Does benign multiple sclerosis today imply benign multiple sclerosis tomorrow?

Whether there is a benign form of multiple sclerosis (MS) continues to be a controversial issue. Varying definitions, inadequacies in measurement tools of MS-related impairment, and differences in the interpretation of the same or similar data by different investigators make this a confusing but important topic for discussion.^1–6 In this issue of Neurology, Sayao et al. report that MS patients with an Expanded Disability Status Scale (EDSS) score of ≤2 or ≤1 or no disability for ≥10 years' duration have a 70%, 90%, and 94% chance, respectively, of remaining benign (EDSS score ≤ 3) 10 years later in a large population-based study in British Columbia. The only factor associated with 20-year EDSS score was the 10-year EDSS score.^7,8 The authors note that although the natural history is favorable for this cohort of patients, not all will remain “well” for the duration of their lives. Indeed, the authors emphasize that even patients with these mildest cases of MS may ultimately do poorly.

As Sayao et al. point out, their results differ somewhat from other studies.^1,2,4,5 A recent population-based Olmsted County MS study reported that 93% (vs 70% in Sayao's study) of patients with EDSS score ≤ 2 for >10 years remained benign (EDSS score ≤ 3) a further 10 years later. The Olmsted County report, though a much smaller study, …