Non-Verbal Episodic Memory Deficits in Primary Progressive Aphasias are Highly Predictive of Underlying Amyloid Pathology

Everyday Memory Disturbance in Primary Progressive Aphasia

INTRODUCTION

Mounting evidence indicates distinct memory profiles among the primary progressive aphasia (PPA) variants. Neuropsychological tests reveal disproportionate memory impairments in the logopenic variant PPA (lv-PPA) relative to the non-fluent variant PPA (nfv-PPA) and semantic variant PPA (sv-PPA). The real-world experience of day-to-day memory disturbances in PPA, however, remains poorly understood.

METHODS

Everyday expressions of memory in 26 lv-PPA, 24 nfv-PPA, and 40 sv-PPA patients, and 70 healthy controls were examined using the Cambridge Behavioural Inventory-Revised (CBI-R) carer questionnaire. Kruskal-Wallis tests compared CBI-R Memory items (1-8) across groups. Receiver operating characteristic curves evaluated the most discriminative items to distinguish lv-PPA from nfv-PPA.

RESULTS

Compared to controls, lv-PPA and sv-PPA patients were reported to experience more day-to-day memory issues (item 1), increased repetition of questions (2), forgetting the names of familiar people and objects (4, 5), and poor concentration (6). lv-PPA patients were also reported to exhibit more occurrences of losing or misplacing items (3) and forgetting the day (7). All PPA groups experienced more confusion in unfamiliar environments (8) than controls. Direct comparisons among PPA groups revealed distinct profiles, with lv-PPA and sv-PPA patients exhibiting more frequent forgetting of names and objects (3, 4) than nfv-PPA, and sv-PPA demonstrating greater day-to-day memory impairment (1), repeated questions (2), and poor concentration (6) compared to nfv-PPA. Forgetting the names of familiar objects (5) was the most sensitive and specific item to distinguish lv-PPA from nfv-PPA.

CONCLUSIONS

Our findings demonstrate distinct day-to-day memory profiles in PPA. Future research should explore the influence of language impairments on these profiles.

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.

The neural substrates of transdiagnostic cognitive-linguistic heterogeneity in primary progressive aphasia

BACKGROUND

Clinical variants of primary progressive aphasia (PPA) are diagnosed based on characteristic patterns of language deficits, supported by corresponding neural changes on brain imaging. However, there is (i) considerable phenotypic variability within and between each diagnostic category with partially overlapping profiles of language performance between variants and (ii) accompanying non-linguistic cognitive impairments that may be independent of aphasia magnitude and disease severity. The neurobiological basis of this cognitive-linguistic heterogeneity remains unclear. Understanding the relationship between these variables would improve PPA clinical/research characterisation and strengthen clinical trial and symptomatic treatment design. We address these knowledge gaps using a data-driven transdiagnostic approach to chart cognitive-linguistic differences and their associations with grey/white matter degeneration across multiple PPA variants.

METHODS

Forty-seven patients (13 semantic, 15 non-fluent, and 19 logopenic variant PPA) underwent assessment of general cognition, errors on language performance, and structural and diffusion magnetic resonance imaging to index whole-brain grey and white matter changes. Behavioural data were entered into varimax-rotated principal component analyses to derive orthogonal dimensions explaining the majority of cognitive variance. To uncover neural correlates of cognitive heterogeneity, derived components were used as covariates in neuroimaging analyses of grey matter (voxel-based morphometry) and white matter (network-based statistics of structural connectomes).

RESULTS

Four behavioural components emerged: general cognition, semantic memory, working memory, and motor speech/phonology. Performance patterns on the latter three principal components were in keeping with each variant's characteristic profile, but with a spectrum rather than categorical distribution across the cohort. General cognitive changes were most marked in logopenic variant PPA. Regardless of clinical diagnosis, general cognitive impairment was associated with inferior/posterior parietal grey/white matter involvement, semantic memory deficits with bilateral anterior temporal grey/white matter changes, working memory impairment with temporoparietal and frontostriatal grey/white matter involvement, and motor speech/phonology deficits with inferior/middle frontal grey matter alterations.

CONCLUSIONS

Cognitive-linguistic heterogeneity in PPA closely relates to individual-level variations on multiple behavioural dimensions and grey/white matter degeneration of regions within and beyond the language network. We further show that employment of transdiagnostic approaches may help to understand clinical symptom boundaries and reveal clinical and neural profiles that are shared across categorically defined variants of PPA.

A cognitive marker for Alzheimer disease pathology in primary progressive aphasia? A validation study in the clinical setting

We validated in the clinical setting a putative clinical marker for a biological diagnosis of primary progressive aphasia (PPA) due to amyloid previously identified in an autopsy cohort and including impaired (score ≤4) digit span (DS) as index of phonological loop dysfunction and broadened criteria for logopenic PPA. In 29 PPA patients with an amyloid-positive (A+) biomarker and 28 PPA patients with an amyloid-negative (A-) biomarker, Receiver Operating Characteristics (ROC) curve analysis showed moderate specificity (71%) but insufficient sensitivity (41%) for the proposed marker. Specificity was particularly poor (58%) for the discrimination between A+ PPA and the A- subgroup with nonfluent PPA. DS may be compromised in both logopenic and nonfluent PPA, whose loci of neurodegeneration lie at the 2 ends of the left fronto-parieto-temporal system that underpins phonology. An Statistical Parametric Mapping (SPM) correlation analysis between DS score and metabolism on brain 18-fluoro-deoxy-glucose positron emission tomography also showed a major contribution of the left frontal cortex to impaired span.

Utility of a Spanish version of Three Words-Three Shapes Test to detect memory impairment in primary progressive aphasia

INTRODUCTION

Three Words-Three Shapes (3W3S) is a bedside test that assesses verbal and non-verbal memory and has proven useful in staging memory decline in amnestic disorders and primary progressive aphasia. Given its simple structure, the 3W3S can be easily adapted to other languages maintaining the original shapes and only modifying the words. We aim to validate a Spanish version of the 3W3S test and establish whether memory loss patterns present in amnesic disorders associated with Alzheimer's etiology and PPA were correctly characterized.

METHOD

The translation and adaptation of the 3W3S were performed according to standardized guidelines and applied to a cohort of patients with Dementia of Alzheimer's type (DAT = 20), mild cognitive impairment (aMCI= 20), primary progressive aphasia (PPA = 20), and healthy controls (HC = 20).

RESULTS

In verbal memory performance, PPA patients' score was lower than that of MCI and HC and similar to DAT's in the effortless encoding (p < 0.001), delayed recall (p < 0.001), and recognition (p < 0.012). For non-verbal performance, PPA patients performed better than DAT and similar to HC and MCI subjects (p < 0.001).

CONCLUSIONS

Results show good applicability of 3W3S to determine memory function in PPA patients, independently from language ability. Visual and verbal components of memory are dissociated in PPA.

Longitudinal changes in behaviour, mood and functional capacity in the primary progressive aphasia variants

Primary progressive aphasia (PPA) is a neurodegenerative clinical syndrome characterised by a progressive decline in speech and language functions. Deficits in behaviour, mood and functional capacity are reported in PPA but are less well understood. This study examined the PPA variants' profiles on these domains at initial presentation and over time and evaluated their relations to overall cognitive ability. Behaviour, mood and functional capacity were measured annually (over ~6 years) in 145 individuals diagnosed with PPA (41 logopenic [lv-PPA], 44 non-fluent [nfv-PPA] and 60 semantic variants [sv-PPA]) using the Cambridge Behavioural Inventory-Revised (CBI-R) carer questionnaire. Overall cognition was assessed annually with the Addenbrooke's Cognitive Examination-III. Distinct profiles were observed across PPA syndromes. Notably, sv-PPA carers reported greater behavioural, eating and motivational disturbances than the other PPA variants throughout the disease course. Reported memory problems were also greater in sv-PPA and lv-PPA than in nfv-PPA across all time points. These disturbances occurred in the context of the sv-PPA group demonstrating a slower rate of cognitive decline than the lv-PPA group and a parallel rate to that found in the nfv-PPA group. Associations between overall cognition and the CBI-R domains were trivial at baseline assessment; however, distinct profiles emerged when mapping each syndrome's overall cognitive decline with their behavioural, mood and functional trajectories. Our findings demonstrate that the evolving behaviour, mood and functional capacity profiles of the PPA variants are distinct and extend beyond the primary disorder of language. These findings have important implications for clinical management and caregiver education in PPA.

The Hong Kong Grocery Shopping Dialog Task (HK-GSDT): A Quick Screening Test for Neurocognitive Disorders

The Hong Kong Grocery Shopping Dialog Task (HK-GSDT) is a short and easy-to-administer cognitive test developed for quickly screening neurocognitive disorders (NCDs). In the test, participants are instructed to do a hypothetical instrumental activity of daily living task of purchasing ingredients for a dish from a grocery store and verbally describe the specific shopping procedures. The current study aimed to validate the test with a sample of 545 Hong Kong older adults (58.8% female; aged 73.4 ± 8.37 years), including 464 adults with normal cognitive function, 39 with mild NCD, and 42 with major NCD. Demographic characteristics (i.e., sex, age, education) and clinical diagnosis of cognitive states (i.e., major NCD, mild NCD, and normal aging) were collected. Cognitive functioning was measured using the HK-GSDT and several standardized NCD-screening tests. The results showed good reliability (i.e., internal consistency) and structural validity in the HK-GSDT. It discriminated among different cognitive conditions, particularly between major NCDs and the other conditions, as effectively as did the existing standardized neurocognitive tests (e.g., Montreal Cognitive Assessment, Hong Kong List Learning Test). Moreover, the HK-GSDT explained additional variance of cognitive condition on top of those standardized neurocognitive tests. These results indicate that the HK-GSDT can be used alone, or in combination with other tests, to screen for NCDs.

Temporal Cortical Thickness and Cognitive Associations among Typical and Atypical Phenotypes of Alzheimer's Disease

Background

The hippocampus and temporal lobe are atrophic in typical amnestic Alzheimer's disease (tAD) and are used as imaging biomarkers in treatment trials. However, a better understanding of how temporal structures differ across atypical AD phenotypes and relate to cognition is needed.

Objective

Our goal was to compare temporal lobe regions between tAD and two atypical AD phenotypes (logopenic progressive aphasia (LPA) and posterior cortical atrophy (PCA)), and assess cognitive associations.

Methods

We age and gender-matched 77 tAD participants to 50 LPA and 27 PCA participants, all of which were amyloid-positive. We used linear mixed-effects models to compare FreeSurfer-derived hippocampal volumes and cortical thickness of entorhinal, inferior and middle temporal, and fusiform gyri, and to assess relationships between imaging and memory, naming, and visuospatial function across and within AD phenotype.

Results

Hippocampal volume and entorhinal thickness were smaller bilaterally in tAD than LPA and PCA. PCA showed greater right inferior temporal and bilateral fusiform thinning and LPA showed greater left middle and inferior temporal and left fusiform thinning. Atypical AD phenotypes differed with greater right hemisphere thinning in PCA and greater left hemisphere thinning in LPA. Verbal and visual memory related most strongly to hippocampal volume; naming related to left temporal thickness; and visuospatial related to bilateral fusiform thickness. Fewer associations remained when examined within AD group.

Conclusion

Atypical AD phenotypes are associated with greater thinning of lateral temporal structures, with relative sparing of medial temporal lobe, compared to tAD. These findings may have implications for future clinical trials in AD.

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.

Utility of the Addenbrooke’s Cognitive Examination III online calculator to differentiate the primary progressive aphasia variants

The Addenbrooke’s Cognitive Examination III is a brief cognitive screening tool that is widely used for the detection and monitoring of dementia. Recent findings suggest that the three variants of primary progressive aphasia can be distinguished based on their distinct profiles on the five subdomain scores of this test. Here, we investigated the utility of the Addenbrooke’s Cognitive Examination III to differentiate the primary progressive aphasia variants based on their item-by-item performance profiles on this test. From these results, we created an interactive primary progressive aphasia Addenbrooke’s Cognitive Examination III calculator which predicts the variant based on a patient’s unique item-by-item profile. Twenty-eight logopenic variant, 25 non-fluent variant and 37 semantic variant primary progressive aphasia patients and 104 healthy controls completed the Addenbrooke’s Cognitive Examination III at first clinical presentation. Multinomial regression analyses were conducted to establish performance profiles among groups, and R Shiny from RStudio was used to create the interactive Addenbrooke’s Cognitive Examination III diagnostic calculator. To verify its accuracy, probability values of the regression model were derived based on a 5-fold cross-validation of cases. The calculator’s accuracy was then verified in an independent sample of 17 logopenic, 19 non-fluent and 13 semantic variant primary progressive aphasia patients and 68 Alzheimer’s disease patients who had completed the Addenbrooke’s Cognitive Examination III (or an older version of this test: Revised) and had in vivo amyloid-PET imaging and/or brain autopsy pathological confirmation. Cross-validation of cases in the calculator model revealed different rates of sensitivity in classifying variants: semantic = 100%, non-fluent = 80.6% and logopenic = 79.9%; healthy controls were distinguished from primary progressive aphasia patients with 100% sensitivity. Verification of in vivo amyloid and/or autopsy-confirmed patients showed that the calculator correctly classified 10/13 (77%) semantic variant, 3/19 (16%) non-fluent variant and 4/17 (24%) logopenic variant patients. Importantly, for patients who were not classified, diagnostic probability values mostly pointed toward the correct clinical diagnosis. Furthermore, misclassified diagnoses of the primary progressive aphasia cohort were rare (1/49; 2%). Although 22 of the 68 Alzheimer’s disease patients (32%) were misclassified with primary progressive aphasia, 19/22 were misclassified with the logopenic variant (i.e. falling within the same neuropathological entity). The Addenbrooke’s Cognitive Examination III primary progressive aphasia diagnostic calculator demonstrates sound accuracy in differentiating the variants based on an item-by-item Addenbrooke’s Cognitive Examination III profile. This calculator represents a new frontier in using data-driven approaches to differentiate the primary progressive aphasia variants.

Verbal Encoding Deficits Impact Recognition Memory in Atypical “Non-Amnestic” Alzheimer’s Disease

Memory encoding and retrieval deficits have been identified in atypical Alzheimer’s disease (AD), including posterior cortical atrophy (PCA) and logopenic variant primary progressive aphasia (lvPPA), despite these groups being referred to as “non-amnestic”. There is a critical need to better understand recognition memory in atypical AD. We investigated performance on the California Verbal Learning Test (CVLT-II-SF) in 23 amyloid-positive, tau-positive, and neurodegeneration-positive participants with atypical “non-amnestic” variants of AD (14 PCA, 9 lvPPA) and 14 amnestic AD participants. Recognition memory performance was poor across AD subgroups but trended toward worse in the amnestic group. Encoding was related to recognition memory in non-amnestic but not in amnestic AD. We also observed cortical atrophy in dissociable subregions of the distributed memory network related to encoding (left middle temporal and angular gyri, posterior cingulate and precuneus) compared to recognition memory (anterior medial temporal cortex). We conclude that recognition memory is not spared in all patients with atypical variants of AD traditionally thought to be “non-amnestic”. The non-amnestic AD patients with poor recognition memory were those who struggled to encode the material during the learning trials. In contrast, the amnestic AD group had poor recognition memory regardless of encoding ability.

Neuroanatomical correlations of visuospatial processing in primary progressive aphasia

Clinical phenotyping of primary progressive aphasia has largely focused on speech and language presentations, leaving other cognitive domains under-examined. This study investigated the diagnostic utility of visuospatial profiles and examined their neural basis among the three main primary progressive aphasia variants. We studied the neuropsychological performances of 118 primary progressive aphasia participants and 30 cognitively normal controls, across 11 measures of visuospatial cognition, and investigated their neural correlates via voxel-based morphometry analysis using visuospatial composite scores derived from principal component analysis. The principal component analysis identified three main factors: visuospatial-executive, visuospatial-memory and visuomotor components. Logopenic variant primary progressive aphasia performed significantly worst across all components; nonfluent/agrammatic variant primary progressive aphasia showed deficits in the visuospatial-executive and visuomotor components compared with controls; and the semantic variant primary progressive aphasia scored significantly lower than nonfluent/agrammatic variant primary progressive aphasia and control in the visuospatial-memory component. Grey matter volumes over the right parieto-occipital cortices correlated with visuospatial-executive performance; volumetric changes in the right anterior parahippocampal gyrus and amygdala were associated with visuospatial-memory function, and visuomotor composite scores correlated significantly with the grey matter volume at the right precentral gyrus. Discriminant function analysis identified three visuospatial measures: Visual Object and Space Perception and Benson figure copy and recall test, which classified 79.7% (94/118) of primary progressive aphasia into their specific variant. This study shows that each primary progressive aphasia variant also carries a distinctive visuospatial cognitive profile that corresponds with grey matter volumetric changes and in turn can be largely represented by their performance on the visuomotor, visuospatial-memory and executive functions.

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.

The Box Task: A novel tool to differentiate the primary progressive aphasias

OBJECTIVE

Differentiating the primary progressive aphasia (PPA) variants in clinical settings remains complex and challenging, especially for the logopenic (lv-PPA) and non-fluent variants (nfv-PPA). Recent studies suggest that visuospatial memory is more compromised in lv-PPA than in nfv-PPA and is relatively spared in the semantic variant (sv-PPA). Accordingly, assessment of visuospatial memory performance may assist in the differential diagnosis of PPA variants. Here, we investigated the utility of a novel computerised visuospatial working memory test-the Box Task-to differentiate the three PPA variants and typical Alzheimer's disease (AD).

METHODS

Eighteen lv-PPA, 14 nfv-PPA, 23 sv-PPA, 33 AD patients, and 32 healthy controls matched for age and education were recruited. All participants completed the computerised Box Task and WMS-III Spatial Span as measures of visuospatial working memory.

RESULTS

The lv-PPA group made significantly more Box Task between-search errors than nfv-PPA, sv-PPA and control groups. The AD group, however, displayed the greatest impairments on this measure relative to the PPA variants. Logistic regression analyses in lv-PPA and nfv-PPA demonstrated that the combination of Box Task between-search error variables (i.e., 4- and 6-box levels) could correctly classify 72% of lv-PPA patients and nearly 79% of nfv-PPA patients. Area under the receiver operator characteristics curve (AUC) analyses revealed the Box Task was more sensitive than Spatial Span at differentiating lv-PPA from nfv-PPA.

CONCLUSIONS

Our findings suggest that a simple, computerised measure of visuospatial working memory-the Box Task-shows potential diagnostic utility in differentiating lv-PPA from the other PPA variants.

Longitudinal cognitive and functional changes in primary progressive aphasia

OBJECTIVE

The variants of primary progressive aphasia (PPA) are predominantly diagnosed on the basis of specific profiles of language impairments. Deficits in other cognitive domains and their evolution over time are less well documented. This study examined the cognitive profiles of the PPA variants over time and determined the contribution of cognition on functional capacity.

METHODS

Longitudinal performance on the Addenbrooke's Cognitive Examination-III (ACE-III) total and cognitive subdomains were investigated in 147 PPA individuals (41 logopenic [lv-PPA], 44 non-fluent [nfv-PPA], and 62 semantic variants [sv-PPA]). The relative contribution of ACE-III subdomain scores to overall functional capacity over time was identified using mixed and hierarchical regression modelling.

RESULTS

The annual rate of global ACE-III decline was twice that in lv-PPA than in nfv-PPA and sv-PPA, despite lv-PPA performing intermediate to the other variants at baseline assessment. Notably, attention and visuospatial subdomains declined faster in lv-PPA than in nfv-PPA and sv-PPA; and memory impairment was more severe in lv-PPA than in nfv-PPA at all time points. Functional decline was comparable across PPA variants; however, the contribution of cognition on functional capacity varied across variants and over time.

CONCLUSION

The cognitive profiles of the PPA variants are distinct at baseline and over time. Crucially, cognitive decline in lv-PPA was more widespread and pervasive than in nfv-PPA and sv-PPA. Our findings also demonstrate the complex interplay between cognition and functional capacity. This study underscores the importance of routinely assessing cognition and functional capacity in PPA to improve diagnostic accuracy and provide targeted support services.

Examining prefrontal contributions to past- and future-oriented memory disturbances in daily life in dementia

Deficits in episodic memory are commonplace in dementia, yet mounting evidence indicates pervasive impairments in future-oriented thinking in these syndromes. How such impairments manifest in the daily lives of people with dementia remain unclear, as do their neural bases. This study aimed to determine the neurocognitive mechanisms of past- and future-oriented memory performance across a large sample of dementia syndromes, each of which is characterised by distinct clinical and cognitive profiles. Carer-rated memory changes in everyday life in Alzheimer's disease, behavioural-variant frontotemporal dementia, semantic dementia, progressive non-fluent aphasia, and logopenic progressive aphasia were assessed using the Prospective and Retrospective Memory Questionnaire (PRM-Q). Participants underwent neuropsychological testing and whole-brain structural MRI. Relative to Controls, past- and future-oriented memory were compromised exclusively in AD and bvFTD, with no impairments reported for the other groups. For AD, atrophy in a distributed network of prefrontal, lateral and medial temporal regions including the hippocampus, correlated with past- and future-oriented memory impairments. In contrast, lateral and medial prefrontal regions correlated with past- and future-oriented memory difficulties in bvFTD. Notably, the orbitofrontal cortex emerged as a common neural substrate implicated in memory disturbances across the AD and bvFTD groups. This study confirms the presence of episodic amnesia in bvFTD across a host of everyday activities, mirroring the profile typically observed in AD. Of note, the orbitofrontal cortex emerged as a common region implicated in past- and future-oriented memory deficits in both patient groups, underscoring a critical role for prefrontal regions in supporting complex aspects of memory function in everyday life.

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.

Visuospatial short-term and working memory disturbance in the primary progressive aphasias: Neuroanatomical and clinical implications

INTRODUCTION

Primary progressive aphasia (PPA) comprises three main variants: logopenic (lv-PPA), non-fluent (nfv-PPA) and semantic variant (sv-PPA). Differentiating the language profiles of the PPA variants remains challenging, especially for lv-PPA and nfv-PPA. As such, diagnostic tools that do not rely on speech and language may offer some utility. Here, we investigated the short-term and working memory profiles of the PPA variants and typical Alzheimer's disease (AD), with a particular interest in the visuospatial system. We hypothesised visuospatial short-term and working memory would be more compromised in lv-PPA and AD than in the other PPA variants, and that this would relate to degeneration of posterior temporoparietal brain regions.

METHOD

Thirty-three lv-PPA, 26 nfv-PPA, 31 sv-PPA and 58 AD patients, and 45 matched healthy controls were recruited. All participants completed the WMS-III Spatial and Digit Span tasks and underwent a structural brain MRI for voxel-based morphometry analyses.

RESULTS

Relative to Controls, Spatial Span Forward (SSF) performance was impaired in lv-PPA and AD but not in nfv-PPA or sv-PPA. In contrast, Digit Span Forward (DSF) performance was impaired in lv-PPA and nfv-PPA (to a similar level), and AD, but was relatively intact in sv-PPA. As expected, most backward span scores across both modalities were lower than forward span scores. Neuroimaging analyses revealed that SSF and SSB performance in all patients combined correlated with grey matter intensity decrease in several clusters located in temporo-parieto-occipital brain regions. Post-hoc group comparisons of these regions showed that grey matter loss was more extensive in the lv-PPA and AD groups than in the nfv-PPA and sv-PPA groups.

CONCLUSIONS

The findings suggest that the visuospatial short-term and working memory profiles of the PPA variants are separable and likely reflect their distinct patterns of temporo-parieto-occipital brain atrophy.

Neuropsychological Similarities and Differences Between Amnestic Alzheimer's Disease and its Non-Amnestic Variants

BACKGROUND

The neuropsychological recognition of early-onset Alzheimer's disease (AD) can be difficult because of non-amnestic variants such as logopenic variant primary progressive aphasia (lvPPA) and posterior cortical atrophy (PCA).

OBJECTIVE

This study evaluated the similarities and differences between typical amnestic AD (tAD) and lvPPA and PCA on a screening neuropsychological battery.

METHODS

We enrolled 51 patients meeting NIA-AA criteria for biomarker-supported AD (amnestic or non-amnestic) and having an age of onset of <65 years of age. Based on additional recommended clinical criteria for lvPPA and PCA, the early-onset AD patients were divided into three groups (28 tAD, 9 lvPPA, 14 PCA) of comparable age and dementia severity. We then analyzed their profiles on a focused, screening neuropsychological battery for early-onset AD.

RESULTS

In addition to greater variance on the Mini-Mental State Examination, the lvPPA and PCA variants had episodic memory impairment that did not significantly differ from the memory impairment in the tAD patients. Despite differences on language and visuospatial tasks, they did not significantly distinguish the lvPPA and PCA from tAD. The lvPPA group, however, was distinguishable by worse performance on measures reflecting working memory (digit span forward, memory registration).

CONCLUSIONS

On neuropsychological screening, all clinical early-onset AD subtypes may have memory impairments. Screening batteries for early-onset AD should also include measures of working memory, which is disproportionately decreased in lvPPA.

Does amnesia specifically predict Alzheimer's pathology? A neuropathological study

Amnesia is a key component of Alzheimer's disease (AD) and the most important feature of its clinical diagnosis but its specificity has recently been challenged. This study investigated the ability of amnesia to predict AD in a clinicopathological dementia series. Ninety-one patients to which free and cued verbal memory assessment was administered during early cognitive decline, were followed until autopsy. Patients' histological diagnoses were classified as pure AD, mixed AD, and non-AD pathologies. Data-driven automated classification procedures explored the correspondence between memory performance and pathological diagnoses. Classifications revealed 3 clusters of performance reflecting different levels of amnesia. Little correspondence between these clusters and the presence of AD pathology was retrieved. A third of patients with pure/mixed AD pathology were non-amnesic at presentation and ≈45% of patients without AD pathology were amnesic. Data-driven prediction of AD pathology based on memory also had a poor accuracy. Free and cued memory assessments are fair tools to diagnose an amnesic syndrome but lack accuracy to predict AD pathology.

A Meta-Analysis of Neuropsychological Functioning in the Logopenic Variant of Primary Progressive Aphasia: Comparison with the Semantic and Non-Fluent Variants

OBJECTIVES

The logopenic variant of primary progressive aphasia (lvPPA) has disparate pathological and anatomical features when compared to the semantic (svPPA) and non-fluent (nfvPPA) variants of PPA. As such, there is increasing need for measures that improve diagnostic accuracy particularly when etiology-specific treatments become available. In the current study, we used meta-analytic methods to establish the neuropsychological profile of lvPPA and compare it to recent findings in svPPA and nfvPPA.

METHODS

We extracted neuropsychological data from 51 publications representing 663 lvPPA patients and 1379 controls. We calculated Hedges' g effect sizes for nine domains of neuropsychological functioning in lvPPA and assessed the influence of demographic, disease, and task characteristics on effect size magnitude. Results obtained in lvPPA were compared to findings in svPPA and nfvPPA.

RESULTS

In lvPPA, the magnitude of deficits in attention, math, visuospatial memory, and executive functioning were as prominent as language deficits. Within the language domain, lvPPA patients demonstrated greater naming than repetition deficits. Compared to svPPA and nfvPPA, lvPPA patients demonstrated greater neuropsychological deficits overall and greater impairment on attention, math, and visual set-shifting tests.

CONCLUSIONS

Tests of attention, delayed visuospatial memory, visual set-shifting, and math distinguish lvPPA from svPPA and nfvPPA likely reflecting the posterior temporoparietal atrophy observed early in the course of lvPPA. These findings support the inclusion of these measures in the clinical neuropsychological assessment of lvPPA and underscore the need for additional clinicopathological and longitudinal studies of arithmetic and visuospatial memory across the PPA variants.

A meta-analysis of neuropsychological, social cognitive, and olfactory functioning in the behavioral and language variants of frontotemporal dementia

BACKGROUND

Though meta-analyses of neuropsychological and social cognitive deficits in behavioral variant frontotemporal dementia (bvFTD) have been conducted, no study has comprehensively characterized and compared the neuropsychological, social cognitive, and olfactory profiles in the behavioral and language variants of FTD.

METHODS

Our search yielded 470 publications meeting inclusion criteria representing 11 782 FTD patients and 19 451 controls. For each domain, we calculated Hedges' g effect sizes, which represent the mean difference between the patient and control group divided by the pooled standard deviation. The heterogeneity of these effects was assessed with Cochran's Q-statistic using a random-effects model. Meta-regressions were employed to analyze the influence of demographic and disease characteristics.

RESULTS

Though semantic variant primary progressive aphasia patients showed the greatest impairment across all task types, the three groups showed similar cognitive effect sizes once contributions from the language subdomain were excluded from analysis. Contrary to expectation, the magnitude of deficits in executive functioning, social cognition and olfaction were comparable between the three subgroups. Among indices, a metric of executive errors distinguished the behavioral variant of FTD from the language phenotypes.

CONCLUSIONS

These data indicate that social cognitive and traditional executive functioning measures may not capture differences between FTD syndromes. These results have important implications for the interpretation of neuropsychological assessments, particularly when applied to the differential diagnosis of FTD. It is hoped that these findings will guide clinical and research assessments and spur new studies focused on improving the measurement of FTD syndromes.

Practical algorithms for amyloid β probability in subjective or mild cognitive impairment

INTRODUCTION

Practical algorithms predicting the probability of amyloid pathology among patients with subjective cognitive decline or mild cognitive impairment may help clinical decisions regarding confirmatory biomarker testing for Alzheimer's disease.

METHODS

Algorithm feature selection was conducted with Alzheimer's Disease Neuroimaging Initiative and Australian Imaging, Biomarkers and Lifestyle Flagship Study of Ageing data. Probability algorithms were developed in Alzheimer's Disease Neuroimaging Initiative using nested cross-validation accompanied by stratified subsampling to obtain 1000 internally validated decision trees. Semi-independent validation was conducted using Australian Imaging, Biomarkers and Lifestyle Flagship Study of Ageing. Independent external validation was conducted in the population-based Mayo Clinic Study of Aging.

RESULTS

Two algorithms were developed using age and normalized immediate recall z-scores, with or without apolipoprotein E ε4 carrier status. Both algorithms had robust performance across data sets and when substituting different recall memory tests.

DISCUSSION

The statistical framework resulted in robust probability estimation. Application of these algorithms may assist in clinical decision-making for further testing to diagnose amyloid pathology.

Fronto-parietal contributions to episodic retrieval-evidence from neurodegenerative disorders

Converging evidence suggests a critical role for the parietal cortices in episodic memory retrieval. Here, we examined episodic memory performance in Corticobasal Syndrome (CBS), a rare neurodegenerative disorder presenting with early parietal atrophy in the context of variable medial temporal lobe damage. Forty-four CBS patients were contrasted with 29 typical Alzheimer's disease (AD), 29 healthy Controls, and 20 progressive supranuclear palsy patients presenting with brainstem atrophy as a disease control group. Participants completed standardized assessments of verbal episodic memory (learning, delayed recall, and recognition), and underwent structural and diffusion-weighted MRI. Selective delayed recall deficits were evident in the CBS group relative to Controls, at an intermediate level to the stark amnesia displayed by AD, and Control-level performance noted in progressive supranuclear palsy. Considerable variability within the CBS group on delayed recall performance led to the identification of memory-spared (N = 19) and memory-impaired (N = 25) subgroups. Whereas CBS-Spared showed no significant memory deficits, the CBS-Impaired subgroup were indistinguishable from typical AD across all episodic memory measures. Whole-brain voxel-based morphometry analyses implicated fronto-parietal and medial temporal regions in delayed recall performance in both the CBS-Impaired and AD groups. Furthermore, diffusion tensor imaging analyses revealed correlations between delayed recall performance and altered structural connectivity between fronto-parietal and frontotemporal regions in the CBS-Impaired group. Our findings underscore the importance of a distributed brain network including frontal, medial temporal, and parietal brain regions in supporting the capacity for successful episodic memory retrieval.

Atypical clinical features associated with mixed pathology in a case of non-fluent variant primary progressive aphasia

A 66-year-old woman presented with agrammatism and apraxia of speech, meeting criteria for non-fluent/agrammatic variant primary progressive aphasia (nfvPPA). However, three years later, she developed frontal/executive, short-term phonological memory, visuospatial, and visual memory deficits suggesting involvement of multiple brain networks. Multimodal neuroimaging showed damage of both fronto-striatal and posterior brain regions. She was found to have multiple pathological processes: corticobasal degeneration (CBD), Alzheimer's disease (AD), and TAR DNA-binding protein (TDP)-43 type A. We hypothesize that cognitive and neuroimaging findings consistent with damage to multiple brain networks, each associated with vulnerability to certain molecular disease subtypes, could indicate mixed pathology.

Episodic memory in mild cognitive impairment inversely correlates with the global modularity of the cerebral blood flow network

Cerebral blood flow (CBF) SPECT is an interesting methodology to study brain connectivity in mild cognitive impairment (MCI) since it is accessible worldwide and can be used as a biomarker of neuronal injury in MCI. In CBF SPECT, connectivity is grounded in group-based correlation networks. Therefore, topological metrics derived from the CBF correlation network cannot be used to support diagnosis and prognosis individually. However, methods to extract the individual patient contribution to topological metrics of group-based correlation networks were developed although not yet applied to MCI patients. Here, we investigate whether the episodic memory of 24 amnestic MCI patients correlates with individual patient contributions to topological metrics of the CBF correlation network. We first compared topological metrics of the MCI group network with the network corresponding to 26 controls. Metrics that showed significant differences were then used for the individual patient contribution analysis. We found that the global network modularity was increased while global efficiency decreased in the MCI network compared to the control. Most importantly, we found that episodic memory inversely correlates with the patient contribution to the global network modularity, which highlights the potential of this approach to develop a CBF connectivity-based biomarker at the individual level.

Amyloid beta-positive subjects exhibit longitudinal network-specific reductions in spontaneous brain activity

Amyloid beta (Aβ) deposition and cognitive decline are key features of Alzheimer's disease. The relationship between Aβ status and changes in neuronal function over time, however, remains unclear. We evaluated the effect of baseline Aβ status on reference region spontaneous brain activity (SBA-rr) using resting-state functional magnetic resonance imaging and fluorodeoxyglucose positron emission tomography in patients with mild cognitive impairment. Patients (N = 62, [43 Aβ-positive]) from the Alzheimer's Disease Neuroimaging Initiative were divided into Aβ-positive and Aβ-negative groups via prespecified cerebrospinal fluid Aβ42 or 18F-florbetapir positron emission tomography standardized uptake value ratio cutoffs measured at baseline. We analyzed interaction of biomarker-confirmed Aβ status with SBA-rr change over a 2-year period using mixed-effects modeling. SBA-rr differences between Aβ-positive and Aβ-negative subjects increased significantly over time within subsystems of the default and visual networks. Changes exhibit an interaction with memory performance over time but were independent of glucose metabolism. Results reinforce the value of resting-state functional magnetic resonance imaging in evaluating Alzheimer''s disease progression and suggest spontaneous neuronal activity changes are concomitant with cognitive decline.

Visuospatial Functioning in the Primary Progressive Aphasias

OBJECTIVES

The aim of this study was to identify whether the three main primary progressive aphasia (PPA) variants would show differential profiles on measures of visuospatial cognition. We hypothesized that the logopenic variant would have the most difficulty across tasks requiring visuospatial and visual memory abilities.

METHODS

PPA patients (n=156), diagnosed using current criteria, and controls were tested on a battery of tests tapping different aspects of visuospatial cognition. We compared the groups on an overall visuospatial factor; construction, immediate recall, delayed recall, and executive functioning composites; and on individual tests. Cross-sectional and longitudinal comparisons were made, adjusted for disease severity, age, and education.

RESULTS

The logopenic variant had significantly lower scores on the visuospatial factor and the most impaired scores on all composites. The nonfluent variant had significant difficulty on all visuospatial composites except the delayed recall, which differentiated them from the logopenic variant. In contrast, the semantic variants performed poorly only on delayed recall of visual information. The logopenic and nonfluent variants showed decline in figure copying performance over time, whereas in the semantic variant, this skill was remarkably preserved.

CONCLUSIONS

This extensive examination of performance on visuospatial tasks in the PPA variants solidifies some previous findings, for example, delayed recall of visual stimuli adds value in differential diagnosis between logopenic variant PPA and nonfluent variant PPA variants, and illuminates the possibility of common mechanisms that underlie both linguistic and non-linguistic deficits in the variants. Furthermore, this is the first study that has investigated visuospatial functioning over time in the PPA variants. (JINS, 2018, 24, 259-268).

Neural Correlates of Verbal Episodic Memory and Lexical Retrieval in Logopenic Variant Primary Progressive Aphasia

Objective: Logopenic variant primary progressive aphasia (lvPPA) is commonly associated with Alzheimer's disease (AD) pathology. But lvPPA patients display different cognitive and anatomical profile from the common clinical AD patients, whose verbal episodic memory is primarily affected. Reports of verbal episodic memory difficulty in lvPPA are inconsistent, and we hypothesized that their lexical retrieval impairment contributes to verbal episodic memory performance and is associated with left middle temporal gyrus atrophy.

Methods: We evaluated patients with lvPPA (n = 12) displaying prominent word-finding and repetition difficulties, and a demographically-matched cohort of clinical Alzheimer's disease (AD, n = 26), and healthy seniors (n = 16). We assessed lexical retrieval with confrontation naming and verbal episodic memory with delayed free recall. Whole-brain regressions related naming and delayed free recall to gray matter atrophy. Medial temporal lobe (MTL) subfields were examined using high in-plane resolution imaging.

Results: lvPPA patients had naming and delayed free recall impairments, but intact recognition memory. In lvPPA, delayed free recall was related to naming; both were associated with left middle temporal gyrus atrophy but not MTL atrophy. Despite cerebrospinal fluid evidence consistent with AD pathology, examination of MTL subfields revealed no atrophy in lvPPA. While AD patients displayed impaired delayed free recall, this deficit did not correlate with naming. Regression analyses related delayed free recall deficits in clinical AD patients to MTL subfield atrophy, and naming to left middle temporal gyrus atrophy.

Conclusion: Unlike amnestic AD patients, MTL subfields were not affected in lvPPA patients. Verbal episodic memory deficit observed in lvPPA was unlikely to be due to a hippocampal-mediated mechanism but appeared to be due to poor lexical retrieval. Relative sparing of MTL volume and intact recognition memory are consistent with previous reports of hippocampal-sparing variant cases of AD pathology, where neurofibrillary tangles are disproportionately distributed in cortical areas with relative sparing of the hippocampus. This suggests that AD neuropathology in lvPPA may originate in neuronal networks outside of the MTL, which deviates from the typical Braak staging pattern of spreading pathology in clinical AD.