Alzheimer's Disease.
This is the most common cause of dementia accounting for at least 50% of all dementia cases. There is a steady progression and worsening of symptoms. Eventually the person with Alzheimer's becomes totally dependent on others for even the most basic of daily care.

Multi Infarct Dementia. (MID).
The name describes the occurrence of small strokes or infarcts in the brain. Where the stroke occurs there is permanent brain damage. People with high blood pressure are more at risk of having strokes, therefore are at greater risk of developing MID.

The risk of developing this disease can be reduced by lifestyle changes eg, attention to diet (reducing fat intake and blood cholesterol levels), not smoking, effective management of diabetes, and regular exercise.

The progression of this disease follows a downward stepwise pattern. As a stroke happens there is a corresponding decline in abilities or worsening of symptoms. The person then seems to recover slightly although never to their previous level of functioning. Then another stroke occurs and the pattern of decline continues. Eventually strokes occur throughout the brain. The symptoms that present as each stroke occurs will depend on which area of brain is damaged. In about 15 - 20% of dementia cases, MID and Alzheimer's occur together.

Wernicke-Korsakoff Syndrome.
This occurs as a result (not in all cases) of alcohol abuse. It is the third most common form of dementia. It is believed that the thiamine (Vitamin B1) deficiency experienced as a result of alcohol addiction may cause short term memory loss and inappropriate responses.

This syndrome accounts for about 5% of all dementia cases seen, although it is the predominant cause of dementia within the Indigenous Peoples in Australia.

There are numerous other diseases causing irreversible dementia. To name a few: *Down's Syndrome; *Huntington's Disease; *AIDS and *Creutzfeld Jakob Disease (the human form of "mad cow disease"); Picks disease and Lewy Body dementia. 10% or less of people with *Parkinson's Disease also develop dementia.

Of special note is Sub-dural Haematoma which is bleeding between the brain and its protective layer as a result of head injury. The collection of blood causes pressure on, and damage to, brain tissue, possibly leading to dementia. The damage may only become apparent some time after the injury occurred eg. Boxer's dementia. If a person has hit their head, get them to a doctor promptly as treatment may prevent permanent damage.

*There are specific organisations dealing with diseases marked with an asterisk.