Seasonal variations in exacerbations and MRI parameters in relapsing-remitting multiple sclerosis.

Environmental factors may be involved in the etiology of multiple sclerosis (MS). We investigate prevalence of exacerbations and MRI findings in a cohort of relapsing-remitting multiple sclerosis patients, for evidence of seasonal variation or cyclic trends. We find only weak evidence of seasonality in our data. Differences in reports of seasonal variation in multiple sclerosis disease activity may be due to regional climatic differences or other geographic variables that change with latitude as well as genetic predisposition.