Multi-parametric [18F]PI-2620 tau PET/MRI for the phenotyping of different Alzheimer's disease variants

PURPOSE

Heterogeneity in clinical phenotypes has led to the description of different phenotypes of Alzheimer's disease (AD). Besides the most frequent amnestic variant of AD (aAD), patients presenting with language deficits are diagnosed with logopenic variant primary progressive aphasia (lvPPA), whereas patients presenting with visual deficits are classified as posterior cortical atrophy (PCA).

METHODS

This study set out to investigate the value of a multi-parametric [18F]PI-2620 tau PET/MRI protocol to distinguish aAD, lvPPA and PCA to support clinical diagnosis in 32 patients. Phenotype-specific information about tau accumulation, relative perfusion, grey matter density, functional network alterations and white matter microstructural alterations was collected.

RESULTS

The aAD patients showed significantly higher tau accumulation, relative hypoperfusion and grey matter density loss in the temporal lobes compared to PCA and lvPPA patients. PCA patients, on the other hand, showed significantly higher tau accumulation in the occipital lobe as compared to aAD patients. Relative hypoperfusion in the occipital lobe and loss of functional connectivity of the posterior cingulate cortex to supplementary visual cortical regions helped to distinguish PCA from lvPPA. Tau accumulation in the cerebellum and microstructural changes in the cingulum were found to help differentiate lvPPA from aAD.

CONCLUSION

This study highlights structural and functional differences between patients with different AD phenotypes. Differences in regional tau PET signals suggest that refinements in the Braak staging system are needed for the non-aAD cases. These patterns of tau accumulation align with the cascading network failure hypothesis, though more research is needed to warrant the here presented results in larger patient cohorts.

Transcranial direct current stimulation over the temporal-parietal junction yields no lexical-semantic effects in logopenic primary progressive aphasia: a double-blind sham-controlled study

Transcranial direct current stimulation (tDCS) has generated some promising outcomes in primary progressive aphasia (PPA). The logopenic variant (lv-PPA), one of the most frequent PPA phenotypes, erodes the temporal-parietal junction (TPJ) generating impaired lexical processing, rapidly extending to semantic deficits. Positive tDCS effects have been reported in several small-cohort studies but there is need for rigorous sham-controlled double-blind investigations to substantiate, or not, beneficial effects. We used a sham-controlled double-blind counter-balanced crossover design with 12 clinically and imaging-characterized lv-PPA patients applying, according to the principle of interhemispheric rivalry, anodal and cathodal tDCS over the left and right TPJ, respectively, as compared to sham. A letter fluency (lexical access), a picture-naming (lexical/semantic access), and a semantic-matching task (semantic access) were applied before and after tDCS. Computational modeling was used to characterize predicted cortical tDCS current distribution. Comparisons of post/pre-tDCS results did not show language improvement in any task. Finite element models showed impact for both tDCS modalities on the TPJ, but with lower radial field-strength when atrophy was implemented in the model. Correlation analyses on individual data, uncorrected for multiples comparisons, suggested that lesser aphasia severity and shorter disease duration are associated with more efficient tDCS effects. Our results showing the absence of significant tDCS outcomes in lv-PPA mitigate previous reports of positive tDCS effects with similar or smaller patient sample sizes, and they demonstrate the need for exploring factors influencing stimulation effects. Findings from computational modelling combined with our uncorrected correlation results suggest that tDCS use might be most appropriate in PPA patients having slight atrophy and aphasia severity. Future studies on larger patient populations are required for robust proof-of-concept regarding therapy use of tDCS in PPA.

Brain Perfusion, Atrophy, and Dopaminergic Changes in Amyloid Negative Logopenic Primary Progressive Aphasia

Although most cases of logopenic variant primary progressive aphasia (lvPPA) are caused by Alzheimer's disease (AD), Lewy body disease (LBD) has also been reported. We assessed brain perfusion, atrophy, dopamine transporter (DAT) uptake, and language function among patients with lvPPA based on beta-amyloid. Thirty-three patients with lvPPA and 28 healthy controls (HCs) underwent MRI, 18F-florbetaben PET, and early- and late-phase DAT PET. All patients completed a language test. General linear models were applied to investigate the association of brain imaging with the aphasia quotient (AQ) and repetition scores. 20 (60.6%) and 13 (39.4%) of the lvPPA patients were amyloid-positive (lvPPAA+) and -negative (lvPPAA-), respectively. Language function was comparable between groups. Compared to HCs, the lvPPAA+ had lower perfusion across widespread brain regions, the lvPPAA- had lower perfusion in the left supramarginal and angular gyri, and both groups had lower DAT in the left caudate and bilateral substantia nigra. In the lvPPAA-, AQ and repetition scores were positively correlated with perfusion in the left temporal and inferior parietal cortices, with perfusion in the left supramarginal gyrus mediating the effect of left substantia nigra DAT. Although AD is the most common underlying pathology of lvPPA, LBD may contribute to the logopenic phenotype.

A new GRN variant in logopenic variant primary progressive aphasia: a case report and literature review

The majority of genetic Primary progressive aphasia (PPA) patients harbor mutations in the granulin (GRN) gene. The present case showed impaired performances in single-word retrieval in spontaneous speech and naming, and repetition. Head MRI revealed marked lateral atrophy in the left parietal cortex. A diagnosis of logopenic variant PPA (lvPPA) was established. Genetic analysis showed a heterozygous 10-bp frameshift deletion in exon 4 of the GRN gene (NM_002087.4), leading to transformation of cysteine into alanine at amino acid 92 and creation of a premature stop codon at position 161. This patient represented a rare case of GRN-associated lvPPA. A new mutation site was detected in exon 4 of GRN gene.

The Functional Origin of Oral Word Production Deficits in the Logopenic Variant of Primary Progressive Aphasia: A Systematic Review

BACKGROUND/OBJECTIVES

Oral word production (OWP) deficits are prominent in the logopenic variant of primary progressive aphasia (lvPPA); however, their functional origin remains unclear. Some studies suggest a lexical, post-lexical, or even a combined functional origin of these deficits. The aim of the present study was to synthesize and analyze the information on the functional origin of the OWP deficits in patients with lvPPA.

METHODS

A quantitative systematic literature review was carried out using four databases: CINAHL, PsycINFO, Linguistics and Language Behavior Abstracts, and PubMed. Fourteen studies, including a total of 243 patients with lvPPA, and reporting results on picture naming and/or word and/or pseudoword repetition, were selected.

RESULTS

The overall findings of this review highlighted that two main functional origins appear to explain the OWP deficits in lvPPA: a lexical impairment affecting lexical processing and a post-lexical impairment affecting phonological short-term memory. Interestingly, the possibility of a third functional origin, affecting the semantic processing level, was also suggested by some studies.

CONCLUSIONS

We concluded that the presence of different functional origins of OWP in this population may be explained, at least partially, by the diversity of assessment tasks used in studies and the varied manipulation and control of psycholinguistic properties of words (e.g., frequency, length), as well as the various interpretations and analyses of the participants' errors. Further studies are needed to substantiate these findings by examining all the components involved in OWP, carefully manipulating the psycholinguistic properties and qualitatively analyzing the errors made by lvPPA participants.

[The experience of diagnosing Alzheimer's disease based on the study of cerebrospinal fluid biomarkers]

OBJECTIVE

To evaluate the frequency of Alzheimer's disease (AD) confirmed by cerebrospinal fluid (CSF) biomarkers in a cohort of patients with classical (amnesic) and atypical phenotypes of this disease.

MATERIAL AND METHODS

The study included 63 patients (24 men and 39 women; median age 65 years [60; 71]). All patients were divided into 3 groups according to the phenotype: a classic amnesic phenotype (n=32), frequent non-amnesic phenotypes (n=21) and rare non-amnesic phenotypes (n=10). All patients underwent lumbar puncture followed by the CSF biomarkers evaluation (beta-amyloid 1-42 (Aβ1-42) and phosphorylated tau protein 181 (p-tau181)) to confirm the AD pathology. The clinical characteristics of each subgroup were studied.

RESULTS

A decreased level of CSF Aβ1-42 in combination with an increased level of p-tau181 was found in 36 patients (57.1%). A change in at least one biomarker was detected in 54 patients (85.7%). The highest frequency of the Alzheimer's type pathology was found in the group with predominant amnestic phenotype (87.5%), as well as in the subgroups with logopenic variant of primary progressive aphasia (lvPPA) (100%) and with posterior cortical atrophy (PCA) (100%). In the group with rare phenotypes, the frequency of AD CSF changes characteristic of AD was 50% for patients with predominant behavioral disorders and 66.7% for corticobasal syndrome.

CONCLUSION

The high frequency of AD CSF biomarkers in both the classical (amnesic) and atypical phenotypes is shown. This indicates the need to expand the use of AD CSF biomarkers for a more reliable assessment of the prevalence of AD In Russia.

Impaired semantic control in the logopenic variant of primary progressive aphasia

We investigated semantic cognition in the logopenic variant of primary progressive aphasia, including (i) the status of verbal and non-verbal semantic performance; and (ii) whether the semantic deficit reflects impaired semantic control. Our a priori hypothesis that individuals with logopenic variant of primary progressive aphasia would exhibit semantic control impairments was motivated by the anatomical overlap between the temporoparietal atrophy typically associated with logopenic variant of primary progressive aphasia and lesions associated with post-stroke semantic aphasia and Wernicke's aphasia, which cause heteromodal semantic control impairments. We addressed the presence, type (semantic representation and semantic control; verbal and non-verbal), and progression of semantic deficits in logopenic variant of primary progressive aphasia. Since most people with logopenic variant of primary progressive aphasia have Alzheimer's disease pathology and are part of a broader multi-dimensional phenotype space encompassing Alzheimer's disease sub-types, we compared semantic performance in logopenic variant of primary progressive aphasia and typical amnestic Alzheimer's disease. Given the differences in lesion and atrophy patterns in semantic aphasia and Wernicke's aphasia versus semantic-dementia/semantic-variant primary progressive aphasia patients, our second aim was to examine atrophy patterns in people with logopenic variant of primary progressive aphasia and typical Alzheimer's disease compared to age-matched controls. Twenty-seven patients participated in the study. People were grouped into those meeting consensus criteria for logopenic variant of primary progressive aphasia (N = 10) and others who may have previously satisfied definitions of logopenic variant of primary progressive aphasia but had progressed with multi-domain cognitive impairments (herein referred to as 'logopenic variant of primary progressive aphasia+'; N = 8). People with typical amnestic Alzheimer's disease (N = 9) were relatively preserved across verbal and non-verbal semantic assessments. Logopenic variant of primary progressive aphasia patients were impaired on both verbal and non-verbal semantic tasks and their impairments showed the hallmark characteristics of a semantic control deficit. Logopenic variant of primary progressive aphasia and logopenic variant of primary progressive aphasia + patients showed effects of varying semantic control demands, positive cueing effects, and correlated performance between semantic and executive tasks. Whole-brain voxel-based morphometry, comparing each of the patient groups to age-matched controls, revealed significantly reduced grey and white matter in the bilateral hippocampi and lateral temporal regions in typical Alzheimer's disease patients. The logopenic variant of primary progressive aphasia group exhibited an asymmetric pattern of reduced grey and white matter intensity in the language-dominant left hemisphere, including a significant portion of the lateral and medial temporal lobe. Logopenic variant of primary progressive aphasia + patients demonstrated reduced grey and white matter in the left temporal lobe extending sub-cortically, anteriorly and posteriorly, as well as right temporal involvement. Our findings could aid diagnostic sub-typing of primary progressive aphasia by adopting semantic control features and offer improved clinical characterization of logopenic variant of primary progressive aphasia in the trajectory of semantic decline.

Primary Progressive Aphasia Lacking Core Features of Nonfluent and Semantic Variants: Clinical, Neuroimaging, and Neuropathologic Features

BACKGROUND AND OBJECTIVES

Evidence has accumulated that the 2011 consensus criteria for primary progressive aphasia (PPA) do not fully capture features of logopenic variant PPA (lvPPA/LPA). We aimed to examine clinical, neuroimaging, and neuropathologic features of PPA lacking features of nonfluent/semantic variants and to provide practical additions to the 2011 consensus criteria.

METHODS

This was a retrospective examination of data from 2 observational cohort studies where patients with PPA were prospectively recruited at Mayo Clinic. Based on performance on 2 cardinal features (repetition and comprehension), patients were classified as: pure-LPA (poor repetition, acceptable comprehension), Wernicke-like (poor in both), anomic-like (acceptable in both), and transcortical sensory aphasia-like (TCSA-like) (acceptable repetition, poor comprehension).

RESULTS

The entire cohort consisted of 102 patients with PPA lacking features of nonfluent/semantic variants (median age at onset 63.5 years, 56% female). Thirty-one patients were followed up at 1 year. Twenty-three patients were included in a neuropathologic cohort. The proportion of repetition-preserved PPA (anomic-like and TCSA-like) was more than double that of repetition-impaired PPA (pure-LPA and Wernicke-like) (73% vs 27%). Regarding clinical course, the anomic-like subgroup was a prodromal state of the pure-LPA or TCSA-like subgroup, whereas the pure-LPA and TCSA-like subgroups were a prodromal state of the Wernicke-like subgroup. There was left temporoparietal atrophy on MRI and/or hypometabolism on 18F-fluorodeoxyglucose-PET in all groups. Furthermore, repetition-impaired PPA showed severe hypometabolism in the left superior temporal lobe associated with repetition ability. Regarding pathologic diagnoses, 70% had Alzheimer disease (AD). The pure-LPA, Wernicke-like, and TCSA-like subgroups all showed AD pathology. Only 53% of the anomic-like subgroup had AD. The remaining 47% showed Pick disease (7%), frontotemporal lobar degeneration with TDP-43-immunoreactive pathology (20%), and Lewy body disease (20%).

DISCUSSION

This observed clinical heterogeneity reflects different time points/severities of the same disease process and hence can be reconceptualized as an AD-related aphasia spectrum, incorporating lvPPA and the 4 subgroups (pure-LPA, Wernicke-like, anomic-like, and TCSA-like). Specifying moderate/severe repetition deficits as a core feature of lvPPA in the 2011 consensus criteria can enhance its pathologic correlations. Recognizing progressive anomic aphasia (anomic-like) as an additional PPA variant could lessen pathologic heterogeneity of lvPPA.

Behavioral Treatment for Speech and Language in Primary Progressive Aphasia and Primary Progressive Apraxia of Speech: A Systematic Review

Primary progressive aphasia (PPA) and primary progressive apraxia of speech (PPAOS) are neurodegenerative syndromes characterized by progressive decline in language or speech. There is a growing number of studies investigating speech-language interventions for PPA/PPAOS. An updated systematic evaluation of the treatment evidence is warranted to inform best clinical practice and guide future treatment research. We systematically reviewed the evidence for behavioral treatment for speech and language in this population. Reviewed articles were published in peer-reviewed journals through 31 May 2021. We evaluated level of evidence, reporting quality, and risk of bias using a modified version of the American Speech-Language Hearing Association (ASHA) Levels of Evidence, an appraisal point system, additional reporting quality and internal/external validity items, and, as appropriate, the Single Case Experimental Design Scale or the Physiotherapy Evidence Database - PsycBITE Rating Scale for Randomized and Non-Randomized Controlled Trials. Results were synthesized using quantitative summaries and narrative review. A total of 103 studies reported treatment outcomes for 626 individuals with PPA; no studies used the diagnostic label PPAOS. Most studies evaluated interventions for word retrieval. The highest-quality evidence was provided by 45 experimental and quasi-experimental studies (16 controlled group studies, 29 single-subject designs). All (k = 45/45) reported improvement on a primary outcome measure; most reported generalization (k = 34/43), maintenance (k = 34/39), or social validity (k = 17/19) of treatment for at least one participant. The available evidence supports speech-language intervention for persons with PPA; however, treatment for PPAOS awaits systematic investigation. Implications and limitations of the evidence and the review are discussed.

The impact of phonological short-term memory impairment on verbal repetition in the logopenic variant of primary progressive aphasia

The logopenic variant of primary progressive aphasia (lvPPA) is characterized mainly by anomia, production of phonological errors, and impairment in repetition of sentences. The functional origin of these language impairments is mainly attributed to the breakdown of phonological short-term memory. The present study examined the effects of phonological short-term memory impairment on language processing in lvPPA. In two studies, 11 participants with lvPPA and 11 healthy control participants were presented with repetition tasks in which the type and length of stimuli and the mode of administration were manipulated. Study 1 aimed to examine the influence of length and lexicality (words vs. pseudowords) on immediate and delayed repetition, whereas Study 2 aimed to examine the influence of length, syntactic complexity (nominalized vs. pronominalized sentences), and serial position on immediate sentence repetition. Study 1 showed that participants' performance with lvPPA was impaired only on immediate repetition of five-syllable pseudowords and on delayed repetition of words and pseudowords. Study 2 showed that participants' performance with lvPPA was impaired in the repetition of nominalized sentences where a recency effect was observed. Repetition of pronominalized sentences was also impaired in the lvPPA group. This study provides additional support for arguments regarding phonological short-term memory as a cause of language impairment in lvPPA. Clinically, the results of the study suggest that instruments for assessing repetition ability in lvPPA should include not only lists of short or long nominalized sentences, but also delayed repetition of words and pseudowords and pronominalized sentences.

Data-driven subtypes of mixed semantic-logopenic primary progressive aphasia: Linguistic features, biomarker profiles and brain metabolic patterns

Mixed primary progressive aphasia (mPPA) accounts for a substantial proportion of primary progressive aphasia (PPA) cases. However, the lack of a standardised definition of this condition has resulted in misclassification of PPA cases. In this study, we enrolled 55 patients diagnosed with PPA, comprising 12 semantic variant (svPPA), 23 logopenic variant (lvPPA), and 20 mPPA cases with linguistic characteristics consistent with both svPPA and lvPPA (s/lvPPA). All patients underwent language assessments, evaluation of Alzheimer's disease biomarkers (via cerebrospinal fluid analysis or Amyloid-PET), and 18F-FDG-PET brain scans. An agglomerative hierarchical clustering (AHC) analysis based on linguistic characteristics revealed two distinct clusters within the s/lvPPA group: cluster k1 (n = 10) displayed an AD-like biomarker profile, with lower levels of Aβ42 and Aβ42/Aβ40 ratio, along with higher levels of t-tau and p-tau compared to cluster k2 (n = 10). Interestingly, k1 exhibited linguistic features that were similar to those of svPPA. Both clusters exhibited extensive temporoparietal hypometabolism. These findings support the hypothesis that a subgroup of s/lvPPA may represent a clinical manifestation of AD-related PPA.

Discriminating nonfluent/agrammatic and logopenic PPA variants with automatically extracted morphosyntactic measures from connected speech

Morphosyntactic assessments are important for characterizing individuals with nonfluent/agrammatic variant primary progressive aphasia (nfvPPA). Yet, standard tests are subject to examiner bias and often fail to differentiate between nfvPPA and logopenic variant PPA (lvPPA). Moreover, relevant neural signatures remain underexplored. Here, we leverage natural language processing tools to automatically capture morphosyntactic disturbances and their neuroanatomical correlates in 35 individuals with nfvPPA relative to 10 healthy controls (HC) and 26 individuals with lvPPA. Participants described a picture, and ensuing transcripts were analyzed via part-of-speech tagging to extract sentence-related features (e.g., subordinating and coordinating conjunctions), verbal-related features (e.g., tense markers), and nominal-related features (e.g., subjective and possessive pronouns). Gradient boosting machines were used to classify between groups using all features. We identified the most discriminant morphosyntactic marker via a feature importance algorithm and examined its neural correlates via voxel-based morphometry. Individuals with nfvPPA produced fewer morphosyntactic elements than the other two groups. Such features robustly discriminated them from both individuals with lvPPA and HCs with an AUC of .95 and .82, respectively. The most discriminatory feature corresponded to subordinating conjunctions was correlated with cortical atrophy within the left posterior inferior frontal gyrus across groups (pFWE < .05). Automated morphosyntactic analysis can efficiently differentiate nfvPPA from lvPPA. Also, the most sensitive morphosyntactic markers correlate with a core atrophy region of nfvPPA. Our approach, thus, can contribute to a key challenge in PPA diagnosis.

Heterogeneity and overlap in the continuum of linguistic profile of logopenic and semantic variants of primary progressive aphasia: a Profile Analysis based on Multidimensional Scaling study

BACKGROUND

Primary progressive aphasia (PPA) diagnostic criteria underestimate the complex presentation of semantic (sv) and logopenic (lv) variants, in which symptoms partially overlap, and mixed clinical presentation (mixed-PPA) and heterogenous profile (lvPPA +) are frequent. Conceptualization of similarities and differences of these clinical conditions is still scarce.

METHODS

Lexical, semantic, phonological, and working memory errors from nine language tasks of sixty-seven PPA were analyzed using Profile Analysis based on Multidimensional Scaling, which allowed us to create a distributed representation of patients' linguistic performance in a shared space. Patients had been studied with [18F] FDG-PET. Correlations were performed between metabolic and behavioral data.

RESULTS

Patients' profiles were distributed across a continuum. All PPA, but two, presented a lexical retrieval impairment, in terms of reduced production of verbs and nouns. svPPA patients occupied a fairly clumped space along the continuum, showing a preponderant semantic deficit, which correlated to fusiform gyrus hypometabolism, while only few presented working memory deficits. Adjacently, lvPPA + presented a semantic impairment combined with phonological deficits, which correlated with metabolism in the anterior fusiform gyrus and posterior middle temporal gyrus. Starting from the shared phonological deficit side, a large portion of the space was occupied by all lvPPA, showing a combination of phonological, lexical, and working memory deficits, with the latter correlating with posterior temporo-parietal hypometabolism. Mixed PPA did not show unique profile, distributing across the space.

DISCUSSION

Different clinical PPA entities exist but overlaps are frequent. Identifying shared and unique clinical markers is critical for research and clinical practice. Further research is needed to identify the role of genetic and pathological factors in such distribution, including also higher sample size of less represented groups.

Primary progressive aphasia: six questions in search of an answer

Here, we review recent progress in the diagnosis and management of primary progressive aphasia-the language-led dementias. We pose six key unanswered questions that challenge current assumptions and highlight the unresolved difficulties that surround these diseases. How many syndromes of primary progressive aphasia are there-and is syndromic diagnosis even useful? Are these truly 'language-led' dementias? How can we diagnose (and track) primary progressive aphasia better? Can brain pathology be predicted in these diseases? What is their core pathophysiology? In addition, how can primary progressive aphasia best be treated? We propose that pathophysiological mechanisms linking proteinopathies to phenotypes may help resolve the clinical complexity of primary progressive aphasia, and may suggest novel diagnostic tools and markers and guide the deployment of effective therapies.

Comparing two picture naming tasks in primary progressive aphasia: Insights from behavioural and neural results

Picture naming tests are widely used to evaluate language impairments in neurodegenerative diseases, especially in Primary Progressive Aphasia (PPA). The available tests differ for many factors affecting the performance, e.g. format of stimuli and their psycholinguistic properties. We aim to identify the most appropriate naming test to be used on PPA according to the clinical and research demands. We investigated the behavioural characteristics, i.e. proportion of correct responses and error type, and their neural correlates in two Italian naming tests, CaGi naming (CaGi) and naming subtest of the Screening for Aphasia in NeuroDegeneration battery (SAND), administered to 52 PPA patients who underwent an FDG-PET scan. We analysed the effectiveness of the tests in distinguishing PPA versus controls and among PPA variants, considering the psycholinguistic variables affecting performance. We explored the brain metabolic correlates of behavioural performance in the tests. SAND, differently from CaGi, has time limits for the response and its items are less frequent and acquired later. SAND and CaGi differed in terms of number of correct responses and error profile, suggesting a higher difficulty to name SAND items compared to CaGi. Semantic errors predominated in CaGi, while anomic and semantic errors were equally frequent in SAND. Both tests distinguished PPA from controls, but SAND outperformed CaGi in discriminating among PPA variants. FDG-PET imaging revealed a shared metabolic involvement of temporal areas associated with lexico-semantic processing, encompassing anterior fusiform, temporal pole, and extending to posterior fusiform in sv-PPA. Concluding, a picture naming test with response time limit and items which are less frequent and acquired later in life, as SAND, may be effective at highlighting subtle distinctions between PPA variants, improving the diagnosis. Conversely, a naming test without time limit for the response, as CaGi, may be useful for a better characterization of the nature of the naming impairment at the behavioural level, eliciting more naming errors than anomia, possibly helping in the development of rehabilitation protocols.

Network anatomy in logopenic variant of primary progressive aphasia

The logopenic variant of primary progressive aphasia (lvPPA) is a neurodegenerative syndrome characterized linguistically by gradual loss of repetition and naming skills resulting from left posterior temporal and inferior parietal atrophy. Here, we sought to identify which specific cortical loci are initially targeted by the disease (epicenters) and investigate whether atrophy spreads through predetermined networks. First, we used cross-sectional structural MRI data from individuals with lvPPA to define putative disease epicenters using a surface-based approach paired with an anatomically fine-grained parcellation of the cortical surface (i.e., HCP-MMP1.0 atlas). Second, we combined cross-sectional functional MRI data from healthy controls and longitudinal structural MRI data from individuals with lvPPA to derive the epicenter-seeded resting-state networks most relevant to lvPPA symptomatology and ascertain whether functional connectivity in these networks predicts longitudinal atrophy spread in lvPPA. Our results show that two partially distinct brain networks anchored to the left anterior angular and posterior superior temporal gyri epicenters were preferentially associated with sentence repetition and naming skills in lvPPA. Critically, the strength of connectivity within these two networks in the neurologically-intact brain significantly predicted longitudinal atrophy progression in lvPPA. Taken together, our findings indicate that atrophy progression in lvPPA, starting from inferior parietal and temporoparietal junction regions, predominantly follows at least two partially nonoverlapping pathways, which may influence the heterogeneity in clinical presentation and prognosis.

Frontotemporal Dementia, Where Do We Stand? A Narrative Review

Frontotemporal dementia (FTD) is a neurodegenerative disease of growing interest, since it accounts for up to 10% of middle-age-onset dementias and entails a social, economic, and emotional burden for the patients and caregivers. It is characterised by a (at least initially) selective degeneration of the frontal and/or temporal lobe, generally leading to behavioural alterations, speech disorders, and psychiatric symptoms. Despite the recent advances, given its extreme heterogeneity, an overview that can bring together all the data currently available is still lacking. Here, we aim to provide a state of the art on the pathogenesis of this disease, starting with established findings and integrating them with more recent ones. In particular, advances in the genetics field will be examined, assessing them in relation to both the clinical manifestations and histopathological findings, as well as considering the link with other diseases, such as amyotrophic lateral sclerosis (ALS). Furthermore, the current diagnostic criteria will be explored, including neuroimaging methods, nuclear medicine investigations, and biomarkers on biological fluids. Of note, the promising information provided by neurophysiological investigations, i.e., electroencephalography and non-invasive brain stimulation techniques, concerning the alterations in brain networks and neurotransmitter systems will be reviewed. Finally, current and experimental therapies will be considered.

Network anatomy in logopenic variant of primary progressive aphasia

The logopenic variant of primary progressive aphasia (lvPPA) is a neurodegenerative syndrome characterized linguistically by gradual loss of repetition and naming skills, resulting from left posterior temporal and inferior parietal atrophy. Here, we sought to identify which specific cortical loci are initially targeted by the disease (epicenters) and investigate whether atrophy spreads through pre-determined networks. First, we used cross-sectional structural MRI data from individuals with lvPPA to define putative disease epicenters using a surface-based approach paired with an anatomically-fine-grained parcellation of the cortical surface (i.e., HCP-MMP1.0 atlas). Second, we combined cross-sectional functional MRI data from healthy controls and longitudinal structural MRI data from individuals with lvPPA to derive the epicenter-seeded resting-state networks most relevant to lvPPA symptomatology and ascertain whether functional connectivity in these networks predicts longitudinal atrophy spread in lvPPA. Our results show that two partially distinct brain networks anchored to the left anterior angular and posterior superior temporal gyri epicenters were preferentially associated with sentence repetition and naming skills in lvPPA. Critically, the strength of connectivity within these two networks in the neurologically-intact brain significantly predicted longitudinal atrophy progression in lvPPA. Taken together, our findings indicate that atrophy progression in lvPPA, starting from inferior parietal and temporo-parietal junction regions, predominantly follows at least two partially non-overlapping pathways, which may influence the heterogeneity in clinical presentation and prognosis.

Dyslexia and dysgraphia of primary progressive aphasia in Chinese: A systematic review

Introduction

Currently, little is known about Chinese-speaking primary progressive aphasia (PPA) patients compared to patients who speak Indo-European languages. We examined the demographics and clinical manifestations, particularly reading and writing characteristics, of Chinese patients with PPA over the last two decades to establish a comprehensive profile and improve diagnosis and care.

Methods

We reviewed the demographic features, clinical manifestations, and radiological features of Chinese-speaking PPA patients from 56 articles published since 1994. We then summarized the specific reading and writing errors of Chinese-speaking patients.

Results

The average age of onset for Chinese-speaking patients was in their early 60's, and there were slightly more male patients than female patients. The core symptoms and images of Chinese-speaking patients were similar to those of patients who speak Indo-European languages. Reading and writing error patterns differed due to Chinese's distinct tone and orthography. The types of reading errors reported in Chinese-speaking patients with PPA included tonal errors, regularization errors, visually related errors, semantic errors, phonological errors, unrelated errors, and non-response. Among these errors, regularization errors were the most common in semantic variant PPA, and tonal errors were specific to Chinese. Writing errors mainly consisted of non-character errors (stroke, radical/component, visual, pictograph, dyskinetic errors, and spatial errors), phonologically plausible errors, orthographically similar errors, semantic errors, compound word errors, sequence errors, unrelated errors, and non-response.

Conclusion

This paper provides the latest comprehensive demographic information and unique presentations on the reading and writing of Chinese-speaking patients with PPA. More detailed studies are needed to address the frequency of errors in reading and writing and their anatomical substrates.

Characterization of the logopenic variant of Primary Progressive Aphasia: A systematic review and meta-analysis

The linguistic and anatomical variability of the logopenic variant of Primary Progressive Aphasia (lv-PPA) as defined by current diagnostic criteria has been the topic of an intense debate. The present review and meta-analysis aims at characterizing the profile of lv-PPA, by a comprehensive analysis of the available literature on the neuropsychological, neuroimaging, electrophysiological, pathological, and genetic features of lv-PPA. We conducted a systematic bibliographic search, leading to the inclusion of 207 papers. Of them, 12 were used for the Anatomical Likelihood Estimation meta-analysis on grey matter revealed by magnetic resonance imaging data. The results suggest that the current guidelines outline a relatively consistent syndrome, characterized by a core set of linguistic and, to a lesser extent, non-linguistic deficits, mirroring the involvement of left temporal and parietal regions typically affected by Alzheimer Disease pathology. Variations of the lv-PPA profile are discussed in terms of heterogeneity of the neuropsychological instruments and the diagnostic criteria adopted.

Silent Pauses and Speech Indices as Biomarkers for Primary Progressive Aphasia

Background and Objectives: Recent studies highlight the importance of investigating biomarkers for diagnosing and classifying patients with primary progressive aphasia (PPA). Even though there is ongoing research on pathophysiological indices in this field, the use of behavioral variables, and especially speech-derived factors, has drawn little attention in the relevant literature. The present study aims to investigate the possible utility of speech-derived indices, particularly silent pauses, as biomarkers for primary progressive aphasia (PPA). Materials and Methods: We recruited 22 PPA patients and 17 healthy controls, from whom we obtained speech samples based on two elicitation tasks, i.e., cookie theft picture description (CTP) and the patients’ personal narration of the disease onset and course. Results: Four main indices were derived from these speech samples: speech rate, articulation rate, pause frequency, and pause duration. In order to investigate whether these indices could be used to discriminate between the four groups of participants (healthy individuals and the three patient subgroups corresponding to the three variants of PPA), we conducted three sets of analyses: a series of ANOVAs, two principal component analyses (PCAs), and two hierarchical cluster analyses (HCAs). The ANOVAs revealed significant differences between the four subgroups for all four variables, with the CTP results being more robust. The subsequent PCAs and HCAs were in accordance with the initial statistical comparisons, revealing that the speech-derived indices for CTP provided a clearer classification and were especially useful for distinguishing the non-fluent variant from healthy participants as well as from the two other PPA taxonomic categories. Conclusions: In sum, we argue that speech-derived indices, and especially silent pauses, could be used as complementary biomarkers to efficiently discriminate between PPA and healthy speakers, as well as between the three variants of the disease.

Case Report: A neurolinguistic and neuroimaging study on a Chinese follow-up case with logopenic-variant of primary progressive aphasia

Primary progressive aphasia (PPA), typically resulting from a neurodegenerative disease, is characterized by a progressive loss of specific language functions while other cognitive domains are relatively unaffected. The logopenic variant, characterized by impairments of word retrieval and sentence repetition along with preserved semantic, syntactic, and motor speech abilities, is the most recently described and remains less understood than other variants due to a comparatively small number of case studies and a lack of investigations with a thorough specification. In this article, we report a 2-year follow-up case study of a 74-year-old Chinese female patient with a logopenic variant of primary progressive aphasia, including its neurolinguistic study, magnetic resonance imaging (MRI), and 11C-Pittsburgh compound B-Positron emission tomography imaging analyses, as well as gene sequencing. This case confirms that, in addition to word-finding and sentence repetition difficulties, the logopenic variant may also present with mild auditory comprehension and naming deficits attributed to impaired access to lexical representations. The observation of clinical treatment suggests the efficacy of memantine hydrochloride tablet and rivastigmine transdermal patch in slowing down the cognitive deterioration of this patient. The description and exploration of this case may shed new insights into a better understanding of the Chinese logopenic variant of primary progressive aphasia.

Understanding the multidimensional cognitive deficits of logopenic variant primary progressive aphasia

The logopenic variant of primary progressive aphasia is characterized by early deficits in language production and phonological short-term memory, attributed to left-lateralized temporoparietal, inferior parietal and posterior temporal neurodegeneration. Despite patients primarily complaining of language difficulties, emerging evidence points to performance deficits in non-linguistic domains. Temporoparietal cortex, and functional brain networks anchored to this region, are implicated as putative neural substrates of non-linguistic cognitive deficits in logopenic variant primary progressive aphasia, suggesting that degeneration of a shared set of brain regions may result in co-occurring linguistic and non-linguistic dysfunction early in the disease course. Here, we provide a Review aimed at broadening the understanding of logopenic variant primary progressive aphasia beyond the lens of an exclusive language disorder. By considering behavioural and neuroimaging research on non-linguistic dysfunction in logopenic variant primary progressive aphasia, we propose that a significant portion of multidimensional cognitive features can be explained by degeneration of temporal/inferior parietal cortices and connected regions. Drawing on insights from normative cognitive neuroscience, we propose that these regions underpin a combination of domain-general and domain-selective cognitive processes, whose disruption results in multifaceted cognitive deficits including aphasia. This account explains the common emergence of linguistic and non-linguistic cognitive difficulties in logopenic variant primary progressive aphasia, and predicts phenotypic diversification associated with progression of pathology in posterior neocortex.

Multimodality Imaging in Primary Progressive Aphasia

Primary progressive aphasia is a clinically and neuropathologically heterogeneous group of progressive neurodegenerative disorders, characterized by language-predominant impairment and commonly associated with atrophy of the dominant language hemisphere. While this clinical entity has been recognized dating back to the 19th century, important advances have been made in defining our current understanding of primary progressive aphasia, with 3 recognized subtypes to date: logopenic variant, semantic variant, and nonfluent/agrammatic variant. Given the ongoing progress in our understanding of the neurobiology and genomics of these rare neurodegenerative conditions, accurate imaging diagnoses are of the utmost importance and carry implications for future therapeutic triaging. This review covers the diverse spectrum of primary progressive aphasia and its multimodal imaging features, including structural, functional, and molecular neuroimaging findings; it also highlights currently recognized diagnostic criteria, clinical presentations, histopathologic biomarkers, and treatment options of these 3 primary progressive aphasia subtypes.

Phenotypic subtypes of progressive dysexecutive syndrome due to Alzheimer's disease: a series of clinical cases

Diagnostic criteria for a progressive dysexecutive syndrome due to Alzheimer's disease (dAD) were proposed. Clinical observations suggest substantial variability in the clinico-radiological profiles within this syndrome. We report a case series of 6 patients with dAD highlighting this heterogeneity. Average age at diagnosis was 57.3 years, and patients were followed annually with clinical, cognitive, and multimodal imaging assessments for an average of 3.7 years. Cases were divided based into three subtypes based on their pattern of FDG-PET hypometabolism: predominantly left parieto-frontal (ldAD), predominantly right parieto-frontal (rdAD), or predominantly biparietal (bpdAD) (n = 2 for each). Prominent executive dysfunction was evidenced in all patients. ldAD cases showed greater impairment on measures of verbal working memory and verbal fluency compared to other subtypes. rdAD cases showed more severe alterations in measures of visual abilities compared to language-related domains and committed more perseverative errors on a measure of cognitive flexibility. bpdAD cases presented with predominant cognitive flexibility and inhibition impairment with relative sparing of working memory and a slower rate of clinical progression. rdAD and bpdAD patients developed neuropsychiatric symptoms, whereas none of the ldAD patients did. For each subtype, patterns of tau deposition relatively corresponded to the spatial pattern of FDG hypometabolism. dAD cases could be differentiated from two clinical cases of atypical AD variants (language and visual) in terms of clinical, cognitive and neuroimaging profiles, suggesting that dAD subtypes represent clinical entities separable from other variants of the disease. The recognition of distinct dAD phenotypes has clinical relevance for diagnosis, prognosis, and symptom management.

Logogenic Primary Progressive Aphasia or Alzheimer Disease: Contribution of Acoustic Markers in Early Differential Diagnosis

The logopenic variant of Primary Progressive Aphasia (lvPPA), a syndromic disorder centered on language impairment, often presents variable underlying neurodegenerative pathologies such as Alzheimer Disease (AD). Actual language assessment tests and lumbar puncture, focused on AD diagnosis, cannot precisely distinguish the symptoms, or predict their progression at onset time. We analyzed acoustic markers, aiming to discriminate lvPPA and AD as well as the influence of AD biomarkers on acoustic profiles at the beginning of the disease. We recruited people with AD (n = 8) and with lvPPA (n = 8), with cerebrospinal fluid biomarker profiles determined by lumbar puncture. The participants performed a sentence repetition task that allows assessing potential lvPPA phonological loop deficits. We found that temporal and prosodic markers significantly differentiate the lvPPA and AD group at an early stage of the disease. Biomarker and acoustic profile comparisons discriminated the two lvPPA subgroups according to their biomarkers. For lvPPA with AD biomarkers, acoustic profile equivalent to an atypical AD form with a specific alteration of the phonological loop is shown. However, lvPPA without AD biomarkers has an acoustic profile approximating the one for DLFT. Therefore, these results allow us to classify lvPPA differentially from AD based on acoustic markers from a sentence repetition task. Furthermore, our results suggest that acoustic analysis would constitute a clinically efficient alternative to refused lumbar punctures. It offers the possibility to facilitate early, specific, and accessible neurodegenerative diagnosis and may ease early care with speech therapy, preventing the progression of symptoms.

Linguistic profiles of variants of primary progressive aphasia

BACKGROUND

Several subtypes of primary progressive aphasia (PPA) have been proposed. Most reports use small samples, and few have included Spanish-speaking participants.

AIM

To analyze the language profile and nonlinguistic deficits in a large sample of PPA Spanish monolingual participants.

METHOD

177 individuals were diagnosed with PPA in a sample consisting of 69 men and 108 women (M_age = 66.40 years, SD = 9.30). The participants were assessed using the Spanish versions of the Western Aphasia Battery Revised (SWAB-R) and the Boston Diagnostic Aphasia Examination (SBDAE). Non-verbal reasoning was evaluated with the Raven's Colored Progressive Matrices.

RESULTS

41.8% of the sample met the criteria for the logopenic variant (lvPPA), while 28.2% met the criteria for semantic (svPPA), 15.3% for lexical (lxvPPA), and 14.7% for nonfluent/agrammatic (nfvPPA) variants. Language difficulties were similar in all variants except for lxvPPA. Scores on Spontaneous Language, Auditory Comprehension, Repetition, and Naming were significantly higher for the lxvPPA group. Raven's Colored Progressive Matrices scores were significantly lower in lvPPA. Years of education correlated with all test scores, while age was negatively associated with naming. When the PPA variants were classified according to the traditional aphasia classification, discrepancies were evident. Furthermore, the most frequent type of aphasia was Amnesic, while the least frequent was Wernicke's aphasia.

CONCLUSION

The SWAB-R is useful in describing the clinical characteristics of aphasia for each variant of PPA, but quantitative scores from this battery are not capable of distinguishing between variants of PPA, with the exception of lxvPPA.

The temporal lobe in typical and atypical Alzheimer disease

Alzheimer disease (AD) is defined neuropathologically by abnormal extra-cellular β-amyloid plaques combined with intraneuronal tau aggregation. Patients sharing the same neuropathological features but presenting different clinical manifestations and evolutions have led to the notion of AD spectrum. This spectrum encompasses typical and atypical forms of AD. For all of them, specific parts of the temporal lobes, as well as their structural and functional connections with other brain regions, are affected. In typical amnestic late-onset Alzheimer's disease (>65 years old; LOAD), tau pathology gradually spreads to the brain from the medial temporal lobe (MTL). MTL is an inhomogeneous structure consisting of several subregions densely connected to each other and to other cortical and subcortical brain regions. These regions play a crucial role in the storage of information in episodic memory. In less common early-onset AD (<65 years old; EOAD), a large proportion of patients presents atypical clinical manifestations, in which memory impairment is not inaugural and predominant. Instead, these patients have predominant and/or isolated deficits in language, visuospatial, motor, or executive/behavioral functions. In atypical variants, brain damage is mainly centered on the posterior regions, with relative sparing of the MTL. However, the temporal lobe also appears to be variably and specifically damaged in some subtypes of EOAD. For example, the left superior temporal gyrus is the core of brain damage in the language variant, as well as the ventral regions of the temporal lobe play an important role in the clinic of the visual variant.

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.

Primary progressive aphasias associated with C9orf72 expansions: Another side of the story

C9orf72 repeat expansions are rarely associated with primary progressive aphasias (PPA). In-depth characterization of the linguistic deficits, and the underlying patterns of grey-matter atrophy in PPA associated with the C9orf72 expansions (PPA-C9orf72) are currently lacking. In this study, we comprehensively analyzed a unique series of 16 patients affected by PPA-C9orf72. Eleven patients were issued from two independent French and Finnish cohorts, and five were identified by means of literature review. Voxel-based morphometry (VBM) studies were performed on three of them. This study depicts the spectrum of C9orf72-related aphasic phenotypes, and illustrates their linguistic presentation. The non-fluent/agrammatic variant was the most frequent phenotype in our series (9/16 patients, 56%), with apraxia of speech being the main defining feature. Left frontal lobe atrophy was present in these subjects, peaking in inferior frontal gyrus. Three patients (19%) showed the semantic variant, with progression of atrophy in temporo-polar regions, later involving orbitofrontal cortex. Anterior temporal lobe dysfunction was also particularly relevant in two patients (12.5%) with mixed forms of PPA. Lastly, two patients (12.5%) had unclassifiable PPA with predominating word-finding difficulties. No PPA-C9orf72 patients in our series fulfilled the criteria of the logopenic variant. Importantly, this study underlines the role of C9orf72 mutation in the disruption of the most anterior parts of the language network, including prefrontal and temporo-polar areas. It provides guidelines for C9orf72 testing in PPA patients, with important clinical impact as gene-specific therapies are upcoming.

Evidence for a pervasive autobiographical memory impairment in Logopenic Progressive Aphasia

Although characterized primarily as a language disorder, mounting evidence indicates episodic amnesia in Logopenic Progressive Aphasia (LPA). Whether such memory disturbances extend to information encoded pre-disease onset remains unclear. To address this question, we examined autobiographical memory in 10 LPA patients, contrasted with 18 typical amnestic Alzheimer's disease and 16 healthy Control participants. A validated assessment, the Autobiographical Interview, was employed to explore autobiographical memory performance across the lifespan under free and probed recall conditions. Relative to Controls, LPA patients showed global impairments across all time periods for free recall, scoring at the same level as disease-matched cases of Alzheimer's disease. Importantly, these retrieval deficits persisted in LPA, even when structured probing was provided, and could not be explained by overall level of language disruption or amount of information generated during autobiographical narration. Autobiographical memory impairments in LPA related to gray matter intensity decrease in predominantly posterior parietal brain regions implicated in memory retrieval. Together, our results suggest that episodic memory disturbances may be an under-appreciated clinical feature of LPA.

Heterogeneity of repetition abilities in logopenic variant primary progressive aphasia

The differential diagnosis of primary progressive aphasia (PPA) is challenging due to overlapping clinical manifestations of the different variants of the disease. This is particularly true for the logopenic variant of PPA (lvPPA), in which such overlap was reported with regard to impairments in repetition abilities. In this study, four individuals with lvPPA underwent standard neuropsychological and language assessments. The influence of psycholinguistic variables on their performance of in word, nonword and sentence repetition tasks was also specifically explored. Some level of heterogeneity was found in cognitive functions and in language. The four participants showed impairment in sentence repetition in which their performance was negatively affected by semantic reversibility and syntactic complexity. This study supports the heterogeneity of lvPPA with respect to the cognitive and linguistic status of participants. It also shows that sentence repetition is influenced not only by length, but also by semantic reversibility and syntactic complexity, two psycholinguistic variables known to place additional demands on phonological working memory.

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.

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.

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.

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.

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.

Motor speech disorders in the nonfluent, semantic and logopenic variants of primary progressive aphasia

OBJECTIVE

Motor speech disorders (MSDs) are characteristic for nonfluent primary progressive aphasia (nfvPPA). In primary progressive aphasia (PPA) of the semantic (svPPA) and of the logopenic type (lvPPA), speech motor function is considered typically intact. However, knowledge on the prevalence of MSDs in svPPA and lvPPA is mainly based on studies with a priori knowledge of PPA syndrome diagnosis. This fully blinded retrospective study aims to provide data on the prevalence of all types of MSDs in a large sample of German-speaking patients with different subtypes of PPA.

METHOD

Two raters, blinded for PPA subtype, independently evaluated connected speech samples for MSD syndrome and severity from 161 patients diagnosed with nfvPPA, svPPA or lvPPA in the database of the German Consortium of Frontotemporal Lobar Degeneration (FTLDc). In case of disagreement, a third experienced rater re-evaluated the speech samples, followed by a consensus procedure. Consensus was reached for 160 patients (74 nfvPPA, 49 svPPA, 37 lvPPA).

MAIN RESULTS

Across all PPA syndromes, 43.8% of the patients showed MSDs. Patients with nfvPPA demonstrated the highest proportion of MSDs (62.2%), but MSDs were also identified in svPPA (26.5%) and lvPPA (29.7%), respectively. Overall, dysarthria was the most common class of MSDs, followed by apraxia of speech. In addition, we identified speech abnormalities presenting as "syllabic speech", "dysfluent speech", and "adynamic speech".

DISCUSSION

Our study confirmed MSDs as frequently occurring in PPA. The study also confirmed MSDs to be most common in patients with nfvPPA. However, MSDs were also found in substantial proportions of patients with svPPA and lvPPA. Furthermore, our study identified speech motor deficits that have not received attention in previous studies on PPA. The results are discussed against the background of the existing literature on MSDs in PPA, including theoretical considerations of the neuroanatomical conditions described for each of the different subtypes of PPA.

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.

Online sentence processing impairments in agrammatic and logopenic primary progressive aphasia: Evidence from ERP

Evidence from psycholinguistic research indicates that sentence processing is impaired in Primary Progressive Aphasia (PPA), and more so in individuals with agrammatic (PPA-G) than logopenic (PPA-L) subtypes. Studies have mostly focused on offline sentence production ability, reporting impaired production of verb morphology (e.g., tense, agreement) and verb-argument structure (VAS) in PPA-G, and mixed findings in PPA-L. However, little is known about real-time sentence comprehension in PPA. The present study is the first to compare real-time semantic, morphosyntactic and VAS processing in individuals with PPA (10 with PPA-G and 9 with PPA-L), and in two groups of healthy (22 young and 19 older) individuals, using event-related potentials (ERP). Participants were instructed to listen to sentences that were either well-formed (n = 150) or contained a violation of semantics (e.g., *Owen was mentoring pumpkins at the party, n = 50), morphosyntax (e.g., *The actors was singing in the theatre, n = 50) or VAS (*Ryan was devouring on the couch, n = 50), and were required to perform a sentence acceptability judgment task while EEG was recorded. Results indicated that in the semantic task both healthy and PPA groups showed an N400 response to semantic violations, which was delayed in PPA and older (vs. younger) groups. Morphosyntactic violations elicited a P600 in both groups of healthy individuals and in PPA-L, but not in PPA-G. A similar P600 response was also found only in healthy individuals for VAS violations; whereas, abnormal ERP responses were observed in both PPA groups, with PPA-G showing no evidence of VAS violation detection and PPA-L showing a delayed and abnormally-distributed positive component that was negatively associated with offline sentence comprehension scores. These findings support characterizations of sentence processing impairments in PPA-G, by providing online evidence that VAS and morphosyntactic processing are impaired, in the face of substantially preserved semantic processing. In addition, the results indicate that on-line processing of VAS information may also be impaired in PPA-L, despite their near-normal accuracy on standardized language tests of argument structure production.

A Reliable and Rapid Language Tool for the Diagnosis, Classification, and Follow-Up of Primary Progressive Aphasia Variants

Background: Primary progressive aphasias (PPA) have been investigated by clinical, therapeutic, and fundamental research but examiner-consistent language tests for reliable reproducible diagnosis and follow-up are lacking.

Methods: We developed and evaluated a rapid language test for PPA (“PARIS”) assessing its inter-examiner consistency, its power to detect and classify PPA, and its capacity to identify language decline after a follow-up of 9 months. To explore the reliability and specificity/sensitivity of the test it was applied to PPA patients (N = 36), typical amnesic Alzheimer's disease (AD) patients (N = 24) and healthy controls (N = 35), while comparing it to two rapid examiner-consistent language tests used in stroke-induced aphasia (“LAST”, “ART”).

Results: The application duration of the “PARIS” was ~10 min and its inter-rater consistency was of 88%. The three tests distinguished healthy controls from AD and PPA patients but only the “PARIS” reliably separated PPA from AD and allowed for classifying the two most frequent PPA variants: semantic and logopenic PPA. Compared to the “LAST” and “ART,” the “PARIS” also had the highest sensitivity for detecting language decline.

Conclusions: The “PARIS” is an efficient, rapid, and highly examiner-consistent language test for the diagnosis, classification, and follow-up of frequent PPA variants. It might also be a valuable tool for providing end-points in future therapeutic trials on PPA and other neurodegenerative diseases affecting language processing.

Quantifying grammatical impairments in primary progressive aphasia: Structured language tests and narrative language production

PURPOSE

This study examined grammatical production impairments in primary progressive aphasia (PPA), as measured by structured tests and narrative samples. We aimed to quantify the strength of the relationship between grammatical measures across tasks, and identify factors that condition it. Three grammatical domains were investigated: overall sentence production, verb morphology, and verb-argument structure.

METHODS

77 participants with PPA (34 PPA-G, 16 PPA-L, 15 PPA-S and 12 other) completed a battery of grammatical tests and a narrative language sample was obtained. Accuracy scores were computed for the language tests and the narrative samples were analyzed for both accuracy of selected narrative variables as well as grammatical diversity across the three grammatical domains. Principal components analysis (PCA) and multiple regression were used to examine cross-task relationships for all measures.

RESULTS

As expected on the basis of classification criteria, accuracy scores were lower for the PPA-G group as compared to the PPA-L and PPA-S participants for overall sentence production and verb morphology, but not argument structure. Grammatical accuracy in narratives strongly predicted overall language test performance in PPA-G, whereas grammatical diversity in narratives did so in PPA-L, and no significant correspondence between narrative and language test performance was found for PPA-S. For individuals with severe grammatical impairments only, error distribution for both morphology and argument structure was strongly associated in structured tasks and narratives.

CONCLUSIONS

Grammatical production in narrative language predicts accuracy elicited with structured language tests in PPA. However, unique narrative production patterns distinguish PPA by subtype: accuracy for PPA-G, and grammatical diversity for PPA-L. The impairment in PPA-G is likely to reflect a core impairment in grammar whereas that of PPA-L may be closely tied to the word retrieval and verbal working memory deficits that characterize this variant. This underscores the theoretical distinction between PPA-L and PPA-G, as well as the importance of including grammatical diversity measures in analyses of language production, especially for patients who do not display frank agrammatism. Further, the results suggest that measures of domain-specific language deficits (i.e., verb morphology vs. argument structure) are robust across tasks only in individuals with severe grammatical impairments.

Language and Speech Markers of Primary Progressive Aphasia: A Systematic Review

Purpose This systematic review aimed to establish language and speech markers to support the clinical diagnosis of primary progressive aphasia (PPA) and its clinical phenotypes. Our first objective was to identify behavioral language and speech markers of early-stage PPA. Our second objective was to identify the electrophysiological correlates of the language and speech characteristics in PPA. Method The databases MEDLINE, Web of Science, and Embase were searched for relevant articles. To identify behavioral markers, the initial subjective complaints and the language and speech deficits detected during the initial diagnostic evaluation were summarized for PPA in general and each clinical variant according to the 2011 consensus diagnostic criteria (nonfluent variant [NFV], semantic variant, and logopenic variant [LV]). To identify electrophysiological markers, the studies in which event-related potentials (ERPs) were elicited by a language or speech paradigm in patients with PPA were included. Results In total, 114 relevant studies were identified, including 110 behavioral studies and only four electrophysiological studies. This review suggests that patients with the semantic variant could be accurately differentiated from the NFV and LV in the initial stages based on the consensus criteria. Nonetheless, the early differentiation between the NFV and LV is not straightforward. In the four electrophysiological studies, differences in the latency, amplitude, and topographical distribution of the semantic N400 component were found between patients with PPA and healthy controls. Conclusions To accurately differentiate the NFV from the LV, it could be important to assess the language and speech degeneration by more specific assessments and by more objective diagnostic methods that offer insights into the language-related processes. Electrophysiological markers of PPA were not identified in this review due to the low number of studies that investigated language-related ERPs. More controlled ERP studies in larger patient cohorts are needed to investigate the diagnostic applicability of language-related ERPs in PPA. Supplemental Material https://doi.org/10.23641/asha.12798080.

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.

Linguistic profiles, brain metabolic patterns and rates of amyloid-β biomarker positivity in patients with mixed primary progressive aphasia

We aimed to detail language profiles, brain metabolic patterns and proportion of Alzheimer's disease biomarkers in a cohort of patients with mixed primary progressive aphasia (mPPA). We considered 58 patients with PPA: 10 with non-fluent/agrammatic variant (nfvPPA), 16 with semantic variant (svPPA), 21 with logopenic variant (lvPPA) and 9 with mPPA. Patients with mPPA were further classified as 4 nf/lvPPA (with prevailing features for nfvPPA and lvPPA) and 5 s/lvPPA (with prevailing features for svPPA and lvPPA). Nf/lvPPA patients were characterized by higher proportion of Naming impairment compared to nfvPPA and more frequent Grammatical Errors and Phonologic Errors than lvPPA. S/lvPPA had higher proportion of impairment in Sentences Repetition compared to svPPA and in Single-word Comprehension compared to lvPPA. 100% of nf/lvPPA and 40% of s/lvPPA had Aβ positive biomarkers. Brain hypometabolic pattern in Nf/lvPPA was consistent with lvPPA, while s/lvPPA had a brain metabolism resembling svPPA. We concluded that nf/lvPPA patients might be considered as PPA variant due to Alzheimer's disease and s/lvPPA group mainly included patients with svPPA.

Limb and face apraxias in frontotemporal dementia: A systematic scoping review

PURPOSE

To investigate the literature for frequencies, profiles and neural correlates of limb and face apraxias in frontotemporal dementia (FTD).

METHOD

The search conducted in Ovid Medline, PsycINFO and Scopus yielded 487 non-duplicate records, and 43 were included in the final analysis.

RESULTS

Apraxias are evident in diverse forms in all clinical variants of FTD within the first four years of the disease. Face apraxia and productive limb apraxia co-occur in the behavioural and nonfluent variants. The logopenic variant resembles Alzheimer's disease in terms of pronounced parietal limb apraxia and absence of face apraxia. The semantic variant exhibits conceptual praxis deficits together with relatively preserved imitation skills. Concerning the genetic variants of FTD, productive limb apraxia is common among carriers of the progranulin gene mutation, and subtle gestural alterations have been documented among carriers of the chromosome 9 open reading frame 72 gene mutation before the expected disease onset. The data on neural correlations suggest that the breakdown of praxis results from bilateral cortical and subcortical damage in FTD and that Alzheimer-type pathology of the cerebrospinal fluid increases the severity of limb apraxia in all of the variants. Face apraxia correlates with degeneration of the medial and superior frontal cortices.

CONCLUSIONS

Each of the clinical variants of FTD exhibits a characteristic profile of apraxias that may support early differentiation between the variants and from Alzheimer's disease. However, the screening procedures developed for stroke populations seem insufficient, and a multifaceted assessment tool is needed. Although valid and practical tests already exist for dementia populations, a concise selection of test items that covers all of the critical domains is called for.