The stages of Alzheimer's disease: a reappraisal

'Stages', as used in clinical practice and research, are defined, their value described, and criteria are proposed for their evaluation. The specific interest is in staging Alzheimer's disease (AD). Two staging systems, one based on the Global Deterioration Scale (GDS) and one based on the Mini-Mental State Exam (MMSE), are compared in terms of these criteria, as an illustration of the process involved. We propose that there is not one unique staging system, that different staging criteria might be appropriate to different research or clinical needs, depending on which part of the temporal course of the disease is of primary interest, and on whether the focus is on cognitive, functional, neurological, behavioral, economic, or other issues. GDS staging seems a better choice for the later stages of AD when the focus is on functional change. MMSE staging seems a better choice for tracking the earlier stages of AD when the focus is on cognitive change.