dementia [Lat.,=being out of the mind], progressive deterioration of intellectual faculties resulting in apathy, confusion, and stupor. In the 17th cent. the term was synonymous with insanity, and the term dementia praecox was used in the 19th cent. to describe the condition now known as schizophrenia. In recent years, the term has generally been used to describe various conditions of mental deterioration occurring in middle to later life. Dementia, in its contemporary usage, is an irreversible condition, and is not applied to states of mental deterioration that may be overcome, such as delirium. The condition is generally caused by deterioration of brain tissue, though it can occassionally be traced to deterioration of the circulatory system. Major characteristics include short- and long-term memory loss, impaired judgement, slovenly appearance, and poor hygiene. Dementia disrupts personal relationships and the ability to function occupationally. Senility (senile dementia) in old age is the most commonly recognized form of dementia, usually occurring after the age of 65. Alzheimer's disease can begin at a younger age, and deterioration of the brain tissue tends to happen much more quickly. Individuals who have experienced cerebrovascular disease (particularly strokes) may develop similar brain tissue deterioration, with symptoms similar to Alzheimer's disease and senile dementia. Other types of dementia include Huntington's disease, Parkinson's disease, and Pick's disease. Some forms of familial Alzheimer's disease are caused by specific dominant gene mutations.

Any of a group of severe mental disorders that have in common symptoms such as hallucinations, delusions, blunted emotions, disorganized thinking, and withdrawal from reality. Five main types are recognized: the paranoid, characterized by delusions of persecution or grandeur combined with unrealistic, illogical thinking and frequent auditory hallucinations; the disorganized (hebephrenic), characterized by disordered speech and behaviour and shallow or inappropriate emotional responses; the catatonic, characterized by motor inflexibility or stupor along with mutism, echolalia, or other speech abnormalities; the simple or undifferentiated type, which conforms to basic definitions of schizophrenia but does not exhibit particular behaviours in the aforementioned types; and the residual type, which is a chronic stage indicating advancement toward later-stage schizophrenia. Schizophrenia seems to occur in 0.5–1percnt of the general population, and more than half of those so diagnosed will eventually recover. There is strong evidence that genetic inheritance plays a role, but no single cause of schizophrenia has been identified. Stressful life experiences may help trigger its onset. Treatment consists of drug therapy and counseling.

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Chronic, usually progressive deterioration of intellectual functions. Most common in the elderly, it usually begins with short-term-memory loss once thought a normal result of aging but now known to result from Alzheimer disease. Other common causes are Pick disease and vascular disease. Dementia also occurs in Huntington chorea, paresis (see paralysis), and some types of encephalitis. Treatable causes include hypothyroidism (see thyroid gland), other metabolic diseases, and some malignant tumours. Treatment may arrest dementia's progress but usually does not reverse it.

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