Use of Envelope Following Response Normative Ranges for Diagnosing Cochlear Deafferentation

Area of Science:

• Auditory Neuroscience
• Audiology
• Clinical Diagnostics

Background:

• Cochlear synaptopathy, a form of cochlear deafferentation, is difficult to diagnose due to a lack of established clinical tools.
• The envelope following response (EFR) shows promise as a diagnostic indicator for deafferentation, but abnormal EFR criteria are not well-defined.

Purpose of the Study:

• To establish normative ranges for EFR magnitude in a low-risk population.
• To compare EFRs in a high-risk population against these normative ranges to identify potential deafferentation.

Main Methods:

• Normative EFR ranges were generated using rectangular amplitude-modulated (RAM) or sinusoidal amplitude-modulated stimuli in young adults with normal hearing and low noise exposure.
• EFRs were measured in military Veterans with normal audiograms but auditory complaints (tinnitus, sound tolerance issues, speech-in-noise difficulties).
• EFR data were adjusted for sex and distortion product otoacoustic emission (DPOAE) levels.

Main Results:

• The 4-kHz RAM EFR provided the greatest distinction between low-risk and high-risk groups, with 31%-34% of Veterans falling below the normative range.
• Adjusting for DPOAEs did not consistently alter normative ranges across different conditions.
• Computational models suggest DPOAE adjustment may be unnecessary for individuals with normal audiograms.

Conclusions:

• Defined normative ranges for the 4-kHz RAM EFR can facilitate clinical identification of cochlear deafferentation in patients with normal audiograms.
• This diagnostic tool could help identify individuals experiencing auditory deficits despite normal hearing thresholds.