Transient ischemic attack (TIA)

Alternative names:

little stroke; mini stroke; TIA

Definition:

A brain disorder caused by temporary disturbance of blood supply to an area of the brain, resulting in a sudden, brief (less than 24 hours, usually less than 1 hour) decrease in brain functions.

Causes, incidence, and risk factors:

The brain requires about 20% of the circulation of blood in the body. The primary blood supply to the brain is through two arteries in the neck (the carotid arteries) which then branch off within the brain to multiple arteries that supply specific areas of the brain. Even 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 commonly include such problems as changes in vision, speech changes, decreased movement or sensation in a part of the body, and changes in the level of consciousness. If the blood flow is decreased for longer than a few seconds, brain cells in the area are destroyed (infarcted) causing permanent damage to that area of the brain or even death. The major causes of loss of blood circulation to areas of the brain are reduced blood flow (ischemia) and bleeding (hemorrhage).

Transient ischemic attack (TIA, "little stroke") is a warning that the body's safety mechanisms are overloaded and indicates that a stroke may be pending. About one-third of the people with TIA will later have a stroke. However, about 80 to 90% of people who have a stroke secondary to atherosclerosis had TIA episodes before their stroke. Approximately one-third of the people with TIA will have recurrent TIAs, and one-third will have only a single episode of TIA. The age of onset varies, but incidence rises dramatically after age 50. TIA is more common among men and African-Americans.

A TIA is caused by a temporary state of reduced blood flow (ischemia) in a portion of the brain. This is most frequently caused by tiny blood clots (microemboli) that temporarily occlude a portion of the brain. The microemboli are caused by atherosclerotic plaque in the arteries that supply the brain. Atherosclerosis ("hardening of the arteries") is a condition where fatty deposits occur on the inner lining of the arteries. 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. Clots (thrombus) may form at the site of the plaque, triggered by irregular blood flow in this location, and the thrombus may occlude the blood vessels in the brain. Pieces of plaque or clots may break off and travel through the bloodstream from distant locations, forming an embolus that can occlude the small arteries, causing TIAs. Occlusions that last for more than a few minutes more commonly cause stroke.

Less common causes of TIA include blood disorders (including polycythemia, 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. Hypotension (low blood pressure) may precipitate symptoms in an individual with a pre-existing vascular lesion.

Risks for TIA include high blood pressure (hypertension), heart disease, migraine headaches, smoking, diabetes mellitus, and increasing age.