Even minimal hearing loss can retard language development
Hearing loss has considerable impact on the overall development of the infant-language development, development of cognition, development of social and emotional competence.
First year of life is a critical period for brain development. Especially development of hearing pathway. Auditory experience during this period has profound influence on the functional development of auditory system and lack of auditory experience can have detrimental effects. This can be understood by this basic neuro developmental phenomenon. At birth, the brain has 100 billion neurons (nerve cells) and they form about 50 trillion connections. The only way the connections can be strengthened is by stimulation – both auditory and sensory. The connections that are not used or stimulated wither away. Now we understand the need for a constant auditory stimulation for optimal development of auditory system, a prerequisite for optimal development of speech and language.
“All children with speech delay should have a hearing assessment as the first investigation. Never ever make a casual statement that “he will be alright” or “he will speak later” without proper assessment.”
Even mild hearing loss if not detected early can significantly retard acquisition of language skill and untreated hearing loss of greater degree have a measurable, even devastating effect on speech and intellectual development. In USA, UK and many other countries, routine screening for hearing of all new-born is made mandatory before discharge from hospital. If by chance it is not accomplished, screening is done at next visit, but never later than one month.
The incidence of hearing loss is found to be in the range of 1-2 per thousand in general population. This is quite high as compared to all other screen-able diseases put together (thyroid disorders, sickle cell anaemia, phenylketonuria etc). When one takes into account the incidence of hearing Loss in high risk babies (babies with birth weight of less than 1500 gms, babies on artificial ventilation for more than 5 days, babies with high bilirubin levels, meningitis, birth asphyxia, ototoxic medications, family history of hearing loss, intrauterine infections, craniofacial anomalies, syndrome associated with hearing loss) have higher incidence of hearing loss (1.5-15%).
It is advisable that all new-borns be screened before discharge from hospital, but at least all high risk new-borns must definitely be screened, because the incidence of hearing loss is 10-20 times higher.
Oto Acoustic Emission (OAE) test is the most widely used screening test carried out on babies shortly after birth. It’s a portable tiny equipment (otoport, otodynamic, UK) and the trained person carries the equipment to the particular hospital to screen for hearing loss. A small ear piece (containing a speaker and microphone) is placed at child’s ear. A clicking sound is played and if the cochlea is working properly, the ear piece will pick up the response and we get a positive response. It works on the principle that a healthy cochlea will produce a faint response when stimulated with sound.
A poor response to an OAE does not necessarily mean that the child is deaf. Background noise, an unsettled body, fluid in ear from birth, cerumen in the ear canal. No aeration of middle ear, all can give an abnormal result. If an abnormal result is obtained, the test must be repeated after 2 weeks. If again abnormal, BERA test has to be undertaken.
All NICU babies should undergo BERA test to rule out auditory neuropathy/ dyssynchrony.
The importance of early identification is emphasized, considering the fact that, if a hearing problem exists, it should be detected and re-mediated at least before six months of age so that language development will occur normally. If detection and remediation is after one year, language development will be adversely affected and if detection is after 2-3 years child will become a deaf mute. Even mild hearing loss, if not detected early, can significantly retard the child’s development, especially speech, language and intellectual development.
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