Natural, innate improvements in multiple sclerosis disability

Background: Improvements in multiple sclerosis (MS) disability have recently been reported in immunomodulatory drug (IMD) clinical trials and observational studies. However, improvements have rarely been examined in natural history or IMD naive patients. We investigated annual and biennial improvements in Expanded Disability Status Scale (EDSS) scores in British Columbia, Canada. Methods: The British Columbian MS database was accessed for definite MS patients (1980-2009). Consecutive IMD-free EDSS scores one and two years apart (+/- 3 months) were examined; improvements (>= 0.5,>= 1,>= 2 EDSS points) and sustained improvements (confirmed at one year) were described. The influence of patient characteristics on improvements was examined using logistic regression. Results: From 16,132 EDSS scores, 7653 yearly and 5845 biennial EDSS intervals were available for 2961 and 2382 patients respectively. Of the yearly intervals, 14.9% showed an improvement (>= 0.5 points), 8.3% >= 1 point and 2.2% >= 2 point improvement, with nearly half being sustained. Corresponding worsenings were observed in 32.9%, 20.5% and 7.9% respectively, with stability in just over half (53%). Biennial findings were similar. Characteristics generally associated with improvements included: female sex, younger age, shorter disease duration, relapsing-onset and presence of moderate disability (compared with mild or advanced) and a previous episode of worsening (disassociated from a relapse). However, improvements were also observed after periods of stability and in primary-progressive MS. Conclusion: Improvements in MS disability over one or two years are not unusual. We suggest the term `innate improvements'. Our findings have implication for the design of clinical trials and observational studies in MS targeting improvements on the EDSS.