Many people assume a loss of mental agility is an evitable part of ageing. In fact, there's no reason why the mind shouldn't remain sharp. But, like any other organ, the brain is susceptible to disease, which can lead to dementia.
Why is dementia linked to age?
The older a person is, the greater the chance they will develop a disease that harms the brain. Diseases that damage the areas which control thinking, memory, reasoning and language can lead to dementia.
The condition is rare in people under the age of 60 - there are about 18,000 people affected in the UK - but affects one person in 20 over the age of 65 and one in five over 80.
Causes of dementia
When someone is diagnosed with dementia it's vital the cause is established as far as possible because in a small number of cases the disease is reversible.
Even when the cause is not reversible, a clear diagnosis is important as different drugs are recommended in different types of dementia.
Diseases resulting in progressive degeneration or death of nerve cells. These include Alzheimer's (which accounts for more than half of all cases), Parkinson's disease, Huntington's disease, Creutzfeldt-Jakob disease and Pick's disease. Another condition, called Lewy Body dementia, affects 20 per cent of people with dementia.
Conditions, such as atherosclerosis, that harm the blood vessels supplying the brain. This type of dementia is known as vascular dementia and accounts for about 20 per cent of dementia cases.
Conditions producing a dementia that can be reversed with treatment. These include hypothyroidism (under-active thyroid), vitamin B12 deficiency, folate deficiency, syphilis of the nervous system, subdural haematoma (a blood clot round the brain, usually following a blow to the head), hypercalcaemia (abnormally high calcium levels), undiagnosed diabetes, brain tumours or infections, and a condition called normal pressure hydrocephalus.
Some medicines can interfere with concentration and memory, producing dementia-like symptoms. These include tranquilisers and sleeping pills, antidepressants, and certain drugs with an anticholinergic effect (for example, some hayfever and cold remedies, some stomach ulcer drugs and treatments for diarrhoea).
Symptoms of dementia
People with dementia often don't look ill, especially in the early stages, and may have no particular symptoms. But family and friends may notice a change in the person's personality, or that they seem to have problems remembering things.
The condition usually progresses slowly, and three types of symptoms may appear:
Cognitive problems - a disturbance of understanding, memory, thinking, calculation, learning capacity, language and judgement
Functional problems - difficulty carrying out complex tasks and, as the condition progresses, difficulty with daily living activities, such as personal hygiene and
Emotional problems - changes in mood, loss of emotional control, and a withdrawal from previous interests, activities and social interactions.
Different types of dementia show slightly different patterns of disease. For example, in Lewy Body dementia, severity varies markedly from day to day, while in Alzheimer's there is only slight variation from day to day.
There is no single test that can identify dementia, although a range of blood tests and sophisticated brain scans increasingly help and are important in ruling out reversible causes.
Diagnosis is made by an assessment of symptoms and the use of brief questionnaires that test ability to remember facts, or draw simple diagrams. An example is the Mini Mental State Examination
Treatment and care
Most types of dementia progress slowly. People may live with the condition for ten years or more, requiring increasing levels of support as they become less independent. By carefully planning the person's environment, and giving structure to their day with supportive activities, it may be possible to reduce the impact of their symptoms.
There has been a lot of debate about the use of drug treatments. While there is no treatment that can cure progressive dementias, drugs (especially a type known as cholinesterase inhibitors) play an important part in controlling symptoms and can enable a person with dementia to live independently in the community for longer before they need nursing home care.
These treatments may also help behavioural symptoms such as restlessness or agitation, and improve the quality of life for the person with dementia and their carers.
Unfortunately, some people don't respond to any existing treatments. Depression is common among people with dementia, and antidepressants can also help to improve symptoms.
Dementia is not part of the normal ageing process - it occurs because of diseases that affect the brain.
In the early stages most people seem quite well, but close family or friends may notice changes.
It's important to try to pin down the type of dementia or its cause because in a few cases it may be reversible. Diagnosis may also determine treatment.
There is no cure for most dementias but a lot can be done to help the person and their relatives maintain their quality of life, and sometimes slow the progression of the disease.