Auditory Neural Responses and Communicative Functioning in Children With Microcephaly Related to Congenital Zika Syndrome.

OBJECTIVES: Children with microcephaly exhibit neurodevelopmental delays and compromised communicative functioning, yielding challenges for clinical assessment and informed intervention. This study characterized auditory neural function and communication abilities in children with microcephaly due to congenital Zika syndrome (CZS). DESIGN: Click-evoked auditory brainstem responses (ABR) at fast and slow stimulation rates and natural speech-evoked cortical auditory evoked potentials (CAEP) were recorded in 25 Brazilian children with microcephaly related to CZS (M age: 5.93 ± 0.62 years) and a comparison group of 25 healthy children (M age: 5.59 ± 0.80 years) matched on age, sex, ethnicity, and socioeconomic status. Communication abilities in daily life were evaluated using caregiver reports on Vineland Adaptive Behavior Scales-3. RESULTS: Caregivers of children with microcephaly reported significantly lower than typical adaptive functioning in the communication and socialization domains. ABR wave I latency did not differ significantly between the groups, suggesting comparable peripheral auditory function. ABR wave V absolute latency and waves I-V interwave latency were significantly shorter in the microcephaly group for both ears and rates. CAEP analyses identified reduced N2 amplitudes in children with microcephaly as well as limited evidence of speech sound differentiation, evidenced mainly by the N2 response latency. Conversely, in the comparison group, speech sound differences were observed for both the P1 and N2 latencies. Exploratory analyses in the microcephaly group indicated that more adaptive communication was associated with greater speech sound differences in the P1 and N2 amplitudes. The trimester of virus exposure did not have an effect on the ABRs or CAEPs. CONCLUSIONS: Microcephaly related to CZS is associated with alterations in subcortical and cortical auditory neural function. Reduced ABR latencies differ from previous reports, possibly due to the older age of this cohort and careful assessment of peripheral auditory function. Cortical speech sound detection and differentiation are present but reduced in children with microcephaly. Associations between communication performance in daily life and CAEPs highlight the value of auditory evoked potentials in assessing clinical populations with significant neurodevelopmental disabilities.

Comprehensive behavioral and physiologic assessment of peripheral and central auditory function in individuals with mild traumatic brain injury.

Auditory complaints are frequently reported by individuals with mild traumatic brain injury (mTBI) yet remain difficult to detect in the absence of clinically significant hearing loss. This highlights a growing need to identify sensitive indices of auditory-related mTBI pathophysiology beyond pure-tone thresholds for improved hearing healthcare diagnosis and treatment. Given the heterogeneity of mTBI etiology and the diverse peripheral and central processes required for normal auditory function, the present study sought to determine the audiologic assessments sensitive to mTBI pathophysiology at the group level using a well-rounded test battery of both peripheral and central auditory system function. This test battery included pure-tone detection thresholds, word understanding in quiet, sentence understanding in noise, distortion product otoacoustic emissions (DPOAEs), middle-ear muscle reflexes (MEMRs), and auditory evoked potentials (AEPs), including auditory brainstem responses (ABRs), middle latency responses (MLRs), and late latency responses (LLRs). Each participant also received magnetic resonance imaging (MRI). Compared to the control group, we found that individuals with mTBI had reduced DPOAE amplitudes that revealed a compound effect of age, elevated MEMR thresholds for an ipsilateral broadband noise elicitor, longer ABR Wave I latencies for click and 4 kHz tone burst elicitors, longer ABR Wave III latencies for 4 kHz tone bursts, larger MLR Na and Nb amplitudes, smaller MLR Pb amplitudes, longer MLR Pa latencies, and smaller LLR N1 amplitudes for older individuals with mTBI. Further, mTBI individuals with combined hearing difficulty and noise sensitivity had a greater number of deficits on thalamic and cortical AEP measures compared to those with only one/no self-reported auditory symptoms. This finding was corroborated with MRI, which revealed significant structural differences in the auditory cortical areas of mTBI participants who reported combined hearing difficulty and noise sensitivity, including an enlargement of left transverse temporal gyrus (TTG) and bilateral planum polare (PP). These findings highlight the need for continued investigations toward identifying individualized audiologic assessments and treatments that are sensitive to mTBI pathophysiology.

The Effects of Middle-ear Stiffness on the Auditory Brainstem Neural Encoding of Phase.

The middle-ear system relies on a balance of mass and stiffness characteristics for transmitting sound from the external environment to the cochlea and auditory neural pathway. Phase is one aspect of sound that, when transmitted and encoded by both ears, contributes to binaural cue sensitivity and spatial hearing. The study aims were (i) to investigate the effects of middle-ear stiffness on the auditory brainstem neural encoding of phase in human adults with normal pure-tone thresholds and (ii) to investigate the relationships between middle-ear stiffness-induced changes in wideband acoustic immittance and neural encoding of phase. The auditory brainstem neural encoding of phase was measured using the auditory steady-state response (ASSR) with and without middle-ear stiffness elicited via contralateral activation of the middle-ear muscle reflex (MEMR). Middle-ear stiffness was quantified using a wideband acoustic immittance assay of acoustic absorbance. Statistical analyses demonstrated decreased ASSR phase lag and decreased acoustic absorbance with contralateral activation of the MEMR, consistent with increased middle-ear stiffness changing the auditory brainstem neural encoding of phase. There were no statistically significant correlations between stiffness-induced changes in wideband acoustic absorbance and ASSR phase. The findings of this study may have important implications for understanding binaural cue sensitivity and horizontal plane sound localization in audiologic and otologic clinical populations that demonstrate changes in middle-ear stiffness, including cochlear implant recipients who use combined electric and binaural acoustic hearing and otosclerosis patients.

Changes in Acoustic Absorbance Pre- and Post-Cochlear Implantation.

PURPOSE: Until recently, there has been little investigation on the effects of cochlear implantation on the transmission of acoustic stimuli through the middle-ear system. Recent studies have shown that cochlear implantation decreases low-frequency acoustic absorbance, consistent with a stiffer middle-ear system postsurgery. The objectives of this study are (a) to investigate the time course of changes in acoustic absorbance post-cochlear implantation in the implanted ear and (b) to compare changes in acoustic absorbance between implanted and nonimplanted ears over time. METHOD: Seventeen adult cochlear implant (CI) recipients within 6 months of device activation participated in this study. Wideband acoustic absorbance was measured in both ears at one to six different time points from pre-implantation up to 6-month postactivation. Analyses examined (a) changes in acoustic absorbance as compared to pre-implantation and (b) differences in acoustic absorbance between implanted and nonimplanted ears over time. RESULTS: Acoustic absorbance in the implanted ear decreased postsurgery for frequencies lower than 1.5 kHz and persisted through at least 6-month postactivation. We also observed that the spectral range of decreased acoustic absorbance in the implanted ear decreased with longer time postsurgery. Differences in acoustic absorbance between implanted and nonimplanted ears occurred over a broad spectral range at the activation time point and persisted through at least 3-month postactivation, though for a narrower spectral range at the later time point. CONCLUSIONS: Cochlear implantation increased middle-ear stiffness as indicated by decreased acoustic absorbance of low-frequency acoustic power. The findings of this study are consistent with those of previous studies and may have important implications toward understanding spatial hearing and programming of acoustic components for CI-combined electric and binaural acoustic stimulation patients.

Cholesteatoma Is Associated With Pediatric Progressive Sensorineural Hearing Loss.

OBJECTIVES: This study identified an association between cholesteatoma and progressive sensorineural hearing loss using a large pediatric longitudinal audiologic dataset. Cholesteatoma is a potential sequela of chronic otitis media with effusion, a commonly observed auditory pathology that can contribute to hearing loss in children. The purpose of this report is to (i) describe the process of identifying the association between cholesteatoma and progressive sensorineural hearing loss in a large pediatric dataset and (ii) describe the audiologic data acquired over time in patients identified with cholesteatoma-associated progressive sensorineural hearing loss. DESIGN: Records of patients included in the Audiologic and Genetics Database (n = 175,215 patients) were examined using specified criteria defining progressive hearing loss. A linear regression model examined the log frequency of all diagnostic codes in the electronic health record assigned to patients for a progressive hearing loss cohort compared with a stable hearing loss group. Based on findings from the linear regression analysis, longitudinal audiometric air (AC) and bone conduction (BC) thresholds were extracted for groups of subjects with cholesteatoma-associated progressive (n = 58 subjects) and stable (n = 55 subjects) hearing loss to further analyze changes in hearing over time. RESULTS: The linear regression analyses identified that diagnostic codes for cholesteatoma were associated with progressive sensorineural hearing loss in children. The longitudinal audiometric data demonstrated within-subject changes in masked BC sensitivity consistent with progressive sensorineural hearing loss in children diagnosed with cholesteatoma. Additional analyses showed that mastoidectomy surgeries did not appear to contribute to the observed progressive hearing loss and that a high number of cholesteatoma patients with progressive hearing loss had normal-hearing thresholds at their first test. CONCLUSIONS: The statistical analyses demonstrated an association between cholesteatoma and pediatric progressive sensorineural hearing loss. These findings inform clinical management by suggesting that children with cholesteatoma diagnoses may be at increased risk for progressive sensorineural hearing loss and should receive continued monitoring even after a normal masked BC baseline has been established.

A prospective study of neurodevelopmental trends between 3 and 24 months in normocephalic infants with prenatal Zika virus exposure: Evidence of emerging communication delays in the NATZIG cohort.

Developmental trends between 3 and 24 months were assessed in 194 normocephalic infants with prenatal Zika virus exposure. Bayley Scales of Infant and Toddler Development Screening Test-3rd Edition cognitive scores remained in the typical range. Communication skills developed at a slower rate suggesting that neurodevelopmental delays may emerge at older ages.

Auditory Neuropathy/Auditory Synaptopathy.

Patients with auditory neuropathy (AN)/auditory synaptopathy (AS) present unique evaluation and management challenges. Communication ability using auditory stimuli varies among patients, with particular difficulty understanding speech in noise. Auditory physiologic responses are key to accurate identification and monitoring of patients with AN/AS. Management approaches should consider individual variation and the possibility of change over time. Many patients with accurately characterized AN/AS demonstrate success with cochlear implants. Areas of discovery, including understanding of synaptic and neural mechanisms, genotype/phenotype relationships, and use of cochlear and cortical evoked potentials, will promote accurate clinical evaluation and management of infants, children, and adults with AN/AS.

Relationships between click auditory brainstem response and speech frequency following response with development in infants born preterm.

The speech evoked frequency following response (sFFR) is used to study relationships between neural processing and functional aspects of speech and language that are not captured by click or toneburst evoked auditory brainstem responses (ABR). The sFFR is delayed, deviant, or weak in school age children having a variety of disorders, including autism, dyslexia, reading and language disorders, in relation to their typically developing peers. Much less is known about the developmental characteristics of sFFR, especially in preterm infants, who are at risk of having language delays. In term neonates, phase locking and spectral representation of the fundamental frequency is developed in the early days of life. Spectral representation of higher harmonics and latencies associated with transient portions of the stimulus are still developing in term infants through at least 10 months of age. The goal of this research was to determine whether sFFR could be measured in preterm infants and to characterize its developmental trajectory in the time and frequency domain. Click ABR and sFFR were measured in 28 preterm infants at ages 33 to 64 weeks gestational age. The sFFR could be measured in the majority of infants at 33 weeks gestational age, and the detectability of all sFFR waves was 100% by 64 weeks gestational age. The latency of all waves associated with the transient portion of the response (waves V, A, and O), and most waves (waves D and E) associated with the quasi-steady state decreased with increasing age. The interpeak wave A-O latency did not change with age, indicating that these waves share a neural generator, or the neural generators are developing at the same rate. The spectral amplitude of F0 and the lower frequencies of the first formant increased with age, but that for higher frequencies of the first formant and higher harmonics did not. The results suggest that the sFFR can be reliably recorded in preterm infants, including those cared for in the neonatal intensive care unit. These findings support that in preterm infants, F0 amplitude continues to develop within the first 6 months of life and develops before efficient representation of higher frequency harmonics. Further research is needed to determine if the sFFR in preterm infants is predictive of long-term language or learning disorders.

Association between ABO blood group status and cochlear/neural function: auditory brainstem response findings.

BACKGROUND: ABO blood group status may be a risk factor for some diseases, including hearing loss. Individuals with blood group O show a higher prevalence of hearing loss after industrial noise exposure. Group O individuals with normal hearing show reduced amplitudes in otoacoustic emission recordings. Whether blood group status affects auditory brainstem responses (ABR), which reflect cochlear hair cell and auditory nerve bioelectric activity, is unclear. AIMS/OBJECTIVES: To compare cochlear and peripheral neural function across ABO blood groups by recording cochlear microphonic (CM) and wave I ABR responses. MATERIAL AND METHODS: Sixty normal-hearing young adults, with 15 participants from each blood group, completed 70 dB nHL click stimulus ABR measures. CM amplitude, wave I amplitude and wave I latency data were obtained for both ears. One-way ANOVA tests compared results across the ABO groups. RESULTS: A statistically significant difference for wave I peak-to-peak amplitudes across the four groups was found. Post-hoc comparisons revealed group O had significantly reduced wave I amplitudes compared to group A participants. A consistent trend of reduced CM amplitudes and prolonged wave I latencies was shown in group O participants. CONCLUSIONS AND SIGNIFICANCE: Emerging evidence exists that ABO blood group status may influence auditory function.

Perspective on the Development of a Large-Scale Clinical Data Repository for Pediatric Hearing Research.

The use of "big data" for pediatric hearing research requires new approaches to both data collection and research methods. The widespread deployment of electronic health record systems creates new opportunities and corresponding challenges in the secondary use of large volumes of audiological and medical data. Opportunities include cost-effective hypothesis generation, rapid cohort expansion for rare conditions, and observational studies based on sample sizes in the thousands to tens of thousands. Challenges include finding and forming appropriately skilled teams, access to data, data quality assessment, and engagement with a research community new to big data. The authors share their experience and perspective on the work required to build and validate a pediatric hearing research database that integrates clinical data for over 185,000 patients from the electronic health record systems of three major academic medical centers.

Early Indices of Reduced Cochlear Function in Young Adults with Type-1 Diabetes Revealed by DPOAE Fine Structure.

BACKGROUND: The relationship between type-1 diabetes mellitus (DM) and cochlear dysfunction remains inconclusive. PURPOSE: The purpose of this study was to examine otoacoustic emissions (OAEs) in normal-hearing young adults with type-1 DM as compared with matched controls and identify potential covariates influencing OAE findings. RESEARCH DESIGN: Cross-sectional study. STUDY SAMPLE: N = 40 young adults aged 18-28 years including individuals with type-1 DM (n = 20) and age-gender matched controls (n = 20) with normal hearing sensitivity. DATA COLLECTION AND ANALYSIS: Measures of pure-tone threshold sensitivity and OAEs, including distortion product otoacoustic emissions (DPOAEs), transient evoked OAEs, and DPOAE fine structure, were compared between groups. Covariates such as noise exposure and DM-related factors (e.g., duration of disease, glycated hemoglobin levels) were considered. Statistical analysis included analysis of variance and linear regression. RESULTS: Measures of hearing sensitivity and auditory function in both groups were comparable for all assays, except DPOAE fine structure. A reduced number of fine structure peaks and component amplitudes were found in the type-1 diabetes DM group with the primary difference in the reflection component. CONCLUSIONS: The results indicate that reduced cochlear function in young adults with type-1 DM can be revealed using DPOAE fine structure, suggesting potential clinical applications of DPOAE fine structure in early identification of cochlear pathology. Potential factors underlying these findings are discussed.

Erythrocyte folate, serum vitamin B12, and hearing loss in the 2003-2004 National Health And Nutrition Examination Survey (NHANES).

BACKGROUND/OBJECTIVES: Studies based on food frequency questionnaires suggest that folate and vitamin B12 intake could protect against hearing loss. We investigated whether erythrocyte folate and serum vitamin B12 levels are independently associated with hearing loss in humans. SUBJECTS/METHODS: Participants in the 2003-2004 US National Health and Nutrition Examination Survey who had data on hearing, folate, and vitamin B12 levels were included. Pure-tone average (PTA) at 0.5, 1.0, 2.0, and 4.0 kHz was computed for each ear. We used weighted logistic regression to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for the relation between quartiles of folate and vitamin B12, and hearing loss (present if PTA > 25 dB in either ear and absent if PTA ≤ 25 dB in both ears). RESULTS: Participants (n = 1149) were 20-69 (mean 42) years old and 16.4% had hearing loss in at least one ear. Our data suggest a U-shaped relationship between folate and hearing loss. Compared to the 1st quartile, the ORs (95% CIs) for hearing loss were 0.87 (0.49-1.53), 0.70 (0.49-1.00), and 1.08 (0.61-1.94) for the 2nd, 3rd, and 4th quartile of erythrocyte folate in analyses adjusted for age, sex, vitamin B12, smoking, alcohol use, body mass index, race/ethnicity, exposure to noise, income, and education. Although we observed inverse associations between vitamin B12 and hearing loss, the associations were not statistically significant (P > 0.05). CONCLUSIONS: Our data show a U-shaped relationship between erythrocyte folate levels and hearing loss, suggesting a need to evaluate whether optimizing blood folate levels could prevent hearing loss.

Noise History and Auditory Function in Young Adults With and Without Type 1 Diabetes Mellitus.

OBJECTIVES: The purpose of this study was to examine the relationship between noise exposure history, type 1 diabetes mellitus (DM), and suprathreshold measures of auditory function. DESIGN: A cross-sectional study was conducted; 20 normal-hearing participants without type 1 DM were matched on age and sex to 20 normal-hearing participants with type 1 DM (n=40). Participants, all having normal audiometric thresholds, completed noise history questionnaires and a battery of auditory physiological tests including transient evoked otoacoustic emissions, distortion product otoacoustic emissions, and auditory brainstem responses (ABR) at 80 dB nHL and at 2 different stimulus rates in both ears. Amplitude and latency for waves I and V are presented. Statistical analysis included analysis of variance and multivariate linear regression. RESULTS: No statistically significant difference for noise exposure history, otoacoustic emissions (OAE), or ABR findings were found between type 1 DM and matched controls. Males and females showed statistically significant differences for OAE amplitudes and ABR amplitude and latencies. However, no statistically significant relationship was found between noise outcomes and OAE or ABR findings. CONCLUSIONS: No statistically significant relationship between noise history and our suprathreshold ABR or OAE findings was indicated for individuals with type 1 DM or matched controls. The lack of evidence of noise related neuropathology might be due to inadequate noise exposure or lack of comorbidities in our DM group. Implications of these findings are discussed.

Heritability of non-speech auditory processing skills.

Recent insight into the genetic bases for autism spectrum disorder, dyslexia, stuttering, and language disorders suggest that neurogenetic approaches may also reveal at least one etiology of auditory processing disorder (APD). A person with an APD typically has difficulty understanding speech in background noise despite having normal pure-tone hearing sensitivity. The estimated prevalence of APD may be as high as 10% in the pediatric population, yet the causes are unknown and have not been explored by molecular or genetic approaches. The aim of our study was to determine the heritability of frequency and temporal resolution for auditory signals and speech recognition in noise in 96 identical or fraternal twin pairs, aged 6-11 years. Measures of auditory processing (AP) of non-speech sounds included backward masking (temporal resolution), notched noise masking (spectral resolution), pure-tone frequency discrimination (temporal fine structure sensitivity), and nonsense syllable recognition in noise. We provide evidence of significant heritability, ranging from 0.32 to 0.74, for individual measures of these non-speech-based AP skills that are crucial for understanding spoken language. Identification of specific heritable AP traits such as these serve as a basis to pursue the genetic underpinnings of APD by identifying genetic variants associated with common AP disorders in children and adults.

Auditory Neuropathy/Dys-Synchrony Disorder: Diagnosis and Management.

Auditory neuropathy/dys-synchrony disorder affects neural responses, either directly or indirectly. Patients may demonstrate good ability to detect sound, but have significant difficulty listening in noise. Clinical auditory physiologic measures are used to characterize cochlear, eighth nerve, and brainstem function, and are needed to accurately identify this disorder. Cochlear implants provide benefit to many patients, and some patients derive benefit from amplification. This disorder can be identified and managed in infants, may have later onset, may be a part of a syndrome, and may include fluctuation in hearing ability.

Estimates of cochlear compression using distortion product otoacoustic emissions and growth of forward masking.

OBJECTIVE: The authors investigated the relationship between behavioral and physiologic estimates of cochlear compression. DESIGN: Cochlear compression was estimated in distortion product otoacoustic emission (DPOAE) fine structure minima and maxima near 4 kHz. The composite DPOAE response and separated generator and reflection components yielded three estimates in four young adults with normal hearing. DPOAE estimates were compared to behavioral compression estimates derived using a growth of forward masking (GOFM) paradigm. The DPOAE primary tone f2 and GOFM signal were identical and selected individually based on placement in a DPOAE fine structure minimum. RESULTS: Across participants, DPOAE compression estimates derived from the generator component were most similar to estimates derived from the GOFM paradigm and did not vary with DPOAE fine structure. CONCLUSIONS: These results suggest that the generator component may provide a quick, reliable estimate of cochlear compression in humans. This may prove useful in populations that cannot give behavioral responses.

A comparison of auditory brain stem responses elicited by click and chirp stimuli in adults with normal hearing and sensory hearing loss.

OBJECTIVES: The aim of this study was to compare the human auditory brain stem response (ABR) elicited by clicks and chirps with overall behavioral hearing thresholds in participants with normal hearing and with sensory hearing loss. The authors hypothesized that ABRs to chirps would be more robust and that thresholds would be more similar to overall behavioral hearing thresholds compared with ABRs to clicks. DESIGN: Twenty-five adults with normal hearing and 25 adults with sensory hearing loss were recruited. Subjects were without middle ear or neurological pathologies at the time of testing. Subjects with sensory hearing loss were separated into mild to moderate hearing loss and mild to severe hearing loss groups. Behavioral hearing thresholds for pure tones were obtained at nine octave and interoctave frequencies ranging from 250 to 8000 Hz; an average of these nine frequencies was calculated for each participant. Evoked potential thresholds were measured by ABRs to click and chirp stimuli. Analyses included wave V absolute latencies and wave V peak-to-peak amplitudes. Thresholds for ABRs to clicks and chirps were compared with each other and with overall behavioral hearing thresholds. RESULTS: ABR thresholds to chirp and click stimuli did not differ significantly for either the normal-hearing or the hearing loss groups. Wave V peak-to-peak amplitude was higher for chirps than clicks, particularly at lower intensities, for all groups. ABR thresholds to chirps were closer to overall behavioral thresholds than clicks in all groups. Moreover, ABR thresholds to chirps did not differ significantly from behavioral thresholds in the two hearing loss groups. CONCLUSIONS: ABRs obtained with chirp stimuli provide an efficient method for estimating hearing thresholds in individuals with normal hearing and sensory hearing loss where broadband signals are selected for testing. ABRs to chirps display higher peak-to-peak amplitudes than those obtained with clicks and may provide responses closer to behavioral thresholds. This information could result in improved accuracy in identifying hearing loss and estimating hearing sensitivity for broadband signals in infants, children, and difficult-to-test older populations.

Effects of age on the tuning of the cVEMP and oVEMP.

OBJECTIVES: The purpose of the present investigation was to define for young, middle-aged, and older adults the optimal frequency (cies) to record both the cervical vestibular-evoked myogenic potential (cVEMP) and the ocular vestibular-evoked myogenic potential (oVEMP). Further, this study aimed to describe age-related changes in the tuning of these two vestibular-evoked myogenic potentials. DESIGN: This was a prospective study. Participants were 39 healthy adults (mean age 46.3 ± 15.7 years; range = 22 to 78 years; 15 men) equally divided into 3 age groups of 13 participants each: young adult (18 to 39 years), middle age (40 to 59 years), and old adult (≥60 years). cVEMPs and oVEMPs were recorded using air-conduction tone bursts at stimulus frequencies of 125, 250, 500, 750, 1000, 1500, and 2000 Hz presented at 127 dB pSPL. RESULTS: There was a significant main effect of age group and frequency on the amplitude of both the cVEMP and the oVEMP. Amplitudes were largest for the Young adult group for the cVEMP and for the young adult and Middle age group for the oVEMP. The largest average peak-to-peak amplitude occurred in response to a 750 Hz tone burst for both responses. No significant differences in mean amplitude of the cVEMP or oVEMP were observed for 500, 750, or 1000 Hz stimuli. There was a significant interaction of age group and frequency for the cVEMP, suggesting a loss of tuning for the old adult group. Compared with the young adult group, the tuning of the cVEMP and oVEMP for the older adjults appeared to shift to a higher frequency. CONCLUSION: There is no sharp tuning in the saccule and utricle. Instead, there is a range of best frequencies that may be used to evoke the cVEMP and oVEMP responses. The results of the present investigation also demonstrate that the optimal stimulus frequency to elicit a VEMP may change with age. Accordingly, 500 Hz may not be the ideal frequency to elicit VEMPs for all age groups. For this reason, in cases where the VEMP response is absent at 500 Hz it is recommended that attempts be made to record the VEMP for tone-burst frequencies of 750 or 1000 Hz.

Hearing loss associated with xylene exposure in a laboratory worker.

BACKGROUND: Xylene is an organic solvent, widely used in histology laboratories and other occupational settings. Research in animals has demonstrated that xylene induces outer hair cell damage. Evidence regarding the effects of xylene in humans is only available from studies investigating workers exposed to mixtures of solvents containing xylene. These data indicate that mixtures of solvents containing xylene may induce hearing loss and central auditory dysfunction. PURPOSE: To comprehensively evaluate the peripheral and central auditory system of a histology laboratory worker exposed to xylene, who had presented with bilateral mild sensorineural hearing loss at an initial assessment. RESEARCH DESIGN: A case report of a male histology laboratory worker who has been exposed to xylene for over 20 yr. RESULTS: A diagnosis of bilateral mild sensorineural hearing loss of cochlear origin was made on the basis of otological, neuroimaging, and audiological examinations. Results indicating the absence of transient-evoked otoacoustic emissions, and auditory brainstem responses as expected for a mild cochlear hearing loss, were obtained. CONCLUSIONS: The observed bilateral mild sensorineural hearing loss was considered to have been induced by xylene exposure, due to the absence of any other etiological factors related to the onset of hearing loss. The results found in this patient are in agreement with animal data indicating xylene-induced ototoxicity. Xylene-exposed individuals should be audiologically monitored on a regular basis.

Normal characteristics of the ocular vestibular evoked myogenic potential.

BACKGROUND: Stimulus-evoked electromyographic changes can be recorded from the extraocular muscles. These short-latency negative-polarity evoked myogenic potentials are called ocular vestibular evoked myogenic potentials (oVEMPs). To date there has not yet been a large-scale study examining the effects of age on the amplitude, latency, threshold, and interaural differences of the oVEMP to air-conducted stimuli. Further, before the oVEMP can become a useful clinical tool, the test-retest reliability of the response must be established. The oVEMP response, once more completely understood, may provide diagnostic information that is complementary to the cervical vestibular evoked myogenic potential (cVEMP; i.e., sternocleidomastoid muscle). PURPOSE: To describe the normal characteristics of oVEMP in a cohort of age-stratified subjects, to assess the test-retest reliability of the oVEMP, and to determine if reference contamination occurs using a common recommended infraorbital reference electrode derivation. RESEARCH DESIGN: A prospective, descriptive study design was used for an investigation with a threefold purpose in which oVEMP recordings were made from the extraocular muscles (e.g., inferior oblique muscle). STUDY SAMPLE: Fifty otologically and neurologically normal adults and children served as subjects. Subjects ranged in age from 8 to 88 yr. DATA COLLECTION AND ANALYSIS: In Investigation 1, oVEMPs were recorded from the ipsilateral and contralateral inferior oblique muscles for all subjects. The stimulus was a 95 dB nHL 500 Hz tone burst. Next, oVEMP thresholds were obtained. Amplitude, latency, and thresholds were tabulated, and descriptive statistics were used to calculate normative values. Age-related differences in oVEMP component latencies, amplitudes, interaural amplitude asymmetries (IAAs), and thresholds were determined using an analysis of variance. In Investigation 2, oVEMPs were recorded twice in 10 subjects, once (test) and once approximately 10 weeks later (retest). Test-retest reliability for the oVEMP peak-to-peak amplitude, n1 latency, p1 latency, n1 threshold, and IAA were assessed with intraclass correlation coefficients (ICCs) calculated using a two-way random-effects, absolute-agreement model. In Investigation 3, a four-channel oVEMP recording was conducted in 10 subjects. Both observational methods and paired-sample t-tests were used to evaluate the effect that reference electrode location had on the oVEMP. RESULTS: oVEMP responses were present bilaterally in 90% of our subjects. The upper limit of oVEMP amplitude asymmetry, defined as the mean plus two standard deviations, was 34% (mean = 14%, SD 10), and the mean n1 latency was 12.5 (SD 1.0) msec. The amplitude of the response significantly decreased and the threshold significantly increased with increasing age, with the greatest age effects occurring in subjects 50 yr and older. Test-retest reliability was acceptable (ICCs for the measurement variables ranged from .53 to .87). Using conventional recommended recording techniques, evidence of reference contamination occurred for all subjects, resulting in a mean amplitude reduction of 30% (range = 18%-43%). CONCLUSIONS: Age results in systematic changes in oVEMP measurement parameters. The test-retest reliability is acceptable, and reference contamination averaging 30% is guaranteed using a second infraorbital electrode as the inverting input (i.e., reference electrode) for bipolar recordings. The oVEMP can be used as a complementary diagnostic tool to the cVEMP in evaluating subjects with suspected peripheral vestibular disorders.