When Are Patients with MS Most Prone to Relapse?

The latitudinal gradient in multiple sclerosis (MS) has been hypothesized to be partially attributable to ultraviolet (UV) light exposure and its effect on vitamin D levels. Investigators used the global MSBase Registry to evaluate seasonal differences in relapses rates across 46 clinical centers in 20 countries. The dataset included 9811 patients who had a total of 32,762 relapses. Daily UV radiation (UVR) was recorded for all locations in the analysis, and UVR trough was determined.

Relapses followed a cyclical pattern, peaking in spring: Relapses were most common around March 7 in the northern hemisphere and September 5 in the southern hemisphere. Mean lag from UV radiation trough to relapse onset peak was 2.7 months, and for every 10 deg…