- Email: [email protected]
Diagnosing hearing problems in children
Current Paediatrics (2000) 10, 200–205 © 2000 Harcourt Publishers Ltd doi:10.1054/ cupe.2000.0099, available online at http://www.idealibrary.com on
Symposium: Hearing problems
Diagnosing hearing problems in children
B. McCormick
those fitted after 6 months.1 Such findings have prompted further debate about the need to introduce neonatal hearing screening programmes at a time when doubts have been cast on the viability of maintaining high-quality community hearing screening programmes in the hands of health visitors. There is general concern about the poor record of success with the Health Visitor Distraction Test (HVDT) as a screening tool when viewed nationwide, rather than in a few locations where it is known to produce good results. It is also argued that hearing problems should be detected before the age at which the distraction test can be performed. Over the next few years there will be a radical change in the way hearing screening services are administered and although there should be long-term benefits there will inevitably be short-term disruptions. It is vital to support health visitors with their training needs during this period of transition. Their enthusiasm is waning with all the criticism they have received and there is a danger that the thousands of deaf babies, born before the neonatal screening screen is in place, will face an even poorer quality of service if standards decline further. There is an urgent need for services to address the current training needs of health visitors and to improve the standards of community hearing screening over the next 5 years or so. There will, after all, be an additional 5000 deaf babies born over that period.
KEY POINTS
• • • •
•
There is an urgent need for health visitors to review their performance with the distraction test and generally to improve standards. The distraction test will be with us for at least another 5 years before it will be replaced by Universal Neonatal Hearing Screening (UNHS). Major sources of funding and additional service planning will be needed before UHNS can be introduced. Services must be family friendly. No child is too young to be considered for hearing aid or cochlear implant assessment. Generally, the younger these devices are supplied, the better the eventual outcome for the child. Audiological test techniques are now very refined and can be applied from a few weeks of age. Cochlear implants will enable many more deaf children to develop spoken language skills and the number of children requiring sign language as their primary means of communication will decline.
INTRODUCTION There is mounting evidence that early detection of hearing problems and prompt remedial treatment can have permanent beneficial effects. Yoshinaga-Itano demonstrated that deaf children fitted with hearing aids before 6 months of age later showed better expressive and receptive language development than
PERMANENT CHILDHOOD DEAFNESS Between one and two children per 1000 population have permanent childhood deafness of sufficient degree to require hearing aids, cochlear implants or a manual means of communication. Thus in the UK, about 1000 new cases will appear each year. According to Davis et al:2
Barry McCormick OBE, PhD, Special Professor in Paediatric Audiology, Queen’s Medical Centre University Hospital NHS Trust, Nottingham, UK. Correspondence to BMCC.
200
Diagnosing hearing problems in children
201
• 840 (84%) will be born deaf; • 50% of these cases will have moderate hearing losses (40–69 dB); • 25% will have severe hearing losses (70–90 dB); • 25% will have profound hearing losses (>90 dB); • An additional 158 (16%) will acquire bilateral deafness before 5 years of age. With the introduction of cochlear implants over the past decade,3,4 many more deaf children will have access to spoken language as their primary means of communication. In the future, very few will be unable to benefit from hearing aids or cochlear implants and there will inevitably be a decline in the numbers requiring sign language as their main means of communication. Some members of the deaf community are very unhappy about their anticipated decline in numbers and they oppose the use of hearing aids and cochlear implants. Over 90% of deaf children are, however, born into hearing families and it is only natural for these families to want their children to be able to hear and share their spoken language through the use of new hearing aid and cochlear implant technology. It is likely that the vast majority of profoundly deaf children, for whom hearing aids are of limited benefit, will be able to make effective use of cochlear implants if the systems are provided early enough in the child’s life. By early in this context, we mean well within the first 5 years of life and preferably within the first 2 years. Current debate about hearing aid provision favours the fitting of these instruments within the first few months of life,1,2 and this argument will, no doubt, extend to cochlear implant provision in the near future. Although it may be desirable to fit these instruments early, our present record of success with early detection of hearing problems is not good and leaves much to be desired across the UK as a whole. It is useful to take stock of the present situation.
THE HISTORY AND FUTURE OF THE HEALTH VISITOR DISTRACTION TEST (HVDT) This test has been with us since the 1940s and was first described by Ewing and Ewing in 1944.5 It was extensively modified and improved by McCormick during the 1980s.6–8 The test works on the principle noted by the Ewings that the normal response for a baby of 6–7 months of age is to turn to locate the source of a sound. By presenting a series of quiet sounds of different frequencies, it is possible to ensure that the child has sufficiently good hearing to develop normal language. The sounds must be presented out of vision and with no inadvertent clues to indicate the presence of the tester behind the child. A typical test situation is shown in Fig. 1. Despite considerable effort with the development of this screening method and a proven track record of
Fig. 1
Typical test arrangement for a distraction test.
success in a few districts,9,10 the general picture nationwide is very disappointing.11,12 The reason for this appears to be a general lack of compliance with welldefined quality standards and poor local training support for health visitors. Davis and Wood9 reported excellent results for the distraction test in the Nottingham district which, over a 4-year period, achieved a coverage of 96% and a sensitivity of 88% for hearing losses greater than 50 dB. The mean age at referral for babies with severe and profound hearing losses was 8 months. Watkins10 reported a distraction test sensitivity of 93% for severe and profound hearing losses. Both of these studies showed that with sufficient support and with thorough training, health visitors could maintain an excellent level of performance with the HVDT. In both studies, however, the test did not perform so well for children with mild or moderate degrees of hearing loss, and if the identification and treatment of babies with lesser degrees of hearing loss is considered to be important within their first year of life, it will be necessary to seek an alternative form of testing. In a follow-up study of the performance of the HVDT in the Nottingham district,13 a decline in the success rate was recorded which was surbsequently attributed to re-organized management arrangements. This resulted in the lack of availability of refresher courses for health visitors over a 2-year period. As soon as this problem was identified and rectified the success rate was restored to the previous good level of performance.14 This did, however, demonstrate the vulnerability of this form of community screening and also the need for each provider unit to have access to a vigilant audiological overview and to a high level of training for health visitors, which is evidently lacking in many areas. In their 1997 Health Technology Assessment Report, Davis et al quoted only the median age of detection for all degrees of hearing loss. Not surprisingly, this painted a very gloomy picture of very late ascertainment of hearing loss nationwide.2 The same
202
Current Paediatrics
picture emerged from a very large regional study reported by Fortnum and Davis.15 They reported a median age of ascertainment of 20 months for all degrees of hearing loss. Hidden within the data is a more enlightening picture of success, with the median age of identification being 11 months for severe hearing loss and 9 months for profound hearing loss. The general conclusion, however, is that all hearing losses should be identified before the age at which the HVDT is performed and universal neonatal hearing screening must be introduced to achieve this objective. This recommendation has been considered and accepted by the National Screening Committee and there will be significant consequences for community and acute services as the focus of attention gradually shifts from the HVDT to the neonatal unit. The reality of the situation is that universal neonatal hearing screening cannot possibly be introduced without the injection of new cash and new resources. It is unlikely that there will be a transfer of funds from the health visitor budgets to the acute sector. There are also other issues to be considered, including the readiness of services to provide a ‘family friendly’ follow-up and audiological diagnostic and hearing aid fitting service for babies of a few weeks of age (during the sensitive parent–child bonding period). The experience base for neonatal screening in a routine service context is limited and the skilled personnel required to satisfy these needs are in short supply in the UK. Assuming that these obstacles will be overcome within the next few years, what options are available for neonatal hearing screening and for confirming the presence of hearing loss in audiology clinics?
NEONATAL HEARING SCREENING TEST METHODS Otoacoustic emissions tests (OAE) This is the most popular form of test because of its ease of application with minimum preparation and short test time. Otoacoustic emissions (cochlear echoes) were first recorded by Kemp16 and are believed to arise from the active biomechanics of the cochlear sensory mechanism at a preneural level. Various portable versions of test equipment are now commercially available. A soft tipped probe arrangement is placed in the ear canal to record the acoustic signals and this forms the only contact with the child (Fig. 2). The emissions are only present if the cochlear is functioning and the test takes only a minute or so to perform. Pilot studies using this method have met with considerable success. It must be remembered, however, that the OAE does not check the entire hearing pathway and it cannot detect retro-cochlea pathologies. Fortunately pure retro-cochlea pathologies are very rare and the vast majority of deafness in childhood should be detectable from the use of OAE measurements.
Fig. 2 Using a hand-held otoacoustic emissions test system on a 7-month-old baby.
Fig. 3 Undertaking a diagnostic distraction test with an electronic noise generator.
Auditory brain stem response testing (ABR) This technique records sound induced electrical activity in the brain utilizing surface mounted electrodes positioned on the scalp. The test has the advantage that it enables hearing to be screened at any predetermined level (mostly 40 dB or 50 dB in practice) and it tests the integrity of the system beyond the cochlea. The test does require more preparation with the need to position the electrodes on the scalp and to obtain a good electrical contact whilst maintaining the baby in a calm and quiet state. The test takes longer to perform than the OAE method, with a typical test time of 20 min rather than a minute or so for the OAE test. The portable auditory response cradle (PARC) This equipment uses microchip technology with transducers positioned around the baby to record behavioural responses to sound. It has the advantage that it records responses though the entire auditory pathway. Problems have been found with the use of an early version of this equipment with special care babies,17 but Tucker and Bhattacharya18 have reported good result in their screening programme.
Diagnosing hearing problems in children
203
A
B
Fig. 5
The use of inset ear phones with a 7-month-old baby.
Diagnostic distraction testing
Fig. 4 A typical set up for a visual reinforcement audiometry test with a lighting up reward adjacent to the speaker.
Nevertheless most workers prefer to use the OAE or ABR methods now that convenient portable versions of the equipment are readily available. BEYOND THE SCREEN—TESTS FOR CONFIRMING THE PRESENCE OF HEARING PROBLEMS Diagnostic auditory brain stem response testing As an objective test of hearing function, the ABR takes pride of place. In skilled hands and in a controlled environment it is possible to record responses very close to the child’s hearing thresholds and this makes the test very useful for application with children who are difficult to test by behavioural means, either because they are very young or because they have other difficulties. The use of click stimuli enable hearing thresholds in the mid to high frequency region (centred on 2.5–3 kHz) to be explored and the use of tone pips enables lower frequency thresholds (around 1 kHz) to be checked.19 It is also possible to undertake bone conduction threshold measurements. If access to skilled behavioural testing is available in an audiology service, the support of diagnostic ABR will be needed in about 3% of cases.20 This figure will rise with the introduction of neonatal hearing screening as more neonates appear for investigation within the system.
The distraction test still has application at the diagnostic level despite the widespread and increasing popularity of visual reinforcement audiometry (VRA). Not all infants will respond to a VRA procedure: when VRA works it is excellent but some children are unresponsive for reasons other than hearing impairment. A big advantage of the distraction test is that the child’s general response state can be checked using other modalities such as visual clues or tactile clues. If a child turns quickly to a touch on the ear, or to an object brought into peripheral vision, but fails to respond to certain sound, then this will indicate the presence of deafness for those sounds. The hearing thresholds for a wide range of frequency-specific sounds can be measured fairly quickly by two skilled testers using sound generators in the typical test situation (shown in Fig. 3). Perhaps the biggest advantages of the distraction test are that the child’s attention can be controlled in a very refined and structured way and a wide and rapidly changing range of calibrated sound stimuli can be used. The sound can also be presented very close to each ear, thus enabling the thresholds in each ear to be checked without having to make physical contact with the child. This is a particularly useful option for babies who are disturbed by the use of headphones or insert earphones but for whom a difference in the responsiveness of the two ears is suspected. Visual reinforcement audiometry (VRA) A typical set-up for VRA is shown in Fig. 4(A,B). The test utilizes a calibrated loudspeaker arrangement for presenting the sounds, and the child’s responses, normally in the form of head turns, are rewarded with some form of visual display, for example a puppet lighting up in a box. The hearing thresholds are chased by varying the stimulus levels in the same way as with the distraction test. The main difference between this form of testing and distraction testing is the absence of a tester behind the child and inclusion
204
Current Paediatrics
Fig. 6 The use of a bone conductor with a 7-month-old baby.
Fig. 8
Undertaking the McCormick Toy Discrimination test.
the child to hear conversational levels of voice, the possibility of cochlear implantation or a sign language approach should be considered. The youngest child to have been implanted in the UK was just 6 months old and babies as young as 6 weeks of age have been supplied with hearing aids.
TESTING OLDER CHILDREN
Fig. 7 Undertaking the performance test using a hand-held warbler.
of a mechanical/electronic response reward system. It is possible to calibrate the speaker (sound field) stimuli very precisely and to measure a child’s hearing thresholds with slightly more precision (5 dB or so). The use of insert earphones (Fig. 5) adds to the precision and enables each ear to be tested independently. It is also possible to utilize a bone conductor (Fig. 6) to chase the bone conduction thresholds. Normally up to 20 responses can be obtained before the child loses interest in the task.
AT WHAT AGE CAN HEARING AIDS AND COCHLEAR IMPLANTS BE PROVIDED? Using a combination of the above objective and behavioural tests it should be possible to obtain sufficient audiological data to know whether hearing aids are needed with babies as young as 6 months and even younger in exceptional circumstances. The investigations can then be repeated with the use of hearing aids and, if the aided hearing thresholds do not enable
This article has concentrated on babies with permanent hearing losses. It must be remembered that 15% of permanent deafness will be postnatally acquired and there must be a system in place to detect these cases. Approximately 6% of all children will experience fluctuating conductive hearing loss at some stage. The techniques for testing infants and toddlers are very straightforward if a child can be conditioned to perform conventional audiometry. In the community it should be possible to obtain an audiogram from a 4-year-old child without too much difficulty. Prior to this the performance test (Fig. 7), which is a simplified form of play audiometry, can be applied by health visitors. In audiology clinics skilled clinicians can sometimes obtain conventional audiometric results with 2-year-old children. Simple speech discrimination testing can be performed in the community by 2 years of age, for example the McCormick Toy Discrimination Test21 (Fig. 8), and most health visitors will have been trained to undertake this form of testing in addition to the performance test. If there are suspicions about any child’s hearing following illness, because of failure to develop clear speech or because of family history of deafness, a screening test should be arranged without delay and a referral made to the audiology clinic if there are any doubts about the responses. Within the constraints of this article it has only been possible to give a general overview of the various test techniques The reader is referred to The Medical Practitioner’s Guide to Paediatric Audiology for more detailed coverage.22
Diagnosing hearing problems in children CONCLUSIONS Radical changes in the way we detect and manage hearing impairment are on the horizon. The way in which this change is managed will determine the future potential of deaf children. Now, more than at any time in the past, the onus is on services to assess their present level of performance, to improve this level urgently in the short term and to prepare for the new neonatal hearing screening service. REFERENCES 1. Yoshinaga-Itano C, Sedey AL, Coulter DK, Mehl AL. Language of early and late identified children with hearing loss. Pediatrics 1998; 102: 1161–1171. 2. Davis A, Bamford J, Wilson I, Ramkalawan T, Forshaw M, Wright S. A critical review of the role of neonatal hearing screening in the detection of congenital hearing-impairment. Health Technol Assessment 1997; 1(10). 3. McCormick B. Cochlear implantation in the UK: a delayed journey on a well marked route. Br J Audiol 1991; 25: 145–149. 4. McCormick B. Paediatric audiology and cochlear implantation in the UK: taking off in the fast lane. Br J Audiol 1997; 31: 303–307. 5. Ewing IR, Ewing AWC. The ascertainment of deafness in infancy and early childhood. J Laryngol Otolo 1944; 309–333. 6. McCormick B. Hearing screening by health visitors: a critical appraisal of the Distraction Test. Health Visitor 1983; 56: 449–451. 7. McCormick B. Evaluation of a warbler in hearing screening tests. Health Visitor 1986; 59: 143–144. 8. McCormick B. Screening for Hearing Impairment in Young Children. London: Whurr Publishers; 1988. 9. Davis A, Wood S. The epidemiology of childhood hearingimpairment: factors relevant to planning of services. Br J Audiol 1992; 26: 77–90.
205
10. Watkin PM, Baldwin M, Laoide S. Parental suspicion and identification of hearing impairment. Arch Dis Child 1990; 65: 846–850. 11. Sutton GJ, Scanlon PE. Health visitor screening versus vigilance: outcomes of programmes for detecting permanent childhood hearing loss in West Berkshire. Br J Audiol 1999; 33: 145–156. 12. Fonseca S, Forsyth H, Grigor J, Lowe J, MacKinnon M, Price E, Rose S, Scanlon P, Umpathy D. Identification of permanent hearing loss in children: are the targets for outcome measures attainable? Br J Audiol 1999; 33: 135–143. 13. Wood S, Davis A, McCormick B. Changing yield of the health visitor distraction test when targeted neonatal screening is introduced into a health district. Br J Audiol 1997; 31: 55–61. 14. McCormick B. Managing the transition to Universal Neonatal Hearing Screening—the missing link. Br J Audiol 2000; 34: 67–70 [letter]. 15. Fortnum H, Davis A. Epidemiology of permanent childhood hearing impairment in Trent Region, 1985–1993. Br J Audiol 1997; 31: 409–446. 16. Kemp DT. Stimulated acoustic emissions from within the human auditory system. J Acoust Soc Am 1978; 64: 1386–1391. 17. McCormick B, Curnock DA, Spavins F. Auditory screening of special care neonates using the Auditory Response Cradle. Arch Dis Child 1984; 59: 1168–1172. 18. Tucker SM, Bhattacharya J. Screening of hearing impairment in the newborn using the Auditory Response Cradle. Arch Dis Child 1992; 67: 911–919. 19. Mason S. Electric response audiometry. In: McCormick B, (ed). Paediatric Audiology 0–5 Years. London: Whurr Publishers; 1993. 20. Mason S, McCormick B, Wood S. The auditory brain stem response (ABR). Arc Dis Child 1998; 63: 465–467. 21. McCormick B. The Toy Discrimination Test: an aid for screening the hearing of children above a mental age of two years. Public Health (London) 1977; 91: 67–73. 22. McCormick B, ed. The Medical Practitioner’s Guide to Paediatric Audiology. Cambridge: Cambridge University Press; 1995.
Symposium: Hearing problems
Diagnosing hearing problems in children
B. McCormick
those fitted after 6 months.1 Such findings have prompted further debate about the need to introduce neonatal hearing screening programmes at a time when doubts have been cast on the viability of maintaining high-quality community hearing screening programmes in the hands of health visitors. There is general concern about the poor record of success with the Health Visitor Distraction Test (HVDT) as a screening tool when viewed nationwide, rather than in a few locations where it is known to produce good results. It is also argued that hearing problems should be detected before the age at which the distraction test can be performed. Over the next few years there will be a radical change in the way hearing screening services are administered and although there should be long-term benefits there will inevitably be short-term disruptions. It is vital to support health visitors with their training needs during this period of transition. Their enthusiasm is waning with all the criticism they have received and there is a danger that the thousands of deaf babies, born before the neonatal screening screen is in place, will face an even poorer quality of service if standards decline further. There is an urgent need for services to address the current training needs of health visitors and to improve the standards of community hearing screening over the next 5 years or so. There will, after all, be an additional 5000 deaf babies born over that period.
KEY POINTS
• • • •
•
There is an urgent need for health visitors to review their performance with the distraction test and generally to improve standards. The distraction test will be with us for at least another 5 years before it will be replaced by Universal Neonatal Hearing Screening (UNHS). Major sources of funding and additional service planning will be needed before UHNS can be introduced. Services must be family friendly. No child is too young to be considered for hearing aid or cochlear implant assessment. Generally, the younger these devices are supplied, the better the eventual outcome for the child. Audiological test techniques are now very refined and can be applied from a few weeks of age. Cochlear implants will enable many more deaf children to develop spoken language skills and the number of children requiring sign language as their primary means of communication will decline.
INTRODUCTION There is mounting evidence that early detection of hearing problems and prompt remedial treatment can have permanent beneficial effects. Yoshinaga-Itano demonstrated that deaf children fitted with hearing aids before 6 months of age later showed better expressive and receptive language development than
PERMANENT CHILDHOOD DEAFNESS Between one and two children per 1000 population have permanent childhood deafness of sufficient degree to require hearing aids, cochlear implants or a manual means of communication. Thus in the UK, about 1000 new cases will appear each year. According to Davis et al:2
Barry McCormick OBE, PhD, Special Professor in Paediatric Audiology, Queen’s Medical Centre University Hospital NHS Trust, Nottingham, UK. Correspondence to BMCC.
200
Diagnosing hearing problems in children
201
• 840 (84%) will be born deaf; • 50% of these cases will have moderate hearing losses (40–69 dB); • 25% will have severe hearing losses (70–90 dB); • 25% will have profound hearing losses (>90 dB); • An additional 158 (16%) will acquire bilateral deafness before 5 years of age. With the introduction of cochlear implants over the past decade,3,4 many more deaf children will have access to spoken language as their primary means of communication. In the future, very few will be unable to benefit from hearing aids or cochlear implants and there will inevitably be a decline in the numbers requiring sign language as their main means of communication. Some members of the deaf community are very unhappy about their anticipated decline in numbers and they oppose the use of hearing aids and cochlear implants. Over 90% of deaf children are, however, born into hearing families and it is only natural for these families to want their children to be able to hear and share their spoken language through the use of new hearing aid and cochlear implant technology. It is likely that the vast majority of profoundly deaf children, for whom hearing aids are of limited benefit, will be able to make effective use of cochlear implants if the systems are provided early enough in the child’s life. By early in this context, we mean well within the first 5 years of life and preferably within the first 2 years. Current debate about hearing aid provision favours the fitting of these instruments within the first few months of life,1,2 and this argument will, no doubt, extend to cochlear implant provision in the near future. Although it may be desirable to fit these instruments early, our present record of success with early detection of hearing problems is not good and leaves much to be desired across the UK as a whole. It is useful to take stock of the present situation.
THE HISTORY AND FUTURE OF THE HEALTH VISITOR DISTRACTION TEST (HVDT) This test has been with us since the 1940s and was first described by Ewing and Ewing in 1944.5 It was extensively modified and improved by McCormick during the 1980s.6–8 The test works on the principle noted by the Ewings that the normal response for a baby of 6–7 months of age is to turn to locate the source of a sound. By presenting a series of quiet sounds of different frequencies, it is possible to ensure that the child has sufficiently good hearing to develop normal language. The sounds must be presented out of vision and with no inadvertent clues to indicate the presence of the tester behind the child. A typical test situation is shown in Fig. 1. Despite considerable effort with the development of this screening method and a proven track record of
Fig. 1
Typical test arrangement for a distraction test.
success in a few districts,9,10 the general picture nationwide is very disappointing.11,12 The reason for this appears to be a general lack of compliance with welldefined quality standards and poor local training support for health visitors. Davis and Wood9 reported excellent results for the distraction test in the Nottingham district which, over a 4-year period, achieved a coverage of 96% and a sensitivity of 88% for hearing losses greater than 50 dB. The mean age at referral for babies with severe and profound hearing losses was 8 months. Watkins10 reported a distraction test sensitivity of 93% for severe and profound hearing losses. Both of these studies showed that with sufficient support and with thorough training, health visitors could maintain an excellent level of performance with the HVDT. In both studies, however, the test did not perform so well for children with mild or moderate degrees of hearing loss, and if the identification and treatment of babies with lesser degrees of hearing loss is considered to be important within their first year of life, it will be necessary to seek an alternative form of testing. In a follow-up study of the performance of the HVDT in the Nottingham district,13 a decline in the success rate was recorded which was surbsequently attributed to re-organized management arrangements. This resulted in the lack of availability of refresher courses for health visitors over a 2-year period. As soon as this problem was identified and rectified the success rate was restored to the previous good level of performance.14 This did, however, demonstrate the vulnerability of this form of community screening and also the need for each provider unit to have access to a vigilant audiological overview and to a high level of training for health visitors, which is evidently lacking in many areas. In their 1997 Health Technology Assessment Report, Davis et al quoted only the median age of detection for all degrees of hearing loss. Not surprisingly, this painted a very gloomy picture of very late ascertainment of hearing loss nationwide.2 The same
202
Current Paediatrics
picture emerged from a very large regional study reported by Fortnum and Davis.15 They reported a median age of ascertainment of 20 months for all degrees of hearing loss. Hidden within the data is a more enlightening picture of success, with the median age of identification being 11 months for severe hearing loss and 9 months for profound hearing loss. The general conclusion, however, is that all hearing losses should be identified before the age at which the HVDT is performed and universal neonatal hearing screening must be introduced to achieve this objective. This recommendation has been considered and accepted by the National Screening Committee and there will be significant consequences for community and acute services as the focus of attention gradually shifts from the HVDT to the neonatal unit. The reality of the situation is that universal neonatal hearing screening cannot possibly be introduced without the injection of new cash and new resources. It is unlikely that there will be a transfer of funds from the health visitor budgets to the acute sector. There are also other issues to be considered, including the readiness of services to provide a ‘family friendly’ follow-up and audiological diagnostic and hearing aid fitting service for babies of a few weeks of age (during the sensitive parent–child bonding period). The experience base for neonatal screening in a routine service context is limited and the skilled personnel required to satisfy these needs are in short supply in the UK. Assuming that these obstacles will be overcome within the next few years, what options are available for neonatal hearing screening and for confirming the presence of hearing loss in audiology clinics?
NEONATAL HEARING SCREENING TEST METHODS Otoacoustic emissions tests (OAE) This is the most popular form of test because of its ease of application with minimum preparation and short test time. Otoacoustic emissions (cochlear echoes) were first recorded by Kemp16 and are believed to arise from the active biomechanics of the cochlear sensory mechanism at a preneural level. Various portable versions of test equipment are now commercially available. A soft tipped probe arrangement is placed in the ear canal to record the acoustic signals and this forms the only contact with the child (Fig. 2). The emissions are only present if the cochlear is functioning and the test takes only a minute or so to perform. Pilot studies using this method have met with considerable success. It must be remembered, however, that the OAE does not check the entire hearing pathway and it cannot detect retro-cochlea pathologies. Fortunately pure retro-cochlea pathologies are very rare and the vast majority of deafness in childhood should be detectable from the use of OAE measurements.
Fig. 2 Using a hand-held otoacoustic emissions test system on a 7-month-old baby.
Fig. 3 Undertaking a diagnostic distraction test with an electronic noise generator.
Auditory brain stem response testing (ABR) This technique records sound induced electrical activity in the brain utilizing surface mounted electrodes positioned on the scalp. The test has the advantage that it enables hearing to be screened at any predetermined level (mostly 40 dB or 50 dB in practice) and it tests the integrity of the system beyond the cochlea. The test does require more preparation with the need to position the electrodes on the scalp and to obtain a good electrical contact whilst maintaining the baby in a calm and quiet state. The test takes longer to perform than the OAE method, with a typical test time of 20 min rather than a minute or so for the OAE test. The portable auditory response cradle (PARC) This equipment uses microchip technology with transducers positioned around the baby to record behavioural responses to sound. It has the advantage that it records responses though the entire auditory pathway. Problems have been found with the use of an early version of this equipment with special care babies,17 but Tucker and Bhattacharya18 have reported good result in their screening programme.
Diagnosing hearing problems in children
203
A
B
Fig. 5
The use of inset ear phones with a 7-month-old baby.
Diagnostic distraction testing
Fig. 4 A typical set up for a visual reinforcement audiometry test with a lighting up reward adjacent to the speaker.
Nevertheless most workers prefer to use the OAE or ABR methods now that convenient portable versions of the equipment are readily available. BEYOND THE SCREEN—TESTS FOR CONFIRMING THE PRESENCE OF HEARING PROBLEMS Diagnostic auditory brain stem response testing As an objective test of hearing function, the ABR takes pride of place. In skilled hands and in a controlled environment it is possible to record responses very close to the child’s hearing thresholds and this makes the test very useful for application with children who are difficult to test by behavioural means, either because they are very young or because they have other difficulties. The use of click stimuli enable hearing thresholds in the mid to high frequency region (centred on 2.5–3 kHz) to be explored and the use of tone pips enables lower frequency thresholds (around 1 kHz) to be checked.19 It is also possible to undertake bone conduction threshold measurements. If access to skilled behavioural testing is available in an audiology service, the support of diagnostic ABR will be needed in about 3% of cases.20 This figure will rise with the introduction of neonatal hearing screening as more neonates appear for investigation within the system.
The distraction test still has application at the diagnostic level despite the widespread and increasing popularity of visual reinforcement audiometry (VRA). Not all infants will respond to a VRA procedure: when VRA works it is excellent but some children are unresponsive for reasons other than hearing impairment. A big advantage of the distraction test is that the child’s general response state can be checked using other modalities such as visual clues or tactile clues. If a child turns quickly to a touch on the ear, or to an object brought into peripheral vision, but fails to respond to certain sound, then this will indicate the presence of deafness for those sounds. The hearing thresholds for a wide range of frequency-specific sounds can be measured fairly quickly by two skilled testers using sound generators in the typical test situation (shown in Fig. 3). Perhaps the biggest advantages of the distraction test are that the child’s attention can be controlled in a very refined and structured way and a wide and rapidly changing range of calibrated sound stimuli can be used. The sound can also be presented very close to each ear, thus enabling the thresholds in each ear to be checked without having to make physical contact with the child. This is a particularly useful option for babies who are disturbed by the use of headphones or insert earphones but for whom a difference in the responsiveness of the two ears is suspected. Visual reinforcement audiometry (VRA) A typical set-up for VRA is shown in Fig. 4(A,B). The test utilizes a calibrated loudspeaker arrangement for presenting the sounds, and the child’s responses, normally in the form of head turns, are rewarded with some form of visual display, for example a puppet lighting up in a box. The hearing thresholds are chased by varying the stimulus levels in the same way as with the distraction test. The main difference between this form of testing and distraction testing is the absence of a tester behind the child and inclusion
204
Current Paediatrics
Fig. 6 The use of a bone conductor with a 7-month-old baby.
Fig. 8
Undertaking the McCormick Toy Discrimination test.
the child to hear conversational levels of voice, the possibility of cochlear implantation or a sign language approach should be considered. The youngest child to have been implanted in the UK was just 6 months old and babies as young as 6 weeks of age have been supplied with hearing aids.
TESTING OLDER CHILDREN
Fig. 7 Undertaking the performance test using a hand-held warbler.
of a mechanical/electronic response reward system. It is possible to calibrate the speaker (sound field) stimuli very precisely and to measure a child’s hearing thresholds with slightly more precision (5 dB or so). The use of insert earphones (Fig. 5) adds to the precision and enables each ear to be tested independently. It is also possible to utilize a bone conductor (Fig. 6) to chase the bone conduction thresholds. Normally up to 20 responses can be obtained before the child loses interest in the task.
AT WHAT AGE CAN HEARING AIDS AND COCHLEAR IMPLANTS BE PROVIDED? Using a combination of the above objective and behavioural tests it should be possible to obtain sufficient audiological data to know whether hearing aids are needed with babies as young as 6 months and even younger in exceptional circumstances. The investigations can then be repeated with the use of hearing aids and, if the aided hearing thresholds do not enable
This article has concentrated on babies with permanent hearing losses. It must be remembered that 15% of permanent deafness will be postnatally acquired and there must be a system in place to detect these cases. Approximately 6% of all children will experience fluctuating conductive hearing loss at some stage. The techniques for testing infants and toddlers are very straightforward if a child can be conditioned to perform conventional audiometry. In the community it should be possible to obtain an audiogram from a 4-year-old child without too much difficulty. Prior to this the performance test (Fig. 7), which is a simplified form of play audiometry, can be applied by health visitors. In audiology clinics skilled clinicians can sometimes obtain conventional audiometric results with 2-year-old children. Simple speech discrimination testing can be performed in the community by 2 years of age, for example the McCormick Toy Discrimination Test21 (Fig. 8), and most health visitors will have been trained to undertake this form of testing in addition to the performance test. If there are suspicions about any child’s hearing following illness, because of failure to develop clear speech or because of family history of deafness, a screening test should be arranged without delay and a referral made to the audiology clinic if there are any doubts about the responses. Within the constraints of this article it has only been possible to give a general overview of the various test techniques The reader is referred to The Medical Practitioner’s Guide to Paediatric Audiology for more detailed coverage.22
Diagnosing hearing problems in children CONCLUSIONS Radical changes in the way we detect and manage hearing impairment are on the horizon. The way in which this change is managed will determine the future potential of deaf children. Now, more than at any time in the past, the onus is on services to assess their present level of performance, to improve this level urgently in the short term and to prepare for the new neonatal hearing screening service. REFERENCES 1. Yoshinaga-Itano C, Sedey AL, Coulter DK, Mehl AL. Language of early and late identified children with hearing loss. Pediatrics 1998; 102: 1161–1171. 2. Davis A, Bamford J, Wilson I, Ramkalawan T, Forshaw M, Wright S. A critical review of the role of neonatal hearing screening in the detection of congenital hearing-impairment. Health Technol Assessment 1997; 1(10). 3. McCormick B. Cochlear implantation in the UK: a delayed journey on a well marked route. Br J Audiol 1991; 25: 145–149. 4. McCormick B. Paediatric audiology and cochlear implantation in the UK: taking off in the fast lane. Br J Audiol 1997; 31: 303–307. 5. Ewing IR, Ewing AWC. The ascertainment of deafness in infancy and early childhood. J Laryngol Otolo 1944; 309–333. 6. McCormick B. Hearing screening by health visitors: a critical appraisal of the Distraction Test. Health Visitor 1983; 56: 449–451. 7. McCormick B. Evaluation of a warbler in hearing screening tests. Health Visitor 1986; 59: 143–144. 8. McCormick B. Screening for Hearing Impairment in Young Children. London: Whurr Publishers; 1988. 9. Davis A, Wood S. The epidemiology of childhood hearingimpairment: factors relevant to planning of services. Br J Audiol 1992; 26: 77–90.
205
10. Watkin PM, Baldwin M, Laoide S. Parental suspicion and identification of hearing impairment. Arch Dis Child 1990; 65: 846–850. 11. Sutton GJ, Scanlon PE. Health visitor screening versus vigilance: outcomes of programmes for detecting permanent childhood hearing loss in West Berkshire. Br J Audiol 1999; 33: 145–156. 12. Fonseca S, Forsyth H, Grigor J, Lowe J, MacKinnon M, Price E, Rose S, Scanlon P, Umpathy D. Identification of permanent hearing loss in children: are the targets for outcome measures attainable? Br J Audiol 1999; 33: 135–143. 13. Wood S, Davis A, McCormick B. Changing yield of the health visitor distraction test when targeted neonatal screening is introduced into a health district. Br J Audiol 1997; 31: 55–61. 14. McCormick B. Managing the transition to Universal Neonatal Hearing Screening—the missing link. Br J Audiol 2000; 34: 67–70 [letter]. 15. Fortnum H, Davis A. Epidemiology of permanent childhood hearing impairment in Trent Region, 1985–1993. Br J Audiol 1997; 31: 409–446. 16. Kemp DT. Stimulated acoustic emissions from within the human auditory system. J Acoust Soc Am 1978; 64: 1386–1391. 17. McCormick B, Curnock DA, Spavins F. Auditory screening of special care neonates using the Auditory Response Cradle. Arch Dis Child 1984; 59: 1168–1172. 18. Tucker SM, Bhattacharya J. Screening of hearing impairment in the newborn using the Auditory Response Cradle. Arch Dis Child 1992; 67: 911–919. 19. Mason S. Electric response audiometry. In: McCormick B, (ed). Paediatric Audiology 0–5 Years. London: Whurr Publishers; 1993. 20. Mason S, McCormick B, Wood S. The auditory brain stem response (ABR). Arc Dis Child 1998; 63: 465–467. 21. McCormick B. The Toy Discrimination Test: an aid for screening the hearing of children above a mental age of two years. Public Health (London) 1977; 91: 67–73. 22. McCormick B, ed. The Medical Practitioner’s Guide to Paediatric Audiology. Cambridge: Cambridge University Press; 1995.