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How Good is Ultrasound at Diagnosing PTA?

Posted by Marco Torres on

Background: The increased utility and accessibility of point-of-care ultrasound (POCUS) has allowed clinicians the freedom to rethink their diagnostic approach for many common diseases, including peritonsillar abscess (PTA). Clinical evaluation may prove difficult since many PTA and peritonsillar cellulitis symptoms overlap. Physical examination is approximately 75% sensitive and 50% specific for identifying PTA. CT and aspiration or drainage are considered the gold standard for diagnosis. Unfortunately, there are limited guidelines from ACEP, SAEM, and AAO-HNS regarding the optimal diagnostic approach for patients with PTA. Moreover, POCUS can be used to augment clinical assessment, and the results may obviate the need for advanced imaging. However, It is unclear how well POCUS performs in ruling in or ruling out the diagnosis of PTA.

Article: Kim DJ et al. Test characteristics of ultrasound for the diagnosis of peritonsillar abscess: A systematic review and meta-analysis. Acad Emerg Med. 2023 Jan 10. Epub ahead of print. PMID: 36625850.

Question: How well does the US perform in diagnosing PTA compared to CT, needle aspiration, or Incision and Drainage?

What They Did:

  • The systematic review was performed in accordance with the PRISMA-DTA guidelines
  • Searched multiple databases, including Ovid MEDLINE, Embase, Cumulative Index to Nursing and Allied Health Literature, the Cochrane Central Register of Controlled Trials, Latin American and Caribbean Health Sciences Literature database, and Web of Science from 1960 to 2020. A repeat search was completed in May 2021 & November 2022.
  • Two investigators independently assessed and screened all studies for eligibility.
  • Two reviewers independently assessed study quality using the QUADAS-2 tool
  • Authors were contacted for any missing or unreported data.
  • Any disagreements resolved through discussion and third-party adjudication when necessary.
  • The trial was registered wIth PROSPERO (CRD42021224241)

Inclusion Criteria:

  • Studies that evaluated the test characteristic of ultrasound in diagnosing PTA compared to the reference standard of CT or the aspiration or drainage of pus.
  • Retrospective, prospective, and RCTs

Exclusion Criteria:

  • Case Reports
  • Case series with 10 or fewer patients
  • Protocol papers
  • Narrative reviews
  • Articles not written in English

Outcomes:

Primary Outcome: Diagnostic accuracy of ultrasound for diagnosing a peritonsillar abscess

Subgroup Analysis:

  • Operator type (radiology vs. POCUS)
  • Scanning technique (intraoral vs. transcervical)

Results:

Study Selection:

  • Authors identified 339 studies and screened 192 abstracts after removing duplicates.
  • 33 studies selected for full review
  • Of those 33 studies, 17 of those met criteria for inclusion
  • Of the 18 studies, 1 was an RCT, 14 were prospective cohort studies, and 3 were retrospective cohort studies
  • Total of 812 patients of whom 541 had PTA from 17 studies.
  • Overall all included studies had some unclear risk or high risk of bias based on the QUADAS-2 assessment.

Sensitivity & Specificity of US for Diagnosis of PTA:

Strengths:

  • Utilized multiple databases to identify a large number of studies
  • Excluded studies with less evidentiary strength
  • Used established guidelines, including PRISMA-DTA, and registered with PROSPERO to reduce reporting biases
  • Multiple statistical analyses were performed to account for possible factors that would contribute to bias (heterogeneity summary using I2 statistics; QUADAS-2 risk of bias assessment)
  • Sound and transparent methodology
  • Included studies from multiple countries
  • Investigators compared ultrasound to an appropriate independent reference standard (in this case, CT vs drainage)
  • Participating patients constituted a representative sample of those presenting with PTA
  • Heterogeneity (I2) was low and < 50%

Limitations:

  • Training & qualification of the sonographers not specified in 13 studies
  • Based on the QUADAS-2 tool for quality assessment, all of the included studies were found to be of high or unclear risk of bias
  • Most of the studies contained small sample sizes, and only one study had a sample size estimate.
  • Low generalizability- studies took place in multiple settings, including ENT, ED, and radiology departments
  • Excluded non-English papers
  • Did not report on investigator agreement of Kappa for included studies
  • Did not search reference lists of included studies for additional papers
  • 53% of enrolled patients came from 2 studies
  • More than half the patients enrolled in the included studies had a PTA, which seems high and suggests non-consecutive enrollment and selection bias
  • Only one included trial was an RCT
  • Confidence intervals were wide, and point estimates were heavily disparate

Discussion:

Bias:

  • Based on a positive LR of 3.51, the post-test probability of having a PTA given a positive US is approximately 80%.
  • However, there is a tremendous amount of bias in the included studies. Furthermore, we have no confidence in the results rendering the numbers meaningless. We need high-quality evidence to provide a definite conclusion.

Does CT Change Management:

  • Peritonsillar infections, including uncomplicated cellulitis, phlegmon, and small and large abscess, exist on a spectrum. Likewise, patients can have many symptoms, including mild tonsillar erythema and swelling or more ominous symptoms like muffled voices, drooling, and trismus. However, clinicians treat many patients without drainage.
  • An extensive systematic review with more than 30,000 patients found no difference in the odds of treatment failure for patients with PTA managed with medical intervention alone or surgically (Forner 2020). However, in a small retrospective study of 214 patients, investigators found that abscesses >2cm in size were more likely to fail antibiotic treatment (Urban 2018). Furthermore, another small retrospective study found that approximately 30% of patients with CT-diagnosed PTA lacked purulence on drainage attempts (Eliason 2023).
  • In some patients, the presence of CT confirmed abscess might not change management. In these patients, a diagnostic US may be enough to confidently forgo CT imaging, as many will improve with medical therapy alone.

First, Do No Harm!

  • We are often uncomfortable with uncertainty and may feel compelled to order a CT scan on patients with PTA. However, CT imaging is not infallible and carries the potential for false negatives and false positives, and beyond statistics, CT imaging is not harmless. The neck and thyroid are particularly vulnerable to radiation (Tipnis et al.). Additionally, potential increases in resource utilization, healthcare expense, and ED length of stay are also essential considerations. Ultrasound has become an extended part of our physical exam. While operator dependent, the dynamic ability of POCUS augments bedside diagnosis and can assist with drainage. Furthermore, we can still perform a CT scan if the US proves inconclusive. In short, there is little downside to utilizing US as an adjunct for PTA diagnosis and management.

Author’s Conclusion: “Ultrasound is an acceptable alternative to computed tomography and incision and drainage for establishing diagnosis of peritonsillar abscess. It has high sensitivity for ruling out PTA but it demonstrates only moderate specificity for ruling in the diagnosis.”

Clinical Bottom Line:

This systematic review and meta-analysis adds to the growing body of evidence in favor of utilizing US for diagnosing PTA. However, there simply is not enough high-quality evidence to provide a definite conclusion. Many questions remain, but in our opinion, the benefits provided by US outweigh any drawbacks. We recommend US as an adjunct diagnostic tool for managing patients with suspected PTA. If inconclusive, order a CT scan.

References:

  1. Forner D, Curry DE, Hancock K, MacKay C, Taylor SM, Corsten M, Trites JR, Rigby MH. Medical Intervention Alone vs Surgical Drainage for Treatment of Peritonsillar Abscess: A Systematic Review and Meta-analysis. Otolaryngol Head Neck Surg. 2020 Nov;163(5):915-922. Epub 2020 Jun 2. PMID: 32482146.
  2. Tipnis SV, Spampinato MV, Hungerford J, Huda W. Thyroid Doses and Risks to Adult Patients Undergoing Neck CT Examinations. AJR Am J Roentgenol. 2015 May;204(5):1064-8. PMID: 25905942.
  3. Urban MJ, Masliah J, Heyd C, Patel TR, Nielsen T. Peritonsillar Abscess Size as a Predictor of Medical Therapy Success. Ann Otol Rhinol Laryngol. 2021 May 12:34894211015590. Epub ahead of print. PMID: 33980073.
  4. Eliason MJ, Wang AS, Lim J, Beegle RD, Seidman MD. Are Computed Tomography Scans Necessary for the Diagnosis of Peritonsillar Abscess? Cureus. 2023 Feb 9;15(2):e34820.. PMID: 36919070

For More Information, Check Out:

Guest Post By:

Alanna Dompkowski, MD
PGY-3, Chief Emergency Medicine Resident
Nuvance Health, Poughkeepsie, New York
Email: alanna.dompkowski@nuvancehealth.org

Melissa Hazlitt, MD
Student Ultrasound Director
Department of Emergency Medicine
Nuvance Health, Poughkeepsie, New York
Email: melissa.hazlitt@nuvancehealth.org

Marco Propersi, DO FAAEM
Vice-Chair/Associate Medical Director
Assistant Residency Program Director
Department of Emergency Medicine
Vassar Brothers Hospital, Poughkeepsie, New York
Twitter: @marco_propersi

Post-Peer Reviewed By: Salim R. Rezaie, MD (Twitter: @srrezaie ), Anand Swaminathan, MD (Twitter: @EMSwami)

The post How Good is Ultrasound at Diagnosing PTA? appeared first on REBEL EM - Emergency Medicine Blog.

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