Just another cellulitis, or not?

This is part of a recurring series examining landmark articles in Emergency Medicine, based on ALiEM’s 52 Articles.

Discussing: Wong, C. Khin, L. Kien-Seng, H. Kok-Chai, T. Cheng-Ooi, L. “The LRINEC (Laboratory Risk Indicator for Necrotizing Fasciitis) score: A tool for distinguishing necrotizing fasciitis from other soft tissue infections.” Crit Care Med, 2004, Vol 32(7). 1535-1541.

Main Points:

  1. Developed in a 2004 retrospective observational study, the LRINEC score uses routine laboratory studies alone (CBC, BMP, CRP) to stratify patients with soft tissue infections into high-, moderate-, and low-risk for necrotizing fasciitis.
  1. Using a cut-off value of 6, the PPV was 92% and NPV was 96%; though approximately 10% of patients with necrotizing fasciitis still had a LRINEC score < 6, stressing that this is only a diagnostic adjunct for what is ultimately a clinical diagnosis.

Background:

Necrotizing fasciitis is a rare, rapidly progressive soft tissue infection that is potentially limb and life threatening. Delayed recognition correlates with a higher mortality rate, though early in its course, the disease may be difficult to distinguish from cellulitis or abscess. The purpose of this study was to develop a diagnostic scoring system to differentiate necrotizing fasciitis from other soft tissue infections.

Details:

This was a retrospective observational study divided into a developmental cohort of 314 patients and validation cohort of 140 patients at two teaching tertiary care hospitals in Singapore. The developmental cohort consisted of 89 consecutive patients admitted for necrotizing fasciitis and 225 control patients randomly selected from patients admitted with severe cellulitis or abscess during that same period.

The definitive diagnosis of necrotizing fasciitis was based on characteristics during operative exploration: the presence of grayish necrotic fascia, demonstration of a lack of resistance of normally adherent muscular fascia to blunt dissection, lack of bleeding of the fascia during dissection, and the presence of foul-smelling “dishwater” pus. The diagnosis of severe cellulitis or abscess was based on clinical impression of severe infection in documentation, the use of parenteral antibiotics for > 48 hours, and abscess (when present) requiring surgical debridement.

Thirteen variables from biochemical and hematologic tests done on admission were analyzed, including age, gender, total WBC, hemoglobin, platelet count, serum sodium, potassium, chloride, glucose, urea, creatinine, CRP, and ESR. To construct a diagnostic scoring system, these factors were entered as categorical variables. Six criteria – total WBC, sodium, glucose, serum creatinine, and CRP – were found to be independently predictive of necrotizing fasciitis, each worth 0, 1, 2, or 4 points for a total of 13 points.

This score was then retrospectively “externally validated” on a separate cohort of 56 consecutive patients with necrotizing fasciitis and 84 control patients with severe cellulitis or abscess seen at a separate hospital during a similar time period.

Patients were classified into three groups: low (LRINEC < or = 5), moderate (LRINEC 6-7), or high (LRINEC > or = 8) risk. These risk groups corresponded to a probability of developing necrotizing soft tissue infections of <50%, 50-75%, and >75%, respectively. A LRINEC score greater than or equal to 6 yielded a PPV of 92% and NPV of 96%. Eighty-nine and 92.9% of patients with necrotizing fasciitis had a LRINEC score of 6 or greater in the developmental and validation cohorts, respectively; whereas only 3.1% and 8.4% of control patients in the corresponding cohorts had a score of 6 or greater. The authors concluded that patients above this cutoff of 6 should be carefully evaluated for the presence of necrotizing fasciitis.

Commentary:

The advantage of the LRINEC score, as the authors mention, is that the variables used are routinely obtained when assessing severe soft tissue infections (CBC, BMP, CRP). Another cited advantage is the potential to detect clinically early cases of necrotizing fasciitis.

There are several limitations. Approximately 15% of the data sets were incomplete with respect to the CRP, and yet in the final model, CRP is the most heavily weighted (four points, with no other variable being weighted more than two points). Other potentially useful laboratory markers, such as CK, were not included in the analysis.

While the LRINEC score may be useful in identifying patients at high risk for necrotizing fasciitis, it is less useful in ruling out the diagnosis. In this study, approximately 10% of patients with necrotizing fasciitis had a LRINEC score of less than 6. This highlights the importance of recognizing the clinical features (toxic-appearing patient, pain out of proportion to skin findings, crepitus, rapid progression, bullous lesions, skin necrosis) of a disease that is ultimately diagnosed only in the operating room.

Results from subsequent studies have been even less optimistic. Based on the cutoff of 6, a small retrospective study in 2009 by MJ Holland yielded a sensitivity of 80%, specificity of 67%, PPV 57%, NPV 86% for diagnosing necrotizing fasciitis. A larger retrospective study by Liao et al. in 2012 demonstrated a sensitivity of 59.2%, specificity of 83.8%, PPV 37.9%, and NPV 92.5%. Finally, there have been no prospective trials yet validating the LRINEC score or demonstrating implementation of the score leads to earlier diagnosis or improved outcomes.

How do/will you use the LRINEC score?

Relevant articles:

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 May; 44(5):928-31.

Liao, Chun-I. Lee, Yi-Kung. Su, Yung-Cheng. Chuang, Chin-Hsiang. Wong, Chun-Hing. “Validation of the laboratory risk indicator for necrotizing fasciitis (LRINEC) score for early diagnosis of necrotizing fasciitis.” Tzu Chi Medical Journal. 2012 24: 73-76.

Holland MJ. “Application of the Laboratory Risk Indicator in Necrotising Fasciitis (LRINEC) score to patients in a tropical tertiary referral centre.” Anaesth Intensive Care. 2009 Jul;37(4):588-92.

Chan, T. Yaghoubian, A. Rosing, D. Kaji, A. deVirgilio, C. “Low sensitivity of physical examination findings in necrotizing soft tissue infection is improved with laboratory values: a prospective study.” Am J Surg. 2008 Dec; 196(6):926-30.

 

Resident author: Roger Wu, MD
Faculty reviewer: Matthew Siket, MD, MS

Leave a Reply