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.