Dementia is an umbrella term that describes a collection of symptoms, not one specific disease. There are more than 100 different diseases that cause dementia. The most common are Alzheimer’s disease, vascular dementia and Lewy body disease.
Alzheimer’s disease is the most common form of dementia. It is more common in older people than younger people, usually coming on after the age of 65. More than 70% of people with dementia have Alzheimer’s disease.
A few people develop Alzheimer’s disease while much younger. It is likely that these people have inherited Alzheimer’s disease due to problems with one or more of their genes.
People with Alzheimer’s disease have, scattered through their brains, deposits of certain proteins and other material that shouldn’t be there. It is likely that these deposits interfere with the way a person thinks and uses their memory.
Apart from the few cases of familial Alzheimer’s disease (Alzheimer’s that is inherited through a faulty gene), the causes of Alzheimer’s disease are unknown.
Alzheimer’s disease results in a progressive worsening of symptoms over 3 to 20 years.
Vascular dementia refers to dementia associated with problems in the circulation of blood to the brain. Some people develop dementia after having lots of small strokes, many of which they would not have even noticed. This is called multi-infarct dementia.
Some people develop dementia because of poor blood flow to the brain, usually due to high blood pressure and thickened arteries. This is called Binswanger's disease or subcortical vascular dementia.
People can also develop dementia after having one large stroke.
Lewy body disease
Lewy body disease is a common form of dementia, similar to Alzheimer’s disease. It is caused by the degeneration and death of nerve cells in the brain. Lewy bodies are unusual round objects that develop within cells in the brain. They probably play a role in killing these cells. It is not clear why they form, nor exactly what they do. It seems they are not inherited.
In frontotemporal dementia, the front and/or sides of the brain are affected more than the back of the brain or the central areas. It affects mood, judgement, behaviour and speech.
Frontotemporal dementias begin more often in the 50s and 60s than other types of dementia. They are also more likely to have a genetic element.
Expert advice - is dementia inevitable?
Although dementia is associated with ageing, it is not inevitable. Learn more from an expert about the risk factors of dementia such as ageing, smoking and high cholesterol and blood pressure.
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Last reviewed: October 2018