Associations between [18F]AV1451 tau PET and CSF measures of tau pathology in a clinical sample

Spatially constrained kinetic modeling with dual reference tissues improves 18F-flortaucipir PET in studies of Alzheimer disease

PURPOSE

Recent studies have shown that standard compartmental models using plasma input or the cerebellum reference tissue input are generally not reliable for quantifying tau burden in dynamic 18F-flortaucipir PET studies of Alzheimer disease. So far, the optimal reference region for estimating 18F-flortaucipir delivery and specific tau binding has yet to be determined. The objective of the study is to improve 18F-flortaucipir brain tau PET quantification using a spatially constrained kinetic model with dual reference tissues.

METHODS

Participants were classified as either cognitively normal (CN) or cognitively impaired (CI) based on clinical assessment. T1-weighted structural MRI and 105-min dynamic 18F-flortaucipir PET scans were acquired for each participant. Using both a simplified reference tissue model (SRTM2) and Logan plot with either cerebellum gray matter or centrum semiovale (CS) white matter as the reference tissue, we estimated distribution volume ratios (DVRs) and the relative transport rate constant R1 for region of interest-based (ROI) and voxelwise-based analyses. Conventional linear regression (LR) and LR with spatially constrained (LRSC) parametric imaging algorithms were then evaluated. Noise-induced bias in the parametric images was compared to estimates from ROI time activity curve-based kinetic modeling. We finally evaluated standardized uptake value ratios at early phase (SUVREP, 0.7-2.9 min) and late phase (SUVRLP, 80-105 min) to approximate R1 and DVR, respectively.

RESULTS

The percent coefficients of variation of R1 and DVR estimates from SRTM2 with spatially constrained modeling were comparable to those from the Logan plot and SUVRs. The SRTM2 using CS reference tissue with LRSC reduced noise-induced underestimation in the LR generated DVR images to negligible levels (< 1%). Inconsistent overestimation of DVR in the SUVRLP only occurred using the cerebellum reference tissue-based measurements. The CS reference tissue-based DVR and SUVRLP, and cerebellum-based SUVREP and R1 provided higher Cohen's effect size d to detect increased tau deposition and reduced relative tracer transport rate in CI individuals.

CONCLUSION

Using a spatially constrained kinetic model with dual reference tissues significantly improved quantification of relative perfusion and tau binding. Cerebellum and CS are the suggested reference tissues to estimate R1 and DVR, respectively, for dynamic 18F-flortaucipir PET studies. Cerebellum-based SUVREP and CS-based SUVRLP may be used to simplify 18F-flortaucipir PET study.

Cortical hypometabolism reflects local atrophy and tau pathology in symptomatic Alzheimer's disease

Posterior cortical hypometabolism measured with [18F]-Fluorodeoxyglucose (FDG)-PET is a well-known marker of Alzheimer's disease-related neurodegeneration, but its associations with underlying neuropathological processes are unclear. We assessed cross-sectionally the relative contributions of three potential mechanisms causing hypometabolism in the retrosplenial and inferior parietal cortices: local molecular (amyloid and tau) pathology and atrophy, distant factors including contributions from the degenerating medial temporal lobe or molecular pathology in functionally connected regions, and the presence of the apolipoprotein E (APOE) ε4 allele. Two hundred and thirty-two amyloid-positive cognitively impaired patients from two cohorts (University of California, San Francisco, UCSF, and Alzheimer's Disease Neuroimaging Initiative, ADNI) underwent MRI and PET with FDG, amyloid-PET using [11C]-Pittsburgh Compound B, [18F]-Florbetapir, or [18F]-Florbetaben, and [18F]-Flortaucipir tau-PET within one year. Standard uptake value ratios (SUVR) were calculated using tracer-specific reference regions. Regression analyses were run within cohorts to identify variables associated with retrosplenial or inferior parietal FDG SUVR. On average, ADNI patients were older and were less impaired than UCSF patients. Regional patterns of hypometabolism were similar between cohorts, though there were cohort differences in regional gray matter atrophy. Local cortical thickness and tau-PET (but not amyloid-PET) were independently associated with both retrosplenial and inferior parietal FDG SUVR (ΔR2 = .09 to .21) across cohorts in models that also included age and disease severity (local model). Including medial temporal lobe volume improved the retrosplenial FDG model in ADNI (ΔR2 = .04, p = .008) but not UCSF (ΔR2 < .01, p = .52), and did not improve the inferior parietal models (ΔR2s < .01, ps > .37). Interaction analyses revealed that medial temporal volume was more strongly associated with retrosplenial FDG SUVR at earlier disease stages (p = .06 in UCSF, p = .046 in ADNI). Exploratory analyses across the cortex confirmed overall associations between hypometabolism and local tau pathology and thickness and revealed associations between medial temporal degeneration and hypometabolism in retrosplenial, orbitofrontal, and anterior cingulate cortices. Finally, our data did not support hypotheses of a detrimental effect of pathology in connected regions or of an effect of the APOE ε4 allele in impaired participants. Overall, in two independent groups of patients at symptomatic stages of Alzheimer's disease, cortical hypometabolism mainly reflected structural neurodegeneration and tau, but not amyloid, pathology.

Optimal Combinations of AT(N) Biomarkers to Determine Longitudinal Cognition in the Alzheimer's Disease

Background: National Institute on Aging-Alzheimer's Association (NIA-AA) proposed the AT(N) system based on β-amyloid deposition, pathologic tau, and neurodegeneration, which considered the definition of Alzheimer's disease (AD) as a biological construct. However, the associations between different AT(N) combinations and cognitive progression have been poorly explored systematically. The aim of this study is to compare different AT(N) combinations using recognized biomarkers within the Alzheimer's Disease Neuroimaging Initiative (ADNI) cohort. Methods: A total of 341 participants were classified into cognitively unimpaired (CU; n = 200) and cognitively impaired (CI; n = 141) groups according to the clinical manifestations and neuropsychological tests. Cerebrospinal fluid (CSF) Aβ42 and amyloid-PET ([18F]flutemetamol) were used as biomarkers for A; CSF phosphorylated tau (p-tau) and tau-PET ([18F]flortaucipir) were used as biomarkers for T; CSF total tau (t-tau), hippocampal volume, temporal cortical thickness, [18F]fluorodeoxyglucose (FDG) PET, and plasma neurofilament light (NfL) were used as biomarkers for (N). Binary biomarkers were obtained from the Youden index and publicly available cutoffs. Prevalence of AT(N) categories was compared between different biomarkers within the group using related independent sample non-parametric test. The relationship between AT(N) combinations and 12-year longitudinal cognition was assessed using linear mixed-effects modeling. Results: Among the CU participants, A-T-(N)- was most common. More T+ were detected using p-tau than tau PET (p < 0.05), and more (N)+ were observed using fluid biomarkers (p < 0.001). A+T+(N)+ was more common in the CI group. Tau PET combined with cortical thickness best predicted cognitive changes in the CI group and MRI predicted changes in the CU group. Conclusions: These findings suggest that optimal AT(N) combinations to determine longitudinal cognition differ by cognitive status. Different biomarkers within a specific component for defining AT(N) cannot be used identically. Furthermore, different strategies for discontinuous biomarkers will be an important area for future studies.

18F-Flortaucipir PET Associations with Cerebrospinal Fluid, Cognition, and Neuroimaging in Mild Cognitive Impairment due to Alzheimer's Disease

BACKGROUND

Tau positron emission tomography (PET) imaging is used in research, but its relation to cerebrospinal fluid (CSF) tau and other Alzheimer's disease (AD)-related clinical measures is unclear in mild cognitive impairment with AD biomarkers (MCI-AD).

OBJECTIVE

To determine associations between 18F-flortaucipir PET and CSF AD biomarkers, cognitive functioning, and neuroimaging measures in MCI-AD.

METHODS

In 29 participants 50 years or older with MCI-AD, 18F-flortaucipir PET, CSF total tau (T-tau), phosphorylated tau181p (P-tau), amyloid-β (Aβ), structural MRI, and neuropsychological testing were collected as baseline assessments of an ongoing clinical trial. 11C-Pittsburgh compound B PET was simultaneously conducted in 20 participants. Associations between 18F-flortaucipir PET and these measures were assessed by multiple linear regression adjusted for potential confounders and using global, lobar, and voxel-wise standardized uptake value ratio (SUVr).

RESULTS

Whole brain 18F-flortaucipir SUVr was significantly associated with CSF T-tau (r = 0.68, p < 0.001) and P-tau (r = 0.42, p = 0.04) after adjusting for age, sex, race, and education, with strongest associations in the temporal region (T-tau: r = 0.69, p < 0.001; P-tau: r = 0.49, p = 0.02). Voxel-wise analysis confirmed these regional associations. 18F-flortaucipir PET was also associated with CSF Aβ (r = -0.45, p = 0.03), episodic memory (r = -0.61, p = 0.001), visuospatial working memory (r = -0.46, p = 0.02), and brain cortical thickness (r = -0.44, p = 0.03) but not hippocampal volume. In the amyloid PET subset, although 11C-PiB PET associated strongly with 18F-flortaucipir (r = 0.79, p≤0.001), associations were stronger between 11C-PiB and key outcomes, compared to 18F-flortaucipir.

CONCLUSION

18F-flortaucipir PET is moderately associated with CSF AD biomarkers and other AD-related phenotypes. The associations in this MCI-AD sample are stronger than previously described in other populations.

Temporal trajectory of biofluid markers in Parkinson's disease

Full dynamics of biofluid biomarkers have been unknown in patients with Parkinson’s disease (PD). Using data from 396 PD patients and 182 controls in the Parkinson's Progression Markers Initiative (PPMI) database, we estimated long-term temporal trajectories of CSF α-synuclein (α-syn), amyloid-β (Aβ), total tau (t-tau), phosphorylated tau (p-tau) and serum neurofilament light chain (NfL) by integrating function between the baseline levels and annual changes. At baseline, PD patients showed lower CSF α-syn, Aβ, t-tau and p-tau levels than those of the controls. In all PD patients, CSF α-syn and Aβ decreased in a negative exponential pattern before the onset of motor symptoms, whereas CSF t-tau and p-tau, and serum NfL increased. Patients with cognitive impairment exhibited faster decline of Aβ and α-syn and faster rise of t-tau, p-tau and NfL, when compared to those without. Similarly, low Aβ group showed earlier decline of α-syn, faster rise of t-tau, p-tau and NfL, and faster decline of cognitive performances, when compared to high Aβ group. Our results suggest that longitudinal changes in biomarkers can be influenced by cognitive impairment and Aβ burden at baseline. PD patients with Aβ pathology may be associated with early appearance of α-synuclein pathology, rapid progression of axonal degeneration and neurodegeneration, and consequently greater cognitive decline.

Proteomic correlates of cortical thickness in cognitively normal individuals with normal and abnormal cerebrospinal fluid beta-amyloid1-42

Cortical atrophy is an early feature of Alzheimer´s disease (AD). The biological processes associated with variability in cortical thickness remain largely unknown. We studied 220 cerebrospinal fluid (CSF) proteins to evaluate biological pathways associated with cortical thickness in 34 brain regions in 79 cognitively normal older individuals with normal (>192 ng/L, n = 47), and abnormal (≤192 ng/L, n = 32) CSF beta-amyloid_1-42 (Aβ₄₂). Interactions for Aβ₄₂ status were tested. Panther GeneOntology and Cytoscape ClueGO analyses were used to evaluate biological processes associated with regional cortical thickness. 170 (77.3 %) proteins related with cortical thickness in at least 1 brain region across the total group, and 171 (77.7 %) proteins showed Aβ₄₂ specific associations. Higher levels of proteins related to axonal and synaptic integrity, amyloid accumulation, and inflammation were associated with thinner cortex in lateral temporal regions, the rostral anterior cingulum, the lateral occipital cortex and the pars opercularis only in the abnormal Aβ₄₂ group. Alterations in CSF proteomics are associated with a regional cortical atrophy in the earliest stages of AD.

Clinical validity of increased cortical uptake of [18F]flortaucipir on PET as a biomarker for Alzheimer's disease in the context of a structured 5-phase biomarker development framework

PURPOSE

In 2017, the Geneva Alzheimer's disease (AD) Biomarker Roadmap initiative adapted the framework of the systematic validation of oncological diagnostic biomarkers to AD biomarkers, with the aim to accelerate their development and implementation in clinical practice. With this work, we assess the maturity of [18F]flortaucipir PET and define its research priorities.

METHODS

The level of maturity of [18F]flortaucipir was assessed based on the AD Biomarker Roadmap. The framework assesses analytical validity (phases 1-2), clinical validity (phases 3-4), and clinical utility (phase 5).

RESULTS

The main aims of phases 1 (rationale for use) and 2 (discriminative ability) have been achieved. [18F]Flortaucipir binds with high affinity to paired helical filaments of tau and has favorable kinetic properties and excellent discriminative accuracy for AD. The majority of secondary aims of phase 2 were fully achieved. Multiple studies showed high correlations between ante-mortem [18F]flortaucipir PET and post-mortem tau (as assessed by histopathology), and also the effects of covariates on tracer binding are well studied. The aims of phase 3 (early detection ability) were only partially or preliminarily achieved, and the aims of phases 4 and 5 were not achieved.

CONCLUSION

Current literature provides partial evidence for clinical utility of [18F]flortaucipir PET. The aims for phases 1 and 2 were mostly achieved. Phase 3 studies are currently ongoing. Future studies including representative MCI populations and a focus on healthcare outcomes are required to establish full maturity of phases 4 and 5.

The validation status of blood biomarkers of amyloid and phospho-tau assessed with the 5-phase development framework for AD biomarkers

PURPOSE

The development of blood biomarkers that reflect Alzheimer's disease (AD) pathophysiology (phosphorylated tau and amyloid-β) has offered potential as scalable tests for dementia differential diagnosis and early detection. In 2019, the Geneva AD Biomarker Roadmap Initiative included blood biomarkers in the systematic validation of AD biomarkers.

METHODS

A panel of experts convened in November 2019 at a two-day workshop in Geneva. The level of maturity (fully achieved, partly achieved, preliminary evidence, not achieved, unsuccessful) of blood biomarkers was assessed based on the Biomarker Roadmap methodology and discussed fully during the workshop which also evaluated cerebrospinal fluid (CSF) and positron emission tomography (PET) biomarkers.

RESULTS

Plasma p-tau has shown analytical validity (phase 2 primary aim 1) and first evidence of clinical validity (phase 3 primary aim 1), whereas the maturity level for Aβ remains to be partially achieved. Full and partial achievement has been assigned to p-tau and Aβ, respectively, in their associations to ante-mortem measures (phase 2 secondary aim 2). However, only preliminary evidence exists for the influence of covariates, assay comparison and cut-off criteria.

CONCLUSIONS

Despite the relative infancy of blood biomarkers, in comparison to CSF biomarkers, much has already been achieved for phases 1 through 3 - with p-tau having greater success in detecting AD and predicting disease progression. However, sufficient data about the effect of covariates on the biomarker measurement is lacking. No phase 4 (real-world performance) or phase 5 (assessment of impact/cost) aim has been tested, thus not achieved.

Application of the ATN classification scheme in a population without dementia: Findings from the EPAD cohort

BACKGROUND

We classified non-demented European Prevention of Alzheimer's Dementia (EPAD) participants through the amyloid/tau/neurodegeneration (ATN) scheme and assessed their neuropsychological and imaging profiles.

MATERIALS AND METHODS

From 1500 EPAD participants, 312 were excluded. Cerebrospinal fluid cut-offs of 1000 pg/mL for amyloid beta (Aß)1-42 and 27 pg/mL for p-tau181 were validated using Gaussian mixture models. Given strong correlation of p-tau and t-tau (R2  = 0.98, P < 0.001), neurodegeneration was defined by age-adjusted hippocampal volume. Multinomial regressions were used to test whether neuropsychological tests and regional brain volumes could distinguish ATN stages.

RESULTS

Age was 65 ± 7 years, with 58% females and 38% apolipoprotein E (APOE) ε4 carriers; 57.1% were A-T-N-, 32.5% were in the Alzheimer's disease (AD) continuum, and 10.4% suspected non-Alzheimer's pathology. Age and cerebrovascular burden progressed with biomarker positivity (P < 0.001). Cognitive dysfunction appeared with T+. Paradoxically higher regional gray matter volumes were observed in A+T-N- compared to A-T-N- (P < 0.001).

DISCUSSION

In non-demented individuals along the AD continuum, p-tau drives cognitive dysfunction. Memory and language domains are affected in the earliest stages.

Subtle cognitive impairment as a marker of Alzheimer's pathologies and clinical progression in cognitively normal individuals

INTRODUCTION

Subtle cognitive impairment (SCI) may appear before pathological changes surpass thresholds for abnormality. We aimed to investigate whether SCI could predict Alzheimer's pathologies and advancement.

METHODS

A total of 816 cognitively normal individuals were enrolled to assess the longitudinal neuropathological and clinical correlates of baseline SCI, via linear mixed-effects and Cox proportional-hazard models. Cross-lagged panel models were used in specific time waves.

RESULTS

SCI individuals had a faster increase in brain amyloid burden and a higher risk of conversion. They also showed greater rates of cerebrospinal fluid (CSF) phosphorylated tau (p-tau)181 increase and glucose metabolism decrease. In addition, baseline SCI predicted worse clinical progression, whereas multi-domain SCI advanced faster compared to the single domain group.

DISCUSSION

Baseline SCI could be an imperative prediction indicator of clinical and pathological progression. It enables cognitive measures to be informative at a very early stage and provided objective criteria for high-risk population screening.

Towards clinical application of tau PET tracers for diagnosing dementia due to Alzheimer's disease

The recent development of several tau positron emission tomography (PET) tracers represents a major milestone for the Alzheimer's disease (AD) field. These tau PET tracers bind tau neurofibrillary tangles, a key neuropathological characteristic of AD that is tightly linked to synaptic loss, brain atrophy, and cognitive decline. It is notable that these tau PET tracers show low uptake in most non-AD tauopathies and other neurodegenerative disorders, resulting in a diagnostic specificity that is superior to that of amyloid beta (Aβ) PET and biofluid markers, especially at an older age when incidental Aβ pathology is common. Furthermore, tau PET tracers diagnostically outperform widely used MRI markers. Given its excellent diagnostic performance due to the combination of high sensitivity and specificity for detecting tau pathology in AD dementia, we hypothesize that tau PET can become an important diagnostic tool in specialized clinics for the differential diagnosis of dementia syndromes where AD is among the major possible underlying diseases.

The Israel Registry for Alzheimer's Prevention (IRAP) Study: Design and Baseline Characteristics

BACKGROUND

Family history of Alzheimer's disease (AD) is associated with increased dementia-risk.

OBJECTIVE

The Israel Registry for Alzheimer's Prevention (IRAP) is a prospective longitudinal study of asymptomatic middle-aged offspring of AD patients (family history positive; FH+) and controls (whose parents have aged without dementia; FH-) aimed to unravel the contribution of midlife factors to future cognitive decline and dementia. Here we present the study design, methods, and baseline characteristics.

METHODS

Participants are members of the Maccabi Health Services, 40-65 years of age, with exquisitely detailed laboratory, medical diagnoses and medication data available in the Maccabi electronic medical records since 1998. Data collected through IRAP include genetic, sociodemographic, cognitive, brain imaging, lifestyle, and health-related characteristics at baseline and every three years thereafter.

RESULTS

Currently IRAP has 483 participants [mean age 54.95 (SD = 6.68) and 64.8% (n = 313) women], 379 (78.5%) FH+, and 104 (21.5%) FH-. Compared to FH-, FH+ participants were younger (p = 0.011), more often males (p = 0.003) and with a higher prevalence of the APOE E4 allele carriers (32.9% FH+, 22% FH-; p = 0.040). Adjusting for age, sex, and education, FH+ performed worse than FH-in global cognition (p = 0.027) and episodic memory (p = 0.022).

CONCLUSION

Lower cognitive scores and higher rates of the APOE E4 allele carriers among the FH+ group suggest that FH ascertainment is good. The combination of long-term historical health-related data available through Maccabi with the multifactorial information collected through IRAP will potentially enable development of dementia-prevention strategies already in midlife, a critical period in terms of risk factor exposure and initiation of AD-neuropathology.

Characterization of Alzheimer's tau biomarker discordance using plasma, CSF, and PET

BACKGROUND

We aimed to investigate the tau biomarker discrepancies of Alzheimer's disease (AD) using plasma tau phosphorylated at threonine 181 (p-tau181), cerebrospinal fluid (CSF) p-tau181, and AV1451 positron emission tomography (PET).

METHODS

In the Alzheimer's Disease Neuroimaging Initiative, 724 non-demented participants were categorized into plasma/CSF and plasma/PET groups. Demographic and clinical variables, amyloid-β (Aβ) burden, flortaucipir-PET binding in Braak regions of interest (ROIs), longitudinal changes in clinical outcomes, and conversion risk were compared.

RESULTS

Across different tau biomarker groups, the proportion of participants with a discordant profile varied (plasma+/CSF- 15.6%, plasma-/CSF+ 15.3%, plasma+/PET- 22.4%, and plasma-/PET+ 6.1%). Within the plasma/CSF categories, we found an increase from concordant-negative to discordant to concordant-positive in the frequency of Aβ pathology or cognitive impairment, rates of cognitive decline, and risk of cognitive conversion. However, the two discordant categories (plasma+/CSF- and plasma-/CSF+) showed comparable performances, resulting in similarly reduced cognitive capacities. Regarding plasma/PET categories, as expected, PET-positive individuals had increased Aβ burden, elevated flortaucipir retention in Braak ROIs, and accelerated cognitive deterioration than concordant-negative persons. Noteworthy, discordant participants with normal PET exhibited reduced flortaucipir uptake in Braak stage ROIs and slower rates of cognitive decline, relative to those PET-positive. Therefore, individuals with PET abnormality appeared to have advanced tau pathological changes and poorer cognitive function, regardless of the plasma status. Furthermore, these results were found only in individuals with Aβ pathology.

CONCLUSIONS

Our results indicate that plasma and CSF p-tau181 abnormalities associated with amyloidosis occur simultaneously in the progression of AD pathogenesis and related cognitive decline, before tau-PET turns positive.

Temporal Correlation of CSF and Neuroimaging in the Amyloid-Tau-Neurodegeneration Model of Alzheimer Disease

OBJECTIVE

To evaluate temporal correlations between CSF and neuroimaging (PET and MRI) measures of amyloid, tau, and neurodegeneration in relation to Alzheimer disease (AD) progression.

METHODS

A total of 371 cognitively unimpaired and impaired participants enrolled in longitudinal studies of AD had both CSF (β-amyloid [Aβ]₄₂, phosphorylated tau₁₈₁, total tau, and neurofilament light chain) and neuroimaging (Pittsburgh compound B [PiB] PET, flortaucipir PET, and structural MRI) measures. The pairwise time interval between CSF and neuroimaging measures was binned into 2-year periods. Spearman correlations identified the time bin when CSF and neuroimaging measures most strongly correlated. CSF and neuroimaging measures were then binarized as biomarker-positive or biomarker-negative using Gaussian mixture modeling. Cohen kappa coefficient identified the time bin when CSF measures best agreed with corresponding neuroimaging measures when determining amyloid, tau, and neurodegeneration biomarker positivity.

RESULTS

CSF Aβ₄₂ and PiB PET showed maximal correlation when collected within 6 years of each other (R ≈ -0.5). CSF phosphorylated tau₁₈₁ and flortaucipir PET showed maximal correlation when CSF was collected 4 to 8 years prior to PET (R ≈ 0.4). CSF neurofilament light chain and cortical thickness showed low correlation, regardless of time interval (R _avg ≈ -0.3). Similarly, CSF total tau and cortical thickness had low correlation, regardless of time interval (R _avg < -0.2).

CONCLUSIONS

CSF Aβ₄₂ and PiB PET best agree when acquired in close temporal proximity, whereas CSF phosphorylated tau precedes flortaucipir PET by 4 to 8 years. CSF and neuroimaging measures of neurodegeneration have low correspondence and are not interchangeable at any time interval.

Recent Advances in Imaging of Preclinical, Sporadic, and Autosomal Dominant Alzheimer's Disease

Observing Alzheimer's disease (AD) pathological changes in vivo with neuroimaging provides invaluable opportunities to understand and predict the course of disease. Neuroimaging AD biomarkers also allow for real-time tracking of disease-modifying treatment in clinical trials. With recent neuroimaging advances, along with the burgeoning availability of longitudinal neuroimaging data and big-data harmonization approaches, a more comprehensive evaluation of the disease has shed light on the topographical staging and temporal sequencing of the disease. Multimodal imaging approaches have also promoted the development of data-driven models of AD-associated pathological propagation of tau proteinopathies. Studies of autosomal dominant, early sporadic, and late sporadic courses of the disease have shed unique insights into the AD pathological cascade, particularly with regard to genetic vulnerabilities and the identification of potential drug targets. Further, neuroimaging markers of b-amyloid, tau, and neurodegeneration have provided a powerful tool for validation of novel fluid cerebrospinal and plasma markers. This review highlights some of the latest advances in the field of human neuroimaging in AD across these topics, particularly with respect to positron emission tomography and structural and functional magnetic resonance imaging.

Association of Cognitive and Behavioral Features Between Adults With Tuberous Sclerosis and Frontotemporal Dementia

Importance

Individuals with tuberous sclerosis complex can develop a progressive neuropsychiatric syndrome known as tuberous sclerosis-associated neuropsychiatric disorders. Tuberous sclerosis-associated neuropsychiatric disorders symptoms overlap with clinical criteria for frontotemporal dementia, yet the association between the 2 has not been explored.

Objective

To investigate the potential association between tuberous sclerosis-associated neuropsychiatric disorders and frontotemporal dementia.

Design, Setting, and Participants

Case-control study that enrolled patients with tuberous sclerosis complex with normal IQs in an observational clinical study at the University of California, San Francisco, from 2017 to 2019 where they underwent a comprehensive clinical evaluation including neuropsychologic testing, cerebral spinal fluid biomarker profiling, and structural neuroimaging. The study included adults who fulfilled the clinical criteria for tuberous sclerosis complex and had normal IQs, had frontotemporal dementia, or were healthy control individuals.

Main Outcomes and Measures

Tuberous sclerosis-associated neuropsychiatric disorders checklist severity score, neuropsychologic test scores, cerebral spinal fluid concentrations of phosphorylated tau181, total tau, amyloid-β 42, and neurofilament light chain. Amyloid and tau positron emission tomography scans were obtained in a subset of patients.

Results

Eighteen patients with tuberous sclerosis complex (mean [SD] age, 48 years [9.54]; 13 women [72%]), 16 with frontotemporal dementia (60 [6.93] years; 7 women [44%]) and 18 healthy control individuals (63 [3.85] years; 9 women [50%]) were included. The tuberous sclerosis-associated neuropsychiatric disorders checklist and neuropsychological test results were not significantly different when the tuberous sclerosis complex and frontotemporal dementia cohorts were compared. The tuberous sclerosis complex cohort exhibited elevated cerebral spinal fluid phosphorylated tau181 and neurofilament light chain with a mean of 32 pg/mL and 2300 pg/mL, respectively, when compared to healthy control individuals. All 3 patients with tuberous sclerosis complex who underwent fluorine 1B-labeled flortaucipir tau positron emission tomographic neuroimaging showed punctate foci of elevated [18F]flortaucipir binding in the frontal and temporal regions.

Conclusions and Relevance

Adults with tuberous sclerosis complex showed phenotypic overlap with frontotemporal dementia. The results support a possible clinical continuum between tuberous sclerosis-associated neuropsychiatric disorders and frontotemporal dementia and highlights a potential pathophysiological link between neurodevelopmental and neurodegenerative processes. Quantitative neuropsychological testing and the tuberous sclerosis-associated neuropsychiatric disorders checklist, potentially supplemented by cerebral spinal fluid and imaging biomarkers, could be used to screen and prognosticate for risk of a neurodegenerative process in adult patients with tuberous sclerosis complex.

Diagnostic Accuracy of Amyloid versus 18 F-Fluorodeoxyglucose Positron Emission Tomography in Autopsy-Confirmed Dementia

OBJECTIVE

The purpose of this study was to compare the diagnostic accuracy of antemortem 11 C-Pittsburgh compound B (PIB) and 18 F-fluorodeoxyglucose (FDG) positron emission tomography (PET) versus autopsy diagnosis in a heterogenous sample of patients.

METHODS

One hundred one participants underwent PIB and FDG PET during life and neuropathological assessment. PET scans were visually interpreted by 3 raters blinded to clinical information. PIB PET was rated as positive or negative for cortical retention, whereas FDG scans were read as showing an Alzheimer disease (AD) or non-AD pattern. Neuropathological diagnoses were assigned using research criteria. Majority visual reads were compared to intermediate-high AD neuropathological change (ADNC).

RESULTS

One hundred one participants were included (mean age = 67.2 years, 41 females, Mini-Mental State Examination = 21.9, PET-to-autopsy interval = 4.4 years). At autopsy, 32 patients showed primary AD, 56 showed non-AD neuropathology (primarily frontotemporal lobar degeneration [FTLD]), and 13 showed mixed AD/FTLD pathology. PIB showed higher sensitivity than FDG for detecting intermediate-high ADNC (96%, 95% confidence interval [CI] = 89-100% vs 80%, 95% CI = 68-92%, p = 0.02), but equivalent specificity (86%, 95% CI = 76-95% vs 84%, 95% CI = 74-93%, p = 0.80). In patients with congruent PIB and FDG reads (77/101), combined sensitivity was 97% (95% CI = 92-100%) and specificity was 98% (95% CI = 93-100%). Nine of 24 patients with incongruent reads were found to have co-occurrence of AD and non-AD pathologies.

INTERPRETATION

In our sample enriched for younger onset cognitive impairment, PIB-PET had higher sensitivity than FDG-PET for intermediate-high ADNC, with similar specificity. When both modalities are congruent, sensitivity and specificity approach 100%, whereas mixed pathology should be considered when PIB and FDG are incongruent. ANN NEUROL 2021;89:389-401.

Radioactive synthesis of tau PET imaging agent 18F-AV-1451 and its role in monitoring the progression of Alzheimer's disease and supporting differential diagnosis

Alzheimer's disease (AD) is on the rise all over the world, and brings with it great challenges to medical care and heavy burdens to family and society. Accurate diagnosis and differential diagnosis are of great importance. Tau positron emission tomography (PET) might offer novel insights and be of great assistance in monitoring disease progression and supporting the differential diagnosis. ¹⁸F-AV-1451, as the first Tau PET imaging agent approved by the Food and Drug Administration (FDA), has been of great potential in clinical trials. Here, we reviewed the synthesis and characteristics of ¹⁸F-AV-1451 and its role in monitoring AD progression and supporting the differential diagnosis.

Comparing ATN-T designation by tau PET visual reads, tau PET quantification, and CSF PTau181 across three cohorts

PURPOSE

To compare rates of tau biomarker positivity (T-status) per the 2018 Alzheimer's Disease (AD) Research Framework derived from [¹⁸F]flortaucipir (FTP) PET visual assessment, FTP quantification, and cerebrospinal fluid (CSF) phosphorylated Tau-181 (PTau181).

METHODS

We included 351 subjects with varying clinical diagnoses from three cohorts with available FTP PET and CSF PTau181 within 18 months. T-status was derived from (1) FTP visual assessment by two blinded raters; (2) FTP standardized uptake value ratio (SUVR) quantification from a temporal meta-ROI (threshold: SUVR ≥1.27); and (3) Elecsys® Phospho-Tau (181P) CSF (Roche Diagnostics) concentrations (threshold: PTau181 ≥ 24.5 pg/mL).

RESULTS

FTP visual reads yielded the highest rates of T+, while T+ by SUVR increased progressively from cognitively normal (CN) through mild cognitive impairment (MCI) and AD dementia. T+ designation by CSF PTau181 was intermediate between FTP visual reads and SUVR values in CN, similar to SUVR in MCI, and lower in AD dementia. Concordance in T-status between modality pairs ranged from 68 to 76% and varied by clinical diagnosis, being highest in patients with AD dementia. In discriminating Aβ + MCI and AD subjects from healthy controls and non-AD participants, FTP visual assessment was most sensitive (0.96) but least specific (0.60). Specificity was highest with FTP SUVR (0.91) with sensitivity of 0.89. Sensitivity (0.73) and specificity (0.72) were balanced for PTau181.

CONCLUSION

The choice of tau biomarker may differ by disease stage and research goals that seek to maximize sensitivity or specificity. Visual interpretations of tau PET enhance sensitivity compared to quantification alone, particularly in early disease stages.

What Is T+? A Gordian Knot of Tracers, Thresholds, and Topographies

In this review we examine, in the context of the amyloid, tau, and neurodegeneration framework, the available evidence and potential alternatives on how to establish tau positivity (T+) for multiple tau-imaging tracers in order to reach a consensus on normal and abnormal tau imaging values that can be universally implemented in clinical research and therapeutic trials.

Imaging of Tau Pathology in Neurodegenerative Diseases: An Update

Pathological accumulated misfolded tau underlies various neurodegenerative diseases and associated clinical syndromes. To diagnose those diseases reliable before death or even at early stages, many different tau-specific radiotracers have been developed in the last decade to be used with positron-emission-tomography. In contrast to amyloid-β imaging, different isoforms of tau exist further complicating radiotracer development. First-generation radiotracers like [¹¹C]PBB3, [¹⁸F]AV1451 and [¹⁸F]THK5351 have been extensively investigated in vitro and in vivo. In Alzheimer's disease (AD), high specific binding could be detected, and evidence of clinical applicability recently led to clinical approval of [¹⁸F]flortaucipir ([¹⁸F]AV1451) by the FDA. Nevertheless, absent or minor binding to non-AD tau isoforms and high off-target binding to non-tau brain structures limit the diagnostic applicability especially in non-AD tauopathies demanding further tracer development. In vitro assays and autoradiography results of next-generation radiotracers [¹⁸F]MK-6240, [¹⁸F]RO-948, [¹⁸F]PM-PBB3, [¹⁸F]GTP-1 and [¹⁸F]PI-2620 clearly indicate less off-target binding and high specific binding to tau neurofibrils. First in human studies have been conducted with promising results for all tracers in AD patients, and also some positive experience in non-AD tauopathies. Overall, larger scaled autoradiography and human studies are needed to further evaluate the most promising candidates and support future clinical approval.

Association of APOE4 and Clinical Variability in Alzheimer Disease With the Pattern of Tau- and Amyloid-PET

OBJECTIVE

To assess whether Alzheimer disease (AD) clinical presentation and APOE4 relate to the burden and topography of β-amyloid (Aβ) and tau pathologies using in vivo PET imaging.

METHODS

We studied 119 Aβ-positive symptomatic patients aged 48-95 years, including 29 patients with logopenic variant primary progressive aphasia (lvPPA) and 21 with posterior cortical atrophy (PCA). Pittsburgh compound B (PiB)-Aβ and flortaucipir (tau)-PET standardized uptake value ratio (SUVR) images were created. General linear models assessed relationships between demographic/clinical variables (phenotype, age), APOE4, and PET (including global cortical and voxelwise SUVR values) while controlling for disease severity using the Clinical Dementia Rating Sum of Boxes.

RESULTS

PiB-PET binding showed a widespread cortical distribution with subtle differences across phenotypes and was unrelated to demographic/clinical variables or APOE4. Flortaucipir-PET was commonly elevated in temporoparietal regions, but showed marked phenotype-associated differences, with higher binding observed in occipito-parietal areas for PCA, in left temporal and inferior frontal for lvPPA, and in medial temporal areas for other AD. Cortical flortaucipir-PET binding was higher in younger patients across phenotypes (r = -0.63, 95% confidence interval [CI] -0.72, -0.50), especially in parietal and dorsal prefrontal cortices. The presence of APOE4 was associated with a focal medial temporal flortaucipir-SUVR increase, controlling for all other variables (entorhinal: + 0.310 SUVR, 95% CI 0.091, 0.530).

CONCLUSIONS

Clinical phenotypes are associated with differential patterns of tau but not amyloid pathology. Older age and APOE4 are not only risk factors for AD but also seem to affect disease expression by promoting a more medial temporal lobe-predominant pattern of tau pathology.

Evaluation of a visual interpretation method for tau-PET with 18F-flortaucipir

INTRODUCTION

Positron emission tomography targeting tau (tau-PET) is a promising diagnostic tool for the identification of Alzheimer's disease (AD). Currently available data rely on quantitative measures, and a visual interpretation method, critical for clinical translation, is needed.

METHODS

We developed a visual interpretation method for 18F-flortaucipir tau-PET and tested it on 274 individuals (cognitively normal controls, patients with mild cognitive impairment [MCI], AD dementia, and non-AD diagnoses). Two readers interpreted 18F-flortaucipir PET using two complementary indices: a global visual score and a visual distribution pattern.

RESULTS

Global visual scores were reliable, correlated with global cortical 18F-flortaucipir standardized uptake value ratio (SUVR) and were associated with clinical diagnosis and amyloid status. The AD-like 18F-flortaucipir pattern had good sensitivity and specificity to identify amyloid-positive patients with AD dementia or MCI.

DISCUSSION

This 18F-flortaucipir visual rating scheme is associated with SUVR quantification, clinical diagnosis, and amyloid status, and constitutes a promising approach to tau measurement in clinical settings.

PET Amyloid and Tau Status Are Differently Affected by Patient Features

BACKGROUND

Amyloid-β (Aβ) plaques and tau neurofibrillary tangles are two neuropathological hallmarks of Alzheimer's disease (AD), which both can be visualized in vivo using PET radiotracers, opening new opportunities to study disease mechanisms.

OBJECTIVE

Our study investigated 11 non-PET factors in 5 categories (including demographic, clinical, genetic, MRI, and cerebrospinal fluid (CSF) features) possibly affecting PET amyloid and tau status to explore the relationships between amyloid and tau pathology, and whether these features had a different association with amyloid and tau status.

METHODS

We included 372 nondemented elderly from the Alzheimer's Disease Neuroimaging Initiative cohort. All underwent PET amyloid and tau analysis simultaneously, and were grouped into amyloid/tau quadrants based on previously established abnormality cut points. We examined the associations of above selected features with PET amyloid and tau status using a multivariable logistic regression model, then explored whether there was an obvious correlation between the significant features and PET amyloid or tau levels.

RESULTS

Our results demonstrated that PET amyloid and tau status were differently affected by patient features, and CSF biomarker features provided most significant values associating PET findings. CSF Aβ42/40 was the most important factor affecting amyloid PET status, and negatively correlated with amyloid PET levels. CSF pTau could significantly influence both amyloid and tau PET status. Besides CSF pTau and Aβ42, APOEɛ4 allele status and Mini-Mental State Examination scores also could influence tau PET status, and significantly correlated with tau PET levels.

CONCLUSION

Our results support that tau pathology possibly affected by Aβ-independent factors, implicating the importance of tau pathology in AD pathogenesis.

A Fragment of S38AA is a Novel Plasma Biomarker of Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease without a cure. The pathological process starts decades before clinical onset, and thus clinical trials of drugs aimed at treating AD should start at a presymptomatic stage. Therefore, it is critical to diagnose AD at an early stage. Tau, phosphorylated tau, and amyloid-β peptide (Aβ) in cerebrospinal fluid (CSF), and positron emission tomography (PET) imaging of Aβ or tau accumulation are supportive biomarkers for AD diagnosis, but there is no reliable presymptomatic diagnostic marker. Since CSF sampling is invasive, and PET imaging is expensive and available only at specialized centers, a reliable blood biomarker has long been sought for. Here we describe a novel extramembrane fragment from solute carrier family 38 member 10 (SLC38A10, S38AA) that we found to be decreased in pyramidal neurons in AD cases by proteomics and immunohistochemical analysis. We detected a S38AA fragment in CSF and found the levels to correlate with severity of AD and APOE genotype. Importantly, the plasma levels of the fragment also showed a significant correlation with Mini-Mental State Examination scores in AD. Moreover, plasma from other neurodegenerative disease was analyzed and the fragment was found to be increased specifically in AD. Interestingly, the fragment is detected in mouse, rat, and monkey, and increases in amyloid precursor protein transgenic mice as the AD-like pathology progresses. We propose that the S38AA fragment in plasma could be a novel quantitative diagnostic marker for AD and potentially a marker of disease progression in AD.

Multimodal in vivo and postmortem assessments of tau in Lewy body disorders

We compared regional retention of ¹⁸F-flortaucipir between 20 patients with Lewy body disorders (LBD), 12 Alzheimer's disease patients with positive amyloid positron emission tomography (PET) scans (AD+Aβ) and 15 healthy controls with negative amyloid PET scans (HC-Aβ). In LBD subjects, we compared the relationship between ¹⁸F-flortaucipir retention and cerebrospinal fluid (CSF) tau, cognitive performance, and neuropathological tau at autopsy. The LBD cohort was stratified using an Aβ42 cut-off of 192 pg/mL to enrich for groups likely harboring tau pathology (LBD+Aβ = 11, LBD-Aβ = 9). ¹⁸F-flortaucipir retention was higher in LBD+AB than HC-Aβ in five, largely temporal-parietal regions with sparing of medial temporal regions. Higher retention was associated with higher CSF total-tau levels (p = 0.04), poorer domain-specific cognitive performance (p = 0.02-0.04), and greater severity of neuropathological tau in corresponding regions. While ¹⁸F-flortaucipir retention in LBD is intermediate between healthy controls and AD, retention relates to cognitive impairment, CSF total-tau, and neuropathological tau. Future work in larger autopsy-validated cohorts is needed to define LBD-specific tau biomarker profiles.

Normalization of CSF pTau measurement by Aβ40 improves its performance as a biomarker of Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD)-related tauopathy can be measured with CSF phosphorylated tau (pTau) and tau PET. We aim to investigate the associations between these measurements and their relative ability to predict subsequent disease progression.

METHODS

In 219 cognitively unimpaired and 122 impaired Alzheimer's Disease Neuroimaging Initiative participants with concurrent amyloid-β (Aβ) PET (18F-florbetapir or 18F-florbetaben), 18F-flortaucipir (FTP) PET, CSF measurements, structural MRI, and cognition, we examined inter-relationships between these biomarkers and their predictions of subsequent FTP and cognition changes.

RESULTS

The use of a CSF pTau/Aβ40 ratio eliminated positive associations we observed between CSF pTau alone and CSF Aβ42 in the normal Aβ range likely reflecting individual differences in CSF production rather than pathology. Use of the CSF pTau/Aβ40 ratio also increased expected associations with Aβ PET, FTP PET, hippocampal volume, and cognitive decline compared to pTau alone. In Aβ+ individuals, abnormal CSF pTau/Aβ40 only individuals (26.7%) were 4 times more prevalent (p <  0.001) than abnormal FTP only individuals (6.8%). Furthermore, among individuals on the AD pathway, CSF pTau/Aβ40 mediates the association between Aβ PET and FTP PET accumulation, but FTP PET is more closely linked to subsequent cognitive decline than CSF pTau/Aβ40.

CONCLUSIONS

Together, these findings suggest that CSF pTau/Aβ40 may be a superior measure of tauopathy compared to CSF pTau alone, and CSF pTau/Aβ40 enables detection of tau accumulation at an earlier stage than FTP among Aβ+ individuals.

PET Tau Imaging and Motor Impairments Differ Between Corticobasal Syndrome and Progressive Supranuclear Palsy With and Without Alzheimer's Disease Biomarkers

Introduction: Frontotemporal lobar degeneration (FTLD)-related syndrome includes progressive supranuclear palsy (PSP) and corticobasal syndrome (CBS). PSP is usually caused by a tauopathy but can have associated Alzheimer's disease (AD) while CBS can be caused by tauopathy, transactive response DNA binding protein 43 kDa, or AD pathology. Our aim was to compare the parkinsonian syndromes presenting without AD biomarkers (CBS/PSP-non-AD) to parkinsonian syndromes with AD biomarkers (CBS/PSP-AD).

Materials and Methods: Twenty-four patients [11 males, 13 females; age (68.46 ± 7.23)] were recruited for this study. The whole cohort was divided into parkinsonian syndromes without AD biomarkers [N = 17; diagnoses (6 CBS, 11 PSP)] and parkinsonian syndromes with AD biomarkers [N = 7; diagnoses (6 CBS-AD, 1 PSP-AD)]. Anatomical MRI and PET imaging with tau ligand [18F]-AV1451 tracer was completed. Cerebrospinal fluid analysis or [18F]-AV1451 PET imaging was used to assess for the presence of AD biomarkers. Progressive supranuclear palsy rating scale (PSPRS) and unified Parkinson's disease rating scale (UPDRS) motor exam were implemented to assess for motor disturbances. Language and cognitive testing were completed.

Results: The CBS/PSP-non-AD group [age (70.18 ± 6.65)] was significantly older (p = 0.028) than the CBS/PSP-AD group [age (64.29 ± 7.32)]. There were no differences between the groups in terms of gender, education, years of disease duration, and disease severity as measured with the Clinical Dementia Rating scale. The CBS/PSP-non-AD group had significantly lower PET Tau Standard Volume Uptake Ratio (SUVR) values compared to the CBS/PSP-AD group in multiple frontal and temporal areas, and inferior parietal (all p < 0.03). The CBS/PSP-non-AD group had significantly higher scores compared to the CBS/PSP-AD group on PSPRS (p = 0.004) and UPDRS motor exam (p = 0.045). The CBS/PSP-non-AD group had higher volumes of inferior parietal, precuneus, and hippocampus (all p < 0.02), but lower volume of midbrain (p = 0.02), compared to the CBS/PSP-AD group.

Discussion: The CBS/PSP-non-AD group had higher motor disturbances compared to the CBS/PSP-AD group; however, both groups performed similarly on neuropsychological measures. The AD biomarker group had increased global uptake of PET Tau SUVR and lower volumes in AD-specific areas. These results show that the presenting phenotype of CBS and PSP syndromes and the distribution of injury are strongly affected by the presence of AD biomarkers.

Characterization of Alzheimer Disease Biomarker Discrepancies Using Cerebrospinal Fluid Phosphorylated Tau and AV1451 Positron Emission Tomography

Importance

Fluid and imaging biomarkers of Alzheimer disease (AD) are often used interchangeably, but some biomarkers may reveal earlier stages of disease.

Objective

To characterize individuals with tau abnormality indicated by cerebrospinal fluid (CSF) assay or positron emission tomography (PET).

Design, Setting, and Participants

Between 2010 and 2019, 322 participants in the Alzheimer's Disease Neuroimaging Initiative (ADNI) underwent CSF and PET assessments of tau pathology. Data-driven, clinically relevant thresholds for CSF phosphorylated tau (P-tau) (≥26.64 pg/mL) and flortaucipir-PET meta-regions of interest (ROI) (standard uptake value ratio ≥1.37) indicated participants' tau status as CSF-/PET-, CSF+/PET-, CSF-/PET+, and CSF+/PET+. Of 1659 ADNI participants with a CSF or flortaucipir assessment, 588 had both measures (1071 were excluded). Among these, 266 were further excluded because they did not have flortaucipir and CSF testing within less than 25 months, leaving 322 for analysis. Of these, 213 were cognitively unimpaired (CU); 98 had mild cognitive impairment (MCI); and 11 had AD dementia.

Main Outcomes and Measures

We compared tau-positive vs tau-negative groups as indicated by either modality or demographic and clinical variables, amyloid β-PET burden, and flortaucipir-PET binding across Braak stage-related ROIs. We also compared 5-year rates of CSF P-tau accumulation and cognitive decline prior to flortaucipir-PET scanning.

Results

Among the 322 study participants, 180 were women (56%), and the mean (SD) age was 73.08 (7.37) years. Two hundred ten participants were CSF-/PET- (65%); 63 were CSF+/PET- (19.5%); 15 were CSF-/PET+ (4.6%); and 34 were CSF+/PET+ (10.5%). Most CSF-/PET+ participants had measures near CSF or PET tau thresholds. The CSF+/PET- participants showed faster 5-year accrual of P-tau and increased flortaucipir-PET binding in early Braak ROIs but similar memory decline compared with CSF-/PET- participants. Tau-positive individuals by either measure showed increased amyloid β-PET burden. All CSF+/PET+ individuals were amyloid-positive, and 26 had MCI or AD dementia (76%). Compared with the CSF-/PET- group, CSF+/PET+ individuals had experienced faster 5-year accrual of CSF P-tau and decline in memory and executive function, resulting in reduced cognitive abilities at the time of flortaucipir-PET assessment.

Conclusions and Relevance

Suprathreshold CSF P-tau without flortaucipir-PET abnormality may indicate a stage of AD development characterized by early tau abnormality without measurable loss in cognitive performance. Persons with both tau CSF and PET abnormality appear to have reduced cognitive capacities resulting from faster antecedent cognitive decline. Elevation of CSF P-tau appears to precede flortaucipir-PET positivity in the progression of AD pathogenesis and related cognitive decline.

The implications of different approaches to define AT(N) in Alzheimer disease

Objective

To compare different β-amyloid (Aβ), tau, and neurodegeneration (AT[N]) variants within the Swedish BioFINDER studies.

Methods

A total of 490 participants were classified into AT(N) groups. These include 53 cognitively unimpaired (CU) and 48 cognitively impaired (CI) participants (14 mild cognitive impairment [MCI] and 34 Alzheimer disease [AD] dementia) from BioFINDER-1 and 389 participants from BioFINDER-2 (245 CU and 144 CI [138 MCI and 6 AD dementia]). Biomarkers for A were CSF Aβ₄₂ and amyloid-PET ([¹⁸F]flutemetamol); for T, CSF phosphorylated tau (p-tau) and tau PET ([¹⁸F]flortaucipir); and for (N), hippocampal volume, temporal cortical thickness, and CSF neurofilament light (NfL). Binarization of biomarkers was achieved using cutoffs defined in other cohorts. The relationship between different AT(N) combinations and cognitive trajectories (longitudinal Mini-Mental State Examination scores) was examined using linear mixed modeling and coefficient of variation.

Results

Among CU participants, A−T−(N)− or A+T−(N)− variants were most common. However, more T+ cases were seen using p-tau than tau PET. Among CI participants, A+T+(N)+ was more common; however, more (N)+ cases were seen for MRI measures relative to CSF NfL. Tau PET best predicted longitudinal cognitive decline in CI and p-tau in CU participants. Among CI participants, continuous T (especially tau PET) and (N) measures improved the prediction of cognitive decline compared to binary measures.

Conclusions

Our findings show that different AT(N) variants are not interchangeable, and that optimal variants differ by clinical stage. In some cases, dichotomizing biomarkers may result in loss of important prognostic information.

Temporal trajectories of in vivo tau and amyloid-β accumulation in Alzheimer's disease

PURPOSE

To investigate the temporal trajectories of tau and amyloid-β (Aβ) accumulation in Alzheimer's disease (AD) by using the longitudinal positron emission tomography (PET) study.

METHODS

A total of 132 participants, who were healthy volunteers or recruited in our memory disorder clinic, completed longitudinal ¹⁸F-flortaucipir and ¹⁸F-florbetaben PET studies with a mean follow-up time of 2 years. Referencing baseline data from 57 Aβ-negative cognitively unimpaired individuals, Z-scores and their annual changes were calculated with the global cortical or regional standardized uptake value ratios measured at baseline and follow-up after correcting for partial volume effect. The temporal trajectories of tau and Aβ burden as a function of time were obtained based on the spline models from the annual changes and baseline Z-score data.

RESULTS

Tau burden first emerged in the Braak's stage I-II regions, followed by stage III-IV regions, and finally in the stage V-VI regions. Time intervals between two time points at which Z-score curves rose above 2 were 17.3 years for the stages I-II and III-IV and 15.2 years for the stages III-IV and V-VI. Rise in the tau curve for stages I-II preceded that for global cortical Aβ, while the rise in global cortical Aβ curve preceded that for global cortical tau. Aβ accumulation rate was attenuated during the surge in tau burden in the global cortex and reached a plateau.

CONCLUSION

Sequential appearance of Aβ and tau accumulation supports a hypothetical dynamic biomarker model and Braak's hierarchical tau spreading model in AD.

Regional [18F]flortaucipir PET is more closely associated with disease severity than CSF p-tau in Alzheimer's disease

Purpose

In vivo Alzheimer’s disease (AD) biomarkers for tau pathology are cerebrospinal fluid (CSF) phosphorylated tau (p-tau) and [¹⁸F]flortaucipir positron emission tomography (PET). Our aim was to assess associations between CSF p-tau with [¹⁸F]flortaucipir PET and the associations of both tau biomarkers with cognition and atrophy.

Methods

We included 78 amyloid positive cognitively impaired patients (clinical diagnoses mild cognitive impairment (MCI, n = 8) and AD dementia (n = 45) and 25 cognitively normal subjects with subjective cognitive decline (SCD) (40% amyloid-positive)). Dynamic 130 min [¹⁸F]flortaucipir PET scans were acquired to generate binding potential (BP_ND) images using receptor parametric mapping and standardized uptake values ratios of 80–100 min (SUVr_80-100min) post injection. We obtained regional BP_ND and SUVr from entorhinal, limbic, and neocortical regions-of-interest (ROIs), closely aligning to the neuropathological tau staging schemes. Cognition was assessed using MMSE and composite scores of four cognitive domains, and atrophy was measured using gray matter volume covering the major brain lobes. First, we used linear regressions to investigate associations between CSF p-tau (independent variable) and tau PET (dependent variable). Second, we used linear regressions to investigate associations between CSF p-tau, tau PET (separate independent variables, model 1), and cognition (dependent variable). We then assessed the independent effects of CSF p-tau and tau PET on cognition by simultaneously adding the other tau biomarker as a predictor (model 2). Finally, we performed the same procedure for model 1 and 2, but replaced cognition with atrophy. Models were adjusted for age, sex, time lag between assessments, education (cognition only), and total intracranial volume (atrophy only).

Results

Higher [¹⁸F]flortaucipir BP_ND was associated with higher CSF p-tau (range of standardized betas (sβ) across ROIs, 0.43–0.46; all p < 0.01). [¹⁸F]flortaucipir BP_ND was more strongly associated with cognition and atrophy than CSF p-tau. When [¹⁸F]flortaucipir BP_ND and CSF p-tau were entered simultaneously, [¹⁸F]flortaucipir BP_ND (range sβ = − 0.20 to – 0.57, all p < 0.05) was strongly associated with multiple cognitive domains and atrophy regions. SUVr showed comparable results to BP_ND.

Conclusion

Regional [¹⁸F]flortaucipir BP_ND correlated stronger with cognition and neurodegeneration than CSF p-tau, suggesting that tau PET more accurately reflects disease severity in AD.

Electronic supplementary material

The online version of this article (10.1007/s00259-020-04758-2) contains supplementary material, which is available to authorized users.

Aβ deposition is associated with increases in soluble and phosphorylated tau that precede a positive Tau PET in Alzheimer's disease

The links between β-amyloid (Aβ) and tau in Alzheimer's disease are unclear. Cognitively unimpaired persons with signs of Aβ pathology had increased cerebrospinal fluid (CSF) phosphorylated tau (P-tau181 and P-tau217) and total-tau (T-tau), which increased over time, despite no detection of insoluble tau aggregates [normal Tau positron emission tomography (PET)]. CSF P-tau and T-tau started to increase before the threshold for Amyloid PET positivity, while Tau PET started to increase after Amyloid PET positivity. Effects of Amyloid PET on Tau PET were mediated by CSF P-tau, and high CSF P-tau predicted increased Tau PET rates. Individuals with MAPT mutations and signs of tau deposition (but without Aβ pathology) had normal CSF P-tau levels. In 5xFAD mice, CSF tau increased when Aβ aggregation started. These results show that Aβ pathology may induce changes in soluble tau release and phosphorylation, which is followed by tau aggregation several years later in humans.

Effect of apolipoprotein E ε4 allele on the progression of cognitive decline in the early stage of Alzheimer's disease

INTRODUCTION

Possession of the apolipoprotein E (APO E) ε4 allele advances amyloid β (Aβ) deposition and symptomatic onset of Alzheimer's disease (AD), whereas its effect on the rate of cognitive decline remained controversial. We examined the effects of APOE ε4 allele on cognition in biomarker-confirmed late mild cognitive impairment (LMCI) and mild AD subjects in the Japanese Alzheimer's Disease Neuroimaging Initiative (J-ADNI) and North American ADNI (NA-ADNI).

METHODS

The "early AD" (ie, combined LMCI and mild AD) cohort of 649 subjects from J-ADNI and NA-ADNI were selected based on positivity of Aβ confirmed by amyloid positron emission tomography (PET) or cerebrospinal fluid testing. The rates of cognitive decline in the Mini Mental State Examination (MMSE), the Clinical Dementia Rating Sum of Boxes (CDR-SB), and the Alzheimer's Disease Assessment Scale-cognitive subscale 13 (ADAS-Cog) from baseline were examined using mixed-effects model. The effect of ε4 on time to conversion to dementia was also analyzed in LMCI using the Kaplan-Meier estimator and log-rank test.

RESULTS

The rates of cognitive decline were not significantly different between ε4 carriers and ε4 non-carriers in the total early AD cohort, which were affected neither by region nor by the number of ε4 alleles. In LMCI, ε4 carriers showed almost the same progression rates as ε4 non-carriers, except for a significantly faster decline in MMSE (P = .0282). Time to conversion to demenita was not significantly different between ε4 carriers and ε4 non-carriers. In ε4-positive mild AD, the rates of decline in MMSE (P = .003) and CDR-SB (P = .0071) were slower than those in ε4 non-carriers.

DISCUSSION

The APOE ε4 allele had little effect on the rates of cognitive decline in the overall biomarker-confirmed early AD, regardless of region and number of ε4 alleles, with a slight variability in different clinical stages, the ε4 allele being slightly accelerative in LMCI, while decelerative in mild AD.

A soluble phosphorylated tau signature links tau, amyloid and the evolution of stages of dominantly inherited Alzheimer's disease

Development of tau-based therapies for Alzheimer's disease requires an understanding of the timing of disease-related changes in tau. We quantified the phosphorylation state at multiple sites of the tau protein in cerebrospinal fluid markers across four decades of disease progression in dominantly inherited Alzheimer's disease. We identified a pattern of tau staging where site-specific phosphorylation changes occur at different periods of disease progression and follow distinct trajectories over time. These tau phosphorylation state changes are uniquely associated with structural, metabolic, neurodegenerative and clinical markers of disease, and some (p-tau217 and p-tau181) begin with the initial increases in aggregate amyloid-β as early as two decades before the development of aggregated tau pathology. Others (p-tau205 and t-tau) increase with atrophy and hypometabolism closer to symptom onset. These findings provide insights into the pathways linking tau, amyloid-β and neurodegeneration, and may facilitate clinical trials of tau-based treatments.

Risk factors for earlier dementia onset in autopsy-confirmed Alzheimer's disease, mixed Alzheimer's with Lewy bodies, and pure Lewy body disease

INTRODUCTION

Clinical Alzheimer's disease (AD) and dementia with Lewy bodies often have mixed AD and Lewy pathology, making it difficult to delineate risk factors.

METHODS

Six risk factors for earlier dementia onset due to autopsy-confirmed AD (n = 647), mixed AD and Lewy body disease (AD + LBD; n = 221), and LBD (n = 63) were entered into multiple linear regressions using data from the National Alzheimer's Coordinating Center.

RESULTS

In AD and AD + LBD, male sex and apolipoprotein E (APOE) ɛ4 alleles each predicted a 2- to 3-year-earlier onset and depression predicted a 3-year-earlier onset. In LBD, higher education predicted earlier onset and depression predicted a 5.5-year-earlier onset.

DISCUSSION

Male sex and APOE ɛ4 alleles increase risk for earlier dementia onset in AD but not LBD. Depression increases risk for earlier dementia onset in AD, LBD, and AD + LBD, but evaluating the course, treatment, and severity is needed in future studies.

Diagnostic value of plasma phosphorylated tau181 in Alzheimer's disease and frontotemporal lobar degeneration

With the potential development of new disease-modifying Alzheimer's disease (AD) therapies, simple, widely available screening tests are needed to identify which individuals, who are experiencing symptoms of cognitive or behavioral decline, should be further evaluated for initiation of treatment. A blood-based test for AD would be a less invasive and less expensive screening tool than the currently approved cerebrospinal fluid or amyloid β positron emission tomography (PET) diagnostic tests. We examined whether plasma tau phosphorylated at residue 181 (pTau181) could differentiate between clinically diagnosed or autopsy-confirmed AD and frontotemporal lobar degeneration. Plasma pTau181 concentrations were increased by 3.5-fold in AD compared to controls and differentiated AD from both clinically diagnosed (receiver operating characteristic area under the curve of 0.894) and autopsy-confirmed frontotemporal lobar degeneration (area under the curve of 0.878). Plasma pTau181 identified individuals who were amyloid β-PET-positive regardless of clinical diagnosis and correlated with cortical tau protein deposition measured by 18F-flortaucipir PET. Plasma pTau181 may be useful to screen for tau pathology associated with AD.

Predicting sporadic Alzheimer's disease progression via inherited Alzheimer's disease-informed machine-learning

Introduction:

Developing cross-validated multi-biomarker models for the prediction of the rate of cognitive decline in Alzheimer’s disease (AD) is a critical yet unmet clinical challenge.

Methods:

We applied support vector regression to AD biomarkers derived from cerebrospinal fluid, structural magnetic resonance imaging (MRI), amyloid-PET and fluorodeoxyglucose positron-emission tomography (FDG-PET) to predict rates of cognitive decline. Prediction models were trained in autosomal-dominant Alzheimer’s disease (ADAD, n = 121) and subsequently cross-validated in sporadic prodromal AD (n = 216). The sample size needed to detect treatment effects when using model-based risk enrichment was estimated.

Results:

A model combining all biomarker modalities and established in ADAD predicted the 4-year rate of decline in global cognition (R² = 24%) and memory (R² =25%) in sporadic AD. Model-based risk-enrichment reduced the sample size required for detecting simulated intervention effects by 50%–75%.

Discussion:

Our independently validated machine-learning model predicted cognitive decline in sporadic prodromal AD and may substantially reduce sample size needed in clinical trials in AD.

Association of Vascular Risk Factors With β-Amyloid Peptide and Tau Burdens in Cognitively Unimpaired Individuals and Its Interaction With Vascular Medication Use

IMPORTANCE

Vascular risk factors are associated with increased risk of Alzheimer disease (AD), but it is unclear whether there is a direct association of these risk factors with AD pathogenesis.

OBJECTIVES

To assess the associations of vascular risk factors with AD pathogenesis in asymptomatic individuals, and to test whether this association is moderated among individuals who use vascular medications.

DESIGN, SETTING, AND PARTICIPANTS

This cross-sectional study used data from the Presymptomatic Evaluation of Experimental or Novel Treatments for Alzheimer Disease (PREVENT-AD) cohort of cognitively unimpaired individuals aged 55 to 82 years with a parental or multiple-sibling history of sporadic AD, who were recruited via advertisement from the greater Montreal, Quebec, Canada, metropolitan area. Participants were enrolled between September 9, 2011, to May, 3, 2017, and stratified by use vs no use of vascular medications. Data were analyzed July 1, 2018, to April 5, 2019.

MAIN OUTCOMES AND MEASURES

Principal analyses investigated associations of total, high-density lipoprotein, and low-density lipoprotein cholesterol levels, systolic and diastolic blood pressure, pulse pressure, and a combined vascular risk score (measured using the Framingham Coronary Risk Profile) with global β-amyloid peptide (Aβ) and entorhinal tau burden as measured by positron emission tomography (PET). Potential moderating associations of use of vascular medications with these associations were examined. Secondary similar analyses considered cerebrospinal fluid (CSF) Aβ1-42 and phosphorylated tau levels.

RESULTS

Among 215 participants (mean [SD] age, 62.3 [5.0] years; 161 [74.8%] women), 120 participants underwent PET, including 75 participants (62.5%) who were not using vascular medications, and 162 participants underwent CSF assessment, including 113 participants (69.8%) who were not using vascular medications. There was an overlap of 67 participants who underwent PET and CSF assessment. Interaction analyses showed that among participants not using vascular medications, higher Aβ deposition as measured by PET was associated with higher total cholesterol level (β = -0.002 [SE, 0.001]; P = .02), low-density lipoprotein cholesterol level (β = -0.002 [SE, 0.001]; P = .006), systolic blood pressure (β = -0.006 [SE, 0.002]; P = .02), pulse pressure (β = -0.007 [SE, 0.002]; P = .004), and Framingham Coronary Risk Profile score (β = -0.038 [SE, 0.011]; P = .001), but such associations were absent in participants who used vascular medications. Interactions were also found between vascular medication use and high-density lipoprotein cholesterol (β = -3.302 [SE, 1.540]; P = .03), low-density lipoprotein cholesterol (β = 1.546 [SE, 0.754]; P = .04), and Framingham Coronary Risk Profile score (β = 23.102 [SE, 10.993]; P = .04) on Aβ1-42 burden as measured in CSF. Higher Framingham Coronary Risk Profile scores were associated with reduced tau burden among participants using vascular medications but not among participants not using vascular medications (interaction, β = -0.010 [SE, 0.005]; P = .046).

CONCLUSIONS AND RELEVANCE

These findings corroborate previously reported associations of vascular risk factors with Aβ burden but not tau burden. However, these associations were found only among individuals who were not using vascular medications. These results suggest that medication use or other control of vascular risk factors should be considered in Alzheimer disease prevention trials.

Intermediate flortaucipir uptake is associated with Aβ-PET and CSF tau in asymptomatic adults

OBJECTIVE

To investigate relationships between flortaucipir (FTP) uptake, age, and established Alzheimer disease (AD) markers in asymptomatic adults at increased risk of AD.

METHODS

One-hundred nineteen individuals with a family history of AD (Presymptomatic Evaluation of Experimental or Novel Treatments of Alzheimer's Disease [PREVENT-AD] cohort, mean age 67 ± 5 years) underwent tau-PET ([¹⁸F]FTP), β-amyloid (Aβ)-PET ([¹⁸F]NAV4694 [NAV]), and cognitive assessment. Seventy-four participants also had CSF phosphorylated tau and total tau data available. We investigated the association between age and FTP in this relatively young cohort of older adults. We also investigated regional FTP standardized uptake value ratio (SUVR) differences between Aβ-positive and Aβ-negative individuals and regional correlations between FTP and NAV retention. In cortical regions showing consistent associations across analyses, we assessed whether FTP was in addition related to CSF tau and cognitive performance. Lastly, we identified the lowest FTP value at which associations with Aβ-PET, CSF, and cognition were detectable.

RESULTS

Increased age was associated only with amygdala and transverse temporal lobe FTP retention. Aβ-positive individuals had higher FTP SUVR values in several brain regions, further showing correlation with NAV load through the cortex. Increased FTP SUVRs in medial temporal regions were associated with increased CSF tau values and worse cognition. The SUVRs at which associations between entorhinal FTP SUVR and other AD markers were first detected differed by modality, with a detection point of 1.12 for CSF values, 1.2 for Aβ-PET, and 1.4 for cognition.

CONCLUSIONS

Relatively low FTP-PET SUVRs are associated with pathologic markers of AD in the preclinical phase of the disease. Adjustment in the tau threshold should be considered, depending on the purpose of the tau classification.

Plasma tau/amyloid-β1-42 ratio predicts brain tau deposition and neurodegeneration in Alzheimer's disease

One of the hallmarks of Alzheimer's disease is abnormal deposition of tau proteins in the brain. Although plasma tau has been proposed as a potential biomarker for Alzheimer's disease, a direct link to brain deposition of tau is limited. Here, we estimated the amount of in vivo tau deposition in the brain by PET imaging and measured plasma levels of total tau (t-tau), phosphorylated tau (p-tau, T181) and amyloid-β1-42. We found significant correlations of plasma p-tau, t-tau, p-tau/amyloid-β1-42, and t-tau/amyloid-β1-42 with brain tau deposition in cross-sectional and longitudinal manners. In particular, t-tau/amyloid-β1-42 in plasma was highly predictive of brain tau deposition, exhibiting 80% sensitivity and 91% specificity. Interestingly, the brain regions where plasma t-tau/amyloid-β1-42 correlated with brain tau were similar to the typical deposition sites of neurofibrillary tangles in Alzheimer's disease. Furthermore, the longitudinal changes in cerebral amyloid deposition, brain glucose metabolism, and hippocampal volume change were also highly associated with plasma t-tau/amyloid-β1-42. These results indicate that combination of plasma tau and amyloid-β1-42 levels might be potential biomarkers for predicting brain tau pathology and neurodegeneration.

Prospective longitudinal atrophy in Alzheimer's disease correlates with the intensity and topography of baseline tau-PET

β-Amyloid plaques and tau-containing neurofibrillary tangles are the two neuropathological hallmarks of Alzheimer's disease (AD) and are thought to play crucial roles in a neurodegenerative cascade leading to dementia. Both lesions can now be visualized in vivo using positron emission tomography (PET) radiotracers, opening new opportunities to study disease mechanisms and improve patients' diagnostic and prognostic evaluation. In a group of 32 patients at early symptomatic AD stages, we tested whether β-amyloid and tau-PET could predict subsequent brain atrophy measured using longitudinal magnetic resonance imaging acquired at the time of PET and 15 months later. Quantitative analyses showed that the global intensity of tau-PET, but not β-amyloid-PET, signal predicted the rate of subsequent atrophy, independent of baseline cortical thickness. Additional investigations demonstrated that the specific distribution of tau-PET signal was a strong indicator of the topography of future atrophy at the single patient level and that the relationship between baseline tau-PET and subsequent atrophy was particularly strong in younger patients. These data support disease models in which tau pathology is a major driver of local neurodegeneration and highlight the relevance of tau-PET as a precision medicine tool to help predict individual patient's progression and design future clinical trials.

Individualized atrophy scores predict dementia onset in familial frontotemporal lobar degeneration

INTRODUCTION

Some models of therapy for neurodegenerative diseases envision starting treatment before symptoms develop. Demonstrating that such treatments are effective requires accurate knowledge of when symptoms would have started without treatment. Familial frontotemporal lobar degeneration offers a unique opportunity to develop predictors of symptom onset.

METHODS

We created dementia risk scores in 268 familial frontotemporal lobar degeneration family members by entering covariate-adjusted standardized estimates of brain atrophy into a logistic regression to classify asymptomatic versus demented participants. The score's predictive value was tested in a separate group who were followed up longitudinally (stable vs. converted to dementia) using Cox proportional regressions with dementia risk score as the predictor.

RESULTS

Cross-validated logistic regression achieved good separation of asymptomatic versus demented (accuracy = 90%, SE = 0.06). Atrophy scores predicted conversion from asymptomatic or mildly/questionably symptomatic to dementia (HR = 1.51, 95% CI: [1.16,1.98]).

DISCUSSION

Individualized quantification of baseline brain atrophy is a promising predictor of progression in asymptomatic familial frontotemporal lobar degeneration mutation carriers.

Tau PET and multimodal brain imaging in patients at risk for chronic traumatic encephalopathy

OBJECTIVE

To characterize individual and group-level neuroimaging findings in patients at risk for Chronic Traumatic Encephalopathy (CTE).

METHODS

Eleven male patients meeting criteria for Traumatic Encephalopathy Syndrome (TES, median age: 64) underwent neurologic evaluation, 3-Tesla MRI, and PET with [18F]-Flortaucipir (FTP, tau-PET) and [11C]-Pittsburgh compound B (PIB, amyloid-PET). Six patients underwent [18F]-Fluorodeoxyglucose-PET (FDG, glucose metabolism). We assessed imaging findings at the individual patient level, and in group-level comparisons with modality-specific groups of cognitively normal older adults (CN). Tau-PET findings in patients with TES were also compared to a matched group of patients with mild cognitive impairment or dementia due to Alzheimer's disease (AD).

RESULTS

All patients with TES sustained repetitive head injury participating in impact sports, ten in American football. Three patients met criteria for dementia and eight had mild cognitive impairment. Two patients were amyloid-PET positive and harbored the most severe MRI atrophy, FDG hypometabolism, and FTP-tau PET binding. Among the nine amyloid-negative patients, tau-PET showed either mildly elevated frontotemporal binding, a "dot-like" pattern, or no elevated binding. Medial temporal FTP was mildly elevated in a subset of amyloid-negative patients, but values were considerably lower than in AD. Voxelwise analyses revealed a convergence of imaging abnormalities (higher FTP binding, lower FDG, lower gray matter volumes) in frontotemporal areas in TES compared to controls.

CONCLUSIONS

Mildly elevated tau-PET binding was observed in a subset of amyloid-negative patients at risk for CTE, in a distribution consistent with CTE pathology stages III-IV. FTP-PET may be useful as a biomarker of tau pathology in CTE but is unlikely to be sensitive to early disease stages.

AD molecular: Imaging tau aggregates with positron emissions tomography

Pathologic aggregates of tau protein are observed in several neurodegenerative diseases and are used to diagnose and stage disease postmortem. Recent advances in positron emission tomography radioligands allow for the detection of aggregated tau proteins in living persons. This chapter describes the development and characterization of several positron emission tomography radioligands used to detect tau pathophysiology in vivo, and how these ligands are being used in clinical aging and neurodegenerative disease research with a focus on imaging tau aggregates in Alzheimer's disease.

Plasma Amyloid Beta and Tau Levels Are Predictors of Post-stroke Cognitive Impairment: A Longitudinal Study

Objectives: Post-stroke cognitive impairment (PSCI) is a common disease that may occur within 3 months after a stroke or even later. However, the mechanism of PSCI development is unclear. The present study investigated whether the levels of plasma amyloid beta-42 (Aβ42) and tau are associated with the onset of PSCI. Methods: Fifty-five patients admitted within 7 days of acute ischemic stroke were enrolled and followed up for 1 year. Montreal Cognitive Assessment (MoCA) was administered at 3 months and 1 year, and plasma Aβ42 and tau levels were determined using an ultrasensitive immunoassay (immunomagnetic reduction) within 7 days of the stroke event and 3 months later. Results: In this study, 13 of 55 patients developed PSCI (MoCA score <23) at 3 months. Seven patients with PSCI at 3 months recovered to a cognitively normal state at 1 year, whereas seven cognitively normal patients developed PSCI at 1 year. The patients with PSCI at 1 year had a higher incidence of cognitive function deterioration between 3 months and 1 year compared with those without PSCI at 1 year. Plasma Aβ42 and tau levels at 3 months were lower in the patients with PSCI at 1 year than in those without PSCI (Aβ42: 15.1 vs. 17.2 pg/mL, P = 0.013; tau: 16.7 vs. 19.9 pg/mL, P = 0.018). Low education levels and pre-existing white matter disease were the most significant predictors of PSCI at 3 months, and poor cognitive performance at 3 months and low plasma Aβ42 and tau levels at 3 months were the most significant predictors of PSCI at 1 year. Conclusion: The pathogenesis of PSCI is complex and changes with time. Ischemia-induced Aβ42/tau pathology might be involved in PSCI development.

A new perspective for advanced positron emission tomography-based molecular imaging in neurodegenerative proteinopathies

Recent studies in neurodegenerative conditions have increasingly highlighted that the same neuropathology can trigger different clinical phenotypes or, vice-versa, that similar phenotypes can be triggered by different neuropathologies. This evidence has called for the adoption of a pathology spectrum-based approach to study neurodegenerative proteinopathies. These conditions share brain deposition of abnormal protein aggregates, leading to aberrant biochemical, metabolic, functional, and structural changes. Positron emission tomography (PET) is a well-recognized and unique tool for the in vivo assessment of brain neuropathology, and novel PET techniques are emerging for the study of specific protein species. Today, key applications of PET range from early research and clinical diagnostic tools to their use in clinical trials for both participants screening and outcome evaluation. This position article critically reviews the role of distinct PET molecular tracers for different neurodegenerative proteinopathies, highlighting their strengths, weaknesses, and opportunities, with special emphasis on methodological challenges and future applications.

Cross-sectional associations between [18F]GTP1 tau PET and cognition in Alzheimer's disease

The regional relationships between tau positron emission tomography (PET) imaging and cognitive impairment in Alzheimer's disease (AD) remain uncertain. We examined cross-sectional associations between cognitive performance, cerebral uptake of the novel tau PET tracer [¹⁸F]GTP1, and other neuroimaging indices ([¹⁸F]florbetapir amyloid PET, magnetic resonance imaging) in 71 participants with normal cognition, prodromal AD, or AD dementia. Greater [¹⁸F]GTP1 uptake was seen with increasing clinical severity and correlated with poorer cognition. [¹⁸F]GTP1 uptake and cortical volume (but not [¹⁸F]florbetapir uptake) were independently associated with cognitive performance, particularly within the temporal lobe. Delayed memory was more specifically associated with temporal [¹⁸F]GTP1 uptake; other domains correlated with a broader range of regional [¹⁸F]GTP1 uptake. These data confirm that [¹⁸F]GTP1 tau PET uptake significantly correlates with cognitive performance in AD, but regional correlations between performance in non-memory cognitive domains were less specific than reported by tau PET imaging studies that included participants with atypical focal cortical AD syndromes. Tau PET imaging may have utility as a surrogate biomarker for clinical AD progression in therapeutic trials of disease-modifying interventions.

Tau covariance patterns in Alzheimer's disease patients match intrinsic connectivity networks in the healthy brain

According to the network model of neurodegeneration, the spread of pathogenic proteins occurs selectively along connected brain regions. We tested in vivo whether the distribution of filamentous tau (measured with [18F]flortaucipir-PET), fibrillar amyloid-β ([11C]PIB-PET) and glucose hypometabolism ([18F]FDG-PET) follows the intrinsic functional organization of the healthy brain. We included 63 patients with Alzheimer's disease (AD; 30 male, 63 ± 8 years) who underwent [18F]flortaucipir, [11C]PIB and [18F]FDG PET, and 1000 young adults (427 male, 21 ± 3 years) who underwent task-free fMRI. We selected six predefined disease epicenters as seeds for whole-brain voxelwise covariance analyses to compare correlated patterns of tracer uptake across AD patients against fMRI intrinsic connectivity patterns in young adults. We found a striking convergence between [18F]flortaucipir covariance patterns and intrinsic connectivity maps (range Spearman rho's: 0.32-0.78, p < .001), which corresponded with expected functional networks (range goodness-of-fit: 3.8-8.2). The topography of amyloid-β covariance patterns was more diffuse and less network-specific, while glucose hypometabolic patterns were more spatially restricted than tau but overlapped with functional networks. These findings suggest that the spatial patterns of tau and glucose hypometabolism observed in AD resemble the functional organization of the healthy brain, supporting the notion that tau pathology spreads through circumscribed brain networks and drives neurodegeneration.