Dementia is a progressive and usually irreversible deterioration in a person's intellectual capacity, memory, thinking and reasoning abilities, which is often associated with changes in personality and impaired social function. The early stages of dementia may be difficult to distinguish from the forgetfulness of normal ageing. In the late stages of severe dementia the sufferer may be unable to exist independently because of mental and physical frailty.

How common is Dementia ?

The risk of developing dementia increases with age; the percentage of people in the population with dementia doubles every five years over the age of 65. At the age of 80, one person in five may be affected. Dementia is the fourth most common cause of death after heart disease, cancer, and stroke. The annual cost of providing care for dementia sufferers in England and Wales has been estimated as over one thousand million pounds per year, exceeding the treatment costs of any other single disorder.

What causes Dementia?

The loss of mental faculties which occurs in dementia is associated with loss of nerve cells in the brain. Many diseases can cause dementia. The great majority of cases,however, are accounted for by three main disorders: Alzheimer's disease, which is the most common, accounting for 50-60% of cases in older people, dementia with Lewy bodies, which accounts for 15-25% of all cases, and vascular dementia, also known as multi-infarct dementia, which also accounts for 15-25%. These three different types of dementia can usually be distinguished from one another by an experienced clinician. Accurate diagnosis is important because the different dementias progress in different ways and may require different types of treatment.

Alzheimer's disease

In Alzheimer's disease, abnormal microscopic structures known as senile plaques and neurofibrillary tangles are deposited in and around nerve cells causing their premature death. Exposure to aluminium in a form which can be absorbed by the body (not aluminium cooking utensils) has also been implicated in the formation of the 'senile plaques', but the role of aluminium in causing Alzheimer's disease remains uncertain. Previous head injuries also seem to be associated with a small increase in the risk of the subsequent development of Alzheimer's disease, perhaps by bringing forward the time of onset of 'senile plaque' deposition in the brain. Recent research has revealed that some Alzheimer' s disease cases have a genetic basis, and if the way these genes exert their effect can be understood,it may greatly help the process of developing treatments which will delay the onset of the disease. Such treatment possibilities are probably still several years away.

Dementia with Lewy bodies

This is a relatively recently described cause of dementia which shares some features with Alzheimer' s disease and some with Parkinson's disease, which is a disorder of movement in which patients become slow, with stiffness and tremor of the limbs and trunk. Lewy bodies are another type of abnormal microscopic structure in the brain. Affected individuals have fluctuating mental symptoms and many experience bouts of confusion, in which they often have hallucinations. Many patients with dementia with Lewy bodies receive a particular class of drugs called neuroleptics for such symptoms, and in approximately 50% of cases there may be serious and sometimes irreversible side effects (neuroleptic sensitivity), including increased confusion, sedation, and an increase in Parkinsonian symptoms.

Vascular Dementia

This is a group of disorders in which brain cells are damaged by abnormal blood circulation to the brain. This may take the form of multiple 'mini-strokes', leading to a step-by-step deterioration. In other cases the small blood vessels become narrowed, leading to a progressive loss of blood supply. High blood pressure, smoking and dietary factors contribute to these forms of dementia. Until recently there have been no known treatments for any of the common forms of dementia. For vascular dementia, the main means of prevention are thought to be the same as for stroke disease, e.g. control of high blood pressure, together with aspirin tablets. Research has demonstrated that in Alzheimer' s disease and dementia with Lewy bodies, some types of nerve cells producing one particular neurotransmitter chemical (acetylcholine) are more affected than others. Recently introduced drug treatments which can boost acetylcholine levels in the brain may improve the symptoms of dementia, e.g. memory loss in some patients, but these new treatments do not appear to halt the underlying disease processes.

Need for more research

The number of people of retirement age in the UK is steadily increasing. Currently they form about 18% of the population, but by the year 2021 they will make up 21%. This means that if research into dementia does not continue and progress, the number of people suffering from the mental decline and helplessness which characterise the condition will increase. Despite the advances of recent years, further research is urgently needed in order to ensure that new and more effective methods of early diagnosis and treatment can be developed.