Test batteries of electrocochleography (EcochG) and evoked otoacoustic emission (e-OAE) were performed in a 57-year-old woman with sensorineural deafness and bilateral facial and vocal cord paralyses.
Recordings of AP, SP and CM were made with the use of the transtympanic needle electrode technique. The e-OAE were recorded with an acoustic probe N-1 inserted into the external ear canal. Click acoustic stimulation was used for the measurement ofAP and SP. Short tone bursts were employed to evoke both e-OAE and CM.
The broad AP waveforms with the monophasic shape in response to click stimulus were observed in both ears.Input-output curves of AP amplitude in both ears showed only H-part, in which the amplitude of N1increased minimally with increasing intensity (L-response). The EcochG data showed enhancement of the negative SP (dominant-SP).
The broadening of the AP, SP waveforms in this case might be due to the superimposition upon the monophasic AP waveform of the dominant-SP.
Delayed CM which followed CM were not recorded in both ears. Detection thresholds of the CM in right ear were almost the same as those of normal subjects andwere about 20 dB higher in the left ear.
Fast and slow components of acoustic oscillation appearing within 20 ms were definitely obtained in this case. The detection thresholds ofboth components, however were raised slightly above those of normal ears.
The conventional psychoacoustic examination and the findings of ABR and SR suggested that the retrocochlear deafness might result mainly from brain stem lesions. The EcochG and e-OAE findingswere also suggestive of the pathphysiology of the cochlea with the impaiment at AP (N1) level and the damaged outer hair cells.
