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Abstract
Background and Objectives To predict when cognitively normal individuals with brain amyloidosis will develop symptoms of Alzheimer disease (AD).
Methods Brain amyloid burden was measured by amyloid PET with Pittsburgh compound B. The mean cortical standardized uptake value ratio (SUVR) was transformed into a timescale with the use of longitudinal data.
Results Amyloid accumulation was evaluated in 236 individuals who underwent >1 amyloid PET scan. The average age was 66.5 ± 9.2 years, and 12 individuals (5%) had cognitive impairment at their baseline amyloid PET scan. A tipping point in amyloid accumulation was identified at a low level of amyloid burden (SUVR 1.2), after which nearly all individuals accumulated amyloid at a relatively consistent rate until reaching a high level of amyloid burden (SUVR 3.0). The average time between levels of amyloid burden was used to estimate the age at which an individual reached SUVR 1.2. Longitudinal clinical diagnoses for 180 individuals were aligned by the estimated age at SUVR 1.2. In the 22 individuals who progressed from cognitively normal to a typical AD dementia syndrome, the estimated age at which an individual reached SUVR 1.2 predicted the age at symptom onset (R2 = 0.54, p < 0.0001, root mean square error [RMSE] 4.5 years); the model was more accurate after exclusion of 3 likely misdiagnoses (R2 = 0.84, p < 0.0001, RMSE 2.8 years).
Conclusion The age at symptom onset in sporadic AD is strongly correlated with the age at which an individual reaches a tipping point in amyloid accumulation.
Glossary
- Aβ=
- β-amyloid;
- AD=
- Alzheimer disease;
- ADRC=
- Alzheimer Disease Research Center;
- CDR=
- Clinical Dementia Rating;
- PiB=
- Pittsburgh compound B;
- RMSE=
- root mean square error;
- SUVR=
- standardized uptake value ratio
Footnotes
Go to Neurology.org/N for full disclosures. Funding information and disclosures deemed relevant by the authors, if any, are provided at the end of the article.
- Received March 22, 2021.
- Accepted in final form August 12, 2021.
- © 2021 American Academy of Neurology
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