Vestibular function in children with auditory neuropathy spectrum disorder

Abstract

Objective

Children with auditory neuropathy spectrum disorder (ANSD) account for about 10% of paediatric patients referred for cochlear implantation. Vestibulopathy may be associated with ANSD, and may have implications when formulating management plans in this patient group. We wanted to determine the incidence and predictive factors for vestibulopathy in this patient group to guide vestibular testing in this patient population, and give insight to the aetiology of ANSD.

Methods

We reviewed the outcomes of vestibular function testing in a cohort of paediatric patients with ANSD.

Results

Probable or definite vestibulopathy was seen in 42% of patients who were tested. Vestibulopathy was associated with medical co-morbidities, but was not associated with imaging findings.

Conclusions

Vestibulopathy is relatively prevalent in this patient group, and should be considered when planning the investigation and management of children with ANSD.

Introduction

Auditory neuropathy spectrum disorder (ANSD) is a syndrome that is increasingly recognised as a major cause of hearing loss in a paediatric population. The term ANSD refers to hearing impairment due to pathology at any point between the inner hair cells, and the distal auditory pathway. It is characterised by a disparity between central measures of hearing such as auditory brainstem responses, and measures of outer hair cell function such as otoacoustic emissions (OAEs), or cochlear microphonics. However, it is important to note that in established ANSD, OAEs may be negative as they may disappear over time. It is thought that ANSD may account for approximately 5–10% [1], [2], [3] of paediatric patients with profound hearing loss.

In addition to its prevalence, ANSD is important for other reasons. Firstly, neonates may ‘pass’ newborn screening programmes with normal OAE responses, but in the presence of auditory neuropathy, they may still have a significant hearing loss [4]. Secondly, ANSD is associated with conditions such as prematurity which may already put the patient at risk of developmental delay. Additional hearing loss may exacerbate this disability. Thirdly, some patients with ANSD may be less amenable to treatment with cochlear implantation [5], [6] and early development of alternative communication strategies may have to be considered.

ANSD is a spectrum of conditions that produce hearing loss distal to the outer hair cells. These include disorders of the inner hair cells, neuropathy in the cochlear or vestibulocochlear nerve, and central pathologies. As the vestibular and auditory systems are intrinsically linked, these conditions can affect the vestibular system. The overlap between auditory and vestibular neuropathies in adult and paediatric patients has previously been demonstrated.

A number of studies have tested the superior vestibular nerve using calorics and clinical examination in patients with ANSD. Starr [7] showed that five of a series of ten had vestibulopathy – three clinical and an additional two subclinical. Sheykholeslami [8] and Kaga [9] demonstrated vestibulopathy in all ANSD patients they assessed (three and five respectively).

The vestibulopathy is frequently subclinical. When testing 14 asymptomatic patients, Fujikawa [10] found nine with evidence of objective vestibulopathy. Indeed, in the largest series, only 18% reported balance difficulties, despite vestibular dysfunction being detected in 44% [11]. Auditory and vestibular neuropathy was frequently associated with peripheral neuropathy, and indeed in this large series, the overlap was noted with 62% of ANSD patients having abnormal somatosensory evoked potentials – a marker for peripheral neuropathy. Masuda [12] showed that vestibular function had declined over time with hearing in three 60 year old patients, and therefore when considering a paediatric population, it is important to consider these patients separately.

Two studies have looked at this association in children using a combination of examination, calorics, pursuit testing, and optokinetic nystagmus. Both Konradson [13] and Akdogan [14] demonstrated normal vestibular function in four and two patients respectively.

The saccule and inferior vestibular nerve have also been investigated. In a trial of eight adults with adult onset auditory neuropathy, the vast majority (81%) of tested ears had concomitant abnormal vestibular evoked myogenic potentials (VEMPs) [15]. In three 19–21 year old patients with recent diagnoses of auditory neuropathy, all had some element of vestibulopathy; one patient had symptomatic vestibular hypofunction, one asymptomatic but clinically detectable, and one was only detectable on objective testing [16]. Sheykholeslami and Kaga’s series mentioned above also included VEMP testing, which was also abnormal in all eight patients. Whereas, in Akdogan’s paediatric series, whilst superior vestibular nerve function was normal, two out of the three patients had abnormal VEMPs.

In summary, whilst there have been investigations of vestibulopathy in adult patients with ANSD, we have very limited information on vestibulopathy in paediatric patients. Given the frequency of subclinical vestibulopathy, all paediatric patients at our institution with ANSD who were referred for consideration of cochlear implantation underwent objective vestibular testing. We summarise the results of the vestibular assessment. We also investigated the past medical history and imaging findings to see if these were associated with vestibulopathy.