Researchers at Washington University School of Medicine in St. Louis have developed an approach to estimating when a person who is likely to develop Alzheimer’s disease, but has no cognitive symptoms, will start showing signs of Alzheimer’s dementia.
The algorithm, available online in the journal Neurology, uses data from a kind of brain scan known as amyloid positron emission tomography (PET) to gauge brain levels of the key Alzheimer’s protein amyloid beta.
In those who eventually develop Alzheimer’s dementia, amyloid silently builds up in the brain for up to two decades before the first signs of confusion and forgetfulness appear. Amyloid PET scans already are used widely in Alzheimer’s research, and this algorithm represents a new way of analyzing such scans to approximate when symptoms will arise. Using a person’s age and data from a single amyloid PET scan, the algorithm yields an estimate of how far a person has progressed toward dementia — and how much time is left before cognitive impairment sets in.
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“I perform amyloid PET scans for research studies, and when I tell cognitively normal individuals about positive results, the first question is always, ‘How long do I have until I get dementia?’,” said senior author Suzanne Schindler, MD, PhD, an assistant professor of neurology. “Until now, the answer I’d have to give was something like, ‘You have an increased risk of developing dementia in the next five years.’ But what does that mean? Individuals want to know when they are likely to develop symptoms, not just whether they are at higher risk.”
Schindler and colleagues analyzed amyloid PET scans from 236 people participating in Alzheimer’s research studies through Washington University’s Charles F. and Joanne Knight Alzheimer Disease Research Center. The participants were an average of 67 years old at the beginning of the study. All participants underwent at least two brain scans an average of 4½ years apart. The researchers applied a widely used metric known as the standard uptake value ratio (SUVR) to the scans to estimate the amount of amyloid in each participant’s brain at each time point.
The researchers also accessed over 1,300 clinical assessments on 180 of the participants. The assessments typically were performed every one to three years. Most participants were cognitively normal at the start of data collection, so the repeated assessments allowed the researchers to pinpoint when each participant’s cognitive skills began to slip.