Background Brain atrophy is increasingly used as an outcome measure in clinical trials in relapsing-remitting multiple sclerosis (RRMS), but little is known about how chronological age interacts with MS-specific effects. For instance, while annual brain atrophy rates typically increase with age in healthy individuals, MS patients tend to exhibit decreasing atrophy rates over time.Methods We investigated the relationship between age and brain volume in a large dataset of 4241 trial participants with RRMS. We used pooled individual-participant data from phase 3 clinical trials with 96 weeks follow-up, which included both active treatment and placebo/comparator arms. Participants were categorised into seven groups based on chronological age (18-24 years, 25-30 years, 31-35 years, 36-40 years, 41-45 years, 46-50 years, 51-56 years). We performed multilevel linear mixed-effects regression analyses to examine differences between age groups in normalised whole brain volume (NWBV), thalamus grey matter volume (NThGMV), grey matter volume (NGMV) and white matter volume at baseline and their changes over follow-up. We also studied how disease duration influenced these relationships using similar models.Results Older participants showed significantly lower NWBV, NGMV and NThGMV at baseline than younger participants. Most importantly, older participants exhibited lower rates of atrophy during follow-up, particularly in the thalamus. This association was consistent across all disease duration subgroups.Conclusions Older participants had more severe atrophy when enrolled into trials, but slower (thalamic) atrophy rates, independent of disease duration over time. Together, these findings emphasise that age should be taken into account when designing clinical trials that use brain atrophy as an outcome measure.

BACKGROUND:Recent studies suggest that disruptions of the blood-cerebrospinal fluid (CSF) barrier within the choroid plexus (ChP) may contribute to multiple sclerosis (MS) pathogenesis. We investigated the relationship between a quantitative marker of ChP enhancement and markers of focal and diffuse brain tissue injury in MS. METHODS:A group of 34 MS participants and 21 healthy participants underwent 7T MRI including magnetization prepared 2 rapid acquisition gradient echoes (MP2RAGE) and fluid attenuated inversion recovery (FLAIR) acquisitions. The MS group received contrast, and delta T1 (ΔT1) maps were computed to assess enhancement. ChP, white matter lesions (WML), normal-appearing white matter (NAWM), and gray matter (GM) were segmented. Pre-contrast quantitative T1 (qT1) values were compared between groups, and linear regression with mean ChP ΔT1 was performed for WML volume and pre-gadolinium (Gd) mean qT1 of WML, NAWM, and GM. RESULTS:Mean qT1 of ChP, NAWM, and GM, as well as ChP volume, were higher in MS compared to controls (p < 0.001). ChP ΔT1 was significantly associated with pre-Gd qT1 of NAWM (β = 0.20, R2 = 0.54, p < 0.001) and GM (β = 0.18, R2 = 0.49, p < 0.001), but not WML volume (p = 0.3) or WML qT1 (p = 0.05). CONCLUSIONS:The association between ChP enhancement and diffuse tissue injury, together with elevated qT1 values and ChP volumes in MS, supports a mechanism of brain injury involving CSF-mediated toxicity distinct from classic lesion pathology in MS.

Introduction TOL a réduit le risque d’aggravation du handicap vs placebo et vs tériflunomide dans les études de phase 3 (SEP-SP sans poussée et SEP-R). Les PRL à l’IRM sont des lésions actives chroniques qui sont corrélées au handicap. Objectifs Le BTKi pouvant moduler la neuro-inflammation liée à la microglie et aux lym B, une analyse post-hoc fut réalisée pour évaluer les PRL comme marqueur pronostique du handicap et de réponse au traitement dans les études TOL. Méthodes HERCULES, GEMINI 1 et 2 étaient des études de phase 3, en double aveugle évaluant TOL (vs placebo [PBO] dans HERCULES et tériflunomide [TER] dans GEMINI 1 et 2).Au total, 39 % des patients HERCULES et 34 % des patients GEMINI étaient suivis dans des centres avec des capacités d’imagerie permettant l’évaluation des PRL. À la suite de précédentes études, il a été analysé l’effet de TOL sur le délai d’apparition d’une aggravation confirmée du handicap à 6 mois (CDW) chez les patients avec 0,1 à 3 ou ≥4 PRL à baseline (BL). Résultats Dans les 2 études, 61 % des patients présentaient des PRL. Dans HERCULES, 40 %, 36 %, et 24 % des patients avaient 0, 1–3, ou ≥4 PRL à BL, respectivement (idem dans GEMINI). Dans HERCULES, TOL semblait atténuer le risque de CDW à 6 mois avec un effet plus important chez les patients ayant plus de PRL à BL, avec une réduction de 54 % chez les patients avec ≥4 PRL. Dans GEMINI, un effet similaire a été observé avec une réduction du risque de 46 % et 49 % chez les patients avec 1–3 et ≥4 PRL, respectivement. Discussion Dans HERCULES et GEMINI, le risque de CDW a augmenté en fonction du nombre de PRL à BL dans les groupes PBO et TER.Chez les patients traités par TOL présentant des PRL dans les études HERCULES et GEMINI, le risque de CDW à 6 mois était numériquement similaire au risque correspondant chez les patients sans PRL. Conclusion Cette analyse post hoc suggère que l’impact de tolébrutinib pourrait être plus important chez les personnes avec un nombre élevé de PRL, ce qui est consistant avec le mécanisme d’action bioactif de tolébrutinib dans le SNC.

Disability worsening is the critical long-term outcome in multiple sclerosis, yet the Expanded Disability Status Scale incompletely captures neurological deterioration and has limited sensitivity in the short time windows of clinical trials. Composite endpoints incorporating functional measures have been proposed to address these limitations, but whether they reliably improve detection of treatment effects has not been established across trials. We conducted a post-hoc analysis of individual patient data from ten phase III randomised controlled trials (ASCEND, BRAVO, CONFIRM, DEFINE, EXPAND, INFORMS, OLYMPUS, OPERA I/II, and ORATORIO; n = 9,369), spanning relapsing-remitting and progressive multiple sclerosis. Confirmed disability worsening was defined using harmonised criteria with the msprog package and confirmed at 24 weeks. Treatment effects were estimated using Cox proportional hazards models and combined across trials in a one-stage individual patient data framework. Composite endpoints were constructed from the Expanded Disability Status Scale, the timed 25-foot walk test, and the nine-hole peg test using logical unions (OR-type), intersections (AND-type), and majority-vote structures. Sensitivity to treatment effect was quantified using Z-scores (the ratio of the pooled log-hazard ratio to its standard error) and compared to the Expanded Disability Status Scale reference using interaction tests. Event rates varied across components: the timed walk test generated the highest rates (up to 46.8%) while the nine-hole peg test generated the lowest (as low as 2.1%). OR-type composite endpoints showed weaker treatment effects than the Expanded Disability Status Scale alone, with the largest reductions in sensitivity observed for endpoints incorporating the timed walk test (ΔZ up to +2.26; interaction p = 0.004). These findings were confirmed across disease subtypes and were pronounced in relapsing-remitting trials, where no composite endpoint outperformed the Expanded Disability Status Scale. In progressive multiple sclerosis, the combination of the Expanded Disability Status Scale and the nine-hole peg test showed numerically stronger treatment effects (ΔZ = −1.65), though interaction tests did not reach statistical significance (p = 0.051). Composite endpoints do not systematically improve treatment effect detection in multiple sclerosis trials. Increased event capture driven by the timed walk test introduces noise that dilutes the treatment signal rather than amplifying it, highlighting that event rate and endpoint quality are not interchangeable. Upper limb function assessed by the nine-hole peg test provides complementary and specific information, particularly in progressive disease. The combination of global disability and upper limb measures represents a promising direction for future endpoint development in progressive multiple sclerosis trials, warranting validation. ### Competing Interest Statement Francesca Bovis and Noemi Montobbio report no competing interest. Alessio Signori received speakers honoraria from Chiesi, Novartis, and Horizon and grant from MSBase, Tomas Kalincik served on scientific advisory boards for MS International Federation and World Health Organisation, BMS, Roche, Janssen, Sanofi Genzyme, Novartis, Merck and Biogen, steering committee for Brain Atrophy Initiative by Sanofi Genzyme, received conference travel, support and/or speaker honoraria from WebMD Global, Eisai, Novartis, Biogen, Roche, Sanofi-Genzyme, Teva, BioCSL and Merck and received research or educational event support from Biogen, Novartis, Genzyme, Roche, Celgene and Merck. Douglas L Arnold reports consulting honoraria from Alexion, Biogen, Celgene, Frequency Therapeutics, GENeuro, Genentech, Merck/EMD Serono, Novartis, Roche, and Sanofi; and ownership interest in NeuroRx. Mar Tintore has received compensation for consulting services, speaking honoraria and research support from Almirall, Bayer Schering Pharma, Biogen-Idec, Genzyme, Immunic Therapeutics, Janssen, Merck-Serono, Novartis, Roche, Sanofi-Aventis, Viela Bio and Teva Pharmaceuticals. Data Safety Monitoring Board for Parexel and UCB Biopharma, Relapse Adjudication Committee for IMCYSE SA. Ludwig Kappos reports receiving honoraria for consulting and/or advisory board services for Actelion, Bayer, BMS, df-mp Molnia & Pohlmann, Celgene, Eli Lilly, EMD Serono, Genentech, Glaxo Smith Kline, Janssen, Japan Tobacco, Merck, MH Consulting, Minoryx, Novartis, F. Hoffmann-La Roche Ltd, Senda Biosciences Inc., Sanofi, Santhera, Shionogi BV, TG Therapeutics, and Wellmera; license fees for Neurostatus UHB products; and grants from Novartis, Innosuisse, and Roche. Maria Pia Sormani reports receiving honoraria for consulting and/or advisory board/lecture services from Biogen, Celgene, GeNeuro, GSK, Immunic, Medday, Merck, Novartis, Roche, and Sanofi. ### Funding Statement This study did not receive any funding ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: All the data have been de-identified. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Individual patient data from these RCTs were made available through the International Progressive MS Alliance (IPMSA) project (award reference number PA-1603-08175). Access requests should be forwarded to the relevant data controllers.

In multiple sclerosis (MS), focal demyelinating lesions disrupt many automated MRI analysis pipelines, most of which are calibrated for anatomically normal brain tissue. Replacement of these pathological voxels with realistic surrogates of healthy tissue restores compatibility with downstream tools, whether for morphometry, tissue segmentation, or longitudinal atrophy studies. In this paper, we introduce a temporal diffusion framework for MS lesion inpainting that operates on pairs of scans from different timepoints of the same patient. Our denoising diffusion probabilistic model (DDPM) is conditioned on (i) binary MS-lesion and (ii) ventricle masks that preserve periventricular geometry, the region where MS lesions are most common and hardest to inpaint. By simultaneously generating anatomically plausible tissue at both timepoints, the method yields lesion-free images suitable for a broad range of analyses, including, but not limited to robust brain volume change estimation. Experiments show that the model learns to inpaint lesions faithfully while maintaining inter-timepoint consistency and overall brain topology.

People with highly active multiple sclerosis benefit from early treatment with highly efficacious disease-modifying therapies. Here we present data on the efficacy of ublituximab versus teriflunomide in a subgroup of participants with highly active disease at baseline. Pooled post hoc analyses of the phase 3 ULTIMATE I (N = 549) and II (N = 545) studies evaluated efficacy measures at weeks 12 and 96 in participants with highly active disease, defined as ≥ 2 relapses in the year prior and ≥ 1 gadolinium-enhancing (Gd+) T1 lesion at baseline. In the highly active disease population, the unadjusted annualized relapse rates (ARR) at week 96 were 0.145 and 0.496 for the ublituximab (n = 88) and teriflunomide (n = 80) groups, respectively (70.8

Image-based personalized medicine has the potential to transform healthcare, particularly for diseases that exhibit heterogeneous progression such as Multiple Sclerosis (MS). In this work, we introduce the first treatment-aware spatio-temporal diffusion model that is able to generate future masks demonstrating lesion evolution in MS. Our voxel-space approach incorporates multi-modal patient data, including MRI and treatment information, to forecast new and enlarging T2 (NET2) lesion masks at a future time point. Extensive experiments on a multi-centre dataset of 2131 patient 3D MRIs from randomized clinical trials for relapsing-remitting MS demonstrate that our generative model is able to accurately predict NET2 lesion masks for patients across six different treatments. Moreover, we demonstrate our model has the potential for real-world clinical applications through downstream tasks such as future lesion count and location estimation, binary lesion activity classification, and generating counterfactual future NET2 masks for several treatments with different efficacies. This work highlights the potential of causal, image-based generative models as powerful tools for advancing data-driven prognostics in MS.

Introduction Les traitements de fond actuels ciblent surtout les poussées, moins efficaces sur le PIRA, qui représente la majorité du handicap. TOL est un BTKi oral qui pénètre le SNC modulant l’activation immunitaire liée à la microglie. Objectifs Dans l’étude de phase 3 HERCULES sur la SEP-SP sans poussées, TOL a réduit le PIRA de 31 %. Évaluer les effets de TOL vs Tériflunomide (TER) sur le PIRA dans les études de phase 3 GEMINI dans la SEP-R. Méthodes GEMINI 1 et 2 étaient des études de phase 3, en double aveugle, chez des patients atteints de SEP-R (âge 18–55 ans, score EDSS ≤5,5, ≥1 poussée dans l’année précédente, ≥2 poussées au cours des 2 années précédentes ou ≥1 lésion T1 Gd+ l’année précédente) qui ont reçu TOL ou TER par voie orale, une fois par jour. Le critère d’évaluation principal était le taux annualisé de poussées et le principal critère d’évaluation secondaire était le délai jusqu’à l’aggravation du handicap confirmée à 6 mois (CDW). Résultats Les essais ont inclus 1873 patients (974 dans GEMINI 1 et 899 dans GEMINI 2), dont 67 % étaient des femmes et 64 % étaient naïfs de traitement. Bien que TOL n’ait pas été supérieur au TER dans la réduction du taux annualisé de poussées, le pourcentage de patients atteints de CDW à 6 mois était de 8,3 % avec TOL et de 11,3 % avec TER (rapport de risque, 0,71 ; IC à 95 %, 0,53 à 0,95) Discussion Comme attendu, la majorité (près de 80 %) des événements de CDW à 6 mois étaient des événements PIRA (défini comme un CDW, sans poussée 90j avant ou après l’apparition du handicap et sans poussée dans les 30j avant la confirmation du handicap), et moins de patients ont présenté des événements PIRA avec TOL (6,4 %) par rapport au TER (8,5 %), ce qui a entraîné une réduction du risque de 27 %. Conclusion Ces données appuient l’observation dans l’étude HERCULES selon laquelle TOL cible les facteurs d’accumulation du handicap qui sont indépendants des effets liés aux poussées.

Background In multiple sclerosis (MS), pathology of both the subpial cortex and subependymal parenchyma has been strongly linked to compartmentalized meningeal inflammation. The topographical distribution of subpial demyelination can be appraised in vivo using surface-based mapping of magnetization transfer saturation (MTsat) in the cortex with 7T MRI. We combined 7T cortical MTsat mapping with [11C]PBR28 PET molecular imaging of microglia to study the potential influence of subcortical microglial inflammation on cortical pathology. Methods Thirty-eight MS patients (median EDSS: 4.0) and 21 healthy controls (HCs) underwent high resolution 7T MRI and [11C]PBR28 PET. Principal component analysis of [11C]PBR28 PET data was used to phenotype patients as having high (MSHigh) or low (MSLow) subcortical inflammation. Quantitative, surface-based measures of cortical myelin were obtained by sampling MTsat maps at 25%-50%-75% depths from the pial surface. Results MSHigh patients presented substantially greater, diffuse reductions in MTsat at all three cortical depths relative to HCs (P < 0.05). Areas of significantly reduced MTsat were greatest at 25% depth in the frontal, parietal and cingulate cortices, occupying nearly 70% of total cortical area and providing evidence of extensive subpial demyelination. Importantly, MSHigh patients presented increased microstructural abnormalities in subcortical regions (P < 0.05), alongside higher Expanded Disability Status Score (EDSS) (P = 0.02), increased odds of progressive MS (odds ratio = 4.85:1 [1.20, 23.26], P = 0.03) and significant cortical atrophy (P = 0.009). Discussion We provide in vivo evidence of a relationship between subcortical microglial inflammation and subpial demyelination in MS that is associated with increased clinical disability.

Motivation Compositional data comprise vectors that describe the constituent parts of a whole. Data arising from various -omics platforms such as 16S and RNA-sequencing are compositional in nature. However, correlations between features on raw counts have no meaningful interpretation. Metrics of proportionality were formulated to address this problem. However, there is an inherent bias that arises when calculating these metrics empirically on count-based measures due to variability in read depths. Results We quantify the bias introduced by empirically calculating proportionality-based association metrics in count data. Additionally, we propose a means of estimating these metrics within a logit-normal multinomial model in pursuit of more accurate estimates. The model-based estimates are shown to outperform empirical estimates in simulated data, and are additionally applied to a mouse embryonic stem-cell single-cell sequencing dataset as well as a pediatric-onset multiple sclerosis metagenomic dataset. Availability and Implementation An R package is available at https://CRAN.R-project.org/package=countprop . Supplementary information Supplementary data are available at Bioinformatics online.

Introduction- Choroid plexus (CP) enlargement on brain MRI has been identified as an emerging neuroinflammatory biomarker in multiple sclerosis (MS), yet its relationship to downstream parenchymal neurochemical abnormalities remains unknown. Proton magnetic resonance spectroscopy (1H MRS) enables non-invasive in vivo quantification of neurometabolites, making it well-suited to probe downstream consequences of CP pathology in MS. Methods- Ultra-high-field 7T 1H MRS was performed in 45 people with MS (pwMS) (28 Relapsing Remitting MS, RRMS; 17 Progressive MS, PMS) and 43 age- and sex-matched healthy controls (HCs) in the posterior cingulate cortex (PCC) and centrum semiovale white matter (CSWM). CP volume, EDSS, and MS Functional Composite measures were also acquired. Group differences in metabolite concentrations were evaluated using Mann-Whitney U tests with correction for multiple comparisons, and associations between CP volume, altered metabolites, and clinical disability and functional measures were investigated. Results- Myo-inositol (mI) was significantly elevated and total N-acetylaspartate was reduced in both MS subtypes, in the CSWM. In PMS, CP volume was positively associated with CSWM mI/total creatine (tCr) (ρ = 0.63, p = 0.008), an association absent in RRMS. Across the combined MS cohort, CP volume correlated significantly with EDSS (ρ = 0.40, p = 0.006). Conclusions- WM mI/tCr was elevated and tNAA/tCr was reduced across MS phenotypes compared with controls, reflecting a dual metabolic signature consistent with concurrent glial overactivation and neuroaxonal compromise. Increased CP volume was associated with greater neurological disability across MS phenotypes. The association of CP enlargement with CSWM mI/tCr in PMS suggests a potential link between CP-mediated periventricular inflammation and progressive WM glial pathology. Collectively, these findings support CP volume as a clinically relevant, non-invasive biomarker and restoring CP integrity as a potential therapeutic target in PMS, where effective treatments remain limited. ### Competing Interest Statement SS, FED, SA, JN and AB have nothing to report. DLA reports consulting fees from Biogen, Biohaven, BMS, Eli Lilly, EMD Serono, Find Therapeutics, Frequency Therapeutics, GSK, Idorsia Pharmaceuticals, Kiniksa Pharmaceuticals, Merck, Novartis, Race to Erase MS, Roche, Sanofi-Aventis, Shionogi, and Xfacto Communications; as well as an equity interest in NeuroRx, a Clario company. SN has received research funding from the Canadian Institutes of Health Research, the National Institutes of Health, the Myelin Repair Foundation, Immunotec, and F. Hoffman LaRoche; he has been a consultant for Sana Biotech and is a part-time employee of NeuroRx Research, a Clario Company. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The study was approved by the Research Ethics Board of the McGill University Health Centre, the McGill University Institutional Review Board, Faculty of Medicine and Health Sciences, and the Aging-Neuroimaging Research Ethics Committee of the CIUSSS du Centre-Sud-de-île-de-Montréal (CIUSSS-CSMTL). Written informed consent was obtained from all participants. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors. Canadian Institutes of Health Research, https://ror.org/01gavpb45, 153005 Réseau en Bio-Imagerie du Quebec, https://ror.org/0271st670 Projets de Recherche Stratégiques et Structurants Fonds de Recherche du Québec - Santé, https://ror.org/02eqrsj93, 352199, 332672 Fondation Courtois

BACKGROUND:Reproducibility and comparability of disability outcomes remain major challenges in multiple sclerosis (MS) research. Definitions of disability progression vary widely across studies, and calculation criteria are often insufficiently documented to enable replication. FRAMEWORK:To address these issues, a consensus process endorsed by the International Advisory Committee on Clinical Trials in MS was conducted to develop practical guidelines for outcome calculation across a range of study designs and research questions. Instead of proposing a single universal endpoint definition, we establish specific recommendations for each use case, within a fixed parameter space derived from extraction and systematisation of common practices for baseline selection, event confirmation, relapse handling, and event categorisation. These criteria are implemented in a shared computational framework, "msprog," available as open-source R and Python software and as a web application. The tool supports different disability scales, facilitates full reporting of parameters, and adapts to both clinical trial and real-world settings. CONCLUSION:The integration of consensus-based guidelines with a standardised, extensible implementation provides a practical basis for consistent and reproducible specification of disability outcomes in MS.

INTRODUCTION:Oxidative stress may contribute to brain injury in the Alzheimer's disease (AD) continuum. The antioxidant glutathione (GSH) can be assessed with magnetic resonance spectroscopy (MRS). Because the relationship between GSH and vascular brain injury is unknown in the AD continuum, we address this gap in mild cognitive impairment (MCI). METHODS:3T Magnetic resonance imaging (MRI)/MRS data were obtained from 31 patients with MCI. GSH and total N-acetylaspartate (tNAA; neuroaxonal integrity marker) were measured in posterior cingulate cortex (PCC) and frontal white matter (FWM). Cerebrovascular injury was assessed using white matter hyperintensity (WMH) volume. Global and regional brain tissue integrity were assessed using normalized brain (NBV) and hippocampal volumes. RESULTS:Significant associations were reported in FWM between GSH/total creatine (tCr) and tNAA/tCr, and between GSH and both WMH and NBV. tNAA, GSH/tCr, and tNAA/tCr were higher in PCC than in FWM. DISCUSSION:Our results suggest that oxidative stress contributes to vascular brain injury in MCI. HIGHLIGHTS:Neuronal, vascular, and oxidative injuries occur in the Alzheimer's disease (AD) spectrum. Glutathione (GSH) is the main endogenous antioxidant in the brain. Brain GSH can be measured with magnetic resonance spectroscopy (MRS). We measured brain GSH level in people with mild cognitive impairment (MCI). Low GSH level was associated with vascular brain injury, neuroaxonal damage, and atrophy.

Abstract: Objective: Recent studies suggest that disruptions of the blood –cerebrospinal fluid barrier within the choroid plexus (ChP) may contribute to MS pathogenesis. We investigated the relationship between a quantitative marker of ChP enhancement and markers of focal and diffuse brain tissue injury in multiple sclerosis (MS). Methods: 34 MS participants underwent 7T MRI including MP2RAGE-based qT1 mapping pre – and post contrast, and FLAIR acquisitions. Delta T1 (ΔT1) maps were calculated by subtraction of post –contrast from co-registered pre-contrast qT1 maps. ChP, white matter lesions (WML), normal–appearing white matter (NAWM) and grey matter (GM) were segmented. Linear regression analyses were conducted between mean ΔT1 values of ChP and (1) WML volume, (2) pre–Gd mean qT1 of WML, (3) pre–Gd mean qT1 of NAWM, and (4) pre–Gd mean qT1 of GM. Results: ΔT1 of ChP was significantly associated with pre–Gd qT1 of NAWM ( β=0.20 , R2 = 0.54, p<0.001) and GM (β = 0.32, R2 = 0.62, p<0.001). No significant associations were found between ChP ΔT1 and WML volume (p = 0.3) or WML qT1 (p = 0.05). Interpretation: The strong associations we observed between the degree of ChP contrast enhancement and markers of diffuse brain tissue injury, combined with a lack of a relationship with lesion volume or qT1 within lesions, support the hypothesis that entry of toxic factors into the CSF via the ChP may constitute an additional mechanism of brain tissue injury distinct from the classic lesion-based pathology of MS. ### Competing Interest Statement S.S., I.T., D.F., C.H.H., H.E.A., E.F., Z.K., D.A.R., G.R.W.M., S.N. have nothing to report. D.L.A. received partial funding for data acquisition from Novartis Canada. ### Funding Statement This study was supported in part by the Canadian Institutes of Health Research, grant #153005 (SN), the United States Department of Defense, Multiple Sclerosis Research Program, Investigator–Initiated Research Award (Award No. W81XWH19–1–0486) (DAR) and an Investigator–Initiated award from Novartis Canada (DLA). SS thanks the Fonds de Recherche Québec – Santé for personal support (scholarship). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The Research Ethics Board of the Montreal Neurological Institute-Hospital gave ethical approval for this work. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes The data that support the findings of this study are not publicly available due to concerns surrounding patient confidentiality but are available from the corresponding author on reasonable request.

BACKGROUND:Interest in progression independent of relapse activity (PIRA) as an endpoint in multiple sclerosis (MS) clinical trials is surging. However, established definitions of PIRA may produce biased treatment effect estimates in the presence of a treatment-induced relapse reduction. METHODS:We applied different definitions of PIRA to pooled data from the OPERA I/II clinical trials (clinicaltrials.gov identifiers: NCT01247324, NCT01412333). Treatment effects on PIRA according to different methods were quantified by hazard ratios (HRs) and risk ratios (RRs). Next, we evaluated the bias in each definition using synthetic Expanded Disability Status Scale (EDSS) data simulating a control and an experimental arm with varying treatment effects on relapses and on PIRA. We quantified the bias by comparing the estimated effect on PIRA with the known true effect. FINDINGS:The pooled OPERA I/II population included 1656 participants. Estimated treatment effects on PIRA varied from a non-significant HR of 0.83 (CI = 0.66-1.04) to an HR of 0.73 (CI = 0.59-0.90) depending on the definition used. Follow-up analyses on simulated data (n = 800 per arm) revealed an underestimation of the true treatment effect on PIRA when using established definitions, with increasing bias as treatment effect on relapses increased. Defining PIRA as complementary to relapse-associated worsening (RAW) provided a less biased and operationally simple alternative. INTERPRETATION:For clinical trials with PIRA as an endpoint, we suggest a "complementary" definition of PIRA, relying on accurate exclusion of RAW promoted by appropriate visit timing. FUNDING:Italian Ministry of University and Research.

Background: Multiple sclerosis (MS) slowly expanding lesions (SELs) are defined on magnetic resonance imaging (MRI) as contiguous regions of pre-existing focal non-contrast-enhancing T2 lesions with constant and concentric local expansion on conventional T1-weighted and T2-weighted images. SELs are associated with an increased risk of disability progression. Methods: Myelin-related changes detected using myelin water fraction (MWF) and magnetisation transfer ratio (MTR) in SELs and T2 lesions were measured over 192 weeks in participants with relapsing MS. Results: In participants with SELs (SEL+), SELs (MWF: 0.12 ± 0.03, MTR: 33.1 ± 3.6 pu) showed reduced myelin measures at baseline compared to T2 lesions (MWF: 0.13 ± 0.02, MTR: 35.1 ± 2.4 pu). In participants without SELs (SEL−), T2 lesions had higher myelin measures (MWF: 0.15 ± 0.02, MTR: 36.2 ± 2.0 pu) compared to T2 lesions in SEL+. Over 4 years, only SELs showed decreases in MWF (−11.4%). The percentage of abnormal voxels within normal-appearing white matter was higher in SEL+ and increased over time (SEL+ MWF Week 0: 0.56%, Week 192: 0.98%; SEL− MWF Week 0: 0.13%, Week 192: 0.25%). Conclusion: Our results indicate progressive focal and global demyelination in SEL+ participants and that the presence of SELs might be a biomarker for participants with ongoing diffuse or smouldering inflammation within the whole brain.

Multiple sclerosis (MS) affects 2.9 million people. Traditional classification of MS into distinct subtypes poorly reflects its pathobiology and has limited value for prognosticating disease evolution and treatment response, thereby hampering drug discovery. Here we report a data-driven classification of MS disease evolution by analyzing a large clinical trial database (approximately 8,000 patients, 118,000 patient visits and more than 35,000 magnetic resonance imaging scans) using probabilistic machine learning. Four dimensions define MS disease states: physical disability, brain damage, relapse and subclinical disease activity. Early/mild/evolving (EME) MS and advanced MS represent two poles of a disease severity spectrum. Patients with EME MS show limited clinical impairment and minor brain damage. Transitions to advanced MS occur via brain damage accumulation through inflammatory states, with or without accompanying symptoms. Advanced MS is characterized by moderate to high disability levels, radiological disease burden and risk of disease progression independent of relapses, with little probability of returning to earlier MS states. We validated these results in an independent clinical trial database and a real-world cohort, totaling more than 4,000 patients with MS. Our findings support viewing MS as a disease continuum. We propose a streamlined disease classification to offer a unifying understanding of the disease, improve patient management and enhance drug discovery efficiency and precision.

Vision-language models have demonstrated impressive capabilities in generating 2D images under various conditions; however the impressive performance of these models in 2D is largely enabled by extensive, readily available pretrained foundation models. Critically, comparable pretrained foundation models do not exist for 3D, significantly limiting progress in this domain. As a result, the potential of vision-language models to produce high-resolution 3D counterfactual medical images conditioned solely on natural language descriptions remains completely unexplored. Addressing this gap would enable powerful clinical and research applications, such as personalized counterfactual explanations, simulation of disease progression scenarios, and enhanced medical training by visualizing hypothetical medical conditions in realistic detail. Our work takes a meaningful step toward addressing this challenge by introducing a framework capable of generating high-resolution 3D counterfactual medical images of synthesized patients guided by free-form language prompts. We adapt state-of-the-art 3D diffusion models with enhancements from Simple Diffusion and incorporate augmented conditioning to improve text alignment and image quality. To our knowledge, this represents the first demonstration of a language-guided native-3D diffusion model applied specifically to neurological imaging data, where faithful three-dimensional modeling is essential to represent the brain's three-dimensional structure. Through results on two distinct neurological MRI datasets, our framework successfully simulates varying counterfactual lesion loads in Multiple Sclerosis (MS), and cognitive states in Alzheimer's disease, generating high-quality images while preserving subject fidelity in synthetically generated medical images. Our results lay the groundwork for prompt-driven disease progression analysis within 3D medical imaging.