Deaf Child Hearing Assessment

Guidelines for the Genetic Evaluation and Triage Paradigm Of Congenital Hearing Loss

Based on the genetic evaluation, if a syndrome is suspected, then test if possible. However, if nonsyndromic pathology is suspected and there is no family history, that is, it is an isolated case, then testing for cytomegalic virus should be done to confirm viral infection that could possibly be transmitted through the mother. Additionally, the GJB2 (connexin 26) gene sequencing mutation should be checked. If a syndrome is suspected and not isolated, only the GJB2 mutation is checked.

If a nonsyndromic cause is suspected and is indicative of an autosomal dominant condition, the connexin 26 mutation should be tested. 

If a mitochondrial mutation is suspected along with nonsyndromic pathology, connexin 26 and mt genes associated with ototoxic responses should be assessed. The patients need to be counseled regarding the range of tools that can help with hearing loss, such as hearing aids, middle ear implants, cochlear implants, and auditory brain stem implants. Proper follow-up is required so that it is known how the parents are coping with the situation, that is, if they are taking active steps in treating their children. This is due to the fact that until hearing is rehabilitated, the speech will not develop.

The Genetic Testing and Triage Paradigm

Genetic counseling and education to ensure that parents and patients understand the findings and limitations. Parents should consider pre-test and post-test counseling. Habilitation options should be provided with a pre-planned follow-up. The patients need to be counseled regarding the range of tools that can help with hearing loss, such as hearing aids, middle ear implants, cochlear implants, and auditory brain stem implants.

Proper follow-up is required so that it is known how the parents are coping with the situation, that is, if they are taking active steps in treating their children. This is because until hearing is rehabilitated, speech will not develop.

Speech And Language Milestones

• From birth to up to 3 months
• The child is startled by loud noise (Moros reflex).
• The child awakens to any sort of sound (Arousal test).
• The child blinks or widens their eyes in response to noises (Cochleo-palpebral reflex).
• Between 3 to 4 months
• The child gets calm or quiet upon hearing the mother’s voice.
• The child responds to new sounds.
• The child actively tries to find the source of sound if not present in sight.
• Between 5 to 6 months
• The child tries to localize the sound.
• The child squeals and babbles.
• Between 6 to 9 months
• The child starts enjoying musical toys.
• The child coos and produces gurgling sounds with inflection.
• The child starts to make bisyllabic sounds like “Mama” or “Dada”.
• Between 12 to 15 months
• The child starts to respond to the name and says words like “Yes” and “No”.
• The child follows simple requests.
• The child uses an expressive vocabulary of 3-5 words.
• The child starts imitating some sounds.
• Between 18 to 24 months
• The child knows body parts.
• The child uses expressive vocabulary with 2-worded phrases (minimum of 20-50 words)
• 50% of the speech is intelligible to the strangers.
• The child is conditioned by auditory clues.
• By 3 years or 36 months
• The child uses expressive vocabulary with 4 to 5 worded sentences.
• Around 80% of speech is still intelligible to strangers.
• Starts to understand some verbs.

Why is Early Intervention Required in a Deaf Child?

Synaptic density is compared at birth, at 6-8 years of age, and at an older age of 14 years. Synaptic density is maximum at 6-8 years of age. Therefore, in early age child must have auditory clues and stimuli and respond to these clues in order for the synapses to form and grow.  Once these synapses are generated, the child needs to be rehabilitated with better ways to develop speech. Early experiences have a decisive impact on the architecture of the brain. In the first year of life, neurons in the auditory brainstem are developing.  Billions of major neural connections are being formed (number of synapses increases 20-fold to 1,000 trillion). The newborn brain is in a subcortical state; Areas of cortex responsible for language are well developed by 12 months of age.

Neural plasticity refers to the adaptability of the brain. The child can have a good adaptability for speech articulation between 2-3 years of age. The child adapts well to listening between 6-8 years of age. Around 2-3 per 1000 newborns will have permanent childhood hearing loss. This is often missed or is realized late by 2 or 3 years. Although it will be difficult to help the patient this late, however, medical intervention can possibly help.

Also Read: Foreign Body in ENT and its Management

Hearing Assessment in Children

The first and most objective test would be an electrophysiological test. These tests will demonstrate the function of the cochlea, and the retro-cochlear pathway. It will help to identify the exact position of the lesion in the hearing pathway. These tests are:

• Otoacoustic Emission (OAE) demonstrates the condition of the outer hair cells (OHC), which are present in the cochlea.
• Brainstem Evoked Response Audiometry (BERA) 
• Cortical Evoked Response Audiometry (CERA)
• Impedance Audiometry provides information about the middle ear. 

BERA and CERA will reveal responses coming from the retro-cochlear pathway (BERA) and the brain (CERA). Behavioral observation audiometry is done to assess-

• 0-6 months: Arousal reflex, auropalpebral reflex, startle reflex, auditory cradle reflex.
• 5-6 months: Free field audiometry.
• 6-24 months: Visual reinforcement audiometry or distraction test.
• >30 months: Conditional technique (Play audiometry).

Newborn Hearing Screening

At birth, three tests can be used to screen the hearing in newborns.

• Otoacoustic emissions (OAE)- Screening test
• Auditory brainstem response (ABR)-Confirmatory test
• Two-stage screening (OAE + ABR)-Conclusive test

We will read about these tests briefly. For much more detailed information, please watch the video from the prepladder video section. 

Otoacoustic Emissions

OAE are impulses generated by the OHC present on the cochlea. The OHC will release impulses that are efferent. So, a probe connected to the external auditory canal will help to identify if the emissions are present or absent. The presence of these emissions will suggest the probability of healthy cochlea is high. If OAE is present, then no other tests need to be performed except in case of suspected syndromic or genetic pathology.

If OAE is absent, then ABR should be performed. In OAE, sounds are presented to the canal using a small microphone to measure OAE responses. The average time to complete the test is 5-15 minutes depending on the child’s cooperation. Middle ear / cochlear defects can be detected, but the hearing threshold cannot be estimated.

Auditory Brainstem Response

The sound is presented using different probes near the ear and forehead, and surface electrodes measure brainstem activity. The measure of electrical activity is in the form of seven waves. When the sound is given, it is measured whether there is latency or a decrease in amplitude of the electrical waves. The average time is 20-30 minutes per baby and it allows the hearing threshold to be estimated. The test provides information about retro cochlear pathology or pathways. During this test, the child needs to be asleep or can be mildly sedated using chlorpheniramine. This test is only confirmatory in nature as it cannot be applied to the general population.

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OAE+ABR

• All babies are screened using OAEs
• Those babies who fail the OAE screening receive an ABR screening prior to leaving the hospital.
• Average test time/baby (25-35 min) 
• Reduces refer rate; useful when follow-up is likely to be difficult or costly
• The initial cost of equipment is higher than OAE or ABR screening alone, but follow-up costs are less.

Frequently Asked Questions

Q: All these tests can be used to screen the hearing in newborns except

1. Otoacoustic emissions (OAE)- Screening test
2. Auditory brainstem response (ABR)-Confirmatory test
3. Two-stage screening (OAE + ABR)-Conclusive test
4. Rinne’s Test

Answer: Rinne’s Test

Q: What is BERA?

Answer: Brainstem Evoked Response Audiometry

Q: What is CERA?

Answer: Cortical Evoked Response Audiometry

Q: What does the BERA test detect?

Answer: It detects hearing ability in newborns.

Q: Can BERA detect autism?

Answer: No, Bera can only find out about the hearing abnormalities in a newborn.

Hope you found this blog helpful for your Pediatric ENT Preparation. For more informative and interesting posts like these, keep reading PrepLadder’s blogs. 

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