Anosmia as an Enantiopathy for Migraines

Abstract

Elimination of olfactory sensory perception with a reduction in odor-induced migraine has not heretofore been reported. Case study: A 64-year-old right-handed woman presented with a history of common migraines since childhood. The headaches were bilateral, throbbing, pulsatile, and without aura and were associated with lightheadedness, photophobia, sonophobia, nausea, and vomiting. They would be precipitated by ambient aromas, such as perfumes and bath products, and she became agoraphobic, fearful of going out of her domicile and being exposed to odors. She avoided stores, perfume counters, and public places; scared that it would initiate a disabling headache. Twenty-five years prior to presentation, the patient fell on ice, striking her head and causing a transient loss of consciousness and persistent absence of smell and taste. From that point forwards, while she would have an occasional headache independent of an odor, she no longer experienced odor-induced headaches. Her agoraphobia had resolved. Since the head trauma, her smell remained at 10% to 20%. Her taste remained at 30% of normal. Abnormalities on neurological examination: Motor examination: Drift testing: Right pronator drift with right abductor digiti minimi sign. Cerebellar examination: Bilateral finger-to-nose dysmetria. Rapid alternating movements: decreased in the left upper extremity. Reflexes: Bilateral upper extremity 3+. Absent bilateral ankle jerks. Bilateral palmomental and Hoffmann reflexes present. Chemosensory testing: Olfaction: Brief Smell Identification Test (B-SIT): 7 (hyposmia), Alcohol Sniff Test: 0 (anosmia). Retronasal Olfaction: Retronasal Smell Index: 4 (hyposmia). Gustation: Propylthiouracil Disc Taste Test: 10 (normogeusia). While performing the B-SIT and sniffing the aroma of rose, the patient noted the sudden onset of a headache, even though she could not detect any odor present. The temporal relationship between loss of sense of smell and elimination of odor-induced migraines suggests a causal relationship. Conscious recognition of odor may induce a stimulus-response paradigm, whereby migraine occurs. Head trauma-induced anosmia, by elimination of conscious perception of the odor, may thus be the modality whereby her headaches resolved. Alternatively, odors may induce an autonomic response, and conscious recognition of such autonomic response may induce a headache. To tergiversate, that the rose aroma in the B-SIT induced a headache, without any conscious detection of the odor, implies that either unconscious perception is enough to precipitate a headache or that these odors act not as odorants, but rather as an exogenous ambient chemical inducing headaches. Possibly the production of temporary anosmia by use of nose clips may be utilized as a prophylactic device for those with odor-induced migraines. Further investigation into this is warranted. No funding.