Right-to-left shunt and migraine: the strength of the relationship.

Several studies have shown that the prevalence of a cardial right-to-left shunt (RLS) in patients with migraine with aura is significantly higher than in patients without migraine. To assess the strength of the possible relationship between RLS and migraine, the literature concerning this subject was systematically reviewed. We identified seven relevant studies. Among patients with RLS migraine with aura was 3.5 times more prevalent than among subjects without RLS [Mantel-Haenszel odds ratio (ORMH) 3.5; 95% confidence interval (CI) 2.1, 5.8]. In patients with ischaemic stroke migraine was more than two times more prevalent in patients with RLS than in patients without RLS (ORMH 2.1; 95% CI 1.6, 2.9). Our review shows that there is a clear association between RLS and migraine, especially migraine with aura. The relationship between RLS and migraine is further substantiated by the observations of disappearance and improvement of migraine symptoms after closure of the foramen ovale. However, the mechanism as well as the question about causality of this association has to be further elucidated.