Cognitive Function and Carotid Artery Disease

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The summary below is from the full report titled "Cognitive Impairment and Decline Are Associated with Carotid Artery Disease in Patients without Clinically Evident Cerebrovascular Disease." It is in the 17 February 2004 issue of Annals of Internal Medicine (volume 140, pages 237-247). The authors are S.C. Johnston, E.S. O'Meara, T.A. Manolio, D. Lefkowitz, D.H. O'Leary, S. Goldstein, M.C. Carlson, L.P. Fried, and W.T. Longstreth Jr.

What is the problem and what is known about it so far?

In atherosclerosis, cholesterol and other fatty substances collect in arteries, causing narrowing or blockages. Risk factors for atherosclerosis include high blood pressure, diabetes, and high cholesterol levels. The carotid arteries are large blood vessels in either side of the neck that bring blood to the brain. Atherosclerosis-related blockages in the carotid arteries (carotid artery stenosis) can lead to low blood flow to the brain and conditions called transient ischemic attacks (TIAs) or stroke. With a TIA, blockage of blood flow to the brain is temporary and the brain suffers no permanent damage. With a stroke, blockage of the blood flow lasts long enough that a section of brain tissue dies. People who have TIAs or stroke can have problems in their memory and thinking (cognitive impairment). It is unknown whether carotid artery stenosis that is not severe enough to result in a TIA or stroke also cause cognitive impairment.

Why did the researchers do this particular study?

To see whether carotid artery stenosis is associated with problems with cognitive function in people who have not had a TIA or stroke.

Who was studied?

4006 right-handed men and women 65 years of age or older who had no history of stroke, TIA, or previous carotid artery surgery. They included only right-handed people because they focused on left carotid artery disease. In right-handed people, the left carotid artery supplies the parts of the brain that control cognitive function. One would expect that left carotid artery stenosis would affect cognitive function.

How was the study done?

The researchers examined the people at the start of the study in 1992–1993. These examinations included questions about heath and ultrasound tests to look at the carotid arteries. If one thinks of the carotid arteries as tubes, ultrasound lets doctors measure the thickness of the walls of the tubes and the percentage of the tube that is blocked. The researchers defined significant carotid artery stenosis as blockages of 75% or more. The researchers measured cognitive function yearly over the next 5 years using a standard test called the Modified Mini-Mental Status Examination.

What did the researchers find?

People with left carotid artery stenosis were more likely to have cognitive impairment and to have worsening cognitive function over time than people who did not have left-sided carotid artery disease. This association remained even when the researchers adjusted for other risk factors for stroke and for right-sided carotid artery disease. This indicates that it was truly left carotid artery stenosis and not just generalized atherosclerosis that was associated with cognitive problems.

What were the limitations of the study?

This study cannot tell us whether fixing the carotid artery blockages through surgery or another method would improve cognitive function in people with carotid artery stenosis.

What are the implications of the study?

Carotid artery disease appears related to cognitive impairment even in people without a history of TIA or stroke. Further research is necessary to learn whether treating carotid artery stenosis can improve cognitive function.