Stroke

Aetiology

There is no single, specific cause of stroke, rather several factors that increase the risk of an individual having a stroke. The more factors a person has, the greater the chance he/she will experience a stroke. The major risk factors include:

• age
• family history
• prior stroke
• transient ischaemic attack , or 'mini strokes': these produce stroke-like symptoms, but no lasting damage
• hypertension
• heart disease
• carotid artery disease
• diabetes mellitus
• cigarette smoking
• excessive alcohol intake
• high plasma cholesterol.

In addition to this, people with a high red blood cell count and people who have sickle cell anaemia are more susceptible to strokes than people who do not have these disorders.

People with a high red blood cell count
A person is at greater risk of having a stroke if they have a moderate or marked increase in their red blood cell count. This is because an increase in the number of red blood cells leads to a thickening of the blood, and this increases the possibility of a blood clot forming.

People with sickle cell anaemia
Sickle cell anaemia is a genetic disorder in which blood cells are sickle shaped, instead of being rounded, resulting in them being less able to carry oxygen to the cells of the body. Sickle cells tend to have higher viscosity than normal red blood cells, and as a result they can adhere to blood vessel walls, which can lead to blockage in a vessel and therefore potentially to a stroke. Therefore, patients with sickle cell anaemia are more susceptible to stroke.

What happens in the brain?

When a stroke occurs, the neurons at the site of attack are killed within minutes. The dying cells release free radicals that destroy neurons in the surrounding area. Without immediate treatment, more and more brain cells will die. The effects of the attack depend on the area of the brain affected by the stroke and the extent of the damage that the attack causes. A stroke in the right hemisphere of the cerebrum often causes paralysis in the left side of the body, and a stroke in the left hemisphere may cause paralysis in the right side of the body. Someone who has a left-hemisphere stroke may also develop problems with their speech. A stroke that takes place in the cerebellum can cause dizziness and vomiting and abnormal reflexes of the head and body. If an attack occurs in the brainstem, the results can be devastating and may result in paralysis in one or both sides of the body or even death.