Chapter 27 Necrotizing Fasciitis

Highlights

• Necrotizing fasciitis is a rare but potentially lethal condition that requires

early recognition and aggressive surgical treatment.

• The Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) criteria use

routine blood test results that can discriminate between necrotizing fasciitis

and severe cellulitis or abscess. The LRINEC criteria still need to be validated

in a larger trial in an external setting before widespread use can be

recommended.

• In a small single-center retrospective study, CT scanning was found to be

100% sensitive with a 100% negative predictive value for necrotizing soft

tissue infections, indicating that CT may be helpful in ruling out necrotizing

fasciitis in the ED.

Background

Necrotizing fasciitis is a rapidly progressive infection involving the fasciaand subcutaneous tissue. Differentiating necrotizing fasciitis from otherskin and soft tissue infections (Figure 27.1) is important in the emergencydepartment (ED), because while necrotizing fasciitis is a rare disease, it resultsin considerable morbidity and mortality. By some reports, mortality fromnecrotizing fasciitis can approach 34%. Necrotizing fasciitis is a surgicallytreated disease, and early recognition and debridement of necrotic fasciaand other involved areas are major determinants of overall outcome (Figure27.2). A delay in debridement has been associated with poorer survival.

Early on, necrotizing fasciitis can be difficult to distinguish from otherforms of soft tissue infections, such as cellulitis and abscess. While computedtomography (CT), magnetic resonance imaging (MRI), and ultrasound havebeen shown to be useful in distinguishing necrotizing fasciitis from otherclinical entities, choice of which patients to perform imaging studies on hasbeen a source of controversy.

Evidence-Based Emergency Care: Diagnostic Testing and Clinical Decision Rules, Second Edition.Jesse M. Pines, Christopher R. Carpenter, Ali S. Raja and Jeremiah D. Schuur.© 2013 John Wiley & Sons, Ltd. Published 2013 by John Wiley & Sons, Ltd.

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228 Chapter 27: Necrotizing Fasciitis

ANATOMY

Epidermis ErysipelasImpetigoFolliculitisEcthymaFurunculosisCarbunculosis

Cellulitis

Necrotizingfasciitis

Myonecrosis(clostridial andnon-clostridial)

Dermis

Skin

Superficial fasciaSubcutaneous tissueSubcutaneous fat,nerves, arteries, veinsDeep fascia

Muscle

SYNDROME

Figure 27.1 Schematic of the different layers of the skin and the correspondinginfections associated with each layer.

(a) (b)

Figure 27.2 (a) A suspected case of necrotizing fasciitis. Left foot shown with oozingwound, dusky skin, and bullae formation. (b) Surgical exploration resulted in extensivedebridement. (Reproduced from [5], Hall et al Principles of Critical Care 3rd edition,Copyright 2005, with permission of The McGraw-Hill Companies).

Chapter 27: Necrotizing Fasciitis 229

Clinical question

Can laboratory tests be reliably used in the ED to distinguish necrotizing fasciitisfrom other skin and soft tissue infections?The Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) investi-gators developed a scoring system to differentiate necrotizing fasciitis fromother skin and soft tissue infections.1 They derived the LRINEC scoring sys-tem in a retrospective cohort of 314 patients and validated it in 140 patientsin two teaching hospitals in Singapore. They included 140 patients who hadnecrotizing fasciitis and 309 patients with severe cellulitis or abscesses. Theyfound that WBC, hemoglobin, sodium, glucose, creatinine, and C-reactiveprotein were associated with a diagnosis of necrotizing fasciitis. They con-structed the LRINEC score through conversion of the independent predictorsof necrotizing fasciitis into an integer scoring system. This scoring system isdetailed in Table 27.1.

Using a cutoff of 6 points or higher, there was a positive predictive valueof 92% and a negative predictive value of 96%. The authors did not reportsensitivities and specificities in their results section. The area under the ROCcurve was 0.98 in the derivation set and 0.976 in the validation cohort,showing a high degree of accuracy in differentiating necrotizing fasciitis fromcellulitis or abscess.

In 2009, a single-center retrospective study was published from Australiathat aimed to externally validate the LRINEC.2 The authors calculated theperformance of a LRINEC score of ≥6 compared with the findings ofa surgical biopsy. In 28 patients who were identified with an admission

Table 27.1 The LRINEC score to differentiatenecrotizing fasciitis from severe cellulitis

Variable, units Score

C-reactive protein,mg/L ≥150

4

WBC (per mm3) 15–25 1WBC (per mm3) >25 2Hemoglobin 11–13.5 1Hemoglobin <11 2Sodium, mmol/L <135 2Creatinine, mg/dL >1.6 2Glucose, mg/dL <180 1

Source: A score ≥6 is a positive test.WBC = white blood cell.

230 Chapter 27: Necrotizing Fasciitis

diagnosis of necrotizing fasciitis, 10 had biopsy-proven necrotizing fasciitis.In this small group of patients using a score ≥6, the LRINEC score had asensitivity of 80%, a specificity of 67%, a positive predictive value of 57%,and a negative predictive value of 86% in distinguishing the patients withproven necrotizing fasciitis from those with severe soft tissue infections. Theauthor concluded that at this cutoff level, the LRINEC score would have onlyminimal effect on posttest probability for having necrotizing fasciitis.

In another 2010 study in France, a LRINEC ≥6 was retrospectively appliedto risk-stratify patients for the diagnosis of necrotizing fasciitis.3 Threecriteria were used: time from initiation of antibiotics to regression of ery-thema, duration of fever, and occurrence of complications (abscess, surgery,septic shock, necrotizing fasciitis, death, and transfer to intensive care).There were several potential predictor variables, including a LRINEC score≥6 at admission. In 50 patients, the authors reported that the complicationrate was higher for patients with a LRINEC score ≥6 (54%) than for patientswith a score <6 (12%, P = 0.008). However, a LRINEC score ≥6 did notappear to be related to an increased duration of erythema or fever.

Clinical question

What are the sensitivity and specificity of CT to rule out necrotizing fasciitis?A recent study investigated the sensitivity of CT to detect necrotizingfasciitis in a single academic medical center from January 2003 to April2009 (all patients were scanned with either 16- or 64-section helical CT).4

They considered a CT result positive if inflamed and necrotic tissue wasdetected with or without gas or fluid collections. The criterion standard fornecrotizing fasciitis was a necrotizing soft tissue infection found on surgicalexploration and pathological analysis, while the diagnosis was excluded ifsurgical exploration or pathological analysis did not find either, or if thepatient improved without surgical exploration. In the 67 patients meetinginclusion criteria, 58 had a surgical exploration, and necrotizing infectionswere found in 25 (43% of the sample). The remainder either had non-necrotizing infections on exploration (33) or were treated non-operativelyand their symptoms resolved. The authors reported that the sensitivity ofCT was 100%, the specificity was 81%, the positive predictive value was76%, and the negative predictive value was 100%. The authors concludedthat a negative CT reliably excludes the diagnosis of necrotizing soft tissueinfections.

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Comment

The LRINEC score had good discrimination in detecting clinically earlycases of necrotizing fasciitis in the derivation and validation cohorts in twoacademic medical centers in Singapore. However, it was not shown to beparticularly helpful in the small Australian study, while it was found to be apredictor of complications in a somewhat larger French study (50 patients).Given the high specificity of the LRINEC to differentiate necrotizing fasciitisfrom other less severe infections, ED physicians may consider using theLRINEC scoring system or the laboratory abnormalities detailed in thescoring system along with their clinical evaluation in identifying high-riskpatients in whom to obtain surgical consultation or further diagnostic studiesto rule out necrotizing fasciitis. We would not recommend using the LRINECto rule out necrotizing fasciitis.

In a single-center study, multidetector CTs were able to reliably distinguishpatients who had necrotizing soft tissue infections. Although it was a smallsample (67 patients), CT showed a perfect ability to rule out necrotizingfasciitis. While we believe that additional studies should be done to confirmthese study findings, at this time, we recommend CT as the initial test ofchoice to rule out necrotizing fasciitis in the ED.

References1. Wong CH, Khin LW, Heng KS et al. The LRINEC (Laboratory Risk Indicator for

Necrotizing Fasciitis) score: A tool for distinguishing necrotizing fasciitis fromother soft tissue infections based on routine laboratory testing. Critical CareMedicine. 2004; 32(7): 1535–41.

2. Holland MJ. Application of the Laboratory Risk Indicator in Necrotising Fasciitis(LRINEC) score to patients in a tropical tertiary referral centre. Anaesthesia andIntensive Care. 2009; 37: 588–92.

3. Corbin V, Vidal M, Beytout J et al. [Prognostic value of the LRINEC score (Labora-tory Risk Indicator for Necrotizing Fasciitis) in soft tissue infections: A prospectivestudy at Clermont-Ferrand University hospital]. Annales de Dermatologie et deVenereologie. 2010 Jan; 137(1): 5–11. [Article in French]

4. Zacharias N, Velmahos GC, Salama A et al. Diagnosis of necrotizing soft tissueinfections by computed tomography. Archives of Surgery. 2010; 145: 452–5.

5. Hall JB, Schmidt GA, Wood L. Principles of critical care. 3rd ed. New York:McGraw-Hill Companies; 2005.