Within-Subject Comparisons of the Auditory Brainstem Response and Uncomfortable Loudness Levels in Ears With and Without Tinnitus in Unilateral Tinnitus Subjects With Normal Audiograms.

OBJECTIVE: To evaluate whether cochlear synaptopathy is a common pathophysiologic cause of tinnitus in individuals with normal audiograms. STUDY DESIGN: Prospective study. SETTING: Tertiary referral center. METHODS: We enrolled 27 subjects with unilateral tinnitus and normal symmetric hearing thresholds, and 27 age- and sex-matched control subjects with normal symmetric hearing thresholds. We measured 1) the amplitudes of waves I and V with 90 dB nHL click stimuli in quiet conditions; 2) the latency shift of wave V with 80 dB nHL click stimuli in background noise, varying from 40 dB HL to 70 dB HL; and 3) uncomfortable loudness levels (UCLs) at 500 Hz and 3000 Hz pure tones. RESULTS: There were no significant differences in the wave V/I amplitude ratio or the latency shift in wave V with increasing noise levels among the tinnitus ears (TEs), nontinnitus ears (NTEs), and control ears. There were no significant differences in UCLs at 500 Hz or 3000 Hz between TEs and NTEs, but the UCLs were lower in TEs (mean 111.3 dB or 104.1 dB) and NTEs (mean 109.4 dB or 100.6 dB) than in control ears (mean 117.9 dB or 114.1 dB, p < 0.017). No subject met our criteria for cochlear synaptopathy or increased central gain in terms of all three parameters. CONCLUSION: Based on these results for UCL, increased central gain is a major mechanism of tinnitus in humans with normal audiograms. However, this compensatory mechanism for reduced auditory input may originate from other pathophysiologic factors rather than from cochlear synaptopathy.

Clinical Application of the Threshold Equalizing Noise Test in Patients with Hearing Loss of Various Etiologies: A Preliminary Study.

BACKGROUND AND OBJECTIVES: We aimed to make a preliminary assessment of the prevalence of cochlear dead regions (DRs) and the factors affecting the results of the threshold-equalizing noise (TEN) test in patients with hearing loss of various etiologies. SUBJECTS AND METHODS: Between May and July 2014, 109 patients (191 ears) with hearing loss who visited our outpatient clinic were prospectively enrolled. Pure tone audiometry and TEN (HL) test were performed for all the patients. DR at each frequency was indicated by masked thresholds of ≥10 dB above the TEN level and ≥10 dB above the absolute threshold. RESULTS: DR was present in 15.7% (n=30) of the 191 ears. According to disease entity, 16.6% of patients with sensorineural hearing loss had a DR. However, DR was absent in patients with chronic otitis media. According to audiometric configurations, DR was most common in moderately severe, flat hearing loss. Significantly worse hearing thresholds for both mean hearing level and hearing threshold at each frequency were found in the presence of DR (p<0.001). Logistic regression analysis showed that only the mean hearing level (odds ratio: 1.053, 95% confidence interval: 1.021-1.085) affected the presence of DR. CONCLUSIONS: Although performance of the TEN test is limited by frequencies and hearing levels, it provides additional information regarding DRs and may therefore have the potential to be used as a prognostic tool for diverse diseases causing hearing loss.