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Types of dementia
There are at least 400 different types of dementia, the most common of which are Alzheimer’s disease and vascular dementia.

There are at least 400 different types of dementia, the most common of which are Alzheimer’s disease and vascular dementia. While some cases of dementia can occur in young people, dementia is most likely to develop in older people over 65. People with Down’s syndrome are more likely to develop dementia as they get older, particularly Alzheimer’s disease. Most dementias are progressive and a person’s function's generally decline over time.

Some of the most common types of dementia are:

Alzheimer’s Disease

Accounting for the majority of cases in older people, the name Alzheimer’s disease is familiar to most people. It often develops slowly, over several years, and in the early stages can be difficult to distinguish from the mild forgetfulness which can be part of normal ageing. Early signs usually include difficulty in forming new memories for recent events. People may also experience difficulty finding the right words, figuring out problems or making decisions and both judging distance and finding the way to familiar places may be affected.
What’s happening in the brain: With Alzheimer’s disease there is a progressive build-up of abnormal clumps of protein that causes damage to the nerve cells in the brain.

Vascular Dementia

This is another common type of dementia but the name is not so well known. It can occur suddenly, for example, following a stroke affecting major blood vessels, or it can occur more gradually and can progress slowly over several years, if smaller and deeper blood vessels are affected. The signs and symptoms can sometimes be difficult to distinguish from Alzheimer’s and other forms of dementia. They can include memory loss, disorientation and problems with communication and changes in how the person walks. More specific symptoms differ depending on which part of the brain is affected. These may include problems with planning and concentrating, or short periods of intense confusion.
What’s happening in the brain: When blood supply to the brain reduces because of narrowing or blockages in blood vessels, brain cells can be damaged. Vascular dementia symptoms can occur suddenly after a major stroke, or over time through a series of small strokes or damage to blood vessels in the brain.

Lewy Body Disease

With Lewy body disease, movements may be affected so people might shuffle as they walk, and be more prone to falls. Some of the symptoms are similar to those who have Parkinson’s disease. People with Lewy body disease may experience periods of severe confusion. They can have hallucinations, seeing or hearing things that aren't really there. Swallowing and sleep patterns can also be affected – people can fall asleep easily during the day but then have disrupted sleep at night.
What’s happening in the brain: With ‘Lewy bodies’ there are abnormal clumps of protein that build up over time in the brain. These protein deposits disrupt nerve cell connections in the brain and cause changes in movement, thinking, behaviour and alertness.

Fronto-temporal Dementia (FTD)

This form of dementia can affect behaviour and personality and language function. Some cases of fronto-temporal dementia are linked to motor neurone disease. With Fronto-temporal dementia the early symptoms vary, depending on which area of the brain is affected. They may include changes in personality or eating patterns, lack of personal awareness (e.g. personal hygiene) or lack of social awareness (e.g. being tactless). In some instance, difficulties speaking or understanding others can be the main presenting features in the early stages.  It is more common in younger people (45-65) but can also develop in older individuals.
What’s happening in the brain: Fronto-temporal Dementia affects the front section of the brain, just behind the forehead and the temporal lobes (over the ears). If the frontal lobes are affected, the person will have increasing difficulty with motivation, planning and organising, controlling emotions and maintaining socially appropriate behaviour. If the temporal lobes are affected the person will have difficulty with speaking and/or understanding language.

Early/Younger Onset Dementia

Although most people who develop dementia are over 65, it can affect younger people too. Most people with early/younger onset dementia are in their 40s or 50s. Since doctors don’t usually suspect dementia, the process of getting a diagnosis can be difficult. People who are diagnosed may have a strong family history of dementia and occasionally genetics may have a role in the development of their condition. Younger onset dementia can also affect those with another health condition such as Parkinson’s disease, multiple sclerosis, Huntington’s disease, HIV or AIDS.