Monthly variation of multiple sclerosis activity in the southern hemisphere: analysis from 996 relapses in Brazil

Background and purpose: Seasonal variations of multiple sclerosis (MS) activity have been reported, however, most data come from studies in the northern hemisphere. Methods: We reviewed medical records of MS patients living in Campinas region, Brazil. The first symptoms' date was defined as the relapse month. Climatic information included UV radiation index, median temperature, rainfall, and humidity. Results: Two hundred and nine patients were included. The incidence of relapses was highest in January (11.2%) and December (10.4%) and lowest in November (5.7%) and October (7.0%) (P < 0.015). The months with highest incidence of relapses (December-January) had higher UV radiation index and humidity rates (P = 0.032 and 0.040, respectively). Conclusion: Most exacerbations were in the spring/summer transition, which also showed higher UV radiation index and humidity rate. Along with other environmental factors, seasonal fluctuation contributes to MS activity.19466066