A relationship between
migraine with aura and the presence of right-to-left shunts has been reported in two studies. Right-to-left shunts are also associated with some forms of
decompression illness. While conducting research in divers with
decompression illness, it was our impression that divers with 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 symptoms. The medical records of the last 200 individuals referred for investigation 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 unconnected 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 (11 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
migraine 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 shunt that was smaller or only seen after a Valsalva manoeuvre (five of 40; 12.5%) or no shunt (one of 80; 1.3%) (P<0.001). Thus individuals with a large right-to-left shunt have an increased prevalence of
migraine with aura in daily life unconnected with diving, and they also have an increased incidence of
migraine aura after dives, but only when the dives liberate venous bubbles. These data suggest the possibility that, in some individuals, right-to-left shunts have a role in the aetiology of
migraine with aura. The observations suggest that paradoxical
gas embolism may precipitate
migraine with aura.