PROGNOSTIC CRITERIA OF SUDDEN DEAFNESS DEDUCED BY ELECTROCOCHLEOGRAPHY
1976 Volume 79 Issue 2 Pages 151-162
Details
1976 Volume 79 Issue 2 Pages 151-162
Auditory nerve action potentials (AP N1) and summating potentials (SP) which were evoked by sound stimuli were investigated at the first attendance on twenty patients of sudden deafness.
A recording was performed by use of the transtympanic needle electrode technique, that is, needle electrode was placed on the promontry through the tympanic membrane and average responses were recorded by a computer.
Sound stimulus used was the sine wave of one cycle (duration 0.25msec).
This type of stimulus was similar to the click in analysis using sound spectrogram.
The patterns of the wave forms of AP and SP response obtained in these cases were divided into the following types.
1. The Dominant -SP: The -SP appears as negative deflection which develops immediately after the start of sound stimuli. The dominant SP having an amplitude almost equal to that of the AP or, having a much higher voltage than that of the normal hearing subject in the segment of High-Response Curve termed by Yoshie (1967)
2. The AP High Response: The wave forms of AP response having a higher amplitude or one almost equal to that of the normal hearing subject in the segment of High-Response Curve.
3. The Decreased AP High Response: The wave forms of AP response having a reduced AP amplitude in the High-Response Curve Segment and loss of the Low-Response Curve Segment.No increment of the N1 amplitude is encountered with increasing intensity.
4. The AP Low Response: The wave forms of AP N1 having a markedly low voltage and delayed latency (>2.5msec) at sound intensity of 90-100dB HL.
5. The +SP: The wave forms of response having a positive deflection that develops immediately after the start of sound stimulus at the intensity of 100dB HL. Neither is the response of AP obtained.
6. The AP and SP No Response: The wave forms of AP and SP responses can not be obtained even at the maximum sound intensity of 100dB HL.
A total of twenty patients with sudden deafness was examined by electrocochleography. Therewas a significant difference of the wave forms recorded between the cases of complete recovery or remarkable improvement and cases of slight improvement or no change.
In four of the seven cases in which complete recovery or remarkable improvement were shown the Dominant -SP was obtained and in the remaining three the AP High Response was obtained.
In cases in which slight improvement or no change was shown Decreased AP High Respnse, AP Low Response, +SP and AP, SP No Response were obtained.
It was concluded that the electrocochleography could be very helpful in estimating the prognosis of sudden deafness during the early stage of the onset
