Don't trust clinical decision rules (even the Alvarado score), and make ultrasound a first-line test
Appendicitis is a difficult diagnosis that is underrated in the ED. It is taught in medical school as a straightforward, common pathology, but experienced physicians know it's not that simple. Correction: It's simple if you perform computed tomography scans on everyone who enters your department.
We owe it to our patients, however, to practice evidence-based medicine. The answer to reduce the miss rate of appendicitis is not just more cowbell (CTs). (Saturday Night Live. https://bit.ly/SNL-Cowbell.) The American College of Emergency Physicians recently released a clinical policy for evaluating and managing appendicitis in the ED.
The policy was developed by a committee of emergency physicians based on a systematic review of the current literature. (ACEP Clinical Policy: Critical Issues in the Evaluation and Management of Emergency Department Patients with Suspected Appendicitis. Feb. 1, 2023; https://bit.ly/4020Sa0.)
Symptoms and signs of appendicitis vary, and even laboratory studies are not helpful. Leukocytosis has a sensitivity of 80% and a specificity of 55%. (Am Surg. 1998;64:983.) Acute appendicitis is unlikely when the WBC count is normal, but “unlikely” is not reassuring enough for most physicians. Physical exam findings are hit or miss, with tenderness at McBurney's point having a sensitivity of 50 percent to 94 percent and a specificity of 75 percent to 86 percent. (Ann R Coll Surg Engl. 1996;78:11; https://bit.ly/3mVX4sv.)
Attempts to reduce radiation exposure and decrease unnecessary workups have led to the development of clinical prediction rules. The Alvarado score is perhaps the most well known and most widely used. (Ann Emerg Med. 1986;15:557.) It is hiding some dark secrets about its legitimacy, however.
The ACEP clinical policy noted that no studies have shown that a clinical prediction score has an adequate likelihood ratio (LR) to rule appendicitis in or out. The only evidence supporting the use of the Alvarado score is a 1986 retrospective study of 305 patients and a 1994 prospective study of 49 patients. That's it.
The score has low diagnostic accuracy, making it insufficient to use alone when assessing the risk of appendicitis. This is especially true for atypical presentations or early in the disease course. ACEP gives clinical decision rules in appendicitis a Level C recommendation.
The policy pays a lot of attention to CT as the most widespread, fastest option available. Its high sensitivity and specificity make it the go-to choice for diagnosis, but it is not without risk. Cost, radiation exposure, and potential for incidental findings are the key drawbacks.
Ultrasound has some obvious advantages to CT. It is cheaper, confers no harm to the patient, and can be performed relatively fast. (Acad Emerg Med. 2018;25:785; https://bit.ly/3JExh0P.) ACEP, the American College of Radiology, and the supporting evidence recommend ultrasound as the first-line test in pediatric patients. (American College of Radiology. Appropriateness Criteria, Variant 4. 2013; https://bit.ly/3TpRCdC; Radiology. 2018;288:717.)
The literature is less clear for adults, and studies are limited. The ACEP policy cites two studies, both of which demonstrated strong specificities (92% and 95%) and LR (7.2 and 17) and are comparable with CT and MRI. (ACEP Clinical Policy: Critical Issues in the Evaluation and Management of Emergency Department Patients with Suspected Appendicitis. Feb 1, 2023; https://bit.ly/4020Sa0.) Unfortunately, the sensitivity was not comparable.
One of the oft-cited limitations for the lower sensitivity of ultrasound is the high rate of equivocal/nondiagnostic examinations. No full or partial visualization of the appendix is a source of confusion for physicians. The current literature greatly varies on how nondiagnostic studies are reported, yet there is hope.
The most recent study was published last December and was not included in the ACEP clinical policy; it was a retrospective design of 508 adults with suspected appendicitis who underwent ultrasound as their first test.
A positive test included any of the following: appendiceal diameter >6 mm, pain with compression, noncompressibility, periappendiceal fluid, and echogenicity. (Emerg Med J. 2022;39:931; http://bit.ly/3TgVai6.) The evaluation was considered nondiagnostic if the appendix was not visualized at all. Importantly, 29 percent of patients who had a nondiagnostic study ended up having appendicitis, emphasizing the need for caution with nondiagnostic ultrasound studies.
Where does this leave us? Do not place much faith in clinical decision rules for appendicitis. The Alvarado score has minimal evidence backing its use, and ACEP agreed it has limited utility. Studies show ultrasound should be first line for diagnostic evaluation of appendicitis in children. Given its high positive predictive value in adults, it should still be considered as a first-line test when it can be readily obtained.
Be cautious when attempting to interpret nondiagnostic evaluations. Serial examinations, observation, and consultation are reasonable alternatives to immediate CT or MRI in the setting of a nondiagnostic appendiceal ultrasound.
Share this article on Twitter and Facebook.
Access the links in EMN by reading this on our website: www.EM-News.com.
Comments? Write to us at [email protected].
Dr. Briggsis an assistant professor of emergency medicine at the University of Tennessee Medical Center in Knoxville. He is the founder, a podcast host, and the editor-in-chief of EM Board Bombs (https://www.emboardbombs.com), a multiplatform educational tool designed to provide board prep and focus on what EPs need to know for the practice of emergency medicine. Follow him on Twitter@blakebriggsmd.