Symmetric corticobasal degeneration (S-CBD)

Atypical findings: Atypical parkinsonian syndromes or Atypical parkinsonian syndromes look-alikes

OBJECTIVE

In parkinsonian syndromes, presentations other than current diagnostic criteria are considered atypical findings. Our goal was to identify and describe the frequency and features of uncommon manifestations of atypical parkinsonian syndromes within our group.

METHODS

We retrospectively retrieved the medical records of all patients admitted to our clinic with parkinsonism between January 2011 and January 2022. We only included patients with atypical parkinsonian syndromes, in which the diagnosis was based on current clinical criteria. We retrospectively analyzed neurological, psychiatric, radiological, and electrophysiological characteristics. Typical and atypical features were classified according to the current clinical criteria and previous reports.

RESULTS

We determined 51 patients with atypical parkinsonian syndromes; 46 were included, whereas five were excluded due to insufficient follow-up. The probable diagnoses were multiple system atrophy (MSA, n = 19), dementia with Lewy bodies (DLB, n = 10), frontotemporal dementia (FTD, n = 10), corticobasal syndrome (CBS, n = 3), progressive supranuclear palsy (PSP, n = 4). The prevalence of atypical findings was similar among different types of atypical parkinsonian syndromes (p = 0.847). Atypical findings were eyelid myoclonus, double vision in MSA; ataxia, myoclonus, and a typical hummingbird sign on MRI in DLB; pyramidal findings and family history in FTD; early onset, family history, and onset with psychiatric findings in PSP-like phenotype. Genetic causes were identified in the FTD-like phenotype with pyramidal findings, whereas symptom onset was early with myoclonus in the PSP-like phenotype.

CONCLUSION

Atypical findings such as abnormal saccades, myoclonus, and ataxia may be a part of degenerative syndromes. However, family history, onset at an earlier age, and specific neurological findings suggest genetic syndromes.

Four-repeat tauopathies and late-onset psychiatric disorders: Etiological relevance or incidental findings?

Argyrophilic grain disease (AGD), progressive supranuclear palsy (PSP) and corticobasal degeneration are four-repeat (4R) tauopathies that develop in the presenium or later. Whether these diseases are associated with the occurrence of late-onset psychiatric disorders remains unclear. To facilitate the accumulation of clinicopathological findings regarding this issue, we here present a selected series of 11 cases that clinically developed psychotic disorder (n = 7; age at onset: 41-75 years), depressive disorder (n = 1; 49 years), bipolar disorder (n = 2; 32 and 37 years) and somatoform disorder (n = 1; 88 years), and had at least one pathological hallmark of these tauopathies. The mean age at death was 74.3 years. No case showed dementia, at least in the early stage of the course. Nine cases had AGD. Granular fuzzy astrocytes in the amygdala were noted in all AGD cases and one non-AGD case. Two AGD cases had tufted astrocytes (TAs) in the amygdala but not in the frontal cortex and striatum. Three AGD and two non-AGD cases had TAs in the frontal cortex and/or striatum but not in the amygdala. One AGD case had a small number of astrocytic plaques in the frontal cortex, striatum and globus pallidus. Only one case was diagnosed as atypical PSP according to the NINDS-PSP neuropathological criteria. No case had high-level Alzheimer's disease pathology, Lewy body disease or limbic-predominant age-related TDP-43 encephalopathy. Two cases had mild neuronal loss in the hippocampus and substantia nigra, respectively. Clinicopathological studies focusing especially on early changes of 4R tauopathies, as well as the development of surrogate markers of these diseases, may be necessary for better understanding of the pathogenic backgrounds of late-onset psychiatric disorders.

Radiological assessment of dementia: the Italian inter-society consensus for a practical and clinically oriented guide to image acquisition, evaluation, and reporting

Background

Radiological evaluation of dementia is expected to increase more and more in routine practice due to both the primary role of neuroimaging in the diagnostic pathway and the increasing incidence of the disease. Despite this, radiologists often do not follow a disease-oriented approach to image interpretation, for several reasons, leading to reports of limited value to clinicians. In our work, through an intersocietal consensus on the main mandatory knowledge about dementia, we proposed a disease-oriented protocol to optimize and standardize the acquisition/evaluation/interpretation and reporting of radiological images. Our main purpose is to provide a practical guideline for the radiologist to help increase the effectiveness of interdisciplinary dialogue and diagnostic accuracy in daily practice.

Results

We defined key clinical and imaging features of the dementias (A), recommended MRI protocol (B), proposed a disease-oriented imaging evaluation and interpretation (C) and report (D) with a glimpse to future avenues (E). The proposed radiological practice is to systematically evaluate and score atrophy, white matter changes, microbleeds, small vessel disease, consider the use of quantitative measures using commercial software tools critically, and adopt a structured disease-oriented report.

Summary statement

In the expanding field of cognitive disorders, the only effective assessment approach is the standardized disease-oriented one, which includes a multidisciplinary integration of the clinical picture, MRI, CSF and blood biomarkers and nuclear medicine.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11547-022-01534-0.

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.

The Significance of Asymmetry in the Assessment of Brain Perfusion in Atypical Tauopathic Parkinsonian Syndromes

Progressive supranuclear palsy syndrome (PSPS) and corticobasal syndrome (CBS) are clinical manifestations of tauopathic Parkinsonian syndromes. Due to their overlapping symptomatology, the differential diagnosis of these entities may be difficult when bounded to clinical assessment. The manifestations are commonly associated with pathological entities—corticobasal degeneration and progressive supranuclear palsy, which are four-repeat tauopathies. In this study, the authors attempted to find whether the asymmetry typically associated with CBS may be feasible in the interpretation of perfusion single-photon computed tomography. The analysis based on the examination of patients with progressive supranuclear palsy—Richardson syndrome (PSP-RS), progressive supranuclear palsy—Parkinsonism predominant (PSP-P), and corticobasal syndrome (CBS) revealed significant asymmetry of perfusion of the amygdala in corticobasal syndrome. The more pronounced abnormalities of perfusion were observed in the left amygdala among patients with more severe Parkinsonian syndromes in CBS on the right. This study shows that the comparison of the perfusion of tauopathic Parkinsonian syndromes should be extended by asymmetry analysis. Interestingly, the differentiating potential of brain perfusion is present in the comparison of CBS and PSP-RS, but not in CBS and PSP-P. This phenomenon could be explained by more distinct asymmetry in the perfusion observed in PSP-P, which diminishes the differentiating potential of this parameter when it comes to the comparison of PSP-P and CBS. To the best of our knowledge, this is the first study evaluating which structures can be interpreted as significantly asymmetrical in the context of perfusion in CBS.

Neuropathology and emerging biomarkers in corticobasal syndrome

Corticobasal syndrome (CBS) is a clinical syndrome characterised by progressive asymmetric limb rigidity and apraxia with dystonia, myoclonus, cortical sensory loss and alien limb phenomenon. Corticobasal degeneration (CBD) is one of the most common underlying pathologies of CBS, but other disorders, such as progressive supranuclear palsy (PSP), Alzheimer's disease (AD) and frontotemporal lobar degeneration with TDP-43 inclusions, are also associated with this syndrome.In this review, we describe common and rare neuropathological findings in CBS, including tauopathies, synucleinopathies, TDP-43 proteinopathies, fused in sarcoma proteinopathy, prion disease (Creutzfeldt-Jakob disease) and cerebrovascular disease, based on a narrative review of the literature and clinicopathological studies from two brain banks. Genetic mutations associated with CBS, including GRN and MAPT, are also reviewed. Clinicopathological studies on neurodegenerative disorders associated with CBS have shown that regardless of the underlying pathology, frontoparietal, as well as motor and premotor pathology is associated with CBS. Clinical features that can predict the underlying pathology of CBS remain unclear. Using AD-related biomarkers (ie, amyloid and tau positron emission tomography (PET) and fluid biomarkers), CBS caused by AD often can be differentiated from other causes of CBS. Tau PET may help distinguish AD from other tauopathies and non-tauopathies, but it remains challenging to differentiate non-AD tauopathies, especially PSP and CBD. Although the current clinical diagnostic criteria for CBS have suboptimal sensitivity and specificity, emerging biomarkers hold promise for future improvements in the diagnosis of underlying pathology in patients with CBS.

Progressive Supranuclear Palsy and Corticobasal Degeneration

Progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD) are neurodegenerative tauopathies with neuronal and glial lesions composed of tau that is composed predominantly of isomers with four repeats in the microtubule-binding domain (4R tau). The brain regions vulnerable to pathology in PSP and CBD overlap, but there are differences, particularly with respect to distribution of neuronal loss, the relative abundance of neuronal and glial lesions, the morphologic features of glial lesions, and the frequency of comorbid pathology. Both PSP and CBD have a wide spectrum of clinical manifestations, including disorders of movement and cognition. Recognition of phenotypic diversity in PSP and CBD may improve antemortem diagnostic accuracy, which tends to be very good for the most common presentation of PSP (Richardson syndrome), but poor for the most characteristic presentation of CBD (corticobasal syndrome: CBS). Development of molecular and imaging biomarkers may improve antemortem diagnostic accuracy. Currently, multidisciplinary symptomatic and supportive treatment with pharmacological and non-pharmacological strategies remains the standard of care. In the future, experimental therapeutic trials will be important to slow disease progression.

Clinical and pathologic features of cognitive-predominant corticobasal degeneration

OBJECTIVE

To describe clinical and pathologic characteristics of corticobasal degeneration (CBD) with cognitive predominant problems during the disease course.

METHODS

In a series of autopsy-confirmed cases of CBD, we identified patients with cognitive rather than motor predominant features (CBD-Cog), including 5 patients thought to have Alzheimer disease (AD) and 10 patients thought to have behavioral variant frontotemporal dementia (FTD). We compared clinical and pathologic features of CBD-Cog with those from a series of 31 patients with corticobasal syndrome (CBD-CBS). For pathologic comparisons between CBD-Cog and CBD-CBS, we used semiquantitative scoring of neuronal and glial lesion types in multiple brain regions and quantitative assessments of tau burden from image analysis.

RESULTS

Five of 15 patients with CBD-Cog never had significant motor problems during their disease course. The most common cognitive abnormalities in CBD-Cog were executive and visuospatial dysfunction. The frequency of language problems did not differ between CBD-Cog and CBD-CBS. Argyrophilic grain disease, which is a medial temporal tauopathy associated with mild cognitive impairment, was more frequent in CBD-Cog. Apathy was also more frequent in CBD-Cog. Tau pathology in CBD-Cog was greater in the temporal and less in perirolandic cortices than in CBD-CBS.

CONCLUSION

A subset of patients with CBD has a cognitive predominant syndrome than can be mistaken for AD or FTD. Our findings suggest that distribution of tau cortical pathology (greater in temporal and less in perirolandic cortices) may be the basis of this uncommon clinical variant of CBD.

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 degeneration and corticobasal syndrome: A review

Corticobasal degeneration (CBD) is a rare neurodegenerative disorder. The most common presentation of CBD is the corticobasal syndrome (CBS), which is a constellation of cortical and extrapyramidal symptoms and signs. Clinical-pathological studies have illustrated that CBD can present with diverse clinical phenotypes, including a non-fluent, agrammatic primary progressive aphasia syndrome, a behavioral, dysexecutive and visuospatial syndrome, as well as a progressive supranuclear palsy-like syndrome. Conversely, multiple pathologies, such as CBD, Alzheimer's disease and progressive supranuclear palsy may underlie a patient with CBS. This clinical-pathological overlap emphasizes the need for biomarkers that will assist in the accurate diagnosis of patients with CBS. This review presents an overview of the pathological, genetic, clinical and therapeutic characteristics of CBD, with an emphasis on the imaging (structural and functional) and biochemical (cerebrospinal fluid) biomarkers of CBD.

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.

FTD spectrum: Neuroimaging across the FTD spectrum

Frontotemporal dementia is a complex and heterogeneous neurodegenerative disease that encompasses many clinical syndromes, pathological diseases, and genetic mutations. Neuroimaging has played a critical role in our understanding of the underlying pathophysiology of frontotemporal dementia and provided biomarkers to aid diagnosis. Early studies defined patterns of neurodegeneration and hypometabolism associated with the clinical, pathological and genetic aspects of frontotemporal dementia, with more recent studies highlighting how the breakdown of structural and functional brain networks define frontotemporal dementia. Molecular positron emission tomography ligands allowing the in vivo imaging of tau proteins have also provided important insights, although more work is needed to understand the biology of the currently available ligands.

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.

Clinical Neurology and Epidemiology of the Major Neurodegenerative Diseases

Neurodegenerative diseases are a common cause of morbidity and cognitive impairment in older adults. Most clinicians who care for the elderly are not trained to diagnose these conditions, perhaps other than typical Alzheimer's disease (AD). Each of these disorders has varied epidemiology, clinical symptomatology, laboratory and neuroimaging features, neuropathology, and management. Thus, it is important that clinicians be able to differentiate and diagnose these conditions accurately. This review summarizes and highlights clinical aspects of several of the most commonly encountered neurodegenerative diseases, including AD, frontotemporal dementia (FTD) and its variants, progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), Parkinson's disease (PD), dementia with Lewy bodies (DLB), multiple system atrophy (MSA), and Huntington's disease (HD). For each condition, we provide a brief overview of the epidemiology, defining clinical symptoms and diagnostic criteria, relevant imaging and laboratory features, genetics, pathology, treatments, and differential diagnosis.

Pathology of Neurodegenerative Diseases

Neurodegenerative disorders are characterized by progressive loss of selectively vulnerable populations of neurons, which contrasts with select static neuronal loss because of metabolic or toxic disorders. Neurodegenerative diseases can be classified according to primary clinical features (e.g., dementia, parkinsonism, or motor neuron disease), anatomic distribution of neurodegeneration (e.g., frontotemporal degenerations, extrapyramidal disorders, or spinocerebellar degenerations), or principal molecular abnormality. The most common neurodegenerative disorders are amyloidoses, tauopathies, α-synucleinopathies, and TDP-43 proteinopathies. The protein abnormalities in these disorders have abnormal conformational properties. Growing experimental evidence suggests that abnormal protein conformers may spread from cell to cell along anatomically connected pathways, which may in part explain the specific anatomical patterns observed at autopsy. In this review, we detail the human pathology of select neurodegenerative disorders, focusing on their main protein aggregates.

Frontotemporal Dementia

Frontotemporal dementia (FTD) is a heterogeneous disorder with distinct clinical phenotypes associated with multiple neuropathologic entities. Presently, the term FTD encompasses clinical disorders that include changes in behavior, language, executive control, and often motor symptoms. The core FTD spectrum disorders include behavioral variant FTD, nonfluent/agrammatic variant primary progressive aphasia, and semantic variant PPA. Related FTD disorders include frontotemporal dementia with motor neuron disease, progressive supranuclear palsy syndrome, and corticobasal syndrome. In this article, the authors discuss the clinical presentation, diagnostic criteria, neuropathology, genetics, and treatments of these disorders.

Astrogliopathy predominates the earliest stage of corticobasal degeneration pathology

SEE KOBYLECKI AND MANN DOI101093/AWW267 FOR A SCIENTIFIC COMMENTARY ON THIS ARTICLE: Animal models have shown that tau seeding and propagation are strain- and neural network-specific. The study of preclinical cases is valuable to gain insights into early pathological features of corticobasal degeneration and its progression. Three preclinical corticobasal degeneration cases and six age-matched end-stage corticobasal degeneration cases were included in this study. Tau immunohistochemistry performed in 20 brain regions and quantitative assessment of regional tau load using image analysis were performed. Semi-quantitative grading of tau-positive cellular lesions and neuronal loss in the frontal, parietal and temporal cortices, striatum, substantia nigra and subthalamic nucleus were assessed. All preclinical cases were clinically asymptomatic but had widespread tau lesions in the typically affected regions in corticobasal degeneration and the pathognomonic astrocytic plaques were the most prominent lesion type in the anterior frontal and striatal regions. Mean total tau load (sum of all regional tau load) of end-stage corticobasal degeneration cases were nine times greater than that of the preclinical cases (P = 0.04) and less tau load was found in all regions of the preclinical cases. An anterior-to-posterior tau load ratio in the frontal cortex in preclinical cases was 12-fold greater than in end-stage corticobasal degeneration cases. Relatively greater tau burden in the anterior frontal cortex, striatum and subthalamic nucleus suggests the striatal afferent connection to the dorsolateral prefrontal cortex and basal ganglia circuitry are the earliest neural network connections affected by corticobasal degeneration-related tau pathology. Differential distribution of the tau pathology to selective cortical regions in these preclinical cases implies phenotypic presentation may be predetermined at a very early stage of the disease process. Neuronal loss of the substantia nigra was either absent or very mild in the preclinical cases and was moderate to severe in end-stage corticobasal degeneration cases (P < 0.05). Our findings suggest that a threshold of pathological burden in the 'right' anatomical regions needs to be reached before the onset of clinical symptoms. The early prominence of the astrocytic plaques in relation to sparse neuronal lesions leads one to speculate that corticobasal degeneration may begin as an astrogliopathy at a very early disease stage but neuronal lesions gradually take over as the predominant lesion type in advanced disease.

Survival in Frontotemporal Dementia Phenotypes: A Meta-Analysis

BACKGROUND

Survival in frontotemporal dementia (FTD) is not well understood. We conducted a mixed effects meta-analysis of survival in FTD to examine phenotype differences and contributory factors.

METHODS

The PubMed, Medline, EMBASE, CINAHL, PsycINFO and Cochrane databases were searched for studies describing survival or natural history of behavioral variant FTD (bvFTD), progressive non-fluent aphasia (PNFA), semantic dementia (SD), FTD with amyotrophic lateral sclerosis (FTD-ALS), progressive supranuclear palsy and corticobasal degeneration. There were no language restrictions.

RESULTS

We included 27 studies (2,462 subjects). Aggregate mean and median survival were derived for each phenotype and, for comparison, Alzheimer's disease (AD) (using data from the selected studies). Survival was shortest in FTD-ALS (2.5 years). Mean survival was longest in bvFTD and PNFA (8 years) and median survival in SD (12 years). AD was comparable in survival to all except FTD-ALS. Age and sex did not affect survival; the education effect was equivocal. Heterogeneity in FTD survival was largely, but not wholly, explained by phenotypes.

CONCLUSIONS

Survival differs for FTD phenotypes but, except for FTD-ALS, compares well to AD survival. Elucidating the potential causes of within-phenotype heterogeneity in survival (such as complicating features and comorbidities) may open up opportunities for tailored interventions.

Alien Limb Syndrome Responsive to Amantadine in a Patient with Corticobasal Syndrome

Background

Corticobasal syndrome (CBS) is a complex neurodegenerative disorder associated with parkinsonism and alien limb syndrome. Dressing and ideomotor apraxia were reportedly responsive to amantadine.

Case Report

A 79-year-old female was referred for evaluation of right hemiparesis. Neurological examination showed dementia, normal ocular movements, mild facial hypomimia, and bradykinesia with right hemiparesis. Nine years later, she developed alien limb syndrome and was diagnosed with CBS. After failure to respond to several medications, alien limb syndrome markedly improved with amantadine.

Discussion

To the best of our knowledge, this is the first report of a consistent response of severe, forced dystonic alien limb syndrome to amantadine in a patient with CBS.

Motor features in posterior cortical atrophy and their imaging correlates

Posterior cortical atrophy (PCA) is a neurodegenerative syndrome characterized by impaired higher visual processing skills; however, motor features more commonly associated with corticobasal syndrome may also occur. We investigated the frequency and clinical characteristics of motor features in 44 PCA patients and, with 30 controls, conducted voxel-based morphometry, cortical thickness, and subcortical volumetric analyses of their magnetic resonance imaging. Prominent limb rigidity was used to define a PCA-motor subgroup. A total of 30% (13) had PCA-motor; all demonstrating asymmetrical left upper limb rigidity. Limb apraxia was more frequent and asymmetrical in PCA-motor, as was myoclonus. Tremor and alien limb phenomena only occurred in this subgroup. The subgroups did not differ in neuropsychological test performance or apolipoprotein E4 allele frequency. Greater asymmetry of atrophy occurred in PCA-motor, particularly involving right frontoparietal and peri-rolandic cortices, putamen, and thalamus. The 9 patients (including 4 PCA-motor) with pathology or cerebrospinal fluid all showed evidence of Alzheimer's disease. Our data suggest that PCA patients with motor features have greater atrophy of contralateral sensorimotor areas but are still likely to have underlying Alzheimer's disease.

Clinicopathologic assessment and imaging of tauopathies in neurodegenerative dementias

Microtubule-associated protein tau encoded by the MAPT gene binds to microtubules and is important for maintaining neuronal morphology and function. Alternative splicing of MAPT pre-mRNA generates six major tau isoforms in the adult central nervous system resulting in tau proteins with three or four microtubule-binding repeat domains. In a group of neurodegenerative disorders called tauopathies, tau becomes aberrantly hyperphosphorylated and dissociates from microtubules, resulting in a progressive accumulation of intracellular tau aggregates. The spectrum of sporadic frontotemporal lobar degeneration associated with tau pathology includes progressive supranuclear palsy, corticobasal degeneration, and Pick’s disease. Alzheimer’s disease is considered the most prevalent tauopathy. This review is divided into two broad sections. In the first section we discuss the molecular classification of sporadic tauopathies, with a focus on describing clinicopathologic relationships. In the second section we discuss the neuroimaging methodologies that are available for measuring tau pathology (directly using tau positron emission tomography ligands) and tau-mediated neuronal injury (magnetic resonance imaging and fluorodeoxyglucose positron emission tomography). Both sections have detailed descriptions of the following neurodegenerative dementias – Alzheimer’s disease, progressive supranuclear palsy, corticobasal degeneration and Pick’s disease.

Corticobasal degeneration with olivopontocerebellar atrophy and TDP-43 pathology: an unusual clinicopathologic variant of CBD

Corticobasal degeneration (CBD) is a disorder affecting cognition and movement due to a progressive neurodegeneration associated with distinctive neuropathologic features, including abnormal phosphorylated tau protein in neurons and glia in cortex, basal ganglia, diencephalon, and brainstem, as well as ballooned neurons and astrocytic plaques. We identified three cases of CBD with olivopontocerebellar atrophy (CBD-OPCA) that did not have α-synuclein-positive glial cytoplasmic inclusions of multiple system atrophy (MSA). Two patients had clinical features suggestive of progressive supranuclear palsy (PSP), and the third case had cerebellar ataxia thought to be due to idiopathic OPCA. Neuropathologic features of CBD-OPCA are compared to typical CBD, as well as MSA and PSP. CBD-OPCA and MSA had marked neuronal loss in pontine nuclei, inferior olivary nucleus, and Purkinje cell layer. Neuronal loss and grumose degeneration in the cerebellar dentate nucleus were comparable in CBD-OPCA and PSP. Image analysis of tau pathology showed greater infratentorial tau burden, especially in pontine base, in CBD-OPCA compared with typical CBD. In addition, CBD-OPCA had TDP-43 immunoreactive neuronal and glial cytoplasmic inclusions and threads throughout the basal ganglia and in olivopontocerebellar system. CBD-OPCA met neuropathologic research diagnostic criteria for CBD and shared tau biochemical characteristics with typical CBD. These results suggest that CBD-OPCA is a distinct clinicopathologic variant of CBD with olivopontocerebellar TDP-43 pathology.

Imaging brain atrophy in progressive supranuclear palsy and corticobasal syndromes: potential for diagnosis and monitoring of disease progression

SUMMARY The progressive supranuclear palsy syndrome (PSPS) and corticobasal syndrome (CBS) are atypical parkinsonian disorders that are both associated with characteristic patterns of atrophy that can be detected on MRI and can be diagnostically useful for the clinician. Much recent work has focused on developing imaging biomarkers, particularly utilizing measurements of the brainstem, which can differentiate PSPS from CBS and other parkinsonian disorders. The utility of longitudinal measures of atrophy as biomarkers of disease progression has also been assessed with a view to how these measures could be utilized in clinical treatment trials. Here, these studies are reviewed and the potential value of imaging biomarkers to aid diagnosis and monitor disease progression in PSPS and CBS will be discussed.

Recent advances in structural MRI in Parkinson’s disease and atypical parkinsonian syndromes

SUMMARY In the past 2 years, technical developments in conventional and advanced MRI, such as ultra-high-field MRI or mapping of brain mineralization, has allowed novel insights into the nature of Parkinson’s disease (PD) and atypical parkinsonian syndromes, which may aid diagnostic accuracy and differential diagnosis. In addition, sophisticated post-processing analyses, such as morphometry- and surface-based classifications and automated whole-brain analyses, have become available; in PD, this has led to direct visualization of structural substantia nigra abnormalities, monitoring disease progression or screening for brain atrophy associated with dementia. Based on conventional MRI, new MRI rating scales have been established for progressive supranuclear palsy and multiple system atrophy and have been further assessed with a view to their diagnostic accuracy. Clinicopathological series of patients with tauopathies imply that correlations between clinical syndromes, imaging patterns and underlying histopathology are not always strong. Here, some of the issues related to conventional and advanced MRI for the diagnostic accuracy of PD and atypical parkinsonian syndromes are reviewed.

The corticobasal syndrome-Alzheimer's disease conundrum

Corticobasal syndrome (CBS), once thought to be pathognomonic for corticobasal degeneration pathology, is increasingly reported with various underlying pathologies. Alzheimer's disease is one such pathology, also once believed to be unique for its clinical syndrome of dementia of the Alzheimer's type. CBS is believed to result from topography of asymmetric parietofrontal cortical lesion involvement, rather than lesion subtype. However, this topographical pattern is strikingly different to that typically associated with AD for unclear reasons. This article will focus on CBS with underlying AD pathology (CBS-AD), and will review associated clinical, imaging and demographic factors. Predicting AD pathology is of marked interest as disease-modifying therapies loom on the horizon, with biomarkers and imaging research underway. By reviewing the literature for CBS-AD case reports and series and contrasting them with CBS with underlying corticobasal degeneration pathology cases, the article aims to examine factors that may predict AD pathology. How AD pathology may produce this clinical phenotype, rather than the prototype dementia of the Alzheimer's type, will also be reviewed.

Frontal asymmetry in behavioral variant frontotemporal dementia: clinicoimaging and pathogenetic correlates

We aimed to assess associations between clinical, imaging, pathologic, and genetic features and frontal lobe asymmetry in behavioral variant frontotemporal dementia (bvFTD). Volumes of the left and right dorsolateral, medial, and orbital frontal lobes were measured in 80 bvFTD subjects and subjects were classified into 3 groups according to the degree of asymmetry (asymmetric left, asymmetric right, symmetric) using cluster analysis. The majority of subjects were symmetric (65%), with 20% asymmetric left and 15% asymmetric right. There were no clinical differences across groups, although there was a trend for greater behavioral dyscontrol in right asymmetric compared with left asymmetric subjects. More widespread atrophy involving the parietal lobe was observed in the symmetric group. Genetic features differed across groups with symmetric frontal lobes associated with C9ORF72 and tau mutations, while asymmetric frontal lobes were associated with progranulin mutations. These findings therefore suggest that neuroanatomical patterns of frontal lobe atrophy in bvFTD are influenced by specific gene mutations.

Neuroimaging in frontotemporal lobar degeneration--predicting molecular pathology

Frontotemporal lobar degeneration (FTLD) encompasses a group of diseases characterized by neuronal loss and gliosis of the frontal and temporal lobes. Almost all cases of FTLD can be classified into three categories on the basis of deposition of one of three abnormal proteins: the microtubule-associated protein tau, TAR DNA-binding protein 43, or fused in sarcoma. The specific diagnoses within each of these three categories are further differentiated by the distribution and morphological appearance of the protein-containing inclusions. Future treatments are likely to target these abnormal proteins; the clinical challenge, therefore, is to be able to predict molecular pathology during life. Clinical diagnosis alone has had variable success in helping to predict pathology, and is particularly poor in the diagnosis of behavioral variant frontotemporal dementia, which can be associated with all three abnormal proteins. Consequently, other biomarkers of disease are needed. This Review highlights how patterns of atrophy assessed on MRI demonstrate neuroanatomical signatures of the individual FTLD pathologies, independent of clinical phenotype. The roles of these patterns of atrophy as biomarkers of disease, and their potential to help predict pathology during life in patients with FTLD, are also discussed.

Staging neurodegenerative disorders: structural, regional, biomarker, and functional progressions

The notion of staging in the neurodegenerative disorders is modulated by the constant and progressive loss of several aspects of brain structural integrity, circuitry, and neuronal processes. These destructive processes eventually remove individuals' abilities to perform at sufficient and necessary functional capacity at several levels of disease severity. The classification of (a) patients on the basis of diagnosis, risk prognosis, and intervention outcome, forms the basis of clinical staging, and (b) laboratory animals on the basis of animal model of brain disorder, extent of insult, and dysfunctional expression, provides the components for the clinical staging and preclinical staging, respectively, expressing associated epidemiological, biological, and genetic characteristics. The major focus of clinical staging in the present account stems from the fundamental notions of Braak staging as they describe the course and eventual prognosis for Alzheimer's disease, Lewy Body dementia, and Parkinson's disease. Mild cognitive impairment, which expresses the decline in episodic and semantic memory performance below the age-adjusted normal range without marked loss of global cognition or activities of daily living, and the applications of longitudinal magnetic resonance imaging, major instruments for the monitoring of either disease progression in dementia, present important challenges for staging concepts. Although Braak notions present the essential basis for further developments, current staging conceptualizations seem inadequate to comply with the massive influx of information dealing with neurodegenerative processes in brain, advanced both under clinical realities, and discoveries in the laboratory setting. The contributions of various biomarkers of disease progression, e.g., amyloid precursor protein, and neurotransmitter system imbalances, e.g., dopamine receptor supersensitivity and interactive propensities, await their incorporation into the existing staging models thereby underlining the ongoing, dynamic feature of the staging of brain disorders.

Clinicopathological correlations in corticobasal degeneration

OBJECTIVE

To characterize cognitive and behavioral features, physical findings, and brain atrophy patterns in pathology-proven corticobasal degeneration (CBD) and corticobasal syndrome (CBS) with known histopathology.

METHODS

We reviewed clinical and magnetic resonance imaging data in all patients evaluated at our center with either an autopsy diagnosis of CBD (n = 18) or clinical CBS at first presentation with known histopathology (n = 40). Atrophy patterns were compared using voxel-based morphometry.

RESULTS

CBD was associated with 4 clinical syndromes: progressive nonfluent aphasia (n = 5), behavioral variant frontotemporal dementia (n = 5), executive-motor (n = 7), and posterior cortical atrophy (n = 1). Behavioral or cognitive problems were the initial symptoms in 15 of 18 patients; less than half exhibited early motor findings. Compared to controls, CBD patients showed atrophy in dorsal prefrontal and perirolandic cortex, striatum, and brainstem (p < 0.001 uncorrected). The most common pathologic substrates for clinical CBS were CBD (35%), Alzheimer disease (AD, 23%), progressive supranuclear palsy (13%), and frontotemporal lobar degeneration (FTLD) with TDP inclusions (13%). CBS was associated with perirolandic atrophy irrespective of underlying pathology. In CBS due to FTLD (tau or TDP), atrophy extended into prefrontal cortex, striatum, and brainstem, whereas in CBS due to AD, atrophy extended into temporoparietal cortex and precuneus (p < 0.001 uncorrected).

INTERPRETATION

Frontal lobe involvement is characteristic of CBD, and in many patients frontal, not parietal or basal ganglia, symptoms dominate early stage disease. CBS is driven by medial perirolandic dysfunction, but this anatomy is not specific to a single underlying histopathology. Antemortem prediction of CBD will remain challenging until clinical features of CBD are redefined, and sensitive, specific biomarkers are identified.

Neuropathological features of corticobasal degeneration presenting as corticobasal syndrome or Richardson syndrome

Patients with corticobasal degeneration can present with several different clinical syndromes, making ante-mortem diagnosis a challenge. Corticobasal syndrome is the clinical phenotype originally described for corticobasal degeneration, characterized by asymmetric rigidity and apraxia, cortical sensory deficits, dystonia and myoclonus. Some patients do not develop these features, but instead have clinical features consistent with the Richardson syndrome presentation of progressive supranuclear palsy, characterized by postural instability, early unexplained falls, vertical supranuclear gaze palsy, symmetric motor disability and dysphagia. The aim of this study was to identify differences in corticobasal degeneration presenting with corticobasal syndrome (n = 11) or Richardson syndrome (n = 15) with respect to demographic, clinical and neuropathological features. Corticobasal degeneration cases were also compared with patients with pathologically proven progressive supranuclear palsy with Richardson syndrome (n = 15). Cases with corticobasal degeneration, regardless of presentation, shared histopathological and tau biochemical characteristics, but they had differing densities of tau pathology in neuroanatomical regions that correlated with their clinical presentation. In particular, those with corticobasal syndrome had greater tau pathology in the primary motor and somatosensory cortices and putamen, while those with Richardson syndrome had greater tau pathology in limbic and hindbrain structures. Compared with progressive supranuclear palsy, patients with corticobasal degeneration and Richardson syndrome had less neuronal loss in the subthalamic nucleus, but more severe neuronal loss in the medial substantia nigra and greater atrophy of the anterior corpus callosum. Clinically, they had more cognitive impairment and frontal behavioural dysfunction. The results suggest that Richardson syndrome can be a clinicopathological presentation of corticobasal degeneration. Atrophy of anterior corpus callosum may be a potential neuroimaging marker to differentiate corticobasal degeneration from progressive supranuclear palsy in patients with Richardson syndrome.

Symmetrical corticobasal syndrome caused by a novel C.314dup progranulin mutation

Corticobasal syndrome (CBS) is characterised by asymmetrical parkinsonism and cognitive impairment. The underlying pathology varies between corticobasal degeneration, progressive supranuclear palsy, Alzheimer’s disease, Creutzfeldt–Jakob disease and frontotemporal lobar degeneration sometimes in association with GRN mutations. A 61-year-old male underwent neurological examination, neuropsychological assessment, MRI, and HMPAO-SPECT at our medical centre. After his death at the age of 63, brain autopsy, genetic screening and mRNA expression analysis were performed. The patient presented with slow progressive walking disabilities, non-fluent language problems, behavioural changes and forgetfulness. His family history was negative. He had primitive reflexes, rigidity of his arms and postural instability. Later in the disease course he developed dystonia of his left leg, pathological crying, mutism and dysphagia. Neuropsychological assessment revealed prominent ideomotor and ideational apraxia, executive dysfunction, non-fluent aphasia and memory deficits. Neuroimaging showed symmetrical predominant frontoparietal atrophy and hypoperfusion. Frontotemporal lobar degeneration (FTLD)-TDP type 3 pathology was found at autopsy. GRN sequencing revealed a novel frameshift mutation c.314dup, p.Cys105fs and GRN mRNA levels showed a 50% decrease. We found a novel GRN mutation in a patient with an atypical (CBS) presentation with symmetric neuroimaging findings. GRN mutations are an important cause of CBS associated with FTLD-TDP type 3 pathology, sometimes in sporadic cases. Screening for GRN mutations should also be considered in CBS patients without a positive family history.

The multiple phenotypes of corticobasal syndrome and corticobasal degeneration: implications for further study

Corticobasal degeneration (CBD) is a complex neurodegenerative disorder which nomenclature of which its nomenclature and characterization continues to evolve. The core clinical features that have been considered characteristic of the disorder include progressive asymmetric rigidity and apraxia, with other findings suggesting additional cortical (e.g., alien limb phenomena, cortical sensory loss, myoclonus, and mirror movements) and basal ganglionic (e.g., bradykinesia, dystonia, and tremor) dysfunctions. The characteristic findings at autopsy are asymmetric cortical atrophy that is typically maximal in the frontoparietal regions, as well as basal ganglia and nigral degeneration. Microscopically, abnormal accumulations of the microtubule-associated tau protein are found in both neurons and glia, and this disorder is now considered one of the "tauopathies." CBD was initially thought to represent a distinct clinicopathologic entity. Recent studies have shown considerable clinicopathologic heterogeneity, leading some to use the term "corticobasal syndrome" (CBS) for the constellation of findings initially considered characteristic of the disorder, and the term "corticobasal degeneration" for the histopathologic disorder. In this review, the multiple phenotypes/syndromes associated with CBD pathology, and multiple diseases associated with the CBS, are presented. The clinicopathologic heterogeneity in CBS/CBD and the implications of this heterogeneity on clinical practice, on understanding the focal/asymmetric cerebral degeneration syndromes, and on future research are all reviewed.

The clinical diagnosis of early-onset dementias: diagnostic accuracy and clinicopathological relationships

Accuracy of clinical diagnosis of dementia is increasingly important for therapeutic and scientific investigations. In this study, we examine diagnostic accuracy in a consecutive series of 228 patients referred to a specialist early-onset dementia clinic, whose brains were subsequently examined at post-mortem. Diagnosis was based on structured history, neurological examination and neuropsychological assessment, with emphasis on qualitative as well as quantitative aspects of performance. Neuroimaging provided support for but did not alter the clinical diagnosis. We set out the principles that guided diagnosis: (i) time course of illness; (ii) weighting of physical, behavioural and cognitive symptoms and signs; (iii) 'anterior' versus 'posterior' hemisphere character of cognitive change; and (iv) specificity of deficit, paying attention to the differentiation between syndromes of frontotemporal lobar degeneration and focal forms of Alzheimer's disease. Forty-two per cent of the patients had clinical diagnoses of one of the syndromes of frontotemporal lobar degeneration, the high proportion reflecting the research interests of the group. Forty-six per cent were diagnosed with Alzheimer's disease and the remaining patients, dementia with Lewy bodies, Creutzfeldt-Jakob disease, vascular or unclassified dementia. Frontotemporal lobar degeneration was identified with 100% sensitivity and 97% specificity and Alzheimer's disease with 97% sensitivity and 100% specificity. Patients with other pathologies were accurately identified on clinical grounds. Examination of subsyndromes of frontotemporal lobar degeneration showed a relatively predictable relationship between clinical diagnosis and pathological subtype. Whereas the behavioural disorder of frontotemporal dementia was associated with tau, transactive response DNA binding protein 43 and fused-in-sarcoma pathology, cases of frontotemporal dementia with motoneuron disease, semantic dementia and, with one exception, progressive non-fluent aphasia were associated with transactive response DNA binding protein 43 pathology, distinguished by ubiquitin subtyping (types B, C and A, respectively). Clinical diagnoses of progressive apraxia, corticobasal degeneration and progressive supranuclear palsy were, with one exception, associated with Pick, corticobasal and progressive supranuclear palsy subtypes of tau pathology, respectively. Unanticipated findings included Alzheimer pathology in two patients presenting with the behavioural syndrome of frontotemporal dementia and corticobasal pathology in four others with clinical frontotemporal dementia. Notwithstanding such anomalies, which serve as a reminder that there is not an absolute concordance between clinical phenotype and underlying pathology, the findings show that dementias can be distinguished in life with a high level of accuracy. Moreover, careful clinical phenotyping allows prediction of histopathological subtype of frontotemporal lobar degeneration. The principles guiding diagnosis provide the foundation for future prospective studies.

Neuropathology of frontotemporal lobar degeneration-tau (FTLD-tau)

A clinically and pathologically heterogeneous type of frontotemporal lobar degeneration has abnormal tau pathology in neurons and glia (FTLD-tau). Familial FTLD-tau is usually due to mutations in the tau gene (MAPT). Even FTLD-tau determined by MAPT mutations has clinical and pathologic heterogeneity. Tauopathies are subclassified according to the predominant species of tau that accumulates, with respect to alternative splicing of MAPT, with tau proteins containing three (3R) or four repeats (4R) of ~32 amino acids in the microtubule binding domain. In Pick's disease (PiD), 3R tau predominates, whereas 4R tau is characteristic of corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP). Depending upon the specific mutation in MAPT, familial FTLD-tau can have 3R, 4R or a combination of 3R and 4R tau. PiD is the least common FTLD-tau characterized by neuronal Pick bodies in a stereotypic neuroanatomical distribution. PSP and CBD are more common than PiD and have extensive clinical and pathologic overlap, with no distinctive clinical syndrome or biomarker that permits their differentiation. Diagnosis rests upon postmortem examination of the brain and demonstration of globose tangles, oligodendroglial coiled bodies and tufted astrocytes in PSP or threads, pretangles and astrocytic plaques in CBD. The anatomical distribution of tau pathology determines the clinical presentation of PSP and CBD, as well as PiD. The basis for this selective cortical vulnerability in FTLD-tau is unknown.

Corticobasal degeneration: a pathologically distinct 4R tauopathy

Corticobasal degeneration (CBD) is a rare, progressive neurodegenerative disorder with onset in the 5(th) to 7(th) decade of life. It is associated with heterogeneous motor, sensory, behavioral and cognitive symptoms, which make its diagnosis difficult in a living patient. The etiology of CBD is unknown; however, neuropathological and genetic evidence supports a pathogenetic role for microtubule-associated protein tau. CBD pathology is characterized by circumscribed cortical atrophy with spongiosis and ballooned neurons; the distribution of these changes dictates the patient's clinical presentation. Neuronal and glial tau pathology is extensive in gray and white matter of the cortex, basal ganglia, diencephalon and rostral brainstem. Abnormal tau accumulation within astrocytes forms pathognomonic astrocytic plaques. The classic clinical presentation, termed corticobasal syndrome (CBS), comprises asymmetric progressive rigidity and apraxia with limb dystonia and myoclonus. CBS also occurs in conjunction with other diseases, including Alzheimer disease and progressive supranuclear palsy. Moreover, the pathology of CBD is associated with clinical presentations other than CBS, including Richardson syndrome, behavioral variant frontotemporal dementia, primary progressive aphasia and posterior cortical syndrome. Progress in biomarker development to differentiate CBD from other disorders has been slow, but is essential in improving diagnosis and in development of disease-modifying therapies.

[Differential diagnosis of parkinsonian syndromes using MRI]

The differential diagnosis of parkinsonian syndromes is considered one of the most challenging in clinical neurology. Despite published consensus operational criteria for the diagnosis of Parkinson's disease (PD) and the various atypical parkinsonian disorders (APD), such as progressive supranuclear palsy (PSP), multiple system atrophy (MSA) and corticobasal degeneration (CBD), the clinical separation of APDs from PD carries a high rate of misdiagnosis. However, the early differentiation between APD and PD, each characterized by a very different natural history, is crucial for determining the prognosis and choosing a treatment strategy. Despite limitations the various modern magnetic resonance imaging (MRI) techniques have undoubtedly added to the differential diagnosis of neurodegenerative parkinsonism. In clinical practice conventional MRI with visual assessment of T2 and T1-weighted imaging is a well established method for the exclusion of symptomatic parkinsonism due to other pathologies and may also point to the diagnosis of APD. Furthermore, advances in MRI techniques, such as diffusion-weighted imaging (DWI), have enabled abnormalities in the basal ganglia and infratentorial brain structures in APD to be quantitatively illustrated.

Imaging correlates of pathology in corticobasal syndrome

BACKGROUND

Corticobasal syndrome (CBS) can be associated with different underlying pathologies that are difficult to predict based on clinical presentation. The aim of this study was to determine whether patterns of atrophy on imaging could be useful to help predict underlying pathology in CBS.

METHODS

This was a case-control study of 24 patients with CBS who had undergone MRI during life and came to autopsy. Pathologic diagnoses included frontotemporal lobar degeneration (FTLD) with TDP-43 immunoreactivity in 5 (CBS-TDP), Alzheimer disease (AD) in 6 (CBS-AD), corticobasal degeneration in 7 (CBS-CBD), and progressive supranuclear palsy in 6 (CBS-PSP). Voxel-based morphometry and atlas-based parcellation were used to assess atrophy across the CBS groups and compared to 24 age- and gender-matched controls.

RESULTS

All CBS pathologic groups showed gray matter loss in premotor cortices, supplemental motor area, and insula on imaging. However, CBS-TDP and CBS-AD showed more widespread patterns of loss, with frontotemporal loss observed in CBS-TDP and temporoparietal loss observed in CBS-AD. CBS-TDP showed significantly greater loss in prefrontal cortex than the other groups, whereas CBS-AD showed significantly greater loss in parietal lobe than the other groups. The focus of loss was similar in CBS-CBD and CBS-PSP, although more severe in CBS-CBD.

CONCLUSIONS

Imaging patterns of atrophy in CBS vary according to pathologic diagnosis. Widespread atrophy points toward a pathologic diagnosis of FTLD-TDP or AD, with frontotemporal loss suggesting FTLD-TDP and temporoparietal loss suggesting AD. On the contrary, more focal atrophy predominantly involving the premotor and supplemental motor area suggests CBD or PSP pathology.