“Consequences of Gaining Olfactory Function After Lifelong Anosmia”, 2021-05-18 (; similar):
We present a rare case in which a patient has gained her smell after lifelong anosmia.
The patient was objectively tested and diagnosed with functional anosmia at age 13 and reported they were experiencing a new sensation of smell at age 22.
Our results show an electrophysiological signal for 2 unimodal odorants. The patient had a retronasal score in the hyposmic range and self-reported the ability to smell non-trigeminal odors, but reported being disturbed by the presence of the new sense and co-occurrence of phantosmia.
We discuss our case in routes of neurogenesis and non-forming memory association with odors.
[Keywords: Anosmia, olfactory recovery, neurogenesis, congenital, new sense, memory, phantosmia]
…As typical with congenital loss, the patient was diagnosed in her early teenage years, most likely after it was brought to her attention that others smell…However, in her mid-20s, she started to perceive odors. From then on, she also perceived an occasional odor phantom, ie. phantosmia, following an odorous sensation, elicited by an odorous stimulus, which could not be switched off. Hence, she experiences an olfactory percept, and then the sensation lingers from that previous exposure even with no airflow. To our knowledge, this is the first report on a patient recovering from lifelong anosmia.
…From an age of 24 years she was able to perceive more and more fragrances with occasional new smell impressions every few weeks. During an interview process, she emphasized that her “new sense” is an annoyance to her with most odor sensations being unpleasant. Only a few fragrances are perceived as pleasant (eg. lavender or curry). To the former, she has experienced more and more unpleasant smells (eg. manure, onion, garlic) than pleasant ones which has increased her anxiety. During the last months, she fainted and connected this collapse to the olfactory stress. Additionally, during the recent olfactory recovery period (~18 months), there have been a few olfactory phantoms (phantosmia II°: intense [8⁄10], unpleasant [−2 on a scale from −5 to +5], lasting minutes to hours, not daily but constant frequency, extremely annoyed by the odor phantom ( et al 2013)). From a follow-up interview (10 days after November visit), the patient reported on the odor phantoms “I often cannot tell whether the smell is real or not. It usually feels just as strong and real as when I actually smell something” and “smells stay in the nose for hours which is stressful”. On a third interview (4 months after November visit), following an odor presentation, a pinch of the nose did not make the smell disappear. Gustatory function has remained unchanged over the years although retronasal aromas have mostly become more pleasant.
…The patient claimed that she could smell half (16) of these odors which included mostly trigeminal (eg. peppermint, clove), but also nontrigeminal odorants (eg. coffee, lilac). Many pleasant ratings for spices were lower than what is commonly found (eg. clove, anise, ginger; ( et al 1984)) and some similar odors were given opposite ratings of liking (low peppermint, but high mint). Supra-threshold taste sprays showed normal taste function (eg. normogeusia) for sweet, bitter, sour, and salty (4⁄4 correct; ( et al 2013)).
…More obvious questions are how it should be possible that (1) somebody without olfactory bulbs should have olfactory percepts, and that (2) a person without a sense of smell from birth should develop olfactory function. At least the former question has been discussed in depth previously ( et al 2020). Among the major ideas were (1) that, although unlikely given the resolution of present MR scans, OBs might have been too small to be detected, (2) that the olfactory sensations are mediated by the trigeminal nerve, which would be astonishing given the many subtle, unimodal odors the patient was able to detect and the electrophysiological response to pure unimodal odorants. In addition, a hypothesis could be that portions of the coding of olfactory information are different from that in other mammals so that some olfactory sensations are possible even without an olfactory bulb.