Alzheimer's disease: A progressive neurologic disease of the brain that leads to the irreversible loss of neurons and dementia. The clinical hallmarks of Alzheimer's disease are progressive impairment in memory, judgment, decision making, orientation to physical surroundings, and language. A working diagnosis of Alzheimer disease is usually made on the basis of the neurologic examination. A definitive diagnosis can be made only at autopsy. On a cellular level, Alzheimer's disease is characterized by unusual helical protein filaments in nerve cells (neurons) of the brain. These odd twisted filaments are called neurofibrillary tangles. On a functional level, there is degeneration of the cortical regions, especially the frontal and temporal lobes, of the brain.

Alzheimer's disease is the most common of all neurodegenerative diseases. It accounts for about two-thirds of cases of dementia with vascular causes and other neurodegenerative diseases making up most of the rest.

The average time of survival from the initial diagnosis of Alzheimer's disease was found (in a study reported in 2004) to be 4.2 years for men and 5.7 years for women. Men had poorer survival across all age groups compared with women and survival was decreased in all age groups compared with the life expectancy of the US population.

The German psychiatrist and pathologist Alois Alzheimer (1864-1915) first described this form of presenile dementia in 1907. (German psychiatrist Emil Kraepelin named the disease in his honor.)

For more information, see: Alzheimer's disease. See also: Alzheimer's disease, early-onset familial.