Abstract
Auditory neuropathy spectrum disorder (ANSD) refers to a range of hearing impairments characterized by deteriorated speech perception, despite relatively preserved pure-tone detection thresholds. Affected individuals usually present with abnormal auditory brainstem responses (ABRs), but normal otoacoustic emissions (OAEs). These electrophysiological characteristics have led to the hypothesis that ANSD may be caused by various dysfunctions at the cochlear inner hair cell (IHC) and spiral ganglion neuron (SGN) levels, while the activity of outer hair cells (OHCs) is preserved, resulting in discrepancies between pure-tone and speech comprehension thresholds. The exact prevalence of ANSD remains unknown; clinical findings show a large variability among subjects with hearing impairment ranging from mild to profound hearing loss. A wide range of prenatal and postnatal etiologies have been proposed. The study of genetics and of the implicated sites of lesion correlated with clinical findings have also led to a better understanding of the molecular mechanisms underlying the various forms of ANSD, and may guide clinicians in better screening, assessment and treatment of ANSD patients. Besides OAEs and ABRs, audiological assessment includes stapedial reflex measurements, supraliminal psychoacoustic tests, electrocochleography (ECochG), auditory steady-state responses (ASSRs) and cortical auditory evoked potentials (CAEPs). Hearing aids are indicated in the treatment of ANSD with mild to moderate hearing loss, whereas cochlear implantation is the first choice of treatment in case of profound hearing loss, especially in case of IHC presynaptic disorders, or in case of poor auditory outcomes with conventional hearing aids.
Highlights
Auditory neuropathy spectrum disorder (ANSD) refers to a range of hearing dysfunctions characterized by compromised signal processing along the auditory nerve or by deficient transmission of this signal to the auditory nerve by the presynaptic inner hair cells (IHCs)
Its diagnosis is in part based on evidence of altered neural processing such abnormal auditory brainstem responses (ABRs), with a reduced or absent wave V, despite evidence of preserved outer hair cells (OHCs) responses, such as otoacoustic emissions (OAEs) and/or cochlear microphonic (CM). [1,2,3,4]
hidden hearing loss (HHL) is associated with well-synchronized ABRs. This auditory processing disorder may be caused by a specific synaptopathy-neuropathy, limited to auditory fibers responding to high intensity sounds with preservation of fibers responding to low intensity sounds [18,19]
Summary
Auditory neuropathy spectrum disorder (ANSD) refers to a range of hearing dysfunctions characterized by compromised signal processing along the auditory nerve or by deficient transmission of this signal to the auditory nerve by the presynaptic inner hair cells (IHCs). HHL is associated with well-synchronized ABRs. HHL is associated with well-synchronized ABRs This auditory processing disorder may be caused by a specific synaptopathy-neuropathy, limited to auditory fibers responding to high intensity sounds with preservation of fibers responding to low intensity sounds [18,19]. This special kind of auditory synaptopathy-neuropathy will be discussed separately because it does not correspond to the currently accepted definition of ANSD where ABRs waves and speech audiometry in quiet are severely deteriorated [20].
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