Objective: To review the literature on auditory dyssynchrony AD or neuropathy which is characterized by absent auditory brainstem responses, normal otoacoustic emissions, and word discrimination disproportional to the pure tone audiogram. Results: Several papers attempt to estimate the prevalence of AD that seems to range between 0. It seems that AD is not a single disease but a spectrum of pathologies that affect the auditory pathway at the level of the inner hair cells, the synapses, or the auditory nerve. Many predisposing or contribution factors have been reported, including prematurity, hyperbilirubinemia, hypoxia, low-birth weight, immunological conditions, infectious diseases, etc. Before proposing any method of management, parents should be informed about the variation among patients and the changes that may appear in some children's audition over time. Sigh language, speech and language therapy, hearing-aids, and cochlear implantation have been used in the treatment of AD.
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Colleague's E-mail is Invalid. Your message has been successfully sent to your colleague. Save my selection. Hood, Linda J. What does that mean? The term auditory dys-synchrony may provide a more comprehensive view of auditory neuropathy. An article by Berlin, Hood, and Rose discusses this recommendation and focuses on two primary underlying reasons. First, the auditory nerve itself may not be affected.
The possibility of a sensory rather than neural disorder is based on a number of factors, including the lack of a Wave I in the electrocochleogram ECochG and the auditory brainstem response ABR , absence of neuropathy in other than auditory systems, and human and animal temporal bones showing specific inner hair cell loss. Second, the term auditory neuropathy may lead clinicians to discount cochlear implants as a management option, even though cochlear implants have proven beneficial in auditory neuropathy patients.
Zeng et al. Certainly, but you also might want to check our earlier review article. The clinical audiologic tests sensitive to this disorder and useful in correctly identifying patients are physiologic measures.
Otoacoustic emissions OAEs reflect outer hair cell function and cochlear microphonics CM are another measure generated at least in part in the outer hair cells. You're correct in thinking that even minor middle ear problems may prevent OAEs from being observed, but there is less effect on the cochlear microphonic.
The CM is one of the electrical responses from the cochlea others are the endocochlear potential and summating potential. However, middle ear problems also attenuate the emission returning from the cochlea outward through the middle ear.
Since the CM is an electrical response, it is recorded by electrodes attached to the scalp, as with the ABR.
In this case, the hair cell response is picked up by the electrodes and thus is not dependent on conduction back out through the middle ear system.
So, in patients with middle ear problems where OAEs are absent, it is often still possible to record the CM and thus have some indication of outer hair cell function. There are several distinct differences between cochlear and neural responses. Use of appropriate recording methods makes it possible to differentiate these responses.
The most direct method to separate these responses is to compare responses obtained with rarefaction polarity stimuli with those obtained with condensation stimuli. Because CMs follow the characteristics of the external stimulus, the direction of the cochlear microphonic peaks will reverse with changes in stimulus polarity.
For higher-frequency stimuli and clicks, neural responses such as the ABR may show slight latency shifts with polarity changes, but they do not invert. Therefore, cochlear and neural components generally can be distinguished based on whether or not the peaks reverse with the stimulus.
Use of alternating polarity stimuli is not recommended since the CM will cancel and not be visible in the averaged response. If responses are obtained without reversing polarity but at several stimulus intensities, it may still be possible to distinguish cochlear from neural components.
The CM decreases in amplitude but does not increase in latency as the stimulus intensity decreases. In contrast, ABR waves increase in latency and decrease in amplitude as the stimulus intensity decreases. Thus, comparison of response latency at various intensities can help distinguish cochlear from neural responses.
Further discussion of these issues can be found in an article by Berlin et al. Is there anything I can do? Yes, there is. Many school systems routinely evaluate middle ear function using tympanometry and MEMRs. If a child has normal middle ear function and absent MEMRs that cannot be explained by peripheral hearing loss, then this information can provide a good first indication of a possible neural dys-synchrony disorder.
Each has several distinguishing characteristics. Have any of these children been found to have OAEs? To address this question, two groups of researchers have tested students at schools for the Deaf.
Yes, there are. First, it is important to note that, while some patients have risk factors related to hearing loss in their history, there are also are a significant number of patients with no risk factors in their history. These include hyperbilirubinemia ranging from just above normal to quite high, premature birth 25 to 36 weeks gestational age , and perinatal asphyxia. Most writers agree with Starr et al. There are several sources of information that support the possible involvement of the inner hair cells.
Absence of inner hair cells with present outer hair cells demonstrated in animal models such as the Bronx waltzer mouse 13 and the Beethoven mouse 14 provides a biological precedence. Recently, this was shown in human infants as well through temporal bone histological studies, 15 providing an important connection to its possible occurrence in humans.
All of the possible sites result in auditory dys-synchrony and suggest similar management needs related to methods of communication. As mentioned earlier, patients vary in demonstration of other peripheral neuropathies.
Some patients have clear hereditary sensory-motor neuropathy. Others have less apparent neuropathy, which is only evident on clinical examination, and still other patients demonstrate no signs of neuropathy.
Often the only complaint of patients in these latter two groups is difficulty hearing or understanding speech, particularly in noise. In an interesting study, Starr et al.
As for clinical audiologic test results, pure-tone thresholds vary widely and, while most patients perform very poorly on word- and sentence-recognition tests, a few patients have some residual speech-recognition ability in quiet. However, in our experience, even those with some speech-recognition ability in quiet are unable to understand words or sentences in competing noise situations.
What patients have in common are findings on physiologic auditory measures consistent with normal outer hair cell function and neural dys-synchrony. Starr et al. It can. Another group is patients who are well fitted with up-to-date hearing aids but, despite good audibility of signals, derive very minimal or no benefit. There is considerable variability among patients related to changes over time. Berlin et al. Progressive loss of peripheral auditory integrity: Some patients show a retrograde loss of cochlear microphonics and OAEs, and become audiologically almost indistinguishable from peripherally deaf children.
Such children have been successfully implanted and perform well with a cochlear implant. Maintain: Some patients maintain cochlear microphonics and OAEs, but do not learn speech and language by auditory means alone. Visual information e. A number of patients in this group are successful cochlear implant users and have moved away from visual cues post-implant.
Worsening with peripheral neuropathy: Some patients show a worsening of symptoms and develop other peripheral neuropathies, such as hereditary motor-sensory neuropathy e. Partial recovery: Some patients seem to recover pure-tone sensitivity and awareness of sound, but continue to show desynchronized ABRs, robust cochlear microphonics, and normal OAEs. Speech and language are delayed, but develop. Hearing aids can improve detection of sound through amplification but, in our experience, are of minimal benefit in improving discrimination.
In the children now approaching whom we follow in our database, we have not seen facilitation of speech and language development with hearing aids alone.
Do they really work with these patients? The underlying physiology in some patients may include absence or malfunction of inner hair cells.
This has been documented in animal models, where the inner hair cells have been destroyed, and in human infant temporal bones. The five children with cochlear implants reviewed by Shallop et al. Shallop et al. Using intraoperative video recording, Shallop and colleagues have observed contraction of the stapedius muscle in response to acoustic stimulation through the cochlear implant electrode array as another demonstration of synchronous response to auditory signals.
Most of the patients who have been implanted have been children and the published reports to date summarize results with children. A few adults have been implanted with generally positive results. While the reports from adults to date have been anecdotal, some report variable benefit when first tuned up, but improved ability to communicate within a short time. Also, like the usual cochlear implant patients, some are able to converse over the telephone. We believe this is because it is difficult or impossible to achieve a clear and consistent auditory signal unless the patient has a cochlear implant in a dys-synchronous auditory system.
We recommend use of visual communication methods such as Cued Speech, sign language, or signed English as a necessary component for language development.
Do management strategies change? While we don't recommend use of auditory information alone pre-implant, we do use an AV approach post-implant and have found this approach successful.
We recommend slowly changing from auditory and visual cues to auditory cues alone post-implant. Abrupt removal of the communication system that a child has depended on prior to receiving a cochlear implant could interrupt smooth continuation of progress. Is there anything available for parents or patients? The web site at Kresge Hearing Research Lab contains information that is updated periodically and links to other web sites; it can be accessed at www. It provides a forum for parents and patients to exchange information.
One of the primary objectives of audiologic testing is to identify auditory pathologies. Years back, armed only with the results of pure-tone air-conduction and bone-conduction thresholds, we usually were able to separate conductive from sensorineural disorders. In the early s, immittance audiometry provided us the ability to further identify specific pathologies within these two general categories and, by the s, the routine use of the ABR further enhanced our ability to identify more subtle pathologies of the cochlea and auditory neural pathways.
Today, with the addition of OAEs to the audiologic test battery, we are able to identify unique pathologies that perhaps would have been misdiagnosed in years past.
This pathology, identified by means of physiologic measures, presents a distinctive pattern when the acoustic reflex, OAEs, ABR, and cochlear microphonic results are compared. A few years ago, Dr. Now, she's back to field queries on recent developments surrounding this unique dysfunction. She is a founder and past president of the American Academy of Audiology. You probably know her best from her book chapters, text books, and the many workshops on auditory physiologic testing that she has conducted in New Orleans and the rest of the world as well.
As you read Dr.
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Auditory Neuropathy AN is a hearing disorder in which the outer hair cells of the cochlea are present and functional, but sound information is not transmitted sufficiently by the auditory nerve to the brain. Hearing loss with AN can range from normal hearing sensitivity to profound hearing loss. A neuropathy usually refers to a disease of the peripheral nerve or nerves, but the auditory nerve itself is not always affected in auditory neuropathy spectrum disorders. These high-risk factors are: hypoxia, low birth weight, premature birth, hyperbilirubinemia, jaundice, and aminoglycoside antibiotic treatments NIDCD, Based on clinical testing of subjects with auditory neuropathy, the disruption in the stream of sound information has been localized to one or more of three probable locations: the inner hair cells of the cochlea, the synapse between the inner hair cells and the auditory nerve, or a lesion of the ascending auditory nerve itself. Diagnosis is possible after a test battery, that must necessarily include the following: the auditory brainstem response and otoacoustic emissions.
Auditory neuropathy is a condition in which patients, on audiologic evaluation, are found to have normal outer hair cell function and abnormal neural function at the level of the eighth nerve. These patients, on clinical testing, are found to have normal otoacoustic emissions, whereas auditory brainstem response audiometry reveals the absence of neural synchrony. Unlike space-occupying lesions, radiologic evaluation reveals normal results. Patients with auditory neuropathy require a different management approach to their auditory and communication problems from approaches used with patients with usual peripheral hearing losses. Users Online:
Auditory Neuropathy/Dys-synchrony and Its Perceptual Consequences
Send correspondence to. The ECAP's characteristics differences at 80 and 35Hz stimulation rate were also not statistically significant. However, a unique clinical procedure cannot be proposed at this point. Clinical Trials: NCT