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Dementia is a syndrome caused by a number of brain disorders which cause memory loss, decline in some other aspect of cognition, and difficulties with activities of daily living.

The symptoms fall into three groups:

  • Cognitive impairment: causing difficulties with memory, language, attention, thinking, orientation, calculation, and problem-solving.

  • Psychiatric or behavioural disturbances: changes in personality, emotional control, and social behaviour; depression, agitation, hallucinations, and delusions.

  • Difficulties with activities of daily living, such as driving, shopping, eating, and dressing.

Deterioration must represent a progressive decline from a previous higher level of functioning, and consciousness should not be clouded (compare with acute confusional state or delirium). Memory loss is typically for recent events and long-term memory can be remarkably intact.

Mild cognitive impairment (MCI) is a decline in cognitive function greater than expected, taking account of the subject's age and education, which is not interfering with activities of daily living. This is often clinically a pre-dementia state.

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Some of the more common causes of dementia are:

Alzheimer's disease (about 50%). Degeneration of the cerebral cortex, with cortical atrophy, neurofibrillary tangles, amyloid plaque formation and reduction in acetylcholine production from affected neurons.
Vascular dementia (about 25%). Brain damage due to cerebrovascular disease: either major stroke, multiple smaller unrecognised strokes (multi-infarct) or chronic changes in smaller vessels (subcortical dementia).
Dementia with Lewy bodies (DLB) (about 15%). Deposition of abnormal protein within neurons in the brain stem and neocortex.
Frontotemporal dementia (less than 5%). Specific degeneration/atrophy of the frontal and temporal lobes of the brain. One type of frontotemporal dementia is Pick's disease, where protein tangles (Pick's bodies) are seen histologically.
Mixed dementia.
Parkinson's disease.
Potentially treatable dementias (fewer than 5%):
Substance misuse
Space-occupying intracranial lesions
Normal pressure hydrocephalus
Vitamin B12 deficiency
Folate deficiency
Genetic causes of dementia such as familial autosomal dominant Alzheimer's disease.

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