Evoluţia hipoacuziei la copiii cu tulburări din spectrul neuropatiei auditive, identificată prin screening neonatal auditiv

Introduction

ANSD (auditory neuropathy spectrum disorders) represent a group of auditory impairments that may be caused by pathologic processes of: internal hair cells of Corti organ, cochlear-neural synaptic space or cochlear nerve fibers. Due to particular aspects in children with auditory neuropathy spectrum disorders consisting in the degree and evolution of hearing loss, audiometric configuration, speech perception and hearing aid benefit^(1-5), there is not yet a consensus in the therapeutic recommendation in newborns with auditory neuropathy^(6,7,8). ANSD could be early identified after the hearing neonatal screening by a comprehensive audiological assessment.

Purpose of the study

The objectives of the current study are: to report our ANSD cases resulting from neonatal hearing screening, to identify and to describe specific patterns of hearing dynamic progress and speech development evolution in ANSD cases diagnosed immediately after our hearing neonatal screening.

Materials and method

The study included all babies referred from maternities and diagnosed with auditory neuropathy in the Audiology Department of Rehabilitation Clinical Hospital Iaşi, Romania, in the last six years. In this period, within the universal auditory newborn screening program in maternities there were tested over 50,000 babies and, after the clinical audiological assessments in the audiology department, we identified and managed newborns with auditory neuropathy spectrum disorders.

ANSD cases were diagnosed on the base of the following clinical criteria: the presence of otoacoustic emissions (at least at birth) and/or abnormal or absent ABR responses, the presence of cochlear microphonics and/or abnormal or absent ABR (auditory brainstem response), mismatches between ABR thresholds and ASSR (auditory steady state response) results or free field behavioral auditory thresholds^(9-12).

The follow-up was done for each child periodically until 18 months (at least three clinical evaluations) for cases fitted by hearing aids and until the cochlear implantation surgery for cases with this indication.

The follow-up of ANSD cases included:

auditory assessment periodic control (every three or four months), including ASSR, ABR (rarefaction and condensation polarity), free-field behavioral audiometry, tympanometry, otoacoustic emissions, free-field behavioral audiometry with hearing aids or cochlear implant;

periodic reports from speech therapy specialist (describing performances with hearing aids or with cochlear implant) regarding tonal perception, message intelligibility according to age and the level of speech production.

Results and discussion

The development of universal auditory newborn screening program allowed us to test in the Department of Audiology 1034 newborns sent from maternities for otoacoustic emissions test and/or for the presence of one or more risk factors. We finally identified 26 children (3%) with auditory neuropathy spectrum disorders (Figure 1). Figure 2 shows the number of newborns identified by audiological testing during 2012 and 2016 in the first clinical phase. In our study there were diagnosed six babies with ANSD, presenting normal tonal hearing, and 20 cases were diagnosed with different degrees of hearing loss (Figure 3). In the group of children with hearing loss, we observed that seven children showed progressive forms, three presented fluctuating forms and ten children showed stable forms (Figure 4). All six cases of ANSD with normal hearing, according to the results of our follow-up process, conserved their auditory thresholds. In four cases, speech development cannot be appreciated yet (age between 8 and 15 months). In other two cases that did not develop speech production, one case showed evidence of a good evolution (Figure 5). An example of a newborn with ANSD and normal hearing is presented in Figure 6, where we can observe the presence of cochlear microphonics even 8 months later than the diagnosis moment. All deaf children were hearing aid fitted, except for those with profound hearing loss with direct indication for cochlear implantation. For mild/moderate/severe hearing loss we used the hearing aids as the first choice. At the follow-up, when we found stable hearing loss thresholds with evidence of auditory gain and good speech development, hearing aids remained the best solution, with a periodic follow-up. When we identified a progressive hearing loss (proved after hearing aid fitted), we recommended unilateral cochlear implantation (the existence of a low speech development rate was not an argument against the evidence of hearing loss progressivity).  In the group of children with hearing loss, we observed three cases with fluctuating hearing loss (Figure 7 represents the fluctuations in ASSR thresholds level in a case with auditory neuropathy). For these children, the evaluation of the limits of fluctuation determined some difficulties for hearing aid fitting, and the evaluation of speech development showed us no evidences of good evolution. Depending on the available time or age of the patient, our indication was for unilateral cochlear implant. In our group, we did not find reversible hearing loss cases. In the group of progressive hearing loss, 57% (9 cases) evolved under acoustic stimulation by hearing aids to profound deafness and cochlear implant indication (Figure 8, Figure 9). The greater the initial diagnosed degree of hearing loss, the more the children have progressed to profound deafness. In cases with bimodal stimulation, two patients refused the contralateral hearing aid after few months from the switch-on of their cochlear implant. They are included among patients with evidence of good performances in speech development (Figure 10). Two patients with cochlear implant indication refused the surgery and they are still hearing aid users, with no evidence of speech development (Figure 11). Four out of seven of cochlear implanted children showed evidence of good speech development until now – following survey is necessary. Patients with ANSD fitted by hearing aid without cochlear implant indication present different levels of progress in speech understanding and production.
 

Conclusions

Universal hearing screening in newborns offers the chance to identify children with auditory neuropathy, requiring a different diagnosis and therapeutic approach compared to patients with regular inner ear hearing loss. Auditory neuropathy spectrum disorders cannot be diagnosed only on the base of screening auditory tests in maternity; the presence of different hearing loss risk fac­tors is an important argument to indicate clinical au­dio­logical tests. ANSD was found in 3% of the newborns referred to our audiology department for clinical audio­lo­gical tests (risk factors or “refer” result in screening tests), 23% presented normal tonal hearing and 77% presented different levels of hearing loss. We found different clinical forms of hearing loss: stable hearing level (16 cases), progressive hearing level (seven cases) and fluctuating hearing level (three cases). Because 35% of the patients with progressing hearing level switched from different degrees of hearing level to the profound one, we consider the periodical follow-up essential in the first 18 months in order to offer the best medical indication and to avoid the delay of appropriate intervention for hearing rehabilitation and speech development.  

Conflict of interests: The authors declare no conflict of interests.