Importance of Vestibulo-ocular Reflex Gain and Refixation Saccade Analysis in Individuals with Auditory Neuropathy Spectrum Disorder

THIEME 146 Original Research Importance of Vestibulo-ocular Reflex Gain and Refixation Saccade Analysis in Individuals with Auditory Neuropathy Spectrum Disorder Sujeet Kumar Sinha1 Anuj Kumar Neupane1 Krithika Gururaj1 1 Department of Audiology, All India Institute of Speech and Hearing, Mysore, Karnataka, India Address for correspondence Sujeet Kumar Sinha, PhD, Department of Audiology, All India Institute of Speech and Hearing, Mysore, Karnataka, India (e-mail: ). Int Arch Otorhinolaryngol 2020;24(2):e146–e154. Abstract Keywords ► auditory neuropathy ► semicircular canals ► vestibulo-ocular reflexes ► saccades ► pure tone threshold Introduction Auditory neuropathy spectrum disorder (ANSD) features the presence of otoacoustic emissions, poor speech identification score and absent auditory brainstem response. Objective The present study was designed to evaluate the functioning of all six semicircular canals in individuals with ANSD and to compare it with those of normalhearing individuals. Methods A total of 50 individuals participated in the present study, in which Group I comprised 25 normal-hearing individuals, and Group II comprised 25 individuals with ANSD. All of the participants underwent case history, pure tone audiometry, immittance, otoacoustic emissions, auditory evoked response and video head impulse test (vHIT). Results The independent sample t-test revealed significantly lower vestibulo-ocular reflex gain values in individuals with ANSD. A presence of 100% corrective refixation saccades was observed in the same group. The Pearson correlation test revealed no significant correlation between vestibulo-ocular reflex (VOR) gain with duration of hearing loss and pure tone thresholds for any of the three orthogonal planes. The chisquared test revealed no association between the VOR gain values and the presence or absence of saccades in any of the semicircular canals (p > 0.05). Conclusion Huge percentages of individuals with ANSD have been found to have associated vestibular dysfunction as well. Therefore, the vHIT can be used as one of the important tests of the vestibular test battery to evaluate all six semicircular canals in individuals with ANSD. Introduction Auditory neuropathy spectrum disorder (ANSD) is characterized by the presence of otoacoustic emissions, the absence of auditory brainstem response, and of poorer speech identification score that does not correlate with the pure tone threshold.1–4 The epidemiological data on ANSD varies across the studies and age groups. In 1979, Davis et al5 reported that 1 in every 200 children with hearing impairment have ANSD. Simi- received March 22, 2018 accepted June 23, 2019 published online November 4, 2019 DOI https://doi.org/ 10.1055/s-0039-1697004. ISSN 1809-9777. larly, in 1999, Berlin6 reported 4% of children with permanent hearing loss with ANSD. In the Indian scenario, it was reported that 1 in every 183 individuals with sensorineural hearing loss has ANSD,7 whereas the prevalence of ANSD was reported to be 2.27% in school-going hearing impaired children.8 The prevalence of vestibular impairment varies across studies. In a retrospective study on 50 individuals with ANSD, 53% of them were found to have vestibular dysfunction with hypoactive caloric response.9 Prabhu et al10 reported that one in five Copyright © 2020 by Thieme Revinter Publicações Ltda, Rio de Janeiro, Brazil Importance of Vestibulo-ocular Reflex Gain and Refixation Saccade Analysis in Individuals individuals with ANSD reported at least one of the vestibular symptoms. A few other studies have also reported affected sacculocollic11–13 and utriculo-ocular pathways14 in these individuals. Also, abnormal response has been reported in the Mann, Romberg and Fukuda stepping tests for eyes closed condition suggesting a possible involvement of peripheral vestibular organs in individuals with ANSD.13 However, earlier studies have also reported variability in vestibular test results in individuals with ANSD. Sinha et al (2013b)13 reported abnormality of cervical vestibular evoked myogenic potentials (cVEMPs) in 82.26% of the ears with ANSD, Ismail et al15 reported absence of cVEMPs in 50% of the ears with ANSD, Kumar et al12 reported abnormal cVEMPs in 65% of the ears with ANSD, and Sinha et al (2013b)13 reported absence of ocular vestibular evoked myogenic potentials (oVEMPs) in 90% of the ears with ANSD. There was a large variability not only in the cVEMPs and oVEMPs, but also in caloric test findings. For example, Starr et al3 reported absent responses to caloric tests in 20% of the participants with ANSD, AbdelNasser et al16 reported reduced caloric responses in 30% of the subjects with ANSD, whereas Sinha et al17 reported reduced caloric responses in 86% of the participants with ANSD. The caloric test is considered as a gold standard test for the evaluation of the 2 lateral semicircular canals in a very low and brief frequency range (0.002–0.004 Hz). However, the frequency range assessed by the caloric test is way below the frequency range to which a normal hearing individual is exposed in everyday life.18 Also, the caloric test does not assess the anterior and the posterior canal. Even after combining the cVEMP, oVEMP and caloric test results, we obtain information about the saccule, the utricle, and only the horizontal semicircular canals. Hence, there is a need to assess the anterior and the posterior canals in individuals with ANSD. Halmagyi et al19 have come up with an advanced noninvasive tool based on the principle of the head impulse test (HIT), known as the video head impulse test (vHIT). The vHIT is a software-based test that consists of goggles with gyroscope to quantify the vestibulo-ocular reflex (VOR) gain function and refixation saccades.20 The vHIT has good test retest reliability21 and good sensitivity in identifying semicircular canal lesions in various clinical populations, such as Meniere disease,22 benign paroxysmal positional vertigo,23 Sinha et al. vestibular neuritis,24 adults with congenital sensorineural hearing loss,25 and in vestibular migraine.26 The inclusion of the vHIT in the vestibular test battery for the diagnosis of vestibular lesions in individuals with ANSD will provide information about all the six semicircular canals. Therefore, the present study aimed at evaluating the functioning of all six semicircular canals in individuals with ANSD and to compare it with those of normal hearing individuals. Vestibulo-ocular reflex gain function and refixation saccades (if any) in both groups were analyzed. The present study also aimed at finding out a correlation between vHIT test findings with duration of disorder and pure tone thresholds and finding out an association between the presence or absence of saccades with VOR gain values in individuals with ANSD (if any). Methods Two groups of individuals were included in the present study. Group I consisted of 25 participants (18 males and 7 females) in the age ra (...truncated)