Across the world, 1 to 3 out of every 1000 children has a hearing defect. While some are congenital or present at birth, some are acquired after birth. That is why, in some countries, like the US, it has become mandatory to screen an infant for hearing defects from 3 months onwards, as early-stage hearing loss can be treated successfully.
Causes for hearing defects in Infants and children
Congenital Hearing loss (present at birth)
- Genetic factors:
- Autosomal recessive hearing loss: Neither parent has hearing loss but carries a gene related to hearing loss that is passed on to the child.
- Autosomal dominant hearing loss: One of the parents has a hearing loss which is passed on to the child.
- Genetic syndromes: Such as Usher syndrome, Down syndrome, Crouzon syndrome, Waardenburg syndrome, Alport syndrome, etc
- Non-genetic factors
- Birth complications and premature birth
- The mother had an infection during pregnancy
- Maternal diabetes
- The use of certain medication by the mother during pregnancy
- Drug, alcohol , tobacco abuse by the mother during pregnancy
- Nervous system or brain disorder
Acquired Hearing loss (developed after birth)
In the first 2 years of the child, several factors can lead to acquired hearing loss that develops gradually. Some of them are:
- A perforated eardrum
- A serious head injury
- Otosclerosis or Meniere’s diseases
- Meningitis, measles, mumps or whooping cough
- An ear infection such as otitis media which is untreated
- Exposure to loud noise, causing noise-induced hearing loss
- Exposure to second-hand smoke
Types of Hearing loss in Infants
- Conductive: Caused by a blockage in the transmission of the sound in the inner ear. This can be treated with medicines or surgery
- Sensori neural: Caused by a damage to, or structural defect in the cochlea or inner ear. This type of hearing loss is permanent
- Mixed: When the child has both conductive and sensori neural defects
- Central: In this, the cochlea is working properly but certain parts of the brain related to hearing are not working properly
Screening Infants for Hearing loss
Infants can be screened or tested for hearing loss at the time of being discharged after birth. In case the Audiologist is not sure about the results, a repeat test is conducted after 2 weeks, and thereafter every 3 months till the defect is confirmed.
The following tests are conducted on infants or children to check for hearing loss. Based on the results, the doctor may conduct a full hearing evaluation thereafter.
- Auditory brainstem response (ABR) test
This procedure tests a baby’s inner ear and lower part of the auditory system (brainstem) for normal speech response. Tiny earphones are placed in the ear canals and small electrodes are placed behind the ears and on the forehead. The technician then sends clicking sounds through the earphones and measures the hearing nerve’s response to the sounds, through the electrodes. The results are compared with normal results displayed on a chart.
- Auditory steady state response (ASSR) test
A test that is carried out after the ABR test to validate the ABR readings… Here again, sounds are passed into the child’s ear canals, while a computer picks up the brain’s response to the sounds. The results are used to categorize the hearing loss as mild, moderate, severe, or profound.
- Central auditory evoked potential (CAEP) test
This is carried out for specific types of hearing loss, and is similar to the ABR and ASSR. However, the readings from the electrodes are used to map the pathways from the brainstem to the auditory cortex, to check if they are working properly.
- Otoacoustic emissions (OAE) test
This test also checks if the hearing pathways are working properly. A tiny probe is placed in the ear canal, after which sound pulses are sent and an echo response from the outer hair cells in the inner ear are recorded and analyzed using software. A normal recording indicates that the outer hair cells are working well.
This procedure is used to check for middle ear problems, such as fluid collecting behind the eardrum. In this test, soft sounds and pressure is applied on the ear, and the movement of the eardrum is recorded.
- Middle ear muscle reflex (MEMR)
As the name indicates, the MEMR is used to check the reflexes of the middle ear to sounds. In a normal ear, these reflexes protect the ear from loud sounds while the same is not true with a middle ear that has defects.
Hearing loss can create physical, mental, emotional and developmental challenges in a child throughout its childhood and in adulthood too. Visit a reputed hospital and have your child screened for hearing loss.