Niraj Kumar Singh

Involvement of peripheral vestibular nerve in individuals with auditory neuropathy

The vestibulocochlear nerve is a sensory nerve that serves the organs of hearing and equilibrium. Neuropathies of the nerve, particularly auditory neuropathy may be caused by primary demyelination or by axonal diseases. In disorders affecting the cochlear nerve, it is probable that the vestibular nerve is involved as well. There are isolated reports of the involvement of the inferior vestibular nerve (using vestibular-evoked myogenic potentials) in individuals with AN. However, there is a dearth of information on the involvement of the superior vestibular nerve and other functions such as optokinetic, saccade and vestibulo-occular reflex. A total of three subjects diagnosed as having auditory neuropathy, underwent an extensive vestibular assessment consisting of clinical tests of stability (Romberg, Fukuda stepping test), administration of dizziness questionnaire developed by Maryland hearing and balance centre, cervical vestibular-evoked myogenic potentials and a standard electronystagmography test battery. In the present study, the entire subject population assessed showed hypofunctional caloric responses and absent VEMPs. Two out of the three subjects were asymptomatic of vestibular dysfunction. On the clinical tests of stability, two subjects showed deviations to the right, while one subject performed normally. Thus, the present study indicates a possible involvement of peripheral vestibular nerve involvement in individuals with auditory neuropathy.

Characterizing the frequency tuning properties of air-conduction ocular vestibular evoked myogenic potentials in healthy individuals

Abstract Objective: Inconsistencies regarding frequency tuning of ocular vestibular evoked myogenic potentials (oVEMP) prompted the present study to aim at characterizing frequency tuning of oVEMP in healthy individuals. Design: Normative study. Study sample: The study was conducted to obtain oVEMP responses from 54 healthy individuals in age range of 18–30 years. The responses were acquired for tone-bursts at octave and mid-octave frequencies from 250 to 2000 Hz from the inferior oblique muscle using contralateral electrode placement. The frequencies were compared for amplitude and threshold. Results: oVEMPs were present in 100% of individuals at or below the frequency of 1000 Hz. The responses had maximum amplitude and lowest thresholds at 500 Hz. There were at least two replicable peak-complexes namely n1-p1 and p1-n2. Both these complexes revealed tuning at 500 Hz. Comparison between the two peak-complexes revealed higher amplitudes and lower thresholds for p1-n2 complex. Conclusions: oVEMPs are tuned to 500 Hz for both peak-complexes, with p1-n2 being more robust. Future studies using the threshold of oVEMP may be better suited to use p1-n2 complex for this purpose, provided vestibular origin of the second complex is proved. Additionally, careful use of tuning property is recommended when evaluating pathological conditions.

Vestibular Evoked Myogenic Potential as a Tool to Identify Vestibular Involvement in Auditory Neuropathy

Abstract Auditory neuropathy is characterized by a unique pattern of hearing loss, absent or severely distorted ABR, preserved OAE, and measurable cochlear microphonics. As the vestibular and cochlear branches are parts of the same fiber bundle system called the vestibulocochlear nerve, it is likely that neuropathy in one (cochlear branch) might also form a feature in the other (vestibular branch). But none of these tests are able to explain the involvement of the vestibular system in these cases. Thus, the present study was undertaken to explore this aspect to determine: (1) the involvement of the vestibular pathway in cases with auditory neuropathy; (2) if there is any relationship between vestibular abnormalities and the symptoms they mimic; and (3) the incidence of vestibular abnormality in patients with auditory neuropathy. Ten subjects (7 male and 3 female) in the age range of 15 to 35 years participated in this study. The test battery administered included pure-tone audiometry, ABR, OAE, Immittance, and VEMP. The results showed: (1) nine out of the 10 subjects showed abnormal or absent VEMP; (2) there is no one-to-one correlation between the abnormal or absent VEMP and the vestibular symptoms that these subjects present; and (3) 80% of the ears with auditory neuropathy showed abnormal VEMP results giving an indication of high incidence of vestibular involvement in the auditory neuropathy population. The present study provides evidence for involvement of the vestibular branch of the VIIIth cranial nerve in a high percentage of the auditory neuropathy population; hence, it is suggested that there is need for vestibular assessment in cases of auditory neuropathy that would help to better understand the disorder. It is also suggested that the term “acoustic neuropathy” be used to indicate those patients in whom only the acoustic nerve is affected and “vestibuloacoustic neuropathy” to label those patients who also show involvement of the vestibular system.

Efficacy of ocular vestibular-evoked myogenic potential in identifying posterior semicircular canal benign paroxysmal positional vertigo.

Objectives: Benign paroxysmal positional vertigo (BPPV) is a unilateral peripheral vestibular pathology, mostly involving the semicircular canals and the otolith organs. Although equivocal findings exist on the utility of cervical vestibular-evoked myogenic potential in identifying BPPV-associated changes in saccule, ocular vestibular-evoked myogenic potential (oVEMP), which is primarily a utricular response, has sparingly been explored in this population. Hence, the present study aimed at examining oVEMP in individuals with BPPV and comparing them with healthy individuals to illustrate its efficacy in identifying BPPV-associated changes in the utricle. Design: Using a case-control design, oVEMPs were elicited by 500 Hz tone bursts at 125 dB peak sound pressure level and recorded bilaterally from 30 individuals with unilateral posterior canal BPPV and 30 age- and gender-matched healthy controls. Results: There were no inter- or intragroup differences in latency aspects (p > 0.05); however, amplitudes were significantly smaller in BPPV ears compared with the non-BPPV ears of individuals with BPPV as well as ears of healthy controls (p < 0.05). Exceptions to this were five participants with BPPV in whom the affected ears demonstrated larger response amplitude (augmentation) than the unaffected ears. Furthermore, there was significantly larger interaural amplitude ratio in individuals with BPPV compared with the healthy controls (p < 0.05). Interaural amplitude ratio produced the largest effect size among the oVEMP parameters for differentiating BPPV from healthy controls. Conclusions: Large asymmetry ratio of oVEMP, usually exceeding 26.8%, is the most potent characteristic of oVEMP in BPPV. Abnormal oVEMP results confirm utricular pathology in ears with BPPV, and therefore, oVEMP can be used as an objective tool with asymmetry ratio as the parameter of choice for the evaluation of utricular function in persons with posterior canal BPPV.

Characterizing the Effects of Frequency on Parameters of Short Tone‑bursts Induced Ocular Vestibular Evoked Myogenic Potentials

Stimulus is the essence of any audiovestibular investigation and ocular vestibular-evoked myogenic potential (oVEMP) would be no different. Several investigations have examined the effect of frequency of stimulus on oVEMP parameters with prime reports concentrated around amplitude and to a lesser extent threshold. Effects of stimulus frequency on latency-related parameters have been sparingly explored with equivocal results. Thus, the aim of this study was to investigate the effects of air-conducted frequency-specific short tone-bursts on latency, amplitude, and threshold-related parameters of various peaks of oVEMP. A normative study was conducted to obtain oVEMP responses from 50 healthy individuals in the age range of 18 - 30 years. Tone-bursts at octave and midoctave frequencies from 250 to 2000 Hz were used to acquire responses from the inferior oblique muscle using contralateral electrode placement. oVEMPs were present in 100% of the individuals at or below the frequency of 1000 Hz. The largest amplitudes and the lowest threshold corresponded to 500 Hz tone-burst, whereas 250 Hz produced largest absolute latencies as well as interpeak latency intervals (P < 0.05). Frequency had no effect on interaural latency difference as well as interaural amplitude ratio. Owing to largest amplitudes and best thresholds, 500 Hz appears better stimuli for clinical recording of oVEMPs. This is true irrespective of the peak complex being assessed is n1p1 or p1n2.

Rise/fall and plateau time optimization for cervical vestibular-evoked myogenic potential elicited by short tone bursts of 500 Hz

Abstract Objective: Literature on clinical utility of cervical vestibular-evoked myogenic potential (cVEMP) has been increasing rapidly, though not without inconsistencies in spite of involving similar populations. Close examination of methods across studies exposed the use of variable stimulus parameters, especially rise/fall time (R/FT) and plateau time (PT) as the possible reason. However the effect of variation in R/FT and PT on cVEMP response parameters has been largely uncharted. Design: The study aimed at evaluating the impact of R/FT and PT on cVEMPs elicited by 500-Hz short tone-bursts (STBs) at 95 dB nHL using R/FT from 1 to 4 ms and PT from 0 to 3 ms. Study sample: 30 healthy individuals with normal audio-vestibular system. Results: Significant prolongation of latencies with increasing R/FT and PT (p < 0.05) was noticed. The amplitude however varied significantly only for some R/FTs and PTs. R/FT of 2 ms, in combination with 1-ms PT, produced large amplitudes with lowest variability in amplitude and latency parameters. Conclusions: R/FT of 2 ms along with PT of 1 ms formed a good amalgamation and could be considered optimum for clinical recording of cVEMPs elicited by 500-Hz STBs, although slight deviances in these parameters might not impact the outcome significantly.

Are cervical vestibular evoked myogenic potentials sensitive to changes in the vestibular system associated with benign paroxysmal positional vertigo

Abstract Objective: This study aimed to correct the notion regarding the efficacy of cervical vestibular evoked myogenic potentials (cVEMP) in identifying benign paroxysmal positional vertigo (BPPV)-associated changes in the peripheral vestibular system. Study design: A static group comparison research design was used to compare the cVEMP results of a group of individuals with BPPV in the age range of 30–60 years against age- and gender-matched healthy individuals. The cVEMP were recorded with tone bursts of 500 Hz gated using a Blackman window. The 95dB nHL tone bursts were presented at the rate of 5.1 Hz. The response was band-pass filtered between 10 and 1500 Hz and amplified by a factor of 5000. The response window was set to 70 ms, which was inclusive of a 15-ms pre-stimulus recording. Results: Responses were analysed for individual peak latencies, peak-to-peak amplitudes, and asymmetry ratio and compared between the groups using mixed analysis of variance and an independent samples t-test. The results revealed no significant difference in the latencies of P13 and N23 (p > 0.05). There was also a lack of difference for peak-to-peak amplitude and asymmetry ratio between the two groups (p > 0.05). Conclusion: There was no difference in the latency or amplitude measures between healthy individuals and the individuals with BPPV, which undermines the utility of cVEMP in identifying changes associated with BPPV in the peripheral vestibular system.

Development of equally intelligible Telugu sentence-lists to test speech recognition in noise

Abstract Objective: To develop sentence lists in the Telugu language for the assessment of speech recognition threshold (SRT) in the presence of background noise through identification of the mean signal-to-noise ratio required to attain a 50% sentence recognition score (SRTn). Design: This study was conducted in three phases. The first phase involved the selection and recording of Telugu sentences. In the second phase, 20 lists, each consisting of 10 sentences with equal intelligibility, were formulated using a numerical optimisation procedure. In the third phase, the SRTn of the developed lists was estimated using adaptive procedures on individuals with normal hearing. Study sample: A total of 68 native Telugu speakers with normal hearing participated in the study. Of these, 18 (including the speakers) performed on various subjective measures in first phase, 20 performed on sentence/word recognition in noise for second phase and 30 participated in the list equivalency procedures in third phase. Results: In all, 15 lists of comparable difficulty were formulated as test material. The mean SRTn across these lists corresponded to −2.74 (SD = 0.21). Conclusions: The developed sentence lists provided a valid and reliable tool to measure SRTn in Telugu native speakers.

The Developement of Hindi Sentence Test for Speech Recognition in Noise

Background : The aim of the study was to develop a test material in Hindi language for assessing sentence recognition threshold in noise. Material and Methods : The study was conducted in two phases. First phase involved three experiments. First experiment consisted of the collection and recording of the sentence material. In the second experiment, sentence perception was assessed at five signal to noise ratios to check for the equalization of sentence material in terms of intelligibilty. This was done on 25 native speakers of Hindi language with normal hearing sensitivity. In the final experiment, 20 different lists with 10 sentences in each were formulated. The second phase of the experiment involved estimation of signal to noise ratio required to obtain 50% correct sentence identification score (SNR 50) and the test reliability of the lists was assessed. The estimation of SNR 50 was done on 30 native speakers of Hindi language with normal hearing sensitivity. Results : Twenty optimized lists were formulated. Lists were found to be of almost equal difficulty and to have good test reliability in normal-hearing listeners. The average SNR50 was -4.56 dB with a standard deviation of 0.45 dB. Conclusions : The developed test provides a reliable means of measuring sentence recognition threshold in noise for native speakers of Hindi.

Altered auditory and vestibular functioning in individuals with low bone mineral density: a systematic review

Alteration in the process of bone remodelling is associated with falls and fractures due to increased bone fragility and altered calcium functioning. The auditory system consists of skeletal structures and is, therefore, prone to getting affected by altered bone remodelling. In addition, the vestibule consists of huge volumes of calcium (CaCO3) in the form of otoconia crystals and alteration in functioning calcium levels could, therefore, result in vestibular symptoms. Thus, the present study aimed at compiling information from various studies on assessment of auditory or vestibular systems in individuals with reduced bone mineral density (BMD). A total of 1977 articles were searched using various databases and 19 full-length articles which reported auditory and vestibular outcomes in persons with low BMD were reviewed. An intricate relationship between altered BMD and audio-vestibular function was evident from the studies; nonetheless, how one aspect of hearing or balance affects the other is not clear. Significant effect of reduced bone mineral density could probably be due to the metabolic changes at the level of cochlea, secondary to alterations in BMD. One could also conclude that sympathetic remodelling is associated with vestibular problems in individual; however, whether vestibular problems lead to altered BMD cannot be ascertained with confidence. The studies reviewed in the article provide an evidence of possible involvement of hearing and vestibular system abnormalities in individuals with reduced bone mineral density. Hence, the assessment protocol for these individuals must include hearing and balance evaluation as mandatory for planning appropriate management.