BrownSound POCUS for Diagnosis of Necrotizing Fasciitis
“Necrotizing fasciitis is characterized by erythema with ill-defined borders, severe pain and tenderness, and excruciating pain out of proportion to the presenting symptoms.”
Necrotizing fasciitis is a life-threatening soft tissue infection that causes necrosis of the muscle fascia and subcutaneous tissues. It often occurs after invasive procedures or minor trauma, and it usually affects the extremities, perineum, and trunk [1,2]. Necrotizing fasciitis is characterized by erythema with ill-defined borders, severe pain and tenderness, and excruciating pain out of proportion to the presenting symptoms. Later in the disease course, blisters, hemorrhagic bullae, and crepitus may be present. The most common predisposing risk factors are diabetes mellitus, immune suppression, end-stage renal failure, and liver cirrhosis [2]. This condition has high morbidity and mortality rates and time to surgical debridement and removal of necrotic tissue is of the essence. Unfortunately, up to 25% of patients with necrotizing fasciitis are misdiagnosed highlighting the importance of prompt evaluation and diagnosis [3].
Necrotizing fasciitis is often diagnosed clinically, but imaging may be helpful in early stages of the disease and to help differentiate from cellulitis. CT, or less commonly MRI, is the mainstay imaging modality for this condition, but time to transport and lack of availability in some emergency departments are limiting factors. Furthermore, using CT exposes patients to ionizing radiation and intravenous contrast. Point-of-care ultrasound (POCUS) is faster and has shown efficacy in diagnosing soft tissue infections [4]. Several studies have specifically evaluated the sensitivity and specificity of POCUS in diagnosing necrotizing fasciitis [5-8]. Two prospective studies demonstrated a sensitivity of 88-100% and specificity of 93-98% for POCUS diagnosis compared to CT and/or surgical impression [5,8].
Necrotizing fasciitis findings on POCUS can be summarized using the “STAFF” mnemonic:
1. S/T for subcutaneous thickening.
2. A for air or emphysema in the subcutaneous tissue, which presents as “dirty shadowing”.
3. FF for fascial fluid layer greater than or equal to 2mm.
https://coreem.net/core/ultrasound-diagnosis-of-necrotizing-soft-tissue-infections/
These pathologic findings can be seen in Figure 2, with Figure 1 showing normal ultrasound findings. Soft tissue gas appears as echogenic foci with posterior dirt shadowing; this is often a late finding of necrotizing fasciitis [8]. Other soft tissue infections like cellulitis may be clinically indistinguishable from necrotizing fasciitis. The presence of fluid tracking along the deep fascial layers is indicative of necrotizing fasciitis rather than cellulitis [8].
It is important to note that if there is high clinical suspicion for necrotizing fasciitis and the ultrasound study is negative, advanced imaging such as CT maybe warranted as patients may require emergency surgical exploration and debridement. Overall, POCUS is a valuable tool for evaluating patients with suspected necrotizing fasciitis and hemodynamically unstable patients unable to undergo CT imaging.
Author: Ogechi Ezemma is a fourth-year medical student at The Warren Alpert Medical School of Brown University.
Faculty Reviewer: Kristin Dwyer, MD, MPH is Assistant Professor of Emergency Medicine at Warren Alpert Medical School of Brown University and Emergency Ultrasound Fellowship Director.
References
1. Wallace HA, Perera TB. Necrotizing Fasciitis. In: StatPearls. Treasure Island (FL): StatPearls Publishing; February 21, 2023.
2. Lancerotto L, Tocco I, Salmaso R, Vindigni V, Bassetto F. Necrotizing fasciitis: classification, diagnosis, and management. J Trauma Acute Care Surg. 2012;72(3):560-566. doi:10.1097/TA.0b013e318232a6b3
3. Hefny AF, Eid HO, Al-Hussona M, Idris KM, Abu-Zidan FM. Necrotizing fasciitis: a challenging diagnosis. Eur J Emerg Med. 2007;14(1):50-52. doi:10.1097/01.mej.0000228447.48276.7b
4. Subramaniam S, Bober J, Chao J, Zehtabchi S. Point-of-care Ultrasound for Diagnosis of Abscess in Skin and Soft Tissue Infections. Acad Emerg Med. 2016;23(11):1298-1306. doi:10.1111/acem.13049
5. Yen ZS, Wang HP, Ma HM, Chen SC, Chen WJ. Ultrasonographic screening of clinically-suspected necrotizing fasciitis. Acad Emerg Med. 2002;9(12):1448-1451. doi:10.1111/j.1553-2712.2002.tb01619.x
6. Lin CN, Hsiao CT, Chang CP, et al. The Relationship Between Fluid Accumulation in Ultrasonography and the Diagnosis and Prognosis of Patients with Necrotizing Fasciitis. Ultrasound Med Biol. 2019;45(7):1545-1550. doi:10.1016/j.ultrasmedbio.2019.02.027
7. Magalhães L, Martins SRP, Nogué R. The role of point-of-care ultrasound in the diagnosis and management of necrotizing soft tissue infections. Ultrasound J. 2020;12(1):3. Published 2020 Jan 23. doi:10.1186/s13089-020-0153-4
8. Lahham S, Shniter I, Desai M, et al. Point of Care Ultrasound in the Diagnosis of Necrotizing Fasciitis. Am J Emerg Med. 2022;51:397-400. doi:10.1016/j.ajem.2021.10.033