Cerebrovascular Disease

Risk Factors

The most important risk factor for stroke, whether infarction or haemorrhage, is hypertension. Cerebral infarction is 5-10 times more common than cerebral haemorrhage. Hypertension is a major risk factor for haemorrhagic strokes and accounts for approximately 50% of cases of cerebral haemorrhage. The risk of stroke is related to the height of blood pressure. Both stroke and hypertension reach major proportions in the elderly

Although hypertension is a major risk factor for cerebral haemorrhage, the part played by hypertension in cerebral infarction is less clear. Chronic hypertension clearly exacerbates atheroma and increases involvement of smaller distal arteries. The relationship between blood pressure and atheroma, however, is complex and also relates to the level of circulating lipoproteins.

The relationship between serum lipids and stroke is less well established than the association with coronary artery disease. Increased dietary lipids, particularly cholesterol and saturated fats correlate with the development of atheroma in the walls of large and medium-sized arteries. Atheroma develops in the carotid arteries at about the same rate as in the coronary arteries. Involvement of the vertebral arteries and vessels of the circle of Willis tends to occur later. Atheroma develops when a high plasma level of low density lipoprotein is associated with excessive amounts of low density lipoprotein-cholesterol within the arterial intima. Normally only small amounts of low density lipoprotein are transported across the vascular endothelium and processes that disrupt the endothelium such as hypertension, free radicals, toxic substances such as cigarette smoke, and hyperlipidaemia are contributory factors.

• Diabetes

Diabetes mellitus increases the incidence of strokes up to 3-fold in both sexes. There is, however, considerable variation in the incidence of cerebral infarction amongst diabetics depending on the level of other risk factors.

• Environmental Factors

• Diets resulting in hyperlipidaemia.

• High salt intake may promote hypertension.

• Smokers have an approximately 3-fold increased risk for subarachnoid haemorrhage and a two-fold increased risk of cerebral infarction. The relationship between smoking and stroke is less clear than that for coronary heart disease and some of the increased risk of stroke relates to the complications of cardiac problems.

In general, stroke incidence tends to increase with weight and this is more marked in women than in men.

• Alcohol

The relationship between alcohol intake and stroke is complex. Small amounts of alcohol appear to decrease the risk of stroke whereas heavy drinking appears to increase the risk up to 2.5-fold.

• Impaired Cardiac Function

The greatest risk factor is atrial fibrillation, due to the increased risk of embolisation. Emboli may also complicate myocardial infarction,cardiac valvular disease, and congestive cardiac disease.

• Carotid Artery Stenosis

The increased risk is particularly marked in those who have previously experienced transient ischaemic attacks.

• Cardiac surgery

• Oral contraceptives with a high oestrogen content

There is an increased risk of transient ischaemic attacks and embolic, thrombotic and haemorrhagic strokes. The risk is greatest over the age of 35, with prolonged use of the contraceptive pill, a history of migraine, cigarette smoking, and the presence of diabetes or hyperlipidaemia.

• Antiphospholipid Autoantibodies

The younger age groups are particularly vulnerable, but the also occur in older patients, and they may be recurrent. There are various syndromes sometimes associated with recurrent thrombosis of arteries and/or veins. Venous thrombosis is the more common and increases the chance of paradoxical embolus. When they involve arteries, the brain is the most common site.

The two most relevant antibodies are anticardiolipin and lupus anticoagulant.

Antiphospholipid antibodies are associated with many disorders including: