Differentiating Necrotizing Fasciitis from other soft tissue infections

Necrotizing fasciitis can be misdiagnosed in about 75% of the cases in the intial stage of the disease. The most consistent feature of early necrotizing fasciitis is the pain out of proportion to swelling or erythema. Other features helping to differentiate from other soft tissue infections are:

  1. Tenderness extending beyond the apparent involved area (due to toxins and enzymes spreading along the fascia below the skin)
  2. Indistinct margins of involvement
  3. Lymhangitis is often absent (infection is in deep fascia rather than skin)
  4. Rapidly progressive despite use of antibiotics

Fever may be present in only 40% of the cases due to masking effect of NSAIDs, steroids and antibiotics. Clinicians should have a higher index of suspicion when patients with diabetes or liver cirrhosis present with cutaneous infection.

finger test for necrotizing fasciitis

Necrotizing fasciitis can be differentiated from cellulitis using ABCDEFG mnemonic.

Adenitis (also lymphangitis) often absent

Bullae (Serous – intermediate stage; Hemorrhagic – late stage)

Crepitus (Late stage)

Dishwater-colored fluid discharge

Extension of tenderness beyond area of involvement and Expanding despite antibiotic use

Finger test

Greater pain than swelling and erythema

Another ABCDE mnemonic for summarizing the relevant clinical features and diagnostic criteria.

  • A ā€“ Anaerobic, Aerobic, Adult, Antibiotics refractory
  • B ā€“ Bacterial synergistic gangrene, group B streptococcus, and Blood count higher than normal
  • C ā€“ Cellulitis, Crepitus, and Coagulopathy
  • Dā€”Dermal gangrene, Delay in presentation almost fatal
  • E ā€“ Erythema with spreading Edema

Stages of Necrotizing Fasciitis

Warm to palpationBlister or Bullae (serous)Hemorrhagic bullae
ErythemaSkin fluctuanceSkin anesthesia
Tenderness to palpation (extending beyond apparent areas of skin involvement)Skin indurationCrepitus
SwellingSkin necrosis with dusky discoloration progressing to frank gangrene

STAFF mnemonic for USG diagnosis to diagnose necrotizing fasciitis

  1. Subcutaneous Thickening
  2. Air [hyperechoic (white) patches, with indistinct, “dirty” shadows]
  3. Fascial Fluid

LRINEC score mnemonic for necrotizing fasciitis


  1. Asif Zubair Bhatti, MD, FRCS, FCPS, James Mcdiarmid, FRCS, FRCS (PLAST), MSc, Necrotizing Fasciitis: An Aid to Prompt Diagnosis, Aesthetic Surgery Journal, Volume 26, Issue 1, January 2006, Page 54, https://doi.org/10.1016/j.asj.2005.11.005
  2. Goh T, Goh LG, Ang CH, Wong CH. Early diagnosis of necrotizing fasciitis. Br J Surg. 2014 Jan;101(1):e119-25. doi: 10.1002/bjs.9371. Epub 2013 Nov 29. PMID: 24338771.
  3. https://med.emory.edu/departments/emergency-medicine/sections/ultrasound/image-of-the-fortnight/miscellaneous/necfasc.html

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