Definition of Transient ischemic attack:

A transient ischemic attack (TIA) is an episode in which a person has stroke -like symptoms for less than 24 hours, usually less than 1-2 hours.

A TIA is often considered a warning sign that a true stroke may happen in the future if something is not done to prevent it.

Causes, incidence, and risk factors:

A transient ischemic attack (TIA) is caused by temporary disturbance of blood supply to an area of the brain, which results in a sudden, brief decrease in brain function. (A decrease in brain function is called a neurologic deficit.)

A TIA is different than a small stroke. The symptoms of TIAs do not last as long as a stroke and do not show changes on CT or MRI scans. (Small strokes do show changes on such tests.)

The temporary loss of blood flow to the brain can be caused by:

• Blood clot within an artery of the brain
• Blood clot that travels to the brain from somewhere else in the body (for example, the heart)
• Injury to blood vessels
• Narrowing of a blood vessel in the brain or leading to the brain

For instance, the temporary disruption in blood flow could be due to a blood clot that occurs and then dissolves.

Less common causes of TIA include:

• An irregular heart rhythm called atrial fibrillation
• Certain blood disorders, including polycythemia, sickle cell anemia, and syndromes where the blood is very thick
• Conditions that cause blood vessels problems such as fibromuscular dysplasia, systemic lupus erythematosus, and syphilis
• Inflammation of the arteries such as arteritis, polyarteritis, and granulomatous angiitis
• Spasm of the small arteries in the brain

Atherosclerosis ("hardening of the arteries") is a condition where fatty deposits occur on the inner lining of the arteries. This condition dramatically increases the risk for both TIAs and stroke. Approximately 80-90% of people who have a stroke due to atherosclerosis had a TIA episode before.

Other risks for TIA include high blood pressure, heart disease, migraine headaches, smoking, diabetes, and increasing age.

About a third of those diagnosed with TIA will later have a stroke. TIAs are more common among men and black people.