What Is Dementia?

Dementia is a condition of the brain, which causes a gradual loss of mental ability. In addition, other features commonly develop such as changes in personality, a decline in social function, and a decline in the ability to look after oneself. There are various different causes of dementia.

Who Gets Dementia?

Dementia usually affects older people and becomes more common with increasing age. Sometime after the age of 65 about 1 in 20 people develop dementia. About 1 in 5 people over the age of 80 have dementia. Rarely, it affects younger people. Dementia is not a normal part of ageing. It is also different to the 'Age Associated Memory Impairment' that is common in older people.

What Causes Dementia?

Dementia can be caused by various diseases, which affect the parts of the brain involved with thought processes. However, most cases are caused by Alzheimer's disease or vascular dementia. All of the types of dementia cause similar symptoms, but some features may point to a particular cause. Therefore, quite often it is not possible to say which disease is causing the dementia in each individual case.

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 reduces. 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. (See separate leaflet called 'Preventing Cardiovascular Diseases'.)

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.

How Does Dementia Progress?

Symptoms tend to develop slowly, often over several years. In the early stages of the disease, many people with mild dementia cope with just a small amount of support and care. As the disease progresses more care is usually needed. A 'typical' person with Alzheimer's disease takes about 8-10 years to go from the first signs of memory problems, to being severely affected, and ultimately to die due to frailty of body and mind. However, the speed of progression of symptoms can vary greatly between different people.

How Is Dementia Diagnosed?

Dementia is suspected by the typical symptoms which are usually reported by a relative or friend. A doctor may do a standard 'memory test' to confirm the diagnosis. However, some other conditions (sometimes treatable) have similar symptoms to dementia. Not all 'confusion' is due to dementia. For example, depression in older people can sometimes cause memory problems. A person who reports a failing memory themselves, rather than a relative or friend, is just as likely to have depression as dementia. Depression is often treatable. Also, some physical problems such as thyroid disorders and brain tumours may cause 'confusion' in an older person and mimic dementia. Some tests may be done if symptoms are not typical, or if other conditions are suspected.