Strokes

David Gull

Strokes are a common cause of severe impairment or death.

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What is a stroke?

Stroke Disability Ischaemia Haemorrhage

There are two different types of stroke. The commonest cause is a blood clot (see Box 1) blocking one of the arteries supplying the brain with blood (ischaemic stroke) - 80% of strokes are caused this way. When the blood vessel becomes blocked, all the brain cells on the far side of the clot are deprived of oxygen. They are rapidly damaged and die . Whatever function this area of brain performed is lost.

Where do the blood clots come from?

As people age, atherosclerotic plaques develop on their artery walls, narrowing the artery diameter. These plaques can cause blood to clot, eventually blocking the blood vessel. If this happens in the brain, it causes a stroke. Alternatively, blood clots can form in other places and be transported until they eventually get stuck in a blood vessel. The carotid arteries and the left chambers of the heart are commonly the origin of these clots. The carotid arteries supply blood to the brain and as we age they tend to accumulate atherosclerotic plaques. Blood dots here do not block these large vessels but tend to break off and are carried up to the brain, where they may lodge in a smaller artery and block it.

When blood clots form in the heart it is usually because the heart is diseased; atrial fibrillation is usually the cause. In a healthy heart, the atria contract regularly, pushing blood into the ventricles. In atrial fibrillation, the atria beat poorly and irregularly, and although blood still flows into the ventricles, blood can pool in the atria where it tends to clot. Clots formed in the left atrium pass into the left ventricle and are ejected into the aorta. Because 20% of the blood in the aorta goes to the brain, these clots have a one in five probability of ending up in the brain. Diseased atrioventricular valves can also cause blood clots to form.

Blood clots can also form in the veins, which carry blood back to the heart - a condition called deep-vein thrombosis or DVT. These blood clots do not cause strokes since they lodge in the lungs, causing a condition called pulmonary embolism; they cannot pass through the lungs to reach the left side of the heart.

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The other major cause of stroke (haemorrhagic stroke) is bleeding into the brain itself. One of the blood vessels in the brain ruptures, commonly caused by longstanding high blood pressure or a weakness in the wall of the blood vessel itself. Blood escapes into the surrounding brain tissue, much as happens when you bruise yourself. While a bruise will heal without any problems, unfortunately the blood damages the brain, causing cells in the affected area to die.

Although the two mechanisms for stroke are different, they produce similar results. In both cases a particular area of brain is damaged and dies, causing particular loss of function. The rest of the brain is unaffected and continues working normally.

isk factors High blood pressure, diabetes and high cholesterol are risk factors for stroke, partly because they damage arteries and worsen atherosclerotic plaques. Smoking increases the chance of having a stroke in several ways.

Some chemicals in the cigarette smoke damage blood vessel walls, others raise blood pressure, and yet other substances in the cigarette affect platelets. The chemicals increase the tendency of platelets to clump together and form blood clots.

Symptoms of stroke The symptoms of stroke are determined by which part of the brain is affected, and how big the damaged area is. To understand the symptoms a stroke can cause, you have to know something about brain structure and function (see figure 1) , Biological SCIencE's ReView

Looking at Figure 1 should make it clear why the symptoms of a stroke are so varied. i\ patient with damage to the motor area will experience weakness of the muscles on the opposite side of the body. [f only a small part of the motor area is involved, perhaps only the face may be affected . However, if the whole motor area is affected, the patient will have complete paralysis of the opposite side of the body. The same principle applies to the sensory area ­ if the left side is affected, the patient has numbness on the right side of the body.

Strokes affecting the cerebellum typically cause problems with coordination. In this case an affected

arm will not lose strength but the patient is unable to control it properly - it simply won't do as it is told.

Strokes affecting the brainstem are often fatal. If the patient survives, a whole range of symptoms can occur.

The brainstem contains important control centres, but also all the communicating neurones connecting the cerebral cortex and the spinal cord. A stroke that affects the pons - a part of the brainstem- can result in the devastating 'locked in' syndrome. Patients are unable to move or speak, only able to move their eyes and blink.

The most distressing part is that the patient is completely conscious and awake. This syndrome occurs because the stroke severs the connections between the cerebral hemispheres - responsible for the voluntary control of movement - and the spinal cord. Whatever the patient would like to do, the brain is no longer connected to the muscles that are responsible for carrying out the actions.

Symptoms can vary depending on whether the stroke affects the left or right cerebral hemisphere. Strokes affecting the left cerebral hemisphere often affect language abilities and can produce several different problems. Patients can have a problem expressing what they want to say, they can't find the right words, can't give objects the correct name. It is frustrating for them, because they know what they want to say but are unable to express themselves. [n severe cases, patients may lose all ability to speak. Other patients may have problems understanding language - they simply cannot comprehend what is said to them and are often unable to follow simple commands, even though they are able to speak sensibly. Problems with reading and writing are also associated with damage to the language centres.

A bizarre syndrome called neglect can occur when a stroke affects the right cerebral hemisphere. The patient loses perception on one side of the body, and sometimes becomes unaware of everything that is happening on that side. Patients may ignore people who are standing

Figure 1 Areas of the human brain viewed (left) from the top and (right) from the left side.

Parietal lobe (sensation)

Longitudinal fissure

Reading comprehension area Occipital lobe (vision)

Motor speech area (controls how speech is produced)

Parietal lobe -!-.,ÂŁ-_--

Occipital lobe

/ Left-hand side

\ Right-hand side

controls right-hand side of body

controls left-hand side of body

April 2012

Temporal lobe (hearing and long-term memory formation)

Sensory speech area (understanding and generation of speech) Pons Medulla oblongata (brainstem ­ controls breathing, heartbeat, blood pressure and maintains alertness)

Cerebellum (coordination of movement and balance)

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and talking to them on the affected side, but interact normally when someone moves to the unaffected side.

They may not recognise the arm on the affected side as being theirs, aqd in extreme cases may tTy to muti.1ate it. \\Then given a plate of food, a patient with neglect will eat precisely half of it, and completely ignore the other halJ of the p.1ate. This is because they do not realise that it is there.

Prevention is better t an cure Simple measures, such as good diet, regular exercise, alcohol in moderation, not being overweight and not smoking, will reduce the chances of stroke (and heart attack). When someone does develop a disease that is a risk factor for stroke, such as high blood pressure, high cholesterol or diabetes, effective treatment will reduce the risk of developing a stroke.

Treatment

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Once a person has had a stroke, the first thing to do is to determine the cause and the second is help recovery.

After a stroke caused by a clot, patients are usually started on drugs such as aspirin to reduce the chance of further strokes. Aspirin works by making the platelets less sticky, making it harder for them to form a blood clot. If the patient has raised cholesterol and blood pressure, he or she is started on medication such as statins, to reduce blood pressure and lower cholesterol (see BIOLOGICAL SCIENCES REVIEW, Vol. 22, No.3, pp. 7-9).

Patients will often have an ultrasound scan of their carotid arteries to check for deposits of plaque. [f there is evidence of narrowing in the carotid artery, it is possible to repair the artery by an operation, which removes the fatty deposits and restores the normal diameter.

Where a clot forming in the heart was the cause of the stroke, a drug called Warfarin is often used. It works by reducing the liver's ability to make one of the proteins needed for blood clotting.

Treatment of the stroke starts as soon as the patient arrives at the hospital. The brain is highly sensitive to lac1< of oxygen; when deprived of oxygen it starts to die within minutes. [n a stroke, a core of brain tissue loses all blood supply and dies almost immediately - nothing can be done to save it. However, around this core there is an area of tissue that dies more slowly - the penumbra.

It is thought that some blood gets through the penumbra and this means that the brain cells are dying more slowly.

Advice from the Stroke Association Suspect a stroke? Act FAST

What is FAST? FAST requires an assessment of three specific symptoms of stroke:

Facial weakness - can the person smile? Has his/her mouth or eye drooped?

• Arm weakness - can the person raise both arms?

Speech problems - can the person speak clearly and understand what you say?

If the answer to any of these is yes, then: • Time to call 999

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Drugs that dissolve blood clots can restore blood flow to this area, and, if administered in time, this area of brain can be saved, thus limiting the damage. The sooner these drugs are administered the better their effect.

Patients who have had a serious stroke face a long recovery and in many cases will never recover completely.

Recovery depends on many things, including the area of brain affected, the patient's age, and how fit he or she was before the stroke. The process of aiding recovery after stroke is called rehabilitation.

Rehabilitation aims to help the patient to make as full a recovery as possible, and to help them live independently. Physiotherapy forms an important part of rehabilitation. Exercising leads to patients seeing an improvement in the muscle power of the affected limb and their ability to use it. This improvement occurs because areas of undamaged brain surrounding the damaged area can, to a limited degree, take over the function of the damaged area. This is called neuroplasticity.

Speech and language therapy is important in helping patients overcome any communication difficulties they may have developed. It also helps with eating - a common problem because strokes can affect the muscles that control swallowing.

Occupational therapists work with stroke patients to help them overcome any disability they are left with .

This can involve anything from simple tools to make everyday activities such as eating, opening jars, and making a cup of tea easier, through to organising major modifications to a patient's house, making it accessible to a wheelchair for example.

Conclusion Stroke is a term for what can be a terrible and disabling condition. It is often fataL and is also the most common cause of disability in the UK. Treatment of stroke is improving, with many exciting developments on the horizon. Stroke is as much of an emergency as a heart attack; urgent medical attention is just as essential as it is for someone with chest pain. Would you recognise the symptoms of stroke? See Box 2.

Dr David Gull trained at the University of Birmingham and is now a clinical teaching fellow at University Hospital Coventry. One of his major interests is stroke.

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• Stroke is the most common cause of disability in the UK. • Stroke is a medical emergency requiring urgent treatment.

• Stroke is most commonly caused by blockage of one of the blood vessels supplying blood to the brain (ischaemic stroke).

• Less commonly, stroke can be caused by bleeding into or

around the brain (haemorrhagic stroke) .

• Symptoms of stroke vary greatly depending on the area of brain affected.

• The FAST test is a good way to quickly identify a person

who may be suffering a stroke.

Biological SCiences Review