Prediction of continuous amyloid PET values by CSF tau measures

Abstract

AbstractBackgroundAlzheimer disease (AD) is a slowly progressive neurodegenerative disorder characterized by the presence of amyloid plaques that can be measured in vivo with positron emission tomography (PET). PET quantifies the lifetime accumulation of amyloid plaques, while cerebrospinal fluid (CSF) biomarkers reflect the production and clearance of Aβ and tau peptides at time of CSF collection. Previous work has demonstrated a relative plateau of CSF values at higher levels of amyloid burden. Our objective was to identify the range of amyloid PET values predicted by CSF measures of tau phosphorylation, which have been found to be strongly associated with amyloid PET burden.MethodCSF was collected within two years of an amyloid PET scan from 417 (63 cognitively impaired) participants enrolled in studies of memory and aging at the Knight Alzheimer Disease Research Center (mean age 69.8 years, standard deviation 8.9 years). PET imaging was performed with Pittsburgh Compound B (PiB). CSF Aβ42, p‐tau181 and Aβ40 were measured with Lumipulse automated immunoassays. The CSF tau phosphorylation occupancies (percent of tau phosphorylated) at T111, T153, T175, T181, S199, S202, T205, S208, T217, and T231 were evaluated with an immunoprecipitation‐mass spectrometry (IPMS) assay. We applied a neural network to generate a simulated PET‐PiB scan and cortical summary estimates using the fluid biomarkers as modeled inputs. We used asymptotic regression to evaluate the range of amyloid PET values predicted by each CSF measure (Figure 1).ResultCombining fluid biomarkers generated a cortical amyloid burden estimate within 12.6% mean average percent error (MAPE). Four of the assessed fluid biomarkers individually generated estimates within 20% MAPE (Figure 2). Of these, CSF Lumipulse p‐tau181/Aβ42, pS208/S208 (%), and pT231/T231 (%) predicted amyloid PET burden up until a high level (3.08 SUVR/91.1 Centiloids; 3.01 SUVR/88.0 Centiloids; 2.79 SUVR/78.1 Centiloids, respectively) (Figure 3). CSF pT217/217 (%) also had high accuracy but a slightly lower prediction threshold (2.65 SUVR/71.8 Centiloids).ConclusionCSF measures including phosphorylated tau predict amyloid PET over different ranges. Combining different measures of CSF tau phosphorylation can generate estimates of cortical amyloid burden. Future work will evaluate the prediction of tau PET by CSF measures.