What is the difference between dementia and Alzheimer’s disease?

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Dementia is an umbrella term used to describe a wide range of symptoms associated with decline in memory and other thinking skills severe enough to reduce a person’s ability to perform everyday activities. Alzheimer’s disease is one cause of dementia and accounts for 60 to 80 percent of cases. Vascular dementia, or dementia due to small stroke-like changes in the brain, is the second most common cause.