Primary Progressive Aphasia: Toward a Pathophysiological Synthesis

Navigating the diagnosis and treatment of primary progressive aphasia: Lived experience of a rural patient

Frontotemporal dementias (FTD) are a group of early-onset neurodegenerative disorders that primarily affect the frontal and temporal lobes, leading to changes in behavior, motor abilities, communication, and executive functions. Primary progressive aphasias (PPA), the language variant of FTD, specifically impair speech and language abilities. The heterogeneous presentation of FTD, particularly PPA, complicates differential diagnosis and treatment selection for healthcare professionals. These challenges are further exacerbated for patients in rural areas due to limited access to specialized healthcare services. This cross-sectional, descriptive case study examines a 76-year-old male patient diagnosed with agrammatic primary progressive aphasia (nfvPPA) living in a rural area in the U.S. We conducted a semi-structured interview with his caregiver to explore the lived experience of being diagnosed and treated for PPA in a rural setting and to identify challenges encountered during the diagnostic and therapeutic processes. Several critical barriers were identified, including poor interprofessional communication, inadequate practitioner-patient and caregiver communication, limited access to educational resources, inconsistent intervention and follow-ups, and restricted healthcare services. To improve the patient and caregiver experience, we propose a collaborative management model centered around speech-language pathologists with expertise in FTD/PPA. This model aims to facilitate smoother navigation of the healthcare system and improve patient outcomes. Effective care management requires clear and continuous communication among providers, patients, caregivers, and other professionals. Additionally, educating and supporting FTD/PPA patients and their families is essential. Research gaps in rural areas regarding diagnosis and treatment outcomes further hinder care, underscoring the need for targeted studies to enhance clinical practices and improve the quality of life for both patients and caregivers.

Atypical Alzheimer's dementia: Addressing the subtypes, epidemiology, atypical presentations, diagnostic biomarkers, and treatment updates

Alzheimer's disease is a progressive neurodegenerative disorder that primarily affects the elderly population; and is characterized by the gradual loss of memory, cognition, and ability to carry out daily activities. However, a growing body of research indicates that there exists a subtype of Alzheimer's disease known as Atypical Alzheimer's disease. Atypical Alzheimer's disease is a rare form of dementia that differs from the typical presentation of Alzheimer's disease, such as variations in the age of onset, distribution of brain pathology, and clinical symptoms. The patients affected have a younger age of onset and have predominantly visual, language, executive function, motor, and behavioral dysfunction. The diagnosis requires a comprehensive neurological evaluation with specific attention to cognitive and behavioral changes while ruling out other potential causes of dementia. Emerging biomarkers including CSF profiles, amyloid and tau PET imaging, and advanced neuroimaging techniques offer promising avenues for improving diagnostic accuracy and understanding disease mechanisms. In this article, we focus on atypical presentations seen in the posterior cortical variant, frontal variant, progressive aphasic variant, corticobasal syndrome and look at the specific biomarkers used in the diagnosis of each variant along with focusing on the treatment of the disease. We also aim to provide an understanding of Atypical Alzheimer's disease, its clinical features, the biomarkers helping in diagnosing the disease, the current treatment guidelines, and the current scientific advancements in the field.

Partial volume effect correction impairs the diagnostic utility of [18F]-THK-5351 PET in nonfluent-agrammatic variant primary progressive aphasia

OBJECTIVES

Partial volume effects in positron emission tomography occur frequently in neurodegenerative diseases due to increasing cortical atrophy during the disease course, and fronto-temporal dementia is often characterized by severe atrophy. The aim of this study was to challenge partial volume effect correction (PVEC) in patients with nonfluent-agrammatic variant primary progressive aphasia (nfv-PPA) imaged with [18F]-THK-5351 PET a marker of reactive neuroinflammatory astrogliosis as well as tau-binding.

METHODS

Patients with nfv-PPA (n = 20) were imaged with [18F]-THK-5351 PET accompanied by structural magnetic resonance tomography imaging (MRI). Region specific cortical grey matter volumes and standard uptake value ratios (SUVr) of the Hammers atlas were compared with eight healthy control (HC) (n = 8) data before and after performing region-based voxel-wise PVEC. We evaluated regional coefficients of variance (CoV) and the number of regions with significant [18F]-THK-5351 PET signal differences between nfv-PPA and controls before and after PVEC. Additionally, a blinded visual read was performed by three nuclear medicine physicians (consensus) before and after PVEC.

RESULTS

Prior to PVEC, [18F]-THK-5351 tracer uptake was significantly higher in the bilateral frontal cortex of patients with nfv-PPA when compared to HC (left > right), despite significant grey matter atrophy in the same brain regions in patients with nfv-PPA. SUVr differences between nfv-PPA and HC were further increased by PVEC in frontal brain regions, but group level variance increased in parallel and reduced the number of significant differences between SUVr of nfv-PPA and HC (uncorrected: 10 significant regions, CoV[nfv-PPA]: 20.8 % ± 4.7 %, CoV[HC]: 7.9 % ± 2.4 %/PVEC: 3 significant regions, CoV[nfv-PPA]: 28.4 % ± 8.9 %, CoV[HC]: 9.8 % ± 2.5 %). Sensitivity/specificity of the visual read for detection of nfv-PPA was 0.85/1.00 without PVEC and 0.85/0.75 with PVEC.

CONCLUSIONS

[18F]-THK-5351 PET facilitates detection of pathological alterations in patients with nfvPPA with severe atrophy. PVEC increases quantitative SUVr differences between patients with nfv-PPA and HC but introduces a parallel increase of variance at the group level. Visual assessment of [18F]-THK-5351 images in patients with nfv-PPA is impaired by PVEC due to loss of specificity and does not support the use of PVEC even in patients with severe atrophy.

Data-driven neuroanatomical subtypes of primary progressive aphasia

The primary progressive aphasias are rare, language-led dementias, with three main variants: semantic, non-fluent/agrammatic and logopenic. Although the semantic variant has a clear neuroanatomical profile, the non-fluent/agrammatic and logopenic variants are difficult to discriminate from neuroimaging. Previous phenotype-driven studies have characterized neuroanatomical profiles of each variant on MRI. In this work, we used a machine learning algorithm known as SuStaIn to discover data-driven neuroanatomical 'subtype' progression profiles and performed an in-depth subtype-phenotype analysis to characterize the heterogeneity of primary progressive aphasia. Our study included 270 participants with primary progressive aphasia seen for research in the UCL Queen Square Institute of Neurology Dementia Research Centre, with follow-up scans available for 137 participants. This dataset included individuals diagnosed with all three main variants (semantic, n = 94; non-fluent/agrammatic, n = 109; logopenic, n = 51) and individuals with unspecified primary progressive aphasia (n = 16). A dataset of 66 patients (semantic, n = 37; non-fluent/agrammatic, n = 29) from the ARTFL LEFFTDS Longitudinal Frontotemporal Lobar Degeneration (ALLFTD) Research Study was used to validate our results. MRI scans were segmented, and SuStaIn was used on 19 regions of interest to identify neuroanatomical profiles independent of the diagnosis. We assessed the assignment of subtypes and stages, in addition to their longitudinal consistency. We discovered four neuroanatomical subtypes of primary progressive aphasia, labelled S1 (left temporal), S2 (insula), S3 (temporoparietal) and S4 (frontoparietal), exhibiting robustness to statistical scrutiny. S1 was correlated strongly with the semantic variant, whereas S2, S3 and S4 showed mixed associations with the logopenic and non-fluent/agrammatic variants. Notably, S3 displayed a neuroanatomical signature akin to a logopenic-only signature, yet a significant proportion of logopenic cases were allocated to S2. The non-fluent/agrammatic variant demonstrated diverse associations with S2, S3 and S4. No clear relationship emerged between any of the neuroanatomical subtypes and the unspecified cases. At first follow-up, subtype assignment was stable for 84% of patients, and stage assignment was stable for 91.9% of patients. We partially validated our findings in the ALLFTD dataset, finding comparable qualitative patterns. Our study, leveraging machine learning on a large primary progressive aphasia dataset, delineated four distinct neuroanatomical patterns. Our findings suggest that separable spatiotemporal neuroanatomical phenotypes do exist within the primary progressive aphasia spectrum, but that these are noisy, particularly for the non-fluent/agrammatic non-fluent/agrammatic and logopenic variants. Furthermore, these phenotypes do not always conform to standard formulations of clinico-anatomical correlation. Understanding the multifaceted profiles of the disease, encompassing neuroanatomical, molecular, clinical and cognitive dimensions, has potential implications for clinical decision support.

Clinical characteristics of semantic variant of primary progressive aphasia with TDP-43- and tau-related gene variants

BACKGROUND

Semantic variant primary progressive aphasia (svPPA) can be inheritable. There is a predictable relationship between the pathological substrate and genetic variants in this condition.

OBJECTIVE

To report a case with svPPA who carried a MAPT gene mutation and to explore clinical differences between svPPA with TDP-43 pathology-related genes and svPPA with tau pathology-related genes.

METHODS

Studies reporting svPPA patients with MAPT, TARDBP, GRN, C9orf72, or TBK1 gene mutations were selected from PubMed and China National Knowledge Infrastructure (CNKI). Of the 109 articles from the literature, 31 reports involving 75 cases provided the outcomes of interest.

RESULTS

Along with the new case, 76 patients (43 males and 33 females) were included in this study. Among them, 34 carried MAPT mutations, 15 with TARDBP mutations, 13 with GRN mutations, 8 with C9orf72 expansions, and 6 with TBK1 mutations. The analysis results revealed that the mean age of onset in the tau pathology-related gene mutation group (50.56 ± 7.46 years) was younger than that in the TDP-43 pathology-related gene mutation group (58.19 ± 7.66 years) (p < 0.001). MAPT and TARDBP mutations were more prevalent in the study population, accounting for 44.7% and 19.7%, respectively. Within the MAPT gene mutation population, P301L accounted for 41.2%, while IVS10 + 16C > T accounted for 38.2%. Among the TARDBP gene mutation carriers, I383V accounted for 73.3%.

CONCLUSIONS

The onset age in svPPA patients with tau pathology-related gene mutations is younger than in those with TDP-43 pathology-related gene mutations. MAPT variants, specifically P301L and IVS10 + 16C > T, as well as TARDBP I383V variant, may have higher mutation frequency in svPPA.

An international core outcome set for primary progressive aphasia (COS-PPA): Consensus-based recommendations for communication interventions across research and clinical settings

INTRODUCTION

Interventions to treat speech-language difficulties in primary progressive aphasia (PPA) often use word accuracy as a highly comparable outcome. However, there are more constructs of importance to people with PPA that have received less attention.

METHODS

Following Core Outcome Set Standards for Development Recommendations (COSSTAD), this study comprised: Stage 1 - systematic review to identify measures; Stage 2 - consensus groups to identify important outcome constructs for people with PPA (n = 82) and care partners (n = 91); Stage 3 - e-Delphi consensus with 57 researchers.

RESULTS

The systematic review identified 84 Outcome Measurement Instruments. Core outcome constructs identified included: (1) Participate in conversations with family and friends, (2) get words out, (3) be more fluent, (4) convey a message by any means, and (5) understand what others are saying. Researchers were unable to reach a consensus on measurement instruments.

DISCUSSION

Further work is required to develop appropriate measurement instruments that address all core outcome constructs important to key stakeholders.

HIGHLIGHTS

We introduce new symptom-led perspectives on primary progressive aphasia (PPA). The focus is on non-fluent/agrammatic (nfvPPA) and semantic (svPPA) variants. Foregrounding of early and non-verbal features of PPA and clinical trajectories is featured. We introduce a symptom-led staging scheme for PPA. We propose a prototype for a functional impairment scale, the PPA Progression Planning Aid.

Advancing Neuropsychological Rehabilitation in Primary Progressive Aphasia Based on Principles of Cognitive Neuroscience: A Scoping Review and Systematic Analysis of the Data

Background/Objectives: This systematic review of neuropsychological rehabilitation strategies for primary progressive aphasia will consider recent developments in cognitive neuroscience, especially neuroimaging techniques such as EEG and fMRI, to outline how these tools might be integrated into clinical practice to maximize treatment outcomes. Methods: A systematic search of peer-reviewed literature from the last decade was performed following the PRISMA guidelines across multiple databases. A total of 63 studies were included, guided by predefined inclusion and exclusion criteria, with a focus on cognitive and language rehabilitation in PPA, interventions guided by neuroimaging, and mechanisms of neuroplasticity. Results: Integration of neuroimaging techniques contributes to the increase in the efficacy of interventions with critical information about the neural mechanisms underlying language deficits in the aphasias. Traditional rehabilitation strategies, technology-assisted interventions, and non-invasive brain stimulation techniques hold considerable promise for language improvement. Neuroimaging was also found to be necessary in subtype-specific differentiation toward tailoring therapeutic intervention. Evidence also shows that directed and sustained interventions using neuroplasticity can have long-term effects in managing the symptoms of PPA. Conclusions: The present review underlines the necessity of including cognitive neuroscience techniques within neuropsychological rehabilitation to enhance therapeutic outcomes in PPA. In addition, neuroimaging modalities such as EEG and fMRI are also of great importance in understanding the underlying neurobiology of language disturbances and guiding tailored interventions. Long-term benefits of these approaches should be evaluated, including their applicability in routine clinical practice.

A call for globally responsive screening materials to account for heterogeneity in dementia syndromes

Effective screening for communicative ability in dementia is vital to drive theoretical understanding and optimize care responsiveness globally. Communication is central to the human experience; however, routine clinical screening for progressive communication change remains limited due to a variety of resource constraints. Other challenges include the subtlety of early communication-led symptoms, heterogeneous underlying pathologies, and a lack of culturally diverse research and tools. To address the scarcity of dedicated assessment resources, future initiatives must maximize responsiveness to and representation of our global population to appropriately respond to the rising, and vastly diverse, dementia crisis.

Bridging the gap between scientific research of rare diseases and the affected patients and families

In 2015, my father was diagnosed with primary progressive aphasia (PPA), a type of frontotemporal dementia that my family and I knew nothing about. Medical professionals told us that there was no research on the disease, and I believed this until very recently. I took a class in neurobiology, leading me to attempt to document this lack of research and create a call to action for the research and treatment of rare disorders. However, I was met with an overwhelming amount of information regarding PPA that I was not expecting to find. I was frustrated that I was not given this information; moreover, I did not understand why it was all being 'hidden' from me. After discussion with my mother, I realized that my science education allowed me to find and interpret this information, but more importantly, that not everyone has this same privilege. My call to action pivoted into a call for better communication and for open access to biomedical information. Regardless of the existence and quality of literature about rare diseases, most of the information is out of reach of the public.The public often does not have the scientific literacy to understand the complexities of the genre that is required for comprehension. I recognize that not every patient and family may wish to access the information generated by biomedical research. I argue that they have a right to examine these findings because they are the ones that are being the most deeply affected by these disorders. While the translation of information may seem cumbersome , the impact it could have on patients, caregivers, and providers is worth the effort.

Study protocol for the Functional Communication Checklist for people living with primary progressive aphasia

This study protocol describes the development of the first instrument of functional communication for people living with primary progressive aphasia (PPA), with future applications to other progressive conditions, with expert validation, item-level reliability analyses, input from partners in research, and outcomes. Progressive conditions like PPA require monitoring, and as such, re-assessment. Re-assessment poses the high risk of being burdensome, destructive, and of little use to the patient. As such, there is a significant need to establish a validated and reliable measure that (1) poses minimal patient burden and (2) captures communication ability in a strengths-based manner for both clinical and research purposes. A strengths-based approach to assessment is widely recognized as the optimal way to promote patient autonomy, minimize harm, and implement functional treatment protocols and strategies. To date, there are no strengths-based assessment tools that were developed for people living with PPA nor ways to efficiently document functional communication performance. This study protocol outlines our work to address this gap in clinical practice and research.

FDG-PET in the diagnosis of primary progressive aphasia: a systematic review

Primary progressive aphasia (PPA) is a disease known to affect the frontal and temporal regions of the left hemisphere. PPA is often an indication of future development of dementia, specifically semantic dementia (SD) for frontotemporal dementia (FTD) and logopenic progressive aphasia (LPA) as an atypical presentation of Alzheimer's disease (AD). The purpose of this review is to clarify the value of 2-deoxy-2-[18F]fluoro-D-glucose (FDG)-positron emission tomography (PET) in the detection and diagnosis of PPA. A comprehensive review of literature was conducted using Web of Science, PubMed, and Google Scholar. The three PPA subtypes show distinct regions of hypometabolism in FDG-PET imaging with SD in the anterior temporal lobes, LPA in the left temporo-parietal junction, and nonfluent/agrammatic Variant PPA (nfvPPA) in the left inferior frontal gyrus and insula. Despite the distinct patterns, overlapping hypometabolic areas can complicate differential diagnosis, especially in patients with SD who are frequently diagnosed with AD. Integration with other diagnostic tools could refine the diagnostic process and lead to improved patient outcomes. Future research should focus on validating these findings in larger populations and exploring the therapeutic implications of early, accurate PPA diagnosis with more targeted therapeutic interventions.

Global perspectives on the management of primary progressive aphasia

Speech-language therapists/pathologists (SLT/Ps) are key professionals in the management and treatment of primary progressive aphasia (PPA), however, there are gaps in education and training within the discipline, with implications for skills, confidence, and clinical decision-making. This survey aimed to explore the areas of need amongst SLT/Ps working with people living with PPA (PwPPA) internationally to upskill the current and future workforce working with progressive communication disorders. One hundred eighty-six SLT/Ps from 27 countries who work with PwPPA participated in an anonymous online survey about their educational and clinical experiences, clinical decision-making, and self-reported areas of need when working with this population. Best practice principles for SLT/Ps working with PwPPA were used to frame the latter two sections of this survey. Only 40.7% of respondents indicated that their university education prepared them for their current work with PwPPA. Competency areas of "knowing people deeply," "practical issues," "connectedness," and "preventing disasters" were identified as the basic areas of priority and need. Respondents identified instructional online courses (92.5%), sample tools and activities for interventions (64.8%), and concrete training on providing care for advanced stages and end of life (58.3%) as central areas of need in their current work. This is the first international survey to comprehensively explore the perspectives of SLT/Ps working with PwPPA. Based on survey outcomes, there is a pressing need to enhance current educational and ongoing training opportunities to better promote the well-being of PwPPA and their families, and to ensure appropriate preparation of the current and future SLT/P workforce.

Advances in semantic dementia: Neuropsychology, pathology & neuroimaging

Semantic dementia is a kind of neurodegenerative disorder, characterized by prominent semantic impairments and anterior temporal lobe atrophy. Since 2010, more studies have devoted to this rare disorder, revealing that it is more complex than we think. Clinical advances include more specific findings of semantic impairments and other higher order cognitive deficits. Neuroimaging techniques can help revealing the different brain networks affected (both structurally and functionally) in this condition. Pathological and genetic studies have also found more complex situations of semantic dementia, which might explain the huge variance existing in semantic dementia. Moreover, the current diagnosis criteria mainly focus on semantic dementia's classical prototype. We further delineated the features of three subtypes of semantic dementia based on atrophy lateralization with three severity stages. In a broader background, as a part of the continuum of neurodegenerative disorders, semantic dementia is commonly compared with other resembling conditions. Therefore, we summarized the differential diagnosis between semantic dementia and them. Finally, we introduced the challenges and achievements of its diagnosis, treatment, care and cross cultural comparison. By providing a comprehensive picture of semantic dementia on different aspects of advances, we hope to deepen the understanding of semantic dementia and promote more inspirations on both clinical and theoretical studies about it.

Differential linguistic features of verbal fluency in behavioral variant frontotemporal dementia and primary progressive aphasia

Frontotemporal dementia (FTD) is an early-onset neurodegenerative disorder with a heterogeneous clinical presentation. Verbal fluency is regularly used as a sensitive measure of language ability, semantic memory, and executive functioning, but qualitative changes in verbal fluency in FTD are currently overlooked. This retrospective study examined qualitative, linguistic features of verbal fluency in 137 patients with behavioral variant (bv)FTD (n = 50), or primary progressive aphasia (PPA) [25 non-fluent variant (nfvPPA), 27 semantic variant (svPPA), and 34 logopenic variant (lvPPA)] and 25 control participants. Between-group differences in clustering, switching, lexical frequency (LF), age of acquisition (AoA), neighborhood density (ND), and word length (WL) were examined in the category and letter fluency with analysis of variance adjusted for age, sex, and the total number of words. Associations with other cognitive functions were explored with linear regression analysis. The results showed that the verbal fluency performance of patients with svPPA could be distinguished from controls and other patient groups by fewer and smaller clusters, more switches, higher LF, and lower AoA (all p < 0.05). Patients with lvPPA specifically produced words with higher ND than the other patient groups (p < 0.05). Patients with bvFTD produced longer words than the PPA groups (p < 0.05). Clustering, switching, LF, AoA, and ND-but not WL-were differentially predicted by measures of language, memory, and executive functioning (range standardized regression coefficient 0.25-0.41). In addition to the total number of words, qualitative linguistic features differ between subtypes of FTD. These features provide additional information on lexical processing and semantic memory that may aid the differential diagnosis of FTD.

'Communication is difficult': Speech, language and communication needs of people with young onset or rarer forms of non-language led dementia

BACKGROUND

People with behavioural variant frontotemporal dementia, Lewy body dementia, posterior cortical atrophy and young onset Alzheimer's disease may experience language and communication difficulties. However, the role of speech and language interventions for people with these non-language led dementias has received little attention.

AIMS

This study aimed to explore the experiences and perspectives of people living with these conditions, and their families, regarding their language and communication difficulties and how speech and language therapy could address these needs.

METHODS

This study employed a qualitative design to explore the experiences of people living with or caring for somebody with behavioural variant frontotemporal dementia, Lewy body dementia, posterior cortical atrophy or young onset Alzheimer's disease, and to understand their opinions about speech and language therapy. Participants were recruited from a support service connected to a dementia clinic to attend one of five focus group meetings. Videorecorded focus groups and interviews were transcribed, and reflexive thematic analysis was used to analyse data from people affected by each type of dementia.

RESULTS

A total of 25 participants were recruited to the study, with representation across the different forms of non-language led dementias. The four main themes identified were: (1) communication difficulties as a key difficulty, (2) loss and loneliness, (3) speech and language therapy, and (4) the role of the caregiver. Sixteen subthemes were also identified which highlighted individual issues across disease types.

DISCUSSION

Although all the forms of dementia studied here are not considered to be language-led, people with these conditions and/or their care partners identified speech, language and communication as common challenges. These communication difficulties were reported to have a negative impact on their social participation and mental health and participants felt speech and language interventions could help. There is a need for research exploring speech and language interventions developed for and with people with non-language led dementias and their care partners, to ensure they meet the needs of the people they are designed for.

WHAT THIS PAPER ADDS

What is already known on the subject People with primary progressive aphasia present with speech, language and communication difficulties, and several speech and language interventions have been developed to meet the needs of this population. However, people with non-language led dementias may also experience speech, language and communication difficulties, and little is known about interventions that may address these difficulties. What this paper adds to existing knowledge People living with or caring for somebody with behavioural variant frontotemporal dementia, Lewy body dementia, posterior cortical atrophy and young onset Alzheimer's disease report experiencing speech, language and communication difficulties that impact on the person with dementia's social participation and mood. Participants in this study also shared their opinions about how speech and language interventions could help, from the earliest stages of the disease. What are the potential or actual clinical implications of this work? Speech and language therapists need to address the individual speech, language and communication needs of people with dementias, even those that are not thought to be language-led. Current speech and language therapy service provision does not meet the needs of people with non-language led dementias and further research is required to develop interventions and services to meet these needs.

COS-PPA: protocol to develop a core outcome set for primary progressive aphasia

INTRODUCTION

The term primary progressive aphasia (PPA) describes a group of language-led dementias. Disease-modifying treatments that delay, slow or reverse progression of PPA are currently lacking, though a number of interventions to manage the symptoms of PPA have been developed in recent years. Unfortunately, studies exploring the effectiveness of these interventions have used a variety of different outcome measures, limiting comparability. There are more constructs, apart from word retrieval, that are important for people with PPA that have not received much attention in the research literature. Existing core outcome sets (COS) for dementia and non-progressive aphasia do not meet the needs of people with PPA, highlighting a need to develop a specific COS for PPA.

METHODS AND ANALYSIS

This protocol describes a three-stage study to identify a COS for PPA interventions in research and clinical practice. The stage 1 systematic review will identify existing speech, language and communication measures used to examine the effectiveness of interventions for PPA in the research literature. Employing a nominal group technique, stage 2 will identify the most important outcomes for people with PPA and their families. The data collected in stages 1 and 2 will be jointly analysed with the project PPI group and will inform the stage 2 modified Delphi consensus study to identify a core outcome measurement set for PPA among a range of research disciplines undertaking intervention studies for people with PPA.

ETHICS AND DISSEMINATION

Ethical approval for stage 2 of the study has been sought individually in each country at collaborating institutions and is stated in detail in the manuscript. Stage 3 has been granted ethical approval by the Chairs of UCL Language and Cognition Department Ethics, Project ID LCD-2023-06. Work undertaken at stages 1, 2 and 3 will be published in open-access peer-reviewed journal articles and presented at international scientific conferences.

PROSPERO REGISTRATION NUMBER

CRD42022367565.

Global Perspectives on the Management of Primary Progressive Aphasia

Speech-language therapists/pathologists (SLT/Ps) are key professionals in the management and treatment of primary progressive aphasia (PPA), however, there are gaps in education and training within the discipline, with implications for skills, confidence, and clinical decision-making. This survey aimed to explore the areas of need amongst SLT/Ps working with people living with PPA (PwPPA) internationally to upskill the current and future workforce working with progressive communication disorders. One hundred eighty-five SLT/Ps from 27 countries who work with PwPPA participated in an anonymous online survey about their educational and clinical experiences, clinical decision-making, and self-reported areas of need when working with this population. Best practice principles for SLT/Ps working with PwPPA were used to frame the latter two sections of this survey. Only 40.7% of respondents indicated that their university education prepared them for their current work with PwPPA. Competency areas of "Knowing people deeply," "Practical issues," "Connectedness," and "Preventing disasters" were identified as the basic areas of priority and need. Respondents identified instructional online courses (92.5%), sample tools and activities for interventions (64.8%), and concrete training on providing care for advanced stages and end of life (58.3%) as central areas of need in their current work. This is the first international survey to comprehensively explore the perspectives of SLT/Ps working with PwPPA. Based on survey outcomes, there is a pressing need to enhance current educational and ongoing training opportunities to better promote the well-being of PwPPA and their families, and to ensure appropriate preparation of the current and future SLT/P workforce.

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.

Development of fidelity of delivery and enactment measures for interventions in communication disorders

OBJECTIVES

This study was part of a process evaluation for a single-blind, randomized controlled pilot study comparing Better Conversations with Primary Progressive Aphasia (BCPPA), an approach to communication partner training, with no speech and language therapy treatment. It was necessary to explore fidelity of delivery (delivery of intervention components) and intervention enactment (participants' use of intervention skills in the form of conversation behaviours comprising facilitators, that enhance the conversational flow, and barriers, that impeded the flow of conversation). This study aimed to: (1) Outline an adapted methodological process that uses video observation, to measure both fidelity of delivery and enactment. (2) Measure the extent to which the BCPPA pilot study was delivered as planned, and enacted.

DESIGN

Observational methods were used alongside statistical analysis to explore the fidelity of intervention and enactment using video recordings obtained from the BCPPA pilot study.

METHODS

A 5-step methodology, was developed to measure fidelity of delivery and enactment for the BCPPA study using video-recorded data. To identify delivery of intervention components, a random sample of eight video recorded and transcribed BCPPA intervention sessions was coded. To examine the enactment of conversation behaviours, 108 transcribed 10 -min-video recorded conversations were coded from 18 participants across the control and intervention group.

RESULTS

Checklists and guidelines for measurement of fidelity of treatment delivery and coding spreadsheets and guidelines for measurement of enactment are presented. Local collaborators demonstrated 87.2% fidelity to the BCPPA protocol. Participants in the BCPPA treatment group increased their use of facilitator behaviours enacted in conversation from a mean of 13.5 pre-intervention to 14.2 post-intervention, whilst control group facilitators decreased from a mean of 15.5 to 14.4, over the same timescale.

CONCLUSIONS

This study proposes a novel and robust methods, using video recorded intervention sessions and conversation samples, to measure both fidelity of intervention delivery and enactment. The learnings from this intervention are transferable to other communication interventions.

Muddles and puzzles: Metaphor use associated with disease progression in Primary Progressive Aphasia

Background

Primary Progressive Aphasia describes a language-led dementia and its variants. There is little research exploring the experiences of living with this disease. Metaphor, words that represent something else, have been studied extensively in health-related narratives to gain a more intimate insight into health experiences.

Aims

This study explored the metaphors used spontaneously by people with PPA, their care partners (family), and speech and language therapists/pathologists (SLT/Ps) providing support along the continuum of care.

Methods & Procedures

This study examined two previously collected data sets comprising naturalistic talk where metaphors were not the specific focus, the first from focus groups conducted with people with PPA and their families and the second from focus groups conducted with SLT/Ps working with people with PPA. Transcribed data were analysed for metaphor use through an iterative narrative approach.

Outcomes & Results

In all, 237 examples of metaphorical language were identified in the data, with 14 metaphors from people with PPA, 116 from the families and 106 from SLT/Ps. Different metaphors were used by participants to describe their experiences depending on which variant of PPA they were living with, and people also described their disease differently over time. SLT/Ps also used metaphors, however, their language reflected the structured, professional perspective of delivering speech and language therapy services.

Conclusions & Implications

SLT/Ps should listen for and recognise the metaphorical language used by people with PPA and their families to ensure therapeutic alignment, see beyond the PPA to recognise the individual's needs, and provide person-centred and empathic support.

Comprehension of acoustically degraded speech in Alzheimer's disease and primary progressive aphasia

Successful communication in daily life depends on accurate decoding of speech signals that are acoustically degraded by challenging listening conditions. This process presents the brain with a demanding computational task that is vulnerable to neurodegenerative pathologies. However, despite recent intense interest in the link between hearing impairment and dementia, comprehension of acoustically degraded speech in these diseases has been little studied. Here we addressed this issue in a cohort of 19 patients with typical Alzheimer's disease and 30 patients representing the three canonical syndromes of primary progressive aphasia (non-fluent/agrammatic variant primary progressive aphasia; semantic variant primary progressive aphasia; logopenic variant primary progressive aphasia), compared to 25 healthy age-matched controls. As a paradigm for the acoustically degraded speech signals of daily life, we used noise-vocoding: synthetic division of the speech signal into frequency channels constituted from amplitude-modulated white noise, such that fewer channels convey less spectrotemporal detail thereby reducing intelligibility. We investigated the impact of noise-vocoding on recognition of spoken three-digit numbers and used psychometric modelling to ascertain the threshold number of noise-vocoding channels required for 50% intelligibility by each participant. Associations of noise-vocoded speech intelligibility threshold with general demographic, clinical and neuropsychological characteristics and regional grey matter volume (defined by voxel-based morphometry of patients' brain images) were also assessed. Mean noise-vocoded speech intelligibility threshold was significantly higher in all patient groups than healthy controls, and significantly higher in Alzheimer's disease and logopenic variant primary progressive aphasia than semantic variant primary progressive aphasia (all P < 0.05). In a receiver operating characteristic analysis, vocoded intelligibility threshold discriminated Alzheimer's disease, non-fluent variant and logopenic variant primary progressive aphasia patients very well from healthy controls. Further, this central hearing measure correlated with overall disease severity but not with peripheral hearing or clear speech perception. Neuroanatomically, after correcting for multiple voxel-wise comparisons in predefined regions of interest, impaired noise-vocoded speech comprehension across syndromes was significantly associated (P < 0.05) with atrophy of left planum temporale, angular gyrus and anterior cingulate gyrus: a cortical network that has previously been widely implicated in processing degraded speech signals. Our findings suggest that the comprehension of acoustically altered speech captures an auditory brain process relevant to daily hearing and communication in major dementia syndromes, with novel diagnostic and therapeutic implications.

Results from a randomised controlled pilot study of the Better Conversations with Primary Progressive Aphasia (BCPPA) communication partner training program for people with PPA and their communication partners

BACKGROUND

There has been a growing focus on functional communication interventions for primary progressive aphasia (PPA). These interventions aim to support individuals to participate in life situations. One such intervention, communication partner training (CPT) aims to change conversation behaviours in both the person with PPA and their communication partner (CP). CPT has a growing evidence base in stroke aphasia; however, these programmes are not designed to meet the needs of people with progressive communication difficulties. To address this, the authors developed a CPT program entitled Better Conversations with PPA (BCPPA) and undertook a pilot trial to establish for a future full trial; predicted recruitment rates, acceptability, an assessment of treatment fidelity and an appropriate primary outcome measure.

METHODOLOGY

This was a single-blind, randomised controlled pilot study comparing BCPPA to no treatment, delivered across 11 National Health Service Trusts in the UK. A random sample of eight recordings of local collaborators delivering the intervention were analysed to examine fidelity. Participants completed feedback forms reporting on acceptability. Pre- and post-intervention measures targeted conversation behaviours, communication goals and quality of life.

RESULTS

Eighteen people with PPA and their CPs (9 randomised to BCPPA, 9 randomised to no treatment) completed the study. Participants in the intervention group rated BCPPA positively. Treatment fidelity was 87.2%. Twenty-nine of 30 intervention goals were achieved or over-achieved and 16 of 30 coded conversation behaviours demonstrated change in the intended direction. The Aphasia Impact Questionnaire was identified as the preferred outcome measure.

CONCLUSION

The first randomised controlled UK pilot study of a CPT program for people with PPA and their families demonstrates BCPPA is a promising intervention. The intervention was acceptable, treatment fidelity high and an appropriate measure identified. Results of this study indicate a future RCT of BCPPA is feasible.

TRIAL REGISTRATION

Registered 28/02/2018 ISRCTN10148247 .

'Like going into a chocolate shop, blindfolded': What do people with primary progressive aphasia want from speech and language therapy?

BACKGROUND

Primary progressive aphasia (PPA) describes a group of language-led dementias. PPAs are complex, diverse and difficult to diagnose, and therefore conventional models of aphasia and dementia treatment do not meet their needs. The research evidence on intervention for PPA is developing, but to date there are only a few case studies exploring the experiences of people with PPA (PwPPA) themselves.

AIMS

To explore the experiences and opinions of PwPPA and their communication partners (CPs) to understand how speech and language therapy (SLT) services can better meet their needs.

METHODS & PROCEDURES

A qualitative research approach was used whereby PwPPA and their friends or family members were recruited to participate in focus groups, via advertisements in the Rare Dementia Support PPA group newsletters. Consenting participants were allocated to attend one of four focus groups hosted on an online video conferencing platform. Participants were asked about their communication difficulties, and how SLT could address these needs. All meetings were transcribed, and data were examined using reflexive thematic analysis.

OUTCOMES & RESULTS

Six PwPPA and 14 CPs representing all three PPA variants and mixed PPA participated in the focus groups. Four main themes were identified during the analysis of the focus group discussions: (1) CPs' burden, (2) adjusting to the diagnosis, (3) communication abilities and difficulties and (4) beyond language. A further 10 subthemes were identified.

CONCLUSIONS & IMPLICATIONS

This study provides a greater understanding of the experiences and needs of PwPPA and their families in relation to SLT. This work underlines the importance of a person-centred approach that considers the broader needs of both the PwPPA and the people around them. This will enable service providers to deliver SLT that meets the needs of PwPPA and their families and will also inform future research in this field.

WHAT THIS PAPER ADDS

What is already known on this subject We know that PwPPA can maintain or even make improvements in word retrieval and speech fluency with SLT exercises. There is also developing evidence of the benefits of interventions such as CP training, communication aid support and other functional interventions. What this paper adds to existing knowledge This study provides an understanding of the experiences and opinions of people living with PPA and their families in relation to SLT. Results demonstrate that PwPPA and their families have to navigate a complex journey, identifying strategies to support communication but also the influence of personality and other cognitive symptoms. SLT was useful, but not always available. What are the potential or actual clinical implications of this work? This study will enable service providers to better plan, justify funding for and delivery of SLT that will meet the needs of PwPPA and their families. Most importantly this work underlines the importance of a person-centred approach, incorporating the broader needs of the person with PPA and those around them.

Symptom-led staging for primary progressive aphasia

The primary progressive aphasias (PPA) present complex and diverse challenges of diagnosis, management and prognosis. A clinically-informed, syndromic staging system for PPA would take a substantial step toward meeting these challenges. This study addressed this need using detailed, multi-domain mixed-methods symptom surveys of people with lived experience in a large international PPA cohort. We administered structured online surveys to caregivers of patients with a canonical PPA syndromic variant (nonfluent/agrammatic (nvPPA), semantic (svPPA) or logopenic (lvPPA)). In an 'exploratory' survey, a putative list and ordering of verbal communication and nonverbal functioning (nonverbal thinking, conduct and wellbeing, physical) symptoms was administered to 118 caregiver members of the UK national PPA Support Group. Based on feedback, we expanded the symptom list and created six provisional clinical stages for each PPA subtype. In a 'consolidation' survey, these stages were presented to 110 caregiver members of UK and Australian PPA Support Groups, and refined based on quantitative and qualitative feedback. Symptoms were retained if rated as 'present' by a majority (at least 50%) of respondents representing that PPA syndrome, and assigned to a consolidated stage based on majority consensus; the confidence of assignment was estimated for each symptom as the proportion of respondents in agreement with the final staging for that symptom. Qualitative responses were analysed using framework analysis. For each PPA syndrome, six stages ranging from 1 ('Very mild') to 6 ('Profound') were identified; earliest stages were distinguished by syndromic hallmark symptoms of communication dysfunction, with increasing trans-syndromic convergence and dependency for basic activities of daily living at later stages. Spelling errors, hearing changes and nonverbal behavioural features were reported at early stages in all syndromes. As the illness evolved, swallowing and mobility problems were reported earlier in nfvPPA than other syndromes, while difficulty recognising familiar people and household items characterised svPPA and visuospatial symptoms were more prominent in lvPPA. Overall confidence of symptom staging was higher for svPPA than other syndromes. Across syndromes, functional milestones were identified as key deficits that predict the sequence of major daily life impacts and associated management needs. Qualitatively, we identified five major themes encompassing 15 subthemes capturing respondents' experiences of PPA and suggestions for staging implementation. This work introduces a prototypical, symptom-led staging scheme for canonical PPA syndromes: the PPA Progression Planning Aid (PPA 2 ). Our findings have implications for diagnostic and care pathway guidelines, trial design and personalised prognosis and treatment for people living with these diseases.

Principles and philosophies for speech and language therapists working with people with primary progressive aphasia: an international expert consensus

PURPOSE

Primary progressive aphasia (PPA) is a language-led dementia associated with Alzheimer's pathology and fronto-temporal lobar degeneration. Multiple tailored speech and language interventions have been developed for people with PPA. Speech and language therapists/speech-language pathologists (SLT/Ps) report lacking confidence in identifying the most pertinent interventions options relevant to their clients living with PPA during their illness trajectory.

MATERIALS AND METHODS

The aim of this study was to establish a consensus amongst 15 clinical-academic SLT/Ps on best practice in selection and delivery of speech and language therapy interventions for people with PPA. An online nominal group technique (NGT) and consequent focus group session were held. NGT rankings were aggregated and focus groups video recorded, transcribed, and reflexive thematic analysis undertaken.

RESULTS

The results of the NGT identified 17 items. Two main themes and seven further subthemes were identified in the focus groups. The main themes comprised (1) philosophy of person-centredness and (2) complexity. The seven subthemes were knowing people deeply, preventing disasters, practical issues, professional development, connectedness, barriers and limitations, and peer support and mentoring towards a shared understanding.

CONCLUSIONS

This study describes the philosophy of expert practice and outlines a set of best practice principles when working with people with PPA.Implications for rehabilitationPrimary progressive aphasia (PPA) describes a group of language led dementias which deteriorate inexorably over time.Providing speech and language therapy for people with PPA is complex and must be person centred and bespoke.This study describes the philosophy of expert practice and outlines a set of best practice principles for speech and language therapists/pathologists working with people with people with PPA.

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.

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.

Comorbid Neurodegeneration in Primary Progressive Aphasia: Clinicopathological Correlations in a Single-Center Study

Introduction. Primary progressive aphasia (PPA) is a clinically variable syndrome manifesting as slow progressive loss of speech and language with multiple underlying neurodegenerative pathologies. Materials and Methods. We included data from nine PPA patients with available autopsies. We then retrospectively reviewed all available medical records, neuropsychology, and MRI results to confirm the corresponding subtypes of PPA and compared them with postmortem neuropathological results. Results. Clinical presentations corresponded to the nonfluent/agrammatic variant in six cases, the semantic variant in one case, the logopenic variant in one case, and the mixed variant (concomitant nonfluent/agrammatic plus semantic variant) in one case. Patients with a broader clinical presentation, i.e., combining manifestations of one PPA subtype and symptoms of another PPA variant, had autopsy comorbidities showing multiple neurodegenerative disorders. Of the nine subjects enrolled in the study, Alzheimer’s disease (AD) was found in eight cases; however, in only one case, AD was detected as an isolated neuropathological substrate of PPA. In eight brain samples, different comorbid neuropathologies were detected: three cases with comorbid AD and dementia with Lewy bodies, two cases with comorbid AD and TDP-43 pathology, one case with comorbid AD and complex tauopathies, and one case with comorbid AD with both tau and TDP-43 deposits. Finally, one case had comorbid tau and TDP-43 pathology but without comorbid AD pathology. Conclusions. Our observation suggests that PPA cases could be more heterogeneous in their etiology than previously thought and underlying neurodegenerative comorbidities should be considered in routine practice, especially if the clinical presentation of PPA is atypical.

miRNA Expression Is Increased in Serum from Patients with Semantic Variant Primary Progressive Aphasia

Primary progressive aphasia (PPA) damages the parts of the brain that control speech and language. There are three clinical PPA variants: nonfluent/agrammatic (nfvPPA), logopenic (lvPPA) and semantic (svPPA). The pathophysiology underlying PPA variants is not fully understood, including the role of micro (mi)RNAs which were previously shown to play a role in several neurodegenerative diseases. Using a two-step analysis (array and validation through real-time PCR), we investigated the miRNA expression pattern in serum from 54 PPA patients and 18 controls. In the svPPA cohort, we observed a generalized upregulation of miRNAs with miR-106b-5p and miR-133a-3p reaching statistical significance (miR-106b-5p: 2.69 ± 0.89 mean ± SD vs. 1.18 ± 0.28, p < 0.0001; miR-133a-3p: 2.09 ± 0.10 vs. 0.74 ± 0.11 mean ± SD, p = 0.0002). Conversely, in lvPPA, the majority of miRNAs were downregulated. GO enrichment and KEGG pathway analyses revealed that target genes of both miRNAs are involved in pathways potentially relevant for the pathogenesis of neurodegenerative diseases. This is the first study that investigates the expression profile of circulating miRNAs in PPA variant patients. We identified a specific miRNA expression profile in svPPA that could differentiate this pathological condition from other PPA variants. Nevertheless, these preliminary results need to be confirmed in a larger independent cohort.

Case Report: Semantic Variant Primary Progressive Aphasia With Impaired Verbal Word Discrimination

Some patients with primary progressive aphasia (PPA) present with various types of hearing deficits. Research on the auditory function and speech sounds in PPA, including temporal, phonemic, and prosodic processing, revealed impairment in some of these auditory processes. Many patients with PPA who present with impaired word recognition subsequently developed non-fluent variant PPA. Herein, we present a patient with semantic variant PPA (svPPA) who demonstrated impaired verbal word discrimination. Audiological examinations revealed normal auditory brainstem responses and slightly impaired pure-tone perception. By contrast, verbal word discrimination and monosyllable identification were impaired, and temporal auditory acuity deteriorated. Analyses of brain magnetic resonance images revealed a significant decrease in the gray matter volume in bilateral superior temporal areas, predominantly on the left, compared with those of patients with typical svPPA, which appeared to be associated with impaired word recognition in our patient.

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.

Language training for oral and written naming impairment in primary progressive aphasia: a review

BACKGROUND

Primary progressive aphasia (PPA) is a neurodegenerative disorder characterized by a gradual, insidious and progressive loss of language abilities, with naming difficulties being an early and persistent impairment common to all three variants. In the absence of effective pharmacological treatments and given the progressive nature of the disorder, in the past few decades, many studies have investigated the effectiveness of language training to minimize the functional impact of word-finding difficulties in daily life.

MAIN BODY

We review language treatments most commonly used in clinical practice among patients with different variants of PPA, with a focus on the enhancement of spoken and written naming abilities. Generalization of gains to the ability to name untrained stimuli or to other language abilities and the maintenance of these results over time are also discussed. Forty-eight studies were included in this literature review, identifying four main types of language treatment: a) lexical retrieval treatment, b) phonological and/or orthographic treatment, c) semantic treatment, and d) a multimodality approach treatment. Overall, language training is able to induce immediate improvements of naming abilities in all variants of PPA. Moreover, despite the large variability among results, generalization and long-term effects can be recorded after the training. The reviewed studies also suggest that one factor that determines the choice of a particular approach is the compromised components of the lexical/semantic processing system.

CONCLUSION

The majority of studies have demonstrated improvements of naming abilities following language treatments. Given the progressive nature of PPA, it is essential to apply language treatment in the early stages of the disease.

Processing of Degraded Speech in Brain Disorders

The speech we hear every day is typically "degraded" by competing sounds and the idiosyncratic vocal characteristics of individual speakers. While the comprehension of "degraded" speech is normally automatic, it depends on dynamic and adaptive processing across distributed neural networks. This presents the brain with an immense computational challenge, making degraded speech processing vulnerable to a range of brain disorders. Therefore, it is likely to be a sensitive marker of neural circuit dysfunction and an index of retained neural plasticity. Considering experimental methods for studying degraded speech and factors that affect its processing in healthy individuals, we review the evidence for altered degraded speech processing in major neurodegenerative diseases, traumatic brain injury and stroke. We develop a predictive coding framework for understanding deficits of degraded speech processing in these disorders, focussing on the "language-led dementias"-the primary progressive aphasias. We conclude by considering prospects for using degraded speech as a probe of language network pathophysiology, a diagnostic tool and a target for therapeutic intervention.