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The word dementia comes from Latin and means "out of the mind." It is used to describe an acquired, persistent, global impairment of cognition/intellectual processes, which is sufficiently severe to interfere with social or occupational function. Dementia, like delirium, is known as a syndrome, that is, it is a collection of symptoms and signs, whose presence can be diagnosed, but the diagnosis does not in and of itself suggest a cause. For example, the syndrome of dementia has a number of causes, including Alzheimer's disease, Lewy body dementia, and fronto-temporal dementia.

Each of the words in the definition is important both for what it says and what it leaves out. Thus "acquired" differentiates dementia, which is usually seen in late life, from lifelong conditions of diminished intellect encountered in people who have grown older. Such people would still be described by their original diagnosis (e.g., cerebral palsy) even after they have become elderly. The most common exception to this general rule is with Down's syndrome, where a genetic abnormality that gives rise to increased amounts of the protein beta-amyloid increases the likelihood that individuals will develop Alzheimer's disease as they grow older. In consequence, the designation of the syndrome describing their cognitive impairment can properly be termed, once they have developed Alzheimer's disease, as a dementia. In other cases, however, the description of the lifelong disorder, if stable, is not described as a dementia.

The word chronic (some definitions use the word persistent) is meant to distinguish dementia from delirium. While delirium is another cause of global cognitive impairment in elderly people, it typically comes on acutely, and generally resolves quickly. Note, however, that an acute onset does not rule out dementia. For example, the dementia seen following stroke can begin suddenly. Similarly, there are other dementias, particularly Creutzfeldt-Jakob disease, and dementia with Lewy bodies, which can seem as though they came on almost out of the blue. Although it is often not stated, chronic generally implies progressive, that is, it is usually the case that the dementia gets worse over time. While there are some dementias (notably the dementia following stroke) that can have prolonged periods of plateau, most dementias follow a characteristic pattern of decline. The pattern of deficits seen as the decline progresses forms the basis of staging the dementia.

The word "global" in the definition of dementia is meant to imply that the dementia cannot be diagnosed when only one aspect of higher cortical function is impaired. Thus, for example, people with language problems (aphasia), even though they typically have great difficulty in expressing themselves, would not meet the criteria for dementia as long as other functions (such as memory) were not impaired.

Impairment of cognition may seem self-evident for a diagnosis of dementia, but its demonstration sometimes is difficult, particularly where the impairment is mild. The special challenge here is the diagnosis of cognitive impairment, which may begin to meet the dementia criteria in someone who is highly educated. Most highly educated people do well on most tests of cognition until a dementia becomes established.

One way to distinguish mild cognitive impairment from the cognitive impairment that is more likely consistent of dementia is to determine the extent to which this impairment interferes with social or occupational function. For example, although many people find as they get older that their memory is not as good as it once was, this does not imply dementia unless the memory loss impairs job performance or social roles.

Impairment of function also underlies the usual method of staging the course of dementia. While a number of formal staging systems exist, most agree on a "pre-dementia" stage, followed by mild, moderate, and then severe dementia. In the pre-dementia stage, the rough rule of thumb is that the cognitive impairment, while giving rise to symptoms, does not yet impair function. By contrast, mild dementia is diagnosed with somewhat greater confidence when impairment in instrumental activities of daily living (such as driving, balancing a check book, following a recipe) is present. Moderate dementia is diagnosed when patients begin to need prompting to carry out their personal care. Typically, prompting is required for them to change their clothes or maintain their grooming. Severe dementia is heralded when, even with prompting, people are no longer able to carry out basic activities of daily living, such as dressing, grooming, and feeding.

Dementia is a common problem among older people, affecting about 10 percent of the population over age sixty. Although dementia is age-related, it is distinct from the normal aging of the brain. Dementia increases the risk of delirium, and is often seen in the face of depression. Patients with severe dementia need to be cared for in nursing homes or in long-term care institutions. Between one-third and one-half of all people with dementia are in institutional long-term care. These facilities are quite costly and make dementia among the most expensive of medical conditions.

People with dementia necessarily have impairment of their cognitive function. Given that good cognitive function is necessary to be competent, a number of ethical issues arise when a person's competence is not assured at the same time that important decisions about the future course need to be made.

While some causes of dementia can be treated, cure is rare, and many types of dementia have no effective treatment. In consequence, in each of these ways discussed above—personal, medical, social, economic, and ethical—dementia poses a considerable challenge to an aging society.



DUNITZ, M. Clinical Diagnosis and Management of Alzheimer's Disease. Edited by S. Gauthier. London: Martin Dunitz, Ltd., 2001.

ROCKWOOD, K., and MACKNIGHT, C. Understanding Dementia. Halifax: Pottersfield, 2001.

WILCOCK, G. K.; BUCKS, R.; and ROCKWOOD, K. Diagnosis and Management of Dementia. Oxford, U.K.: Oxford University Press, 1999.

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