A New Biological Definition of Alzheimer Disease

This transcript has been edited for clarity.

This is the Medscape Neurology Minute. I'm Dr Alan Jacobs.

Researchers from the National Institute of Aging Alzheimer's Association Research Framework have just released a new biological definition of Alzheimer disease.^[2] The shift defines Alzheimer disease from the current symptomatic behavioral one with biomarker confirmation to a strictly biological construct.

In 2011, new diagnostic guidelines for Alzheimer disease arose, including three stages: preclinical, mild cognitive impairment (MCI), and dementia.^[2] Now, the definition of Alzheimer disease in living people is biological, by pathologic brain changes or their biomarkers; and degree of cognitive impairment are now symptoms and signs of the disease, not its definition.

A new nomenclature uses ATN as its conceptual framework, with "A" referring to beta amyloid measured by PET scan or cerebrospinal fluid (CSF), "T" referring to tau pathology measured by CSF or PET, and "N" referring to neurodegeneration or neuronal injury and dysfunction measured by MRI or CSF.

The new labels include Alzheimer's pathologic change when only amyloid is present, and Alzheimer disease when both amyloid and pathologic tau are present. Both are now phases of the Alzheimer's continuum.

Every research participant now has both a biomarker profile and a cognitive stage—for example, Alzheimer disease with MCI, instead of the old label: MCI due to Alzheimer disease.

This has been the Medscape Neurology Minute. I'm Dr Alan Jacobs.

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Cite this: Alan R. Jacobs. A New Biological Definition of Alzheimer Disease - Medscape - Feb 20, 2019.