Although
stroke is a leading cause of death and disability in the United States, a
relatively small proportion of all disabling strokes are due to Carotid Artery
Stenosis (CAS).
The
most commonly used screening test for severe CAS (60% to 99% stenosis) is
duplex ultrasonography. The accuracy of
carotid duplex ultrasonography, by using digital subtraction angiography as the
reference standard, estimate the sensitivity to be 86% to 90% and the
specificity to be 87% to 94% for detecting CAS greater than 70%. The estimated
sensitivity and specificity of carotid duplex ultrasonography to detect CAS of
60% or more are approximately 94% and 92%, respectively. In 1996, the USPSTF reviewed the evidence for
screening for bruits on physical examination and found that the test had poor
reliability and poor sensitivity. Good evidence indicates that duplex ultrasonography
has moderate sensitivity and specificity but yields many false-positive
results. A positive result on duplex ultrasonography is often confirmed by digital
subtraction angiography, which is more accurate but is associated with
complications. Given these facts, some people with a false-positive test
results may receive unnecessary carotid endarterectomy surgery.
The evidence analyzed by the U.S. Preventive Services Task Force (USPSTF) indicates that in selected, high-risk trial participants with
asymptomatic severe CAS, carotid endarterectomy by select surgeons reduces the
5-year absolute incidence of all strokes or peri-operative death by
approximately 5%. These benefits would be less among asymptomatic people in the
general population. For the general primary care population, the benefits are
judged to be no greater than small.
Therefore
evidence indicates that both the testing strategy and the treatment with
carotid endarterectomy can cause harms. A testing strategy that includes
angiography will itself cause some strokes. A testing strategy that does not
include angiography will cause some strokes by leading to carotid
endarterectomy in people who do not have severe CAS. In excellent centers,
carotid endarterectomy is associated with a 30-day stroke or mortality rate of
about 3%; some areas have higher rates. These harms are judged to be no less
than small.
