Auditory neuropathy/auditory dys-synchrony detected by universal newborn hearing screening

Summary

The implementation of neonatal hearing screening has enabled early detection and intervention in hearing loss. The use of otoacoustic emissions (OAE) and auditory brainstem response testing in universal screening has led to the recognition of this recently described disorder called auditory neuropathy/auditory dys-synchrony (AN/AD). This diagnosis indicates that the infant has significant hearing loss despite having normal outer hair cells in the cochlea. We reviewed the characteristics and natural history of nine infants detected to have AN/AD from universal newborn hearing screening in a national pediatric hospital. Fifty-two cases of hearing loss were detected from 14,807 consecutively screened cases. Of the 52 cases, 9 had electrophysiological test results consistent with AN/AD. They include both premature infants who had major neonatal complications and term infants with no perinatal complications. Six cases had bilateral and three cases had unilateral findings. We suggest that AN/AD can occur in low-risk infants and hence screening of high-risk cases alone is insufficient. Our findings are discussed with reference to the current literature.

Introduction

Objective physiological hearing assessments are used in newborn hearing screening because behavioral testing is unreliable. Two common assessments used are the otoacoustic emissions (OAE) and the automated auditory brainstem response (Auto-ABR). The OAE test is a quick and inexpensive method but it has a high false positive rate; and of more concern is the possibility of false negatives, such as in the case of auditory neuropathy/auditory dys-synchrony (AN/AD).

The term auditory neuropathy was first used by Starr et al. [1] in 1996 to describe 10 patients who had acquired hearing impairment in the presence of normal cochlear outer hair cells. All went on to develop a peripheral neuropathy later in life. Starr et al. [1] attributed the hearing loss to a generalized neuropathic disorder and he suggested that the lesion might be in the auditory nerve. In 1996, Kaga et al. [2] also described two patients with absent auditory brain response (ABR) but almost normal OAE. In addition, one patient had vestibular problems. These patients were diagnosed to have auditory nerve disease due to an unknown cause.

In 1997, Deltenre et al. [3] reported three cases of infants who had hearing loss detected early following major neonatal events. They showed the same pattern of absent auditory brainstem response but with preserved cochlear outer hair cell function. Doyle et al. [4] in 1998 described eight children who had hearing loss disproportionate to the normal OAE and cochlear microphonics. Five had reverse sloping hearing loss, two had predominantly high-frequency hearing loss and one had a mild flat pattern. The pattern of test results suggested neuropathy of the cochlear nerve and implied a neural deafness as opposed to a sensory deafness.

Hood [5] describes auditory neuropathy as being distinguished from other types of auditory abnormalities by the presence of normal OAE, absent middle ear muscle reflex and auditory brain response in the presence of normal radiological results. ABR testing showed that this disorder was distinct from a central deafness and the lesion potentially could be anywhere from the inner hair cells to the auditory cortex. In 2001, Berlin et al. [6] recommended that the term auditory neuropathy/auditory dys-synchrony be used because the presence of poor synchrony of the auditory nerve suggests a more logical connection to viable management options. The pattern of AN/AD has been seen in varied presentations from neonates to adults with acquired hearing loss. Hence, AN/AD is not a diagnosis, but a presentation now readily identified with OAE and ABR screening. It is not a new disease, but an entity, which is recognized because of improvements in hearing assessment.

Since mid 2002, universal newborn hearing screening has been implemented in Kandang Kerbau Women's and Children's Hospital (KKWCH), Singapore with the use of Auto-ABR testing. We present nine cases of newborns detected to have auditory test patterns consistent with AN/AD over 1 year. This pattern consisted of absent ABR in the presence of normal OAE.