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Dementia is an acquired, diffuse, and usually progressive impairment of the content of consciousness. Dementia differs from other disorders of cognitive function, such as coma (see Chapter 3, Coma) or confusional states (see Chapter 4, Confusional States), in that in dementia, the level of consciousness (wakefulness or arousal) is preserved.

Although the prevalence of dementia increases with advancing age (Figure 5-1), dementia is not an invariable consequence of aging, and results instead from diseases involving the cerebral cortex, its subcortical connections, or both. Normal aging may be associated with minor alterations in neurologic function (Table 5-1) and with neuroanatomic changes, such as enlargement of cerebral ventricles and cortical sulci seen on CT or MRI. However, these alone do not imply cognitive deficits.

Figure 5-1.

Relationship between advancing age and incidence and prevalence of dementia. (Data from Lobo A, Launer LJ, Fratiglioni L, et al. Prevalence of dementia and major subtypes in Europe. Neurology. 2000;54(11 Suppl 5):S4-9 and Fratiglioni L, Launer LJ, Andersen K, et al. Incidence of dementia and major subtypes in Europe. Neurology. 2000;54(11 Suppl 5):S10-15.)

Table 5-1.Neurologic Changes in Normal Aging.

Several syndromes have been recognized as possible precursors to dementia.

Mild cognitive impairment (MCI) refers to cognitive deficits in one or more spheres that are objectively demonstrable and more severe than customarily seen with normal aging, but that do not interfere significantly with daily function. Patients with MCI have an increased risk (~7-10% per year) of developing dementia, most often Alzheimer disease.

Subjective cognitive decline describes self-reported cognitive deterioration, typically affecting memory, which cannot be verified objectively. The risk of dementia, especially Alzheimer disease, is increased, especially with symptoms that have been present for <5 years, begin at >60 years of age, cause patients concern, or are confirmed by family members or others.

Motoric cognitive risk syndrome is characterized by subjective cognitive complaints, slow gait, and increased risk of progression to dementia. Factors associated with motoric cognitive risk syndrome include obesity, stroke, Parkinson disease, physical inactivity, depression, and low educational attainment.

Whereas dementia affects multiple spheres of cognitive function, more limited cognitive disorders may also occur. These include deficits ...

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