A 52 year old female presents via EMS after being found down outside. Medical history is notable for reported insulin-dependent diabetes. The patient is found to have altered mental status on presentation, and is unable to provide further history. Vitals are notable for heart rate of 138, blood pressure 92/50, and temperature of 102.1F; POC blood glucose shows blood sugar over 600. On physical exam, patient is found to have hemorrhagic bullae of her left lower extremity with palpable crepitus. Labs in the emergency department are notable for WBC of 36k, anion gap of 30, and lactate of 2.5.
Point-of-care ultrasound of the left lower extremity is shown below. What is the most likely diagnosis, and what findings on the ultrasound imaging support this?
Answer: Necrotizing Fasciitis; “dirty shadowing”
- Subcutaneous air results will appear as hyperechoic lines on soft tissue ultrasound, with “dirty shadowing” of tissue/structures deep to the air.
- These hyperechoic lines are seen at the borders between air and soft-tissue, due to a scattering of ultrasound waves that occurs at these boundaries.
- Additional findings of necrotizing fasciitis on ultrasound include a “cobblestone” appearance of the subcutaneous tissue with abnormal fluid collections. These findings are not specific to necrotizing fasciitis, however.
References:
Tso DK, Singh AK. Necrotizing fasciitis of the lower extremity: imaging pearls and pitfalls. Br J Radiol. 2018 Jul;91(1088):20180093. doi: 10.1259/bjr.20180093. Epub 2018 Mar 28. PMID: 29537292; PMCID: PMC6209465.
Buttar S, Cooper D Jr, Olivieri P, Barca M, Drake AB, Ku M, Rose G, Siadecki SD, Saul T. Air and its Sonographic Appearance: Understanding the Artifacts. J Emerg Med. 2017 Aug;53(2):241-247. doi: 10.1016/j.jemermed.2017.01.054. Epub 2017 Mar 31. PMID: 28372830.
