Alzheimer disease is a progressive loss of mental function, characterized by degeneration of brain tissue, including loss of nerve cells, the accumulation of an abnormal protein called beta-amyloid, and the development of neurofibrillary tangles.
Alzheimer disease is a type of dementia, which is a slow, progressive decline in mental function including memory, thinking, judgment, and the ability to learn.
In 60 to 80% of older people with dementia, Alzheimer disease is the cause. It is rare among people younger than 65. It becomes more common with increasing age. About 11% of people aged 65 or older and about 32% of those aged 85 or older have Alzheimer disease. It affects more women than men, partly because women live longer. In 2015 in the United States, an estimated 5.3 million people had Alzheimer disease. The number of people with Alzheimer disease is expected to greatly increase as the proportion of older people increases.
Dementia is a slow, progressive decline in mental function including memory, thinking, judgment, and the ability to learn.
Dementia occurs primarily in people older than 65. Dementia, particularly the disruptive behavior that often accompanies it, is the reason for more than 50% of admissions to nursing homes. However, dementia is a disorder and is not a part of normal aging. Many people over 100 do not have dementia.
Dementia differs from delirium, which is characterized by an inability to pay attention, disorientation, an inability to think clearly, and fluctuations in the level of alertness.
Juebin Huang, MD, PhD – Merck Maual – Consumer Version - http://www.merckmanuals.com