Purpose: The lack of a means to diagnose cochlear synaptopathy, a type of cochlear deafferentation, prevents clinicians from identifying patients with this auditory deficit and providing them with appropriate treatments. The envelope following response (EFR) has potential as a diagnostic indicator of deafferentation. However, it is not clear what constitutes an abnormal EFR. The objectives of this study were to establish normative ranges for EFR magnitude in a population at low risk for cochlear synaptopathy and then compare EFRs from a population at high risk for synaptopathy to those normative ranges.
Method: The low-risk sample consisted of young adults with normal audiograms, minimal reported lifetime noise exposure, and no auditory complaints. Normative ranges were generated using rectangular amplitude-modulated (RAM) or sinusoidal amplitude-modulated EFR stimuli and were adjusted for sex and distortion product otoacoustic emission (DPOAE) levels. The high-risk sample consisted of military Veterans with normal audiograms who reported at least one auditory complaint (tinnitus, decreased sound tolerance, or speech-in-noise difficulty).
Results: The RAM EFR normative ranges for a 4-kHz carrier resulted in the biggest separation of the low- and high-risk samples, with 31%-34% of Veterans falling below the lower bound of the normative range. There were no consistent effects of DPOAE adjustment on the normative ranges across sex and stimulus condition, and computational modeling suggests that adjusting for DPOAEs may not be necessary in individuals with normal audiograms.
Conclusion: EFR normative ranges for the 4-kHz RAM EFR will allow for the clinical identification of patients with normal audiograms who may have significant degrees of cochlear deafferentation.
Supplemental material: https://doi.org/10.23641/asha.32347524.