Association between migraine and asthma: matched case-control study

BACKGROUND Earlier studies have suggested a link between asthma and severe headache, and also between migraine and wheezing illness. Recent analysis have also shown an increase of asthma among cases with a prior history of migraine but without a history of hay fever, allergic rhinitis or eczema. AIM To examine whether there is an association between migraine and asthma in the United Kingdom. DESIGN OF STUDY Matched case-control study using the General Practice Research Database (GPRD). SETTING Practices in the United Kingdom providing data on 5,110,619 patients to the GPRD. METHOD The subjects were the patients with one or more diagnoses of migraine plus treatment for migraine. Each case was matched by general practice, sex, and age, with one control who had never been given a diagnosis of migraine. Case and control groups were compared for prevalence of asthma, chronic obstructive pulmonary disease, respiratory symptoms treated with inhalers or hay fever. Investigations were carried out to determine whether the association between migraine and asthma was stronger among patients with hayfever or those without hayfever, and whether patients with migraine had an increased prescription of other (non-migraine and non-asthma) medications. RESULTS Among 64 678 case-control pairs, the relative risk of asthma in patients with migraine was 1.59 (95% CI = 1.54 to 1.65) among definite cases, and 0.75 (95% CI = 0.67 to 0.83) among those whose selection as case included beta-blocker prophylaxis. Among definite migraine cases, relative risks of chronic obstructive pulmonary disease, respiratory symptoms, eczema, and hay fever (pollinosis), were all raised (at 1.22, 1.85, 1.55, and 1.67, respectively). The association between migraine and asthma was stronger in patients without a diagnosis of hay fever, than in those with hayfever (relative risk = 1.32 and 1.19, respectively). The relative risk of prescription for a range of non-migraine, non-asthma medications was raised, the exception being anti-diabetic medication. CONCLUSION This large case-control study provides evidence for an association between migraine and asthma. Frequent attendance at a general practice surgery may confound this association. However, if the association is real, its elucidation may help the understanding of disease mechanisms shared by migraine and asthma.