A Comparison of Clinical Diagnostic Classification Criteria Used in Longitudinal Cohort Studies of the Alzheimer's Disease Continuum: A Systematic Review.

Alzheimer's is a progressive disease, with a long preclinical phase of many decades. Accurate classification within longitudinal cohort studies is crucial for understanding disease progression and for the comparability and collaboration across studies. The main objective of this systematic review was to identify and compare the diagnostic criteria used in prospective population study cohorts centering on the Alzheimer's disease clinical continuum in older adults. A review was performed of cohort studies started in the year 2000 or later, with a follow-up duration of at least 3 years among people aged between 50 and 85 years old living in the community. Original studies were searched in MEDLINE, Embase, Cochrane, PsycINFO, and Web of Science. Two independent reviewers agreed on the final selection of 28 studies covering 25 cohorts. One study was identified by three independent judges as having methodological limitations due to inadequate reporting as per the modified NIH quality assessment tool. Data was extracted from each included study using a standardized extraction form. In general, the studies followed fewer than 1500 participants. The results showed convergence in the choice of diagnostic classification criteria among the 25 cohorts studied especially for the later stages of AD, while criteria for the earliest stages showed greater variability. Only five cohorts studied were concerned with the follow-up of the full spectrum of the disease. Our study may help to put in place a unified set of clinical diagnostic criteria across the continuum of Alzheimer's disease, rather than criteria developed specifically for a given study.