Auditory Brainstem Response: Cochlear Health Indicator

A new study has established clear normative ranges for a key auditory brainstem response (ABR) measurement, providing clinicians with a potential tool to diagnose cochlear deafferentation—a hidden hearing loss—in patients with normal hearing tests. Published in the *American Journal of Audiology*, the research from the VA National Center for Rehabilitative Auditory Research offers a method to identify individuals whose hearing complaints may stem from damage to the nerve connections in the inner ear, even when their standard audiogram appears perfect.

Building a Baseline for a Hidden Problem

Sean D. Kampel, Garnett P. McMillan, and their team set out to solve a persistent clinical puzzle. Cochlear synaptopathy, the loss of connections between inner hair cells and the auditory nerve, does not raise thresholds on a standard hearing test. However, evidence links this “hidden” deafferentation to real-world difficulties like understanding speech in noise, tinnitus, and decreased sound tolerance. Until now, there has been no validated way to diagnose this condition in individual patients.

The researchers’ first objective was to establish what a “normal” ABR Wave I amplitude looks like in people at very low risk for such damage. Wave I amplitude is a sensitive electrophysiological measure of the synchronized response of the auditory nerve. Their low-risk sample included 169 young, non-Veteran adults. All had pristine audiograms, minimal history of noise exposure, and no self-reported auditory complaints like tinnitus or hyperacusis.

They measured Wave I amplitudes in response to 2, 4, and 8 kHz tonebursts. To account for known biological variables, they generated normative ranges that were statistically adjusted for sex and for average distortion product otoacoustic emission (DPOAE) levels, a measure of outer hair cell health.

Testing the Norms on a High-Risk Population

The critical test was applying these new normative ranges to a group likely to have hidden damage. For this, the team studied 91 military Veterans. All Veterans had clinically normal audiograms, but each reported at least one auditory complaint—such as tinnitus, hyperacusis, or difficulty with speech in noise—making them a high-risk sample for cochlear deafferentation.

The results were revealing. The DPOAE-adjusted normative ranges successfully distinguished the low-risk from the high-risk groups. But a more significant finding emerged: adjusting for outer hair cell function might not be needed. The data suggested this adjustment could even be problematic, potentially muddying the diagnostic picture.

A simpler model, using normative ranges adjusted only for the patient’s sex, proved equally effective. This sex-specific approach cleanly separated the two populations. The signal was strongest at 8 kHz, a frequency region vulnerable to noise damage. Using a 105 dB peSPL 8-kHz toneburst, 51% of the high-risk Veteran sample fell below the normal range, indicating a high degree of probable cochlear deafferentation.

A Practical Tool for Clinicians and Patients

The practical implication of this work is direct. For clinicians seeing patients with hearing complaints but normal audiograms, the study provides a validated framework. “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,” the authors conclude.

This moves the field from theory to application. A patient presenting with tinnitus, hyperacusis, and anxiety after noise exposure, for instance, can now be assessed with an objective measure that correlates with their subjective experience. It validates their condition and steers management strategies. The ABR test itself is a standard clinical tool, making this diagnostic step highly feasible in audiology practices.

The finding that DPOAE adjustment may be unnecessary simplifies the protocol. It suggests that Wave I amplitude is specifically tracking the neural element of hearing—the synaptopathy—independent of outer hair cell function. This strengthens its role as a pure indicator of the auditory nerve’s health. For more on how ABR is used as an indicator of hearing loss, you can explore our related resource.

Validating the Invisible Injury

This research, accessible via PMID: 42635501 or DOI: 10.1044/2026_AJA-25-00296, represents a significant advance in auditory diagnostics. It gives a name and a measure to a problem that was previously only inferred. For the individual struggling with misophonia or the inability to follow conversations in busy rooms, a diagnosis of cochlear deafferentation can be the first step toward targeted rehabilitation and coping strategies.

The study also highlights a clear demographic need, showing a high prevalence of this hidden damage in a Veteran population with normal hearing thresholds. By providing a clear, sex-specific normative benchmark, Kampel and colleagues have equipped clinicians with a vital tool to bridge the gap between a patient’s lived experience and the binary result of a standard hearing test.