Temporal trends of disability progression in multiple sclerosis: findings from British Columbia, Canada (1975-2009)

Background: Recent natural history studies suggest that multiple sclerosis (MS) is a more slowly progressing disease than previously thought. These observations are from studies separated by time, geography and methodological approach. Objectives: We investigated whether MS disease progression has changed over time in British Columbia, Canada. Methods: The British Columbia MS database was queried for relapsing-onset MS patients with symptom onset from 1975 to < 1995, first assessed within 15 years from onset and with at least two Expanded Disability Status Scale (EDSS) scores. Latest follow-up was to 2009. Patients were grouped by 5-year onset intervals (1975 to < 1980, 1980 to < 1985, 1985 to < 1990, 1990 to < 1995). Outcome was defined as time to reach sustained and confirmed EDSS 6 within 15 years of disease duration. Kaplan-Meier analysis was used to compare: the proportion of patients reaching EDSS 6 (primary analysis) and the time to EDSS 6 (secondary analysis) across the time-period groups. Results: A total of 2236 relapsing-onset MS patients (73.4% female; mean age at onset: 32.3 +/- 8.8 years) were included. No significant temporal trend was found in the proportion of patients reaching EDSS 6 within 15 years from onset (28.5%, 26.4%, 27.7%, 22.3% for intervals 1975 to < 1980, 1980 to < 1985, 1985 to < 1990, 1990 to < 1995, respectively; p = 0.09) or in survival curves for time to reach the outcome (p = 0.14). Conclusions: Rates of disease progression remained relatively stable over two decades of MS onset in British Columbia, Canada. Our results suggest that differences in disease progression findings between natural history studies may be related to factors other than time period.