title: Disability as an outcome in MS clinical trials.
abstract: BACKGROUND
  Inferences about long-term effects of therapies in multiple sclerosis (MS) have been based on surrogate markers studied in short-term trials. Preventing progressive disability is the key therapeutic goal but there remains no validated definition for its measurement in a trial context. Meanwhile, MS trials continue to shorten and to depend on unvalidated surrogates. Since there have been no treatment claims for improving unremitting disability, worsening of disability in the placebo/control arm must occur for effectiveness on this outcome to be shown.
  
  
  METHODS
  We examined widely-used clinical surrogates of long-term disability progression in individual patients with MS within a unique database from the placebo arms of 31 randomized clinical trials.
  
  
  RESULTS
  Detection of treatment effects in secondary progressive MS trials is undermined by noise in disability measurement. Whereas existing measures can be partially validated in secondary progressive MS, this is not the case in relapsing-remitting MS. Here, examination of widely used definitions of treatment failure demonstrated that disability progression was no more likely than similarly defined improvement. Existing definitions of disease progression in short-term intervention trials in relapsing-remitting patients reflect random variation, measurement error, and remitting relapses.
  
  
  CONCLUSIONS
  Clinical surrogates of unremitting disability used in trials of relapsing-remitting multiple sclerosis cannot be validated. Trials have been too short or degrees of disability change too small to measure the key outcomes. These analyses highlight the difficulty in determining effectiveness of therapy in chronic diseases.
authors.affiliation: University of Oxford Department of Clinical Neurology, Level 3, West Wing, John Radcliffe Hospital, Oxford OX3 9DU, UK. george.ebers@clneuro.ox.ac.uk
authors.forename: G C
authors.initials: GC
authors.lastname: Ebers
authors.forename: L
authors.initials: L
authors.lastname: Heigenhauser
authors.forename: M
authors.initials: M
authors.lastname: Daumer
authors.forename: C
authors.initials: C
authors.lastname: Lederer
authors.forename: J H
authors.initials: JH
authors.lastname: Noseworthy
mesh_terms: D000293:Adolescent; D000328:Adult; D015415:Biomarkers / Q000032:analysis*; D002648:Child; D002675:Child, Preschool; D016208:Databases, Factual / Q000706:statistics & numerical data; D004185:Disability Evaluation; D018450:Disease Progression; D023381:Endpoint Determination / Q000379:methods*; D006801:Humans; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000188:drug therapy*; D020529:Multiple Sclerosis, Relapsing-Remitting / Q000188:drug therapy; D010043:Outcome and Process Assessment, Health Care / Q000379:methods*; D016032:Randomized Controlled Trials as Topic / Q000706:statistics & numerical data*
chemical_list: D015415:Biomarkers