Amyloid positron emission tomography (PET) data are commonly expressed as binary measures of cortical deposition. However, not all individuals with high cortical amyloid will experience a rapid cognitive decline

Motivated by postmortem data, we evaluated a three-stage PET classification: low cortical; high cortical, low striatal; and high cortical, high striatal amyloid; hypothesizing this model could better reflect Alzheimer's dementia progression than a model based only on cortical measures.

Researchers explored an alternative PET measure seeking to stage Aβ pathology in vivo based on the established Thal-Phase postmortem ordinal system for regional extent of Aβ pathology.

They evaluated the predictive value of a PET measure from the striatum, a subcortical structure in which Aβ is typically detected at autopsy only after cortical deposition and in which corresponding PET measures are readily available.

Results

They classified PET data from 1433 participants (646 normal, 574 mild cognitive impairment, and 213 AD), explored the successive involvement of cortex and striatum using 3-year follow-up PET data, and evaluated the associations between PET stages, hippocampal volumes, and cognition.

Follow-up data indicated that PET detects amyloid first in cortex and then in the striatum. Our three-category staging including striatum better predicted hippocampal volumes and subsequent cognition than a three-category staging including only cortical amyloid.

PET can evaluate amyloid expansion from cortex to subcortex. Using the striatal signal as a marker of advanced amyloidosis may increase predictive power in Alzheimer's dementia research.