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Persistence of otoacoustic emissions in children with auditory neuropathy spectrum disorders
International Journal of Pediatric Otorhinolaryngology 77 (2013) 703–706
Contents lists available at SciVerse ScienceDirect
International Journal of Pediatric Otorhinolaryngology journal homepage: www.elsevier.com/locate/ijporl
Persistence of otoacoustic emissions in children with auditory neuropathy spectrum disorders Hossam Sanyelbhaa Talaat a,*, Lobna Hamed Khalil b,1, Ahmed H. Khafagy c,2, Mariyam M. Alkandari d,3, Ahmed M. Zein a,4 a
Audiology Unit, ENT Department, Menoufiya University, Egypt Audiology Unit, ENT Department, Ain Shams University, Egypt ENT Department Ain Shams University, Egypt d Sheikh Salem Al Ali Center for Audiology and Speech, Sabah Medical Area, Kuwait b c
A R T I C L E I N F O
A B S T R A C T
Article history: Received 5 January 2013 Received in revised form 16 January 2013 Accepted 18 January 2013 Available online 12 February 2013
Objectives: Many studies confirmed the disappearance of otoacoustic emissions in some of the patients with auditory neuropathy spectrum disorder, yet the data about the incidence rate of such disappearance is scanty or even absent. This study aims to test the persistence of transient evoked otoacoustic emissions in patients with auditory neuropathy spectrum disorder over few years. Methods: The study group consisted of 77 subjects (31 females and 46 males). Their ages ranged from 4 to 9 years (5.5 1.5). All the subjects were previously diagnosed to have auditory neuropathy spectrum disorder affecting both ears. Transient evoked otoacoustic emissions test results of the recent follow up sessions were compared with their initial diagnostic evaluation sessions done 3–6 years ago (3.7 0.8), in order to test the persistence of the emissions and the reduction of emissions level. Results: The transient evoked otoacoustic emissions level was reduced in the follow up visit compared to the initial study group. The transient evoked otoacoustic emissions level showed insignificant reduction (less than 3 dB) in 77.3% of the ears in the study group, and significant reduction (i.e. 3 dB or more) in 20.8%, and was absent in 1.9%. The transient evoked otoacoustic emissions level reduction in the different study subgroups was homogenous; gender (males versus females) laterality (right versus left ears) incubated to neonatal intensive care unit versus those non incubated all showed no significant differences in transient evoked otoacoustic emissions level reduction. Moreover, the duration of auditory neuropathy spectrum disorder was not correlated to the degree of transient evoked otoacoustic emissions reduction. Those fitted with hearing aids had more reduction in their transient evoked otoacoustic emissions level compared with those not fitted with hearing aids. Conclusions: (1) Transient evoked otoacoustic emissions was still detected in 98.1% of patients with auditory neuropathy spectrum disorder few years after the diagnosis. (2) Those fitted with hearing aids showed the most pronounced reduction in transient evoked otoacoustic emissions level. ß 2013 Elsevier Ireland Ltd. All rights reserved.
Keywords: Auditory neuropathy spectrum disorder (ANSD) Transient evoked otoacoustic emissions (TEOAEs) Disappearance of TEOAEs in ANSD
1. Introduction and rationale * Corresponding author at: ENT Department, Hadiclinic Hospital, Elgabriya, Kuwait. Tel.: +965 66753572. E-mail addresses: [email protected] (H. Sanyelbhaa Talaat), [email protected] (L.H. Khalil), [email protected] (A.H. Khafagy), [email protected] (M.M. Alkandari), [email protected] (A.M. Zein). 1 Address: ENT Department, Faculty of Medicine, Abbasia, Cairo, Egypt. Tel.: +20 195041332. 2 Address: ENT Department, Faculty of Medicine, Abbasia, Cairo, Egypt. Tel.: +20 965 97215597. 3 Address: Sheikh Salem Al Ali Center for Audiology & Speech, Shewikh, Kuwait. Tel.: +965 99610624. 4 Address: ENT Department, Faculty of Medicine, Shebien Elkoom, Egypt. Tel.: +20 1004299201. 0165-5876/$ – see front matter ß 2013 Elsevier Ireland Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijporl.2013.01.022
Auditory neuropathy spectrum disorder (ANSD) is a hearing disorder resulting from lesions involving auditory nerve fibers themselves (postsynaptic ANSD), the inner hair cells (IHCs) or their synapses with auditory nerve terminals (presynaptic ANSD) [1]. The disruption of auditory nerve function underlies both the absence of or profound alterations in auditory brainstem responses (ABR) and the preservation of cochlear receptor outer hair cell activities; this is indicated by the detection of otoacoustic emissions (OAEs), and by recording of cochlear microphonics (CM) [2]. On long term follow up for patients with ANSD the ABR remains abnormal and the OAEs continue to be present, but in
704
H. Sanyelbhaa Talaat et al. / International Journal of Pediatric Otorhinolaryngology 77 (2013) 703–706
some patients the OAEs may also disappear over time [3]. It has been suggested that conventional amplification may be beneficial in patients with ANSD after the disappearance of OAEs [4]. Though many studies confirmed the disappearance of OAEs in some of the patients of with ANSD, yet the data about the incidence rate of such disappearance is scanty or even absent. This study aims to compare the transient evoked otoacoustic emissions testing (TEOAEs) of patients with ANSD in the recent follow up sessions with their initial diagnostic evaluation sessions done few years ago in order to test the persistence of TEOAEs over years.
attending their follow up sessions in our centers during May through November 2012. The inclusion criteria of the study group included the following: - The diagnosis of ANSD was established for at least 3 years. - Their initial evaluations in the medical records show absent ABR waves and intact TEOAEs. - Type (A) tympanogram on the day of follow up session. 3. Methods 3.1. Transient evoked otoacoustic emissions testing
2. Materials and methods 2.1. Subjects This study was conducted at 4 audiology centers in Egypt and Kuwait. Meoufiya and Ain Shams University Hospitals, Egypt. Hadiclinic and Salem Al-Ali center, Kuwait. The study was approved by the Research Ethics Committee of the participating centers. The study group consisted of 77 subjects (31 females and 46 males). Their ages ranged from 4 to 9 years (mean age 5.5 years, standard deviation 1.5 years). All the subjects were previously diagnosed to have ANSD affecting both ears and were
[(Fig._1)TD$IG]
Multi-centers participated in this study resulting in heterogeneity regarding the TEOAEs recording systems and the testing paradigms. Every effort was done to ensure that every subject in the study group had his recent TEOAEs assessment with the same equipment and testing paradigm used in his initial diagnosis session. For the entire study group, the click stimulus was in the 0.7–4 kHz frequency range at an intensity of 83 dB SPL (3dB). The results were presented in dB as an average for 4 frequency bands range 1, 2, 3 and 4 kHz. In order to consider otoacoustic emission positive, the mean TEOAE amplitude at the frequency band should be either 6 dB or 3 dB with reproducibility 50% according to the used recording system.
Fig. 1. Example for calculating the TEamp for one ear in the study.
H. Sanyelbhaa Talaat et al. / International Journal of Pediatric Otorhinolaryngology 77 (2013) 703–706
705
Table 2 The change in TEOAEs amplitude in the study group.
3.2. Comparison criteria of TEOAEs The TEOAEs results of both the initial diagnosis and recent follow up evaluation sessions were compared as regards amplitude. For every ear TEamp was calculated as follows: (1) Over all emissions level = (the sum of TEOAEs level in frequency bands 1, 2, 3 and 4 kHz showing positive emissions)/4 NB. Any frequency band not showing positive emission was considered as (2) TEamp = The over all emission level of the initial evaluation the over all emission level of the recent evaluation.
If the TEamp was less than 3 dB such reduction in emission level was considered insignificant as it may be attributed to test–retest variability. Fig. 1 shows an example for calculating the TEamp for one ear in the study. 4. Results
Absent TEOAEs Reduced amplitudea Insignificantb amplitude reduction Total a b
Percent
3 32 119 154
1.9 20.8 77.3 100
TEamp 3 dB. TEamp <3 dB.
Table 3 The mean and standard deviation of reduction in emissions level (TEamp) in the different study subgroups regarding gender, ear laterality, incubation and hearing aid fitting.
Gender Laterality NICU Hearing aids
4.1. Etiology of ANSD
Number
Subgroup
TEamp/ear
Males (n = 92 ears) Females (n = 62 ears) Right (n = 77 ears) Left (n = 77 ears) Incubated (n = 90 ears) Non incubated (n = 64 ears) Fitted (n = 18 ears) Non Fitted (n = 136 ears)
1.8 2.6 1.6 2.3 1.7 2.2 1.8 2.7 1.9 3.3 2.1 2.9 3.4 4.2 1.5 2.1
t-Test reveal statistical significant difference only when comparing ears fitted with hearing aid with those non fitted (P < 0.001).
Hyperbilirubinaemia, prematurity, low birth weight or neonatal sepsis were reported in 45children (58.4%). Most of the patients had more than one risk factor e.g. low birth weight together with hyperbilirubinaemia. They all were incubated. 32 children (41.6%) showed no disorder would be suggested as etiology for ANSD (Table 1) 4.2. TEOAEs amplitude The Over all emission level of the TEOAEs in the initial diagnostic evaluation session was 14.5 2.9 dB, in the follow up evaluation session it was 12.2 4.7 dB, Paired t-Test revealed high statistical difference (P < 0.01). Table 2 shows categorical classification of the study group as regards the TEOAEs level reduction; absent, significant reduction or insignificant reduction. Two patients showed absent TEOAEs, one of them had neonatal hyperbilirubinaemia and was fitted bilaterally with high gain hearing aids, the emission were absent bilaterally. The other one had idiopathic ANSD and was not fitted with hearing aid, the emissions were absent in the left ear. 4.3. Effect of gender, ear laterality and hearing aid use Eleven children were fitted with hearing aids, seven of them were fitted binaurally and four were fitted monaurally. In order to study the possible effect of gender, ear laterality, hearing aid fitting and admission to the NICU on the persistence of the otoacoustic emissions the changes in each group were averaged and compared with the other group, e.g. the TEamp of the right ears are averaged and compared to the averaged TEamp of the left ears (Table 3).
Table 1 The possible etiology of ANSD in the study. Risk factor
Number
%
Idiopathic Hyperbilirubinaemia Low birth weight Prematurity Neonatal sepsis
32 39 25 18 3
41.6 50.6 32.5 23.4 3.9
The total number in this table is more than 77 patients as most of the subjects showed more than one risk factor.
4.4. Correlation between duration of the diagnosis and TEOAEs consistency The mean age of the subjects in the study group was 5.5 1.5 years; the range of duration of ANSD diagnosis was 3–6 years (3.7 0.8). Correlation between the duration of ANSD diagnosis and TEamp was done. r = 0.1459 (P > 0.05) which indicates absence of correlation. 5. Discussion It has been reported that on long term follow up for patients with ANSD OAEs may disappear over time [3]. Studying the disappearance of OAEs in some patients with ANSD would consolidate our understanding for the etiology and management of ANSD. One explanation for such phenomenon is that the pathological process may initially predominantly affect the IHCs, sparing most of the OHCs. later with the advance of the condition the OHCs may become involved as well, with ensuing disappearance of OAEs. Genetic ANSD due to abnormality in the gene encoding otoferlin (OTOF), is a well known example for such condition [8]. Hearing aid fitting may be another cause for the impairment of OAEs as the loud sounds delivered by the hearing aid may induce acoustic trauma to the OHCs. Evoked otoacoustic emissions are invaluable diagnostic tool used for monitoring the outer hair cells (OHCs) function. TEOAEs are more sensitive than DPOAEs for assessment of hearing at the range of 1–2 kHz. While DPOAEs are superior to TEOAEs for assessment of hearing at frequencies above 2 kHz [6]. In this study TEOAEs were applied as the majority of our ANSD patients were diagnosed using TEOAEs. TEOAE amplitude is highly reliable. The highest reliability is obtained on retest without probe-refitting, but decreases when there is probe refitting. Changing the position and the fit of the probe may affect the level of background noise in the ear canal, which interferes with the responses mainly at low frequencies and can also influence the interaction of the resonances of the outer ear and acoustic stimuli [7]. The analyzing bandwidth is another variable affecting the TEOAE reliability. According to Marshall & Heller intrasubject test–retest standard deviations were 1.4, and
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H. Sanyelbhaa Talaat et al. / International Journal of Pediatric Otorhinolaryngology 77 (2013) 703–706
1.8 dB for 1, and 1/6 octave analyzing bandwidths, respectively [8]. In this study only reduction of emission level 3 dB was considered significant, as many studies indicated that the intrasubject test–rest difference of the TEOAEs level may be up to 3 dB or even more [7,8]. 5.1. Reduction of TEOAEs level It is established that TEOAEs levels in neonates are larger than in older children, and larger in children than in adults [9]. These differences in TEOAEs levels across age groups have most often been attributed to anatomic changes in the outer or middle ear systems that occur with development. Ear canal diameter and length increase with development, as dose middle ear volume [10]. This increase in external canal and middle ear volume changes the external canal resonance, renders the recording probe more far from the generators of OAEs, and increases the volume of measuring cavity with subsequent reduction of the measured OAEs SPL. Such OAEs level reduction may explain, in part, the reduced TEOAEs level in this study (Table 2). Subjects participating in this study were diagnosed to have ANSD during their infancy and early childhood. And their follow up sessions were undertaken few years later. It is expected that their TEOAEs level would be reduced as their ears reach the adult size. Three ears (1.9%) of 2 subjects in the study showed absent TEOAEs in the follow up, such finding cannot be considered a normal process related to maturation of the middle and external ears. This is mostly either due to ongoing pathological process or effect of improper amplification. Unfortunately no further analysis can be done to suggest the factors contributing for the loss of TEOAEs because of the small number of ears showing absent TEOAEs. 5.2. Factors affecting reduction of TEOAEs level Hearing aids fitting is one of the habilitative/rehabilitative procedures used for management of ANSD. Berlin et al. conducted a retrospective analysis of 260 patients with ANSD, hearing aid outcomes were reported for 85 patients. It was surmised that 14% of patients gained benefit from amplification as manifested by increased functional interactions or language acquisition, while the remaining patients reportedly showed little (25%) or no benefit (61%) with hearing aids [11]. In the current study 18 ears (11.7%) were fitted with hearing aids. The reduction of TEOAEs level in these ears was greater than it was in non fitted ears. The difference was found statistically significant (Table 3). Two ears of these 18 ears had absent
TEOAEs. These data emphasize the possible role of amplification in reducing the OAEs level in ANDS. * In the current study the TEOAEs level reduction was not related to gender or ear laterality. More over those with idiopathic ANSD had the same degree of TEOAEs level reduction as those who were incubated because of hyperbilirubinaemia, prematurity, etc. The duration of ANSD diagnosis was found to be not correlated to the reduction in TEOAEs level (P > 0.05) this may be explained by the fact that the range of duration of diagnosis was 3–6 years (3.7 0.8). such range is contracted and render the study group of homogenous duration of diagnosis. May be in other studies with longer duration and wider duration range there would be positive correlation between reduction of TEOAEs level and duration of diagnosis. 6. Conclusion 1 TEOAEs was still detected in 98.1% of patients with ANSD after 3– 6 years of the diagnosis. The TEOAEs level was reduced by less than 3 dB in 77.3% of the study group, and 3 dB or more in 20.8%. 2 Hearing aid fitting affects the TEOAEs level in patients with ANSD. References [1] A. Starr, F. Zeng, H. Michalewski, T. Moser, Perspectives on auditory neuropathy: disorders of inner hair cell, auditory nerve, and their synapse, in: A.I. Basbaum, et al. (Eds.), The Senses: A Comprehensive Reference, New York, Academic Press, 2008, pp. 397–412. [2] R. Santarelli, Information from cochlear potentials and genetic mutations helps localize the lesion site in auditory neuropathy, Genome Med. 2 (12) (2010) 91. [3] A. Shoup, R. Rosser, Audiologic evaluation of special population, in: R. Rosser, M. Valanete, Hosford-Dunn (Eds.), Audiology: Diagnosis, Thieme, New York, 2007, pp. 314–335. [4] P. Deltenre, A.L. Mansbach, C. Bozet, F. Christiaens, P. Barthelemy, D. Paulissen, T. Renglet, Auditory neuropathy with preserved cochlear microphonics and secondary loss of otoacoustic emissions, Audiology 38 (4) (1999) 187–195. [6] M. Gorga, S. Neely, B. Bergman, K. Beauchaine, J. Kaminski, J. Peters, L. Schulte, W. Jesteadt, A comparison of transient-evoked and distortion product otoacoustic emissions in normal-hearing and hearing-impaired subjects, J. Acoust. Soc. Am. 94 (5) (1993) 2639–2648. [7] F. Zhao, D. Stephens, Test–retest variability of distortion-product otoacoustic emissions in human ears with normal hearing, Scand. Audiol. 28 (3) (1999) 171–178. [8] L. Marshall, L. Heller, Reliability of transient-evoked otoacoustic emissions, Ear Hear. 17 (3) (1996) 237–254. [9] B.A. Prieve, T.S. Fitzgerald, L.E. Schulte, Basic characteristics of click-evoked otoacoustic emissions in infants and children, J. Acoust. Soc. Am. 102 (1997) 2860–2880. [10] D.H. Keefe, J.C. Bulen, K.H. Arehart, E.M. Burns, Ear-canal impedance and reflection coefficient in human infants and adults, J. Acoust. Soc. Am. 94 (1993) 2617– 2638. [11] C. Berlin, L. Hood, T. Morlet, D. Wilensky, L. Li, K.R. Mattingly, J. Taylor-Jeanfreau, Multi-site diagnosis and management of 260 patients with auditory neuropathy/ dys-synchrony (auditory neuropathy spectrum disorder), Int. J. Audiol. 49 (1) (2010) 30–43.
Contents lists available at SciVerse ScienceDirect
International Journal of Pediatric Otorhinolaryngology journal homepage: www.elsevier.com/locate/ijporl
Persistence of otoacoustic emissions in children with auditory neuropathy spectrum disorders Hossam Sanyelbhaa Talaat a,*, Lobna Hamed Khalil b,1, Ahmed H. Khafagy c,2, Mariyam M. Alkandari d,3, Ahmed M. Zein a,4 a
Audiology Unit, ENT Department, Menoufiya University, Egypt Audiology Unit, ENT Department, Ain Shams University, Egypt ENT Department Ain Shams University, Egypt d Sheikh Salem Al Ali Center for Audiology and Speech, Sabah Medical Area, Kuwait b c
A R T I C L E I N F O
A B S T R A C T
Article history: Received 5 January 2013 Received in revised form 16 January 2013 Accepted 18 January 2013 Available online 12 February 2013
Objectives: Many studies confirmed the disappearance of otoacoustic emissions in some of the patients with auditory neuropathy spectrum disorder, yet the data about the incidence rate of such disappearance is scanty or even absent. This study aims to test the persistence of transient evoked otoacoustic emissions in patients with auditory neuropathy spectrum disorder over few years. Methods: The study group consisted of 77 subjects (31 females and 46 males). Their ages ranged from 4 to 9 years (5.5 1.5). All the subjects were previously diagnosed to have auditory neuropathy spectrum disorder affecting both ears. Transient evoked otoacoustic emissions test results of the recent follow up sessions were compared with their initial diagnostic evaluation sessions done 3–6 years ago (3.7 0.8), in order to test the persistence of the emissions and the reduction of emissions level. Results: The transient evoked otoacoustic emissions level was reduced in the follow up visit compared to the initial study group. The transient evoked otoacoustic emissions level showed insignificant reduction (less than 3 dB) in 77.3% of the ears in the study group, and significant reduction (i.e. 3 dB or more) in 20.8%, and was absent in 1.9%. The transient evoked otoacoustic emissions level reduction in the different study subgroups was homogenous; gender (males versus females) laterality (right versus left ears) incubated to neonatal intensive care unit versus those non incubated all showed no significant differences in transient evoked otoacoustic emissions level reduction. Moreover, the duration of auditory neuropathy spectrum disorder was not correlated to the degree of transient evoked otoacoustic emissions reduction. Those fitted with hearing aids had more reduction in their transient evoked otoacoustic emissions level compared with those not fitted with hearing aids. Conclusions: (1) Transient evoked otoacoustic emissions was still detected in 98.1% of patients with auditory neuropathy spectrum disorder few years after the diagnosis. (2) Those fitted with hearing aids showed the most pronounced reduction in transient evoked otoacoustic emissions level. ß 2013 Elsevier Ireland Ltd. All rights reserved.
Keywords: Auditory neuropathy spectrum disorder (ANSD) Transient evoked otoacoustic emissions (TEOAEs) Disappearance of TEOAEs in ANSD
1. Introduction and rationale * Corresponding author at: ENT Department, Hadiclinic Hospital, Elgabriya, Kuwait. Tel.: +965 66753572. E-mail addresses: [email protected] (H. Sanyelbhaa Talaat), [email protected] (L.H. Khalil), [email protected] (A.H. Khafagy), [email protected] (M.M. Alkandari), [email protected] (A.M. Zein). 1 Address: ENT Department, Faculty of Medicine, Abbasia, Cairo, Egypt. Tel.: +20 195041332. 2 Address: ENT Department, Faculty of Medicine, Abbasia, Cairo, Egypt. Tel.: +20 965 97215597. 3 Address: Sheikh Salem Al Ali Center for Audiology & Speech, Shewikh, Kuwait. Tel.: +965 99610624. 4 Address: ENT Department, Faculty of Medicine, Shebien Elkoom, Egypt. Tel.: +20 1004299201. 0165-5876/$ – see front matter ß 2013 Elsevier Ireland Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijporl.2013.01.022
Auditory neuropathy spectrum disorder (ANSD) is a hearing disorder resulting from lesions involving auditory nerve fibers themselves (postsynaptic ANSD), the inner hair cells (IHCs) or their synapses with auditory nerve terminals (presynaptic ANSD) [1]. The disruption of auditory nerve function underlies both the absence of or profound alterations in auditory brainstem responses (ABR) and the preservation of cochlear receptor outer hair cell activities; this is indicated by the detection of otoacoustic emissions (OAEs), and by recording of cochlear microphonics (CM) [2]. On long term follow up for patients with ANSD the ABR remains abnormal and the OAEs continue to be present, but in
704
H. Sanyelbhaa Talaat et al. / International Journal of Pediatric Otorhinolaryngology 77 (2013) 703–706
some patients the OAEs may also disappear over time [3]. It has been suggested that conventional amplification may be beneficial in patients with ANSD after the disappearance of OAEs [4]. Though many studies confirmed the disappearance of OAEs in some of the patients of with ANSD, yet the data about the incidence rate of such disappearance is scanty or even absent. This study aims to compare the transient evoked otoacoustic emissions testing (TEOAEs) of patients with ANSD in the recent follow up sessions with their initial diagnostic evaluation sessions done few years ago in order to test the persistence of TEOAEs over years.
attending their follow up sessions in our centers during May through November 2012. The inclusion criteria of the study group included the following: - The diagnosis of ANSD was established for at least 3 years. - Their initial evaluations in the medical records show absent ABR waves and intact TEOAEs. - Type (A) tympanogram on the day of follow up session. 3. Methods 3.1. Transient evoked otoacoustic emissions testing
2. Materials and methods 2.1. Subjects This study was conducted at 4 audiology centers in Egypt and Kuwait. Meoufiya and Ain Shams University Hospitals, Egypt. Hadiclinic and Salem Al-Ali center, Kuwait. The study was approved by the Research Ethics Committee of the participating centers. The study group consisted of 77 subjects (31 females and 46 males). Their ages ranged from 4 to 9 years (mean age 5.5 years, standard deviation 1.5 years). All the subjects were previously diagnosed to have ANSD affecting both ears and were
[(Fig._1)TD$IG]
Multi-centers participated in this study resulting in heterogeneity regarding the TEOAEs recording systems and the testing paradigms. Every effort was done to ensure that every subject in the study group had his recent TEOAEs assessment with the same equipment and testing paradigm used in his initial diagnosis session. For the entire study group, the click stimulus was in the 0.7–4 kHz frequency range at an intensity of 83 dB SPL (3dB). The results were presented in dB as an average for 4 frequency bands range 1, 2, 3 and 4 kHz. In order to consider otoacoustic emission positive, the mean TEOAE amplitude at the frequency band should be either 6 dB or 3 dB with reproducibility 50% according to the used recording system.
Fig. 1. Example for calculating the TEamp for one ear in the study.
H. Sanyelbhaa Talaat et al. / International Journal of Pediatric Otorhinolaryngology 77 (2013) 703–706
705
Table 2 The change in TEOAEs amplitude in the study group.
3.2. Comparison criteria of TEOAEs The TEOAEs results of both the initial diagnosis and recent follow up evaluation sessions were compared as regards amplitude. For every ear TEamp was calculated as follows: (1) Over all emissions level = (the sum of TEOAEs level in frequency bands 1, 2, 3 and 4 kHz showing positive emissions)/4 NB. Any frequency band not showing positive emission was considered as (2) TEamp = The over all emission level of the initial evaluation the over all emission level of the recent evaluation.
If the TEamp was less than 3 dB such reduction in emission level was considered insignificant as it may be attributed to test–retest variability. Fig. 1 shows an example for calculating the TEamp for one ear in the study. 4. Results
Absent TEOAEs Reduced amplitudea Insignificantb amplitude reduction Total a b
Percent
3 32 119 154
1.9 20.8 77.3 100
TEamp 3 dB. TEamp <3 dB.
Table 3 The mean and standard deviation of reduction in emissions level (TEamp) in the different study subgroups regarding gender, ear laterality, incubation and hearing aid fitting.
Gender Laterality NICU Hearing aids
4.1. Etiology of ANSD
Number
Subgroup
TEamp/ear
Males (n = 92 ears) Females (n = 62 ears) Right (n = 77 ears) Left (n = 77 ears) Incubated (n = 90 ears) Non incubated (n = 64 ears) Fitted (n = 18 ears) Non Fitted (n = 136 ears)
1.8 2.6 1.6 2.3 1.7 2.2 1.8 2.7 1.9 3.3 2.1 2.9 3.4 4.2 1.5 2.1
t-Test reveal statistical significant difference only when comparing ears fitted with hearing aid with those non fitted (P < 0.001).
Hyperbilirubinaemia, prematurity, low birth weight or neonatal sepsis were reported in 45children (58.4%). Most of the patients had more than one risk factor e.g. low birth weight together with hyperbilirubinaemia. They all were incubated. 32 children (41.6%) showed no disorder would be suggested as etiology for ANSD (Table 1) 4.2. TEOAEs amplitude The Over all emission level of the TEOAEs in the initial diagnostic evaluation session was 14.5 2.9 dB, in the follow up evaluation session it was 12.2 4.7 dB, Paired t-Test revealed high statistical difference (P < 0.01). Table 2 shows categorical classification of the study group as regards the TEOAEs level reduction; absent, significant reduction or insignificant reduction. Two patients showed absent TEOAEs, one of them had neonatal hyperbilirubinaemia and was fitted bilaterally with high gain hearing aids, the emission were absent bilaterally. The other one had idiopathic ANSD and was not fitted with hearing aid, the emissions were absent in the left ear. 4.3. Effect of gender, ear laterality and hearing aid use Eleven children were fitted with hearing aids, seven of them were fitted binaurally and four were fitted monaurally. In order to study the possible effect of gender, ear laterality, hearing aid fitting and admission to the NICU on the persistence of the otoacoustic emissions the changes in each group were averaged and compared with the other group, e.g. the TEamp of the right ears are averaged and compared to the averaged TEamp of the left ears (Table 3).
Table 1 The possible etiology of ANSD in the study. Risk factor
Number
%
Idiopathic Hyperbilirubinaemia Low birth weight Prematurity Neonatal sepsis
32 39 25 18 3
41.6 50.6 32.5 23.4 3.9
The total number in this table is more than 77 patients as most of the subjects showed more than one risk factor.
4.4. Correlation between duration of the diagnosis and TEOAEs consistency The mean age of the subjects in the study group was 5.5 1.5 years; the range of duration of ANSD diagnosis was 3–6 years (3.7 0.8). Correlation between the duration of ANSD diagnosis and TEamp was done. r = 0.1459 (P > 0.05) which indicates absence of correlation. 5. Discussion It has been reported that on long term follow up for patients with ANSD OAEs may disappear over time [3]. Studying the disappearance of OAEs in some patients with ANSD would consolidate our understanding for the etiology and management of ANSD. One explanation for such phenomenon is that the pathological process may initially predominantly affect the IHCs, sparing most of the OHCs. later with the advance of the condition the OHCs may become involved as well, with ensuing disappearance of OAEs. Genetic ANSD due to abnormality in the gene encoding otoferlin (OTOF), is a well known example for such condition [8]. Hearing aid fitting may be another cause for the impairment of OAEs as the loud sounds delivered by the hearing aid may induce acoustic trauma to the OHCs. Evoked otoacoustic emissions are invaluable diagnostic tool used for monitoring the outer hair cells (OHCs) function. TEOAEs are more sensitive than DPOAEs for assessment of hearing at the range of 1–2 kHz. While DPOAEs are superior to TEOAEs for assessment of hearing at frequencies above 2 kHz [6]. In this study TEOAEs were applied as the majority of our ANSD patients were diagnosed using TEOAEs. TEOAE amplitude is highly reliable. The highest reliability is obtained on retest without probe-refitting, but decreases when there is probe refitting. Changing the position and the fit of the probe may affect the level of background noise in the ear canal, which interferes with the responses mainly at low frequencies and can also influence the interaction of the resonances of the outer ear and acoustic stimuli [7]. The analyzing bandwidth is another variable affecting the TEOAE reliability. According to Marshall & Heller intrasubject test–retest standard deviations were 1.4, and
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1.8 dB for 1, and 1/6 octave analyzing bandwidths, respectively [8]. In this study only reduction of emission level 3 dB was considered significant, as many studies indicated that the intrasubject test–rest difference of the TEOAEs level may be up to 3 dB or even more [7,8]. 5.1. Reduction of TEOAEs level It is established that TEOAEs levels in neonates are larger than in older children, and larger in children than in adults [9]. These differences in TEOAEs levels across age groups have most often been attributed to anatomic changes in the outer or middle ear systems that occur with development. Ear canal diameter and length increase with development, as dose middle ear volume [10]. This increase in external canal and middle ear volume changes the external canal resonance, renders the recording probe more far from the generators of OAEs, and increases the volume of measuring cavity with subsequent reduction of the measured OAEs SPL. Such OAEs level reduction may explain, in part, the reduced TEOAEs level in this study (Table 2). Subjects participating in this study were diagnosed to have ANSD during their infancy and early childhood. And their follow up sessions were undertaken few years later. It is expected that their TEOAEs level would be reduced as their ears reach the adult size. Three ears (1.9%) of 2 subjects in the study showed absent TEOAEs in the follow up, such finding cannot be considered a normal process related to maturation of the middle and external ears. This is mostly either due to ongoing pathological process or effect of improper amplification. Unfortunately no further analysis can be done to suggest the factors contributing for the loss of TEOAEs because of the small number of ears showing absent TEOAEs. 5.2. Factors affecting reduction of TEOAEs level Hearing aids fitting is one of the habilitative/rehabilitative procedures used for management of ANSD. Berlin et al. conducted a retrospective analysis of 260 patients with ANSD, hearing aid outcomes were reported for 85 patients. It was surmised that 14% of patients gained benefit from amplification as manifested by increased functional interactions or language acquisition, while the remaining patients reportedly showed little (25%) or no benefit (61%) with hearing aids [11]. In the current study 18 ears (11.7%) were fitted with hearing aids. The reduction of TEOAEs level in these ears was greater than it was in non fitted ears. The difference was found statistically significant (Table 3). Two ears of these 18 ears had absent
TEOAEs. These data emphasize the possible role of amplification in reducing the OAEs level in ANDS. * In the current study the TEOAEs level reduction was not related to gender or ear laterality. More over those with idiopathic ANSD had the same degree of TEOAEs level reduction as those who were incubated because of hyperbilirubinaemia, prematurity, etc. The duration of ANSD diagnosis was found to be not correlated to the reduction in TEOAEs level (P > 0.05) this may be explained by the fact that the range of duration of diagnosis was 3–6 years (3.7 0.8). such range is contracted and render the study group of homogenous duration of diagnosis. May be in other studies with longer duration and wider duration range there would be positive correlation between reduction of TEOAEs level and duration of diagnosis. 6. Conclusion 1 TEOAEs was still detected in 98.1% of patients with ANSD after 3– 6 years of the diagnosis. The TEOAEs level was reduced by less than 3 dB in 77.3% of the study group, and 3 dB or more in 20.8%. 2 Hearing aid fitting affects the TEOAEs level in patients with ANSD. References [1] A. Starr, F. Zeng, H. Michalewski, T. Moser, Perspectives on auditory neuropathy: disorders of inner hair cell, auditory nerve, and their synapse, in: A.I. Basbaum, et al. (Eds.), The Senses: A Comprehensive Reference, New York, Academic Press, 2008, pp. 397–412. [2] R. Santarelli, Information from cochlear potentials and genetic mutations helps localize the lesion site in auditory neuropathy, Genome Med. 2 (12) (2010) 91. [3] A. Shoup, R. Rosser, Audiologic evaluation of special population, in: R. Rosser, M. Valanete, Hosford-Dunn (Eds.), Audiology: Diagnosis, Thieme, New York, 2007, pp. 314–335. [4] P. Deltenre, A.L. Mansbach, C. Bozet, F. Christiaens, P. Barthelemy, D. Paulissen, T. Renglet, Auditory neuropathy with preserved cochlear microphonics and secondary loss of otoacoustic emissions, Audiology 38 (4) (1999) 187–195. [6] M. Gorga, S. Neely, B. Bergman, K. Beauchaine, J. Kaminski, J. Peters, L. Schulte, W. Jesteadt, A comparison of transient-evoked and distortion product otoacoustic emissions in normal-hearing and hearing-impaired subjects, J. Acoust. Soc. Am. 94 (5) (1993) 2639–2648. [7] F. Zhao, D. Stephens, Test–retest variability of distortion-product otoacoustic emissions in human ears with normal hearing, Scand. Audiol. 28 (3) (1999) 171–178. [8] L. Marshall, L. Heller, Reliability of transient-evoked otoacoustic emissions, Ear Hear. 17 (3) (1996) 237–254. [9] B.A. Prieve, T.S. Fitzgerald, L.E. Schulte, Basic characteristics of click-evoked otoacoustic emissions in infants and children, J. Acoust. Soc. Am. 102 (1997) 2860–2880. [10] D.H. Keefe, J.C. Bulen, K.H. Arehart, E.M. Burns, Ear-canal impedance and reflection coefficient in human infants and adults, J. Acoust. Soc. Am. 94 (1993) 2617– 2638. [11] C. Berlin, L. Hood, T. Morlet, D. Wilensky, L. Li, K.R. Mattingly, J. Taylor-Jeanfreau, Multi-site diagnosis and management of 260 patients with auditory neuropathy/ dys-synchrony (auditory neuropathy spectrum disorder), Int. J. Audiol. 49 (1) (2010) 30–43.