ARTICLE IN BRIEF
A review of published research by the US Preventive Services Task Force found no evidence that ultrasound screening reduced the risk of stroke. The review also found no advantage in doing carotid endarterectomy (CEA) or stenting instead of medical therapy in asymptomatic patients.
Ultrasound screening for carotid artery stenosis in people who are asymptomatic probably does more harm than good, according to an updated clinical guideline developed by the US Preventive Services Task Force.
A review of published research that was used to develop the guidelines found no evidence that such ultrasound screening reduced the risk of stroke. The review of the medical literature also found no advantage in doing carotid endarterectomy (CEA) or stenting instead of medical therapy in asymptomatic patients. (The guideline did not focus on management of symptomatic cases.)
“Noninvasive screening with ultrasonography would result in many false-positive results,” which in turn could lead to more testing and procedures that carry risks, the review noted.
The review noted that the incidence of carotid artery stenosis is estimated to be about 1 percent in the general population. Using that rate, and a specificity of 92 percent for the screening, the researchers calculated that if 100,000 adults were screened, “it would result in 940 true-positive results, and 7,920 false-positive results.”
“When you look at the overall evidence, it looks like there may be greater harm than benefit from screening the general population,” said Dan E. Jonas, MD, MPH, an associate professor in the Division of General Medicine at the University of Carolina, Chapel Hill, who was the lead author of the review.
“Some people would suffer stroke or death because of screening and intervention,” Dr. Jonas told Neurology Today.
The new clinical guideline, along with the review of the research on carotid artery stenosis screening and intervention, were published online July 8 ahead of the print edition of the Annals of Internal Medicine.
The US Preventive Services Task Force, which is an independent panel made up of experts in prevention, evidence-based medicine, and primary care, periodically evaluates the benefits and risks of preventive screenings and other services, and makes recommendations for clinical practice. The panel last weighed in on ultrasound screening for carotid artery stenosis in asymptomatic patients in 2007, and the new update found little reason to change that recommendation against screening.
The updated clinical guideline on carotid artery screening was based on a systematic review of research on screening and interventions, including some studies published as recently as earlier this year.
Dr. Jonas and his research team analyzed 78 published articles on 56 studies, but they found the medical literature lacking in some regards. There were no trials that compared screening to no screening, and none that compared stenting with medical therapy, or assessed the value of intensification of medical therapy.
They noted that findings that may have pointed to a benefit from CEA and stenting in reducing the risk of stroke may not be relevant today, in part because medical management of patients has improved. Also, the studies, which involved highly selected doctors, may have produced better results than real-life practice.
“Current evidence does not establish incremental overall benefits of CEA, stenting, or intensification of medical therapy,” they reported.
The task force, in its guideline, noted that research has shown that carotid artery stenosis is more common in older adults, smokers, as well as people with hypertension and heart disease. But, it said that research “has not shown any single risk factor or clinically useful risk stratification tool that can reliably and accurately distinguish between persons who have clinically important carotid artery stenosis and those who do not.”
“Although screening with ultrasonography has few direct harms, all screening strategies, including those with or without confirmatory tests...have imperfect sensitivity and could lead to unnecessary surgery and result in serious harms, including death, stroke, and myocardial infarction,” the Task Force said.
It also noted “there is no evidence that screening by auscultation of the neck is accurate or provides benefit.”
The task force said that none of the reviewed studies examined the direct harms of screening, although they said that follow-up testing using angiography, which is now less common, carried a risk of stroke of about 1.2 percent. The review found that the 30-day rates of stroke or death after CEA in control trials or cohort studies were 2.4 percent and 3.3 percent respectively, Dr. Jonas said. For stenting, rates were 3.1 percent and 3.8 percent respectively.
Experts who were not involved with the review noted that people can now more readily get screened for carotid artery disease because of mobile ultrasound units that are sometimes set up at health fairs, community centers, libraries, and even outside stores. So-called “executive physicals” will often offer carotid artery screening as well as whole-body screening. The ultrasound tests may be portrayed as innocuous, but what seems like a simple, cheap, and harmless test can set off a cascade of follow-up appointments and tests.
Pierre Fayad, MD, FAAN, a professor of neurology and director of the Stroke Center at the University of Nebraska Medical Center in Omaha, said he has had patients come in for a consultation after getting a bad result from a carotid artery screening done elsewhere. Some patients were scared by what they were told was a severe stenosis that ended up being less severe on other confirmatory tests, he said. He has also seen patients who were sent for urgent surgery based on the results, and had a stroke as a result of the procedure.
On the other hand, a screening test that shows no significant carotid artery stenosis could offer false reassurance to a patient who has risk factors for cardiovascular disease — such as high blood pressure and elevated cholesterol — that need to be well managed with medication, Dr. Fayad said. It is estimated that about 10 percent of ischemic strokes are caused by carotid artery stenosis.
“The bottom line is we really don't know which patients with an asymptomatic carotid stenosis are most at risk of stroke,” Dr. Fayad told Neurology Today. “Medical management has gotten so good at controlling risk factors for cardiovascular disease that doing a procedure for asymptomatic carotid artery disease is much harder to justify.”
Philip B. Gorelick, MD, MPH, FAAN, a professor of translational and molecular science at Michigan State University, told Neurology Today that he hopes that the guideline will draw attention to the downsides of what can happen “when the ultrasound truck pulls up to your local shopping mall or church and offers a battery of tests.” A “bad” result, he said, could make people “think they have a ticking time bomb in their neck and they have to do something about it.”
Dr. Gorelick, who favors aggressive medical management of most asymptomatic patients, said the upcoming Carotid Revascularization Endarterectomy versus Stent 2 Trial (CREST 2) should provide much-needed information on the benefits of intervention versus medical management. The trial will compare carotid artery stenting plus aggressive medical therapy versus aggressive medical therapy alone, and CEA plus aggressive medical therapy versus aggressive medical therapy alone in persons with asymptomatic carotid stenosis of at least 70 percent (as determined by duplex ultrasound and one other confirmatory test).
Dr. Gorelick said further research is needed to help identify which subset of patients might benefit from carotid artery screening, as well as those most likely to benefit from an interventional procedure. “We are moving in the direction of what makes sense for each individual patient as well as what will help them and not harm them,” he said.
EXPERTS: SCREENING FOR ASYMPTOMATIC CAROTID ARTERY STENOSIS