Definition of dementia from the National Institute of Neurological Disorders and Stroke. (NINDS).
Dementia is the loss of cognitive functioning—the ability to think, remember, problem solve or reason—to such an extent that it interferes with a person’s daily life and activities. 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 daily living.
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Functions affected 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. Signs and symptoms of dementia result when once-healthy neurons (nerve cells) in the brain stop working, lose connections with other brain cells, and die.
While everyone loses some neurons as they age, people with dementia experience far greater loss. Unlike dementia, age-related memory loss isn’t disabling. While dementia is more common with advanced age (as many as half of all people age 85 or older may have some form of dementia), it is not normal part of aging. Many people live into their 90s and beyond without any signs of dementia.
The causes of dementia can vary. Many people with dementia have both Alzheimer’s disease and one or more closely related disorders that share brain scanning or clinical (and sometimes both) features with Alzheimer’s disease. When a person is affected by more than one dementia disorder, the dementia can be referred to as a mixed dementia.
Some people may have mixed dementia caused by Alzheimer’s-related neurodegenerative processes, vascular disease-related processes, or another neurodegenerative condition. Many other conditions such as Creutzfeldt-Jakob disease, Huntington’s Disease, and chronic traumatic encephalopathy can cause dementia or dementia-like symptoms.
Risk factors for dementia include advancing age, stroke, high blood pressure, poorly controlled diabetes, and a thickening of blood vessel walls (atherosclerosis). Other dementias include frontotemporal disorders, vascular dementia, and Lewy body dementia.