Necrotizing fasciitis producing gas in the soft tissues as seen on CT scan Necrotizing fasciitis as seen on ultrasound Micrograph of necrotizing fasciitis, showing necrosis (center of image) of the dense connective tissue, i.e. fascia, interposed between fat lobules (top-right and bottom-left of image), H&E stain Early diagnosis is difficult, as the disease often looks early on like a simple superficial skin infection. While a number of laboratory and imaging modalities can raise the suspicion for necrotizing fasciitis, none can rule it out. The gold standard for diagnosis is a surgical exploration in a setting of high suspicion. When in doubt, a small incision can be made into the affected tissue, and if a finger easily separates the tissue along the fascial plane, the diagnosis is confirmed and an extensive debridement should be performed. Medical imaging Imaging has a limited role in the diagnosis of necrotizing fasciitis. The time delay in performing imaging is a major concern. Plain radiography may show subcutaneous emphysema (gas in the subcutaneous tissue), which is strongly suggestive of necrotizing changes, but it is not sensitive enough to detect all the cases, because necrotizing skin infections caused by bacteria other than clostridial infections usually do not show subcutaneous emphysema. If the diagnosis is still in doubt, computed tomography (CT) scans and magnetic resonance imaging (MRI) are more sensitive modalities than plain radiography. However, both the CT scan and MRI are not sensitive enough to rule out necrotizing changes completely. CT scan may show fascial thickening, edema, subcutaneous gas, and abscess formation. In MRI, when fluid collection with deep fascia involvement occurs, thickening or enhancement with contrast injection, necrotizing fasciitis should be strongly suspected. Meanwhile, ultrasonography can show superficial abscess formation, but is not sensitive enough to diagnose necrotizing fasciitis. CT scan is able to detect about 80% of cases, while MRI may pick up slightly more. Scoring system A white blood cell count greater than 15,000 cells/mm3 and serum sodium level less than 135 mmol/l have a sensitivity of 90% in detecting the necrotizing soft tissue infection. It also has a 99% chance of ruling out necrotizing changes if the values have shown otherwise. Various scoring systems are being developed to determine the likelihood of getting necrotizing fasciitis, but a scoring system developed by Wong and colleagues in 2004 is the most commonly used. It is the laboratory risk indicator for necrotizing fasciitis (LRINEC) score, which can be used to stratify by risk those people having signs of severe cellulitis or abscess to determine the likelihood of necrotizing fasciitis being present. It uses six laboratory values: C-reactive protein, total white blood cell count, hemoglobin, sodium, creatinine, and blood glucose. A score of 6 or more indicates that necrotizing fasciitis should be seriously considered. The scoring criteria are: * CRP (mg/L) ≥150: 4 points * WBC count (×103/mm3) * 25: 2 points * Hemoglobin (g/dl) * >13.5: 0 points * 11–13.5: 1 point * 141: 2 points * Glucose (mmol/l) >10: 1 point However, the scoring system has not been validated. The values would be falsely positive if any other inflammatory conditions are present. Therefore, the values derived from this scoring system should be interpreted with caution. About 10% of patients with necrotizing fasciitis in the original study still had a LRINEC score <6. A validation study showed that patients with a LRINEC score ≥6 have a higher rate of both death and amputation.
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