Translating pathology in multiple sclerosis: the combination of postmortem imaging, histopathology and clinical findings

Micro-diffusely abnormal white matter: An early multiple sclerosis lesion phase with intensified myelin blistering

OBJECTIVE

Multiple sclerosis (MS) is a chronic central nervous system disease whose white matter lesion origin remains debated. Recently, we reported subtle changes in the MS normal appearing white matter (NAWM), presenting with an increase in myelin blisters and myelin protein citrullination, which may recapitulate some of the prodromal degenerative processes involved in MS pathogenesis. Here, to clarify the relevance of these changes for subsequent MS myelin degeneration we explored their prevalence in WM regions characterized by subtly reduced myelination (dubbed as micro-diffusely abnormal white matter, mDAWM).

METHODS

We used an in-depth (immuno)histochemistry approach in 27 MS donors with histological presence of mDAWM and 5 controls. An antibody panel against degenerative markers was combined and the presence of myelin/axonal aberrations was analyzed and compared with the NAWM from the same cases/slices/regions.

RESULTS

mDAWM-defined areas exhibit ill-defined borders, no signs of Wallerian degeneration, and they associate with visible veins. Remarkably, such areas present with augmented myelin blister frequency, enhanced prevalence of polar myelin phospholipids, citrullination, and degradation of myelin basic protein (MBP) when compared with the NAWM. Furthermore, enhanced reactivity of microglia/macrophages against citrullinated MBP was also observed in this tissue.

INTERPRETATION

We report a new histologically defined early phase in MS lesion formation, namely mDAWM, which lacks signs of Wallerian pathology. These results support the prelesional nature of the mDAWM. We conceptualize that evolution to pathologically evident lesions comprises the previously documented imbalance of axo-myelinic units (myelin blistering) leading to their degeneration and immune system activation by released myelin components.

Measuring Pathology in Patients with Multiple Sclerosis Using Positron Emission Tomography

PURPOSE OF REVIEW

Multiple sclerosis is characterized by a diverse and complex pathology. Clinical relapses, the hallmark of the disease, are accompanied by focal white matter lesions with intense inflammatory and demyelinating activity. Prevention of these relapses has been the major focus of pharmaceutical development, and it is now possible to dramatically reduce this inflammatory activity. Unfortunately, disability accumulation persists for many people living with multiple sclerosis owing to ongoing damage within existing lesions, pathology outside of discrete lesions, and other yet unknown factors. Understanding this complex pathological cascade will be critical to stopping progressive multiple sclerosis. Positron emission tomography uses biochemically specific radioligands to quantitatively measure pathological processes with molecular specificity. This review examines recent advances in the understanding of multiple sclerosis facilitated by positron emission tomography and identifies future avenues to expand understanding and treatment options.

RECENT FINDINGS

An increasing number of radiotracers allow for the quantitative measurement of inflammatory abnormalities, de- and re-myelination, and metabolic disruption associated with multiple sclerosis. The studies have identified contributions of ongoing, smoldering inflammation to accumulating tissue injury and clinical worsening. Myelin studies have quantified the dynamics of myelin loss and recovery. Lastly, metabolic changes have been found to contribute to symptom worsening. The molecular specificity facilitated by positron emission tomography in people living with multiple sclerosis will critically inform efforts to modulate the pathology leading to progressive disability accumulation. Existing studies show the power of this approach applied to multiple sclerosis. This armamentarium of radioligands allows for new understanding of how the brain and spinal cord of people is impacted by multiple sclerosis.

A comparative assessment of myelin-sensitive measures in multiple sclerosis patients and healthy subjects

INTRODUCTION

Multiple Sclerosis (MS) is a common neurological disease primarily characterized by myelin damage in lesions and in normal - appearing white and gray matter (NAWM, NAGM). Several quantitative MRI (qMRI) methods are sensitive to myelin characteristics by measuring specific tissue biophysical properties. However, there are currently few studies assessing the relative reproducibility and sensitivity of qMRI measures to MS pathology in vivo in patients.

METHODS

We performed two studies. The first study assessed of the sensitivity of qMRI measures to MS pathology: in this work, we recruited 150 MS and 100 healthy subjects, who underwent brain MRI at 3 T including quantitative T1 mapping (qT1), quantitative susceptibility mapping (QSM), magnetization transfer saturation imaging (MTsat) and myelin water imaging for myelin water fraction (MWF). The sensitivity of qMRIs to MS focal pathology (MS lesions vs peri-plaque white/gray matter (PPWM/PPGM)) was studied lesion-wise; the sensitivity to diffuse normal appearing (NA) pathology was measured using voxel-wise threshold-free cluster enhancement (TFCE) in NAWM and vertex-wise inflated cortex analysis in NAGM. Furthermore, the sensitivity of qMRI to the identification of lesion tissue was investigated using a voxel-wise logistic regression analysis to distinguish MS lesion and PP voxels. The second study assessed the reproducibility of myelin-sensitive qMRI measures in a single scanner. To evaluate the intra-session and inter-session reproducibility of qMRI measures, we have investigated 10 healthy subjects, who underwent two brain 3 T MRIs within the same day (without repositioning), and one after 1-week interval. Five region of interest (ROIs) in white and deep grey matter areas were segmented, and inter- and intra- session reproducibility was studied using the intra-class correlation coefficient (ICC). Further, we also investigated the voxel-wise reproducibility of qMRI measures in NAWM and NAGM.

RESULTS

qT1 and QSM showed the highest sensitivity to distinguish MS focal WM and cortical pathology from peri-plaque WM (P < 0.0001), although QSM also showed the highest variance when applied to lesions. MWF and MTsat exhibited the highest sensitivity to NAWM pathology (P < 0.01). On the other hand, qT1 appeared to be the most sensitive measure to NAGM pathology (P < 0.01). All myelin-sensitive qMRI measures exhibited high inter/intra sessional ICCs in various WM and deep GM ROIs, in NAWM and in NAGM (ICC 0.82 ± 0.12).

CONCLUSION

This work shows that the applied qT1, MWF, MTsat and QSM are highly reproducible and exhibit differential sensitivity to focal and diffuse WM and GM pathology in MS patients.

Artificial double inversion recovery images can substitute conventionally acquired images: an MRI-histology study

Cortical multiple sclerosis lesions are disease-specific, yet inconspicuous on magnetic resonance images (MRI). Double inversion recovery (DIR) images are sensitive, but often unavailable in clinical routine and clinical trials. Artificially generated images can mitigate this issue, but lack histopathological validation. In this work, artificial DIR images were generated from postmortem 3D-T1 and proton-density (PD)/T2 or 3D-T1 and 3D fluid-inversion recovery (FLAIR) images, using a generative adversarial network. All sequences were scored for cortical lesions, blinded to histopathology. Subsequently, tissue samples were stained for proteolipid protein (myelin) and scored for cortical lesions type I-IV (leukocortical, intracortical, subpial and cortex-spanning, respectively). Histopathological scorings were then (unblinded) compared to MRI using linear mixed models. Images from 38 patients (26 female, mean age 64.3 ± 10.7) were included. A total of 142 cortical lesions were detected, predominantly subpial. Histopathology-blinded/unblinded sensitivity was 13.4/35.2% for artificial DIR generated from T1-PD/T2, 14.1/41.5% for artificial DIR from T1-FLAIR, 17.6/49.3% for conventional DIR and 10.6/34.5% for 3D-T1. When blinded to histopathology, there were no differences; with histopathological feedback at hand, conventional DIR and artificial DIR from T1-FLAIR outperformed the other sequences. Differences between histopathology-blinded/unblinded sensitivity could be minified through adjustment of the scoring criteria. In conclusion, artificial DIR images, particularly generated from T1-FLAIR could potentially substitute conventional DIR images when these are unavailable.

Myelin Quantification in White Matter Pathology of Progressive Multiple Sclerosis Post-Mortem Brain Samples: A New Approach for Quantifying Remyelination

Multiple sclerosis (MS) is a demyelinating and neurodegenerative disease of the central nervous system (CNS). Repair through remyelination can be extensive, but quantification of remyelination remains challenging. To date, no method for standardized digital quantification of remyelination of MS lesions exists. This methodological study aims to present and validate a novel standardized method for myelin quantification in progressive MS brains to study myelin content more precisely. Fifty-five MS lesions in 32 tissue blocks from 14 progressive MS cases and five tissue blocks from 5 non-neurological controls were sampled. MS lesions were selected by macroscopic investigation of WM by standard histopathological methods. Tissue sections were stained for myelin with luxol fast blue (LFB) and histological assessment of de- or remyelination was performed by light microscopy. The myelin quantity was estimated with a novel myelin quantification method (MQM) in ImageJ. Three independent raters applied the MQM and the inter-rater reliability was calculated. We extended the method to diffusely appearing white matter (DAWM) and encephalitis to test potential wider applicability of the method. Inter-rater agreement was excellent (ICC = 0.96) and there was a high reliability with a lower- and upper limit of agreement up to −5.93% to 18.43% variation in myelin quantity. This study builds on the established concepts of histopathological semi-quantitative assessment of myelin and adds a novel, reliable and accurate quantitative measurement tool for the assessment of myelination in human post-mortem samples.

Complement-associated loss of CA2 inhibitory synapses in the demyelinated hippocampus impairs memory

The complement system is implicated in synapse loss in the MS hippocampus, but the functional consequences of synapse loss remain poorly understood. Here, in post-mortem MS hippocampi with demyelination we find that deposits of the complement component C1q are enriched in the CA2 subfield, are linked to loss of inhibitory synapses and are significantly higher in MS patients with cognitive impairments compared to those with preserved cognitive functions. Using the cuprizone mouse model of demyelination, we corroborated that C1q deposits are highest within the demyelinated dorsal hippocampal CA2 pyramidal layer and co-localized with inhibitory synapses engulfed by microglia/macrophages. In agreement with the loss of inhibitory perisomatic synapses, we found that Schaffer collateral feedforward inhibition but not excitation was impaired in CA2 pyramidal neurons and accompanied by intrinsic changes and a reduced spike output. Finally, consistent with excitability deficits, we show that cuprizone-treated mice exhibit impaired encoding of social memories. Together, our findings identify CA2 as a critical circuit in demyelinated intrahippocampal lesions and memory dysfunctions in MS.

Quantitative magnetic resonance imaging towards clinical application in multiple sclerosis

Quantitative MRI provides biophysical measures of the microstructural integrity of the CNS, which can be compared across CNS regions, patients, and centres. In patients with multiple sclerosis, quantitative MRI techniques such as relaxometry, myelin imaging, magnetization transfer, diffusion MRI, quantitative susceptibility mapping, and perfusion MRI, complement conventional MRI techniques by providing insight into disease mechanisms. These include: (i) presence and extent of diffuse damage in CNS tissue outside lesions (normal-appearing tissue); (ii) heterogeneity of damage and repair in focal lesions; and (iii) specific damage to CNS tissue components. This review summarizes recent technical advances in quantitative MRI, existing pathological validation of quantitative MRI techniques, and emerging applications of quantitative MRI to patients with multiple sclerosis in both research and clinical settings. The current level of clinical maturity of each quantitative MRI technique, especially regarding its integration into clinical routine, is discussed. We aim to provide a better understanding of how quantitative MRI may help clinical practice by improving stratification of patients with multiple sclerosis, and assessment of disease progression, and evaluation of treatment response.

Whole brain 3D MR fingerprinting in multiple sclerosis: a pilot study

Background

MR fingerprinting (MRF) is a novel imaging method proposed for the diagnosis of Multiple Sclerosis (MS). This study aims to determine if MR Fingerprinting (MRF) relaxometry can differentiate frontal normal appearing white matter (F-NAWM) and splenium in patients diagnosed with MS as compared to controls and to characterize the relaxometry of demyelinating plaques relative to the time of diagnosis.

Methods

Three-dimensional (3D) MRF data were acquired on a 3.0T MRI system resulting in isotropic voxels (1 × 1 × 1 mm³) and a total acquisition time of 4 min 38 s. Data were collected on 18 subjects paired with 18 controls. Regions of interest were drawn over MRF-derived T₁ relaxometry maps encompassing selected MS lesions, F-NAWM and splenium. T₁ and T₂ relaxometry features from those segmented areas were used to classify MS lesions from F-NAWM and splenium with T-distributed stochastic neighbor embedding algorithms. Partial least squares discriminant analysis was performed to discriminate NAWM and Splenium in MS compared with controls.

Results

Mean out-of-fold machine learning prediction accuracy for discriminant results between MS patients and controls for F-NAWM was 65 % (p = 0.21) and approached 90 % (p < 0.01) for the splenium. There was significant positive correlation between time since diagnosis and MS lesions mean T2 (p = 0.015), minimum T1 (p = 0.03) and negative correlation with splenium uniformity (p = 0.04). Perfect discrimination (AUC = 1) was achieved between selected features from MS lesions and F-NAWM.

Conclusions

3D-MRF has the ability to differentiate between MS and controls based on relaxometry properties from the F-NAWM and splenium. Whole brain coverage allows the assessment of quantitative properties within lesions that provide chronological assessment of the time from MS diagnosis.

Axonal degeneration as substrate of fractional anisotropy abnormalities in multiple sclerosis cortex

Cortical microstructural abnormalities are associated with clinical and cognitive deterioration in multiple sclerosis. Using diffusion tensor MRI, a higher fractional anisotropy has been found in cortical lesions versus normal-appearing cortex in multiple sclerosis. The pathological substrates of this finding have yet to be definitively elucidated. By performing a combined post-mortem diffusion tensor MRI and histopathology study, we aimed to define the histopathological substrates of diffusivity abnormalities in multiple sclerosis cortex. Sixteen subjects with multiple sclerosis and 10 age- and sex-matched non-neurological control donors underwent post-mortem in situ at 3 T MRI, followed by brain dissection. One hundred and ten paraffin-embedded tissue blocks (54 from multiple sclerosis patients, 56 from non-neurological controls) were matched to the diffusion tensor sequence to obtain regional diffusivity measures. Using immunohistochemistry and silver staining, cortical density of myelin, microglia, astrocytes and axons, and density and volume of neurons and glial cells were evaluated. Correlates of diffusivity abnormalities with histological markers were assessed through linear mixed-effects models. Cortical lesions (77% subpial) were found in 27/54 (50%) multiple sclerosis cortical regions. Multiple sclerosis normal-appearing cortex had a significantly lower fractional anisotropy compared to cortex from non-neurological controls (P = 0.047), whereas fractional anisotropy in demyelinated cortex was significantly higher than in multiple sclerosis normal-appearing cortex (P = 0.012) but not different from non-neurological control cortex (P = 0.420). Compared to non-neurological control cortex, both multiple sclerosis normal-appearing and demyelinated cortices showed a lower density of axons perpendicular to the cortical surface (P = 0.012 for both) and of total axons (parallel and perpendicular to cortical surface) (P = 0.028 and 0.012). In multiple sclerosis, demyelinated cortex had a lower density of myelin (P = 0.004), parallel (P = 0.018) and total axons (P = 0.029) versus normal-appearing cortex. Regarding the pathological substrate, in non-neurological controls, cortical fractional anisotropy was positively associated with density of perpendicular, parallel, and total axons (P = 0.031 for all). In multiple sclerosis, normal-appearing cortex fractional anisotropy was positively associated with perpendicular and total axon density (P = 0.031 for both), while associations with myelin, glial and total cells and parallel axons did not survive multiple comparison correction. Demyelinated cortex fractional anisotropy was positively associated with density of neurons, and total cells and negatively with microglia density, without surviving multiple comparison correction. Our results suggest that a reduction of perpendicular axons in normal-appearing cortex and of both perpendicular and parallel axons in demyelinated cortex may underlie the substrate influencing cortical microstructural coherence and being responsible for the different patterns of fractional anisotropy changes occurring in multiple sclerosis cortex.

Cortical axonal loss is associated with both gray matter demyelination and white matter tract pathology in progressive multiple sclerosis: Evidence from a combined MRI-histopathology study

Background:

Neuroaxonal degeneration is one of the hallmarks of clinical deterioration in progressive multiple sclerosis (PMS).

Objective:

To elucidate the association between neuroaxonal degeneration and both local cortical and connected white matter (WM) tract pathology in PMS.

Methods:

Post-mortem in situ 3T magnetic resonance imaging (MRI) and cortical tissue blocks were collected from 16 PMS donors and 10 controls. Cortical neuroaxonal, myelin, and microglia densities were quantified histopathologically. From diffusion tensor MRI, fractional anisotropy, axial diffusivity (AD), radial diffusivity (RD), and mean diffusivity (MD) were quantified in normal-appearing white matter (NAWM) and white matter lesions (WML) of WM tracts connected to dissected cortical regions. Between-group differences and within-group associations were investigated through linear mixed models.

Results:

The PMS donors displayed significant axonal loss in both demyelinated and normal-appearing (NA) cortices (p < 0.001 and p = 0.02) compared with controls. In PMS, cortical axonal density was associated with WML MD and AD (p = 0.003; p = 0.02, respectively), and NAWM MD and AD (p = 0.04; p = 0.049, respectively). NAWM AD and WML AD explained 12.6% and 22.6%, respectively, of axonal density variance in NA cortex. Additional axonal loss in demyelinated cortex was associated with cortical demyelination severity (p = 0.002), explaining 34.4% of axonal loss variance.

Conclusion:

Reduced integrity of connected WM tracts and cortical demyelination both contribute to cortical axonal loss in PMS.

Post-Mortem MRI and Histopathology in Neurologic Disease: A Translational Approach

In this review, combined post-mortem brain magnetic resonance imaging (MRI) and histology studies are highlighted, illustrating the relevance of translational approaches to define novel MRI signatures of neuropathological lesions in neuroinflammatory and neurodegenerative disorders. Initial studies combining post-mortem MRI and histology have validated various MRI sequences, assessing their sensitivity and specificity as diagnostic biomarkers in neurologic disease. More recent studies have focused on defining new radiological (bio)markers and implementing them in the clinical (research) setting. By combining neurological and neuroanatomical expertise with radiological development and pathological validation, a cycle emerges that allows for the discovery of novel MRI biomarkers to be implemented in vivo. Examples of this cycle are presented for multiple sclerosis, Alzheimer's disease, Parkinson's disease, and traumatic brain injury. Some applications have been shown to be successful, while others require further validation. In conclusion, there is much to explore with post-mortem MRI and histology studies, which can eventually be of high relevance for clinical practice.

Structural network topology relates to tissue properties in multiple sclerosis

OBJECTIVE

Abnormalities in segregative and integrative properties of brain networks have been observed in multiple sclerosis (MS) and are related to clinical functioning. This study aims to investigate the micro-scale correlates of macro-scale network measures of segregation and integration in MS.

METHODS

Eight MS patients underwent post-mortem in situ whole-brain diffusion tensor (DT) imaging and subsequent brain dissection. Macro-scale structural network topology was derived from DT data using graph theory. Clustering coefficient and mean white matter (WM) fiber length were measures of nodal segregation and integration. Thirty-three tissue blocks were collected from five cortical brain regions. Using immunohistochemistry micro-scale tissue properties were evaluated, including, neuronal size, neuronal density, axonal density and total cell density. Nodal network properties and tissue properties were correlated.

RESULTS

A negative correlation between clustering coefficient and WM fiber length was found. Higher clustering coefficient was associated with smaller neuronal size and lower axonal density, and vice versa for fiber length. Higher whole-brain WM lesion load was associated with higher whole-brain clustering, shorter whole-brain fiber length, lower neuronal size and axonal density.

CONCLUSION

Structural network properties on MRI associate with neuronal size and axonal density, suggesting that macro-scale network measures may grasp cortical neuroaxonal degeneration in MS.

Visualization of the Breakdown of the Axonal Transport Machinery: a Comparative Ultrastructural and Immunohistochemical Approach

Axonal damage is a major factor contributing to disease progression in multiple sclerosis (MS) patients. On the histological level, acute axonal injury is most frequently analyzed by anti-amyloid precursor protein immunohistochemistry. To what extent this method truly detects axonal injury, and whether other proteins and organelles are as well subjected to axonal transport deficits in demyelinated tissues is not known. The aim of this study was to correlate ultrastructural morphology with the immunohistochemical appearance of acute axonal injury in a model of toxin-induced oligodendrocyte degeneration. C57BL/6J mice were intoxicated with 0.25% cuprizone to induce demyelination. The corpus callosum was investigated by serial block-face scanning electron microscopy (i.e., 3D EM), immunohistochemistry, and immunofluorescence microscopy. Brain tissues of progressive MS patients were included to test the relevance of our findings in mice for MS. Volumes of axonal swellings, determined by 3D EM, were comparable to volumes of axonal spheroids, determined by anti-APP immunofluorescence stains. Axonal swellings were present at myelinated and non-myelinated axonal internodes. Densities of amyloid precursor protein (APP)⁺ spheroids were highest during active demyelination. Besides APP, vesicular glutamate transporter 1 and mitochondrial proteins accumulated at sites of axonal spheroids. Such accumulations were found as well in lesions of progressive MS patients. In this correlative ultrastructural-immunohistochemical study, we provide strong evidence that breakdown of the axonal transport machinery results in focal accumulations of mitochondria and different synaptic proteins. We provide new marker proteins to visualize acute axonal injury, which helps to further understand the complex nature of axonal damage in progressive MS.

Lipid biochemical changes detected in normal appearing white matter of chronic multiple sclerosis by spectral coherent Raman imaging

Multiple sclerosis (MS) exhibits demyelination, inflammatory infiltration, axonal degeneration, and gliosis, affecting widespread regions of the central nervous system (CNS). While white matter MS lesions have been well characterized pathologically, evidence indicates that the MS brain may be globally altered, with subtle abnormalities found in grossly normal appearing white matter (NAWM). These subtle changes are difficult to investigate by common methods such as histochemical stains and conventional magnetic resonance imaging. Thus, the prototypical inflammatory lesion likely represents the most obvious manifestation of a more widespread involvement of the CNS. We describe the application of spectral coherent anti-Stokes Raman Scattering (sCARS) microscopy to study such changes in chronic MS tissue particularly in NAWM. Subtle changes in myelin lipid biochemical signatures and intra-molecular disorder of fatty acid acyl chains of otherwise normal-appearing myelin were detected, supporting the notion that the biochemical involvement of the MS brain is far more extensive than conventional methods would suggest.

The Role of T1-Weighted Derived Measures of Neurodegeneration for Assessing Disability Progression in Multiple Sclerosis

Introduction

Multiple sclerosis (MS) is characterised by the accumulation of permanent neurological disability secondary to irreversible tissue loss (neurodegeneration) in the brain and spinal cord. MRI measures derived from T1-weighted image analysis (i.e., black holes and atrophy) are correlated with pathological measures of irreversible tissue loss. Quantifying the degree of neurodegeneration in vivo using MRI may offer a surrogate marker with which to predict disability progression and the effect of treatment. This review evaluates the literature examining the association between MRI measures of neurodegeneration derived from T1-weighted images and disability in MS patients.

Methods

A systematic PubMed search was conducted in January 2017 to identify MRI studies in MS patients investigating the relationship between “black holes” and/or atrophy in the brain and spinal cord, and disability. Results were limited to human studies published in English in the previous 10 years.

Results

A large number of studies have evaluated the association between the previous MRI measures and disability. These vary considerably in terms of study design, duration of follow-up, size, and phenotype of the patient population. Most, although not all, have shown that there is a significant correlation between disability and black holes in the brain, as well as atrophy of the whole brain and grey matter. The results for brain white matter atrophy are less consistently positive, whereas studies evaluating spinal cord atrophy consistently showed a significant correlation with disability. Newer ways of measuring atrophy, thanks to the development of segmentation and voxel-wise methods, have allowed us to assess the involvement of strategic regions of the CNS (e.g., thalamus) and to map the regional distribution of damage. This has resulted in better correlations between MRI measures and disability and in the identification of the critical role played by some CNS structures for MS clinical manifestations.

Conclusion

The evaluation of MRI measures of atrophy as predictive markers of disability in MS is a highly active area of research. At present, measurement of atrophy remains within the realm of clinical studies, but its utility in clinical practice has been recognized and barriers to its implementation are starting to be addressed.

The clinico-radiological paradox of cognitive function and MRI burden of white matter lesions in people with multiple sclerosis: A systematic review and meta-analysis

BACKGROUND

Moderate correlation exists between the imaging quantification of brain white matter lesions and cognitive performance in people with multiple sclerosis (MS). This may reflect the greater importance of other features, including subvisible pathology, or methodological limitations of the primary literature.

OBJECTIVES

To summarise the cognitive clinico-radiological paradox and explore the potential methodological factors that could influence the assessment of this relationship.

METHODS

Systematic review and meta-analysis of primary research relating cognitive function to white matter lesion burden.

RESULTS

Fifty papers met eligibility criteria for review, and meta-analysis of overall results was possible in thirty-two (2050 participants). Aggregate correlation between cognition and T2 lesion burden was r = -0.30 (95% confidence interval: -0.34, -0.26). Wide methodological variability was seen, particularly related to key factors in the cognitive data capture and image analysis techniques.

CONCLUSIONS

Resolving the persistent clinico-radiological paradox will likely require simultaneous evaluation of multiple components of the complex pathology using optimum measurement techniques for both cognitive and MRI feature quantification. We recommend a consensus initiative to support common standards for image analysis in MS, enabling benchmarking while also supporting ongoing innovation.

Imaging Central Nervous System Demyelination and Remyelination by Positron-Emission Tomography

Positron Emission Tomography (PET), an imaging technique based on the injection of radiotracers directed against specific biological targets within brain tissues, within brain tissues, is a specific and sensitive technique which offers the unique opportunity to quantify myelin dynamics in the central nervous system. Several stilbene and benzothiazole derivatives have been repurposed to image myelin by PET. In demyelinating and dysmyelinating models, selected radiotracers were shown to reliably quantify demyelination and remyelination, allowing a translational approach in humans. A pilot study in subjects with active relapsing MS using PET and the most available benzothiazole derivative, [¹¹C]PIB, supported the hypothesis that this technique is able to quantify myelin content in multiple sclerosis (MS) lesions and to capture dynamic demyelination and remyelination over time. This study highlighted for the first time in vivo the prognostic value of individual profiles of remyelination on the disease course. In future, the clinical application of myelin PET will be pushed forward thanks to the availability of novel fluorinated tracers for myelin, together with the setting up of non invasive quantification procedures and the use of powerful PET-MR systems. This will enable to address in vivo critical unanswered questions about the pathogenesis of remyelination, and to measure the efficacy of emerging promyelinating drugs in early-phase therapeutic trials.

Postmortem validation of MRI cortical volume measurements in MS

Grey matter (GM) atrophy is a prominent aspect of multiple sclerosis pathology and an important outcome in studies. GM atrophy measurement requires accurate GM segmentation. Several methods are used in vivo for measuring GM volumes in MS, but assessing their validity in vivo remains challenging. In this postmortem study, we evaluated the correlation between postmortem MRI cortical volume or thickness and the cortical thickness measured on histological sections. Sixteen MS brains were scanned in situ using 3DT1-weighted MRI and these images were used to measure regional cortical volume using FSL-SIENAX, FreeSurfer, and SPM, and regional cortical thickness using FreeSurfer. Subsequently, cortical thickness was measured histologically in 5 systematically sampled cortical areas. Linear regression analyses were used to evaluate the relation between MRI regional cortical volume or thickness and histological cortical thickness to determine which postprocessing technique was most valid. After correction for multiple comparisons, we observed a significant correlation with the histological cortical thickness for FSL-SIENAX cortical volume with manual editing (std. β = 0.345, adjusted R(2)  = 0.105, P = 0.005), and FreeSurfer cortical volume with manual editing (std. β = 0.379, adjusted R(2)  = 0.129, P = 0.003). In addition, there was a significant correlation between FreeSurfer cortical thickness with manual editing and histological cortical thickness (std. β = 0.381, adjusted R(2)  = 0.130, P = 0.003). The results support the use of FSL-SIENAX and FreeSurfer in cases of severe MS pathology. Interestingly none of the methods were significant in automated mode, which supports the use of manual editing to improve the automated segmentation. Hum Brain Mapp 37:2223-2233, 2016. © 2016 Wiley Periodicals, Inc.

Can MS lesion stages be distinguished with MRI? A postmortem MRI and histopathology study

In multiple sclerosis (MS), a histopathological distinction is made between different stages of white matter (WM) lesions. These lesions are characterized as preactive, active, chronic active or chronic inactive, depending on the degree of microglia activation and degree of demyelination. The different lesions are not distinguishable on conventional magnetic resonance imaging (MRI) scans at standard clinical field strengths, but might be distinguished using more advanced, quantitative MRI methods, such as T1 relaxation time (T1-RT) mapping. To investigate this, postmortem brain material from 20 MS patients was investigated, using both T1-RT MRI at 1.5T and histopathology. The brain material contained a total of 9 preactive, 18 active, 30 chronic active and 14 chronic inactive lesions, as well as 38 areas of normal appearing WM (NAWM). Our results show that, at 1.5T, T1-RT qMRI can only distinguish between categories NAWM/preactive, active and chronic WM lesions. Advanced imaging at standard field strengths, such as conventional imaging measures, is therefore insufficient to differentiate the WM lesions in MS, and higher field strengths may be required to achieve better pathological differentiation of these lesions.

What drives MRI-measured cortical atrophy in multiple sclerosis?

BACKGROUND

Cortical atrophy, assessed with magnetic resonance imaging (MRI), is an important outcome measure in multiple sclerosis (MS) studies. However, the underlying histopathology of cortical volume measures is unknown.

OBJECTIVE

We investigated the histopathological substrate of MRI-measured cortical volume in MS using combined post-mortem imaging and histopathology.

METHODS

MS brain donors underwent post-mortem whole-brain in-situ MRI imaging. After MRI, tissue blocks were systematically sampled from the superior and inferior frontal gyrus, anterior cingulate gyrus, inferior parietal lobule, and superior temporal gyrus. Histopathological markers included neuronal, axonal, synapse, astrocyte, dendrite, myelin, and oligodendrocyte densities. Matched cortical volumes from the aforementioned anatomical regions were measured on the MRI, and used as outcomes in a nested prediction model.

RESULTS

Forty-five tissue blocks were sampled from 11 MS brain donors. Mean age at death was 68±12 years, post-mortem interval 4±1 hours, and disease duration 35±15 years. MRI-measured regional cortical volumes varied depending on anatomical region. Neuronal density, neuronal size, and axonal density were significant predictors of GM volume.

CONCLUSIONS

In patients with long-standing disease, neuronal and axonal pathology are the predominant pathological substrates of MRI-measured cortical volume in chronic MS.

Do low field magnetic resonance imaging abnormalities correlate with macroscopical and histological changes within the equine deep digital flexor tendon?

Correlating magnetic resonance (MR) imaging and histopathological findings is essential to validate low field MR imaging in lame horses. This study aimed to compare signal changes in the deep digital flexor tendon (DDFT) of the distal limb on low field MR imaging with macroscopical and histological findings. Cadaver limbs from lame horses with DDFT lesions were selected. The DDFT MR imaging findings and histopathological results were graded, and macroscopical abnormalities were recorded. There was a strong correlation between MR imaging and histopathology grades (rs = 0.76, p < 0.001) in the foot. There was moderate agreement (Kappa statistic 0.52) between the MR and histopathology grades; agreement was superior further proximal in the foot. The presence and severity of pathology in the DDFT are well represented by the presence and severity of MR imaging signal changes. The study supports the use of low field MR imaging for diagnosis of equine distal limb DDFT lesions.

Postmortem magnetic resonance imaging to guide the pathologic cut: individualized, 3-dimensionally printed cutting boxes for fixed brains

Interfacing magnetic resonance imaging (MRI) with pathology is critically important for understanding the pathologic basis of MRI signal changes in vivo and for clinicopathologic correlations. Postmortem MRI is an intermediate step in this process; unfortunately, however, relating the data to standard pathologic sections, which are relatively thick and often nonparallel, is both time-consuming and insufficiently accurate. The aim of this project was to develop technology to integrate postmortem, high-resolution, whole-brain MRI into the planning and execution of pathologic analysis through precise localization of the target and coordinates of cut. Compared with standard pathologic sectioning, the use of an individualized, 3-dimensionally printed cutting box-designed based on postmortem MRI of formalin-fixed whole brains-improved the speed, quality, and accuracy of radiologic-pathologic correlations and, specifically, the histopathologic localization of imaging findings. The technology described herein is easily implemented, applicable to any brain disorder, and potentially extendable to other organs. From the point of view of the pathologist, this technique can improve localization of small or subtle abnormalities, whereas from the point of view of the radiologist, it has the potential to improve understanding of MRI signal changes observed in diseases.

MRI evaluation of grey matter atrophy and disease course in multiple sclerosis: an overview of current knowledge

Multiple sclerosis (MS) is characterized by chronic inflammation of the central nervous system, and magnetic resonance imaging (MRI) is used as both a diagnostic tool and a parameter in the clinical evaluation. Multiple sclerosis was long regarded as a disease of the white matter (WM) in the brain, which can be visualized by the standard MRI used in daily practice. There is an increasing amount of evidence that grey matter (GM) pathology plays a role from the start of the MS disease and throughout the clinical course. Grey matter atrophy, both cortical and central, is present in the early course of MS and is also related above all to cognitive decline, but also to the development of physical disability as measured by EDSS. In this article, we give an overview of GM atrophy in MS evaluated by MRI and the relation to the clinical course in MS.

Ex vivo MR volumetry of human brain hemispheres

PURPOSE

The aims of this work were to (a) develop an approach for ex vivo MR volumetry of human brain hemispheres that does not contaminate the results of histopathological examination, (b) longitudinally assess regional brain volumes postmortem, and (c) investigate the relationship between MR volumetric measurements performed in vivo and ex vivo.

METHODS

An approach for ex vivo MR volumetry of human brain hemispheres was developed. Five hemispheres from elderly subjects were imaged ex vivo longitudinally. All datasets were segmented. The longitudinal behavior of volumes measured ex vivo was assessed. The relationship between in vivo and ex vivo volumetric measurements was investigated in seven elderly subjects imaged both antemortem and postmortem.

RESULTS

This approach for ex vivo MR volumetry did not contaminate the results of histopathological examination. For a period of 6 months postmortem, within-subject volume variation across time points was substantially smaller than intersubject volume variation. A close linear correspondence was detected between in vivo and ex vivo volumetric measurements.

CONCLUSION

Regional brain volumes measured with this approach for ex vivo MR volumetry remain relatively unchanged for a period of 6 months postmortem. Furthermore, the linear relationship between in vivo and ex vivo MR volumetric measurements suggests that this approach captures information linked to antemortem macrostructural brain characteristics.

Neuropathologic correlates of hippocampal atrophy in the elderly: a clinical, pathologic, postmortem MRI study

The volume of the hippocampus measured with structural magnetic resonance imaging (MRI) is increasingly used as a biomarker for Alzheimer's disease (AD). However, the neuropathologic basis of structural MRI changes in the hippocampus in the elderly has not been directly assessed. Postmortem MRI of the aging human brain, combined with histopathology, could be an important tool to address this issue. Therefore, this study combined postmortem MRI and histopathology in 100 elderly subjects from the Rush Memory and Aging Project and the Religious Orders Study. First, to validate the information contained in postmortem MRI data, we tested the hypothesis that postmortem hippocampal volume is smaller in subjects with clinically diagnosed Alzheimer's disease compared to subjects with mild or no cognitive impairment, as observed in antemortem imaging studies. Subsequently, the relations of postmortem hippocampal volume to AD pathology, Lewy bodies, amyloid angiopathy, gross infarcts, microscopic infarcts, and hippocampal sclerosis were examined. It was demonstrated that hippocampal volume was smaller in persons with a clinical diagnosis of AD compared to those with no cognitive impairment (P = 2.6×10⁻⁷) or mild cognitive impairment (P = 9.6×10⁻⁷). Additionally, hippocampal volume was related to multiple cognitive abilities assessed proximate to death, with its strongest association with episodic memory. Among all pathologies investigated, the most significant factors related to lower hippocampal volume were shown to be AD pathology (P = 0.0018) and hippocampal sclerosis (P = 4.2×10⁻⁷). Shape analysis allowed for visualization of the hippocampal regions most associated with volume loss for each of these two pathologies. Overall, this investigation confirmed the relation of hippocampal volume measured postmortem to clinical diagnosis of AD and measures of cognition, and concluded that both AD pathology and hippocampal sclerosis affect hippocampal volume in old age, though the impacts of each pathology on the shape of the hippocampus may differ.

The neuropathological basis of clinical progression in multiple sclerosis

Multiple sclerosis is the major inflammatory condition affecting the central nervous system (CNS) and is characterised by disseminated focal immune-mediated demyelination. Demyelination is accompanied by variable axonal damage and loss and reactive gliosis. It is this pathology that is thought to be responsible for the clinical relapses that often respond well to immunomodulatory therapy. However, the later secondary progressive stage of MS remains largely refractory to treatment and it is widely suggested that accumulating axon loss is responsible for clinical progression. Although initially thought to be a white matter (WM) disease, it is increasingly apparent that extensive pathology is also seen in the grey matter (GM) throughout the CNS. GM pathology is characterised by demyelination in the relative absence of an immune cell infiltrate. Neuronal loss is also seen both in the GM lesions and in unaffected areas of the GM. The slow progressive nature of this later stage combined with the presence of extensive grey matter pathology has led to the suggestion that neurodegeneration might play an increasing role with increasing disease duration. However, there is a paucity of studies that have correlated the pathological features with clinical milestones during secondary progressive MS. Here, we review the contributions that the various types of pathology are likely to make to the increasing neurological deficit in MS.

Advances in the application of MRI to amyotrophic lateral sclerosis

IMPORTANCE OF THE FIELD: With the emergence of therapeutic candidates for the incurable and rapidly progressive neurodegenerative condition of amyotrophic lateral sclerosis (ALS), it will be essential to develop easily obtainable biomarkers for diagnosis, as well as monitoring, in a disease where clinical examination remains the predominant diagnostic tool. Magnetic resonance imaging (MRI) has greatly developed over the past thirty years since its initial introduction to neuroscience. With multi-modal applications, MRI is now offering exciting opportunities to develop practical biomarkers in ALS. AREAS COVERED IN THIS REVIEW: The historical application of MRI to the field of ALS, its state-of-the-art and future aspirations will be reviewed. Specifically, the significance and limitations of structural MRI to detect gross morphological tissue changes in relation to clinical presentation will be discussed. The more recent application of diffusion tensor imaging (DTI), magnetic resonance spectroscopy (MRS), functional and resting-state MRI (fMRI & R-fMRI) will be contrasted in relation to these more conventional MRI assessments. Finally, future aspirations will be sketched out in providing a more disease mechanism-based molecular MRI. WHAT THE READER WILL GAIN: This review will equip the reader with an overview of the application of MRI to ALS and illustrate its potential to develop biomarkers. This discussion is exemplified by key studies, demonstrating the strengths and limitations of each modality. The reader will gain an expert opinion on both the current and future developments of MR imaging in ALS. TAKE HOME MESSAGE: MR imaging generates potential diagnostic, prognostic and therapeutic monitoring biomarkers of ALS. The emerging fusion of structural, functional and potentially molecular imaging will improve our understanding of wider cerebral connectivity and holds the promise of biomarkers sensitive to the earliest changes.

Evaluation of multiple sclerosis diagnostic criteria in Suzhou, China--risk of under-diagnosis in a low prevalence area

OBJECTIVE

To evaluate the discharge diagnosis of demyelinating diseases in the central nervous system (CNS) and analyze the predictive value of the new diagnostic criteria in Suzhou, China.

MATERIALS AND METHODS

We collected clinical information and data of laboratory examinations for all cases with a diagnosis of various demyelinating diseases in the CNS. All data were reviewed individually by four senior neurologists, and a diagnosis was finally given to each patient according to the McDonald criteria and the Poser criteria for multiple sclerosis (MS).

RESULTS

In the analysis, 176 patients with a diagnosis of demyelinating diseases in the CNS at discharge were included. In 82 patients with a diagnosis of MS at discharge, the MS diagnosis was confirmed for 74 patients according to the McDonald criteria for MS, and the positive predictive value for the discharge diagnosis of MS was 90.2% (74/82). According to the Poser criteria, 61 patients were diagnosed as MS. The consistency of the two diagnostic criteria for MS was 78.4%, based on the results of the evaluation.

CONCLUSIONS

Under-diagnosis of MS could be one of the explanations for the low prevalence of MS in China. Compared to the Poser criteria, the McDonald criteria had a higher sensitivity for the diagnosis of MS.