Asymptomatic carotid stenosis increases risk for cognitive dysfunction

Image: PD

Key study points:

1. Patients with asymptomatic carotid stenosis, unilateral or bilateral, are at higher risk for cognitive deficits than those without carotid stenosis.

2. The domains affected are dependent on the hemisphere involved and the degree of cerebral hypoperfusion resulting from the stenosis.

Primer: Carotid artery stenosis, or narrowing of the carotid artery, is a well-recognized cause of ischemic stroke.  The most common cause of carotid stenosis is build-up of atherosclerotic plaque on the luminal (inner) surface of the vessel.  In many patients this is asymptomatic, as blood flow past the stenosis is sufficient to meet the brain’s needs.  In some instances, however, fragments of the plaque break off and embolize to smaller vessels in the brain.  These can initially cause transient ischemic attacks (TIAs) consisting of monocular blindness or other stroke-like symptoms that last less than 24 hours.  In more severe cases, flow in cerebral vessels can be permanently occluded, causing ischemic stroke.

Symptomatic carotid stenosis is generally treated with medical therapy (anti-coagulation and anti-hypertensives) followed by surgical removal of the carotid lumen via carotid endarterectomy depending on degree of stenosis and the patient’s co-morbidities.  However, the surgical management of asymptomatic carotid stenosis (ACS) is controversial.  While the presence of ACS is a predictor of future ischemic events, surgical management carries risks that are difficult to balance against risk of future stroke.  As such, the pathophysiology and sequelae of ACS have been the subject of intense scrutiny.  Recently, cognitive dysfunction has been identified in patients considered to have ACS, suggesting that it may not be asymptomatic after all.  Moreover, it has been suggested that cognitive dysfunction may serve as a diagnostic indicator of ACS, as well as a prognostic variable to determine who may benefit the most from intervention.

Background reading:

1. Inzitari D, Eliasziw M, Gates P, et al. The causes and risk of stroke in patients with asymptomatic internal-carotid-artery stenosis.  NEJM 2000;342(23):1693-1700.

2. Goessens BM, Visseren FL, Kappelle LJ, et al. Asymptomatic carotid artery stenosis and the risk of new vascular events in patients with manifest arterial disease: the SMART study. Stroke 2007;38:1470 –1475.

3. Johnston SC, O’Meara ES, Manolio TA, et al. Cognitive impairment and decline are associated with carotid artery disease in patients without clinically evident cerebrovascular disease. Ann Intern Med 2004;140:237–247

This [cross-sectional cohort] study: The study examined 333 patients referred to an Italian vascular neurology clinic by their primary care doctors for carotid stenosis screening due to vascular risk factors.  All patients underwent initial carotid ultrasound, and only those with with ≥60% stenosis of one or both internal carotid arteries (ICAs) were included.  Enrolled patients underwent neuropsychological testing designed to assess the function of both cerebral hemispheres, as well as transcranial Doppler studies to assess cerebral perfusion.

127 patients had bilateral ACS while 150 had unilateral stenosis. Patients with bilateral or left ACS scored significantly worse on measures of left hemisphere function.  Conversely, patients with bilateral or right ACS scored significantly worse on measures of right hemisphere function.  Moreover, these findings were significantly associated with the degree of cerebral perfusion impairment in patients with bilateral ACS.  Notably, patients with bilateral ACS but preserved cerebral perfusion to both hemispheres scored comparably to the patients without carotid stenosis.

In sum: Asymptomatic carotid artery stenosis, and more importantly the resulting reduced cerebral perfusion, was found to be associated with poorer cognitive function in the hemisphere ipsilateral to the stenotic artery. Impaired cognitive function was particularly evident in patients with bilateral ACS in cases where both hemispheres were found to be hypoperfused.  On the other hand, cognition in patients with bilateral carotid stenosis was comparable to that in those without carotid stenosis as long as sufficient cerebral perfusion was maintained.  Stressing the subtle nature of deficits, the authors note that while these changes were significant, they were not detectable on the mini-mental status exam, the most commonly used tool for mental status assessment in the clinical setting.

This study was limited by a lack of imaging data, which does not allow the authors to evaluate performance in the context of existing lesions (e.g. previous strokes, which would be more common in patients with ACS). Additionally, the data obtained represent only one time point in each patient’s disease course, limiting the ability to prognosticate based upon the findings.  Nonetheless, the presence of significant cognitive deficits patients with ACS (with compromised perfusion) underscores the need for detailed evaluation and more well-defined management criteria in this population.

 Click to read the study, published online ahead of print in Neurology

By [JD] and [RR]

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