Early Hearing and Communication Development

Chapter V: Assessment

Audiologic Assessment

Authors: Dr. Martyn Hyde and Dr. David Brown

Context

Audiologic assessment here refers to detailed determination of the hearing status of an infant. Three routes to audiologic assessment include universal newborn hearing screening (UNHS), surveillance of children at risk for permanent childhood hearing impairment (PCHI), and risk-based referral. Respectively, these cover neonates who express congenital PCHI, infants at risk for late-onset or progressive impairment, and infants at risk through postnatal risk discovery or new risk events. Most audiologic assessment candidates arise through UNHS, and are accessible under 3 months corrected age (see Prieve et al.¹). Surveillance and postnatal risk routes may yield candidates at any time throughout infancy (age 0-24 months). For a comprehensive overview, see Thompson et al.²

Audiologic assessment must be as accurate as possible.³ Errors have occurred in the past, with significant consequences for affected children and families. The importance of high quality test protocols applied consistently and program wide, adequate tester training and skills maintenance, as well as rigorous quality management, cannot be overstated. Definitive quantification of hearing may require several test sessions, either to improve audiometric accuracy or completeness, or to monitor possible changes in hearing. The later audiologic assessments may occur after provision of amplification or other communication enhancement strategies.

Objectives

The purpose of the audiologic assessment is to provide the audiometric information that is necessary and sufficient to fully inform the subsequent course of events, which may include medical diagnosis and treatment, prognosis, provision of assistive technology such as hearing aids, and/or communication development options. There are two kinds of measurement in common use: (i) estimates of perceptual threshold for pure tones at specific frequencies; and (ii) measures of function of specific parts of the auditory system. The latter measurements can inform about the site of dysfunction (e.g., middle ear, cochlear, retrocochlear) and the related type of dysfunction (e.g., conductive, sensory, neural, mixed). Also, the relationships among the measurements can help to validate the overall inferences about hearing status.

Age at Assessment

The chronological and developmental age of the infant affects the choice of tests. For infants under about 9 months developmental age, behavioural observation audiometry (BOA) is often recommended as the assessment tool of choice. However, there is clear evidence that BOA is not a reliable procedure.⁴ It is widely recommended that audiologic assessment in such infants must be based on physiologic measures.⁵ These include: threshold estimation by evoked potentials (EPs); acoustic immittance and middle ear muscle reflexes; transient-evoked or distortion product-evoked otoacoustic emissions (TEOAE or DPOAE); and testing the functional integrity of the afferent cochleoneural pathways by cochlear microphonic potentials (CM) and also by the auditory brainstem response (ABR). A limitation of electrophysiologic audiometry is that EPs are epiphenomena of hearing and so their relationship to perception is not causal, but correlational. Thus, EP thresholds are proxy statistical estimators of actual perceptual thresholds.

At 6-9 months' developmental age, most infants can give reliable hearing thresholds using operant-conditioned head-turn responses - visual reinforcement audiometry (VRA). Infants with multiple disorders or severe cognitive disorders may not be testable behaviourally, and it may be necessary to resort to physiologic methods of estimating perceptual thresholds.

Electrophysiologic Threshold Estimation

Hearing threshold estimates are required at a set of frequencies, typically in the range 0.5 through 4 kHz. This range includes frequencies that are important for speech perception as well as for detailed specification of hearing aids, and which are conventionally required for medical evaluation. Of the many EPs that can be elicited from the cochlea to the cerebral cortex, only the frequency-specific (FS) ABR and auditory steady state responses (ASSR) are appropriate candidates for threshold estimation.⁶

Auditory Brainstem Response

ABR thresholds can be measured for click and tonepip stimuli. The click excites a broad cochlear region, so click ABRs cannot provide accurate, frequency-specific audiometry.^6-8 In contrast, there is evidence that tonepip ABRs can yield clinically acceptable estimates of puretone thresholds by air conduction (AC), but only given appropriate test protocols and tester skills.⁹ The key elements of the test protocol are that the infant must be in natural or sedated sleep, recording electrodes must be properly positioned and have low and approximately equal contact impedances. In addition, recording bandwidth must be from about 30-1,500 Hz, the data window must be at least 25 milliseconds (ms) in length, the gain and artifact rejection limits must be set appropriately, and averages must be of at least 2,000 accepted sweeps with replication.⁶ Because test time is limited, the stimulation rate must be at least 30 per second and the selection strategies for stimulus frequency, intensity and route must be very efficient. It is necessary to restrict testing to only those frequencies and routes of stimulation that are required for clinical decision making. Furthermore, in order to resolve the conductive and sensorineural components of hearing impairment, testing by bone conduction (BC) may be necessary.^10-13 Data on the accuracy of BC FS-ABR threshold estimates are limited, as is the dynamic range of BC stimulation.

Errors in FS-ABR threshold estimation are reported to arise most commonly from misjudgment of response presence or absence.⁶ Currently, reliable and well-validated objective statistical response detection algorithms are not widely available clinically. Thus, it is essential that testers be properly trained in test conduct and response recognition, that caseloads are sufficient to maintain skills, and that ABR results be assessed critically in the light of all other sources of evidence.

ABR thresholds are not equal to perceptual thresholds, and it is necessary to adjust for bias when estimating true hearing levels. FS-ABR thresholds are biased positively by about 0-20 dB, the exact amount depending on the stimulus frequency and possibly on stimulus level.^6,9 Due to this bias and the intensity limitations of the transducer, it is not possible to resolve hearing impairments greater than about 80 dBHL by tonepip ABR techniques.

Careful attention to stimulus calibration is essential. Levels may be expressed in dB peak equivalent sound pressure level (SPL) in the individual infant ear, in a standard coupler that simulates an average adult ear, or in dBnHL (normal hearing level). Neither dBnHL nor dBHL (hearing level, as defined by the American National Standards Institute (ANSI) in American National Standard S3.6-1996) is directly applicable to thresholds in young infants. An unresolved question is whether it is necessary to apply SPL adjustments reflecting the acoustical properties of the average infant ear, or to take real ear SPL measurements, in order to express infant hearing thresholds appropriately (see, for example, Sininger et al.¹⁴).

In the vast majority of infants under about 6 months of age, successful FS-ABR can be accomplished during natural sleep. However, it can be difficult to test infants over 4 months in natural sleep, and those over 6 months will most likely require sedation or light, general anesthesia. While electroencephalogram (EEG) conditions in sedated sleep are usually very good, test efficiency remains an important consideration, because the duration of sedated sleep can be unpredictable and limited.

Click Auditory Brainstem Response and Auditory Neuropathy

The click ABR has limited clinical value for diagnostic audiometric assessment. For example, the latency of wave I or wave V can imply a significant conductive impairment component, and this is informative if BC threshold measurements prove impractical in a given infant. Also, if EEG conditions were marginal, the click ABR might be detected when tonepip ABRs were not, because of the superior neuronal synchrony induced by a click. However, these applications are relevant only if sedated testing for FS-ABR is deemed to be unfeasible.

The click ABR is useful to detect cochleoneural dysfunction beyond the level of the cochlear outer hair cells. The most common cause is auditory neuropathy (AN), which is a set of cochleoneural transduction disorders that have in common reduced temporal synchrony of afferent neuronal activity.¹⁵ This leads to absence or gross abnormality of the ABR, and its predictive accuracy for hearing threshold is lost.

Most infants who have AN are graduates of neonatal intensive care units (NICUs).¹⁶ AN usually yields absent ABRs, present otoacoustic emissions (OAEs), absent acoustic middle ear muscle reflexes, and any degree of hearing impairment from mild to profound.^17,18 OAEs may be absent or may decline over time, but cochlear microphonic potentials (CM) are present. Accordingly, an appropriate sub-protocol for CM measurement is essential. When AN is detected, ABR thresholds are usually not measurable and in any event are not reliable, whereas behavioural thresholds, such as by VRA, are more accurate. AN typically imposes an auditory perceptual deficit in the temporal resolution of complex signals such as speech. It is reported that about 50% of infants with AN receive significant benefit from hearing aids¹⁹ but, currently, the prediction of such benefit is difficult. A substantial proportion of infants with AN appear to do well with cochlear implants.

Emerging Technology: Auditory Steady State Response

The auditory steady state response (ASSR) is an evoked potential that is recorded from the scalp and, like the ABR, can be used to estimate auditory thresholds.²⁰ It is frequency specific and can be elicited at a single frequency or at multiple frequencies simultaneously.²¹ The ASSR has been measured in newborns, children and adults^22,23 when asleep or awake.^24,25 The stimulus is a tone that is amplitude- and/or frequency-modulated, evoking periodic scalp potentials at the modulation frequency. The stimulus activates a place on the basilar membrane determined by the carrier frequencies, typically 0.5, 1, 2, and 4 kHz.²⁶ The ASSR is usually displayed as amplitude and phase spectra of the response and background noise. Presence or absence of response is determined statistically, which makes the ASSR an objective test.^22,27 The multi-frequency stimulus/multi-ear stimulation technique has the potential to shorten the time needed to determine auditory thresholds,²⁸ relative to FS-ABR, which would be a major advantage given the time pressures in infant testing. However, this advantage would be gained only if no substantial interaction occurs between the responses for multiple frequencies and ears. Further analysis of the techniques and large-scale clinical trials are required to quantify the usefulness of this technique.

Otoacoustic Emissions

Otoacoustic emissions (OAEs) are sounds produced by the cochlea and recordable in the ear canal.²⁹ Since the cochlea is developed by 34 weeks' gestation, OAEs can be measured in newborns.³⁰ The two types of OAEs in common clinical use are transient-evoked OAE (TEOAE) and distortion product-evoked OAE (DPOAE).²⁹ TEOAEs are normally elicited by clicks and comprise a complex waveform lasting up to about 15 ms and reflecting progressive activation of the cochlear partition from base (high frequency) to apex (low frequency). Response components associated with various frequency regions of the cochlea are extracted by spectral analysis. DPOAEs are elicited by simultaneously stimulating the cochlea with two tones (at frequencies f1 and f2) making the response frequency specific. The result is an emission at 2f1-f2 caused by intermodulation distortion occurring on the basilar membrane of the cochlea.

OAEs are useful for screening, in part because they are an objective and frequency-specific measure.²⁹ However, they are limited as a tool for detailed audiologic assessment, because they relate more to cochlear function than to audiometric threshold. OAE measures cannot predict an individual's puretone threshold, so they are considered as a test of cochlear function from which inferences can be drawn about hearing status.³¹ OAEs are typically not present in ears with significant negative middle ear pressure, middle ear effusion or permanent, conductive disorders.^32,33 In ears with sensorineural impairment, OAEs may or may not be present depending upon the frequency and severity of the impairment. An absent OAE suggests a severity of at least 30-35 dBHL in the frequency region of the OAE, but only if the impairment is of cochlear origin.^34,35 Regardless of the true size of the cochlear impairment component, even a slight conductive impairment could abolish the OAE, and there is no direct clue from the OAE itself about the impairment type. However, OAEs are a useful contributor to the audiometric assessment process by providing a limited cross-check of the EP or VRA results.

Middle Ear Analysis

Middle ear analysis (MEA) typically includes tympanometry and acoustic middle ear muscle reflex (MEMR) measurement (see ASHA³⁶ for review). Basic tympanometry yields acoustic immittance versus static pressure, and the parameters of the relation reflect the middle ear function. The most common inferences relate to middle ear pressure and to fluid in the middle ear, associated with otitis media (OM). These findings increase the likelihood of conductive hearing impairment (CHI), and thereby provide a weak inferential cross-check on a conductive component measured by ABR or VRA. It should be noted that reflexes are absent even with a slight conductive hearing loss.

The differential diagnostic value of MEA lies in four inferences. First, finding a significant conductive impairment component by ABR implies middle ear abnormality, so normal MEA would suggest that the ABR results be examined critically (especially BC ABR results). Second, BC stimulus levels above about 50 dBnHL are not achievable, so air-bone gaps cannot be measured accurately when AC thresholds are above 50 dB. Abnormal MEA implies a possible conductive component. Third, abnormal MEA is often associated with reduced or absent OAE, so when MEA is abnormal, absence of OAE has little diagnostic value in assessment of possible AN. Fourth, presence of an acoustic reflex (AR) is normally associated with AC thresholds not greater than 10 dB below the AR threshold, so an inference of severe hearing impairment or greater by ABR must be examined very critically if an AR is observed. Conversely, absence of the AR is not informative about thresholds if the tympanometry is markedly abnormal.

To optimize these cross-checks, MEA probe frequency should be much higher than the conventional 226 Hz used in adult testing.³⁷ There is fair evidence that in infants under about 7 months of age, a normal 226 Hz immittance curve can be obtained despite the presence of middle ear fluid.³⁸ A probe tone frequency of 678 Hz or greater reduces these false-negative findings.^39,40 Similarly, ARs are frequently absent in young infants with 226 Hz probes, but not with higher frequency probes.⁴¹ Thus, use of high-frequency probes is likely to improve the diagnostic value of MEA in young infants.

Visual Reinforcement Audiometry

Visual reinforcement audiometry (VRA) procedures in common use are less than optimal because they involve sound field stimuli and/or speech stimuli which has limited value for precise threshold estimation. These VRA methods, therefore, do not measure ear-specific and frequency-specific thresholds accurately. However, Widen et al.⁴² describe VRA procedures that make obtaining these measurements possible at 8-12 months in over 90% of candidates, given skilled testers and a high quality protocol. Key elements of a high quality protocol are: stimulation by insert earphones at key frequencies; use of frequent, valid control trials; and careful documentation of the sequence of stimulus, control and response events. Infrastructural aspects, such as the use of two properly trained testers, appropriate test environment, and optimal conditioning, reinforcement and distraction methods, are also important.

Minimum response levels (MRLs) obtained by VRA are likely to be biased positively, relative to true perceptual thresholds.⁴³ The bias will be small if and only if the infant has adequate cognitive, visual and motor function and is well conditioned, the assessment of which is partly subjective but can be made more reliable and verifiable by careful response documentation. In infants for whom adequate operant conditioning cannot be established, one may always resort to ABR methods, bearing in mind an increasingly likely need for sedation in infants over about 6 months of age.

Audiologic assessment based on VRA should include OAE and MEA testing wherever feasible. If cognitive development and responsiveness are deemed sufficient for accurate VRA, then normal OAEs and VRA threshold elevation beyond about 45 dBHL are clearly discrepant, in which case AN is a possibility and ABR testing is indicated, usually under sedation. As was the case for ABR threshold inferences, abnormal tympanometry precludes inferences from OAE and from AR absence. Given normal tympanometry, AR presence should prompt careful review of the significance of a finding of severe or profound hearing impairment by VRA.

Auditory Brainstem Response / Visual Reinforcement Audiometry Relationships

In the present, programmatic context, VRA will be used most frequently in infants with prior ABR audiometry, and often after fitting of hearing aids. If the VRA and ABR thresholds differ significantly, questions arise about hearing aid adjustment as well as diagnostic and prognostic significance of the possible "changes." Available data are limited, but discrepancy clearly demands careful review of the quality of all audiometric findings. Consistent and reliable VRA thresholds well below ABR estimates should lead to revised management based on the VRA, but the validity of the VRA reliability judgment is crucial. When VRA thresholds are higher than ABR thresholds, the latter must be carefully reviewed for false-positive response identification, and re-testing under sedation may be indicated. The potential for progressive impairment requires careful and sustained audiometric monitoring.

Finally, it is known that the age period between about 18 and 30 months can be problematic for reliable audiometry. The child's attention may not be sustainable for operant conditioning, yet adequate cooperation for play audiometry may not yet be readily achieved. Frequency-specific ABR testing under sedation remains a viable option for the determination of hearing thresholds across all age groups, if neuropathy is not suspected.

Conclusions

• Complete audiologic assessment, which can be achieved in healthy children under 6 months of age, is essential to appropriate hearing aid fitting and to family decisions about communication development options.
• Further studies are needed to determine the true prevalence of congenital, late-onset, progressive and acquired impairment, and to clarify its relationship to risk indicators.
• Existing literature is unclear with respect to the management of auditory neuropathy (AN) and the value of auditory steady state response (ASSR) testing.

Key References

1. Prieve B, Dalzell L, Berg A, et al. The New York State universal newborn hearing screening demonstration project: outpatient outcome measures. Ear Hearing. 2000 Apr;21(2):104-17.
2. Thompson DC, McPhillips H, Davis RL, et al. Universal Newborn Hearing Screening. JAMA. 2001 Oct;286:2000-10.
3. Gravel JS. Potential pitfalls in the audiological assessment of infants and young children. In: Seewald RC, Gravel JS, editors. A Sound Foundation Through Early Amplification 2001. Phonak AG; 2002. p. 85-102.
4. Gravel JS. Audiologic assessment for the fitting of hearing instruments: Big challenges from tiny ears. In: Seewald RC, editor. A Sound Foundation Through Early Amplification. Phonak AG; 2000. p. 33-46.
5. Joint Committee on Infant Hearing. Year 2000 Position Statement: Principles and Guidelines for Early Hearing Detection and Intervention Programs. Am J Audiol. 9:9-29.
6. Stapells DR, Oates P. Estimation of the pure-tone audiogram by the auditory brainstem response: a review. Audiol Neuro-Otol. 1997;2:257-80.
7. Durieux-Smith A, Picton TW, Bernard P, et al. Prognostic validity of brainstem electric response audiometry in infants of a neonatal intensive care unit. Audiology. 1991;30(5):249-65.
8. Hyde ML, Riko K, Malizia K. Audiometric accuracy of the click ABR in infants at risk for hearing loss. J Am Acad Audiol. 1990;1:59-66.
9. Stapells DR. Threshold estimation by the tone-evoked auditory brainstem response; a literature meta-analysis. J Speech Lang Pathol Audiol. 2000 Jun;24:74-83.
10. Cone-Wesson B, Ramirez GM. Hearing sensitivity in newborns estimated from ABRs to bone-conducted sounds. J Am Acad Audiol. 1997 Oct;8(5):299-307.
11. Foxe JJ, Stapells DR. Normal infant and adult auditory brainstem responses to bone-conducted tones. Audiology. 1993;32(2):95-109.
12. Kramer SJ. Frequency-specific auditory brainstem responses to bone-conducted stimuli. Audiology. 1992;31(2):61-71.
13. Yang EY, Stuart A, Mencher GT, et al. Auditory brainstem responses to airand bone-conducted clicks in the audiological assessment of at-risk infants. Ear Hearing. 1993 Jun;14(3):175-82.
14. Sininger YS, Abdala C, Cone-Wesson B. Auditory threshold sensitivity of the human neonate as measured by the auditory brainstem response. Hearing Res. 1997;104:27-38.
15. Starr A, Picton TW, Sininger Y, et al. Auditory neuropathy. Brain. 1996 Jun;119:741-53.
16. Mehl AL, Thomson V. The Colorado Newborn Hearing Screening Project, 1992-1999: On the threshold of effective population-based universal newborn hearing screening. Pediatrics. 2002;109(1):E7.
17. Brown DK, Dort JC. Auditory Neuropathy: When test results conflict. J Otolaryngol. 2001;30(1):46-51.
18. Sininger Y, Oba S. Patients with Auditory Neuropathy: Who are they and what can they hear? In: Sininger Y, Starr A, editors. Auditory Neuropathy: A New Perspective on Hearing Disorders. San Diego: Singular; 2001. p. 15-36.
19. Rance G, Beer DE, Cone-Wesson B, et al. Clinical findings for a group of infants and young children with auditory neuropathy. Ear Hearing. 1999;20:238-52.
20. Lins OG, Picton T. Auditory steady-state responses to multiple simultaneous stimuli. Electroen Clin Neuro. 1995;96(5):420-32.
21. Dimitrijevic A, John M, van Roon P, Picton T. Human auditory steady-state responses to tones independently modulated in both frequency and amplitude. Ear Hearing. 2001;22(2):100-11.
22. Lins OG, Picton T, Boucher B, et al. Frequency-specific audiometry using steady-state responses. Ear Hearing. 1996;17(2):81-96.
23. Rance G, Rickards F, Cohen L, et al. The automated prediction of hearing thresholds in sleeping subjects using auditory steady-state evoked potentials. Ear Hearing. 1995;16(5):499-507.
24. Levi EC, Folsom RC, Dobie RA. Amplitude-modulation following response (AMFR): effects of modulation rate, carrier frequency, age, and state. Hearing Res. 1993;68(1):42-52.
25. Cohen LT, Rickards FW, Clark GM. A comparison of steady-state evoked potentials to modulated tones in awake and sleeping humans. J Acoust Soc Am. 1991;90(5):2467-79.
26. Picton TW, John M, Dimitrijevic A, et al. Human auditory steady-state responses. Int J Audiol. 2003;42:117-219.
27. Picton TW, Durieux-Smith A, Champagne SC, et al. Objective evaluation of aided thresholds using auditory steady-state responses. J Am Acad Audiol. 1998;9:315-31.
28. John MS, Lins O, Boucher B, Picton T. Multiple auditory steady-state responses (MASTER): stimulus and recording parameters. Audiology. 1998;37(2):59-82.
29. Probst R. Otoacoustic Emissions: an overview. In: Pfaltz CR, editor. New Aspects of Cochlear Mechanics and Inner Ear Pathophysiology. Advanced Otorhinolaryngology. Basel: Karger; 1990. p. 1-91.
30. Eggermont JJ, Brown DK, Ponton C, Kimberley B. Comparison of distortion product otoacoustic emission (DPOAE) and auditory brainstem response (ABR) traveling wave delay measurements suggests frequency-specific synapse maturation. Ear Hearing. 1996;17(5):386-94.
31. Kimberley BP, Hernadi I, Lee A, Brown DK. Predicting pure tone thresholds in normal and hearing-impaired ears with distortion product emission and age. Ear Hearing. 1994;15(3):199-209.
32. Koivunen P, Uhari M, Laitakari K, et al. Otoacoustic emissions and tympanometry in children with otitis media. Ear Hearing. 2000;21(3):212-7.
33. Sutton GJ, Gleadle P, Rowe SJ. Tympanometry and otoacoustic emissions in a cohort of special care neonates. Brit J Audiol. 1996 Feb;30(1):9-17.
34. Gorga MP, Neely S, Ohlrich B, et al. From laboratory to clinic: a large-scale study of distortion product otoacoustic emissions in ears with normal hearing and ears with hearing loss. Ear Hearing. 1997;18(6):440-55.
35. Harris FP, Probst R. Otoacoustic Emissions and Audiometric Outcomes. In: Robinette MS, Glattke TJ, editors. Otoacoustic Emissions: Clinical Applications. New York: Thieme; 1997. p. 151-80.
36. ASHA Tutorial: tympanometry. Working group on aural acoustic immittance measurements. J Speech Hear Disord. 1988;53:354-77.
37. Meyer SE, Jardine CA, Deverson W. Developmental changes in tympanometry: a case study. Brit J Audiol. 1997 Jun;31(3):189-95.
38. Paradise JL, Smith CG, Bluestone CD. Tympanometric detection of middle ear effusion in infants and young children. Pediatrics. 1976 Aug;58(2):198-210.
39. Hunter LL, Margolis RH. Multifrequency tympanometry. Current clinical application. Am J Audiol. 1992 Jul;1:33-43.
40. Holte L, Margolis RH, Cavanaugh RM Jr. Developmental changes in multifrequency tympanograms. Audiology. 1991;30(1):1-24.
41. Marchant CD, McMillan PM, Shurin PA, et al. Objective diagnosis of otitis media in early infancy by tympanometry and ipsilateral acoustic reflex thresholds. J Pediatr. 1986 Oct;109(4):590-5.
42. Widen JE, Folsom RC, Cone-Wesson B, et al. Identification of neonatal hearing impairment: hearing status at 8 to 12 months corrected age using a visual reinforcement audiometry protocol. Ear Hearing. 2000 Oct;21(5):471-87.
43. Gravel JS, Wallace IF. Audiologic management of otitis media. In: Bess FH, editor. Children with Hearing Loss: Contemporary Trends. Nashville, TN: Bill Wilkerson Center Press; 1998. p. 215-30.

Medical Evaluation of a Child with Bilateral Sensorineural Hearing Impairment

Authors: Dr. Brian Westerberg, Dr. Sanjay Morzaria, Dr. Frederick Kozak and Dr. David Price

Universal newborn hearing screening (UNHS) programs target earliest identification of sensorineural hearing impairment (SNHI) and facilitate entry into an early hearing and communication development (EHCD) program. As such, clinicians will encounter children with SNHI at a younger age. Medical evaluation of a newborn with hearing impairment should be initiated prior to 3 months of age and intervention initiated prior to 6 months of age. Establishing the etiology for SNHI is important to allow patients at risk for SNHI to be identified early, to allow physicians to intervene against the causative factor (i.e., stop potentially ototoxic drug therapy), and to provide the patient and family with prognostic information.

A detailed history, physical examination and audiological evaluation are the most important steps in diagnosing the etiology of SNHI.¹ Many syndromes and infectious etiologies can be diagnosed by these methods. This critical review provides a discussion of the etiology of childhood bilateral SNHI (>40 dBHL) and a review of processes for diagnostic evaluation.

Etiology of Bilateral Sensorineural Hearing Impairment

Advances in genetic testing and aggressive management of perinatal infections have altered the frequency of diagnoses of etiologies of SNHI.^2-8 Recent studies suggest that autosomal recessive genes are responsible for most cases of unknown etiology (i.e., connexin 26 (cx26), see below). The etiologic categories and their prevalence are:

1. Unknown (37.7%)
2. Genetic - nonsyndromic (29.2%) and syndromic (3.2% - e.g., Waardenburg syndrome)
3. Nongenetic - prenatal (12% - e.g., rubella, cytomegalovirus), perinatal (9.6% - e.g., prematurity, asphyxia, kernicterus), postnatal (8.2% - e.g., meningitis). Auditory neuropathy (AN) is presumed to be a nongenetic postnatal cause. Its frequency and etiology requires further study.

Presentation of Common Etiologies

The presentation of the more common etiologies of bilateral SNHI and the results of investigations are discussed in this section.

Unknown

With careful investigation, a presumptive cause can be determined in some children with bilateral SNHI previously labeled as "unknown."^8,9 Genetic nonsyndromic is often the presumed cause following the obtaining of further details regarding family history.

A recent study¹⁰ retrospectively tested stored neonatal blood of children diagnosed with SNHI, and identified five children (12% of children with SNHI) believed to have SNHI secondary to intrauterine cytomegalovirus (CMV) infection (four unilateral and one bilateral hearing impairment). The role of prenatal infections is an area that requires further investigation.

Genetic Nonsyndromic

Most of the nonsyndromic recessive gene mutations produce congenital profound deafness, although there is variation. Genetic nonsyndromic hearing impairment is highly heterogeneous. At the time of this review, 30 recessive genes have been localized with 7 of the genes identified; 39 dominant genes have been localized with 11 identified; and 7 X-linked genes have been localized with one identified.¹¹

The most common recessive nonsyndromic mutation is in the beta-2 gene on chromosome 13 that produces the protein connexin 26 (cx26). Mutations in the cx26 gene produce hearing impairments with considerable range in severity, from the mild-moderate range to profound. Cx26 forms gap junctions between cells and is thought to help recirculation of ions in the cochlear endolymph.¹² Mutations in this gene account for half of all nonsyndromic recessive deafness, meaning that they cause 30-50% of genetic nonsyndromic deafness. The carrier frequency in European populations is about one in forty.¹³

Genetic Syndromic

An example within this classification is Waardenburg syndrome, an autosomal dominant syndrome with variable penetrance.¹⁴ Clinical features include lateral displacement of the medial canthi of the eyelids, high nasal root, hypertrichosis, confluent eyebrows, pigmentary disorders and SNHI. Hearing impairment, unilateral or bilateral, occurs in 30-50% of patients with Waardenburg syndrome.¹⁵ The possibility that such features may appear fortuitously in some family members can make it difficult to ascertain whether the syndrome is present. There are several classifications for Waardenburg syndrome, defined by physical characteristics. Individuals with dystopia canthorum have Type 1. SNHI occurs in about 20% of individuals with Type 1. Patients without dystopia canthorum (Type 2) have a 50% prevalence of SNHI and the hearing impairment is more likely to be progressive.¹⁶ The SNHI may be unilateral or bilateral.^15,17 A radiological abnormality of the inner ear was detected in 17% of patients.¹⁸ Genetic testing is possible for Waardenburg syndrome (i.e., PAX3, EDNRB, EDN3; Smith et al.¹⁹) but not widely available. The sensitivity and specificity of genetic testing for this condition is not well described in the literature.

Nongenetic

Prematurity

Prematurity is defined as birth before completion of the 37th week of gestation. Although several risk factors for SNHI, such as perinatal hypoxia, sepsis and kernicterus, may be present in premature neonates, prematurity constitutes a unique reliable risk indicator. Premature infants are 20 times more likely to be severely hearing impaired than infants of normal weight and gestational age.²⁰ The mechanism for this is not well understood, but is believed to involve recurrent apnea attacks. The natural history of the SNHI associated with prematurity has not been well described. If the potential for prematurity cannot be established prior to birth, based on risk factors or ultrasound dating, there are characteristic neonatal signs and symptoms which include: weak cry, hypotonia, abnormal posturing and poor feeding.^21-23 The reliability of these clinical measures is not well described.

Asphyxia

There is evidence that birth asphyxia can result in damage to the central auditory pathways and to the cochlea. Autopsy studies have shown ischemic lesions of the cortical gray matter, basal ganglia and brainstem in infants with perinatal asphyxia.²⁴ The severity of pathologic findings correlates with the duration of hypoxia.²⁵ The pathophysiology would indicate that the hearing impairment is present at birth. However, the natural history of the SNHI is not well described in the literature.

Meningitis

SNHI secondary to meningitis is due to cochlear damage with a reduction in neurons in the spiral ganglia and destruction of outer and inner hair cells.²⁶ Most patients with meningitis sustain permanent, bilateral, severe-profound SNHI, but in a series of 64 cases of meningococcal meningitis, 38% had bilateral asymmetric SNHI and 11% exhibited a unilateral SNHI.²⁷ The reported incidence of SNHI after meningitis has varied from 3-40%, with most reports clustered in the 15-20% range.²⁸ Eighty-nine percent of those who suffered post-meningitic hearing impairment contracted meningitis before the age of 3 years.²⁹ Post-meningitic hearing impairment has been described as occurring as late as six months after an episode of meningitis, although patients who exhibit a normal auditory brainstem response (ABR) after the first few days of hospitalization and antibiotic therapy are unlikely to develop SNHI.³⁰

Kernicterus

Hyperbilirubinemia is defined as a serum bilirubin greater than 1.5mg/100ml.³¹ Hyperbilirubinemia during the first week of life is most often due to overproduction of bilirubin through hemolysis and defective conjugation. Kernicterus defines a syndrome of neurologic sequelae secondary to bilirubin crossing the blood-brain barrier. It is often seen at values greater than 1.8-2.0mg/100ml. Early symptoms and signs include extreme jaundice, absent Moro (startle) reflex, poor suck and lethargy. Late features include high-pitched cry, arched back with neck hyperextension (opisthotonos), bulging fontanel and seizures.³² The association of kernicterus with SNHI is well documented and believed to be secondary to deposition of bilirubin in the cochlear nuclei and basal ganglia.³³ It is also associated with auditory neuropathy (see below).

Rubella

Defects attributed to congenital rubella infection include SNHI, cataracts, micro-phthalmia, buphthalmos, ventricular septal defect, pulmonary stenosis, microcephaly, cerebral palsy, mental retardation, thrombocytopenic purpura, rash, hepatomegaly, splenomegaly and osteopathy.³⁴ Not all associated defects present concurrently. In fact, 40% of children included in the National Congenital Rubella Surveillance Program (NCRSP) had a single organ defect,³⁵ and hearing impairment is present as an isolated defect in 22% of children.³⁶ The greatest risk occurs with maternal infection during the first trimester.³⁷ This risk has been estimated in various prospective studies to be between 60% and 90%.^38,39

SNHI is the most common defect secondary to intrauterine exposure to rubella. It is usually bilateral but can be unilateral. Reported damage to the auditory system has included degenerative and inflammatory changes affecting the organ of Corti, stria vascularis, Reisener's membrane and the tectorial membrane. ⁴⁰

In some children with SNHI secondary to rubella, it may be possible to elicit a maternal history of contact with rubella or of a rash during pregnancy. However, 24% of mothers of children registered with the NCRSP were unable to give any history of contact, rash or illness during pregnancy.³⁵ In a proportion of children with no evidence of damage other than a hearing impairment, there may be signs of rubella retinopathy to indicate that a congenital infection has taken place. The retinopathy is the result of alternate areas of hyperpigmentation and hypopigmentation, and the appearance is described as a "salt and pepper" effect. It does not usually affect visual acuity. Fifty percent of patients with congenital rubella display the typical retinopathy.⁴¹ Sera obtained in pregnancy which show seroconversion or a significant rise in antibody titre, and detection of specific IgM antibody provide evidence of definite infection.⁴² Demonstration of rubella-specific IgM in cord serum is diagnostic of a congenital infection, as immunoglobulin of the IgM class does not cross the placental barrier.

With routine immunization programs, rubella as a cause for SNHI has practically been eradicated in developed countries.

Auditory Neuropathy

The syndrome of auditory neuropathy (AN) has only recently been described. AN is defined by the presence of otoacoustic emissions (OAEs), an abnormal ABR, absence of middle ear muscle responses and elevated or absent behavioral responses to sound. Speech intelligibility is affected out of proportion to pure tone thresholds.^43,44

The audiometric pattern is variable but typically demonstrates a rising or flat configuration. The hearing may fluctuate over time. Children with AN can achieve favourable results with cochlear implantation.⁴⁵

AN has been associated with hyperbilirubinemia, neurodegenerative diseases, neuro-metabolic diseases, demyelinating diseases, hereditary motor sensory neuropathology (e.g., Charcot-Marie-Tooth syndrome), inflammatory neuropathy, hydrocephalus, severe and/or pervasive developmental delay, ischemic-hypoxic neuropathy, encephalopathy, meningitis and cerebral palsy.⁴⁶ A genetic factor may exist as AN has been described in families.⁴⁷ The postulated site of lesion is the inner hair cell/cochlear afferent system.⁴⁸

Diagnostic Yield of Tests Used to Determine the Etiology of Sensorineural Hearing Impairment

When ordering investigations for SNHI, the clinician needs to know what the diagnostic certainty is associated with a positive or negative test result.

Genetic Testing

Studies have shown that the carrier rate for the 35delG mutation of connexin 26 (cx26) is between 2% and 3%, similar to the carrier rate for the gene for cystic fibrosis. The polymerase chain reaction assay for cx26 has a sensitivity and specificity of 97.4% and 96.9%, respectively.¹³ In addition to its high yield, proponents of early genetic testing advocate its minimal morbidity. Although blood sampling allows for a greater yield of DNA, buccal smears are an alternative means of obtaining DNA.⁴⁹ Interest in the role of genetic testing continues to expand.

CT Scan

Radiological abnormalities may be present on CT scans in up to 37% of children with SNHI.⁵⁰ Large vestibular aqueducts (LVA) are the most common isolated findings, followed by lateral semicircular canal dysplasia, otic capsular lucency, small internal auditory canals and hypoplastic cochlea. At least 40% of patients with LVA will develop profound SNHI.⁵¹ The presence of LVA may also indicate additional malformations and has been associated with stapes gusher syndrome, lateral semicircular canal dysplasia and Mondini deformity.⁵²

Laboratory Studies

The low diagnostic yield for blood tests (CBC, platelet count, autoimmune evaluation and blood glucose), in the absence of other specific disease manifestations, does not justify their routine use.

The diagnosis of Pendred syndrome depends on the demonstration of the triad of congenital SNHI, goitre and abnormal perchlorate discharge test.⁵³ Given the rare abnormalities on thyroid function studies, they should only be performed in the presence of clinical signs and symptoms of hypothyroidism, presence of goitre, or when there is radiological evidence of LVA or Mondini deformity.

Other Studies

An electrocardiogram (ECG) may be valuable to detect conduction abnormalities associated with Jervell Lange Neilson (JLN) syndrome. It is a rare disorder with an estimated incidence of one to six cases per million.⁵⁴ However, in a review of the reported cases of JLN ("hereditary Q-T prolongation syndrome"), the frequency in deaf children was found to be 0.3%.⁵⁵ Identification of patients with JLN can be lifesaving. An ECG is particularly valuable when a history of syncope, arrhythmias, or a family history of sudden death in a young child is elicited.

Urinalysis alone may not be adequate for the diagnosis of Alport syndrome. Examination of urine for glomerular basement membrane proteins, however, did provide a high diagnostic yield.^56,57 However, the cost of this test may be prohibitive to be used for routine screening. An unanswered question is the value of detecting hematuria and/or proteinuria on routine urinalysis. Routine urinalysis is inexpensive and simple to perform. Its role relative to the child with SNHI is unresolved.

Conclusions

• Medical evaluation of an infant with hearing impairment should be initiated at less than 3 months of age and intervention should be started by 6 months of age.
• Common etiologies of bilateral sensorineural hearing impairment (SNHI) include nonsyndromic gene mutations (such as connexin 26 (cx26) mutations), genetic syndromes (such as Waardenburg syndrome) and nongenetic causes involving preterm birth, asphyxia, meningitis, kernicterus, intrauterine infection and auditory neuropathy (AN).
• There is a need for evidence-based rational decision strategies, embracing history taking, physical examination, risk assessment and genetic testing and their interpretation, in children with bilateral SNHI.

Key References

1. Tomaski SM, Grundfast KM. A stepwise approach to the diagnosis and treatment of hereditary hearing loss. Pediatr Clin N Am. 1999;46:35-48.
2. Dutta PK, Banerjee A. An epidemiological study of hearing loss in a slum in Pune. Indian J Public Health. 1991;4:108-12.
3. Karikoski JO, Martilla TI. Prevalence of childhood hearing impairment in southern Finland. Scand Audiol. 1995;24:237-41.
4. Kiese-Himmel C, Schroff J, Kruse E. Identification and diagnostic evaluation of hearing impairments in early childhood in German-speaking infants. Eur Arch Oto-Rhino-L. 1997;254:133-9.
5. Naarden KV, Decoufle P, Caldwell K. Prevalence and characteristics of children with serious hearing impairment in metropolitan Atlanta, 1991-1993. Pediatrics. 1999;103:570-3.
6. Parving A, Hauch AM. The causes of profound hearing impairment in a school for the deaf - a longitudinal study. Brit J Audiol. 1994;28:63-69.
7. Zakzouk SM. Epidemiology and etiology of hearing impairment among infants and children in a developing country. J Otolaryngol. 1997;6:335-44.
8. Zakzouk SM, Al-Anazy F. Sensorineural hearing impaired children with unknown causes: a comprehensive etiological study. Int J Pediatr Otorhi. 2002;64:17-21.
9. Parving A. Inherited low-frequency hearing loss. A new mixed conductive sensorineural entity? Scand Audiol. 1984;13(1):47-56.
10. Barbi M, Binda S, Caroppo S, et al. A wider role for congenital cytomegalovirus infection in sensorineural hearing loss. Pediatr Infect Dis J. 2003;22(1):39-42.
11. Van Camp G, Smith RJH. Hereditary Hearing Loss [monograph on the Internet]. Available from: <http://webhost.ua.ac.be/hhh/main.html>.
12. Kikuchi T, Kimura RS, Paul DS, et al. Gap junction systems in the mammalian cochlea. Brain Res Rev. 2000;32:163-6.
13. Green GE, Scott DA, McDonald JM, et al. Carrier rates in the Midwestern United States for GJB2 mutations causing inherited deafness. JAMA. 1999;281:2211-6.
14. Waardenburg PJ. A new syndrome combining developmental anomalies of the eyelids, eyebrows and nasal root with pigmentary defects of the iris and head hair and with congenital deafness. Am J Hum Genet. 1951;3:195-253.
15. Hageman MJ, Delleman JW. Heterogeneity in Waardenburg Syndrome. Am J Hum Genet. 1977;29:468-85.
16. Hildesheimer M, Maayan Z, Muchnik C, at al. Auditory and vestibular findings in Waardenburg's Type 2 syndrome. J Laryngol Otol. 1989;103:1130-3.
17. National Institute on Deafness and Other Communication Disorders [homepage on the Internet]. 2003. Available from: <http://www.nidcd.nih.gov/health/hearing/waard.asp>.
18. Oysu C, Oysu A, Aslan I, Tinaz M. Temporal bone imaging findings in Waardenburg's syndrome. Int J Pediatr Otorhi. 2001;58(3):215-21.
19. Smith SD, Schaefer GB, Horton MB, et al. Medical genetic evaluation for the etiology of hearing loss in children. J Commun Disord. 1998;31:371-88.
20. Southall DP, Richards JM, Rhoden KJ, et al. Prolonged apnea and cardiac arrhythmias in infants discharged from neonatal intensive care units. Pediatrics. 1982;70:844-51.
21. American College of Obstetricians and Gynecologists. Home uterine activity monitoring. Committee opinion no. 172. Washington, DC: ACOG; 1996.
22. Canadian Preterm Labor Investigators Group. Treatment of preterm labor with the beta-adrenergic agonist ritodrine. N Engl J Med. 1992;327:308-12.
23. Creasy RK, Herron MA. Prevention of preterm birth. Semin Perinatol. 1981;5:295-302.
24. Wigglesworth JS, Pape KE. An integrated model for hemmorhage and ischemic lesions in the newborn brain. Early Hum Dev. 1978;2:179-99.
25. Pape KE, Wigglesworth JS. Hemmorhage, Ischemia and the Perinatal Brain. London: Heinemann Medical (for) Spastic International Medical Publications, Lippincott; 1979.
26. Paparella MM, Capps MJ. Sensorineural deafness in children - no genetic. Otolaryng Head Neck. 1973.
27. Moss TD. Outcome of meningococcal Group B meningitis. Arch Dis Child. 1982;57:616-21.
28. Hinojosa R, Lindsay JR. Profound deafness, associated sensory and neural degeneration. Arch Otolaryngol. 1980;106;193-209.
29. Brookhauser PE, Worthington DW, Kelly WJ. The pattern and stability of postmeningitic hearing loss in children. Laryngoscope. 1988;98:940.
30. Rosenhall U, Nylen O, Lindberg J, et al. Auditory function after Haemophilus influenzae meningitis. Acta Oto-Laryngol. 1978;85:243-7.
31. Odell GB. Neonatal hyperbilirubinemia. New York: Grune and Stratton; 1980.
32. Billings R. Rh incompatability [mongraph on the Internet]. 2003. Available from: <http://www.1uphealth.com/health/rh_incompatibility_diagnosis_tests.html>.
33. Keaster J, Hyman CB, Harris I. Hearing problems subsequent to neonatal hemolytic disease or hyperbilirubinemia. Am J Dis Child. 1969;117:406-10.
34. Dudgeon JA. Congenital rubella: a preventable disease. Postgrad Med J. 1972;3:7-11.
35. Sheppard S. National Congenital Rubella Surveillance Program, 1971-1981. Proceedings of the Scientific Meeting of the British Association of Audiological Physicians and Community Pediatric Group; 1981.
36. Balkany TJ, Luntz M. Diagnosis and management of sensorineural hearing disorders. In: Lalwani AK, Grundfast KM, editors. Pediatric Otology and Neurotology. Philadelphia, PA; 1998. p. 397-403.
37. Siegel M, Fuerst HT, Guinee UF. Rubella epidemicity and embryopathy. Results of a long-term study. Am J Dis Child. 1971;121:469-73.
38. Hurley R. Virus infections in pregnancy and the puerperium. Recent Advances in Clinical Virology. 1983.
39. Dudgeon JA. Laboratory studies in congenital rubella deafness. Int J Audiol. 1970;9:68-76.
40. Grumpel S. Clinical and social status of patients with congenital rubella. Arch Dis Child. 1972;47:330-7.
41. Schei HG, Albert DM. Adler's textbook of ophthalmology. W.B. Saunders; 1986.
42. Tobin JOH. Viruses and Deafness. Proceedings of the Scientific Meeting of the British Association of Audiological Physicians and Community Pediatric Group; 1981.
43. Starr A, Picton TW, Sininger Y, et al. Auditory neuropathy. Brain. 1996 Jun;119(3):741-53.
44. Berlin CI, Morlet T, Hood LJ. Auditory neuropathy/dyssynchrony: its diagnosis and management. Pediatr Clin of N Am. 2003 Apr;50(2):331-40,vii-viii.
45. Buss E, Labadie RF, Brown CJ, et al. Outcome of cochlear implantation in pediatric auditory neuropathy. Otol Neurotol. 2002 May;23(3):328-32.
46. Campbell KCM, Mullin-Derrick G. Otoacoustic Emissions [monograph on the Internet]. 2002 Jul. Available from: <http://www.emedicine.com>.
47. Madden C, Rutter M, Hilbert L, et al. Clinical and audiological features in auditory neuropathy. Arch Otolaryngol. 2002 Sep;128(9):1026-30.
48. Sawada S, Mori N, Mount RJ, Harrison RV. Differential vulnerability of inner and outer hair cell systems to chronic mild hypoxia and glutamate ototoxicity: insights into the cause of auditory neuropathy. J Otolaryngol. 2001 Apr;30(2):106-14.
49. Greinwald JH, Hartnick CJ. The evaluation of children with sensorineural hearing loss. Arch Otolaryngol. 2002;128:84-87.
50. Mafong DD, Shin EJ, Lalwani AK. Use of laboratory evaluation and radiologic imaging in the diagnostic evaluation of children with SNHL. Laryngoscope. 2002;112:1-7.
51. Reilly GP, Lalwani AK, Jackler RK. Congenital anomalies of the inner ear. In: Lalwani AK, Grundfast KM, editors. Pediatric Otology and Neurotology. Philadelphia, PA; 1998. p. 201-10.
52. Shirazi A, Fenton JE, Fagan PA. Large vestibular aqueduct syndrome and stapes fixation. J Laryngol Otol. 1994;108:989-90.
53. Fugazzola L, Mannavola D, Cerutti N, et al. Molecular analysis of the Pendred's syndrome gene and magnetic resonance imaging studies of the inner ear are essential for the diagnosis of true Pendred's syndrome. J Clin Endocr Metab. 2000;85(7):2469-75.
54. Fraser GR, Froggart P, James TN. Congenital deafness associated with ECG abnormalities: a recessive syndrome. Q J Med. 1964;33:361-85.
55. Hashiba K. Hereditary QT prolongation syndrome in Japan: Genetic analysis and pathological findings of the conducting system. Jpn Circulation J. 1978;42:1133-50.
56. Bartosch B, Vycudilik W, Popow C, Lubec G. Urinary 3-hydroxyproline excretion in Alport's syndrome: a non-invasive screening test? Arch Dis Child. 1991 Feb;66(2):248-51.
57. Lubec G, Balzar E, Weissenbacher G, Syre G. Urinary excretion of glomerular basement membrane antigens in Alport's syndrome. A new diagnostic approach. Arch Dis Child. 1978 May;53(5):401-6.

Additional References

Management of Middle Ear Disease in Children Less than 2 Years of Age with Sensorineural Hearing Impairment

Authors: Dr. Brian Westerberg, Dr. Sanjay Morzaria, Dr. Frederick Kozak, and Dr. David Price

Seventy to ninety percent of children will experience fluctuating conductive hearing impairment (CHI) secondary to otitis media with effusion (OME) with or without acute otitis media (AOM) in their first two years of life. The child less than 2 years of age with fluctuating CHI and underlying sensorineural hearing impairment (SNHI) presents a challenging diagnostic and therapeutic dilemma. Given the attention to and implementation of early hearing and communication development (EHCD) programs, physicians are increasingly requested to review young children and infants to assess and manage medical conditions associated with hearing impairment.

Measures of speech and language development have been shown to be negatively correlated with duration of time spent with OME in a child's first years of life.^1,2 Fluctuating CHI may have a greater effect on speech discrimination than a comparable SNHI.³ The conditions that cause CHI affect the performance of various diagnostic tests,⁴ further compromise hearing in a child with SNHI and lead to delays in diagnosis and hearing and communication development options.⁵ Otoacoustic emissions (OAEs), for example, can be influenced by debris in the ear canal and the presence of middle ear fluid.⁶

This critical review focuses on the child with fluctuating CHI and SNHI. It does not address the management of children with permanent CHI (e.g., secondary to congenital ossicular fixation or external auditory canal atresia). These conditions pose less of a management dilemma for the physician and audiologist, and are beyond the scope of this review. In addition, the modification of behavioural and environmental risk factors for OME and AOM is not comprehensively addressed. Current evidence suggests the risk of AOM or OME in an otherwise healthy child 1 to 3 years of age is increased with exposure to passive smoking, group daycare attendance and bottle feeding.⁷ The rationale for modification of these risk factors applies equally well to children with and without SNHI. Finally, audiological tests for OME were also not specifically reviewed, i.e., tympanometry. It is recognized that these tests are an important adjunct to clinical examination.

Diagnosis of Otitis Media with Effusion

Accurate assessment of OME may prevent delays in diagnosis and unnecessary treatment of children with a permanent childhood hearing impairment (PCHI). Pneumatic otoscopy is strongly recommended by the Otitis Media Guideline Panel⁷ for the diagnostic evaluation of OME in otherwise healthy children ages 1 to 3 years, as this allows the observer to directly see the effect of positive and negative pressure on the mobility of the tympanic membrane.

There is no published literature regarding the accuracy of pneumatic otoscopy in diagnosing OME in a child less than 2 years of age with SNHI. Studies in healthy children suggest a sensitivity of 85-98% and a specificity of 71-90%.^8-10 As with other procedures, tester training significantly improves diagnostic accuracy.¹¹ Clinical examination results should be interpreted in conjunction with audiological assessments performed when diagnosing OME. Tympanometry and acoustic reflexometry are possible in children less than 2 years of age. Of note, the diagnostic agreement among the three tests is poor in the newborn period,¹² but improves significantly after 2 to 3 months of age.¹³

Middle Ear Fluid: Prevalence and Clearance

Most newborns referred for audiologic diagnostic evaluation from EHCD programs are subsequently found not to have PCHI. Retained amniotic fluid is a hypothesized cause for false-positive results on newborn hearing screening. Amniotic fluid takes many days to clear from the newborn's middle ear (see Figure 1).

Figure 1: Natural History of Clearance of Amniotic Fluid from the Middle Ear following Birth

The peak prevalence of OME occurs between 6 and 12 months of age and is significantly more common in high-risk born infants.¹⁶ Unilateral OME will clear after an average of five weeks with or without a history of AOM; bilateral OME will clear on average nine weeks following AOM, and after eight weeks without a history of AOM.¹⁷

Managing Otitis Media with Effusion

Many clinicians recommend an aggressive approach to the management of OME in a child with an underlying SNHI. Developing guidelines for the treatment of children with OME and co-existing SNHI requires extrapolation from studies on otherwise healthy children. However, many experts recommend more aggressive management.¹⁸

Ventilation Tubes

Bilateral myringotomy and ventilation tube (BM&T) placement reduce the mean duration of OME over the year following their placement from 277 days to 142 days and result in improved hearing thresholds by a mean of 5-6 dB.¹⁹ However, some of the complications of ventilation tubes are associated with CHI, i.e., otorrhea and perforations (2.2% for short-term tubes; 16.6% for long-term tubes).²⁰

Behavioural problems may be more common in children with OME and improvement of the CHI by BM&T may improve the behavioural problems.²¹ Verbal and expressive language scores in children with OME may be delayed compared to healthy children.²² There is some evidence to suggest that BM&T will improve these measures as well.

Many physicians advocate an aggressive approach to children with OME and underlying SNHI. Based on this review, if OME persists for eight to twelve weeks, BM&T with short-term tubes (lower complication rate) should be discussed with the parents.

Antibiotics

Antibiotics offer a small short-term increase in the likelihood of resolution of OME in otherwise healthy children.¹⁸ Seven children require treatment with an antibiotic for one to benefit - number needed to treat (NNT) = 7. This small benefit must be weighed against the potential adverse effects of antibiotic use which includes an increase in bacterial resistance to the antibiotic in the child's community.

In a child with co-existing SNHI and OME for four to six weeks, a course of 10 days of a first-line antibiotic (amoxicillin 40-80 mg/kg/day) may be warranted.

Other Treatments

Adenoidectomy is not indicated in this age group for the treatment of OME due to a lack of studies to support its efficacy.⁷ Steroids, antihistamine-decongestants and tonsillectomy are not recommended.⁷

Management of Acute Otitis Media

Fluctuating CHI secondary to AOM in the child less than 2 years of age is presumed to cause similar problems to that caused by OME. Concerns of a lower rate of clinical resolution, and possibly an increased risk of complications from AOM in children less than 2 years compared to children more than 2 years of age, currently justify a 10-day course of a first-line antibiotic (amoxicillin 40-80 mg/kg/day).²³ Treatment should be individualized, as some children may be at a greater risk of long-term complications of middle ear disease warranting more aggressive treatment of AOM. For example, Canadian Inuit children may have a greater risk of developing CHI as a result of middle ear disease.²⁴

A child with three or more episodes of AOM in six months, or four or more episodes in one year, can be managed with either prophylactic antibiotics or BM&T.¹⁸ If BM&T is considered to be necessary in a child with underlying SNHI, intubation with short-term rather than long-term ventilation tubes is indicated given the lower risk of chronic perforation.²⁰ Alternatively, a child with recurrent AOM can be treated with a trial of one to six months of prophylactic antibiotics (amoxicillin 20 mg/kg/day). This would avoid the risk of otorrhea and/or perforation secondary to BM&T but may increase the development of resistant bacteria in the community. There is good justification for restricting the use of prophylactic antibiotics due to an increase in bacterial resistance in the community following widespread use.

Conjugate pneumococcal vaccine will reduce the overall risk of AOM by 6-7%, the risk of pneumococcal AOM by 25% and the need for BM&T by 20% in healthy children who are less than 3 years of age.^25,26 Prevention of AOM in children with SNHI may be an additional reason to implement publicly-funded programs with this vaccine, if not universally, then for those at higher risk of the detrimental effects of AOM. Similarly, influenza vaccine, in particular intranasal formulations, may be beneficial in reducing the risk of AOM in children.²⁷ Vaccinated children had 6-30% fewer episodes of AOM compared to controls, although the study was not specifically designed to assess reduction in episodes of AOM. Further studies in this area are required.

Conclusions

• 70-90% of children will experience fluctuating conductive hearing impairment (CHI) secondary to otitis media with effusion (OME), with or without acute otitis media (AOM) in the first two years of life.
• Pneumatic otoscopy is recommended for the clinical evaluation of OME in otherwise healthy children under 2 years of age who have sensorineural hearing impairment (SNHI).
• Unilateral OME clears after an average of five weeks with or without a history of AOM, and bilateral OME clears on average after eight to nine weeks.
• Bilateral myringotomy and ventilation tube (BM&T) placement reduces the mean duration of OME and improves hearing thresholds, as well as some behavioural problems and expressive language scores in some children.
• Antibiotic therapy and conjugate pneumococcal vaccine should be considered in relation to middle ear disease in children.
• Further research is needed to explain the natural history of OME in children with SNHI, optimal antibiotic regimes and complications of myringotomy tubes.

Key References

1. Friel-Patti S, Finitzo T. Language learning in a prospective study of otitis media with effusion in the first two years of life. J Speech Hear Res. 1990;33:188-94.
2. Teele DW, Klein JO, Chase C, et al; Greater Boston Otitis Media Study Group. Otitis media in infancy and intellectual ability, school achievement, speech, and language at age 7 years. J Infect Dis. 1990;162:685-94.
3. Katz J. The effects of conductive hearing loss on auditory function. American Speech-Language-Hearing Association 1978;20:879-86.
4. Levi H, Adelman C, Geal-Dor M, et al. Transient evoked otoacoustic emissions in newborns in the first 48 hours after birth. Audiology. 1997;36:181-6.
5. Watkin PM, Baldwin M. Confirmation of deafness in infancy. Arch Dis Child. 1999;81:380-9.
6. Proschel U, Eysholdt U. Evoked otoacoustic emissions in children in relation to middle ear impedance. Folia Phoniatr. 1993;45:288-94.
7. Stool SE, Berg AO, Berman S, et al.; Otitis Media Guideline Panel. Otitis media with effusion in young children. Clinical Practice Guideline, Number 12. AHCPR Publication No. 94-0622. Rockville, MD: Agency for Health Care Policy and Research, Clinical Practice Guideline, Public Health Service, U.S. Department of Health and Human Services; 1994 Jul.
8. Mains BT, Toner JG. Pneumatic otoscopy: Study of inter-observer variability. J Laryngol Otol. 1989,103:1134-5.
9. Vaughan-Jones R, Mills RP. The Welch Allyn Audioscope and Microtymp: their accuracy and that of pneumatic otoscopy, tympanometry and pure tone audiometry as predictors of otitis media with effusion. J Laryngol Otol. 1992;106:600-2.
10. Nozza RJ, CD Bluestone, Kardatzke D, Bachman R. Identification of middle ear effusion by aural acoustic admittance and otoscopy. Ear Hearing. 1994;15(4):310-23.
11. Silva AB, Hotaling AJ. A protocol for otolaryngology-head and neck resident training in pneumatic otoscopy. Int J Pediatr Otorhi. 1997;40:125-31.
12. Roberts DG, Johnson CE, Carlin SA, et al. Resolution of middle ear effusion in newborns. Arch Pediat Adol Med. 1995;149:873-7.
13. Marchant CD, McMillan PM, Shurin PA, et al. Objective diagnosis of otitis media in early infancy by tympanometry and ipsilateral acoustic reflex thresholds. J Pediatr. 1986;109:590-5.
14. Doyle KJ, Rodgers P, Fujikawa S, Newman E. External and middle ear effects on infant hearing screening test results. Otolaryng Head Neck. 2000;122:477-81.
15. Cavanaugh RM. Pneumatic otoscopy in healthy full-term infants. Pediatrics. 1987;79:520-3.
16. Engel J, Anteunis L, Volovics A, et al. Prevalence rates of otitis media with effusion from 0 to 2 years of age: healthy-born versus high-risk-born infants.
    Int J Pediatr Otorhi. 1999;47:243-51.
17. Hogan SC, Stratford KJ, Moore DR. Duration and recurrence of otitis media with effusion in children from birth to 3 years: prospective study using monthly otoscopy and tympanometry. Brit Med J. 1997;314:350-5.
18. Rosenfeld RM, Bluestone CD, editors. Evidence-based otitis media. Hamilton: B.C. Decker Inc.; 1999.
19. Rovers MM, Straatman H, Ingels K, et al. The effect of short-term ventilation tubes versus watchful waiting on hearing in young children with persistent otitis media with effusion: a randomized trial. Ear Hearing. 2001;22:191-9.
20. Kay D, Nelson M, Rosenfeld RM. Meta-analysis of tympanostomy tube sequelae. Otolaryng Head Neck. 2001;124:374-80.
21. Wilks J, Maw R, Peters TJ, et al. Randomised controlled trial of early surgery versus watchful waiting for glue ear: the effect on behavioural problems in pre-school children. Clin Otolaryngol. 2000;25:209-14.
22. Maw R, Wilks J, Harvey I, et al. Early surgery compared with watchful waiting for glue ear and effect on language development in preschool children: a randomised trial. Lancet. 1999;353:960-3.
23. Rosenfeld RM, Casselbrant ML, Hannley MT. Implications of the AHRQ evidence report on acute otitis media. Otolaryng Head Neck. 2001;125:440-8.
24. Moore JA. Comparison of risk of conductive hearing loss among three ethnic groups of Arctic audiology patients. J Speech Lang Hear R. 1999 Dec;42(6):1311-22.
25. National Advisory Committee on Immunization. Advisory Committee Statement (ACS), Statement on recommended use of pneumococcal conjugate vaccine. Canadian Communicable Disease Report - Supplement. 2002 Jan;28:ACS-2.
26. Eskola J, Kilpi T, Palmu A, et al.; Finnish Otitis Media Study Group. Efficacy of a pneumococcal conjugate vaccine against acute otitis media. N Engl J Med. 2001;344(6):403-9.
27. Belshe RB, Mendelman PM, Treanor J, et al. The efficacy of live attenuated, cold-adapted, trivalent, intranasal influenzavirus vaccine in children. N Engl J Med. 1998;338:1405-12.

Additional References

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