Seasonality and clinical characteristics of MS in an equatorial country

•Seasonality has been linked to the risk of MS in countries from higher latitudes.•Some studies show some influence of the season of birth in the course of MS.•In a sample of patients from an equatorial country, no relationship was found between month and season of birth and the course of MS. Month and season of birth have been associated with risk of multiple sclerosis (MS), but there is relatively little evidence regarding their influence on the timing and severity of disease at onset. To assess whether month and season of birth influence the age and phenotype at onset of MS as well as its severity in a cohort of Colombian patients. This study is an analysis on MS cases only, drawn from a previously published case-control study. MS cases confirmed with current diagnostic criteria cared for at least once in our center were included. We assessed the influence of the month and season of birth in the age at MS onset, MS severity score, and age-related MS severity score using multiple and pairwise comparisons. Age at onset was also studied using Kaplan–Meier survival estimates compared with the log-rank test. The likelihood of progressive MS onset was evaluated with OR estimated from logistic regression models adjusted for age at onset and sex. 668 MS cases were included. No significant differences were found in the age at MS onset according to month of birth or season of birth. Neither month of birth nor season of birth conferred significant differences in MS severity score or age-related MS severity score. No significant association was found between month (ORs ranging from 0.62 to 3.11, none significant) or season of birth (OR 0.91; 95 %CI: 0.46–1.84) with primary progressive MS. The month or season of birth do not appear to influence the age onset and phenotype of MS in our country.