Visuoperception test predicts pathologic diagnosis of Alzheimer disease in corticobasal syndrome

The Graded Incomplete Letters Test (GILT): a rapid test to detect cortical visual loss, with UK Biobank implementation

Impairments of object recognition are core features of neurodegenerative syndromes, in particular posterior cortical atrophy (PCA; the 'visual-variant Alzheimer's disease'). These impairments arise from damage to higher-level cortical visual regions and are often missed or misattributed to common ophthalmological conditions. Consequently, diagnosis can be delayed for years with considerable implications for patients. We report a new test for the rapid measurement of cortical visual loss - the Graded Incomplete Letters Test (GILT). The GILT is an optimised psychophysical variation of a test used to diagnose cortical visual impairment, which measures thresholds for recognising letters under levels of increasing visual degradation (decreasing "completeness") in a similar fashion to ophthalmic tests. The GILT was administered to UK Biobank participants (total n=2,359) and participants with neurodegenerative conditions characterised by initial cortical visual (PCA, n=18) or memory loss (typical Alzheimer's disease, n=9). UK Biobank participants, including both typical adults and those with ophthalmological conditions, were able to recognise letters under low levels of completeness. In contrast, participants with PCA consistently made errors with only modest decreases in completeness. GILT sensitivity to PCA was 83.3% for participants reaching the 80% accuracy cut-off, increasing to 88.9% using alternative cut-offs (60% or 100% accuracy). Specificity values were consistently over 94% when compared to UK Biobank participants without or with documented visual conditions, regardless of accuracy cut-off. These first-release UK Biobank and clinical verification data suggest the GILT has utility in both rapidly detecting visual perceptual losses following posterior cortical damage and differentiating perceptual losses from common eye-related conditions.

Relationships between PET and blood plasma biomarkers in corticobasal syndrome

INTRODUCTION

Corticobasal syndrome (CBS) can result from underlying Alzheimer's disease (AD) pathologies. Little is known about the utility of blood plasma metrics to predict positron emission tomography (PET) biomarker-confirmed AD in CBS.

METHODS

A cohort of eighteen CBS patients (8 amyloid beta [Aβ]+; 10 Aβ-) and 8 cognitively unimpaired (CU) individuals underwent PET imaging and plasma analysis. Plasma concentrations were compared using a Kruskal-Wallis test. Spearman correlations assessed relationships between plasma concentrations and PET uptake.

RESULTS

CBS Aβ+ group showed a reduced Aβ42/40 ratio, with elevated phosphorylated tau (p-tau)181, glial fibrillary acidic protein (GFAP), and neurofilament light (NfL) concentrations, while CBS Aβ- group only showed elevated NfL concentration compared to CU. Both p-tau181 and GFAP were able to differentiate CBS Aβ- from CBS Aβ+ and showed positive associations with Aβ and tau PET uptake.

DISCUSSION

This study supports use of plasma p-tau181 and GFAP to detect AD in CBS. NfL shows potential as a non-specific disease biomarker of CBS regardless of underlying pathology.

HIGHLIGHTS

Plasma phosphorylated tau (p-tau)181 and glial fibrillary acidic protein (GFAP) concentrations differentiate corticobasal syndrome (CBS) amyloid beta (Aβ)- from CBS Aβ+. Plasma neurofilament light concentrations are elevated in CBS Aβ- and Aβ+ compared to controls. Plasma p-tau181 and GFAP concentrations were associated with Aβ and tau positron emission tomography (PET) uptake. Aβ42/40 ratio showed a negative correlation with Aβ PET uptake.

Visuospatial cognition in acute unilateral peripheral vestibulopathy

Background

This study aims to investigate the presence of spatial cognitive impairments in patients with acute unilateral peripheral vestibulopathy (vestibular neuritis, AUPV) during both the acute phase and the recovery phase.

Methods

A total of 72 AUPV patients (37 with right-sided AUPV and 35 with left-sided AUPV; aged 34-80 years, median 60.5; 39 males, 54.2%) and 35 healthy controls (HCs; aged 43-75 years, median 59; 20 males, 57.1%) participated in the study. Patients underwent comprehensive neurotological assessments, including video-oculography, video head impulse and caloric tests, ocular and cervical vestibular-evoked myogenic potentials, and pure-tone audiometry. Additionally, the Visual Object and Space Perception (VOSP) battery was used to evaluate visuospatial perception, while the Block design test and Corsi block-tapping test assessed visuospatial memory within the first 2 days (acute phase) and 4 weeks after symptom onset (recovery phase).

Results

Although AUPV patients were able to successfully perform visuospatial perception tasks within normal parameters, they demonstrated statistically worse performance on the visuospatial memory tests compared to HCs during the acute phase. When comparing right versus left AUPV groups, significant decreased scores in visuospatial perception and memory were observed in the right AUPV group relative to the left AUPV group. In the recovery phase, patients showed substantial improvements even in these previously diminished visuospatial cognitive performances.

Conclusion

AUPV patients showed different spatial cognition responses, like spatial memory, depending on the affected ear, improving with vestibular compensation over time. We advocate both objective and subjective visuospatial assessments and the development of tests to detect potential cognitive deficits after unilateral vestibular impairments.

Neuropsychological Assessment in the Distinction Between Biomarker Defined Frontal-Variant of Alzheimer's Disease and Behavioral-Variant of Frontotemporal Dementia

BACKGROUND

Frontal-variant of Alzheimer's disease (fvAD) was purposed for patients with AD pathology that, despite the typical amnestic presentation, show early and progressive deterioration of behavior and executive functions, closely resembling the behavioral-variant of frontotemporal dementia (bvFTD). This leads to a challenging differential diagnosis where neuropsychological evaluation and in vivo pathological evidence are essential.

OBJECTIVE

To evaluate the contribution of a comprehensive neuropsychological assessment (NP) battery in distinguishing between fvAD-dementia and bvFTD supported by cerebrospinal fluid (CSF) biomarkers.

METHODS

We included 40 patients with a baseline NP profile with prominent early executive and/or behavioral dysfunction, who meet both diagnosis of bvFTD and fvAD-dementia, according to international criteria. All patients underwent comprehensive NP assessment and CSF-AD biomarker evaluation. Neuropsychological domains as well as clinical and sociodemographic features, and APOE genotype were compared between groups.

RESULTS

21 patients (52.5%) met the biological criteria for AD (decreased Aβ42 together with increased T-tau or P-tau in CSF) and were therefore classified as fvAD (mean age was 64.57, with 47.6% female). There were no differences between groups regarding age/age-at-onset, gender, or educational level. Regarding neuropsychological profile, performances in language and memory functions were equivalent in both groups. Significant differences were found in visuo-constructional abilities (p = 0.004), Trail Making Test A (p < 0.001), and Raven's Colored Progressive Matrices (p = 0.019), with fvAD patients showing worst performances.

CONCLUSION

In patients with an early prominent frontal profile, a higher impairment in attention and visuo-spatial functions, signaling additional right hemisphere fronto-parietal dysfunction, point towards a diagnosis of fvAD-dementia and may be useful in clinical practice.

Clinical Spectrum of Tauopathies

Tauopathies are both clinical and pathological heterogeneous disorders characterized by neuronal and/or glial accumulation of misfolded tau protein. It is now well understood that every pathologic tauopathy may present with various clinical phenotypes based on the primary site of involvement and the spread and distribution of the pathology in the nervous system making clinicopathological correlation more and more challenging. The clinical spectrum of tauopathies includes syndromes with a strong association with an underlying primary tauopathy, including Richardson syndrome (RS), corticobasal syndrome (CBS), non-fluent agrammatic primary progressive aphasia (nfaPPA)/apraxia of speech, pure akinesia with gait freezing (PAGF), and behavioral variant frontotemporal dementia (bvFTD), or weak association with an underlying primary tauopathy, including Parkinsonian syndrome, late-onset cerebellar ataxia, primary lateral sclerosis, semantic variant PPA (svPPA), and amnestic syndrome. Here, we discuss clinical syndromes associated with various primary tauopathies and their distinguishing clinical features and new biomarkers becoming available to improve in vivo diagnosis. Although the typical phenotypic clinical presentations lead us to suspect specific underlying pathologies, it is still challenging to differentiate pathology accurately based on clinical findings due to large phenotypic overlaps. Larger pathology-confirmed studies to validate the use of different biomarkers and prospective longitudinal cohorts evaluating detailed clinical, biofluid, and imaging protocols in subjects presenting with heterogenous phenotypes reflecting a variety of suspected underlying pathologies are fundamental for a better understanding of the clinicopathological correlations.

Neuropsychological deficits in Posterior Cortical Atrophy and typical Alzheimer's disease: A meta-analytic review

AIMS

To identify cognitive tests that best differentiate between Posterior Cortical Atrophy (PCA) and typical Alzheimer's Disease (tAD), as well as PCA and healthy control (HC) participants.

METHOD

Medline, PsycInfo and Web of Science were systematically searched using terms related to PCA, tAD, and cognitive testing. Seventeen studies were identified, including 441 PCA, 391 tAD, and 284 HC participants. Standardised effect sizes of mean scores were calculated to measure performance differences on cognitive tests for PCA versus tAD and PCA versus HC groups. Meta-analyses used a random effects model.

RESULTS

The most discriminating cognitive tests for PCA and tAD presentations were measures of visuospatial function and verbal memory. Large, significant effect sizes were produced for all measures of visuospatial function, most notably for Rey-Osterrieth Copy (Hedges' g = -2.79), VOSP Fragmented letters (Hedges' g = -1.73), VOSP Dot Counting (Hedges' g = -1.74), and VOSP Cube Analysis (Hedges' g = -1.98). For measures of verbal memory, the RAVLT delay and Digit Span Backwards produced significant medium effects (Hedges' g = .62 and -.56, respectively).

CONCLUSION

Establishing a common framework for testing individuals with PCA has important implications for diagnosis and treatment, and forms a practical objective for future research. Findings from this meta-analysis suggest that measures of visuospatial function and verbal memory would form an important part of this framework.

Visuospatial dysfunction is associated with posterior distribution of white matter damage in non-demented cerebral amyloid angiopathy

BACKGROUND AND PURPOSE

Cerebral amyloid angiopathy (CAA) is a well-recognized contributor to cognitive decline in the elderly. The posterior cortical predilection of CAA pathology would cause visuospatial dysfunction, which is still underexplored. We aimed to investigate whether the visuospatial dysfunction in CAA is associated with the posterior distribution of small vessel disease (SVD) imaging markers.

METHODS

We recruited 60 non-demented CAA cases from a Chinese prospective cohort and 30 cases with non-CAA SVD as controls. We used the Visual Object and Space Perception (VOSP) battery to evaluate visuospatial abilities, and multivariable regression models to assess their associations with SVD imaging markers.

RESULTS

There was visuospatial dysfunction, especially visual object perception impairment, in CAA compared to controls (Z-score of VOSP: -0.11 ± 0.66 vs. 0.22 ± 0.54, p = 0.023). The VOSP score in CAA was independently related to the fronto-occipital gradient of white matter hyperintensity volumes (coefficient = 0.03, 95% confidence interval [CI] = 0.003-0.05, p = 0.030) and mean fractional anisotropy values on diffusion tensor imaging (coefficient = 4.72, 95% CI = 0.97-8.48, p = 0.015), but not the severity of global SVD imaging markers or the gradient of lobar cerebral microbleeds with adjustments for age and global cognition score.

CONCLUSIONS

This finding suggests that the damage of posterior white matter rather than global disease severity may be a major contributor to visuospatial dysfunction in CAA.

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

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

FDG-PET Patterns Predict Amyloid Deposition and Clinical Profile in Corticobasal Syndrome

BACKGROUND

Corticobasal syndrome (CBS) is an atypical parkinsonian syndrome related to multiple underlying pathologies.

OBJECTIVE

To investigate if individual brain [¹⁸ F]fluorodeoxyglucose-positron emission tomography (FDG-PET) patterns could distinguish CBS due to Alzheimer's disease (AD) from other pathologies based on [¹¹ C]Pittsburgh Compound-B (PIB)-PET.

METHODS

Forty-five patients with probable CBS were prospectively evaluated regarding cognitive and movement disorders profile. They underwent FDG-PET and were distributed into groups: likely related to AD (CBS FDG-AD) or likely non-AD (CBS FDG-nonAD) pathology. Thirty patients underwent PIB-PET on a hybrid PET-magnetic resonance imaging equipment to assess their amyloid status. FDG and PIB-PET images were classified individually based on visual and semi-quantitative analysis, blinded to each other. Quantitative group analyses were also performed.

RESULTS

CBS FDG-AD group demonstrated worse cognitive performances, mostly concerning attention, memory, visuospatial domains, and displayed more myoclonus and hallucinations. The non-AD metabolic group presented more often limb dystonia, ocular motor dysfunction, motor perseveration, and dysarthria. All patients classified as CBS FDG-AD tested positive at PIB-PET compared to 3 of 20 in the non-AD group. The individual FDG-PET classification demonstrated 76.92% of sensitivity, 100% of specificity and positive predictive value and 88.5% of balanced accuracy to detect positive PIB-PET scans. Individuals with positive and negative PIB-PET showed hypometabolism in posterior temporoparietal areas and in thalamus and brainstem, respectively, mainly contralateral to most affected side, disclosing possible metabolic signatures of CBS variants.

CONCLUSION

FDG-PET was useful to predict AD and non-AD CBS variants depicting their specific degeneration patterns, different clinical features, and brain amyloid deposition. © 2020 International Parkinson and Movement Disorder Society.

Reliability and Feasibility of the Memory Associative Test TMA-93

BACKGROUND

Memory tests focused on binding may be more sensitive to diagnose Alzheimer's disease (AD) at an early phase. TMA-93 examines relational binding by images.

OBJECTIVE

Evaluate the reliability (internal consistency and inter-rater and test-retest reliability) and feasibility of the TMA-93 in a clinic setting with low-educated individuals and limited face-to-face time per patient.

METHODS

The study was undertaken in a neurology outpatient clinic of a hospital in Southern Spain. The internal consistency of the TMA-93 was estimated in 35 patients with amnestic mild cognitive impairment (aMCI) and 40 healthy controls (HCs). The inter-rater reliability (by two raters) and feasibility (by recording the percentage of participants who completed the test, and by timing the administration time) were evaluated in HCs (n = 16), aMCI patients (n = 18), and mild dementia patients (n = 15). The test-retest reliability for the TMA-93 total score was studied in 51 HCs tested by the same examiner 2-4 months apart. The internal consistency was estimated by Cronbach's alpha. The inter-rater and test-retest reliability was quantified by the intraclass correlation coefficient (ICC). The administration time was compared by diagnosis.

RESULTS

The internal consistency was "optimal" (Cronbach's alpha = 0.936). The test-retest reliability was "good" [ICC = 0.802 (CI 95%  = 0.653-0.887)]. The inter-rater reliability was "optimal" [ICC = 0.999, (CI 95%  = 0.999-1)]. All participants completed the test. The administration time ranged from less than 3 min in HCs to 6 min in aMCI patients, and 7 min in mild dementia patients.

CONCLUSION

Good feasibility and reliability support using the TMA-93 for examining visual relational binding, particularly in the context of low-educational attainment and limited time per patient.

Latent atrophy factors related to phenotypical variants of posterior cortical atrophy

OBJECTIVE

To determine whether atrophy relates to phenotypical variants of posterior cortical atrophy (PCA) recently proposed in clinical criteria (i.e., dorsal, ventral, dominant-parietal, and caudal) we assessed associations between latent atrophy factors and cognition.

METHODS

We employed a data-driven Bayesian modeling framework based on latent Dirichlet allocation to identify latent atrophy factors in a multicenter cohort of 119 individuals with PCA (age 64 ± 7 years, 38% male, Mini-Mental State Examination 21 ± 5, 71% β-amyloid positive, 29% β-amyloid status unknown). The model uses standardized gray matter density images as input (adjusted for age, sex, intracranial volume, MRI scanner field strength, and whole-brain gray matter volume) and provides voxelwise probabilistic maps for a predetermined number of atrophy factors, allowing every individual to express each factor to a degree without a priori classification. Individual factor expressions were correlated to 4 PCA-specific cognitive domains (object perception, space perception, nonvisual/parietal functions, and primary visual processing) using general linear models.

RESULTS

The model revealed 4 distinct yet partially overlapping atrophy factors: right-dorsal, right-ventral, left-ventral, and limbic. We found that object perception and primary visual processing were associated with atrophy that predominantly reflects the right-ventral factor. Furthermore, space perception was associated with atrophy that predominantly represents the right-dorsal and right-ventral factors. However, individual participant profiles revealed that the large majority expressed multiple atrophy factors and had mixed clinical profiles with impairments across multiple domains, rather than displaying a discrete clinical-radiologic phenotype.

CONCLUSION

Our results indicate that specific brain behavior networks are vulnerable in PCA, but most individuals display a constellation of affected brain regions and symptoms, indicating that classification into 4 mutually exclusive variants is unlikely to be clinically useful.

Clinicopathologic subtype of Alzheimer's disease presenting as corticobasal syndrome

INTRODUCTION

The corticobasal syndrome (CBS) is associated with several neuropathologic disorders, including corticobasal degeneration and Alzheimer's disease (AD).

METHOD

In this report, we studied 43 AD patients with CBS (AD-CBS) and compared them with 42 AD patients with typical amnestic syndrome (AD-AS), as well as 15 cases of corticobasal degeneration and CBS pathology.

RESULTS

Unlike AD-AS, AD-CBS had prominent motor problems, including limb apraxia (90%), myoclonus (81%), and gait disorders (70%). Alien limb phenomenon was reported in 26% and cortical sensory loss in 14%. Language problems were also more frequent in AD-CBS, and memory impairment was less frequent. AD-CBS had more tau pathology in perirolandic cortices but less in superior temporal cortex than AD-AS. In addition, AD-CBS had greater neuronal loss in the substantia nigra.

DISCUSSION

AD-CBS is a clinicopathological subtype of AD with an atypical distribution of Alzheimer-type tau pathology. Greater neuronal loss in the substantia nigra may contribute to Parkinsonism which is not a feature of typical AD.

FDG-PET patterns associated with underlying pathology in corticobasal syndrome

OBJECTIVE

To evaluate brain ¹⁸Fluorodeoxyglucose PET (FDG-PET) differences among patients with a clinical diagnosis of corticobasal syndrome (CBS) and distinct underling primary pathologies.

METHODS

We studied 29 patients with a diagnosis of CBS who underwent FDG-PET scan and postmortem neuropathologic examination. Patients were divided into subgroups on the basis of primary pathologic diagnosis: CBS-corticobasal degeneration (CBS-CBD) (14 patients), CBS-Alzheimer disease (CBS-AD) (10 patients), and CBS-progressive supranuclear palsy (CBS-PSP) (5 patients). Thirteen age-matched healthy patients who underwent FDG-PET were the control group (HC). FDG-PET scans were compared between the subgroups and the HC using SPM-12, with a threshold of p _FWE < 0.05.

RESULTS

There were no differences in Mattis Dementia Rating Scale or finger tapping scores between CBS groups. Compared to HC, the patients with CBS presented significant hypometabolism in frontoparietal regions, including the perirolandic area, basal ganglia, and thalamus of the clinically more affected hemisphere. Patients with CBS-CBD showed a similar pattern with a more marked, bilateral involvement of the basal ganglia. Patients with CBS-AD presented with posterior, asymmetric hypometabolism, including the lateral parietal and temporal lobes and the posterior cingulate. Finally, patients with CBS-PSP disclosed a more anterior hypometabolic pattern, including the medial frontal regions and the anterior cingulate. A conjunction analysis revealed that the primary motor cortex was the only common area of hypometabolism in all groups, irrespective of pathologic diagnosis.

DISCUSSION AND CONCLUSIONS

In patients with CBS, different underling pathologies are associated with different patterns of hypometabolism. Our data suggest that FDG-PET scans could help in the etiologic diagnosis of CBS.

Consensus classification of posterior cortical atrophy

INTRODUCTION

A classification framework for posterior cortical atrophy (PCA) is proposed to improve the uniformity of definition of the syndrome in a variety of research settings.

METHODS

Consensus statements about PCA were developed through a detailed literature review, the formation of an international multidisciplinary working party which convened on four occasions, and a Web-based quantitative survey regarding symptom frequency and the conceptualization of PCA.

RESULTS

A three-level classification framework for PCA is described comprising both syndrome- and disease-level descriptions. Classification level 1 (PCA) defines the core clinical, cognitive, and neuroimaging features and exclusion criteria of the clinico-radiological syndrome. Classification level 2 (PCA-pure, PCA-plus) establishes whether, in addition to the core PCA syndrome, the core features of any other neurodegenerative syndromes are present. Classification level 3 (PCA attributable to AD [PCA-AD], Lewy body disease [PCA-LBD], corticobasal degeneration [PCA-CBD], prion disease [PCA-prion]) provides a more formal determination of the underlying cause of the PCA syndrome, based on available pathophysiological biomarker evidence. The issue of additional syndrome-level descriptors is discussed in relation to the challenges of defining stages of syndrome severity and characterizing phenotypic heterogeneity within the PCA spectrum.

DISCUSSION

There was strong agreement regarding the definition of the core clinico-radiological syndrome, meaning that the current consensus statement should be regarded as a refinement, development, and extension of previous single-center PCA criteria rather than any wholesale alteration or redescription of the syndrome. The framework and terminology may facilitate the interpretation of research data across studies, be applicable across a broad range of research scenarios (e.g., behavioral interventions, pharmacological trials), and provide a foundation for future collaborative work.

Neuropsychological assessment and differential diagnosis in young-onset dementias

Although Alzheimer's disease is the most common cause of dementia in the elderly, there are several conditions (ie, frontotemporal dementia or Huntington's disease) associated with a relatively earlier onset. This article provides arguments in favor of a comprehensive neuropsychological assessment in the differential diagnosis of young-onset dementia, as episodic memory impairment is not observed early in the course of most types of young-onset dementia that predominantly affect the domains of behavior, executive, language, and/or motor function.