Diagnosis

The diagnosis is clinical. If there is a strong clinical suspicion of the diagnosis, then urgent exploratory surgery is required - regardless of any test results. (1)

There must be a low threshold for diagnosis if the following features are present: (2)

• skin changes:
  • erythema
  • low-grade cellulitis
  • cyanotic discolouration or ecchymosis
  • epidermolysis or bullae
  • skin necrosis
  • anaesthesia of skin beyond the margin of surface colour change
  • crepitus
• a hard, indurated feel to the subcutaneous tissue which is present beyond the visible limits of skin involvement
• pain out of proportion to the visible surface changes
• signs of systemic toxicity with altered mental status, fever, shock or acute renal failure
• minimal improvement despite initial antibiotic therapy

A number of blood investigations may support the diagnosis. (3) Imaging should not delay the patient progressing to theatre for rapid, adequate debridement.

However, imaging may show soft-tissue gas, which is highly suggestive of the diagnosis and may also demonstrate abnormalities in the involved soft tissue. (2) Computed tomography (CT) is typically the radiological test of choice (1) although both CT and magnetic resonance imaging (MRI) offer higher sensitivity than x-ray. However, MRI may be difficult to organise in an emergency and is not recommended as the first-line imaging technique. (MRI scans may help to show the extent of tissue involvement but may not be accurate and should not delay surgery.)

(Do not use a plain x-ray to rule out the diagnosis because X-ray is frequently normal during the early stages. (4) )

Bedside ultrasound may be performed if the patient is clinically unstable. (2)

Reference:

1. Diab J, Bannan A, Pollitt T. Necrotising fasciitis. BMJ. 2020 Apr 27;369:m1428.
2. Sartelli M, Guirao X, Hardcastle TC, et al. 2018 WSES/SIS-E consensus conference: recommendations for the management of skin and soft-tissue infections. World J Emerg Surg. 2018 Dec 14;13:58.
3. Anaya DA, Dellinger EP; Necrotizing soft-tissue infection: diagnosis and management. Clin Infect Dis. 2007 Mar 1;44(5):705-10.
4. Hua C, Urbina T, Bosc R, et al. Necrotising soft-tissue infections. Lancet Infect Dis. 2023 Mar;23(3):e81-e94.