1086 patients were included (1017 with relapsing-remitting and 69 with secondary progressive MS [SPMS]). 74.9% were female and 91.5% were white. Mean age was 40.0 (SD 10.2) and median disease duration was 5.1 years (IQR 1.4 to 11.6). Median EDSS was 1.5 (IQR 1 to 2.5). ARR during the first three years after FV was 0.27. A multiple regression model predicted 10.3% of the variance in relapses. Younger age, non-SPMS diagnosis, and relapses in the year before FV were significantly predictive of relapses after FV.

We model the three-year ARR for a real-world sample of relapsing-onset MS patients at the time of their first clinic visit. The sample was limited to patients on low-efficacy therapy prior to 2010 to reduce confounding from treatment. While age and progressive disease were inversely correlated with relapses, as expected, most of the variance in relapses was unexplained. Relapses in the year prior to FV, but not total relapses, were correlated with future relapses. Whether relapses ‘cluster’ is an area for future study.