Ototoxicity | |
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Specialty | Otorhinolaryngology |
Ototoxicity is the property of being toxic to the ear (oto-), specifically the cochlea or auditory nerve and sometimes the vestibular system, for example, as a side effect of a drug. The effects of ototoxicity can be reversible and temporary, or irreversible and permanent. It has been recognized since the 19th century. [1] There are many well-known ototoxic drugs used in clinical situations, and they are prescribed, despite the risk of hearing disorders, for very serious health conditions. [2] Ototoxic drugs include antibiotics (such as gentamicin, streptomycin, tobramycin), loop diuretics (such as furosemide), and platinum-based chemotherapy agents (such as cisplatin and carboplatin). A number of nonsteroidal anti-inflammatory drugs (NSAIDS) have also been shown to be ototoxic. [3] [4] This can result in sensorineural hearing loss, dysequilibrium, or both. Some environmental and occupational chemicals have also been shown to affect the auditory system and interact with noise. [5]
Ototoxicity results in cochlear and/or vestibular dysfunction which can manifest as sensorineural hearing loss, tinnitus, hyperacusis, dizziness, vertigo, or imbalance. [6] [7] Presentation of symptoms vary in singularity, onset, severity and reversibility. [6]
Ototoxicity-induced hearing loss typically impacts the high frequency range, affecting above 8000 Hz prior to impacting frequencies below. [8] There is not global consensus on measuring severity of ototoxicity-induced hearing loss as there are many criteria available to define and measure ototoxicity-induced hearing loss. [9] [10] Guidelines and criteria differ between children and adults. [8]
There are at least 13 classifications for ototoxicity. [11] Examples of ototoxicity grades for hearing loss are the National Cancer Institute's Common Terminology Criteria for Adverse Events (CTCAE), Brock's Hearing Loss Grades, Tune grading system, and Chang grading system. [9]
National Cancer Institute (NCI) Common Terminology Criteria for Adverse Events (CTCAE) (as described in the American Academy of Audiology Ototoxicity Monitoring Guidelines from 2009): [8]
Brock's Hearing Loss Grades (as described in the American Academy of Audiology Ototoxicity Monitoring Guidelines from 2009): [8]
Chang grading system (as reported in Ganesan et al., 2018): [9]
Tune grading system (as reported in Ganesan et al., 2018): [9]
Hyperacusis is abnormally increased sensitivity to intensity (perceived as loudness) to what is typically deemed as normal/tolerable loudness.
Vestibular symptoms from ototoxicity, which would specifically be vestibulotoxicity, can include general dizziness, vertigo, imbalance, and oscillopsia.
Antibiotics in the aminoglycoside class, such as gentamicin and tobramycin, may produce cochleotoxicity through a poorly understood mechanism. [12] It may result from antibiotic binding to NMDA receptors in the cochlea and damaging neurons through excitotoxicity. [13] Aminoglycoside-induced production of reactive oxygen species may also injure cells of the cochlea. [14] Once-daily dosing [15] and co-administration of N-acetylcysteine [16] may protect against aminoglycoside-induced ototoxicity. The anti-bacterial activity of aminoglycoside compounds is due to inhibition of ribosome function and these compounds similarly inhibit protein synthesis by mitochondrial ribosomes because mitochondria evolved from a bacterial ancestor. [17] Consequently, aminoglycoside effects on production of reactive oxygen species as well as dysregulation of cellular calcium ion homeostasis may result from disruption of mitochondrial function. [18] Ototoxicity of gentamicin can be exploited to treat some individuals with Ménière's disease by destroying the inner ear, which stops the vertigo attacks but causes permanent deafness. [19] Due to the effects on mitochondria, certain inherited mitochondrial disorders result in increased sensitivity to the toxic effects of aminoglycosides.
Macrolide antibiotics, including erythromycin, are associated with reversible ototoxic effects. [20] The underlying mechanism of ototoxicity may be impairment of ion transport in the stria vascularis. [20] Predisposing factors include renal impairment, hepatic impairment, and recent organ transplantation. [20]
Certain types of diuretics are associated with varying levels of risk for ototoxicity. Loop and thiazide diuretics carry this side effect. The loop diuretic furosemide is associated with ototoxicity, particularly when doses exceed 240 mg per hour. [21] The related compound ethacrynic acid has a higher association with ototoxicity, and is therefore used only in patients with sulfa allergies. Diuretics are thought to alter the ionic gradient within the stria vascularis. [22] Bumetanide confers a decreased risk of ototoxicity compared to furosemide. [20]
Platinum-containing chemotherapeutic agents, including cisplatin and carboplatin, are associated with cochleotoxicity characterized by progressive, high-frequency hearing loss with or without tinnitus (ringing in the ears). [23] Ototoxicity is less frequently seen with the related compound oxaliplatin. [24] The severity of cisplatin-induced ototoxicity is dependent upon the cumulative dose administered [25] and the age of the patient, with young children being most susceptible. [26] The exact mechanism of cisplatin ototoxicity is not known. The drug is understood to damage multiple regions of the cochlea, causing the death of outer hair cells, as well as damage to the spiral ganglion neurons and cells of the stria vascularis. [27] Long-term retention of cisplatin in the cochlea may contribute to the drug's cochleotoxic potential. [28] Once inside the cochlea, cisplatin has been proposed to cause cellular toxicity through a number of different mechanisms, including through the production of reactive oxygen species. [29] The decreased incidence of oxaliplatin ototoxicity has been attributed to decreased uptake of the drug by cells of the cochlea. [24] Administration of amifostine has been used in attempts to prevent cisplatin-induced ototoxicity, but the American Society of Clinical Oncology recommends against its routine use. [30]
The vinca alkaloids, [31] [32] [33] including vincristine, [34] are also associated with reversible ototoxicity. [20]
Topical skin preparations such as chlorhexidine and ethyl alcohol have the potential to be ototoxic should they enter the inner ear through the round window membrane. [20] This potential was first noted after a small percentage of patients undergoing early myringoplasty operations experienced severe sensorineural hearing loss. It was found that in all operations involving this complication the preoperative sterilization was done with chlorhexidine. [35] The ototoxicity of chlorhexidine was further confirmed by studies with animal models. [20]
Several other skin preparations have been shown to be potentially ototoxic in the animal model. These preparations include acetic acid, propylene glycol, quaternary ammonium compounds, and any alcohol-based preparations. However, it is difficult to extrapolate these results to human ototoxicity because the human round window membrane is much thicker than in any animal model. [20]
At high doses, quinine, aspirin and other salicylates may also cause high-pitch tinnitus and hearing loss in both ears, typically reversible upon discontinuation of the drug. [20] Erectile dysfunction medications may have the potential to cause hearing loss. [36] However the link between erectile dysfunction medications and hearing loss remains uncertain. [37]
Previous noise exposure has not been found to potentiate ototoxic hearing loss. [38] [39] The American Academy of Audiology includes in their position statement that exposure to noise at the same time as aminoglycosides may exacerbate ototoxicity. The American Academy of Audiology recommends people being treated with ototoxic chemotherapeutics avoid excessive noise levels during treatment and for several months following cessation of treatment. Opiates in combination with excessive noise levels may also have an additive effect on ototoxic hearing loss. [40]
Ototoxic effects are also seen with quinine, pesticides, solvents, asphyxiants, and heavy metals such as mercury and lead. [5] [20] [41] [42] When combining multiple ototoxicants, the risk of hearing loss becomes greater. [43] [44] [45] As these exposures are common, this hearing impairment can affect workers in many occupations and industries. [46] [47] This risk probably been overlook because individual hearing tests conducted on workers, pure tone audiometry, does not allow one to determine if a hearing effects are a consequence of noise or chemical exposure. [48]
Examples of activities that often have exposures to both noise and solvents include: [49]
Ototoxic chemicals in the environment (from contaminated air or water) or in the workplace interact with mechanical stresses on the hair cells of the cochlea caused by noise in different ways. For mixtures containing organic solvents such as toluene, styrene or xylene, the combined exposure with noise increases the risk of occupational hearing loss in a synergistic manner. [5] [50] The risk is greatest when the co-exposure is with impulse noise. [51] [52] Carbon monoxide has been shown to increase the severity of the hearing loss from noise. [50] Given the potential for enhanced risk of hearing loss, exposures and contact with products such as fuels, paint thinners, degreasers, white spirits, exhaust, should be kept to a minimum. [53] Noise exposures should be kept below 85 decibels, and the chemical exposures should be below the recommended exposure limits given by regulatory agencies.
Drug exposures mixed with noise potentially lead to increased risk of ototoxic hearing loss. Noise exposure combined with the chemotherapeutic cisplatin puts individuals at increased risk of ototoxic hearing loss. [38] Noise at 85 dB SPL or above added to the amount of hair cell death in the high frequency region of the cochlea in chinchillas. [54]
The hearing loss caused by chemicals can be very similar to a hearing loss caused by excessive noise. A 2018 informational bulletin by the US Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH) introduces the issue, provides examples of ototoxic chemicals, lists the industries and occupations at risk and provides prevention information. [55]
Several guidelines have been published around the world, though there is not consensus on one universally agreed-upon protocol. [10] [11]
Guidelines released:
Auditory testing involved in ototoxicity monitoring/management (OtoM) is typically general audiological evaluation, high frequency audiometry (HFA), and otoacoustic emissions (OAEs). [57] [56] High frequency audiometry evaluates hearing thresholds beyond 8000 Hz, which is the typical cut-off for conventional audiometry. [57] It is recommended a baseline evaluation be performed prior to treatment beginning. [57] [56]
There are several guidelines on what constitutes a significant change in hearing [57] [59] which can indicate further action must be taken, whether that be to implement aural rehabilitation or adjust the source of ototoxic exposure (eg. chemotherapy). With pure tone audiometry, ASHA considers a significant change to have occurred if there is a: [60] [56]
If using distortion product ototoacoustic emissions (DPOAEs), a significant shift is observed if there is a reduction in amplitude by 6 dB or more than the baseline within the sensitive range of ototoxicity. [60]
Vestibular tests for vestibulotoxicity specifically can include caloric testing, rotational testing, vestibular evoked myogenic potentials (VEMPs), and computerized dynamic posturography (CDP); however, there are no globally accepted guidelines for monitoring/management of vestibular function during or following ototoxic treatments. [57] [61]
Hearing loss is a partial or total inability to hear. Hearing loss may be present at birth or acquired at any time afterwards. Hearing loss may occur in one or both ears. In children, hearing problems can affect the ability to acquire spoken language, and in adults it can create difficulties with social interaction and at work. Hearing loss can be temporary or permanent. Hearing loss related to age usually affects both ears and is due to cochlear hair cell loss. In some people, particularly older people, hearing loss can result in loneliness.
Tinnitus is a variety of sound that is heard when no corresponding external sound is present. Nearly everyone experiences faint "normal tinnitus" in a completely quiet room; but it is of concern only if it is bothersome, interferes with normal hearing, or is associated with other problems. The word tinnitus comes from the Latin tinnire, "to ring". In some people, it interferes with concentration, and can be associated with anxiety and depression.
Aminoglycoside is a medicinal and bacteriologic category of traditional Gram-negative antibacterial medications that inhibit protein synthesis and contain as a portion of the molecule an amino-modified glycoside (sugar). The term can also refer more generally to any organic molecule that contains amino sugar substructures. Aminoglycoside antibiotics display bactericidal activity against Gram-negative aerobes and some anaerobic bacilli where resistance has not yet arisen but generally not against Gram-positive and anaerobic Gram-negative bacteria.
The acoustic reflex is an involuntary muscle contraction that occurs in the middle ear in response to loud sound stimuli or when the person starts to vocalize.
Sensorineural hearing loss (SNHL) is a type of hearing loss in which the root cause lies in the inner ear, sensory organ, or the vestibulocochlear nerve. SNHL accounts for about 90% of reported hearing loss. SNHL is usually permanent and can be mild, moderate, severe, profound, or total. Various other descriptors can be used depending on the shape of the audiogram, such as high frequency, low frequency, U-shaped, notched, peaked, or flat.
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.
An audiogram is a graph that shows the audible threshold for standardized frequencies as measured by an audiometer. The Y axis represents intensity measured in decibels (dB) and the X axis represents frequency measured in hertz (Hz). The threshold of hearing is plotted relative to a standardised curve that represents 'normal' hearing, in dB(HL). They are not the same as equal-loudness contours, which are a set of curves representing equal loudness at different levels, as well as at the threshold of hearing, in absolute terms measured in dB SPL.
Noise health effects are the physical and psychological health consequences of regular exposure to consistent elevated sound levels. Noise from traffic, in particular, is considered by the World Health Organization to be one of the worst environmental stressors for humans, second only to air pollution. Elevated workplace or environmental noise can cause hearing impairment, tinnitus, hypertension, ischemic heart disease, annoyance, and sleep disturbance. Changes in the immune system and birth defects have been also attributed to noise exposure.
Noise-induced hearing loss (NIHL) is a hearing impairment resulting from exposure to loud sound. People may have a loss of perception of a narrow range of frequencies or impaired perception of sound including sensitivity to sound or ringing in the ears. When exposure to hazards such as noise occur at work and is associated with hearing loss, it is referred to as occupational hearing loss.
Pure-tone audiometry is the main hearing test used to identify hearing threshold levels of an individual, enabling determination of the degree, type and configuration of a hearing loss and thus providing a basis for diagnosis and management. Pure-tone audiometry is a subjective, behavioural measurement of a hearing threshold, as it relies on patient responses to pure tone stimuli. Therefore, pure-tone audiometry is only used on adults and children old enough to cooperate with the test procedure. As with most clinical tests, standardized calibration of the test environment, the equipment and the stimuli is needed before testing proceeds. Pure-tone audiometry only measures audibility thresholds, rather than other aspects of hearing such as sound localization and speech recognition. However, there are benefits to using pure-tone audiometry over other forms of hearing test, such as click auditory brainstem response (ABR). Pure-tone audiometry provides ear specific thresholds, and uses frequency specific pure tones to give place specific responses, so that the configuration of a hearing loss can be identified. As pure-tone audiometry uses both air and bone conduction audiometry, the type of loss can also be identified via the air-bone gap. Although pure-tone audiometry has many clinical benefits, it is not perfect at identifying all losses, such as ‘dead regions’ of the cochlea and neuropathies such as auditory processing disorder (APD). This raises the question of whether or not audiograms accurately predict someone's perceived degree of disability.
Hearing conservation programs are designed to prevent hearing loss due to noise. Hearing conservation programs require knowledge about risk factors such as noise and ototoxicity, hearing, hearing loss, protective measures to prevent hearing loss at home, in school, at work, in the military and, and at social/recreational events, and legislative requirements. Regarding occupational exposures to noise, a hearing conservation program is required by the Occupational Safety and Health Administration (OSHA) "whenever employee noise exposures equal or exceed an 8-hour time-weighted average sound level (TWA) of 85 decibels (dB) measured on the A scale or, equivalently, a dose of fifty percent." This 8-hour time-weighted average is known as an exposure action value. While the Mine Safety and Health Administration (MSHA) also requires a hearing conservation program, MSHA does not require a written hearing conservation program. MSHA's hearing conservation program requirement can be found in 30 CFR § 62.150, and is very similar to the OSHA hearing conservation program requirements. Therefore, only the OSHA standard 29 CFR 1910.95 will be discussed in detail.
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 fatigue is defined as a temporary loss of hearing after exposure to sound. This results in a temporary shift of the auditory threshold known as a temporary threshold shift (TTS). The damage can become permanent if sufficient recovery time is not allowed before continued sound exposure. When the hearing loss is rooted from a traumatic occurrence, it may be classified as noise-induced hearing loss, or NIHL.
Occupational hearing loss (OHL) is hearing loss that occurs as a result of occupational hazards, such as excessive noise and ototoxic chemicals. Noise is a common workplace hazard, and recognized as the risk factor for noise-induced hearing loss and tinnitus but it is not the only risk factor that can result in a work-related hearing loss. Also, noise-induced hearing loss can result from exposures that are not restricted to the occupational setting.
Acoustic trauma is the sustainment of an injury to the eardrum as a result of a very loud noise. Its scope usually covers loud noises with a short duration, such as an explosion, gunshot or a burst of loud shouting. Quieter sounds that are concentrated in a narrow frequency may also cause damage to specific frequency receptors. The range of severity can vary from pain to hearing loss.
Causes of hearing loss include ageing, genetics, perinatal problems, loud sounds, and diseases. For some kinds of hearing loss the cause may be classified as of unknown cause.
Safe listening is a framework for health promotion actions to ensure that sound-related recreational activities do not pose a risk to hearing.
Ototoxicity is defined as the toxic effect on the functioning of the inner ear, which may lead to temporary or permanent hearing loss (cochleotoxic) and balancing problems (vestibulotoxic). Drugs or pharmaceutical agents inducing ototoxicity are regarded as ototoxic medications.