- Written by Ethan Abbott
For this week’s question:
A 25 yo male with no PMH presents the SBH ED 2 with a painful “spider bite” on his left arm that has been present for 3 days. The patient reports pain, redness, and swelling at the site. He has attempted to open up the lesion with a needle, but without relief. On exam there is a 3 x 3 cm raised lesion that is tender to palpation, fluctuant, and mild surrounding erythema. You suspect there is an abscess present. You decide to use the ultrasound to confirm your suspicions. What is the utility of ultrasound in this scenario?
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Answer: The physical exam is not always reliable for distinguishing the presence of an abscess or drainable collection or differentiating the lesion from a cellulitis. Soft tissue point-of-care ultrasound has emerged as a method to help identify patients who may benefit from incision and drainage. But what is the sensitivity and specificity of ultrasound for distinguishing an abscess from a cellulitis?
A recent systematic review in the October 2017 Annals of Emergency Medicine entitled, “What Is the Utility of Ultrasonography for the Identification of Skin and Soft Tissue Infections in the Emergency Department?” found strong support for the use of ultrasound in these clinical scenarios. The authors found a sensitivity of 97% and specificity of 83% for identifying abscess versus cellulitis from a pooled analysis of 5 studies. The data was however, heterogeneous and did include a significant number of pediatric patients. These studies also did not address patient outcomes, antibiotic use, return visits, or hospital admissions.
Reference: Gottlieb M, Pandurangadu AV. What Is the Utility of Ultrasonography for the Identification of Skin and Soft Tissue Infections in the Emergency Department? Ann Emerg Med. 2017 Oct;70(4):580-582.