Rapid cognitive decline: searching for a definition and predictive factors among elderly with Alzheimer's disease.

The pattern and rate of cognitive decline in AD patients is far from uniform. In clinical practice, certain patients present episodes of rapid cognitive loss, whereas others deteriorate more progressively. At present time, there is little known about rapid decline in cognitive function in patients with AD, and moreover among older population. The main objective of this review was to elaborate a proposal of definition of rapid cognitive decline in order to facilitate its applicability into ordinary medical practice and to be relevant for clinical-decision making in old patients with AD. After the literature review, our results from longitudinal prospective studies and our clinical practice experience, we propose the following definition of rapid cognitive decline: a four-point or greater loss on the MMSE within six months and the loss of at least one point on the MMSE during the following six months. After ELSA cohort's results, 11% of an AD population of 312 patients were rapid cognitive decliners, complying with our proposed definition. They represent a non-negligible proportion of the population afflicted by AD.