Chapter 101 - Necrotizing soft tissue infections Flashcards
Give a definition of Necrotizing soft tissue infection (NSTI)
Subset of soft tissue infections involving skin, SQ tissue, muscle and fascia that cause vascular occlusion, ischemia, and necrosis
Give a definition of Toxic shock syndrome (TSS)
Acute, severe, systemic inflammatory response initiated by a microbial infection at a normally sterile site, usually exotoxin-releasing Staphylococcus or Streptococcus spp
What is the mortality rate associated with NSTI in humans? With TSS?
- 12-41.6% (improved outcome with early debridement)
- 35%
What are the risk factors identified in human medicine?
Age (>50 yo), atherosclerosis, peripheral vascular disease, obesity, trauma, hypoalbuminemia, diabetes mellitus, glucorticoid usage
What are the 4 categories (types) of NSTI?
- I: polymicrobial (mixed anaerobes and aerobes, usually >4 organisms)
- II: Monomicrobial (commonly beta-hemolytic Streptococcus)
- III: Gram-negative monomicrobials (such as Clostridia, often marine-related organisms)
- IV: Fungal (such as Candida)
Why extremities and truncal regions are more susceptible to widespread infection and necrotizing fasciitis?
Because of the lack of fibrous attachements acting like a boundary between the subcutaneous and fascial tissue to limit spread of organisms
Angiothrombotic microbial invasion with liquefactive necrosis of which layers is a key pathologic process of NSTI?
Superficial fascia and soft tissue
What are the clinical signs potentially associated with TSS and NSTI?
Skin changes (bruising, edema, cellulitis, SQ emphysema, cutaneous bullae), respiratory signs, increased urination frequency, signs of malaise
Give 2 hallmarks of NSTI
Rapid progression, disproportionate localized pain
What does LRINEC stand for?
Laboratory Risk Indicator for NECrotizing fasciitis: diagnostic scoring system based on measurement of C-reactive protein, WBC, hemoglobin, sodium, creatinine and glucose in human patients
What are the features suggestive of NSTI on CT-scan? Ruling out NSTI?
- Asymmetric fascial thickening, hypodermal fat inflammation, gas in the soft tissue plane
- Absence of deep fascial involvement
What does require a definitive diagnosis of TSS? NSTI?
- Positive microbial culture (streptococcus or staphylococcus) and evidence of septic shock
- Histopathologic findings including fascial necrosis and myonecrosis, angiothrombotic microbial invasion, liquefactive necrosis
What is the most important part of NSTI treatment?
Surgical debridement (within 4-6 hours after presentation)
When should the bacterial and fungal cultures be submitted?
ASAP before injectable broad-spectrum antibiotic coverage is instituted AND after surgery from the debrided tissue
Which antibiotic remains effective during the stationary phase of a group A streptococcal organisms, inhibits streptococcal M-protein synthesis, and suppresses lipopolysaccharide-induced monocytes synthesis of tumor necrosis factor, provides coverage for anaerobic organisms
Clindamycin (recommended in combination with an aminoglycoside or 3rd generation cephalosporin)
