In most cases, the symptoms of dementia progress gradually, often over a period of several years. The early signs - usually memory problems - are normally subtle and may not be immediately obvious.

The symptoms of dementia can vary greatly, but those with dementia often have one or more of the following:

• problems with memory - this may include forgetting the names of people they know well, or forgetting where they live. Normally, recent memories are affected first, with memories of events further in the past only affected once the dementia becomes more developed. As dementia progresses, memory loss may affect memories of recent events so completely that the person appears to be living in the past - they may even think of themselves as young and not recognise their true age.
• problems with speech and language - they may forget simple words, may use the wrong words without noticing, or their conversation may become simplified, repetitive or irrelevant.
• confusion - they may become confused in new surroundings or by new people, or about who or where they are. They may lose track of time so that they are unsure what day it is, or even whether it is morning or afternoon.
• changes in mood or behaviour - they may become irritable or aggressive. As dementia progresses they may lose their normal inhibitions and begin to say or do inappropriate or antisocial things; in some cases this can include inappropriate sexual behaviour. They may lose interest in the outside world or their own care, giving up interests and hobbies, paying little attention to their personal hygiene, or forgetting to wash or change their clothes.
• difficulty performing simple tasks they may have difficulty doing everyday tasks such as cooking a meal. They may begin cooking and then wander away, forgetting what they were doing, or they may prepare a meal and then forget to serve it.
• problems learning new information, ideas or skills.

Some types of dementia can cause less common symptoms, including:

• hallucinations,
• obsessive or repetitive behaviour,
• the belief that they have done or experienced things that never happened (confabulation),
• disturbed sleep, or sleeping in the daytime and being awake at night,
• depression,
• physical deterioration, loss of appetite, loss of weight and increased vulnerability to infection, and
• incontinence.

If dementia becomes severe, it can cause other symptoms, including:

• difficulty with swallowing,
• difficulty changing position or moving from place to place without assistance, and
• complete loss of short-term and long-term memory.

Sometimes, those with dementia are unaware that they have any symptoms, especially symptoms that affect behaviour.

Many conditions (such as depression) have symptoms similar to dementia, so it is important not to assume that someone has dementia just because they have some of the symptoms above.

Dementia develops when cells in the parts of your brain involved with mental ability become damaged. Damage to these cells can be caused by:

• diseases and infections that affect the brain, such as Alzheimer's disease or meningitis,
• pressure on the brain, for example from a brain tumour,
• lack of blood and oxygen supply to the brain, for example due to stroke, and
• head injury.

The most common type of dementia is that caused by Alzheimer's disease, which is responsible for about 60% of all cases. The cause of Alzheimer's disease is unknown, except for a very small percentage of cases that are inherited.

About 20% of all cases of dementia are vascular dementias, the name given to dementia caused by poor circulation of blood in the brain. There are a number of different types of vascular dementia, the most common being multi-infarct dementia, where the small blood vessels in the brain becoming narrowed or blocked. The cells in the brain supplied by these blood vessels become starved of the blood and oxygen they need, and become damaged or die. This is like having a series of small strokes in the brain.

The risk of developing vascular dementia is increased by the same things that increase the risk of stroke and heart disease. These include high blood pressure, diabetes, smoking, poor diet and excessive alcohol intake.

Other less common types of dementia include:

• Lewy body dementia,
• dementia caused by Picks disease,
• dementia caused by Huntington's disease,
• dementia caused by Creutzfeldt-Jakob disease (CJD),
• dementia caused by the advanced stages of syphilis or HIV/AIDS,
• dementia caused by hypothyroidism (under-activity of the thyroid gland),
• dementia caused by build-up of fluid within the skull leading to pressure on the brain (hydrocephalus),
• dementia caused by infections of the brain, such as meningitis or encephalitis,
• dementia as part of a neurological (brain) illness, such as Parkinson's disease or multiple sclerosis,
• dementia caused by reaction to a medication, or to an interaction of two or more medications,
• dementia caused by long-term alcohol misuse,
• dementia caused by use of illegal drugs, and
• dementia caused by lack of certain hormones or nutrients, especially B vitamins.

Dementia usually develops slowly, with mild early symptoms, so diagnosing dementia in its early stages can be difficult. It is normally diagnosed initially by the most common symptoms, such as memory loss. The diagnosis can be confirmed with a careful physical and mental examination and simple memory and mental ability tests that check things such as the ability to read, write or calculate.

However, as different types of dementia have similar symptoms, it can be more difficult to diagnose the precise type or cause. Blood tests, X-rays, or a CT or MRI scan of the brain may be necessary to provide more information.

Further tests may be needed to make sure that the person does not have a condition which can produce symptoms similar to dementia, such as depression or a severe urine or chest infection.

As those with dementia are often unaware they have a problem, many people with dementia are brought to medical attention by a caring relative or friend.

Most types of dementia cannot be cured. The exceptions are:

• those dementias related to vitamin or hormone deficiency, which can be treated with supplements,
• those related to head injury, hydrocephalus or tumour, which may be treatable with surgery,
• those related to medication, which can be treated by altering the medication, and
• those related to infections, where treating the infection will normally cure the dementia.

Alzheimers disease cannot be cured. However, for some people in the early and middle stages of the disease, the medicines donepezil, rivastigmine and galantamine may help prevent some symptoms from becoming worse for a period of time. A new medicine called memantine may have the same effect for some people who have moderate or severe Alzheimers disease.

Medical researchers are currently investigating other medical treatments, including anti-oxidants, brain stem cell therapy and a vaccination to stop the build up of plaques in the brain (a hallmark of Alzheimers disease).

There is some evidence that the herbal remedy Ginkgo biloba can delay the progression of dementia for some of those with Alzheimer's disease or vascular dementia, and even make a small improvement in symptoms such as forgetfulness and confusion. However, more research is needed.

It is thought that mental activity can help to slow the progress of some types of dementia, so you should encourage someone with dementia to stay mentally and physically active and ensure their environment is stimulating. Puzzles, games (particularly memory games), reading and simple mental arithmetic are good choices, but its important not to overwhelm them with too many demands, or unrealistic demands, as this may only frustrate them.

A technique called reality orientation may help some people with dementia. It uses repetition to help the memory and involves regularly reminding the person of information such as the time, date, where they are and important information for that day, such as a visit to see a friend. The information could be given verbally by a carer, or be written on a board in their home where they will see it regularly. The aim of reality orientation is to help people understand their situation by reminding them or telling them about what's going on.

Many of those with dementia in the early and intermediate stages are able to cope well in their own home, due to the familiar surroundings. Others may need more frequent supervision, full time care in the home, or care in a residential or nursing home.

Support and care is the most important part of treatment for dementia. Many people with dementia are cared for in the community, often by a relative or friend. However, caring for a person with dementia can be very difficult. Support and advice for those caring for someone with dementia is available from the following sources:

• district nurses, who can advise on day-to-day nursing care,
• community psychiatric nurses, who can advise on caring for someone with a mental illness,
• social services, who can help with care in the home, day-care centres, respite care and benefits,
• voluntary organisations - in most areas of the UK there are organisations that provide support and advice for carers of people with dementia. See the Selected links section of this article for more information.

There is no known way to prevent Alzheimer's disease, the most common cause of dementia. However, you can reduce the risk of vascular dementia by maintaining a healthy lifestyle, including:

• quitting smoking,
• doing regular exercise,
• eating a low-fat, balanced diet, and
• drinking no more than the safe recommended limits of alcohol.

The information shown here is Crown copyright and has been reproduced with the permission of NHS Direct. Last updated June 2007.