To ascertain the contribution of relapse associated disability in RMS using long term data collected in our clinic.

The natural history of relapsing MS (RMS) is being newly defined in the treatment era.  Treatments affect both relapse related disability and short term worsening, but measurements of long term outcomes remain a challenge.

Retrospective study of a cohort of consecutively newly diagnosed RMS patients, (n=176) was undertaken, measuring all confirmed changes in disability up to 15 years after onset.   Worsening was assessed yearly and in 5 year epochs and was attributed to either relapse (RW) or slow progression (PW), or a combination of both.

At data lock 139/176 (79%) of patients were still actively followed, with EDSS available for year10 post onset in 145/176 (82%) of patients and year 15 post onset EDSS was available for 83 patients (average follow up entire group 12 years post onset).   RW accounted for a large proportion of worsening seen in the first 15 years of  RMS. RW was less frequent over time, but accounted for most EDSS changes in the first decade of MS (167/267, 63% of all EDSS changes), and remained important even in years 11-15 (17/50, 34% of all EDSS changes).   Median change in disability due to RW vs PW was similar over the entire 15 years. 

Worsening of treated MS was associated with relapses in many RMS patients throughout the first 15 years after onset, suggesting an opportunity for long term benefit through relapse reduction.  Worsening due to slow progression played an increasing role over time.