A Tour around Stroke

(Date of publication 17 June 2005)

A 'stroke' is a fairly innocuous term for what can be a terrifying medical emergency – perhaps the American use of 'brain attack' is more appropriate. The condition can strike without warning, has a significant mortality and leaves many of its victims permanently disabled. It is caused by a sudden interruption of the blood supply to a part of the brain, the effects depending upon the region that is affected and the severity of the interruption.

There are two main categories. An ischaemic stroke occurs when a blood vessel supplying brain tissue becomes blocked (for example, by an embolus or thrombus) and the bloodflow is impaired. Brain cells and tissue beyond the blockage begin to die within minutes from the lack of oxygen and nutrients, creating an infarct. About 80% of strokes fall into this category. Here is a CT scan of a brain that suffered an ischaemic stroke because of occlusion of the left middle cerebral artery. The reduced activity in an affected area can be readily seen in this example.

Haemorrhagic strokes, which account for the other 20%, occur when a blood vessel ruptures and bleeds, again depriving brain tissue of oxygen and nutrients. If the bleeding originates from blood vessels within the brain, it is termed an intracerebral haemorrhage; the cause is often hypertension, there are usually no warning signs and bleeding may be severe. By contrast, in a subarachnoid haemorrhage, blood occupies the space between the brain and the meninges, the membranes which cover its surface. Here are some CT scans and colour photographs of a subarachnoid haemorrhage that was caused by an aneurysm, or weakened artery wall.

This Loyola University site lists the risk factors which increase the likelihood of having a stroke, helpfully dividing them into those that can and cannot be modified. High blood pressure, cigarette smoking, lack of exercise and obesity are placed firmly in the former category! The common symptoms of stroke include sudden neurological effects such as weakness or numbness, confusion, difficulty speaking or understanding, dizziness and headaches, but there may also be nausea, fever or fainting. Prompt, accurate diagnosis is essential, so that appropriate treatment can be started at the earliest possible moment. The various tests and procedures that may be employed to rule out other conditions and determine the type of stroke – including a physical examination, blood tests and imaging techniques – are briefly described on this neurologychannel page.

The medical treatment of stroke is discussed on the emedicine site, which divides it up into primary and secondary prevention, acute treatment and chronic treatment. Coverage is quite comprehensive; the rationale and clinical trials underlying therapies such as platelet antiaggregants, statins, antihypertensives and thrombin inhibitors are outlined. As surgical measures are not included, you will have to go here to learn about carotid endarterectomy, the removal of atheromatous plaque from the carotid artery. In carefully selected patients this procedure can be highly beneficial, reducing the 2-year risk of stroke from more than 1 in 4 to less than 1 in 10.

One major advance in the treatment of ischaemic stroke has been the use of tissue plasminogen activator (t-PA) to dissolve blood clots, which was introduced in the 1990s. It must be given intravenously within 3 hours of the onset of symptoms. Although it does not significantly decrease subsequent mortality, some 11% to 13% more patients make a full recovery. In view of the action of this agent, which makes bleeding a major side effect, it must not be administered to any patient with a haemorrhagic stroke. A full list of the exclusion criteria is given on the Postgraduate Medicine site, which also has a detailed account of t-PA patient management and the prevention of complications.

A number of authorities take the view that the value of t-PA therapy is not proven, and argue that aspirin provides greater benefit at far less risk – read this article by Jerome R. Hoffman, Professor of Medicine and Emergency Medicine at UCLA. However, late last year a trial demonstrated that the combination of t-PA with ultrasound brought much greater benefits than t-PA alone; 49% of patients who received the combination showed dramatic clinical improvement and little or no blockage within two hours of the start of therapy, compared to 30% of those who received t-PA alone. Also, a more potent agent has been developed from the saliva of vampire bats; desmoteplase (DSPA) can be used up to 9 hours after the onset of symptoms, has much greater clot-busting properties than t-PA (13,000:72), and unlike t-PA has no effect on two brain receptors that cause cellular damage .

For victims of intracerebral haemorrhage, which has a greater mortality rate than ischaemic strokes, major benefits have been demonstrated by the use of Factor VIIa, traditionally used to counter bleeding episodes in haemophiliacs. A multi-centre study in 20 countries showed that the drug reduces the amount of blood that leaks into the brain by 50%, decreases mortality and improves neurological and clinical outcomes. If you want to hear the actual presentation announcing the results at the International Stroke Conference last February, click here.

Perhaps the most innovative potential future treatment for stroke is the mobilisation of the brain's own stem cells. It has been shown that new neurons are produced from stem cells in response to injury, but it is not yet known whether they are functional or if they can migrate to the site of injury and replace those which have died. Thus the development of therapies is a long way off, but providing you have the Adobe Acrobat reader, you can read about some very exciting possibilities here.

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