Patients with COVID-19-associated olfactory impairment also show impaired trigeminal function

Abstract

Objective: Next to olfactory function, the nose can also perceive chemestetic sensations mediated by the trigeminal nerve. While olfactory dysfunction as a symptom of COVID-19 is well described, there has been little research on the limitation of other nasal sensory inputs due to SARS-CoV-2 infection. The aim of this study was to determine possible limitations of nasal chemesthesis after COVID-19 infection by a psychophysiological diagnostic tool.

Methods: In 65 patients with a PCR-confirmed, former COVID-19 disease, olfaction was tested by means of a sniffin' sticks test, tasting by taste sprays and chemesthesis with a menthol dilution series. The subjective self-assessment of the patients was recorded via a questionnaire.

Results: We found a restriction of nasal chemesthesis and the extent correlated with the loss of smell, as well as with the values of the taste score, but not with subjective self-assessment.

Conclusion: Not only the ability to smell and taste, but also nasal chemesthesis is affected by COVID-19.

Keywords: Chemesthesis; SARS-CoV-2; Smell disorders; Sniffin’ Sticks; Trigeminal nerve.

Fig. 1

Schematic procedure for determining the chemesthesis threshold with example values entered. Starting with the weakest concentration of menthol (“1″), the next higher concentration was offered until the subject felt trigeminal irritation three times in a row. This was the first turning point until the subject did not register correct perceptions three times in a row and thus the next turning point towards stronger concentrations was reached. This procedure was repeated until seven turning points were recorded. The threshold was calculated from the mean value of the last four turning points. 1–16 = concentrations of the methanol solution, 1 = strongest, 16 = weakest concentration. + = subject felt a trigeminal sensation (cooling, burning). - = subject did not indicate a trigeminal sensation. The ellipses mark the last four turning points. The grey line follows the direction of the testing.

Fig. 2

Except for two subjects with anosmia, the other participants had TDI scores in the hypo- or normosmic range. The graph illustrates the correlation between the TDI and the chemesthesis score.