- Email: [email protected]
Cochlear microphonics in sensorineural hearing loss: Lesson from newborn hearing screening
International Journal of Pediatric Otorhinolaryngology (2008) 72, 1281—1285
www.elsevier.com/locate/ijporl
CASE REPORT
Cochlear microphonics in sensorineural hearing loss: Lesson from newborn hearing screening Ansar Ahmmed a,*, Christopher Brockbank a, June Adshead b a b
Lancashire Teaching Hospitals NHS Foundation Trust, Preston, United Kingdom Sefton Paediatric Audiology Service, Southport, United Kingdom
Received 17 January 2008; received in revised form 5 May 2008; accepted 9 May 2008
KEYWORDS Cochlear microphonics; Auditory neuropathy; Auditory Dyssynchrony; Auditory brainstem response; Newborn Hearing Screening Programme; Sensorineural hearing loss; Enlarged vestibular aqueduct
Summary The diagnostic dilemma surrounding the presence of cochlear microphonics (CM) coupled with significantly elevated auditory brainstem response (ABR) thresholds in babies failing the newborn hearing screening is highlighted. A case report is presented where initial electo-diagnostic assessment could not help in differentiating between Auditory Neuropathy/Auditory Dys-synchrony (AN/AD) and sensorineural hearing loss (SNHL). In line with the protocol and guidelines provided by the national Newborn Hearing Screening Programme in the UK (NHSP) AN/AD was suspected in a baby due to the presence of CM at 85 dBnHL along with click evoked ABR thresholds of 95 dBnHL in one ear and 100 dBnHL in the other ear. Significantly elevated thresholds for 0.5 and 1 kHz tone pip ABR fulfilled the audiological diagnostic criteria for AN/AD. However, the possibility of a SNHL could not be ruled out as the 85 dBnHL stimuli presented through inserts for the CM would have been significantly enhanced in the ear canals of the young baby to exceed the threshold level of the ABR that was carried out using headphones. SNHL was eventually diagnosed through clinical and family history, physical examination and imaging that showed enlarged vestibular aqueducts. Presence of CM in the presence of very high click ABR thresholds only suggests a pattern of test results and in such cases measuring thresholds for 0.5 and 1 kHz tone pip ABR may not be adequate to differentiate between SNHL and other conditions associated with AN/AD. There is a need for reviewing the existing AN/AD protocol from NHSP in the UK and new research to establish parameters for CM to assist in the differential diagnosis. A holistic audiological and medical approach is essential to manage babies who fail the newborn hearing screening. # 2008 Elsevier Ireland Ltd. All rights reserved.
1. Introduction * Corresponding author at: Lancashire Teaching Hospitals NHS Foundation Trust, Paediatric Audiology Centre, Fulwood Clinic, 4, Lytham Road, Fulwood, Preston PR2 8FH, United Kingdom. Tel.: +44 1772 401310; fax: +44 1772 713237. E-mail address: [email protected] (A. Ahmmed).
The hearing of all babies is now screened in the UK through the national universal Newborn Hearing Screening Programme (NHSP). Despite some studies unable to show superior language outcome between those detected with hearing loss at a
0165-5876/$ — see front matter # 2008 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ijporl.2008.05.003
1282 mean age of 6.6 months following newborn screening and those not screened and hearing loss detected at a mean age of 16.5 months [1], it is generally accepted that newborn hearing screening is an effective screening programme [2] with the primary goal of early detection and management of significant permanent hearing impairment. The early detection of hearing impairment has introduced issues that are distinctly separate from the hearing screening per se but intimately related to the ultimate success of the screening programme such as the challenges of fitting and managing hearing aids in young infants, support for such children and their families from education and social services, medical assessment and aetiological investigations and so on. These issues are evaluated and addressed in the UK through a NHSP quality assurance mechanism. One of the issues that have significant impact on the audiological as well as medical diagnosis and management in the post-screen failure phase include a pattern of electro-diagnostic test results where otoacoustic emissions (OAE) and/or cochlear microphonics (CM) are present along with absent or abnormal morphology of auditory brainstem response (ABR) at high stimulus levels. The term Auditory Neuropathy or Auditory De-synchrony (AN/ AD is used for such patterns of test results that occur in a small number of children with different conditions requiring different management and with different outcomes [3—6]. The NHSP in the UK has a protocol and policy for assessing and managing AN/ AD which suggests that either AN/AD or Sensorineural hearing loss (SNHL) should be suspected when either OAE or CM is present along with absent/ abnormal ABR response to air conduction click of 80 dBnHL or above [4,5]. In such a situation the distinction between SNHL and AN/AD is made by 1 kHz tone pip ABR, with a diagnosis of SNHL if response is better or present and a likely diagnosis of AN/AD if the response is still poor or absent [4,5]. It is crucial that a distinction between AN/AD and SNHL is made soon after the screen failure as the management and outcome in terms of audiological, early support and medical intervention will be significantly different. We present the findings from a baby that suggests that the mere presence of CM in the presence of significantly elevated click and 1 kHz tone pip ABR thresholds do not always rule out SNHL. The diagnostic dilemma and subsequent findings will reiterate the importance of a holistic audiological and medical assessment and management of children who fail the newborn hearing screening, a review of existing AN/AD protocol from NHSP and further research.
A. Ahmmed et al. Table 1 Diagnostic ABR thresholds following failing hearing screening Mode and side of stimulus
Stimuli
Threshold (dBnHL)
Bone
Click
>55
Right air conduction
Click 1 kHz tone 0.5 kHz tone
95 95 95
Left air conduction
Click 1 kHz tone 0.5 kHz tone
100 95 95
2. Case report 2.1. History Child AB was born at 38 weeks of gestation following an uncomplicated pregnancy and normal vaginal delivery. She was a healthy baby without any postnatal problems and was referred to our centre after failing her newborn hearing screening test. The electro-diagnostic assessments in the post screen failure period included air conduction ABR test using click and tone pips of 0.5 and 1 kHz and bone conduction ABR using click (Table 1) and measurement of CM from both ears. The CM traces from the left ear is shown in Fig. 1. OAE responses were absent but both the ears showed CM that reversed with changes in the stimulus polarity. ABR thresholds were way above 80 dBnHL for clicks and 0.5 and 1 kHz tone pips. In view of the results and the existing NHSP protocol/policy for AN/AD we adhere to in our centre the likelihood of AN/AD had to be considered in the initial clinical management and aetiological investigation [4,5]. AB, with the above electro-diagnostic test results, was seen along with her parents in the multidisciplinary tertiary paediatric audiology clinic involving Audiologist, Health Visitor, Audio-vestibular Physician and Teacher for the hearing impaired when she was about 6 weeks of age. She had no apparent behavioural response to sounds. Examination showed no dysmorphic features or any other abnormal physical findings. Both the tympanic membranes looked healthy and were mobile with Type A tympanograms.
2.2. Family history Father has unilateral moderate SNHL. There were no other known medical conditions that ran through the family. The cause of the fathers hearing loss was not investigated in the past. Examination at the time of baby daughter’s consultation it was found that he had synophrys and very blue irides.
Cochlear microphonics in sensorineural hearing loss
1283 Table 2 Visual reinforcement audiometry at 7 months of age Left insert (dB HL) Right insert (dB HL)
Fig. 1 Cochlear microphonics tracings from the left ear to 85 dBnHL. Note the reversal in the polarity of cochlear microphonic waves with condensation (Con) and the rarefraction (Rar) clicks.
2.3. Audiological/medical considerations and investigations In view of the presence of CM and poor ABR threshold AN/AD could not be ruled out. The baby did not have any neonatal history that usually accompanies, but not essential for, a diagnosis of auditory neuropathy [6,7]. The ABR was carried out using headphones while the CM was recorded using insert earphones, which meant that the actual intensity levels in the child’s ear canal could have been 10— 20 dB higher raising the possibility that CM in this child was generated at intensity levels above the ABR threshold. The NHSP AN/AD protocol only checks for CM at one intensity level of 80 or 85 dBnHL and no information regarding the CM threshold is available. The possibility of a SNHL could not therefore be ruled out. In view of the different possibilities to account for the audiological impairment detailed aetiological investigations had to be considered. The assessments included a detailed Paediatric examination, Ophthalmic assessment, MRI and CT scan of her inner ears and brain, ECG for QTc interval, TORCH, Urine for red cell and sugar, and hearing test of the parents and siblings.
0.5 kHz
1 kHz
2 kHz
4 kHz
90 90
85 90
90 105
85 115 NR
the child less than optimal recommended care if she had a SNHL instead of conditions that are more commonly associated with AN/AD and defeat the purpose of early detection and management ethos of the NHSP [2]. Secondly, there was also the management option with cochlear implant to consider. Thirdly, it was difficult to answer the parental question as to how long they may have to wait for a recovery, in case maturation of the auditory system was responsible for the impairment. The time can vary from 12 to 18 months [5] and the parents felt such information was vague and meaningless in the face of the uncertainty of diagnosis. Additionally, they were also anxious about the other possible causes of AN/AD and most appropriate intervention. Parents opted for a cautious amplification on one side only until a definitive diagnosis was reached. The unaided behavioural hearing thresholds at 7 months of age using insert visual reinforcement audiometry (VRA) were not significantly different from the ABR test results. The tympanic membranes were healthy with normal tympanograms. The VRA thresholds are given in Table 2.
2.5. Diagnosis and review of management Paediatric assessment showed no health issues other than the hearing impairment. MRI and CT scans showed bilateral enlarged vestibular aqueduct (EVA). Fig. 2 shows the EVAs in the two ears in the CT scan. MRI scan showed normal white matter myelination pattern and normal brain structures in addition to the EVA. In view of the findings in the CT and MRI scans, baby’s medical and family history noted earlier it was concluded that SNHL could give an AN/AD pattern of test results. In view of the child’s hearing loss associated with EVA and
2.4. Initial audiological considerations and management In the absence of a definite audiological diagnosis in this early stage deciding a management option for the child proved difficult. Firstly, in accordance to the NHSP AN/AD policy, a conservative approach with initial low gain hearing and a wait for a behavioural hearing threshold measurement for re-programming the aids would be appropriate [5]. However, such a management option would give
Fig. 2 Axial CT scan showing enlarged vestibular aqueducts in both the ears.
1284
A. Ahmmed et al.
Table 3 Binaural aided responses in the free field at 9 months of age 0.5 kHz 35 dB HL
1 kHz 45 dB HL
2 kHz 50 dB HL
4 kHz 70 dB HL
father’s hearing loss associated with synophrys and blue irides Waardenburg syndrome was considered as a possibility. Genetic referral was made for further investigation. Bilateral hearing aids were now fitted with gains appropriate for the behavioural hearing threshold. The parents were happy to notice responses to sounds with the hearing aids. At 9 months of age aided responses using VRA in the free field suggested poor responses for high frequency sounds compared to low frequency sounds (see Table 3). Referral to the regional Paediatric Cochlear Implant Programme was made to see if cochlear implant would give better access to high frequency sounds, which are important for optimal speech and language development.
3. Conclusion This case raises a number of important issues relevant to the management of some children who fail the newborn hearing screen. AN/AD is characterised by impairment of peripheral auditory function with preservation of outer hair cell (OHC) integrity, usually indicated by the detection of OAEs. OAE is absent in a large numbers of subject with AN, and the diagnosis in such cases depends on detection of CM in surface recordings [8]. In accordance with the present definition and diagnostic criteria, as laid in the NHSP guidelines and protocols in the UK, AN/AD had to be considered in our baby due to the presence of CM and poor ABR threshold exceeding 80 dBnHL [4,5]. The presence of CM in surface recordings has been considered a distinctive sign of OHC activity in auditory neuropathy but recent studies disputes such a claim [7]. CM is almost always detected in transtympanic electrocochleography in ears with varying degrees of SNHL including profound deafness [7,9]. The absence of CM in surface recording in some SNHL can be attributed to lower signal to noise ratio compared to transtympanic recordings [7]. SNHL with recruitment cause enhanced CM [10]. AN/AD and a number of central nervous system pathologies also facilitates CM recording due to impaired activity in the auditory efferent pathways to the cochlea [7]. In cases with relevant history and more typical findings of abnormal or absent ABR in the presence of OAE the diagnosis of AN/AD is
straightforward. However, in cases where ABR is present at very high stimulus intensity along with CM, as reported in this present case, the diagnosis of AN/AD is difficult and other possibilities needs to be considered. It would be very helpful to find out if there are any CM parameters that may distinguish between SNHL and the more typical cases of AN/AD. Transtympanic recording shows that CM is present at lower stimulus levels than that required for generating compound action potential (CAP) in subjects with elevated CAP thresholds. On the contrary in subjects with normal CAP thresholds the CM threshold was a lot higher than the CAP threshold [7]. Information regarding different parameters of CM using transtympanic recordings in normal hearing and hearing impairment including AN/AD is now available but such data are not available for surface recordings [7]. In accordance to the NHSP policy the CM in the baby in this case report was recorded from surface electrodes in response to 85 dBnHL clicks presented via insert earphones and the ABR was recorded separately using headphones. This caused a problem in directly comparing the actual intensity of the stimuli in the child’s ear canal that generated the CM to that of the ABR threshold. The 85 dBnHL click stimuli presented through inserts in the small ear canals of the young baby is most likely to increase the actual level of sound the child receives to about 100—105 dBnHL, raising possibility that CM was generated at levels above the ABR threshold, and hence suggesting SNHL. It is vital to note here that if the child did not have other clinical and imaging evidence to suggest SNHL the diagnosis on the basis of ABR and CM would have been very difficult and definitely delayed. The 80—85 dBnHL click stimuli for CM may be adequate for diagnosing AN/AD where ABR is absent around 100 dBnHL [5] but if AN/AD is to be considered when ABR threshold just exceeds 80 dBnHL (using headphones) the click stimuli for CM (using insert earphones) needs to be less than 80— 85 dBnHL to ensure that the CM is not generated at intensities above the ABR threshold. Our centre follows the national NHSP protocol/policy for AN/ AD and did not use lower intensity levels in the case reported. Consequently, we cannot comment if CM would have been recordable at intensity levels lower than the ABR threshold. Recording ABR and cochlear CM simultaneously using insert earphones, a method suggested by Berlin et al. [11], could give a clearer picture about the relationship between the stimulus levels generating ABR and CM. Many centres avoid inserts for ABR measurements due to calibration issues. The CM threshold is also not measured in the NHSP protocol we follow and therefore we could not compare the
Cochlear microphonics in sensorineural hearing loss CM threshold with that of the ABR threshold. Further research and guidance is required regarding the advantages of insert earphones in ABR measurement and the usefulness of CM threshold or other relevant parameters in differentiating between AN/AD and other types of hearing loss associated with CM in surface recordings. Our case shows that SNHL can present with AN/AD pattern of test results and that tone pip ABR at 1 kHz is not an adequate measure to differentiate between SNHL and AN/AD as suggested in the NHSP protocol [4]. We suggest that the existing NHSP policy and protocol for AN/AD in the UK [4,5] is reviewed in light of the above discussion. This case study stresses the importance of early medical history, examination and investigation in establishing the cause of hearing impairment that can change the audiological management option very dramatically. A diagnosis of SNHL was made from the family history, relevant physical features and findings of the MRI and CTscans. EVAs can be missed in milder cases without the expertise of an experienced Neuroradiologist [12]. We emphasise the need for the availability of such expertise throughout the country for the NHSP to be meaningful for the hearing impaired children and their families. The importance of a holistic approach in identifying syndromic conditions with atypical presentations is also demonstrated here. The father has one major (SNHL) and two minor (Blue Irides and Synophrys) Waardenburg Consortium criteria to suggest a diagnosis of Waardenburg type 1 syndrome [13]. In the absence of dystopia canthorum Waardenburg type II syndrome is, however, more likely but the father did not qualify Lui et al. criteria for type II Waardenburg syndrome [14]. The child’s hearing loss gave father the 2nd major criteria required for a diagnosis of type II Waardenburg syndrome [14]. EVA is seen in Waardenburg syndrome and such a finding strengthened the diagnostic criteria [15]. The findings of the child in this case report not only helped in the aetiological diagnosis of her hearing loss but also helped in solving the uncertainty surrounding her dads hearing loss. This case report should remind us that syndromic conditions may not present with all the common features of the condition, such as white forelock of hair or heterochromia irides in Waardenburg syndrome.
1285
References [1] E. Fitzpatrick, A. Durieux-Smith, A. Eriks-Brophy, J. Olds, R. Gaines, The impact of newborn hearing screening on communication development, J. Med. Screen. 14 (3) (2007) 123— 131. [2] C. Yoshinaga-Itano, From screening to early identification and intervention: discovering predictors to successful outcomes for children with significant hearing loss, J. Deaf Stud. Deaf Educ. 8 (1) (2003) 11—30. [3] A. Starr, Y. Sininger, T. Nguyen, H.J. Michalewski, S. Oba, C. Abdala, Cochlear receptor (microphonic and summating potentials, otoacoustic emissions) and auditory pathway (auditory brain stem potentials) activity in auditory neuropathy, Ear Hear. 22 (2) (2001) 91—99. [4] S. Wood, Auditory neuropathy policy-Appendix 1 (time line). Posted 17/12/04 NHSP web site. http://hearing.screening.nhs.uk/cms.php?folder=84. [5] G. Sutton (Ed.), Assessment and Management of Auditory Neuropathy/Auditory Dys-synchrony. A Recommended Protocol. October27, 2004. NHSP web site. [6] G. Parker, Personal communication, Auditory Neuropathy Policy–—Main Text, posted 17/12/04, NHSP website. http://hearing.screening.nhs.uk/cms.php?folder=84. [7] R. Santarelli, P. Scimemi, E. Dal Monte, E. Arslan, Cochlear microphonic potential recorded by transtympanic electrocochleography in normally hearing and hearing-impaired ears, Acta Otorhinolaryngol. Ital. 26 (2006) 78—95. [8] G. Rance, D.E. Beer, B. Cone-Wesson, R.K. Shepherd, R.C. Dowell, A.M. King, et al., Clinical findings for a group of infants and young children with auditory neuropathy, Ear Hear. 20 (1999) 238—252. [9] R. Schoonhoven, P.J.J. Lamore ´, J.A.P.M. De Laat, J.J. Grote, The prognostic value of electrocochleography in severely hearing impaired infants, Audiology 38 (1999) 141—154. [10] C. Liu, X. Chen, L. Xu, Cochlear microphonics and recruitment, Acta Otolaryngol. 112 (2) (1992) 215—220. [11] C.I. Berlin, J. Bordelon, P. St John, D. Wilensky, A. Hurley, E. Kluka, et al., Reversing click polarity may uncover auditory neuropathy in infants, Ear Hear. 19 (1998) 37—47. [12] D.E. Bamiou, P. Phelps, T. Sirimanna, Temporal bone computed tomography findings in bilateral sensorineural hearing loss, Arch. Dis. Child. 82 (2000) 257—260. [13] L.A. Farrer, K.M. Grundfast, J. Amos, K.S. Arnos, J.H. Asher, P. Beighton, et al., Waardenburg syndrome (WS) type 1 is caused by defects in multiple loci, one of which is near ALPP on chromosome 2: first report of the WS Consortium, Am. J. Hum. Genet. 50 (1992) 902—913. [14] X.Z. Liu, V.E. Newton, A.P. Read, Waardenburg syndrome Type 2: phenotypic findings and diagnostic criteria, Am. J. Med. Genet. 55 (1995) 95—100. [15] J.A. Gonza ´lez-Garcı´a, A. Iba ´n ˜ez, R. Ramı´rez-Camacho, A. Rodrı´guez, J.R. Garcı´a-Berrocal, A. Trinidad, Enlarged vestibular aqueduct: looking for genotypic—phenotypic correlations, Eur. Arch. Otorhinolaryngol. 263 (11) (2006) 971— 976.
Available online at www.sciencedirect.com
www.elsevier.com/locate/ijporl
CASE REPORT
Cochlear microphonics in sensorineural hearing loss: Lesson from newborn hearing screening Ansar Ahmmed a,*, Christopher Brockbank a, June Adshead b a b
Lancashire Teaching Hospitals NHS Foundation Trust, Preston, United Kingdom Sefton Paediatric Audiology Service, Southport, United Kingdom
Received 17 January 2008; received in revised form 5 May 2008; accepted 9 May 2008
KEYWORDS Cochlear microphonics; Auditory neuropathy; Auditory Dyssynchrony; Auditory brainstem response; Newborn Hearing Screening Programme; Sensorineural hearing loss; Enlarged vestibular aqueduct
Summary The diagnostic dilemma surrounding the presence of cochlear microphonics (CM) coupled with significantly elevated auditory brainstem response (ABR) thresholds in babies failing the newborn hearing screening is highlighted. A case report is presented where initial electo-diagnostic assessment could not help in differentiating between Auditory Neuropathy/Auditory Dys-synchrony (AN/AD) and sensorineural hearing loss (SNHL). In line with the protocol and guidelines provided by the national Newborn Hearing Screening Programme in the UK (NHSP) AN/AD was suspected in a baby due to the presence of CM at 85 dBnHL along with click evoked ABR thresholds of 95 dBnHL in one ear and 100 dBnHL in the other ear. Significantly elevated thresholds for 0.5 and 1 kHz tone pip ABR fulfilled the audiological diagnostic criteria for AN/AD. However, the possibility of a SNHL could not be ruled out as the 85 dBnHL stimuli presented through inserts for the CM would have been significantly enhanced in the ear canals of the young baby to exceed the threshold level of the ABR that was carried out using headphones. SNHL was eventually diagnosed through clinical and family history, physical examination and imaging that showed enlarged vestibular aqueducts. Presence of CM in the presence of very high click ABR thresholds only suggests a pattern of test results and in such cases measuring thresholds for 0.5 and 1 kHz tone pip ABR may not be adequate to differentiate between SNHL and other conditions associated with AN/AD. There is a need for reviewing the existing AN/AD protocol from NHSP in the UK and new research to establish parameters for CM to assist in the differential diagnosis. A holistic audiological and medical approach is essential to manage babies who fail the newborn hearing screening. # 2008 Elsevier Ireland Ltd. All rights reserved.
1. Introduction * Corresponding author at: Lancashire Teaching Hospitals NHS Foundation Trust, Paediatric Audiology Centre, Fulwood Clinic, 4, Lytham Road, Fulwood, Preston PR2 8FH, United Kingdom. Tel.: +44 1772 401310; fax: +44 1772 713237. E-mail address: [email protected] (A. Ahmmed).
The hearing of all babies is now screened in the UK through the national universal Newborn Hearing Screening Programme (NHSP). Despite some studies unable to show superior language outcome between those detected with hearing loss at a
0165-5876/$ — see front matter # 2008 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ijporl.2008.05.003
1282 mean age of 6.6 months following newborn screening and those not screened and hearing loss detected at a mean age of 16.5 months [1], it is generally accepted that newborn hearing screening is an effective screening programme [2] with the primary goal of early detection and management of significant permanent hearing impairment. The early detection of hearing impairment has introduced issues that are distinctly separate from the hearing screening per se but intimately related to the ultimate success of the screening programme such as the challenges of fitting and managing hearing aids in young infants, support for such children and their families from education and social services, medical assessment and aetiological investigations and so on. These issues are evaluated and addressed in the UK through a NHSP quality assurance mechanism. One of the issues that have significant impact on the audiological as well as medical diagnosis and management in the post-screen failure phase include a pattern of electro-diagnostic test results where otoacoustic emissions (OAE) and/or cochlear microphonics (CM) are present along with absent or abnormal morphology of auditory brainstem response (ABR) at high stimulus levels. The term Auditory Neuropathy or Auditory De-synchrony (AN/ AD is used for such patterns of test results that occur in a small number of children with different conditions requiring different management and with different outcomes [3—6]. The NHSP in the UK has a protocol and policy for assessing and managing AN/ AD which suggests that either AN/AD or Sensorineural hearing loss (SNHL) should be suspected when either OAE or CM is present along with absent/ abnormal ABR response to air conduction click of 80 dBnHL or above [4,5]. In such a situation the distinction between SNHL and AN/AD is made by 1 kHz tone pip ABR, with a diagnosis of SNHL if response is better or present and a likely diagnosis of AN/AD if the response is still poor or absent [4,5]. It is crucial that a distinction between AN/AD and SNHL is made soon after the screen failure as the management and outcome in terms of audiological, early support and medical intervention will be significantly different. We present the findings from a baby that suggests that the mere presence of CM in the presence of significantly elevated click and 1 kHz tone pip ABR thresholds do not always rule out SNHL. The diagnostic dilemma and subsequent findings will reiterate the importance of a holistic audiological and medical assessment and management of children who fail the newborn hearing screening, a review of existing AN/AD protocol from NHSP and further research.
A. Ahmmed et al. Table 1 Diagnostic ABR thresholds following failing hearing screening Mode and side of stimulus
Stimuli
Threshold (dBnHL)
Bone
Click
>55
Right air conduction
Click 1 kHz tone 0.5 kHz tone
95 95 95
Left air conduction
Click 1 kHz tone 0.5 kHz tone
100 95 95
2. Case report 2.1. History Child AB was born at 38 weeks of gestation following an uncomplicated pregnancy and normal vaginal delivery. She was a healthy baby without any postnatal problems and was referred to our centre after failing her newborn hearing screening test. The electro-diagnostic assessments in the post screen failure period included air conduction ABR test using click and tone pips of 0.5 and 1 kHz and bone conduction ABR using click (Table 1) and measurement of CM from both ears. The CM traces from the left ear is shown in Fig. 1. OAE responses were absent but both the ears showed CM that reversed with changes in the stimulus polarity. ABR thresholds were way above 80 dBnHL for clicks and 0.5 and 1 kHz tone pips. In view of the results and the existing NHSP protocol/policy for AN/AD we adhere to in our centre the likelihood of AN/AD had to be considered in the initial clinical management and aetiological investigation [4,5]. AB, with the above electro-diagnostic test results, was seen along with her parents in the multidisciplinary tertiary paediatric audiology clinic involving Audiologist, Health Visitor, Audio-vestibular Physician and Teacher for the hearing impaired when she was about 6 weeks of age. She had no apparent behavioural response to sounds. Examination showed no dysmorphic features or any other abnormal physical findings. Both the tympanic membranes looked healthy and were mobile with Type A tympanograms.
2.2. Family history Father has unilateral moderate SNHL. There were no other known medical conditions that ran through the family. The cause of the fathers hearing loss was not investigated in the past. Examination at the time of baby daughter’s consultation it was found that he had synophrys and very blue irides.
Cochlear microphonics in sensorineural hearing loss
1283 Table 2 Visual reinforcement audiometry at 7 months of age Left insert (dB HL) Right insert (dB HL)
Fig. 1 Cochlear microphonics tracings from the left ear to 85 dBnHL. Note the reversal in the polarity of cochlear microphonic waves with condensation (Con) and the rarefraction (Rar) clicks.
2.3. Audiological/medical considerations and investigations In view of the presence of CM and poor ABR threshold AN/AD could not be ruled out. The baby did not have any neonatal history that usually accompanies, but not essential for, a diagnosis of auditory neuropathy [6,7]. The ABR was carried out using headphones while the CM was recorded using insert earphones, which meant that the actual intensity levels in the child’s ear canal could have been 10— 20 dB higher raising the possibility that CM in this child was generated at intensity levels above the ABR threshold. The NHSP AN/AD protocol only checks for CM at one intensity level of 80 or 85 dBnHL and no information regarding the CM threshold is available. The possibility of a SNHL could not therefore be ruled out. In view of the different possibilities to account for the audiological impairment detailed aetiological investigations had to be considered. The assessments included a detailed Paediatric examination, Ophthalmic assessment, MRI and CT scan of her inner ears and brain, ECG for QTc interval, TORCH, Urine for red cell and sugar, and hearing test of the parents and siblings.
0.5 kHz
1 kHz
2 kHz
4 kHz
90 90
85 90
90 105
85 115 NR
the child less than optimal recommended care if she had a SNHL instead of conditions that are more commonly associated with AN/AD and defeat the purpose of early detection and management ethos of the NHSP [2]. Secondly, there was also the management option with cochlear implant to consider. Thirdly, it was difficult to answer the parental question as to how long they may have to wait for a recovery, in case maturation of the auditory system was responsible for the impairment. The time can vary from 12 to 18 months [5] and the parents felt such information was vague and meaningless in the face of the uncertainty of diagnosis. Additionally, they were also anxious about the other possible causes of AN/AD and most appropriate intervention. Parents opted for a cautious amplification on one side only until a definitive diagnosis was reached. The unaided behavioural hearing thresholds at 7 months of age using insert visual reinforcement audiometry (VRA) were not significantly different from the ABR test results. The tympanic membranes were healthy with normal tympanograms. The VRA thresholds are given in Table 2.
2.5. Diagnosis and review of management Paediatric assessment showed no health issues other than the hearing impairment. MRI and CT scans showed bilateral enlarged vestibular aqueduct (EVA). Fig. 2 shows the EVAs in the two ears in the CT scan. MRI scan showed normal white matter myelination pattern and normal brain structures in addition to the EVA. In view of the findings in the CT and MRI scans, baby’s medical and family history noted earlier it was concluded that SNHL could give an AN/AD pattern of test results. In view of the child’s hearing loss associated with EVA and
2.4. Initial audiological considerations and management In the absence of a definite audiological diagnosis in this early stage deciding a management option for the child proved difficult. Firstly, in accordance to the NHSP AN/AD policy, a conservative approach with initial low gain hearing and a wait for a behavioural hearing threshold measurement for re-programming the aids would be appropriate [5]. However, such a management option would give
Fig. 2 Axial CT scan showing enlarged vestibular aqueducts in both the ears.
1284
A. Ahmmed et al.
Table 3 Binaural aided responses in the free field at 9 months of age 0.5 kHz 35 dB HL
1 kHz 45 dB HL
2 kHz 50 dB HL
4 kHz 70 dB HL
father’s hearing loss associated with synophrys and blue irides Waardenburg syndrome was considered as a possibility. Genetic referral was made for further investigation. Bilateral hearing aids were now fitted with gains appropriate for the behavioural hearing threshold. The parents were happy to notice responses to sounds with the hearing aids. At 9 months of age aided responses using VRA in the free field suggested poor responses for high frequency sounds compared to low frequency sounds (see Table 3). Referral to the regional Paediatric Cochlear Implant Programme was made to see if cochlear implant would give better access to high frequency sounds, which are important for optimal speech and language development.
3. Conclusion This case raises a number of important issues relevant to the management of some children who fail the newborn hearing screen. AN/AD is characterised by impairment of peripheral auditory function with preservation of outer hair cell (OHC) integrity, usually indicated by the detection of OAEs. OAE is absent in a large numbers of subject with AN, and the diagnosis in such cases depends on detection of CM in surface recordings [8]. In accordance with the present definition and diagnostic criteria, as laid in the NHSP guidelines and protocols in the UK, AN/AD had to be considered in our baby due to the presence of CM and poor ABR threshold exceeding 80 dBnHL [4,5]. The presence of CM in surface recordings has been considered a distinctive sign of OHC activity in auditory neuropathy but recent studies disputes such a claim [7]. CM is almost always detected in transtympanic electrocochleography in ears with varying degrees of SNHL including profound deafness [7,9]. The absence of CM in surface recording in some SNHL can be attributed to lower signal to noise ratio compared to transtympanic recordings [7]. SNHL with recruitment cause enhanced CM [10]. AN/AD and a number of central nervous system pathologies also facilitates CM recording due to impaired activity in the auditory efferent pathways to the cochlea [7]. In cases with relevant history and more typical findings of abnormal or absent ABR in the presence of OAE the diagnosis of AN/AD is
straightforward. However, in cases where ABR is present at very high stimulus intensity along with CM, as reported in this present case, the diagnosis of AN/AD is difficult and other possibilities needs to be considered. It would be very helpful to find out if there are any CM parameters that may distinguish between SNHL and the more typical cases of AN/AD. Transtympanic recording shows that CM is present at lower stimulus levels than that required for generating compound action potential (CAP) in subjects with elevated CAP thresholds. On the contrary in subjects with normal CAP thresholds the CM threshold was a lot higher than the CAP threshold [7]. Information regarding different parameters of CM using transtympanic recordings in normal hearing and hearing impairment including AN/AD is now available but such data are not available for surface recordings [7]. In accordance to the NHSP policy the CM in the baby in this case report was recorded from surface electrodes in response to 85 dBnHL clicks presented via insert earphones and the ABR was recorded separately using headphones. This caused a problem in directly comparing the actual intensity of the stimuli in the child’s ear canal that generated the CM to that of the ABR threshold. The 85 dBnHL click stimuli presented through inserts in the small ear canals of the young baby is most likely to increase the actual level of sound the child receives to about 100—105 dBnHL, raising possibility that CM was generated at levels above the ABR threshold, and hence suggesting SNHL. It is vital to note here that if the child did not have other clinical and imaging evidence to suggest SNHL the diagnosis on the basis of ABR and CM would have been very difficult and definitely delayed. The 80—85 dBnHL click stimuli for CM may be adequate for diagnosing AN/AD where ABR is absent around 100 dBnHL [5] but if AN/AD is to be considered when ABR threshold just exceeds 80 dBnHL (using headphones) the click stimuli for CM (using insert earphones) needs to be less than 80— 85 dBnHL to ensure that the CM is not generated at intensities above the ABR threshold. Our centre follows the national NHSP protocol/policy for AN/ AD and did not use lower intensity levels in the case reported. Consequently, we cannot comment if CM would have been recordable at intensity levels lower than the ABR threshold. Recording ABR and cochlear CM simultaneously using insert earphones, a method suggested by Berlin et al. [11], could give a clearer picture about the relationship between the stimulus levels generating ABR and CM. Many centres avoid inserts for ABR measurements due to calibration issues. The CM threshold is also not measured in the NHSP protocol we follow and therefore we could not compare the
Cochlear microphonics in sensorineural hearing loss CM threshold with that of the ABR threshold. Further research and guidance is required regarding the advantages of insert earphones in ABR measurement and the usefulness of CM threshold or other relevant parameters in differentiating between AN/AD and other types of hearing loss associated with CM in surface recordings. Our case shows that SNHL can present with AN/AD pattern of test results and that tone pip ABR at 1 kHz is not an adequate measure to differentiate between SNHL and AN/AD as suggested in the NHSP protocol [4]. We suggest that the existing NHSP policy and protocol for AN/AD in the UK [4,5] is reviewed in light of the above discussion. This case study stresses the importance of early medical history, examination and investigation in establishing the cause of hearing impairment that can change the audiological management option very dramatically. A diagnosis of SNHL was made from the family history, relevant physical features and findings of the MRI and CTscans. EVAs can be missed in milder cases without the expertise of an experienced Neuroradiologist [12]. We emphasise the need for the availability of such expertise throughout the country for the NHSP to be meaningful for the hearing impaired children and their families. The importance of a holistic approach in identifying syndromic conditions with atypical presentations is also demonstrated here. The father has one major (SNHL) and two minor (Blue Irides and Synophrys) Waardenburg Consortium criteria to suggest a diagnosis of Waardenburg type 1 syndrome [13]. In the absence of dystopia canthorum Waardenburg type II syndrome is, however, more likely but the father did not qualify Lui et al. criteria for type II Waardenburg syndrome [14]. The child’s hearing loss gave father the 2nd major criteria required for a diagnosis of type II Waardenburg syndrome [14]. EVA is seen in Waardenburg syndrome and such a finding strengthened the diagnostic criteria [15]. The findings of the child in this case report not only helped in the aetiological diagnosis of her hearing loss but also helped in solving the uncertainty surrounding her dads hearing loss. This case report should remind us that syndromic conditions may not present with all the common features of the condition, such as white forelock of hair or heterochromia irides in Waardenburg syndrome.
1285
References [1] E. Fitzpatrick, A. Durieux-Smith, A. Eriks-Brophy, J. Olds, R. Gaines, The impact of newborn hearing screening on communication development, J. Med. Screen. 14 (3) (2007) 123— 131. [2] C. Yoshinaga-Itano, From screening to early identification and intervention: discovering predictors to successful outcomes for children with significant hearing loss, J. Deaf Stud. Deaf Educ. 8 (1) (2003) 11—30. [3] A. Starr, Y. Sininger, T. Nguyen, H.J. Michalewski, S. Oba, C. Abdala, Cochlear receptor (microphonic and summating potentials, otoacoustic emissions) and auditory pathway (auditory brain stem potentials) activity in auditory neuropathy, Ear Hear. 22 (2) (2001) 91—99. [4] S. Wood, Auditory neuropathy policy-Appendix 1 (time line). Posted 17/12/04 NHSP web site. http://hearing.screening.nhs.uk/cms.php?folder=84. [5] G. Sutton (Ed.), Assessment and Management of Auditory Neuropathy/Auditory Dys-synchrony. A Recommended Protocol. October27, 2004. NHSP web site. [6] G. Parker, Personal communication, Auditory Neuropathy Policy–—Main Text, posted 17/12/04, NHSP website. http://hearing.screening.nhs.uk/cms.php?folder=84. [7] R. Santarelli, P. Scimemi, E. Dal Monte, E. Arslan, Cochlear microphonic potential recorded by transtympanic electrocochleography in normally hearing and hearing-impaired ears, Acta Otorhinolaryngol. Ital. 26 (2006) 78—95. [8] G. Rance, D.E. Beer, B. Cone-Wesson, R.K. Shepherd, R.C. Dowell, A.M. King, et al., Clinical findings for a group of infants and young children with auditory neuropathy, Ear Hear. 20 (1999) 238—252. [9] R. Schoonhoven, P.J.J. Lamore ´, J.A.P.M. De Laat, J.J. Grote, The prognostic value of electrocochleography in severely hearing impaired infants, Audiology 38 (1999) 141—154. [10] C. Liu, X. Chen, L. Xu, Cochlear microphonics and recruitment, Acta Otolaryngol. 112 (2) (1992) 215—220. [11] C.I. Berlin, J. Bordelon, P. St John, D. Wilensky, A. Hurley, E. Kluka, et al., Reversing click polarity may uncover auditory neuropathy in infants, Ear Hear. 19 (1998) 37—47. [12] D.E. Bamiou, P. Phelps, T. Sirimanna, Temporal bone computed tomography findings in bilateral sensorineural hearing loss, Arch. Dis. Child. 82 (2000) 257—260. [13] L.A. Farrer, K.M. Grundfast, J. Amos, K.S. Arnos, J.H. Asher, P. Beighton, et al., Waardenburg syndrome (WS) type 1 is caused by defects in multiple loci, one of which is near ALPP on chromosome 2: first report of the WS Consortium, Am. J. Hum. Genet. 50 (1992) 902—913. [14] X.Z. Liu, V.E. Newton, A.P. Read, Waardenburg syndrome Type 2: phenotypic findings and diagnostic criteria, Am. J. Med. Genet. 55 (1995) 95—100. [15] J.A. Gonza ´lez-Garcı´a, A. Iba ´n ˜ez, R. Ramı´rez-Camacho, A. Rodrı´guez, J.R. Garcı´a-Berrocal, A. Trinidad, Enlarged vestibular aqueduct: looking for genotypic—phenotypic correlations, Eur. Arch. Otorhinolaryngol. 263 (11) (2006) 971— 976.
Available online at www.sciencedirect.com