Neonatal audiological screening with otoemissions


               The refinement of the method and the achievement of a more precise definition of peripheral auditory function is now widely felt in the scientific field in view of the social impact that hearing impairment entails. An increasing awareness (by the scientific world) of the repercussions of congenital neuro-sensory hearing loss on the social and relational insertion of the individual together with the evidence of the opportunities offered by early intervention, have made possible the development of programs aimed at optimizing the universal neonatal audiological screening procedure. The opportunities offered by the development of new technologies in this field make it possible to concentrate efforts towards the objectives of safer preventive intervention. Out of a thousand newborns, 1-3 per thousand have various types and degrees of hearing loss. This percentage increases to 4 to 6 per thousand in infants at risk, as noted in the Neonatal Intensive Care Units. Recent studies have shown that selective screenings based on audiological risk criteria lead to the failure to identify about half of congenital hearing loss (the prevalence of which is around 1-2 cases per 1000 healthy infants and around 4-5% of infants considered to be at audiological risk according to the 10 criteria of the Joint Commitee on Infant Hearing’s Position Statement). Currently the average age of identification of congenital hearing loss is between 24 and 30 months of life: between 24-30 months for severe and deep hearing loss; even over 3 years for moderate and severe ones.As is known the first three years of life are fundamental for the development of interneuronal circuits and therefore for the acquisition of auditory memory and language. The total or partial lack of acoustic inputs during this phase therefore leads to a permanent and significant reduction in psycholinguistic and relational capacity with consequent difficulties of socio-cultural integration of the individual. It is now well known that hearing loss during the first years of life interferes with the development of language. Reduced auditory stimulation has negative effects on the development of the cerebral auditory cortex, as well as on the child’s social, emotional and cognitive development. Early identification of moderate or severe hearing loss can prevent the aforementioned damage. The critical period for the development of speech and language is considered around 2-3 years of life. The average age of identification of possible hearing damage in Europe and the United States remains around 3 years, with the exception of those areas where auditory screening of newborns is not carried out. The implementation of an audiological screening programme in infants and any early intervention reduce the resulting damage. The detection of otoacustic emissions or cochlear echoes or otoemissions are the test of choice for audiological screening, in particular for universal neonatal screening. In 1978 Kemp registered the presence of acoustic energy emitted by the ears with normal hearing. Otoemissions are acoustic signals that can be recorded in the external acoustic meato that can be spontaneous (SOAEs), evoked by transient stimuli (TEOAEs) or distortion products (DPOAEs). They are determined by the hydrodynamic and mechanical properties of the screw; appear to be produced by the microactive processes of external ciliate cells (electro, cellular chemo). They are therefore expressions of cochlear functionality. It should be emphasized that the cochlea at birth is already ripe. TEAOs are beeps that can be recorded in the external ear canal that appear after sending a series of clicks and that have a duration of more than 10 ms. They are found in 98-100% of normoacusic adult subjects with an audiometric threshold equal to or less than 30-40 dB HL; they are not evoked in the presence of pathologies of the middle ear; they do not give information about the type or level of hearing loss, but represent, in essence, an index of normalization of the external ciliate cells of the cochlea. In case of partial or total absence, true or presumed absence of the otoemissions, a 3-month life check is scheduled that provides for the determination of the threshold of auditory evoked potentials (ABR) and, in case of confirmation of hearing loss, a new test, the ASSR with subsequent possible prosthesis of the small patient. In conclusion, TEOAEs represent, today, the test of choice for universal neonatal audiological screening, for the low cost, for the accuracy, the nothingness and for the speed of execution. In addition, in the newborn, the size of the responses is greater than that of the adult and therefore very well assessable. The nest is the ideal place to carry out screening as it is possible to ensure a wide coverage of the study population. In addition, newborns in the first days of life have long periods of sleep and therefore the test can be performed more easily. The incidence of middle ear diseases in the first days of life is extremely low and, as a result, these pathologies have little chance of influencing the results of screening. Unfortunately, late-onset hearing loss is lost. In order to organise all screening steps, all the necessary resources must be available to complete it: level I (Screening of nest otohemissions), Level II (ABR examination), Level III (ASSR examination and impedenzometry). It is necessary to raise awareness of the community both outside and in the Hospital, with all forms of advertising (newspapers, radio, local television). Contact family doctors, obstetricians and local pediatricians; organize informative conferences, meetings with mothers-to-be, involve obstetricians, pediatricians, neonatologists, child watchers, auxiliaries in the Hospital. The positive aspects of this test are the speed of execution, the low cost, the reliability and the little or no invasiveness. The equipment used is not bulky, transportable and easy to handle. Universal neonatal screening carried out with otoemissions evoked by transient can appreciably decrease the age of diagnosis of childhood hearing loss. The American Academy of Pediatrics considers TEOAEs to be a valid method for neonatal auditory screening for high test reliability, low invasiveness, low cost, handling. The prevalence of childhood deafness is however higher than that of other congenital diseases for which newborns are already routinely screened such as:- phenylchetonuria (1/10,000 births)- congenital hypothyroidism (1/3000 births). In Italy, unfortunately, there is no specific legislation to promote neonatal hearing screening. The European Conference on the State of Neonatal Auditory Screening (May 1998, Milan) promotes and hopes to apply it in all the countries of the Community; this screening is mandatory in the USA and has recently been adopted by the Campania Region in all points of birth, public and private, of its territory. In Italy the average age of diagnosis of deep childhood deafness is around 3 years; suspicion often arises from the recognition of the child’s failure to learn spoken language. Early diagnosis, around 12 months of age, allows the rehabilitation prosthetic therapy necessary to prevent the consequent speech disorders to be implemented. It is therefore a secondary prevention, aimed at avoiding the consequences of a pathology and not a primary prevention aimed at avoiding pathology.

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