Dr. Prasad Kelkar*, M.S. (ENT) Diplomate NB**
Fellow (Fisch International Microsurgical Foundation).*, Fellow (Fisch International Microsurgical Foundation).**
Hearing impairment or deafness is an unforeseen misery. Helen Keller, a powerful symbol of triumph over adversity and a leader and legend of the blindness field said, " the problems of deafness are deeper and more complex, if not more important than those of blindness. Deafness is much worse misfortune, for it means, the most vital stimulus - the sound of voice - that brings speech and language, sets thoughts astir and keeps us in intellectual company of the man".

A neonate or a child with complaints of inability to hear, lack of response to loud sound, poor speech and language development is relatively common complaint in pediatric out patient department. It is often difficult and time taking to assess such a child in pediatric OPD.

This article addresses the importance of early detection of hearing loss, different investigations and various modalities of management of pediatric hearing loss. Incidence - Sensory organ of hearing is fully developed at birth; however the neural maturation (i.e., myelination and synaptic development) of the brainstem and auditory cortical connections continue for the first 2 to 3 years. It is important to realize that the postnatal development of auditory system depends upon normal hearing.

If there is unidentified and untreated hearing loss in an infant, it results in structural changes in the cortical auditory connections and is clinically evident as delayed speech and language development.

Incidence of significant bilateral hearing loss is estimated to be 0.1 to 0.3% in the well-baby nursery population and 2 to 4% in neonatal intensive care unit population. This incidence in the second group is on the rise due to survival of more and more of the LBW babies.

Risk factors for hearing loss in neonate - Joint Committee on Infant Hearing (JCIH) - a Team of Experts from American Academy of Pediatrics, has defined various risk factors for hearing impairment in NICU graduates like:
  1. History of hereditary hearing impairment
  2. Rubella or other nonbacterial intrauterine fetal infections during pregnancy
  3. Defect of ear, nose and throat (including cleft palate)
  4. Birth weight of less than 1500 gm
  5. Bilirubin level greater than 20 mg/dl serum
  6. The level of hyperbilirubinemia requiring exchange transfusion. Bacterial meningitis in the neonatal period
  7. Severe asphyxia including infants with APGAR scores of 0 to 3 minutes after birth, who fail to begin spontaneous respiration by 10 minutes and infants with hypotonia persisting to 2 hours of age

Most infants in NICU fall into one or more of the "High-Risk" category.

Before considering various investigations for detection of hearing loss, it is important to know the development of the child in response to sound as most of the clinical tests done depend on the age of the child.
Development of the Child in response to Sound
From Birth to 3 months - Startles to loud noise, awakens to sounds, blinks or widens eyes in response (reflex) to noises.

3 to 4 months - Quiets to mother's voice, stops playing, listens to new sounds, looks for source of new sounds not in sight.

6 to 9 months - Enjoys musical toys, says "mama" Coos and gurgles with inflection.

12 to 15 months - Responds to his or her name, follows simple requests, Uses expressive vocabulary of 3 to 5 words, imitates some sounds.

18 to 24 months - Knows body parts, Uses expressive vocabulary 2-word phrases (minimum of 20 to 50 words), 50% of speech intelligible to strangers.

By 36 months - Uses expressive vocabulary of 4 to 5-word sentences (approximately 500 words), Speech is 80% intelligible to strangers understands some verbs.
Newborn and Childhood Hearing Testing
The Joint Committee on Infant Hearing 1994 position statement recognizes the need for early detection and states "Because normal hearing is critical for speech and oral language development as early as the first six months of life, it is desirable to identify infants with hearing loss before three months of age".

Various Clinical tests which can be performed in OPD setting are:

0-4 months: Auropalpebral Reflex, Startle response, Arousal

5-12 months: Distraction Test - This is a simple test which can be the mother's lap. One person (distracter) tries to divert the attention of baby. The other person (Tester) makes a sound (Drum-low freq. Sound, Rattle-mid freq. Sound, Bell-high freq. Sound) at a distance of 1 meter behind the child and child response to the sound in the form of head turn, eye turn, frowning is noted.

12-24 months: Free field audiometry, Visual reinforcement audiometry

24-48 months: Play Audiometry

48 months: Pure tone audiometry, Speech audiometry

84 months: Central auditory test

Objective tests - All the clinical tests have a drawback that they are subjective, often difficult to do in unco-operative children. Therefore, there is a need of the objective test which can detect the hearing in pediatric population independent of the patient response. This problem is solved by two objective tests:
  1. Brain Stem Evoked Response Audiometry
  2. Otoacoustic emissions
Brain Stem Evoked Response Audiometry (BERA)
It is a gold standard objective test for the identification and quantification of hearing impairment. It is noninvasive and unaffected by sleep or drugs.

Principle - BERA follows same principle as EEG. Whenever sound stimulus is presented to the test ear, the electrical activity evoked by sound travels from one neuronal centre to other in a fixed manner which can be recorded and can be graphically presented as waveforms.

Procedure - BERA test can be performed as an OPD procedure in which child is sedated and a click sound is presented to the test ear. Sound evoked EEG activity is recorded by surface electrodes placed on the scalp.

Reading of BERA waves - BERA records electrical activity in first 10 msec of the sound stimulus. Normal BERA consists of five positive peaks. Out of which wave V is most prominent and consistent peak. Sound stimulus of 120dB is given to the test ear and slowly the intensity of the sound is reduced. Various parameters like latency, amplitude, wave morphology are studied to know the threshold of hearing.
Normal BERA waves (I-V)
Otoacoustic emission (OAE) - It is one of the useful screening tool for detection of hearing loss. Those babies with absent OAE are subjected for BERA test. The concept of OAE is that certain sounds generated by the inner ear can be recorded. The sounds may be spontaneous or evoked. How these sounds are produced and why they are not produced in people with SNHL is unclear, but they do correlate very well with hearing loss.

Also a test for newborn screening, the OAE can be performed quickly and inexpensively by personnel with relatively little training. An earphone is simply placed over the ear of a resting neonate, and the machine produces and records the evoked response. Sensitivity and specificity reported with evoked OAE are 100% and 82% respectively.
Management of conductive hearing loss resulting from otitis media or its sequelae is done with a course of appropriate antibiotic treatment. Ultimately, myringotomy or ventilation tubes may be necessary. If the hearing loss continues, amplification with a hearing aid may be needed. Conductive hearing loss that results from obstruction of the auditory canal by cerumen or a foreign body should be treated by removing the obstruction.

Hearing Aids: They form mainstay of rehabilitation of children with hearing loss. Behind the ear, hearing aids provide better speech clarity as compared to body wear type. Modern hearing aids can selectively amplify a specified range of frequencies more than others rather than all frequencies equally. Electronic hearing aids comprise three basic components: a microphone, an amplifier and a receiver, which are housed in a plastic case, designed to fit behind or in the ear. Ear moulds are necessary for proper fitting of hearing aid.

Cochlear Implants: There are subsets of individuals with moderately severe to profound sensorineural hearing loss who do not get sufficient benefit from hearing aids and are thus not able to develop good speech or language. Such individuals require cochlear implantation. Cochlear implant is a medical device which provides hearing sensation for people who have moderately severe to profound sensorineural hearing loss. It is designed to bypass the damaged parts of inner ear (i.e. cochlea) and send electrical stimulation directly to the auditory nerve, which is interpreted as sound by the brain. Even in the congenitally deaf, the auditory nerve pathways are viable and once the presence of a normal cochlea and auditory nerve is confirmed by CT and MRI respectively and mental retardation is ruled out, the patient is taken up for cochlear implantation. Intensive auditory training is required postoperatively, which require the parents to be highly motivated. The earlier the cochlear implantation is done, more is the beneficial effect, as we are making maximum use of developing neurons in the child's brain. Youngest age at which children have been implanted is 6 months.

Early identification and rehabilitation of the children with hearing loss is the key to success in the management of such patients. Identification of hearing loss before 1st year of age often results in normal speech and language development. Combination of behavioural and objective tests helps in proper assessment of the child. Brainstem evoked response audiometry (BERA) is the important objective test for identification and quantification of the hearing loss.
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