An examination of tinnitus and cochlear functionality in both hearing impaired and normally hearing individuals : the relationship between tinnitus and cochlear functions in individuals with hearing impairment and those with normal hearing

Abstract

Purpose: The evaluation of peripheral hearing organ function is vital for determining the pathophysiology of tinnitus and for establishing appropriate treatment strategies. This research seeks to investigate cochlear functions in tinnitus patients, irrespective of whether they have hearing loss. Methods: In this study, participants suffering from tinnitus were divided into two groups: the first study group (SG-I) consisted of 20 individuals who had associated hearing loss (HL). In contrast, the second group (SG-II) included 20 individuals without hearing loss. A control group (CG) was formed with 20 normal-hearing participants who did not have tinnitus. The tinnitus-related discomfort levels were evaluated using the Tinnitus Handicap Inventory (THI). Alongside pure-tone audiometry, Otoacoustic Emissions (OAE) were conducted to assess cochlear functions and to identify any dead regions (DR). Additionally, Threshold Equalizing Noise (TEN) was employed in the evaluation. Results: The analysis revealed a threshold shift in subjects from SG-I when evaluated using Transient Evoked Otoacoustic Emissions (TEN), with these levels showing statistically significant differences from both SG-I and the control group (CG). Furthermore, SG-I exhibited both threshold shifts and distortion responses (DR) as indicated by TEN. In contrast, Transient Otoacoustic Emissions (TEOAE) did not present any significant differences between SG-II and CG. The findings for Distortion Product Otoacoustic Emissions (DPOAE) in SG-II demonstrated significant decreases in emission amplitudes at 6 and 8 kHz. Conclusion: Conventional testing methods are suitable for evaluating tinnitus patients with hearing loss. Nevertheless, for patients with normal hearing experiencing tinnitus, the use of additional assessments such as Otoacoustic Emissions (OAE) and Tone-Evoked Noise (TEN) enables a more precise evaluation of the peripheral hearing mechanisms. The limited or absent otoacoustic emissions (OAEs) observed in the SG-I group indicate a potential reduction or loss of functionality in the outer hair cells (OHC) at the tested frequency. In contrast, an increase in the thresholds of the tone-equalizing noise (TEN) test points to a possible dysfunction in the inner hair cells (IHC).