Normative Ranges for Auditory Brainstem Response Wave I Amplitude: A Potential Diagnostic Indicator of Cochlear Deafferentation

PURPOSE: While cochlear synaptopathy has limited impact on auditory thresholds, there is increasing evidence that cochlear deafferentation is associated with auditory perceptual deficits. However, there is currently no means for diagnosing synaptopathy or deafferentation in individual patients. The objectives of this study were to establish normative ranges for auditory brainstem response (ABR) Wave I amplitude, a measure sensitive to synaptopathy in animals, in a population at low risk for cochlear deafferentation and then compare a population at high risk for deafferentation to the normative ranges. METHOD: The low-risk sample consisted of 169 non-Veteran young adults with normal audiograms, minimal self-reported noise exposure history, and no auditory complaints (tinnitus, decreased sound tolerance, or speech perception in noise difficulty). ABR Wave I amplitude normative ranges were generated for 2, 4, and 8 kHz tonebursts and were statistically adjusted for sex and average distortion product otoacoustic emission (DPOAE) levels. Ninety-one military Veterans with normal audiograms and at least one auditory complaint were included in the high-risk comparison sample. RESULTS: While the DPOAE-adjusted ABR normative ranges were effective at distinguishing between the low- and high-risk samples, the results also indicated that adjusting the ABR normative ranges for outer hair cell dysfunction may not be necessary and could be problematic. ABR normative ranges that were adjusted only for sex were able to differentiate between the low- and high-risk samples, with 51% of the high-risk sample falling below the normative ranges for a 105 dB peak equivalent sound pressure level 8-kHz toneburst. CONCLUSION: In patients with normal audiograms, sex-specific ABR Wave I amplitude normative ranges can be used by clinicians to identify patients with high degrees of cochlear deafferentation.