Allergy, histamine 1 receptor blockers, and the risk of multiple sclerosis

Background: It is unclear whether allergic diseases are associated with multiple sclerosis (MS), but histamine 1 receptor blockers, used in the treatment of allergic conditions, decreased the severity of experimental autoimmune encephalomyelitis (an animal model of MS). Objective: To assess the association of allergy history and use of histamine 1 receptor blockers with the risk of MS. Methods: Using a case-control study nested in the United Kingdom-based General Practice Research Database cohort, the authors identified 163 incident cases of MS with at least 3 years of follow-up before their first symptoms (index date). Up to 10 controls matched to the cases by age, sex, general practice, and time in the cohort were selected. Previous history of allergic disease and use of histamine 1 receptor blockers in the 3 years before the index date were assessed through computerized medical records. Results: History of any allergic condition in the 3 years before the index date was not associated with MS risk (adjusted odds ratio [OR] 1.2, 95% CI 0.8 to 1.8). However, use of sedating histamine 1 receptor blockers was associated with decreased MS risk (adjusted OR 0.2, 95% CI 0.1 to 0.8). Conclusion: These results do not support a strong link between allergic conditions and multiple sclerosis (MS) risk but suggest a possible beneficial effect of antihistamines on the onset of MS.