Researchers at Washington University in St. Louis, MO, analyzed amyloid accumulation in 236 individuals who underwent more than one amyloid PET scan on average 4.5 years apart. The team measured standardized uptake value ratio (SUVR) on amyloid-PET scans to estimate the amount of amyloid in each participant's brain at each time point, according to a study published September 9 in Neurology
Most participants were cognitively normal at the start of the study, so repeated assessments allowed the researchers to pinpoint when each participant's cognitive skills began to slip.
The researchers identified what they described as a tipping point in amyloid accumulation at a low level of amyloid burden, measured at an SUVR of 1.2, after which nearly all individuals accumulated amyloid at a relatively consistent rate until reaching a high level of amyloid burden, at an SUVR of 3.
Longitudinal clinical diagnoses for 180 individuals in the study were aligned by the estimated age at SUVR 1.2. In the 22 participants who progressed from cognitively normal to a typical Alzheimer's disease dementia, the estimated age at which an individual reached SUVR 1.2 predicted their ages at symptom onset.
"Individuals want to know when they are likely to develop symptoms, not just whether they are at higher risk," said senior author Dr. Suzanne Schindler, PhD, an assistant professor of neurology, in a news release from the university.
The study's clinical significance may apply when doctors are discussing positive Alzheimer's disease test results with cognitively normal patients, Schindler concluded.
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