Delineating the sites and progression of in vivo atrophy in multiple system atrophy using fluid-registered MRI

Imaging markers of disease progression in multiple system atrophy

Different neuroimaging modalities hold potential as surrogate markers of underlying neurodegeneration in multiple system atrophy (MSA) and may reflect cell loss, altered glucose metabolism, microglial proliferation, astroglial activation, and nigrostriatal denervation. Multiple studies have demonstrated that serial structural and functional imaging studies are capable of demonstrating neurodegeneration in MSA patients quantitatively, which allows sample size estimates based on rates of progression of these neuroimaging markers. This review summarizes recent research findings as a tool to assess longitudinal changes of serial neuroimaging-derived parameters in MSA.

An update on advances in magnetic resonance imaging of multiple system atrophy

In this review, we describe how different neuroimaging tools have been used to identify novel MSA biomarkers, highlighting their advantages and limitations. First, we describe the main structural MRI changes frequently associated with MSA including the 'hot cross-bun' and 'putaminal rim' signs as well as putaminal, pontine, and middle cerebellar peduncle (MCP) atrophy. We discuss the sensitivity and specificity of different supra- and infratentorial changes in differentiating MSA from other disorders, highlighting those that can improve diagnostic accuracy, including the MCP width and MCP/superior cerebellar peduncle (SCP) ratio on T1-weighted imaging, raised putaminal diffusivity on diffusion-weighted imaging, and increased T2* signal in the putamen, striatum, and substantia nigra on susceptibility-weighted imaging. Second, we focus on recent advances in structural and functional MRI techniques including diffusion tensor imaging (DTI), resting-state functional MRI (fMRI), and arterial spin labelling (ASL) imaging. Finally, we discuss new approaches for MSA research such as multimodal neuroimaging strategies and how such markers may be applied in clinical trials to provide crucial data for accurately selecting patients and to act as secondary outcome measures.

A novel tract imaging technique of the brainstem using phase difference enhanced imaging: normal anatomy and initial experience in multiple system atrophy

OBJECTIVES

To develop a new tract imaging technique for visualising small fibre tracts of the brainstem and for detecting the abnormalities in multiple system atrophy of the cerebellar type (MSA-C) using a phase difference enhanced (PADRE) imaging technique, in which the phase difference between the target and surrounding tissue is selectively enhanced.

METHODS

Two neuroradiologists compared the high-spatial-resolution PADRE imaging, which was acquired from six healthy volunteers, three patients with MSA-C, and 7 patients with other types of neurodegenerative diseases involving the brainstem or cerebellum.

RESULTS

Various fine fibre tracts in the brainstem, the superior and inferior cerebellar peduncles, medial lemniscus, spinothalamic tract, medial longitudinal fasciculus, central tegmental tract, corticospinal tract and transverse pontine fibres, were identified on PADRE imaging. PADRE imaging from MSA-C demonstrated the disappearance of transverse pontine fibres and significant atrophy of the inferior cerebellar peduncles, while the superior cerebellar peduncles were intact. PADRE imaging also demonstrated that the transverse pontine fibres and inferior cerebellar peduncle were not involved in the other neurodegenerative diseases.

CONCLUSION

PADRE imaging can offer a new form of tract imaging of the brainstem and may have the potential to reinforce the clinical utility of MRI in differentiating MSA from other conditions.

Assessing disease progression with MRI in atypical parkinsonian disorders

During the last decade, novel MR techniques have become available to support the early differential diagnosis of Parkinsonism and also to generate MR surrogate markers of disease progression. The article reviews the current state of the art focusing on three atypical parkinsonian disorders: multiple system atrophy (MSA), progressive supranuclear palsy (PSP), and dementia with Lewy bodies (DLB).

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.

Visualization and quantification of disease progression in multiple system atrophy

To visualize and quantify disease progression in multiple system atrophy (MSA) from cerebellar type (MSA-C), we combined two magnetic resonance imaging (MRI) techniques, voxel-based morphometry (VBM) and 3D-based volumetry. Patients suffering from MSA-C (n = 14) were imaged twice with an interval of 2.0 +/- 0.2 years. We first applied VBM to map brain morphology changes between MSA patients and controls and to identify brain areas that showed a significant amount of atrophy. Using 3D-based volumetry, we confirmed that in MSA-C patients, the brainstem including medulla and pons, vermis and cerebellar hemispheres, caudate nucleus and putamen showed significant atrophy compared with controls. Next, we used 3D-based volumetry to analyze the atrophy rates. Atrophy rates in patients with MSA were significantly different from controls for putamen (-11.4% +/- 2.6%/year), vermis (-12.3% +/- 2.9%/year), and cerebellar hemispheres (-6.6% +/- 1.1%/year). The results show that 3D-based MRI volumetry is a tool that allows the disease progression of MSA to be followed over a time period of 2 years and suggest that it may serve as a surrogate marker in clinical trials to measure disease progression.

The “Cross” Signs in Patients With Multiple System Atrophy: A Quantitative Study

Patients with multiple system atrophy (MSA) may show the "cross" sign in the pontine base that has been considered as an expression of the degeneration of pontine neurons and transverse pontocerebellar fibers. However, correlations between pontine base atrophy and existence of "cross" sign have not been fully investigated. The authors studied 68 patients with MSA (47 MSA-C [predominantly cerebellar ataxia], 21 MSA-P [predominantly parkinsonism], mean [+/-SD ] 58.7 +/- 10.9 years). T1-weighted (T1W) sagittal and axial images and T2-weighted (T2W) axial images were obtained for all patients and controls. To measure the areas of pontine basis and cerebellar vermis, the authors used midsagittal T1W images and analyzed a bit map transformed on a computer. They classified atrophy in the pontine base into 3 grades. There is significant correlation between atrophies of pontine base and existence of the cross sign. All patients with a smaller area of pontine base 2 standard deviations below those of normal controls had the cross sign. This supports that existence of the cross sign depends only on the extent of pontine base atrophies.

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.

Anisotropic multi-scale fluid registration: evaluation in magnetic resonance breast imaging

Registration using models of compressible viscous fluids has not found the general application of some other techniques (e.g., free-form-deformation (FFD)) despite its ability to model large diffeomorphic deformations. We report on a multi-resolution fluid registration algorithm which improves on previous work by (a) directly solving the Navier-Stokes equation at the resolution of the images, (b) accommodating image sampling anisotropy using semi-coarsening and implicit smoothing in a full multi-grid (FMG) solver and (c) exploiting the inherent multi-resolution nature of FMG to implement a multi-scale approach. Evaluation is on five magnetic resonance (MR) breast images subject to six biomechanical deformation fields over 11 multi-resolution schemes. Quantitative assessment is by tissue overlaps and target registration errors and by registering using the known correspondences rather than image features to validate the fluid model. Context is given by comparison with a validated FFD algorithm and by application to images of volunteers subjected to large applied deformation. The results show that fluid registration of 3D breast MR images to sub-voxel accuracy is possible in minutes on a 1.6 GHz Linux-based Athlon processor with coarse solutions obtainable in a few tens of seconds. Accuracy and computation time are comparable to FFD techniques validated for this application.

Mapping the onset and progression of atrophy in familial frontotemporal lobar degeneration

BACKGROUND

Frontotemporal lobar degeneration (FTLD) may be inherited as an autosomal dominant disease. Studying patients "at risk" for developing FTLD can provide insights into the earliest onset and evolution of the disease.

METHOD

We carried out approximately annual clinical, MRI, and neuropsychological assessments on an asymptomatic 51 year old "at risk" family member from a family with FTLD associated with ubiquitin-positive and tau-negative inclusion bodies. We used non-linear (fluid) registration of serial MRI to determine areas undergoing significant regional atrophy at different stages of the disease.

RESULTS

Over the first 26 months of the study, the patient remained asymptomatic, but subsequently developed progressive speech production difficulties, and latterly severe orofacial dyspraxia, dyscalculia, frontal executive impairment, and limb dyspraxia. Regional atrophy was present prior to the onset of symptoms, and was initially centred on the left dorsolateral prefrontal cortex and the left middle frontal gyrus. Latterly, there was increasing asymmetric left frontal and parietal atrophy. Imaging revealed excess and increasing global atrophy throughout the study. Neuropsychological evaluation revealed mild intellectual impairment prior to the onset of these clinical symptoms; frontal executive and left parietal impairment subsequently emerged, culminating in widespread cognitive impairment. Fluid registered MRI allowed the emerging atrophy patterns to be delineated.

CONCLUSION

We have demonstrated the onset and progressive pattern of in vivo atrophy in familial FTLD using fluid registered MRI and correlated this with the clinical features. Fluid registered MRI may be a useful technique in assessing patterns of focal atrophy in vivo and demonstrating the progression of degenerative diseases.

How to diagnose multiple system atrophy

The diagnosis of multiple system atrophy (MSA) in life remains entirely clinical. Consensus diagnostic criteria have been developed, but their use does not particularly render a diagnosis of MSA more accurate than are clinicians' diagnoses. Some patients may not fulfill the stipulated core diagnostic criteria, yet display many so-called red flags pointing toward MSA. The additional usefulness of these red flags and of a variety of investigations currently is being investigated, with a view to some of them being incorporated in future sets of diagnostic criteria.

Young onset dementia

Young onset dementia is a challenging clinical problem with potentially devastating medical and social consequences. The differential diagnosis is wide, and includes a number of rare sporadic and hereditary diseases. However, accurate diagnosis is often possible, and all patients should be thoroughly investigated to identify treatable processes. This review presents an approach to the diagnosis, investigation, and management of patients with young onset dementia, with particular reference to common and treatable causes.