Anosmia (also known as anosphresia or olfactory anesthesia) is the complete absence of the sense of smell.
In addition to anosmia, there is also hyposmia (a.k.a. microsmia or olfactory hypoesthesia) representing a diminished sense of smell and parosmia (a.k.a. dysosmia or paraosmia) referring to any pathology of the olfactory system 1,5. Phantosmia is the experience of a smell being present without an actual stimulus, i.e. an olfactory hallucination 5. For completion, normosmia is the state of having normal olfactory function.
It is estimated that the point prevalence of an impaired sense of smell is as much as 19.1% adult population and four-fifths of over 75-year-olds 2.
The underlying causes of anosmia have been traditionally subdivided into 2,5:
- conductive: an obstruction to the passage of odorants, or
- sensorineural: dysfunction of the olfactory neurons or olfactory nerve (I)
- central: dysfunction of the olfactory processing systems of the CNS
- systemic pathologies with olfactory complications, e.g. granulomatosis with polyangiitis
- postoperative, for example nasal surgery
- medications, e.g. antibiotics (aminoglycosides, penicillins, macrolides, tetracyclines), amino ester anesthetics (e.g. procaine), propylthiouracil
- viral infections e.g. coronaviruses,
- neurological disease, primarily neurodegenerative, e.g. Parkinson disease, Alzheimer disease, also stroke, myasthenia gravis
- head injury
- intracranial lesions
- toxins, e.g. heavy metals, solvents (e.g. toluene, ammonia, benzene)
- genetic, e.g. Kallmann syndrome
It is increasingly clear that this anatomical approach to the etiology of olfactory dysfunction is limited, and ultimately unhelpful, as underlying diseases, e.g. chronic rhinosinusitis, may cause loss of smell via both obstructive and neural mechanisms 5.
History and etymology
Anosmia is derived from Classical Greek roots. "οσμη" (osme) means an aroma/scent, and "αν" (an) is a prefix used to indicate negation 4.
- 1. William Alexander Newman Dorland. Dorland's Illustrated Medical Dictionary. (2018) ISBN: 9781416023647
- 2. Walker A, Pottinger G, Scott A, Hopkins C. Anosmia and loss of smell in the era of covid-19. (2020) BMJ (Clinical research ed.). 370: m2808. doi:10.1136/bmj.m2808 - Pubmed
- 3. Meng X, Deng Y, Dai Z, Meng Z. COVID-19 and anosmia: A review based on up-to-date knowledge. (2020) American journal of otolaryngology. 41 (5): 102581. doi:10.1016/j.amjoto.2020.102581 - Pubmed
- 4. James Morwood, John Taylor. Pocket Oxford Classical Greek Dictionary. (2002) ISBN: 9780198605126
- 5. Hummel T, Whitcroft KL, Andrews P, et al. Position paper on olfactory dysfunction. (2017) Rhinology. Supplement. 54 (26): 1-30. doi:10.4193/Rhino16.248 - Pubmed