Association between FDG uptake, CSF biomarkers and cognitive performance in patients with probable Alzheimer's disease

Multi-modal cross-attention network for Alzheimer's disease diagnosis with multi-modality data

Alzheimer's disease (AD) is a neurodegenerative disorder, the most common cause of dementia, so the accurate diagnosis of AD and its prodromal stage mild cognitive impairment (MCI) is significant. Recent studies have demonstrated that multiple neuroimaging and biological measures contain complementary information for diagnosis. Many existing multi-modal models based on deep learning simply concatenate each modality's features despite substantial differences in representation spaces. In this paper, we propose a novel multi-modal cross-attention AD diagnosis (MCAD) framework to learn the interaction between modalities for better playing their complementary roles for AD diagnosis with multi-modal data including structural magnetic resonance imaging (sMRI), fluorodeoxyglucose-positron emission tomography (FDG-PET) and cerebrospinal fluid (CSF) biomarkers. Specifically, the imaging and non-imaging representations are learned by the image encoder based on cascaded dilated convolutions and CSF encoder, respectively. Then, a multi-modal interaction module is introduced, which takes advantage of cross-modal attention to integrate imaging and non-imaging information and reinforce relationships between these modalities. Moreover, an extensive objective function is designed to reduce the discrepancy between modalities for effectively fusing the features of multi-modal data, which could further improve the diagnosis performance. We evaluate the effectiveness of our proposed method on the ADNI dataset, and the extensive experiments demonstrate that our MCAD achieves superior performance for multiple AD-related classification tasks, compared to several competing methods. Also, we investigate the importance of cross-attention and the contribution of each modality to the diagnostics performance. The experimental results demonstrate that combining multi-modality data via cross-attention is helpful for accurate AD diagnosis.

24S-Hydroxycholesterol Is Associated with Agitation Severity in Patients with Moderate-to-Severe Alzheimer's Disease: Analyses from a Clinical Trial with Nabilone

Background:

Agitation is a prevalent and difficult-to-treat symptom of Alzheimer’s disease (AD). The endocannabinoid system (ECS) has been a target of interest for the treatment of agitation. However, ECS signaling may interact with AD-related changes in brain cholesterol metabolism. Elevated brain cholesterol, reflected by reduced serum 24-S-hydroxycholesterol (24S-OHC), is associated with reduced membrane fluidity, preventing ligand binding to cannabinoid receptor 1.

Objective:

To assess whether 24S-OHC was associated with agitation severity and response to nabilone.

Methods:

24S-OHC was collected from AD patients enrolled in a clinical trial on nabilone at the start and end of each phase. This allowed for the cross-sectional and longitudinal investigation between 24S-OHC and agitation (Cohen Mansfield Agitation Inventory, CMAI). Post-hoc analyses included adjustments for baseline standardized Mini-Mental Status Exam (sMMSE), and analyses with CMAI subtotals consistent with the International Psychogeriatric Association (IPA) definition for agitation (physical aggression and nonaggression, and verbal aggression).

Results:

24S-OHC was not associated with CMAI scores cross-sectionally or longitudinally, before and after adjusting for baseline sMMSE. However, 24S-OHC was associated with greater CMAI IPA scores at baseline (F(1,36) = 4.95, p = 0.03). In the placebo phase only, lower 24S-OHC at baseline was associated with increases in CMAI IPA scores (b = –35.2, 95% CI –65.6 to –5.0, p = 0.02), and decreases in 24S-OHC were associated with increases in CMAI IPA scores (b = –20.94, 95% CI –57.9 to –4.01, p = 0.03).

Conclusion:

24S-OHC was associated with agitation severity cross-sectionally, and longitudinally in patients with AD. However, 24S-OHC did not predict treatment response, and does not change over time with nabilone.

Hybrid imaging in dementia: A semi-quantitative (18F)-fluorodeoxyglucose positron emission tomography/magnetic resonance imaging approach in clinical practice

Neurodegenerative disorders may demonstrate typical lobar and regional patterns of volume loss with corresponding decreased glucose metabolism. In this retrospective study, we correlated semi-quantitative volumetric changes utilizing NeuroQuant morphometric analysis with decreased fluorodeoxyglucose (FDG) uptake age-matched calculated z-scores utilizing ¹⁸F-FDG positron emission tomography/magnetic resonance imaging (PET/MRI). Eighty-nine patients (mean age 71.4) with clinical findings suggestive of various subtypes of dementia underwent PET/MR brain imaging. Cases were categorized as follows: Alzheimer's dementia (AD), frontotemporal lobar degeneration (FTLD), dementia with Lewy bodies (DLB), and corticobasal degeneration (CBD). NeuroQuant software provided semi-quantitative assessment of lobar-specific patterns of volume loss compared to age-matched controls. MIMneuro software provided semi-quantitative FDG uptake data, with metabolic z-scores generated in comparison to age-matched controls. Volumetric and metabolic data were then correlated for statistical significance. In 29 AD cases, Pearson correlation coefficient between z-score and lobar volume was 0.3 (P = 0.120) and 0.38 (P < 0.05), for parietal and temporal lobes, respectively. In 34 FTLD cases, it was 0.35 (P = 0.051) and 0.02 (P = 0.916), for frontal and temporal lobes, respectively. In 14 DLB cases, it was 0.42 (P = 0.130), 0.5 (P = 0.067), and 0.22 (P = 0.447) for the occipital lobes, middle occipital gyrus, and parietal lobes, respectively. In 12 CBD cases, it was 0.58 (P < 0.05) for the superior parietal lobule. Semi-quantitative (F18)-FDG PET/MRI analysis demonstrated a positive relationship between volumetric loss and hypometabolism within certain lobar-specific regions, depending on neurodegenerative disorder subtype. Our findings may add diagnostic confidence in the accurate imaging diagnosis of neurodegenerative disease.

The relationship between CSF biomarkers and cerebral metabolism in early-onset Alzheimer's disease

PURPOSE

One can reasonably suppose that cerebrospinal spinal fluid (CSF) biomarkers can identify distinct subgroups of Alzheimer's disease (AD) patients. In order to better understand differences in CSF biomarker patterns, we used FDG PET to assess cerebral metabolism in CSF-based subgroups of AD patients.

METHODS

Eighty-five patients fulfilling the criteria for probable early-onset AD (EOAD) underwent lumbar puncture, brain ¹⁸F-FDG PET and MRI. A cluster analysis was performed, with the CSF biomarkers for AD as variables. Vertex-wise, partial-volume-corrected metabolic maps were computed for the patients and compared between the clusters of patients. Linear correlations between each CSF biomarker and the metabolic maps were assessed.

RESULTS

Three clusters emerged. The "Aβ42" cluster contained 32 patients with low levels of Aβ42, while tau and p-tau remained within the normal range. The "Aβ42 + tau" cluster contained 41 patients with low levels of Aβ42 and high levels of tau and p-tau. Lastly, the "tau" cluster contained 12 patients with very high levels of tau and p-tau and low-normal levels of Aβ42. There were no inter-cluster differences in age, sex ratio, educational level, APOE genotype, disease duration or disease severity. The "Aβ42 + tau" and "tau" clusters displayed more marked frontal hypometabolism than the "Aβ42" cluster did, and frontal metabolism was significantly negatively correlated with the CSF tau level. The "Aβ42" and "Aβ42 + tau" clusters displayed more marked hypometabolism in the left occipitotemporal region than the "tau" cluster did, and metabolism in this region was significantly and positively correlated with the CSF Aβ42 level.

CONCLUSION

The CSF biomarkers can be used to identify metabolically distinct subgroups of patients with EOAD. Future research should seek to establish whether these biochemical differences have clinical consequences.

[The importance of molecular imaging (PET) in the diagnostics of dementia]

Due to the expanding older population and increasing prevalence of dementia and currently lacking curative therapy but potentially conceivable availability of molecular-specific treatment to delay the progression of cognitive decline, the early diagnosis of cognitive deficits and their etiological differential diagnosis becomes increasingly more important. The advances in nuclear medicine diagnostics in the field of neurodegenerative diseases within the last few years have been substantial. In this article the relevance of these technologies in the diagnostic process of dementia is described.

Current Role for Biomarkers in Clinical Diagnosis of Alzheimer Disease and Frontotemporal Dementia

Purpose of review Alzheimer's disease (AD) and frontotemporal dementia can often be diagnosed accurately with careful clinical history, cognitive testing, neurological examination, and structural brain MRI. However, there are certain circumstances wherein detection of specific biomarkers of neurodegeneration or underlying AD pathology will impact the clinical diagnosis or treatment plan. We will review the currently available biomarkers for AD and frontotemporal dementia (FTD) and discuss their clinical importance. Recent findings With the advent of ¹⁸F-labeled tracers that bind amyloid plaques, amyloid PET is now clinically available for the detection of amyloid pathology and to aid in a biomarker-supported diagnosis of AD or mild cognitive impairment (MCI) due to AD. It is not yet possible to test for the specific FTD pathologies (tau or TDP-43); however, a diagnosis of FTD may be "imaging supported" based upon specific MRI or FDG-PET findings. Cerebrospinal fluid measures of amyloid-beta, total-tau, and phospho-tau are clinically available and allow detection of both of the cardinal pathologies of AD: amyloid and tau pathology. Summary It is appropriate to pursue biomarker testing in cases of MCI and dementia when there remains diagnostic uncertainty and the result will impact diagnosis or treatment. Practically speaking, due to the rising prevalence of amyloid positivity with advancing age, measurement of biomarkers in cases of MCI and dementia is most helpful in early-onset patients, patients with atypical clinical presentations, or when considering referral for AD clinical trials.

Imaging Biomarkers in Alzheimer's Disease: A Practical Guide for Clinicians

Although recent developments in imaging biomarkers have revolutionized the diagnosis of Alzheimer’s disease at early stages, the utility of most of these techniques in clinical setting remains unclear. The aim of this review is to provide a clear stepwise algorithm on using multitier imaging biomarkers for the diagnosis of Alzheimer’s disease to be used by clinicians and radiologists for day-to-day practice. We summarized the role of most common imaging techniques and their appropriate clinical use based on current consensus guidelines and recommendations with brief sections on acquisition and analysis techniques for each imaging modality. Structural imaging, preferably MRI or alternatively high resolution CT, is the essential first tier of imaging. It improves the accuracy of clinical diagnosis and excludes other potential pathologies. When the results of clinical examination and structural imaging, assessed by dementia expert, are still inconclusive, functional imaging can be used as a more advanced option. PET with ligands such as amyloid tracers and ¹⁸F-fluorodeoxyglucose can improve the sensitivity and specificity of diagnosis particularly at the early stages of the disease. There are, however, limitations in using these techniques in wider community due to a combination of lack of facilities and expertise to interpret the findings. The role of some of the more recent imaging techniques including tau imaging, functional MRI, or diffusion tensor imaging in clinical practice, remains to be established in the ongoing and future studies.

Concordance between brain 18F-FDG PET and cerebrospinal fluid biomarkers in diagnosing Alzheimer's disease

OBJECTIVES

Cortical posterior hypometabolism on PET imaging with ¹⁸F-FDG (FDG-PET), and altered levels of Aß_1-42 peptide, total Tau (tTau) and phosphorylated Tau (pTau) proteins in cerebrospinal fluid (CSF) are established diagnostic biomarkers in Alzheimer's disease (AD). An evaluation has been made of the concordance and relationship between the results of FDG-PET and CSF biomarkers in symptomatic patients with suspected AD.

MATERIAL AND METHODS

A retrospective review was carried out on 120 patients with cognitive impairment referred to our Cognitive Neurology Unit, and who were evaluated by brain FDG-PET and a lumbar puncture for CSF biomarkers. In order to calculate their Kappa coefficient of concordance, the result of the FDG-PET and the set of the three CSF biomarkers in each patient was classified as normal, inconclusive, or AD-compatible. The relationship between the results of both methods was further assessed using logistic regression analysis, including the Aß_1-42, tTau and pTau levels as quantitative predictors, and the FDG-PET result as the dependent variable.

RESULTS

The weighted Kappa coefficient between FDG-PET and CSF biomarkers was 0.46 (95% CI: 0.35-0.57). Logistic regression analysis showed that the Aß_1-42 and tTau values together were capable of discriminating an FDG-PET result metabolically suggestive of AD from one non-suggestive of AD, with a 91% sensitivity and 93% specificity at the cut-off line Aß_1-42=44+1.3×tTau.

CONCLUSIONS

The level of concordance between FDG-PET and CSF biomarkers was moderate, indicating their complementary value in diagnosing AD. The Aß_1-42 and tTau levels in CSF help to predict the patient FDG-PET cortical metabolic status.

What are the Most Frequently Impaired Markers of Neurodegeneration in ADNI Subjects?

The aim of this study was to examine the relationship between cerebrospinal fluid (CSF) levels of biomarkers for Alzheimer's disease (AD) (Aβ1-42, t-tau, and p-tau) and 18Fluorodeoxyglucose positron emission tomography (FDG-PET) hypometabolism in subjects from the Alzheimer's Disease Neuroimaging Initiative, and specifically to determine which index of neurodegeneration was most frequently affected. The secondary objective was to determine the most frequently hypometabolic region in patients with a CSF AD signature (abnormal Aβ1-42 and abnormal p-tau). We included the 372 subjects (85 normal subjects, 212 patients with mild cognitive impairment, and 75 patients with AD) with a CSF biomarker dosage (Aβ1-42, t-tau, and p-tau) and brain FDG-PET. The relationship between FDG-PET metabolism (in five regions of interest (ROI) known to be damaged in AD) and CSF t-tau and p-tau levels was studied as a function of CSF Aβ1-42 status. FDG-PET hypometabolism and CSF t-tau and p-tau levels were correlated only in patients with an abnormal CSF Aβ1-42 level (t-tau: R2 = 0.044, p = 0.001; p-tau: R2 = 0.02, p = 0.03). In the latter patients, CSF p-tau was the most frequently (p = 0.0001) abnormal neurodegeneration marker (p-tau: 92.8%; FDG-PET: 56.5%; CSF t-tau: 59.1%). Within the five ROI of FDG PET, the angular gyrus metabolism (R2 = 0.149; p = 0.0001) was selected as the most tightly associated with CSF AD signature. The relation between CSF markers of neurodegeneration (p-tau and t-tau) and brain hypometabolism (in FDG-PET) is conditioned by presence of amyloid abnormality. This finding supports the current physiopathological model of AD. P-tau is the most frequently impaired biomarker. Using FDG PET angular gyrus hypometabolism is the most sensitive to CSF-biomarker-defined AD.

CSF Biomarkers and Its Associations with 18F-AV133 Cerebral VMAT2 Binding in Parkinson's Disease-A Preliminary Report

OBJECTIVE

Cerebrospinal fluid (CSF) biomarkers, such as α-synuclein (α-syn), amyloid beta peptide 1-42 (Aβ1-42), phosphorylated tau (181P) (p-tau), and total tau (t-tau), have long been associated with the development of Parkinson disease (PD) and other neurodegenerative diseases. In this investigation, we reported the assessment of CSF biomarkers and their correlations with vesicular monoamine transporter 2 (VMAT2) bindings measured with 18F-9-fluoropropyl-(+)-dihydrotetrabenazine (18F-AV133) that is being developed as a biomarker for PD. We test the hypothesis that monoaminergic degeneration was correlated with CSF biomarker levels in untreated PD patients.

METHODS

The available online data from the Parkinson's Progression Markers Initiative study (PPMI) project were collected and analyzed, which include demographic information, clinical evaluations, CSF biomarkers (α-syn, Aβ1-42, p-tau, and t-tau), 18F-AV133 brain PET, and T1 weighted MRIs. Region of interest (ROI) and voxel-wise Pearson correlation between standardized uptake value ratio (SUVR) and CSF biomarkers were calculated.

RESULTS

Our major findings are: 1) Compared with controls, CSF α-syn and tau levels decreased significantly in PD; 2) α-syn was closely correlated with Aβ1-42 and tau in PD, especially in early-onset patients; and 3) hypothesis-driven ROI analysis found a significant negative correlation between CSF Aβ1-42 levels and VMAT2 densities in post cingulate, left caudate, left anterior putamen, and left ventral striatum in PDs. CSF t-tau and p-tau levels were significantly negatively related to VMAT2 SUVRs in substantia nigra and left ventral striatum, respectively. Voxel-wise analysis showed that left caudate, parahippocampal gyrus, insula and temporal lobe were negatively correlated with Aβ1-42. In addition, superior frontal gyrus and transverse temporal gyrus were negatively correlated with CSF p-tau levels.

CONCLUSION

These results suggest that monoaminergic degeneration in PD is correlated with CSF biomarkers associated with cognitive impairment in neurodegenerative diseases including Alzheimer's disease. The association between loss of dopamine synaptic function and pathologic protein accumulations in PD indicates an important role of CSF biomarkers in PD development.

Longitudinal Partial Volume Correction in 2-[18F]-Fluoro-2-Deoxy-D-Glucose Positron Emission Tomography Studies of Alzheimer Disease

OBJECTIVE

To investigate partial volume correction (PVC) of 2-[F]-fluoro-2-deoxy-D-glucose positron emission tomography in Alzheimer disease in a longitudinal context.

METHODS

A total of 115 participants were included, including 55 controls, 53 patients with mild cognitive impairment, and 7 patients with dementia of the Alzheimer type. Imaging was performed at baseline and 24 months. Partial volume corrected vs uncorrected rates of longitudinal change were compared for mesial temporal and cortical regions of interest.

RESULTS

Partial volume correction increased apparent uptake, and this effect was greater at 24 months compared with baseline. Partial volume correction decreased the rate of decline, causing an apparent increase in uptake at 24 months compared with baseline. This effect was correlated with the structural atrophy.

CONCLUSIONS

These findings suggest that applying PVC in a longitudinal context in Alzheimer disease might produce unpredictable results. Accordingly, both PVC corrected and uncorrected data should be reported to ensure that the results are physiologically plausible.

The mediational effects of FDG hypometabolism on the association between cerebrospinal fluid biomarkers and neurocognitive function

Positive cerebrospinal fluid (CSF) biomarkers of tau and amyloid beta42 suggest possible active underlying Alzheimer's disease (AD) including neurometabolic dysfunction and neurodegeneration leading to eventual cognitive decline. But the temporal relationship between CSF, imaging markers of neural function, and cognition has not been described. Using a statistical mediation model, we examined relationships between cerebrospinal fluid (CSF) analytes (hyperphosphorylated tau (p-Tau(181p)), β-amyloid peptides 1-42 (Aβ(1-42)), total tau (t-Tau), and their ratios); change in cognitive function; and change in [18F]fluorodeoxyglucose (FDG) uptake using positron emission tomography (PET). We hypothesized that a) abnormal CSF protein values at baseline, result in cognitive declines by decreasing neuronal glucose metabolism across time, and b) the role of altered glucose metabolism in the assumed causal chain varies by brain region and the nature of CSF protein alteration. Data from 412 individuals participating in Alzheimer's Disease Neuroimaging (ADNI) cohort studies were included in analyses. At baseline, individuals were cognitively normal (N = 82), or impaired: 241 with mild cognitive impairment, and 89 with Alzheimer's disease. A parallel-process latent growth curve model was used to test mediational effects of changes in regional FDG-PET uptake over time in relation to baseline CSF biomarkers and changes in cognition, measured with the 13-item Alzheimer Disease's Assessment Scale-cognitive subscale (ADAS-Cog). Findings suggested a causal sequence of events; specifically, FDG hypometabolism acted as a mediator between antecedent CSF biomarker alterations and subsequent cognitive impairment. Higher baseline concentrations of t-Tau, and p-Tau(181p) were more predictive of decline in cerebral glucose metabolism than lower baseline concentrations of Aβ(1-42). FDG-PET changes appeared to mediate t-Tau or t-Tau/Aβ(1-42)-associated cognitive change across all brain regions examined. Significant direct effects of alterations in Aβ(1-42) levels on hypometabolism were observed in a single brain region: middle/inferior temporal gyrus. Results support a temporal framework model in which reduced CSF amyloid-related biomarkers occur earlier in the pathogenic pathway, ultimately leading to detrimental cognitive effects. Also consistent with this temporal framework model, baseline markers of neurofibrillary degeneration predicted changes in brain glucose metabolism in turn causing longitudinal cognitive changes, suggesting that tau-related burden precedes neurometabolic dysfunction. While intriguing, the hypothesized mediational relationships require further validation.

Memory loss in Alzheimer's disease

Loss of memory is among the first symptoms reported by patients suffering from Alzheimer's disease (AD) and by their caretakers. Working memory and long-term declarative memory are affected early during the course of the disease. The individual pattern of impaired memory functions correlates with parameters of structural or functional brain integrity. AD pathology interferes with the formation of memories from the molecular level to the framework of neural networks. The investigation of AD memory loss helps to identify the involved neural structures, such as the default mode network, the influence of epigenetic and genetic factors, such as ApoE4 status, and evolutionary aspects of human cognition. Clinically, the analysis of memory assists the definition of AD subtypes, disease grading, and prognostic predictions. Despite new AD criteria that allow the earlier diagnosis of the disease by inclusion of biomarkers derived from cerebrospinal fluid or hippocampal volume analysis, neuropsychological testing remains at the core of AD diagnosis.

Neuroimaging in dementia

Over the last few years, advances in neuroimaging have generated biomarkers, which increase diagnostic certainty, provide valuable information about prognosis, and suggest a particular pathology underlying the clinical dementia syndrome. We aim to review the evidence for use of already established imaging modalities, along with selected techniques that have a great potential to guide clinical decisions in the future. We discuss structural, functional and molecular imaging, focusing on the most common dementias: Alzheimer's disease, fronto-temporal dementia, dementia with Lewy bodies and vascular dementia. Finally, we stress the importance of conducting research using representative cohorts and in a naturalistic set up, in order to build a strong evidence base for translating imaging methods for a National Health Service. If we assess a broad range of patients referred to memory clinic with a variety of imaging modalities, we will make a step towards accumulating robust evidence and ultimately closing the gap between the dramatic advances in neurosciences and meaningful clinical applications for the maximum benefit of our patients.

Fluid biomarkers for diagnosing dementia: rationale and the Canadian Consensus on Diagnosis and Treatment of Dementia recommendations for Canadian physicians

Fluid biomarkers improve the diagnostic accuracy in dementia and provide an objective measure potentially useful as a therapeutic response in clinical trials. The role of fluid biomarkers in patient care is a rapidly evolving field. Here, we provide a review and recommendations regarding the use of fluid biomarkers in clinical practice as discussed at the Fourth Canadian Consensus Conference on the Diagnosis and Treatment of Dementia (CCCDTD4) convened in Montreal, 4 to 5 May 2012. At present, there is no consensus regarding the optimal methodology for conducting quantification of plasma amyloid-beta (Aβ) peptides. In addition, since there is insufficient evidence supporting clinical applications for plasma Aβ-peptide measures, the CCCDTD4 does not recommended plasma biomarkers either for primary care or for specialists. Evidence for CSF Aβ1-42, total tau and phosphorylated tau in the diagnosis of Alzheimer pathology is much stronger, and can be considered at the tertiary care level for selected cases to improve diagnostic certainty, particularly in those cases presenting atypical clinical features.

PET/CT in diagnosis of dementia

Clinical use of positron emission tomography (PET) is now well established in neurodegenerative disorders, especially in the diagnosis of dementia. Measurement of cerebral glucose metabolism is of significant value, and it facilitates early diagnosis, appropriate differential diagnosis, and the evaluation of drug treatment in patients with dementia. In addition, tracers offer new perspectives for studying the neuropathology of underlying dementia, such as the accumulation of amyloid proteins, tau-proteins, or the presence of neuroinflammation. Finally, PET tracer studies of different neurotransmitter systems in dementia may not only increase the understanding of pathophysiologic mechanisms of the different disorders, but also improve diagnostic accuracy. In conclusion, PET imaging with different tracers offers reliable biomarkers in dementia, which can assist clinicians in the diagnosis of different dementing disorders, especially in the situation of overlapping phenotypes.