Imaging the tip of the iceberg: visualization of cortical lesions in multiple sclerosis

Detection and quantification of regional cortical gray matter damage in multiple sclerosis utilizing gradient echo MRI

Cortical gray matter (GM) damage is now widely recognized in multiple sclerosis (MS). The standard MRI does not reliably detect cortical GM lesions, although cortical volume loss can be measured. In this study, we demonstrate that the gradient echo MRI can reliably and quantitatively assess cortical GM damage in MS patients using standard clinical scanners. High resolution multi-gradient echo MRI was used for regional mapping of tissue-specific MRI signal transverse relaxation rate values (R2(*)) in 10 each relapsing-remitting, primary-progressive and secondary-progressive MS subjects. A voxel spread function method was used to correct artifacts induced by background field gradients. R2(*) values from healthy controls (HCs) of varying ages were obtained to establish baseline data and calculate ΔR2(*) values - age-adjusted differences between MS patients and HC. Thickness of cortical regions was also measured in all subjects. In cortical regions, ΔR2(*) values of MS patients were also adjusted for changes in cortical thickness. Symbol digit modalities (SDMT) and paced auditory serial addition (PASAT) neurocognitive tests, as well as Expanded Disability Status Score, 25-foot timed walk and nine-hole peg test results were also obtained on all MS subjects. We found that ΔR2(*) values were lower in multiple cortical GM and normal appearing white matter (NAWM) regions in MS compared with HC. ΔR2(*) values of global cortical GM and several specific cortical regions showed significant (p < 0.05) correlations with SDMT and PASAT scores, and showed better correlations than volumetric measures of the same regions. Neurological tests not focused on cognition (Expanded Disability Status Score, 25-foot timed walk and nine-hole peg tests) showed no correlation with cortical GM ΔR2(*) values. The technique presented here is robust and reproducible. It requires less than 10 min and can be implemented on any MRI scanner. Our results show that quantitative tissue-specific R2(*) values can serve as biomarkers of tissue injury due to MS in the brain, including the cerebral cortex, an area that has been difficult to evaluate using standard MRI.

Regional Distribution and Evolution of Gray Matter Damage in Different Populations of Multiple Sclerosis Patients

BACKGROUND

Both gray-matter (GM) atrophy and lesions occur from the earliest stages of Multiple Sclerosis (MS) and are one of the major determinants of long-term clinical outcomes. Nevertheless, the relationship between focal and diffuse GM damage has not been clarified yet. Here we investigate the regional distribution and temporal evolution of cortical thinning and how it is influenced by the local appearance of new GM lesions at different stages of the disease in different populations of MS patients.

METHODS

We studied twenty MS patients with clinically isolated syndrome (CIS), 27 with early relapsing-remitting MS (RRMS, disease duration <5 years), 29 with late RRMS (disease duration ≥ 5 years) and 20 with secondary-progressive MS (SPMS). The distribution and evolution of regional cortical thickness and GM lesions were assessed during 5-year follow-up.

RESULTS

The results showed that new lesions appeared more frequently in hippocampus and parahippocampal gyri (9.1%), insula (8.9%), cingulate cortex (8.3%), superior frontal gyrus (8.1%), and cerebellum (6.5%). The aforementioned regions showed the greatest reduction in thickness/volume, although (several) differences were observed across subgroups. The correlation between the appearance of new cortical lesions and cortical thinning was stronger in CIS (r2 = 50.0, p<0.001) and in early RRMS (r2 = 52.3, p<0.001), compared to late RRMS (r2 = 25.5, p<0.001) and SPMS (r2 = 6.3, p = 0.133).

CONCLUSIONS

We conclude that GM atrophy and lesions appear to be different signatures of cortical disease in MS having in common overlapping spatio-temporal distribution patterns. However, the correlation between focal and diffuse damage is only moderate and more evident in the early phase of the disease.

Ultra-High-Field MRI Visualization of Cortical Multiple Sclerosis Lesions with T2 and T2*: A Postmortem MRI and Histopathology Study

BACKGROUND AND PURPOSE

At 7T MR imaging, T2*-weighted gradient echo has been shown to provide high-resolution anatomic images of gray matter lesions. However, few studies have verified T2*WI lesions histopathologically or compared them with more standard techniques at ultra-high-field strength. This study aimed to determine the sensitivity of T2WI and T2*WI sequences for detecting cortical GM lesions in MS.

MATERIALS AND METHODS

At 7T, 2D multiecho spin-echo T2WI and 3D gradient-echo T2*WI were acquired from 27 formalin-fixed coronal hemispheric brain sections of 15 patients and 4 healthy controls. Proteolipid-stained tissue sections (8 μm) were matched to the corresponding MR images, and lesions were manually scored on both MR imaging sequences (blinded to histopathology) and tissue sections (blinded to MR imaging). The sensitivity of MR imaging sequences for GM lesion types and white matter lesions was calculated. An unblinded retrospective scoring was also performed.

RESULTS

If all cortical GM lesions were taken into account, the T2WI sequence detected slightly more lesions than the T2*WI sequence: 28% and 16%, respectively (P = .054). This difference disappeared when only intracortical lesions were considered. When histopathologic information (type, location) was revealed to the reader, the sensitivity went up to 84% (T2WI) and 85% (T2*WI) (not significant). Furthermore, the false-positive rate was 8.6% for the T2WI and 10.5% for the T2*WI sequence.

CONCLUSIONS

There is no strong advantage of the T2*WI sequence compared with a conventional T2WI sequence in the detection of cortical lesions at 7T. Retrospectively, a high percentage of lesions could be detected with both sequences. However, many lesions are still missed prospectively. This could possibly be minimized with better a priori observer training.

Periventricular lesions correlate with cortical thinning in multiple sclerosis

OBJECTIVE

It has been suggested recently that cortical pathology in multiple sclerosis (MS) may, at least partly, be caused by factors in cerebrospinal fluid (CSF). We thus hypothesized that MS-related tissue changes in compartments close to the CSF, such as periventricular lesions, might correlate with cortical pathology.

METHODS

We investigated a cohort of 160 patients, comprising 91 with a clinically isolated syndrome (CIS) and 69 with relapsing-remitting MS (RRMS; mean age: CIS: 31.4 ± 9.0; RRMS: 33.0 ± 8.7 years; mean disease duration: CIS: 7.2 ± 15 months; RRMS: 8.0 ± 6.5 years, Expanded Disability Status Scale (median, min-max): CIS: 1, 0-3.5; RRMS: 1.25, 0-4) with 3.0T magnetic resonance imaging. MS lesions were segmented semiautomatically on fluid-attenuated inversion recovery images. To quantify periventricular lesion load (PV-LL), we generated ventricle masks and dilated them by a voxel factor of 3. Lesions within the dilated ventricle margin were classified as periventricular. Cortical thinning was assessed by cortical mean thickness (CMT) and compared to data from 58 healthy controls (HCs; mean age: 29.1 ± 7.4 years).

RESULTS

Compared to HC, CIS and (even more so) RRMS patients demonstrated significantly reduced CMT. Even after controlling for ventricular volume and total lesion load, increased periventricular lesion occupancy (percentage of PV-LL) significantly correlated with decreased CMT in RRMS (r = -0.295; p = 0.015), but not in CIS (r = 0.032; p = 0.768) patients.

INTERPRETATION

The correlation between increased periventricular lesion burden and decreased CMT indicative of subpial cortical pathology supports the concept that common CSF-mediated factors might play a role in the accumulation of damage to gray and white matter in MS.

Magnetization transfer ratio in lesions rather than normal-appearing brain relates to disability in patients with multiple sclerosis

Magnetization transfer ratio (MTR) is a semi-quantitative measure that seems to correlate with the degree of myelin loss and generally tissue destruction in multiple sclerosis (MS). Our objective was to comprehensively assess the MTR of lesions and normal appearing (NA) tissue separately in the white matter (WM), the cortex, the thalamus and the basal ganglia (BG) and determine their relative contribution to disability. In this cross-sectional study 71 patients were included (59 with relapsing-remitting MS, 12 with secondary progressive MS). We used a three-dimensional MTR sequence with high spatial resolution, based on balanced steady-state free precession. Mean MTR was calculated for lesions and NA tissue separately for each tissue type. Lesional MTR was lower than normal-appearing MTR in WM, cortex and thalamus. In the regression analysis, MTR of cortical lesions (β = -0.23, p = 0.05) and MTR of WML (β = -0.21, p = 0.08) were related by trend to the expanded disability status scale. MTR of WML significantly predicted the paced auditory serial-addition test (β = 0.35, p = 0.004). MTR of normal-appearing tissue did not relate to any outcome. Our results suggest that MTR of lesions in the white matter and cortex rather than of normal-appearing tissue relates to disability in patients with MS.

Exploring the origins of grey matter damage in multiple sclerosis

Multiple sclerosis is characterized at the gross pathological level by the presence of widespread focal demyelinating lesions of the myelin-rich white matter. However, it is becoming clear that grey matter is not spared, even during the earliest phases of the disease. Furthermore, grey matter damage may have an important role both in physical and cognitive disability. Grey matter pathology involves both inflammatory and neurodegenerative mechanisms, but the relationship between the two is unclear. Histological, immunological and neuroimaging studies have provided new insight in this rapidly expanding field, and form the basis of the most recent hypotheses on the pathogenesis of grey matter damage.

A gradient in cortical pathology in multiple sclerosis by in vivo quantitative 7 T imaging

We used a surface-based analysis of T2* relaxation rates at 7 T magnetic resonance imaging, which allows sampling quantitative T2* throughout the cortical width, to map in vivo the spatial distribution of intracortical pathology in multiple sclerosis. Ultra-high resolution quantitative T2* maps were obtained in 10 subjects with clinically isolated syndrome/early multiple sclerosis (≤ 3 years disease duration), 18 subjects with relapsing-remitting multiple sclerosis (≥ 4 years disease duration), 13 subjects with secondary progressive multiple sclerosis, and in 17 age-matched healthy controls. Quantitative T2* maps were registered to anatomical cortical surfaces for sampling T2* at 25%, 50% and 75% depth from the pial surface. Differences in laminar quantitative T2* between each patient group and controls were assessed using general linear model (P < 0.05 corrected for multiple comparisons). In all 41 multiple sclerosis cases, we tested for associations between laminar quantitative T2*, neurological disability, Multiple Sclerosis Severity Score, cortical thickness, and white matter lesions. In patients, we measured, T2* in intracortical lesions and in the intracortical portion of leukocortical lesions visually detected on 7 T scans. Cortical lesional T2* was compared with patients' normal-appearing cortical grey matter T2* (paired t-test) and with mean cortical T2* in controls (linear regression using age as nuisance factor). Subjects with multiple sclerosis exhibited relative to controls, independent from cortical thickness, significantly increased T2*, consistent with cortical myelin and iron loss. In early disease, T2* changes were focal and mainly confined at 25% depth, and in cortical sulci. In later disease stages T2* changes involved deeper cortical laminae, multiple cortical areas and gyri. In patients, T2* in intracortical and leukocortical lesions was increased compared with normal-appearing cortical grey matter (P < 10(-10) and P < 10(-7)), and mean cortical T2* in controls (P < 10(-5) and P < 10(-6)). In secondary progressive multiple sclerosis, T2* in normal-appearing cortical grey matter was significantly increased relative to controls (P < 0.001). Laminar T2* changes may, thus, result from cortical pathology within and outside focal cortical lesions. Neurological disability and Multiple Sclerosis Severity Score correlated each with the degree of laminar quantitative T2* changes, independently from white matter lesions, the greatest association being at 25% depth, while they did not correlate with cortical thickness and volume. These findings demonstrate a gradient in the expression of cortical pathology throughout stages of multiple sclerosis, which was associated with worse disability and provides in vivo evidence for the existence of a cortical pathological process driven from the pial surface.

Cortical Ischemic Lesion Burden Measured by DIR Is Related to Carotid Artery Disease Severity

Background: Over time, exposure to cerebrovascular risk factors and carotid artery disease may cause multiple asymptomatic brain cortical and subcortical microinfarcts, which are commonly found at brain autopsy. So far, lack of convenient neuroimaging tools limited the investigation of grey matter ischemic damage in vivo. We applied the Double Inversion Recovery (DIR) sequence to explore the impact of carotid artery disease on intracortical ischemic lesion load in vivo, taking into account the impact of demographic characteristics and vascular risk factors. Methods: DIR was acquired in 62 patients with common cerebrovascular risk factors stratified in three groups according to carotid artery disease severity. Intracortical lesions scored on DIR (DIRlns) were classified by vascular territory, lobe and hemisphere. White matter hyperintensities (WMHs) volume was also quantified on Fluid Attenuated Inversion Recovery sequence (FLAIR). Results: Among demographic characteristics and cerebrovascular risk variables explored, General Linear Model indicated that age and carotid artery disease were significantly associated to DIRlns. After correcting for age, DIRlns load was found to be significantly dependent on carotid artery stenosis severity (F(2, 58) = 5.56, p = 0.006). A linear positive correlation between DIRlns and WMHs was found after correcting for age (p = 0.003). Conclusions: Carotid disease severity is associated with DIRlns accrual. Microembolism and impaired cerebral hemodynamics may act as physiopathological mechanisms underlying cortical ischemic damage. The role of other factors, such as small vessel disease and the possible interaction with carotid disease, remains to be further explored.

7 Tesla magnetic resonance imaging to detect cortical pathology in multiple sclerosis

BACKGROUND

Neocortical lesions (NLs) are an important pathological component of multiple sclerosis (MS), but their visualization by magnetic resonance imaging (MRI) remains challenging.

OBJECTIVES

We aimed at assessing the sensitivity of multi echo gradient echo (ME-GRE) T2*-weighted MRI at 7.0 Tesla in depicting NLs compared to myelin and iron staining.

METHODS

Samples from two MS patients were imaged post mortem using a whole body 7 T MRI scanner with a 24-channel receive-only array. Isotropic 200 micron resolution images with varying T2* weighting were reconstructed from the ME-GRE data and converted into R2* maps. Immunohistochemical staining for myelin (proteolipid protein, PLP) and diaminobenzidine-enhanced Turnbull blue staining for iron were performed.

RESULTS

Prospective and retrospective sensitivities of MRI for the detection of NLs were 48% and 67% respectively. We observed MRI maps detecting only a small portion of 20 subpial NLs extending over large cortical areas on PLP stainings. No MRI signal changes suggestive of iron accumulation in NLs were observed. Conversely, R2* maps indicated iron loss in NLs, which was confirmed by histological quantification.

CONCLUSIONS

High-resolution post mortem imaging using R2* and magnitude maps permits detection of focal NLs. However, disclosing extensive subpial demyelination with MRI remains challenging.

Challenges in multiple sclerosis; how to define occurence of progression

The challenges in MS are related to number of controversies in various aspects of disease but the relationship between relapses and disability progression, or aspects of MS as an inflammatory and/or neurodegenerative disease are extremely important because of its implications on prognosis and therapy of MS. MS was classically regarded as white matter inflammatory disease, while disability progression, brain and spinal cord atrophy were regarded as a consequence of global inflammation of NAWM and secondary involvement of grey matter. More recent histopathology studies, but also new, modern MRI techniques changed this view in MS as a prominent grey and white matter disease. Inflammatory demyelination of grey matter occurs early in MS sometimes even before occurrence of white matter lesions. Inspite of early therapy of MS with immunomodulatory drugs disability progression and neurodegeneration are still important and common part of MS pathogenesis. This indicate that treatment is not adequate to the predicted severity of MS, or perhaps to the basic pathogenetic mechanisms in MS. Beside acute clinical symptoms, conclusions about the severity of the disease are reflection of MRI sensitivity to detect focal WM lesions and insensitivity to detect grey matter lesions which correlate better with clinical symptoms. All presented studies and evaluations point to the necessity of changing the established diagnostic evaluation and treatment in MS. At the earliest stage of MS as well as in follow up of disease it would be necessary to apply a new MRI techniques more available for clinical practice such as DIR brain MR imaging at 3T because of their sensitivity to detect grey matter lesions. In patient with present cortical lesions even in earliest stages of MS depending on severity of grey matter involvement more efficacious therapy like second or even third line therapy should start.

Gray matters in multiple sclerosis: cognitive impairment and structural MRI

Multiple sclerosis (MS) is an immune-mediated disease affecting central nervous system (CNS). Although MS is classically considered a white matter (WM) disease, the involvement of gray matter (GM) in the pathogenic process has been confirmed by pathology studies and MRI studies. Impairment of cognitive domains such as memory, mental processing speed, attention, and executive function can occur from the early stage of the disease and tends to worsen over time, despite stable physical symptoms. WM demyelination is moderately correlated with CI, suggesting that probably WM abnormalities alone cannot fully explain the extent of clinical symptoms in MS, including CI. Several MRI techniques have shown the involvement of GM in MS and the association between GM damage, physical disability, and CI. The aim of this review is to provide an overview of CI and GM damage assessed by structural brain MRI.

Improved detection of focal cortical lesions using 7T magnetisation transfer imaging in patients with multiple sclerosis

BACKGROUND

Cortical lesions account for a larger proportion of brain demyelination than white matter (WM) lesions. They are often missed on conventional MRI. Recently studies improved the detection of cortical lesions using 7T T2(⁎), 7T MPRAGE and 3T DIR but it seems that we are still able to detect only "the tip of the iceberg". In this study we report for the first time the systematic use of high resolution MTR in MS and compare MTR lesion detection with 7T MPRAGE, 7T T2(⁎) and 3T 3D DIR.

OBJECTIVES

We report the use of high resolution, fast, magnetisation transfer imaging (MTI) at 7T in MS focusing on the detection of cortical lesions.

SUBJECTS AND METHODS

Eighteen patients with MS were scanned (Expanded Disability Status Scale score: 3.0, mean age: 48 years, mean disease duration: 7.25 years). The scans were compared to nine healthy control subjects (mean age 36.5 years).

DATA ACQUISITION

We acquired 7T MPRAGE images, 7T MTR maps, 7T T2(⁎)and 3T 3D DIR. The WM was segmented from the MPRAGE and removed to obtain only the cortical grey matter ribbon (cGMR) mask. The mask was then applied to the different modalities (MPRAGE, MTR, DIR, T2(⁎)w) previously registered onto the MPRAGE volume. The analysis of the cGMR was performed by two observers blinded to the disease state.

RESULTS

In patients with MS 365 lesions in total were detected with 7T MTR (mean 20.28 lesions per patient), 289 lesions were detected with 7T MPRAGE (mean 16.06 lesions) and 231 lesions were detected with 7T T2(⁎) (mean 12.83 lesions). In the 8 MS subjects who had 3T 3D DIR acquired on the same day, a total of 136 lesions (mean 17 lesions per patient) were detected as opposed to 171 lesions with 7T MTR, 147 lesions were detected with 7T MPRAGE and 126 lesions with 7T T2(⁎) in the same patients.

CONCLUSION

We found that 7T MTR, in less than 10min scanning time, was able to detect cortical lesions. In this study we found that 7T MTR was better in detecting intracortical lesions in comparison with 7T T2(⁎), 7T MPRAGE, and 3T 3D DIR. since only a very few intracortical lesions were detected in healthy controls in our blind assessment, it is likely that the lesions detected represent focal grey matter demyelination. High resolution MT imaging has especially revealed cortical changes that have not been recognised by other MR sequences. MTR maps were noisier than MPRAGE, T2(⁎) and DIR, but also better in localising cortical lesions. As MTR is more pathologically specific than other sequences in detecting tissue myelination, it raises the possibility that high resolution MTR will be able to demonstrate cortical remyelination in vivo.

The changing clinical course of multiple sclerosis: a matter of gray matter

OBJECTIVE

Clinical and neuroimaging parameters predictive of the changing clinical course of multiple sclerosis (MS) from relapsing-remitting to secondary progressive have not been clarified yet. We specifically designed a prospective 5-year longitudinal study aimed at assessing demographic, clinical, and magnetic resonance imaging (MRI) parameters that could predict the changing clinical course of MS.

METHODS

At study entry and after 5 years, clinical and MRI (ie, gray matter and white matter lesions, including spinal cord lesions, and global and regional cortical thinning) parameters were assessed in a training set of 334 consecutive relapsing-remitting MS patients and in an independent validation set of 84 relapsing-remitting MS patients.

RESULTS

Sixty-six (19.7%) relapsing-remitting MS patients changed their clinical course during the study and entered into the secondary progressive phase. Age (p = 0.001, odds ratio [OR] = 1.2), cortical lesion volume (p < 0.001, OR = 1.7), and cerebellar cortical volume (p < 0.001, OR = 0.2) at study entry were found to predict the changing clinical course. The model including only these 3 variables correctly identified 252 of 268 (94.0%) patients who maintained the relapsing-remitting course and 58 of 66 (87.8%) patients who became secondary progressive (cross-validated error rate = 7.2%). When applied on the validation set, the model obtained a similar error rate (8.4%).

INTERPRETATION

A prediction model based on age, cortical lesion load, and cerebellar cortical volume suitably explains the probability of relapsing-remitting MS patients evolving into the progressive phase. Gray matter damage appears to play a pivotal role in determining the changing clinical course of MS.

Gray Matter Pathology in MS: Neuroimaging and Clinical Correlations

It is abundantly clear that there is extensive gray matter pathology occurring in multiple sclerosis. While attention to gray matter pathology was initially limited to studies of autopsy specimens and biopsies, the development of new MRI techniques has allowed assessment of gray matter pathology in vivo. Current MRI techniques allow the direct visualization of gray matter demyelinating lesions, the quantification of diffuse damage to normal appearing gray matter, and the direct measurement of gray matter atrophy. Gray matter demyelination (both focal and diffuse) and gray matter atrophy are found in the very earliest stages of multiple sclerosis and are progressive over time. Accumulation of gray matter damage has substantial impact on the lives of multiple sclerosis patients; a growing body of the literature demonstrates correlations between gray matter pathology and various measures of both clinical disability and cognitive impairment. The effect of disease modifying therapies on the rate accumulation of gray matter pathology in MS has been investigated. This review focuses on the neuroimaging of gray matter pathology in MS, the effect of the accumulation of gray matter pathology on clinical and cognitive disability, and the effect of disease-modifying agents on various measures of gray matter damage.

Neurodegeneration and inflammation in hippocampus in experimental autoimmune encephalomyelitis induced in rats by one--time administration of encephalitogenic T cells

Cognitive dysfunction is relatively frequent in multiple sclerosis (MS) and it happens from the early stages of the disease. There is increasing evidence that the grey matter may be involved in autoimmune inflammation during relapses of MS. The purpose of this study was to evaluate if a single transfer of encephalitogenic T cells, mimicking a relapse of MS, may cause hippocampal damage and memory disturbances in rats. Lewis rats were injected with anti-MBP CD4+ T cells, that induced one-phase autoimmune encephalomyelitis (EAE) with full recovery from motor impairments at 10-15 days. The spatial learning and memory were tested by the Morris water maze test in control and EAE animals, 30 and 90 days post-induction (dpi). The neural injury and inflammation was investigated in the hippocampus by immunohistochemistry and quantitative analyses. There was a marked decrease in the number of CA1 and CA4 pyramidal neurons 5 dpi. The loss of neurons then aggravated till the 90 dpi. An increase in microglial and astroglial activation and in pro-inflammatory cytokines mRNA expression in the hippocampus, were present 30 and 90 dpi. Nerve growth factor and brain-derived neurotrophic factor mRNA levels were also significantly elevated. The water maze test, however, did not reveal memory deficits. The present data indicate that a single transfer of autoimmune T cells results in preserved inflammation and probable on-going neuronal injury in the hippocampus, long after recovery from motor disturbances. These findings suggest that any relapse of the MS may start the neurodegenerative process in the hippocampus, which is not necessarily connected with memory deficits.

Callosal atrophy in multiple sclerosis is related to cognitive speed

BACKGROUND

Long-term changes regarding corpus callosum area (CCA) and information processing speed in cognitive and sensory-motor tasks have rarely been studied in multiple sclerosis (MS).

OBJECTIVE AND METHODS

Information processing speed in cognitive (Symbol Digit Modalities Test, SDMT), sensory (visual and auditory reaction time) and motor (finger-tapping speed, FT; right and left hand) tasks as well as auditory inter-hemispheric transfer (verbal dichotic listening, VDL) was related to CCA, measured by MRI at baseline and at follow-up after nine years in 22 patients with MS. Possible confounding by demographic (age, gender and education), clinical (symptom onset, duration, severity of disease) and relative brain volume (RBV) as well as T2 lesion load was taken into account.

RESULTS

The smaller the CCA at baseline, the slower was SDMT performance at baseline. In a similar way, CCA at follow-up was associated with poor SDMT result at follow-up. Furthermore, the higher the annual rate of change in CCA, the poorer was performance in VDL on the left ear and the more pronounced was the right ear advantage. A positive relationship between performance in VDL right ear and annual rate of change in RBV was also seen. Sensory-motor tests were not significantly associated with CCA. T2 lesion load at baseline was associated with FT performance at baseline. Demographic, clinical and radiological (RBV and T2 lesion load) characteristics did not confound the significant relation between CCA and SDMT.

CONCLUSIONS

CCA unlike RBV and T2 lesion load was associated with SDMT, which indicated a marked cognitive rather than perceptual-motor component.

Sulcal and gyral crown cortical grey matter involvement in multiple sclerosis: A magnetisation transfer ratio study

BACKGROUND

Histopathology has demonstrated extensive cortical grey matter (GM) demyelination in multiple sclerosis (MS), and suggests that sulcal folds may be preferentially affected, particularly in progressive MS. This has not been confirmed in vivo, and it is not known if it is relevant to clinical status.

OBJECTIVES

To determine sulcal and gyral crown magnetisation transfer ratio (MTR) in MS cortical GM, and the MTR associations with clinical status.

METHODS

We measured sulcal and gyral crown cortical GM MTR values in 61 MS patients and 32 healthy controls. Disability was measured using Expanded Disability Status Scale and Multiple Sclerosis Functional Composite scores.

RESULTS

MTR values were reduced in sulcal and gyral crown regions in all MS subtypes, more so in secondary progressive (SP) MS than relapsing remitting (RR) MS, and similarly in primary progressive (PP) MS and RRMS. Sulcal MTR was lower than gyral crown MTR in controls, PPMS and RRMS patients, but not in SPMS. MTR correlated with clinical status in RRMS and SPMS, but not PPMS.

CONCLUSIONS

Cortical pathology, as reflected by MTR, is present in all MS subtypes and most pronounced in SPMS. A preferential disease effect on sulcal cortical regions was not observed. Cortical MTR abnormalities appear to be more clinically relevant in relapse-onset rather than progressive-onset MS.

Bimonthly Evolution of Cortical Atrophy in Early Relapsing-Remitting Multiple Sclerosis over 2 Years: A Longitudinal Study

We investigated the evolution of cortical atrophy in patients with early relapsing-remitting (RR) multiple sclerosis (MS) and its association with lesion volume (LV) accumulation and disability progression. 136 of 181 RRMS patients who participated in the Avonex-Steroids-Azathioprine study were assessed bimonthly for clinical and MRI outcomes over 2 years. MS patients with disease duration (DD) at baseline of ≤24 months were classified in the early group (DD of 1.2 years, n = 37), while patients with DD > 24 months were classified in the late group (DD of 7.1 years, n = 99). Mixed effect model analysis was used to investigate the associations. Significant changes in whole brain volume (WBV) (P < 0.001), cortical volume (CV) (P < 0.001), and in T2-LV (P < 0.001) were detected. No significant MRI percent change differences were detected between early and late DD groups over 2 years, except for increased T2-LV accumulation between baseline and year 2 in the early DD group (P < 0.01). No significant associations were found between changes in T2-LV and CV over the followup. Change in CV was related to the disability progression over the 2 years, after adjusting for DD (P = 0.01). Significant cortical atrophy, independent of T2-LV accumulation, occurs in early RRMS over 2 years, and it is associated with the disability progression.

Grey matter damage in multiple sclerosis: a pathology perspective

Over the past decade, immunohistochemical studies have provided compelling evidence that gray matter (GM) pathology in multiple sclerosis (MS) is extensive. Until recently, this GM pathology was difficult to visualize using standard magnetic resonance imaging (MRI) techniques. However, with newly developed MRI sequences, it has become clear that GM damage is present from the earliest stages of the disease and accrues with disease progression. GM pathology is clinically relevant, as GM lesions and/or GM atrophy were shown to be associated with MS motor deficits and cognitive impairment. Recent autopsy studies demonstrated significant GM demyelination and microglia activation. However, extensive immune cell influx, complement activation and blood-brain barrier leakage, like in WM pathology, are far less prominent in the GM. Hence, so far, the cause of GM damage in MS remains unknown, although several plausible underlying pathogenic mechanisms have been proposed. This paper provides an overview of GM damage in MS with a focus on its topology and histopathology.

Clinically feasible MTR is sensitive to cortical demyelination in MS

OBJECTIVE

Presently there is no clinically feasible imaging modality that can effectively detect cortical demyelination in patients with multiple sclerosis (MS). The objective of this study is to determine if clinically feasible magnetization transfer ratio (MTR) imaging is sensitive to cortical demyelination in MS.

METHODS

MRI were acquired in situ on 7 recently deceased patients with MS using clinically feasible sequences at 3 T, including relatively high-resolution T1-weighted and proton density-weighted images with/without a magnetization transfer pulse for calculation of MTR. The brains were rapidly removed and placed in fixative. Multiple cortical regions from each brain were immunostained for myelin proteolipid protein and classified as mostly myelinated (MM(ctx)), mostly demyelinated (MD(ctx)), or intermediately demyelinated (ID(ctx)). MRIs were registered with the cortical sections so that the cortex corresponding to each cortical section could be identified, along with adjacent subcortical white matter (WM). Mean cortical MTR normalized to mean WM MTR was calculated for each cortical region. Linear mixed-effects models were used to test if mean normalized cortical MTR was significantly lower in demyelinated cortex.

RESULTS

We found that mean normalized cortical MTR was significantly lower in cortical tissue with any demyelination (ID(ctx) or MD(ctx)) compared to MM(ctx) (demyelinated cortex: least-squares mean [LSM] = 0.797, SE = 0.007; MM(ctx): LSM = 0.837, SE = 0.006; p = 0.01, n = 89).

CONCLUSIONS

This result demonstrates that clinically feasible MTR imaging is sensitive to cortical demyelination and suggests that MTR will be a useful tool to help detect MS cortical lesions in living patients with MS.

MRI in multiple sclerosis: a review of the current literature

PURPOSE OF REVIEW

This review summarizes the recent data pertaining to the use of magnetic resonance imaging (MRI) in assessing brain and spinal cord involvement in multiple sclerosis (MS).

RECENT FINDINGS

Using MRI as a tool, investigators have made progress recently in understanding the substrate and mechanisms underlying the development and evolution of focal lesions and diffuse damage in MS. The application of refined MRI sequences has markedly improved the characterization of focal lesions, in particular cortical lesions. Promising improvements have been made to clarify the pathological specificity and sensitivity of MRI techniques by performing combined histopathologic-MRI correlation studies. The use of high-field (3 T) and ultra-high-field (UHF; >3 T) MRI has further facilitated the detection of both gray matter and white matter microstructural damage, and elucidated the topographic relationship of overt damage to venous blood vessels. The development of advanced MRI postprocessing tools has led to additional progress in detecting clinically relevant regional gray matter and white matter damage.

SUMMARY

MRI continues to play a pivotal role in the investigation of MS. Ongoing advances in MRI technology should further expand the current understanding of pathologic disease mechanisms and improve diagnostic, prognostic, and monitoring ability in patients with MS.

Quantitative magnetic resonance imaging of cortical multiple sclerosis pathology

Although significant improvements have been made regarding the visualization and characterization of cortical multiple sclerosis (MS) lesions using magnetic resonance imaging (MRI), cortical lesions (CL) continue to be under-detected in vivo, and we have a limited understanding of the causes of GM pathology. The objective of this study was to characterize the MRI signature of CLs to help interpret the changes seen in vivo and elucidate the factors limiting their visualization. A quantitative 3D high-resolution (350 μm isotropic) MRI study at 3 Tesla of a fixed post mortem cerebral hemisphere from a patient with MS is presented in combination with matched immunohistochemistry. Type III subpial lesions are characterized by an increase in T1, T2 and M0, and a decrease in MTR in comparison to the normal appearing cortex (NAC). All quantitative MR parameters were associated with cortical GM myelin content, while T1 showed the strongest correlation. The histogram analysis showed extensive overlap between CL and NAC for all MR parameters and myelin content. This is due to the poor contrast in myelin content between CL and NAC in comparison to the variability in myelo-architecture throughout the healthy cortex. This latter comparison is highlighted by the representation of T1 times on cortical surfaces at several laminar depths.

Grey matter lesions in MS: from histology to clinical implications

Although multiple sclerosis (MS) is a chronic inflammatory-demyelinating disease of the white matter (WM) of the central nervous system, several pathological and magnetic resonance imaging (MRI) studies have shown that a large amount of lesions are located in the cortical and deep gray matter. The histopathological and immunological characteristics of cortical lesions differ significantly from those located in the WM, which suggests a location-dependent expression of the MS immunopathological process. More recently, the availability of not-conventional MRI sequences having higher sensitivity for the gray matter has allowed to depict in vivo a portion of such lesions. The available MRI data obtained on large cohorts of patients, having different clinical forms of the disease, indicate that cortical lesions can be detected early in the disease course, sometimes even before the appearance of WM lesions, and correlate with the severity of physical disability and cognitive impairment, and with the evolution of the disease toward the secondary progressive phase. This review provides a summary of the main histopathological and MRI findings of cortical lesions in MS and discusses their possible clinical implications.

Low degree of cortical pathology is associated with benign course of multiple sclerosis

BACKGROUND

Although a more favorable course of multiple sclerosis is associated with a low degree of cortical pathology, only longitudinal studies could definitely confirm this association.

MATERIALS AND METHODS

We followed 95 early relapsing-remitting MS (RRMS; median Expanded Disability Status Scale (EDSS) = 1.5, mean disease duration = 3.1 ± 1.3 years) and 45 benign MS patients (EDSS ≤ 3.0, disease duration ≥ 15 years, normal cognition) for 6 years, with EDSS evaluations every 6 months and brain magnetic resonance imaging (MRI) at baseline and then yearly.

RESULTS

At baseline, we detected 406 cortical lesions (CLs) in 67/95 (70.5%) early RRMS and in 24/45 (53.3%) benign MS patients (p = 0.046). After 6 years, the appearance of new CLs was observed in 80/95 (84.2%; 518 CLs) of our early RRMS and in 25/45 (55.5%; 63 CLs; p < 0.001) benign MS patients. At baseline, after corrections for age and disease duration, we observed a cortical thinning of several frontal and temporal regions in our RRMS study patients, compared to the benign MS patients (p ranging between 0.001-0.05). After 6 years, the cortical thinning had increased significantly in several cortices of RRMS patients, but only in the occipital-temporal (p = 0.036) and superior parietal gyrus (p = 0.035) of those with benign MS. Stepwise regression analysis revealed the CL volume (p = 0.006) and the cortical thickness of the temporal middle (p < 0.001), insular long (p < 0.001), superior frontal (p < 0.001) and middle frontal gyri (p < 0.001) as the most sensitive independent predictors of a favorable disease course.

CONCLUSIONS

Our data confirmed that a significantly milder cortical pathology characterizes the most favorable clinical course of MS. Measures of focal and diffuse grey matter should be combined to increase the accuracy in the identification of a benign MS course.

Multicontrast MR imaging at 7T in multiple sclerosis: highest lesion detection in cortical gray matter with 3D-FLAIR

BACKGROUND AND PURPOSE

7T MR imaging has led to improved detection and classification of cortical MS lesions, mainly based on T2*-weighted gradient-echo sequences. Depiction of cortical GM by using the recommended MS imaging protocol has not yet been investigated at 7T. We aimed to investigate prospectively which recommended sequence for clinical use has the highest value at 7T, in terms of GM and WM lesion detection.

MATERIALS AND METHODS

Thirty-seven patients with MS (mean age, 43.8 years; 25 women) and 7 healthy controls (mean age, 40.4 years; 5 women) underwent multicontrast 7T MR imaging including the recommended clinical 2D-T2WI, 3D-T1WI, 3D-FLAIR, and GM-specific 3D-DIR. Lesions were scored and categorized anatomically by 3 raters, in consensus. The value of sequences was evaluated lesion-wise and patient-wise (Wilcoxon signed-rank test).

RESULTS

At 7T, 3D-FLAIR detected the highest number of total cortical GM lesions (217), 89% more than 3D-DIR and 87% and 224% more than 2D-T2WI and 3D-T1WI. Patient-wise analysis showed that this difference between 3D-FLAIR and 3D-DIR was statistically significant (P<.04), and most pronounced for the number of mixed lesions (P<.03). 3D-FLAIR also detected the highest number of total WM lesions (2605), but the difference with 3D-DIR and 3D-T1WI was not significant.

CONCLUSIONS

When using recommended clinical sequences at 7T, the best way to detect cortical GM lesions is with 3D-FLAIR and not by GM-specific 3D-DIR or by conventional 2D-T2WI and 3D-T1WI sequences.

Clinical applications of imaging disease burden in multiple sclerosis: MRI and advanced imaging techniques

This review will address the critical role of radiographic techniques in monitoring multiple sclerosis disease course and response to therapeutic interventions using conventional imaging. We propose an algorithm of obtaining a contrast-enhanced brain MRI 6 months after starting a disease-modifying therapy, and considering a gadolinium-enhancing lesion on that scan to indicate suboptimal response to therapy. New or enlarging T2 lesions should be followed on scans at 6-month intervals to assess for change, and the presence of one or more enhancing lesions on a 6- or 12-month scan, or two or more new or enlarging T2 lesions on a 12-month scan should prompt consideration of therapy change. New techniques such as PET imaging, magnetic resonance spectroscopy, magnetic resonance relaxometry, iron-sensitive imaging and perfusion MRI will also be overviewed, with their potential roles in monitoring disease course and activity.

Association between pathological and MRI findings in multiple sclerosis

The identification of pathological processes that could be targeted by therapeutic interventions is a major goal of research into multiple sclerosis (MS). Pathological assessment is the gold standard for such identification, but has intrinsic limitations owing to the limited availability of autopsy and biopsy tissue. MRI has gained a leading role in the assessment of MS because it allows doctors to obtain an ante mortem picture of the degree of CNS involvement. A number of correlative pathological and MRI studies have helped to define in vivo the pathological substrates of MS in focal lesions and normal-appearing white matter, not only in the brain, but also in the spinal cord. These studies have resulted in the identification of aspects of pathophysiology that were previously neglected, including grey matter involvement and vascular pathology. Despite these important achievements, numerous open questions still need to be addressed to resolve controversies about how the pathology of MS results in fixed neurological disability.

Gray matter imaging in multiple sclerosis: what have we learned?

At the early onset of the 20^th century, several studies already reported that the gray matter was implicated in the histopathology of multiple sclerosis (MS). However, as white matter pathology long received predominant attention in this disease, and histological staining techniques for detecting myelin in the gray matter were suboptimal, it was not until the beginning of the 21^st century that the true extent and importance of gray matter pathology in MS was finally recognized. Gray matter damage was shown to be frequent and extensive, and more pronounced in the progressive disease phases. Several studies subsequently demonstrated that the histopathology of gray matter lesions differs from that of white matter lesions. Unfortunately, imaging of pathology in gray matter structures proved to be difficult, especially when using conventional magnetic resonance imaging (MRI) techniques. However, with the recent introduction of several more advanced MRI techniques, the detection of cortical and subcortical damage in MS has considerably improved. This has important consequences for studying the clinical correlates of gray matter damage. In this review, we provide an overview of what has been learned about imaging of gray matter damage in MS, and offer a brief perspective with regards to future developments in this field.