The assessment of olivocochlear function in neonates with real-time distortion product otoacoustic emissions.

OBJECTIVES/HYPOTHESIS: Otoacoustic emissions (OAE) can be suppressed with activation of the medial olivocochlear neural pathway by stimulation of the contralateral ear. The primary objective of this study was to assess the feasibility of using olivocochlear mediated OAE suppression to test neonatal hearing with a novel device that detects changes in distortion product (DP)OAE level with high temporal resolution. The secondary objective was to investigate whether temporal parameters of the response can be determined with this technique and used in the assessment of neonates at risk of auditory neuropathy spectrum disorder (ANSD).

STUDY DESIGN

Prospective translational study of novel hearing assessment technique.

METHODS

There were 46 neonates tested in a clinic or neonatal intensive care unit (NICU). DPOAE were recorded in real time with narrow band pass digital filtering (1 ms temporal resolution) during presentation of an intermittent contralateral broadband noise stimulus. Magnitude and latency of the contralateral suppression response were compared with hearing outcome (auditory brainstem response screen and clinical follow-up) and risk factors for hearing loss, particularly hyperbilirubinemia as a risk factor for ANSD.

RESULTS

: Contralateral suppression was identified in all of 38 neonates with detectable DPOAE and normal hearing, most reliably at f(2) = 4.4 kHz (average values = 1 dB suppression from DP level of 14 dB SPL using 0.55 s contralateral stimulus at 50 dB SPL). Sensorineural hearing loss was identified in three cases (6.5%) and ANSD in five cases (11% of all neonates tested). Contralateral suppression was absent in two of the ANSD cases (one associated with cochlear nerve aplasia, the other with hyperbilirubinemia) and present in three. The median latency for onset of contralateral suppression was 60 ms and offset latency 83 ms. The latency for offset of suppression was longer in neonates who required treatment for hyperbilirubinemia at 123 ms (P = .02, Mann-Whitney rank sum test). Latency measurements were determined with high intraobserver reliability (Pearson product moment correlation coefficient > 0.96).

CONCLUSIONS

Contralateral suppression of real-time DPOAE can reliably be identified in neonates. This is likely a manifestation of olivocochlear activity, although middle ear muscle reflexes might contribute to suppression in some circumstances. The technique provides a feasible objective test of hearing in neonates that can be applied in the NICU setting without sedation. The presence of a response indicates detection of sound by the contralateral ear and effective brainstem transmission of neural signals, therefore providing a more sensitive test of hearing than OAE alone. The high temporal resolution of the technique allows measurement of latency of the response. These benefits help to identify neonates at risk of ANSD and have the potential to provide prognostic information that will assist in the management of this unpredictable disorder. Further development of the technique is indicated with regard to determination of hearing threshold, frequency specific testing, and automation of response detection.