Auditory neuropathy: case study with hyperbilirubinemia.

Auditory neuropathy (AN) has been described in the literature as presenting with a combination of audiometric findings that include elevated behavioral audiometric thresholds, auditory brainstem response findings that are not consistent with audiometric findings, poor speech recognition, and present otoacoustic emissions (OAEs) and/or cochlear microphonics. Since the availability of clinical OAE testing, AN has come to be identified with increasing frequency; however, incidence and prevalence figures are unavailable. There is a great deal of discussion about the accurate diagnosis of AN, its characteristics, and its treatment. Some of this discussion is occurring on the Internet and over the telephones. The need to continue to provide information in accessible peer-reviewed journals is paramount. Following a review of the literature, a case study is presented of a boy who was diagnosed with AN as a newborn. He experienced hyperbilirubinemia and other neonatal health complications. His educational intervention was managed elsewhere until recently. Information is presented about the progression of the case over a 5-year period that includes audiologic data and communication development results.

Management of the child with sensorineural hearing loss. Medical, surgical, hearing aids, cochlear implants.

Optimal comprehensive management of a child with SNHL involves constructive dialogue and coordination with the child's family and teachers. Not all children with SNHL benefit from conventional amplification, even after parents have invested significant amounts of money in hearing aids. Parents may encounter frustration and disappointment if their children fail to achieve communicative and academic goals they have established in their own mind. If the child is a potential candidate for cochlear implantation, this decision not only involves the risks (albeit modest) of surgery but also often a substantial financial commitment to help defray the cost of this sophisticated electronic device. The parents may encounter conflicting advice from friends and members of the adult deaf community about the benefit of cochlear implantation. Throughout the course of all of these difficult considerations, the health professionals caring for a child with hearing loss should be a source for information, guidance, and support to the family.

Longitudinal study of FM system use in nonacademic settings: effects on language development.

OBJECTIVE: The overall objective of the present study was to assess the efficacy of FM system use in the home setting for a group of preschool children with mild-to-severe sensorineural hearing loss. Changes in language acquisition were monitored and compared with similar measures from a group of children who used hearing aids. Secondarily, the perceived benefits and practical problems associated with FM system use across a variety of nonacademic situations were documented. DESIGN: Ten children with mild-to-severe sensorineural hearing loss participated in a 2-yr longitudinal study investigating the efficacy of FM system use in the home setting. The subjects were divided into two groups: one group was instructed to use FM systems at home as often as possible while the other used only their personal hearing aids. Changes in language acquisition were monitored in both groups. Subjective benefit and the practical problems associated with use of FM systems outside of traditional academic environments were monitored via daily use logs, a weekly observation inventory, and a situational listening profile. RESULTS: The majority of children in both groups improved in all measures of language development over the study interval. Although there were relatively large individual differences in performance for some measures, no statistically significant differences between the FM and hearing aid users were found. However, some children in the FM group made unusually large gains in some aspects of language development over the study interval. In addition, both parents and children reported benefits of FM system use in specific listening situations. Throughout the 2-yr study, a number of practical problems associated with FM system use outside the classroom were identified. CONCLUSIONS: Formal language measures did not yield significant differences between the FM and HA groups, but some subjects had rates of language acquisition which suggested that FM system use may be beneficial in selected cases. In addition, subjective reports of FM system benefit suggest that appropriate use of the device may facilitate effective communication in a variety of listening situations. Although recent advances in FM system design may minimize some of the factors that reportedly restricted consistent FM use in this study, the complexities associated with the modes of operation and problems with FM interference remain issues that require consistent audiologic monitoring of FM system use in nonacademic environments.

Preliminary descriptions of transient-evoked and distortion-product otoacoustic emissions from graduates of an intensive care nursery.

Transient-evoked (TEOAE) and distortion-product otoacoustic emissions (DPOAE) were measured in 51 graduates of an intensive care nursery and compared to data obtained from 80 normal-hearing children and adults. All infants had click-evoked auditory brainstem responses (ABR) at 30 dB nHL or less while the older subjects had pure-tone thresholds of 20 dB HL or less for octave frequencies from 250 to 8000 Hz. OAE data were collected using commercially available devices. All data were analyzed in terms of emission amplitude, emission-to-noise ratio, and response reproducibility as a function of frequency. DPOAEs were measured at three points per octave between f2 frequencies of approximately 500 and 8000 Hz. TEOAEs were elicited by clicks and were analyzed in both octave and 1/3-octave bands centered at frequencies from 500 to 4000 Hz, as well as in the broadband condition. In addition, stimulus amplitudes for the clicks used to elicit TEOAEs were analyzed within octave and 1/3-octave bands to determine whether any age-related differences in responses can be accounted for on the basis of stimulus differences. Both emission amplitude and noise amplitude were greater in neonates than adults, although there was variability across frequency. Emission-to-noise ratio and response reproducibility were more similar between groups. For TEOAEs, high-frequency emission-to-noise ratios were larger in neonates compared to older subjects, while the reverse was true in the lower frequencies. Less obvious frequency effects were observed for DPOAEs. These findings are discussed in relation to the potential use of OAEs as screening measures for neonatal hearing loss.

Towards understanding the limits of distortion product otoacoustic emission measurements.

Distortion product otoacoustic emission (DPOAE) data were obtained with a custom-designed system from 20 subjects with normal hearing. Cavity measurements, using this system and an Etymotic ER-10B low-noise microphone system, resulted in estimates of recording system distortion of -20 dB SPL for f2 frequencies ranging from 500 to 8000 Hz, and primary levels ranging from 20 to 75 dB SPL (L2 = L1-10 dB). Using this system it was possible to automatically adjust averaging time in order to obtain the same residual noise levels across frequencies. In all subjects with normal hearing, DPOAEs were measurable over a wide range of primary levels for octave f2 frequencies from 1000 to 8000 Hz, but not at 500 Hz. At 500 Hz, only half of the normal-hearing subjects produced DPOAEs that were above the noise floor. When they did, DPOAE amplitude was less than that observed at higher f2 frequencies. While the cause for response absence in some normal ears may have been due to residual noise, the reduced amplitude suggests that the other factors influence the measurement of DPOAEs at low frequencies. This result may be due to reduced cochlear production of DPOAEs at lower frequencies or reduced transmission through the middle ear.

A comparison of transient-evoked and distortion product otoacoustic emissions in normal-hearing and hearing-impaired subjects.

The ability of transient-evoked otoacoustic emissions (TEOAEs) and distortion product otoacoustic emissions (DPOAEs) to distinguish normal hearing from hearing impairment was evaluated in 180 subjects. TEOAEs were analyzed into octave or one-third octave bands for frequencies ranging from 500 to 4000 Hz. Decision theory was used to generate receiver operating characteristic (ROC) curves for each of three measurements (OAE amplitude, OAE/noise, reproducibility) for each OAE measure (octave TEOAEs, 1/3 octave TEOAEs, DPOAEs), for octave frequencies from 500 to 4000 Hz, and for seven audiometric criteria ranging from 10 to 40 dB HL. At 500 Hz, TEOAEs and DPOAEs were unable to separate normal from impaired ears. At 1000 Hz, both TEOAE measures were more accurate in identifying hearing status than DPOAEs. At 2000 Hz, all OAE measures performed equally well. At 4000 Hz, DPOAEs were better able to distinguish normal from impaired ears. Almost without exception, measurements of OAE/noise and reproducibility performed comparably and were superior to measurements of OAE amplitude, although the differences were small. TEOAEs analyzed into octave bands showed better performance than TEOAEs analyzed into 1/3 octaves. Under standard test conditions, OAE test performance appears to be limited by background noise, especially for the low frequencies.

Otoacoustic emissions from normal-hearing and hearing-impaired subjects: distortion product responses.

Distortion product otoacoustic emissions (DPOAE) were measured in normal-hearing and hearing-impaired human subjects. Analyses based on decision theory were used to evaluate DPOAE test performance. Specifically, relative operating characteristic (ROC) curves were constructed and the areas under these curves were used to estimate the extent to which normal and impaired ears could be correctly identified by these measures. DPOAE amplitude and DPOAE/noise measurements were able to distinguish between normal and impaired subjects at 4000, 8000, and, to a lesser extent, at 2000 Hz. The ability of these measures to distinguish between groups decreased, however, as frequency and audiometric criterion used to separate normal and hearing-impaired ears decreased. At 500 Hz, performance was no better than chance, regardless of the audiometric criterion for normal hearing. Cumulative distributions of misses (hearing-impaired ears incorrectly identified as normal hearing) and false alarms (normal-hearing ears identified as hearing impaired) were constructed and used to evaluate test performance for a range of hit rates (i.e., the percentage of correctly identified hearing-impaired ears). Depending on the desired hit rate, criterion values of -5 to -12 dB SPL for DPOAE amplitudes and 8 to 15 dB for DPOAE/noise accurately distinguished normal-hearing ears from those with thresholds greater than 20 dB HL for the two frequencies at which performance was best (4000 and 8000 Hz). It would appear that DPOAE measurements can be used to accurately identify the presence of high-frequency hearing loss, but are not accurate predictors of hearing status at lower frequencies, at least for the conditions of the present measurements.

A comparison of auditory brain stem response thresholds and latencies elicited by air- and bone-conducted stimuli.

Auditory brain stem responses (ABRs) were measured for stimuli presented both by air conduction and by bone conduction. Stimuli included clicks and tone bursts at octave frequencies from 250 to 4000 Hz. ABR thresholds were comparable for air- and bone-conducted stimuli. Wave V latencies were longer for bone-conducted stimuli compared to similar responses for air conduction. This effect was evident for both clicks and tone bursts. The fact that these latency differences were largely independent of stimulus spectrum suggests that they are not due to differences between the frequency responses of air and bone conduction transducers. This finding is expected when one considers the interaction between output, threshold, and frequency for both transducer types. These data also suggest that there are inherent differences in transmission by air and bone conduction that affect response latency but are unrelated to the amplitude spectrum in the signal.

Equivalent ear canal volumes in children pre- and post-tympanostomy tube insertion.

Pre- and postoperative equivalent ear canal volume measures were obtained from a group of 334 children ranging in age from 6 weeks to 6.7 years. The purpose of the study was to develop volumetric guidelines for the determination of tympanostomy tube patency. For children 4 years and older, almost no ambiguity existed in making this determination accurately. For younger children, the pre- and postoperative distributions overlap. A criterion value of greater than or equal to 1.0 cm3 as an indicator of a tympanic membrane perforation appears to yield the lowest possible error rate. When both pre- and postoperative measures are available, a difference of greater than or equal to 0.4 cm3 can be used in conjunction with the absolute value to identify a patent tympanostomy tube.

Auditory brainstem responses elicited by 1000-Hz tone bursts in patients with sensorineural hearing loss.

Auditory brainstem responses were measured in response to 1000-Hz tone bursts from 115 patients with sensorineural hearing loss, presumably of cochlear origin. Mean wave V latencies and variability were comparable to those observed in normal hearing subjects for similar stimuli. The range of interaural differences in wave V latencies for 1000-Hz tone bursts were slightly greater than those observed for clicks, which may not be surprising, given the greater variability in wave V latencies for tonal stimulation, even in normal-hearing subjects. These differences, however, were not affected either by the magnitude or symmetry of hearing loss for frequencies at and above 1000 Hz. These data suggest that tone burst ABRs might be useful in otoneurologic evaluations, especially for patients with asymmetric hearing loss.

Effects of stimulus phase on the latency of the auditory brainstem response.

Auditory brainstem responses were measured in five normal-hearing subjects, using single-cycle sinusoids at octave frequencies ranging from 250 to 2000 Hz. These sinusoids, gated with Blackman functions, were presented either at 0 or 180 degree phase and were varied in level from 90 dB SPL to threshold in 10-dB steps. Stimulus phase affected wave V latencies for low-frequency stimuli, with the effect decreasing as frequency increased. These data are thought to represent an evoked potential manifestation of known phase-locking abilities within the auditory system.

The identification and diagnosis of hearing loss in infants.

The goal of early identification of hearing loss is being reached gradually. The technological options for assessing hearing loss in neonates and infants are expanding to the point that we are now capable of identifying hearing loss, regardless of developmental level. The latest revision of the JCIH (1991) risk criteria, in conjunction with an increasing number of statewide programs, provides optimism for meeting the goal of finding and remediating hearing loss early in the first year of life.

Auditory brainstem responses from children three months to three years of age: normal patterns of response. II.

Auditory brainstem responses (ABR) were measured in 535 children from 3 months to 3 years of age. The latencies reported in this paper should be unaffected by peripheral hearing loss because each child had bilateral wave V responses at 20 dB HLn. Wave V latencies decreased as age increased, at least to 18 months of age, while little or no change was noted in wave I latencies over the same age range. Thus, interpeak latency differences followed the same developmental time course as wave V. The shapes of wave V latency-level functions were comparable across age groups. These results suggest that changes in wave V latency with age are due to central (neural) factors and that age-appropriate norms should be used in evaluations of ABR latencies in children. Interaural differences in absolute wave V latencies and interpeak latency differences were similar to those observed in infants and adults, indicating that response symmetry is independent of age. Statistical analyses suggested that the distributions of absolute and relative latency measurements are normal, making it possible to describe norms in terms of means and standard deviations. A simple model is described that accounts accurately for changes in mean wave V latencies as function of age from preterm through the first three years of life.