Transient ischaemic attack is a warning sign that a stroke may just be around the corner.
A TRANSIENT ischaemic attack (TIA) is due to a temporary interruption of the blood supply to part of the brain, leading to a “mini-stroke”. Its features are similar to that of a stroke, but the duration is about a few minutes. The TIA is usually resolved within 24 hours.
TIAs provide a warning that further TIAs or a stroke is on the way. Its incidence is not well known as many people who have TIA do not seek medical attention. However, strokes are the third most common cause of death in Malaysia. It is estimated that there are about 52,000 strokes per annum, i.e. strokes occur in six persons every hour.
It has been estimated that without treatment, the likelihood is one in 10 that a stroke will occur within a month after a TIA. As strokes lead to disability and even death in some instances, TIAs should be treated as seriously as strokes. Its early investigation and treatment will markedly reduce the risk of another TIA or stroke.
Anatomy of a TIA
The brain receives its blood supply primarily from the carotid arteries in the front of the neck and secondarily from the vertebral arteries in front of the backbone. These arteries branch into smaller vessels that supply blood to all parts of the brain.
One of these smaller blood vessels gets blocked off during a TIA. This blockage is temporary, lasting a few minutes, and the blood supply is restored soon after, unlike a stroke, in which the blockage lasts a longer period of time. The lack of a constant supply of oxygen-rich blood leads to damage, and later, death of the brain cells.
The blockage is due either to a narrowing of the arteries or as a result of a blood clot formed elsewhere in the body getting into the brain’s arteries to reach a blood vessel small enough to block its passage.
The brain’s arteries are narrowed or blocked by cholesterol deposits (plaques) on its inner lining due to atherosclerosis. Everyone’s arteries get narrower with age, but the process is hastened by factors like high blood pressure, poorly controlled diabetes, raised blood cholesterol, obesity, smoking, excessive alcohol intake, obesity, and a family history of diabetes or heart disease.
TIAs can also result from blood conditions like leukaemia, abnormally thickened blood (polycythaemia), or overproduction of platelets (thrombocythemia).
A TIA can result from blood clots formed in an artery (from elsewhere in the body), which gets “thrown” off (emboli) and eventually blocks the brain’s blood supply. This may be due to irregular heartbeats, the causes of which include high blood pressure, coronary artery disease, disease of the heart’s mitral valve, overactive thyroid gland and excessive alcohol intake.
It is rare that a brain haemorrhage causes a TIA.
TIAs, like strokes, are preventable as lifestyle changes can reduce many of the risk factors. However, there are some risk factors that are not preventable. They include:
·Age – The risks are increased in the older person, although TIAs can occur at any age, including the young.
·Gender – Men are more likely to have TIAs than pre-menopausal women. However, the likelihood of TIA and stroke increases in postmenopausal women. Although the reason for this is not well elucidated, it is believed that the female hormones, oestrogen and progesterone, affect the elasticity of the body’s ateries.
·Ethnicity – The risks are increased in Indians and Malays because the incidence of diabetes and hypertension are higher in these groups.
·Medical history – The risks are increased if one has had a heart attack, stroke or TIA.
·Family history – The risks are increased if a close relative has had a TIA or stroke.
There are several other factors (preventable) that increase the risks of TIAs and strokes. They include:
·High blood pressure (hypertension) is the single most important risk factor. The hypertension leads to extra strain on the arteries, causing them to narrow or be easily blocked.
·Diet – Atherosclerosis is more likely to develop with a diet high in saturated fats and excessive salt intake.
·Diabetes increases the likelihood of TIA because of the increased risk of atherosclerosis.
·Smoking doubles the likelihood of TIA or stroke because the chemicals in the cigarette smoke cause thickening of the arteries, thereby increasing the likelihood of clotting.
Features of TIA
The features vary depending on the part of the brain that is affected and the extent to which it is affected.
The common features of TIAs and strokes are:
·Face – There may be an inability to smile, open the mouth or the face or eye may hang downwards.
·Arms – There may be an inability to lift one or both arms due to numbness or weakness.
·Legs – There may be an inability to move one or both legs due to numbness or weakness.
·Speech – There may be slurring of speech or an inability to talk at all although awake.
Other features may include sudden vision loss, dizziness, difficulty talking and understanding what others say, difficulty swallowing, balancing problems, sudden headache, and blacking out.
Immediate medical attention should be sought if one has or knows another person who has features of a TIA. This will reduce the likelihood of another TIA or stroke.
The diagnosis of a TIA is made by history taking and physical examination even if one thinks that the symptoms have gone. The objective is to check the patient’s neurological status and to rule out other conditions which may have caused the symptoms.
If a TIA is suspected, a referral will be made to a physician, geriatrician or neurologist for further evaluation. This should be done within a week of the occurrence of a TIA and immediately if there is more than one TIA in a period of seven days.
There are several investigations that are carried out after a TIA to check for the underlying conditions that may have caused it. They include:
·Blood tests like clotting factors, glucose, cholesterol
·Electrocardiogram to detect any abnormal heart rhythms
·Chest x-ray may be done to exclude other medical conditions
The common methods of brain imaging are computerised tomography (CT) scan and magnetic resonance imaging (MRI).
The CT scan involves multiple x-ray imaging to produce detailed three dimensional images of the brain and will provide information about factors that may have caused the TIA, e.g. haemorrhage or tumour. The MRI involves use of magnetic and radio waves to produce detailed images of the brain.
Both the CT scan and MRI are used to take images of the brain’s blood vessels as well the blood vessels in the neck that connect the heart and the brain’s blood vessels. This procedure, called a CT or MR angiogram, involves injecting a dye into a vein in the arm.
The brain imaging modality used depends on the availability of CT scan and/or MRI.
Other investigations of the cardiovascular system will be carried out to determine the cause of the TIA. It includes ultrasound examination of the heart (echocardiogram) or carotid artery in the neck (Doppler scan). It can also include injecting dye into the carotid or vertebral arteries (arteriography) to enable a detailed examination of the arteries in the brain.
The management of TIA will be discussed in a subsequent article.
Source: Dr Milton Lum