Blood supply to the brain may be interrupted by arteries furring up with ATHEROSCLEROSIS (which is accelerated by HYPERTENSION and DIABETES MELLITUS, both of which are associated with a higher incidence of strokes) or being occluded by blood clots arising from distant organs such as infected heart valves or larger clots in the heart (see BLOOD CLOT; THROMBOSIS). Hearts with an irregular rhythm are especially prone to develop clots. Patients with thick or viscous blood, clotting disorders or those with inflamed arteries – for example, in SYSTEMIC LUPUS ERYTHEMATOSUS (SLE) – are particularly in danger of having strokes. Bleeding into the brain arises from areas of weakened blood vessels (arteriovenous malformations or arterial microaneurysms), many of which may be congenital.

Minor episodes due to temporary lack of blood supply and oxygen (called TRANSIENT ISCHAEMIC ATTACKS (TIA)) are manifested by short-lived weakness or numbness in an arm or leg; these may lead to no further problem, but often precede a more significant stroke. Strokes cause sudden weakness or complete paralysis of the muscles controlled by the part of the brain affected, as well as sensory changes (e.g. numbness or tingling). In the worst cases these symptoms and signs may be accompanied by loss of consciousness. If the stroke affects the area of the brain controlling the larynx and throat, the patient may suffer slurring or loss of speech and difficulty in initiating swallowing. When the face is involved, the mouth may droop and the patient dribble. Strokes caused by haemorrhage may be preceded by headaches. Rarely, strokes are complicated by epileptic fits (see EPILEPSY). If, on the other hand, numerous small clots develop in the brain rather than one major event, this may manifest itself as a gradual deterioration in the patient's mental function, leading to DEMENTIA.

Tests on the heart, MAGNETIC RESONANCE IMAGING (MRI), COMPUTED TOMOGRAPHY (CT) or ultrasonic scans (see ULTRASOUND) on arteries in the neck may indicate the original sites of distantly arising clots. Blood tests may show increased thickness or tendency to clotting, and the diagnosis of general medical conditions can explain the presence of inflamed arteries which are prone to block. Brain imaging by MRI may show the position and size of the damaged brain tissue and can usually distinguish between a clot or infarct and a rupture of, and haemorrhage from, a blood vessel in the brain.

It is best to try to reduce the risk of a stroke, for example by controlling diabetes or high blood pressure. Treatment with ANTICOAGULANTS (including aspirin) may prevent the formation of clots in those at risk. In some individuals, surgery on the carotid artery to remove a blockage or the insertion of a STENT may prevent further problems.

If someone has an ischaemic stroke (that is not one caused by haemorrhage) and comes under medical care within 4½ hours, then they may be helped by a ‘clot-busting’ drug such as TISSUE PLASMINOGEN ACTIVATOR. If the risk of a haemorrhagic stroke has been confirmed by finding an aneurysm in a brain blood vessel, surgical intervention may be needed.

But for many patients, once the stroke has occurred, there is no effective treatment to reduce the damage to brain tissue. Function will return to the affected part of the body only if and when the brain recovers and messages are again sent down the appropriate nerves. Simple movements are more likely to recover than delicate ones, and sophisticated functions have the worst outlook. Thus, movement of the thigh may improve more easily than fine movements of fingers, and any speech impairment is more likely to be permanent. A rehabilitation team can help to compensate for any disabilities the subject may have. Physiotherapists maintain muscle tone and joint flexibility, whilst waiting for power to return; occupational therapists advise about functional problems and supply equipment to help patients overcome their disabilities; and speech therapists help with difficulties in swallowing, improve the clarity of remaining speech or offer alternative methods of communication. District nurses or home helps can provide support to those caring for victims of stroke at home. Advice about strokes may be obtained from the Stroke Association (www.stroke.org.uk).