Clinical significance of olfactory event-related potentials related to orthonasal and retronasal olfactory testing

OBJECTIVE: The purpose of this study was to evaluate the likelihood of recording olfactory event-related potentials (OERPs) in patients with an olfactory dysfunction and to correlate the electrophysiological responses to orthonasal and retronasal olfactory testing. DESIGN/MATERIALS AND METHODS: This was a prospective study of 65 patients with different origins of their olfactory loss. Orthonasal olfactory function was assessed with the "Sniffin' Sticks" test (orthonasal score; maximal score 48) and retronasal olfactory function with odorized powders presented intraorally (retronasal score; maximal score 20). The OERPs were obtained after presentation of 2-phenyl ethyl alcohol, the selected olfactory stimulus. Causes of olfactory dysfunction included postinfectious olfactory loss (n = 15), head trauma (n = 26), nasal polyposis (n = 15), and mixed causes (idiopathic, toxic, drug induced) (n = 9). RESULTS: Based on orthonasal testing, 32 and 33 patients were diagnosed with anosmia and hyposmia, respectively. Twenty-two patients from the hyposmic group demonstrated reliable OERPs. No OERPs were recorded in the anosmic group. Prevalence of OERPs in a cohort of patients with olfactory dysfunction was 33.8% (22 of 65). Median score (expressed as the percentage of the maximal score that could be obtained theoretically) in which OERPs were recorded was 50% (24 of 48) with orthonasal testing and 80% (16 of 20) with retronasal testing. CONCLUSIONS: Patients with olfactory dysfunction usually demonstrate OERPs in one third of the cases. When olfactory dysfunction is in the range that separates normosmic subjects from anosmic patients, patients may have identifiable OERPs. Interpretation of both orthonasal and retronasal psychophysical olfactory testing should be supported by the recording of OERPs in a clinical setting.