Transient ischemic attacks are caused when blood flow to parts of the brain are restricted for brief periods of time. 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.
Transient ischemic 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 break off and lodge in the small blood vessels of the brain
- Spasms in the walls of the arteries
- High blood pressure
- Conditions in which the blood flows but does not have enough oxygen to nourish the brain. This can happen when a person is severely anemic, has carbon monoxide poisoning or has a condition that produces abnormal blood cells or clotting function, such as leukemia or polycythemia.
A transient ischemic attack starts suddenly and typically lasts between two and 30 minutes. Rare cases can last more than two hours. Its effects vary, depending on what part of the brain is deprived of blood and oxygen.
Many different symptoms can occur, including:
- Weakness or paralysis of an arm or leg or one side of the body
- Loss of (or abnormal) sensations in an arm, 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 of a transient ischemic attack are similar to those of a stroke, but are temporary and reversible. However, these kind of attacks tend to recur. A person may have several in one day or only two or three in several years. About one-third of the time, a transient ischemic attack is followed by a stroke. Roughly half of such strokes occur within a year of having a transient ischemic attack.
Many disorders have symptoms similar to those of transient ischemic attacks, such as seizures, tumors, migraines or abnormal blood sugar levels. 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 where there is brain damage, are not useful for diagnosing transient ischemic attacks where there is no permanent brain damage.
If the blockage occurs in one or both carotid arteries, several techniques can be used to confirm transient ischemic attacks. (When these arteries are affected, common symptoms include 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 scans and Doppler flow studies 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 done if there is a severe narrowing of the artery. In a cerebral angiography, a fluid is injected into an artery while X-rays of the head and neck are taken.
Ultrasound scans and Doppler flow studies are less helpful in assessing the vertebral arteries. In that case, MRI and angiography are the only sure ways to verify that a vertebral artery is diseased. However, while surgery may be used to correct blockages of the carotid arteries, this approach may not be viable for vertebral artery blockages.
Treatment of transient ischemic attacks is aimed at preventing stroke. The major risk factors for stroke are high blood pressure, high cholesterol levels, smoking and diabetes. Eliminating or reducing these risk factors is the first step in preventing strokes. Other steps that may be taken include:
- Drugs to reduce the ability of the blood to clot, which is a major cause of stroke. This may be as simple as an aspirin (half of an adult tablet or one children's tablet a day), or 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. This option 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.
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