Mild cognitive impairment: transition between aging and Alzheimer's disease.

The concept of the boundary between normal aging and early Alzheimer's disease is a focus of a great deal of research in the field of aging and dementia. Presumably there is a continuum of function between normality and the earliest signs of Alzheimer's disease. This transitional condition has been labeled mild cognitive impairment. Mild cognitive impairment refers to individuals who have a memory impairment greater than what one would expect for age, yet general cognitive function is preserved. Similarly activities of daily living are normal. However, the memory function of these individuals is abnormal for age and education. These subjects do not meet criteria for Alzheimer's disease. When mild cognitive impairment subjects are followed longitudinally, they tend to convert to clinically probable Alzheimer's disease as a rate of 10-15% per year. This is in contrast to normal elderly subjects who will develop Alzheimer's disease at a rate of 1-2% per year. Certain predictor variables are available to determine which subjects are more likely to progress at a rapid rate. Mild cognitive impairment is an important topic for research in aging and dementia and has also become the subject of several multicenter treatment trials.