BACKGROUND: It was suggested that right-to-left shunt (RLS) may be highly prevalent in chronic migraine (CM) patients, indicating that patent foramen ovale (PFO) might be an aggravating and chronifying factor of migraine. Since a high proportion of chronic migraineurs also have medication-overuse headache (MOH), one may wonder if they have a more severe form of the disorder and more frequently a PFO.

OBJECTIVE: The objective of this study is to determine the prevalence and grade of RLS in patients suffering from CM and MOH.

METHODS: A cross-sectional multicenter study of air-contrast transcranial Doppler was conducted in 159 patients with CM ( N  = 57) or MOH ( N  = 102) attending a tertiary headache clinic.

RESULTS: The prevalence of RLS in CM was 37% (11% large shunts) and in MOH patients 31% (13% large shunts). There was no difference between the two groups ( P  = 0.49).

CONCLUSION: RLS prevalence in CM is within the upper range of those reported in episodic migraine without aura or in the general population, and not higher in MOH. PFO is thus unlikely to have a significant causal role in these chronic headaches.