Use of Envelope Following Response Normative Ranges for Diagnosing Cochlear Deafferentation
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Purpose
The lack of a means for diagnosing 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 response. 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.
Methods
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 (SAM) 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 SAM EFR normative ranges for a 4 kHz carrier resulted in the biggest separation of the low-and high-risk samples, with 36% 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 SAM EFR will allow for clinical identification of patients with normal audiograms who have significant degrees of cochlear deafferentation.
