What is a TIA?

TIA is an acronym for “Transient Ischemic Attack.” The term was coined in the 1950s to designate a clinical stroke-like event that resolved completely, with no residual signs or symptoms. Early on, there was much disagreement about how long an event could last and still be called a “TIA,” but ultimately the time limit for symptoms was officially defined as 24 hours.

The motivation behind creating the concept of TIA was to call public attention to an important warning that a stroke may be imminent. TIA might be thought of as an invitation to avoid having a stroke. It is an invitation that should not be ignored. The odds of having a stroke after a TIA are approximately as follows:

The symptoms of a TIA are the same as those of a stroke, except that they are transient. Symptoms include:

TIA is often caused by a blood clot that temporarily blocks an artery, but it may also be caused by a spasm of arteries or by sluggish flow in a blood vessel that is narrowed. Sometimes it can be mimicked by things that do not involve a disturbed circulation, such as a seizure or low blood sugar. Although 24 hours is the maximal duration, most TIAs are considerably briefer, lasting less than an hour.

Like a stroke, a TIA should be considered an emergency. One should seek medical evaluation as soon as possible. It is important to stress that TIA is a diagnosis that can be properly made only in retrospect. When one is in the midst of a TIA (i.e., the symptoms have not yet resolved), there is no way of being certain that the symptoms will ever go away.

The aims of medical management of TIA are like those that one adopts when trying to prevent a recurrent stroke. In all cases, potential stroke risk factors should be sought and modified if they are present. Specific treatment recommendations for an individual will depend on identifying the mechanism of the TIA. Two common mechanisms are blood clots that migrate to the brain from the heart or large arteries in the neck, and sluggish blood flow through small blood vessels within the brain.

When the concept of TIA was formulated, we had almost nothing in the way of imaging or laboratory tests to confirm that clinical symptoms were, in fact, due to a disturbance of circulation. With modern imaging techniques such as CT and MRI scans, we are able to identify hemorrhages, tumors, and other disorders that may masquerade as TIA. These techniques also reveal that 15-20% of TIAs are actually strokes, even though the signs and symptoms have subsided.

Given these considerations, basing the definition of TIA on clinical criteria and an arbitrary 24-hour time limit is seen as outdated, confusing, and potentially misleading. It is proposed that TIA be redefined according to imaging and physiologic evidence. If such evidence shows that the event was a stroke, it should be called a stroke, even if all signs and symptoms have subsided.