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Transient Ischemic Attacks
A transient ischemic attack (TIA) is a disturbance in brain function that typically lasts less than 1 hour and results from a temporary blockage of the brain’s blood supply.
The cause and symptoms of a TIA are the same as those of an ischemic stroke.
TIAs differ from ischemic strokes because symptoms usually resolve within 1 hour and no permanent brain damage occurs.
Symptoms suggest the diagnosis, but brain imaging is also done.
Other imaging tests and blood tests are done to diagnose the cause of the TIA.
Controlling high blood pressure, high cholesterol levels, and high blood sugar levels and not smoking are recommended.
Drugs to make blood less likely to clot and sometimes surgery (carotid endarterectomy) or angioplasty are used to reduce the risk of stroke after a TIA.
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. The risk increases as early as 2 days after 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 TIAs do not seem to cause permanent brain damage. That is, TIA symptoms resolve completely and quickly, and few or no brain cells died—at least not enough to cause any changes that can be detected by brain imaging.
Causes of TIAs and ischemic strokes are mostly the same (see Ischemic Stroke : Causes). 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 (usually in the neck), travels through the bloodstream (becoming an embolus), and lodges in an artery that supplies the brain.
If the arteries to the brain are already narrowed (as in people with atherosclerosis), other conditions occasionally cause TIAs. These conditions include a very low oxygen level in the blood (as may result from a lung disorder), a severe deficiency of red blood cells (anemia), carbon monoxide poisoning, thickened blood (as in polycythemia), or very low blood pressure (hypotension).
Symptoms of a TIA develop suddenly. They are identical to those of an ischemic stroke (see Ischemic Stroke : Symptoms) but are temporary and reversible. They usually last 2 to 30 minutes and resolve completely within 1 hr. TIAs recur in about 5% of people with atherosclerosis. People may have several in 1 day or only two or three in several years.
When heard through a stethoscope, turbulent blood flow produces a murmur as blood tumbles over an abnormal heart valve. A similar sound called a bruit is heard as blood goes through a narrowed or irregular artery. A bruit indicates that atherosclerosis, which is a major risk factor for transient ischemic attack or stroke, is present within the blood vessel.
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.
Doctors suspect a TIA if symptoms of a stroke develop, particularly if they resolve in less than 1 hour. Doctors may be unable to tell a stroke from a TIA before symptoms resolve. They evaluate people who have symptoms of a TIA or stroke rapidly. People who have had a TIA are usually admitted in the hospital, at least for a short time, to do tests and to see whether a stroke occurs soon after the 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-weighted MRI, can show areas of brain tissue that are not functioning and thus help doctors diagnose a TIA (or an ischemic stroke). However, diffusion-weighted 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 to evaluate blood flow through arteries), magnetic resonance angiography (see Magnetic resonance angiography), or CT angiography (see CT angiography) may be done.
Treatment of TIAs is aimed at preventing a stroke. It is the same as that after an ischemic stroke (see Ischemic Stroke : Treatment).
The first step in preventing a stroke is to control, if possible, the major risk factors for it: high blood pressure (see High Blood Pressure : Treatment), high cholesterol levels (see Dyslipidemia : Treatment), smoking, and diabetes (see Diabetes Mellitus (DM) : Treatment of Diabetes).
Taking an antiplatelet drug, such as aspirin, a combination tablet of low-dose aspirin plus dipyridamole, clopidogrel, or clopidogrel plus aspirin, reduces the chance that clots will form and cause TIAs or ischemic strokes. Antiplatelet drugs make platelets less likely to clump and form clots. (Platelets are tiny cell-like particles in the blood that help it clot in response to damaged blood vessels.)
If a blood clot from the heart caused the TIA, anticoagulants, such as warfarin, are given to make blood less likely to clot. Dabigatran, apixaban, and rivaroxaban are new anticoagulants that are sometimes used instead of warfarin.
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 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 is typically not done because the operation is riskier when it is done in arteries other than the internal carotid arteries.
If people are not healthy enough to have surgery, angioplasty with stenting (see Figure: Understanding Percutaneous Coronary Intervention (PCI)) may be done. For this procedure, a 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.
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