Point/Counterpoint: Is screening for asymptomatic carotid artery stenosis justified?
By R. Eugene Zierler, M.D.
To most vascular specialists, the concept of detecting asymptomatic carotid stenosis and intervening to prevent stroke makes intuitive sense, but is it consistent with the evidence? In 2007, the USPSTF concluded that the general asymptomatic adult population should not be screened for carotid stenosis, and this recommendation has been reiterated in a 2014 draft recommendation statement.1,2 Other groups, including our own Society for Vascular Surgery, have published similar recommendations.3,4
Arguments in favor of screening for asymptomatic carotid stenosis are often based on the results of randomized controlled trials such as the Asymptomatic Carotid Atherosclerosis Study, which was reported in 1995.5 However, while these trials are historically important, they are no longer clinically relevant. Surgical and catheter-based interventions for carotid atherosclerosis have evolved significantly in the last 2 decades, but the outcomes associated with modern intensive medical therapy have also improved dramatically.6,7 It is not clear that carotid endarterectomy or stenting is superior to current medical management for asymptomatic carotid stenosis, and new trials such as the recently announced CREST-2 are designed to answer these important questions.
The relatively poor reliability and accuracy of duplex ultrasound as a screening test for carotid stenosis is a major theme in the USPSTF draft recommendations, but in spite of this criticism, carotid duplex scanning has served as a clinically valuable method for classifying the severity of carotid stenosis for more than 30 years.8 As pointed out by others, the best way to ensure quality in the vascular laboratory is to recognize the importance of certified vascular sonographers, accredited vascular laboratories, and qualified medical staff. But despite high-quality ultrasound testing, relying on carotid stenosis as a marker of stroke risk has significant limitations. While there is an association between the degree of carotid stenosis and risk of stroke, many patients with severe carotid stenosis do not have strokes and some with moderate stenosis do have strokes. For example, it was reported that 61% of the symptomatic patients in the North American Symptomatic Carotid Endarterectomy Trial had less than 50% carotid stenosis.9 This suggests that stenosis severity alone does not identify those patients who are at the highest risk for stroke. Fortunately, the concept of the "vulnerable plaque" is promising as a means for more accurate risk stratification, and features such as intraplaque hemorrhage and thin or ruptured fibrous caps do correlate with a high risk for stroke.10 Experience has shown that these features can be characterized by ultrasound.11
So although screening of the general population for asymptomatic carotid stenosis is not justified, there still may be subgroups of patients with specific risk factors and plaque features that could benefit from early intervention, and future clinical trials will establish whether or not this hypothesis has merit. Until more data are available the issue of screening for asymptomatic carotid stenosis will continue to provoke debate on multiple levels. Carotid disease screening is not covered by insurance, so cost and ability to pay are key factors to consider. In these discussions, the health of the patient and the population must always be the first priority, and clinical decision-making should be evidence based.
Dr. Zierler is professor of surgery at the University of Washington and medical director of the D.E. Strandness Jr. Vascular Laboratory at the university’s medical center and Harborview Medical Center, Seattle. He is also an associate medical editor of Vascular Specialist.
References
1. Ann. Intern. Med. 2007;147:860-70.
2. uspreventiveservicestaskforce.org/.htm.
3. JACC 2011;57:e16-94.
4. J. Vasc. Surg. 2011;54:e1-31.
5. JAMA 1995:273:1421-8.
6. Circulation 2013;127:739-42.
7. Stroke 2009;40:e573-83.
8. Vasc. Endovascular Surg. 2012;46:466-74.
9. N. Engl. J. Med. 1998;339:1415-25.
10. Imaging Med. 2010;2:63-75.
11. J. Vasc. Surg. 2010;52:1486-96.
