Detection of disability worsening in relapsing-remitting multiple sclerosis patients. A real-world roving EDSS-Expanded Disability Status Scale reference analysis from the Italian Multiple Sclerosis Register

Background and purpose: In relapsing-remitting multiple sclerosis patients (RRMS) disability progressively accumulates over time. To compare the cumulative probability of six-month confirmed disability-worsening events using a fixed baseline or a roving Expanded Disability Status Scale (EDSS) reference, in a real-world setting. Methods: A cohort of 7,964 RRMS patients followed for two or more years, with EDSS scores recorded every six months, was selected from the Italian Multiple Sclerosis (MS) Register. The overall probability of confirmed disability-worsening events and of confirmed disability-worsening events unrelated to relapse was evaluated using as reference a fixed baseline EDSS score or a roving EDSS score in which the increase had to be separated from the last EDSS assessment by at least 6 or 12 months. Results: Using a fixed baseline EDSS reference, the cumulative probability of six-year overall confirmed disability-worsening events was 33.2%; that of events unrelated to relapse was 10.9% (33% of overall confirmed disability-worsening events). Using a roving EDSS the proportions were respectively 35.2% and 21.3% (61% of overall confirmed disability-worsening events). Conclusions: In a real-world setting, in RRMS patients roving EDSS reference scores appear to be more sensitive for detecting confirmed disability-worsening events unrelated to relapse.