Onset of Dysosmia with Covid-19 Infection
While loss of smell is a common symptom following Covid-19 infection, occurring in as many as 68% of patients who experience this infection, patients also experience distortions of smell that fall under the general category of dysosmia.
Dysosmia falls into two major forms: PHANTOSMIA – an onset of a distorted smell in the absence of any transient odor, and ALIOSMIA – onset of a distorted smell which occurs in the presence of ambient odors. Both PHANTOSMIA and ALIOSMIA are repugnant. They can be transient or persistent and they are usually obnoxious and unpleasant. They are commonly described as chemical, burned, rotten or pungent. Many patients have difficulty in describing these sensations since they have never experienced such sensations prior to the onset of Covid-19 infection.
These distortions may occur spontaneously and can be transient. However, in some patients these distortions can be permanent and can significantly disrupt personal life causing disturbances in the ability to eat, drink and pursue normal life goals.
However, the most common occurrence of dysosmia follows the onset of loss of smell following Covid-19 infection. While smell loss may be transient with the patient recovering smell function, patients may subsequently only experience the distortion and not the smell loss.
The mechanism of the onset of the dysosmia is related to a significant decrease in the brain GABA (gamma amino-butyric acid) the normal inhibitory brain neurotransmitter. With the diminution of this neurochemical neurotransmitter distortions can occur. Treatment with GABAergic drugs or repetitive transcranial magnetic stimulations (rTMS) can increase brain GABA and inhibit the dysosmia.
See: Henkin RI, Potolicchio SJ, Levy LM. Improvement in smell and taste dysfunction after repetitive transcranial magnetic stimulation. Am J Otolaryngol. 2011;32:38-46 and Henkin RI, Potolicchio SJ, Levy LM. Olfactory hallucinations without clinical motor activity: a comparison of unirhinal with birhinal phantosmia. Brain Sci. 2013;3:1483-1553.