CHAPTER – 1INTRODUCTION Hearing plays a significant role inlanguage and intellectual development.
The impact of early diagnosis andrehabilitation of newborns with hearing loss cannot be overstated. Since thedisease develops gradually over years while first signs can be detected early;therefore early screening is the best way of prevention of advanced hearingdisorders. Congenital and acquired hearing loss in newborns and children canlead to deficiencies and defects in the evolution of speech, poor educationalfunction, and lifelong social non-concurrence and emotional distress.Pediatricians are required to identify at-risk children, intervene in a timelyand effective manner, and refer patients as necessary.The importance of earlydiagnosis is cle ar, but diagnosis and treatment in the 1st months of life is a recent concept.Theinitial signs of hearing loss are very subtle and systematic neonatal hearingscreening is the most effective tool for early detection of it. Hearing lossaffects around 3 out of every 1000 live births.
Hearing is essential forspeech and language development, communication and learning. Children withhearing loss continue to be under identified and underserved population andtheir life is affected both quantitatively and qualitatively. Hearing loss inchildren constitutes a considerable handicap because it is an invisibledisability that can compromise their optimal development and personalachievement. The prevalence of congenital hearing loss has been estimated to be 1.
2 – 5.7 per thousand live births Earlydetection and appropriate treatment provides the best choice maximizing the critical period of hearing and thereby availing the resources to improvehearing and oral communication skills.On the other hand late detection and treatment leaves the children with poorspeech development and school achievement. Programmes that focus on detectinghearing disabilities at an early part of life help in improving the overalldevelopment of the child in cognitive, motor and social domain.The incidence of sensorineuralhearing loss is approximately 1-3/1,000 newborns.
This is 1/1,000 about severeto deep deafness (70 db or greater). Therefore, only 2-5% of newborns hasdeafness or hearing loss and the remaining (95-98%) are normal.50% of childrenwith a severe to profound congenital hearing loss have no risk factors fordeafness.
This means that screening of at-risk children only misses 50% ofcongenital hearing loss. For this reason, screening of all newborns has beenrecommended.Both the auditory brainstemresponse (ABR) and the otoacoustic emission (OAE) test are used to screenhearing in newborns. The OAE test measures the response of the cochlea to noiseemitted by a microphone in the external ear canal and reflects the status ofthe peripheral auditory system and the outer hair cells. The ABR test uses asurface electrode to measure neural activity in the cochlea, auditory nerve andbrainstem in response to acoustic stimuli, reflecting the status of theperipheral auditory system, the eighth nerve and the auditory brainstem.Recommended Protocol for Infant AudiologicAssessmentThe following protocol was developed tofacilitate the diagnosisof hearing loss, medical clearance for amplification, and use ofamplification for infants with hearing loss by three months of age. Anaudiologist should have the necessary equipment (ABR with bone conduction andtone bursts, OAE, high frequency tympanometry) and be experienced in theassessment of infants. Infants should obtain a diagnostic assessment after afailed/referred (that is, an abnormal) newborn hearing screen.
A hearing screenis considered failed when one or both ears do not pass the hospital screen oroutpatient re-screen. Within the first two months of life, the proceduresoutlined below in Step I and Step II, should be completed on all infantsreferred from the screening process. Use the Newborn Audiological AssessmentChecklist found in Appendix 1 to assure that all recommended follow-upactivities have been completed. The activities outlined in Step III, forchildren with confirmed hearing loss, should occur by three months of age.
Forinfants who pass both ABR and OAEs (robust responses at 3 or more frequencies),parents should receive information about hearing, speech, and languagemilestones and information regarding risk indicators for progressive hearingloss. Parents should be instructed that, if questions about their child’shearing or speech and language development arise at any point, their childshould receive an age-appropriate audiologic assessment.For infants who pass both ABR and OAEs (robust responsesat 3 or more frequencies), parents should receive information abouthearing, speech, and language milestones and information regarding riskindicators forprogressive hearing loss. Parents should be instructed that, ifquestions abouttheir child’s hearing or speech and language development arise at any point,their child should receive an age-appropriate audiologic assessment.
Infants who pass ABR but who do not pass OAEsmay have external and/or middle ear pathology and should be referred to aphysician experienced in evaluating external and middle ear function ininfants. A repeat audiologic assessment should be completed after thisevaluation. The assessment should occur by three months of age and shouldinclude repeat OAEs. Infants who pass OAEs but who do not pass ABRshould continue with the recommended assessments outlined in Step II below.Infants who fail both OAEs and ABR in one or both ears should continue with therecommended assessments as outlined in Step II.Definition ofThreshold In theNHSP AC click ABR protocol4 the definition of ABR threshold is “the lowest level atwhich a clear response is present, with the absence of a recordable responseat a level 5 or 10dB below the threshold, obtained under good recording conditions.The provisional NHSP definition for the ASSR threshold, for each frequencytested, is the equivalent to this, i.
e. the lowest level at which the target responseat a level 5 or 10dB below this threshold, obtained under good recording conditions(defined as p >0.02 with the noise floor <10nV). There should also be a responsemeeting the p<0.02 criteria at 5 or 10dB above threshold. If threshold is at themaximum stimulus level there should be a further run at the maximum stimuluslevel meeting the p<0.
02 criteria instead of the run at 5 or 10dB above threshold.response criteria value of p<0.02 is obtained, with the absence of arecordable. Otoacoustic emissions (OAEs) are low-intensitysounds emitted by functioning outer hair cells of the cochlea. OAEs aremeasured by acoustic stimuli such as a series of very brief clicks to the ear through a probe that isinserted in the outer third of the ear canal. The probe contains loudspeakersthat generate the clicks and a microphone for measuring the resulting OAEs.
OAEtesting requires no behavioral or interactive feedback by the individual beingtested. OAEs are used as a screening test for hearing in newborns. Otherpotential applications of OAE testing include screening children or at-riskpopulations for hearing loss, and characterizing sensitivity and functionalhearing loss and differentiating sensory from neural components in people withknown hearing loss.
OAE devices use either transient evoked OAE(TEOAE) or distortion product EOE (DPOAE) technology. TEOAE devices emit asingle brief click that covers a broad frequency range. DPOAE devices emit two brief tonesset at two separate frequencies. TEOAEs are used to screen infants, validate other tests, andassess cochlear function, and DPOAEs are used to assess cochlear damage,ototoxicity, and noise-induced damage. Spontaneous otoacoustic emissions(SOAEs) are sounds emitted without an acoustic stimulus (i.e.
, spontaneously).Stimulus-frequency otoacoustic emissions (SFOAEs) are sounds emitted inresponse to a continuous tone. At present, SOAEs and SFOAEs are not usedclinically. There is inadequate evidence that hearing screening with OAEs issuperior to screening audiometry in improving health outcomes such as timelyfacilitation of speech, language, and communication skills in older children oradults.
Otoacoustic emissions (OAEs) testing as adiagnostic service is medically necessary for the evaluation of hearing loss in one or more ofthe following: Infantsover 90 days old and children up to 4 years of age, children and adults who are or who are unableto cooperate with other methods of hearing testing (e.g. individuals with autismor stroke), children with developmentalor delayed speech or language disorders, individuals with tinnitus, acoustictrauma, noise induced hearing loss, or sudden hearing loss, individuals withabnormal auditory perception, individuals with sensorineural hearing loss, individuals with abnormal auditory functionstudies or failed hearing exam, potentially malingering individuals who may befeigning a hearing loss, monitoring ofototoxicity in patients before, during, and after administration of agentsknown to be ototoxic (e.g., aminoglycosides, chemotherapy agents) A study which involved 53,781 newborns provideda direct comparison of hearing impairment detection rates during periods ofnewborn hearing screening and no screening in the same hospitals (WessexUniversal Hearing Screening Trial, 1998). Those infants born during a period ofscreening underwent a two-stage screening test, with transient evokedotoacoustic emissions (TEOAE) at birth, followed by automated auditorybrainstem response (AABR) before discharge if the first screen was failed. If the secondscreen was also failed, the babies were referred to an audiologist at 6 to 12weeks of age. In this study, 4% of infants with hearing loss were missed duringthe screening period, while 27% were missed during the period of no screening.
This study did notprovide data on clinical outcomes such as speech and language development inscreened versusunscreened children. Another group of investigators comparedclinical outcomes, including speech and language development, in 25 infants whowere screened as part of the Colorado Universal Newborn Screening program withoutcomes in 25 matched infants who were born in a hospital without a universalnewborn hearing screening program (Yoshinaga-Itano et al., 2000). This studyfound that children who were identified as hearing impaired through the newbornhearing screening program had significantly better scores on tests of speechand language development than did children who were identified later.There are many behavioral and electrophysiological assessmentmethods for screening of hearing in neonates.
Behavioral techniques have a highnumber of false negative results. As electrophysiologic methods with greatersensitivity and specificity, the following may be used: auditory brainstemresponse (ABR) automated auditory brainstem response (AABR) and evokedoto-acoustic emissions (EOAE). ABR and OAE are used for universal hearingscreening. However, it is better to minimize false-positive results indeveloping a more reliable newborn hearing screening program. OAE and ABR toolsare evolving and becoming more and more automated.
Determining which of them ismost effective is interesting.ABR is a standard and very precise test in determining the averagethreshold of frequencies at 2000-4000 Hz. The differences in the size of theexternal auditory canal and in the placement and type of earphone can producesmall differences in the stimulus and therefore can lead to false negativeresults in mild hearing losses. False positive results of it seem to be fewer.OAE tests are generally thought to be easier to administer and faster. The timeneeded for screening test is variable.
However, the average time to carry outautomated ABR testing ranges from 8 to 15 min, and conventional OAE tests take2 to 13 minThis measures not only theintegrity of the inner ear, but also the auditory pathway. It can thereforedetect the rare condition of auditory neuropathy, in children who are deaf buthave normal OAE’s (because the cochlea is normal). The stimulus (either clicksor tones) is presented using either earphones or an ear canal probe, and theelectrophysiological response from the brainstem is detected by scalpelectrodes. Automated devices allow screening to be performed bynon-specialists. Responses from a large number of stimulus presentations areaveraged and the automated screener uses a response algorithm to produce a’pass’ or ‘refer’ result.
The “pass” level is set at about 35 decibels. Thistest takes 15-20 min, but once again this time may be longer if a child isrestless, and does not include time for discussion and preparation before thetest.DPOAE test performance was compromised at 1.1kHz. In view of the different test performance characteristics across thefrequencies, the use of a fixed SNR as a pass criterion for all frequencies inDPOAE assessments is not recommended. When compared to pure tone plustympanometry results, the DPOAEs showed deterioration in test performance,suggesting that the use of DPOAEs alone might miss children with subtle middleear dysfunction.
However, when the results of a test protocol, whichincorporates both DPOAEs and tympanometry, were used in comparison with thegold standard of pure-tone screening plus tympanometry, test performance wasenhanced. The investigators concluded that In view of its high performance, theuse of a protocol that includes both DPOAEs and tympanometry holds promise as auseful tool in the hearing screening of schoolchildren, includingdifficult-to-test children.Early diagnosis and immediate intervention play important role inthe development and prognosis of children with hearing loss and decrease theimpact of the condition on the child’s social, emotional, intellectual andlinguistic development This study addressed thefollowing question with respect to neonatal screening: To evaluate out the efficacy of Auditory Brainstem Response (ABR), Distortion Product OtoacousticEmission (DPOAE) and Auditory Steady State Response, in screening the hearingloss in Indian population, and toknow among all above test is morespecific and sensitive in screening the hearing loss in Indian population. This can help to betterdiagnosis and better prognosis. Purposeof study: The main purpose of this study is to This staddressed the following question with respect to neonatal screening: To evaluate the efficacy of auditory Brainstem Response (ABR), Distortion Product OtoacousticEmission (DPOAE) and Auditory Steady State Response, in screening the hearingloss in Indian population, and toknow among all above test is morespecific and sensitive in screening the hearing loss in Indian population.
Also to compare theresult between demographic variable such as Type of delivery,Birth weight, APGAR Score, Family history, Age of the Mother, Hypertension,Diabetes and Delivery This can help to better diagnosis and better prognosis.Implicationof the Study: Early diagnosis and acute intervention playsan important role in the development andprognosis of children with hearing loss and decrease the impact of thecondition on the child’s social, emotional, intellectual and linguisticdevelopment. Better form of screening will give exact level of hearing loss andpathology that will help for early diagnosis and better treatment. This studyhelped to know better form of neonatal screening which can help to earlydiagnosis and early interventions.