Most diagnostic criteria for the dementia syndrome stipulate that two or more cognitive functions must be sufficiently impaired so as to interfere with social and/ or occupational functioning and that there must not be clouding of consciousness. Clouding of consciousness, particularly in the context of a sudden onset of confusion, disorientation, hallucinations, disturbance in attention, or marked behavior change, is typically indicative of delirium (also termed acute confusional state). Delirium may be caused by an acute or chronic systemic illness (e.g., bacterial infection, hypoglycemia), adverse effects of medication, or serious neurological event requiring immediate medical attention. Untreated, these illnesses may result in death or irreversible impairment.
The risk of developing dementia increases markedly with age in later adulthood and is the single most prevalent category of mental illness for older persons. Worldwide, between 10 and 15% of persons over the age of 65 show at least mild dementia and approximately 6% show severe dementia. After age 65, dementia prevalence doubles approximately every 5 years. Overall, dementia is somewhat more common among women and may be more common in community-dwelling older black Americans. Prevalence for other nonwhite ethnic and racial groups is difficult to estimate due to the small number of adequate epide-miological studies. Annual incidence of new cases of dementia is also age-related, estimated to steadily increase from 0.33% at age 65 to 8.68% for those 95 years of age and older. A family history is a risk factor for dementia, increasing with the number of first-degree relatives similarly affected. Low educational background or low lifetime occupational attainment also increases the risk of dementia diagnosis. Studies have suggested that higher levels of education and higher levels of linguistic ability in early adulthood may be protective against the development of dementia, although controversy concerning this conclusion still remains.
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