The older you get, the greater the risk of having a stroke. About 75% of all people who have a stroke are older than 65 years. There is also an increased risk of lipohyalinosis with advancing age.
Family history is another factor that cannot be changed; the risk of having a stroke is greater if a family member has had a stroke or TIA of any cause.
Controllable risk factors
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Hypertension
This is probably the single most important factor in stroke development. Hypertension affects the walls of arteries in several ways:
The wall can become thickened, narrowing the space available for blood flow
The function of the cells lining the artery is compromised
Although thickened, the wall becomes weaker, and can form blowouts – these are called aneurysms
The development of atheroma with cholesterol plaques is hastened
The risk of clot formation within the artery is much increased
Lipohyalinosis can occur – this condition is a buildup of a lipid plus a form of degeneration of the artery. It often affects the small arteries deep inside the brain. Strokes due to this are called “Lacunar infarcts”.
It is clear thus, that strict control of hypertension is an extremely important factor, especially in persons known to be at risk of developing strokes. Managementof hypertension may include lifestyle changes such as weight loss and exercise, plus medical therapy.
Cardiovascular disease
The development of atheroma affects cerebral arteries as well, but it also contributes in other ways.
Atheromatous plaque is the commonest cause of localised narrowing of arteries, especially the larger arteries, which are often the source of emboli blocking brain arteries. High LDL is thus a recognised risk factor.
Atheromatous Coronary Artery Disease (CAD) is the commonest cause of heart attacks, which can also contribute to hypoperfusion at the time of an infarct.
Heart failure as a result of atheromatous disease can lead to sluggish blood flow, with an increased risk of clots forming and lodging in the brain arteries.
Heart rhythm disturbances, notably Atrial Fibrillation (AF), often result from atheromatous disease. This AF is the commonest source of clots in the heart, and a very common cause of stroke.
Other heart problems, such as valve disease and cardiomyopathy are also associated with an increased risk of stroke.
Smoking
This is an established risk factor for stroke, mainly because it promotes atheroma, and increases the clotting ability of blood. Nicotine also causes arteries to constrict, and raises the pulse rate and blood pressure: all these factors combine to increase the workload of the heart and reduce blood flow to the brain.
It is very obvious that stopping smoking is a smart choice.
TIA
As already described, this is medical emergency. Without treatment of underlying causes, there is a 20% recurrence rate within 90 days. Commonly, the follow-up incident is a full-blown stroke, which could have been totally avoidable.
Diabetes
Poorly controlled diabetes increases the rate and severity of atherosclerosis, and promotes blood clotting. It is also associated with obesity and hypertension.
Blood disorders
In general, blood and coagulation disorders are not common primary causes for stroke or TIA, but should be considered in younger persons, ie under the age of 45.
Polycythaemia: This is a condition in which there is an excess of red blood cells : the ensuing hyperviscosity of the blood is a risk for clot formation.
Sickle cell anaemia: this genetically determined abnormality can result in excess clot formation, especially in small vessels.
Clotting disorders: Genetic deficiency of some clotting factors increase the risk of bleeding.
Others
Severe migraines may lead to a stroke in susceptible persons – this is a rare condition.
The use of oral contraceptives, especially in smokers, is associated with an increased risk of stroke.
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