[Rare audiometry findings in progressive, monosymptomatic low frequency deafness].

BACKGROUND

Objective audiometric methods such as the measurement of otoacoustic emissions and auditory evoked potentials (click evoked and notched-noise auditory evoked brainstem potentials, auditory evoked cortical potentials) can provide helpful information. However, information derived from the individual test is limited and each method contains specific restrictions. To illustrate the possible audiometric pitfalls this work presents a case history.

CASE REPORT

The puretone audiometry showed a severe hearing loss at low frequencies up to 2 kHz, a slight hearing loss for higher frequencies up to 6 kHz and almost normal hearing thresholds above 6 kHz. Transitory evoked otoacoustic emissions could not be detected. While the auditory evoked brainstem responses (ABR) using click-stimuli showed a normal pattern no reproducible responses could be derived using the notched-noise technique. Auditory evoked cortical potentials exhibited a normal N1/P2-complex and were detectable down to stimulus levels 0-20 dB above the individual hearing threshold.

DISCUSSION

Click-evoked auditory evoked brainstem potentials are widely regarded as the "gold-standard" of objective audiometry. The example presented in this work shows that in special cases it may provide false negative results. In these special cases auditory tone-evoked cortical potentials may provide better objective information. When objectively assessing the determination of the hearing threshold it may be necessary not only to use all electrophysiological measurements but also to know their methodical restrictions and pitfalls.