Dementia is a pattern of mental decline caused by different diseases or conditions. Most commonly, dementia occurs when brain nerve cells (neurons) die, and connections between neurons are interrupted. These disruptions have a variety of causes and usually cannot be reversed.
Among the causes of dementia:
Alzheimer's disease causes about 40% to 45% of all dementias.
Vascular disease, such as stroke, causes about 20%.
Lewy body disease, which causes neurons in the brain to degenerate, causes another 20% of dementias.
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