Cited by 448Dementia and Cognitive Impairment ResearchAlzheimer's disease research and treatmentsMedical Imaging Techniques and Applications

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Positron Emission Tomography Imaging With [ 18 F]flortaucipir and Postmortem Assessment of Alzheimer Disease Neuropathologic Changes

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Abstract

Importance: Positron emission tomography (PET) may increase the diagnostic accuracy and confirm the underlying neuropathologic changes of Alzheimer disease (AD). Objective: To determine the accuracy of antemortem [ 18 F]flortaucipir PET images for predicting the presence of AD-type tau pathology at autopsy. Design, Setting, and Participants: This diagnostic study (A16 primary cohort) was conducted from October 2015 to June 2018 at 28 study sites (27 in US sites and 1 in Australia). Individuals with a terminal illness who were older than 50 years and had a projected life expectancy of less than 6 months were enrolled. All participants underwent [ 18 F]flortaucipir PET imaging, and scans were interpreted by 5 independent nuclear medicine physicians or radiologists. Supplemental autopsy [ 18 F]flortaucipir images and pathological samples were also collected from 16 historically collected cases. A second study (FR01 validation study) was conducted from March 26 to April 26, 2019, in which 5 new readers assessed the original PET images for comparison to autopsy. Main Outcomes and Measures: [ 18 F]flortaucipir PET images were visually assessed and compared with immunohistochemical tau pathology. An AD tau pattern of flortaucipir retention was assessed for correspondence with a postmortem B3-level (Braak stage V or VI) pathological pattern of tau accumulation and to the presence of amyloid-β plaques sufficient to meet the criteria for high levels of AD neuropathological change. Success was defined as having at least 3 of the 5 readers above the lower bounds of the 95% CI for both sensitivity and specificity of 50% or greater. Results: A total of 156 patients were enrolled in the A16 study and underwent [ 18 F]flortaucipir PET imaging. Of these, 73 died during the study, and valid autopsies were performed for 67 of these patients. Three autopsies were evaluated as test cases and removed from the primary cohort (n = 64). Of the 64 primary cohort patients, 34 (53%) were women and 62 (97%) were white; mean (SD) age was 82.5 (9.6) years; and 49 (77%) had dementia, 1 (2%) had mild cognitive impairment, and 14 (22%) had normal cognition. Prespecified success criteria were met for the A16 primary cohort. The flortaucipir PET scans predicted a B3 level of tau pathology, with sensitivity ranging from 92.3% (95% CI, 79.7%-97.3%) to 100.0% (95% CI, 91.0%-100.0%) and specificity ranging from 52.0% (95% CI, 33.5%-70.0%) to 92.0% (95% CI, 75.0%-97.8%). A high level of AD neuropathological change was predicted with sensitivity of 94.7% (95% CI, 82.7%-98.5%) to 100.0% (95% CI, 90.8%-100.0%) and specificity of 50.0% (95% CI, 32.1%-67.9%) to 92.3% (95% CI, 75.9%-97.9%). The FR01 validation study also met prespecified success criteria. Addition of the supplemental autopsy data set and 3 test cases, which comprised a total of 82 patients and autopsies for both the A16 and FR01 studies, resulted in improved specificity and comparable overall accuracy. Among the 156 enrolled participants, 14 (9%) experienced at least 1 treatment-emergent adverse event. Conclusions and Relevance: This study’s findings suggest that PET imaging with [ 18 F]flortaucipir could be used to identify the density and distribution of AD-type tau pathology and the presence of high levels of AD neuropathological change, supporting a neuropathological diagnosis of AD.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

In a prospective autopsy-validated diagnostic study, [18F]flortaucipir PET visual reads detected B3-level tau neurofibrillary tangles and high Alzheimer disease neuropathologic change with high sensitivity and moderate-to-high specificity. A second independent reader validation study confirmed the findings, and quantitative SUVR analysis also showed high specificity.

Key findings

In the A16 primary cohort (n = 64), flortaucipir PET met prespecified success criteria for detecting B3 NFT score: sensitivity ranged from 92.3% (95% CI, 79.7%-97.3%) to 100.0% (95% CI, 91.0%-100.0%) and specificity from 52.0% (95% CI, 33.5%-70.0%) to 92.0% (95% CI, 75.0%-97.8%) across 5 readers; majority read sensitivity was 92.3% and specificity 80.0%. For high ADNC, sensitivity ranged from 94.7% (95% CI, 82.7%-98.5%) to 100.0% (95% CI, 90.8%-100.0%) and specificity from 50.0% (95% CI, 32.1%-67.9%) to 92.3% (95% CI, 75.9%-97.9%); majority read sensitivity was 94.7% and specificity 80.8%.

  • In the full autopsy data set (n = 82), B3 sensitivity ranged from 89.1% (95% CI, 77.0%-95.3%) to 93.5% (95% CI, 82.5%-97.8%) and specificity from 66.7% (95% CI, 50.3%-79.8%) to 94.4% (95% CI, 81.9%-98.5%); high ADNC sensitivity ranged from 95.1% (95% CI, 83.9%-98.7%) to 97.6% (95% CI, 87.4%-99.6%) and specificity from 65.9% (95% CI, 50.5%-78.4%) to 90.2% (95% CI, 77.5%-96.1%). Majority read results were B3 sensitivity 89.1% and specificity 86.1%, and high ADNC sensitivity 95.1% and specificity 82.9%.
  • The FR01 validation study also met prespecified success criteria. Interrater reliability was high: A16 all read scans (n = 105) showed 89.9% agreement (Fleiss κ, 0.80; P < .001), A16 primary cohort scans (n = 64) showed 88.4% agreement (Fleiss κ, 0.74; P < .001), and FR01 (n = 82) had Fleiss κ 0.82 (P < .001).
  • Quantitative SUVR analysis in 60 of 67 scans meeting quality criteria established an optimal cut point greater than 1.113, yielding sensitivity of 84.2% for B3 NFT score and 86.5% for high ADNC, with 100% specificity for both. Safety: 14 of 156 enrolled participants (9%) had at least 1 treatment-emergent adverse event; agitation (n = 3) and headache (n = 2) were most common, and 3 participants (2%) had serious adverse events within 48 hours, including 2 deaths reported as not associated with study drug or procedure.

Methods

This multicenter diagnostic study (A16 primary cohort; NCT02516046) enrolled participants older than 50 years with terminal illness and projected life expectancy less than 6 months, ranging from clinically normal cognition to dementia, at 28 sites (27 US, 1 Australia) from October 2015 through June 2018. The A16 primary cohort included 64 participants with valid evaluable flortaucipir images and autopsy; the full autopsy data set included 82 cases (64 primary cohort, 2 evaluable test cases, 16 supplemental historically collected autopsy cases), and a separate FR01 validation study (NCT03901092) reinterpreted 82 images.

  • PET imaging was acquired for 20 minutes (4 × 5-minute frames) beginning approximately 80 minutes after intravenous 370 (±10%) MBq [18F]flortaucipir; scans were visually rated by 5 blinded nuclear medicine physicians or radiologists as negative, moderate, or advanced AD tau pattern, and quantitative SUVRs used a PERSI white matter reference region and a weighted neocortical target.
  • Neuropathological assessment was performed by 2 blinded authors using NIA–AA guidelines, with AT8 immunohistochemistry for Braak NFT staging and 6E10 for amyloid plaque; primary comparisons were flortaucipir PET classification against B3 NFT score (Braak V-VI) and high ADNC level. Analyses calculated sensitivity, specificity, accuracy, predictive values, and likelihood ratios per reader and for majority read, with Wilson 95% CIs, Fleiss and simple κ statistics, and ROC analysis for the SUVR cut point.

Limitations

The paper states that the A16 cohort was older than typical symptomatic AD trial populations, had more advanced clinical disease with only 1 case of mild cognitive impairment, and lacked racial/ethnic diversity; visual reads showed best accuracy for the most advanced NFT tau load and ADNC, and earlier AD stages may meet intermediate pathological criteria or have neuritic plaque without substantial tau. The paper also states that up to 2 of 5 readers did not meet statistical specificity criteria for primary outcomes, largely from overcalling small noncontiguous temporal lobe activity, and that read errors may relate to imprecise cerebellar reference region drawing; subcortical [18F]flortaucipir retention appeared to represent off-target binding of unknown source.

  • The paper states that larger sample sizes are needed to confirm high specificity for distinguishing AD from non-AD tau pathologies.
  • Evident from the text: the primary cohort lacked structural imaging and used PET-to-PET registration; the full autopsy data set combined primary, test-case, and historically collected supplemental cases, and cognitively normal participants could remain eligible for autopsy regardless of time from scan to autopsy, which may introduce heterogeneity.

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Integrity signals

Registry

Crossref · 10.1001/jamaneurol.2020.0528

Cites

63 of 63 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Figures

Figure 1. Positron Emission Tomography With [18F]flortaucipir Visual Read Categories and Comparative Histologic Structure Three cases representing the 3 levels of visual reads and corresponding histologic sections from the superior or middle temporal (sup/middle temp) gyrus (Braak region of interest [ROI] 7) and middle frontal gyrus (Braak ROI 6) stained for neurofibrillary tangles (NFTs) with AT8 antibodies and for amyloid plaque with 6E10 antibodies. Images presented in a blue-green-red-yellow color scale, with cortical counts scaled to 1.65 × the mean cerebellar counts (eAppendix in the Supplement). A indicates anterior; AD, Alzheimer disease; L, left; P, posterior; R, right.
Figure 1. Positron Emission Tomography With [18F]flortaucipir Visual Read Categories and Comparative Histologic Structure Three cases representing the 3 levels of visual reads and corresponding histologic sections from the superior or middle temporal (sup/middle temp) gyrus (Braak region of interest [ROI] 7) and middle frontal gyrus (Braak ROI 6) stained for neurofibrillary tangles (NFTs) with AT8 antibodies and for amyloid plaque with 6E10 antibodies. Images presented in a blue-green-red-yellow color scale, with cortical counts scaled to 1.65 × the mean cerebellar counts (eAppendix in the Supplement). A indicates anterior; AD, Alzheimer disease; L, left; P, posterior; R, right.CC BY-NC-ND · PubMed Central
Figure 2. Braak Neurofibrillary Tangle (NFT) Scores vs Majority Read Interpretations for the A16 Primary Cohort (n = 64) AD, Alzheimer disease; Advanced AD, consistent with advanced AD tau pattern; Moderate AD, consistent with moderate AD tau pattern; and Negative AD, not consistent with AD tau pattern.
Figure 2. Braak Neurofibrillary Tangle (NFT) Scores vs Majority Read Interpretations for the A16 Primary Cohort (n = 64) AD, Alzheimer disease; Advanced AD, consistent with advanced AD tau pattern; Moderate AD, consistent with moderate AD tau pattern; and Negative AD, not consistent with AD tau pattern.CC BY-NC-ND · PubMed Central
Figure 3. Consortium to Establish a Registry for Alzheimer Disease (CERAD) Amyloid Plaque Scores vs Braak Neurofibrillary Tangle (NFT) Scores A16 primary cohort. CERAD amyloid plaque scores vs Braak NFT stages (highest score from both hemispheres), categorized by clinical diagnosis and flortaucipir majority visual read category. Data points were randomly scattered within each grid square to minimize overlap for presentation purposes. AD, Alzheimer disease; Adv, consistent with advanced AD tau pattern; CN, cognitively normal; MCI, mild cognitive impairment; Mod, consistent with moderate AD tau pattern; Negative, not consistent with AD tau pattern; and ODD, other non-AD dementia diagnoses. All PET image reads represent the majority read interpretation for each image.
Figure 3. Consortium to Establish a Registry for Alzheimer Disease (CERAD) Amyloid Plaque Scores vs Braak Neurofibrillary Tangle (NFT) Scores A16 primary cohort. CERAD amyloid plaque scores vs Braak NFT stages (highest score from both hemispheres), categorized by clinical diagnosis and flortaucipir majority visual read category. Data points were randomly scattered within each grid square to minimize overlap for presentation purposes. AD, Alzheimer disease; Adv, consistent with advanced AD tau pattern; CN, cognitively normal; MCI, mild cognitive impairment; Mod, consistent with moderate AD tau pattern; Negative, not consistent with AD tau pattern; and ODD, other non-AD dementia diagnoses. All PET image reads represent the majority read interpretation for each image.CC BY-NC-ND · PubMed Central

Verification

Claims the paper makes

40 Own result · 28 Not checked yet · 16 Own interpretation · 10 Own method · 4 No basis given · 2 Supported · 1 Supported so far

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  • The paper relies on this without support.

    Tau pathology does not change substantially between antemortem flortaucipir positron emission tomography imaging and postmortem assessment.

    “Participants with cognitive impairment who did not come to autopsy within 9 months after the flortaucipir scan were either removed from the study or required to undergo a repeat flortaucipir scan for comparison with the neuropathological result. Cognitively normal patients remained eligible for autopsy, regardless of the time from scan to autopsy.”
    “After removal of the 3 test cases, the remaining 64 participants were included in the A16 primary cohort, with autopsy occurring a mean (SD) 16.2 (15.0) hours from the recorded time of death and 2.6 (2.14) months after [18F]flortaucipir imaging.”
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  1. Fleisher, 2018, Tau PET imaging as a screening tool for clinical trials of disease modifying therapies., J Prev Alzheimers Dis, 5, S17

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Metadata

Authors
Fleisher, A. S., Pontecorvo, M. J., Devous, M. D., Lu, M., Arora, A. K., Truocchio, S. P., Aldea, P., Flitter, M., Locascio, T., Devine, M., Siderowf, A., Beach, T. G., Montine, T. J., Serrano, G. E., Curtis, C., Perrin, A., Salloway, S., Daniel, M., Wellman, C., Joshi, A. D., Irwin, D. J., Lowe, V. J., Seeley, W. W., Ikonomovic, M. D., Masdeu, J. C., Kennedy, I., Harris, T., Navitsky, M., Southekal, S., Mintun, M. A., & A16 Study Investigators
Affiliations
  • Avid Radiopharmaceuticals (United States) (US)
  • University of Pennsylvania (US)
  • Banner Sun Health Research Institute (US)
  • Stanford University (US)
  • Waypoint Research, Windermere, Florida
  • Banner Alzheimer’s Institute (US)
  • Butler Hospital (US)
  • Pacific Research Network, San Diego, California
  • Hospice of the Western Reserve (US)
  • ImaginAb (United States) (US)
  • Mayo Clinic (US)
  • University of California, San Francisco (US)
  • University of Pittsburgh, Pittsburgh
  • Houston Methodist (US)
Corresponding author
Fleisher, Adam S.
Venue
JAMA Neurology
Published
2020-07-01
Volume
77
Issue
7
Pages
829
ISSN
2168-6149 (ISSN-L)
OpenAlex
W3019122005
Cited by
448
References
63
Citations by year
2026: 68 · 2025: 77 · 2024: 69 · 2023: 57 · 2022: 79 · 2021: 67 · 2020: 30
FWCI
42.50
Type
journal article
Language
en
Open access
Licence
cc-by-nc-nd
Locations
  • JAMA Neurology (publishedVersion, cc-by-nc-nd)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
Funders
  • National Institute on Aging (R01AG034676, U01AG006786, P01AG066597, R01AG054449, R01AG011378, P30AG019610, R01AG041851, P01AG019724, P30AG062422, P50AG023501, P50AG016574)
  • National Institute of Neurological Disorders and Stroke (R01NS089544, R21NS094489, R01NS089757, R01NS097495)
Topics
  • Health Sciences › Medicine › Psychiatry and Mental health › Dementia and Cognitive Impairment Research
  • Life Sciences › Neuroscience › Cellular and Molecular Neuroscience › Alzheimer's disease research and treatments
  • Health Sciences › Medicine › Radiology, Nuclear Medicine and Imaging › Medical Imaging Techniques and Applications
Keywords
18F-flortaucipir, Alzheimer's disease, tau PET imaging, postmortem neuropathology, Braak stages, amyloid plaques, diagnostic accuracy, immunohistochemistry, terminal illness, dementia, neurodegeneration biomarkers, amyloid PET, FDG-PET, neuroimaging validation
MeSH terms
Aged, Aged, 80 and over, Alzheimer Disease, Autopsy, Brain, Carbolines, Contrast Media, Female, Humans, Male, Sensitivity and Specificity, Amyloid beta-Peptides, Neurofibrillary Tangles, tau Proteins, Radiopharmaceuticals, Positron-Emission Tomography, Plaque, Amyloid, Neuroimaging

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