Comparison of auditory electrophysiological responses in normal-hearing patients with and without tinnitus

Introduction: Tinnitus is a disturbing symptom and is often the main reason for otology referral. It is usually associated with hearing loss of varying aetiology, and is thought to begin in the cochlea, with later abnormal central activity. We hypothesise that tinnitus without hearing loss may be caused by central and subcortical abnormalities and altered outer hair cell function. Aim: To compare the auditory brainstem responses, middle latency responses and otoacoustic emissions in normal-hearing individuals with and without tinnitus. Methodology: The audiological test results of 25 normal hearing subjects with tinnitus (age 18-45 years) were determined, and compared with those of a control group. Results: A statistically significant difference was found between study group tinnitus ears vs control group ears, as regards wave I latency prolongation, shortening of wave V and absolute I-III and I-V interpeak latency, enlargement of wave Na and Pa amplitude, and distortion product and transient evoked otoacoustic emission signal-to-noise ratios. There was no statistically significant difference between unilateral vs bilateral tinnitus ears. Conclusion: The pathogenesis and optimum management of tinnitus are still unclear. It often occurs with primary ear disease, usually associated with hearing loss, but may occur in patients with normal hearing. Observed changes in auditory brainstem and middle latency responses indicate central auditory alterations. Tinnitus involves both peripheral and central activity, and complete audiological and neurophysiological investigation is required. Management should be based on both audiological and neurophysiological findings.