EDSS variability before randomization may limit treatment discovery in primary progressive MS

Background:Baseline Expanded Disability Status Scale (EDSS) is usually based on a single measurement. Here we evaluated whether using a baseline EDSS derived from two pre-treatment measurements improves the detection of progression events and the ability to demonstrate a therapeutic effect in delaying MS disability progression.Methods:Real data from OLYMPUS, a phase II/III randomized, placebo-controlled trial of rituximab in patients with primary progressive multiple sclerosis (PPMS), as well as simulated data were analyzed. Several definitions of baseline EDSS were used to capture sustained disability progression (SDP) events. Variations in the EDSS were estimated by linear mixed-effect models.Results:Selecting the higher of two baseline EDSS scores lowered the number of SDP events in both treatment groups, so decreasing sensitivity, and reduced the number of false SDP events, so increasing specificity. Conversely, selecting the lower of two baseline scores increased sensitivity but decreased specificity...