xRead - Olfactory Disorders (September 2023)

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Headache

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reality, more than one trigger can be involved, although complexities abound. For example, migrai neurs who experience auras tend to be more likely to experience a migraine attack after physical activ ity, although compared to olfactory and stress trig gers, only a small proportion of migraine patients without auras have a crisis after such activity. 35 The main odorant that triggered the migraine cri sis of our sample was perfume, a phenomenon reported by others. 6,19,36 We also demonstrated that patients without auras had a higher probability of having perfume as a trigger than those with auras ( P 5 .02). Lima et al 11 have found the same three main odors that we found as being capable of trigger ing a migraine crisis, namely, perfume, cigarette smoke, and cleaning products. Since the odors that trigger the crisis and cause osmophobia are the same, common neurological pathways may well be involved. Other research reported that patients with epi sodic migraine have similar olfactory function as age and sex-matched controls in interictal periods, but a minority exhibited microsmia (lower scores on the University of Pennsylvania Smell Identification Test) during acute attacks. 23 In our study, migraineurs reported having less olfactory acuity using a VAS, dur ing interictal periods, which contrasts to Marmura et al 23 findings. Moreover, there was no difference in self-reported olfactory acuity between the patients with and without auras, although patients who experi enced osmophobia and odor-triggered migraine attacks consistently reported having less olfactory function than migraineurs who did not experience these symp toms. However, it is important to emphasize that we did not use any olfactory test besides the VAS. Phantosmia, considered to be a sensation of odors in the absence of a stimulus, was a rare olfac tory symptom in this study. Interestingly, it was positively related to subjects who have less than 10 crises of migraine per year ( P 5 .01) and subjects with IOH ( P 5 .001). In that context, we character ized olfactory hallucination as an experience of a smell that does not exist right before the crisis, ie, as a kind of aura, as noted by some authors. 28,37 The few migraineurs who experienced an olfactory hallucination found the odor sensation to have a burning and/or putrid-like character.

reported to date. This suggests that osmophobia is as frequent as photophobia and phonophobia in this disease and should be considered as one of its defining features. The lower prevalence rates reported in other studies, which range from 43% 9 to 81.7%, 10 may reflect the fact that, in many cases, different types of populations (eg, only females) 10 or smaller numbers of subjects 9 were studied. Our research confirms the findings of other studies that osmophobia is not specifically related to whether a patient experiences auras or not. 6,9,25 Other olfaction-related symptoms were some what less frequently observed in this study. Among them, our finding of a 14% prevalence rate for IOH is considerably lower than the prevalence rate of 35.2% reported by Demarquay et al 22 for migrain eurs. This investigator found a positive association between odor-induced headaches and IOH patients. In his analysis, those who had IOH also had high rates of odor-induced headaches. Paradoxically, we found the opposite: 93% of no IOH subjects had odor-triggered migraine, while 68% of IOH subjects had odor triggered migraine ( P 5 .002). Moreover, we found that patients with no IOH are more likely to experience osmophobia ( P 5 .002). The basis for this stark discrepancy is not clear, although the ques tions used in our questionnaire were different from those used by Demarquay et al. 22 They asked wheth er the patients regarded themselves as clearly hyper sensitive to odors between attacks and these data were completed using a previously validated chemi cal odor intolerance index. Our findings, along with those of others, clearly demonstrate that odors, like stress, 7,11,32,33 can be a very prevalent trigger of migraine. 11,32 Chakra varty 34 hypothesized that every migraine crisis has a trigger, internal or external, identifiable or not. According to his thinking, triggers induce cortical spreading depression in a hyper-excitable cortex of a migraineurs, beginning the pain process. In our study, 97% of the patients who had stress as a trig ger also had odor as a trigger, suggesting that these two triggers may be related. Interestingly, migrai neurs who have odor as a trigger were also found to have food as a trigger ( P 5 .01), conceivably reflecting the odorous elements of foodstuffs. In