Transient Ischemic Attack
A transient ischemic attack is a brief episode during which parts of the brain do not receive enough blood. Because the blood supply is restored quickly, brain tissue does not die as it does in a stroke. These attacks are often early warning signs of a stroke.
Symptoms of Transient Ischemic Attack
A transient ischemic attack starts suddenly and lasts about two to 30 minutes. (Rarely, some can last more than two hours.) The effects vary depending on what part of the brain is deprived of blood and oxygen. Symptoms of an attack can include:
- Loss of (or abnormal) sensations in an arm, leg or one side of the body
- Weakness or paralysis of an arm or leg or one side of the body
- Partial loss of vision or hearing
- Double vision
- Slurred speech
- Problems thinking of or saying the right word
- Inability to recognize parts of the body
- Unusual movements
- Loss of bladder control
- Imbalance and falling
The symptoms are similar to those of a stroke, but they do not last and are reversible. However, these attacks tend to recur. A person may have several in a day or only two or three in several years. In approximately one-third of cases, a transient ischemic attack is followed by a stroke, and roughly half of such strokes occur within a year of having an attack.
Causes and Risk Factors for Transient Ischemic Attack
Such attacks can be caused by a variety of factors, including:
- Small pieces of fatty material or calcium that have built up on an artery wall and then broken off and lodged in the small blood vessels of the brain
- Cerebral artery stenosis
- Spasms in the walls of the arteries
- High blood pressure
- A lack of oxygen in the blood flowing to the brain, which can occur when a person is severely anemic, has carbon monoxide poisoning or has leukemia or polycythemia (a condition that produces abnormal blood cells and clotting function).
Diagnosing Transient Ischemic Attack
Many disorders (seizures, tumors, migraines or abnormal blood sugar levels) have symptoms similar to those of transient ischemic attacks. While sudden neurologic symptoms suggest clues about which area of the brain is affected, careful evaluation is necessary. Tools like computed tomography (CT) or magnetic resonance imaging (MRI) scans, which are useful in diagnosing a stroke involving brain damage, are not useful for diagnosing transient ischemic attacks that caused no permanent brain damage. Several techniques can be used to confirm an attack if the blockage occurs in one or both carotid arteries, common signs of which can be blindness in one eye, weakness or sensation abnormalities. Diagnostic techniques include:
- Listening to the sound of the blood flow in the carotid arteries using a stethoscope. The uneven flow creates sounds (bruits). However, bruits can be present without any significant blockage.
- Ultrasound scan and Doppler flow study. These tests are done at the same time to measure the size of the blockage and how much blood can flow around it.
- An MRI scan or cerebral angiography can be performed if a severe narrowing of the artery is present. In a cerebral angiography, a fluid is injected into an artery while X-rays of the head and neck are taken.
- Computed tomography (CT) angiography
Treating Transient Ischemic Attack
Treatment of transient ischemic attacks is aimed at preventing stroke. The major risk factors for stroke are:
- High blood pressure
- High cholesterol levels
Other approaches to treating or preventing transient ischemic attack:
- If the transient ischemic attack is due to carotid artery stenosis, treatment may include or carotid artery stenting
- Drugs to reduce the ability of the blood to clot. This may be as simple as an aspirin (half of an adult tablet or one children's tablet) a day, or it may mean taking anticoagulants (such as heparin or warfarin). Sometimes dipyridamole is prescribed, but it is not as effective for most people. Ticlopidine may be given to people who do not tolerate aspirin well.
- Surgery may be considered if more than 70% of the vessel is blocked and the person has had stroke-like symptoms in the past six months. Because the usual operation (an endarterectomy) involves a one to two percent risk of causing a stroke, the benefits need to be carefully weighed against the risks in the case of small blockages.