INTRODUCTION — Hearing loss is a common problem that everyone experiences from time to time. Most commonly it occurs when flying or traveling up a mountain, and a full sensation develops in the ears, leading to the feeling of wanting to pop the ears open in order to hear better. Diminished hearing may also occur during an ear infection. These causes of hearing loss are usually short-lived. The other extreme is the permanent sensorineural hearing loss that occurs with aging, which we will all experience to some degree. The causes of hearing loss are reviewed here, along with brief discussions of the management of certain conditions.
The evaluation of hearing loss in adults and the screening and evaluation of hearing loss in children are discussed separately:
●(See "Evaluation of hearing loss in adults".)
●(See "Sudden sensorineural hearing loss in adults: Evaluation and management".)
●(See "Hearing loss in children: Etiology".)
●(See "Hearing loss in children: Screening and evaluation".)
●(See "Screening the newborn for hearing loss".)
EPIDEMIOLOGY — Hearing loss is a common chronic impairment, particularly for older adults. In the Beaver Dam cohort in the United States, the prevalence of hearing loss, defined by audiometry, increased steadily with age [1]:
●3 percent ages 21 to 34
●6 percent ages 35 to 44
●11 percent ages 44 to 54
●25 percent ages 55 to 64
●43 percent ages 65 to 84
Worldwide, estimates from the World Health Organization are that hearing loss affects 538 million people [2].
ANATOMY AND PHYSIOLOGY — The ear is divided into three segments (figure 1):
●The outer ear, comprising the auricle and ear canal
●The middle ear, comprising the tympanic membrane (TM), ossicles, and the middle ear space
●The inner ear, comprising the cochlea, semicircular canals, and internal auditory canals
Anatomically, the auricle, or outer ear, is a uniquely constructed organ. It is perfectly designed to "catch" incoming sound waves and then funnel them down the external auditory canal (EAC). Sound waves vibrate the TM, causing motion of the ossicles that results in the piston-like effect of the stapes. The piston motion of the stapes then pushes the inner ear fluid around the two-and-one-half turns of the cochlea. Frequency-specific movement sets up fluid waves within the cochlea, which in turn sets into motion the organ of Corti (figure 2). The organ of Corti movement bends the stereocilia, depolarizing the subsequent action of the auditory message traveling through the hair cells via the cochlear (auditory) nerve to the brain. The brain organizes the information into what we perceive as complex sounds.
CLASSIFICATION — Hearing loss may be classified into three types:
●Sensorineural, involving the inner ear, cochlea, or the auditory nerve.
●Conductive, involving any cause that in some way limits the amount of external sound from gaining access to the inner ear. Examples include cerumen impaction, middle ear fluid, or ossicular chain fixation (lack of movement of the small bones of the ear).
●Mixed loss, which is a combination of conductive and sensorineural hearing loss.
The evaluation necessary to make these classifications is discussed separately. (See "Evaluation of hearing loss in adults".)
A number of abnormalities may lead to hearing loss of each type (table 1). Conductive hearing loss is usually related to abnormalities of the outer or middle ear; sensorineural hearing loss is related to inner-ear pathology.
OUTER EAR CAUSES — All hearing loss related to the outer ear is by nature a conductive hearing loss.
Congenital — The external auditory canal (EAC) develops from the 8th to 28th week of gestation; problems can occur anytime during this developmental phase. Microtia, the absence or malformation of the auricle, may cause mild to moderate conductive hearing loss. Atresia or significant stenosis of the EAC causes moderate to maximal (60 dB) conductive hearing loss.
The auricle itself forms from remnants of the first and second branchial arch during the 12th and 20th weeks; it is possible to have a normal auricle but an atretic canal. Unilateral atresia or significant stenosis of the EAC is much more common than bilateral disease.
Atresia malformations of the EAC occur in approximately 1 per 10,000 births and are usually associated with other craniofacial abnormalities such as Treacher-Collins syndrome, Robin sequence, or Crouzon syndrome [3-6]. The severity of the atresia determines how well the child hears and whether surgical intervention (repair or BAHA implant) may provide some benefit. Some patients with congenital atresia have associated inner ear abnormalities, but these abnormalities typically do not cause sensorineural hearing loss [7].
Hearing loss in children is discussed separately. (See "Hearing loss in children: Etiology" and "Hearing loss in children: Screening and evaluation" and "Hearing loss in children: Treatment".)
Infection — Infections may lead to blockage of the EAC due to the accumulation of debris, edema, or inflammation. Otitis externa usually develops as a result of local trauma coupled with contamination by bacteria (or occasionally fungi) after swimming, showering, or exposure to hot humid conditions. Significant edema of the EAC occurs; the canal is often also filled with squamous and purulent debris. The most common symptoms are otalgia, pruritus, discharge, and hearing loss. (See "External otitis: Pathogenesis, clinical features, and diagnosis".)
Trauma — Penetrating trauma to the external auditory canal or meatus due to a bullet, knife, or fracture may cause mild or profound conductive hearing loss, depending upon the degree of EAC occlusion. Ototopical drops prevent otitis externa; EAC stenting is required initially to ensure that the EAC does not develop significant stenosis. Surgical intervention is reserved for cases of stenosis.
Tumor — The most common malignant tumor of the EAC is squamous cell carcinoma [8-10]. This and other tumors of the EAC, such as basal cell carcinoma and melanoma, typically cause conductive hearing loss due to occlusion of the canal. Initially, cancer of the EAC is usually misdiagnosed as otitis externa. However, after multiple failed attempts at treatment with ototopical drops and antibiotics, a biopsy of the EAC should be obtained. Treatment of these malignant tumors is usually surgical with adjuvant radiation therapy as needed.
Benign bony growths may also occlude the EAC with a resulting conductive hearing loss. The two most common benign growths are exostosis and osteoma.
Exostosis — Exostosis or multiple benign bony growths of the EAC most commonly occur in individuals who have had repeated exposure to cold water (picture 1). They almost always form in the suture lines of the EAC bones. Surgical intervention with removal of the exostosis is performed when the exostoses become so large that they occlude the canal (picture 2), and infections begin to develop because of retained skin and cerumen [11-13].
Osteoma — Osteoma is a solitary bony growth that is most commonly attached to the tympanosquamous suture line; it usually is found more towards the meatus compared with exostoses that are typically more medial and closer to the tympanic membrane (TM). Similar to exostoses, osteomas are not treated until they become so large that they affect hearing by occlusion or repeated infections because debris cannot exit the EAC [14].
Benign polyps — Benign polyps may occur as a result of other otologic conditions, such as chronic ear infections or cholesteatoma. Occasionally, benign polyps can grow large enough to obscure the lumen of the EAC (picture 3).
Systemic disease — Diabetes mellitus and other immunocompromised states can predispose to developing necrotizing otitis externa, which in turn can cause conductive hearing loss due to occlusion of the EAC. (See "External otitis: Pathogenesis, clinical features, and diagnosis".)
Dermatologic — Certain skin diseases, such as psoriasis, may cause scaling and edema of the EAC and meatus. Treatment is usually with steroid ointments or creams. (See "Treatment of psoriasis in adults".)
Cerumen — Some patients are not able to clear cerumen on their own or use Q-tips that push the cerumen down the ear canal. These individuals may need periodic cleaning of the cerumen to enhance their auditory capabilities. (See "Cerumen".)
MIDDLE EAR CAUSES — As with the outer ear, all hearing loss associated with the middle ear is conductive hearing loss.
Congenital — Atresia or malformation of the ossicular chain can cause conductive hearing loss. Abnormal development of the ossicular chain is almost impossible to see on otoscopic examination; computed tomography (CT) scanning is virtually always needed in order to make this diagnosis and, in some cases, exploratory tympanostomy may be required for diagnosis.
The most common ossicular abnormality observed is a missing or malalignment of the crura of the stapes. However, it is usually an abnormal incus or malleoincudal joint that causes the conductive hearing loss. One other malformation of the ossicles that can occur is fixation of the malleoincudal joint or one of the ossicles to the scutal or attic ridge [15].
Treatment of any of these abnormalities consists of either hearing amplification or surgical intervention to restore mobility of the ossicular chain. Surgical treatment may include ossiculoplasty, performed to restore the ability of the ossicular chain to move as a unit.
Eustachian tube dysfunction — Eustachian tube dysfunction can cause perceived hearing loss. Eustachian tube dysfunction occurs commonly in the setting of a viral upper respiratory infection (URI) or sinusitis, and it can also occur with allergies. Evaluation and management of eustachian tube dysfunction is discussed in detail separately. (See "Eustachian tube dysfunction".)
Infection — Otitis media (OM) is a common childhood disorder that also frequently occurs in adults [16]. Approximately 80 to 90 percent of all children will have developed at least one episode of OM by the time they enter school [17].
Otitis media is normally associated with pain, fever, and ear fullness as well as decreased hearing (see "Acute otitis media in adults" and "Chronic otitis media, cholesteatoma, and mastoiditis in adults"). Conductive hearing loss occurs because fluid filling the middle ear space prevents the tympanic membrane (TM) from vibrating adequately, thereby diminishing movement of the ossicular chain [18-20].
The middle ear may still be filled with serous or thick, tenacious fluid after the acute infection has been successfully treated. This lingering fluid resolves within four to six weeks in 70 percent of cases [21]. By an additional 12 weeks, 85 to 90 percent of all children or adults who have chronic serous OM resolve the condition on their own. However, in the 10 to 15 percent in whom the fluid does not clear, it needs to be removed and the middle ear aerated in order to promote healing and resolution of any conductive hearing loss [22]. The fluid is usually cleared by either myringotomy and pressure equalization tube placement or myringotomy and aspiration.
Most adults do not tolerate fluid in the middle ear space for any longer than two to four weeks; the increased pressure, decreased hearing, and tinnitus that this can create drives many adults to undergo myringotomy and aspiration much sooner than would be recommended for children. In children, we usually wait for at least two-and-one-half to three months before considering myringotomy and tube placement for chronic OM, unless we know the child has an existing sensorineural hearing loss and a history of poor eustachian tube function [23].
Tumors — Malignant tumors such as Langerhans cell histiocytosis (including the Letterer-Siwe variant) or squamous cell carcinoma may cause conductive hearing loss. However, these entities are relatively rare when compared with benign cholesteatoma or otosclerosis.
Cholesteatoma — Cholesteatoma is a growth of desquamated, stratified, squamous epithelium within the middle ear space (picture 4). As keratin desquamates from the epithelial lining of the sac, it gradually enlarges with eventual erosion of the ossicular chain, mastoid, and external auditory canal (EAC). Formation of a cholesteatoma typically occurs after a retraction pocket has formed in the posterior/superior quadrant, often the result of poor eustachian tube function. It may also occur after TM trauma, such as a traumatic, inflammatory, or iatrogenic perforation.
Left untreated, cholesteatomas may erode the tegmen (the bony covering of the middle fossa), the sigmoid sinus, or even the inner ear. Thus, untreated cholesteatomas can result in lateral sinus thrombosis, sepsis, brain abscess, sensorineural hearing loss, vertigo, disequilibrium, facial paralysis, and even death [22,24]. Treatment is surgical, usually involving a tympanomastoidectomy.
Otosclerosis — Otosclerosis is a bony overgrowth that involves the footplate of the stapes. As the overgrowth develops, the stapes can no longer function as a piston, but rather rocks back and forth and eventually becomes totally fixated. Conduction gradually becomes worse until a maximal conductive hearing loss of 60 dB is reached.
Initial treatment for otosclerosis and the accompanying hearing loss involves either hearing amplification or surgical replacement of the stapes bone with a prosthesis. This can be achieved with a small hole created in the footplate of the stapes, or a portion of the footplate of the stapes is completely removed (stapedectomy). In both instances, the bulk of the stapes superstructure is removed. A piston prosthesis is then placed from the incus into the surgically created opening, which returns the piston-like action of the ossicular chain. In cases of advanced otosclerosis, cochlear implantation may be considered [25].
Oral sodium fluoride therapy has been advocated for the treatment of otosclerosis, particularly in France [26]; this treatment is not widely used in the United States. There is only limited evidence of efficacy from controlled trials [27,28]. Fluoride therapy can cause significant side effects, including gastrointestinal symptoms and lower extremity pain, and it has a narrow therapeutic window. In the absence of further data from well-performed randomized clinical trials, we do not recommend the routine use of sodium fluoride for otosclerosis.
Tympanic membrane perforation — Conductive hearing loss due to TM perforation is common (picture 5). The degree of conductive hearing loss depends upon the size and location of the perforation. Small perforations and those located in the anterior/inferior quadrant cause the least amount of conductive hearing loss; near total or posterior/superior quadrant perforations have a much higher chance of causing significant hearing loss [29].
TM perforations can be caused by many events, including blast injury, barotrauma (see 'Middle ear barotrauma' below), foreign body trauma, temporal bone fractures, ear infections, or self-inflicted trauma from a Q-tip or other object; or the hole may persist after myringotomy or after tubes fall out. After an acute perforation, the ear needs to be examined under the microscope to ensure that skin is not trapped on the undersurface of the TM, since trapped skin could lead to cholesteatoma formation. Documentation of a patient's auditory status also is mandatory for any newly diagnosed perforation.
Most acute TM perforations heal on their own or with the aid of a paper or biogenic film patch. Occasionally surgical correction is required, usually with a temporalis muscle fascia graft. Repair of the perforation often corrects the conductive hearing loss [30,31].
Temporal bone trauma from fractures or blunt injuries may also cause TM perforation, but the sequelae of ossicular discontinuity must be considered in these situations, particularly if the perforation heals and the patient still has residual hearing loss. This type of hearing loss can eventually attain a level of a 60 dB (maximal) conductive loss. The diagnosis of ossicular discontinuity is often made with CT scan, and/or by demonstrating high compliance of the TM with pneumoscopy once the perforation heals.
Middle ear barotrauma — Barotrauma occurs when a patient is exposed to a sudden, large change in ambient pressure, often during diving or flying. Middle ear pressure becomes more positive with respect to ambient pressure during ascent until the eustachian tube is forced open. On descent, ambient pressure exceeds middle ear pressure until swallowing opens the eustachian tube. (See "Ear barotrauma".)
Pressure in the middle ear normally equilibrates with ambient pressure via the eustachian tube. However, if upon descent with flying or diving this equalization is prevented by mucosal edema secondary to an URI, pregnancy, or anatomic variations, the negative relative pressure in the middle ear can lead to its filling with serous fluid or blood or to inward rupture of the TM [32,33]. Symptoms vary from a sensation of pressure to hearing loss and pain, which may suddenly be relieved with rupture of the TM. Acute unilateral TM rupture can also produce vertigo, nausea, and disorientation due to leakage of cold water into the middle ear and uneven caloric stimulation. Overpressurization of the middle ear can occur during ascent with flying or diving, but TM rupture is rare.
Treatment of middle ear barotrauma consists of topical and systemic decongestants, analgesics, and antihistamines. Antibiotics should be used if purulent otorrhea is observed [34]. Most TM ruptures heal spontaneously, if normal eustachian tube function is restored and infection is controlled. Patients with middle ear barotrauma should be evaluated for inner ear barotrauma. (See 'Inner ear barotrauma' below.)
Vascular — Jugulotympanic paragangliomas (previously referred to as glomus tympanicum or glomus jugulare tumors) are highly vascular, typically benign paragangliomas that arise either from the promontory of the middle ear or the adventitia of the dome of the jugular bulb. As tympanic tumors grow, they tend to fill the middle ear, with resultant pulsatile tinnitus with or without conductive hearing loss. They also erode bone as they enlarge, especially inferiorly, causing damage to cranial nerves. In addition, tumors may impede upon the ossicular chain and TM, thereby decreasing motility of either or both structures. (See "Paragangliomas: Epidemiology, clinical presentation, diagnosis, and histology", section on 'Definition and anatomic origin' and "Paragangliomas: Epidemiology, clinical presentation, diagnosis, and histology", section on 'Head and neck paragangliomas'.)
Jugulotympanic paragangliomas can be identified by pneumoscopy. A reddish mass may be seen behind the TM that blanches when positive air pressure is instilled into the ear canal (picture 6).
The treatment of jugulotympanic paragangliomas has traditionally been complete surgical removal [35,36]. Surgery, however, is associated with significant cranial nerve deficits that are unavoidable much of the time. Many surgeons have now started primary treatment with stereotactic radiation therapy [37,38].
INNER EAR CAUSES — Disorders of the inner ear normally cause a sensorineural hearing loss. The etiology may be associated with the cochlea, eighth nerve, internal auditory canal, or brain.
Congenital or hereditary — Congenital hearing loss will be defined as any hearing loss that occurs at or shortly after birth that may be due to either a hereditary or non-hereditary cause. Non-hereditary etiologies involve an insult to the developing cochlea, including viral infections such as cytomegalovirus (CMV), hepatitis, rubella, toxoplasmosis, HIV, and syphilis. Some medications also may have a teratogenic effect on the developing ear of the fetus, including recreational drugs, alcohol, quinine, and retinoic acid.
Sensorineural hearing loss can be inherited in an autosomal dominant or recessive pattern; 90 percent is autosomal recessive, so that the children often have normal hearing parents [39-41]. Mutations in a second gene (modifier gene) may worsen the degree of hearing loss produced by certain mutations [42]. Sensorineural hearing loss also may be part of a syndrome or occur as a spontaneous mutation. The hearing deficit may be present at birth, progressive from birth, or present when the child is older, such as years 5 to 6, during teens, or even in early adult life. One clue to the presence of hereditary sensorineural hearing loss is that there is no set pattern; it may fluctuate, progress, or remain stable. The most common testable genetic defect is an abnormal connexin 26; clinical implications in terms of genetic screening remain unclear [43,44].
Congenital malformations of the inner ear also occur; these include anything from complete atresia to a common cavity of the cochlea. The most common malformation is a Mondini, where the normal two-and-one-half turns of the cochlea are replaced by one to one-and-one-half turns.
Patients who have congenital anomalies of either the inner or the middle ear may also develop perilymphatic fistulas (PLFs). PLFs alone can cause progressive or fluctuating sensorineural hearing loss [45,46]. Thus, surgical exploration and repair of PLFs may be indicated in patients who exhibit fluctuating or progressive sensorineural hearing loss.
Hearing loss in children is discussed separately. (See "Hearing loss in children: Etiology" and "Hearing loss in children: Screening and evaluation" and "Hearing loss in children: Treatment".)
Presbycusis — Presbycusis, or age-related hearing loss, is a common cause of hearing loss worldwide. The hallmark of presbycusis is the progressive, symmetric loss of high-frequency hearing over many years in an older adult. One analysis of 605 older individuals from a large cohort study who had audiologic and cognitive testing done showed an association between a decrease in hearing with decreases in a measure of nonverbal executive function and psychomotor speed. Therefore, it is important to identify and treat hearing loss early [47]. (See "Presbycusis".)
Common complaints associated with presbycusis include the inability to hear or understand speech in a crowded or noisy environment, difficulty understanding consonants, and the inability to hear high-pitched voices or noises. Tinnitus is often present and may be described as either a roaring sound, crickets, or bells in the ear. (See "Etiology and diagnosis of tinnitus".)
Hearing aids are able to benefit most patients with presbycusis. The progression of hearing loss rarely becomes so severe that hearing aids are not effective in restoring the ability to communicate. At times, hearing amplification is not tolerated by patients either because they produce too much ear wax, which plugs the device; the meatus is too small; or the device has increased static or noise. The aid may also cause discomfort, and it is a cosmetic concern to many patients. Cochlear implantation may benefit patients of any age who are not helped by hearing aids. Specific issues related to hearing amplification are discussed separately, including identification of appropriate candidates, choosing the type of hearing aid, and fitting. (See "Hearing amplification in adults".)
Patients with unilateral or asymmetric high-frequency sensorineural hearing loss do not fall into the category of typical presbycusis. These patients all deserve further and full otologic evaluations [48]. (See "Evaluation of hearing loss in adults".)
Infection — The most common infection of the inner ear in adults is viral cochleitis; in young children, it is meningitis [49]. Meningitis can access the cochlea by way of cerebrospinal fluid (CSF)-perilymph fluid connection and cause a profound sensorineural hearing loss by destroying the inner ear hair cells. (See "Neurologic complications of bacterial meningitis in adults", section on 'Sensorineural hearing loss'.)
Those who have suffered severe or profound sensorineural hearing loss due to meningitis or other causes may still be able to hear with cochlear implants. Cochlear implants are useful for any patient with moderate to severe or profound bilateral sensorineural hearing loss with speech scores (AZ Bio sentence testing in quiet or noise) as high as 50 percent in best aided conditions [50,51]. The implant consists of an electrode array of either 22 or 16 channels that is inserted into the cochlea. The patient then wears a processor, much like a behind-the-ear hearing aid, which is connected to the implanted device underlying the skin via a magnet. Patients who seem to get the most benefit from a cochlear implant are postlingual adults who have profound sensorineural hearing loss bilaterally.
Viral cochleitis usually manifests as a sudden sensorineural hearing loss [52,53]; vertigo, facial paralysis, or pain occur rarely. Other causes of sudden sensorineural hearing loss (table 2) such as acoustic neuroma, PLF, Meniere disease, vascular insufficiency, multiple sclerosis, and other central etiologies are only going to be discovered on magnetic resonance imaging (MRI). Thus, although the primary etiology of sudden sensorineural hearing loss is almost always viral or a vascular ischemic event, patients with this presentation need to undergo audiometric evaluation as well as an MRI with gadolinium. (See "Sudden sensorineural hearing loss in adults: Evaluation and management".)
Meniere disease — Patients with Meniere disease complain of episodic spells of vertigo that last for hours, associated with aural fullness, tinnitus, and sensorineural hearing loss. Occasionally the auditory system is affected in what is commonly called cochlear Meniere or cochlear hydrops; in these cases, the patients experience episodic hearing loss that recovers within a 12- to 24-hour period, usually with associated aural fullness and tinnitus. The spells of hearing loss may occur on a daily, weekly, or monthly basis. The hearing loss is almost always low frequency. Over time and with repeated attacks, the hearing deficit can become permanent and may even eventually involve all frequencies [54,55]. The diagnosis and management of Meniere disease are discussed separately. (See "Meniere disease: Evaluation, diagnosis, and management".)
Noise exposure — Everyday noise exposure, compounded over time, has an impact upon our ability to hear. Excessive noise can ultimately affect the degree of the presbycusis that develops. Constant exposure to loud noises can cause high-frequency sensorineural hearing loss (figure 3).
Nearly one in four (24 percent) adults aged 20 to 69 in the United States have evidence of noise-induced hearing loss based upon 2011 to 2012 data from the National Health and Nutrition Examination Survey (NHANES) [56]. Among those who reported exposure to loud noise at work, 33 percent had impaired hearing.
The mechanism by which excessive noise induces hearing loss includes direct mechanical damage of cochlear structures and metabolic overload due to overstimulation [57,58]. Some potential metabolic effects are excess nitric oxide release that can damage hair cells, generation of oxygen free radicals that become toxic to membranes, and low magnesium concentrations that weaken hair cells by reducing the concentration of intracellular calcium.
The United States Occupational Safety and Health Administration (OSHA) has set standards and guidelines for noise exposure in order to protect workers. All employees who are exposed to a greater than 85 dB time-weighted average must be enrolled in a hearing conservation program and provided hearing protection. Furthermore, OSHA's standards limit employees' exposure to noise. As an example, if the time-weighted average is 90 dB (which is equivalent to the noise made by a power lawn mower), they may be exposed to that noise for eight hours; at 95 dB, only four hours of exposure is allowed; at 100 dB, only two hours are allowed [59].
Exposure to loud noise in daily life is common. As an example, at recreational sporting events such as college basketball games, people may be exposed to average sound levels of 81 to 96 dB, with peak sound levels of 105 to 124 dB [60]. At some live music performances, average continuous sound levels have been recorded at 112 dB, with an average maximum sound level of 127 dB [61]. Hearing protection in the form of muffs or plugs is highly recommended anytime a person may be exposed to such noise levels.
In addition, a short blast of loud noise also can cause severe to profound sensorineural hearing loss, tinnitus, pain, or hyperacusis (over-sensitivity to a range of sounds). This usually involves exposure to noise greater than 120 to 155 dB.
Inner ear barotrauma — Barotrauma occurs when a patient is exposed to a sudden, large change in ambient pressure, often during diving or flying. Middle ear pressure becomes more positive with respect to ambient pressure during ascent until the eustachian tube is forced open. On descent, ambient pressure exceeds middle ear pressure until swallowing opens the eustachian tube. (See "Ear barotrauma".)
Inner ear barotrauma is a fairly uncommon injury but should be excluded in all cases of middle ear barotrauma [62] (see 'Middle ear barotrauma' above). It can occur following the development of a sudden pressure differential between the inner and middle ear, leading to rupture of the round or oval window. The main symptoms are tinnitus, vertigo, and hearing loss, which in turn can cause disorientation and panic. The resulting labyrinthine fistula and leakage of perilymph can result in permanent inner ear damage. The primary treatment of this complication is complete bed rest with head elevation to avoid increases in CSF pressure, which can increase the leakage of perilymph [63]. Deteriorating inner ear function generally requires tympanotomy and patching of the round or oval window.
Trauma — Penetrating trauma typically causes sensorineural or mixed hearing loss. These injuries are usually due to gunshot wounds that upon impact cause significant temporal bone fractures.
Blunt trauma can result in sensorineural loss due to concussive forces of the inner ear fluids, which may cause a shearing effect on the cochlear organ of Corti. Blunt trauma may also lead to longitudinal or transverse temporal bone fracture [64].
●The longitudinal type is most common (80 percent). It is usually caused by a blow to the temporal parietal region (image 1) [65]. Hearing loss is typically conductive and associated with tympanic membrane (TM) perforations and blood in the middle ear space.
●A transverse fracture occurs following a blow to the occipital or frontal region (image 2). Fractures of this type usually run through the inner ear with the result of a "dead" ear. If hearing is preserved to some degree, the most common reason for a conductive hearing loss is an ossicular injury, typically due to separation of the incudal stapedial joint and/or incus dislocation. Surgery does not correct these types of sensorineural hearing loss but can for conductive losses; if there is bilateral profound sensorineural hearing loss, a cochlear implant may be a viable option.
Tumors — Most tumors of the inner ear are benign, although malignant tumors such as squamous cell carcinoma, sarcomas, and adenoid carcinoma rarely occur with bony involvement. Benign bony tumors including fibrous dysplasia and Paget disease are also rare.
The most common tumor that causes sensorineural hearing loss is an acoustic neuroma (image 3). This is a benign tumor that usually originates from the vestibular portion of the eighth cranial nerve. The most common complaint is an asymmetric or unilateral sensorineural hearing loss, which occurs in 90 percent of all patients [66]. Other symptoms include unilateral tinnitus, disequilibrium, dizziness, lipomas, or headaches. Additional findings may include facial hyperesthesias or facial muscular twitching. (See "Vestibular schwannoma (acoustic neuroma)".)
Endocrine/systemic/metabolic — Various metabolic abnormalities have been known to either cause or be associated with sensorineural hearing loss. Thus, an evaluation of an unexplained sensorineural hearing loss should involve a complete laboratory evaluation to include the following:
●Measurement of blood sugar; small vessel disease as a result of diabetic vasculopathy can cause cochlear ischemia
●Complete blood count (CBC) with differential; anemia or a white blood cell dyscrasia may lead to sensorineural hearing loss by an unknown mechanism that may involve decreased oxygenation, microblockage of vessels, or infection
●Thyroid function tests to rule out hyper or hypothyroidism
●Serologic test for syphilis
Diabetes has been associated with an approximately twofold increase in the prevalence of low- and mid-frequency hearing impairment in adults; this might relate to the impact of diabetes on the vascular or neural components of the inner ear [67]. There is conflicting observational evidence about whether increased serum folate levels are associated with a decreased risk of age-related hearing loss [68,69]. A randomized trial in the Netherlands found a slightly slower decline in low-frequency hearing with three years of supplementation with folic acid 800 mcg [70]; additional studies are needed before folate supplementation can be recommended for the purpose of preventing hearing loss.
Autoimmune hearing loss — Autoimmune hearing loss was first described in 1979 [71]. It is usually bilateral, asymmetric, sensorineural hearing loss that is either fluctuating or progressive in nature. The autoimmune inner ear disease may be limited just to the ear, or it may be part of an overall systemic problem such as granulomatosis with polyangiitis, Cogan syndrome, rheumatoid arthritis, systemic lupus erythematosus, polyarteritis nodosa, or relapsing polychondritis. (See "Cogan syndrome" and "Clinical manifestations of relapsing polychondritis".)f
A number of studies are consistent with autoimmune hearing loss, including an elevated erythrocyte sedimentation rate (ESR), antinuclear antibody (ANA), and rheumatoid factor (RF). One of the more controversial tests is the detection of a cochlear autoantibody, a 68 kilodalton protein [72].
Autoimmune hearing loss is typically first treated with high-dose glucocorticoids (60 to 80 mg prednisone) every morning for two to three weeks. This often results in significant recovery of hearing. As an example, in a study that excluded patients with Cogan syndrome, 58 percent of patients treated with 60 mg of prednisone for one month experienced improvement in hearing [73]. Steroids are then tapered gradually until hearing loss recurs, thereby establishing an appropriate chronic steroid dose [74].
Cytotoxic medications such as cyclophosphamide, methotrexate, or azathioprine may be used if corticosteroids fail [75,76]. However, a randomized trial found no benefit to methotrexate therapy when used as steroid-sparing maintenance therapy in patients who had experienced improvement during one month of treatment with prednisone [73].
Iatrogenic — Iatrogenic inner ear injuries may occur during surgical procedures such as tympanomastoidectomy or stapedectomy; following radiation therapy, either for intracranial or nasopharyngeal tumors; or they may be medication-related. (See "Delayed complications of cranial irradiation", section on 'Ototoxicity' and "Treatment of early and locoregionally advanced nasopharyngeal carcinoma" and 'Ototoxic substances' below.)
Ototoxic substances — A number of ototoxic drugs and heavy metals can cause hearing loss [77]. Antibiotics and chemotherapeutic agents are among the most commonly used drugs that cause hearing loss. The hearing loss caused by antibiotic or chemotherapeutic agents usually begins at high frequencies; with continued medication use, the hearing loss will become more pronounced and may even continue to worsen for a time after the drug is discontinued. Any sensorineural hearing loss associated with antibiotic or chemotherapeutic drugs is permanent.
●Several antibiotics cause ototoxicity. All oral aminoglycosides are ototoxic. Some aminoglycosides are more vestibulotoxic than cochleotoxic. The relative order of cochleotoxicity is gentamicin > tobramycin > amikacin > neomycin. Ototopical aminoglycoside drops have the potential to cause ototoxicity. These include gentamicin, tobramycin, and Cortisporin (which contains neomycin). However, there are few case reports of sensorineural hearing loss with the use of ototopical medication and, in those, it is not clear that the drops were the cause. The reason it is believed that these medications do not have their normal ototoxic effect is that the inflamed mucosa within the ear prevents significant drug penetration into the oval and round windows [78]. (See "Pathogenesis and prevention of aminoglycoside nephrotoxicity and ototoxicity".)
●Other oral antibiotics that can cause ototoxicity include erythromycin and tetracycline. These drugs have a more pronounced ototoxic effect in patients with impaired kidney function. (See "Tetracyclines".)
●Many chemotherapeutic agents are known to cause hearing loss. The worst ototoxicity occurs with cisplatin. Other commonly used agents with ototoxicity are fluorouracil, bleomycin, and nitrogen mustard.
●High-dose aspirin (6 to 8 g/day) or other salicylates can cause hearing loss, but this is reversible with discontinuation of the drug. In an observational study in men, regular use of standard-dose aspirin, acetaminophen, or nonsteroidal antiinflammatory drugs (NSAIDs; ≥2 times/week) was also associated with an increased risk of hearing loss, particularly in those less than 50 years old [79]. Similar findings were found in women for acetaminophen and ibuprofen, but not aspirin [80].
●Phosphodiesterase 5 inhibitors stimulate downstream events in the cyclic guanosine monophosphate (cGMP) pathway thought to damage cochlear hair cells [81]. In a large population-based sample, sildenafil use was associated with hearing loss [82]. Hearing loss has also been reported with tadalafil or vardenafil [83].
●Antimalarial medications such as quinine and chloroquine may also cause sensorineural hearing loss and tinnitus but, similar to salicylates, these effects are usually reversible.
●Loop diuretics may cause temporary hearing loss and tinnitus [84].
●Cocaine, both intranasal and intravenous, has been associated with unilateral or bilateral sensorineural hearing loss in case reports [85].
●Heavy metals, including lead, mercury, cadmium, and arsenic, can all lead to hearing loss [86].
●Exposure to aromatic solvents, including toluene and styrene, may cause hearing loss due to cochleotoxic effects as well as alterations of the middle ear acoustic reflex [87].
Neurogenic — Several neurologic disorders may cause sensorineural hearing loss:
●Cerebrovascular accident or transient ischemic attack. (See "Stroke: Etiology, classification, and epidemiology" and "Definition, etiology, and clinical manifestations of transient ischemic attack".)
●Arnold-Chiari malformations may stretch the auditory vestibular nerve, thereby causing hearing loss and/or vestibular complaints [88]. The malformation may be decompressed with restoration of hearing.
●Multiple sclerosis is another disease that can initially present as a sudden sensorineural hearing loss and/or vertigo [89] (see "Sudden sensorineural hearing loss in adults: Evaluation and management" and "Manifestations of multiple sclerosis in adults"). The hearing loss may be temporary or permanent.
●Otosyphilis is a rare cause of sudden unilateral or bilateral sensorineural hearing loss. The hearing loss is sometimes accompanied by vertigo or tinnitus, and it may be reversible when promptly recognized and treated [90]. (See "Neurosyphilis".)
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Hearing loss and hearing disorders in adults".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, “The Basics” and “Beyond the Basics.” The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on “patient info” and the keyword(s) of interest.)
●Basics topics (see "Patient education: Age-related hearing loss (presbycusis) (The Basics)" and "Patient education: Ear wax impaction (The Basics)" and "Patient education: Ruptured eardrum (The Basics)")
SUMMARY AND RECOMMENDATIONS
●Anatomy and physiology of hearing loss – Hearing loss may be due to outer, middle, or inner ear etiologies (figure 1 and table 1). (See 'Anatomy and physiology' above.)
●Causes of conductive and sensorineural hearing loss – All outer and middle ear causes of hearing loss result in conductive hearing loss; nearly all inner ear causes result in sensorineural hearing loss (table 1 and table 2). (See 'Outer ear causes' above and 'Middle ear causes' above and 'Inner ear causes' above.)
