Evaluation of idiopathic olfactory loss with chemosensory event‐related potentials and magnetic resonance imaging

Abstract

Background Idiopathic olfactory loss (IOL) accounts for a sizable fraction of olfactory dysfunction, but very little is known about its etiology and electrophysiological changes in the olfactory pathway. Methods We analyzed the physiology of IOL using chemosensory event‐related potentials (ERPs) (olfactory and trigeminal: oERP and tERP) and olfactory pathway magnetic resonance imaging (MRI) measured in adult patients with IOL and healthy controls. Subjective olfactory function was measured by Toyota and Takagi (T&T) olfactometry and Sniffin’ Sticks (SS). Results Olfactory function was worse in patients with IOL compared to controls (T&T, p < 0.001; SS, p < 0.001). oERPs could be evoked in 17 IOL patients. Signals in these patients showed lower amplitude in the N 1 and P 2 waves than controls ( p < 0.05 for both), but there were no difference in latency between the 2 groups ( p > 0.05). tERP were detected in all patients and controls; there were no differences in latency and nor amplitude between the 2 groups ( p > 0.05). The olfactory bulb (OB) volume was significantly smaller in the IOL group than controls ( p < 0.001), but there was no difference in the olfactory sulcus depth between groups ( p > 0.05). Better olfactory function was associated with increasing magnitude of N 1 amplitude in oERPs ( p < 0.05) and increasing OB volume ( p < 0.05). Conclusion IOL patients show neurophysiologic deficits and some anatomic differences compared to healthy controls.