Necrotizing soft tissue infection (a spectrum of disease including necrotizing fasciitis, necrotizing cellulitis, and necrotizing myositis) is a highly lethal bacterial illness. Without emergent surgical debridement, the mortality rate for this condition approaches 100%. Even with early surgical debridement, broad spectrum antimicrobial therapy, and aggressive physiologic support, the mortality rate for necrotizing soft tissue infection is approximately 24%. Despite the seriousness of necrotizing soft tissue infection, it is often missed in its early stages, perhaps because of clinicians’ inexperience with this relatively rare disease. There are only an estimated 500 to 1500 cases per year in the US – around 3.5 cases per 100,000 patients. A standardized diagnostic tool called the Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC score) has been demonstrated to be highly specific, and its use can help save lives by aiding in the early diagnosis of this serious condition.
Given the significant morbidity and mortality of necrotizing soft tissue infections, providers should have a high index of suspicion with certain history and physical exam findings. Risk factors for necrotizing infections include trauma, injection drug use, and chronic debilitating conditions like HIV, alcoholism, diabetes, obesity, liver cirrhosis, and heart disease (a population of patients seen disproportionately by trauma units). The most common early symptoms on admission are tenderness and pain disproportionate to the patient’s clinical appearance, erythema, and tachycardia. Interestingly, only a third of patients in one large case series presented with fever. Patients often deteriorate quickly, showing tense edema over affected regions, ecchymosis, blistering/bullae, and crepitus from subcutaneous gas. Patients can progress rapidly into severe sepsis, and the infection spreads rapidly along facial planes in just hours. In the setting of a strongly positive history and physical, further diagnostic studies should not delay the initiation of surgical management. Only gross surgical and pathological findings of extensive tissue destruction, thrombosis of blood vessels, abundant foul-smelling exudate, bacteria spreading along fascial planes, and infiltration of acute inflammatory cells can establish the formal diagnosis.
Imaging may also be used to aid in the diagnosis necrotizing soft tissue infections. The visualization of subcutaneous air on X-Ray, CT, or MRI is a specific but insensitive indicator for necrotizing infection. Soft tissue swelling is the most common finding and is very nonspecific. The absence of gas on diagnostic imaging should not delay surgical intervention in the setting of high clinical suspicion.
Once clinical suspicion has been aroused, six easily obtained lab values can be plugged into LRINEC score to help determine the probability of necrotizing soft tissue infections:
A score of ≥6 on the LRINEC is associated with increased risk for both mortality and amputation from necrotizing soft tissue disease. It has a positive predictive value of 92% and a negative predictive value of 96%. It is a highly specific but a relatively insensitive test. It can be appropriately used to confirm a clinical suspicion of necrotizing soft tissue infection. The only way to prevent significant morbidity and mortality from necrotizing soft tissue infection is to quickly begin treatment with early surgical debridement, broad spectrum antibiotics, and aggressive physiologic correction of sepsis. A LRINEC score of 6 or greater can and should help expedite the decision to begin the definitive operative management of necrotizing soft tissue infection.
References:
1. Anaya DA, Dellinger EP. Necrotizing soft tissue infection: diagnosis and management. Clin Infect Dis. 2007;44(5):705–10. Epub 2007 Jan 22.
2. Wong CH, Khin LW, Heng KS, Tan KC, Low CO. The LRINEC (laboratory risk indicator for necrotizing fasciitis) score: a tool for distinguishing necrotizing fasciitis from other soft tissue infections. Crit Care Med. 2004;32(7):1535–41.
3. Su YC, Chen HW, Hong YC, Chen CT, Hsiao CT, Chen IC. Laboratory risk indicator for necrotizing fasciitis score and the outcomes. ANZ J Surg. 2008 Nov;78(11):968-72.
4. Up to Date: Necrotizing Soft Tissue infections
Post Submitted by John Hayes - MS4
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