Relationship between migraine and cardiac and pulmonary right-to-left shunts

A relationship between migraine with aura and the presence of right-re-left shunts has been reported in two studies. Right-to-left shunts are also ass ociated with some forms of decompression illness. While conducting research in divers with decompression illness, it was our impression that divers wi th a large shunt often had a history of migraine with aura in everyday life and after dives. Therefore we routinely asked all divers about migraine sy mptoms. The medical records of the last 200 individuals referred for invest igation of decompression illness were reviewed to determine the association between right-to-left shunts and migraine aura after diving, and migraine in daily life unconnected with diving. Migraine with aura in daily life unc onnected with diving occurred significantly more frequently in individuals who had a large shunt which was present at rest (38 of 80; 47.5%) compared with those who had a shunt which was smaller or only seen after a Valsalva manoeuvre (four of 40; 10%) or those with no shunt (I I of 80; 13.8%) (P < 0.001). Hemiplegic migraine occurred in 10 divers, each of whom had a shunt that was present at rest; in eight of these cases the shunt was large. The prevalence of migraine without aura was similar in all groups. Post-dive m igraine aura was significantly more frequent in individuals who had a large shunt present at rest (21 of 80; 26.3%) compared with those who had a shun t that was smaller or only seen after a Valsalva manoeuvre (five of 40; 12. 5%) or no shunt tone of 80; 1.3%) (P < 0.001). Thus individuals with a larg e right-to-left shunt have an increased prevalence of migraine with aura in daily life unconnected with diving, acid they also have an increased incid ence of migraine aura after dives, but only when the dives liberate venous bubbles. These data suggest the possibility that, in some individuals, righ t-to-left shunts have a role in the aetiology of migraine with aura. The ob servations suggest that paradoxical gas embolism may precipitate migraine w ith aura.