Oct 12 (Reuters) - A stroke is caused by an interruption of blood supply to the brain, usually because a blood vessel is blocked by a clot. Less commonly, the blood vessel ruptures. The blockage or rupture stops blood reaching parts of the brain, depriving it of the oxygen it needs. Nerve cells in the affected area of the brain can't work and die within minutes. When nerve cells stop, the part of the body they control can't work. The devastating effects of a severe stroke are often permanent because dead brain cells aren't replaced. EFFECTS AND SEVERITY The effects of a stroke depend on which part of the brain is injured and how severely it is affected. A very severe stroke can quickly kill. Stroke is the third most common cause of death in developed countries, after coronary heart disease and cancer. It is the second most common cause of death worldwide and in developing countries. Worldwide, 3 million women and 2.5 million men die from stroke each year. Women account for about 6 in 10 stroke deaths. Even where advanced technology and facilities are available, 60 percent of those who suffer a stroke die or become dependent. RISK FACTORS The most important modifiable cause of stroke is high blood pressure. For every 10 people who die of stroke, four could have been saved if their blood pressure had been regulated. For those under 65, two fifths of stroke deaths are linked to smoking. Other modifiable risk factors include unhealthy diet, high salt intake, underlying heart disease, irregular heart beat (atrial fibrillation), diabetes, high blood lipids and obesity. Risk of a stroke increases when a person is over 55, is male, has had a previous stroke or has a family history of the disease. Stroke is more common in men than women, but more women than men die from stroke. TYPES OF STROKE - Ischemic stroke, caused by blockage of a blood vessel, is most common and accounts for 80 to 90 percent of all strokes. It occurs when a blood clot forms and blocks flow in an artery bringing blood to part of the brain. Blood clots usually form in arteries damaged by fatty buildups, called atherosclerosis. When the blood clot forms within an artery of the brain, it is called cerebral thrombotic stroke. These often occur at night or first thing in the morning. A wandering clot (embolus) or some other particle that forms away from the brain, usually in the heart, may also cause an ischemic stroke. This is called cerebral embolism. The clot is carried by the bloodstream until it lodges in an artery leading to or in the brain, blocking the flow of blood. The most common cause of these emboli is blood clots that form during atrial fibrillation. - Hemorrhagic strokes, which have a much higher fatality rate than strokes caused by clots, occur when a blood vessel inside the brain or on the brain's surface ruptures and bleeds into the space between the brain and the skull. Hemorrhage (or bleeding) into the brain occurs when the wall of the artery is weakened by high blood pressure or deposition of amyloid. Amyloid is a protein complex related to Alzheimer's disease. Hemorrhage on the brain's surface can be caused by a head injury or a burst aneurysm. Aneurysms are blood-filled pouches that balloon out from weak spots in the artery wall. They're often caused or made worse by high blood pressure. Aneurysms aren't always dangerous, but if one bursts in the brain, they cause a hemorrhagic stroke. SYMPTOMS The most common symptom of a stroke is sudden weakness or numbness of the face, arm or leg, most often on one side of the body. Other symptoms include: confusion, difficulty speaking or understanding speech; difficulty seeing with one or both eyes; difficulty walking, dizziness, loss of balance or coordination; severe headache with no known cause; fainting or unconsciousness. DON'T WAIT About one third of all strokes are preceded by one or more "mini-strokes", or transient ischemic attacks (TIAs). The symptoms of TIAs are identical to those of stroke. However, TIAs last a few minutes to several hours, always with complete recovery within 24 hours, so it is easy to ignore them. But the underlying problem continues and TIAs are often early warning signs of more serious strokes in the future. Recognising and responding to the warning signs gives the patient the best chance of recovery. Patients often do not seek help for a day or more after the first symptoms. That reduces the effectiveness of treatment. (Sources: Department of Medicine at the University of Hong Kong, American Stroke Association, American Heart Association, World Health Organisation, National Stroke Association, Stanford Stroke Centre)
