Understanding children’s hearing loss
Hearing is fundamental to a child’s speech development. If you have any doubt about your child’s hearing it’s best to get them tested as soon as possible. In the particular case of children, it is necessary to be aware of expected speech and language skills at different ages, since these are strong indicators of their hearing development.
Symptoms of hearing loss in children
If you think your child might have a hearing problem , answering these questions will help:
- Do your child’s language skills appear to be delayed or inappropriate for his or her age? (If you are not sure, please refer to the Age- related acoustic behavior table.)
- Does your child have trouble understanding speech correctly?
- Does your child behave unresponsively to loud sounds or sleep through them?
- Does your child have difficulties imitating sounds?
- Is your child unable to locate the source of a sound?
- Do you feel that your child withdraws him- or herself in group settings?
- Has your child had frequent ear infections?
If you answered ‘yes’ to any of the questions, there is a chance that your child may have some degree of hearing loss. We urge you to have a hearing test conducted by a Hearing Care Professional. You should do so even if the above test does not indicate a hearing deficiency in your child but you still have doubts. It is important that you address your child’s potential hearing loss quickly in order to avoid difficulties in language acquisition and learning. The earlier it is diagnosed, the earlier appropriate intervention measures can be taken and the sooner he or she will be able to enjoy the colorful sounds of the world.
Causes for hearing impairment in children
When something is wrong with their child’s hearing, parents usually try to understand the origin of the hearing loss.
The causes of infantile hearing impairment are diverse. The main ones are high-risk pregnancies, different infectious diseases, taking certain medications, and alcohol or drug abuse during pregnancy. Additionally, although less common, hereditary irregularities and infantile meningitis are also possible causes.
Risk factors which can cause hearing loss before, during or shortly after birth:
- Weight at birth below 1,500 g and/or birth before the 32nd week of pregnancy
- Lack of oxygen or respiratory standstill
- Administration of ototoxic medicines (loop diuretics, aminoglycosides)
- Mechanical birth injuries
In many children, the hearing impairment occurs after birth. Examples are:
- In babies and infants afflicted by bacterial meningitis or encephalitis
- After severe cases of measles or mumps
- After accidents
- Following chemotherapy
- After chronic ear inflammations
- In children who suffer from certain syndromes (e.g. Moebius syndrome, congenital multiple arthrogryposis, etc.)
One should also consider the possibility of hearing damage in:
- Children with minor and severe middle ear malformations (e.g. Franceschetti’s syndrome)
- Children with cerebral motor disturbances
- Children in whom speech does not develop at all or not any further
- Children exhibiting abnormal behavior, i.e. by being very loud, aggressive or completely still
Types of hearing loss
Hearing loss can occur in either one of two ways, or a combination of both.
Conductive hearing loss
Conductive hearing loss occurs when the outer or middle ear is dysplastic or does not work properly. Consequently, sound waves cannot be efficiently conducted to the inner ear. In case of a temporary dysfunction, it is often possible to correct conductive hearing loss with surgery and/or treatment with medication.
Common causes of conductive hearing loss include:
- Injury of the outer ear itself
- Blockage of the ear canal due to ear wax (cerumen) or other small objects like food, beads or insects
- Infections of the outer or middle ear
- Perforation of the tympanic membrane
- Congenital deformities (e.g. Down syndrome, Franceschetti syndrome, Treacher Collins syndrome or Achondroplasia (dwarfism)
The audiogram below demonstrates conductive hearing loss. In this example, the inner ear works properly but something inhibits sound from getting through the outer/middle ear to the inner ear.
The hearing loss displayed above ranges from 30 to 50 dB HL in the right ear and between 35 and 45 dB in the left ear. This individual would only be able to perceive fragments of normal speech, which has a loudness level of about 65 dB. A normal hearing person has a dynamic range of up to 65 dB between listening threshold (at 0 dB) and speech level (at 65 dB). The person with the described hearing loss only has a dynamic range of about 20 dB. This difference of about 45 dB must be amplified to enable the person to perceive speech and sounds appropriately.
Depending on the general diagnosis, the necessary amplification is usually provided by:
- Conventional hearing instruments (sometimes not possible due to chronic inflammation, effusion and/or dysplasia of the outer ear/ear canal)
- Bone conduction hearing instruments: Behind-the-ear shell with a vibrating transducer, placed on the skull using a headband or retainer
- Bone anchored hearing aid (BAHA): A vibrating hearing solution which is attached to the skull using a screw which is implanted behind the ear
If the inner ear is unimpaired, bone conduction hearing solutions do not deliver any amplification. Their task is only to make sounds audible by an adequate vibration of the skull, which transfers the sound information directly to the inner ear. Starting from there, the hearing process continues normally.
Sensorineural hearing loss
Sensorineural hearing loss is the most common type of hearing loss. It has its origin in the inner ear or along the auditory nerve. Most commonly, the damage occurs in the inner ear (cochlea). In this instance, the hair cells in the cochlea are damaged and cannot transmit neuro-electrical impulses to the brain. Sensorineural hearing loss can be congenital (present at birth) or acquired after birth.
Common congenital causes include:
- Hereditary factors
- Viral infections
- Birth trauma such as anoxia
Acquired causes include:
- Reactions to ototoxic drugs (damaging to the hearing system)
- Head injury
- Noise exposure
- Ear infections
- Other diseases
The audiogram displays a sloping hearing loss from 20 dB HL in the low frequencies up to 75 dB HL in the higher frequencies and (nearly) equal in both ears. Such a hearing loss can usually be amplified sufficiently by using conventional hearing instruments.
If sensorineural hearing loss in speech relevant frequencies exceeds values of about 80 to 90 dB HL, it might become difficult to make speech adequately audible. The reason here is that even though the person suffers from profound hearing loss, he/she nevertheless regards extremely loud sounds just as uncomfortable as a normal hearing person would. The challenge here is to fit the complete speech spectrum into the individual’s residual dynamic hearing range. If this range is reduced to 10 – 20 dB, conventional hearing instruments cannot provide sufficient amplification anymore.
In these cases a cochlear implant (CI) might be the solution. A cochlear implant processes sounds and transforms them directly into electric impulses. The cochlear implant replaces the functionality of the inner ear. The electric impulses directly stimulate the auditory nerve. The auditory process in the brain is thus triggered. However, for the brain to interpret sounds correctly, patients need to have either adequate former listening experiences, or should be treated with a CI within the first four years of life.
Even under ideal conditions, patients provided with a cochlear implant need a lot of auditory training and continuous support. Even then, there is no guarantee that a CI works to every patient’s satisfaction
Mixed hearing loss
If air conduction and bone conduction measurement values exceed 20 dB HL, and the difference between the two is more than 15 dB, this is called a mixed hearing loss. Such hearing loss is treated according to the severity, the given anatomic structures, and other possible influence factors. Therefore, all of the hearing solutions mentioned previously might apply here:
- Conventional hearing instruments
- Bone conduction hearing instruments
- Bone-anchored hearing instruments (BAHA)
- Cochlear implants (CI)
Selecting the right method for treatment of a mixed hearing loss depends on the degree of the conductive and sensorineural components of the given hearing loss.
Degrees of hearing loss in children
Different levels of hearing loss are referred to as degrees, depending on the severity of impairment.
|Degrees of hearing loss||Hearing threshold (in decibels, dB)||Ability to hear speech|
|None||0 – 15 dB||Your child experiences no perceptible difficulty.|
|Minimal hearing loss||16 – 25 dB||Comparable to lightly plugging both ears with your fingers. Your child has difficulty hearing very soft speech or speech from a distance. It is harder to hear when there is background noise, like in an auditorium, classroom or dining room. Hearing instruments might be useful, but this depends on the individual..|
|Mild hearing loss||26 – 40 dB||Similar to minimal hearing loss, but with effects that are greater in degree. Your child may hear speech, but certain segments, especially short words, word endings and indistinct word sounds, tend to drop out. Background noise in classrooms and in other listening environments makes it even more difficult for the child to hear. Hearing instruments are usually recommended.|
|Moderate hearing loss||41 – 55 dB||Your child may miss over 50% of speech, and even more with the presence of background noise. Thus, hearing instruments are necessary to provide amplification. Otherwise, children may have limited vocabulary, produce faint or unclear articulation of speech sounds and develop limited communication skills. They may also have “flat” speech melody/intonation with only little inflection due to their inability to properly monitor their own voice.|
|Moderate to severe hearing loss||56 – 70 dB||Most sounds are not audible to the child. Speech and language skills may not fully develop without proper and early amplification through hearing instruments. The child may also need support from speech and language therapists.|
|Severe to profound hearing loss||71 dB and above||Most environmental sounds and even speech are almost inaudible. Speech is unlikely to develop without amplification through hearing instruments or other interventions.|
In addition, children might also be referred to programs that offer specialized instruction in various supportive and alternative communication methods (e.g. lip reading, sign language).
|Fluctuating hearing loss||Children who frequently have middle ear infections (otitis media) with fluid build-up in the middle ear (effusion) may experience varying degrees of hearing loss. These episodes of temporary hearing loss may last for several months or even longer. Although the hearing loss is mostly temporary and thus reversible, the child’s speech and language skills may still be affected if the reduced hearing ability persists over a certain period of time. The child may “hear,” but will constantly miss certain fragments of information.|
|High-frequency hearing loss||1,500 – 8000 Hz||The child experiences difficulty perceiving consonant sounds. Significant portions of important information may be lost from the speech signal. High levels of background noise will make it even harder to understand speech. This is because background noise contains a lot of low-frequency sounds that are perceived normally by the child, whereas the high frequencies, which are affected by the hearing loss, carry most of the information necessary for speech intelligibility.|
|Unilateral hearing loss||One ear has normal hearing, while the other has a hearing loss, which can create an imbalance in hearing. The child may have difficulties locating sound sources and voices. In addition, the child may have difficulty separating soft-spoken speech from background noise, especially if the speech is originating from the side with hearing loss. A hearing instrument is sometimes recommended. Ongoing audiological monitoring is very important to ensure effective intervention if a hearing loss should develop in the ear with normal hearing or if the existing hearing loss worsens.|