[A new definition for Alzheimer's disease].

In 2007 and 2010, the International Working Group on Research Criteria for Alzheimer's Disease introduced a new conceptual framework that included a diagnostic algorithm covering early prodromal stages. There is a growing consensus that Alzheimer's disease (AD) should be considered as a clinical-biological entity characterized by: i) a well-defined clinical phenotype (an amnestic syndrome of the hippocampal type in typical AD), and ii) biomarkers, especially pathophysiological biomarkers, of the underlying disease process. The IWG criteria created the possibility for AD to be diagnosed prior to the onset of dementia, and also integrated biomarkers into the diagnostic framework. Although these criteria were intended for research purposes, they are increasingly used in expert centers for early diagnosis, for example of young-onset AD and complex cases (posterior cortical atrophy, primary progressive aphasia, etc.), where biomarkers can improve the diagnostic accuracy. In this article we present this new approach, together with the results of ongoing validation studies and data obtained by a French research team.