What causes dementia depends on the type of dementia. Below are the main types of dementia and their causes:
Alzheimer’s disease is the most common cause of dementia. Alzheimer’s disease is caused by an abnormal protein which surrounds brain cells and another protein that damages their internal structure. In time, chemical connections between brain cells are lost and cells begin to die. The reduced connections between brain cells affect day-to-day memory, difficulties in finding the right words, solving problems, making decisions, or perceiving things in three dimensions.
Vascular dementia occurs if the oxygen supply to the brain is reduced because of narrowing or blockage of blood vessels. It causes some brain cells to become damaged or die. The symptoms can occur suddenly (after a large stroke) or they can develop over time because of a series of small strokes. The symptoms of vascular dementia vary and may be similar to the symptoms of Alzheimer’s disease. Many people have difficulties with problem-solving, planning, concentrating or thinking quickly. They may also experience short periods of confusion.
Mixed dementia – describes 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.
Dementia with Lewy bodies – this type of dementia is caused by 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 difficulty judging distances. A person’s day-to-day memory is not usually affected in the same way as 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 this type of dementia, the front and side parts of the brain are damaged. Clumps of abnormal proteins form inside brain cells, causing them to die. Initially, changes in personality and behaviour may be the most obvious signs. Depending on which areas of the brain are damaged, the person may forget the meaning of words, or have difficulty with fluent speech.
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