Auditory brainstem response in unilateral tinnitus patients: does symmetrical hearing thresholds and within-subject comparison affect responses?

Objective: In recent studies, cochlear synaptopathy has been suggested as a potential pathophysiology mechanism for tinnitus, which occurs in individuals with normal hearing thresholds. Auditory Brainstem Response (ABR) is a noninvasive method frequently used in the literature to evaluate cochlear synaptopathy in tinnitus patients. However, possible factors such as high-frequency pure-tone hearing thresholds, age, gender, and head characteristics that may affect ABR were not considered sufficiently in previous studies. Therefore, the present study aims to evaluate tinnitus ears and non-tinnitus ears with ABR in unilateral chronic tinnitus patients with symmetrical hearing. Methods: Twenty unilateral chronic tinnitus patients having normal pure-tone average with symmetrical hearing thresholds was included in the study. Subjects were evaluated with 0.25–16 kHz pure-tone audiometry, Tinnitus Handicap Inventory (THI) and ABR were administered. All ears were evaluated monaurally using click stimuli at 80 dB nHL, alternating polarity (21.1 rate/s, 2000 sweeps). Results: Wave I amplitude of the ABR and the ratio of III/I, V/I, and V/III wave amplitudes from tinnitus ears was higher than non-tinnitus ears. At the same time, there was a positive correlation between THI and V–I and V–III interpeak latency range, and a negative correlation between V/III wave amplitude ratio. Conclusion: ABR can be used as an evaluation method to provide evidence that the neural organizations of individuals with chronic tinnitus differ in certain regions in their auditory pathways. The correlation between THI and ABR findings suggests that there may be a connection between tinnitus distress and the neural organization of the auditory system.