Infectious Disease · Soft Tissue Infections
The facts most likely to be tested
The definitive treatment for necrotizing fasciitis is emergent surgical debridement and should never be delayed for imaging.
Physical exam findings often show pain out of proportion to physical exam findings in the early stages of infection.
The presence of crepitus or subcutaneous emphysema on physical exam or imaging is highly specific for gas-forming organisms like *Clostridium perfringens*.
The LRINEC score (Laboratory Risk Indicator for Necrotizing Fasciitis) utilizes C-reactive protein, leukocyte count, hemoglobin, sodium, creatinine, and glucose to risk-stratify patients.
Type I necrotizing fasciitis is a polymicrobial infection typically involving a mix of aerobic and anaerobic bacteria often seen in patients with diabetes mellitus.
Type II necrotizing fasciitis is typically monomicrobial and most commonly caused by Group A Streptococcus (*Streptococcus pyogenes*).
Patients with necrotizing fasciitis frequently present with systemic toxicity, including hypotension, tachycardia, and altered mental status due to rapid progression to septic shock.
Vignette unlocked
A 54-year-old male with a history of poorly controlled diabetes presents to the emergency department with a 24-hour history of rapidly worsening right leg pain. On examination, the patient is febrile and tachycardic with a blood pressure of 90/60 mmHg. The right lower extremity shows erythema, edema, and dusky skin changes extending to the mid-thigh, with pain out of proportion to physical exam. Palpation reveals crepitus over the calf, and the patient appears confused.
What is the most appropriate next step in management?
Emergent surgical debridement
The patient presents with classic signs of necrotizing fasciitis, including crepitus and pain out of proportion to exam; the most critical step is immediate surgical intervention to remove necrotic tissue.
Full handout
High yield triage
Etiology / Epidemiology
Most common in diabetes mellitus and immunocompromised patients; often follows minor trauma or surgery.
Clinical Manifestations
Pain out of proportion to exam; crepitus and skin bullae are pathognomonic.
Diagnosis
Clinical diagnosis; surgical exploration is the gold standard.
Treatment
Immediate surgical debridement and broad-spectrum antibiotics.
Prognosis
High mortality; LRINEC score helps risk stratification.
Full handout
Epidemiology & Etiology
Predominantly affects patients with diabetes, peripheral vascular disease, or chronic alcohol use. Often caused by Group A Streptococcus (Type I) or polymicrobial flora (Type II). Entry is typically via minor skin breaks or surgical sites.
Pertinent Anatomy
Infection spreads rapidly along the superficial fascia plane, sparing the underlying muscle initially. This anatomical separation explains why skin findings often appear deceptively mild compared to deep tissue destruction.
Pathophysiology
Bacterial enzymes (hyaluronidase) facilitate rapid fascial plane dissection. This leads to thrombosis of subcutaneous vessels, causing tissue ischemia and necrosis. The resulting gas gangrene (in clostridial cases) produces subcutaneous air.
Clinical Manifestations
Early signs include pain out of proportion to physical exam. Look for rapidly spreading erythema, skin bullae, and crepitus. Systemic signs include septic shock and multi-organ failure.
Diagnosis
Diagnosis is primarily clinical; do not delay for imaging. Surgical exploration is the gold standard. The LRINEC score (Laboratory Risk Indicator for Necrotizing Fasciitis) uses CRP, WBC, hemoglobin, sodium, creatinine, and glucose to assess risk.
Treatment
Immediate surgical debridement is mandatory. Empiric therapy includes vancomycin plus piperacillin-tazobactam or a carbapenem. Do not delay surgery for imaging; hemodynamic stabilization is critical.
Prognosis
Mortality rates remain high, often exceeding 20-30%. Survivors frequently require amputation or extensive skin grafting. Monitor for sepsis and acute kidney injury.
Differential Diagnosis
Cellulitis: lacks pain out of proportion and systemic toxicity
Gas gangrene: presence of clostridial myonecrosis
Pyomyositis: infection localized to the muscle belly
Toxic shock syndrome: systemic hypotension without localized fascial necrosis
Erysipelas: superficial dermal infection with well-demarcated borders