Preclinical Alzheimer disease—the challenges ahead

Pathological changes underlying Alzheimer disease (AD) begin more than 10 years before clinical presentation, and the need for early therapeutic intervention is becoming increasingly recognized. Reisa Sperling and colleagues consider challenges to such an approach—including the difficulty of defining preclinical AD, and ethical issues associated with disclosing information on AD biomarker status to healthy individuals—and discuss possible ways to overcome these hurdles. There is growing recognition that the pathophysiological process of Alzheimer disease (AD) begins many years prior to clinically obvious symptoms, and the concept of a presymptomatic or preclinical stage of AD is becoming more widely accepted. Advances in biomarker studies have enabled detection of AD pathology in vivo in clinically normal older individuals. The predictive value of these biomarkers at the individual patient level, however, remains to be elucidated. The ultimate goal of identifying individuals in the preclinical stages of AD is to facilitate early intervention to delay and perhaps even prevent emergence of the clinical syndrome. A number of challenges remain to be overcome before this concept can be validated and translated into clinical practice.