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Tinnitus in Normal-Hearing Individuals: Is Outer Hair Cell Dysfunction the Mechanism?
Theognosia Chimona1, Maria Vrentzou1, Emmanouel Erotokritakis2
1ENT Department of Chania General Hospital, 73133 Chania, Greece.
Journal of Clinical Medicine
|August 14, 2025
Summary
Individuals with normal hearing and tinnitus exhibit reduced otoacoustic distortion product emissions (DPOAEs) compared to those without tinnitus. Tinnitus pitch often aligns with frequencies showing abnormal DPOAEs, suggesting cochlear dysfunction.
Area of Science:
- Otoacoustic Emissions
- Auditory Neuroscience
- Tinnitus Research
Background:
- Cochlear injury is a known cause of tinnitus in hearing-impaired individuals.
- Tinnitus can also occur in individuals with normal hearing, indicating other underlying mechanisms.
- Otoacoustic distortion product emissions (DPOAEs) are objective measures of outer hair cell function in the cochlea.
Purpose of the Study:
- To evaluate DPOAEs in individuals with normal hearing who perceive tinnitus.
- To investigate the relationship between DPOAE measurements and tinnitus characteristics in normal-hearing individuals.
Main Methods:
- Prospective study comparing a tinnitus group (TG, n=34) with normal hearing to a control group (CG, n=10) with normal hearing and no tinnitus.
- Participants underwent otolaryngological examination, pure tone audiometry, and DPOAE recording (DP-gram).
- Tinnitus history, self-rated loudness, and Tinnitus Handicap Inventory (THI-G) were assessed in the TG.
Main Results:
- Mean DPOAE amplitudes were significantly lower in the TG compared to the CG at low and high frequencies.
- Tinnitus pitch matching frequently occurred at frequencies with abnormal or absent DPOAEs.
- Abnormal DPOAEs around 4000 Hz correlated with sudden onset tinnitus and severe disability (THI-G > 58).
- Pathological DPOAEs at ≥6000 Hz were associated with gradual onset tinnitus.
Conclusions:
- Normal-hearing individuals with tinnitus demonstrate reduced DPOAE amplitudes, particularly at low and high frequencies, compared to their non-tinnitus counterparts.
- The frequency of tinnitus perception often corresponds to areas of abnormal DPOAEs, suggesting localized cochlear dysfunction.
- DPOAE measurements may provide objective insights into the pathophysiology of tinnitus in normal-hearing individuals.
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