What is Dementia? by Professor Sir Muir Gray

Many people, including many members of the medical profession are confused about dementia and its relationship to Alzheimer's disease. If you consult the World Health Organisation (WHO) International Classification of Diseases it says that Dementia is classified as an 'organic mental disorder' namely one caused by damage to the brain, as distinct from schizophrenia which is a disorder of the mind.  For diagnosis of dementia the WHO require evidence of:

• A decline in memory, which can be 'mild', 'moderate' or 'severe' and
• A decline in other cognitive abilities characterized by deterioration in judgement and thinking, such as planning and organising and again this deterioration can be graded 'mild', 'moderate' or 'severe' 

However, the full WHO definition is not easy reading except for scientists so here are some shorter definitions.

Dementia is a condition that some people develop in old age. This is characterised by confusion and memory problems and its effect on the individual affected is determined by the degree of severity of the dementia, their personality before the dementia developed and by their social circumstances and support. Alzheimer's Disease is a disease of the brain of unknown cause and is one of the principal causes of dementia but it seems that there are some people who do develop Alzheimer's Disease but who develop no symptoms of dementia. Vascular dementia is the other principal cause of dementia and results from impairments of the supply of oxygen rich blood to the brain, due to disease affecting the arteries of the brain. These two conditions often occur together. The relationship between these three conditions is best explained with a diagram. The other causes of dementia are a set of less common diseases such as Picks Disease or some types of Parkinson's Disease. There is one more term which we need to explain that you may see in the newspapers or on the web 'Mild Cognitive Impairment'.

Mild Cognitive Impairment (MCI) This is a more problematic term. The American Alzheimer's Association and the Alzheimer's Societies of Canada and the UK define it as a disorder that:

• causes more serious cognitive changes than are observed in normal ageing but are
• changes not severe enough to interfere with daily life or independent function.

The Alzheimer's Society UK emphasises that the benefit of diagnosing MCI is that the person can be helped to reduce the risk of developing dementia. The diagnosis of MCI does not mean that the person will develop dementia but that, in the words of the American Association they are 'more likely to develop Alzheimer's or other dementias than people without MCI.' but the Canadian Society also points out that some people with MCI will improve.