Congenital hearing losses with onset in childhood, rather than at birth, arise from genetic susceptibility to deterioration in cochlear hearing levels over time. This may be hearing loss in isolation or as part of a genetic syndrome. Example of genetic syndromes with progressive hearing loss include Alport’s syndrome with renal abnormalities, Usher’s syndrome with loss of vision, and Down’s syndrome (trisomy 21) associated with early conductive hearing loss and abnormal aging. The onset of a hearing loss may be first indication of a wider genetic condition; therefore, careful and thorough investigation of each case is important. The period from birth to 3 years is the critical period for speech and language acquisition, and the aim of newborn hearing screening is for early identified children to have age-appropriate language by school entry. 8 Speech is acquired through hearing and its more active counterpart of listening. There is no part of the child’s day in which it is not important for the child to be able to hear sounds in the environment. The neural processes for binaural hearing, localization skills, listening in noise, and applying auditory attention are laid down in the early years of life. Even a fluctuating conductive hearing loss from middle ear effusion can delay or obstruct these processes for later auditory learning potential. 9 A typical vocabulary size at school entry is between 5,000 and 20,000 words, depending on the richness of language exposure at home, but, by adulthood, it may be 60,000. 10 Most of these words have not been taught but have been acquired through overhearing and tangential learning. Language level and hearing ability predict later acquired literacy skills as the school curriculum is mainly delivered through audition. 11 The scores by children in standardized attainment scores used in Britain for schools are influenced by the noise levels in the classroom, even when controlled for socioeconomic group. 12 This demonstrates the importance of being able to overhear speech by different talkers as a foundation skill for literacy, academic, and social achievement. One of the recent themes being reported in the research literature on hearing impairment is that children with hearing loss often have subtle difficulties in peer-group situations, even if their language skills are age-appropriate on assessment. 13 The evidence is clear: the impact of hearing loss in early life, even for short periods, is wide-ranging and has long-term effects on achievement and life choices. Tips and Tricks Avoid simplified phrases such as “speech is coming on well” unless there are specific measures from standardized evaluations such as language scores. Comments may be quoted out of context and be overinterpreted as meaning “no intervention is required.” The medical doctor’s statements carry very high credibility and may be hard to counterbalance by the relevant professional working with the family thereafter. As the focus of screening for hearing loss is now on identifying children with bilateral permanent hearing loss at birth (with concurrent improvements in outcomes for these infants), how is the much larger group of children, with later and possibly fluctuating hearing loss, picked up? Some may have had no period of illness, for example, those with later onset genetic deafness or chronic noninfective middle ear effusion. The screening of hearing at school entry is no longer standard practice in most countries. A wide-ranging yet methodical system of surveillance is necessary, usually through primary practitioners and family doctors leading on to ear, nose, and throat (ENT)/audiology and pediatric referrals. Hearing deficits may be noticed by parents and carers. When a parent expresses concern about their child’s hearing, there is almost always a hearing or communication impairment. The tendency is for families to assume that their child hears well unless they have clear indications to the contrary. Thus, if parents specifically express concerns about their child’s hearing, this is a red flag for there being a problem. It may not be hearing—sometimes it is a more generalized communication difficulty—but it is always important to arrange hearing assessment if parents or carers are questioning hearing. Tips and Tricks If parents or teachers are concerned about hearing, this is a red flag. The child needs full and accurate assessment of hearing in each ear. A fuller communication assessment is needed if hearing is found to be normal. The converse is not true; parents, teachers, and carers may not always be aware that a child has poor hearing. If there is any doubt, refer for early assessment. Otoacoustic emission (OAE) testing is a noninvasive and simple method for recording reflected sound generated by the normal activity of the outer hair cells in the cochlea (refer to ▶ 13 for more on screening tests). The OAE is typically absent for hearing loss of 25 to 30 dB HL or above or when there is middle ear effusion, which makes it highly suitable for screening for hearing loss in early life. OAEs are generated by the outer hair cells in the cochlea and therefore this test is not sensitive to cases with normal cochlear function but with an auditory neuropathy (refer to ▶ 13, Chapter 14.4.3, and ▶ Fig. 14.7) in which the transmission of neural information is compromised. The techniques used for hearing assessment depend upon the age and developmental status of the child. In the first few months of life, up to approximately 4 months of age, auditory brainstem response (ABR) testing is used. This is typically needed for newborn babies who have failed the preliminary screening tests, typically OAE (see ▶ 13). Electrodes are attached to the vertex, high forehead, and mastoid of the baby’s head. These record the electroencephalogram (EEG) activity that is time-locked to the presentation of short acoustic signals, either clicks or tone bursts, to the ear. Use of averaging and filtering of the EEG allows the auditory neural potentials from the brainstem pathways to be extracted and analyzed in response to acoustic signals of different intensities and frequencies. ABR therefore reflects early hearing levels for detection and transduction of sound signals within the cochlea and onto the central neural pathways. This type of electrophysiologic testing is used to define the extent and type of hearing loss in each ear for infants referred from NHSPs. ABR testing is carried out in natural sleep (easier to arrange up to 12 weeks of age) or under sedation or general anesthetic in the older child ( ▶ Fig. 14.1). Fig. 14.1 Newborn undergoing auditory brainstem response. New methods of electrophysiologic testing are being developed including auditory steady-state responses (ASSRs) and cortical evoked response audiometry (CERA). CERA has the benefit of allowing speech sounds to be presented through hearing aids worn by the infant during the test to assess the effectiveness of the hearing aid fitting in the first months of life. 14 Acoustic reflex thresholds give additional diagnostic information along with evoked potential measurement of the cochlear microphonic component of the ABR. Auditory neuropathy is present in approximately 1 in 10 children with permanent hearing loss from birth. 15 There are updated prevalence data from NHSPs and full information on all aspects relevant to a newborn hearing screening and follow-up assessment and habilitation services given on the UK Web site (hearing.screening.nhs.uk/publications). Tips and Tricks Cases in which a hearing impairment has been misdiagnosed tend to arise from overreliance on a single method of assessment without any functional observation, or when insufficient attention is paid to parents’ report of poor hearing responses in the case history, regardless of whether the infant passed the NHSP screen at birth. As the infant develops, from approximately 6 months of age, behavioral tests are used to measure hearing levels. The aim of all behavioral testing is to define the minimal sound levels detected across a range of frequencies, in each ear separately for air-conduction and bone-conduction signals, that is, to determine hearing thresholds for the child that correspond to pure-tone audiometric (PTA) readings in older children and adults. Visual reinforcement audiometry (VRA) is appropriate from approximately 6 months to approximately 30 months of developmental age. In this test technique, the infant is conditioned to associate the presentation of a specific frequency of sound to a visual reward by turning his/her head toward the lighting up of a toy or activation of a video clip. Once the association of sound has been paired to the visual reward, the intensity level of the signal is reduced until the child no longer responds. The intensity is then increased in incremental steps until the infant makes a head turn on hearing the signal. There is a skill in providing the appropriate engagement of attention for the child for this type of testing and an established test protocol is followed to avoid for random head turns being interpreted as hearing responses by well-intentioned but invalid testing. 16 Sounds are presented to each ear separately through inserts for air conduction and for bone conduction to derive a full audiogram for each child. This type of testing has now replaced traditional techniques of unconditioned testing, for example, distraction testing or observation of responses in the sound field. 17 From approximately 2 years of age, conditioned play audiometry (CPA) responses in which the child learns to make play-based responses when a sound is presented are used. Testing with headphones or insert earphones and bone conduction is necessary to determine whether the hearing loss is conductive, mixed, or sensorineural in nature. Once a child reaches approximately 5 years of age, he/she will typically be able to perform the PTA similar to an adult, possibly pressing a button or making a response with a toy. Tips and Tricks It is important to be aware that children with sensorineural hearing loss (SNHL) will also have episodes of middle ear effusion and that flat tympanometry does not imply that a hearing loss is solely due to middle ear effusion. If a mixed hearing loss is misidentified as a conductive hearing loss, grommet insertion may be arranged with only limited improvements in hearing, and the opportunity to identify and treat more severe hearing loss may be delayed. All test techniques require the first signal to be clearly audible to demonstrate the child’s role in the game. Thus, the starting stimulus must be demonstrably audible to the child, and the toys need to be engaging and appropriately motivating for the developmental age of the child. A clear understanding of typical developmental milestones and profiles through infancy and early life is a great asset for people carrying out efficient pediatric audiology, as 40% of the cases with PCHI have additional cognitive, sensory, and developmental impairments. The audiogram is a chart showing the sensitivity of hearing in each ear, mainly across the frequency range important for understanding speech (Box 14.1). The reduced sensitivity is measured in decibels hearing level (dB HL), with the standard for normal hearing shown by a straight line at zero (0 dB) on the y-axis. Box 14.1 Interpreting the Audiogram The PTA defines the lowest (quietest) level at which a pure-tone signal is detected, in each ear, when other sounds are absent. Standards are applied for test rooms so that they are appropriately quiet (BS EN ISO 8253–1:1998) and there is a specified procedure that must be used for results to be comparable across different test sessions (e.g., BSA, 2011). 18 Most decisions on management for hearing loss are predicated on the hearing thresholds shown by the audiogram. It is therefore crucial that the audiogram is an accurate representation of hearing thresholds, regardless of the test technique used to derive it. It is much more important that there are two or three frequencies reliably derived than that more frequencies are represented but with poor reliability. Common sources of error in testing are that visual cues are available to the child, (e.g., seeing hand movements for presenting the sound, or that the tester looks toward the child) or that a poor tester presents tones with regular timing patterns so the child is able to correctly guess when to make a response. It is crucial that in the initial conditioning of the child’s response to the presented signal, the tone is clearly audible to the child and that no assumptions are made about the child’s hearing status prior to completing the testing. The full audiogram may be derived by VRA or by conditioned responses over several test sessions. The audiogram reflects the hearing detection levels for the child and therefore also the sounds that are inaudible. The constraints on the child’s listening skill development arising from lack of experience in hearing speech and environmental sounds are important. Limited hearing inevitably also restricts the auditory feedback that a child has for his/her own vocalizations in his own babbling and early speech sounds. 21 However, the audiogram does not measure an individual child’s potential ability to differentiate and recognize complex signals of speech in daily life once hearing amplification or surgery is performed. The range of variables that are known to impact on speech understanding include use of visual cues, cognitive ability, speech and language level, personality type, parent engagement, and communication modes at home. Thus, a mild or moderate audiogram configuration may be debilitating for one child, but have relatively less impact on another child. In a study by Taylor, 22 no correlation was found between the three-frequency pure-tone average and performance on speech in noise scores for 100 adult listeners, thus highlighting the variable impact of hearing loss for different individuals. The extent of hearing loss is traditionally described as normal, mild, moderate, severe, and profound, in line with categories shown in ▶ Fig. 14.2. However, hearing loss tends to vary across frequencies and so may be normal in the low frequencies, mild to moderate in the midfrequencies, and severe in the high frequencies (as shown in ▶ Fig. 14.2 for a typical age-related hearing loss configuration), making audiometric categorization meaningless. Fig. 14.2 Audiometric classifications for extent of hearing loss. In the United Kingdom, the British Society Audiology (BSA) guidelines 18 quantify hearing loss according to the thresholds obtained in a PTA with similar categories given by the American Speech-Language-Hearing Association guidelines in the United States. 19 However,, these have limited value in understanding the impact of hearing loss for a child on the basis of these simple descriptors. ▶ Fig. 14.3 shows the typical speech spectrum for conversational-level speech on the audiogram format, with different speech sounds (or phonemes) included to represent their acoustic features across intensity and frequency. In terms of the functional effect of hearing loss categories, it can be seen that a mild hearing loss may reduce half of the audible information in conversational-level speech, or more for quiet speech or when at a distance. A moderate loss may make distant speech inaudible and degrade the quieter parts of conversational speech even at close range. A severe hearing loss makes speech inaudible even at close range, though the child may be able to hear some of his/her own vocalizations. A profound hearing loss prevents the child from hearing his/her own speech or that of others at all without hearing aid or cochlear implant (CI) amplification. The hearing loss may be: Conductive ( ▶ Fig. 14.4). Sensorineural ( ▶ Fig. 14.5, ▶ Fig. 14.6). Mixed conductive and sensorineural. Auditory neuropathy ( ▶ Fig. 14.7). Knowing the type of hearing loss is crucial for considering appropriate options for management and also for predicting the levels of amplification required to reduce the sound deprivation from hearing loss. Children need to experience sound in both ears to derive localization skills and meaning as the basis of speech understanding and also to alert them to oncoming sounds. The development of the brain and neural networks for audition is highly influenced by exposure to the auditory environment and so preschool hearing loss impacts on the rate and progress of sound learning, with the size of a child’s vocabulary in the first year of school predicting future reading comprehension. 20 Tips and Tricks Be careful with the use of the word mild based on audiogram thresholds. This can be misinterpreted by parents and carers as implying a condition with minimal impact on the child. Parents look to medical practitioners to give clear, evidence-based information for their options for interventions. Fig. 14.3 An audiogram with the average speech spectrum for conversational-level speech shown between the two curved lines with different speech sounds of English and some environmental sound sources. Fig. 14.4 Audiometric examples of bilateral conductive hearing loss, mild to moderate on the left and mild on the right. Fig. 14.5 Audiometric examples of bilateral sensorineural loss, moderate to severe on the left and severe to profound on the right. Fig. 14.6 Audiometric examples of unilateral left hearing loss, no masking done. Triangles relate to right hearing levels. Needs masking to define true left hearing, which is the dead ear. Fig. 14.7 Possible configuration of auditory neuropathy spectrum disorder audiogram, with otoacoustic emission present and absent auditory brainstem responses. The use of speech recognition testing is important within the test battery as a more holistic measure of the functional impact of hearing loss on the child. Assessment of the child’s speech discrimination can be included, using live voice testing, from approximately 3 years’ development age to demonstrate the impact on speech understanding and to provide audiological certainty across different audiology test techniques. This is usually done by presenting a set of pictures or items that are familiar to the child. An item is asked for (“Where’s the duck?”) without giving lipreading cues or looking toward the target item. The lowest speech level at which the child can consistently identify all the items is measured on a sound-level meter. The choice of items is important: a choice between “coat, goat, note, and boat” gives much more specific information than a choice between “cup, shoe, biscuit, and butterfly,” in which the target items have different vowels and syllable numbers. Speech testing is important in that it demonstrates to parents the impact of hearing loss on the child, which may be subtle in real-life situations, and gives a measure of disability for considering urgency of intervention. A helpful way of predicting the impact of a level of hearing loss for a child is to consider the proportion of speech information that is inaudible to him/her with his/her hearing deficit on the audiogram. The speech spectrum can be represented on the audiogram as a shaded area covering the frequencies range 125 to 8,000 Hz and the intensity range from 20 to 60 dB ( ▶ Fig. 14.8). Fig. 14.8 Minimum audible field for combined male and female speech presented at 65-dB level. Note that although the measured level is reported as 65 dB from a sound-level meter, most of the speech information is between 30 and 40 dB and some of the high frequency cues are below 20 dB, requiring hearing levels of below 20 dB to accurately hear all the speech sounds. All of the shaded speech area needs to be audible for a child to accurately follow conversational-level speech in quiet listening conditions. If a child has a flat hearing loss of 60 dB, it is more meaningful to say that only 10% of the information in speech (or SII) is audible than to say that he/she has 60% hearing loss, which might be interpreted as meaning he/she hears 40% of speech (see Boothroyd and Gatty 23 for more information). Tips and Tricks In general, reporting hearing levels as a percentage equivalent to the extent of hearing loss is misleading and should be avoided, for example, saying that 60-dB hearing loss is the same as 60% hearing loss. This underrepresents the huge functional impact of the hearing loss on a child’s speech understanding. The important point about the speech spectrum (sometimes called the speech banana), which is used to derive the SII, is that greater importance is attributed to mid- and high-frequency components than to low-frequency components because mid- and high-frequency speech sounds (e.g., t, p, k, s, sh) carry more meaning than low-frequency speech sounds (e.g., u, ee, oh, m) in spoken language. For example, if a child has high-frequency hearing loss, he/she may have an SII score of only 45 (i.e., only 45% of the information in speech is audible), and yet to the parents the child appears to respond well to sounds and talking around him/her. This is because the child hears that someone is talking from hearing vowel sounds, voice quality, and intonation but cannot recognize and understand the words that were said through hearing alone. A test battery approach is used to assess middle ear function and hearing threshold levels. Tympanometry is used to assess middle ear function and the mobility of the eardrum. This objective test confirms the presence of middle ear effusion when tympanometry shows a flat compliance trace ( ▶ Fig. 14.9). OAEs also make a helpful contribution to the test battery results to define the type of hearing loss for any individual case. Tips and Tricks It is important that ENT practitioners occasionally observe the types of testing used in their departments to appraise the quality , competence, and reliability of the testing performed and thereby to be aware of potential errors in threshold measurements and appropriateness of referrals to audiology. Systems of peer review are commonly arranged between pediatric audiology teams to share new techniques and encourage reflective practice. Fig. 14.9 Tympanogram. (a) Normal. There is a prominent, sharp peak between +100 and –100 daPa. (b) Flat compliance trace of middle ear effusion, indicating immobility of the tympanic membrane. (Reproduced from Probst R, Grevers G, Iro H. Basic Otorhinolaryngology: A Step-by-Step Learning Guide. Stuttgart/New York; Thieme: 2006, with permission.)
14.2 What Is the Impact of Hearing Loss for Children?
14.3 Diagnosis of Acquired Hearing Loss
14.3.1 Objective Hearing Assessment in the Early Months of Life
Screening Tests
Objective Assessment of Hearing Loss
Auditory Brainstem Response or Brainstem Evoked Response Audiometry
Auditory Steady-State Responses and Cortical Evoked Response Audiometry
Acoustic Reflex Thresholds and Auditory Neuropathy
14.3.2 Behavioral Hearing Tests
Visual Reinforcement Audiometry
Conditioned Play Audiometry
Pure-Tone Audiogram
Quantifying Extent of Hearing Loss
Speech Discrimination Testing
Speech Intelligibility Index
14.3.3 Measuring Middle Ear Function
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