Evaluation of cochlear function, hidden hearing loss, and auditory temporal processing in tinnitus patients with normal audiograms

Abstract

Introduction and objective

Some patients complain of tinnitus despite having normal conventional audiograms. However, normal audiograms do not exclude the presence of subtle cochlear or neural damage. The study's objective was to assess cochlear function and the cochlear nerve in tinnitus patients with normal audiograms, as well as assessing temporal processing in these patients.

Materials and Methods

The study included a total of 40 participants: 20 tinnitus patients with normal audiograms and 20 healthy controls without tinnitus. All participants underwent otoscopic examination, tympanometry, acoustic reflex (AR) testing, pure-tone audiometry, extended high-frequency (EHF) audiometry, distortion product otoacoustic emissions (DPOAEs), auditory brainstem response (ABR), and auditory temporal processing assessments, including the auditory fusion test–revised and the pitch pattern sequence test.

Results

The tinnitus group showed significant findings across multiple tests, including: elevated EHF thresholds and reduced DPOAE amplitudes (indicating cochlear dysfunction); reduced acoustic reflex responses and delayed ABR wave I latency (suggesting cochlear nerve/synapse involvement); and poorer performance in auditory temporal processing tests.

Conclusions

Our findings provide compelling clinical evidence for subtle, measurable peripheral (cochlear and neural) and central auditory dysfunction in tinnitus patients with normal audiograms. These deficits in the auditory system are essential components of tinnitus pathology and require the integration of advanced audiological assessments for proper diagnosis and management.