The wound was left open for 6 more days. On hospital day 9, operative exploration revealed no necrotizing fasciitis. The fascia and skin wound were then closed (eFigure 3).
Cultures from the fascia grew the GAS bacteria Streptococcus pyogenes (S pyogenes), which was sensitive to penicillin. The blood cultures from admission were sterile. A test for Epstein-Barr virus immunoglobulin M antibody was negative. The patient was discharged after 10 days in the hospital to complete a 2-week course of IV penicillin. Two months later he resumed playing tennis and returned to his clinical duties.
Discussion
In the U.S., there are approximately 3.5 cases of invasive GAS infection per 100,000 persons.1 Type I NSTI is polymicrobial (aerobic and anaerobic organisms). Risk factors include recent surgery, immunocompromised states, drug use, diabetes mellitus, and traumatic wounds.2 Type II NSTI is caused by GAS or other β-hemolytic streptococci either alone or in association with another organism, most commonly Staphylococcus aureus. Type II NSTI is classically found on the extremities and occurs in young, healthy, immunocompetent patients—such as this patient.3
The portal of entry in nearly half of type II NSTI is unknown; minor local trauma is often suspected.4 However, cases have been reported in which the only identifiable source was a preceding sore throat.4 The origin of this patient’s GAS remains unknown, but perhaps his pharyngitis led to transient bacteremia, which then seeded his injured thigh muscle. An in vitro model demonstrated that injured muscles increase surface expression of the cytoskeletal protein vimentin, which binds GAS.5 Exotoxins and endotoxins produced by S pyogenes may lead to microvascular thrombosis, tissue ischemia, liquefactive necrosis, and systemic release of cytokines followed by systemic illness, multiorgan dysfunction, and death.6
The Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score was developed to aid in early diagnosis of NSTI.7 It was derived from a series of 2,555 patients admitted with cellulitis or abscesses at a single institution. Scores > 8 have a positive predictive value of 93% for NSTI. This patient had a LRINEC score of 9. Radiographs or computed tomography scans may demonstrate soft-tissue air collections but lack sensitivity and are often nondiagnostic.8,9 T1-weighted magnetic resonance imaging can delineate the anatomic extent of soft-tissue infections but is time consuming and may delay treatment.10 When the pretest probability is high, proceeding directly to the OR for direct visualization and possible debridement is advisable. Histologic features of necrotizing fasciitis include inflammation with polymorphonuclear cells and necrosis of the subcutaneous fat and fascia with relative sparing of the muscle.11Necrotizing soft-tissue infection requires early surgical debridement and broad-spectrum antibiotic coverage. Without surgical debridement, the mortality rate approaches 100%.2 Antibiotics should include activity against Gram-positive, Gram-negative, and anaerobic organisms. The duration of antibiotic therapy has not been defined and is dependent on the patient’s clinical status. Adjunctive treatment options may include IV immunoglobulin and hyperbaric oxygen therapy, although the data supporting their utility are limited.12,13
Conclusion
Despite the LRINEC scoring systems and advanced imaging, necrotizing fasciitis remains challenging to diagnose in a timely manner. In this case, close monitoring of the patient facilitated timely evaluation and treatment of a fatal disease.