Dementia is the loss of cognitive functioning—thinking, remembering, and reasoning—and behavioral abilities to such an extent that it severely interferes with a person’s daily life and activities. These functions include memory, language skills, visual perception, problem solving, self-management, and the ability to focus and pay attention. Some people with dementia cannot control their emotions, and their personalities may change. Dementia ranges in severity from the mildest stage, when it is just beginning to affect a person’s functioning, to the most severe stage, when the person must depend completely on others for basic activities of living.

While dementia is more common as people grow older, it is not a normal part of aging. Many people live into their 90s and beyond without any signs of dementia. The causes of dementia can vary, depending on the types of brain changes that may be taking place. Alzheimer’s disease is the most common cause of dementia in older adults. Other dementias include:

• Lewy body dementia
• Frontotemporal disorders
• Vascular dementia

Doctors have identified many other conditions that can cause dementia or dementia-like symptoms. These conditions include:

• Argyrophilic grain disease, a common, late-onset degenerative disease
• Creutzfeldt-Jakob disease, a rare brain disorder
• Huntington’s disease, an inherited, progressive brain disease
• Chronic traumatic encephalopathy (CTE), caused by repeated traumatic brain injury
• HIV-associated dementia (HAD)

To diagnose dementia, doctors first assess whether a person has an underlying treatable condition such as abnormal thyroid function, normal pressure hydrocephalus, or a vitamin deficiency that may relate to cognitive difficulties. Early detection of symptoms is important, as some causes can be treated. In many cases, the specific type of dementia a person has may not be confirmed until after the person has died and the brain is examined.