Short- and long-term memory impairment is the most prominent symptom of dementia. It ranges from inability to learn new information, to think problems through or to complete complex tasks, to inability to remember past personal history. There may also be impairment in abstract thinking or in judgement. Dementia may disturb higher cortical function affecting language and motor activities. Personality change happens often involving either an alteration or an accentuation of paranoid, inappropriate or bizarre behaviour.
Deteriorating intellectual capacity may be caused by a variety of diseases and disorders. The US National Institute on Aging states that some 100 conditions which mimic serious disorders are actually reversible. These are sometimes called "pseudodementias," and are often treatable. Examples of conditions causing reversible symptoms of dementia are: (1) reactions to medications (sedatives, hypnotics, neuroleptics, antihypertensives and antiarthritic medications); (2) emotional distress ([eg] depression or major life changes); (3) metabolic disturbances ([eg] renal failure, liver failure, electrolyte imbalances, hypoglycemia, hypercalcemia, hepatic diseases or pancreatic disorders); (4) Undetected problems of vision or hearing may result in inappropriate responses, misinterpreted as dementia; (5) nutritional deficiencies; (6) endocrine abnormalities (hypothyroidism, hyperthyroidism, parathyroid disturbances or adrenal abnormalities can cause confusion which mimics dementia) (7) older persons can develop infections which produce a sudden onset of a confusional state; (8) subdural haematoma (blood clot on the surface of the brain); (9) normal pressure hydrocephalus; (10) brain tumours; (11) atherosclerosis, causing a series of small strokes occurs (multi-infarct dementia).