A stroke is the loss of brain tissue from a lack of oxygenated blood to the affected area. It can occur in two ways - from a clot or a hemorrhage.

Strokes caused by clots are called ischemic strokes. They usually develop when an area of a blood vessel feeding the brain is narrowed by atherosclerosis (fatty deposits on the arterial wall). A clot that develops at the site of the narrowed vessel (known as a cerebral thrombosis) can block the flow of blood. Brain tissue fed by the artery at a point beyond the blockage is starved for oxygen and dies. A blood clot can also form in another area of the body (commonly, somewhere in the heart), break loose and travel in the bloodstream - eventually becoming caught in a narrowed brain artery and blocking the flow of blood. This type of blockage is called a cerebral embolism. Ischemic strokes are the most common form of stroke, accounting for about 83 percent of all cases.

Clots caused by bleeding are known as hemorrhagic strokes. They occur when a weak blood vessel feeding the brain ruptures. Hemorrhagic strokes are less common than ischemic strokes (accounting for only 17 percent of cases), but are usually more deadly.

According to the American Stroke Association, every year about 700,000 Americans experience a stroke. It's the third leading cause of death in this country (after heart disease and cancer) and the leading cause of long-term disability.

Regaining Movement After a Stroke

A stroke can cause muscle weakness in some areas of the body, leading to some degree of paralysis or problems with movement. Lack of movement can cause the supporting structures in the area to become tight and pull the limb into an awkward position (a condition called spasticity). If the muscles aren't stretched, the limb can be permanently "frozen" in an abnormal position.

Rehabilitation therapists work with stroke patients to increase range of motion in affected limbs, reduce spasticity and improve mobility. However, it's not an easy process. After a stroke, some of the muscles in a limb may be weak while others are strong. So it can be more difficult to use weaker muscles.

Researchers at the Medical College of Wisconsin are studying the effects of BOTOX(r) injections for stroke patients with arm spasticity. BOTOX is a purified form of the toxin produced by a strain of bacteria that causes food poisoning, called Botulinum.

Using a special needle, doctors inject small amounts of BOTOX into the target muscle. The needle contains an electronic sensor that shows where the BOTOX will be most effective. Once inside the muscle, the drug is taken up by the nerves, where it blocks the transmission of acetylcholine, a chemical needed for the muscle to contract. That causes the muscle to temporarily relax, or weaken, and makes it easier for patients to use the weaker muscles.

After a BOTOX injection, patients undergo physical therapy and exercises to gain strength in the weaker muscles. Technicians use 3-D analysis to measure and chart the patient's progress.

The effects of BOTOX last for about three to four months and patients can be re-injected if necessary. Doctors need to be careful not to give BOTOX too frequently because the body can build a tolerance to the drug, making it ineffective.

SOURCES

National Stroke Association, http://www.stroke.org