Normobaric hypoxia and nitroglycerin as trigger factors for migraine.

Migraine prevalence is increased in high-altitude populations and symptoms of acute mountain sickness mimic migraine symptoms. Here we tested whether normobaric hypoxia may trigger migraine attacks. As positive control we used nitrolgycerin (NTG), which has been shown to induce migraine attacks in up to 80% of migraineurs. Sixteen patients (12 females, mean age 28.9 +/- 7.2 years) suffering from migraine with (n = 8) and without aura (n = 8) underwent three different provocations (normobaric hypoxia, NTG and placebo) in a randomized, cross-over, double dummy design. Each provocation was performed on a separate day. The primary outcome measure was the proportion of patients developing a migraine attack according to the criteria of the International Headache Society within 8 h after provocation onset. Fourteen patients completed all three provocations. Migraine was provoked in six (42%) patients by hypoxia, in three (21%) by NTG and in two (14%) by placebo. The differences among groups were not significant (P = 0.197). The median time to attacks was 5 h. In conclusion, the (remarkably) low response rate to NTG is surprising in view of previous data. Further studies are required to establish fully the potency of hypoxia in triggering migraine attacks.