Episodes of temporary loss of function in one area of the brain resulting from a reduced blood supply to the brain
In a transient ischaemic attack, part of the brain suddenly and briefly fails to function properly because it is temporarily deprived of oxygen by blockage of its arterial blood supply. Transient ischaemic attacks can last for anything from a few seconds to 1 hour and have no after-effects. If the symptoms persist for longer than 24 hours, the attack is classified as a stroke.
In the UK, an estimated 1 in 2,500 people each year has a transient ischaemic attack, more commonly after the age of 45. Attacks are three times more common in men. It is important that a transient ischaemic attack is not ignored because there is a strong possibility that it may be followed by a stroke. Without treatment, about 1 in 3 people who has an attack goes on to have a stroke later on.
Two conditions can lead to blockage of an artery supplying the brain. A blood clot, called a thrombus, may develop in an artery, or a fragment from a blood clot, called an embolus, may detach itself from elsewhere in the body and travel in the blood to block an artery (see Thrombosis and embolism).
A thrombus usually forms in blood vessels that are affected by atherosclerosis, a condition in which fatty deposits build up in the vessel wall. People at increased risk of atherosclerosis include smokers and those who have a high-fat diet. People who have an inherited tendency towards high levels of fat (see Inherited hyperlipidaemias) or people with diabetes mellitus are at risk. High blood pressure (see Hypertension) increases the risk of atherosclerosis.
The emboli that cause transient ischaemic attacks usually originate in the heart, the aorta (the main artery of the body), or the carotid or vertebral arteries in the neck. Blood clots are more likely to form in the heart if it has been damaged by a heart attack (see Myocardial infarction), if the heartbeat is irregular (see Atrial fibrillation), or if the heart valves are damaged or have been replaced (see Heart valve disorders). Sickle-cell disease can also increase the risk of transient ischaemic attacks because abnormally shaped red blood cells tend to clump together and block blood vessels.
The symptoms of a transient ischaemic attack usually develop suddenly and are often short-lived, lasting for only a few minutes. Symptoms vary depending on which part of the brain is affected and may include the following:
Loss of vision in one eye or blurred vision in both.
Difficulty in finding the right words.
Problems understanding what other people are saying.
Numbness or pins and needles on one side of the body.
Weakness or paralysis on one side of the body, affecting one or both limbs.
Feeling of unsteadiness and general loss of balance.
Although the symptoms of transient ischaemic attacks disappear within an hour, attacks tend to recur. People may have a number of attacks in one day or over several days. Sometimes, several years may elapse between attacks.
Transient ischaemic attacks themselves causes no permanent after-effects but people who have them are at increased risk of stroke and it is therefore important to seek urgent medical help.
Your doctor will carry out a physical examination, which will include checking your blood pressure, heart rhythm, and neurological function. He or she may arrange for CT scanning or MRI of your brain to look for other causes of your symptoms. You might also have ultrasound scanning of the arteries in your neck (see Carotid Doppler scanning) to look for narrowing. If these arteries are significantly narrowed, further imaging tests will be carried out to assess the severity of the narrowing. For example, you may have MRA (magnetic resonance angiography, a form of MRI) or cerebral angiography.
Tests to look for the source of the blood clots include echocardiography, which is used to look at the structure of your heart and the movement of its valves. Your heart rate may also be monitored for 24 hours to look for irregularities in your heart rhythm (see Ambulatory ECG).
You may have blood tests to look for other factors that increase the risk of having a transient ischaemic attack, such as diabetes mellitus and hyperlipidaemias. Blood tests may also be used to check for blood disorders that increase the risk of a clot forming.
Once a transient ischaemic attack has been diagnosed, the aim of treatment is to reduce your risk of having a stroke in the future. You will be advised to reduce the amount of fat in your diet and, if you smoke, you should stop. If you have diabetes mellitus, you should make sure your blood glucose levels are well controlled. Your doctor will prescribe appropriate drugs to treat high blood pressure (see Antihypertensive drugs) or an irregular heartbeat (see Antiarrhythmic drugs) if you have either of these conditions.
Treatment after a transient ischaemic attack can be as simple as taking half an aspirin daily to help to prevent blood clots from forming inside blood vessels. Other drugs that help to prevent blood clotting, such as warfarin, may be prescribed if emboli originate from clots that have formed in the heart.
If your doctor finds that the arteries in your neck are severely narrowed, he or she may suggest that you have a surgical procedure called a carotid endarterectomy to clear fatty deposits from the narrowed arteries. Alternatively, you may be referred for a surgical procedure called balloon angioplasty, in which a small balloon is inserted into the affected artery or arteries. Once in place, the balloon is inflated to open up the narrowed section of artery. Both of these procedures increase the diameter of the blood vessel and improve the blood supply to the brain.
Transient ischaemic attacks may occur intermittently over a long period or they may stop spontaneously. Of those people who have a transient ischaemic attack, about 1 in 5 will have a stroke within a year. The more frequently you have transient ischaemic attacks, the higher your risk of having a stroke in the future. However, if you take appropriate steps to change aspects of your lifestyle, such as giving up smoking and adopting a low-fat diet, you will reduce the risk of having further transient ischaemic attacks or a stroke.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.