Diagnosing Dementia in the Clinical Setting: Can Amyloid PET Provide Additional Value Over Cerebrospinal Fluid?

Brain Amyloid in Sporadic Young Onset Alzheimer’s Disease

Background: Controversy exists as to the role of the amyloid-β (Aβ) peptide in the pathophysiology of Alzheimer’s disease (AD). Objective: To clarify the effect of age on Aβ deposition in sporadic AD by exploring the degree of amyloid burden in patients with sporadic young onset AD (YOAD). Methods: Patients were diagnosed with YOAD with dementia starting before the age of 65 years (N = 42; males = 20, females = 22). A cross-sectional analysis of amyloid binding using positron emission tomography (PET) imaging was performed using the C-Pittsburgh Compound B (PiB). The global standardized uptake value ratios (gSUVR) were examined using the Wilcoxon two-sample test, as were the cognitive scores between disease and healthy control populations. Differences in PiB retention in different anatomical areas were compared using the Kruskal-Wallis test. The contrast in APOE genotyping between groups was calculated with Fisher’s Exact Test. Results: Women had a median gSUVR = 2.68±0.73 and 73% had at least one APOE ɛ4 allele. Men had gSUVR = 2.37±0.54, with 80% having at least one APOE ɛ4 allele. The gSUVRs were significantly higher than the control populations for men and women and had significantly greater frequency of APOE ɛ4. Men and women analyzed together had significantly greater amyloid burden and APOE ɛ4 allele frequencies than controls, but no differences existed between them in gSUVR nor in the anatomical distribution of amyloid uptake. Conclusion: Men and women with YOAD have greater amyloid uptake than controls and have more APOE ɛ4 alleles. Our findings suggest that the Aβ peptide is operational in young onset dementia and driven by the APOE ɛ4 allele.

Clinical impact of amyloid PET using 18F-florbetapir in patients with cognitive impairment and suspected Alzheimer's disease: a multicenter study

OBJECTIVE

Amyloid positron emission tomography (PET) can reliably detect senile plaques and fluorinated ligands are approved for clinical use. However, the clinical impact of amyloid PET imaging is still under investigation. The aim of this study was to evaluate the diagnostic impact and clinical utility in patient management of amyloid PET using ¹⁸F-florbetapir in patients with cognitive impairment and suspected Alzheimer's disease (AD). We also aimed to determine the cutoffs for amyloid positivity for quantitative measures by investigating the agreement between quantitative and visual assessments.

METHODS

Ninety-nine patients suspected of having AD underwent ¹⁸F-florbetapir PET at five institutions. Site-specialized physicians provided a diagnosis of AD or non-AD with a percentage estimate of their confidence and their plan for patient management in terms of medication, prescription dosage, additional diagnostic tests, and care planning both before and after receiving the amyloid imaging results. A PET image for each patient was visually assessed and dichotomously rated as either amyloid-positive or amyloid-negative by four board-certified nuclear medicine physicians. The PET images were also quantitatively analyzed using the standardized uptake value ratio (SUVR) and Centiloid (CL) scale.

RESULTS

Visual interpretation obtained 48 positive and 51 negative PET scans. The amyloid PET results changed the AD and non-AD diagnosis in 39 of 99 patients (39.3%). The change rates of 26 of the 54 patients (48.1%) with a pre-scan AD diagnosis were significantly higher than those of 13 of the 45 patients with a pre-scan non-AD diagnosis (χ² = 5.334, p = 0.0209). Amyloid PET results also resulted in at least one change to the patient management plan in 42 patients (42%), mainly medication (20 patients, 20%) and care planning (25 patients, 25%). Receiver-operating characteristic analysis determined the best agreement of the quantitative assessments and visual interpretation of PET scans to have an area under the curve of 0.993 at an SUVR of 1.19 and CL of 25.9.

CONCLUSION

Amyloid PET using ¹⁸F-florbetapir PET had a substantial clinical impact on AD and non-AD diagnosis and on patient management by enhancing diagnostic confidence. In addition, the quantitative measures may improve the visual interpretation of amyloid positivity.

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.

Outcomes of clinical utility in amyloid-PET studies: state of art and future perspectives

PURPOSE

To review how outcomes of clinical utility are operationalized in current amyloid-PET validation studies, to prepare for formal assessment of clinical utility of amyloid-PET-based diagnosis.

METHODS

Systematic review of amyloid-PET research studies published up to April 2020 that included outcomes of clinical utility. We extracted and analyzed (a) outcome categories, (b) their definition, and (c) their methods of assessment.

RESULTS

Thirty-two studies were eligible. (a) Outcome categories were clinician-centered (found in 25/32 studies, 78%), patient-/caregiver-centered (in 9/32 studies, 28%), and health economics-centered (5/32, 16%). (b) Definition: Outcomes were mainly defined by clinical researchers; only the ABIDE study expressly included stakeholders in group discussions. Clinician-centered outcomes mainly consisted of incremental diagnostic value (25/32, 78%) and change in patient management (17/32, 53%); patient-/caregiver-centered outcomes considered distress after amyloid-pet-based diagnosis disclosure (8/32, 25%), including quantified burden of procedure for patients' outcomes (n = 8) (1/8, 12.5%), impact of disclosure of results (6/8, 75%), and psychological implications of biomarker-based diagnosis (75%); and health economics outcomes focused on costs to achieve a high-confidence etiological diagnosis (5/32, 16%) and impact on quality of life (1/32, 3%). (c) Assessment: all outcome categories were operationalized inconsistently across studies, employing 26 different tools without formal rationale for selection.

CONCLUSION

Current studies validating amyloid-PET already assessed outcomes for clinical utility, although non-clinician-based outcomes were inconsistent. A wider participation of stakeholders may help produce a more thorough and systematic definition and assessment of outcomes of clinical utility and help collect evidence informing decisions on reimbursement of amyloid-PET.

Matching Clinical Diagnosis and Amyloid Biomarkers in Alzheimer's Disease and Frontotemporal Dementia

BACKGROUND

The aims of this study were to compare the diagnostic accuracy, sensitivity, specificity, and positive and negative predictive values (PPV, NPV) of different cerebrospinal fluid (CSF) amyloid biomarkers and amyloid-Positron Emission Tomography (PET) in patients with a clinical diagnosis of Alzheimer's disease (AD) and Frontotemporal Dementia (FTD); to compare concordance between biomarkers; and to provide an indication of their use and interpretation.

METHODS

We included 148 patients (95 AD and 53 FTD), who underwent clinical evaluation, neuropsychological assessment, and at least one amyloid biomarker (CSF analysis or amyloid-PET). Thirty-six patients underwent both analyses. One-hundred-thirteen patients underwent Apolipoprotein E (ApoE) genotyping.

RESULTS

Amyloid-PET presented higher diagnostic accuracy, sensitivity, and NPV than CSF Aβ_1-42 but not Aβ_42/40 ratio. Concordance between CSF biomarkers and amyloid-PET was higher in FTD patients compared to AD cases. None of the AD patients presented both negative Aβ biomarkers.

CONCLUSIONS

CSF Aβ_42/40 ratio significantly increased the diagnostic accuracy of CSF biomarkers. On the basis of our current and previous data, we suggest a flowchart to guide the use of biomarkers according to clinical suspicion: due to the high PPV of both amyloid-PET and CSF analysis including Aβ_42/40, in cases of concordance between at least one biomarker and clinical diagnosis, performance of the other analysis could be avoided. A combination of both biomarkers should be performed to better characterize unclear cases. If the two amyloid biomarkers are both negative, an underlying AD pathology can most probably be excluded.

Reciprocal Incremental Value of 18F-FDG-PET and Cerebrospinal Fluid Biomarkers in Mild Cognitive Impairment Patients Suspected for Alzheimer's Disease and Inconclusive First Biomarker

BACKGROUND

In Alzheimer's disease (AD) diagnosis, both cerebrospinal fluid (CSF) biomarkers and FDG-PET sometimes give inconclusive results.

OBJECTIVE

To evaluate the incremental diagnostic value of FDG-PET over CSF biomarkers, and vice versa, in patients with mild cognitive impairment (MCI) and suspected AD, in which the first biomarker resulted inconclusive.

METHODS

A consecutive series of MCI patients was retrospectively selected from two Memory Clinics where, as per clinical routine, either the first biomarker choice is FDG-PET and CSF biomarkers are only used in patients with uninformative FDG-PET, or vice versa. We defined criteria of uncertainty in interpretation of FDG-PET and CSF biomarkers, according to current evidence. The final diagnosis was established according to clinical-neuropsychological follow-up of at least one year (mean 4.4±2.2).

RESULTS

When CSF was used as second biomarker after FDG-PET, 14 out of 36 (39%) received informative results. Among these 14 patients, 11 (79%) were correctly classified with respect to final diagnosis, thus with a relative incremental value of CSF over FDG-PET of 30.6%. When FDG-PET was used as second biomarker, 26 out of 39 (67%) received informative results. Among these 26 patients, 15 (58%) were correctly classified by FDG-PET with respect to final diagnosis, thus with a relative incremental value over CSF of 38.5%.

CONCLUSION

Our real-world data confirm the added values of FDG-PET (or CSF) in a diagnostic pathway where CSF (or FDG-PET) was used as first biomarkers in suspected AD. These findings should be replicated in larger studies with prospective enrolment according to a Phase III design.

Amyloid PET imaging in clinical practice

Amyloid positron emission tomography (PET) imaging enables in vivo detection of brain Aβ deposition, one of the neuropathological hallmarks of Alzheimer's disease. There is increasing evidence to support its clinical utility, with major studies showing that amyloid PET imaging improves diagnostic accuracy, increases diagnostic certainty and results in therapeutic changes. The Amyloid Imaging Taskforce has developed appropriate use criteria to guide clinicians by predefining certain scenarios where amyloid PET would be justified. This review provides a practical guide on how and when to use amyloid PET, based on the available research and our own experience. We discuss its three main appropriate indications and illustrate these with clinical cases. We stress the importance of a multidisciplinary approach when deciding who might benefit from amyloid PET imaging. Finally, we highlight some practical points and common pitfalls in its interpretation.

Why Is Amyloid-β PET Requested After Performing CSF Biomarkers?

BACKGROUND

Amyloid-β positron emission tomography (PET) and cerebrospinal fluid (CSF) Aβ42 are considered interchangeable for clinical diagnosis of Alzheimer's disease.

OBJECTIVE

To explore the clinical reasoning for requesting additional amyloid-β PET after performing CSF biomarkers.

METHODS

We retrospectively identified 72 memory clinic patients who underwent amyloid-β PET after CSF biomarkers analysis for clinical diagnostic evaluation between 2011 and 2019. We performed patient chart reviews to identify factors which led to additional amyloid-β PET. Additionally, we assessed accordance with appropriate-use-criteria (AUC) for amyloid-β PET.

RESULTS

Mean patient age was 62.0 (SD = 8.1) and mean Mini-Mental State Exam score was 23.6 (SD = 3.8). CSF analysis conflicting with the clinical diagnosis was the most frequent reason for requesting an amyloid-β PET scan (n = 53, 74%), followed by incongruent MRI (n = 16, 22%), unusual clinical presentation (n = 11, 15%) and young age (n = 8, 11%). An amyloid-β PET scan was rarely (n = 5, 7%) requested in patients with a CSF Aβ+/tau+ status. Fifteen (47%) patients with a post-PET diagnosis of AD had a predominantly non-amnestic presentation. In n = 11 (15%) cases, the reason that the clinician requested amyloid-β was not covered by AUC. This happened most often (n = 7) when previous CSF analysis did not support current clinical diagnosis, which led to requesting amyloid-β PET.

CONCLUSION

In this single-center study, the main reason for requesting an amyloid-β PET scan after performing CSF biomarkers was the occurrence of a mismatch between the primary clinical diagnosis and CSF Aβ/tau results.

The Incremental Diagnostic Value of [18F]Florbetaben PET and the Pivotal Role of the Neuropsychological Assessment in Clinical Practice

BACKGROUND

Amyloid pathology is a key feature of Alzheimer's disease (AD) and can be assessed in vivo with amyloid positron emission tomography (PET) imaging.

OBJECTIVE

The objective of this study was to evaluate the incremental value of a PET scan with [18F]florbetaben, in terms of changes of diagnosis, diagnostic confidence, and treatment plan when added to a standardized diagnostic workup for cognitive disorders, with particular focus on the role of the neuropsychological assessment, including the Free and Cued Selective Reminding Test (FCSRT).

METHODS

A total of 104 patients (69 mild cognitive impairment, 35 dementia), with diagnostic uncertainty after diagnostic workup, were recruited from our memory clinic. [18F]florbetaben PET scans were interpreted as amyloid negative or positive on the basis of a semi-quantitative visual rating. Clinical diagnosis and diagnostic confidence for AD or non-AD dementia were rated before and after PET result disclosure, as was the impact of PET on the patient management plan.

RESULTS

There were 69/104 (66%) [18F]florbetaben positive scans, 51/62 (82%) patients were suspected as having AD before the PET scan and 18/42 (43%) were not. Overall, the data obtained at PET changed 18/104 diagnoses (17%) and increased diagnostic confidence from 69.1±8.1% to 83.5±9.1 (p < 0.001), with the greatest impact on diagnosis and confidence in PET negative patients with an initial diagnosis of AD (p < 0.01) and in early-onset patients (p = 0.01).

CONCLUSION

Amyloid PET represents a source of added value in dementia diagnosis, with a significant effect on diagnosis and diagnostic confidence. However, the use of a complete neuropsychological assessment has an add-on value on limiting the amyloid PET influence on change of diagnosis, and the real impact of amyloid PET should always be weighed up together with an accurate standardized diagnostic workup.

Plasma amyloid assay as a pre-screening tool for amyloid positron emission tomography imaging in early stage Alzheimer's disease

INTRODUCTION

Due to the high cost and high failure rate of ascertaining amyloid positron emission tomography positivity (PET+) in patients with earlier stage Alzheimer's disease (AD), an effective pre-screening tool for amyloid PET scans is needed.

METHODS

Patients with mild cognitive impairment (n = 33, 24.2% PET+, 42% females, age 74.4 ± 7.5, MMSE 26.8 ± 1.9) and mild dementia (n = 19, 63.6% PET+, 36.3% females, age 73.0 ± 9.3, MMSE 22.6 ± 2.0) were recruited. Amyloid PET imaging, Apolipoprotein E (APOE) genotyping, and plasma amyloid β (Aβ)_1-40, Aβ_1-42, and total tau protein quantification by immunomagnetic reduction (IMR) method were performed. Receiver operating characteristics (ROC) analysis and Youden's index were performed to identify possible cut-off points, clinical sensitivities/specificities, and areas under the curve (AUCs).

RESULTS

Amyloid PET+ participants had lower plasma Aβ_1-42 levels than amyloid PET-negative (PET-) subjects. APOE ε4 carriers had higher plasma Aβ_1-42 than non-carriers. We developed an algorithm involving the combination of plasma Aβ_1-42 and APOE genotyping. The success rate for detecting amyloid PET+ patients effectively increased from 42.3 to 70.4% among clinically suspected MCI and mild dementia patients.

CONCLUSIONS

Our results demonstrate the possibility of utilizing APOE genotypes in combination with plasma Aβ_1-42 levels as a pre-screening tool for predicting the positivity of amyloid PET findings in early stage dementia patients.

Association of Amyloid Positron Emission Tomography With Changes in Diagnosis and Patient Treatment in an Unselected Memory Clinic Cohort: The ABIDE Project

Importance

Previous studies have evaluated the diagnostic effect of amyloid positron emission tomography (PET) in selected research cohorts. However, these research populations do not reflect daily practice, thus hampering clinical implementation of amyloid imaging.

Objective

To evaluate the association of amyloid PET with changes in diagnosis, diagnostic confidence, treatment, and patients' experiences in an unselected memory clinic cohort.

Design, Setting, and Participants

Amyloid PET using fluoride-18 florbetaben was offered to 866 patients who visited the tertiary memory clinic at the VU University Medical Center between January 2015 and December 2016 as part of their routine diagnostic dementia workup. Of these patients, 476 (55%) were included, 32 (4%) were excluded, and 358 (41%) did not participate. To enrich this sample, 31 patients with mild cognitive impairment from the University Medical Center Utrecht memory clinic were included. For each patient, neurologists determined a preamyloid and postamyloid PET diagnosis that existed of both a clinical syndrome (dementia, mild cognitive impairment, or subjective cognitive decline) and a suspected etiology (Alzheimer disease [AD] or non-AD), with a confidence level ranging from 0% to 100%. In addition, the neurologist determined patient treatment in terms of ancillary investigations, medication, and care. Each patient received a clinical follow-up 1 year after being scanned.

Main Outcomes and Measures

Primary outcome measures were post-PET changes in diagnosis, diagnostic confidence, and patient treatment.

Results

Of the 507 patients (mean [SD] age, 65 (8) years; 201 women [39%]; mean [SD] Mini-Mental State Examination score, 25 [4]), 164 (32%) had AD dementia, 70 (14%) non-AD dementia, 114 (23%) mild cognitive impairment, and 159 (31%) subjective cognitive decline. Amyloid PET results were positive for 242 patients (48%). The suspected etiology changed for 125 patients (25%) after undergoing amyloid PET, more often due to a negative (82 of 265 [31%]) than a positive (43 of 242 [18%]) PET result (P < .01). Post-PET changes in suspected etiology occurred more frequently in patients older (>65 years) than younger (<65 years) than the typical age at onset of 65 years (74 of 257 [29%] vs 51 of 250 [20%]; P < .05). Mean diagnostic confidence (SD) increased from 80 (13) to 89 (13%) (P < .001). In 123 patients (24%), there was a change in patient treatment post-PET, mostly related to additional investigations and therapy.

Conclusions and Relevance

This prospective diagnostic study provides a bridge between validating amyloid PET in a research setting and implementing this diagnostic tool in daily clinical practice. Both amyloid-positive and amyloid-negative results had substantial associations with changes in diagnosis and treatment, both in patients with and without dementia.

Incremental value of amyloid-PET versus CSF in the diagnosis of Alzheimer's disease

PURPOSE

To compare the incremental diagnostic value of amyloid-PET and CSF (Aβ42, tau, and phospho-tau) in AD diagnosis in patients with mild cognitive impairment (MCI) or mild dementia, in order to improve the definition of diagnostic algorithm.

METHODS

Two independent dementia experts provided etiological diagnosis and relative diagnostic confidence in 71 patients on 3 rounds, based on (1) clinical, neuropsychological, and structural MRI information alone; (2) adding one biomarker (CSF amyloid and tau levels or amyloid-PET with a balanced randomized design); and (3) adding the other biomarker.

RESULTS

Among patients with a pre-biomarker diagnosis of AD, negative PET induced significantly more diagnostic changes than amyloid-negative CSF at both rounds 2 (CSF 67%, PET 100%, P = 0.028) and 3 (CSF 0%; PET 78%, P < 0.001); PET induced a diagnostic confidence increase significantly higher than CSF on both rounds 2 and 3.

CONCLUSIONS

Amyloid-PET should be prioritized over CSF biomarkers in the diagnostic workup of patients investigated for suspected AD, as it provides greater changes in diagnosis and diagnostic confidence.

TRIAL REGISTRATION

EudraCT no.: 2014-005389-31.

Clinical applicability of diagnostic biomarkers in early-onset cognitive impairment

BACKGROUND AND PURPOSE

Several diagnostic biomarkers are currently available for clinical use in early-onset cognitive impairment. The decision on which biomarker is used in each patient depends on several factors such as its predictive value or tolerability.

METHODS

There were a total of 40 subjects with early-onset cognitive complaints (<65 years of age): 26 with Alzheimer's disease (AD), five with frontotemporal dementia and nine with diagnostic suspicion of non-neurodegenerative disorder. Clinical and neuropsychological evaluation, lumbar puncture for cerebrospinal fluid (CSF) AD core biochemical marker determination, medial temporal atrophy evaluation on magnetic resonance imaging, amyloid-positron emission tomography (PET) and ¹⁸ F-fluorodeoxyglucose-PET were performed. Neurologists provided pre- and post-biomarker diagnosis, together with diagnostic confidence and clinical/therapeutic management. Patients scored the tolerability of each procedure.

RESULTS

Cerebrospinal fluid biomarkers and amyloid-PET increased diagnostic confidence in AD (77.4%-86.2% after CSF, 92.4% after amyloid-PET, P < 0.01) and non-neurodegenerative conditions (53.6%-75% after CSF, 95% after amyloid-PET, P < 0.05). Biomarker results led to diagnostic (32.5%) and treatment (32.5%) changes. All tests were well tolerated.

CONCLUSIONS

Biomarker procedures are well tolerated and have an important diagnostic/therapeutic impact on early-onset cognitive impairment.

A Review of Diagnostic Impact of Amyloid Positron Emission Tomography Imaging in Clinical Practice

BACKGROUND

Molecular imaging of brain amyloid for the diagnosis of Alzheimer's disease (AD) using positron emission tomography (PET) has been approved for use in clinical practice by the Food and Drug Administration (FDA) since 2012. However, the clinical utility and diagnostic impact of amyloid PET imaging remain controversial. We conducted a review of the recent studies investigating clinical utility of amyloid PET imaging with focus on changes in diagnosis, diagnostic confidence, and patient management.

SUMMARY

A total of 16 studies were included in the final analysis. Overall rate of changes in diagnosis after amyloid PET ranged from 9 to 68% (pooled estimate of 31%, 95% CI 23-39%). All studies reported overall increase in diagnostic confidence or diagnostic certainty after amyloid PET. Changes in patient management ranged from 37 to 87%; the most common type of change in management reported was either the initiation or discontinuation of planned AD medications. Key Messages: Amyloid PET imaging led to moderate to significant changes in diagnosis, diagnostic confidence, and subsequent patient management. It may be most useful in patients with high level of diagnostic uncertainty even after the completing the standard workup.

New PET markers for the diagnosis of dementia

PURPOSE OF REVIEW

To present the new PET markers that could become in the coming years, relevant to advanced clinical approaches to dementia diagnosis, drug trials, and treatment strategies and discuss their advantages and limitations.

RECENT FINDINGS

The most advanced new PET tracers are the markers of the amyloid plaques, the τ compounds and the tracers of the translocator protein as markers of neuroinflammation. The main advantages but also the weaknesses of each of these markers are discussed. The main pitfall remains the heterogeneity of the available results that cast doubt to a rapid introduction of these new ligands in clinical practice.

SUMMARY

With the advent of biomarkers in clinical management and findings of molecular neuroimaging studies in the evaluation of patients with suspected dementia, the impact of functional neuroimaging has increased considerably these last years and has been integrated into many clinical guidelines in the field of dementia. In addition to conventional single PET brain perfusion and dopaminergic neurotransmission, 18F-fluorodeoxyglucose (18F-FDG) PET is used in advanced diagnosis procedures. Furthermore, new tracers are being developed to quantify key neuropathological features in the brain tissue as highly specific diagnosis is crucial to comply with the global medical and public health objectives in this domain. A strategic road map for further developments, adapted from the approach to cancer biomarkers, should be proposed so as to optimize the rationale of the PET-based molecular diagnosis of Alzheimer's disease and related disorders.

Clinical utility of amyloid PET imaging with (18)F-florbetapir: a retrospective study of 100 patients

BACKGROUND AND OBJECTIVE

Amyloid-positron emission tomography (PET) imaging (API) detects amyloid-beta pathology early in the course of Alzheimer's disease (AD) with high sensitivity and specificity. (18)F-florbetapir (Amyvid) is an amyloid-binding PET ligand with a half-life suitable for clinical use outside of the research setting. How API affects patient investigation and management in the 'real-world' arena is unknown. To address this, we retrospectively documented the effect of API in patients in the memory clinic.

METHODS

We reviewed the presenting clinical features, the pre-API and post-API investigations, diagnosis and outcomes for the first 100 patients who had API as part of their routine work-up at the Imperial Memory Centre, a tertiary referral clinic in the UK National Health Service.

RESULTS

API was primarily used to investigate patients with atypical clinical features (56 cases) or those that were young at onset (42 cases). MRI features of AD did not always predict positive API (67%), and 6 of 23 patients with MRIs reported as normal were amyloid-PET positive. There were significantly more cases categorised as non-AD dementia post-API (from 11 to 23). Patients investigated when API was initially available had fewer overall investigations and all patients had significantly fewer investigations in total post-API.

CONCLUSIONS

API has a clear impact on the investigation of young-onset or complex dementia while reducing the overall burden of investigations. It was most useful in younger patients, atypical presentations or individuals with multiple possible causes of cognitive impairment.

A Systematic Review and Aggregated Analysis on the Impact of Amyloid PET Brain Imaging on the Diagnosis, Diagnostic Confidence, and Management of Patients being Evaluated for Alzheimer's Disease

BACKGROUND

Amyloid PET (aPET) imaging could improve patient outcomes in clinical practice, but the extent of impact needs quantification.

OBJECTIVE

To provide an aggregated quantitative analysis of the value added by aPET in cognitively impaired subjects.

METHODS

Systematic literature searches were performed in Embase and Medline until January 2017. 1,531 cases over 12 studies were included (1,142 cases over seven studies in the primary analysis where aPET was the key biomarker; the remaining cases included as defined groups in the secondary analysis). Data was abstracted by consensus among two observers and assessed for bias. Clinical utility was measured by diagnostic change, diagnostic confidence, and patient management before and after aPET. Three groups were further analyzed: control patients for whom feedback of aPET scan results was delayed; aPET Appropriate Use Criteria (AUC+) cases; and patients undergoing additional FDG/CSF testing.

RESULTS

For 1,142 cases with only aPET, 31.3% of diagnoses were revised, whereas 3.2% of diagnoses changed in the delayed aPET control group (p < 0.0001). Increased diagnostic confidence following aPET was found for 62.1% of 870 patients. Management changes with aPET were found in 72.2% of 740 cases and in 55.5% of 299 cases in the control group (p < 0.0001). The diagnostic value of aPET in AUC+ patients or when FDG/CSF were additionally available did not substantially differ from the value of aPET alone in the wider population.

CONCLUSIONS

Amyloid PET contributed to diagnostic revision in almost a third of cases and demonstrated value in increasing diagnostic confidence and refining management plans.

Clinical Use and Utility of Amyloid Imaging

Currently, 3 amyloid PET tracers are approved and commercially available for clinical use. They allow for the accurate in vivo detection of amyloid plaques, one hallmark of Alzheimer disease. Here, we review the current knowledge on the clinical use and utility of amyloid imaging. Appropriate use criteria for the clinical application of amyloid imaging are established, and most currently available data point to their validity. Visual amyloid image analysis is highly standardized. Disclosure of amyloid imaging results is desired by many cognitively impaired subjects and seems to be safe once appropriate education is delivered to the disclosing clinicians. Regarding clinical utility, increasing evidence points to a change in diagnosis via amyloid imaging in about 30% of cases, to an increase in diagnostic confidence in about 60% of cases, to a change in patient management in about 60% of cases, and specifically to a change in medication in about 40% of cases. Also, amyloid imaging results seem to have a relevant impact on caregivers. Further, initial simulation studies point to a potential positive effect on patient outcome and to cost effectiveness of amyloid imaging. These features, however, will require confirmation in prospective clinical trials. More work is also required to determine the clinical utility of amyloid imaging specifically in subjects with mild cognitive impairment and in comparison with or in conjunction with other Alzheimer disease biomarkers. In summary, the clinical use of amyloid imaging is being studied, and the currently available data point to a relevant clinical utility of this imaging technique. Ongoing research will determine whether this accurate and noninvasive approach to amyloid plaque load detection will translate into a benefit to cognitively impaired subjects.

Strategic roadmap for an early diagnosis of Alzheimer's disease based on biomarkers

The diagnosis of Alzheimer's disease can be improved by the use of biological measures. Biomarkers of functional impairment, neuronal loss, and protein deposition that can be assessed by neuroimaging (ie, MRI and PET) or CSF analysis are increasingly being used to diagnose Alzheimer's disease in research studies and specialist clinical settings. However, the validation of the clinical usefulness of these biomarkers is incomplete, and that is hampering reimbursement for these tests by health insurance providers, their widespread clinical implementation, and improvements in quality of health care. We have developed a strategic five-phase roadmap to foster the clinical validation of biomarkers in Alzheimer's disease, adapted from the approach for cancer biomarkers. Sufficient evidence of analytical validity (phase 1 of a structured framework adapted from oncology) is available for all biomarkers, but their clinical validity (phases 2 and 3) and clinical utility (phases 4 and 5) are incomplete. To complete these phases, research priorities include the standardisation of the readout of these assays and thresholds for normality, the evaluation of their performance in detecting early disease, the development of diagnostic algorithms comprising combinations of biomarkers, and the development of clinical guidelines for the use of biomarkers in qualified memory clinics.

Comparison of CSF markers and semi-quantitative amyloid PET in Alzheimer's disease diagnosis and in cognitive impairment prognosis using the ADNI-2 database

BACKGROUND

The relative performance of semi-quantitative amyloid positron emission tomography (PET) and cerebrospinal fluid (CSF) markers in diagnosing Alzheimer's disease (AD) and predicting the cognitive evolution of patients with mild cognitive impairment (MCI) is still debated.

METHODS

Subjects from the Alzheimer's Disease Neuroimaging Initiative 2 with complete baseline cognitive assessment (Mini Mental State Examination, Clinical Dementia Rating [CDR] and Alzheimer's Disease Assessment Scale-Cognitive Subscale [ADAS-cog] scores), CSF collection (amyloid-β1-42 [Aβ], tau and phosphorylated tau) and 18F-florbetapir scans were included in our cross-sectional cohort. Among these, patients with MCI or substantial memory complaints constituted our longitudinal cohort and were followed for 30 ± 16 months. PET amyloid deposition was quantified using relative retention indices (standardised uptake value ratio [SUVr]) with respect to pontine, cerebellar and composite reference regions. Diagnostic and prognostic performance based on PET and CSF was evaluated using ROC analysis, multivariate linear regression and survival analysis with the Cox proportional hazards model.

RESULTS

The cross-sectional study included 677 participants and revealed that pontine and composite SUVr values were better classifiers (AUC 0.88, diagnostic accuracy 85%) than CSF markers (AUC 0.83 and 0.85, accuracy 80% and 75%, for Aβ and tau, respectively). SUVr was a strong independent determinant of cognition in multivariate regression, whereas Aβ was not; tau was also a determinant, but to a lesser degree. Among the 396 patients from the longitudinal study, 82 (21%) converted to AD within 22 ± 13 months. Optimal SUVr thresholds to differentiate AD converters were quite similar to those of the cross-sectional study. Composite SUVr was the best AD classifier (AUC 0.86, sensitivity 88%, specificity 81%). In multivariate regression, baseline cognition (CDR and ADAS-cog) was the main predictor of subsequent cognitive decline. Pontine and composite SUVr were moderate but independent predictors of final status and CDR/ADAS-cog progression rate, whereas baseline CSF markers had a marginal influence. The adjusted HRs for AD conversion were 3.8 (p = 0.01) for PET profile, 1.2 (p = ns) for Aβ profile and 1.8 (p = 0.03) for tau profile.

CONCLUSIONS

Semi-quantitative amyloid PET appears more powerful than CSF markers for AD grading and MCI prognosis in terms of cognitive decline and AD conversion.