A Closer Look At A Rapid And Cost-Effective Alternative For Diagnosing Necrotizing Fasciitis

Necrotizing fasciitis is a severe life and limb-threatening infection of the fascia and subcutaneous tissues. Regardless of many advances in medical care, the mortality rate of necrotizing soft tissue infections has not decreased in the last 30 years and remains at 25 to 35 percent.^1,2 The mortality rate is directly related to the time to surgical intervention and early diagnosis and aggressive surgical intervention are the main factors leading to favorable outcomes.^3-8

Early diagnosis of necrotizing fasciitis is critical to reducing the mortality rate but differentiating this infection from other soft tissue infections, including cellulitis and abscess, can be very difficult. Characteristic early symptoms of necrotizing fasciitis are rapidly worsening pain out of proportion to exam findings, anxiety and diaphoresis, which is often associated with a recent break in the skin.⁹ Local erythema, edema and pain are the classic early signs of necrotizing fasciitis and are identical to other soft tissue infections.⁹ Authors have reported that low percentages, less than 50 percent, of patients exhibit the classic early signs and symptoms of necrotizing fasciitis.^3,5 Comorbid diseases leading to immune compromised states can contribute to atypical presentation of necrotizing fasciitis, leading to potential delays in diagnosis.¹⁰ 

The Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score emerged to address the critical need for early diagnosis of necrotizing fasciitis and the difficulty in distinguishing this disease from other soft tissue infections.¹¹ The LRINEC score is useful in distinguishing necrotizing infection from other soft tissue infections and offers a rapid and cost-effective alternative to other diagnostic modalities such as magnetic resonance imaging (MRI) and biopsy. 

One would determine the LRINEC score as follows:¹¹

1. C-reactive protein (CRP) > 150 mg/L: 4 points
2. White blood cell (WBC) count (x 103 mm³)
   • < 15: 0 points
   • 15-25: 1 point
   • >25: 2 points
3. Hemoglobin (g/dL)
   • >13.5: 0 points
   • 11-13.5: 1 point
   • <11: 2 points
4. Sodium < 135 mmol/L: 2 points
5. Creatinine > 1.6 mg/dL (141 mmol/L): 2 points
6. Glucose > 180 mg/dL (10 mmol/L): 1 point

A LRINEC score > 6 has a positive predictive value of 92 percent and a negative predictive value of 96 percent for necrotizing fasciitis, and should raise the suspicion of necrotizing fasciitis. A score > 8 is strongly predictive of necrotizing fasciitis with a positive predictive value of 93.4 percent and a 95 percent confidence interval.

One would classify patients into one of three groups based on their score:¹¹

Low risk: LRINEC score < 5, <50 percent risk for necrotizing fasciitis

Moderate risk: LRINEC score 6-7, 50-75 percent risk for necrotizing fasciitis

High risk: LRINEC score > 8, 75 percent risk for necrotizing fasciitis

While the LRINEC tool can be useful in separating early cases of necrotizing fasciitis from other non-necrotizing soft tissue infections, it is not without limitations. In Wong’s original study, approximately 10 percent of patients with a LRINEC score < 6 still had necrotizing fasciitis and subsequent studies have questioned the sensitivity of the LRINEC score to rule out cases of necrotizing fasciitis.^11-13 This highlights that the LRINEC score cannot rule out the diagnosis of necrotizing fasciitis. However, in cases of low clinical suspicion, a low LRINEC score can provide reassurance that a soft tissue infection is unlikely to be necrotizing. 

Given the high mortality rate associated with necrotizing fasciitis, one should maintain a low degree of clinical suspicion for the presence of this disorder. The LRINEC score is a useful tool to aid in diagnosis and management with emergent surgical intervention recommended for suspected cases. It is important to remember a LRINEC score > 6 is a reasonable cutoff to rule in necrotizing fasciitis but a value < 6 does not rule out the diagnosis.

References

1.      Anaya DA, McMahon K, Nathens AB, Sullivan SR, Foy H, Bulger E. Predictors of mortality and limb loss in necrotizing soft tissue infections. Arch Surg. 2005;140(2):151-157; discussion 158.

2.      Corona PS, Erimeiku F, Reverte-Vinaixa MM, Soldado F, Amat C, Carrera L. Necrotising fasciitis of the extremities: implementation of new management technologies. Injury. 2016;47(Suppl 3):S66-S71.

3.      McHenry CR, Piotrowski JJ, Petrinic D, Malangoni MA. Determinants of mortality for necrotizing soft-tissue infections. Ann Surg. 1995;221(5):558-563; discussion 563-555.

4.      Voros D, Pissiotis C, Georgantas D, Katsaragakis S, Antoniou S, Papadimitriou J. Role of early and extensive surgery in the treatment of severe necrotizing soft tissue infection. Br J Surg. 1993;80(9):1190-1191.

5.      Wong CH, Chang HC, Pasupathy S, Khin LW, Tan JL, Low CO. Necrotizing fasciitis: clinical presentation, microbiology, and determinants of mortality. J Bone Joint Surg Am. 2003;85-A(8):1454-1460.

6.      Bilton BD, Zibari GB, McMillan RW, Aultman DF, Dunn G, McDonald JC. Aggressive surgical management of necrotizing fasciitis serves to decrease mortality: a retrospective study. Am Surg. 1998;64(5):397-400; discussion 400-391.

7.      Roje Z, Roje Z, Matic D, Librenjak D, Dokuzovic S, Varvodic J. Necrotizing fasciitis: literature review of contemporary strategies for diagnosing and management with three case reports: torso, abdominal wall, upper and lower limbs. World J Emerg Surg. 2011;6(1):46.

8.      Kalaivani V, Hiremath BV, Indumathi VA. Necrotising soft tissue infection-risk factors for mortality. J Clin Diagn Res. 2013;7(8):1662-1665.

9.      Puvanendran R, Huey JC, Pasupathy S. Necrotizing fasciitis. Can Fam Physician. 2009;55(10):981-987.

10.    Sarani B, Strong M, Pascual J, Schwab CW. Necrotizing fasciitis: current concepts and review of the literature. J Am Coll Surg. 2009;208(2):279-288.

11.    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):1535-1541.

12.    Burner E, Henderson SO, Burke G, Nakashioya J, Hoffman JR. Inadequate sensitivity of laboratory risk indicator to rule out necrotizing fasciitis in the emergency department. West J Emerg Med. 2016;17(3):333-336.

13.    Wilson MP, Schneir AB. A case of necrotizing fasciitis with a LRINEC score of zero: clinical suspicion should trump scoring systems. J Emerg Med. 2013;44(5):928-931.