Alzheimer's disease
This causes about 6 in 10 cases of dementia. It is named after the doctor who first described it. In Alzheimer's disease the brain shrinks (atrophies) and the number of nerve fibres in the brain gradually reduce. The amount of some brain chemicals (neurotransmitters) is also reduced, in particular one called acetylcholine. These chemicals help to send messages between brain cells. Tiny deposits or 'plaques' also form throughout the brain. It is not known why these changes in the brain occur, or exactly how they cause dementia.
There is no way of predicting who will develop Alzheimer's disease. It is not hereditary and anyone may develop it.
Vascular ('blood vessel') dementia
This causes about 2 in 10 cases of dementia. This is due to problems with the small blood vessels in the brain. The most common type is called 'multi-infarct' dementia. In effect, this is like having many tiny strokes throughout the 'thinking' part of the brain. A stroke is when a blood vessel 'blocks' and stops the blood getting past. So, the section of brain supplied by that blood vessel is damaged or dies. As each 'infarct' occurs, some more brain tissue is damaged. So the mental ability gradually declines.
The risk of developing vascular dementia is increased by the same things that increase the risk of stroke. For example: high blood pressure, smoking, high cholesterol level, lack of exercise, etc.
Other causes of dementia
Over 60 diseases can cause dementia. Many are rare, and in many the dementia is just part of other problems and symptoms. In most cases the dementia cannot be prevented or reversed. In some disorders the dementia can be prevented, or stopped from getting worse if treated. For example, some cases of dementia are caused by alcohol abuse or infections such as syphilis, both of which can be treated.
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