International Journal of Pediatric Otorhinolaryngology
Review articleAuditory neuropathy in a low-risk population: A review of the literature
Introduction
With newborn hearing screening (NHS) programs we are able to identify permanent childhood hearing impairment soon after birth to allow early intervention. With the introduction of NHS, hearing screening program sensitivity and specificity have improved greatly when compared to earlier methods. However not all children with hearing loss are identified early. Hearing loss may go undetected, not only because of the type of hearing loss (progressive or delayed onset), but also as a result of the type of hearing screening used.
In the well baby population in The Netherlands (and several other countries), transient evoked oto-acoustic emissions (OAE) are used in the first stages of the screening program. Hearing impairment due to dysfunction of the inner hair cells or the central nervous system may go unnoticed when OAE-screening is used. The constituents of the present newborn hearing screening program in The Netherlands were chosen on the basis of a modelling-study on cost-effectiveness in which several hearing screening program options were evaluated [1].
The presence of adequately functioning outer hair cells (shown by the presence of OAE or cochlear microphonics) but abnormally functioning inner hair cells, or dysfunctioning or aberrant nerve connections, is defined as auditory neuropathy [2]. The functioning of the latter can be evaluated by (automated) auditory brainstem response (A-ABR). Therefore auditory neuropathy is defined as an abnormal ABR in the presence of a normal OAE. Reported risk factors for auditory neuropathy include, among others, hyperbilirubinemia and admission to a neonatal intensive care unit (NICU) [3], [4], [5], [6], [7]. In The Netherlands NICU-babies (about 3% of births), are screened in a separate neonatal hearing screening program, using only A-ABR screening. This differs from the well baby population, which is screened using OAE in the first stages of the screening program.
In order to estimate the contribution of cases of auditory neuropathy to the false negative rate of the OAE based screening program in the healthy neonatal population, it is essential to gain insight into the prevalence of auditory neuropathy in this group. Therefore, the objective of this study was to collect all available evidence on the prevalence of auditory neuropathy in well babies.
Section snippets
Methods
A review of the literature was conducted using the databases PubMed and EMBASE. These literature databases were searched for articles published from January 1996 to December 2010. This time frame was chosen because the first reports on auditory neuropathy emerged in 1996 [8]. The search strategy (including Medical Subject Headings (MeSH) terms and keywords ‘Auditory disease’, ‘Prevalence’ and ‘Child’ and their relevant synonyms) used for PubMed is shown in Table 1. EMBASE was searched using
Results
Using this search strategy we found 519 citations. Of these citations a total of only 4 original studies met the inclusion criteria (Fig. 1). Table 2 shows the characteristics of the included studies. All four studies were conducted during the last decade [11], [12], [13], [14]. Scrutiny of the population details in the studies revealed selection bias, since ‘contamination’ with non-well babies was present. Elimination of these children led to a pooled prevalence of auditory neuropathy in well
Discussion and conclusion
Based on the available studies we found that the reported pooled prevalence of auditory neuropathy in the well baby population varies strongly, between 0.06 and 0.3 per 1000 children. One should, however, be careful when interpreting the results since there is (1) not much evidence available and (2) the available evidence is heterogeneous.
Although the body of knowledge on the audiological, neurophysiological and clinical findings in auditory neuropathy is large [2], [15], [16], [17], [18] the
Contributors
AO and AM conceived the study. AK and GZ selected the literature and conducted the analyses. AK drafted the manuscript with input from the other co-authors. All authors contributed in critically revising the article for important intellectual content, and approved the version submitted for publication. All authors had full access to the data (including statistical reports and tables) in the study and can take responsibility for the integrity of the data and the accuracy of the data analysis.
Conflict of interest
We declare we have no conflicts of interest.
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