INTRODUCTION — Hearing loss in the first years of life can cause delays in speech, language, and cognitive development [1]. Speech and language delays secondary to hearing loss are often preventable [2,3]. Thus, early identification of hearing loss, whether it is permanent (usually sensorineural) or temporary (usually conductive), is the key to a child's success with communication [4-7].
Clinically significant hearing loss occurs in 1 to 2 per 1000 newborns and in 2 per 1000 young children. However, nearly all children develop transient hearing loss related to middle ear infections during the period from birth to 11 years of age [8]. Knowledge of the etiology of the hearing loss, particularly if genetic, can inform genetic counseling and assist in the development of the optimal habilitation plan for the patient [9,10].
The etiology of hearing loss in children are reviewed here (table 1). The evaluation and treatment of hearing loss are discussed separately. (See "Hearing loss in children: Screening and evaluation" and "Hearing loss in children: Treatment".)
DEFINITIONS — The following terms are used throughout this topic:
●Conductive hearing loss – Conductive hearing loss is caused by a problem of the outer or middle ear that interferes with conduction of sound to the inner ear. It can occur at any location from the outer ear (pinna, external auditory canal) to the stapes footplate and oval window. In children, conductive hearing loss is most often transient (eg, otitis media with effusion), but it can be permanent (eg, aural atresia or chronic adhesive otitis media). Causes of conductive hearing loss are described below. (See 'Conductive hearing loss' below.)
●Sensorineural hearing loss (SNHL) – SNHL is hearing loss resulting from damage, disease, or other disorders affecting the inner ear (eg, the cochlea) and/or the auditory nerve (cranial nerve VIII).
•SNHL due to disorders of the inner ear – Numerous conditions (congenital or acquired) are associated with SNHL. The causes are discussed below. (See 'Sensorineural hearing loss' below.)
•Auditory neuropathy spectrum disorder (ANSD) – In ANSD (also called auditory neuropathy, neural synchrony disorder, neural dyssynchrony, and paradoxical hearing loss), the cochlea can detect sound, but there is a problem sending the signal to the brain. ANSD is characterized by normal otoacoustic emissions (suggesting normal outer hair cell function from the cochlea) but abnormal auditory brainstem response. The abnormality may be anatomically located from the inner hair cells of cochlea to the cochlear nerve of cranial nerve VIII.
•"Retrocochlear" hearing loss – "Retrocochlear" refers to lesions proximal to the cochlea. We define "retrocochlear" hearing loss as hearing loss resulting from abnormalities of the eighth cranial nerve. The most common retrocochlear lesion is a vestibular schwannoma. However, there is overlap between retrocochlear hearing loss and ANSD, and the terms are used somewhat inconsistently in the medical literature. Some resources use the term "retrocochlear" more broadly to describe other abnormalities of the auditory central nervous system.
●Mixed hearing loss – Mixed hearing loss refers to a combination of conductive and sensorineural hearing loss.
ANATOMY AND PHYSIOLOGY — The ear is divided into three anatomic segments (figure 1A-B):
●Outer ear, comprising the auricle and external auditory canal (EAC)
●Middle ear, comprising the tympanic membrane, ossicles, and the middle ear space
●Inner ear, comprising the cochlea, semicircular canals, and internal auditory canals
Anatomically, the auricle has a unique structure. It "catches" incoming sound waves and then funnels them down the EAC. Sound waves vibrate the tympanic membrane, causing motion of the ossicles that results in a movement of the stapes footplate. Movement of the stapes is transmitted to the inner ear fluid as a traveling wave that propagates around the two and one-half turns of the cochlea. Frequency-specific movement of the organ of Corti bends the stereocilia, causing depolarization of the inner and outer hair cells and creating electrical impulses transmitted via the auditory nerve to the brain. The brain organizes the information into what we perceive as complex sounds.
CONDUCTIVE HEARING LOSS — Conductive hearing loss is caused by a mechanical problem of the outer or middle ear that interferes with conduction of sound to the inner ear. It can occur at any location from the outer ear (pinna, external auditory canal) to the stapes footplate and oval window. Examples include cerumen impaction, middle ear fluid, and ossicular chain fixation (table 1).
Outer ear — Congenital anomalies, infections, and trauma to the outer ear can cause conductive hearing loss.
Obstruction — The EAC may be obstructed by cerumen or bony growths:
●Cerumen – This is the most common cause of EAC obstruction. Thus, it is important to clear the EAC of cerumen for accurate pediatric audiologic testing.
●Exostoses – Exostoses are benign broad-based osseous lesions often presenting after a history of chronic cold water exposure (eg, cold water swimming). These lesions are frequently multiple and bilateral, usually diagnosed in teenagers or young adults, and far more common in males.
●Osteomas – Osteomas are benign solitary smooth-round osseous lesions occurring at the tympanosquamous and tympanomastoid suture lines inside the bony EAC. These lesions usually present in middle age, although they may also occur in children.
Infection — Otitis externa can lead to blockage of the EAC caused by the accumulation of debris, edema, or inflammation. Otitis externa can develop after local EAC trauma or impacted cerumen becomes contaminated by bacteria (or occasionally fungi) after swimming, showering, or exposure to hot and humid conditions. The canal is often filled with squamous and purulent debris, and significant edema of the EAC occurs. The most common symptoms are otalgia (often severe), pruritus, discharge, and hearing loss. (See "External otitis: Pathogenesis, clinical features, and diagnosis".)
Trauma — Penetrating trauma to the EAC or meatus may cause mild to severe conductive hearing loss, depending upon the degree of EAC injury and occlusion.
Congenital malformations — The external auditory canal (EAC) develops from the 8th to the 28th week of gestation. Problems can occur anytime during this developmental phase. Microtia, the absence or malformation of the auricle, may be associated with mild to moderate conductive hearing loss, whereas atresia or significant stenosis of the EAC causes moderate to maximal (60 decibels [dB]) conductive hearing loss. 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 is bilateral atresia.
Congenital abnormalities of the outer ear may occur in isolation or may be part of a broader clinical syndrome (table 2). Outer ear malformations are reviewed in greater detail separately. (See "Congenital anomalies of the ear", section on 'Outer ear malformations'.)
Middle ear — Conductive hearing loss associated with the middle ear may be caused by infection, congenital anomalies, tympanic membrane perforation, or tumors.
Infection — Acute otitis media (AOM) is the most common childhood disorder associated with conductive hearing loss. By the age of three years, most children will experience at least one episode of AOM and many will have experienced at least three episodes (See "Acute otitis media in children: Epidemiology, microbiology, and complications", section on 'Epidemiology'.)
Conductive hearing loss occurs in AOM because fluid filling the middle ear space prevents the tympanic membrane from vibrating adequately, thereby diminishing movement of the ossicular chain. The hearing loss persists as long as fluid fills the middle ear space. The median loss is 25 dB, which is similar to the degree of hearing loss associated with the use of ear plugs. (See "Acute otitis media in children: Epidemiology, microbiology, and complications", section on 'Hearing loss'.)
Despite adequate therapy, middle ear effusion persists in many patients, a condition called otitis media with effusion (OME) or serous otitis media. In most cases, OME resolves spontaneously over approximately six weeks. Some children, particularly those at risk for speech delays or learning problems, may benefit from tympanostomy tube placement. This issue is discussed in greater detail separately. (See "Otitis media with effusion (serous otitis media) in children: Clinical features and diagnosis" and "Otitis media with effusion (serous otitis media) in children: Management".)
Tympanic membrane perforation — Conductive hearing loss caused by tympanic membrane perforation is common. 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 a lesser degree of conductive hearing loss. Near-total or posterior/superior quadrant perforations are more likely to cause significant hearing loss.
Tympanic membrane perforations can be caused by many events, including blast injury, barotrauma, foreign body trauma, temporal bone fractures, ear infections, self-inflicted trauma from a cotton-tipped applicator or other object (picture 1); or the hole may persist after tympanostomy tubes fall out. In a study of 602 children presenting to the emergency department with traumatic tympanic membrane perforation, more than one-half of the injuries occurred in children <6 years old [11]. Foreign bodies (especially cotton-tipped applicators) were the most common cause in children <12 years old; whereas the leading cause in children 13 to 18 years old was water trauma (ie, from forced pressure of water to the head during diving or waterskiing, barotrauma [eg, scuba-related], or injury from otitis externa following swimming).
After an acute perforation, the ear should be examined to ensure that the perforation heals without cholesteatoma formation. Documentation of a patient's auditory status also is mandatory for any newly-diagnosed perforation. (See "Cholesteatoma in children".)
Trauma — Blunt trauma can lead to temporal bone fracture, usually by a blow to the temporal parietal region (image 1). Hearing loss due to temporal bone fracture is typically conductive and associated with tympanic membrane perforations and blood in the middle ear space. Conductive hearing loss can occur with ossicular injury, typically due to separation of the incudostapedial joint and/or incus dislocation. Otic capsule fractures are more frequently associated with sensorineural hearing loss, facial nerve injury, or cerebrospinal fluid leak. (See 'Sensorineural hearing loss' below.)
Evaluation and management of middle ear trauma is discussed in greater detail separately. (See "Evaluation and management of middle ear trauma".)
Tumors — Malignant tumors, such as squamous cell carcinoma and proliferative disorders, including Langerhans cell histiocytosis, can cause conductive hearing loss. However, these entities are relatively rare when compared with nonmalignant cholesteatoma or otosclerosis.
●Cholesteatoma – Cholesteatoma is a benign growth of stratified, squamous epithelium filled with desquamated cells and keratin (picture 2). As keratin desquamates from the epithelial lining of the sac, it gradually enlarges, with eventual erosion of the ossicular chain, mastoid air cells, and EAC. Formation of a cholesteatoma typically occurs after a retraction pocket has formed in the posterior/superior quadrant of the tympanic membrane, usually the result of poor Eustachian tube function. It may also occur after tympanic membrane trauma, such as a traumatic, inflammatory, or iatrogenic perforation. A small percentage of cholesteatomas are congenital and occur most commonly in the anterior superior portion of the middle ear space, where they appear as a whitish pearl behind an intact tympanic membrane. (See "Cholesteatoma in children".)
●Otosclerosis – Otosclerosis is an abnormality of bone remodeling that produces overgrowth of sclerotic, hypervascular bone. It has a predilection for the footplate of the stapes. As the overgrowth develops, stapes motion is impaired and ossicular vibrations are not effectively transmitted to the inner ear fluid. Conduction gradually becomes worse until a maximal conductive hearing loss of 60 dB is reached. In most affected patients, the conductive hearing loss progresses gradually over several decades and eventually includes a significant sensorineural component. Otosclerosis is uncommon in children and very rarely recognized in the first decade of life.
Congenital malformations — Congenital malformations of the ossicles may cause conductive hearing loss. Ossicular and other middle ear malformations occur as part of syndromes (eg, Treacher Collins, branchio-oto-renal, Stickler, velocardiofacial (DiGeorge), Beckwith-Wiedemann) and, occasionally, as isolated events. They may or may not be associated with EAC stenosis and/or microtia.
The most common abnormalities of the ossicles are fixation of the malleus and/or incus, incudostapedial discontinuity, and stapes fixation. These defects in the middle ear's conducting mechanism cause hearing losses ranging from minor to maximal (60 dB) and have important effects on communication and learning.
Osteogenesis imperfecta is an autosomal dominant condition associated with fragile bones that fracture easily. Children with this disorder may develop ossicular dislocation, stapes fixation, or fracture of the ossicles, resulting in a conductive hearing loss. (See "Osteogenesis imperfecta: An overview".)
SENSORINEURAL HEARING LOSS — Sensorineural hearing loss (SNHL) results from damage, disease, or other disorders affecting the inner ear (cochlea) and/or the auditory nerve. SNHL can be categorized as congenital (including both hereditary and nonhereditary causes) and acquired (table 1).
Congenital — Congenital hearing loss is any hearing loss that is identified at or shortly after birth. It may be hereditary or nonhereditary. Nonhereditary etiologies involve an insult to the developing cochlea, such as intrauterine infection, medications, or toxins that have a teratogenic effect on the developing ear of the fetus (eg, alcohol, methyl mercury, quinine, trimethadione, retinoic acid, and maternal thyroid peroxidase autoantibodies) [10,12].
Infection — Congenital infection caused by cytomegalovirus (CMV), toxoplasmosis, rubella, or syphilis is associated with SNHL. The hearing loss in these conditions frequently is progressive or delayed in onset, emphasizing the need for universal newborn hearing screening and continued monitoring of children with known congenital infections. (See "Screening tests in children and adolescents", section on 'Hearing screen' and "Screening the newborn for hearing loss".)
●Congenital CMV infection (cCMV) – cCMV is the leading infectious cause of congenital SNHL [13]. SNHL can occur in infants with overtly symptomatic infection (symptomatic cCMV) and in those who lack apparent symptoms (asymptomatic cCMV). CMV-associated hearing loss is highly variable and can be progressive or delayed and unilateral or bilateral. Early treatment with antiviral therapy has been shown to improve hearing outcomes for neonates with congenital CMV infection. This is discussed separately. (See "Congenital cytomegalovirus infection: Clinical features and diagnosis" and "Congenital cytomegalovirus infection: Management and outcome", section on 'Antiviral treatment'.)
Importantly, an isolated finding of hearing loss in an infant with otherwise asymptomatic congenital CMV infection does not exclude genetic causes of hearing loss, which should also be considered [14]. (See "Hearing loss in children: Screening and evaluation", section on 'Identifying the etiology'.)
●Congenital toxoplasmosis – SNHL can occur in children with congenital toxoplasmosis, although the exact incidence is unclear [15]. The hearing loss can be delayed and progressive [16], and the hearing prognosis may be improved if the infection is diagnosed prenatally or shortly after birth and prompt treatment is provided [15]. (See "Congenital toxoplasmosis: Clinical features and diagnosis", section on 'Clinical features' and "Congenital toxoplasmosis: Treatment, outcome, and prevention", section on 'Treatment'.)
●Congenital rubella – Hearing loss affects 68 to 93 percent of children with congenital rubella. It is usually profound and bilateral and sometimes progressive [10]. (See "Congenital rubella".)
●Congenital syphilis – SNHL is a late manifestation of congenital syphilis, typically developing suddenly at 8 to 10 years of age. The higher frequencies are affected first; normal conversational tones are affected later. SNHL in this setting is the result of inflammation from untreated disease and can be prevented by appropriate therapy before three months of age. (See "Congenital syphilis: Clinical manifestations, evaluation, and diagnosis", section on 'Late congenital syphilis'.)
●Congenital Zika virus infection – SNHL has been reported in 5 to 10 percent of infants with congenital Zika virus infection. SNHL occurs predominantly in infants with severe central nervous system involvement. (See "Congenital Zika virus infection: Clinical features, evaluation, and management of the neonate", section on 'Clinical findings'.)
Malformations — Congenital malformations (dysplasias) of the inner ear cause SNHL. High-resolution computed tomographic and magnetic resonance imaging techniques can identify subtle variations in anatomy that my lead to variable degrees of hearing loss. Children with hereditary (genetic) SNHL have a high incidence of minor malformations of the semicircular canals, cochlea, and internal auditory canal. Inner ear malformation are discussed in greater detail separately. (See "Congenital anomalies of the ear", section on 'Inner ear malformations'.)
Perilymph fistula — Perilymph fistula (PLF) is a leak of inner ear fluid through a defect in the otic capsule. Leaks at the round window membrane or the oval window annular ligament may occur. PLFs permit communication between the middle ear and the inner ear. They can be caused by trauma or by a congenital defect of the stapes footplate.
PLF is uncommon and difficult to diagnose. Typical symptoms include fluctuating severe SNHL, dysequilibrium, and aural fullness. Exploratory surgery performed by an otolaryngologist may be necessary to provide a definite diagnosis and to repair the leak.
Hereditary — Hereditary (genetic) bilateral SNHL occurs in approximately 1 in 2000 births [8]. In developed countries, it accounts for 50 to 60 percent of cases of SNHL in children [17]. Approximately one-third are syndromic (associated with other abnormalities (table 3)) and two-thirds nonsyndromic [18-20].
The hearing deficit in hereditary hearing loss (HHL) may be present at birth (congenital), progressive from birth, or it may develop when the child is older.
Approximately 80 percent of cases of HHL are inherited in an autosomal recessive pattern, 15 percent are autosomal dominant, 2 percent are X-linked (mainly recessive) [21], and 1 percent are mitochondrial [18]. A complete list is available on the Hereditary Hearing Loss website. Because HHL is most often inherited as an autosomal recessive trait, many children with HHL will not have affected relatives.
The identification of genetic causes of hearing loss has improved the understanding of the biology of hearing and deafness and has changed the evaluation of children with congenital hearing loss. Next to the audiogram, comprehensive genetic testing has become a critical tool in the diagnosis, evaluation, and management of the hearing-impaired child, particularly in children with bilateral SNHL [22,23]. The approach to genetic testing in children with SNHL is reviewed separately. (See "Hearing loss in children: Screening and evaluation", section on 'Genetic testing'.)
Syndromic sensorineural hearing loss — Approximately one-third of HHL is syndromic (associated with other abnormalities) (table 3). The more common syndromes include:
●Syndromes with an autosomal recessive inheritance pattern:
•Usher syndrome, a form of retinitis pigmentosa, which is associated with progressive vision loss (see "Retinitis pigmentosa: Clinical presentation and diagnosis")
•Pendred syndrome, in which SNHL is accompanied by thyroid disease or goiter
•Alport, which can have variable inheritance patterns and is associated with a family or personal history of kidney disease (see "Clinical manifestations, diagnosis, and treatment of Alport syndrome (hereditary nephritis)")
•Jervell-Lange-Nielsen syndrome (long QT syndrome with deafness) (See "Congenital long QT syndrome: Epidemiology and clinical manifestations".)
●Syndromes with an autosomal dominant inheritance pattern:
•Waardenburg syndrome types I and II, which are associated with pigmentary abnormalities (picture 3) (see "The genodermatoses: An overview", section on 'Waardenburg syndrome')
•Alport (which can have variable inheritance patterns) or branchio-oto-renal syndrome, both of which are associated with a family or personal history of kidney disease (see "Clinical manifestations, diagnosis, and treatment of Alport syndrome (hereditary nephritis)")
•Neurofibromatosis I and II (See "Neurofibromatosis type 1 (NF1): Pathogenesis, clinical features, and diagnosis" and "NF2-related schwannomatosis (formerly neurofibromatosis type 2)".)
●Syndromes with an X-linked inheritance pattern:
•Alport syndrome (which can have variable inheritance patterns) (see "Clinical manifestations, diagnosis, and treatment of Alport syndrome (hereditary nephritis)")
•Hunter syndrome (mucopolysaccharidosis 2) (see "Mucopolysaccharidoses: Clinical features and diagnosis", section on 'MPS type II (Hunter syndrome)')
●Other syndromes that lack a clear or consistent inheritance pattern include:
•CHARGE syndrome, which is associated with choanal atresia, colobomas, heart defects, intellectual disability, genital hypoplasia, and ear anomalies (see "Congenital anomalies of the ear", section on 'Ear anomalies in CHARGE and DiGeorge syndromes')
•Hemifacial microsomia, which is characterized by mandibular hypoplasia, orbital distortion, and ear anomalies(picture 4) (see "Syndromes with craniofacial abnormalities", section on 'Craniofacial microsomia')
●Mitochondrial disorders – Mitochondrial inheritance accounts for less than 1 percent of all HHL. Transmission occurs through the maternal lineage. Hearing loss may be isolated or associated with other features of mitochondrial disorders such as lactic acidosis, encephalopathy, myopathy, seizures, ophthalmoplegia, diabetes mellitus, cardiomyopathy, stroke-like episodes, ataxia, and optic atrophy [24]. (See "Approach to the metabolic myopathies".)
Advances are being made in the understanding of the molecular biology of hearing [25-29]. As examples:
●Autosomal recessive Alport syndrome is associated with mutations in the alpha-3 or alpha-4 chains of type IV collagen [30]. The defect in hearing, as well as the associated renal disease, is caused by impaired formation of a unique type of collagen. (See "Genetics, pathogenesis, and pathology of Alport syndrome (hereditary nephritis)".)
●The defect in Jervell-Lange-Nielsen syndrome, which typically presents with bilateral profound SNHL and long QT on electrocardiogram, involves potassium conductance and impaired endolymph production [31]. (See "Congenital long QT syndrome: Pathophysiology and genetics".)
Nonsyndromic sensorineural hearing loss — Most children with HHL (approximately two-thirds) have nonsyndromic causes. These are increasingly recognized as causes of HHL in children and the list of genes that have been linked to HHL continues to expand. Approximately 120 genes have been linked with nonsyndromic HHL [24,32]. The two genetic variants that are identified most commonly are:
●GJB2 – Mutations in the GJB2 gene that encodes the protein connexin 26 (CX26) on chromosome 13 cause nearly one-half of all bilateral severe to profound congenital hearing loss in nonsyndromic children [19,27,33,34]. Mutations in this gene are also an occasional cause of autosomal dominant hearing loss that is often associated with palmoplantar keratoderma [35,36].
●STRC – The most common cause of mild to moderate nonsyndromic recessive hearing loss is mutation of the STRC gene. This gene encodes the protein stereocilin, which is often deleted together with the neighboring gene, CATSPER2 [37]. Males deleted of both copies of STRC and CATSPER2 have infertility as well as mild to moderate hearing loss; females only have hearing loss [37].
Both of these have an autosomal recessive inheritance pattern. Other forms of nonsyndromic HHL can have an autosomal recessive or autosomal dominant inheritance pattern. X-link inheritance is uncommon, but at least five genes with this an X-linked pattern have been reported [32,38]. Nonsyndromic autosomal dominant disorders that cause progressive SNHL may present with early onset (during the first decade of life) or delayed onset (during the second or third decade) [18].
A complete list of genes linked to HHL is available on the Hereditary Hearing Loss website.
Acquired sensorineural hearing loss — Causes of acquired SNHL include prematurity, infection, hyperbilirubinemia, ototoxins, noise, and tumors.
Prematurity — Approximately 0.5 to 2.4 percent of very low birth weight (<1500 g) infants develop SNHL [39,40]. The risk of hearing loss increases with decreasing birth weight and gestational age [40].
The high rate of hearing loss among preterm infants has been linked to several factors, including administration of ototoxic drugs, such as aminoglycoside antibiotics, ambient noise produced by the incubator [41], and perinatal complications (eg, hypoxia, acidosis, and hyperbilirubinemia) [42,43]. Continued improvements in obstetrical and newborn care have led to decreased mortality in premature infants. As further advances are made in this area, decreased mortality will pose an increased risk of developmental disabilities, including hearing loss, for premature and low birth weight babies [44,45]. (See "Care of the neonatal intensive care unit graduate", section on 'Hearing'.)
Universal newborn hearing screening is recommended for all newborns, and this is particularly important in preterm neonates. Newborn hearing screening is discussed separately. (See "Screening the newborn for hearing loss".)
Hyperbilirubinemia — Hyperbilirubinemia in newborns can result from isoimmune hemolytic disease (eg, ABO blood group incompatibility), enzymatic defects (eg, glucose-6-phosphate-dehydrogenase deficiency), sepsis, increased enterohepatic circulation (eg, breast milk jaundice), and numerous other causes that are reviewed separately. (See "Etiology and pathogenesis of neonatal unconjugated hyperbilirubinemia", section on 'Causes of significant unconjugated neonatal hyperbilirubinemia'.)
Severe hyperbilirubinemia can lead to SNHL because bilirubin is toxic to the cochlear nuclei and the auditory neural pathways (ie, auditory neuropathy). The risk of hearing loss is greatest in infants with hyperbilirubinemia above the threshold for exchange transfusion (figure 2) [46]. In one study of 100 neonates with severe hyperbilirubinemia (ie, at or above the threshold for exchange transfusion), 28 percent were found to have evidence of auditory toxicity [47]. In addition, preterm infants with prolonged hyperbilirubinemia, particularly if it coincides with episodes of acidosis, appear to be at increased risk for SNHL [48]. (See "Risk factors, clinical manifestations, and neurologic complications of neonatal unconjugated hyperbilirubinemia", section on 'Incidence'.)
Infection — Bacterial meningitis is the most common cause of postnatally acquired deafness in childhood [49,50]. The reported frequency of persistent hearing loss varies from 2.5 to 18 percent in survivors [49-52]. Another 10 percent of children have transient hearing loss [52]. (See "Bacterial meningitis in children: Neurologic complications".)
SNHL occurs early in the course of bacterial meningitis (within the first 48 hours), with possible recovery or worsening during the first two weeks of illness [53,54]. Permanent hearing loss may be caused by damage to the cochlea, labyrinth, or eighth cranial nerve from direct bacterial invasion or the inflammatory response elicited by the infection [51,55]. Labyrinthitis detected by gadolinium-enhanced magnetic resonance imaging early in the course of disease is predictive of the development of SNHL [56].
In some studies, treatment with dexamethasone very early in the course of meningitis decreased the incidence of hearing loss and neurologic sequelae, especially when the causative pathogen was Haemophilus influenzae type b. Whether dexamethasone reduced the rate of hearing loss with other bacterial etiologies is less certain. This issue is discussed separately. (See "Bacterial meningitis in children: Dexamethasone and other measures to prevent neurologic complications".)
Children who have had bacterial meningitis should have a prompt and complete hearing evaluation initially and regular follow-up if the evaluation is abnormal. These children may be candidates for early cochlear implantation (before the onset of cochlear ossification). (See "Hearing loss in children: Screening and evaluation".)
Ototoxic drugs — Ototoxic drugs, such as aminoglycosides, high-dose intravenous loop diuretics, and chemotherapeutic agents, such as cisplatin, can cause significant hearing loss [57,58]. The hearing loss caused by antibiotic or chemotherapeutic agents usually begins at high frequencies. The hearing loss becomes more pronounced with continued use and may even continue to worsen after the drug is discontinued. SNHL associated with many of these drugs is permanent.
●Aminoglycosides – All aminoglycosides are ototoxic. Some are more vestibulotoxic than cochleotoxic. In addition, renal impairment may increase the chance of ototoxicity. The relative order of cochleotoxicity is gentamicin>tobramycin>amikacin>neomycin. Individuals with mutations in some of the mitochondrial genes have a genetic predisposition to the development of ototoxicity when exposed to even small doses of aminoglycosides [59,60]. (See "Pathogenesis and prevention of aminoglycoside nephrotoxicity and ototoxicity".)
Otoacoustic emissions, which reflect the functional status of the outer hair cells in the cochlea, are a sensitive measure of the early effects of aminoglycoside-induced injury to the peripheral auditory system [61] and may be useful in monitoring cochlear function during ototoxic treatment. (See "Hearing loss in children: Screening and evaluation", section on 'Otoacoustic emissions'.)
●Other antibiotics – Other antibiotics that can cause ototoxicity include the macrolides (erythromycin, clarithromycin, and azithromycin), vancomycin, and tetracycline. These drugs may have a more pronounced ototoxic effect in patients with impaired renal function.
●Chemotherapeutic agents – Numerous chemotherapeutic agents can cause hearing loss. The most common ones are cisplatin, 5-fluorouracil (5-FU), bleomycin, and nitrogen mustard. Of these, the risk of clinically significant hearing loss is greatest with cisplatin, as discussed separately. (See "Overview of neurologic complications of platinum-based chemotherapy", section on 'Ototoxicity'.)
●Salicylates – Aspirin and other nonsteroidal antiinflammatory drugs can cause hearing loss that is reversible with discontinuation of the drug. The etiology is believed to be enzymatic inhibition, which occurs only at very high doses (eg, 6 to 8 g/day of aspirin).
●Other medications – Antimalarial medications, such as quinine and chloroquine, can cause SNHL and tinnitus, but as with salicylates, these effects are usually reversible. High-dose intravenous loop diuretics are an additional cause of temporary hearing loss and tinnitus [62]. The risk is increased if the patient is also receiving other ototoxins, such as an aminoglycoside [58].
Noise exposure — Noise exposure is the most common modifiable cause of hearing loss in children. Constant exposure to loud noises, as may occur with personal listening devices [63], can cause high-frequency SNHL. In the United States, the estimated prevalence of noise-induced hearing loss (NIHL) in one or both ears among children aged 6 to 19 years is 12.5 percent; for adolescents aged 12 to 19 years, the estimated prevalence is 20 percent [64]. The figure represents a typical audiogram of noise-induced SNHL (figure 3). The worst hearing loss is at 4000 Hz; it improves at 8000 Hz. However, hearing at higher frequencies will decline over time.
The mechanism by which excessive noise induces hearing loss includes direct mechanical damage of cochlear structures and metabolic overload caused by overstimulation [65]. Some potential metabolic effects are excess nitric oxide release, which 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 Occupational Safety and Health Administration (OSHA) and National Institute for Occupational Safety and Health (NIOSH) have set standards and guidelines for noise exposure in order to protect workers in the United States. OSHA requires all employees who are exposed to a greater than 85 decibel (dB) time-weighted average (85 dBA) to be enrolled in a hearing conservation program and provided with hearing protection. OSHA also limits employee's exposure to noise as follows: eight hours of exposure to 90 dBA (which is equivalent to the noise made by a power lawn mower); four hours of exposure to 95 dBA; two hours of exposure to 100 dBA; and so on [66]. NIOSH limits noise exposure as follows: eight hours to 85 dBA, four hours to 88 dBA, two hours to 91 dBA, and so on [67].
The OSHA and NIOSH standards are not necessarily applicable to portable music-listening devices, since music differs from industrial noise spectrally and temporally [63]. However, studies documenting the output levels of various portable listening devices (compact disc [CD] players and digital music players) have been used to develop safety guidelines based upon NIOSH standards [68,69].
●For the typical listener, listening to a portable listening device with supra-aural headphones (earphones that sit on top of the ear) at 60 percent maximum volume should be limited to less than one hour per day in order to reduce the risk of NIHL [68].
●For the typical listener, listening to a digital music player with the earphones that came with the device at 70 percent of maximum volume should be limited to less than 4.6 hours per day, and at 80 percent of maximum volume should be limited to less than 1.2 hours per day in order to reduce the risk of NIHL [69].
The listening times should be adjusted according to presence of other risk factors for hearing loss (eg, ototoxic drugs) [68].
A short blast of loud noise also can cause severe to profound SNHL, pain, or hyperacusis (loudness intolerance). This reaction usually involves exposure to noise greater than 120 to 155 dB (eg, an ambulance siren or a firecracker). Thus, hearing protection in the form of muffs or plugs is highly recommended any time a person is exposed to loud noises.
Another important consequence of noise exposure is that is can cause "hidden hearing loss" (ie, a deficit that is not apparent on a standard audiogram but that affects an individual's ability to extract meaning from sounds in the presence of background noise). Believed to be a synaptopathy, hidden hearing loss reflects defects in cochlear transmission of acoustic signals [70,71].
Trauma — Trauma to the temporal bone usually causes sensorineural or mixed hearing loss. Both penetrating and blunt trauma can result in temporal bone fractures. Penetrating trauma is typically due to gunshot wounds and blunt trauma to blows to the occipital or frontal regions. Temporal bone fractures that violate the otic capsule may run through the inner ear and result in a "dead" ear (image 1). Blunt trauma also causes SNHL when concussive forces are exerted on the inner ear fluids, causing a shearing effect on the cochlear organ of Corti. (See "Evaluation and management of middle ear trauma" and "Skull fractures in children: Clinical manifestations, diagnosis, and management".)
Tumors — The most common tumor that causes SNHL is a vestibular schwannoma (acoustic neuroma), which is rare in children except in those with NF2-related schwannomatosis (NF2). These benign tumors usually originate from the vestibular portion of the eighth cranial nerve. Acoustic neuromas associated with NF2 are typically bilateral and asymmetric [72]. Other symptoms and signs include tinnitus, disequilibrium, dizziness, headaches, facial hyperesthesia, facial muscular twitching, and facial paresis/paralysis. (See "Vestibular schwannoma (acoustic neuroma)".)
Heavy metals — Cadmium, mercury, and arsenic may have toxic effects on cochlear cells, and mercury exposure may cause delayed auditory brainstem evoked potentials [73]. In addition, lead can have neurotoxic effects. In a series of 2535 adolescents aged 12 to 19 years, those with a blood lead level of ≥2 mcg/dL had a twofold increased odds of high-frequency hearing loss compared with those with a lead level <1 mcg/dL [74].
CENTRAL AUDITORY DISORDERS
Cortical deafness — Cortical deafness refers to hearing loss associated with brain injury or disease. The abnormality may be due to global brain injury or lesions in areas involved in auditory neural processing, from the cochlear nucleus of the brainstem to the primary auditory complex in the temporal lobe of the brain. Patients with cortical deafness may have profound hearing loss despite having normal peripheral auditory systems.
Central auditory processing disorder — Central auditory processing disorder (CAPD) refers to inefficient and/or ineffective processing and utilization of auditory information by the central nervous system. CAPD may be clinically significant in that patients have normal hearing sensitivity yet have difficulty interpreting sounds in complex situations such as speech or with background noise. However, it is challenging to distinguish CAPD from other language and learning disabilities, and there is ongoing controversy as to whether CAPD truly represents a distinct clinical entity [75,76]. There is considerable variation in criteria used to define and diagnose CAPD. The diagnosis cannot be made with audiologic testing alone and usually requires a battery of behavioral tests [77]. (See "Etiology of speech and language disorders in children", section on 'Central auditory processing disorder'.)
SUMMARY
●Significant hearing loss is uncommon in newborns and young children. However, nearly all children develop transient hearing loss related to ear infections during early childhood. Hearing loss in the first years of life can cause delays in speech, language, and cognitive development. The causes of hearing loss in infancy and childhood are diverse (table 1). Knowledge of the etiology of the hearing loss, particularly if genetic, can facilitate genetic counseling and assist in the development of the optimal habilitation plan for the child. (See 'Introduction' above.)
●The ear is divided into three segments (figure 1A-B) (see 'Anatomy and physiology' above):
•Outer ear, comprising the auricle and ear canal
•Middle ear, comprising the tympanic membrane, ossicles, and middle ear space
•Inner ear, comprising the cochlea, semicircular canals, and internal auditory canals
●Conductive hearing loss is caused by a mechanical problem of the outer or middle ear that interferes with conduction of sound to the inner ear. It can occur at any location from the outer ear (pinna, external auditory canal) to the stapes footplate and oval window. Common examples include cerumen impaction, middle ear fluid, and ossicular chain fixation. Other causes are summarized in the table (table 1). (See 'Conductive hearing loss' above.)
●Sensorineural hearing loss (SNHL) results from damage, disease, or other disorders affecting the inner ear (eg, the cochlea) and/or the auditory nerve. SNHL can be categorized as congenital (including both hereditary and nonhereditary causes) and acquired (see 'Sensorineural hearing loss' above):
•Hereditary causes account for 50 to 60 percent of cases of SNHL; approximately one-third are syndromic (associated with other abnormalities (table 3)) and two-thirds nonsyndromic. The hearing deficit in hereditary hearing loss may be present at birth (congenital), progressive from birth, or develop when the child is older. (See 'Hereditary' above.)
•Nonhereditary etiologies of congenital SNHL involve an insult to the developing cochlea, such as intrauterine infection, medications, or toxins that have a teratogenic effect on the developing ear of the fetus. (See 'Congenital' above.)
•Causes of acquired SNHL include prematurity, infection, hyperbilirubinemia, ototoxins, noise, trauma, and tumors (table 1). (See 'Acquired sensorineural hearing loss' above.)
●Central causes of hearing loss include cortical deafness (ie, deafness associated with brain injury) and central auditory processing disorder (CAPD). CAPD refers to inefficient and/or ineffective processing and utilization of auditory information by the central nervous system. There is considerable variation in criteria used to define and diagnose CAPD, and it is challenging to distinguish CAPD from other language and learning disabilities. (See 'Central auditory disorders' above.)
