Supplementary Material for: Upper Respiratory Infections and MRI Activity in Relapsing-Remitting Multiple Sclerosis

Background: Although clinical reports have suggested a relationship between systemic infections and multiple sclerosis (MS) relapses, MRI evidence supporting an association is conflicting. Here we evaluated the temporal relationship between upper respiratory infections (URIs) and MRI activity in relapsing-remitting (RR) MS. Methods: We combined individual data on URI with data on active lesions in pre-scheduled MRI examinations performed every 4 weeks for 28 weeks in 69 patients. A 4-week at-risk (AR) period started, by definition, 1 week before the onset of a URI. We recorded the relationship between the number of active lesions in each MRI with (1) the number of days of AR time in the immediately preceding 4-week period and (2) the number of days passed since the onset of a preceding URI. Results: Average MRI lesions/day showed no difference between AR (0.0764) and not-AR (0.0774) periods. The number of lesions in 483 pre-scheduled MRI examinations did not correlate with the AR proportion in the prior 4-week period (rho = -0.03), and time from URI onset did not correlate with lesion number on the next MRI examination (rho = 0.003). Conclusion: The occurrence of a URI did not increase the risk of MRI activity evaluated in an adjacent 4-week window in RRMS.