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Invited Commentary
May 2016

Screening for Asymptomatic Carotid Artery Stenosis: Evidence-Based Opinion

Author Affiliations
  • 1Department of Neurology, Kentucky Neuroscience Institute, University of Kentucky, Lexington
JAMA Intern Med. 2016;176(5):633-634. doi:10.1001/jamainternmed.2016.0857

Evidence-based medicine is a linchpin of contemporary clinical practice. It requires “the integration of the best research evidence with clinical expertise and the patient’s unique values and circumstances.”1(p1) The task can be daunting for busy clinicians, leading to the development of a plethora of clinical guidelines intended to provide recommendations aimed at optimizing patient care by summarizing and evaluating the available evidence supporting or refuting the use of diagnostic studies or therapeutic approaches. As of January 2016, the US Agency for Healthcare Research and Quality listed 3348 guidelines related to diseases or conditions, 8163 addressing treatments or interventions, and 1203 focused on health services administration.2 As with the underlying research itself, however, clinical practice guidelines can vary in quality, which led to efforts to set standards to ensure their value.3(pp75-107)

For any given problem, different professional societies, and indeed panels within single societies, can disagree on recommendations. Because the framing of clinical questions and the implications and interpretation of the underlying data may vary depending on context and other factors, guideline recommendations on a specific issue may differ in minor or substantial ways among different statements. Depending on when they were written and other factors, these documents can lack uniformity. There are a myriad of other potential reasons for the disparities among guidelines, which can then understandably lead to considerable uncertainty and variability in clinical practice.

Against this background, Keyhani et al4 evaluated screening for asymptomatic stenosis of the extracranial carotid artery. The authors noted that although there are several relevant guidelines, the recommendations lack consistency. For example, the American Institute of Ultrasound Medicine concluded that carotid artery screening is indicated for patients with a carotid bruit whereas the US Preventive Services Task Force (USPSTF) states that the procedure is not recommended in this setting. Table 1 of Keyhani et al4 gives the similarities and differences between these 2 sets of guidelines and recommendations from the American Heart Association/American Stroke Association (AHA/ASA) and collaborating organizations.

It is notable that both the USPSTF and the AHA/ASA guidelines agree that there is no benefit for routine screening of populations with no clinical manifestations or risk factors for atherosclerosis. With an estimated population attributable risk of carotid stenosis for stroke in those older than 60 years of 0.9%, the prevalence of asymptomatic carotid stenosis would need to be 14 times greater to reach a level similar to hyperlipidemia and more than 100 times greater to carry a risk similar to hypertension.5 The USPSTF found no validated risk stratification tool or physical finding, including the presence of a cervical bruit, that was useful for identifying those who do or do not have a clinically important asymptomatic carotid artery stenosis.6 Yet such screenings are offered in a variety of settings.5

Screening for a disease or condition is rational only if its identification has a meaningful effect on patient management. Epidemiological studies conducted over the last 3 decades such as the Evans County, Georgia, study find that an anterior cervical bruit is an indicator of generalized atherosclerosis and is a greater risk factor for death due to coronary heart disease than stroke.7 In the Evans County, Georgia, study, of the strokes that did occur, the type and location frequently did not correlate with the bruit. Therefore, the detection of a cervical bruit might reasonably prompt aggressive identification and treatment of other vascular risk factors.

Clinical trials comparing carotid endarterectomy plus best medical therapy with best medical therapy alone were conducted 1 to 3 decades ago.8 On the basis of these trials, current guidelines recommend revascularization for selected patients with an asymptomatic carotid artery stenosis.9 It has been noted, however, that best medical therapy has evolved since these clinical trials were conducted and that they may no longer have external validity.8 Because clinical equipoise now exists, studies such as the Carotid Revascularization Endarterectomy vs Stent Trial 2 (CREST-2) are reevaluating the benefit of both carotid endarterectomy and carotid artery stenting in addition to contemporary best medical therapy compared with best medical therapy alone.

In their retrospective study using data from the Veterans Health Administration, Keyhani et al4 sought to better understand why asymptomatic patients who had undergone carotid revascularization had received carotid artery imaging. Because of the uncertainty related to the interpretation and application of the underlying data, Keyhani et al4 first performed expert reviews of potential indications for carotid artery screening, classifying them as appropriate, inappropriate, or uncertain. The uncertain categorization was used if all raters deemed the indication uncertain or if consensus on appropriateness was not reached. They found that only 5.4% of carotid imaging studies were performed for indications that all raters agreed were appropriate, with 11.3% completed for inappropriate reasons and 83.4% done for uncertain purposes. As discussed herein, the high proportion of carotid imaging studies performed for uncertain indications is not entirely surprising. Their analysis does not address the use of the screening procedure in the larger group of asymptomatic patients who did not undergo a revascularization intervention. The proportions of patients in this population who have the test performed for inappropriate or uncertain reasons might be even higher than in those who underwent revascularization.

Specific educational programs, the use of alerts embedded into the electronic health record, and audits with feedback, among other interventions, may be helpful in reducing inappropriate testing. The more difficult issue is addressing the large number of tests conducted for purposes considered by the expert panel to be uncertain. In this situation, physicians face a dilemma when caring for individual patients. Should a screening test be performed in the face of equivocal, limited, or conflicting data regarding the intervention that would be considered if the condition was detected? To what degree should the potential for false-positive or false-negative test results and the attendant need for confirmatory testing be factored into the decision? How should inconsistent guideline recommendations be balanced? How are these complicated issues best presented and discussed with patients who look to their clinician for guidance? To some extent, despite the available evidence from randomized trials and practice guidelines, whether to proceed with testing can be a matter of informed opinion. In the setting of uncertainty, however, a conservative approach to screening and referral to a center participating in a relevant clinical trial seems the most appropriate strategy.

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Article Information

Corresponding Author: Larry B. Goldstein, MD, Department of Neurology, Kentucky Neuroscience Institute, University of Kentucky, 740 S Limestone St, L445, Lexington, KY 40536 (larry.goldstein@uky.edu).

Published Online: April 18, 2016. doi:10.1001/jamainternmed.2016.0857.

Conflict of Interest Disclosures: None reported.

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