Auditory Neuropathy Spectrum Disorder (ANSD) is a hearing disorder characterized by dysfunction of the auditory nerve and/or synapses of the inner hair cells and auditory nerve, and normal or near normal outer hair cell function. Children with ANSD can present with a wide range of behavioral hearing levels (normal to profound hearing loss), difficulty hearing in noise, and unexpectedly poor speech recognition abilities for the degree of hearing loss. ANSD is thought to account for roughly 10% of new infant hearing loss diagnosis (Uus and Bamford, 2005). It can be unilateral or bilateral.

ANSD can be misinterpreted as profound sensorineural hearing loss if proper testing and/or interpretation are not performed. The recommended test battery to correctly diagnose ANSD is: (1) otoacoustic emission (OAE) testing to assess outer hair cell function, (2) auditory brainstem response (ABR) testing to assess auditory nerve function and outer hair cell function, specifically looking for a Cochlear Microphonic (CM). OAEs are frequently normal or near normal for infants with ANSD; however, OAE responses may disappear over time (Starr et al., 1996). The ABR test is absent or severely abnormal in all infants with ANSD. The ABR may appear flat with no peaks, reveal presence of waves I-III but nothing after, or reveal poorly synchronized later peaks that appear only at high intensity levels. As well, the ABR will reveal a Cochlear Microphonic (CM) when the test is performed correctly. To search for a CM, a single-polarity click stimulus should be run at a high intensity level (80-90 dB nHL) in separate trials through insert earphones (Starr et al, 2001; Berlin et al, 1998). The CM will reverse polarity with the polarity reversal of the click stimulus. Essentially, a mirror image of the CM should be visible. One run should also be completed with no sound to differentiate CM from stimulus artifact. Absence of acoustic reflex thresholds can be used in conjunction with OAE and ABR testing to diagnose ANSD. However, caution should be used when working with infants, as normative data do not exist for acoustic reflex threshold using a 1000-Hz probe tone (recommended for tympanometric studies in infants).

Infant hearing screen protocols (JCIH, 2007) were revised in 2007 and the targeted definition of hearing loss was expanded to include "neural hearing loss" or ANSD. JCIH recommended infants who stay in the NICU for more than 5 days should receive an ABR screen because an OAE screen will fail to detect ANSD in this population. Many well-baby nurseries continue to use an OAE screen protocol. Even if the baby earns a "pass" on the initial OAE screen, ANSD may be present and will be missed. In South Carolina, all infants (well-baby nursery and NICU) receive an ABR initial screen. However, when a "refer" result is obtained, they are often rescreened with OAE at an outpatient clinic. Again, ANSD will be missed. Babies who fail the initial ABR screen should not be rescreened and "passed" with OAE because those infants can have ANSD. Management of ANSD is challenging. Because these children present with an abnormal ABR, it is impossible to determine their actual hearing thresholds until they are developmentally capable of performing sound booth testing using Visual Reinforcement Audiometry test methods. Otherwise normal developing children typically begin VRA at age 6 months. Once stable hearing thresholds can be obtained, amplification may be considered. Hearing aids should not be fit prior to obtaining several consistent audiograms in separate testing sessions. Reliable hearing thresholds must be ascertained to accurately program the hearing aids. One study noted improvement in audiological thresholds in 50% of infants with ANSD within 15 months of diagnosis (Madden et al., 2002). Given the likelihood for fluctuation in hearing levels, children with ANSD should undergo frequent audiological evaluations. Often, children with ANSD will be successful with hearing aids. However, if the child's speech perception abilities are not progressing well following a consistent, well-fit hearing aid trial, a cochlear implant might be warranted. Recent literature suggested the importance of MRI prior to cochlear implantation to rule out aplasia/agenesis of the cochlear nerve (Buchman et al., 2006) for children with ANSD. It has been reported that regardless of sensory aid (hearing aid or cochlear implant), children with ANSD may not perform as well as their matched peers with sensorineural hearing loss (Rance and Barker, 2008).

In summary, children with ANSD present with a spectrum of hearing and speech difficulties. As well, outcomes with hearing aids and/or cochlear implants are difficult to predict. Proper diagnosis is essential to the care of this population. A pediatric audiologist and an otolaryngologist with significant experience with pediatric hearing loss should manage these children