What’s that smell?

by Deena Kuruvilla, MD

Migraine is associated with a number of disabling aura symptoms such as visual changes, focal numbness, focal weakness and speech changes as well as associated symptoms such as photophobia, phonophobia, nausea and osmophobia. Osmophobia, a sensitivity to smell, is frequently described in 95% of migraine patients and is known to trigger or worsen attacks. Specific odors known to trigger attacks include perfumes, cigarette smoke, motor vehicle exhaust and some cleaning products and foods.

Another way in which smell is involved is through olfactory hallucinations during a migraine attack (OHM). While these cases are much rarer, patients actually smell specific things that are not smelled by the people around them and are associated with their headaches. In this month’s edition of Cephalalgia, Dr. Mainardi and colleagues give us insight into OHM. OHM occur in 0.1% of adults and 3.9% of children with migraines. OHM has not been as well characterized as osmophobia, so this article describes the specific features of eleven patients with migraine with and without aura, with OHM. The patients were followed for 25 months and asked to keep a detailed headache diary. Over this period, 831 migraine attacks (migraine without aura= 728, migraine with aura = 103) were reported and of these 141 were associated with OHM. The smells would last between three minutes and twenty-four hours on average. In this particular study among patients with OHM, the patients most commonly had migraine without aura and all had less than fifteen headache days monthly. To make sure to rule out other causes for OHM such a temporal lobe epilepsy, the most common cause, the patients had unremarkable physical exams, routine blood tests, brain imaging and electroencephalograms. In most of the patients in the study, OHM occurred during the attacks without aura. Interestingly, photophobia and phonophobia were associated with migraines in all eleven patients but osmophobia was only present in six of eleven cases. Olfactory hallucinations were undesirable in eight patients and they described them as burnt wood, smoke, gas, rotten meat, metallic and sulphur. The smell was pleasant in two patients, who smelled melon, bananas, jasmine and vanilla. While these smells usually occur before or during a migraine attack, they have not been classified as aura. While this study gives us a view into OHM, larger studies are needed to make an accurate description of this feature.