Does the Multiple Sclerosis Impact Scale-29 (MSIS-29) have the range to capture the experience of fully ambulatory multiple sclerosis patients? Learnings from the ASCLEPIOS studies

BACKGROUND: Trials of disease-modifying therapies (DMTs) for multiple sclerosis (MS) often include patients with minimal disability. Patient-reported outcome instruments used in these trials have often not captured physical and psychological treatment effects concomitant with observed clinical benefits. OBJECTIVE: To examine whether the Multiple Sclerosis Impact Scale-29 (MSIS-29) captures changes in the impact of MS in a sample of patients enrolled in the Phase 3 ASCLEPIOS studies (ofatumumab vs. teriflunomide). METHODS: Measurement properties (i.e. item fit, reliability, and targeting) of the MSIS-29 were analyzed using Rasch measurement theory (RMT) in data from two phase 3 ofatumumab clinical trials including patients with relapsing-remitting or secondary progressive MS (N = 1882). Targeting of the MSIS-29 items to the patient population was explored within groups categorized by Expanded Disability Status Scale (EDSS) scores. RESULTS: Under RMT analyses, both the Physical and Psychological Impact scales of the MSIS-29 were not appropriately targeted to the overall sample of patients. In particular, 49% and 30% of patients with an EDSS score ≤ 2.5 had fewer physical and psychological impacts, respectively, than would typically be captured by these MSIS-29 items compared to patients with EDSS scores of ≥ 3. CONCLUSION: The MSIS-29 is commonly used to evaluate the patient-reported physical and psychological impact of MS. However, it may be limited in evaluating changes associated with DMTs in patients with minimal disability.