What is dementia?

3. What causes dementia?

There are many diseases that result in dementia. The most common types of dementia are outlined below:

  • Alzheimer’s disease – This is the most common cause of dementia. In Alzheimer’s disease, an abnormal protein surrounds brain cells and another protein damages their internal structure. In time, chemical connections between brain cells are lost and cells begin to die. Problems with day-to-day memory are often the first thing to be noticed, but other symptoms may include difficulties finding the right words, solving problems, making decisions, or perceiving things in three dimensions.
  • Vascular dementia – If the oxygen supply to the brain is reduced because of narrowing or blockage of blood vessels, some brain cells become damaged or die. This is what happens in vascular dementia. The symptoms can occur suddenly, following one large stroke. Or they can develop over time, because of a series of small strokes. Vascular dementia can also be caused by disease affecting the small blood vessels deep in the brain, known as subcortical vascular dementia. The symptoms of vascular dementia vary and may overlap with those of Alzheimer’s disease. Many people have difficulties with problem-solving or planning, thinking quickly and concentrating. They may also have short periods when they get very confused.
  • Mixed dementia – This is when someone has more than one type of dementia, and a mixture of the symptoms of those types. It is common for someone to have both Alzheimer’s disease and vascular dementia together.
  • Dementia with Lewy bodies – This type of dementia involves tiny abnormal structures (Lewy bodies) forming inside brain cells. They disrupt the chemistry of the brain and lead to the death of brain cells. Early symptoms can include alertness that varies over the course of the day, hallucinations, and difficulties judging distances. A person’s day-to-day memory is usually affected less than in the early stages of Alzheimer’s disease. Dementia with Lewy bodies is closely related to Parkinson’s disease and often has some of the same symptoms, including difficulty with movement.
  • Frontotemporal dementia (including Pick’s disease) – In frontotemporal dementia, the front and side parts of the brain are damaged. Clumps of abnormal proteins form inside brain cells, causing them to die. At first, changes in personality and behaviour may be the most obvious signs. Depending on which areas of the brain are damaged, the person may have difficulties with fluent speech or forget the meaning of words.

The symptoms of these types of dementia are often different in the early stages but become more similar in the later stages. This is because more of the brain is damaged as the different diseases progress. In the later stages of dementia, the person will need more and more support to carry out everyday tasks. However, many people with dementia live well for years after their diagnosis. Information, advice and support are available for the person and their carer to help them live well with dementia.

For more information see our page on the brain and dementia.

Rarer causes of dementia

There are many other diseases that can lead to dementia. These are rare – together they account for only about 5 per cent of all dementia. They tend to be more common among younger people with dementia (under the age of 65). These rarer causes include corticobasal degeneration, progressive supranuclear palsy, HIV infection, Niemann-Pick disease type C, and Creutzfeldt-Jakob disease (CJD).

Some people with Parkinson’s disease or Huntington’s disease develop dementia as the illness gets worse. People with Down’s syndrome are also at a particular risk of developing Alzheimer’s disease as they get older. For more information see our page on rarer causes of dementia.

Mild cognitive impairment

Some people have problems with their memory or thinking but these are not bad enough to affect their everyday life. In this case, a doctor may diagnose them with mild cognitive impairment (MCI). This is not a type of dementia, but research shows that people with MCI have an increased risk of going on to develop dementia.

However, MCI can also be caused by other conditions such as anxiety, depression, physical illness and the side effects of medication. Because of this, some people with MCI do not go on to develop dementia, and a small number of people will even get better. For more information see our page on mild cognitive impairment.