What Is It?

Dementia is a pattern of mental decline caused by different diseases or conditions. Most commonly, dementia occurs when brain nerve cells (neurons) die, and connections between neurons are interrupted. These disruptions have a variety of causes and usually cannot be reversed.

Among the causes of dementia:

  • Alzheimer's disease causes about 40% to 45% of all dementias.

  • Vascular disease, such as stroke, causes about 20%.

  • Lewy body disease, which causes neurons in the brain to degenerate, causes another 20% of dementias.

Other conditions that can cause dementia include:

  • Creutzfeldt-Jakob disease

  • Traumatic head injury

  • Acquired immunodeficiency syndrome

  • Alcohol abuse

  • Degenerative diseases, such as Huntington's disease and Pick's disease

  • Brain abscess

  • Multiple sclerosis

  • More than 50 other rare degenerative conditions

In rare cases, dementia is caused by a treatable condition, and it may be partially or entirely reversed if the condition is diagnosed and treated early:

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