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Cognition may be altered by neurodegenerative, vascular, traumatic, anoxic, infectious, and toxic pathophysiological processes. Treating pain in such patients poses challenges, because memory loss, language and speech deficits, and altered levels of consciousness may impair patient ability to communicate meaningful discomfort.1 Patients with cognitive deficits are less likely to ask for and to receive analgesia, and they may be predisposed to exacerbations of mental and behavioral aberrance given standard analgesic regimens.15

Cognitive impairment, being difficult to measure and lacking definitive diagnostic criteria, has been reported at varying rates in several epidemiological studies.612,1924 Published prevalence rates span from 2% to 20%. The most descriptive population-based studies have estimated the prevalence in persons 70 or older to be between 14% and 18%.611 Estimates for incidence rates differ similarly. Elderly populations between the ages of 65 to 75 years have been reported to have incidence rates of 14 to 111 per 1,000 persons in a given year.1118 The Mayo Clinic Study of Aging reported 5% to 6% incidence rates per year in those aged 70 and older.16

Cognitive impairment is a complex demonstrable syndrome with diverse and changing appearances, including emotional symptoms, and cannot be restricted to memory or other focal deficit such as impaired executive function. Only 6% of memory dysfunctions are isolated in cases of subclinical cognitive deficit. One working criterion for mild cognitive impairment (MCI) established in 2003 applied a stepwise algorithm based on three diagnostic features. The first is the patient who appears to lack “normality” but is not demented in appearance. The second is cognitive decline indicated by the patient and/or an informant report and objective cognitive tests. Lastly, the patient is reported to exhibit preserved basic activities of daily living but has minimal impairment in complex instrumental functions.12,16,1926

Cognitive impairments, in degrees from mild to severe, are associated with several risk variables. Chronically elevated blood pressure, midlife diabetes mellitus, obesity, cardiac disease, history of stroke, alcohol abuse, alcoholism, drug addiction, apolipoprotein E epsilon 4 genotypes, and male gender are some of the factors that increase risk for cognitive impairment in various degrees of severity.911,1924 In addition the compromise of several organ systems may lead to cognitive impairments. The most common neurologic causes are dementias; these conditions are most often diagnosed as Alzheimer's disease, Lewy body disease, Pick's disease, Huntington's disease, Parkinson's disease, cerebellar degeneration, and supranuclear palsy. Cerebrovascular accidents are among the most common causes of cerebral damage leading to impaired cognitive function. Head trauma may also compromise cortical function, perception, storage of information, and overall function. Poisoning by carbon monoxide may induce a state of cerebral dysfunction. Furthermore, electrolyte abnormalities such as severe hyponatremia may result in seizure and cognitive impairment. Organ failure, anoxia, and infectious processes ...

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