Objective: To evaluate disease status after 20 years in a cohort defined as "benign multiple sclerosis (MS)" (Expanded Disability Status Scale [EDSS] score < or = 3) at 10 years from onset.
Methods: Patients with an EDSS score < or = 3 at 10 (+/- 1) years from onset were selected from the British Columbia MS clinic database. The 20-year EDSS score was the primary outcome. Potential risk factors differentiating those who "continued benign" (EDSS score < or = 3.0) from those who were "no longer benign" (EDSS score > 3.0) at 20 years, including age at onset, onset symptoms, and 10-year EDSS score, were analyzed, and lower 10-year EDSS score cutoffs were investigated.
Results: Twenty-year EDSS scores were obtained for 169 of 200 patients (84.5%); of these, 88 (52.1%) continued benign, but 36 (21.3%) progressed to require the use of a cane (EDSS score > or = 6). Conversion to secondary progressive MS occurred in 45 of 196 patients (23%) with a relapsing-remitting onset. The only variable associated with disease progression at 20 years was the 10-year EDSS score (p < 0.0005); no 10-year EDSS score seemed ideal in predicting benign status, and an EDSS score < or = 2 resulted in 32% becoming no longer benign.
Discussion: At 10 years from onset, neither an Expanded Disability Status Scale (EDSS) score < or = 3 nor an EDSS score < or = 2 adequately represented "benign multiple sclerosis (MS)" because an appreciable proportion of patients progressed in disease severity. Appropriate and reliable criteria to identify which patients with MS remain with mild disability over the long term have yet to be determined.