Introduction: The high prevalence of patent foramen ovale in migraine with aura (MWA) seems to be well established; yet, the possible relation between the magnitude of the right-to-left shunt (RLS) and MWA is not so clear. As a hypothesis, if the RLS played a precipitating role, subjects with a larger degree of shunt might experience a higher number of seizures. We examine this possible relationship between the magnitude of the shunt and the incidence of seizures.
Patients and methods: We examined a series of 72 patients with MWA to obtain the frequencies of seizures (dividing them into three groups of increasing frequency), history and precipitating factors. The presence and magnitude of the RLS were later determined by means of transcranial Doppler ultrasonography, following a method that had previously been validated. Univariate analysis was then used to evaluate the possible association between the magnitude of the shunt and the frequency of seizures.
Results: The mean age was 36 years. RLS appeared in 44 patients (61.1%) and followed a 'shower/curtain' pattern in 38% of cases. Frequency of seizures was low in 27%, medium in 45% and high in 27% of patients. Frequency was not associated with the magnitude of the shunt even when only high-frequency cases were considered. High frequency was associated, however, with certain precipitating factors.
Conclusions: Our study confirms the existence of a high prevalence of RLS in patients with MWA, but no association was found between the magnitude of the shunt and the frequency of the seizures. As discussed here, these findings are partly at odds with a 'threshold' type of association or mechanism that precipitates seizures.