|Year : 2020 | Volume
| Issue : 1 | Page : 16-20
Prevalence of cochlear dead regions in hearing-impaired patients
Asmaa Moaty1, Medhat Fathy Yousef2, Ayman Abd Alaziz3, Abd Allatif Elrasheedy3
1 Department of Otorhinolaryngology, Audiology Unit, Menoufia University Hospital, Menoufia, Egypt
2 Department of Otorhinolaryngology, Audiology Unit, Menoufia University Hospital, Menoufia, Egypt; King Abdullah Ear Specialist Center, Audiology Unit, King Abdulaziz University Hospital, King Saud University, Riyadh, KSA
3 Department of Otorhinolaryngology, Menoufia University, Menoufia, Egypt
|Date of Submission||08-Nov-2019|
|Date of Decision||27-Nov-2019|
|Date of Acceptance||28-Nov-2019|
|Date of Web Publication||01-Jun-2020|
Dr. Medhat Fathy Yousef
King Abdullah Ear Specialist Center, Audiology Unit, King Abdulaziz University Hospital, King Saud University, Riyadh, KSA
Source of Support: None, Conflict of Interest: None
Objective: The aim is to study the prevalence of dead regions in the cochlea in hearing-impaired patients with different audiometric configurations and to study the speech discrimination scores in dead regions of the cochlea. Materials and Methods: Eighty participants, with age ranging from 18 to 50 years, were divided into control group (30 normal-hearing participants) and study group (50 patients suffering from sensorineural hearing loss). All participants in the study were submitted to the following: medical and audiological history, otological examination, basic audiological evaluation in the form of pure-tone audiometry and tympanometry, auditory brainstem response, and the threshold-equalizing noise (TEN) test. Results: Thirty-nine patients in the study group gave negative results of TEN test and 11 patients gave positive results of TEN test. Conclusions: The prevalence of dead regions of the cochlea in this study was 22%. Dead regions in the cochlea were more common in patients with sloping, long-standing hearing loss and in high frequencies.
Keywords: Cochlea, dead region, hearing loss, threshold-equalizing noise test
|How to cite this article:|
Moaty A, Yousef MF, Alaziz AA, Elrasheedy AA. Prevalence of cochlear dead regions in hearing-impaired patients. Saudi J Otorhinolaryngol Head Neck Surg 2020;22:16-20
|How to cite this URL:|
Moaty A, Yousef MF, Alaziz AA, Elrasheedy AA. Prevalence of cochlear dead regions in hearing-impaired patients. Saudi J Otorhinolaryngol Head Neck Surg [serial online] 2020 [cited 2020 Jul 16];22:16-20. Available from: http://www.sjohns.org/text.asp?2020/22/1/16/285555
| Introduction|| |
A dead region of the cochlea is a region where there are no functioning inner hair cells and/or auditory neurons. It is described in terms of the range of characteristic frequencies in the cochlea that would normally be associated with that region., A sound wave that should do vibration at that dead region, will not produce any significant neural activity. However, this signal could be detected by the neighboring inner hair cells and neurons which is called off-place listening.
The auditory performance may vary from one person to another according to the presence or absence of dead regions even if those persons have identical audiograms. The presence of cochlear dead regions can have several perceptual consequences such as distorted perception of pure tones, rapid growth of loudness, and abnormal pitch perception. Moreover, the presence or absence of dead regions has essential implications for the fitting of hearing aids. If there are one or more extensive dead regions, the benefit of a hearing aid and aided speech intelligibility are likely to be poor., Dead regions may also have a significant impact on speech perception by cochlear implant listeners.
Researchers have used various indirect psychophysical methods to estimate the presence and extent of dead regions. Two methods are widely used, which are the psychophysical tuning curves and the threshold-equalizing noise (TEN) test. The TEN (HL) test was developed by Moore et al. to detect cochlear dead regions. The TEN (HL) test involves the measurement of pure-tone thresholds in the presence of broadband noise spectrally shaped to produce equal masked thresholds across frequencies. At a specific frequency, dead regions can be detected by elevated thresholds in the presence of this masking noise.,
There is no general consensus about the prevalence of the dead regions among participants with sensorineural hearing loss (SNHL) as many researchers have published inconsistent findings regarding this issue.,, It has been noted that dead regions could be found with hearing loss of severe degree or worse  and/or moderate degree or better., Moreover, a steep sloping SNHL can be accompanied by a dead region in the high-frequency range but not considered as a reliable landmark for the presence of the dead regions. In this context, it is undeniable that studying the existence of the dead regions of the cochlea in SNHL would be of the utmost interest.
This study was designed to assess the prevalence of the dead regions in the cochlea in hearing-impaired patients with different audiometric configurations using TEN (HL) test and to study the speech intelligibility in patients with dead regions.
| Materials and Methods|| |
Two groups were included in this study; the control group and the study group; demographic data are demonstrated in [Table 1]. The study group consists of 50 participants with SNHL of different etiologies with no restrictions regarding the audiometric level or configuration except the exclusion of severe to profound cases and asymmetrical hearing loss. We also included 30 participants of normal-hearing sensitivity in our study to serve as control group. All participants in this study were recruited from the outpatient audiology clinic of our tertiary hospital in addition to normal volunteers. The age of selected candidates that were included in this study ranged from 18 to 60 years, and they were 39 males and 41 females. The study was approved by the ethical committee of the hospital and patient consent was taken from each participant.
|Table 1: Comparison between the studied groups regarding demographic data|
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Two sessions were arranged for each participant:
The first session
During this session, detailed medical and audiological history was taken from each patient. Otological examinations were performed. Basic audiological evaluations were carried out that include: (a) pure-tone audiometry, (b) speech audiometry: speech reception threshold using Arabic spondee words and word discrimination score using Arabic phonetically balanced words. (c) Immittancemetry: tympanometry and acoustic reflex threshold. The hearing impairment was classified according to its configuration into: (i) Flat: when there is ≤5 dB average difference per octave, (ii) sloping: when there is ≥6 dB rise or fall per octave, and (iii) reverse sloping: when there is better hearing in the high frequencies.
The second session
Auditory brainstem response
Auditory brainstem response (ABR) was carried out for measuring wave I latency. Clicks stimuli were used at a rate of 19.30 pulses/s at 90 dBnHL to the participants ipsilaterally through (TDH 49) earphones. One thousand responses were differentially amplified through a bandpass filter from 100 to 3000 Hz. The analysis time was 20 msec, and two different recordings were obtained.
Threshold-equalizing noise (HL)
The TEN (HL) test was also done during the same session. This test required a two-channel audiometer since the level of the noise masker and of the tone signal needs to be separately controlled. The output from the CD player was fed to the left and right line inputs on the audiometer. The first track contains a calibration tone. The controls on the audiometer were used to adjust the levels of the tone and the noise to the desired values. The following steps are involved in performing the TEN (HL) test: 1 –Play track 1 and set the audiometer so that both VU meters read 0 dB, 2 – The right channel (which contains noise) is turned off. Using the tone input from the left channel, the absolute thresholds are measured for each ear at each test frequency (500, 750, 1000, 1500, 2000, 3000, and 4000 HZ), 3 – The two channels are mixed, and the desired noise level (dB/ERB) is set using the right channel attenuator. Two noise levels were used 50- and 70-dB HL, 4 – The masked threshold is measured for each ear at each frequency. A dead region at a specific frequency is indicated by a masked threshold that is at least 10 dB above the absolute threshold and 10 dB above the nominal noise level per ERB. Both absolute and masked thresholds can be measured using standard audiometric methods.
All statistical analysis was carried out using the SPSS (Statistical Package of Social Science software, Version 23, IBM Corp., Armonk, New York, USA). Nonparametric tests were used due to the nature of ordinal and categorical data. The qualitative data were expressed as number and percentage and analyzed using the Chi-square test. ANOVA test was used for the analysis of the variances. Comparison between the studied groups was carried out using the Kruskal–Wallis test. Furthermore, Mann–Whitney test (U-test) was used to compare between the two subgroups. Correlation analysis for the quantitative variables was carried out using the Pearson correlation coefficient. Statistical significance was considered with a value of P < 0.05.
| Results|| |
The present study included 80 participants, divided into control and study groups; The control group: comprised 30 participants with normal-hearing sensitivity, the study group: comprised 50 participants suffering from SNHL, this group was further subdivided according to the results of TEN test into two subgroups: subgroup A: represents 39 participants with negative results of TEN test, subgroup B: represents 11 participants with positive TEN test results. Demographic data are demonstrated in [Table 1]. Insignificant differences exist between the control and the study subgroups as regards age and gender distribution.
Prevalence of dead regions
All the study group participants did TEN test without difficulty except 8 participants who gave inconclusive results (The masked threshold of the signal is within 10 dB of the absolute threshold but is 10 dB or more above the level of noise) during the first trial. On retesting, 6 patients gave the same results, but the other two patients changed from positive to negative results. All the participants in the control group had negative results of TEN test. In the study group, 16/100 ears had positive results of TEN test represented in 31 frequencies.
In the current study, the prevalence of the dead regions is 22%. The distribution of the dead regions according to the number of affected frequencies is demonstrated in [Figure 1]. Among the TEN (HL) positive participants, 5/11 (45%) showed dead regions in both ears, whereas 6/11 (55%) had dead regions only in one ear (all were in the left ear). The mean value of threshold and threshold shift among right and left ears in positive frequencies are shown in [Table 2]. The distribution of dead regions along different frequencies is illustrated in [Figure 2]. As regards the existence of dead region in different audiometric configuration of hearing loss [Figure 3], the majority (69%) of ears with dead regions had sloping high-frequency SNHL. On the other hand, no patients with flat configuration hearing loss had been found to have dead regions in the current study. Furthermore, dead regions were reported in moderately severe degree of hearing loss, less common in moderate degree, and not found in mild degree of hearing loss [Table 2].
|Figure 1: The distribution of ears according to the number of affected frequencies with dead regions|
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|Table 2: Mean value of threshold and threshold shift among right and left ears in positive frequencies in subgroup B|
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|Figure 2: The distribution of ears with dead regions along the different frequencies|
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|Figure 3: Distribution of dead regions according to audiometric configurations of hearing loss|
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Dead region and hearing loss duration
The duration of hearing loss in the study group is demonstrated in [Table 1]. The mean duration of hearing loss in subgroup B was significantly higher than that of subgroup A. However, using the Pearson correlation coefficient, there is a weak positive correlation between duration of hearing loss and threshold shift at all frequencies in subgroup B.
Dead region and speech discrimination
Both subgroups A and B had significantly lower score than that obtained from the control group (P< 0.001). However, there was no statistically significant difference when comparing subgroups A and B (P > 0.05).
Dead region and latency of wave I of auditory brainstem response
ABR was used to look for wave I latency in all participants. The mean value of wave I latency in subgroup A and B was significantly higher than that of controls (P< 0.001). No statistically significant difference was found between subgroup A and B (P > 0.05). Using the Pearson correlation coefficient, weak positive correlation between latency of wave I and threshold shift had been detected at all frequencies in subgroup B.
| Discussion|| |
The diagnosis of cochlear dead regions is important for the treatment and management of hearing loss, optimal aural rehabilitation, medico-legal cases, and when assessing candidacy for cochlear implants. In the present study, we have assessed the prevalence of dead regions in the cochlea in hearing-impaired participants with different audiometric configurations using TEN (HL) tests. We found that 39 participants from the study group had negative results of TEN (HL) test, whereas only 11 participants had positive TEN (HL) test. The overall prevalence of dead regions (22%) in this study is lower than that reported in the previous study of Vinay and Moore, who reported that the prevalence of dead regions is 57% among their studied cases. There are several possible explanations for the discrepancy between the two studies such as difference in the sample size, the selection criteria, and the degree of SNHL of the selected participants.
Interestingly, our results indicated that dead regions are more common in sloping SNHL. This is consistent with the previous observations of Markessis et al. who reported that 87% of adults with a steeply sloping moderate-to-severe hearing loss met the criteria for a dead region for at least one frequency. Furthermore, our results demonstrated that dead regions are more common at high frequencies. In general, low-frequency dead regions are less frequently encountered than high-frequency dead regions in adults with acquired hearing loss. One possible explanation for this can be the high susceptibility of cochlear basal fibers to damage by a variety of agents such as acoustic trauma and ototoxic drugs., Another important finding is that TEN (HL) test positive participants had a longer history of hearing loss than those that had negative TEN (HL) test. This is in line with the findings of Moore, who reported that dead regions in the cochlea are prevalent in long-standing SNHL.
Our results also demonstrated a statistically significant difference between speech discrimination scores of the study group and that of the control (P< 0.001). However, there was no statistically significant difference between TEN (HL) positive and negative participants regarding speech discrimination scores in quiet. Our finding is not in agreement with Baer et al. who reported that the participants with dead regions extracted little or no information from frequencies that were healthy inside the dead regions. This can be explained by the redundancy of test material used in quiet while in the study of Baer et al. redundancy of speech was reduced by changing cutoff frequencies of speech and low pass filtering of speech.
We also found that there was a statistically significant increase in the latencies of wave I of ABR induced by click stimuli in the study group compared with those of the control group. However, no significant difference was detected between TEN (HL) positive and negative participants in the study group. These results could be explained by using the broad-spectrum click stimulus and thereby stimulates the entire cochlear partition. Evidently, this sharply contrasts results reported by Abdel Rahmanan et al. who indicated longer latencies of wave I of ABR in patients with dead regions. One might surmise that they obtained this result due to using tone burst ABR in their study, which is frequency specific. Taken together, our results indicate that we cannot rely on click ABR or speech discrimination scores in quiet in the diagnosis of dead regions.
The test-retest reliability of the TEN (HL) test was debatable when a dead region was found at a single isolated frequency and in cases with inconclusive results. In the study, some patients with inconclusive results have changed to negative results on retesting. Hence, our findings support the conclusions of another study carried out by Cairns et al. who indicated that on repeating TEN (HL) test for patients with unexpected dead regions at a single isolated frequency, some ears have changed their results from positive to negative dead regions.
From a clinical perspective, there were some practical obstacles associated with TEN (HL) test that had been reported during the current study. Some participants, especially older adults, reported fatigue because of the loud levels of uninterrupted broadband noise during or following the test. In addition, the test is difficult to be understood by children. An intrinsic limitation of TEN (HL) test, which used in the present study, is that masked thresholds can be obtained up to 4 KHz only. This means that any information about the dead regions beyond this level would be missing. Furthermore, there is a limitation in the assessment of threshold as the maximum threshold that can be used in this TEN (HL) test is 90 dB HL.
| Conclusions|| |
The current study indicated that the prevalence of the dead regions of the cochlea was 22%. Dead regions can be unilateral or bilateral, either single or multiple. Importantly, our data show that dead regions in the cochlea are more prevalent in high frequency long-standing SNHL. Speech discrimination scores in quiet cannot be used to assess speech intelligibility in patients with dead regions. Taken together, our data recommend the integration of TEN (HL) test in the routine battery of evaluation of participants with SNHL who are candidates for hearing aid fitting, especially suspected patients of dead regions.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]