POCUS for the PTA

September 18, 2023

Written by Megan Hilbert

Spoon Feed
While it doesn’t have great specificity, the sensitivity of ultrasound makes it a viable first step in making the diagnosis of peritonsillar abscess.

Sore throats and sound waves
In Emergency Medicine, not all sore throats and “hot potato” voices are the same. It is important to establish the diagnosis of peritonsillar abscess (PTA) to prevent potential sequelae, such as airway obstruction and erosion of the carotid sheath.

Physical exam is not particularly adept at establishing the diagnosis of PTA, with a sensitivity of 75% and specificity of 50%. While CT is accurate at making the diagnosis, it exposes the patient to increased cost, ED length of stay, and radiation. This systematic review evaluated the efficacy of ultrasound for making this diagnosis and compared the intra-oral to the trans-cervical technique. They included 17 studies, 812 patients, and found that radiology-performed studies had greater sensitivity (89%) than POCUS (74%). Within POCUS, there was higher sensitivity and lower specificity with the intra-oral technique, but this was not statistically significant. The authors suggest that ultrasound (regardless of approach) is a valid option for making this diagnosis.

Some concerns – none of the included studies had a low risk of bias. There is also an inherent patient selection bias (particularly with the intra-oral technique) given that trismus frequently prevents completion of this POCUS approach. Finally, not all departments have access to an endo-cavitary probe for the intra-oral technique. Given the similar test characteristics, however, it appears that the trans-cervical technique is a viable alternative.

How will this change my practice?
If I have time and PTA is on my differential, I will make a more concerted effort to complete a POCUS to establish the diagnosis of PTA. Having said that, if I don’t find convincing evidence to rule this diagnosis in, but still have a high clinical suspicion, I will likely still plan to complete a CT.

Editor’s note: Prevalence (pre-test probability) of disease in this meta-analysis was 541/812 (67%). With a positive trans-cervical US (positive likelihood ratio 4.3), the post-test probability of disease is 90%. This would make me more confident to put a needle in it. ~Clay Smith

Source
Test characteristics of ultrasound for the diagnosis of peritonsillar abscess: A systematic review and meta-analysis. Acad Emerg Med. 2023 Aug;30(8):859-869. doi: 10.1111/acem.14660. Epub 2023 Jan 30.