Is mild cognitive impairment bridging the gap between normal aging and Alzheimer's disease?

Mild cognitive impairment (MCI) is one label applied to cognitive dysfunction that is beyond normal aging but of insufficient magnitude to qualify for the diagnosis dementia. Various opinions exist about the proportion of people who fall in this boundary condition, the rate at which they will progress to a full dementia syndrome, and the nature and extent of cognitive impairment at the time of MCI diagnosis. There are at least four important dimensions along which studies of boundary conditions must be compared in order to understand the discrepant findings. The first is the population frame sampled to establish MCI cohorts. The second is the nature of memory complaints. The third and fourth respectively, are the type of memory assessment and number and type of other cognitive domains assessed to identify and follow these groups. The contributions of each of these dimensions to the diagnosis of MCI and it's outcome are discussed.