Contralateral suppression of distortion-product otoacoustic emissions: A potential diagnostic tool to evaluate the vestibular nerve

The amplitude of distortion-product otoacoustic emission (DPOAE) is suppressed in one ear when the contralateral ear is subjected to sound stimulation. Contralateral suppression of DPOAE is the phenomenon resulted by the efferent cochlear innervation on the outer hair cells via medial olivocochlear bundle (MOCB) and inferior vestibular nerve. We assumed that DPOAE would not be suppressed by contralateral sound stimulation in patients with vestibular nerve lesion as long as the specific pathway conveying that efferent innervation is affected. To test this hypothesis, we compared the amount of DPOAE contralateral suppression in patients with vestibular neuritis and healthy controls. Twenty healthy volunteers without hearing loss and vestibulopathy, and 13 patients with vestibular neuritis were recruited. DP audiogram was measured without contralateral sound stimulation and then with contralateral sound stimulation (70 dB HL of 2 kHz narrow band noise, NBN). The suppression value of DPOAE was evaluated according to the f2 frequency and was defined as the amount of DPOAE suppression: An-Ao, where An represents the DPOAE amplitude in the presence of contralateral NBN, and Ao represents the DPOAE amplitude in the absence of NBN. Cervical vestibular evoked myogenic potential (cVEMP) was performed in some patients with vestibular neuritis. The suppression values of DPOAE were compared between groups and were analyzed according to the results of cVEMP. The amount of suppression of DPOAE during contralateral sound stimulation was significantly reduced in the patient group compared to control at the f2 frequencies of 1257, 1587, and 2002 Hz (P = 0.045, P < 0.001, P = 0.009, respectively). However, the results of contralateral suppression of DPOAE were not consistent with the results of cVEMP in this study. Efferent cochlear innervation was affected in vestibular neuritis. Evaluation of contralateral suppression of DPOAE can be a potential diagnostic tool to evaluate the functional integrity of the vestibular nerve. Further studies are necessary to clarify this mechanism. (C) 2013 Elsevier Ltd. All rights reserved.