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A transient ischemic attack (TIA) is a disturbance in brain function that lasts less than 1 hour and results from a temporary blockage of the brain's blood supply.
TIAs may be a warning sign of an impending ischemic stroke. People who have had a TIA are much more likely to have a stroke than those who have not. About half of these strokes occur within 1 year of the TIA, and many occur within a few days of the TIA. Recognizing a TIA and having the cause identified can help prevent a stroke.
TIAs are most common among middle-aged and older people.
TIAs differ from ischemic strokes because, after a TIA, symptoms resolve completely and quickly. Experts used to think that symptoms resolved more quickly because TIAs did not cause any permanent brain damage. That is, no brain cells died. However, most experts now think that TIAs are small ischemic strokes. That is, in TIAs, as in ischemic strokes, brain cells die. The difference is that in TIAs, the damage is usually very small.
Causes
Causes of TIAs and ischemic strokes are mostly the same. Most TIAs occur when a piece of a blood clot (thrombus) or of fatty material (atheroma, or plaque) due to atherosclerosis breaks off from the heart or from the wall of an artery, travels through the bloodstream (becoming an embolus), and lodges in an artery that supplies the brain (see Stroke (CVA): Causes). Occasionally, TIAs result from a very low oxygen level in the blood, a severe deficiency of red blood cells (anemia), carbon monoxide poisoning, thickened blood (as in polycythemia), or very low blood pressure (hypotension), especially when the arteries to the brain are already narrowed (as in people with atherosclerosis).
Symptoms
Symptoms of a TIA develop suddenly. They are identical to those of an ischemic stroke (see Stroke (CVA): Ischemic Stroke) but are temporary and reversible. They usually last less than 5 minutes and not longer than 1 hour. TIAs recur in about 5% of people with atherosclerosis. People may have several in 1 day or only two or three in several years.
Diagnosis
People who have a sudden symptom similar to any symptom of a stroke, even if it quickly resolves, should go immediately to an emergency department. Such a symptom suggests a TIA. However, other disorders, including seizures, brain tumors, migraine headaches, and abnormally low levels of sugar in the blood (hypoglycemia), cause similar symptoms, so further evaluation is needed.
If doctors suspect that a TIA has occurred, they evaluate people rapidly, usually in the hospital, because a stroke may occur soon after a TIA. Doctors check for risk factors for stroke by asking people questions, reviewing their medical history, and doing blood tests.
Imaging tests, such as computed tomography (CT) or magnetic resonance imaging (MRI), are done to check for evidence of a stroke, bleeding, and brain tumors. A specialized type of MRI, called diffusion MRI, can show areas of brain tissue that are not functioning and thus help doctors diagnose a TIA (or an ischemic stroke). However, diffusion MRI is not always available.
Other imaging tests help determine whether an artery to the brain is blocked, which artery is blocked, and how complete the blockage is. These tests provide images of the arteries that carry blood through the neck to the brain (the internal carotid arteries and the vertebral arteries) and the arteries of the brain (such as the cerebral arteries). Color Doppler ultrasonography (used only for the internal carotid arteries), magnetic resonance angiography (see Common Imaging Tests: Magnetic Resonance Angiography (MRA)), or CT angiography (see Common Imaging Tests: CT Angiography) may be done. Sometimes if the stroke is severe, cerebral angiography (using a dye injected through a catheter) is done (see Common Imaging Tests: CT Angiography).
Treatment
Treatment of TIAs is aimed at preventing a stroke. It is the same as that after an ischemic stroke.
The first step in preventing a stroke is to control, if possible, the major risk factors for it: high blood pressure, high cholesterol levels, smoking, and diabetes. Taking an antiplatelet drug, such as aspirin, a combination tablet of low-dose aspirin plus dipyridamole, or clopidogrel, reduces the chance that clots will form and cause TIAs or ischemic strokes. (Platelets are tiny cell-like particles in the blood that help it clot in response to damaged blood vessels.)
The degree of narrowing in the carotid arteries helps doctors estimate the risk of a stroke or subsequent TIAs and thus determine the treatment. If people are thought to be at high risk (for example, if the carotid artery is narrowed at least 70%), an operation to widen the artery (called carotid endarterectomy) may be done to reduce the risk (see Stroke (CVA): Surgery). Carotid endarterectomy usually involves removing atheromas and clots in the internal carotid artery. However, the operation can trigger a stroke because the operation may dislodge clots or other material that can then travel through the bloodstream and block an artery. However, after the operation, the risk of stroke is lower for several years than it is when drugs are used.
In other narrowed arteries, such as the vertebral arteries, endarterectomy may not be possible because the operation is riskier to perform in these arteries than in the internal carotid arteries.
If people are not healthy enough to have surgery, angioplasty with stenting (see Coronary Artery Disease:Overview of Coronary Artery Disease ) may be done. For this procedure, a thin, flexible tube (catheter) with a balloon at its tip is threaded into the narrowed artery. The balloon is then inflated for several seconds to widen the artery. To keep the artery open, doctors insert a tube made of wire mesh (a stent) into the artery.
Last full review/revision November 2007 by Elias A. Giraldo, MD, MS
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