BackgroundThe long-term disease trajectory of people living with multiple sclerosis (MS) can be improved by initiating efficacious treatment early. More quantitative evidence is needed on factors that affect a patient's risk of disability worsening or possibility of improvement to inform timely treatment decisions.MethodsWe developed a multistate model to quantify the influence of demographic, clinical, and imaging factors on disability worsening and disability improvement simultaneously across the disability spectrum as measured by the Expanded Disability Status Scale (EDSS). We used clinical trial data from the Novartis-Oxford MS database including ~130,000 EDSS assessments from ~8000 patients, spanning all MS phenotypes.ResultsHigher brain volume was positively associated with disability improvement at all disability levels (hazard ratio (HR) = 1.09-1.19; 95% credible interval (CI) = 1.02-1.27). Higher T2 lesion volume was negatively associated with disability improvement up to EDSS 6 (HR = 0.80-0.89; 95% CI = 0.75-0.94). Older age, time since first symptoms, and the number of relapses in the past year were confirmed as predictors of future disability worsening.ConclusionsBrain damage was identified as the most consistent factor limiting the patient's probability for improvements from the earliest stages and across the whole course of MS. Protecting brain integrity early in MS should have greater weight in clinical decision-making.