Background: The current study attempted to assess efferent auditory system functioning in individuals with auditory neuropathy spectrum disorder (ANSD) using a new approach, contralateral suppression of SOAE, which has not yet been extensively researched.
Methods: Spontaneous otoacoustic emissions (SOAEs) were recorded in a total of 62 ears, divided into 2 groups. Group I comprised of 31 ears with normal hearing (NH), while group II consisted of 31 ears with ANSD. All the participants considered for the study were in the age range of 18-45 years. Synchronized SOAE were recorded using the ILO V6 OAE instrument with and without noise (broadband noise, 50 dB SPL) in the contralateral ear. The frequency and amplitude shifts secondary to the introduction of contralateral noise were analyzed.
Results: The results of the study showed a statistically significant high-frequency shift of SOAE with contralateral noise for the NH and ANSD groups. In addition, the NH group also exhibited a statistically significant reduction in SOAE amplitude in contralateral noise conditions. Such a reduction in SOAE amplitude was not observed in individuals with ANSD.
Conclusion: The absence of suppression of SOAE amplitude suggests efferent damage in individuals with ANSD. The shift in SOAE frequency toward higher frequency in the ANSD group, which is similar to NH group, is suggestive of differential allotment of medial olivocochlear (MOC) mechanism in individuals with ANSD, which codes for contralateral frequency changes and not for amplitude changes.