The added value of 18-fluorodeoxyglucose-positron emission tomography in the diagnosis of the behavioral variant of frontotemporal dementia

Data-driven analysis of regional brain metabolism in behavioral frontotemporal dementia and late-onset primary psychiatric diseases with frontal lobe syndrome: A PET/MRI study

Late-onset primary psychiatric disease (PPD) and behavioral frontotemporal dementia (bvFTD) present with a similar frontal lobe syndrome. We compare brain glucose metabolism in bvFTD and late-onset PPD and investigate the metabolic correlates of cognitive and behavioral disturbances through FDG-PET/MRI. We studied 37 bvFTD and 20 late-onset PPD with a mean clinical follow-up of three years. At baseline evaluation, metabolism of the dorsolateral, ventrolateral, orbitofrontal regions and caudate could classify the patients with a diagnostic accuracy of 91% (95% CI: 0.81-0.98%). 45% of PPD showed low-grade hypometabolism in the anterior cingulate and/or parietal regions. Frontal lobe metabolism was normal in 32% of genetic bvFTD and bvFTD with motor neuron signs. Hypometabolism of the frontal and caudate regions could help in distinguishing bvFTD from PPD, except in cases with motor neuron signs and/or genetic bvFTD for which brain metabolism may be less informative.

Relationship between Neuroimaging and Cognition in Frontotemporal Dementia: A [18 F]FDG PET and Structural MRI Study

Background

Frontotemporal dementia (FTD) is a clinically and pathologically heterogeneous condition with a prevalence comparable to Alzheimer's Disease for patients under sixty-five years of age. Gray matter (GM) atrophy and glucose hypometabolism are important biomarkers for the diagnosis and evaluation of disease progression in FTD. However, limited studies have systematically examined the association between cognition and neuroimaging in FTD using different imaging modalities in the same patient group.

Methods

We examined the association of cognition using Montreal Cognitive Assessment (MoCA) with both GM volume and glucose metabolism using structural magnetic resonance imaging (MRI) and 18F-fluorodeoxyglucose positron emission tomography scanning ([18F]FDG PET) in 21 patients diagnosed with FTD. Standardized uptake value ratio (SUVR) using the brainstem as a reference region was the primary outcome measure for [18F]FDG PET. Partial volume correction was applied to PET data to account for disease-related atrophy.

Results

Significant positive associations were found between whole-cortex GM volume and MoCA scores (r = 0.461, p = 0.035). The association between whole-cortex [18F]FDG SUVR and MoCA scores was not Significant (r = 0.374, p = 0.094). GM volumes of the frontal cortex (r = 0.540, p = 0.011), caudate (r = 0.616, p = 0.002), and insula (r = 0.568, p = 0.007) were also Significantly correlated with MoCA, as were SUVR values of the insula (r = 0.508, p = 0.018), thalamus (r = 0.478, p = 0.028), and posterior cingulate cortex (PCC) (r = 0.472, p = 0.030).

Discussion

Whole-cortex atrophy is associated with cognitive dysfunction, and this effect is larger than for cortical hypometabolism as measured with [18F]FDG PET. At the regional level, focal atrophy and/or hypometabolism in the frontal lobe, insula, PCC, thalamus, and caudate seem to imply the importance of these regions for the decline of cognitive function in FTD. Furthermore, these results highlight how functional and structural changes may not overlap and might contribute to cognitive dysfunction in FTD in different ways. Our findings provide insight into the relationships between structural, metabolic, and cognitive changes due to FTD.

The use of neuroimaging techniques in the early and differential diagnosis of dementia

Dementia is a leading cause of disability and death worldwide. At present there is no disease modifying treatment for any of the most common types of dementia such as Alzheimer's disease (AD), Vascular dementia, Lewy Body Dementia (LBD) and Frontotemporal dementia (FTD). Early and accurate diagnosis of dementia subtype is critical to improving clinical care and developing better treatments. Structural and molecular imaging has contributed to a better understanding of the pathophysiology of neurodegenerative dementias and is increasingly being adopted into clinical practice for early and accurate diagnosis. In this review we summarise the contribution imaging has made with particular focus on multimodal magnetic resonance imaging (MRI) and positron emission tomography imaging (PET). Structural MRI is widely used in clinical practice and can help exclude reversible causes of memory problems but has relatively low sensitivity for the early and differential diagnosis of dementia subtypes. 18F-fluorodeoxyglucose PET has high sensitivity and specificity for AD and FTD, while PET with ligands for amyloid and tau can improve the differential diagnosis of AD and non-AD dementias, including recognition at prodromal stages. Dopaminergic imaging can assist with the diagnosis of LBD. The lack of a validated tracer for α-synuclein or TAR DNA-binding protein 43 (TDP-43) imaging remain notable gaps, though work is ongoing. Emerging PET tracers such as 11C-UCB-J for synaptic imaging may be sensitive early markers but overall larger longitudinal multi-centre cross diagnostic imaging studies are needed.

The Behavioral Variant Frontotemporal Dementia Phenocopy Syndrome: A Review

OBJECTIVES

The relatively recent identification of a subgroup of patients with apparent behavioral variant frontotemporal dementia (bvFTD) that fails to progress with time has led to a reevaluation of our understanding of bvFTD, and a growing body of research that attempts to characterize the mimic or "phenocopy" syndrome. In this article, we review the literature relating to the phenocopy syndrome, focusing in particular on distinguishing characteristics and potential etiologies.

METHODS

Published articles were identified via a systematic search of PubMed and Embase. Observational and interventional studies, case reports, and case series were sought for inclusion.

RESULTS

While bvFTD and the phenocopy syndrome are clinically indistinguishable at initial presentation, the presence or absence of characteristic changes on neuroimaging predicts 2 very different illness trajectories. The etiology for the phenocopy presentation remains uncertain. It is likely that the syndrome represents a heterogenous assortment of clinical frontal syndromes encompassing atypical neurodegenerative, psychiatric, psychological, and as yet unknown neuropsychiatric causes.

CONCLUSIONS

Although the prognosis of the phenocopy syndrome is generally held to be more favorable than that of bvFTD, patients and families are subject to major disruption in their relationships and social and occupational functioning. Early recognition is crucial to facilitate timely interventions aimed at maintaining relationships, roles, and quality of life of those affected.

FDG-PET in presymptomatic C9orf72 mutation carriers

OBJECTIVE

Our aim is to investigate patterns of brain glucose metabolism using fluorodeoxyglucose positron emission tomography (FDG-PET) in presymptomatic carriers of the C9orf72 repeat expansion to better understand the early preclinical stages of frontotemporal dementia (FTD).

METHODS

Structural MRI and FDG-PET were performed on clinically asymptomatic members of families with FTD caused by the C9orf72 repeat expansion (15 presymptomatic mutation carriers, C9orf72+; 20 non-carriers, C9orf72-). Regional glucose metabolism in cerebral and cerebellar gray matter was compared between groups.

RESULTS

The mean age of the C9orf72+ and C9orf72- groups were 45.3 ± 10.6 and 56.0 ± 11.0 years respectively, and the mean age of FTD onset in their families was 56 ± 7 years. Compared to non-carrier controls, the C9orf72+ group exhibited regional hypometabolism, primarily involving the cingulate gyrus, frontal and temporal neocortices (left > right) and bilateral thalami.

CONCLUSIONS

The C9orf72 repeat expansion is associated with changes in brain glucose metabolism that are demonstrable up to 10 years prior to symptom onset and before changes in gray matter volume become significant. These findings indicate that FDG-PET may be a particularly sensitive and useful method for investigating and monitoring the earliest stages of FTD in individuals with this underlying genetic basis.

Neurofilaments as Emerging Biomarkers of Neuroaxonal Damage to Differentiate Behavioral Frontotemporal Dementia from Primary Psychiatric Disorders: A Systematic Review

The behavioral variant of frontotemporal dementia (bvFTD) is a clinical syndrome resulting from various causes of neuronal demises associated with frontotemporal lobar degeneration. Symptoms include behavioral and personality changes, social cognitive impairment, and executive function deficits. There is a significant clinical overlap between this syndrome and various primary psychiatric disorders (PPD). Structural and functional neuroimaging are considered helpful to support the diagnosis of bvFTD, but their sensitivity and specificity remain imperfect. There is growing evidence concerning the potential of neurofilaments as biomarkers reflecting axonal and neuronal lesions. Ultrasensitive analytic platforms have recently enabled neurofilament light chains’ (NfL) detection not only from cerebrospinal fluid but also from peripheral blood samples in FTD patients. In this short review, we present recent advances and perspectives for the use of NfL assessments as biomarkers of neuroaxonal damage to differentiate bvFTD from primary psychiatric disorders.

Frontal hypometabolism in neurocognitive disorder with behavioral disturbance

Criteria for the behavioral variant of frontotemporal dementia (bvFTD) include decreased frontal metabolism. FDG-PET was used to investigate whether patients with neurocognitive disorder and behavioral disturbance (bvNCD) who did not fulfill three bvFTD criteria had characteristic brain metabolic pattern. Methods: Patients were referred from memory clinic to nuclear medicine for differential diagnosis of NCD with dysexecutive syndrome and predominant mild frontal atrophy. Patients were classified into two groups before FDG-PET, probable bvFTD (n = 25) or bvNCD (n = 27) when only two bvFTD criteria were met. Results: Voxel-based and multivariate PLS analyses of FDG-PET did not show significant between-group difference at inclusion. After 4.8 years of follow-up, most patients with probable bvFTD received the same diagnosis, 3 remained very stable and one participant was given a psychiatric diagnosis. Five patients with bvNCD fulfilled criteria for probable bvFTD at 4.4 years mean follow up, while 2 participants remained very stable and 3 received alternative neurological or psychiatric diagnoses. When initial FDG-PET were compared between groups stratified at follow up (26 bvFTD versus 17 bvNCD), there was a trend (p<.001uncorrected) for lower prefrontal with relatively preserved premotor metabolism in bvFTD compared to bvNCD. Twelve bvNCD participants had neuropsychological testing before inclusion. They all presented executive dysfunction and normal visuospatial performance, and most (n = 9) had memory encoding impairment. Conclusion: Frontal hypometabolism was observed in a dysexecutive presentation of frontal neurodegenerative disorder (bvNCD) that did not fulfill all clinical criteria for bvFTD.

Molecular and Anatomical Imaging of Dementia With Lewy Bodies and Frontotemporal Lobar Degeneration

Dementia with Lewy bodies (DLB) and frontotemporal lobar degeneration (FTLD) are common causes of dementia. Early diagnosis of both conditions is challenging due to clinical and radiological overlap with other forms of dementia, particularly Alzheimer's disease (AD). Structural and functional imaging combined can aid differential diagnosis and help to discriminate DLB or FTLD from other forms of dementia. Imaging of DLB involves the use of ¹²³I-FP-CIT SPECT and ¹²³I-metaiodobenzylguanidine (¹²³I-MIBG), both of which have an established role distinguishing DLB from AD. AD is also characterised by more pronounced atrophy of the medial temporal lobe structures when compared to DLB and these can be assessed at MR using the Medial Temporal Atrophy Scale. ¹⁸F-FDG-PET is used as a supportive biomarker for the diagnoses of DLB and can distinguish DLB from AD with high accuracy. Polysomnography and electroencephalography also have established roles in the diagnoses of DLB. FTLD is a heterogenous group of neurodegenerative disorders characterised pathologically by abnormally aggregated proteins. Clinical subtypes include behavioral variant FTD (bvFTD), primary progressive aphasia (PPA), which can be subdivided into semantic variant PPA (svPPA) or nonfluent agrammatic PPA (nfaPPA) and FTD associated with motor neuron disease (FTD-MND). Structural imaging is often the first step in making an image supported diagnoses of FTLD. Regional patterns of atrophy can be assessed on MR and graded according to the global cortical atrophy scale. FTLD is typically associated with atrophy of the frontal and temporal lobes. The patterns of atrophy are associated with the specific clinical subtypes, underlying neuropathology and genetic mutations although there is significant overlap. ¹⁸F-FDG-PET is useful for distinguishing FTLD from other forms of dementia and focal areas of hypometabolism can often precede atrophy identified on structural MR imaging. There are currently no biomarkers with which to unambiguously diagnose DLB or FTLD and both conditions demonstrate a wide range of heterogeneity. A combined approach of structural and functional imaging improves diagnostic accuracy in both conditions.

Frontotemporal Dementia and Late-Onset Bipolar Disorder: The Many Directions of a Busy Road

It is a common pathway for patients with the behavioral variant of frontotemporal dementia (bvFTD) to be first misdiagnosed with a primary psychiatric disorder, a considerable proportion of them being diagnosed with bipolar disorder (BD). Conversely, not rarely patients presenting in late life with a first episode of mania or atypically severe depression are initially considered to have dementia before the diagnosis of late-onset BD is reached. Beyond some shared features that make these conditions particularly prone to confusion, especially in the elderly, the relationship between bvFTD and BD is far from simple. Patients with BD often have cognitive complaints as part of their psychiatric disorder but are at an increased risk of developing dementia, including FTD. Likewise, apathy and disinhibition, common features of depression and mania, respectively, are among the core features of the bvFTD syndrome, not to mention that depression may coexist with dementia. In this article, we take advantage of the current knowledge on the neurobiology of these two nosologic entities to review their historical and conceptual interplay, highlighting the clinical, genetic and neuroimaging features that may be shared by both disorders or unique to each of them.

Recommendations to distinguish behavioural variant frontotemporal dementia from psychiatric disorders

The behavioural variant of frontotemporal dementia (bvFTD) is a frequent cause of early-onset dementia. The diagnosis of bvFTD remains challenging because of the limited accuracy of neuroimaging in the early disease stages and the absence of molecular biomarkers, and therefore relies predominantly on clinical assessment. BvFTD shows significant symptomatic overlap with non-degenerative primary psychiatric disorders including major depressive disorder, bipolar disorder, schizophrenia, obsessive-compulsive disorder, autism spectrum disorders and even personality disorders. To date, ∼50% of patients with bvFTD receive a prior psychiatric diagnosis, and average diagnostic delay is up to 5-6 years from symptom onset. It is also not uncommon for patients with primary psychiatric disorders to be wrongly diagnosed with bvFTD. The Neuropsychiatric International Consortium for Frontotemporal Dementia was recently established to determine the current best clinical practice and set up an international collaboration to share a common dataset for future research. The goal of the present paper was to review the existing literature on the diagnosis of bvFTD and its differential diagnosis with primary psychiatric disorders to provide consensus recommendations on the clinical assessment. A systematic literature search with a narrative review was performed to determine all bvFTD-related diagnostic evidence for the following topics: bvFTD history taking, psychiatric assessment, clinical scales, physical and neurological examination, bedside cognitive tests, neuropsychological assessment, social cognition, structural neuroimaging, functional neuroimaging, CSF and genetic testing. For each topic, responsible team members proposed a set of minimal requirements, optimal clinical recommendations, and tools requiring further research or those that should be developed. Recommendations were listed if they reached a ≥ 85% expert consensus based on an online survey among all consortium participants. New recommendations include performing at least one formal social cognition test in the standard neuropsychological battery for bvFTD. We emphasize the importance of 3D-T1 brain MRI with a standardized review protocol including validated visual atrophy rating scales, and to consider volumetric analyses if available. We clarify the role of 18F-fluorodeoxyglucose PET for the exclusion of bvFTD when normal, whereas non-specific regional metabolism abnormalities should not be over-interpreted in the case of a psychiatric differential diagnosis. We highlight the potential role of serum or CSF neurofilament light chain to differentiate bvFTD from primary psychiatric disorders. Finally, based on the increasing literature and clinical experience, the consortium determined that screening for C9orf72 mutation should be performed in all possible/probable bvFTD cases or suspected cases with strong psychiatric features.

Update on PET in neurodegenerative and neuroinflammatory disorders manifesting on a behavioural level: imaging for differential diagnosis

PURPOSE OF REVIEW

To give an update on recent findings concerning the use of PET for differential diagnosis in neurodegenerative and neuroinflammatory disorders manifesting on a behavioural level.

RECENT FINDINGS

Although accurate differential diagnosis of dementia can be achieved by imaging disease-specific patterns of cerebral glucose metabolism with [F]fluorodeoxyglucose ([F]FDG)-PET, the diagnostic impact of [F]FDG-PET in primary psychiatric disorders is limited. Amyloid-beta PET provides an incremental value beyond [F]FDG-PET in the differential diagnosis of dementia and was proposed as a biomarker defining the so-called Alzheimer continuum. Recently developed tau-specific tracers might also aid in the diagnostic process (biological definition of Alzheimer's disease together with amyloid-beta). Surpassing the diagnostic accuracy of other techniques, such as MRI, [F]FDG-PET has also gained widespread clinical use for diagnosis and follow-up of paraneoplastic and autoimmune disorders of the central nervous system (CNS) as an important differential diagnosis for rapid progressive dementia and subacute onset of psychiatric syndromes.

SUMMARY

Molecular neuroimaging with PET is an established method for the differential diagnosis of neurodegenerative and autoimmune CNS disorders manifesting on a behavioural level with significant therapeutic and prognostic impact. Future prospective studies are needed to define the value of tau imaging for diagnosis and prognosis in neurodegenerative disorders.

Diagnostic Value of Diffusion Tensor Imaging and Positron Emission Tomography in Early Stages of Frontotemporal Dementia

BACKGROUND

Due to suboptimal sensitivity and specificity of structural and molecular neuroimaging tools, the diagnosis of behavioral variant frontotemporal dementia (bvFTD) remains challenging.

OBJECTIVE

Investigation of the sensitivity of diffusion tensor imaging (DTI) and fluorodeoxyglucose positron emission tomography (FDG-PET) to detect cerebral alterations in early stages of bvFTD despite inconspicuous conventional MRI.

METHODS

Thirty patients with early stages of bvFTD underwent a detailed neuropsychological examination, cerebral 3T MRI with DTI analysis, and FDG-PET. After 12 months of follow-up, all patients finally fulfilled the diagnosis of bvFTD. Individual FDG-PET data analyses showed that 20 patients exhibited a "typical" pattern for bvFTD with bifrontal and/or temporal hypometabolism (bvFTD/PET+), and that 10 patients showed a "non-typical"/normal pattern (bvFTD/PET-). DTI data were compared with 42 healthy controls in an individual and voxel-based group analysis. To examine the clinical relevance of the findings, associations between pathologically altered voxels of DTI or FDG-PET results and behavioral symptoms were estimated by linear regression analyses.

RESULTS

DTI voxel-based group analyses revealed microstructural degeneration in bifrontal and bitemporal areas in bvFTD/PET+ and bvFTD/PET- groups. However, when comparing the sensitivity of individual DTI data analysis with FDG-PET, DTI appeared to be less sensitive. Neuropsychological symptoms were considerably related to neurodegeneration within frontotemporal areas identified by DTI and FDG-PET.

CONCLUSION

DTI seems to be an interesting tool for detection of functionally relevant neurodegenerative alterations in early stages of bvFTD, even in bvFTD/PET- patients. However, at a single subject level, it seems to be less sensitive than FDG-PET. Thus, improvement of individual DTI analysis is necessary.

The Use of Biomarkers and Genetic Screening to Diagnose Frontotemporal Dementia: Evidence and Clinical Implications

Within the wide range of neurodegenerative brain diseases, the differential diagnosis of frontotemporal dementia (FTD) frequently poses a challenge. Often, signs and symptoms are not characteristic of the disease and may instead reflect atypical presentations. Consequently, the use of disease biomarkers is of importance to correctly identify the patients. Here, we describe how neuropsychological characteristics, neuroimaging and neurochemical biomarkers and screening for causal gene mutations can be used to differentiate FTD from other neurodegenerative diseases as well as to distinguish between FTD subtypes. Summarizing current evidence, we propose a stepwise approach in the diagnostic evaluation. Clinical consensus criteria that take into account a full neuropsychological examination have relatively good accuracy (sensitivity [se] 75–95%, specificity [sp] 82–95%) to diagnose FTD, although misdiagnosis (mostly AD) is common. Structural brain MRI (se 70–94%, sp 89–99%) and FDG PET (se 47–90%, sp 68–98%) or SPECT (se 36–100%, sp 41–100%) brain scans greatly increase diagnostic accuracy, showing greater involvement of frontal and anterior temporal lobes, with sparing of hippocampi and medial temporal lobes. If these results are inconclusive, we suggest detecting amyloid and tau cerebrospinal fluid (CSF) biomarkers that can indicate the presence of AD with good accuracy (se 74–100%, sp 82–97%). The use of P-tau₁₈₁ and the Aβ_1–42/Aβ_1–40 ratio significantly increases the accuracy of correctly identifying FTD vs. AD. Alternatively, an amyloid brain PET scan can be performed to differentiate FTD from AD. When autosomal dominant inheritance is suspected, or in early onset dementia, mutation screening of causal genes is indicated and may also be offered to at-risk family members. We have summarized genotype–phenotype correlations for several genes that are known to cause familial frontotemporal lobar degeneration, which is the neuropathological substrate of FTD. The genes most commonly associated with this disease (C9orf72, MAPT, GRN, TBK1) are discussed, as well as some less frequent ones (CHMP2B, VCP). Several other techniques, such as diffusion tensor imaging, tau PET imaging and measuring serum neurofilament levels, show promise for future implementation as diagnostic biomarkers.

FTD spectrum: Neuroimaging across the FTD spectrum

Frontotemporal dementia is a complex and heterogeneous neurodegenerative disease that encompasses many clinical syndromes, pathological diseases, and genetic mutations. Neuroimaging has played a critical role in our understanding of the underlying pathophysiology of frontotemporal dementia and provided biomarkers to aid diagnosis. Early studies defined patterns of neurodegeneration and hypometabolism associated with the clinical, pathological and genetic aspects of frontotemporal dementia, with more recent studies highlighting how the breakdown of structural and functional brain networks define frontotemporal dementia. Molecular positron emission tomography ligands allowing the in vivo imaging of tau proteins have also provided important insights, although more work is needed to understand the biology of the currently available ligands.

Psychological and Cognitive Markers of Behavioral Variant Frontotemporal Dementia-A Clinical Neuropsychologist's View on Diagnostic Criteria and Beyond

Behavioral variant frontotemporal dementia (bvFTD) is the second leading cognitive disorder caused by neurodegeneration in patients under 65 years of age. Characterized by frontal, insular, and/or temporal brain atrophy, patients present with heterogeneous constellations of behavioral and psychological symptoms among which progressive changes in social conduct, lack of empathy, apathy, disinhibited behaviors, and cognitive impairments are frequently observed. Since the histopathology of the disease is heterogeneous and identified genetic mutations only account for ~30% of cases, there are no reliable biomarkers for the diagnosis of bvFTD available in clinical routine as yet. Early detection of bvFTD thus relies on correct application of clinical diagnostic criteria. Their evaluation however, requires expertise and in-depth assessments of cognitive functions, history taking, clinical observations as well as caregiver reports on behavioral and psychological symptoms and their respective changes. With this review, we aim for a critical appraisal of common methods to access the behavioral and psychological symptoms as well as the cognitive alterations presented in the diagnostic criteria for bvFTD. We highlight both, practical difficulties as well as current controversies regarding an overlap of symptoms and particularly cognitive impairments with other neurodegenerative and primary psychiatric diseases. We then review more recent developments and evidence on cognitive, behavioral and psychological symptoms of bvFTD beyond the diagnostic criteria which may prospectively enhance the early detection and differential diagnosis in clinical routine. In particular, evidence on specific impairments in social and emotional processing, praxis abilities as well as interoceptive processing in bvFTD is summarized and potential links with behavior and classic cognitive domains are discussed. We finally outline both, future opportunities and major challenges with regard to the role of clinical neuropsychology in detecting bvFTD and related neurocognitive disorders.

Phenocopy syndrome of behavioral variant frontotemporal dementia: a systematic review

Background

The phenocopy syndrome of behavioral variant of frontotemporal dementia (phFTD) refers to patients presenting with neuropsychiatric symptoms mimicking the behavioral variant frontotemporal dementia (bvFTD), but lacking frontotemporal atrophy/hypometabolism on neuroimaging and not evolving to dementia during the follow-up. It is important to recognize phFTD for clinical and research purposes.

Objective

The aim of this study was to perform a systematic review of the available literature on phFTD taking into account its clinical, cognitive, imaging, genetic, and pathological features.

Methods and results

We searched for the following terms in two electronic databases (PubMed and Scopus): “frontotemporal dementia and slowly progressive,” “frontotemporal dementia and phenocopy,” “frontotemporal dementia and non-progressive,” “frontotemporal dementia and benign progression,” and “frontotemporal dementia and benign.” We did not include review articles. Papers had to be written in English, French, Portuguese, or Spanish. Overall, 235 studies were retrieved in the initial search. A total of 31 studies composed the final selection, comprising 292 patients. Patients with phFTD are predominantly male and have no major cognitive deficits, with globally preserved executive functions and episodic memory. Some cases (n = 7) of slowly progressive FTD have been associated with C9orf72 genetic expansion. There are only four reports of phFTD neuropathological data, with two patients with no neurodegenerative findings and two with frontotemporal lobar degeneration with ubiquitin-positive inclusions.

Conclusion

The neurobiological underpinnings of phFTD remain unknown. It is controversial whether phFTD belongs to the FTD spectrum. Studies with biomarkers and pathological data are needed to solve the phFTD conundrum.

Individual Prediction of Behavioral Variant Frontotemporal Dementia Development Using Multivariate Pattern Analysis of Magnetic Resonance Imaging Data

BACKGROUND

Patients with behavioral variant of frontotemporal dementia (bvFTD) initially may only show behavioral and/or cognitive symptoms that overlap with other neurological and psychiatric disorders. The diagnostic accuracy is dependent on progressive symptoms worsening and frontotemporal abnormalities on neuroimaging findings. Predictive biomarkers could facilitate the early detection of bvFTD.

OBJECTIVE

To determine the prognostic accuracy of clinical and structural MRI data using a support vector machine (SVM) classification to predict the 2-year clinical follow-up diagnosis in a group of patients presenting late-onset behavioral changes.

METHODS

Data from 73 patients were included and divided into probable/definite bvFTD (n = 18), neurological (n = 28), and psychiatric (n = 27) groups based on 2-year follow-up diagnosis. Grey-matter volumes were extracted from baseline structural MRI scans. SVM classifiers were used to perform three binary classifications: bvFTD versus neurological and psychiatric, bvFTD versus neurological, and bvFTD versus psychiatric group(s), and one multi-class classification. Classification performance was determined for clinical and neuroimaging data separately and their combination using 5-fold cross-validation.

RESULTS

Accuracy of the binary classification tasks ranged from 72-82% (p < 0.001) with adequate sensitivity (67-79%), specificity (77-88%), and area-under-the-receiver-operator-curve (0.80-0.9). Multi-class accuracy ranged between 55-59% (p < 0.001). The combination of clinical and voxel-wise whole brain data showed the best performance overall.

CONCLUSION

These results show the potential for automated early confirmation of diagnosis for bvFTD using machine learning analysis of clinical and neuroimaging data in a diverse and clinically relevant sample of patients.

Dual-phase [18F]florbetapir in frontotemporal dementia

PURPOSE

The PET tracer [18F]florbetapir is a specific fibrillar amyloid-beta (Aβ) biomarker. During the late scan phase (> 40 min), it provides pathological information about Aβ status. Early scan phase (0-10 min) can provide FDG-'like' information. The current investigation tested the feasibility of using florbetapir as a dual-phase biomarker in behavioural variant frontotemporal dementia (bvFTD).

METHODS

Eight bvFTD patients underwent [18F]florbetapir and [18]FDG-PET scans. Additionally, ten healthy controls and ten AD patients underwent florbetapir-PET only. PET data were acquired dynamically for 60-min post-injection. The bvFTD PET data were used to define an optimal time window, representing blood flow-related pseudo-metabolism ('pseudo-FDG'), of florbetapir data that maximally correlated with the corresponding real FDG SUVR (40-60 min) in a composite neocortical FTD region.

RESULTS

A 2 to 5-min time window post-injection of the florbetapir-PET data provided the largest correlation (Pearson's r = 0.79, p = 0.02) to the FDG data. The pseudo-FDG images demonstrated strong internal consistency with actual FDG data and were also visually consistent with the bvFTD patients' hypometabolic profiles. The ability to identify bvFTD from blind visual rating of pseudo-FDG images was consistent with previous reports using FDG data (sensitivity = 75%, specificity = 85%).

CONCLUSIONS

This investigation demonstrates that early phase florbetapir uptake shows a reduction of frontal lobe perfusion in bvFTD, similar to metabolic findings with FDG. Thus, dynamic florbetapir scans can serve as a dual-phase biomarker in dementia patients to distinguish FTD from AD and cognitively normal elderly, removing the need for a separate FDG-PET scan in challenging dementia cases.

Clinical utility of FDG-PET for the differential diagnosis among the main forms of dementia

AIM

To assess the clinical utility of FDG-PET as a diagnostic aid for differentiating Alzheimer's disease (AD; both typical and atypical forms), dementia with Lewy bodies (DLB), frontotemporal lobar degeneration (FTLD), vascular dementia (VaD) and non-degenerative pseudodementia.

METHODS

A comprehensive literature search was conducted using the PICO model to extract evidence from relevant studies. An expert panel then voted on six different diagnostic scenarios using the Delphi method.

RESULTS

The level of empirical study evidence for the use of FDG-PET was considered good for the discrimination of DLB and AD; fair for discriminating FTLD from AD; poor for atypical AD; and lacking for discriminating DLB from FTLD, AD from VaD, and for pseudodementia. Delphi voting led to consensus in all scenarios within two iterations. Panellists supported the use of FDG-PET for all PICOs-including those where study evidence was poor or lacking-based on its negative predictive value and on the assistance it provides when typical patterns of hypometabolism for a given diagnosis are observed.

CONCLUSION

Although there is an overall lack of evidence on which to base strong recommendations, it was generally concluded that FDG-PET has a diagnostic role in all scenarios. Prospective studies targeting diagnostically uncertain patients for assessing the added value of FDG-PET would be highly desirable.

Screening for Emotional Expression in Frontotemporal Dementia: A Pilot Study

Objective

Although emotional blunting is a core feature of behavioral variant frontotemporal dementia (bvFTD), there are no practical clinical measures of emotional expression for the early diagnosis of bvFTD.

Method

Three age-matched groups (bvFTD, Alzheimer's disease (AD), and healthy controls (HC)) of eight participants each were presented with real-life vignettes varying in emotional intensity (high versus low) with either negative or positive outcomes. This study evaluated verbal (self-reports of distress) and visual (presence or absence of facial affect) measures of emotional expression during the vignettes.

Results

The bvFTD patients did not differ from the AD and HC groups in reported distress or in the amount of facial affect during vignettes with high emotional intensity or type of outcome. However, the bvFTD patients reported significantly less distress and had correspondingly few facial affective expressions when compared on vignettes of low intensity.

Conclusions

Patients with bvFTD require a high intensity of emotional stimulus and are significantly hyporesponsive to low-intensity stimuli. Simple screening or observations of verbal and facial responsiveness to mildly arousing stimuli may aid in differentiating bvFTD from normal subjects and patients with other dementias. Future studies can investigate whether delivering information with high emotional intensity can facilitate communication with patients with bvFTD.

Skin Conduction Levels Differentiate Frontotemporal Dementia From Alzheimer's Disease

Patients with behavioral variant frontotemporal dementia (bvFTD) and Alzheimer's disease (AD) differ in basic emotional tone. Skin conduction levels (SCLs), a measure of sympathetic tone, may be a sensitive test for discriminating these two dementias early in their course. Previous research has shown differences in resting SCLs between patients with bvFTD and AD, but no study has evaluated the discriminability of SCLs during different environmental conditions. The authors compared bvFTD patients (N=8), AD patients (N=10), and healthy control subjects (N=9) on SCL measures pertaining to real-life vignettes or scenarios differing in valence and emotional intensity. The SCLs among the bvFTD patients were decreased across all conditions, whereas the SCLs among the AD patients were increased compared with control participants. On analysis, the SCLs in response to emotional stimuli differentiated bvFTD from AD with an area under the receiver operator characteristic curve of 95.3%. At a cutoff ≤0.77 μS, emotional vignettes distinguished bvFTD from AD with a sensitivity of 86% and a specificity of 96%. These preliminary results indicate the potential utility of SCLs for differentiating bvFTD from AD early in their course, regardless of environmental condition.

Impact of Imaging and Cerebrospinal Fluid Biomarkers on Behavioral Variant Frontotemporal Dementia Diagnosis within a Late-Onset Frontal Lobe Syndrome Cohort

BACKGROUND

The criteria for behavioral variant frontotemporal dementia (bvFTD) incorporate MRI and [18F]-FDG-PET. Cerebrospinal fluid (CSF) analysis is merely advised for excluding Alzheimer's disease.

AIMS

We aimed to assess the impact of biomarkers on diagnostic certainty and contingent changes of bvFTD diagnosis within the clinically relevant neuropsychiatric differential diagnosis of subjects with a late-onset frontal lobe syndrome (LOF).

METHODS

We included 137 patients with LOF, aged 45-75 years, 72% males. Biomarker disclosure was considered contributing after any substantial difference in diagnostic certainty or a diagnostic change. Percentages of contributing biomarkers were compared between three major diagnostic groups (bvFTD, psychiatry, other neurological disorders). Certainty levels in stable diagnostic groups were compared to those with a diagnostic change.

RESULTS

Biomarkers contributed in 53, 60 and 41% of the LOF patients for MRI, [18F]-FDG-PET and CSF, respectively. Biomarkers changed the diagnosis in 14% of cases towards bvFTD and in 13% from bvFTD into an alternative. Those that changed had a lower level of a priori diagnostic certainty compared to stable diagnoses.

CONCLUSION

Our study not only supports the widely accepted use of MRI and [18F]-FDG-PET in diagnosing or excluding bvFTD, but also shows that CSF biomarkers aid clinicians in the diagnostic process.

Frontotemporal Dementia: An Updated Clinician's Guide

Today, frontotemporal dementia (FTD) remains one of the most common forms of early-onset dementia, that is, before the age of 65, thus posing several diagnostic challenges to clinicians since symptoms are often mistaken for psychiatric or neurological diseases causing a delay in correct diagnosis, and the majority of patients with FTD present with symptoms at ages between 50 and 60. Genetic components are established risk factors for FTD, but the influence of lifestyle, comorbidity, and environmental factors on the risk of FTD is still unclear. Approximately 40% of individuals with FTD have a family history of dementia but less than 10% have a clear autosomal dominant pattern of inheritance. Lack of insight is often an early clue to FTD. A tailored treatment option at an early phase can mitigate suffering and improve patients' and caregivers' quality of life.

Structural and functional brain abnormalities place phenocopy frontotemporal dementia (FTD) in the FTD spectrum

Purpose

‘Phenocopy’ frontotemporal dementia (phFTD) patients may clinically mimic the behavioral variant of FTD (bvFTD), but do not show functional decline or abnormalities upon visual inspection of routine neuroimaging. We aimed to identify abnormalities in gray matter (GM) volume and perfusion in phFTD and to assess whether phFTD belongs to the FTD spectrum. We compared phFTD patients with both healthy controls and bvFTD patients.

Materials & methods

Seven phFTD and 11 bvFTD patients, and 20 age-matched controls underwent structural T1-weighted magnetic resonance imaging (MRI) and 3D pseudo-continuous arterial spin labeling (pCASL) at 3T. Normalized GM (nGM) volumes and perfusion, corrected for partial volume effects, were quantified regionally as well as in the entire supratentorial cortex, and compared between groups taking into account potential confounding effects of gender and scanner.

Results

PhFTD patients showed cortical atrophy, most prominently in the right temporal lobe. Apart from this regional atrophy, GM volume was generally not different from either controls or from bvFTD. BvFTD however showed extensive frontotemporal atrophy. Perfusion was increased in the left prefrontal cortex compared to bvFTD and to a lesser extent to controls.

Conclusion

PhFTD and bvFTD show overlapping cortical structural abnormalities indicating a continuum of changes especially in the frontotemporal regions. Together with functional changes suggestive of a compensatory response to incipient pathology in the left prefrontal regions, these findings are the first to support a possible neuropathological etiology of phFTD and suggest that phFTD may be a neurodegenerative disease on the FTD spectrum.

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Both phFTD and bvFTD show frontotemporal cortical structural abnormalities.

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PhFTD shows left frontal hyperperfusion, suggestive of functional compensation.

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Overlapping findings in phFTD and bvFTD findings suggest a common disease spectrum.

Genetic and degenerative disorders primarily causing dementia

Neuroimaging comprises a powerful set of instruments to diagnose the different causes of dementia, clarify their neurobiology, and monitor their treatment. Magnetic resonance imaging (MRI) depicts volume changes with neurodegeneration and inflammation, as well as abnormalities in functional and structural connectivity. MRI arterial spin labeling allows for the quantification of regional cerebral blood flow, characteristically altered in Alzheimer's disease, diffuse Lewy-body disease, and the frontotemporal dementias. Positron emission tomography allows for the determination of regional metabolism, with similar abnormalities as flow, and for the measurement of β-amyloid and abnormal tau deposition in the brain, as well as regional inflammation. These instruments allow for the quantification in vivo of most of the pathologic features observed in disorders causing dementia. Importantly, they allow for the longitudinal study of these abnormalities, having revealed, for instance, that the deposition of β-amyloid in the brain can antecede by decades the onset of dementia. Thus, a therapeutic window has been opened and the efficacy of immunotherapies directed at removing β-amyloid from the brain of asymptomatic individuals is currently being tested. Tau and inflammation imaging, still in their infancy, combined with genomics, should provide powerful insights into these disorders and facilitate their treatment.

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

The new diagnostic criteria for Alzheimer's disease (AD) acknowledges the interest given to biomarkers to improve the specificity in subjects with dementia and to facilitate an early diagnosis of the pathophysiological process of AD in the prodromal or pre-dementia stage. The current availability of PET imaging biomarkers of synaptic dysfunction (PET-FDG) and beta amyloid deposition using amyloid-PET provides clinicians with the opportunity to apply the new criteria and improve diagnostic accuracy in their clinical practice. Therefore, it seems essential for the scientific societies involved to use the new clinical diagnostic support tools to establish clear, evidence-based and agreed set of recommendations for their appropriate use. The present work includes a systematic review of the literature on the utility of FDG-PET and amyloid-PET for the diagnosis of AD and related neurodegenerative diseases that occur with dementia. Thus, we propose a series of recommendations agreed on by the Spanish Society of Nuclear Medicine and Spanish Society of Neurology as a consensus statement on the appropriate use of PET imaging biomarkers.