Frequent Amyloid Deposition Without Significant Cognitive Impairment Among the Elderly

Abstract

Despite the strong association of amyloid burden and Alzheimer disease (AD), it has also long been recognized that a significant number of individuals without clinical evidence of AD have amyloid deposition at death.¹ The ability to identify the proportion of cognitively normal elderly persons with amyloid in their brains, as well as the ability to characterize the relationship of amyloid deposition to cognition function, has historically been limited by the fact that amyloid load was typically determined at autopsy. Nevertheless, through autopsy studies, the prevalence of amyloid burden among cognitively normal elderly persons has been estimated to be more than 25%.^2-4 This number rivals the combined prevalence of mild cognitive impairment (MCI) (approximately 19%⁵) and AD (approximately 13%⁶). If true, this implies that approximately 50% of people older than 65 years have amyloid deposition in their brains and that about half of these people are asymptomatic. These possibilities have important implications when considering strategies for future prevention trials.