Hearing impairment is a common problem in children with developmental disabilities or who have multiple complex medical issues or disabilities. In many cases, however, hearing loss is overlooked because of the difficulty of assessing children who cannot speak, move, follow directions, or maintain concentration throughout a hearing test. Other disabilities, such as autism or physical disabilities, may make standard indicators of hearing milestones difficult to interpret for both parents and professionals.
Children with certain congenital or genetic disorders, as well as children with a history of birth complications, are especially prone to hearing loss. Please see Table 1 for a list of conditions that are associated with hearing loss. If a child has one or more of these conditions, a comprehensive hearing screening should be performed. Similarly, any child who is not meeting age appropriate speech and hearing milestones should be screened for hearing loss.
Table 1: At Risk Conditions for Hearing Loss¹
- Family history of hearing loss
- In utero infection such as toxoplasmosis, rubella, CMV, herpes, or syphilis
- Ear and/or craniofacial differences
- High bilirubin levels, especially if exchange transfusion was required
- Low birth weight (less than 1500 g)
- Bacterial meningitis
- Low Apgar scores or birth complications
- Respiratory distress at birth
- On a ventilator for 10 or more days
- Use of a medication such as gentamicin that can cause hearing loss
- A genetic condition associated with hearing loss (such as Down syndrome) or features suggestive of a genetic condition
- Persistent or frequent ear infections
- Head trauma or fracture
- Infectious diseases such as meningitis, mumps, or measles
- Neurodegenerative disorders
- Brain injury
- Failure to meet speech or hearing milestones
Hearing tests for children with developmental or complex disabilities can be difficult to administer and interpret. The remainder of this article will describe the subjective and objective tests currently available to assess any child, regardless of disability.
Testing for typically developing children over the age of about a year typically involves subjective hearing testing. Children ages one to four use conditioned or play-based responses to assess hearing. For example, a preschooler can be taught to place a block in a jar every time he hears a sound through earphones. A younger child might be trained to turn and look at a light-up toy when she hears a sound. While imprecise, these screening tools can provide basic information on hearing loss. A child’s attention span and behavior may limit the ability to obtain valuable results.
Once a typically developing child reaches age four, testing is performed using standard behavioral audiometry, with the child raising his hand when he hears a sound through earphones, or in some cases, through bone vibration.
Many children with multiple or developmental disabilities are unable to perform successfully on these tests. A child with cerebral palsy, for example, may not have the fine motor skills to lift or drop a block. Or a child with autism may not be able to tolerate the aural stimuli or respond consistently or appropriately to sounds. Some children with cognitive deficits may not be able to learn the trained responses they need to give in response to the aural stimuli. In these and similar other cases, more objective testing is of value.
There are several different tests that can be performed on children unable or unwilling to complete regular audiometry. These include Otoacoustic Emission (OAE) testing, Auditory Brainstem Response (ABR), and Auditory Steady-State Response (ASSR).
Otoacoustic Emission Testing (OAE)
The inner ear or cochlea actually generates a small sound. In children with healthy ears, this sound can be evoked by providing a click or tone in the ear, and a small microphone measures whether the small sound is produced or not. If it does not occur, this suggests that the middle or inner ear is not functioning appropriately.
This hearing test is valuable because it is simple to do on a child of any age, can be performed during sleep, is very fast, tests each ear separately, and is objective. A small probe is placed in the child’s ear that uses tones at various frequencies (high and low sounds) to detect the possibility of hearing loss. A child will receive a report stating whether or not he passed or failed each frequency tested in each ear. This test is commonly performed on all newborns in many states.
There are limitations to this test. It is not effective if the child is moving or crying, and fluid in the ears will make the results unreliable, as it blocks transmission of the tones or reception of the OAEs. It only assesses frequency loss, and cannot quantify if a child can hear soft or loud sounds. Furthermore, it does not detect any cortical hearing issues or hearing problems that are caused by damage to the nerves transmitting sound to the brain or the brain’s processing areas for sound.
Auditory Brainstem Response (ABR)
An ABR is a more comprehensive test of hearing that uses electrodes on the head to sense whether sounds travel appropriately through the auditory nerve into the brainstem.
This test requires the child to be still and quiet for about an hour, so children who are too young to remain quiet are often sedated during the test. Most children between the ages of about three months and eight years will require sedation. Sleeping infants and older children without behavioral or developmental issues can be tested without sedation. A shorter automated type of this test may also be used in newborn screening programs.
During the test, electrodes are placed on the child’s head while different tones are played in each ear. The brain’s response to each tone is recorded and allows an audiologist to determine what frequencies a child can hear (high or low sounds in hertz) and how loud the sounds must be for the child to hear them (volume in decibels). Some ABR testing, particularly the abbreviated form used for newborn screening, is automated, but more comprehensive diagnostic testing requires an audiologist to interpret the brain waveforms to determine whether a child can hear a particular frequency and volume.
This test does have some limitations. It will not identify cortical processing issues and cannot be performed accurately if there is fluid in the ears. It is possible to perform the test using bone conduction (vibration of the bones in the skull) instead of air conduction (tones in the ear) for children who have persistent problems with fluid or cannot be tested in the traditional way due to malformations of the ear.
Auditory Steady-State Response (ASSR)
The ASSR is a newer test that is closely related to the ABR and may be performed in conjunction with it. It also uses electrodes and tones played in the ear, but uses repeated tones instead of single abrupt tones. It can better identify specific frequency problems, especially in children with severe or profound hearing loss. It also uses statistical analysis to interpret brainstem responses instead of relying on an audiologist to interpret waveforms. This test may provide quicker and more accurate results for children with significant hearing loss.
If your child does not seem to hear you, does not turn to loud sounds, has speech problems, or has one of the above listed conditions in Table 1, comprehensive testing for hearing loss is definitely worthwhile. There are many adaptations, ranging from sign language to hearing aids and cochlear implants, that can improve hearing for many children. Improving hearing will often help a child make progress in other developmental domains, including speech, communication, behavior, and learning. Get your child tested!