VI Threshold Auditory Adaptation Measured by Tone Decay Test and Békésy Audiometry

Auditory adaptation testing as a tool for investigating tinnitus origin: two patients with vestibular schwannoma

OBJECTIVE

To enhance the understanding of tinnitus origin by disseminating two case studies of vestibular schwannoma (VS) involving behavioural auditory adaptation testing (AAT).

DESIGN

Retrospective case study.

STUDY SAMPLE

Two adults who presented with unilateral, non-pulsatile subjective tinnitus and bilateral normal-hearing sensitivity. At the initial evaluation, the otolaryngologic and audiologic findings were unremarkable, bilaterally. Upon retest, years later, VS was identified.

RESULTS

At retest, the tinnitus disappeared in one patient and was slightly attenuated in the other patient. In the former, the results of AAT were positive for left retrocochlear pathology; in the latter, the results were negative for the left ear although a moderate degree of auditory adaptation was present despite bilateral normal-hearing sensitivity. Imaging revealed a small VS in both patients, confirmed surgically.

CONCLUSION

Behavioural AAT in patients with tinnitus furnishes a useful tool for exploring tinnitus origin. Decrease or disappearance of tinnitus in patients with auditory adaptation suggests that the tinnitus generator is the cochlea or the cochlear nerve adjacent to the cochlea. Patients with unilateral tinnitus and bilateral, symmetric, normal-hearing thresholds, absent other audiovestibular symptoms, should be routinely monitored through otolaryngologic and audiologic re-evaluations. Tinnitus decrease or disappearance may constitute a red flag for retrocochlear pathology.

[On the interpretation of Békésy audiograms (author's transl)]

A group of 112 subjects with sensorineural hearing loss was checked by an audiological test battery consisting of: pure tone audiometry, SISI Test, tone decay test and fixed frequency Békésy audiometry. Classification of Békésy tracings by two audiologists showes good agreement when introducing a hybrid type I/II, which completes Jerger's classification system of types I--IV. The results of our investigation exhibit no significant differences of manual pure tone threshold and automatic tracing contrary to some other authors. Finally the correlation of diagnosis and type of Békésy audiogram is discussed.