Hood and Morlet (2012) report that auditory neuropathy spectrum disorder (ANSD) is characterized by intact outer hair cells (OHCs, evidenced through present otoacoustic emissions and/or present cochlear microphonic) and the absence (or very poor morphology) of an auditory brainstem response (ABR). Of note, ANSD generally presents with absent (or elevated) ipsi and contralateral middle ear reflexes. In the presence of ANSD, word recognition scores and pure tones may present anywhere from normal to profound hearing loss ranges. Most often, children with ANSD and normal (or near normal) pure-tone thresholds perform very poorly in the presence of background noise. The reported incidence of ANSD varies from 10 percent of all people with severe-to-profound hearing loss to 15 percent (or more) of people with hearing loss.
Of clinical and diagnostic importance, Hood and Morlet report one way to separate the cochlear microphone (CM) from the ABR is to compare responses from rarefaction and condensation stimuli. The CM reverses (inverts) with the change in polarity and CM latencies do not increase in latency as stimulus intensity decreases.
Hood and Morlet report that some infants with a diagnosis of ANSD appear to "outgrow" ANSD over time, as evidenced by their ABRs. Specifically, children with hyperbilirubinemia and/or jaundice may have a better chance of improving (or normalizing their ANSD) over time. Hood and Morlet review several other reports that indicate and document recovery from ANSD. The authors note that individualized management of the child with ANSD is needed and multiple dilemmas are faced by clinicians managing ANSD. Specifically, amplification may damage functioning OHCs, while the benefits obtained vary greatly and are essentially unpredictable. Clinicians using amplification for children with ANSD may be providing amplification to an auditory system that does not require it, or they may provide amplification that remains unclear and/or meaningless to the child.
(Editor's Note: The implications of potentially reversible ANSD for children who receive cochlear implants due to an ANSD diagnosis will also merit additional concerns and discussion.) Hood and Morlet report that ANSD management should be focused on "the global communication skills and abilities of the patient necessary to acquire language, become literate, and be self-sufficient."
For More Information, References and Recommendations
Hood LJ, Morlet T. (2012) Current Issues in Auditory Neuropathy Spectrum Disorder. In Tremblay KE, Burkard, RF. Eds. Translational Perspectives in Auditory Neuroscience. Plural Publishing.