Progression of Microstructural Degeneration in Progressive Supranuclear Palsy and Corticobasal Syndrome: A Longitudinal Diffusion Tensor Imaging Study

Abnormal structural‒functional coupling patterning in progressive supranuclear palsy is associated with diverse gradients and histological features

The anatomy of the brain supports inherent processes, fostering mental abilities and eventually facilitating adaptive behavior. Recent studies have shown that progressive supranuclear palsy (PSP) is accompanied by alterations in functional and structural networks. However, how the structure and function of PSP coordinates change is not clear, and the relationships between structural‒functional coupling (SFC) and the gradient of hierarchical structure and cellular histology remain largely unknown. Here, we use neuroimaging data from two independent cohorts and a public histological dataset to investigate the relationships among the cellular histology, hierarchical structure, and SFC of PSP patients. We find that the SFC of the entire cortex in PSP is severely disrupted, with higher coupling in the visual network (VN). Moreover, coupling differences in PSP follow a macroscopic organizational principle from unimodal to transmodal gradients. Finally, we elucidate greater laminar differentiation in VN regions sensitive to SFC changes in PSP, which is related mainly to the higher cellular density and smaller size of the internal-granular layer. In conclusion, our findings provide an interpretable framework for understanding SFC changes in PSP and provide new insights into the consistency of structural and functional changes in PSP regarding hierarchical structure and cellular histology.

Transcriptional expression patterns of the cortical morphometric similarity network in progressive supranuclear palsy

BACKGROUND

It has been demonstrated that progressive supranuclear palsy (PSP) correlates with structural abnormalities in several distinct regions of the brain. However, whether there are changes in the morphological similarity network (MSN) and the relationship between changes in brain structure and gene expression remain largely unknown.

METHODS

We used two independent cohorts (discovery dataset: PSP: 51, healthy controls (HC): 82; replication dataset: PSP: 53, HC: 55) for MSN analysis and comparing the longitudinal changes in the MSN of PSP. Then, we applied partial least squares regression to determine the relationships between changes in MSN and spatial transcriptional features and identified specific genes associated with MSN differences in PSP. We further investigated the biological processes enriched in PSP-associated genes and the cellular characteristics of these genes, and finally, we performed an exploratory analysis of the relationship between MSN changes and neurotransmitter receptors.

RESULTS

We found that the MSN in PSP patients was mainly decreased in the frontal and temporal cortex but increased in the occipital cortical region. This difference is replicable. In longitudinal studies, MSN differences are mainly manifested in the frontal and parietal regions. Furthermore, the expression pattern associated with MSN changes in PSP involves genes implicated in astrocytes and excitatory and inhibitory neurons and is functionally enriched in neuron-specific biological processes related to synaptic signaling. Finally, we found that the changes in MSN were mainly negatively correlated with the levels of serotonin, norepinephrine, and opioid receptors.

CONCLUSIONS

These results have enhanced our understanding of the microscale genetic and cellular mechanisms responsible for large-scale morphological abnormalities in PSP patients, suggesting potential targets for future therapeutic trials.

Distinct spatiotemporal atrophy patterns in corticobasal syndrome are associated with different underlying pathologies

Objective

To identify imaging subtypes of the cortico-basal syndrome (CBS) based solely on a data-driven assessment of MRI atrophy patterns, and investigate whether these subtypes provide information on the underlying pathology.

Methods

We applied Subtype and Stage Inference (SuStaIn), a machine learning algorithm that identifies groups of individuals with distinct biomarker progression patterns, to a large cohort of 135 CBS cases (52 had a pathological or biomarker defined diagnosis) and 252 controls. The model was fit using volumetric features extracted from baseline T1-weighted MRI scans and validated using follow-up MRI. We compared the clinical phenotypes of each subtype and investigated whether there were differences in associated pathology between the subtypes.

Results

SuStaIn identified two subtypes with distinct sequences of atrophy progression; four-repeat-tauopathy confirmed cases were most commonly assigned to the Subcortical subtype (83% of CBS-PSP and 75% of CBS-CBD), while CBS-AD was most commonly assigned to the Fronto-parieto-occipital subtype (81% of CBS-AD). Subtype assignment was stable at follow-up (98% of cases), and individuals consistently progressed to higher stages (100% stayed at the same stage or progressed), supporting the model's ability to stage progression.

Interpretation

By jointly modelling disease stage and subtype, we provide data-driven evidence for at least two distinct and longitudinally stable spatiotemporal subtypes of atrophy in CBS that are associated with different underlying pathologies. In the absence of sensitive and specific biomarkers, accurately subtyping and staging individuals with CBS at baseline has important implications for screening on entry into clinical trials, as well as for tracking disease progression.

Magnetic Resonance Imaging and Nuclear Imaging of Parkinsonian Disorders: Where do we go from here?

Parkinsonian disorders are a heterogeneous group of incurable neurodegenerative diseases that significantly reduce quality of life and constitute a substantial economic burden. Nuclear imaging (NI) and magnetic resonance imaging (MRI) have played and continue to play a key role in research aimed at understanding and monitoring these disorders. MRI is cheaper, more accessible, nonirradiating, and better at measuring biological structures and hemodynamics than NI. NI, on the other hand, can track molecular processes, which may be crucial for the development of efficient diseasemodifying therapies. Given the strengths and weaknesses of NI and MRI, how can they best be applied to Parkinsonism research going forward? This review aims to examine the effectiveness of NI and MRI in three areas of Parkinsonism research (differential diagnosis, prodromal disease identification, and disease monitoring) to highlight where they can be most impactful. Based on the available literature, MRI can assist with differential diagnosis, prodromal disease identification, and disease monitoring as well as NI. However, more work is needed, to confirm the value of MRI for monitoring prodromal disease and predicting phenoconversion. Although NI can complement or be a substitute for MRI in all the areas covered in this review, we believe that its most meaningful impact will emerge once reliable Parkinsonian proteinopathy tracers become available. Future work in tracer development and high-field imaging will continue to influence the landscape for NI and MRI.

Fiber-specific micro- and macroscopic white matter alterations in progressive supranuclear palsy and corticobasal syndrome

Progressive supranuclear palsy (PSP) and corticobasal syndrome (CBS) are characterized by progressive white matter (WM) alterations associated with the prion-like spreading of four-repeat tau, which has been pathologically confirmed. It has been challenging to monitor the WM degeneration patterns underlying the clinical deficits in vivo. Here, a fiber-specific fiber density and fiber cross-section, and their combined measure estimated using fixel-based analysis (FBA), were cross-sectionally and longitudinally assessed in PSP (n = 20), CBS (n = 17), and healthy controls (n = 20). FBA indicated disease-specific progression patterns of fiber density loss and subsequent bundle atrophy consistent with the tau propagation patterns previously suggested in a histopathological study. This consistency suggests the new insight that FBA can monitor the progressive tau-related WM changes in vivo. Furthermore, fixel-wise metrics indicated strong correlations with motor and cognitive dysfunction and the classifiability of highly overlapping diseases. Our findings might also provide a tool to monitor clinical decline and classify both diseases.

Uncovering spatiotemporal patterns of atrophy in progressive supranuclear palsy using unsupervised machine learning

To better understand the pathological and phenotypic heterogeneity of progressive supranuclear palsy and the links between the two, we applied a novel unsupervised machine learning algorithm (Subtype and Stage Inference) to the largest MRI data set to date of people with clinically diagnosed progressive supranuclear palsy (including progressive supranuclear palsy-Richardson and variant progressive supranuclear palsy syndromes). Our cohort is comprised of 426 progressive supranuclear palsy cases, of which 367 had at least one follow-up scan, and 290 controls. Of the progressive supranuclear palsy cases, 357 were clinically diagnosed with progressive supranuclear palsy-Richardson, 52 with a progressive supranuclear palsy-cortical variant (progressive supranuclear palsy-frontal, progressive supranuclear palsy-speech/language, or progressive supranuclear palsy-corticobasal), and 17 with a progressive supranuclear palsy-subcortical variant (progressive supranuclear palsy-parkinsonism or progressive supranuclear palsy-progressive gait freezing). Subtype and Stage Inference was applied to volumetric MRI features extracted from baseline structural (T1-weighted) MRI scans and then used to subtype and stage follow-up scans. The subtypes and stages at follow-up were used to validate the longitudinal consistency of subtype and stage assignments. We further compared the clinical phenotypes of each subtype to gain insight into the relationship between progressive supranuclear palsy pathology, atrophy patterns, and clinical presentation. The data supported two subtypes, each with a distinct progression of atrophy: a 'subcortical' subtype, in which early atrophy was most prominent in the brainstem, ventral diencephalon, superior cerebellar peduncles, and the dentate nucleus, and a 'cortical' subtype, in which there was early atrophy in the frontal lobes and the insula alongside brainstem atrophy. There was a strong association between clinical diagnosis and the Subtype and Stage Inference subtype with 82% of progressive supranuclear palsy-subcortical cases and 81% of progressive supranuclear palsy-Richardson cases assigned to the subcortical subtype and 82% of progressive supranuclear palsy-cortical cases assigned to the cortical subtype. The increasing stage was associated with worsening clinical scores, whilst the 'subcortical' subtype was associated with worse clinical severity scores compared to the 'cortical subtype' (progressive supranuclear palsy rating scale and Unified Parkinson's Disease Rating Scale). Validation experiments showed that subtype assignment was longitudinally stable (95% of scans were assigned to the same subtype at follow-up) and individual staging was longitudinally consistent with 90% remaining at the same stage or progressing to a later stage at follow-up. In summary, we applied Subtype and Stage Inference to structural MRI data and empirically identified two distinct subtypes of spatiotemporal atrophy in progressive supranuclear palsy. These image-based subtypes were differentially enriched for progressive supranuclear palsy clinical syndromes and showed different clinical characteristics. Being able to accurately subtype and stage progressive supranuclear palsy patients at baseline has important implications for screening patients on entry to clinical trials, as well as tracking disease progression.

Neuroimaging in Dementia

OBJECTIVE

Neurodegenerative diseases are significant health concerns with regard to morbidity and social and economic hardship around the world. This review describes the state of the field of neuroimaging measures as biomarkers for detection and diagnosis of both slowly progressing and rapidly progressing neurodegenerative diseases, specifically Alzheimer disease, vascular cognitive impairment, dementia with Lewy bodies or Parkinson disease dementia, frontotemporal lobar degeneration spectrum disorders, and prion-related diseases. It briefly discusses findings in these diseases in studies using MRI and metabolic and molecular-based imaging (eg, positron emission tomography [PET] and single-photon emission computerized tomography [SPECT]).

LATEST DEVELOPMENTS

Neuroimaging studies with MRI and PET have demonstrated differential patterns of brain atrophy and hypometabolism in different neurodegenerative disorders, which can be useful in differential diagnoses. Advanced MRI sequences, such as diffusion-based imaging, and functional MRI (fMRI) provide important information about underlying biological changes in dementia and new directions for development of novel measures for future clinical use. Finally, advancements in molecular imaging allow clinicians and researchers to visualize dementia-related proteinopathies and neurotransmitter levels.

ESSENTIAL POINTS

Diagnosis of neurodegenerative diseases is primarily based on symptomatology, although the development of in vivo neuroimaging and fluid biomarkers is changing the scope of clinical diagnosis, as well as the research into these devastating diseases. This article will help inform the reader about the current state of neuroimaging in neurodegenerative diseases, as well as how these tools might be used for differential diagnoses.

Digital Histological Study of Neocortical Grey and White Matter Tau Burden Across Tauopathies

3R/4R-tau species are found in Alzheimer disease (AD) and ∼50% of Lewy body dementias at autopsy (LBD+tau); 4R-tau accumulations are found in progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD). Digital image analysis techniques can elucidate patterns of tau pathology more precisely than traditional methods but repeatability across centers is unclear. We calculated regional percentage areas occupied by tau pathological inclusions from the middle frontal cortex (MFC), superior temporal cortex (STC), and angular gyrus (ANG) from cases from the University of Pennsylvania and the University of California San Diego with AD, LBD+tau, PSP, or CBD (n = 150) using QuPath. In both cohorts, AD and LBD+tau had the highest grey and white matter tau burden in the STC (p ≤ 0.04). White matter tau burden was relatively higher in 4R-tauopathies than 3R/4R-tauopathies (p < 0.003). Grey and white matter tau were correlated in all diseases (R2=0.43-0.79, p < 0.04) with the greatest increase of white matter per unit grey matter tau observed in PSP (p < 0.02 both cohorts). Grey matter tau negatively correlated with MMSE in AD and LBD+tau (r = -4.4 to -5.4, p ≤ 0.02). These data demonstrate the feasibility of cross-institutional digital histology studies that generate finely grained measurements of pathology which can be used to support biomarker development and models of disease progression.

Diffusion tractography of superior cerebellar peduncle and dentatorubrothalamic tracts in two autopsy confirmed progressive supranuclear palsy variants: Richardson syndrome and the speech-language variant

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Different changes in DTI metrics in SCP and DRTT can be seen across PSP subtypes.

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DRTT tractography reconstructions demonstrated specific changes in PSP-RS.

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DTI and clinical PSP scores are specifically linked across each PSP variant.

Background

Progressive supranuclear palsy (PSP) is a 4-repeat tauopathy with neurodegeneration typically observed in the superior cerebellar peduncle (SCP) and dentatorubrothalamic tracts (DRTT). However, it is unclear how these tracts are differentially affected in different clinical variants of PSP.

Objectives

To determine whether diffusion tractography of the SCP and DRTT can differentiate autopsy-confirmed PSP with Richardson’s syndrome (PSP-RS) and PSP with predominant speech/language disorder (PSP-SL).

Methods

We studied 22 autopsy-confirmed PSP patients that included 12 with PSP-RS and 10 with PSP-SL. We compared these two groups to 11 patients with autopsy-confirmed Alzheimer’s disease with SL problems, i.e., logopenic progressive aphasia (AD-LPA) (disease controls) and 10 healthy controls. Whole brain tractography was performed to identify the SCP and DRTT, as well as the frontal aslant tract and superior longitudinal fasciculus. We assessed fractional anisotropy and mean diffusivity for each tract. Hierarchical linear modeling was used for statistical comparisons, and correlations were assessed with clinical disease severity, ocular motor impairment, and parkinsonism. DRTT connectomics matrix analysis was also performed across groups.

Results

The SCP showed decreased fractional anisotropy for PSP-RS and PSP-SL and increased mean diffusivity in PSP-RS, compared to controls and AD-LPA. Right DRTT fibers showed lower fractional anisotropy in PSP-RS and PSP-SL compared to controls and AD-LPA, with PSP-RS also showing lower values compared to PSP-SL. Reductions in connectivity were observed in infratentorial DRTT regions in PSP-RS vs cortical regions in PSP-SL. PSP-SL showed greater abnormalities in the frontal aslant tract and superior longitudinal fasciculus compared to controls, PSP-RS, and AD-LPA. Significant correlations were observed between ocular motor impairment and SCP in PSP-RS (p = 0.042), and DRTT in PSP-SL (p = 0.022). In PSP-SL, the PSP Rating Scale correlated with the SCP (p = 0.045) and DRTT (p = 0.008), and the Unified Parkinson’s Disease Rating Scale correlated with the DRTT (p = 0.014).

Conclusions

Degeneration of the SCP and DRTT are diagnostic features of both PSP-RS and PSP-SL and associations with clinical metrics validate the role of these tracts in PSP-related clinical features, particularly in PSP-SL.

Advanced diffusion imaging to track progression in Parkinson's disease, multiple system atrophy, and progressive supranuclear palsy

Advanced diffusion imaging which accounts for complex tissue properties, such as crossing fibers and extracellular fluid, may detect longitudinal changes in widespread pathology in atypical Parkinsonian syndromes. We implemented fixel-based analysis, Neurite Orientation and Density Imaging (NODDI), and free-water imaging in Parkinson's disease (PD), multiple system atrophy (MSAp), progressive supranuclear palsy (PSP), and controls longitudinally over one year. Further, we used these three advanced diffusion imaging techniques to investigate longitudinal progression-related effects in key white matter tracts and gray matter regions in PD and two common atypical Parkinsonian disorders. Fixel-based analysis and free-water imaging revealed longitudinal declines in a greater number of descending sensorimotor tracts in MSAp and PSP compared to PD. In contrast, only the primary motor descending sensorimotor tract had progressive decline over one year, measured by fiber density (FD), in PD compared to that in controls. PSP was characterized by longitudinal impairment in multiple transcallosal tracts (primary motor, dorsal and ventral premotor, pre-supplementary motor, and supplementary motor area) as measured by FD, whereas there were no transcallosal tracts with longitudinal FD impairment in MSAp and PD. In addition, free-water (FW) and FW-corrected fractional anisotropy (FAt) in gray matter regions showed longitudinal changes over one year in regions that have previously shown cross-sectional impairment in MSAp (putamen) and PSP (substantia nigra, putamen, subthalamic nucleus, red nucleus, and pedunculopontine nucleus). NODDI did not detect any longitudinal white matter tract progression effects and there were few effects in gray matter regions across Parkinsonian disorders. All three imaging methods were associated with change in clinical disease severity across all three Parkinsonian syndromes. These results identify novel extra-nigral and extra-striatal longitudinal progression effects in atypical Parkinsonian disorders through the application of multiple diffusion methods that are related to clinical disease progression. Moreover, the findings suggest that fixel-based analysis and free-water imaging are both particularly sensitive to these longitudinal changes in atypical Parkinsonian disorders.

A data-driven model of brain volume changes in progressive supranuclear palsy

The most common clinical phenotype of progressive supranuclear palsy is Richardson syndrome, characterized by levodopa unresponsive symmetric parkinsonism, with a vertical supranuclear gaze palsy, early falls and cognitive impairment. There is currently no detailed understanding of the full sequence of disease pathophysiology in progressive supranuclear palsy. Determining the sequence of brain atrophy in progressive supranuclear palsy could provide important insights into the mechanisms of disease progression, as well as guide patient stratification and monitoring for clinical trials. We used a probabilistic event-based model applied to cross-sectional structural MRI scans in a large international cohort, to determine the sequence of brain atrophy in clinically diagnosed progressive supranuclear palsy Richardson syndrome. A total of 341 people with Richardson syndrome (of whom 255 had 12-month follow-up imaging) and 260 controls were included in the study. We used a combination of 12-month follow-up MRI scans, and a validated clinical rating score (progressive supranuclear palsy rating scale) to demonstrate the longitudinal consistency and utility of the event-based model's staging system. The event-based model estimated that the earliest atrophy occurs in the brainstem and subcortical regions followed by progression caudally into the superior cerebellar peduncle and deep cerebellar nuclei, and rostrally to the cortex. The sequence of cortical atrophy progresses in an anterior to posterior direction, beginning in the insula and then the frontal lobe before spreading to the temporal, parietal and finally the occipital lobe. This in vivo ordering accords with the post-mortem neuropathological staging of progressive supranuclear palsy and was robust under cross-validation. Using longitudinal information from 12-month follow-up scans, we demonstrate that subjects consistently move to later stages over this time interval, supporting the validity of the model. In addition, both clinical severity (progressive supranuclear palsy rating scale) and disease duration were significantly correlated with the predicted subject event-based model stage (P < 0.01). Our results provide new insights into the sequence of atrophy progression in progressive supranuclear palsy and offer potential utility to stratify people with this disease on entry into clinical trials based on disease stage, as well as track disease progression.

Temporal Progression Patterns of Brain Atrophy in Corticobasal Syndrome and Progressive Supranuclear Palsy Revealed by Subtype and Stage Inference (SuStaIn)

Differentiating corticobasal degeneration presenting with corticobasal syndrome (CBD-CBS) from progressive supranuclear palsy with Richardson's syndrome (PSP-RS), particularly in early stages, is often challenging because the neurodegenerative conditions closely overlap in terms of clinical presentation and pathology. Although volumetry using brain magnetic resonance imaging (MRI) has been studied in patients with CBS and PSP-RS, studies assessing the progression of brain atrophy are limited. Therefore, we aimed to reveal the difference in the temporal progression patterns of brain atrophy between patients with CBS and those with PSP-RS purely based on cross-sectional data using Subtype and Stage Inference (SuStaIn)—a novel, unsupervised machine learning technique that integrates clustering and disease progression modeling. We applied SuStaIn to the cross-sectional regional brain volumes of 25 patients with CBS, 39 patients with typical PSP-RS, and 50 healthy controls to estimate the two disease subtypes and trajectories of CBS and PSP-RS, which have distinct atrophy patterns. The progression model and classification accuracy of CBS and PSP-RS were compared with those of previous studies to evaluate the performance of SuStaIn. SuStaIn identified distinct temporal progression patterns of brain atrophy for CBS and PSP-RS, which were largely consistent with previous evidence, with high reproducibility (99.7%) under cross-validation. We classified these diseases with high accuracy (0.875) and sensitivity (0.680 and 1.000, respectively) based on cross-sectional structural brain MRI data; the accuracy was higher than that reported in previous studies. Moreover, SuStaIn stage correctly reflected disease severity without the label of disease stage, such as disease duration. Furthermore, SuStaIn also showed the genialized performance of differentiation and reflection for CBS and PSP-RS. Thus, SuStaIn has potential for improving our understanding of disease mechanisms, accurately stratifying patients, and providing prognoses for patients with CBS and PSP-RS.

Evolving concepts in progressive supranuclear palsy and other 4-repeat tauopathies

Tauopathies are classified according to whether tau deposits predominantly contain tau isoforms with three or four repeats of the microtubule-binding domain. Those in which four-repeat (4R) tau predominates are known as 4R-tauopathies, and include progressive supranuclear palsy, corticobasal degeneration, argyrophilic grain disease, globular glial tauopathies and conditions associated with specific MAPT mutations. In these diseases, 4R-tau deposits are found in various cell types and anatomical regions of the brain and the conditions share pathological, pathophysiological and clinical characteristics. Despite being considered 'prototype' tauopathies and, therefore, ideal for studying neuroprotective agents, 4R-tauopathies are still severe and untreatable diseases for which no validated biomarkers exist. However, advances in research have addressed the issues of phenotypic overlap, early clinical diagnosis, pathophysiology and identification of biomarkers, setting a road map towards development of treatments. New clinical criteria have been developed and large cohorts with early disease are being followed up in prospective studies. New clinical trial readouts are emerging and biomarker research is focused on molecular pathways that have been identified. Lessons learned from failed trials of neuroprotective drugs are being used to design new trials. In this Review, we present an overview of the latest research in 4R-tauopathies, with a focus on progressive supranuclear palsy, and discuss how current evidence dictates ongoing and future research goals.

Multiparametric magnetic resonance imaging and positron emission tomography findings in neurodegenerative diseases: Current status and future directions

Neurodegenerative diseases (NDDs) are characterized by progressive neuronal loss, leading to dementia and movement disorders. NDDs broadly include Alzheimer's disease, frontotemporal lobar degeneration, parkinsonian syndromes, and prion diseases. There is an ever-increasing prevalence of mild cognitive impairment and dementia, with an accompanying immense economic impact, prompting efforts aimed at early identification and effective interventions. Neuroimaging is an essential tool for the early diagnosis of NDDs in both clinical and research settings. Structural, functional, and metabolic imaging modalities, including magnetic resonance imaging (MRI) and positron emission tomography (PET), are widely available. They show encouraging results for diagnosis, monitoring, and treatment response evaluation. The current review focuses on the complementary role of various imaging modalities in relation to NDDs, the qualitative and quantitative utility of newer MRI techniques, novel radiopharmaceuticals, and integrated PET/MRI in the setting of NDDs.

Imaging of Substantia Nigra in Parkinson's Disease: A Narrative Review

Parkinson's disease (PD) is a progressive neurodegenerative disorder, characterized by motor and non-motor symptoms due to the degeneration of the pars compacta of the substantia nigra (SNc) with dopaminergic denervation of the striatum. Although the diagnosis of PD is principally based on a clinical assessment, great efforts have been expended over the past two decades to evaluate reliable biomarkers for PD. Among these biomarkers, magnetic resonance imaging (MRI)-based biomarkers may play a key role. Conventional MRI sequences are considered by many in the field to have low sensitivity, while advanced pulse sequences and ultra-high-field MRI techniques have brought many advantages, particularly regarding the study of brainstem and subcortical structures. Nowadays, nigrosome imaging, neuromelanine-sensitive sequences, iron-sensitive sequences, and advanced diffusion weighted imaging techniques afford new insights to the non-invasive study of the SNc. The use of these imaging methods, alone or in combination, may also help to discriminate PD patients from control patients, in addition to discriminating atypical parkinsonian syndromes (PS). A total of 92 articles were identified from an extensive review of the literature on PubMed in order to ascertain the-state-of-the-art of MRI techniques, as applied to the study of SNc in PD patients, as well as their potential future applications as imaging biomarkers of disease. Whilst none of these MRI-imaging biomarkers could be successfully validated for routine clinical practice, in achieving high levels of accuracy and reproducibility in the diagnosis of PD, a multimodal MRI-PD protocol may assist neuroradiologists and clinicians in the early and differential diagnosis of a wide spectrum of neurodegenerative disorders.

Case Report: Barely Able to Speak, Can't Stop Echoing: Echolalic Dynamic Aphasia in Progressive Supranuclear Palsy

The diagnostic criteria for progressive supranuclear palsy (PSP) incorporate two speech-language disturbances (SLDs), non-fluent/agrammatic primary progressive aphasia and progressive apraxia of speech, but overlook the inclusion of other SLDs, including dynamic aphasia (DA). Thus, there is a need to reappraise the broad spectrum of SLDs in PSP to include other presenting phenotypes. Here we report findings from the study of two elderly patients with PSP presenting with DA and irrepressible echolalia. Both patients had markedly impoverished verbal production, but their performance in other tasks (repetition and naming) and auditory comprehension were preserved or only mildly impaired. Experimental tests of DA revealed impaired word and sentence generation in response to verbal and non-verbal stimuli. Additional language and cognitive testing revealed different types of echolalia (mitigated, automatic, and echoing approval) as well as impaired inhibitory control and social cognition (mentalizing). Both patients had negative neuropsychiatric alterations (i.e., apathy, aspontaneity, and indifference/emotional flatness). Brain magnetic resonance imaging in both patients showed atrophy of the midbrain tegmentum and superior medial frontal cortex suggestive of PSP, yet further evaluation of the neural correlates using multimodal neuroimaging and neuropathological data was not performed. However, based on the already known neural basis of DA and echolalia in PSP and stroke, we suggest that, in the present cases, neurodegeneration in the midbrain tegmentum, superior medial frontal lobe, and caudate nucleus was responsible for DA and that decreased activity in these regions may play a permissive role for eliciting verbal echoing via disinhibition of the perisylvian speech-language network.

Cellular Biology of Tau Diversity and Pathogenic Conformers

Tau accumulation is a prominent feature in a variety of neurodegenerative disorders and remarkable effort has been expended working out the biochemistry and cell biology of this cytoplasmic protein. Tau's wayward properties may derive from germline mutations in the case of frontotemporal lobar degeneration (FTLD-MAPT) but may also be prompted by less understood cues—perhaps environmental or from molecular damage as a consequence of chronological aging—in the case of idiopathic tauopathies. Tau properties are undoubtedly affected by its covalent structure and in this respect tau protein is not only subject to changes in length produced by alternative splicing and endoproteolysis, but different types of posttranslational modifications that affect different amino acid residues. Another layer of complexity concerns alternate conformations—“conformers”—of the same covalent structures; in vivo conformers can encompass soluble oligomeric species, ramified fibrillar structures evident by light and electron microscopy and other forms of the protein that have undergone liquid-liquid phase separation to make demixed liquid droplets. Biological concepts based upon conformers have been charted previously for templated replication mechanisms for prion proteins built of the PrP polypeptide; these are now providing useful explanations to feature tau pathobiology, including how this protein accumulates within cells and how it can exhibit predictable patterns of spread across different neuroanatomical regions of an affected brain. In sum, the documented, intrinsic heterogeneity of tau forms and conformers now begins to speak to a fundamental basis for diversity in clinical presentation of tauopathy sub-types. In terms of interventions, emphasis upon subclinical events may be worthwhile, noting that irrevocable cell loss and ramified protein assemblies feature at end-stage tauopathy, whereas earlier events may offer better opportunities for diverting pathogenic processes. Nonetheless, the complexity of tau sub-types, which may be present even within intermediate disease stages, likely mitigates against one-size-fits-all therapeutic strategies and may require a suite of interventions. We consider the extent to which animal models of tauopathy can be reasonably enrolled in the campaign to produce such interventions and to slow the otherwise inexorable march of disease progression.

The physiological roles of tau and Aβ: implications for Alzheimer's disease pathology and therapeutics

Tau and amyloid beta (Aβ) are the prime suspects for driving pathology in Alzheimer's disease (AD) and, as such, have become the focus of therapeutic development. Recent research, however, shows that these proteins have been highly conserved throughout evolution and may have crucial, physiological roles. Such functions may be lost during AD progression or be unintentionally disrupted by tau- or Aβ-targeting therapies. Tau has been revealed to be more than a simple stabiliser of microtubules, reported to play a role in a range of biological processes including myelination, glucose metabolism, axonal transport, microtubule dynamics, iron homeostasis, neurogenesis, motor function, learning and memory, neuronal excitability, and DNA protection. Aβ is similarly multifunctional, and is proposed to regulate learning and memory, angiogenesis, neurogenesis, repair leaks in the blood-brain barrier, promote recovery from injury, and act as an antimicrobial peptide and tumour suppressor. This review will discuss potential physiological roles of tau and Aβ, highlighting how changes to these functions may contribute to pathology, as well as the implications for therapeutic development. We propose that a balanced consideration of both the physiological and pathological roles of tau and Aβ will be essential for the design of safe and effective therapeutics.

Dentatorubrothalamic tract reduction using fixel-based analysis in corticobasal syndrome

PURPOSE

The word "fixel" refers to the specific fiber population within each voxel, and fixel-based analysis (FBA) is a recently developed technique that facilitates fiber tract-specific statistical analysis. The aim of the paper is to apply FBA to detect impaired fibers for corticobasal syndrome (CBS) especially in regions that contain multiple crossed fibers.

METHODS

FBA was performed in cohorts of participants clinically diagnosed with CBS (n = 10) and Parkinson's disease (n = 15) or in healthy controls (n = 9). The parameters of the diffusion weighted image were echo time, 83 ms; time, 8123.6 ms; flip angle, 90°; section thickness, 2 mm; b = 1000 s/mm²; and 32 axes. Diffusion tensor analysis was conducted using tract-based spatial statistics (TBSS), and white matter volume was estimated via voxel-based morphometry.

RESULTS

A comparison of PD or HC to CBS revealed a significant difference in the dentatorubrothalamic tract of the brainstem in FBA in addition to the affected regions in voxel-based morphometry and TBSS (family-wise error-corrected p < 0.05). Reduction of the white matter fibers crossing the brainstem could not be detected via microstructural changes identified using TBSS, but it was detected using FBA.

CONCLUSION

FBA has some advantages in determining the distribution of corticobasal syndrome lesions.

Diffusion Tensor Imaging in Parkinson's Disease and Parkinsonian Syndrome: A Systematic Review

Diffusion tensor imaging (DTI) allows measuring fractional anisotropy and similar microstructural indices of the brain white matter. Lower than normal fractional anisotropy as well as higher than normal diffusivity is associated with loss of microstructural integrity and neurodegeneration. Previous DTI studies in Parkinson's disease (PD) have demonstrated abnormal fractional anisotropy in multiple white matter regions, particularly in the dopaminergic nuclei and dopaminergic pathways. However, DTI is not considered a diagnostic marker for the earliest Parkinson's disease since anisotropic alterations present a temporally divergent pattern during the earliest Parkinson's course. This article reviews a majority of clinically employed DTI studies in PD, and it aims to prove the utilities of DTI as a marker of diagnosing PD, correlating clinical symptomatology, tracking disease progression, and treatment effects. To address the challenge of DTI being a diagnostic marker for early PD, this article also provides a comparison of the results from a longitudinal, early stage, multicenter clinical cohort of Parkinson's research with previous publications. This review provides evidences of DTI as a promising marker for monitoring PD progression and classifying atypical PD types, and it also interprets the possible pathophysiologic processes under the complex pattern of fractional anisotropic changes in the first few years of PD. Recent technical advantages, limitations, and further research strategies of clinical DTI in PD are additionally discussed.

Eye movements and association with regional brain atrophy in clinical subtypes of progressive supranuclear palsy

OBJECTIVE

To investigate oculomotor impairment in subtypes of progressive supranuclear palsy (PSP) and its associations with clinical features and regional brain volumes in PSP.

METHODS

We compared the video-oculography (VOG) findings of 123 PSP patients, consisting of 66 PSP-Richardson syndrome (PSP-RS), 28 PSP-parkinsonism (PSP-P), and 29 PSP-progressive gait freezing (PSP-PGF), along with 80 Parkinson's disease (PD) patients. We also investigated the associations of the VOG results with clinical features (disease duration, PSP rating scales [PSPRS] scores for dysphagia and postural stability) in the subtypes of PSP patients and with regional volumes in the brainstem, including the midbrain, pons, medulla, and the superior cerebellar peduncle (SCP), among the patients who had MRI images at the time of VOG (30 PSP).

RESULTS

All of the three subtypes of PSP patients showed slower vertical saccades and smooth pursuit than that of the PD patients (adjusted p < 0.05). Among the PSP subtypes, saccadic peak velocity, saccadic accuracy, and pursuit gain were significantly decreased in patients with the PSP-RS compared to those with the PSP-PGF (adjusted p < 0.05). In multiple linear regression model, vertical saccadic velocity, latency, accuracy, and pursuit gain were associated with the PSPRS score for dysphagia (adjusted p < 0.05), and a decrease in vertical saccadic speed and accuracy was associated with SCP atrophy (corrected p < 0.05).

CONCLUSIONS

This study demonstrated the severity of oculomotor dysfunction in differentiating the subtypes of PSP and its significant relationships with the dysphagia symptom and SCP volume in PSP.

The Progressive Supranuclear Palsy: Past and Present Aspects

Objectives: Recently, new criteria for sensitive and specific clinical diagnosis of progressive supranuclear palsy (PSP) have been addressed while distinct clinical phenotypes of the disorder have been increasingly described in the literature. This study aimed to describe past and present aspects of the disease as well as to highlight the cognitive and behavioral profile of PSP patients in relation to the underlying pathology, genetics and treatment procedures.Methods: A Medline and Scopus search was performed to identify articles published on this topic. Articles published solely in English were considered.Results: The most common clinical characteristics of PSP included early postural instability and falls, vertical supranuclear gaze palsy, parkinsonism with poor response to levodopa and pseudobulbar palsy. Frontal dysfunction and verbal fluency deficits were the most distinct cognitive impairments in PSP while memory, visuospatial and social cognition could also be affected. Apathy and impulsivity were also present in PSP patients and had significant impact on relatives and caregivers.Conclusions: PSP is a neurodegenerative disorder with prominent tau neuropathology. Movement, motivation and communication impairments in patients with PSP may limit participation in everyday living activities. Comprehensive neuropsychological assessments are of significant importance for PSP cognitive evaluation. Pharmacologic and non-pharmacologic approaches could be applied in order to relieve patients and improve quality of life.Clinical Implications: Executive dysfunction is the most notable cognitive impairment and dominates the neuropsychological profile of patients with PSP.

Corticobasal degeneration

Corticobasal degeneration (CBD) is a rare neurodegenerative disease characterized by the predominance of pathological 4 repeat tau deposition in various cell types and anatomical regions. Corticobasal syndrome (CBS) is one of the clinical phenotypes associated with CBD pathology, manifesting as a progressive asymmetric akinetic-rigid, poorly levodopa-responsive parkinsonism, with cerebral cortical dysfunction. CBD can manifest as several clinical phenotypes, and similarly, CBS can also have a pathologic diagnosis other than CBD. This chapter discusses the clinical manifestations of pathologically confirmed CBD cases, the current diagnostic criteria, as well as the pathologic and neuroimaging findings of CBD/CBS. At present, therapeutic options for CBD remain symptomatic. Further research is needed to improve the clinical diagnosis of CBD, as well as studies on disease-modifying therapies for this relentlessly progressive neurodegenerative disorder.

Corticobasal syndrome: neuroimaging and neurophysiological advances

Corticobasal degeneration (CBD) is a neurodegenerative condition characterized by 4R tau protein deposition in several brain regions that clinically manifests itself as a heterogeneous atypical parkinsonism typically expressed in adulthood. The prototypical clinical phenotype of CBD is corticobasal syndrome (CBS). Important insights into the pathophysiological mechanisms underlying motor and higher cortical symptoms in CBS have been gained by using advanced neuroimaging and neurophysiological techniques. Structural and functional neuroimaging studies often show asymmetric cortical and subcortical abnormalities, mainly involving perirolandic and parietal regions and basal ganglia structures. Neurophysiological investigations including electroencephalography and somatosensory evoked potentials provide useful information on the origin of myoclonus and on cortical sensory loss. Transcranial magnetic stimulation demonstrates heterogeneous and asymmetric changes in the excitability and plasticity of primary motor cortex and abnormal hemispheric connectivity. Neuroimaging and neurophysiological abnormalities in multiple brain areas reflect asymmetric neurodegeneration, leading to asymmetric motor and higher cortical symptoms in CBS.

MRI-based neuroimaging: atypical parkinsonisms and other movement disorders

PURPOSE OF REVIEW

MRI has become a well established technical tool for parkinsonism both in the diagnostic work-up to differentiate between causes and to serve as a neurobiological marker. This review summarizes current developments in the advanced MRI-based assessment of brain structure and function in atypical parkinsonian syndromes and explores their potential in a clinical and neuroscientific setting.

RECENT FINDINGS

Computer-based unbiased quantitative MRI analyses were demonstrated to guide in the discrimination of parkinsonian syndromes at single-patient level, with major contributions when combined with machine-learning techniques/support vector machine classification. These techniques have shown their potential in tracking the disease progression, perhaps also as a read-out in clinical trials. The characterization of different brain compartments at various levels of structural and functional alterations can be provided by multiparametric MRI, including a growing variety of diffusion-weighted imaging approaches and potentially iron-sensitive and functional MRI.

SUMMARY

In case that the recent advances in the MRI-based assessment of atypical parkinsonism will lead to standardized protocols for image acquisition and analysis after the confirmation in large-scale multicenter studies, these approaches may constitute a great achievement in the (operator-independent) detection, discrimination and characterization of degenerative parkinsonian disorders at an individual basis.

Atrophy in midbrain & cerebral/cerebellar pedunculi is characteristic for progressive supranuclear palsy - A double-validation whole-brain meta-analysis

OBJECTIVE

Progressive supranuclear palsy (PSP) is an atypical parkinsonian syndrome characterized by vertical gaze palsy and postural instability. Midbrain atrophy is suggested as a hallmark, but it has not been validated systematically in whole-brain imaging.

METHODS

We conducted whole-brain meta-analyses identifying disease-related atrophy in structural MRI. Eighteen studies were identified (N = 315 PSP, 393 controls) and separated into gray or white matter analyses (15/12). All patients were diagnosed according to the National Institute of Neurological Disorders and Stroke and the Society for PSP (NINDS-SPSP criteria, Litvan et al. (1996a)), which are now considered as PSP-Richardson syndrome (Höglinger et al., 2017). With overlay analyses, we double-validated two meta-analytical algorithms: anatomical likelihood estimation and seed-based D mapping. Additionally, we conducted region-of-interest effect size meta-analyses on radiological biomarkers and subtraction analyses differentiating PSP from Parkinson's disease.

RESULTS

Whole brain meta-analyses revealed consistent gray matter atrophy in bilateral thalamus, anterior insulae, midbrain, and left caudate nucleus. White matter alterations were consistently detected in bilateral superior/middle cerebellar pedunculi, cerebral pedunculi, and midbrain atrophy. Region-of-interest meta-analyses demonstrated that midbrain metrics generally perform very well in distinguishing PSP from other parkinsonian syndromes with strong effect sizes. Subtraction analyses identified the midbrain as differentiating between PSP and Parkinson's disease.

CONCLUSIONS

Our meta-analyses identify gray matter atrophy of the midbrain and white matter atrophy of the cerebral/cerebellar pedunculi and midbrain as characteristic for PSP. Results support the incorporation of structural MRI data, and particularly these structures, into the revised PSP diagnostic criteria.

Tau and Axonal Transport Misregulation in Tauopathies

Tau is a microtubule-associated protein that is involved in both normal and pathological processes in neurons. Since the discovery and characterization of tau over 40 years ago, our understanding of tau's normal functions and toxic roles in neurodegenerative tauopathies has continued to expand. Fast axonal transport is a critical process for maintaining axons and functioning synapses, critical subcellular compartments underlying neuronal connectivity. Signs of fast axonal transport disruption are pervasive in Alzheimer's disease and other tauopathies and various mechanisms have been proposed for regulation of fast axonal transport by tau. Post-translational modifications of tau including phosphorylation at specific sites, FTDP-17 point mutations, and oligomerization, confer upon tau a toxic effect on fast axonal transport. Consistent with the well-established dependence of axons on fast axonal transport, these disease-related modifications are closely associated temporally and spatially with axonal degeneration in the early disease stages. These factors position tau as a potentially critical factor mediating the disruption of fast axonal transport that precedes synaptic dysfunction and axonal degeneration at later disease stages. In this chapter, we review the evidence that tau affects fast axonal transport and examine several potential mechanisms proposed to underlie this toxicity.

Difficulties in the diagnosis of four repeats (4R) tauopathic parkinsonian syndromes

Corticobasal Degeneration Degeneration (CBD) and Progressive Supranuclear Palsy (PSP) are types of four repeats (4R) tauopathies, which are associated to parkinsonian syndromes. The aim of the work is to analyze cases of patients of the Department of Neurology, overlapping of syndromes related to both pathologies and to show that most likely CBS and PSP are not lineary related to their commonly associated syndromes i.e. adequately corticobasal syndromes and progressive supranuclear palsy syndromes. In the context of each patient factors in favor of most likely CBS, PSP or both diseases are discussed and analyzed using contemporary criteria. This work discusses multidimensional aspect of the examination of five patient aged 64 to 83 - 4 females and 1 male with 4R tauopathies and difficulties in distinguishing both diseases. The duration of the disease varied from 1 to 5 years. Each patient after neurological examination was assessed using magnetic resonance imaging (MRI) and psychological test. Examination of all patients was extended using single photon emission computer tomography (SPECT) to reveal the usefulness of this tool in differentiation of diseases was done. The outcome of this examination was verified with prior clinical manifestation of patients and morphological abnormalities in magnetic resonance imaging. Autopsies were not conducted.

Tracking brain damage in progressive supranuclear palsy: a longitudinal MRI study

OBJECTIVES

In this prospective, longitudinal, multiparametric MRI study, we investigated clinical as well as brain grey matter and white matter (WM) regional changes in patients with progressive supranuclear palsy-Richardson's syndrome (PSP-RS).

METHODS

Twenty-one patients with PSP-RS were evaluated at baseline relative to 36 healthy controls and after a mean follow-up of 1.4 years with clinical rating scales, neuropsychological tests and MRI scans.

RESULTS

Relative to controls, patients with PSP-RS showed at baseline a typical pattern of brain damage, including midbrain atrophy, frontal cortical thinning and widespread WM involvement of the main infratentorial and supratentorial tracts that exceeded cortical damage. Longitudinal study showed that PSP-RS exhibited no further changes in cortical thinning, which remained relatively focal, while midbrain atrophy and WM damage significantly progressed. Corpus callosum and frontal WM tract changes correlated with the progression of both disease severity and behavioural dysfunction.

CONCLUSIONS

This study demonstrated the feasibility of carrying out longitudinal diffusion tensor MRI in patients with PSP-RS and its sensitivity to identifying the progression of pathology. Longitudinal midbrain volume loss and WM changes are associated with PSP disease course.

Cognitive dysfunction in corticobasal degeneration

Corticobasal degeneration (CBD) was originally described as a distinct clinicopathological entity in 1967. Since then, different phenotypic presentations have emerged as possible manifestations of CBD histopathological findings. In addition, pathophysiological findings and the molecular basis have been delineated and several aspects of its cognitive manifestations have been clarified. Thus, not only the spectrum of what is currently designated as CBD has expanded, but overlap with other degenerative and even secondary disorders has made clinical diagnostic certainty even more challenging in the absence of specific and readily-available markers. Cognitive deficits in CBD are now recognized as a frequent initial presentation and may appear up to eight years before the motor symptoms, depending on the phenotypic variant. Characteristic cognitive features of CBD involve language deficits, visuospatial and executive dysfunctions, apraxia, and behavioral disorders. Semantic and episodic memories are usually preserved, while language is often impaired in the early stages.

Axonal Degeneration in Tauopathies: Disease Relevance and Underlying Mechanisms

Tauopathies are a diverse group of diseases featuring progressive dying-back neurodegeneration of specific neuronal populations in association with accumulation of abnormal forms of the microtubule-associated protein tau. It is well-established that the clinical symptoms characteristic of tauopathies correlate with deficits in synaptic function and neuritic connectivity early in the course of disease, but mechanisms underlying these critical pathogenic events are not fully understood. Biochemical in vitro evidence fueled the widespread notion that microtubule stabilization represents tau's primary biological role and that the marked atrophy of neurites observed in tauopathies results from loss of microtubule stability. However, this notion contrasts with the mild phenotype associated with tau deletion. Instead, an analysis of cellular hallmarks common to different tauopathies, including aberrant patterns of protein phosphorylation and early degeneration of axons, suggests that alterations in kinase-based signaling pathways and deficits in axonal transport (AT) associated with such alterations contribute to the loss of neuronal connectivity triggered by pathogenic forms of tau. Here, we review a body of literature providing evidence that axonal pathology represents an early and common pathogenic event among human tauopathies. Observations of axonal degeneration in animal models of specific tauopathies are discussed and similarities to human disease highlighted. Finally, we discuss potential mechanistic pathways other than microtubule destabilization by which disease-related forms of tau may promote axonopathy.

Longitudinal white matter change in frontotemporal dementia subtypes and sporadic late onset Alzheimer's disease

Background

Degradation of white matter microstructure has been demonstrated in frontotemporal lobar degeneration (FTLD) and Alzheimer's disease (AD). In preparation for clinical trials, ongoing studies are investigating the utility of longitudinal brain imaging for quantification of disease progression. To date only one study has examined sample size calculations based on longitudinal changes in white matter integrity in FTLD.

Objective

To quantify longitudinal changes in white matter microstructural integrity in the three canonical subtypes of frontotemporal dementia (FTD) and AD using diffusion tensor imaging (DTI).

Methods

60 patients with clinical diagnoses of FTD, including 27 with behavioral variant frontotemporal dementia (bvFTD), 14 with non-fluent variant primary progressive aphasia (nfvPPA), and 19 with semantic variant PPA (svPPA), as well as 19 patients with AD and 69 healthy controls were studied. We used a voxel-wise approach to calculate annual rate of change in fractional anisotropy (FA) and mean diffusivity (MD) in each group using two time points approximately one year apart. Mean rates of change in FA and MD in 48 atlas-based regions-of-interest, as well as global measures of cognitive function were used to calculate sample sizes for clinical trials (80% power, alpha of 5%).

Results

All FTD groups showed statistically significant baseline and longitudinal white matter degeneration, with predominant involvement of frontal tracts in the bvFTD group, frontal and temporal tracts in the PPA groups and posterior tracts in the AD group. Longitudinal change in MD yielded a larger number of regions with sample sizes below 100 participants per therapeutic arm in comparison with FA. SvPPA had the smallest sample size based on change in MD in the fornix (n = 41 participants per study arm to detect a 40% effect of drug), and nfvPPA and AD had their smallest sample sizes based on rate of change in MD within the left superior longitudinal fasciculus (n = 49 for nfvPPA, and n = 23 for AD). BvFTD generally showed the largest sample size estimates (minimum n = 140 based on MD in the corpus callosum). The corpus callosum appeared to be the best region for a potential study that would include all FTD subtypes. Change in global measure of functional status (CDR box score) yielded the smallest sample size for bvFTD (n = 71), but clinical measures were inferior to white matter change for the other groups.

Conclusions

All three of the canonical subtypes of FTD are associated with significant change in white matter integrity over one year. These changes are consistent enough that drug effects in future clinical trials could be detected with relatively small numbers of participants. While there are some differences in regions of change across groups, the genu of the corpus callosum is a region that could be used to track progression in studies that include all subtypes.

•

We show longitudinal change in white matter in frontotemporal lobar degeneration (FTLD) and Alzheimer’s disease (AD).

•

We use diffusion tensor imaging (DTI) to quantify rate of white matter degeneration in FTLD and AD.

•

In preparation for clinical trials, utility of longitudinal DTI as surrogate marker of therapeutic efficacy is investigated.

•

We produce sample sizes based on rate of change in DTI metrics in the three canonical subtypes of FTLD and AD.

Mild Cognitive Impairment and Progression to Dementia in Progressive Supranuclear Palsy

BACKGROUND

Cognitive deficits are common in progressive supranuclear palsy (PSP), but their relevance and the progression to dementia are still poorly described. The recently revised criteria for PSP consider cognitive dysfunction in the diagnostic work-up.

METHODS

The study retrospectively evaluated a series of 99 PSP patients with Richardson syndrome (PSP-RS), subgrouped according to cognitive and behavioural performances into PSP with normal cognition (PSP-NC), PSP with mild cognitive impairment (PSP-MCI), and PSP with dementia (PSP-D). The progression to dementia at the 3-year follow-up was assessed.

RESULTS

At baseline, 15.2% of patients were classified as PSP-NC, 43.4% as PSP-MCI, and 41.4% as PSP-D. During the 3-year follow-up, 21 out of 29 patients, previously classified as PSP-NC or PSP-MCI, converted to dementia, with an incidence rate of 241 per 1,000 patients/year. Nineteen out of 21 PSP patients (90%) developed the behavioural variant frontotemporal dementia phenotype. The only factor associated with conversion to dementia was MCI diagnosis at baseline (p = 0.023).

CONCLUSION

Cognitive decline occurs in a great proportion of PSP-RS patients early during the disease course. In the absence of a specific phenotype, the diagnosis of MCI might identify PSP patients at greatest risk of developing dementia and should be considered further in the diagnostic assessment.

18F-AV-1451 binds to motor-related subcortical gray and white matter in corticobasal syndrome

OBJECTIVE

To investigate tau distribution in patients with corticobasal syndrome (CBS) using ¹⁸F-AV-1451 PET.

METHODS

Six consecutively recruited patients with CBS and 20 age-matched healthy controls underwent 2 PET scans with ¹⁸F-AV-1451 (for tau) and ¹⁸F-florbetaben (for β-amyloid). We compared standardized uptake value ratio maps of the ¹⁸F-AV-1451 PET images between the patients with CBS and controls.

RESULTS

Compared to controls, patients with CBS exhibited asymmetrically increased ¹⁸F-AV-1451 binding in the putamen, globus pallidus, and thalamus contralateral to the clinically more affected side and in the ipsilateral globus pallidus and dentate nucleus. Voxel-based comparison additionally showed asymmetrically increased ¹⁸F-AV-1451 binding in the focal regions of the precentral gray and white matter and in the midbrain, predominantly in the contralateral side. ¹⁸F-AV-1451 binding in the precentral white matter correlated with motor severity.

CONCLUSIONS

¹⁸F-AV-1451 asymmetrically binds to motor-related subcortical gray and white matter structures in patients with CBS. This pattern corresponds to tau pathology distribution in postmortem studies, and motor deficit in patients with CBS may be associated with tau accumulation predominantly in the subcortical white matter underlying the motor cortex, leading to disruptions in motor-related networks.

Radiological biomarkers for diagnosis in PSP: Where are we and where do we need to be?

PSP is a pathologically defined neurodegenerative tauopathy with a variety of clinical presentations including typical Richardson's syndrome and other variant PSP syndromes. A large body of neuroimaging research has been conducted over the past two decades, with many studies proposing different structural MRI and molecular PET/SPECT biomarkers for PSP. These include measures of brainstem, cortical and striatal atrophy, diffusion weighted and diffusion tensor imaging abnormalities, [18F] fluorodeoxyglucose PET hypometabolism, reductions in striatal dopamine imaging and, most recently, PET imaging with ligands that bind to tau. Our aim was to critically evaluate the degree to which structural and molecular neuroimaging metrics fulfill criteria for diagnostic biomarkers of PSP. We queried the PubMed, Cochrane, Medline, and PSYCInfo databases for original research articles published in English over the past 20 years using postmortem diagnosis or the NINDS-SPSP criteria as the diagnostic standard from 1996 to 2016. We define a five-level theoretical construct for the utility of neuroimaging biomarkers in PSP, with level 1 representing group-level findings, level 2 representing biomarkers with demonstrable individual-level diagnostic utility, level 3 representing biomarkers for early disease, level 4 representing surrogate biomarkers of PSP pathology, and level 5 representing definitive PSP biomarkers of PSP pathology. We discuss the degree to which each of the currently available biomarkers fit into this theoretical construct, consider the role of biomarkers in the diagnosis of Richardson's syndrome, variant PSP syndromes and autopsy confirmed PSP, and emphasize current shortfalls in the field. © 2017 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Advances in progressive supranuclear palsy: new diagnostic criteria, biomarkers, and therapeutic approaches

Progressive supranuclear palsy (PSP), previously believed to be a common cause of atypical parkinsonism, is now recognised as a range of motor and behavioural syndromes that are associated with a characteristic 4-repeat tau neuropathology. New research criteria that recognise early presentations of PSP and operationalise diagnosis of the full spectrum of clinical phenotypes have been reported. The Movement Disorders Society PSP diagnostic criteria include syndromes with few or mild symptoms that are suggestive of underlying PSP pathology and could provide an opportunity for earlier therapeutic interventions in the future. These criteria also include definitions for variant PSP syndromes with different patterns of movement, language, or behavioural features than have been conclusively associated with PSP pathology. Data from new diagnostic biomarkers can be combined with the clinical features of disease to increase the specificity of the new criteria for underlying PSP pathology. Because PSP is associated with tau protein abnormalities, there is growing interest in clinical trials of new tau-directed therapies. These therapies are hypothesised to have disease-modifying effects by reducing the concentration of toxic forms of tau in the brain or by compensating for loss of tau function. Since tau pathology is also central to Alzheimer's disease and chronic traumatic encephalopathy, a successful tau therapeutic for PSP might inform treatment of other neurodegenerative diseases.

Functional disconnection of thalamic and cerebellar dentate nucleus networks in progressive supranuclear palsy and corticobasal syndrome

AIM

To assess functional rearrangement following neurodegeneration in the thalamus and dentate nucleus in patients with progressive supranuclear palsy (PSP) and corticobasal syndrome (CBS).

METHODS

We recruited 19 patients with PSP, 11 with CBS and 14 healthy subjects. All the subjects underwent resting-state (rs) fMRI using a 3T system. Whole brain functional connectivity of the thalamus and dentate nucleus were calculated by means of a seed-based approach with FEAT script in FSL toolbox. Thalamic volume was calculated by means of FIRST, and the dentate area by means of Jim software.

RESULTS

Both thalamic volume and dentate area were significantly smaller in PSP and CBS patients than in healthy subjects. No significant difference emerged in thalamic volume between PSP and CBS patients, whereas dentate area was significantly smaller in PSP than in CBS. Thalamic functional connectivity was significantly reduced in both patient groups in various cortical, subcortical and cerebellar areas. By contrast, changes in dentate nucleus functional connectivity differed in PSP and CBS: it decreased in subcortical and prefrontal cortical areas in PSP, but increased asymmetrically in the frontal cortex in CBS.

CONCLUSIONS

Evaluating the dentate nucleus size and its functional connectivity may help to differentiate patients with PSP from those with CBS.