Background and Objectives
Clinical trials in relapsing-remitting multiple sclerosis (RRMS) usually use the Expanded Disability Status Scale (EDSS) as their primary disability outcome measure, while the more recently developed outcomes timed 25-ft walk (T25FW) and 9-hole peg test (NHPT) may be more useful and patient relevant. The objective of this work was to compare the EDSS to the T25FW and NHPT in a large RRMS randomized controlled trial (RCT) dataset.
We used the dataset from Combination Therapy in Patients With Relapsing-Remitting Multiple Sclerosis (CombiRx) (clinicaltrials.gov identifier NCT00211887), a large phase 3 RCT, to compare the EDSS to the alternative outcomes T25FW and NHPT. We investigated disability worsening vs similarly defined improvement, unconfirmed vs confirmed and sustained disability change, and the presentation methods cumulative Kaplan-Meier survival curves vs cross-sectional disability worsening.
CombiRx included 1,008 participants. A comparison of confirmed and sustained worsening events showed that, throughout the trial, there were substantially fewer sustained than confirmed events, with a positive predictive value of confirmed for sustained worsening at 24 months of 0.73 for the EDSS, 0.73 for the T25FW, and 0.8 for the NHPT. More concerning were the findings that worsening on the EDSS occurred as frequently as similarly defined improvement throughout the 3 years of follow-up and that improvement rates increased in parallel with worsening rates. The T25FW showed low improvement rates of <10% throughout the trial. We also found that Kaplan-Meier survival analysis, the standard presentation and analysis method in modern RRMS trials, yields exaggerated estimates of disability worsening. With the Kaplan-Meier method, the proportion of patients with worsening events steadily increases until it reaches several-fold the number of events seen with more conservative analysis methods. For 3-month confirmed disability worsening up to 36 months, the Kaplan-Meier method yields 2.6-fold higher estimates for the EDSS, 2.9-fold higher estimates for the T25FW, and 5.1-fold higher estimates for the NHPT compared to a more conservative presentation of the same data.
Our analyses raise concerns about using the EDSS as the standard disability outcome in RRMS trials and suggest that the T25FW may be a more useful measure. These findings are relevant for the design and critical appraisal of RCTs.