Patients with hypersensitivity to these agents may be treated either with an aminoglycoside or a fluoroquinolone, plus metronidazole.

Antibiotic treatment should be tailored to Gram stain, culture, and sensitivity results when available. In the setting of known group A streptococcal or other beta-hemolytic streptococcal infection, treatment may be narrowed to the combination of penicillin (4 million units intravenously every four hours in adults >60 kg in weight and with normal renal function) and clindamycin (600 to 900 mg intravenously every eight hours) [30]. Therapy against MRSA may be discontinued after methicillin-resistant staphylococcal infection has been excluded.

The optimal duration of antibiotic treatment has not been defined in clinical trials. Antibiotics should be continued until no further debridements are needed and the patient’s hemodynamic status has normalized; this duration must be tailored to individual patient circumstances

Source

• UpToDate