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  • Progressive intellectual decline.

  • Not due to delirium or psychiatric disease.

  • Age is the main risk factor, followed by family history and vascular disease risk factors.


Dementia is a progressive decline in intellectual function that is severe enough to compromise social or occupational functioning. Mild cognitive impairment describes a decline that has not resulted in a change in the level of function. Although a few patients identify a precipitating event, most experience an insidious onset and gradual progression of symptoms.

Dementia typically begins after age 60, and the prevalence doubles approximately every 5 years thereafter; in persons aged 85 and older, around half have dementia. The prevalence of Alzheimer dementia is predicted to be 15 million by 2060 in the United States. In most cases, the cause of dementia is acquired, either as a sporadic primary neurodegenerative disease or as the result of another disorder, such as stroke (Table 24–6). Other risk factors for dementia include family history, diabetes mellitus, cigarette smoking, hypertension, obesity, a history of significant head injury, and hearing loss. Vitamin D deficiency and chronic sleep deprivation may also increase the risk of dementia. Dementia is more prevalent among women, but this may be accounted for by their longer life expectancy. Physical activity seems to be protective; education, ongoing intellectual stimulation, and social engagement may also be protective, perhaps by promoting cognitive reserve, an improved capacity to compensate for insidious neurodegeneration.

Table 24–6.Common causes of age-related dementia (listed by prevalence).

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