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. The cause may be several dysfunctions of the inner hair cells of the cochlea or spiral ganglion neuron levels. [1] 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. [2] Prevalence in the population is relatively unknown. Neonates with high risk factors for hearing loss have a prevalence of up to 40% (Vignesh, Jaya, & Muraleedharan 2016). These high-risk factors are: hypoxia, low birth weight, premature birth, hyperbilirubinemia, jaundice, and aminoglycoside antibiotic treatments (NIDCD, 2018).
Hair cell | |
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![]() Three rows of outer hair cells in the organ of Corti, one row of inner hair cells. | |
Identifiers | |
MeSH | C538268 |
Anatomical terms of neuroanatomy |
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. [3]
Diagnosis is possible after a test battery, that must necessarily include the following: the auditory brainstem response and otoacoustic emissions. Auditory brainstem response should be tested with both polarities (helps in identifying cochlear microphonics). [4]
Auditory neuropathy can be diagnosed with a battery of tests including otoacoustic emissions (OAE), auditory brainstem response (ABR), and acoustic reflexes. The classic AN paradigm would include present OAEs indicating normal outer hair cell function, absent or abnormal ABR with presence of the cochlear microphonic, and absent acoustic reflexes. Other tests would include pure-tone and speech audiometry. AN patients can have a range of hearing thresholds with difficulty in speech perception. Patients with auditory neuropathy spectrum disorders have to date never been shown to have normal middle ear muscle reflexes at 95 dB HL or less despite having normal otoacoustic emissions. [5]
Auditory neuropathy can occur spontaneously, or in combination with diseases like Charcot-Marie-Tooth disease and Friedreich's ataxia. AN can have either congenital or acquired causes. AN can be due to genetic factors in syndromic, non-syndromic, and mitochondrial related patterns. Approximately 40% of AN cases are estimated to have a genetic cause. [6]
It appears that regardless of the audiometric pattern (hearing thresholds) or of their function on traditional speech testing in quiet the vast majority of those affected have very poor hearing in background noise situations. [7]
When testing the auditory system, there is no characteristic presentation on the audiogram.
When diagnosing a patient with auditory neuropathy, there is no characteristic level of functioning either. Patients can present with relatively little dysfunction other than problems of hearing speech in noise, or can present as completely deaf and gaining no useful information from auditory signals.
Hearing aids are sometimes prescribed, with mixed success. [8] FM systems in combination with hearing aids or cochlear implants could increase success of these amplification devices. Some people with auditory neuropathy obtain cochlear implants, also with mixed success. [8] [9]
Universal newborn hearing screenings are mandated in a majority of the United States. These screenings include OAE testing – otoacoustic emissions, which are sounds generated from the cochlea transmitted across the middle ear to the external ear canal, where they can be recorded. It assesses functionality of the cochlea, but not the auditory nerve. An ABR (auditory brainstem response) is required to assess that the sound is successfully transmitted through the nerve to the brain. In most parts of Australia, hearing screening via ABR testing is mandated, meaning that essentially all congenital (i.e., not those related to later onset degenerative disorders) auditory neuropathy cases should be diagnosed at birth.
Auditory neuropathy is sometimes difficult to catch right away, even with these precautions in place. Parental suspicion of a hearing loss is a trustworthy screening tool for hearing loss, too; if it is suspected, that is sufficient reason to seek a hearing evaluation from an audiologist. [10]
This is a glossary of medical terms related to communication disorders which are psychological or medical conditions that could have the potential to affect the ways in which individuals can hear, listen, understand, speak and respond to others.
The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus. A core component of the cochlea is the organ of Corti, the sensory organ of hearing, which is distributed along the partition separating the fluid chambers in the coiled tapered tube of the cochlea.
A cochlear implant (CI) is a surgically implanted neuroprosthesis that provides a person who has moderate-to-profound sensorineural hearing loss with sound perception. With the help of therapy, cochlear implants may allow for improved speech understanding in both quiet and noisy environments. A CI bypasses acoustic hearing by direct electrical stimulation of the auditory nerve. Through everyday listening and auditory training, cochlear implants allow both children and adults to learn to interpret those signals as speech and sound.
The vestibulocochlear nerve or auditory vestibular nerve, also known as the eighth cranial nerve, cranial nerve VIII, or simply CN VIII, is a cranial nerve that transmits sound and equilibrium (balance) information from the inner ear to the brain. Through olivocochlear fibers, it also transmits motor and modulatory information from the superior olivary complex in the brainstem to the cochlea.
The auditory system is the sensory system for the sense of hearing. It includes both the sensory organs and the auditory parts of the sensory system.
Audiology is a branch of science that studies hearing, balance, and related disorders. Audiologists treat those with hearing loss and proactively prevent related damage. By employing various testing strategies, audiologists aim to determine whether someone has normal sensitivity to sounds. If hearing loss is identified, audiologists determine which portions of hearing are affected, to what degree, and where the lesion causing the hearing loss is found. If an audiologist determines that a hearing loss or vestibular abnormality is present, they will provide recommendations for interventions or rehabilitation.
An otoacoustic emission (OAE) is a sound that is generated from within the inner ear. Having been predicted by Austrian astrophysicist Thomas Gold in 1948, its existence was first demonstrated experimentally by British physicist David Kemp in 1978, and otoacoustic emissions have since been shown to arise through a number of different cellular and mechanical causes within the inner ear. Studies have shown that OAEs disappear after the inner ear has been damaged, so OAEs are often used in the laboratory and the clinic as a measure of inner ear health.
Audiometry is a branch of audiology and the science of measuring hearing acuity for variations in sound intensity and pitch and for tonal purity, involving thresholds and differing frequencies. Typically, audiometric tests determine a subject's hearing levels with the help of an audiometer, but may also measure ability to discriminate between different sound intensities, recognize pitch, or distinguish speech from background noise. Acoustic reflex and otoacoustic emissions may also be measured. Results of audiometric tests are used to diagnose hearing loss or diseases of the ear, and often make use of an audiogram.
Presbycusis, or age-related hearing loss, is the cumulative effect of aging on hearing. It is a progressive and irreversible bilateral symmetrical age-related sensorineural hearing loss resulting from degeneration of the cochlea or associated structures of the inner ear or auditory nerves. The hearing loss is most marked at higher frequencies. Hearing loss that accumulates with age but is caused by factors other than normal aging is not presbycusis, although differentiating the individual effects of distinct causes of hearing loss can be difficult.
The auditory brainstem response (ABR), also called brainstem evoked response audiometry (BERA) or brainstem auditory evoked potentials (BAEPs) or brainstem auditory evoked responses (BAERs) is an auditory evoked potential extracted from ongoing electrical activity in the brain and recorded via electrodes placed on the scalp. The measured recording is a series of six to seven vertex positive waves of which I through V are evaluated. These waves, labeled with Roman numerals in Jewett and Williston convention, occur in the first 10 milliseconds after onset of an auditory stimulus. The ABR is considered an exogenous response because it is dependent upon external factors.
Cortical deafness is a rare form of sensorineural hearing loss caused by damage to the primary auditory cortex. Cortical deafness is an auditory disorder where the patient is unable to hear sounds but has no apparent damage to the structures of the ear. It has been argued to be as the combination of auditory verbal agnosia and auditory agnosia. Patients with cortical deafness cannot hear any sounds, that is, they are not aware of sounds including non-speech, voices, and speech sounds. Although patients appear and feel completely deaf, they can still exhibit some reflex responses such as turning their head towards a loud sound.
An auditory brainstem implant (ABI) is a surgically implanted electronic device that provides a sense of sound to a person who is profoundly deaf, due to retrocochlear hearing impairment. In Europe, ABIs have been used in children and adults, and in patients with neurofibromatosis type II.
Hearing, or auditory perception, is the ability to perceive sounds through an organ, such as an ear, by detecting vibrations as periodic changes in the pressure of a surrounding medium. The academic field concerned with hearing is auditory science.
Auditory neuropathy spectrum disorder (ANSD) is a specific form of hearing loss defined by the presence of normal or near-normal otoacoustic emissions (OAEs) but the absence of normal middle ear reflexes and severely abnormal or completely absent auditory brainstem response (ABRs).
Electrocochleography is a technique of recording electrical potentials generated in the inner ear and auditory nerve in response to sound stimulation, using an electrode placed in the ear canal or tympanic membrane. The test is performed by an otologist or audiologist with specialized training, and is used for detection of elevated inner ear pressure or for the testing and monitoring of inner ear and auditory nerve function during surgery.
The frequency following response (FFR), also referred to as frequency following potential (FFP) or envelope following response (EFR), is an evoked potential generated by periodic or nearly-periodic auditory stimuli. Part of the auditory brainstem response (ABR), the FFR reflects sustained neural activity integrated over a population of neural elements: "the brainstem response...can be divided into transient and sustained portions, namely the onset response and the frequency-following response (FFR)". It is often phase-locked to the individual cycles of the stimulus waveform and/or the envelope of the periodic stimuli. It has not been well studied with respect to its clinical utility, although it can be used as part of a test battery for helping to diagnose auditory neuropathy. This may be in conjunction with, or as a replacement for, otoacoustic emissions.
An audiologist, according to the American Academy of Audiology, "is a person who, by virtue of academic degree, clinical training, and license to practice and/or professional credential, is uniquely qualified to provide a comprehensive array of professional services related to the prevention of hearing loss and the audiologic identification, assessment, diagnosis, and treatment of persons with impairment of auditory and vestibular function, and to the prevention of impairments associated with them."
Audiology and hearing health professionals in India is made up of Indian healthcare professional that focus on audiological and hearing problems.
Sharon G. Kujawa is a clinical audiologist, Director of Audiology Research at the Massachusetts Eye and Ear Infirmary, Associate Professor of Otology and Laryngology at Harvard Medical School, and Adjunct Faculty of Harvard-MIT Health Sciences and Technology.and specialist in otolaryngology, Her specialty is the effects of noise exposure and aging on auditory function.
Computational audiology is a branch of audiology that employs techniques from mathematics and computer science to improve clinical treatments and scientific understanding of the auditory system. Computational audiology is closely related to computational medicine, which uses quantitative models to develop improved methods for general disease diagnosis and treatment.