Assistive devices for patients with auditory neuropathy: hearing aid use

Auditory Neuropathy (AN) is a hearing disorder characterized by disruption of temporal coding of acoustic signals in the auditory nerve resulting from lesions involving auditory nerve fibers, the inner hair cells or their synapses with auditory nerve terminals. Disruption of auditory nerve discharge underlies both the absence of auditory brainstem responses (ABRs) and impairment of speech perception. AN may be underlain by genetic disorders or result from a wide range of other etiologies. It can be identified either as an isolated disorder (isolated AN) or associated with multisystem involvement (non-isolated AN). Effectiveness and choice of assistive devices depend crucially upon etiology, site of lesion and stage of the disease. Cochlear implants constitute an effective rehabilitative tool able to restore speech perception in many patients with genetic AN, especially those affected by the isolated form of the disorder. Hearing aids have been used by patients with isolated AN who were submitted to cochlear implantation with improvement in pure tone sensitivity. Some children with isolated AN have proved to be good hearing users, showing satisfactory open-set speech perception abilities in the aided condition. Moreover, over 50% of children discharged from Neonatal Intensive Care Units (NICUs) showing the electrophysiological profile of AN (absent ABRs, presence of OAEs) benefit from hearing aid use, the provision of amplification resulting in remarkable improvement in speech perception. It can be concluded that differences in cochlear implant outcome or hearing aid use in patients with AN are related to the pathophysiological mechanisms underlying alteration of auditory nerve discharge associated with individual etiologies.