Recommendations for the use of PET imaging biomarkers in the diagnosis of neurodegenerative conditions associated with dementia: SEMNIM and SEN consensus

Connectivity and Patterns of Regional Cerebral Blood Flow, Cerebral Glucose Uptake, and Aβ-Amyloid Deposition in Alzheimer's Disease (Early and Late-Onset) Compared to Normal Ageing

PURPOSE

The aim of this study was to investigate the differences in early (EOAD) and late (LOAD) onset of Alzheimer´s disease, as well as glucose uptake, regional cerebral blood flow (R1), amyloid depositions, and functional brain connectivity between normal young (YC) and Old Controls (OC).

METHODOLOGY

The study included 22 YC (37 ± 5 y), 22 OC (73 ± 5.9 y), 18 patients with EOAD (63 ± 9.5 y), and 18 with LOAD (70.6 ± 7.1 y). Patients underwent FDG and PIB PET/CT. R1 images were obtained from the compartmental analysis of the dynamic PIB acquisitions. Images were analyzed by a voxel-wise and a VOI-based approach. Functional connectivity was studied from the R1 and glucose uptake images.

RESULTS

OC had a significant reduction of R1 and glucose uptake compared to YC, predominantly at the dorsolateral and mesial frontal cortex. EOAD and LOAD vs. OC showed a decreased R1 and glucose uptake at the posterior parietal cortex, precuneus, and posterior cingulum. EOAD vs. LOAD showed a reduction in glucose uptake and R1 at the occipital and parietal cortex and an increased at the mesial frontal and temporal cortex. There was a mild increase in an amyloid deposition at the frontal cortex in LOAD vs. EOAD. YC presented higher connectivity than OC in R1 but lower connectivity considering glucose uptake. Moreover, EOAD and LOAD showed a decreased connectivity compared to controls that were more pronounced in glucose uptake than R1.

CONCLUSION

Our results demonstrated differences in amyloid deposition and functional imaging between groups and a differential pattern of functional connectivity in R1 and glucose uptake in each clinical condition. These findings provide new insights into the pathophysiological processes of AD and may have an impact on patient diagnostic evaluation.

Brain SPECT as a Biomarker of Neurodegeneration in Dementia in the Era of Molecular Imaging: Still a Valid Option?

Biomarkers are playing a progressively leading role in both clinical practice and scientific research in dementia. Although amyloid and tau biomarkers have gained ground in the clinical community in recent years, neurodegeneration biomarkers continue to play a key role due to their ability to identify different patterns of brain involvement that sign the transition between asymptomatic and symptomatic stages of the disease with high sensitivity and specificity. Both ¹⁸F-FDG positron emission tomography (PET) and perfusion single photon emission computed tomography (SPECT) have proved useful to reveal the functional alterations underlying various neurodegenerative diseases. Although the focus of nuclear neuroimaging has shifted to PET, the lower cost and wider availability of SPECT make it a still valid alternative for the study of patients with dementia. This review discusses the principles of both techniques, compares their diagnostic performance for the diagnosis of neurodegenerative diseases and highlights the role of SPECT to characterize patients from low- and middle-income countries, where special care of additional costs is particularly needed to meet the new recommendations for the diagnosis and characterization of patients with dementia.

Clinical Impact of PET With 18F-FDG and 11C-PIB in Patients With Dementia in a Developing Country

Introduction: The objective of this study was to evaluate the clinical impact PET with ¹⁸F-FDG and ¹¹C-PIB in patients with dementia in a developing country.

Methodology: Retrospective study of the patients referred for the evaluation of dementia to the only PET center in Uruguay. A total of 248 patients were identified, from which 70 patients were included based on the availability of medical history and clinical follow-up. Main outcomes included change in diagnosis, diagnostic dilemma and AD treatment. We evaluated the association of clinical outcomes with PET concordance with baseline diagnosis, diagnostic dilemma, level of education, AD pathology/Non-AD pathology (AD/Non-AD), baseline diagnosis and ¹¹C-PIB PET result.

Results: Baseline clinical diagnosis was concordant with ¹⁸F-FDG and ¹¹C-PIB PET results in 64.7 and 77.1% of the patients, respectively. Change in diagnosis after PET was identified in 30.0% of the patients and was associated with discordant ¹⁸F-FDG (p = 0.002) and ¹¹C-PIB (p < 0.001) PET results, previous diagnostic dilemma (p = 0.005), low education (p = 0.027), Non-AD baseline diagnosis (p = 0.027), and negative ¹¹C-PIB PET result (p < 0.001). Only the last variable remained significant in the multivariate analysis (adjusted p = 0.038). Diagnostic dilemma decreased after PET from 15.7 to 7.1% (p = 0.11) and was associated with Non-AD diagnosis (p = 0.002) and negative ¹¹C-PIB PET result (p = 0.003). Change in AD treatment after PET occurred in 45.7% of the patients.

Conclusion:¹⁸F-FDG and ¹¹C-PIB PET had a significant clinical impact in terms of change in diagnosis and treatment in patients with dementia in a developing country, similar to that reported in high-income countries.

The use of systematic review evidence to support the development of guidelines for positron emission tomography: a cross-sectional survey

OBJECTIVES

To examine to what degree guidelines for PET and PET/CT used systematic review evidence.

METHODS

The latest version of guidelines for PET, PET/CT or PET/MRI published in English in PubMed until December 2019 was analysed in two categories: (1) for indications, if mainly discussing the appropriate use of PET in diverse conditions; (2) for procedures, if providing step-by-step instructions for imaging. We surveyed the general characteristics and the use of systematic review evidence for developing recommendations across all guidelines, and surveyed the citation of evidence for five recommendation topics in guidelines for procedures.

RESULTS

Forty-seven guidelines, published between 2004 and 2020, were included. Guidelines for indications were developed mainly on systematic reviews (13 of 19, 68.4%). Among those, 12 (63.2%) reported the level of evidence, 4 (21.1%) reported the strength of recommendations, 3 (15.8%) described external review and 7 (36.8%) involved methodologists. Guidelines for procedures were seldom developed on systematic reviews (1 of 27, 3.7%). Among those, 1 (3.7%) reported the level of evidence, 1 (3.7%) reported the strength of recommendations, 3 (11.1%) described external review and 1 (3.7%) involved methodologists. Systematic review evidence was cited by 2 (7.4%) procedure guidelines per recommendation topic in median.

CONCLUSION

The use of systematic review evidence for developing recommendations among PET or PET/CT guidelines was suboptimal. While our survey is an icebreaking attempt to explore a key element (i.e. use of systematic review evidence) for developing nuclear medicine guidelines, assessments of other domains of guideline quality may help capture the entire picture.

KEY POINTS

• The use of systematic review evidence for developing recommendations among guidelines for PET or PET/CT was suboptimal. • Only 13 (68.4%) guidelines for indications and 1 (3.7%) guideline for procedures systematically reviewed the literature during guideline development. • For each recommendation topic we examined, only a median of 2 (7.4%) procedure guidelines cited systematic review evidence.

CCCDTD5: Clinical role of neuroimaging and liquid biomarkers in patients with cognitive impairment

Since 1989, four Canadian Consensus Conferences on the Diagnosis and Treatment of Dementia (CCCDTDs) have provided evidence-based dementia diagnostic and treatment guidelines for Canadian clinicians and researchers. We present the results from the Neuroimaging and Fluid Biomarkers Group of the 5th CCCDTD (CCCDTD5), which addressed topics chosen by the steering committee to reflect advances in the field and build on our previous guidelines. Recommendations on Imaging and Fluid Biomarker Use from this Conference cover a series of different fields. Prior structural imaging recommendations for both computerized tomography (CT) and magnetic resonance imaging (MRI) remain largely unchanged, but MRI is now more central to the evaluation than before, with suggested sequences described here. The use of visual rating scales for both atrophy and white matter anomalies is now included in our recommendations. Molecular imaging with [18F]-fluorodeoxyglucose ([18F]-FDG) Positron Emisson Tomography (PET) or [99mTc]-hexamethylpropyleneamine oxime/ethylene cysteinate dimer ([99mTc]-HMPAO/ECD) Single Photon Emission Tomography (SPECT), should now decidedly favor PET. The value of [18F]-FDG PET in the assessment of neurodegenerative conditions has been established with greater certainty since the previous conference, and it has now been recognized as a useful biomarker to establish the presence of neurodegeneration by a number of professional organizations around the world. Furthermore, the role of amyloid PET has been clarified and our recommendations follow those from other groups in multiple countries. SPECT with [123I]-ioflupane (DaTscanTM) is now included as a useful study in differentiating Alzheimer's disease (AD) from Lewy body disease. Finally, liquid biomarkers are in a rapid phase of development and, could lead to a revolution in the assessment AD and other neurodegenerative conditions at a reasonable cost. We hope these guidelines will be useful for clinicians, researchers, policy makers, and the lay public, to inform a current and evidence-based approach to the use of neuroimaging and liquid biomarkers in clinical dementia evaluation and management.

Early epigenetic changes of Alzheimer's disease in the human hippocampus

The discovery of new biomarkers would be very valuable to improve the detection of early Alzheimer's disease (AD). DNA methylation marks may serve as epigenetic biomarkers of early AD. Here we identified epigenetic marks that are present in the human hippocampus from the earliest stages of AD. A previous methylome dataset of the human AD hippocampus was used to select a set of eight differentially methylated positions (DMPs) since early AD stages. Next, bisulphite pyrosequencing was performed in an expanded homogeneous cohort of 18 pure controls and 35 hippocampal samples with neuropathological changes of pure AD. Correlation between DNA methylation levels in DMPs and phospho-tau protein burden assessed by immunohistochemistry in the hippocampus was also determined. We found four DMPs showing higher levels of DNA methylation at early AD stages compared to controls, involving ELOVL2, GIT1/TP53I13 and the histone gene locus at chromosome 6. DNA methylation levels assessed by bisulphite pyrosequencing correlated with phospho-tau protein burden for ELOVL2 and HIST1H3E/HIST1H3 F genes. In this discovery study, a set of four epigenetic marks of early AD stages have been identified in the human hippocampus. It would be worth studying in-depth the specific pathways related to these epigenetic marks. These early alterations in DNA methylation in the AD hippocampus could be regarded as candidate biomarkers to be explored in future translational studies.

ABBREVIATIONS

AD: Alzheimer's disease; DMPs: Differentially methylated positions; CSF: Cerebrospinal fluid; βA42: β-amyloid 42; PET: positron emission tomography; 5mC: 5-methyl cytosine; CpG: cytosine-guanine dinucleotides; ANK1: ankyrin-1; BIN1: amphiphysin II; p-tau: hyperphosphorylated tau; CERAD: Consortium to Establish A Registry for Alzheimer's Disease; SD: standard deviation; ANOVA: one-way analysis of variance; VLCFAs: very long-chain fatty acids; DHA: docosahexaenoic acid; mTOR: mechanistic target of rapamycin.

Assessment of the appropriate use criteria for amyloid PET in an unselected memory clinic cohort: The ABIDE project

INTRODUCTION

The objective of this study was to assess the usefulness of the appropriate use criteria (AUC) for amyloid imaging in an unselected cohort.

METHODS

We calculated sensitivity and specificity of appropriate use (increased confidence and management change), as defined by Amyloid Imaging Taskforce in the AUC, and other clinical utility outcomes. Furthermore, we compared differences in post-positron emission tomography diagnosis and management change between "AUC-consistent" and "AUC-inconsistent" patients.

RESULTS

Almost half (250/507) of patients were AUC-consistent. In both AUC-consistent and AUC-inconsistent patients, post-positron emission tomography diagnosis (28%-21%) and management (32%-17%) change was substantial. The Amyloid Imaging Taskforce's definition of appropriate use occurred in 55/507 (13%) patients, detected by the AUC with a sensitivity of 93%, and a specificity of 56%. Diagnostic changes occurred independently of AUC status (sensitivity: 57%, specificity: 53%).

DISCUSSION

The current AUC are not sufficiently able to discriminate between patients who will benefit from amyloid positron emission tomography and those who will not.

PISCOM: a new procedure for epilepsy combining ictal SPECT and interictal PET

PURPOSE

We present a modified version of the SISCOM procedure that uses interictal PET instead of interictal SPECT for seizure onset zone localization. We called this new nuclear imaging processing technique PISCOM (PET interictal subtracted ictal SPECT coregistered with MRI).

METHODS

We retrospectively studied 23 patients (age range 4-61 years) with medically refractory epilepsy who had undergone MRI, ictal SPECT, interictal SPECT and interictal FDG PET and who had been seizure-free for at least 2 years after surgical treatment. FDG PET images were reprocessed (rFDG PET) to assimilate SPECT features for image subtraction. Interictal SPECT and rFDG PET were compared using statistical parametric mapping (SPM). PISCOM and SISCOM images were evaluated visually and using an automated volume of interest-based analysis. The results of the two studies were compared with each other and with the known surgical resection site.

RESULTS

SPM showed no significant differences in cortical activity between SPECT and rFDG PET images. PISCOM and SISCOM showed equivalent results in 17 of 23 patients (74%). The seizure onset zone was successfully identified in 19 patients (83%) by PISCOM and in 17 (74%) by SISCOM: in 15 patients (65%) the two techniques showed concordant successful results. The volume of interest-based analysis showed no significant differences between PISCOM and SISCOM in identifying the extension of the seizure onset zone. However, PISCOM showed a lower amount of indeterminate activity due to propagation, background or artefacts.

CONCLUSION

Preliminary findings of this initial proof-of-concept study suggest that perfusion and glucose metabolism in the cerebral cortex can be correlated and that PISCOM may be a valid technique for identification of the seizure onset zone. However, further studies are needed to validate these results.

Beta-amyloid imaging in dementia

Alzheimer's disease (AD) is a neurodegenerative disorder associated with extracellular plaques, composed of amyloid-beta (Aβ), in the brain. Although the precise mechanism underlying the neurotoxicity of Aβ has not been established, Aβ accumulation is the primary event in a cascade of events that lead to neurofibrillary degeneration and dementia. In particular, the Aβ burden, as assessed by neuroimaging, has proved to be an excellent predictive biomarker. Positron emission tomography, using ligands such as ¹¹C-labeled Pittsburgh Compound B or ¹⁸F-labeled tracers, such as ¹⁸F-florbetaben, ¹⁸F-florbetapir, and ¹⁸F-flutemetamol, which bind to Aβ deposits in the brain, has been a valuable technique for visualizing and quantifying the deposition of Aβ throughout the brain in living subjects. Aβ imaging has very high sensitivity for detecting AD pathology. In addition, it can predict the progression from mild cognitive impairment to AD, and contribute to the development of disease-specific therapies.

Small-molecule PET Tracers for Imaging Proteinopathies

In this chapter, we provide a review of the challenges and advances in developing successful PET imaging agents for 3 major types of aggregated amyloid proteins: amyloid-beta (Aβ), tau, and alpha-synuclein (α-syn). These 3 amyloids are involved in the pathogenesis of a variety of neurodegenerative diseases, referred to as proteinopathies or proteopathies, that include Alzheimer disease, Lewy body dementias, multiple system atrophy, and frontotemporal dementias, among others. In the Introduction section, we briefly discuss the history of amyloid in neurodegenerative diseases and describe why progress in developing effective imaging agents has been hampered by the failure of crystallography to provide definitive ligand-protein interactions for rational radioligand design efforts. Instead, the field has relied on largely serendipitous, trial-and-error methods to achieve useful and specific PET amyloid imaging tracers for Aβ, tau, and α-syn deposits. Because many of the proteopathies involve more than 1 amyloid protein, it is important to develop selective PET tracers for the different amyloids to help assess the relative contribution of each to total amyloid burden. We use Pittsburgh compound B to illustrate some of the critical steps in developing a potent and selective Aβ PET imaging agent. Other selective Aβ and tau PET imaging compounds have followed similar pathways in their developmental processes. Success for selective α-syn PET imaging agents has not been realized yet, but work is ongoing in multiple laboratories throughout the world. In the tau sections, we provide background regarding 3-repeat (3R) and 4-repeat (4R) tau proteins and how they can affect the binding of tau radioligands in different tauopathies. We review the ongoing efforts to assess the properties of tau ligands, which are useful in 3R, 4R, or combined 3R-4R tauopathies. Finally, we describe in the α-syn sections recent attempts to develop selective tracers to image α-synucleinopathies.