POCUS for Abscess - Is It Accurate?

Written by Clay Smith

Spoon Feed
Point of care ultrasound (POCUS) wasn’t better than physician judgment when they were certain an abscess was present, but it was of some value in equivocal cases, though far from a gold standard.

Why does this matter?
Back in ancient times, we used to stick an 18ga needle into an equivocal skin infection; aspiration of pus meant it was an abscess; no pus meant no abscess. POCUS offers a kinder, gentler approach to help us see below the surface. But is it accurate?

POCUS not exactly awesome for soft tissue…
This was a prospective study evaluating the impact of bedside ultrasound on skin/soft tissue infection (SSTI) management. In 1,216 patients, the physicians were uncertain if an abscess was present 8.6% of the time and certain one was present 91.4% of the time. When clinicians were certain, ultrasound added little to the diagnostic accuracy. In the 105 patients in which the clinician was uncertain, diagnostic accuracy of ultrasound was poor: 68.5% sensitive and 80.4% specific. However, it changed management in 25 of these patients. But wait…management was changed inappropriately in 16% (4/25) of the cases. If you know there is an abscess, why would you use ultrasound anyway? It seems most helpful in equivocal cases. What I take home is that ultrasound may bring clarity in uncertain cases, but it is far from a gold standard.

Another Spoonful
Emergency Medicine Cases has a great podcast on skin and soft tissue infections.

Source
Effect of Initial Bedside Ultrasonography on Emergency Department Skin and Soft Tissue Infection Management. Ann Emerg Med. 2019 Mar 26. pii: S0196-0644(19)30104-0. doi: 10.1016/j.annemergmed.2019.02.002. [Epub ahead of print]

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