Necrotizing Fasciitis
- Type I = Mixed aerobic and anaerobic infection. Typically occurs after surgery, in patients with Diabetes or Peripheral Vascular Disease. Can occur in extremities, trunk, perineum (Fournier’s Gangrene), or head and neck. Blood cultures are positive ~20% of the time.
- Type II = Monomicrobial infection due to Group A Strep. Recently, more and more reports of Type II NF due to Community-acquired MRSA, but Strep is still by far more common. Unlikely Type I NF, Type II occurs in any age group and in otherwise healthy patients. Risk factors include blunt trauma, IV drug use, lacerations, surgery, burns, chickenpox. Type II NF is complicated by toxic shock syndrome in up to 50% of cases. Blood cultures are usually positive (~60%).
Signs and symptoms of Necrotizing Fasciitis
Presents as severe cellulitis, but with pain out of proportion to exam, with signs of severe systemic toxicitiy. Suggestive labs include not only exaggerated signs of infection (e.g. high WBC, ESR/CRP) and organ dysfunction (e.g. renal failure) but also sometimes elevated CK, indicating tissue necrosis.
A restrospective risk score was developed and published in Critical Care Medicine in 2004 that can be useful, called the LRINEC (Laboratory Risk Indicator for Necrotizing Fasciitis).
1. CRP > 15 – 4 pts
2. WBC 15-25 – 1 pt, >25 – 2 pts
3. Hb 11-13.5 – 1 pt, <11 – 2 pts
4. Na < 135 – 2 pts
5. Cr >1.6 – 2 pts
6. Glucose > 180 – 1 pt
A score of 6 or more should generally prompt surgical exploration (PPV of 92%, NPV of 96%). However, nothing should replace your clinical judgement – i.e. if you strongly suspect nec fasc, even with a LRINEC score <6, you should be pushing for your surgery colleagues to act regardless!
Management:
1) Hemodynamic support – they require massive amounts of IVFs and usually pressors as well.
2) Surgery – for Strep TSS associated with invasive soft tissue infection, this is absolutely necessary, and the earlier the better. With abxs alone, mortality is basically 100%. Surgical exploration with biopsy and gram stain can often provide early definitive diagnosis.
3) Antibiotics
- Beta-lactam – Group A strep is uniformly sensitive to PCN. For staph, depends on MRSA or not: Nafcillin vs Vancomycin.
- Clindamycin – more effective than beta-lactams against Group A strep in invasive infections. Rationale is the so-called “Eagle Effect” described by Eagle in the 1950s – once there is a high inoculum of Strep and it reaches the stationary phase of growth, Strep does not express PCN-binding proteins and thus is less susceptible to beta-lactams. Clindamycin is not affected by inoculum size or stage of growth, suppresses synthesis of bacterial toxins, has a longer post-Abx effect than Beta-lactams, and may event modulate the immune response by suppressing TNF production.
- Linezolid - similar to Clindamycin, has anti-toxin effect that is likely more efficacious than Vancomycin or beta-lactams.
4) IVIG – small amounts of conflicting data on the efficacy, but generally is recommended. Rationale is that the immunoglobulins “soak up” the bacterial toxins and also modulate the immune response.
(Chanu Rhee MD, 1/7/11)