Can we predict benign multiple sclerosis? Results of a 20-year long-term follow-up study

Benign multiple sclerosis (MS) is a discussed clinical entity, with variable reported prevalence (6-64%) requiring at least 5-10 years of clinical observation. Moreover, many benign patients progress with time becoming no longer benign (NLB). The objective of this study is to compare benign MS patients (EDSS ≤3, 10 years from disease onset) who still fulfilled the definition at 20 years to those NLB. In our retrospective study based on Ottawa Hospital MS Clinic database, 175 benign patients fulfilled the inclusion criteria (clinically definite MS, EDSS ≤3 at 10 years, disease onset from 1983 to 1993, and clinical assessments performed at 10 ± 1 and 20 ± 1 years from onset). Out of the identified patients, 66.3% remained benign at 20 years; however, by changing the definition for benign to EDSS ≤2 or ≤1 at 10 years, they increased to 71.9 and 81.6%, respectively. Female sex, EDSS ≤1 at 10 years, and a pure sensory onset were associated with a benign course, while a pure motor onset with an NLB condition. According to multivariate analysis, an EDSS ≤2 at 10 years predicted a long-term benign course. Our study questions the current definition of "benign" MS, suggesting a more stringent EDSS cutoff at 10 years to predict long-term benign prognosis.