The assumption that TIAs are simply mild ischemic strokes is widespread and thus, they are often referred to as “mini-strokes.” TIAs are thought to occur when a blood clot temporarily clogs an artery, blocking blood flow to the brain. The symptoms are the same as for stroke but are temporary. Most of them last less than five minutes. Unlike stroke, TIA doesn’t permanently injure the brain.
Although most strokes are not preceded by TIAs, more than one-third of people who have had one or more TIAs will later have a stroke, according to American Stroke Association statistics.
A team of Danish researchers noticed that some patients seemed to experience a cluster of TIAs with the same symptoms – indicating that the same part of the brain is affected. In addition, the deficits in speech and motor ability that were observed sometimes reflected that large areas of the brain were involved. However, because they were TIAs, the events left no permanent disability. So, they began looking for possible differences in the causes of TIAs and stroke.
“It was hard for us to believe that those events were caused by blood clots forming and dissolving in the same part of the brain again and again,” explains lead researcher Tom S. Olsen, M.D., Ph.D., chairman of the department of neurology, Gentofte University Hospital in Hellerup, Denmark.
They used data from the community-based prospective Copenhagen Stroke Study to compare the risk factor profiles and short- and long-term outcomes of 154 individuals who had TIAs with 482 who had experienced mild strokes.
“If TIAs are ‘just’ small strokes, one might expect similarities in the risk-factor profile and the outcome of patients with TIAs and mild stroke,” he notes.
Instead, they found differences. TIA patients were half as likely to have diabetes (9 percent vs. 18 percent) and half as likely to have claudication – narrowing of the leg arteries, which indicates atherosclerosis throughout the body (7 percent vs. 15 percent).
“A different risk-factor profile may indicate that some TIAs have a different cause than strokes,” he says. “It is clear that many transient ischemic attacks are due to blood clots. But it could be that some of them are due to spasm of brain arteries instead of a clot.” If some TIAs are not caused by blood clots, then aspirin therapy, which makes the blood less likely to clot, cannot be expected to prevent them, he notes.
“In addition, our results may mean that patients with TIAs should not be included in randomized trials of drugs to prevent stroke,” Olsen says. “This is important because it raises the question: Does spontaneous vasospasm (the sudden constriction of a blood vessel that reduces blood flow) play a role in TIAs and maybe even stroke?”
Even though risk factors are different, both events can be deadly. Short-term mortality rates indicated that 1.3 percent of TIA patients died, as did 2.3 percent of the minor stroke patients. After five years the survival rates were virtually the same for both conditions – 57.9 percent of TIA patients and 56.8 percent of those who had a minor stroke were alive five years later.
Symptoms of stroke are:
Sudden numbness or weakness of the face, arm or leg, especially on one side of the body.
Sudden confusion, trouble speaking or understanding.
Sudden trouble seeing in one or both eyes.
Sudden trouble walking, dizziness, loss of balance or coordination.
Sudden, severe headache with no known cause.
The symptoms are the same for TIA, but are temporary.
Co-authors are Lars P. Kammersgaard, M.D.; Henrik S. Jorgensen, M.D., Ph.D.; Hirofumi Nakayama, M.D., Ph.D.; Palle M. Pedersen, M.A., Ph.D.; and Hans O. Raaschou, M.D.