LETTERS

Neuroimmunology Unit, Blizard Institute, BMJ: first published as 10.1136/bmj.m4739 on 8 December 2020. Downloaded from London E1 2AT, UK PAROSMIA [email protected] Cite this as: BMJ 2020;371:m4739 Parosmia: treatment, mechanism, and types http://dx.doi.org/10.1136/bmj.m4739 Published: 08 December 2020 Christopher Hawkes honorary professor of neurology Rimmer states that there is no cure for parosmia,1 which is correct, but there are drugs that neurologists and ear, nose, and throat specialists have used for decades. These include sodium valproate (to be avoided in women with childbearing potential), gabapentin, and pregabalin. I am not aware of a formal trial of any of these, but they seem to work quite well. The probable mechanism of parosmia is ephaptic firing in demyelinated neurones—that is, a form of short circuiting.2 After the olfactory neurones remyelinate, the afferent signal is no longer distorted and the symptom disappears, a process that can take years but usually occurs eventually. Cacosmia is a form of parosmia that entails an unpleasant hallucination—as most are. I have never come across a pleasant parosmia, although it does happen. The illusion of an odour (phantosmia) that occurs without sniffing can represent an epileptic phenomenon and indicate the presence of a tumour, usually malignant, in the medial temporal pole.

Competing interests: None declared.

1 Rimmer A. Sixty seconds on . . . parosmia. BMJ 2020;371:m4332. doi: 10.1136/bmj.m4332 pmid: 33168519 2 Hawkes CH, Doty RL. Smell and taste disorders Cambridge University Press, 2018doi: 10.1017/9781139192446.

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