Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia in older people. Dementia is a brain disorder that makes it hard for a person to carry out normal daily activities. Symptoms of dementia include changes in memory, personality, and behavior.

There are other conditions besides AD that can cause dementia. For example, small strokes or changes in the brain's blood supply can cause multi-infarct or vascular dementia. Some causes of dementia are reversible, such as drug reactions, dehydration, and thyroid problems.

AD affects the parts of the brain that control thought, memory, and language. It is a slow disease that starts with mild memory problems and leads to severe brain damage. People with AD lose their abilities at different rates. AD can last from 3 to 20 years or more after the onset of symptoms. It is not yet clear what causes AD and there is no known cure.

An estimated 4 million people in the U.S. suffer from AD. The disease usually begins after age 60, and the risk of AD goes up with age. However, some cases of AD occur in younger people. About one in ten persons over 65 have AD, and nearly half of those age 85 and older may have the disease. But AD is not a normal part of aging.

AD is named after Dr. Alois Alzheimer, a German doctor. In 1906, Dr. Alzheimer noticed changes in the brain tissue of a woman who had died of an unusual mental illness. He found abnormal clumps (now called neuritic plaques) and tangled bundles of fibers (now called neurofibrillary tangles). Today, these plaques and tangles in the brain are considered hallmarks of AD.

Scientists have found other changes in the brains of people with AD. There is a loss of nerve cells in areas of the brain that are vital to memory and other mental abilities. There also are lower levels of chemicals in the brain that carry complex messages back and forth among nerve cells. AD may disrupt normal thinking and memory by blocking these messages in the brain.