Wednesday, March 11, 2009 13:06

As we discussed earlier, there is a second type of stroke-like event: Transient Ischaemic Attacks (TIAs). These are exactly what they seem. Transient, meaning they don’t last long; ischaemic, meaning the blood supply has been cut off; attacks, meaning episodes. In other words, TIAs are like repeated strokes, which then go away after a matter of minutes or hours.

In a TIA, a tiny clump of cells forms in the blood, then jams in one of the smaller arteries in the brain. This temporarily interrupts the blood supply to a small area of the brain, which immediately ceases to function properly. However, the clump quickly disperses and the blood supply is restored. During the short time the clump is in place the patient experiences the symptoms of a stroke, which then go away again. The difference between a TIA and a stroke is that a TIA spontaneously resolves – usually within twenty-four hours, and often within a few minutes.

We think now that TIAs are caused by little clumps of platelets; these are tiny cells in the blood that initiate blood clotting. Under some circumstances platelets stick together too easily, forming little clumps which are small enough to pass round the general circulation, but can get jammed in the smaller arteries.

Most cells in the body can function for a short time without a blood supply, so platelet clumps like this can block blood vessels in the muscles, the bones, or the skin without causing symptoms; by the time they are likely to cause symptoms they will have dispersed. However, because nervous tissue cannot function for even a few minutes without an intact blood supply, even a small clot interrupts the workings of the brain. As the clot disperses, the blood supply returns, and that area of the brain starts working properly again.

TIAs are exactly like small strokes which come and go. A patient suddenly finds he has lost the use of an arm or a leg; he can’t speak properly or understand what someone else is saying; shortly afterwards the power returns to the muscles, the speech comes back, and comprehension returns.


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