|Year : 2012 | Volume
| Issue : 2 | Page : 72-75
Electrocochleography in individuals with Meniere's disease
Prawin Kumar1, Pallavi Peepal2
1 Department of Audiology, All India Institute of Speech and Hearing, Mysore, India
2 Audiology section, Phonak Pvt Ltd, New Delhi, India
|Date of Web Publication||6-Sep-2012|
Department of Audiology, All India Institute of Speech and Hearing, Manasagangothri, Mysore - 570006, Karnataka
Source of Support: None, Conflict of Interest: None
Background: Electrocochleography (ECochG) is a useful tool helping in the diagnosis of Meniere's disease (MD). Extra-tympanic ECochG is a non-invasive technique to record the amplitude of summating potential (SP) alone or the amplitude ratio of SP and action potential (AP). Objectives: The present study was aimed to measure the SP and AP amplitudes alone and the ratio (SP/AP) in individuals with normal hearing and in those with MD. Materials and Methods: A total of 63 ears from 34 individuals with normal hearing and those with MD were selected for the study. Individuals with MD had hearing impairment in the range of mild to moderate sensorineural hearing loss. Extra-tympanic non-invasive ECochG recording was done for all the participants. Results: The results of the study revealed that in individuals with normal hearing, 75.75% of the individual ear had SP responses noticeable, whereas in individuals with MD, only 46.66% had SP waveforms present. Further, the mean latency and amplitude of SP were found to be 0.93 msec and 0.29 μV, respectively, in Meniere's ear, whereas in normal ears, they were 0.64 msec and 0.11 μV, respectively. In addition to that, a significant difference in SP/AP amplitude ratio between individuals with normal hearing and those with MD was also reported. Conclusion: Therefore, from the present study one can conclude that the SP values increase both in terms of latency and amplitude in pathological condition. Also, it can be concluded that SP/AP amplitude ratio can help in differentiating individuals with MD from individuals with normal hearing.
Keywords: Action potential, Extra-tympanic, Meniere′s disease, Summating potential, Trans-tympanic
|How to cite this article:|
Kumar P, Peepal P. Electrocochleography in individuals with Meniere's disease. Indian J Otol 2012;18:72-5
| Introduction|| |
Electrocochleography (ECochG) is a measurement of stimulus-related electrical potentials, which include the cochlear microphonics (CM), summating potentials (SP), and compound action potentials (AP) of the auditory nerve. This is an ideal test for the diagnosis of Meniere's disease. It is thought to reflect changes in the anatomic position of the hair cells. This bias in the position of the hair cell is what is expected to occur in active Meniere's disease.  Thus, ECochG focuses on amplitude measure of SP alone or the amplitude ratio of SP and AP. The purpose of measuring ECochG includes monitoring of cochlear and auditory nerve function during surgery, which could result in compromising of these functions and improving the ease with which wave I is identified during ABR testing.  Another area of clinical interest and application of the ECochG response is in differential diagnosis of Meniere's disease. 
ECochG is reported to be an important tool in the diagnosis/assessment/monitoring of Meniere's disease.  In another study, conventional analysis of the click-evoked ECochG included measurement of the amplitudes of SP and AP to derive the SP/AP amplitude ratio. It was documented that an amplitude ratio where SP is elevated relative to AP may be a positive finding for endolymphatic hydrops in individuals suspected of having Meniere's disease. 
In 2010, a survey study was done for evaluating the clinical use of ECochG for diagnosis/treatment of Meniere's disease among members of the American Otological Society (AOS) and American Neurotology Society (ANS). Findings of the survey indicated that in suspected cases of Meniere's disease, 45.5% of respondents did not use ECochG at all, 17.5% used ECochG routinely, and 37.1% used it only in questionable cases. Most respondents (73.2%) thought that ECochG is a test of indeterminate value. Only 3.6% required an abnormal ECochG to diagnose endolymphatic hydrops. Still, 77.9% thought that ECochG findings do fluctuate with activity of the disorder, but only 18.0% agreed that when the ECochG reverts to normal, one can predict remission of symptoms. They concluded that among AOS/ANS members, there is low clinical use of ECochG in diagnosis/management of Meniere's disease. For approximately half of the respondents, ECochG has no role in their clinical practice. 
It can be concluded from the given literature that diagnostic value of ECochG is a matter of controversies. Some authors found the utility of SP/AP amplitude ratio and the amplitude in Meniere's disease, whereas others support the fact that sensitivity and specificity of ECochG is very less in diagnosing Meniere's disease.
Need for the study
Several researchers reported that the SP amplitude in ECochG is high in individuals with Meniere's disease, ,, but other reports contradict the significance of such findings and refer to the large individual variation in SP. , Thus, the value of recording of SP amplitude as a diagnostic tool to identify Meniere's disease has been set in question. Therefore, there is a need for further investigation to study SP recording using extra-tympanic method in individuals with Meniere's disease.
The SP and AP amplitude ratio gives an important indication of the Meniere's disease. , Hence, there is a need to study SP/AP amplitude ratio in Meniere's disease and to compare with non-Meniere's disease individuals.
Aim of the study
The purpose of this study was to find the diagnostic value of ECochG in Meniere's disease. Specifically, the main aims were to study the SP and AP amplitude and the ratio (SP/AP) between the two potentials in individuals with normal hearing and in those with Meniere's disease.
| Materials and Methods|| |
The present study was carried out with the aim to study the SP and AP amplitude and the SP/AP amplitude ratio in individuals with normal hearing and in those with Meniere's disease.
There were two groups of participants, individuals with normal hearing (control group) and individuals with Meniere's disease (experimental group). A detailed case history was taken for each participant in each group. Individuals in both the groups with any otologic and neurologic conditions were excluded from the study.
A total of 33 ears of 10 females and 7 males were considered in this group. All individuals were within the age range of 20-40 years, with a mean age of 22.2 years. They all had pure tone thresholds better than 15 dB HL at octave frequencies between 250 Hz to 8000 Hz in both the ears. The overall mean pure tone average (0.5 kHz, 1 kHz, and 2 kHz) was 6.01 dB HL. They had no indication of middle ear pathology, revealed by "A" type tympanogram with present reflexes.
A total of 30 ears of 9 females and 8 males, with a mean age of 32.1 years, were considered. The pure tone thresholds were within the range of mild to moderate (26-55 dB HL) at octave frequencies between 250 Hz to 8000 Hz. The overall mean pure tone average (0.5 kHz, 1 kHz, and 2 kHz) of all individuals was 35.69. They had no indication of middle ear pathology, as per immittance finding. Auditory brainstem response and otoacoustic emissions were done on each individual to rule out retrocochlear pathology and those individuals with an indication of retrocochlear pathology were excluded. They all had at least three of the four hallmark symptoms (tinnitus, vertigo, fluctuating hearing loss, and fullness) used in the diagnosis of Meniere's disease.  A detailed case history was taken for each individual and the individuals who fulfilled the above-mentioned criteria along with the ENT provisional diagnosis of Meniere's disease were included.
A calibrated two-channel clinical audiometer OB-922 with TDH-39 headphones and bone vibrator BC-71 was used for pure tone audiometry. A calibrated immittance meter, GSI-TYMPSTAR was used to assess the middle ear functioning of the individuals. Otodynamic ILO-V6 software and accompanying hardware was used to record otoacoustic emissions. ABR software installed in Bio-logic Navigator Pro AEP (version 7.0) system was used to record and analyze the waveforms of ABR. Bio-logic inserts earphones were used for ABR recording. ECochG (TM recording) software installed in Bio-logic Navigator Pro AEP (version 7.0) systems was used to record and analyze the findings of ECochG. Bio-logic inserts earphones and a Tiptrode were used for recording ECochG.
All individuals were tested in an acoustically sound treated room with adequate illuminations as per American National Standard Institute (ANSI) (1991). Pure tone thresholds were obtained at octave frequencies between 250 Hz and 8 kHz for air conduction and between 250 Hz and 4 kHz for bone conduction thresholds. Tympanometry was carried out with a probe tone frequency of 226 Hz, and acoustic reflexes thresholds were measured for 500 Hz, 1 kHz, 2 kHz, and 4 kHz ipsilaterally and contralaterally. Otoacoustic emissions (OAE) were obtained using click stimuli presented at 70 dB SPL. The probe tip was positioned in the external ear canal and was adjusted to give flat stimulus spectrum across the frequency range. Responses with reproducibility more than and equal to 80% were accepted. ABR recording was obtained to rule out retro-cochlear pathology.
For recording ECochG, individuals were made to relax on a reclining chair. ECochG was recorded from one channel. The site of electrode placement was prepared with skin preparation gel. Silver chloride electrode with conducting gel and a Tiptrode were used for recording ECochG. It was ensured that impedance for each electrode was less than 5 kW. The test protocols for ECochG recording are mentioned in [Table 1].
| Results and Discussion|| |
The results obtained in the present study are discussed here. The data obtained were subjected to statistical analysis using the SPSS (version 10.0) software. The analysis was done to obtain information on the following measurements:
The above measurements were analyzed using descriptive statistics, parametric tests which included independent sample t-test, and non-parametric tests such as Wilcoxon signed rank test.
- The SP and AP amplitude and latency difference between the two groups.
- The SP/AP amplitude ratio in both the groups.
ECochG in individuals with normal hearing and in those with meniere's disease
ECochG waveforms were recorded in individuals with normal hearing and in those with MD. Twenty-five ears out of 33 ears could be traced for SP waveform, indicating that 75.75% of the individual ear had SP waveforms. Literature also suggests that only for 60% individuals SP is traceable in normal hearing individuals. , The mean and standard deviation for SP and AP are given in [Table 2].
|Table 2: Mean and standard deviation (SD) of SP and AP in individuals with normal hearing and those with Meniere's disease|
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In individuals with normal hearing
Several researchers reported that the range of the latency of SP varied from 0.64 to 1.11 msec, with a mean latency of 0.87 sec. , The latency value of SP in the present study is also in consonance with earlier reports. Similarly the amplitude of SP in the present study varied from 0.04 to 0.55 μV. Literature also indicates almost similar findings ranging between 0.04 V and 1.30 μV. ,, In the present study, extra-tympanic electrode placement has been used, whereas majority of the studies have recorded ECochG with trans-tympanic electrode placements. It can be illustrated that because of differences in electrode placement, literature suggests higher amplitude and shorter latencies compared to the present study. ,,
In individuals with meniere's disease
SP and AP waveforms of ECochG were recorded. Twenty-two ears out of 30 ears (73.33%) had AP waveforms; however, only 14 ears out of 30 ears (46.66%) had SP waveforms. The mean latency and the standard deviation are given in [Table 2].
In the present study, the mean latency and amplitude of SP were 0.93 msec and 0.29 μV, respectively, in the experimental group, whereas in the control group they were 0.64 msec and 0.11 μV, respectively. It indicates the SP values increase both in terms of latency and amplitude in pathological condition. These findings could be explained by the fact that the SP is thought to result from the sum of the alternating current (AC) of the CM, resulting in a direct current (DC) shift from the baseline. This shift is exacerbated by asymmetrical basilar membrane movement, as found in hydrops.  Hence, the amplitude of SP in the experimental group is abnormally larger than in the control group.
The SP and AP amplitude and latency difference between individuals with normal hearing and individuals with Meniere's disease
The difference of SP and AP amplitude and latency between the two groups was statistically analyzed using independent single t-test and the results are summarized in [Table 3].
|Table 3: The significant difference in SP and AP amplitude between individuals with normal hearing and those with Meniere's disease (significance <0.05)|
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[Table 3] shows that the SP amplitude was significantly different in both the groups, whereas no significant difference was found in SP latency. However, significant difference was reported for both amplitude and latency for AP in both groups. The present finding is in consonance with previous reports, [10, 16, 18] but few of them found a significant difference in the SP latency too. This could be explained by the difference in the methodology because studies have been done by using trans-tympanic recording rather than extra-tympanic recording as used in the present study.
The SP/AP amplitude ratio comparison between individuals with normal hearing and individuals with meniere's disease
The SP/AP amplitude ratio was measured separately for each group. The mean SP/AP amplitude ratio for control group ear was 0.12, whereas the mean SP/AP amplitude ratio for experimental group was 0.28. In the present study, the SP/ AP amplitude ratio in the control group was little lower than the value mentioned in literature using extra-tympanic recording. Researches using either extra-tympanic recording or trans-tympanic recording accept the fact that SP/AP ratio considerably differentiates individuals with Meniere's disease from normal group individuals and the same findings are also illustrated from the present study. ,,,
The difference in SP/AP amplitude ratio of each group was measured by using Wilcoxon signed rank test. It was found that there was a significant difference (Z = 2.98, P = 0.003, P < 0.05) in SP/AP amplitude ratio between control and experimental groups. Hence, with these findings it can be concluded that SP/ AP amplitude ratio can differentiate individuals with Meniere's disease from normal hearing individuals.
| Conclusion|| |
The purpose of the present study was to find the diagnostic value of ECochG in Meniere's disease. ECochG was used in individuals with normal hearing (control group) and individuals with Meniere's disease (experimental group). The mean latency and amplitude of SP were 0.93 msec and 0.29 μV, respectively, in Meniere's ear, whereas in normal ear, they were 0.64 msec and 0.11 μV, respectively. Furthermore, a significant difference in SP/AP amplitude ratio across the control and experimental groups was also reported. Therefore, from the present study one can conclude that the SP values increase both in terms of latency and amplitude in pathological condition. In addition, it can also be concluded that SP/AP amplitude ratio can help in differentiating individuals with Meniere's disease from normal group individuals.
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[Table 1], [Table 2], [Table 3]