Usefulness and feasibility of psychophysical and electrophysiological olfactory testing in the rhinology clinic

Olfactory dysfunction may be assessed in the clinic with psychophysical testing and electrophysiological recording. Chemosensory event-related potentials (CSERPs) constitute an objective method to assess chemosensory function. Olfactory and trigeminal stimuli activate chemoreceptors from the olfactory neuroepithelium and from the nasal mucosa to evoke an electrophysiological response respectively called olfactory (OERPs) and trigeminal ERPs (TERPs). The purpose of this study is to assess the usefulness and feasibility of these diagnostic tools in the rhinology clinic and to correlate these results to the olfactory disorder aetiology.

This study encompasses a cohort of 229 patients with a complaint of olfactory dysfunction from different origins. Orthonasal (Sniffing stick test with the treshold-discrimination-identification score: maximal score 48) and retronasal olfactory (maximal score 20) testing as well as CSERPs both after olfactory and trigeminal stimuli have been routinely performed. Olfactory dysfunction aetiologies were as follows: congenital (Cong.), chronic rhinosinusitis (CRS), idiopathic (Idiop.), post-medication (PM), neurologic (Neuro.), post-traumatic (PT) and post-infection (PI).

Mean orthonasal and retronasal scores were respectively: 11.8 and 10.1 for Cong., 18.5 and 13.1 for CRS, 15.6 and 10.4 for Idiop., 15.3 and 10.2 for PM, 17 and 10.6 for Neuro., 15 and 9.9 for PT and 18.3 and 12 for PI. Correlations between orthonasal and retronasal scores were present for all subgroups except congenital and chronic rhinosinusitis subgroups. Orthonasal and retronasal scores were different (p < 0.05) when comparing CRS vs Cong., CRS vs PT and PT vs PI. Technical problems (olfactometer or olfactory stimulation, EEG amplifier,...) and patients discomfort (anxiety, stress,...) did not allow to draw any conclusion in 2 patients. Three patients after olfactory stimulus and 6 patients after trigeminal stimulus demonstrated too much eye blinking or muscular artifacts that did not allow us to perform electrophysiological analysis and averaging as 60% of artifact-free recording was not achieved. Olfactory ERPs were recorded in 28% of the patients and trigeminal ERPs were obtained in almost every patient (95%). There was no statistical difference between each subgroup regarding the presence or absence of OERPs.

Psychophysical olfactory testing is a useful method to assess olfactory function in patients with olfactory loss and may help us to obtain a semi-objective and a basal evaluation of the olfactory performances. Feasibility and usefulness of CSERPs are also underlined in this study with only a limited number of patients who did not complete the examination. Psychophysical testing gives different results according to the aetiology of the olfactory disorder, which was not the case for electrophysiological recording. Olfactory acuity assessment should be based on psychophysical and CSERPs evaluation in a clinical setting.