Asymmetry and heterogeneity of Alzheimer's and frontotemporal pathology in primary progressive aphasia

Clinical and neuroimaging characteristics of primary progressive aphasia

The chapter covers the clinical syndrome of a primary progressive aphasia (PPA), the demographics of this rare neurodegenerative disease, defining clinical and neuroanatomic characteristics of each PPA variant, disease progression, and behavioral features. The chapter begins with a brief introduction that includes references to seminal papers that defined this clinical syndrome and its three variants. The classic PPA subtypes discussed in the chapter are semantic variant PPA (svPPA), nonfluent/agrammatic PPA (nfaPPA), and logopenic variant PPA (lvPPA). The key language and cognitive characteristics, and language tasks that can elicit these language impairments, are detailed. Overlap in the clinical profiles of the PPA variants, which make differential diagnosis challenging, are explained. Disease progression is described, revealing that the PPA variants become more similar over time. Although PPA is language-predominant dementia, there are behavioral manifestations, particularly in svPPA. Changes in behavior in this variant are addressed as well as behavioral changes in nfaPPA and lvPPA that are less well recognized. The patterns of atrophy in the left temporal, parietal, and/or frontal cortices unique to each PPA variant are described. The underlying neuropathologies of the PPA variants are discussed, specifically tauopathies and non-tauopathies associated with svPPA and nfaPPA and Alzheimer's disease pathology in lvPPA.

Breakdown of specific functional brain networks in clinical variants of Alzheimer's disease

Alzheimer's disease (AD) is characterized by different clinical entities. Although AD phenotypes share a common molecular substrate (i.e., amyloid beta and tau accumulation), several clinicopathological differences exist. Brain functional networks might provide a macro-scale scaffolding to explain this heterogeneity. In this review, we summarize the evidence linking different large-scale functional network abnormalities to distinct AD phenotypes. Specifically, executive deficits in early-onset AD link with the dysfunction of networks that support sustained attention and executive functions. Posterior cortical atrophy relates to the breakdown of visual and dorsal attentional circuits, while the primary progressive aphasia variant of AD may be associated with the dysfunction of the left-lateralized language network. Additionally, network abnormalities might provide in vivo signatures for distinguishing proteinopathies that mimic AD, such as TAR DNA binding protein 43 related pathologies. These network differences vis-a-vis clinical syndromes are more evident in the earliest stage of AD. Finally, we discuss how these findings might pave the way for new tailored interventions targeting the most vulnerable brain circuit at the optimal time window to maximize clinical benefits.

Language changes in Alzheimer's disease: A systematic review of verb processing

Alzheimer's disease (AD) results in language impairments and higher-level communication problems. Research into the language of people with AD (pwAD) has mainly focused on nouns; however, improved understanding of verb processing by pwAD could improve diagnostic assessments and communicative interventions. This systematic review synthesizes findings of AD's effects on verbs from single-word, sentence, and discourse tasks. Review of 57 studies revealed that pwAD were less accurate than controls on single-word tasks and less accurate with verbs than nouns on these tasks. They had difficulty comprehending sentences featuring multiple verbs or verbs with reversible thematic roles. Discourse production by pwAD was marked by vagueness, including declines in total output and propositional content and a preference for generic verbs and simple syntax. Few studies examining sentence production or discourse comprehension were found. Future research should address relationships between long-term memory and language preservation as well as verb use in discourse.

Beyond the average patient: how neuroimaging models can address heterogeneity in dementia

Dementia is a highly heterogeneous condition, with pronounced individual differences in age of onset, clinical presentation, progression rates and neuropathological hallmarks, even within a specific diagnostic group. However, the most common statistical designs used in dementia research studies and clinical trials overlook this heterogeneity, instead relying on comparisons of group average differences (e.g. patient versus control or treatment versus placebo), implicitly assuming within-group homogeneity. This one-size-fits-all approach potentially limits our understanding of dementia aetiology, hindering the identification of effective treatments. Neuroimaging has enabled the characterization of the average neuroanatomical substrates of dementias; however, the increasing availability of large open neuroimaging datasets provides the opportunity to examine patterns of neuroanatomical variability in individual patients. In this update, we outline the causes and consequences of heterogeneity in dementia and discuss recent research that aims to tackle heterogeneity directly, rather than assuming that dementia affects everyone in the same way. We introduce spatial normative modelling as an emerging data-driven technique, which can be applied to dementia data to model neuroanatomical variation, capturing individualized neurobiological 'fingerprints'. Such methods have the potential to detect clinically relevant subtypes, track an individual's disease progression or evaluate treatment responses, with the goal of moving towards precision medicine for dementia.

Clinicopathological heterogeneity of Alzheimer's disease with pure Alzheimer's disease pathology: Cases associated with dementia with Lewy bodies, very early-onset dementia, and primary progressive aphasia

We report four cases depicting the heterogeneity of Alzheimer's disease (AD) associated with pure AD pathology. Case 1 was a 77-year-old man with a false positive diagnosis of dementia with Lewy bodies with reduced dopamine transporter uptake activity of the striatum but no Lewy body pathology. There were tau deposits in the large neurons in the putamen, which may be related to the development of parkinsonism. Case 2 was an AD patient in his early 30s who presented with a psychotic episode and a cognitive decline, and later developed myoclonus and seizures. He demonstrated considerable amyloid-beta deposits in the cerebral cortex, including cotton wool plaques, basal ganglia, and cerebellum. Tau deposits were also abundant in the cerebral neocortex, hippocampus, basal ganglia, and brain stem. Case 3 was a 60-year-old woman who exhibited typical symptoms characteristic of the logopenic variant of primary progressive aphasia (lvPPA). Case 4 was a 68-year-old man who exhibited the semantic variant of primary progressive aphasia (svPPA) plus repetition impairment, a rare case associated with AD pathology. In addition to tau pathology, astrocytic pathology was prominent in the white matter and cortical layers of the left temporoparietal cortices. While the main AD lesion in case 4 was evaluated by tau accumulation and astrogliosis in the left temporal lobe, that in case 3 in was evaluated by the same points in the left parietal lobe. Within the spectrum of lvPPA, case 4 may be regarded as a temporal variant of lvPPA presenting svPPA. The pathology of PPA associated with AD may have broader clinical manifestations than that in previously described cases. Case 4 also showed pathological features characteristic of cerebral amyloid angiopathy throughout the cerebral cortex. The distribution of tau and astrocytic pathologies in the cerebral cortex, basal ganglia, brain stem, and cerebellum may explain the various symptoms of atypical pure AD patients.

Retina tissue validation of optical coherence tomography determined outer nuclear layer loss in FTLD-tau

Alzheimer's disease (AD) is associated with inner retina (nerve fiber and ganglion cell layers) thinning. In contrast, we have seen outer retina thinning driven by photoreceptor outer nuclear layer (ONL) thinning with antemortem optical coherence tomography (OCT) among patients considered to have a frontotemporal degeneration tauopathy (FTLD-Tau). Our objective was to determine if postmortem retinal tissue from FTLD-Tau patients demonstrates ONL loss observed antemortem on OCT. Two probable FTLD-Tau patients that were deeply phenotyped by clinical and genetic testing were imaged with OCT and followed to autopsy. Postmortem brain and retinal tissue were evaluated by a neuropathologist and ocular pathologist, respectively, masked to diagnosis. OCT findings were correlated with retinal histology. The two patients had autopsy-confirmed FTLD-Tau neuropathology and had antemortem OCT measurements showing ONL thinning (66.9 μm, patient #1; 74.9 μm, patient #2) below the 95% confidence interval of normal limits (75.1-120.7 μm) in our healthy control cohort. Postmortem, retinal tissue from both patients demonstrated loss of nuclei in the ONL, matching ONL loss visualized on antemortem OCT. Nuclei counts from each area of ONL loss (2 - 3 nuclei per column) seen in patient eyes were below the 95% confidence interval (4 - 8 nuclei per column for ONL) of 3 normal control retinas analyzed at the same location. Our evaluation of retinal tissue from FTLD-Tau patients confirms ONL loss seen antemortem by OCT. Continued investigation of ONL thinning as a biomarker that may distinguish FTLD-Tau from other dementias is warranted.

Clinical Characteristic in Primary Progressive Aphasia in Relation to Alzheimer's Disease Biomarkers

BACKGROUND

Primary progressive aphasia (PPA) is associated with amyloid-β (Aβ) pathology. However, clinical feature of PPA based on Aβ positivity remains unclear.

OBJECTIVE

We aimed to assess the prevalence of Aβ positivity in patients with PPA and compare the clinical characteristics of patients with Aβ-positive (A+) and Aβ-negative (A-) PPA. Further, we applied Aβ and tau classification system (AT system) in patients with PPA for whom additional information of in vivo tau biomarker was available.

METHODS

We recruited 110 patients with PPA (41 semantic [svPPA], 27 non-fluent [nfvPPA], 32 logopenic [lvPPA], and 10 unclassified [ucPPA]) who underwent Aβ-PET imaging at multi centers. The extent of language impairment and cortical atrophy were compared between the A+ and A-PPA subgroups using general linear models.

RESULTS

The prevalence of Aβ positivity was highest in patients with lvPPA (81.3%), followed by ucPPA (60.0%), nfvPPA (18.5%), and svPPA (9.8%). The A+ PPA subgroup manifested cortical atrophy mainly in the left superior temporal/inferior parietal regions and had lower repetition scores compared to the A-PPA subgroup. Further, we observed that more than 90% (13/14) of the patients with A+ PPA had tau deposition.

CONCLUSION

Our findings will help clinicians understand the patterns of language impairment and cortical atrophy in patients with PPA based on Aβ deposition. Considering that most of the A+ PPA patents are tau positive, understanding the influence of Alzheimer's disease biomarkers on PPA might provide an opportunity for these patients to participate in clinical trials aimed for treating atypical Alzheimer's disease.

Posterior Cingulate Cortex Hypometabolism in Non-Amnestic Variants of Alzheimer's Disease

BACKGROUND

Hypometabolism of the posterior cingulate cortex (PCC) is an important diagnostic feature of late-onset, amnestic Alzheimer's disease (AD) measured with 18F-fluorodeoxyglucose positron emission tomography (FDG-PET). However, it is unclear whether PCC hypometabolism has diagnostic value in young-onset, non-amnestic variants of AD, which exhibit less pathology in the hippocampus and default mode network.

OBJECTIVE

Evaluate the prevalence and diagnostic value of PCC hypometabolism in non-amnestic variants of AD.

METHODS

We retrospectively identified 60 patients with young-onset, atypical dementia who have undergone a detailed clinical evaluation, FDG-PET, and an amyloid biomarker (amyloid-PET or cerebrospinal fluid analysis). We quantitatively analyzed regional hypometabolism in 70 regions of interest (ROI) using the MIMneuro® software.

RESULTS

Based on a cut-off of z-score < -1.5 for significant PCC hypometabolism, the prevalence of PCC hypometabolism in non-amnestic variants of AD was 65% compared to 28% in clinical variants of frontotemporal dementia (FTD). The ROI with the maximal hypometabolism was the dominant middle temporal gyrus in the language variant of AD (mean z score -2.28), middle occipital gyrus in PCA (-3.24), middle temporal gyrus in frontal AD (-2.70), and angular gyrus in corticobasal syndrome due to AD (-2.31). The PCC was not among the 10 most discriminant regions between non-amnestic variants of AD versus clinical variants of FTD.

CONCLUSION

We conclude that PCC hypometabolism is not a discriminant feature to distinguish non-amnestic variants of AD from clinical variants of FTD-and should be interpreted with caution in patients with young-onset, non-amnestic dementia.

Relationships among tau burden, atrophy, age, and naming in the aphasic variant of Alzheimer's disease

INTRODUCTION

Examination of pathologic, anatomic, and cognitive relationships has been limited in primary progressive aphasia (PPA) with underlying Alzheimer's disease (AD) neuropathology.

METHODS

Spatial relationships between tau positron emission tomography (PET), cortical thickness, age, and naming on the Boston Naming Test (BNT) in PPA with biomarker evidence of AD (PPA-AD) were examined.

RESULTS

Higher tau PET burden was associated with atrophy and younger age. There was a significant left-lateralized relationship between lower BNT and more atrophy, and between lower BNT and increased tau burden. Variance in naming was primarily shared between tau and atrophy (51%), but naming was uniquely explained more by atrophy (32%) than tau (16%). Higher left anterior temporal tau burden was associated with greater 1-year rate of decline in naming.

DISCUSSION

PPA-AD has a similar relationship between abnormal biomarkers as first described in amnestic AD, with differing spatial extent, reflecting the left-lateralized nature of the language network.

Clinical Characterization of Atypical Primary Progressive Aphasia in a 3-Year Longitudinal Study: A Case Report

The logopenic variant of primary progressive aphasia (lvPPA) is the most recent variant of primary progressive aphasia (PPA) to be identified; thus far, it has been poorly investigated. Despite being typically associated with Alzheimer disease (AD), lvPPA has recently been linked to frontotemporal lobe degeneration (FTLD), with distinctive cognitive and neural features that are worthy of further investigation. Here, we describe the neuropsychological and linguistic profile, as well as cerebral abnormalities, of an individual exhibiting PPA and carrying a pathogenetic variant in the GRN gene, from a 3-year longitudinal perspective. The individual's initial profile resembled lvPPA because it was characterized by word-finding difficulties and phonological errors in spontaneous speech in addition to sentence repetition and phonological short-term memory impairments. The individual's structural and metabolic imaging data demonstrated left temporal and bilateral frontal atrophy and hypometabolism, respectively. On follow-up, as the pathology progressed, dysprosody, stereotypical speech patterns, agrammatism, and orofacial apraxia appeared, suggesting an overlap with the nonfluent variant of PPA (nfvPPA). Severe sentence comprehension impairment also became evident. Our longitudinal and multidisciplinary diagnostic approach allowed us to better characterize the progression of a GRN-positive lvPPA profile, providing neuropsychological and imaging indicators that might be helpful to improve classification between different PPA variants and to address a nosological issue. Finally, we discuss the importance of early diagnosis of PPA given the possible overlap between different PPA variants during the progression of the pathology.

Tau and MAPT genetics in tauopathies and synucleinopathies

MAPT encodes the microtubule-associated protein tau, which is the main component of neurofibrillary tangles (NFTs) and found in other protein aggregates. These aggregates are among the pathological hallmarks of primary tauopathies such as frontotemporal dementia (FTD). Abnormal tau can also be observed in secondary tauopathies such as Alzheimer's disease (AD) and synucleinopathies such as Parkinson's disease (PD). On top of pathological findings, genetic data also links MAPT to these disorders. MAPT variations are a cause or risk factors for many tauopathies and synucleinopathies and are associated with certain clinical and pathological features in affected individuals. In addition to clinical, pathological, and genetic overlap, evidence also suggests that tau and alpha-synuclein may interact on the molecular level, and thus might collaborate in the neurodegenerative process. Understanding the role of MAPT variations in tauopathies and synucleinopathies is therefore essential to elucidate the role of tau in the pathogenesis and phenotype of those disorders, and ultimately to develop targeted therapies. In this review, we describe the role of MAPT genetic variations in tauopathies and synucleinopathies, several genotype-phenotype and pathological features, and discuss their implications for the classification and treatment of those disorders.

Altered Spontaneous Brain Activity in Subjects With Different Cognitive States of Biologically Defined Alzheimer's Disease: A Surface-Based Functional Brain Imaging Study

Background: Before the apparent cognitive decline, subjects on the course of Alzheimer's disease (AD) can have significantly altered spontaneous brain activity, which could be potentially used for early diagnosis. As previous studies investigating local brain activity may suffer from the problem of cortical signal aliasing during volume-based analysis, we aimed to investigate the cortical functional alterations in the AD continuum using a surface-based approach. Methods: Based on biomarker profile "A/T," we included 11 healthy controls (HC, A-T-), 22 preclinical AD (CU, A+T+), 33 prodromal AD (MCI, A+T+), and 20 AD with dementia (d-AD, A+T+) from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database. The amplitude of low-frequency fluctuation (ALFF) method was used to evaluate the changes of spontaneous brain activity, which was performed in the classic frequency band (0.01-0.08 Hz), slow-4 (0.027-0.073 Hz) band, and slow-5 (0.01-0.027 Hz) band. Results: Under classic frequency band and slow-4 band, analysis of covariance (ANCOVA) showed that there were significant differences of standardized ALFF (zALFF) in the left posterior cingulate cortex (PCC) among the four groups. The post-hoc analyses showed that under the classic frequency band, the AD group had significantly decreased zALFF compared with the other three groups, and the cognitively unimpaired (CU) group had decreased zALFF compared with the healthy control (HC) group. Under the slow-4 band, more group differences were detected (HC > CU/MCI > d-AD). The accuracy of classifying CU, mild cognitive impairment (MCI), and AD from HC by left PCC activity under the slow-4 band were 0.774, 0.744, and 0.920, respectively. Moreover, the zALFF values of the left PCC had significant correlations with cerebrospinal fluid (CSF) biomarkers and neuropsychological tests. Conclusions: Spontaneous brain activity in the left PCC may decrease in preclinical AD when cognitive functions were relatively normal. The combination of a surfaced-based approach and specific frequency band analysis may increase sensitivity for the identification of preclinical AD subjects.

Longitudinal naming and repetition relates to AD pathology and burden in autopsy-confirmed primary progressive aphasia

INTRODUCTION

In primary progressive aphasia (PPA) patients with autopsy-confirmed Alzheimer's disease (AD) or frontotemporal lobar degeneration (FLTD), we tested how the core clinical features of logopenic PPA-naming and repetition-change over time and relate to pathologic burden.

METHODS

In PPA with AD (n = 13) or FTLD (n = 16) pathology, Boston Naming Test and Forward Digit Span measured longitudinal naming and repetition; as reference, Mini-Mental State Examination (MMSE) measured global cognition. Pathologic burden in left peri-Sylvian regions was related to longitudinal cognitive decline.

RESULTS

PPA with AD showed greater decline in naming (P = 0.021) and repetition (P = 0.020), compared to FTLD; there was no difference in MMSE decline (P = 0.99). Across all PPA, declining naming (P = 0.0084) and repetition (P = 0.011) were associated with angular, superior-middle temporal (naming P = 0.014; repetition P = 0.011) and middle frontal (naming P = 0.041; repetition P = 0.030) pathologic burden.

DISCUSSION

Unique longitudinal profiles of naming and repetition performance in PPA with AD are related to left peri-Sylvian pathology.

A Spanish Neuropsychological Battery Discriminates Between the Behavioral Variant of Frontotemporal Dementia and Primary Progressive Aphasia in a Colombian Sample

The differential diagnosis among the behavioral variant of frontotemporal dementia FTD (bvFTD) and the linguist one primary progressive aphasia (PPA) is challenging. Presentations of dementia type or variants dominated by personality change or aphasia are frequently misinterpreted as psychiatric illness, stroke, or other conditions. Therefore, it is important to identify cognitive tests that can distinguish the distinct FTD variants to reduce misdiagnosis and best tailor interventions. We aim to examine the discriminative capacity of the most frequently used cognitive tests in their Spanish version for the context of dementia evaluation as well as the qualitative aspects of the neuropsychological performance such as the frequency and type of errors, perseverations, and false positives that can best discriminate between bvFTD and PPA. We also described mood and behavioral profiles of participants with mild to moderate probable bvFTD and PPA. A total of 55 subjects were included in this cross-sectional study: 20 with PPA and 35 with bvFTD. All participants underwent standard dementia screening that included a medical history and physical examination, brain MRI, a semistructured caregiver interview, and neuropsychological testing. We found that bvFTD patients had worse performance in executive function tests, and the PPA presented with the lower performance in language tests and the global score of Mini-Mental State Examination (MMSE). After running the linear discriminant model, we found three functions of cognitive test and subtests combination and three functions made by the Montreal Cognitive Assessment (MoCA) language subtest and performance errors that predicted group belonging. Those functions were more capable to classify bvFTD cases rather than PPA. In conclusion, our study supports that the combination of an individual test of executive function and language, MoCA's subtest, and performance errors as well have good accuracy to discriminate between bvFTD and PPA.

The Combination of Metabolic Posterior Cingulate Cortical Abnormalities and Structural Asymmetries Improves the Differential Diagnosis Between Primary Progressive Aphasia and Alzheimer's Disease

Differential diagnosis between primary progressive aphasia (PPA) and Alzheimer's disease (AD) could be difficult if based on clinical grounds alone. We evaluated the combination of proton MR spectroscopy of posterior cingulate cortex (PCC) and quantitative structural imaging asymmetries to differentiate PPA from AD patients. A greater left-lateralized temporo-parietal atrophy (higher accuracy for the PCC, 81.4%) and metabolic neurodegenerative changes in PCC (accuracy 76.8%) was demonstrated in PPA versus AD. The combined multiparametric approach increased the accuracy to 94%in the differential diagnosis between these two neurodegenerative diseases.

Clinical, Imaging, and Pathologic Characteristics of Patients With Right vs Left Hemisphere-Predominant Logopenic Progressive Aphasia

OBJECTIVE

To assess and compare demographic, clinical, neuroimaging, and pathologic characteristics of a cohort of patients with right hemisphere-predominant vs left hemisphere-predominant logopenic progressive aphasia (LPA).

METHODS

This is a case-control study of patients with LPA who were prospectively followed at Mayo Clinic and underwent [¹⁸F]-fluorodeoxyglucose (FDG) PET scan. Patients were classified as rLPA if right temporal lobe metabolism was ≥1 SD lower than left temporal lobe metabolism. Patients with rLPA were frequency-matched 3:1 to typical left-predominant LPA based on degree of asymmetry and severity of temporal lobe metabolism. Patients were compared on clinical, imaging (MRI, FDG-PET, β-amyloid, and tau-PET), and pathologic characteristics.

RESULTS

Of 103 prospectively recruited patients with LPA, 8 (4 female) were classified as rLPA (7.8%); all patients with rLPA were right-handed. Patients with rLPA had milder aphasia based on the Western Aphasia Battery-Aphasia Quotient (p = 0.04) and less frequent phonologic errors (p = 0.015). Patients with rLPA had shorter survival compared to typical LPA: hazard ratio 4.0 (1.2-12.9), p = 0.02. There were no other differences in demographics, handedness, genetics, or neurologic or neuropsychological tests. Compared to the 24 frequency-matched patients with typical LPA, patients with rLPA showed greater frontotemporal hypometabolism of the nondominant hemisphere on FDG-PET and less atrophy in amygdala and hippocampus of the dominant hemisphere. Autopsy evaluation revealed a similar distribution of pathologic findings in both groups, with Alzheimer disease pathologic changes being the most frequent pathology.

CONCLUSIONS

rLPA is associated with less severe aphasia but has shorter survival from reported symptom onset than typical LPA, possibly related to greater involvement of the nondominant hemisphere.

Longitudinal decline in spoken word recognition and object knowledge in primary progressive aphasia

The premise of this study is that spoken word recognition and object knowledge are impaired in semantic variant primary progressive aphasia (PPA) (svPPA) and are spared in logopenic variant (lvPPA) and nonfluent agrammatic primary progressive aphasia (nfaPPA) at disease onset. Over time, however, there may be heterogeneity in these abilities in lvPPA and nfaPPA. We hypothesized that individuals with svPPA would demonstrate poorer performance on baseline spoken word recognition and object knowledge than those with lvPPA and nfaPPA) as documented in the literature, but that rates of decline over time on spoken word recognition and object knowledge would be similar in all 3 PPA variants because these become less distinguishable with disease progression.The aim of this study was to investigate longitudinal patterns of decline in spoken word recognition and object knowledge across PPA variants.Ninety-five individuals with PPA completed the Semantic Word Picture Matching and Semantic Associates tests at baseline to establish expected performance in these areas. Thirty-five individuals completed follow-up testing.The distributions of trichotomized mean rates of decline in object knowledge were similar for lvPPA and svPPA (P = .05). There were weak negative correlations between symptom duration and baseline scores on Semantic Word Picture Matching (r[37] = -0.399, P = .01), and baseline scores on Semantic Associates (r[37] = -0.394, P = .01) in lvPPA.Degradation of spoken word recognition and object knowledge occurs over time in lvPPA. Further investigation of the receptive language deficits in PPA is warranted to characterize language changes that lessen the distinctions between PPA variants with disease progression.

Clinical diagnosis of Alzheimer's disease: recommendations of the International Working Group

In 2018, the US National Institute on Aging and the Alzheimer's Association proposed a purely biological definition of Alzheimer's disease that relies on biomarkers. Although the intended use of this framework was for research purposes, it has engendered debate and challenges regarding its use in everyday clinical practice. For instance, cognitively unimpaired individuals can have biomarker evidence of both amyloid β and tau pathology but will often not develop clinical manifestations in their lifetime. Furthermore, a positive Alzheimer's disease pattern of biomarkers can be observed in other brain diseases in which Alzheimer's disease pathology is present as a comorbidity. In this Personal View, the International Working Group presents what we consider to be the current limitations of biomarkers in the diagnosis of Alzheimer's disease and, on the basis of this evidence, we propose recommendations for how biomarkers should and should not be used for diagnosing Alzheimer's disease in a clinical setting. We recommend that Alzheimer's disease diagnosis be restricted to people who have positive biomarkers together with specific Alzheimer's disease phenotypes, whereas biomarker-positive cognitively unimpaired individuals should be considered only at-risk for progression to Alzheimer's disease.

Longitudinal Amyloid-β PET in Atypical Alzheimer's Disease and Frontotemporal Lobar Degeneration

BACKGROUND

Rates of amyloid-β (Aβ) accumulation have been characterized across the cognitively normal to typical Alzheimer's dementia spectrum, but little is known about Aβ accumulation in atypical Alzheimer's disease (AD) and other neurodegenerative diseases, such as frontotemporal lobar degeneration (FTLD).

OBJECTIVE

We aimed tocharacterize longitudinal Aβ accumulation anddetermine the influence of age, apolipoprotein E (APOE) genotype, disease duration, and sexin atypical AD and FTLD.

METHODS

322 patients (138 atypical AD, 184 FTLD) underwent Pittsburgh compound B PET scanning, with 73 having serialPiB-PET scans (42 atypical AD, 31 FTLD). Global Aβ standard uptake value ratios were calculated for every scan. Mixed effects models were used to assess the effect of age, APOE genotype, disease duration, and sex on baseline and change measures of Aβ.

RESULTS

Atypical AD showed higher baseline Aβ than FTLD. Rate of Aβ accumulation was not associated with baseline Aβ in either group. Older age was associated with greater baseline Aβ and faster rates of accumulation in FTLD. In patients under age 70, atypical AD showed faster rates of accumulation than FTLD. APOEɛ4 genotype was associated with greater baseline Aβ in FTLD but did not influence rates of accumulation. Rates of Aβ accumulation were faster in FTLD patents with time from onset-to-PET≤4 years. Female sex was associated with faster rates of accumulation in atypical AD.

CONCLUSION

Accumulation of Aβ is observed in atypical AD and FTLD, although different demographic factors influence accumulation in these diseases providing insight into potentially different biological mechanisms of Aβ deposition.

Primary Progressive Aphasia Associated With GRN Mutations: New Insights Into the Nonamyloid Logopenic Variant

OBJECTIVE

To determine relative frequencies and linguistic profiles of primary progressive aphasia (PPA) variants associated with GRN (progranulin) mutations and to study their neuroanatomic correlates.

METHODS

Patients with PPA carrying GRN mutations (PPA-GRN) were selected among a national prospective research cohort of 1,696 patients with frontotemporal dementia, including 235 patients with PPA. All patients with amyloid-positive CSF biomarkers were excluded. In this cross-sectional study, speech/language and cognitive profiles were characterized with standardized evaluations, and gray matter (GM) atrophy patterns using voxel-based morphometry. Comparisons were performed with controls and patients with sporadic PPA.

RESULTS

Among the 235 patients with PPA, 45 (19%) carried GRN mutations, and we studied 32 of these. We showed that logopenic PPA (lvPPA) was the most frequent linguistic variant (n = 13, 41%), followed by nonfluent/agrammatic (nfvPPA; n = 9, 28%) and mixed forms (n = 8, 25%). Semantic variant was rather rare (n = 2, 6%). Patients with lvPPA, qualified as nonamyloid lvPPA, presented canonical logopenic deficit. Seven of 13 had a pure form; 6 showed subtle additional linguistic deficits not fitting criteria for mixed PPA and hence were labeled as logopenic-spectrum variant. GM atrophy involved primarily left posterior temporal gyrus, mirroring neuroanatomic changes of amyloid-positive-lvPPA. Patients with nfvPPA presented agrammatism (89%) rather than apraxia of speech (11%).

CONCLUSIONS

This study shows that the most frequent PPA variant associated with GRN mutations is nonamyloid lvPPA, preceding nfvPPA and mixed forms, and illustrates that the language network may be affected at different levels. GRN testing is indicated for patients with PPA, whether familial or sporadic. This finding is important for upcoming GRN gene-specific therapies.

Accuracy of MRI Classification Algorithms in a Tertiary Memory Center Clinical Routine Cohort

BACKGROUND

Automated volumetry software (AVS) has recently become widely available to neuroradiologists. MRI volumetry with AVS may support the diagnosis of dementias by identifying regional atrophy. Moreover, automatic classifiers using machine learning techniques have recently emerged as promising approaches to assist diagnosis. However, the performance of both AVS and automatic classifiers have been evaluated mostly in the artificial setting of research datasets.

OBJECTIVE

Our aim was to evaluate the performance of two AVS and an automatic classifier in the clinical routine condition of a memory clinic.

METHODS

We studied 239 patients with cognitive troubles from a single memory center cohort. Using clinical routine T1-weighted MRI, we evaluated the classification performance of: 1) univariate volumetry using two AVS (volBrain and Neuroreader™); 2) Support Vector Machine (SVM) automatic classifier, using either the AVS volumes (SVM-AVS), or whole gray matter (SVM-WGM); 3) reading by two neuroradiologists. The performance measure was the balanced diagnostic accuracy. The reference standard was consensus diagnosis by three neurologists using clinical, biological (cerebrospinal fluid) and imaging data and following international criteria.

RESULTS

Univariate AVS volumetry provided only moderate accuracies (46% to 71% with hippocampal volume). The accuracy improved when using SVM-AVS classifier (52% to 85%), becoming close to that of SVM-WGM (52 to 90%). Visual classification by neuroradiologists ranged between SVM-AVS and SVM-WGM.

CONCLUSION

In the routine practice of a memory clinic, the use of volumetric measures provided by AVS yields only moderate accuracy. Automatic classifiers can improve accuracy and could be a useful tool to assist diagnosis.

A systematic review of atypical Alzheimer's disease including behavioural and psychological symptoms

Alzheimer's disease (AD) is the commonest cause of dementia, characterized by the clinical presentation of progressive anterograde episodic memory impairment. However, atypical presentation of patients is increasingly recognized. These atypical AD include logopenic aphasia, behavioural variant AD, posterior cortical atrophy, and corticobasal syndrome. These atypical AD are more common in patients with young onset AD before the age of 65 years old. Since medical needs (including the behavioural and psychological symptoms of dementia) of atypical AD patients could be different from typical AD patients, it is important for clinicians to be aware of these atypical forms of AD. In addition, disease modifying treatment may be available in the future. This review aims at providing an update on various important subtypes of atypical AD including behavioural and psychological symptoms.

Asymmetry of Hippocampal Tau Pathology in Primary Age-Related Tauopathy and Alzheimer Disease

Primary age-related tauopathy (PART) is a neurodegenerative entity defined as neurofibrillary degeneration generally restricted to the medial temporal region (Braak stage I-IV) with complete or near absence of diffuse and neuritic plaques. Symptoms range in severity but are generally milder and later in onset than in Alzheimer disease (AD). Recently, an early predilection for neurofibrillary degeneration in the hippocampal CA2 subregion has been demonstrated in PART, whereas AD neuropathologic change (ADNC) typically displays relative sparing of CA2 until later stages. In this study, we utilized a semiquantitative scoring system to evaluate asymmetry of neurofibrillary degeneration between left and right hippocampi in 67 PART cases and 17 ADNC cases. 49% of PART cases demonstrated asymmetric findings in at least one hippocampal subregion, and 79% of the asymmetric cases displayed some degree of CA2 asymmetry. Additionally, 19% of cases revealed a difference in Braak score between the right and left hippocampi. There was a significant difference in CA2 neurofibrillary degeneration (p = 0.0006) and CA2/CA1 ratio (p < 0.0001) when comparing the contralateral sides, but neither right nor left was more consistently affected. These data show the importance of analyzing bilateral hippocampi in the diagnostic evaluation of PART and potentially of other neurodegenerative diseases.

Functional decline in the aphasic variant of Alzheimer's disease

INTRODUCTION

Primary progressive aphasia (PPA) is a clinical dementia syndrome associated with frontotemporal lobar degeneration (FTLD) or Alzheimer's disease (AD). Impairment in activities of daily living is essential for dementia diagnosis, yet less is known about the neuropathologic impact on functional decline in PPA, especially over time.

METHODS

Activities of Daily Living Questionnaire (ADLQ) ratings were compared by suspected underlying pathology between 17 PPA^Aβ+ and 11 PPA^Aβ- participants at 6-month intervals for 2 years using a linear mixed-effects model. A general linear model examined associations between functional decline and cortical thickness at baseline.

RESULTS

Groups did not differ in demographics or aphasia severity at baseline, yet overall and subdomain scores of the ADLQ were significantly worse for PPA^Aβ+ compared to PPA^Aβ- (P = .015) at each interval across 18 months.

DISCUSSION

Functional decline appears more pronounced and disrupts more aspects of life activities for individuals with non-semantic PPA with suspected AD versus non-AD neuropathology.

Interference Resolution in Nonfluent Variant Primary Progressive Aphasia: Evidence From a Picture-Word Interference Task

BACKGROUND

Picture-word interference tasks have been used to investigate (a) the time course of lexical access in individuals with primary progressive aphasia (PPA) and (b) how these individuals resolve competition during lexical selection.

OBJECTIVE

To investigate the time course of Greek-speaking individuals with PPA to produce grammatical gender-marked determiner phrases by examining their picture-naming latencies in the context of distractor words.

METHOD

Eight individuals with nonfluent variant PPA (nfv-PPA; M age = 62.8 years) and eight cognitively intact controls (M age = 61.1 years) participated in our study. In a picture-word interference task, the study participants named depicted objects by producing determiner + noun sequences. Interference was generated by manipulating the grammatical gender of the depicted objects and distractor words. Two stimulus onset asynchronies were used: +200 ms and +400 ms.

RESULTS

The individuals with nfv-PPA exhibited longer picture-naming latencies than the controls (P = 0.003). The controls exhibited interference from incongruent distractors at both asynchronies (P < 0.001); the individuals with PPA exhibited interference from incongruent distractors only at the +400-ms interval (P = 0.002). The gender-congruency effect was stronger for the individuals with PPA than for the controls at the +400-ms interval (P = 0.05); the opposite pattern was observed at the +200-ms interval (P = 0.024).

CONCLUSION

Gender interference resolution was abnormal in the individuals with nfv-PPA. The results point to deficits in lexicosyntactic networks that compromised the time course of picture-naming production.

Language impairment in progressive supranuclear palsy and corticobasal syndrome

Although commonly known as movement disorders, progressive supranuclear palsy (PSP) and corticobasal syndrome (CBS) may present with changes in speech and language alongside or even before motor symptoms. The differential diagnosis of these two disorders can be challenging, especially in the early stages. Here we review their impact on speech and language. We discuss the neurobiological and clinical-phenomenological overlap of PSP and CBS with each other, and with other disorders including non-fluent agrammatic primary progressive aphasia and primary progressive apraxia of speech. Because language impairment is often an early and persistent problem in CBS and PSP, there is a need for improved methods for language screening in primary and secondary care, and more detailed language assessments in tertiary healthcare settings. Improved language assessment may aid differential diagnosis as well as inform clinical management decisions.

Lewy Body Disease is a Contributor to Logopenic Progressive Aphasia Phenotype

OBJECTIVE

The objective of this study was to describe clinical features, [18 F]-fluorodeoxyglucose (FDG)-positron emission tomography (PET) metabolism and digital pathology in patients with logopenic progressive aphasia (LPA) and pathologic diagnosis of diffuse Lewy body disease (DLBD) and compare to patients with LPA with other pathologies, as well as patients with classical features of probable dementia with Lewy bodies (pDLB).

METHODS

This is a clinicopathologic case-control study of 45 patients, including 20 prospectively recruited patients with LPA among whom 6 were diagnosed with LPA-DLBD. We analyzed clinical features and compared FDG-PET metabolism in LPA-DLBD to an independent group of patients with clinical pDLB and regional α-synuclein burden on digital pathology to a second independent group of autopsied patients with DLBD pathology and antemortem pDLB (DLB-DLBD).

RESULTS

All patients with LPA-DLBD were men. Neurological, speech, and neuropsychological characteristics were similar across LPA-DLBD, LPA-Alzheimer's disease (LPA-AD), and LPA-frontotemporal lobar degeneration (LPA-FTLD). Genetic screening of AD, DLBD, and FTLD linked genes were negative with the exception of APOE ε4 allele present in 83% of LPA-DLBD patients. Seventy-five percent of the patients with LPA-DLBD showed a parietal-dominant pattern of hy pometabolism; LPA-FTLD - temporal-dominant pattern, whereas LPA-AD showed heterogeneous patterns of hypometabolism. LPA-DLBD had more asymmetrical hypometabolism affecting frontal lobes, with relatively spared occipital lobe in the nondominantly affected hemisphere, compared to pDLB. LPA-DLBD had minimal atrophy on gross brain examination, higher cortical Lewy body counts, and higher α-synuclein burden in the middle frontal and inferior parietal cortices compared to DLB-DLBD.

INTERPRETATION

Whereas AD is the most frequent underlying pathology of LPA, DLBD can also be present and may contribute to the LPA phenotype possibly due to α-synuclein-associated functional impairment of the dominant parietal lobe. ANN NEUROL 2021;89:520-533.

Frontotemporal lobar degeneration proteinopathies have disparate microscopic patterns of white and grey matter pathology

Frontotemporal lobar degeneration proteinopathies with tau inclusions (FTLD-Tau) or TDP-43 inclusions (FTLD-TDP) are associated with clinically similar phenotypes. However, these disparate proteinopathies likely differ in cellular severity and regional distribution of inclusions in white matter (WM) and adjacent grey matter (GM), which have been understudied. We performed a neuropathological study of subcortical WM and adjacent GM in a large autopsy cohort (n = 92; FTLD-Tau = 37, FTLD-TDP = 55) using a validated digital image approach. The antemortem clinical phenotype was behavioral-variant frontotemporal dementia (bvFTD) in 23 patients with FTLD-Tau and 42 with FTLD-TDP, and primary progressive aphasia (PPA) in 14 patients with FTLD-Tau and 13 with FTLD-TDP. We used linear mixed-effects models to: (1) compare WM pathology burden between proteinopathies; (2) investigate the relationship between WM pathology burden and WM degeneration using luxol fast blue (LFB) myelin staining; (3) study regional patterns of pathology burden in clinico-pathological groups. WM pathology burden was greater in FTLD-Tau compared to FTLD-TDP across regions (beta = 4.21, SE = 0.34, p < 0.001), and correlated with the degree of WM degeneration in both FTLD-Tau (beta = 0.32, SE = 0.10, p = 0.002) and FTLD-TDP (beta = 0.40, SE = 0.08, p < 0.001). WM degeneration was greater in FTLD-Tau than FTLD-TDP particularly in middle-frontal and anterior cingulate regions (p < 0.05). Distinct regional patterns of WM and GM inclusions characterized FTLD-Tau and FTLD-TDP proteinopathies, and associated in part with clinical phenotype. In FTLD-Tau, WM pathology was particularly severe in the dorsolateral frontal cortex in nonfluent-variant PPA, and GM pathology in dorsolateral and paralimbic frontal regions with some variation across tauopathies. Differently, FTLD-TDP had little WM regional variability, but showed severe GM pathology burden in ventromedial prefrontal regions in both bvFTD and PPA. To conclude, FTLD-Tau and FTLD-TDP proteinopathies have distinct severity and regional distribution of WM and GM pathology, which may impact their clinical presentation, with overall greater severity of WM pathology as a distinguishing feature of tauopathies.

Uniform data set language measures for bvFTD and PPA diagnosis and monitoring

INTRODUCTION

The Frontotemporal Lobar Degeneration Module (FTLD-MOD) includes a neuropsychological battery designed to assess the clinical features of FTLD, although much is unknown about its utility. We investigated FTLD-MOD and Uniform Data Set 3.0 (UDS) language tests for differential diagnosis and disease monitoring.

METHODS

Linear regressions compared baseline performances in 1655 National Alzheimer's Coordinating Center participants (behavioral variant frontotemporal dementia (bvFTD, n = 612), semantic variant primary progressive aphasia (svPPA, n = 168), non-fluent/agrammatic variant PPA (nfvPPA, n = 168), logopenic variant PPA (lvPPA, n = 109), and controls (n = 581)). Sample sizes to detect treatment effects were estimated using longitudinal data.

RESULTS

Among PPAs, the FTLD-MOD language tasks and UDS Multilingual Naming Test accurately discriminated svPPA. Number Span Forward best discriminated lvPPA; Phonemic:Semantic Fluency ratio was excellent for nfvPPA classification. UDS fluency and naming measures required the smallest sample size to detect meaningful change.

DISCUSSION

The FTLD-MOD and UDS differentiated among PPA subtypes. UDS 3.0 measures performed best for longitudinal monitoring.

Translating amyloid PET of different radiotracers by a deep generative model for interchangeability

It is challenging to compare amyloid PET images obtained with different radiotracers. Here, we introduce a new approach to improve the interchangeability of amyloid PET acquired with different radiotracers through image-level translation. Deep generative networks were developed using unpaired PET datasets, consisting of 203 [¹¹C]PIB and 850 [¹⁸F]florbetapir brain PET images. Using 15 paired PET datasets, the standardized uptake value ratio (SUVR) values obtained from pseudo-PIB or pseudo-florbetapir PET images translated using the generative networks was compared to those obtained from the original images. The generated amyloid PET images showed similar distribution patterns with original amyloid PET of different radiotracers. The SUVR obtained from the original [¹⁸F]florbetapir PET was lower than those obtained from the original [¹¹C]PIB PET. The translated amyloid PET images reduced the difference in SUVR. The SUVR obtained from the pseudo-PIB PET images generated from [¹⁸F]florbetapir PET showed a good agreement with those of the original PIB PET (ICC = 0.87 for global SUVR). The SUVR obtained from the pseudo-florbetapir PET also showed a good agreement with those of the original [¹⁸F]florbetapir PET (ICC = 0.85 for global SUVR). The ICC values between the original and generated PET images were higher than those between original [¹¹C]PIB and [¹⁸F]florbetapir images (ICC = 0.65 for global SUVR). Our approach provides the image-level translation of amyloid PET images obtained using different radiotracers. It may facilitate the clinical studies designed with variable amyloid PET images due to long-term clinical follow-up as well as multicenter trials by enabling the translation of different types of amyloid PET.

The current international consensus criteria can lead to under and over-diagnosis of primary progressive aphasia variants

In the field of primary progressive aphasia (PPA), the most recent international consensus criteria of 2011 for diagnosis and variant classification have been shown not to capture accurately the whole range of PPA patients. Up to 30-40% of PPA patients appear not to satisfy the criteria of the three 'classical' PPA variants (non-fluent/agrammatic, logopenic, semantic) and are labelled either 'mixed PPA' or 'unclassifiable PPA'. Based on the PPA literature since 2011, this article discusses why patients might be under-diagnosed with respect to the three PPA variants, thus leading to the default concept of 'mixed/unclassifiable PPA' and, conversely, why the non-fluent/agrammatic variant appears to be over-diagnosed. It analyses and attempts to show how to resolve these issues, and it accordingly proposes clinical criteria, which are more inclusive to diminish the proportion of so-called mixed/unclassifiable PPA diagnoses and to reduce the proportion of questionable non-fluent/agrammatic diagnoses, which frequently correspond to progressive speech apraxia, rather than to aphasia.

Memory Resilience in Alzheimer Disease With Primary Progressive Aphasia

OBJECTIVE

To determine whether memory is preserved longitudinally in primary progressive aphasia (PPA) associated with Alzheimer disease (AD) and to identify potential factors that maintain memory despite underlying neurofibrillary degeneration of mediotemporal memory areas.

METHODS

Longitudinal memory assessment was done in 17 patients with PPA with autopsy or biomarker evidence of AD (PPA-AD) and 14 patients with amnestic dementia of the Alzheimer type with AD at autopsy (DAT-AD).

RESULTS

In PPA-AD, episodic memory, tested with nonverbal items, was preserved at the initial testing and showed no decline at retesting 2.35 ± 0.78 years later, at which time symptoms had been present for 6.26 ± 2.21 years. In contrast, language functions declined significantly during the same period. In DAT-AD, both verbal memory and language declined with equal severity. Although imaging showed asymmetric left-sided mediotemporal atrophy in PPA-AD, autopsy revealed bilateral hippocampo-entorhinal neurofibrillary degeneration at Braak stages V and VI. Compared to DAT-AD, however, the PPA-AD group had lower incidence of APOE ε4 and of mediotemporal TAR DNA-binding protein 43 (TDP-43) pathology.

CONCLUSIONS

Memory preservation in PPA is not just an incidental finding at onset but a core feature that persists for years despite the hippocampo-entorhinal AD neuropathology that is as severe as that of DAT-AD. Asymmetry of mediotemporal atrophy and a lesser impact of APOE ε4 and of TDP-43 on the integrity of memory circuitry may constitute some of the factors underlying this resilience. Our results also suggest that current controversies on memory in PPA-AD reflect inconsistencies in the diagnosis of logopenic PPA, the clinical variant most frequently associated with AD.

CLINICALTRIALSGOV IDENTIFIER

NCT00537004 and NCT03371706.

Primary Progressive Aphasia: Toward a Pathophysiological Synthesis

PURPOSE OF REVIEW

The term primary progressive aphasia (PPA) refers to a diverse group of dementias that present with prominent and early problems with speech and language. They present considerable challenges to clinicians and researchers.

RECENT FINDINGS

Here, we review critical issues around diagnosis of the three major PPA variants (semantic variant PPA, nonfluent/agrammatic variant PPA, logopenic variant PPA), as well as considering 'fragmentary' syndromes. We next consider issues around assessing disease stage, before discussing physiological phenotyping of proteinopathies across the PPA spectrum. We also review evidence for core central auditory impairments in PPA, outline critical challenges associated with treatment, discuss pathophysiological features of each major PPA variant, and conclude with thoughts on key challenges that remain to be addressed. New findings elucidating the pathophysiology of PPA represent a major step forward in our understanding of these diseases, with implications for diagnosis, care, management, and therapies.

Cross-sectional and longitudinal medial temporal lobe subregional atrophy patterns in semantic variant primary progressive aphasia

T1-magnetic resonance imaging (MRI) studies report early atrophy in the left anterior temporal lobe, especially the perirhinal cortex, in semantic variant primary progressive aphasia (svPPA). Improved segmentation protocols using high-resolution T2-MRI have enabled fine-grained medial temporal lobe (MTL) subregional measurements, which may provide novel information on the atrophy pattern and disease progression in svPPA. We aimed to investigate the MTL subregional atrophy pattern cross-sectionally and longitudinally in patients with svPPA as compared with controls and patients with Alzheimer's disease (AD). MTL subregional volumes were obtained using the Automated Segmentation for Hippocampal Subfields software from high-resolution T2-MRIs in 15 svPPA, 37 AD, and 23 healthy controls. All MTL volumes were corrected for intracranial volume and parahippocampal cortices for slice number. Longitudinal atrophy rates of all subregions were obtained using an unbiased deformation-based morphometry pipeline in 6 svPPA patients, 9 controls, and 12 AD patients. Cross-sectionally, significant volume loss was observed in svPPA compared with controls in the left MTL, right cornu ammonis 1 (CA1), Brodmann area (BA)35, and BA36 (subdivisions of the perirhinal cortex). Compared with AD patients, svPPA patients had significantly smaller left CA1, BA35, and left and right BA36 volumes. Longitudinally, svPPA patients had significantly greater atrophy rates of left and right BA36 than controls but not relative to AD patients. Fine-grained analysis of MTL atrophy patterns provides information about the evolution of atrophy in svPPA. These results indicate that MTL subregional measures might be useful markers to track disease progression or for clinical trials in svPPA.

Pattern of cortical thinning in logopenic progressive aphasia patients in Thailand

Background

Logopenic progressive aphasia (LPA) is an uncommon neurodegenerative disorder primarily characterized by word-finding difficulties and sentence repetition impairment. Prominent cortical atrophy around left temporo-parietal junction (TPJ) is a classical imaging feature of LPA. This study investigated cortical thinning pattern in clinically diagnosed LPA patients using non-demented subjects as a control group. We also aimed to explore whether there was prominent thinning of other cortical area additional to the well-recognized left TPJ.

Methods

Thicknesses of all cortical regions were measured from brain magnetic resonance images using an automated command on Freesurfer software. Cortical thickness of the LPA and control groups were compared by two methods: 1) using a general linear model (GLM) in SPSS software; and 2) using a vertex-by-vertex GLM, performed with Freesurfer’s QDEC interface.

Results

Besides the well-recognized left TPJ, cortical regions that were significantly thinner in the LPA group by both comparison methods included left caudal middle frontal gyrus (CMFG) (p = 0.006 by SPSS, p = 0.0003 by QDEC), left rostral middle frontal gyrus (p = 0.001 by SPSS, p = 0.0001 by QDEC), left parahippocampal gyrus (p = 0.008 by SPSS, p = 0.005 by QDEC) and right CMFG (p = 0.005 by SPSS, p = 0.0001 by QDEC).

Conclusions

Our results demonstrated that thinning of middle frontal gyri may be an additional feature in clinically diagnosed LPA patients. Involvement of left parahippocampal gyrus may reflect the underlying neuropathology of Alzheimer’s disease in majority of the LPA patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-020-02039-x.

Accumulation of neurofibrillary tangles and activated microglia is associated with lower neuron densities in the aphasic variant of Alzheimer's disease

The neurofibrillary tangles (NFT) and amyloid-ß plaques (AP) that comprise Alzheimer's disease (AD) neuropathology are associated with neurodegeneration and microglial activation. Activated microglia exist on a dynamic spectrum of morphologic subtypes that include resting, surveillant microglia capable of converting to activated, hypertrophic microglia closely linked to neuroinflammatory processes and AD neuropathology in amnestic AD. However, quantitative analyses of microglial subtypes and neurons are lacking in non-amnestic clinical AD variants, including primary progressive aphasia (PPA-AD). PPA-AD is a language disorder characterized by cortical atrophy and NFT densities concentrated to the language-dominant hemisphere. Here, a stereologic investigation of five PPA-AD participants determined the densities and distributions of neurons and microglial subtypes to examine how cellular changes relate to AD neuropathology and may contribute to cortical atrophy. Adjacent series of sections were immunostained for neurons (NeuN) and microglia (HLA-DR) from bilateral language and non-language regions where in vivo cortical atrophy and Thioflavin-S-positive APs and NFTs were previously quantified. NeuN-positive neurons and morphologic subtypes of HLA-DR-positive microglia (i.e., resting [ramified] microglia and activated [hypertrophic] microglia) were quantified using unbiased stereology. Relationships between neurons, microglia, AD neuropathology, and cortical atrophy were determined using linear mixed models. NFT densities were positively associated with hypertrophic microglia densities (P < 0.01) and inversely related to neuron densities (P = 0.01). Hypertrophic microglia densities were inversely related to densities of neurons (P < 0.01) and ramified microglia (P < 0.01). Ramified microglia densities were positively associated with neuron densities (P = 0.02) and inversely related to cortical atrophy (P = 0.03). Our findings provide converging evidence of divergent roles for microglial subtypes in patterns of neurodegeneration, which includes hypertrophic microglia likely driving a neuroinflammatory response more sensitive to NFTs than APs in PPA-AD. Moreover, the accumulation of both NFTs and activated hypertrophic microglia in association with low neuron densities suggest they may collectively contribute to focal neurodegeneration characteristic of PPA-AD.

Nosology of Primary Progressive Aphasia and the Neuropathology of Language

Primary progressive aphasia (PPA) is a dementia syndrome associated with several neuropathologic entities, including Alzheimer's disease (AD) and all major forms of frontotemporal lobar degeneration (FTLD). It is classified into subtypes defined by the nature of the language domain that is most impaired. The asymmetric neurodegeneration of the hemisphere dominant for language (usually left) is one consistent feature of all PPA variants. This feature offers unique opportunities for exploring mechanisms of selective vulnerability in neurodegenerative diseases and the neuroanatomy of language. This chapter reviews some of the current trends in PPA research as well as the challenges that remain to be addressed on the nosology, clinicopathologic correlations, and therapy of this syndrome.

Dementia with aphasia and mirror phenomenon: examination of the mechanism using neuroimaging and neuropsychological findings: a case report

BACKGROUND

Aphasia often appears in persons living with dementia; however, aphasia and the mirror phenomenon are rarely present at the same time.

CASE PRESENTATION

Here, we report a case of fluent conversation with a person in a mirror or a magazine, and examine the underlying mechanism using brain imaging and neuropsychological findings. We found that the appearance of the mirror phenomenon may be associated with a visuospatial dysfunction caused by a decreased function of the posterior region of the right temporal and parietal lobe. Moreover, active talking to a person in a mirror or a person in a magazine could be associated with disinhibition caused by a decline in bilateral frontal lobe function.

CONCLUSIONS

This case represents a very valuable and interesting presentation because it is the first report of a long-term follow-up of the course of dementia using neurological imaging, and of the neuropsychological analysis of the mechanism of conversation with a mirror image combined with aphasia.

Diagnostic Assessment in Primary Progressive Aphasia: An Illustrative Case Example

Purpose Diagnosis and classification of primary progressive aphasia (PPA) requires confirmation of specific speech and language symptoms, highlighting the important role of speech-language pathologists in the evaluation process. The purpose of this case report is to inform speech-language pathologists regarding current practices for diagnostic assessment in PPA, describing standard approaches as well as complementary, state-of-the-art procedures that may improve diagnostic precision. Method We describe the diagnostic evaluation of a 49-year-old woman with complaints of progressive word-finding difficulty. She completed standard neurological, neuropsychological, and speech-language evaluations, as well as magnetic resonance and positron emission tomography imaging of her brain. In addition, a history of developmental speech, language, and learning abilities was obtained, as well as genetic testing and assessment of cerebrospinal fluid biomarkers. We discuss the evaluation results in the context of the most current research related to PPA diagnosis. Conclusion Detailed behavioral assessment, thorough intake of symptom history and neurodevelopmental differences, multimodal neuroimaging, and comprehensive examination of genes and biomarkers are of paramount importance for detecting and characterizing PPA, with ramifications for early behavioral and/or pharmacological intervention. Supplemental Material https://doi.org/10.23641/asha.12771113.

Altered functional connectivity of cortical networks in semantic variant Primary Progressive Aphasia

As their illness progresses, patients with the semantic variant of Primary Progressive Aphasia (svPPA) frequently exhibit peculiar behaviors indicative of altered visual attention or an increased interest in artistic endeavors. In the present study, we examined changes within and between large-scale functional brain networks that may explain this altered visual behavior. We first examined the connectivity of the visual association network, the dorsal attention network, and the default mode network in healthy young adults (n = 89) to understand the typical architecture of these networks in the healthy brain. We then compared the large-scale functional connectivity of these networks in a group of svPPA patients (n = 12) to a group of age-matched cognitively normal controls (n = 30). Our results showed that the between-network connectivity of the dorsal attention and visual association networks was elevated in svPPA patients relative to controls. We further showed that this heightened between-network connectivity was associated with a decrease in the within-network connectivity of the default mode network, possibly due to progressive degeneration of the anterior temporal lobes in svPPA. These results suggest that focal neurodegeneration can lead to the reorganization of large-scale cognitive networks beyond the primarily affected network(s), possibly contributing to cognitive or behavioral changes that are commonly present as part of the clinical phenotype of svPPA.

Establishing two principal dimensions of cognitive variation in logopenic progressive aphasia

Logopenic progressive aphasia is a neurodegenerative syndrome characterized by sentence repetition and naming difficulties arising from left-lateralized temporoparietal atrophy. Clinical descriptions of logopenic progressive aphasia largely concentrate on profiling language deficits, however, accumulating evidence points to the presence of cognitive deficits even on tasks with minimal language demands. Although non-linguistic cognitive deficits in logopenic progressive aphasia are thought to scale with disease severity, patients at discrete stages of language dysfunction display overlapping cognitive profiles, suggesting individual-level variation in cognitive performance, independent of primary language dysfunction. To address this issue, we used principal component analysis to decompose the individual-level variation in cognitive performance in 43 well-characterized logopenic progressive aphasia patients who underwent multi-domain neuropsychological assessments and structural neuroimaging. The principal component analysis solution revealed the presence of two, statistically independent factors, providing stable and clinically intuitive explanations for the majority of variance in cognitive performance in the syndrome. Factor 1 reflected 'speech production and verbal memory' deficits which typify logopenic progressive aphasia. Systematic variations were also confirmed on a second, orthogonal factor mainly comprising visuospatial and executive processes. Adopting a case-comparison approach, we further demonstrate that pairs of patients with comparable Factor 1 scores, regardless of their severity, diverge considerably on visuo-executive test performance, underscoring the inter-individual variability in cognitive profiles in comparably 'logopenic' patients. Whole-brain voxel-based morphometry analyses revealed that speech production and verbal memory factor scores correlated with left middle frontal gyrus, while visuospatial and executive factor scores were associated with grey matter intensity of right-lateralized temporoparietal, middle frontal regions and their underlying white matter connectivity. Importantly, logopenic progressive aphasia patients with poorer visuospatial and executive factor scores demonstrated greater right-lateralized temporoparietal and frontal atrophy. Our findings demonstrate the inherent variation in cognitive performance at an individual- and group-level in logopenic progressive aphasia, suggesting the presence of a genuine co-occurring cognitive impairment that is statistically independent of language function and disease severity.

Parallels between retinal and brain pathology and response to immunotherapy in old, late-stage Alzheimer's disease mouse models

Despite growing evidence for the characteristic signs of Alzheimer's disease (AD) in the neurosensory retina, our understanding of retina-brain relationships, especially at advanced disease stages and in response to therapy, is lacking. In transgenic models of AD (APPSWE/PS1∆E9; ADtg mice), glatiramer acetate (GA) immunomodulation alleviates disease progression in pre- and early-symptomatic disease stages. Here, we explored the link between retinal and cerebral AD-related biomarkers, including response to GA immunization, in cohorts of old, late-stage ADtg mice. This aged model is considered more clinically relevant to the age-dependent disease. Levels of synaptotoxic amyloid β-protein (Aβ)1-42, angiopathic Aβ1-40, non-amyloidogenic Aβ1-38, and Aβ42/Aβ40 ratios tightly correlated between paired retinas derived from oculus sinister (OS) and oculus dexter (OD) eyes, and between left and right posterior brain hemispheres. We identified lateralization of Aβ burden, with one-side dominance within paired retinal and brain tissues. Importantly, OS and OD retinal Aβ levels correlated with their cerebral counterparts, with stronger contralateral correlations and following GA immunization. Moreover, immunomodulation in old ADtg mice brought about reductions in cerebral vascular and parenchymal Aβ deposits, especially of large, dense-core plaques, and alleviation of microgliosis and astrocytosis. Immunization further enhanced cerebral recruitment of peripheral myeloid cells and synaptic preservation. Mass spectrometry analysis identified new parallels in retino-cerebral AD-related pathology and response to GA immunization, including restoration of homeostatic glutamine synthetase expression. Overall, our results illustrate the viability of immunomodulation-guided CNS repair in old AD model mice, while shedding light onto similar retino-cerebral responses to intervention, providing incentives to explore retinal AD biomarkers.

Dementia with Lewy bodies presenting as Logopenic variant primary progressive Aphasia

We report a patient presenting with clinical features of logopenic variant primary progressive aphasia (lvPPA) who was later diagnosed with probable dementia with Lewy bodies. LvPPA is a neurodegenerative disease that is characterized by anomia, word-finding difficulty, impaired comprehension, and phonological errors. The most common underlying pathology for lvPPA is Alzheimer's disease. However, our patient with clinical features of logopenic progressive aphasia was later diagnosed with probable dementia with Lewy bodies. This case demonstrates that lvPPA can also be an initial manifestation of a phenotype of dementia with Lewy bodies.

The reliability and heritability of cortical folds and their genetic correlations across hemispheres

Cortical folds help drive the parcellation of the human cortex into functionally specific regions. Variations in the length, depth, width, and surface area of these sulcal landmarks have been associated with disease, and may be genetically mediated. Before estimating the heritability of sulcal variation, the extent to which these metrics can be reliably extracted from in-vivo MRI must be established. Using four independent test-retest datasets, we found high reliability across the brain (intraclass correlation interquartile range: 0.65-0.85). Heritability estimates were derived for three family-based cohorts using variance components analysis and pooled (total N > 3000); the overall sulcal heritability pattern was correlated to that derived for a large population cohort (N > 9000) calculated using genomic complex trait analysis. Overall, sulcal width was the most heritable metric, and earlier forming sulci showed higher heritability. The inter-hemispheric genetic correlations were high, yet select sulci showed incomplete pleiotropy, suggesting hemisphere-specific genetic influences.

Isolation and characterization of antibody fragments selective for human FTD brain derived TDP-43 variants

BACKGROUND

Frontotemporal dementia (FTD) is the second leading cause of early onset dementia following Alzheimer's disease. It involves atrophy of the frontal and temporal regions of the brain affecting language, memory, and behavior. Transactive response DNA-binding protein 43 (TDP-43) pathology is found in most FTD and ALS cases. It plays a role in transcription, translation and serves as a shuttle between the nucleus and cytoplasm. Prior to its aggregation, TDP-43 exists as polyubiquitinated, hyperphosphorylated C-terminal fragments that correlate well with FTD disease progression. Because of the importance of TDP-43 in these diseases, reagents that can selectively recognize specific toxic TDP variants associated with onset and progression of FTD can be effective diagnostic and therapeutic tools.

RESULTS

We utilized a novel atomic force microscopy (AFM) based biopanning protocol to isolate single chain variable fragments (scFvs) from a phage display library that selectively bind TDP variants present in human FTD but not cognitively normal age matched brain tissue. We then used the scFvs (FTD-TDP1 through 5) to probe post-mortem brain tissue and sera samples for the presence of FTD related TDP variants. The scFvs readily selected the FTD tissue and sera samples over age matched controls. The scFvs were used in immunohistochemical analysis of FTD and control brain slices where the reagents showed strong staining with TDP in FTD brain tissue slice. FTD-TDP1, FTD-TDP2, FTD-TDP4 and FTD-TDP5 all protected neuronal cells against FTD TDP induced toxicity suggesting potential therapeutic value.

CONCLUSIONS

These results show existence of different disease specific TDP variants in FTD individuals. We have identified a panel of scFvs capable of recognizing these disease specific TDP variants in postmortem FTD tissue and sera samples over age matched controls and can thus serve as a biomarker tool.

Neurofilament Light Chain Related to Longitudinal Decline in Frontotemporal Lobar Degeneration

Objective

Accurate diagnosis and prognosis of frontotemporal lobar degeneration (FTLD) during life is an urgent concern in the context of emerging disease-modifying treatment trials. Few CSF markers have been validated longitudinally in patients with known pathology, and we hypothesized that CSF neurofilament light chain (NfL) would be associated with longitudinal cognitive decline in patients with known FTLD-TAR DNA binding protein ~43kD (TDP) pathology.

Methods

This case-control study evaluated CSF NfL, total tau, phosphorylated tau, and β-amyloid_1-42 in patients with known FTLD-tau or FTLD-TDP pathology (n = 50) and healthy controls (n = 65) and an extended cohort of clinically diagnosed patients with likely FTLD-tau or FTLD-TDP (n = 148). Regression analyses related CSF analytes to longitudinal cognitive decline (follow-up ∼1 year), controlling for demographic variables and core AD CSF analytes.

Results

In FTLD-TDP with known pathology, CSF NfL is significantly elevated compared with controls and significantly associated with longitudinal decline on specific executive and language measures, after controlling for age, disease duration, and core AD CSF analytes. Similar findings are found in the extended cohort, also including clinically identified likely FTLD-TDP. Although CSF NfL is elevated in FTLD-tau compared with controls, the association between NfL and longitudinal cognitive decline is limited to executive measures.

Conclusion

CSF NfL is associated with longitudinal clinical decline in relevant cognitive domains in patients with FTLD-TDP after controlling for demographic factors and core AD CSF analytes and may also be related to longitudinal decline in executive functioning in FTLD-tau.

Longitudinal flortaucipir ([18F]AV-1451) PET uptake in semantic dementia

To assess volume loss and flortaucipir uptake in patients with semantic dementia (SD) over time. Eight SD patients (3 female) underwent clinical evaluations, flortaucipir positron emission tomography, and brain magnetic resonance imaging at 2 visits. Voxel-level comparisons of magnetic resonance imaging gray and white matter volume loss and flortaucipir positron emission tomography uptake were performed in SPM12, comparing SD patients to controls at each visit. T-tests on difference images and paired t-tests of flortaucipir uptake were also performed. At the voxel level, SD patients showed asymmetric, bilateral gray volume loss in the temporal lobes, which, via visual inspection, extended posteriorly at follow-up. White matter loss and flortaucipir uptake were noted in SD patients in the left temporal lobe only, which appeared to extend posteriorly, without involvement of the right hemisphere at follow-up. Longitudinal analyses did not support significant changes in flortaucipir uptake between visits. The biological mechanisms of flortaucipir signal in suspected underlying TAR-DNA binding protein 43 pathology are unknown. A 1-year interval is not sufficient time to demonstrate significant longitudinal flortaucipir uptake changes in SD.

Familial language network vulnerability in primary progressive aphasia

OBJECTIVE

To investigate evidence of the potential role of early cortical vulnerability in the development of primary progressive aphasia (PPA).

METHOD

A woman with a diagnosis of PPA and her 9 adult siblings, 7 with developmental language disabilities, underwent neuropsychological testing, structural MRI, and resting-state fMRI. Whole-exome sequencing was conducted for genes associated with dyslexia or with neurodegenerative dementia.

RESULTS

The siblings demonstrated lower verbal than nonverbal cognitive test scores in a developmental dyslexia pattern. On structural MRI, although the siblings did not differ from controls in total brain volume, the left hemisphere language area volume was significantly smaller than the right. Furthermore, cortical connectivity between the left superior temporal area, previously identified as the region of peak atrophy in the proband early in the course of illness, and adjacent language network components, including the planum temporale, was decreased in the siblings. No distinctive genetic signatures were identified.

CONCLUSION

This report further supports the hypothesis that at least some cases of PPA may be based on a familial language network vulnerability that interferes with the acquisition of language in some members and that makes the language network a locus of least resistance to the effects of an independently late-arising neurodegenerative disease in others. This association offers a conceptual model to explain why identical neurodegenerative diseases may selectively target the language network in some individuals while targeting networks that regulate memory or behavior in others. The genetic basis for this vulnerability remains to be determined.