If your grandfather suffers from dementia, he has a brain disorder that's causing him to gradually lose his memory and become disoriented and confused.

Although dementia is most common in elderly people, it's not a normal part of growing older but a syndrome caused by brain disease or injury. Dementia gets its name from the Latin words de, or "without," and mens, or "mind," which join together to mean "madness," although in English, dementia is not the same thing as madness. One example of an illness that causes dementia is Alzheimer's disease.

Definitions of dementia
  1. noun
    mental deterioration of organic or functional origin
    synonyms: dementedness
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    Korsakoff's psychosis, Korsakoff's syndrome, Korsakov's psychosis, Korsakov's syndrome, alcohol amnestic disorder, alcoholic dementia, polyneuritic psychosis
    dementia observed during the last stages of severe chronic alcoholism; involves loss of memory for recent events although long term memory is intact
    presenile dementia
    dementia with onset before the age of 65
    senile dementia, senile psychosis
    dementia of the aged; results from degeneration of the brain in the absence of cerebrovascular disease
    Alzheimer's, Alzheimer's disease, Alzheimers
    a progressive form of presenile dementia that is similar to senile dementia except that it usually starts in the 40s or 50s; first symptoms are impaired memory which is followed by impaired thought and speech and finally complete helplessness
    Pick's disease
    a progressive form of presenile dementia found most often in middle-aged and elderly women and characterized by degeneration of the frontal and temporal lobes with loss of intellectual ability and transitory aphasia
    type of:
    relatively permanent disorder of the mind
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