|Dementia is a general term describing a group of disorders in which memory and thought processes (cognition) become impaired for a period of at least 6 months. Unlike mental retardation, dementia involves a change in thinking abilities relative to baseline.|
Dementia can be caused by about 50 different disorders, but 50% to 70% of cases are caused by Alzheimer's disease, and 20% to 30% by vascular disease. In many forms of dementia, such as Alzheimer's disease, Lewy body disease, and other neurodegenerative disorders, symptoms develop slowly, are relatively stable rather than fluctuating, and continue into a slow decline. However, other forms of dementia, such as vascular dementia associated with small strokes (multi-infarct dementia) may begin abruptly and worsen in stepwise fashion, with relative stability between each decline. In dementia secondary to head trauma or encephalitis, memory problems are worst at the outset, and remain relatively stable or may even improve with time.
Impaired memory is a prominent and early symptom of dementia. New skills and knowledge are difficult to learn, while old skills and knowledge are eventually lost. Valuables may be lost, such as a wallet or keys. The person may become lost, even in familiar surroundings. Late in dementia, individuals may forget their occupation, family members, or even their name. Other symptoms are difficulty naming objects or people (anomia), rambling speech, difficulty performing certain activities (apraxia), or failure to recognize certain objects (agnosia). Executive functions, such as thinking abstractly, planning, and initiating complex activities, can be impaired. Poor judgment and insight are common. The individual usually has little or no awareness of memory loss or other abnormalities. Individuals have an unrealistic view of their capabilities or their future. For example, they may talk of starting a business or driving. There can be mood and sleep disturbances. False beliefs (delusions) are common, especially paranoid delusions involving others stealing from them or conspiring against them. Individuals with dementia may have further deterioration of cognitive abilities with stress, either physical stress such as a viral illness or minor surgery, or psychological stress such as bereavement.
Alzheimer's disease is the most common cause of dementia, followed by Lewy body disease (DSM-IV-TR 832). Other possibilities include stroke and Parkinson's disease, Huntington's disease, brain injury, tumor, infection (AIDS, syphilis), autoimmune diseases such as lupus, hypothyroidism or other endocrine diseases, liver disease, a neurological disease such as multiple sclerosis, normal pressure hydrocephalus, or heavy metal poisoning with lead or mercury. Dementia could also be a long-lasting effect of drug or alcohol abuse.
Risk: The occurrence of dementia increases with age. The age of onset is usually late in life, with the highest risk above 85 years.
Incidence and Prevalence: Prevalence ranges from about 1.5% for individuals age 65 to 69, up to 16% to 25% for those over 85 (DSM-IV-TR 832).