Change in disability in patients with multiple sclerosis: a 20-year prospective population-based analysis

Background: In patients with multiple sclerosis (MS), the natural history of the disease is of considerable importance to predict and understand long- term outcome and inform choices made by patients and clinicians. This information should ideally be derived from data that reflects the entire disease course. Methods: In this study, morbidity data from a prevalent cohort established in 1985 have been re-examined after an interval of 20 years to assess factors that may be important in determining outcome. Results: Of 379 patients who fulfilled criteria for definite or probable MS in the original population-based cohort, 221 (58.3%) had died, 149 (39.3%) were alive and 9 (2.4%) were untraceable. Mean Expanded Disability Status Scale (EDSS) score in 1985 was 5.15 (SD 2.7, range 0-9.5) and 8.01 (SD 2.6, range 0-10) in those alive in 2005. Mean worsening of EDSS scores in surviving patients was +3.02 EDSS points, but 14.0% had worsened by,1 EDSS point over 20 years. 61.4% of patients with EDSS 3.5-5.5 and 82.2% of those with an EDSS of (3 in 1985 had an EDSS of >= 6 after 20 years. Lower baseline EDSS scores (p < 0.0001), higher pyramidal functional system score (p = 0.02) and a greater number of functional systems involved (p = 0.001) were significantly more likely to be associated with greater worsening of disability. Of those with benign disease in 1985, only 19% remained benign after 20 years of follow-up; however, 12.6% of patients had minimal disability after at least 20 years after their disease onset and 14% of patients failed to worsen by >= 1 EDSS point. Conclusions: This study emphasises the importance of long- term epidemiological studies and the development of clinically relevant measures that effectively predict outcome and can guide decisions on therapeutic management.