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Types of Dementia

Dementia occurs as the result of physical changes in the structure of the brain. We do not yet know what causes some types of dementia and with conditions such as Alzheimer’s or Vascular Dementia it may be a combination of factors.


Alzheimer’s Disease

The most common form of dementia, accounting for somewhere between 50-75% of all dementias. Caused by plaques and tangles in the brain.
The onset of Alzheimers disease is often hard to pinpoint as it begins so subtly. Usually memory and learning problems occur early on, though people behave normally in social situations even late in the condition. The progression is gradual and smooth without plateaus. About 80% of people with Alzheimers Disease develop psychological and / or behavioural problems such as depression or apathy early on and psychosis, irritability, agitation or wandering in the mid-late stages. With severe Alzheimers Disease incontinence, gait disturbance, difficulty swallowing, and seizures occur.

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Vascular Dementia

Caused by damage to the blood vessels supplying the brain, this may be due to smoking, high blood pressure, diabetes or high levels of fats in the blood. Dementia causes gradual deterioration in attention, decision-making, memory and learning, language, perception and/or social behaviour. In particular, compared with other forms of dementia, there are more marked problems with attention and/or frontal-executive function (judgement, planning and decision-making).

A person’s abilities may fluctuate more with vascular dementia than Alzheimers disease. The course of the condition is very variable and may depend on what can be done to improve blood supply.

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Lewy Body Dementia

Lewy body disease is a type of dementia, in which Lewy Bodies form on the cortex of the brain causing degeneration and death of nerve cells.

Some specific features that occur regularly in Lewy body disease and not in other types of dementia are: Parkinson’s disease-like symptoms (tremor, shuffling, stiffness, slow walking, quiet speech and loss of facial expression) visual hallucinations (seeing things that aren’t there) and fluctuations in levels of awareness and alertness.

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Frontotemporal Dementia

Frontotemporal dementia (FTD) is an umbrella term for a group of disorders affecting the frontal and temporal lobes of the brain and is the cause of at least 12% of all dementia cases, possibly more since it is difficult to diagnose. The frontal and temporal regions of the brain can be affected by other forms of dementia. For example, Alzheimers disease can start in the frontal region and poor blood supply to these lobes can occur in vascular dementia. However, generally there are three recognised forms of frontotemporal dementia.

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Behavioural-variant frontotemporal dementia

In this condition there are early changes in behaviour, personality and executive function, that is, poor reasoning, judgement and decision-making. The behaviour and personality changes may include apathy, disinhibition (e.g. tactless, socially-inappropriate behaviour), loss of empathy and social interest. The person may develop repeated, pointless movements or sayings. Eating patterns change and the person shows a tendency to always put something in their mouth (hyperorality). The person is not usually aware of problems and may make disastrous personal or financial decisions due to poor judgement and loss of inhibitions

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Language variants of Frontotemporal dementia

There are two sorts of Frontotemporal dementia that initially affect language, called Primary Progressive Aphasia (PPA):

    • In the semantic variant – The first symptoms are a decline in language skills so that the person has trouble producing words, naming things and structuring sentences. People may struggle to find and understand and pronounce words, especially the ones they do not use very often. The meaning of words can be lost, but grammar remains intact.
    • Non-fluent variation of primary progressive aphasia – In this condition, speech is slow, laboured and halting and words may be left out and grammar misused. People might have trouble understanding complex sentences. People can retain their writing skills for a long time, but spelling and reading can be impaired.

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Young Onset Dementia

Dementia is often thought of as an older person’s disease. However, about 12% of people who get dementia are under the age of 65; these people are referred to as having “younger onset”, or sometimes, “early-onset”, dementia.

Because of the relative rarity, dementia symptoms in younger people are often missed or put down to something else (e.g. work stress, burnout or depression).

Furthermore the proportion of people with the Frontotemporal type of dementia is much greater than in older people with dementia. This is readily mistaken for psychiatric illness, another reason for the diagnosis to be delayed.

Dementia of any type can begin at a younger age. However, Frontotemporal dementia is a common cause of younger-onset dementia.

Some people have a family history of young onset dementia; rare familial forms of Alzheimers or Frontotemporal dementia can afflict people in their 40s or 50s. Huntington’s chorea, a genetic condition, often leads to young onset dementia. People with a history of head injury or Down syndrome are more prone to younger onset dementia. However, people with none of these risk factors can still, inexplicably, develop dementia before the age of 65.

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Alcohol Induced Dementia

Caused by excessive alcohol use over a long period of time. Men aged between 45 and 65 tend to be the ones who develop this type of dementia, although it can affect women and people in younger or older age groups. While younger people tend to consume more alcohol, older people in New Zealand are drinking more than previously as the baby-boomer cohort comes through.

Alcohol-related brain disorders (ARBD) are different in that they are potentially reversible if the person stops drinking. The deterioration stops and some (though usually not all) cognitive function can be regained with abstinence.

There are two factors that cause brain damage if someone abuses alcohol. The first is the direct toxic effect of alcohol on cells. This causes nerve cell death with brain shrinkage and can affect other organs such as the heart, hence reducing blood supply to the brain.

The second factor is a deficiency of vitamin B1 (thiamine) which is important for brain function. Many people who drink heavily neglect their diet and thus become B1 deficient. As well, alcohol irritates the stomach lining making it harder to absorb vitamins. However, with replacement of thiamine, brain function may be preserved.

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