Association between seasonal factors and multiple sclerosis.

Multiple sclerosis (MS) is a chronic inflammatory disease that affects the central nervous system. MS is causing progressive and relapsing neurological disability, due to demyelination and axonal damage. The etiopathogenesis of MS is poorly understood. A number of environmental factors have been previously suggested, including: month of birth, vitamin D levels, smoking and viral infections. Previous studies assessing seasonal variation of relapses in multiple sclerosis have had conflicting results. The aim of this review is to assess the association between seasonal factors and MS, in terms of disease onset, relapses and activity.