Key points
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Early diagnosis of pediatric hearing loss is possible and desirable.
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Measurement tools are available to diagnosis all types of hearing loss in children of all ages.
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Medical and surgical intervention and rehabilitation can begin at a very young age because of the ability to measure hearing loss effectively.
| ABR | Auditory brainstem response |
| BOA | Behavioral observation audiometry |
| CAPD | Central auditory processing disorder |
| CPA | Conditioned play audiometry |
| OAE | Otoacoustic emissions |
| SRT | Speech reception threshold |
Introduction
The goal of pediatric audiologic assessment is to determine if a hearing loss exists and to diagnose the type, degree, and specific nature of the hearing loss. The types of hearing loss include conductive, sensorineural, and mixed; the degree is defined in Table 1 .
| Hearing Level (dB) | Classification of Hearing Loss |
|---|---|
| ≤0–15 | Normal hearing |
| 16–25 | Slight hearing loss |
| 26–40 | Mild hearing loss |
| 41–55 | Moderate hearing loss |
| 56–70 | Moderately severe hearing loss |
| 71–90 | Severe hearing loss |
| 91+ | Profound hearing loss |
The accuracy of the results is crucial because the treatment plan depends on the outcome of the diagnosis. To choose appropriate techniques, consideration must be given to the child’s age, developmental status, physical status, and functional age level. Best practices involve using a test battery approach and not relying solely on one measure to avoid the possibility of error by using the cross-check principle.
Introduction
The goal of pediatric audiologic assessment is to determine if a hearing loss exists and to diagnose the type, degree, and specific nature of the hearing loss. The types of hearing loss include conductive, sensorineural, and mixed; the degree is defined in Table 1 .
| Hearing Level (dB) | Classification of Hearing Loss |
|---|---|
| ≤0–15 | Normal hearing |
| 16–25 | Slight hearing loss |
| 26–40 | Mild hearing loss |
| 41–55 | Moderate hearing loss |
| 56–70 | Moderately severe hearing loss |
| 71–90 | Severe hearing loss |
| 91+ | Profound hearing loss |
The accuracy of the results is crucial because the treatment plan depends on the outcome of the diagnosis. To choose appropriate techniques, consideration must be given to the child’s age, developmental status, physical status, and functional age level. Best practices involve using a test battery approach and not relying solely on one measure to avoid the possibility of error by using the cross-check principle.
Screening for hearing loss
Early detection of any amount and type of hearing loss leads to earlier intervention increasing the possibility that a child can reach his or her developmental potential in all areas. Mandatory newborn hearing screening has significantly reduced the age at which hearing loss is identified, from approximately 14 months of age for significant hearing loss and from 2.5 years of age for less severe degrees of hearing loss to ideally 3 months of age. Late identification of hearing loss causes a lag in the needed medical and audiologic treatment and increases the possibility of delayed linguistic and overall development. Because approximately 2 to 3 per 1000 babies in the United States are born with some amount of hearing loss in one or both ears, the value of newborn hearing screening programs is evident. Currently in the United States, 95% of newborn babies are screened before hospital discharge, although follow-up of all children has been more difficult to achieve. Screening is most frequently accomplished using either auditory brainstem response (ABR) testing and/or otoacoustic emissions (OAEs) testing and is performed ideally before the newborn leaves the hospital.
Otoacoustic Emissions
OAEs are sounds given off by outer hair cells when the cochlea is stimulated by sound. The movement of outer hair cells produces an inaudible sound that echoes back into the middle ear, which can be measured with a small microphone inserted into the ear canal. The status of the middle ear affects OAEs and can prevent their detection while assisting in the diagnosis of middle ear effusion or other middle ear conditions that cause conductive hearing loss.
Auditory Brainstem Response
ABR measures the auditory nerve and brain’s response to sound. It uses surface electrodes placed on the head to measure the coordinated electrical activity of the auditory nerve and brainstem relay pathways when the ear is stimulated by sound. Measuring the threshold (minimum sound intensity to elicit the electrical response) greatly assists in the diagnosis of sensorineural hearing loss.
These two screening techniques can lead to the diagnosis of mild to profound hearing loss be they conductive or sensorineural in nature (and are covered in greater depth later in the article). A definitive diagnosis requires follow-up after hospital discharge. According to the Joint Committee on Infant Hearing 2007 Position Statement, all infants should have access to hearing screening by 1 month of age. If the infant did not pass the hearing screening and subsequent rescreenings, a diagnostic audiologic evaluation and medical evaluation should be performed to confirm the presence of hearing loss by 3 months of age. All infants with confirmed hearing loss should receive intervention by 6 months of age.
Behavioral audiometry
Although these objective electrophysiologic measures provide an estimate of hearing levels, they are not a substitute for behavioral testing. The diagnosis of hearing loss requires at least ear-specific pure tone air and bone testing, which can be accomplished using age-dependent measures. Because behavioral testing is not a viable approach in infants, behavioral observation audiometry (BOA) is often used as an adjunct to electrophysiologic methods when the infant is younger than the age of 6 months. Although BOA does not provide ear-specific information or information regarding absolute thresholds, it does assess the infant’s reflexive response to auditory stimuli including warbled pure tones, narrow-band noise, and speech signals presented through speakers in a sound field. Reflexive responses include full body startle, head/limb reflex, and eye blink. Attentive responses include motion cessation; eye widening; and in older infants smiling, laughing, pointing, and the cessation/initiation of crying or babbling. In general, the responses should be seen within a few seconds of the stimulus presentation ( Table 2 ).
| Age | Auditory Maturation |
|---|---|
| 0–4 mo | Newborn behavioral responses to auditory stimulus are limited to reflexive actions |
| 4–7 mo |
|
| 7 mo | Localize sound source in lower plane (looking downward) |
| 9 mo | Locate sound source when presented above head height |
| 12 mo | Locate sound source in any plane on either side of the body easily and briskly |
From the age of approximately 6 months to 2 years, visual reinforcement audiometry is used to estimate auditory thresholds based on responses that have been shown to be closely aligned with pure tone thresholds obtained with the standard hand raising technique used in older children and adults. The goal is to obtain ear- and frequency-specific information before the child loses interest. The method requires that a child turn her or his head toward the sound source that is coupled with conditioned reinforcement, such as a lighted toy. In an ideal situation, two audiologists are used: one to initiate the stimulus and the second to observe the child’s response. The response should be time-locked to within a few seconds of the stimulus presentation for it to be considered a true response. The paradigm is stimulus-response-reinforcement: a stimulus (either a pure tone or speech) is presented and the child learns that a response (turning head toward stimulus source) will result in reinforcement, usually an animated toy enclosed in smoked plexiglass. Note that some children are frightened by some animations so alternatives should be available. To obtain ear-specific information insert earphones or standard headphones should be used. Either is acceptable depending on the will of the child. It is also possible that some children will not accept any form of earphone and sound field testing will have to be substituted. In this case, the results are a reflection of the better hearing ear only. Results should be combined with OAEs, tympanometry, and reflexes to obtain a total picture regarding hearing status.
Conditioned Play Audiometry
Conditioned play audiometry (CPA) is the next level of behavioral testing and can often be used with children 2 years of age through 4 to 5 years of age. The primary goal of CPA is to obtain ear- and frequency-specific thresholds via air and bone conduction allowing for the diagnosis of conductive, sensorineural, or mixed hearing loss. For air conduction testing, insert earphones should be used, whereas a bone oscillator is placed for bone conduction testing. The test used a form of operant conditioning where the child is taught to wait, listen for a tone or speech signal, and then perform an activity as a response. Most popular tasks include putting a block in a box, pegs in a board, or doing a simple puzzle. In some situations with the consent of the parent or guardian, the child can be offered a tangible item (ie, food or candy) as a reward. It is important not only to choose a task that the child can perform with ease but also to switch tasks often to avoid boredom. As with all the evaluation procedures, CPA needs to be combined with OAEs, tympanometry, and reflexes to obtain a complete picture. There can also be situations where the child because of the existence of multiple disabilities and/or delays cannot respond adequately. In these cases, ABR testing is recommended to obtain a clearer picture of hearing status.
By 5 years of age in a child with average cognitive abilities and some extra encouragement, children should be able to be tested using standard pure tone testing techniques, such as hand-raising or button pushing, and ear-specific air and bone conduction thresholds should be obtained with relative ease.
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