What is transient ischaemic attack?
A transient ischaemic attack is a "mini-stroke" caused by temporary disturbance of blood supply to an area of the brain, resulting in a sudden, brief decrease in brain function. It lasts less than 24 hours, usually less than one hour.
What is the cause?
A transient ischaemic attack (TIA) is caused by an interruption of blood flow to brain cells. If the symptoms resolve completely in under 24 hours, this is called a TIA or "mini stroke." If the symptoms do not resolve, the event is called a stroke.
A brief interruption to the blood flow can cause a decrease in brain function (neurologic deficit). Symptoms vary with the area of the brain affected and may include changes in vision, speech or comprehension, vertigo, decreased movement or sensation in a part of the body, or changes in the level of consciousness. If the blood flow is decreased for a sufficient period, brain cells in the area die (infarct), causing permanent damage to that area of the brain or even death.
The loss of blood circulation to the brain can be caused by the following:
- narrowing of a blood vessel
- blood clotting within an artery of the brain
- blood clot travelling to the brain from somewhere else in the body (e.g., heart)
- a blood disease, cancer, and others
- inflammation of blood vessels
- injury to blood vessels
Atherosclerosis (hardening of the arteries) is a condition where fatty deposits occur on the inner lining of the arteries, which dramatically increases the risk for both TIAs and stroke. Atherosclerotic plaque is formed when damage occurs to the lining of an artery. Platelets clump around the area of injury as a normal part of the clotting and healing process. Cholesterol and other fats also collect at this site, forming a mass within the lining of the artery. A clot (thrombus) may form at the site of the plaque, triggered by irregular blood flow in this location, and the thrombus may then block blood vessels in the brain. Pieces of plaque or clots can also break off and travel through the bloodstream from distant locations, forming an embolus that can block the small arteries, causing TIAs.
Less common causes of TIA include blood disorders (including polycythaemia, sickle cell anemia, and hyperviscosity syndromes where the blood is very thick), spasm of the small arteries in the brain, abnormalities of blood vessels caused by disorders such as fibromuscular dysplasia, inflammation of the arteries (arteritis, polyarteritis, granulomatous angiitis), systemic lupus erythematosus, and syphilis. Other risks for TIA include high blood pressure (hypertension), heart disease, migraine headaches, smoking, diabetes mellitus, and increasing age.
What are the symptoms?
Symptoms of TIA are the same as those that occur in stroke and include the sudden development of:
- numbness and tingling
- weakness, heavy feeling of extremities
- speech difficulty (garbled speech or slurred speech)
- decreased, double or loss of vision,
- loss of balance
- lack of coordination
- gait changes, staggering
- falling (caused by weakness in the legs)
Additional symptoms that may be associated with this disease:
- facial paralysis
- eye pain
The symptoms begin suddenly, last only a short time (from a few minutes to 24 hours) and disappear completely. Symptoms may occur again at a later time. Specific symptoms vary depending on the location, the degree of vessel involvement, and the extent of collateral circulation.
What is the diagnosis?
A detailed and complete history is vital to the diagnosis, because the specific deficits demonstrated help the physician determine which area of the brain was affected. Often, the diagnosis may rest on the history alone, as symptoms and signs may have completely disappeared by the time one gets to the hospital.
A physical examination includes a neurologic examination, which may be abnormal during an episode but normal after the episode has passed. It may also be used to rule out a stroke in evolution rather than TIA. Blood pressure may be high.
Tests for TIA may include tests to determine the cause and extent of blood vessel involvement, and to rule out stroke or other disorder that may cause the symptoms. CBC and PT tests are used to rule out haematologic disease. Head CT scan or cranial MRI are used to rule out focal lesions as the cause of symptoms. An ultrasound may be performed if there is suspected carotid stenosis. An echocardiogram may be performed to look for a source of embolism. A cerebral arteriogram may be performed if there is suspected localised blood vessel disease, such as carotid artery stenosis (hardening) or vasculitis (inflammation of the blood vessels in the brain). Other tests and procedures may be performed to determine underlying disorders and to rule out other disorders that may cause the symptoms. This may include examination for hypertension, heart disease, diabetes, high blood lipids, vasculitis, and peripheral vascular disease.
What is the treatment?
The goal of treatment is to improve the arterial blood supply to the brain and prevent the development of a stroke. Treatment of recent TIA (within the prior 48 hours) usually requires admission to the hospital for evaluation of the specific cause and determination of long-term treatment. Underlying disorders should be treated appropriately, including such disorders as hypertension, heart disease, diabetes, arthritis, and blood disorders. Smoking should be stopped.
Treatment of symptoms of blood disorders (such as erythrocytosis, thrombocytosis, or polycythaemia vera, which include an increase in the number of some types of blood cells) may include phlebotomy, hydration, and treatment of the underlying blood disorder. Antihypertensive medications may be used to control high blood pressure. Medications to lower cholesterol may be useful in reducing high blood cholesterol levels.
Platelet inhibitors and anticoagulant medications (blood thinners) may be used to reduce clotting. Aspirin is the most commonly used medication; others include dipyridamole, clopidogrel, Aggrenox or heparin, coumadin, or other similar medications. Treatment may be continued for an indefinite time period.
A reduced amount of sodium in the diet to help control high blood pressure; diet for diabetics; reduced dietary fat, or other dietary changes may be recommended.
Surgery (carotid endarterectomy, removal of atherosclerotic plaque from the carotid arteries in the neck) may be appropriate for some people, particularly those with carotid artery stenosis of greater than 70% of the artery and without coexisting terminal disease or dementia.
What are the complications?
- TIA recurrence
- Injury that occurs from falls
- Bleeding as a result of anti-coagulant medications
How can TIA be prevented?
Prevention of TIA includes controlling the risk factors. Hypertension, diabetes, heart disease, and other associated disorders should be treated as appropriate. Smoking should be stopped. The use of blood thinners may prevent strokes in some patients who have blood clots or atrial fibrillation. Carotid endarterectomy in select patients may prevent stroke.