May headache triggered by odors be regarded as a differentiating factor between migraine and other primary headaches?

Objectives The objective of this article is to characterize olfactory stimulation as a trigger of headaches attacks and differentiation between migraine and other primary headaches. Participants and methods The study was prospective and experimental, with comparison of groups. A total of 158 volunteers (73 men and 85 women) were diagnosed with primary headaches, according to the criteria of the International Classification of Headache Disorders, Third Edition (beta version) (ICHD-3β). The study was conducted by two examiners; one of them was assigned to diagnose the presence and type of primary headache, while the other was responsible for exposing the volunteers to odor and recording the effects of this exposure. Results Of the 158 volunteers with headache, there were 72 (45.6%) cases of migraine and 86 (54.4%) with other primary headaches. In both groups, there were differences in headache characteristics (χ 2 = 4.132; p = 0.046). Headache attacks (25/72; 34.7%) and nausea (5/72; 6.9%) were triggered by odor only in patients with migraine, corresponding to 19.0% (30/158) of the sample, but in none with other primary headaches (χ 2 = 43.78; p < 0.001). Headache occurred more often associated with nausea ( p = 0.146) and bilateral location ( p = 0.002) in migraineurs who had headache triggered by odor. Headache was triggered after 118 ± 24.6 min and nausea after 72.8 ± 84.7 min of exposure to odor. Conclusions The odor triggered headache attacks or nausea only in migraineurs. Therefore, headache triggered by odors may be considered a factor of differentiation between migraine and other primary headaches and this trigger seems very specific of migraine.