The American Academy of Neurology is proposing a new classification scheme to describe Alzheimer’s biomarkers. Biomarkers have become an essential component of Alzheimer disease (AD) research and also in cognitive aging research. A number of current issues suggest that a new descriptive classification scheme for these biomarkers would be useful.
The proposed format is called the “A/T/N” system in which 7 major AD biomarkers are divided into 3 binary categories based on the nature of the pathophysiology that each measures. “A” refers to the value of a b-amyloid biomarker (amyloid PET or CSF Ab42); “T,” the value of a tau biomarker (CSF phospho tau, or tau PET); and “N,” biomarkers of neurodegeneration or neuronal injury ([18F]-fluorodeoxyglucose–PET, structural MRI, or CSF total tau). Each biomarker category is rated as positive or negative. An individual score might appear as A+/T+/N-, or A+/T-/N-, etc.
Temporal ordering of mechanisms underlying AD pathogenesis are ignored. It includes all individuals in any population regardless of the mix of biomarker findings and therefore is suited to population studies of cognitive aging. It does not specify disease labels and thus is not a diagnostic classification system. It is a descriptive system for categorizing multidomain biomarker findings at the individual person level in a format that is easy to understand and use. Given the present lack of consensus among AD specialists on terminology across the clinically normal to dementia spectrum, a biomarker classification scheme will have broadest acceptance if it is independent from any one clinically defined diagnostic scheme.
Source: Neurology® 2016;87:1–9