Dementia: Significant loss of intellectual abilities such as memory capacity, severe enough to interfere with social or occupational functioning.

Criteria for the diagnosis of dementia include impairment of attention, orientation, memory, judgment, language, motor and spatial skills, and function. By definition, dementia is not due to major depression or schizophrenia.

Dementia is reported in as many as 1% of adults 60 years of age. It has been estimated that the frequency of dementia doubles every five years after 60 years of age.

Alzheimer's disease is the most common cause of dementia. There are many other causes of dementia, including (in alphabetical order): AIDS (due to HIV infection), alcoholism (the dementia is due to thiamine deficiency), brain injury, brain tumors, Creutzfeldt-Jakob disease, dementia with Lewy bodies (tiny round structures made of proteins that develop within nerve cells in the brain), drug toxicity, encephalitis, meningitis, Pick disease (a slowly progressive deterioration of social skills and changes in personality leading to impairment of intellect, memory, and language), syphilis, thyroid disease (hypothyroidism) and vascular dementia (damage to the blood vessels leading to the brain).