Measurement of subtle auditory deficit in tinnitus patients with normal audiometric thresholds using evoked otoacoustic emissions and threshold equalizing noise tests

Introduction: The general consensus on the roles of hearing loss in triggering tinnitus seems not applicable in patients with normal hearing thresholds. The absence of hearing loss on the audiogram in this group of patients poses a serious challenge to the cochlear theories in explaining tinnitus generation in this group of patients. Objective: To scrutinize auditory functioning in a sample of tinnitus subjects with normal hearing thresholds and non-tinnitus normally hearing control participants using transient evoked and distortion product otoacoustic emission (TEOAE and DPOAE) and Threshold Equalising Noise (TEN) test. Methods: Twenty-seven tinnitus adult patients with normal hearing thresholds and 27 normally hearing volunteers were tested with TEOAE, DPOAE and TEN test. Results: Abnormal TEOAE was significantly more in tinnitus group than in controls. No significant difference was observed in DPOAE and TEN test. Only one patient was found with a positive TEN test result, who was confirmed by Magnetic Resonance Imaging to have acoustic neuroma on the affected ear. Conclusion: These results suggest the possible existence of subtle auditory deficit in normally hearing tinnitus patients, which may be an early sign of diseases that are only diagnosed after the onset of hearing loss.