Amyloid PETs are commonly negative in suspected Alzheimer’s disease with an increase in CSF phosphorylated-tau protein concentration but an Aβ42 concentration in the very high range: a prospective study

Correlation Between Amyloid PET Imaging and Discordant Cerebrospinal Fluid Biomarkers Results in Patients with Suspected Alzheimer's Disease

BACKGROUND

Although the concordance between cerebrospinal fluid (CSF) Alzheimer's disease (AD) biomarkers and amyloid-PET findings is well known, there are no data regarding the concordance of amyloid-PET with inconclusive CSF values of amyloid-β (Aβ)1 - 42 and p-tau for the diagnosis of AD.

OBJECTIVE

To investigate the relationship between the amyloid-PET results with discordant AD biomarkers values in CSF (Aβ1 - 42+/p-tau-or Aβ1 - 42-/p-tau+).

METHODS

An observational retrospective study, including 62 patients with mild cognitive impairment (32/62) or dementia (30/62), suspicious of AD who had undergone a lumbar puncture to determine CSF AD biomarkers, and presented discordant values in CSF between Aβ1 - 42 and p-tau (Aβ1 - 42+/p-tau-or Aβ1 - 42-/p-tau+). All of them, underwent an amyloid-PET with 18F-Florbetaben. An extensive neuropsychological testing as part of their diagnostic process (MMSE and TMA-93), was performed, and it was also obtained the Global Deterioration Scale.

RESULTS

Comparing the discordant CSF results of each patient with the cerebral amyloid-PET results, we found that in the group with Aβ1 - 42+ and p-tau-CSF values, the amyloid-PET was positive in 51.2% and negative in 48.8% of patients, while in the group with Aβ1 - 42-and p-Tau+ CSF values, the amyloid-PET was positive in 52.6% of patients and negative in 47.4% of them. No significant association was found (p = 0.951) between the results of amyloid-PET and the two divergent groups in CSF.

CONCLUSIONS

No significant relationship was observed between the results of discordant AD biomarkers in CSF and the result of amyloid-PET. No trend in amyloid-PET results was observed in relation to CSF biomarker values.

Discordant Amyloid Status Diagnosis in Alzheimer’s Disease

Introduction: Early and accurate Alzheimer’s disease (AD) diagnosis has evolved in recent years by the use of specific methods for detecting its histopathological features in concrete cases. Currently, biomarkers in cerebrospinal fluid (CSF) and imaging techniques (amyloid PET) are the most used specific methods. However, some results between both methods are discrepant. Therefore, an evaluation of these discrepant cases is required. Objective: The aim of this work is to analyze the characteristics of cases showing discrepancies between methods for detecting amyloid pathology. Methodology: Patients from the Neurology Department of La Fe Hospital (n = 82) were diagnosed using both methods (CSF biomarkers and amyloid-PET). Statistical analyses were performed using logistic regression, and sex and age were included as covariables. Additionally, results of standard neuropsychological evaluations were taken into account in our analyses. Results: The comparison between CSF biomarker (Aβ42) and amyloid PET results showed that around 18% of cases were discrepant—mainly CFS-negative and PET-positive cases had CSF levels close to the cut-off point. In addition, a correlation between the episodic memory test and CSF biomarkers levels was observed. However, the same results were not obtained for other neuropsychological domains. In general, CSF- and PET-discrepant cases showed altered episodic memory in around 66% of cases, while 33% showed normal performance. Conclusions: In common clinical practice at tertiary memory centers, result discrepancies between tests of amyloid status are far more common than expected. However, episodic memory tests remain an important support method for AD diagnosis, especially in cases with discrepant results between amyloid PET and CSF biomarkers.

Plasma Amyloid Concentration in Alzheimer's Disease: Performance of a High-Throughput Amyloid Assay in Distinguishing Alzheimer's Disease Cases from Controls

Background:

Collection of cerebrospinal fluid (CSF) for measurement of amyloid-β (Aβ) species is a gold standard in Alzheimer’s disease (AD) diagnosis, but has risks. Thus, establishing a low-risk blood Aβ test with high AD sensitivity and specificity is of outmost interest.

Objective:

We evaluated the ability of a commercially available plasma Aβ assay to distinguish AD patients from biomarker-healthy controls.

Method:

In a case-control design, we examined plasma samples from 44 AD patients (A + N+) and 49 controls (A–N–) from a memory clinic. AD was diagnosed using a combination of neuropsychological examination, CSF biomarker analysis and brain imaging. Total Aβ₄₀ and total Aβ₄₂ in plasma were measured through enzyme-linked immunosorbent assay (ELISA) technology using ABtest40 and ABtest42 test kits (Araclon Biotech Ltd.). Receiver operating characteristic (ROC) analyses with outcome AD were performed, and sensitivity and specificity were calculated.

Results:

Plasma Aβ_42/40 was weakly positively correlated with CSF Aβ_42/40 (Spearman’s rho 0.22; p = 0.037). Plasma Aβ_42/40 alone was not able to statistically significantly distinguish between AD patients and controls (AUC 0.58; 95% CI 0.46, 0.70). At a cut-point of 0.076 maximizing sensitivity and specificity, plasma Aβ_42/40 had a sensitivity of 61.2% and a specificity of 63.6%.

Conclusion:

In this sample, the high-throughput blood Aβ assay was not able to distinguish well between AD patients and controls. Whether or not the assay may be useful in large-scale epidemiological settings remains to be seen.

Prognostic Impact of 18-F-Florbetaben Amyloid PET Imaging in Patients with Isolated Increases in Cerebrospinal Fluid Phospho-Tau Biomarkers: A Longitudinal Study

This longitudinal study evaluates the prognostic impact of amyloid PET in patients suspected of Alzheimer's disease and presenting with isolated cerebrospinal fluid (CSF) increases in P-Tau proteins (NCT02556502). The rate of conversion, based on the DSM-5 criteria and all collected data (average follow-up of 39.2±13.2 months), was determined by a panel of experts blinded to the PET results and was 75%(6/8) for positive and 35%(6/17) for negative baseline amyloid PET. In this population with isolated CSF increases in P-Tau, a positive baseline amyloid PET was associated with greater than twice the proportion of dementia conversions within the following three years.

Association between CSF Aβ42 and amyloid negativity in patients with different stage mild cognitive impairment

Whether the cerebrospinal fluid (CSF) biomarkers of amyloid-positive and amyloid-negative patients with mild cognitive impairment (MCI) or Alzheimer's disease (AD) are significantly different is still unknown. The purpose of this study is to compare the differences in CSF total tau, P-tau and Aβ42 in patients with amyloid-positive positron emission tomography (PET) and amyloid-negative PET, and to explore related risk factors in cognitive normal (CN), early MCI (EMCI), late MCI (LMCI) and AD. 558 participants (140 CN; 233 EMCI; 125 LMCI; 60 AD) were recruited in this study from the AD Neuroimaging Initiative (ADNI) database. The associations between CSF biomarkers were assessed by partial correlation analysis. The relations between significant variables were determined by multinomial logistic regression. Compared with amyloid-positive PET patients, patients with amyloid-negative PET had higher CSF Aβ42 and lower P-tau in the whole samples. The concentration of Aβ42 in the positive amyloid PET was significantly different in different groups, but not the negative amyloid PET (CN vs. LMCI; CN vs. AD; EMCI vs. AD, all P < 0.05). When amyloid PET was positive, a weak correlation was found between the levels of Aβ42 and P-tau only in CN group. However, a moderate degree of correlation between Aβ42 and P-tau was found in EMCI and LMCI when amyloid PET was negative. After covariates adjustment, CSF Aβ42 was significantly associated with EMCI [adjusted odds ratio (OR) = 0.99, 95 % confidence interval (CI) = 0.99-1.00, P = 0.02) and LMCI (adjusted OR = 0.99, 95 % CI = 0.99-1.00, P = 0.007)] in patients with negative amyloid PET, not in patients with positive amyloid PET. Our findings highlight that Aβ42 had strong correlations with other biomarkers and might help reduce risk of EMCI or LMCI in patients with amyloid negativity.

Clinical impact of digital and conventional PET control databases for semi-quantitative analysis of brain 18F-FDG digital PET scans

PURPOSE

Digital PET cameras markedly improve sensitivity and spatial resolution of brain ¹⁸F-FDG PET images compared to conventional cameras. Our study aimed to assess whether specific control databases are required to improve the diagnostic performance of these recent advances.

METHODS

We retrospectively selected two groups of subjects, twenty-seven Alzheimer's Disease (AD) patients and twenty-two healthy control (HC) subjects. All subjects underwent a brain ¹⁸F-FDG PET on a digital camera (Vereos, Philips®). These two group (AD and HC) are compared, using a Semi-Quantitative Analysis (SQA), to two age and sex matched controls acquired with a digital PET/CT (Vereos, Philips®) or a conventional PET/CT (Biograph 6, Siemens®) camera, at group and individual levels. Moreover, individual visual interpretation of SPM T-maps was provided for the positive diagnosis of AD by 3 experienced raters.

RESULTS

At group level, SQA using digital controls detected more marked hypometabolic areas in AD (+ 116 cm³ at p < 0.001 uncorrected for the voxel, corrected for the cluster) than SQA using conventional controls. At the individual level, the accuracy of SQA for discriminating AD using digital controls was higher than SQA using conventional controls (86% vs. 80%, p < 0.01, at p < 0.005 uncorrected for the voxel, corrected for the cluster), with higher sensitivity (89% vs. 78%) and similar specificity (82% vs. 82%). These results were confirmed by visual analysis (accuracies of 84% and 82% for digital and conventional controls respectively, p = 0.01).

CONCLUSION

There is an urgent need to establish specific digital PET control databases for SQA of brain ¹⁸F-FDG PET images as such databases improve the accuracy of AD diagnosis.