Pathological substrate for regional distribution of increased atrophy rates in progressive supranuclear palsy

Somatosensory area 3b is selectively unaffected in corticobasal syndrome: combining MRI and histology

An increasing number of neuroimaging studies addressing patients with corticobasal syndrome use macroscopic definitions of brain regions. As a closer link to functionally relevant units, we aimed at identifying magnetic resonance-based atrophy patterns in regions defined by probability maps of cortical microstructure. For this purpose, three analyses were conducted: (1) Whole-brain cortical thickness was compared between 36 patients with corticobasal syndrome and 24 controls. A pattern of pericentral atrophy was found, covering primary motor area 4, premotor area 6, and primary somatosensory areas 1, 2, and 3a. Within the central region, only area 3b was without atrophy. (2) In 18 patients, longitudinal measures with follow-ups of up to 59 months (mean 21.3 ± 15.4) were analyzed. Areas 1, 2, and 6 showed significantly faster atrophy rates than primary somatosensory area 3b. (3) In an individual autopsy case, longitudinal in vivo morphometry and postmortem pathohistology were conducted. The rate of magnetic resonance-based atrophy was significantly correlated with tufted-astrocyte load in those cytoarchitectonically defined regions also seen in the group study, with area 3b being selectively unaffected.

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.

Social cognitive deficits and their neural correlates in progressive supranuclear palsy

Although progressive supranuclear palsy is defined by its akinetic rigidity, vertical supranuclear gaze palsy and falls, cognitive impairments are an important determinant of patients’ and carers’ quality of life. Here, we investigate whether there is a broad deficit of modality-independent social cognition in progressive supranuclear palsy and explore the neural correlates for these. We recruited 23 patients with progressive supranuclear palsy (using clinical diagnostic criteria, nine with subsequent pathological confirmation) and 22 age- and education-matched controls. Participants performed an auditory (voice) emotion recognition test, and a visual and auditory theory of mind test. Twenty-two patients and 20 controls underwent structural magnetic resonance imaging to analyse neural correlates of social cognition deficits using voxel-based morphometry. Patients were impaired on the voice emotion recognition and theory of mind tests but not auditory and visual control conditions. Grey matter atrophy in patients correlated with both voice emotion recognition and theory of mind deficits in the right inferior frontal gyrus, a region associated with prosodic auditory emotion recognition. Theory of mind deficits also correlated with atrophy of the anterior rostral medial frontal cortex, a region associated with theory of mind in health. We conclude that patients with progressive supranuclear palsy have a multimodal deficit in social cognition. This deficit is due, in part, to progressive atrophy in a network of frontal cortical regions linked to the integration of socially relevant stimuli and interpretation of their social meaning. This impairment of social cognition is important to consider for those managing and caring for patients with progressive supranuclear palsy.

Cortical atrophy differentiates Richardson's syndrome from the parkinsonian form of progressive supranuclear palsy

To determine whether brain atrophy differs between the two subtypes of progressive supranuclear palsy (PSP), Richardson's syndrome (PSP-RS), and PSP parkinsonism (PSP-P), and whether such atrophy directly relates to clinical deficits and the severity of tau deposition. We compared 24 pathologically confirmed PSP cases (17 PSP-RS and 7 PSP-P) with 22 controls from a Sydney brain donor program. Volume loss was analyzed in 29 anatomically discrete brain regions using a validated point-counting technique, and tau-immunoreactive neurons, astrocytes and oligodendrocytes/threads semiquantified. Correlations between the two pathological measures and the presence or absence of cardinal PSP symptoms were investigated. Cortical atrophy was more severe in PSP-RS than PSP-P and affected more frontal lobe regions (frontal pole, inferior frontal gyrus). The supramarginal gyrus was atrophic in both subtypes. Additionally, atrophy of the internal globus pallidus, amygdala, and thalamus was more severe in PSP-RS. As expected, more severe frontal lobe tau pathology differentiated PSP-RS from PSP-P. No correlations were found between the degree of atrophy and severity of tau pathology in any region assessed, or between the severity of atrophy or tau pathology and the presence or absence of cardinal PSP symptoms. Our study shows that thalamocortical atrophy is a defining feature of PSP-RS, but this atrophy does not correlate with the presence of any specific cardinal clinical feature. Interestingly, there is a disassociation between tau pathology and atrophy in the brain regions affected in PSP-RS that requires further investigation.

Serial volumetric MRI in Parkinsonian disorders

Tracking progression in neurodegenerative diseases is hampered by the limitations of the clinical rating scales, which are seldom linear, suffer from floor and ceiling effects, lack the ability to distinguish symptomatic change from disease modification, and are limited by imperfect intra- and inter-rater reliability. The promise of an era of neuroprotective therapies renders urgent the search for reliable measures of progression. Biomarkers have the potential to enhance several aspects of both therapeutic trials and clinical practice. MRI-based measures of cerebral volume can provide a surrogate for neuronal loss and several techniques have been applied to elucidate disease processes, aid diagnosis, and enable monitoring of progression in a variety of Parkinsonian disorders, including Parkinson's disease, dementia with Lewy bodies, multiple system atrophy, progressive supranuclear palsy and Huntington's disease. We review the approaches to, and findings revealed by, serial volumetric MRI in these disorders.

MRI derived brain atrophy in PSP and MSA-P

Progressive supranuclear palsy (PSP) and multiple system (MSA) atrophy are associated with progressive brain atrophy. Serial MRI can be applied in order to measure this change in brain volume and to calculate atrophy rates. We evaluated MRI derived whole brain and regional atrophy rates as potential markers of progression in PSP and the Parkinsonian variant of multiple system atrophy (MSA-P). 17 patients with PSP, 9 with MSA-P and 18 healthy controls underwent two MRI brain scans. MRI scans were registered, and brain and regional atrophy rates (midbrain, pons, cerebellum, third and lateral ventricles) measured. Sample sizes required to detect the effect of a proposed disease-modifying treatment were estimated. The effect of scan interval on the variance of the atrophy rates and sample size was assessed. Based on the calculated yearly rates of atrophy, for a drug effect equivalent to a 30% reduction in atrophy, fewer PSP subjects are required in each treatment arm when using midbrain rather than whole brain atrophy rates (183 cf. 499). Fewer MSA-P subjects are required, using pontine/cerebellar, rather than whole brain atrophy rates (164/129 cf. 794). A reduction in the variance of measured atrophy rates was observed with a longer scan interval. Regional rather than whole brain atrophy rates calculated from volumetric serial MRI brain scans in PSP and MSA-P provide a more practical and powerful means of monitoring disease progression in clinical trials.

Rates of cerebral atrophy differ in different degenerative pathologies

Neurodegenerative disorders are pathologically characterized by the deposition of abnormal proteins in the brain. It is likely that future treatment trials will target the underlying protein biochemistry and it is therefore increasingly important to be able to distinguish between different pathologies during life. The aim of this study was to determine whether rates of brain atrophy differ in neurodegenerative dementias that vary by pathological diagnoses and characteristic protein biochemistry. Fifty-six autopsied subjects were identified with a clinical diagnosis of dementia and two serial head MRI. Subjects were subdivided based on pathological diagnoses into Alzheimer's disease, dementia with Lewy bodies (DLB), mixed Alzheimer's disease/DLB, frontotemporal lobar degeneration with ubiquitin-only-immunoreactive changes (FTLD-U), corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP). Twenty-five controls were matched by age, gender and scan interval, to the study cohort. The boundary-shift integral was used to calculate change over time in whole brain (BBSI) and ventricular volume (VBSI). All BSI results were annualized by adjusting for scan interval. The rates of whole brain atrophy and ventricular expansion were significantly increased compared to controls in the Alzheimer's disease, mixed Alzheimer's disease/DLB, FTLD-U, CBD and PSP groups. However, atrophy rates in the DLB group were not significantly different from control rates of atrophy. The largest rates of atrophy were observed in the CBD group which had a BBSI of 2.3% and VBSI of 16.2%. The CBD group had significantly greater rates of BBSI and VBSI than the DLB, mixed Alzheimer's disease/DLB, Alzheimer's disease and PSP groups, with a similar trend observed when compared to the FTLD-U group. The FTLD-U group showed the next largest rates with a BBSI of 1.7% and VBSI of 9.6% which were both significantly greater than the DLB group. There was no significant difference in the rates of atrophy between the Alzheimer's disease, mixed Alzheimer's disease/DLB and PSP groups, which all showed similar rates of atrophy; BBSI of 1.1, 1.3 and 1.0% and VBSI of 8.3, 7.2 and 10.9%, respectively. Rates of atrophy therefore differ according to the pathological diagnoses and underlying protein biochemistry. While rates are unlikely to be useful in differentiating Alzheimer's disease from cases with mixed Alzheimer's disease/DLB pathology, they demonstrate important pathophysiological differences between DLB and those with mixed Alzheimer's disease/DLB and Alzheimer's disease pathology, and between those with CBD and PSP pathology.

The Role of Conventional MR and CT in the Work-Up of Dementia Patients

Dementia is a clinical syndrome with many causes. There often is overlap in the clinical manifestations of various forms of dementia, making them difficult to categorize. Neuroimaging can play an important role in distinguishing one form of dementia from another. Advanced imaging techniques continue to provide greater insight into the underlying pathologic processes in patients who have dementia. Conventional MRI and CT, however, still can contribute useful information when interpreting radiologists are familiar with the patterns of volume loss and signal or density changes that are characteristic of various forms of dementia.

Longitudinal MRI in progressive supranuclear palsy and multiple system atrophy: rates and regions of atrophy

The rate of brain atrophy and its relationship to clinical disease progression in progressive supranuclear palsy (PSP) and multiple system atrophy (MSA) is not clear. Twenty-four patients with PSP, 11 with MSA-P (Parkinsonian variant), 12 with Parkinson's disease, and 18 healthy control subjects were recruited for serial MRI scans, clinical assessments and formal neuropsychological evaluations in order to measure brain atrophy during life and its association with disease progression in PSP and MSA-P. Serial scans were registered and rates of whole brain atrophy calculated from the brain-boundary shift integral. Regional rates of atrophy were calculated in the brainstem (midbrain and pons), the cerebellum, the lateral and third ventricles as well as frontal and posterior inferior brain regions, by locally registering to a region of interest in order to derive a local boundary shift integral (BSI). 82% of recruited subjects completed serial MRI scans (17 PSP, 9 MSA-P, 9 Parkinson's disease patients and 18 healthy controls). Mean (SD) annualized rates of whole-brain atrophy were greatest in PSP: 1.2% (1.0%), three times that in controls. Mean (SD) midbrain atrophy rates in PSP, 2.2% (1.5%), were seven times greater than in healthy controls. In MSA-P, atrophy rates were greatest in the pons: 4.5% (3.2%), over 20 times that in controls and three times the rate of pontine atrophy in PSP. Atrophy rates in Parkinson's disease were not significantly different from control rates of atrophy. Variability in the atrophy rates was lower when calculated using the BSI rather than manual measurements. Worsening motor deficit was associated with midbrain atrophy in PSP, and ponto-cerebellar atrophy in MSA-P. Worsening executive dysfunction was associated with increased rates of frontal atrophy in PSP. Cerebellar atrophy rates were better discriminators of MSA-P than cross-sectional volumes. We confirm that serial MRI can be applied to measure whole brain and regional atrophy rates in PSP and MSA-P. Regional rather than whole-brain atrophy rates better discriminate PSP and MSA-P from healthy controls. Clinico-radiological associations suggest these regional atrophy rates have potential as markers of disease progression in trials of novel therapies.

The role of conventional MR and CT in the work-up of dementia patients

Neuroimaging can play an important role in distinguishing one form of dementia from another. Advanced imaging techniques continue to provide greater insight into the underlying pathologic processes in patients who have dementia. Conventional MRI and CT, however, can contribute useful information when interpreting radiologists are familiar with the patterns of volume loss and signal or density changes that are characteristic of various forms of dementia.

Pathological aging of the brain: an overview

The number of elderly people is increasing rapidly and, therefore, an increase in neurodegenerative and cerebrovascular disorders causing dementia is expected. Alzheimer disease (AD) is the most common cause of dementia. Vascular dementia, dementia with Lewy bodies, and frontotemporal dementia are the most frequent causes after AD, but a large proportion of patients have a combination of degenerative and vascular brain pathology. Characteristic magnetic resonance (MR) imaging findings can contribute to the identification of different diseases causing dementia. The MR imaging protocol should include axial T2-weighted images (T2-WI), axial fluid-attenuated inversion recovery (FLAIR) or proton density-weighted images, and axial gradient-echo T2*-weighted images, for the detection of cerebrovascular pathology. Structural neuroimaging in dementia is focused on detection of brain atrophy, especially in the medial temporal lobe, for which coronal high resolution T1-weighted images perpendicular to the long axis of the temporal lobe are extremely important. Single photon emission computed tomography and positron emission tomography may have added value in the diagnosis of dementia and may become more important in the future, due to the development of radioligands for in vivo detection of AD pathology. New functional MR techniques and serial volumetric imaging studies to identify subtle brain abnormalities may also provide surrogate markers for pathologic processes that occur in diseases causing dementia and, in conjunction with clinical evaluation, may enable a more rigorous and early diagnosis, approaching the accuracy of neuropathology.