CONGENITAL HEARING LOSS
Congenital hearing loss — hearing loss present at birth—occurs when the ability of the ear to convert the vibratory mechanical energy of sound into the electrical energy of nerve impulses is impaired. Congenital hearing loss is one of the most prevalent chronic conditions in children.
TYPES OF HEARING LOSS:
Hearing loss is categorized according to the site of the lesion; into conductive hearing loss where the outer or middle ear are affected and into sensorineural hearing loss where the inner ear, auditory nerve or central auditory pathway are affected. Mixed hearing loss is defined as conductive and sensorineural hearing loss.
In conductive hearing loss, sound waves cannot propagate through the ear, either secondary to maldevelopment of the middle ear, the external ear or both, or following transient obstruction of the middle ear caused by effusion (as in the case of otitis media) .
Sensorineural hearing loss can be further subdivided in sensory hearing loss (when the hair cells are affected), central hearing loss when the cause is located along the central auditory pathway or Auditory Neuropathy Spectrum Disorder.
Auditory Neuropathy Spectrum Disorder may be caused by a primary lesion located in the inner hair cells, in the auditory nerve of intervening synapse and may also include damage to neuronal populations in the auditory pathway.
According to NHS data 1 to 2 babies in every 1,000 are born with permanent hearing loss in 1 or both ears. This increases to about 1 in every 100 babies who have spent more than 48 hours in intensive care. In Nepal it tends to be much higher but due to lack of hearing screening in new born we cannot have the exact data for Nepal. All such cases end-up having very severe speech/language impairment and become what in popular parlance is called "deaf-mutes”. The curse of "deaf-mutlsm" can be definitely prevented by early detection of deafness followed by efficient and timely management. For this we need to establish the UNIVERSAL NEWBORN HEARING SCREENING PROGRAM in our country, so that, like most of the advanced countries, we too have a legislation that mandates a hearing screening test for all newborns before they are discharged from the maternity ward.
RISK FACTOR FOR CONGENITAL HEARING LOSS:
1. Positive family history of permanent congenital hearing loss (1.43% of children with positive family history has hearing loss)
2. Admission to a neonatal ICU
3. Premature babies with low birth weight
4. Medical intervention in ICU like assisted (ventilation, venous access, aminoglycoside use)
5. Duration of hospitalization of >=12 days
CAUSES OF CONGENITAL HEARING LOSS:
It is due to genetic mutation affecting any component of hearing pathway. It can be either syndromic (associated with other physical abnormalities) or nonsyndromic (80% of it are congenital and 20%of it are progressive with later age of onset)
It includes congenital infection like Cytomegalovirus, Rubella, Toxoplasma gondii, Treponema pallidum, herpes simplex virus.
In the past targeted screening of neonate were performed like those who have family history of hearing loss or craniofacial abnormality or admitted to NICU. Now a days Universal Neonatal Hearing Screening programme is introduced in many developed countries which uses 2 phase screening paradigm.
Perform otoacoustic emission (OAE) on newborn 16-24 hours or may be upto 24 hours after birth. If baby pass this test they have normal hearing but if it is fail repeat test is done on 7th day. If baby passes on 7th day they have normal hearing but if baby fails this test baby is suspected to have hearing loss. Then BERA(Brainstem evoked response audiometry) test is performed which must be done before baby is 2 months of age so that if hearing deficit is there hearing aid can be fitted. These babies with hearing loss should undergo behavioral audiometry at 8 months, 12 months, 24 months and 36 months so that hearing threshold is updated for correction of hearing amplification. Those babies who pass the test they should have regular reassessment in a presence of risk factor.
If the neonate fails the universal neonatal screening programme then etiological workup can be done like
1. Screening for congenital infection
2. Imaging of inner ear
3. Genetic testing
4. Ophthalmologic screening
5. Kidney USG
7. Thorough clinical examination for syndromic cause of congenital hearing loss
By doing etiological workup we can :
1. Provide answer to cause of hearing loss to parents
2. Provide accurate and precise genetic counselling
3. Provide relief from guilt of parents
4. Aid in management of hearing loss like hearing aid or cochlear implant or adapted educational method
5. Prediction of progression of hearing loss to certain extent
6. Identify coexisting medical problems that needs to be treated
7. Secure preventable risk factors for future hearing deterioration
Non-surgical treatment: Treatment of congenital cytomegalovirus infection can be done with antiviral medicine. Similarly other congenital infections can be treated.
Restoration of hearing:
Conventional hearing aids
Bone anchored hearing aids
Other surgical treatments specific for the disease
QUALITY OF LIFE:
If the congenital hearing loss is identified before 6 months then children will have better receptive and expressive skills. If they are not treated before that they will fall behind their normal hearing peers in reading skills, cognition, socioemotional development. These children will have modest educational achievement and employment levels.
NEONATAL HEARING SCREENING PROGRAMME:
Human brain can develop language skills up to 3.5 years only .If children cannot hear by this age his language will not develop and he will be deaf mute. Newborn hearing screening programme has found to be extremely cost effective and instrumental in preventing deaf mutism in many countries. So we need to establish UNIVERSAL NEWBORN HEARING SCREENING programme in our country like most of the advanced countries .The long term benefits of this has been well established.
(Dr. Dev is Consultant ENT in National ENT Centre)