Delayed visual maturation associated with auditory neuropathy/dyssynchrony

Auditory neuropathy: endocochlear lesion or temporal processing impairment? Implications for diagnosis and management

BACKGROUND/OBJECTIVE

Auditory neuropathy/dys-synchrony, characterized by absent auditory brainstem responses, normal otoacoustic emissions or cochlear microphonics, and word discrimination disproportional to the pure-tone audiogram, may be accompanied by perceptual consequences that could jeopardize language acquisition in affected children. However, the related evidence is constantly changing leading to a serious debate. The aim of the present paper is to review the current knowledge on auditory neuropathy/dys-synchrony, and to present the therapeutic strategies that can be employed in its management, taking into account the potentially underlying pathophysiology.

MATERIALS/METHODS

Literature review from Medline and database sources. Related books were also included.

STUDY SELECTION

Controlled clinical trials, prospective and retrospective cohort studies, nested-based case-control and analytical family studies, laboratory and electrophysiological studies, animal models, case-reports, joint statements and review articles.

DATA SYNTHESIS

Auditory neuropathy/dys-synchrony, in contrast to what is widely believed, is a very frequent disease, responsible for approximately 8% of newly diagnosed cases of hearing loss in children per year. Hyperbilirubinemia and hypoxia represent major risk factors, whereas generalized neuropathic disorders, or a genetic substrate involving the otoferlin gene, are responsible for the phenotype of auditory neuropathy/dys-synchrony in certain cases. Auditory nerve myelinopathy and/or desynchrony of neural discharges are the most probable underlying pathophysiologic mechanisms. Genetic testing may be helpful in cases of non-syndromic prelingual children. Auditory neuropathy/dys-synchrony management aims at restoring the compromised processing of auditory information, either through conventional amplification and/or alternative forms of communication, or by cochlear implantation (combined with intensive speech and language therapy).

CONCLUSION

Auditory neuropathy/dys-synchrony is more frequent than considered in the past, especially amongst hearing-impaired children. Accurate diagnosis, based on subjective and objective hearing assessment techniques (including the various electrophysiological assessment measures), and timely treatment of the affected children is of paramount importance, with hearing aids, intensive speech and language therapy (and sign language when indicated) providing the mainstay of habilitation, and cochlear implantation representing a valid therapeutic alternative.

Prevalence of auditory neuropathy/synaptopathy in a population of children with profound hearing loss

OBJECTIVE

To examine the prevalence of auditory neuropathy/synaptopathy (AN/AS) in a cohort of children with profound hearing loss.

METHODS

From 1997 until 2004, 5190 children, aged 1-15 years, whose hearing ability was uncertain or who had risk factors for hearing impairment were investigated with subjective and objective hearing tests. Three thousand four hundred and fifteen from these children were screened for AN/AS using pure-tone audiometry, impedance measurement, transient evoked otoacoustic emissions (TEOAE) and click-evoked auditory brainstem responses (ABR).

RESULTS

From 3415 patients who participated in an ABR and TEOAE assessment, 379 children showed absent or elevated (> or = 80 dB nHL) ABR thresholds. Within this group we found 32 cases with evidence of AN/AS via visible TEOAE and/or cochlear microphonics (CM) coupled with absent ABR. In the remaining 3036 children, AN/AS, could be ruled out by means of detectable ABR-thresholds and coherent findings in pure-tone audiometry and TEOAE assessment. This results in a prevalence of AN/AS of 0.94% within the group at risk for hearing loss, compared to 8.44% among profoundly hearing impaired children.

CONCLUSION

This study shows that AN/AS is a common finding in the population of hearing impaired infants. In the majority of our AN/AS children (50%, n=16), an early audiological diagnosis was made under the age of 12 months. Therefore, clinicians and other health care professionals should generally be sensitised for AN/AS in infants, so that an appropriate treatment can promptly be initiated. Further research on clinical and pathophysiological aspects is necessary to better identify and manage patients suffering from AN/AS.