Causes of Transient ischaemic attack

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A TIA occurs when blood supply to the brain is temporarily disrupted. The most common cause is that the blood vessels supplying blood to the brain are blocked. This may be because of a narrowing of the arteries themselves, or because the substances in the arteries (blood cells and fatty deposits) have formed a clot.

Narrowing of the arteries is frequently due to atherosclerosis, a common degenerative disease of the arteries. In atherosclerosis, fatty plaques (atheroma) develop on the inner lining so that the normal flow of blood is reduced. High cholesterol levels will also narrow arteries, because cholesterol forms fatty deposits that line the inside of the arteries.

About 25% of TIAs are attributable to high blood pressure. This condition encourages atherosclerosis and weakens the blood vessels. A clot causing blockage in a blood vessel, called a thromboembolism, may be caused by a number of factors including:

A heart condition such as atrial fibrillation, in which the heartbeat is irregular, or congestive heart muscle disease, when the heart does not pump blood effectively;
Blood conditions such as sickle cell anaemia, leukaemia, high levels of fat in the blood (hyperlipidaemia), abnormally thickened blood (polycythaemia) or overproduction of platelets (thrombocyaemia);
Infections such as phlebitis, which inflames blood vessel walls and encourages formation of clots.
Diabetes mellitus, which can lead to narrowing of blood vessels and poor circulation.

Sometimes a TIA occurs when a blood clot from a blood vessel in another part of the body moves upwards into one of the brain's arteries. Very rarely, symptoms of a TIA are due to bleeding (haemorrhage) in the brain.