Association between allergies and multiple sclerosis: a systematic review and meta-analysis.

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system that expresses a typical type 1 immune response (Th1). Allergies, on the other hand, present with high levels of type 2 (Th2) cytokines. Some authors observed that Th1 and Th2 diseases could coexist in the same subject. Besides its biological plausibility, the association between MS and allergies remains controversial. The aim of this systematic review and meta-analysis was to determine if there is an association between allergic diseases and MS. All clinical and epidemiological studies on patients with MS published up to July 2009, that assessed the association between allergic diseases and MS were reviewed. A total of 1010 articles were retrieved from search, and ten epidemiological studies were included in the analysis. The results showed that there is no evidence supporting an association between allergic diseases (OR: 0.91; CI 95%: 0.68-1.23), asthma (OR: 0.83; CI 95%: 0.48-1.44), allergic rhinitis (OR: 0.81; CI 95%: 0.59-1.12), eczema (OR: 0.93; CI 95%: 0.71-1.23) and MS. Additional prospective studies in this field might help to elucidate the nature of these associations.