Stroke is one of the leading causes of death and disability in the United States, according to the U.S. Preventive Services Task Force (USPSTF). But strokes that result from large artery atherothrombotic disease, such as carotid artery stenosis (CAS), in asymptomatic patients account for only a small portion of all strokes.
On July 8, the USPSTF released its recommendation(www.uspreventiveservicestaskforce.org) against screening for asymptomatic CAS in the general adult population. The recommendation updates the USPSTF's 2007 CAS screening statement, which also recommended that adults should not be screened for the condition. The AAFP mirrored this latest recommendation, as it did the task force's 2007 recommendation.
The Case Against Screening for CAS
CAS is the atherosclerotic narrowing of the extracranial carotid arteries -- specifically, the internal carotid arteries or the common and internal carotid arteries, according to the USPSTF evidence report(www.uspreventiveservicestaskforce.org). The USPSTF reviewed ample evidence that showed both testing for and treating CAS can harm patients. This included 78 published articles that reported on 56 studies.
- The USPSTF has released its recommendation against screening for asymptomatic carotid artery stenosis (CAS) in the general adult population, and the AAFP has mirrored this recommendation.
- The USPSTF reviewed ample evidence that showed both testing for and treating CAS can harm patients.
- Instead of screening for asymptomatic CAS, physicians may wish to address the main treatable risk factors for stroke: hypertension, diabetes, smoking and high cholesterol.
The best available data from U.S. studies found that the prevalence of CAS (defined as 70 percent to 99 percent stenosis) is only 0.5 percent to 1 percent, according to the report. On top of that, evidence showed that the incidence of stroke caused by CAS has been decreasing in the past couple of decades, which the report attributes to advances in medical therapy. Research also could not accurately distinguish between people who had CAS and those who did not.
The argument against screening for CAS in the general population starts with the fact that the most applicable screening test for CAS, ultrasonography, has proven to yield many false-positives in these patients.
"The screening tests for carotid artery stenosis may be unreliable in the asymptomatic adult, so a patient may not have significant stenosis, but may undergo an intervention because the screening test was inaccurate," said Jennifer Frost, M.D., medical director for the AAFP Health of the Public and Science Division.
According to a 1995 study titled "Endarterectomy for Asymptomatic Carotid Artery Stenosis(jama.jamanetwork.com)" that was referenced in the report, use of this type of screening in a population of 100,000 adults with a prevalence of 1 percent would result in 940 true-positive results and 7,920 false-positive results. If all positive results were then followed up by magnetic resonance angiography, many patients would be sent for unnecessary intervention, the study found. This then could lead to dangerous and unnecessary treatments.
The most common treatment for CAS is carotid endarterectomy (CEA), a surgical procedure that carries significant risk, including stroke, myocardial infarction and cranial nerve injury, Frost said. "In fact, studies showed that patients with carotid stenosis who underwent CEA had a higher incidence of stroke than those who simply had medical therapy."
Overall, the USPSTF concluded that the harms of screening for asymptomatic CAS outweighed the benefits.
For the same reasons discussed above, the AAFP has added the recommendation to not screen for CAS in asymptomatic adult patients to its Choosing Wisely list of 15 tests and procedures that both family physicians and patients should carefully consider before integrating them into a treatment plan.
Focusing on Other Stroke Risk Factors
Instead of screening for asymptomatic CAS, Frost recommends focusing on treating other major risk factors for stroke, especially high blood pressure. The main treatable risk factors for stroke are hypertension, diabetes, smoking and high cholesterol, which are also major risk factors for heart disease. Risk increases with age, and African Americans and Hispanics are at higher risk than Caucasians, she added.
"A common primary care patient who would be at a high risk of stroke is a 70-year-old male with uncontrolled (high) blood pressure and tobacco use," Frost said. "Normalizing his blood pressure and getting him to stop smoking would significantly decrease his risk. But this is not always simple. It is frequently not just an issue of adjusting medication."
Smoking cessation is challenging, especially for someone who has been smoking most of his life, she said. He also may need assistance in paying for his medication, and changes in his diet and physical activity would also be important, she added.
Beyond recommending that the patient should quit smoking, the family physician also needs to provide the patient with support to enable him to succeed, Frost said. "This may involve medications, counseling, support groups and/or frequent follow-up. The patient-centered medical home is the best place to provide these services to ensure that the patient receives the treatment, support and follow-up that he needs."
The other risk factors also can be managed in the setting of the medical home. "Knowing a patient's cholesterol level and other risk factors will guide the family physician in prescribing appropriate statin therapy, as well as lifestyle modification," said Frost. "Monitoring and controlling a diabetic's blood sugar is essential in reducing the risk of stroke, as well as other complications associated with diabetes."
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