Should someone without symptoms but biomarkers be diagnosed with AD?

There is an effort underway to define “prodromal” or “preclinical” Alzheimer’s disease (AD).  If someone has particular biomarkers (including tau in cerebrospinal fluid and amyloid seen on a special PET scan) but no memory loss (or other clinical symptoms of Alzheimer’s), there is a proposal to diagnose these people as having “Alzheimer’s disease.”

A recent blog post on Alzforum discusses the controversy around this:

While the proposed revisions [to the AD diagnostic criteria] have garnered praise from researchers for more accurately reflecting the underlying biology of the disease, they also have sparked criticism for advancing toward clinical use what were previously research criteria. …  Some Alzheimer’s researchers remain troubled by the idea of defining people with plaque buildup in their brain, but no symptoms, as having AD. Many others have been moving in this direction for years. Writing for the group Methods for Longitudinal Studies in Dementia (Melodem), Deborah Blacker of Massachusetts General Hospital, Boston, noted that a diagnosis of AD can still induce dread, and might confuse patients and family members. “Many of us would prefer a term like brain amyloidosis or the neuropathologists’ ‘Alzheimer disease neuropathologic changes’ to stress the difference,” she wrote (see comment under Working Group Meetings on Melodem page).

No doubt the same controversy will appear in the Parkinson’s community.  Should someone with alpha-synuclein in the skin and a positive DaTscan but without bradykinesia or rigidity be diagnosed with “preclinical” PD or “preclinical” Lewy body disease?
– Robin