Correlates of MS disability assessed in vivo using aggregates of MR quantities

Machine learning-optimized Combinatorial MRI scale (COMRISv2) correlates highly with cognitive and physical disability scales in Multiple Sclerosis patients

Composite MRI scales of central nervous system tissue destruction correlate stronger with clinical outcomes than their individual components in multiple sclerosis (MS) patients. Using machine learning (ML), we previously developed Combinatorial MRI scale (COMRISv1) solely from semi-quantitative (semi-qMRI) biomarkers. Here, we asked how much better COMRISv2 might become with the inclusion of quantitative (qMRI) volumetric features and employment of more powerful ML algorithm. The prospectively acquired MS patients, divided into training (n = 172) and validation (n = 83) cohorts underwent brain MRI imaging and clinical evaluation. Neurological examination was transcribed to NeurEx™ App that automatically computes disability scales. qMRI features were computed by lesion-TOADS algorithm. Modified random forest pipeline selected biomarkers for optimal model(s) in the training cohort. COMRISv2 models validated moderate correlation with cognitive disability [Spearman Rho = 0.674; Lin's concordance coefficient (CCC) = 0.458; p < 0.001] and strong correlations with physical disability (Spearman Rho = 0.830-0.852; CCC = 0.789-0.823; p < 0.001). The NeurEx led to the strongest COMRISv2 model. Addition of qMRI features enhanced performance only of cognitive disability model, likely because semi-qMRI biomarkers measure infratentorial injury with greater accuracy. COMRISv2 models predict most granular clinical scales in MS with remarkable criterion validity, expanding scientific utilization of cohorts with missing clinical data.

Quantitative magnetization transfer imaging in relapsing-remitting multiple sclerosis: a systematic review and meta-analysis

Myelin-sensitive MRI such as magnetization transfer imaging has been widely used in multiple sclerosis. The influence of methodology and differences in disease subtype on imaging findings is, however, not well established. Here, we systematically review magnetization transfer brain imaging findings in relapsing-remitting multiple sclerosis. We examine how methodological differences, disease effects and their interaction influence magnetization transfer imaging measures. Articles published before 06/01/2021 were retrieved from online databases (PubMed, EMBASE and Web of Science) with search terms including 'magnetization transfer' and 'brain' for systematic review, according to a pre-defined protocol. Only studies that used human in vivo quantitative magnetization transfer imaging in adults with relapsing-remitting multiple sclerosis (with or without healthy controls) were included. Additional data from relapsing-remitting multiple sclerosis subjects acquired in other studies comprising mixed disease subtypes were included in meta-analyses. Data including sample size, MRI acquisition protocol parameters, treatments and clinical findings were extracted and qualitatively synthesized. Where possible, effect sizes were calculated for meta-analyses to determine magnetization transfer (i) differences between patients and healthy controls; (ii) longitudinal change and (iii) relationships with clinical disability in relapsing-remitting multiple sclerosis. Eighty-six studies met inclusion criteria. MRI acquisition parameters varied widely, and were also underreported. The majority of studies examined the magnetization transfer ratio in white matter, but magnetization transfer metrics, brain regions examined and results were heterogeneous. The analysis demonstrated a risk of bias due to selective reporting and small sample sizes. The pooled random-effects meta-analysis across all brain compartments revealed magnetization transfer ratio was 1.17 per cent units (95% CI -1.42 to -0.91) lower in relapsing-remitting multiple sclerosis than healthy controls (z-value: -8.99, P < 0.001, 46 studies). Linear mixed-model analysis did not show a significant longitudinal change in magnetization transfer ratio across all brain regions [β = 0.12 (-0.56 to 0.80), t-value = 0.35, P = 0.724, 14 studies] or normal-appearing white matter alone [β = 0.037 (-0.14 to 0.22), t-value = 0.41, P = 0.68, eight studies]. There was a significant negative association between the magnetization transfer ratio and clinical disability, as assessed by the Expanded Disability Status Scale [r = -0.32 (95% CI -0.46 to -0.17); z-value = -4.33, P < 0.001, 13 studies]. Evidence suggests that magnetization transfer imaging metrics are sensitive to pathological brain changes in relapsing-remitting multiple sclerosis, although effect sizes were small in comparison to inter-study variability. Recommendations include: better harmonized magnetization transfer acquisition protocols with detailed methodological reporting standards; larger, well-phenotyped cohorts, including healthy controls; and, further exploration of techniques such as magnetization transfer saturation or inhomogeneous magnetization transfer ratio.

An In-vivo 1H-MRS short-echo time technique at 7T: Quantification of metabolites in chronic multiple sclerosis and neuromyelitis optica brain lesions and normal appearing brain tissue

Magnetic Resonance Spectroscopy (MRS) allows for the non-invasive quantification of neurochemicals and has the potential to differentiate between the pathologically distinct diseases, multiple sclerosis (MS) and AQP4Ab-positive neuromyelitis optica spectrum disorder (AQP4Ab-NMOSD). In this study we characterised the metabolite profiles of brain lesions in 11 MS and 4 AQP4Ab-NMOSD patients using an optimised MRS methodology at ultra-high field strength (7T) incorporating correction for T2 water relaxation differences between lesioned and normal tissue. MS metabolite results were in keeping with the existing literature: total N-acetylaspartate (NAA) was lower in lesions compared to normal appearing brain white matter (NAWM) with reciprocal findings for myo-Inositol. An unexpected subtlety revealed by our technique was that total NAA differences were likely driven by NAA-glutamate (NAAG), a ubiquitous CNS molecule with functions quite distinct from NAA though commonly quantified together with NAA in MRS studies as total NAA. Surprisingly, AQP4Ab-NMOSD showed no significant differences for total NAA, NAA, NAAG or myo-Inositol between lesion and NAWM sites, nor were there any differences between MS and AQP4Ab-NMOSD for a priori hypotheses. Post-hoc testing revealed a significant correlation between NAWM Ins:NAA and disability (as measured by EDSS) for disease groups combined, driven by the AP4Ab-NMOSD group. Utilising an optimised MRS methodology, our study highlights some under-explored subtleties in MRS profiles, such as the absence of myo-Inositol concentration differences in AQP4Ab-NMOSD brain lesions versus NAWM and the potential influence of NAAG differences between lesions and normal appearing white matter in MS.

Comparison of diffusion-weighted imaging and enhanced T1-weighted sequencing in patients with multiple sclerosis

Introduction The purpose of this study was to assess whether demographic, brain anatomical regions and contrast enhancement show differences in multiple sclerosis (MS) patients with increased diffusion lesions (ID group) compared with diffusion restriction (DR group). Method MRI protocol comprised T1- and T2-weighted sequences with and without gadolinium (Gd), and sagittal three-dimensional FLAIR sequence, DWI and ADC maps were prospectively performed in 126 MS patients from January to December 2015. The investigation was conducted to evaluate differences in demographic, cord and brain regional, technical, and positive or negative Gd contrast imaging parameters in two groups of ID and DR. Statistical analysis was performed by using SPSS. Results A total of 9.6% of patients showed DR. In the DR group, 66.6% of the patients showed contrast enhancement of plaques, whereas 29.2% of the IR group showed enhancement of plaques. The most prevalent group was non-enhanced plaques in the ID group, followed by Gd-enhanced plaques in the ID group. Patients in the ID group (90.4%) were significantly more than in the DR group (9.6%). Out of the 40 patients with Gd-enhanced plaques, 80.5% was from the ID group and 19.5% from the DR group. Conclusion MRI of the brain, unlike of the cord, with Gd demonstrates significant difference in enhancement between the two groups ( p < 0.05). No significant difference was seen in demographic, cord and brain regional, and technical parameters, EDSS, disease duration, and attack rate as well as demographic and regional parameters between the ID and decrease diffusion groups ( p > 0.05).

The Relationship Between Brain MR Spectroscopy and Disability in Multiple Sclerosis: 20-Year Data from the U.S. Glatiramer Acetate Extension Study

BACKGROUND AND PURPOSE

Conventional MRI techniques do not necessarily provide information about multiple sclerosis (MS) disease pathology or progression. Nonconventional MRI techniques, including proton magnetic resonance spectroscopy (¹H‐MRS), are increasingly used to improve the qualitative and quantitative specificity of MR images. This study explores potential correlations between MRI measures of disease and disability progression as measured by the Expanded Disability Status Scale (EDSS), Functional Systems (FS), and ambulation index scores in a unique cohort of MS patients treated with glatiramer acetate that has been closely monitored for over 20 years.

METHODS

This was a multicenter, open‐label, cross‐sectional MRI substudy among participants in the GA‐9004 open‐label extension of the 36‐month, double‐blind GA‐9001 study, timed to coincide with the prospectively planned 20‐year clinical exam.

RESULTS

Of 64 patients who participated in the MRI substudy, results are presented for the 39 patients (61%) who had a ¹H‐MRS assessment at 20 years of treatment. Both total N‐acetylaspartate relative to total creatinine (tNAA/tCr) concentration ratio and T1 lesion volume were found to be robustly associated with disability levels with different statistical approaches. Gray matter (GM) volume was found to be a more consistent parameter than white matter (WM) volume for disability allocation. The elastic net algorithm showed a trade‐off between WM and GM volumes for disability estimation when different disability definitions were used.

CONCLUSIONS

Among patients with MS receiving long‐term glatiramer acetate therapy, consistent effects on disability levels indicated by EDSS and pyramidal FS score thresholds were found for tNAA/tCr concentration ratio and T1 lesion volume.

An MRI-defined measure of cerebral lesion severity to assess therapeutic effects in multiple sclerosis

Assess the sensitivity of the Magnetic Resonance Disease Severity Scale (MRDSS), based on cerebral lesions and atrophy, for treatment monitoring of glatiramer acetate (GA) in relapsing-remitting multiple sclerosis (MS). This retrospective non-randomized pilot study included patients who started daily GA [n = 23, age (median, range) 41 (26.2, 53.1) years, Expanded Disability Status Scale (EDSS) score 1.0 (0, 3.5)], or received no disease-modifying therapy (noDMT) [n = 21, age 44.8 (28.2, 55.4), EDSS 0 (0, 2.5)] for 2 years. MRDSS was the sum of z-scores (normalized to a reference sample) of T2 hyperintense lesion volume (T2LV), the ratio of T1 hypointense LV to T2LV (T1/T2), and brain parenchymal fraction (BPF) multiplied by negative 1. The two groups were compared by Wilcoxon rank sum tests; within group change was assessed by Wilcoxon signed rank tests. Glatiramer acetate subjects had less progression than noDMT on T1/T2 [(median z-score change (range), 0 (−1.07, 1.20) vs. 0.41 (−0.30, 2.51), p = 0.003)] and MRDSS [0.01 (−1.33, 1.28) vs. 0.46 (−1.57, 2.46), p = 0.01]; however, not on BPF [0.12 (−0.18, 0.58) vs. 0.10 (−1.47,0.50), p = 0.59] and T2LV [−0.03 (−0.90, 0.57) vs. 0.01 (−1.69, 0.34), p = 0.40]. While GA subjects worsened only on BPF [0.12 (−0.18, 0.58), p = 0.001], noDMT worsened on BPF [0.10 (−1.47, 0.50), p = 0.002], T1/T2 [0.41 (−0.30, 2.51), p = 0.0002], and MRDSS [0.46 (−1.57, 2.46), p = 0.0006]. These preliminary findings show the potential of two new cerebral MRI metrics to track MS therapeutic response. The T1/T2, an index of the destructive potential of lesions, may provide particular sensitivity to treatment effects.

Novel composite MRI scale correlates highly with disability in multiple sclerosis patients

Understanding genotype-phenotype relationships or development/validation of biomarkers requires large multicenter cohorts integrated by universal quantification of crucial phenotypical traits, such as central nervous system (CNS) tissue destruction. We hypothesized that mathematical modeling-guided combination of biologically meaningful, semi-quantitative MRI elements characterized by high signal-to-noise ratio will provide such reliable, universal tool for measuring CNS tissue destruction. We retrospectively graded 15 elements in MRI scans performed in 419 untreated subjects with or without neurological diseases, while being blinded to their prospectively acquired clinical scores. We then used 305 subjects for disability-guided mathematical modeling to select and combine MRI elements that had non-redundant contributions to clinical disability, resulting in Combinatorial MRI Scale (COMRIS). We validated our model on the remaining 114 independent subjects. COMRIS requires 5-10 min per scan on average to compute and demonstrates highly significant (p < 0.0001) and validation-consistent Spearman correlation coefficients (0.75, 0.76, and 0.65) for the expanded disability status scale (EDSS), Scripps neurological rating scale (SNRS), and symbol digit modality test (SDMT) measures of neurological disability, respectively. Because COMRIS is not greatly influenced by MRI scanners or protocols and can be computed even in the presence of some motion artifacts, it does not require censoring out patients and it provides comparable results across different cohorts. As such, it represents a broadly available clinical and research tool that can facilitate multicenter research studies and comparative analyses across patient cohorts and research projects.

An expanded composite scale of MRI-defined disease severity in multiple sclerosis: MRDSS2

The objective of this study was to test a new version of the Magnetic Resonance Disease Severity Scale (MRDSS2), incorporating cerebral gray matter (GM) and spinal cord involvement from 3 T MRI, in modeling the relationship between MRI and physical disability or cognitive status in multiple sclerosis (MS). Fifty-five MS patients and 30 normal controls underwent high-resolution 3 T MRI. The patients had an Expanded Disability Status Scale score of 1.6±1.7 (mean±SD). The cerebral normalized GM fraction (GMF), the T2 lesion volume (T2LV), and the ratio of T1 hypointense LV to T2LV (T1/T2) were derived from brain images. Upper cervical spinal cord area (UCCA) was obtained from spinal cord images. A within-subject d-score (difference of MS from normal control) for each MRI component was calculated, equally weighted, and summed to form MRDSS2. With regard to the relationship between physical disability and MRDSS2 or its individual components, MRI–Expanded Disability Status Scale correlations were significant for MRDSS2 (r=0.33, P=0.013) and UCCA (r=−0.33, P=0.015), but not for GMF (P=0.198), T2LV (P=0.707), and T1/T2 (P=0.240). The inclusion of UCCA appeared to drive this MRI–disability relationship in MRDSS2. With regard to cognition, MRDSS2 showed a larger effect size (P=0.035) than its individual components [GMF (P=0.081), T2LV (P=0. 179), T1/T2 (P=0.043), and UCCA (P=0.818)] in comparing cognitively impaired with cognitively preserved patients (defined by the Minimal Assessment of Cognitive Function in MS). Both cerebral lesions (T1/T2) and atrophy (GMF) appeared to drive this relationship. We describe a new version of the MRDSS, which has been expanded to include cerebral GM and spinal cord involvement. MRDSS2 has concurrent validity with clinical status.

Insights from magnetic resonance imaging

Recent years have witnessed impressive advancements in the use of magnetic resonance imaging (MRI) for the assessment of patients with multiple sclerosis (MS). Complementary to the clinical evaluation, conventional MRI (cMRI) provides crucial pieces of information for the diagnosis of MS, the understanding of its natural history, and monitoring the efficacy of experimental treatments. Measures derived from cMRI present clear advantages over the clinical assessment, including their more objective nature and an increased sensitivity to MS-related changes. However, the correlation between these measures and the clinical manifestations of the disease remains weak, and this can be explained, at least partially, by the limited ability of cMRI to characterize and quantify the heterogeneous features of MS pathology. Quantitative MR-based techniques have the potential to overcome the limitations of cMRI. Magnetization transfer MRI, diffusion-weighted and diffusion tensor MRI with fiber tractography, proton magnetic resonance spectroscopy, T1 and T2 relaxation time measurement, and functional MRI are contributing to elucidate the mechanisms that underlie injury, repair, and functional adaptation in patients with MS. All conventional and nonconventional MR techniques will benefit from the use of high-field MR systems (3.0T or more).

Gradient echo magnetic resonance imaging correlates with clinical measures and allows visualization of veins within multiple sclerosis lesions

BACKGROUND

Conventional magnetic resonance imaging (MRI) methods do not quantify the severity of multiple sclerosis (MS) white matter lesions or measure pathology within normal-appearing white matter (NAWM).

OBJECTIVE

Gradient Echo Plural Contrast Imaging (GEPCI), a fast MRI technique producing inherently co-registered images for qualitative and quantitative assessment of MS, was used to 1) correlate with disability; 2) distinguish clinical MS subtypes; 3) determine prevalence of veins co-localized within lesions in WM.

METHODS

Thirty subjects representing relapsing-remitting MS (RRMS), secondary progressive MS (SPMS) and primary progressive MS (PPMS) subtypes were scanned with clinical and GEPCI protocols. Standard measures of physical disability and cognition were correlated with magnetic resonance metrics. Lesions with central veins were counted for RRMS subjects.

RESULTS

Tissue damage load (TDL-GEPCI) and lesion load (LL-GEPCI) derived with GEPCI correlated better with MS functional composite (MSFC) measures and most other neurologic measures than lesion load derived with FLAIR (LL-FLAIR). GEPCI correctly classified clinical subtypes in 70% subjects. A central vein could be identified in 76% of WM lesions in RRMS subjects on GEPCI T2*-SWI images.

CONCLUSION

GEPCI lesion metrics correlated better with neurologic disability than lesion load derived using FLAIR imaging, and showed promise in classifying clinical subtypes of MS. These improvements are likely attributable to the ability of GEPCI to quantify tissue damage.

Metabolomic approach to human brain spectroscopy identifies associations between clinical features and the frontal lobe metabolome in multiple sclerosis

Proton magnetic resonance spectroscopy ((1)H-MRS) is capable of noninvasively detecting metabolic changes that occur in the brain tissue in vivo. Its clinical utility has been limited so far, however, by analytic methods that focus on independently evaluated metabolites and require prior knowledge about which metabolites to examine. Here, we applied advanced computational methodologies from the field of metabolomics, specifically partial least squares discriminant analysis and orthogonal partial least squares, to in vivo (1)H-MRS from frontal lobe white matter of 27 patients with relapsing-remitting multiple sclerosis (RRMS) and 14 healthy controls. We chose RRMS, a chronic demyelinating disorder of the central nervous system, because its complex pathology and variable disease course make the need for reliable biomarkers of disease progression more pressing. We show that in vivo MRS data, when analyzed by multivariate statistical methods, can provide reliable, distinct profiles of MRS-detectable metabolites in different patient populations. Specifically, we find that brain tissue in RRMS patients deviates significantly in its metabolic profile from that of healthy controls, even though it appears normal by standard MRI techniques. We also identify, using statistical means, the metabolic signatures of certain clinical features common in RRMS, such as disability score, cognitive impairments, and response to stress. This approach to human in vivo MRS data should promote understanding of the specific metabolic changes accompanying disease pathogenesis, and could provide biomarkers of disease progression that would be useful in clinical trials.

Advanced magnetic resonance imaging in pediatric multiple sclerosis

This review summarizes results from studies that have applied advanced magnetic resonance (MR) imaging techniques to patients with pediatric-onset multiple sclerosis (MS), and includes a discussion of cortical imaging techniques, volumetry, magnetization transfer and diffusion tensor imaging, proton magnetic resonance spectroscopy, and functional MR imaging. Multicenter studies on the sensitivity of these techniques to natural history of disease and treatment response are required before their implementation into clinical practice.

Revisiting brain atrophy and its relationship to disability in multiple sclerosis

Background

Brain atrophy is a well-accepted imaging biomarker of multiple sclerosis (MS) that partially correlates with both physical disability and cognitive impairment.

Methodology/Principal Findings

Based on MRI scans of 60 MS cases and 37 healthy volunteers, we measured the volumes of white matter (WM) lesions, cortical gray matter (GM), cerebral WM, caudate nucleus, putamen, thalamus, ventricles, and brainstem using a validated and completely automated segmentation method. We correlated these volumes with the Expanded Disability Status Scale (EDSS), MS Severity Scale (MSSS), MS Functional Composite (MSFC), and quantitative measures of ankle strength and toe sensation. Normalized volumes of both cortical and subcortical GM structures were abnormally low in the MS group, whereas no abnormality was found in the volume of the cerebral WM. High physical disability was associated with low cerebral WM, thalamus, and brainstem volumes (partial correlation coefficients ∼0.3–0.4) but not with low cortical GM volume. Thalamus volumes were inversely correlated with lesion load (r = −0.36, p<0.005).

Conclusion

The GM is atrophic in MS. Although lower WM volume is associated with greater disability, as might be expected, WM volume was on average in the normal range. This paradoxical result might be explained by the presence of coexisting pathological processes, such as tissue damage and repair, that cause both atrophy and hypertrophy and that underlie the observed disability.

Magnetic resonance disease severity scale (MRDSS) for patients with multiple sclerosis: a longitudinal study

BACKGROUND

We previously described a composite MRI scale combining T1-lesions, T2-lesions and whole brain atrophy in multiple sclerosis (MS): the magnetic resonance disease severity scale (MRDSS).

OBJECTIVE

Test strength of the MRDSS vs. individual MRI measures for sensitivity to longitudinal change.

METHODS

We studied 84 MS patients over a 3.2±0.3 year follow-up. Baseline and follow-up T2-lesion volume (T2LV), T1-hypointense lesion volume (T1LV), and brain parenchymal fraction (BPF) were measured. MRDSS was the combination of standardized T2LV, T1/T2 ratio and BPF.

RESULTS

Patients had higher MRDSS at follow-up vs. baseline (p<0.001). BPF decreased (p<0.001), T1/T2 increased (p<0.001), and T2LV was unchanged (p>0.5). Change in MRDSS was larger than the change in MRI subcomponents. While MRDSS showed significant change in relapsing-remitting (RR) (p<0.001) and secondary progressive (SP) phenotypes (p<0.05), BPF and T1/T2 ratio changed only in RRMS (p<0.001). Longitudinal change in MRDSS was significantly different between RRMS and SPMS (p=0.0027); however, change in the individual MRI components did not differ. Evaluation with respect to predicting on-study clinical worsening as measured by EDSS revealed a significant association only for T2LV (p=0.038).

CONCLUSION

Results suggest improved sensitivity of MRDSS to longitudinal change vs. individual MRI measures. MRDSS has particularly high sensitivity in RRMS.

Multiple Sclerosis Severity Scale and whole-brain N-acetylaspartate concentration for patients' assessment

BACKGROUND

The ability to predict the course of multiple sclerosis (MS) is highly desirable but lacking.

OBJECTIVE

To test whether the MS Severity Scale (MSSS) and global neuronal viability, assessed through the quantification of the whole-brain N-acetylaspartate concentration (WBNAA), concur or complement the assessment of individual patients' disease course.

METHODS

The MSSS and average WBNAA loss rate (ΔWBNAA, extrapolated based on one current measurement and the assumption that at disease onset neural sparing was similar to healthy controls, obtained with proton magnetic resonance (MR) spectroscopy and magnetic resonance imaging (MRI)) from 61 patients with MS (18 male and 43 female) with long disease duration (15 years or more) were retrospectively examined. Some 27 patients exhibited a 'benign' disease course, characterized by an Expanded Disability Status Scale score (EDSS) of 3.0 or less, and 34 were 'non-benign': EDSS score higher than 3.0.

RESULTS

The two cohorts were indistinguishable in age and disease duration. Benign patients' EDSS and MSSS (2.1 ± 0.7, 1.15 ± 0.60) were significantly lower than non-benign (4.6 ± 1.0, 3.6 ± 1.2; both p < 10(-4)). Their respective average ΔWBNAA, 0.10 ± 0.16 and 0.11 ± 0.12 mM/year, however, were not significantly different (p > 0.7). While MSSS is both sensitive to (92.6%) and specific for (97.0%) benign MS, ΔWBNAA is only sensitive (92.6%) but not specific (2.9%).

CONCLUSION

Since the WBNAA loss rate is similar in both phenotypes, the only difference between them is their clinical classification, characterized by MSSS and EDSS. This may indicate that 'benign' MS probably reflects fortuitous sparing of clinically eloquent brain regions and better utilization of brain plasticity.

The generation and validation of white matter connectivity importance maps

Both the size and location of injury in the brain influences the type and severity of cognitive or sensorimotor dysfunction. However, even with advances in MR imaging and analysis, the correspondence between lesion location and clinical deficit remains poorly understood. Here, structural and diffusion images from 14 healthy subjects are used to create spatially unbiased white matter connectivity importance maps that quantify the amount of disruption to the overall brain network that would be incurred if that region were compromised. Some regions in the white matter that were identified as highly important by such maps have been implicated in strategic infarct dementia and linked to various attention tasks in previous studies. Validation of the maps is performed by investigating the correlations of the importance maps' predicted cognitive deficits in a group of 15 traumatic brain injury patients with their cognitive test scores measuring attention and memory. While no correlation was found between amount of white matter injury and cognitive test scores, significant correlations (r>0.68, p<0.006) were found when including location information contained in the importance maps. These tools could be used by physicians to improve surgical planning, diagnosis, and assessment of disease severity in a variety of pathologies like multiple sclerosis, trauma, and stroke.

In vivo evidence of disseminated subpial T2* signal changes in multiple sclerosis at 7 T: a surface-based analysis

Cortical subpial demyelination is frequent in multiple sclerosis (MS) and is closely associated with disease progression and poor neurological outcome. Although cortical lesions have been difficult to detect using conventional MRI, preliminary data using T2*-weighted imaging at ultra-high field 7T MRI showed improved sensitivity for detecting and categorizing different histological types of cortical MS lesions. In this study we combined high-resolution 7T MRI with a surface-based analysis technique to quantify and map subpial T2*-weighted signal changes in seventeen patients with MS. We applied a robust method to register 7T data with the reconstructed cortical surface of each individual and used a general linear model to assess in vivo an increase in subpial T2*-weighted signal in patients versus age-matched controls, and to investigate the spatial distribution of cortical subpial changes across the cortical ribbon. We also assessed the relationship between subpial T2* signal changes at 7T, Expanded Disability Status Scale (EDSS) score and white matter lesion load (WMLL). Patients with MS showed significant T2*-weighted signal increase in the frontal lobes (parsopercularis, precentral gyrus, middle and superior frontal gyrus, orbitofrontal cortex), anterior cingulate, temporal (superior, middle and inferior temporal gyri), and parietal cortices (superior and inferior parietal cortex, precuneus), but also in occipital regions of the left hemisphere. We found significant correlations between subpial T2*-weighted signal and EDSS score in the precentral gyrus (ρ=0.56, P=0.02) and between T2*-weighted signal and WMLL in the lateral orbitofrontal, superior parietal, cuneus, precentral and superior frontal regions. Our data support the presence of disseminated subpial increases in T2* signal in subjects with MS, which may reflect the diffuse subpial pathology described in neuropathology.

Global N-acetylaspartate declines even in benign multiple sclerosis

BACKGROUND AND PURPOSE

Neuro-axonal damage is a well known sequelae of MS pathogeneses. Consequently, our aim was to test whether the ∼20% of patients with MS exhibiting a clinically benign disease course also have minimal neural dysfunction as reflected by the global concentration of their MR imaging marker NAA.

MATERIALS AND METHODS

Q(NAA) was obtained with nonlocalizing whole-head (1)H-MR spectroscopy in 43 patients with benign RRMS (30 women, 13 men; mean age, 44.7 ± 7.3 years of age) with 21.0 ± 4.4 years (range, 15-35 years) of disease duration from the first symptom and an EDSS score of 1.9 (range, 0-3). Q(NAA) was by divided by the brain volume (from MR imaging segmentation) to normalize it into WBNAA. All participants gave institutional review board-approved written informed consent, and the study was HIPAA compliant.

RESULTS

The patients' lesion load was 12.2 ± 7.7 cm(3). Their 8.3 ± 1.8 mmol/L WBNAA was 35% lower than that in controls (P < .001). Individual average loss rates (absolute loss compared with controls divided by disease duration) clustered around 0.22 ± 0.09 mmol/L/year (1.7%/year, assuming monotonic decline). This rate could be extrapolated from that already reported for patients with RRMS of much shorter disease duration. WBNAA did not correlate with lesion load or EDSS.

CONCLUSIONS

Normal WBNAA is not characteristic of benign MS and is not an early predictor of its course. These patients, therefore, probably benefit from successful compensation and sparing of eloquent regions. Because they may ultimately have a rapid decline once their brain plasticity is exhausted, they may benefit from treatment options offered to more affected patients.

In vivo quantitative evaluation of brain tissue damage in multiple sclerosis using gradient echo plural contrast imaging technique

Conventional MRI based on weighted spin-echo (SE) images aids in the diagnosis of multiple sclerosis (MS); however, MRI markers derived from SE sequences provide limited information about lesion severity and correlate poorly with patient disability assessed with clinical tests. In this study, we introduced a novel method [based on quantitative R2* (1/T2*) histograms] for estimating the severity of brain tissue damage in MS lesions. We applied at 1.5T an advanced, multi-gradient echo MRI technique [gradient echo plural contrast imaging (GEPCI)] to obtain images of the brains of healthy control subjects and subjects with MS. GEPCI is a simple yet robust technique allowing simultaneous acquisition of inherently co-registered quantitative T2* and FLAIR-like maps, along with T1-weighted images within a clinically acceptable time frame. Images obtained with GEPCI appear highly similar to standard scans; hence, they can be used in a reliable and conventional way for a clinical evaluation of the disease. Yet, the main advantage of GEPCI approach is its quantitative nature. Analysis of R2* histograms of white matter revealed a difference in the distribution between healthy subjects and subjects with MS. Based on this difference, we developed a new method for grading the severity of tissue damage [tissue damage score (TDS)] in MS lesions. This method also provides a tissue damage load (TDL) assessing both lesion load and lesion severity, and a mean tissue damage score (MTDS) estimating the average MS lesion damage. We found promising correlations between the results derived from this method and the standard measure of clinical disability.

Multiple sclerosis lesions: insights from imaging techniques

The hallmark of multiple sclerosis (MS) pathology is the presence of inflammatory demyelinated lesions distributed throughout the CNS. Along with more diffuse tissue abnormalities, it is considered one of the major determinants of neurological deficit in MS. Conventional MRI has contributed to improve our understanding of MS pathology and has provided objective and reliable measures to monitor the effect of treatments. Advanced MRI techniques have offered the opportunity to quantify pathological changes in lesions, as well as in normal-appearing brain tissue and to characterize their dynamics. This review will discuss the characteristics and development of MS lesions and the contribution of conventional and quantitative MRI techniques to understanding pathological changes associated with them.

A multiparametric evaluation of regional brain damage in patients with primary progressive multiple sclerosis

The purpose of this study is to define the topographical distribution of gray matter (GM) and white matter (WM) damage in patients with primary progressive multiple sclerosis (PPMS), using a multiparametric MR-based approach. Using a 3 Tesla scanner, dual-echo, 3D fast-field echo (FFE), and diffusion tensor (DT) MRI scans were acquired from 18 PPMS patients and 17 matched healthy volunteers. An optimized voxel-based (VB) analysis was used to investigate the patterns of regional GM density changes and to quantify GM and WM diffusivity alterations of the entire brain. In PPMS patients, GM atrophy was found in the thalami and the right insula, while mean diffusivity (MD) changes involved several cortical-subcortical structures in all cerebral lobes and the cerebellum. An overlap between decreased WM fractional anisotropy (FA) and increased WM MD was found in the corpus callosum, the cingulate gyrus, the left short temporal fibers, the right short frontal fibers, the optic radiations, and the middle cerebellar peduncles. Selective MD increase, not associated with FA decrease, was found in the internal capsules, the corticospinal tracts, the superior longitudinal fasciculi, the fronto-occipital fasciculi, and the right cerebral peduncle. A discrepancy was found between regional WM diffusivity changes and focal lesions because several areas had DT MRI abnormalities but did not harbor T2-visible lesions. Our study allowed to detect tissue damage in brain areas associated with motor and cognitive functions, which are known to be impaired in PPMS patients. Combining regional measures derived from different MR modalities may be a valuable tool to improve our understanding of PPMS pathophysiology.

In vivo imaging of cortical pathology in multiple sclerosis using ultra-high field MRI

OBJECTIVE

We used ultra-high field MRI to visualize cortical lesion types described by neuropathology in 16 patients with multiple sclerosis (MS) compared with 8 age-matched controls; to characterize the contrast properties of cortical lesions including T2*, T2, T1, and phase images; and to investigate the relationship between cortical lesion types and clinical data.

METHODS

We collected, on a 7-T scanner, 2-dimensional fast low-angle shot (FLASH)-T2*-weighted spoiled gradient-echo, T2-weighted turbo spin-echo (TSE) images (0.33 x 033 x 1 mm(3)), and a 3-dimensional magnetization-prepared rapid gradient echo.

RESULTS

Overall, 199 cortical lesions were detected in patients on both FLASH-T2* and T2-TSE scans. Seven-tesla MRI allowed for characterization of cortical plaques into type I (leukocortical), type II (intracortical), and type III/IV (subpial extending partly or completely through the cortical width) lesions as described histopathologically. Types III and IV were the most frequent type of cortical plaques (50.2%), followed by type I (36.2%) and type II (13.6%) lesions. Each lesion type was more frequent in secondary progressive than in relapsing-remitting MS. This difference, however, was significant only for type III/IV lesions. T2*-weighted images showed the highest, while phase images showed the lowest, contrast-to-noise ratio for all cortical lesion types. In patients, the number of type III/IV lesions was associated with greater disability (p < 0.02 by Spearman test) and older age (p < 0.04 by Spearman test).

CONCLUSIONS

Seven-tesla MRI detected different histologic cortical lesion types in our small multiple sclerosis (MS) sample, suggesting, if validated in a larger population, that it may prove a valuable tool to assess the contribution of cortical MS pathology to clinical disability.

In-vivo evidence for stable neuroaxonal damage in the brain of patients with benign multiple sclerosis

OBJECTIVE

The term benign multiple sclerosis (BMS) is referred to patients who have a mild or absent disability several years after disease clinical onset. Axonal damage can be measured in vivo using proton MR spectroscopy ((1)H-MRS). In this study, we quantified the severity of "global" axonal damage in BMS and early relapsing-remitting (RR) MS patients, using whole brain N-acetylaspartate (WBNAA) (1)H-MRS, to better elucidate the structural correlates of a non-disabling disease evolution.

METHODS

WBNAA concentration was measured in 37 patients with BMS (mean disease duration 22.3 years) and 17 patients with early RRMS (mean disease duration 4.0 years), using an unlocalized (1)H-MRS sequence. Dual echo and T1-weighted scans were also obtained to measure T2-hyperintense lesion volume (TLV) and normalized brain volume (NBV).

RESULTS

TLV was higher in BMS (mean TLV = 13.1 mL) than in early RRMS patients (mean TLV = 7.2 mL) (P = 0.018), whereas neither NBV (mean NBV: 1491.0 mL in BMS vs 1520.3 mL in RRMS) nor WBNAA concentration (mean WBNAA: 10.5 mmol in BMS vs 11.4 mmol in RRMS) significantly differed between the two groups. In MS patients, no correlation was found between WBNAA concentration and Expanded Disability Status Scale (EDSS), TLV and NBV.

CONCLUSIONS

The similar WBNAA concentrations seen in BMS and early RRMS patients fit with the notion that a non-disabling long-term evolution of MS may be due, at least in part, to non-progression of pathology. Such a condition seems to be independent from MRI-visible lesions burden.

Spinal-cord MRI in multiple sclerosis: conventional and nonconventional MR techniques

Multiple sclerosis is a diffuse disease of the central nervous system, and MRI of the spinal cord is highly recommended in the clinical evaluation of patients suspected of having multiple sclerosis. Within the new diagnostic criteria, spinal cord MRI increases sensitivity and possibly specificity for MS, but further work is needed to investigate other criteria that may give greater weight to the presence of cord lesions in patients with clinically isolated syndromes or suspected relapsing-remitting multiple sclerosis. Techniques should be further studied and validated in studies comparing these techniques with clinical status and histopathology, however.

Predicting clinical progression in multiple sclerosis with the magnetic resonance disease severity scale

BACKGROUND

Individual magnetic resonance imaging (MRI) disease severity measures, such as atrophy or lesions, show weak relationships to clinical status in patients with multiple sclerosis (MS).

OBJECTIVE

To combine MS-MRI measures of disease severity into a composite score.

DESIGN

Retrospective analysis of prospectively collected data.

SETTING

Community-based and referral subspecialty clinic in an academic hospital.

PATIENTS

A total of 103 patients with MS, with a mean (SD) Expanded Disability Status Scale (EDSS) score of 3.3 (2.2), of whom 62 (60.2%) had the relapsing-remitting, 33 (32.0%) the secondary progressive, and 8 (7.8%) the primary progressive form.

MAIN OUTCOME MEASURES

Brain MRI measures included baseline T2 hyperintense (T2LV) and T1 hypointense (T1LV) lesion volume and brain parenchymal fraction (BPF), a marker of global atrophy. The ratio of T1LV to T2LV (T1:T2) assessed lesion severity. A Magnetic Resonance Disease Severity Scale (MRDSS) score, on a continuous scale from 0 to 10, was derived for each patient using T2LV, BPF, and T1:T2.

RESULTS

The MRDSS score averaged 5.1 (SD, 2.6). Baseline MRI and EDSS correlations were moderate for BPF, T1:T2, and MRDSS and weak for T2LV. The MRDSS showed a larger effect size than the individual MRI components in distinguishing patients with the relapsing-remitting form from those with the secondary progressive form. Models containing either T2LV or MRDSS were significantly associated with disability progression during the mean (SD) 3.2 (0.3)-year observation period, when adjusting for baseline EDSS score.

CONCLUSION

Combining brain MRI lesion and atrophy measures can predict MS clinical progression and provides the basis for developing an MRI-based continuous scale as a marker of MS disease severity.

Axonal injury detected by in vivo diffusion tensor imaging correlates with neurological disability in a mouse model of multiple sclerosis

Recent studies have suggested that axonal damage, and not demyelination, is the primary cause of long-term neurological impairment in multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE). The axial and radial diffusivities derived from diffusion tensor imaging have shown promise as non-invasive surrogate markers of axonal damage and demyelination, respectively. In this study, in vivo diffusion tensor imaging of the spinal cords from mice with chronic EAE was performed to determine if axial diffusivity correlated with neurological disability in EAE assessed by the commonly used clinical scoring system. Axial diffusivity in the ventrolateral white matter showed a significant negative correlation with EAE clinical score and was significantly lower in mice with severe EAE than in mice with moderate EAE. Furthermore, the greater decreases in axial diffusivity were associated with greater amounts of axonal damage, as confirmed by quantitative staining for non-phosphorylated neurofilaments (SMI32). Radial diffusivity and relative anisotropy could not distinguish between the groups of mice with moderate EAE and those with severe EAE. The results further the notion that axial diffusivity is a non-invasive marker of axonal damage in white matter and could provide the necessary link between pathology and neurological disability.

Magnetic resonance imaging metrics and their correlation with clinical outcomes in multiple sclerosis: a review of the literature and future perspectives

Magnetic resonance imaging (MRI) has revolutionized the diagnosis and management of patients with multiple sclerosis (MS). Conventional MRI metrics are employed as primary endpoints in proof-of-concept clinical trials evaluating new drugs for MS and as secondary endpoints in definitive phase III trials. Metrics derived from non-conventional MRI techniques are now emerging and hold significant promise since they appear to be more correlated with the most disabling features of MS. However, none of these has been approved for use as a surrogate endpoint for accumulation of physical disability, which is the most important clinical endpoint of this disease. Taking into account the large numbers of patients needed, the extensive exposure to placebo, and the relatively long duration required for phase III clinical trials to show a meaningful effect on progression of disability, the need for a valid, reliable, and objective paraclinical marker of disease evolution cannot be overemphasized. This paper reviews the most up-to-date data regarding MRI techniques, their relationship with central nervous system pathology, as well as with clinical endpoints, and proposes future insights into the use of MRI metrics as surrogate endpoints in clinical trials of MS.

Clinically benign multiple sclerosis despite large T2 lesion load: can we explain this paradox?

Magnetic resonance imaging (MRI) techniques such as magnetization transfer imaging and magnetic resonance spectroscopy (MRS) may reveal otherwise undetectable tissue damage in multiple sclerosis (MS) and can serve to explain more severe disability than expected from conventional MRI. That an inverse situation may exist where non-conventional quantitative MRI and MRS metrics would indicate less abnormality than expected from T2 lesion load to explain preserved clinical functioning was hypothesized. Quantitative MRI and MRS were obtained in 13 consecutive patients with clinically benign MS (BMS; mean age 44 +/- 9 years) despite large T 2 lesion load and in 15 patients with secondary progressive MS (SPMS; mean age 47 +/- 6 years) matched for disease duration. The magnetization transfer ratio (MTR), magnetization transfer rate (kfor), brain parenchymal fraction (BPF) and brain metabolite concentrations from proton MRS were determined. BMS patients were significantly less disabled than their SPMS counterparts (mean expanded disability status score: 2.1 +/- 1.1 versus 6.2 +/- 1.1; P < 0.001) and had an even somewhat higher mean T2 lesion load (41.2 +/- 27.1 versus 27.9 +/- 24.8 cm3; P = 0.19). Normal appearing brain tissue histogram metrics for MTR and kfor, mean MTR and kfor of MS lesions and mean BPF were similar in BMS and SPMS patients. Levels of N-acetyl-aspartate, choline and myoinositol were comparable between groups. This study thus failed to explain the preservation of function in our BMS patients with large T2 lesion load by a higher morphologic or metabolic integrity of the brain parenchyma. Functional compensation must come from other mechanisms such as brain plasticity.

Interferon Beta-1b may reverse axonal dysfunction in multiple sclerosis

Progression of the disability of multiple sclerosis (MS) is thought to be related to axonal damage that is seen even in normal appearing white matter (NAWM) of patients' brains. Interferon beta (IFNβ) treatment for MS reduces the frequency of clinical exacerbations and the appearance of new inflammatory demyelinating lesions on magnetic resonance imaging (MRI). However, the effect of IFNβ treatment on axonal damage in MS is not known. The present study aimed to assess the effect of IFNβ on axonal function by comparing the data from localised single voxel proton MR spectroscopy (MRS) performed on eight MS patients given IFNβ-1b treatment and 11 untreated patients. Brain MRI and MRS were performed before the initiation of IFNβ-1b treatment and 24 months after treatment initiation. Levels of N-acetylaspartate (NAA), choline-containing compounds (Cho) and creatine (Cr) were calculated as the areas under their peaks shown on MRS and the ratios of NAA/Cr and Cho/Cr were calculated. In the patients treated with IFNβ-1b there was a significant increase in the ratio of NAA/Cr in NAWM (p=0.028) at 24 months after the initiation of treatment. In contrast, there was no significant change in the NAA/Cr ratio in the untreated patients. These results suggest that IFNβ-1b treatment might recover axonal function in NAWM of MS patients.

The contribution of diffusion-weighted MR imaging in multiple sclerosis during acute attack

PURPOSE

The aims of the study are firstly, to determine the difference in diffusion-weighted imaging (DWI) in normal appearing white matter (NAWM) between patients with acute multiple sclerosis (MS) and controls; secondly, to determine whether there is a correlation between EDSS scores and DWI in acute plaques and also NAWM.

MATERIALS AND METHOD

Out of 50 patients with acute MS attack, 35 patients had active plaques with diffuse or ring enhancement on postcontrast images. Eighteen healthy volunteers constituted the control group. While 26 of 35 had relapsing-remitting, 9 had secondary progressive MS. Apparent diffusion coefficients (ADC) of the active plaques, NAWM at the level of centrum semiovale and occipital horn of lateral ventricle in the patients and NAWM in control group were measured. ADC values of active plaques were compared with WM of the patients and the control group. The relationship of ADC value of active plaques and WM in MS with expanded disability status scale (EDSS) was investigated by using Mann-Whitney U-test.

RESULTS

Of 63 plaques totally, 26 and 37 of the active plaques had diffuse and ring enhancement, respectively. There was no statistically significant difference between ADC value of active plaques and EDSS (p>0.05). However, there was a statistically significant difference between ADC value of WM occipital horn and EDSS (p<0.05). ADC value of active plaques were higher than WM in both groups (p<0.001). The difference between ADC value of WM at the centrum semiovale (p<0.05) and occipital horns (p<0.001) in patients and controls was statistically significant. There was no statistically significant difference between EDSS scores, ADC value at centrum semiovale and WM around occipital horn and active plaques in subgroups (p>0.05).

CONCLUSION

Apparently normal tissue in MS patients may show early abnormalities when investigated carefully enough, and there is an even though moderate correlation between EDSS and ADC values and early alterations of ADC value are starting in the occipital white matter along the ventricles. This has to be verified in larger series.

Diffusion tensor MRI in multiple sclerosis

During the last 10 years, thanks to the development of sophisticated acquisition schemes and the application of novel image analysis and postprocessing, diffusion tensor (DT) magnetic resonance imaging (MRI) has increasingly been applied to the study of multiple sclerosis (MS). DT MRI proved to be able to detect and quantify tissue damage within and outside T2-visible MS lesions. In addition, DT MRI has been shown to be sensitive to the evolution of MS damage over short-term periods of time, and therefore holds promise to provide us with in vivo correlates of MS clinical severity, as well as predictors of long-term disease evolution. Recent developments of the technique, such as DT tractography, are likely to improve dramatically our understanding of the mechanisms associated to the accumulation of MS disability. Unresolved issues to be addressed include the definition of the actual features underlying diffusion changes in MS and the potential of DT MRI in the differential diagnosis between MS and other demyelinating conditions. The best acquisition and postprocessing strategies for DT MRI studies of MS also remain a matter of debate. Moreover, the precision and accuracy of DT MRI scans in detecting longitudinal, MS-related changes need to be further investigated. This is a pivotal issue for a future application of DT MRI to the monitoring of MS evolution in large-scale clinical trials and, possibly, in individual patients.

The role of hereditary spastic paraplegia related genes in multiple sclerosis. A study of disease susceptibility and clinical outcome

Multiple sclerosis (MS) is a common inflammatory disease of the central nervous system unsurpassed for its variability in disease outcome. It has been observed that axonal loss in MS is significant and that irreversible clinical disability relates to such axonal loss. The clinical similarities between Hereditary Spastic Paraplegia (HSP) and progressive MS, along with their analogous profiles of axonal loss in the long tracts, make the genes known to cause HSP biologically relevant candidates for the study of clinical outcome in MS. A cohort of sporadic MS cases and a set of unaffected controls were used to determine the role of HSP genes on MS susceptibility and disease severity. The MS cases were taken from opposite extremes of the putative distribution of long-term outcome using the most stringent clinical criteria to date. Genotyping the two sets of MS patients and controls could not provide any evidence to suggest that genes involved in the pathogenesis of HSP (Paraplegin, NIPA1, KIF5A, HSPD1, Atlastin, Spartin, Spastin, PLP1, L1CAM, Maspardin and BSCL2) play a role in susceptibility to, or modifying the course of, MS, although small effects of these genes cannot be ruled out.

Structural and functional surrogates of cognitive impairment at the very early stage of multiple sclerosis

Following our previous reports based on parametric MRI methods (T(2)-weighted MRI, statistical mapping analysis of magnetization transfer ratio images and functional MRI) applied to a population of 18 patients with clinically isolated syndrome suggestive of multiple sclerosis, we have reviewed the possible structural and functional surrogates of MS that could explain the subtle cognitive impairment related to attention and working memory deficits evaluated with paced auditory serial addition test (PASAT). We propose that the brain substrates underlying cognitive impairment observed at the very early stage of MS are multifactorial. Several components could influence PASAT performances in patients: i) the extent of diffuse white matter damage, ii) the location of visible and non visible lesions, iii) the connectivity efficiency between distant brain functional areas involved in working memory processes and iv) the cortical reorganization. Nevertheless, individually, each of these parameters may have few influences on PASAT performance in patients. Using a multiregression model built with independent MR parameters, a very good evaluation of PASAT scores has been obtained in this limited number of patients explaining 90% of the variance. In conclusion, the different aspects of tissue and functional pathological brain underpinnings must be accounted to monitor accurately new therapeutic strategies for the treatment of early cognitive deficits related to MS.

Multiple sclerosis trial designs for the 21st century: building on recent lessons

Starting with the first positive pilot study of glatiramer acetate, trial design in multiple sclerosis has advanced considerably over the past two decades, successively building and improving on previous successes in the implementation and analysis of new clinical trials. Most of these trials have been successful and this has led to the regulatory approval and commercial availability of six agents for the treatment of multiple sclerosis. During this period, outcome measures have been validated to determine the efficacy and safety of such agents, notably those useful in reducing the inflammatory aspects of disease. These include measurements of relapse reduction (annualized relapse rate, time to first relapse, proportion of subjects relapse free), disability (change in EDSS score, change in MSFC score) and MRI metrics (measurements of gadolinium-enhancing lesions, T1 and T2 lesion load). Recent trial design has shown that one can answer some clinical questions after one year on study and that these results may be predictive of more robust two-year trial data. The other important recent lesson involves emergence of rare complications of immunomodulatory therapy, namely progressive multifocal leucoencephalopathy with natalizumab that blocks the access of immune cells to the nervous system. In addition to the increased need for enhanced safety assessment, this issue will have an impact both on the study of combination therapies and on the use of combinations in clinical practice.

1H-MRS quantification of tNA and tCr in patients with multiple sclerosis: a meta-analytic review

Meta-analysis was performed on the results of 75 comparisons from the 30 peer-reviewed publications that used proton magnetic resonance spectroscopy (1H-MRS) or spectroscopic imaging to (i) quantify the mean concentrations of total creatine (tCr, found in neurons, astrocytes and oligodendrocytes), and/or total N-acetyl groups (tNA, found only in neurons), in the lesional and/or non-lesional white matter (WM) and/or the grey matter (GM) of patients with multiple sclerosis (MS) and (ii) compare these values with those in the homologous tissues of normal controls (NC). For mean [tNA] values, there was (i) a large-effect-sized overall decrease in patients' lesional WM relative to NC WM (25 comparisons), (ii) a medium-effect-sized overall decrease in patients' non-lesional WM relative to NC WM (36 comparisons) and (iii) a medium-effect-sized overall decrease in patients' GM relative to NC GM (14 comparisons). Patients' mean [tNA] values were sometimes statistically normal but were never statistically increased. For mean [tCr] values, there was (i) no statistically significant overall change in the patients' lesional WM relative to NC WM (24 comparisons), although statistically significant increases and decreases were sometimes found, (ii) a medium-effect-sized overall increase in patients' non-lesional WM relative to NC WM (33 comparisons) and (iii) no statistically significant overall change in patients' GM relative to NC GM (12 comparisons), although a significant decrease was found in one comparison. Of 41 comparisons with statistically significant changes, 38 combined in a way that would probably result in decreased mean [tNA]/[tCr] ratios such that (i) 66% had statistically decreased mean [tNA] and statistically unchanged mean [tCr] values, (ii) 13% had statistically decreased mean [tNA] and statistically increased mean [tCr] values and (iii) 21% had statistically unchanged mean [tNA] values and statistically increased mean [tCr] values. Of the 25 comparisons that came from studies that also analysed [tNA]/[tCr] ratios, the direction of change in mean [tNA] values and mean [tNA]/[tCr] ratios was concordant in 84%. In comparisons that quantified both [tNA] and [tCr], there was a similar amount of variability in both measures in each of the different tissue types studied, both in patients and NCs. Together, these results suggest that within-voxel tNA/tCr ratios can be interpreted as valid and accurate surrogate measures of 'cerebral tissue integrity'-with decreased tNA/tCr ratios indicating some combination of neuroaxonal disturbance, oligodendroglial disturbance, and astrocytic proliferation. These results also suggest that, although within-voxel tNA/tCr ratios are not perfect indicators of [tNA] content, they do represent a practical compromise to acquiring surrogate measures of within-voxel neuroaxonal integrity.

Magnetic Resonance Spectroscopy

Magnetic resonance spectroscopy (MRS) complements magnetic resonance imaging (MRI) as a non-invasive means for the characterization of tissue. While MRI uses the signal from hydrogen protons to form anatomic images, proton MRS uses this information to determine the concentration of brain metabolites such as N-acetyl aspartate (NAA), choline (Cho), creatine (Cr) and lactate in the tissue examined. The most widely used clinical application of MRS has been in the evaluation of central nervous system disorders.MRS has its limitations and is not always specific but, with good technique and in combination with clinical information and conventional MRI, can be very helpful in diagnosing certain entities. For example, a specific pattern of metabolites can be seen in disorders such as Canavan's disease, creatine deficiency, and untreated bacterial brain abscess. MRS may also be helpful in the differentiation of high grade from low grade brain tumors, and perhaps in separating recurrent brain neoplasm from radiation injury.

Mean diffusivity and fractional anisotropy histogram analysis of the cervical cord in MS patients

The spinal cord is frequently involved in multiple sclerosis (MS), and cord damage may be an important contributor to disability. Diffusion tensor magnetic resonance imaging (DT-MRI) provides quantitative information about the structural and orientational features of the central nervous system. In order to assess whether diffusion tensor-derived measures of cord tissue damage are related to clinical disability, mean diffusivity (MD) and fractional anisotropy (FA) histograms from the cervical cord were acquired from a large cohort of MS patients. Diffusion-weighted sensitivity-encoded (SENSE) echo planar images of the cervical cord, and brain dual-echo and diffusion-weighted scans were acquired from 44 patients with MS and 17 healthy controls. Cord and brain MD and FA histograms were produced. An analysis of variance model, adjusting for cord volume and patient age, was used to compare cord DT-MRI parameters from controls and patients. A multivariate linear regression model was used to identify DT-MRI variables independently associated with disability. Average cervical cord FA was significantly lower in MS patients compared to controls. Cord cross-sectional area, average FA and average MD were all significantly correlated with the degree of disability (r values ranging from 0.36 to 0.51). The multivariate linear regression model retained average cord FA and average brain MD as variables independently associated with disability, with a correlation coefficient of 0.73 (P < 0.001). DT-MRI reveals a loss of cervical cord tissue structure in MS patients. The strong correlation found between a composite DT-MRI score and disability suggests that a full and accurate assessment of cervical cord damage in MS provides information that usefully contributes to an explanation of the clinical manifestations of the disease.

Magnetic resonance spectroscopy of normal appearing white matter in early relapsing-remitting multiple sclerosis: correlations between disability and spectroscopy

Background

What currently appears to be irreversible axonal loss in normal appearing white matter, measured by proton magnetic resonance spectroscopy is of great interest in the study of Multiple Sclerosis. Our aim is to determine the axonal damage in normal appearing white matter measured by magnetic resonance spectroscopy and to correlate this with the functional disability measured by Multiple Sclerosis Functional Composite scale, Neurological Rating Scale, Ambulation Index scale, and Expanded Disability Scale Score.

Methods

Thirty one patients (9 male and 22 female) with relapsing remitting Multiple Sclerosis and a Kurtzke Expanded Disability Scale Score of 0–5.5 were recruited from four hospitals in Andalusia, Spain and included in the study. Magnetic resonance spectroscopy scans and neurological disability assessments were performed the same day.

Results

A statistically significant correlation was found (r = -0.38 p < 0.05) between disability (measured by Expanded Disability Scale Score) and N-Acetyl Aspartate (NAA/Cr ratio) levels in normal appearing white matter in these patients. No correlation was found between the NAA/Cr ratio and disability measured by any of the other disability assessment scales.

Conclusions

There is correlation between disability (measured by Expanded Disability Scale Score) and the NAA/Cr ratio in normal appearing white matter. The lack of correlation between the NAA/Cr ratio and the Multiple Sclerosis Functional Composite score indicates that the Multiple Sclerosis Functional Composite is not able to measure irreversible disability and would be more useful as a marker in stages where axonal damage is not a predominant factor.

Volumetric quantitation by MRI in primary progressive multiple sclerosis: volumes of plaques and atrophy correlated with neurological disability

In primary progressive multiple sclerosis (PPMS) abnormalities in brain magnetic resonance imaging (MRI) differ from abnormalities in other subtypes of multiple sclerosis (MS). It was investigated whether the extent of brain and spinal cord MRI abnormalities is reflected in the neurological disability in PPMS. Focal and diffuse changes and atrophy in central nervous system (CNS) in patients with PPMS (n = 28) and healthy controls (n = 20) were assessed by semi-automatic MRI segmentation and volumetric analysis. The measurements were related to neurological disability as expressed by the expanded disability status scale (EDSS), the regional functional scoring system (RFSS), the arm index and the ambulation index. Plaques in T1- and/or T2-weighted images were seen in all brains, while spinal plaques were detected in 23 of 28 patients (82%). The total volumes of brain and spinal cord were significantly smaller in patients than in controls (P = 0.001 and 0.000, respectively). The volumes of T1 or T2 lesions in the brain correlated to the ambulation index (r = 0.51, P = 0.005 and r = 0.53, P = 0.004, respectively). No correlations were detected between MRI measurements and total EDSS score, but relative brain atrophy correlated inversely with the total RFSS scores, poor arm index and higher cerebral disturbances (r = -0.53, P = 0.004; r = -0.53, P = 0.004; and r = -0.52, P = 0.005, respectively). Although the number of spinal T2 lesions correlated with sensory disturbances (r = 0.60, P = 0.001), no correlations were found between EDSS subscores and spinal cord atrophy. These findings show that marked atrophy of brain and spinal cord detected by volumetric quantitation correlates with neurological disability. This observation indicates the importance of neurodegenerative events in PPMS.

Comparisons of Regional White Matter Diffusion in Healthy Neonates and Adults Performed with a 3.0-T Head-only MR Imaging Unit

PURPOSE

To evaluate the normal brains of adults and neonates for regional and age-related differences in apparent diffusion coefficient (ADC) and fractional anisotropy (FA).

MATERIALS AND METHODS

Eight healthy adults and 20 healthy neonates were examined with a 3.0-T head-only magnetic resonance (MR) imaging unit by using a single-shot diffusion-tensor sequence. Trace ADC maps, FA maps, directional maps of the putative directions of white matter (WM) tracts, and fiber-tracking maps were obtained. Regions of interest-eight in WM and one in gray matter (GM)-were predefined for the ADC and FA measurements. The Student t test was used to compare FA and ADC between adults and neonates, whereas the Tukey multiple-comparison test was used to compare FA and ADC in different brain regions in the adult and neonate groups.

RESULTS

A global elevation in ADC (P <.001) in both GM and WM and a reduction in FA (P <.001) in WM were observed in neonates as compared with these values in adults. In addition, significant regional variations in FA and ADC were observed in both groups. Regional variations in FA and ADC were less remarkable in adults, whereas neonates had consistently higher FA values and lower ADC values in the central WM as compared with these values in the peripheral WM. Fiber tracking revealed only major WM tracts in the neonates but fibers extending to the peripheral WM in the adults.

CONCLUSION

There were regional differences in FA and ADC values in the neonates; such variations were less remarkable in the adults.

Directional diffusion in relapsing-remitting multiple sclerosis: A possible in vivo signature of Wallerian degeneration

PURPOSE

To examine the role of directional dependence of the apparent diffusion coefficients in the evaluation of normal-appearing brain regions of patients with relapsing-remitting multiple sclerosis.

MATERIALS AND METHODS

The role of diffusion tensor eigenvalues was investigated in the normal-appearing brain regions for 18 patients with relapsing-remitting multiple sclerosis and 15 age-matched normal controls.

RESULTS

The isotropic apparent diffusion was increased in all regions. However, reduced anisotropy was significant only in regions with high anisotropy, including the corpus callosum and the internal capsule, and was due to increased diffusion tensor eigenvalues corresponding to diffusion transverse to the fibers without significant increase along the fibers. This characteristic pattern of changes in diffusion tensor eigenvalues has been observed previously in cases of Wallerian degeneration. Low-anisotropy regions corresponded to gray matter and gray/white interface regions. Since fiber tract orientations are not determined for regions of low anisotropy, this characteristic pattern of diffusion change is not detectable in these regions.

CONCLUSION

Examination of diffusion tensor eigenvectors may provide insight into the changes observed in diffusion and a signature of Wallerian degeneration in the normal-appearing white matter of relapsing-remitting multiple sclerosis patients.

Spinal-cord MRI in multiple sclerosis

The potential of MRI of the spinal cord as a diagnostic tool in MS has recently gained much interest. Dual echo spin echo MRI is most sensitive for the detection of spinal-cord abnormalities, which range from multiple focal lesions to confluent areas of high signal intensity. In some patients, commonly those with primary progressive disease, diffuse areas of slightly increased signal intensity are found. Disappointingly, the relation between MRI findings and clinical disability is weak. Studies relating MRI findings with histopathology have revealed substantial axonal loss in the spinal cords of patients with MS, whether focal lesions are present of not. Further, diffuse cord atrophy is found in advanced MS, which may reflect axonal loss. In the diagnostic setting, spinal-cord imaging is valuable. First, asymptomatic spinal-cord lesions are very rare in disorders other than MS. For example, in a patient with equivocal brain findings such as an elderly patient with vascular-ischaemic lesions, a normal spinal-cord examination can help rule out MS. Second, presence of asymptomatic spinal lesions may help confirm a diagnosis of MS when few or no brain lesions are present.

Interventions for the prevention of brain atrophy in multiple sclerosis : current status

The assessment of brain volume changes on serial magnetic resonance imaging (MRI) scans can provide an objective measure of the neurodegenerative component of multiple sclerosis (MS) pathology. Results from placebo-controlled and crossover clinical trials indicate that immunomodulating (e.g. recombinant interferon-beta [IFNbeta]-1a [Rebif] and IFNbeta-1b [Betaferon] and glatiramer acetate [Copaxone]) and immunosuppressive (e.g. cladribine and alemtuzumab) treatments for relapsing-remitting (RR) and secondary progressive MS lack substantial efficacy in preventing the development of brain atrophy, despite the marked effects of these treatments on clinical and MRI outcomes of disease activity. A modest but significant treatment effect on brain atrophy has been reported for patients with RRMS only in one trial of IFNbeta-1a (Avonex) and in another study of long-term corticosteroid therapy.Failure to find a significant treatment benefit in preventing brain atrophy might be the result of inadequate trial designs, including their relatively short durations, which may not be adequate to reveal beneficial effects in a chronic disease like MS. Alternatively, such a failure might indicate that treatments proven to be effective in reducing MS-related inflammation are unable to act with the same efficacy on the most severe and disabling pathological substrates of the disease. The modest correlation between MRI enhancement frequency and brain atrophy observed in the placebo groups of several trials also fits with the concept that the suppression of inflammatory activity in MS is not fully and rapidly associated with a similar effect on the global neurodegenerative process of the disease.

The use of quantitative magnetic-resonance-based techniques to monitor the evolution of multiple sclerosis

Conventional MRI can improve accuracy in the diagnosis of multiple sclerosis (MS) and monitor the efficacy of experimental treatments. However, conventional MRI provides only gross estimates of the extent and nature of tissue damage associated with this disease. Other quantitative magnetic-resonance-based techniques have the potential to overcome the limitations of conventional MRI and, as a consequence, to improve our understanding of the natural history of MS. Magnetisation-transfer, diffusion-weighted, and functional MRI--as well as proton magnetic-resonance spectroscopy--are helping us to elucidate the mechanisms that underlie injury, repair, and functional adaptation in patients with MS. These techniques are substantially changing our understanding of how MS causes irreversible disability and should be used more extensively in clinical trials and in studies of disease progression.

Axonal injury in multiple sclerosis

The pivotal role of axons in the pathophysiology and pathogenesis of multiple sclerosis (MS) is increasingly becoming the focus of our attention. Axonal injury, considered at one time to be a late phenomenon, is now recognized as an early occurrence in the inflammatory lesions of MS. There is converging evidence from histopathologic, as well as magnetic resonance imaging and magnetic resonance spectroscopy studies, that axons play a crucial and dynamic role during the evolution of MS pathology and the development of clinical disability. It has been repeatedly demonstrated that neurologic functional impairment correlates best with axonal, rather than myelin, injury. The pathophysiology of axonal injury remains speculative. Although generally considered to be sequelae of demyelination, it is possible that axonal injury in MS is indeed a primary event. The discovery that axonal injury can be reversible has provided an impetus to institute early therapy. The finding that irreversible axonal transection occurs in early lesions has underscored now, more than ever before, the need to curtail inflammation and the need to institute early treatment with disease-modifying agents. The axon will undoubtedly remain the focus of our attention regarding research on MS now and in the future.