Study of cochlear microphonic potentials in auditory neuropathy

Unraveling Cochlear Dynamics: The Effect of Clicks, Tone Burst Frequencies, Polarity, and Stimulus Rates on Cochlear Microphonics in Individuals with Normal Hearing

Background

Despite cochlear microphonic's potential clinical application, especially in ANSD diagnosis, the optimal parameters to record cochlear microphonics and the effect of various stimulus parameters are not well understood yet, which makes its recording a difficult procedure. The present study was undertaken to determine the effect of stimulus polarity, rate, stimulus type, and stimulus frequency on different aspects of cochlear microphonics, which could help to decide an optimal stimulus parameter that can be used to record CM.

Methods

The study involved 32 normal-hearing adults. CM was recorded from these individuals using extratympanic CM measurement from the ear canal independently for tone burst frequencies (500 Hz, 1 kHz, 4 kHz & 8 kHz) and click stimuli having rarefaction and condensation polarity at 30.1/sec and 59.1/sec repetition rates. Amplitude and latency were measured from the recorded waveforms and compared across and between stimulus conditions.

Results

Results reveal that stimulus frequency and stimulus type have a significant effect on different parameters of CM. However, there was no significant effect of stimulus polarity and rate of stimulus on the amplitude and latency of cochlear microphonics. The amplitude and latency of the cochlear microphonics are inversely proportional to the stimulus frequency.

Conclusion

Hence, the study suggests the use of low-frequency tone burst (500 Hz/1 kHz) to elicit robust CM, which has greater application in the assessment of cochlear functioning over OAE as the latter gets affected by environmental and physiological noise and also due to middle ear pathology.

Electrode Montage for Bilateral Cervical Vestibular-Evoked Myogenic Potential Testing

BACKGROUND

 Cervical vestibular-evoked myogenic potentials (cVEMPs) are predominantly ipsilateral, myogenic responses originating from saccular activation. Some individuals have contralateral-crossed cVEMP responses with monaural air-conducted stimulation (ACS) which can contaminate cVEMP responses with bilateral stimulation. While the origin of the contralateral-crossed response is under debate, its presence has implications for cVEMP testing with midline bone conduction vibration (BCV).

PURPOSE

 The purpose of this study was to determine the origin of the contralateral-crossed cVEMP response. It was hypothesized that the crossed response is due to electrode contamination and would disappear with a modified electrode montage.

RESEARCH DESIGN

 This is a cross-sectional research study.

STUDY SAMPLE

 Fifteen healthy participants (30 ears; mean age: 27.4 19-39; 10 females).

DATA COLLECTION AND ANALYSIS

 Participants completed cVEMP testing using three stimulation methods (monoaural ACS, binaural ACS, and midline BCV) and two electrode montages (sternum reference and Fp reference).

RESULTS

 In the monoaural ACS with sternum reference condition, 53.3% ears had contralateral-crossed cVEMP responses that were in-phase with the ipsilateral response for all but three ears. Whereas in the monoaural ACS with Fp reference condition, 3% had a contralateral-crossed cVEMP response. ACS and BCV cVEMP corrected amplitudes were significantly larger in the sternum reference conditions, which is attributed to artificial enhancement from the in-phase contralateral-crossed responses.

CONCLUSIONS

 The significant reduction of contralateral-crossed responses in the Fp reference condition suggests that the contralateral-crossed cVEMP response is due to reference electrode contamination and may be a more appropriate reference placement when completing cVEMPs with midline BCV.

Do cochlear microphonics evoked by narrow-band chirp stimuli affect the objective detection of auditory steady-state responses?

OBJECTIVE

It has recently been discussed whether hearing screening and hearing threshold assessment can accurately be completed using automated ASSR methods for children with auditory neuropathy spectrum disorder (ANSD). Possible causes for the claimed potential failures were investigated here.

DESIGN

The study is based on the analysis of stored ASSR raw data.

STUDY SAMPLE

This study reviewed raw ASSR data from 274 patients with a total of 5809 individual recordings.

RESULTS

Cochlear microphonics (CM) were found in 18 of the 274 patient records. Four of these 18 were obtained from patients with ANSD. One patient with ANSD without click auditory brainstem responses up to 100 dBnHL demonstrated clear ASSR responses from 65 dBnHL upwards. Where click stimulation suggests an auditory nerve defect, narrow-band chirps were shown to evoke ASSR in certain patients. CMs are elicited by narrow-band chirps in the same way as by broadband stimuli. CM residuals as well as a presumed enlarged wave I with absent neural responses, always accompanied by CM, were found as possible causes of misinterpretation at high stimulus levels. A CM detector was created.

CONCLUSIONS

The CM detector, indicating the presence of CM, will prevent misinterpretation of clinical ASSR results.

Duration of Cochlear Microphonics in Click and Toneburst-Evoked Auditory Brainstem Response in Individuals With Auditory Neuropathy Spectrum Disorder and Normal Hearing

The presence of ringing cochlear microphonics (CM) with an absence of auditory brainstem response (ABR) is an indicator of auditory neuropathy spectrum disorder (ANSD). The duration of CM may vary based on the stimuli used to elicit the response. Generally, ABR is recorded using clicks with very limited use of tonebursts. Thus, this study aims to understand the duration of CM in individuals with ANSD and normal hearing in response to clicks, 500 Hz toneburst, and 4000 Hz toneburst using ABR. Results show that individuals with ANSD have a longer duration of CM than those with normal hearing. The presence of CM was more evident in response to toneburst stimuli than clicks, with 500 Hz being commonly eliciting more CM in both groups. The difference in duration of CM was statistically significant in individuals with ANSD with longer duration obtained for 500 Hz followed by clicks and 4000 Hz toneburst. The duration of the stimuli used plays an important role in revealing the CM while recording ABR. This indicates that the use of toneburst, particularly low frequency such as 500 Hz, will be clinically useful in identifying ANSD especially when otoacoustic emissions are compromised.

The audiological characteristics of infant auditory neuropathy patients without otoacoustic emission

Objective

To explore the audiological characteristics of infant auditory neuropathy (AN) patients with cochlear microphonic (CM) recorded but absent otoacoustic emission (OAE), clinically reducing the rate of missed diagnosis of AN.

Methods

We retrospectively analyzed the audiological characteristics of infant AN patients in our medical center between 2003 and 2020. A total of 18 infant AN patients were OAE absent group, with CM present and distortion product otoacoustic emission (DPOAE) absent in both ears. A total of 44 infant AN patients were OAE present group, with CM and DPOAE present in both ears.

Results

(1) The found age in OAE absent group was 0.9 (0.02) years old, which was younger than 1.11 (1.63) years old in OAE present group (p = .041). (2) The CM threshold of OAE absent group was 80 (10) dB nHL, which was significantly higher (p < .001) than OAE present group. CM amplitude were smaller (p < .05), and CM duration were shorter (p < .05) in OAE absent group. (3) The thresholds of auditory steady-state response (ASSR) at 0.5, 1, 2, and 4 kHz were 94 (10), 94 (10), 87 (20), and 81 (10) dB HL cg, respectively in OAE absent group, which were higher than those in OAE present group (p < .01).

Conclusions

Infant AN patients with CM present and OAE absent showed earlier detection and different audiological performance, which was manifested in ASSR thresholds, audiometric configurations and CM performance. CM thresholds were increased, amplitude and duration were decreased, non-linearity of I/O function was reduced.

Level of Evidence

4.

Use of an Extra-Tympanic Membrane Electrode to Record Cochlear Microphonics with Click, Tone Burst and Chirp Stimuli

This study determined electrocochleography (ECochG) parameter settings to obtain cochlear microphonics (CM) with less invasive flexible extra-tympanic membrane electrodes. In 24 adult normal-hearing subjects, CMs were elicited by presenting click stimuli at 100 dBnHL, tone bursts (2 kHz) and broadband (BB) CE-chirps^® LS (Interacoustics, Middelfart, Denmark), both at 80 dBnHL. Different high-pass filters (HPFs) (3.3 Hz and 100 Hz, respectively) were used to investigate response quality of the CM. CMs were successfully obtained in 92–100% with click-, 75–83% with 2 kHz tone burst- and 58–63% with CE-chirp^®-LS stimuli. Click stimuli elicited significantly larger CM amplitudes compared to 2 kHz tone bursts and BB CE-chirp^® LS (Interacoustics, Middelfart, Denmark). No significant differences were found between the two different high-pass filter (HPF) settings. The present study shows that it is possible to obtain clear CMs with the flexible extra-tympanic membrane electrodes using click stimuli. In contrast to 2 kHz tone bursts and CE-chirp^® (Interacoustics, Middelfart, Denmark) LS, clicks show a significantly higher success rate and are the preferred stimuli to confirm the presence or absence of CMs.

Auditory Neuropathy Spectrum Disorders: From Diagnosis to Treatment: Literature Review and Case Reports

Auditory neuropathy spectrum disorder (ANSD) refers to a range of hearing impairments characterized by deteriorated speech perception, despite relatively preserved pure-tone detection thresholds. Affected individuals usually present with abnormal auditory brainstem responses (ABRs), but normal otoacoustic emissions (OAEs). These electrophysiological characteristics have led to the hypothesis that ANSD may be caused by various dysfunctions at the cochlear inner hair cell (IHC) and spiral ganglion neuron (SGN) levels, while the activity of outer hair cells (OHCs) is preserved, resulting in discrepancies between pure-tone and speech comprehension thresholds. The exact prevalence of ANSD remains unknown; clinical findings show a large variability among subjects with hearing impairment ranging from mild to profound hearing loss. A wide range of prenatal and postnatal etiologies have been proposed. The study of genetics and of the implicated sites of lesion correlated with clinical findings have also led to a better understanding of the molecular mechanisms underlying the various forms of ANSD, and may guide clinicians in better screening, assessment and treatment of ANSD patients. Besides OAEs and ABRs, audiological assessment includes stapedial reflex measurements, supraliminal psychoacoustic tests, electrocochleography (ECochG), auditory steady-state responses (ASSRs) and cortical auditory evoked potentials (CAEPs). Hearing aids are indicated in the treatment of ANSD with mild to moderate hearing loss, whereas cochlear implantation is the first choice of treatment in case of profound hearing loss, especially in case of IHC presynaptic disorders, or in case of poor auditory outcomes with conventional hearing aids.

The Prevalence and Causes of Auditory Neuropathy/Dys-synchrony (AN/AD) in Children with Hearing Impairment

There are a wide variety of hearing impairments that part of it is auditory neuropathy/dys-synchrony (AN/AD). So, the object of this study was determination the prevalence and causes of AN/AD in children with hearing impairment. This study was a descriptive cross-sectional survey. The sample size consisted of 105 hearing impairment children. All them were under hearing screening tests (tympanometry), distortion and transient evoked otoacoustic emissions (DPOAEs + TEOAE) and automated auditory brainstem response (AABR). If they were suspected to AN/AD, for complete diagnostic measurements were referred to our hospital. Four cases (8 ears) with AN/AD were diagnosed, which had an average age 37 months (SD = 8.67). So, the prevalence of AN/AD was 3.8 % among hearing impaired children. The findings of this study showed that there are the relationships between AN/AD and fluctuating hearing loss, acoustic reflex, high bilirubin, blood exchange after birth, neonatal intensive (NICU) care unit (P < 0.05). The simultaneous use of both ABR and OAE tests in the birth screening provide much more useful information than when each of these tests is used alone.

Clinical relationship between auditory neuropathy and nervous system diseases

Objective:

To explore the clinical relationship between auditory neuropathy (AN) and nervous system diseases.

Methods:

A total of 134 AN patients who were treated in our hospital from December 2011 to April 2016 were selected. Then 120 cases (240 ears) with complete data of pure tone audiometry and acoustic immittance test were selected as an AN1 group, which was compared with 30 patients (49 ears) with general sensorineural hearing loss (SHL) in regard to the results of pure tone audiometry and acoustic immittance test. On the other hand, 79 cases (158 ears) of the 134 patients with complete data of DP otoacoustic emission test were selected as an AN2 group, which was compared with 30 normal subjects (60 ears) regarding the results of DP otoacoustic emission test.

Results:

Increases in the pure-tone hearing threshold by air conduction of AN1 group significantly exceeded those of SHL group at 0.125 and 0.25 kHz (low frequency) (P<0.05). The former group had significantly lower values at 1.0, 2.0 kHz (moderate frequency) and 4.0, 8.0 kHz (high frequency) (P<0.05). Of 134 patients, 14 (19 ears) had evoked V wave upon auditory brainstem response, whereas no waves after I wave were evoked in other tested ears. Distortion product (DP) otoacoustic emissions could all be evoked. AN2 group had significantly higher amplitudes of DP-gram than those of normal control group at 0.5 and 0.7 kHz (low frequency) (P<0.05). Except for three cases of unsteady walking and 10 of dizziness, others did not suffer from typical symptoms of vertigo attack. As to caloric test-induced electronystagmograms, there were 30 bilaterally normal cases (75.0%), one case of left-side semicircular canal paresis (25%) and nine cases of bilateral semicircular canal paresis (22.5%). Four patients with other nervous system diseases were complicated with AN. Other nervous system disorders included three cases of optic nerve atrophy and 7 of lower limb nerve damage.

Conclusion:

According to characteristic hearing dysfunction, AN may occur in the afferent pathway of acoustic nerve, probably accompanied by the pathological changes of efferent nerve in the olivocochlear system inside the brainstem.