CHAPTER 88

Hearing Impairments

Patricia Padlipsky, MD, FAAP

Any amount of hearing loss, whether unilateral or bilateral, can cause a significant childhood disability that can compromise speech and language development, academic performance, and social and emotional development. It is essential to identify hearing loss as soon as possible to implement early intervention, which has been shown to prevent many adverse consequences. Children may be born with a hearing deficit (ie, congenital deafness), or they may acquire the condition during childhood (ie, late-onset deafness). Hearing loss also may be progressive and not identified on early screening. Hearing loss can be classified as conductive, sensorineural, mixed, or auditory neuropathy spectrum disorder (ANSD). Hearing loss is further described by the degree of loss, whether mild (26–40 dB loss), moderate (40–70 dB loss), severe (71–90 dB loss), or profound (>90 dB loss). The most important period for speech and language development is from birth to 3 years of age. Reduced hearing acuity in both ears or even 1 ear during this time can significantly interfere with this important process (see Chapter 33). Therefore, the primary care physician must have a clear understanding of when to suspect impaired hearing in infancy and early childhood and must be familiar with the identification of, evaluation methods for, and treatment options for hearing loss.

Epidemiology

The prevalence of congenital deafness in children is approximately 0.1%. In other words, 1 in 1,000 children is born with severe to profound hearing loss. The prevalence increases to 6 in 1,000 when all degrees of hearing loss, mild to profound, are considered. By age 18 years, it is estimated that 17 in 1,000 children have some degree of permanent hearing loss. This increase over time reflects the addition of patients with progressive, acquired, or late-onset genetic causes. Diagnostic findings for ANSD often are not conclusive in newborns because language skills are still developing and not aberrant at the time of newborn screening.

Prior to the initiation of newborn hearing screening, the average age at diagnosis of most children who were born with hearing impairment was 2 to 3 years. Since the advent of such screening, however, the average age at diagnosis has dropped to 2 to 3 months. Currently, all 50 states have a universal newborn hearing screening as well as early hearing detection and intervention programs. More than 95% of all newborns are screened, and 74% of those found to have hearing impairment have entered an intervention program by 6 months of age. As with any screening program, however, some newborns are missed, especially with at-home births. Additionally, as many as 40% of identified newborns are currently lost to follow-up, and some forms of early-onset hearing loss are not apparent at birth. Therefore, careful assessment of hearing and language development by the medical professional is essential at each patient encounter.

More than 90% of children with deafness are born to hearing parents. An estimated 20% to 30% of children with hearing impairment develop the condition during childhood. Of these, 70% of children with acquired hearing loss are initially identified by parents rather than physicians. Any concern by parents that their child might have a hearing problem should be taken seriously by the physician and objective testing performed. Risk factors for acquired hearing loss in childhood include persistent otitis media with effusion, history of head trauma, bacterial meningitis, and identification of syndromes or neurologic disorders associated with hearing loss.

Graduates of the neonatal intensive care unit are at significantly increased risk for sensorineural hearing loss (SNHL) and ANSD, with reported rates of SNHL and ANSD of 16.7 and 5.6 per 1,000 infants, respectively, compared with an estimated incidence of ANSD in a well-baby population of 0.06 per 1,000 infants. Diagnostic findings for ANSD often are not conclusive in newborns because language skills are still developing and not aberrant at the time of newborn screening. Associated factors, such as preterm birth (birth weight <1,500 g [<3.3 lb]), hyperbilirubinemia, prolonged mechanical ventilation, extracorporeal membrane oxygenation treatment, perinatal asphyxia, exposure to ototoxic drugs, and neonatal sepsis increase the risk for ANSD. Other factors associated with deafness in childhood include meningitis, parental consanguinity, craniofacial malformations, congenital viral infections, exposure to chemotherapy, and a family history of deafness.

Clinical Presentation

The newborn may present to the primary care physician having had an abnormal newborn hearing screening test. The initial newborn screening is mandated by 1 month of age, with definite testing by an audiologist for abnormal tests by 3 months of age. Intervention should begin by 6 months. For the infant who passes hearing testing but has positive risk factors for hearing impairment (Box 88.1), communication skills should be assessed at every well-child visit and diagnostic audiologic assessment should be done by 24 to 30 months of age.

In the unscreened population or for children with progressive or acquired hearing loss, parents are often the first to suspect hearing loss. A parent may be concerned that the toddler is indicating needs by grunting and pointing rather than using words or that the child does not seem to respond to sounds. Children with hearing impairments frequently present to physicians with delayed speech or speech impediments; children produce what they hear.

Normal speech volumes range from 30 to 50 dB, whereas typical street traffic volume is approximately 60 dB. Standard telephone rings and shouts are approximately 80 dB, and lawnmowers are approximately 90 dB. Therefore, children with a 50-dB hearing loss may hear their mother when she yells at them and may startle when the telephone rings. However, they do not hear most conver-sational speech, and they may not always hear the teacher in a classroom, especially if they are not in the front and in the setting of significant extraneous noise. This can result in behavioral problems, such as inattention, temper tantrums, and aggressive play with other children (Box 88.2).

Abbreviation: SNHL, sensorineural hearing loss.

Worsening speech or school performance may herald long-standing or progressive mild-to-moderate hearing loss. Other presentations of mild or progressive hearing loss may consist of either withdrawal from social activities and playing alone or playing the television and music at increasingly loud volumes.

Hearing impairment can be particularly difficult to recognize in infants younger than 6 months because they may have no obvious symptoms of a hearing deficit. They may startle to moderately loud noises and begin to vocalize as other infants do (Figure 88.1). If the history is suggestive of a hearing deficit or a parent or caregiver expresses concern, audiologic testing should be performed.

Pathophysiology

Mechanism of Hearing

Sounds in the form of pressure waves are carried from the environment through the external auditory canal to the tympanic membrane (TM). These waves are converted to mechanical vibrations by the ossicles, and the mechanical vibrations are then transmitted from the TM to the inner ear, where they are transformed to fluid vibrations. Finally, these fluid vibrations are converted into nerve impulses by nerve endings within the organum spirale located in the cochlea in the inner ear. These impulses are conducted via the auditory nerve to the auditory cortex (Figure 88.2).

Hearing impairments can be classified according to the part of the auditory system affected or by the cause of the hearing loss.

Types of Hearing Loss

A conductive hearing loss (CHL) denotes an abnormality from the pinna, external auditory canal, TM, or middle-ear ossicles. Conductive hearing loss can occur in congenital anomalies, such as atresia, impacted cerumen, otitis externa, serous otitis media, otitis media with effusion, TM perforation, ossicular discontinuity, and otosclerosis. An SNHL is an abnormality that affects the cochlea, inner ear, or auditory nerve. Congenital infections, anomalies, genetic disorders, and loud noise result in this type hearing loss. The loss of cochlear function, usually from damage to sensory hair cells in the organum spirale, is the main cause of permanent childhood hearing loss. A mixed disorder has characteristics of both conductive and sensorineural losses. In retrocochlear hearing loss, the auditory nerve, brain stem, or cortex is affected. This includes ANSD noted in neonates after neonatal intensive care unit stays. In auditory neuropathy, sound enters the ear normally, but because of damage to the inner ear or the hearing nerve, sound is not organized in a way that the brain can understand.

Figure 88.1. Loudness of everyday sounds.

Figure 88.2. Sound waves (represented by arrows) passing through the external ear into the middle ear.

Etiology of Hearing Impairment

The causes of hearing loss can be broadly divided into genetic and acquired and further divided into congenital and/or progressive (Table 88.1). Of the 1 in 1,000 individuals born with severe to profound hearing loss, the cause is genetic in approximately 50%, nongenetic in approximately 25%, and idiopathic in approximately 25%. Of the 50% with a genetic cause, the hearing loss is syndromic in 30% and nonsyndromic in 70%. More than 500 forms of syndromic hearing loss exist, each with associated clinical features. Most of these syndromes are rare. Waardenburg syndrome is the most common type of autosomal dominant syndrome with SNHL. Usher syndrome and Pendred syndrome with goiter are examples of autosomal recessive syndrome with SNHL. Down (ie, trisomy 21) syndrome and oculoauriculovertebral dysplasia (ie, Goldenhar syndrome) often have associated hearing impairment. Alport syndrome with progressive SNHL and nephritis is also well recognized and is X-linked. Most cases of genetic hearing loss are nonsyndromic, however, and result from a single gene defect encoding connexin 26 protein. This recessive disorder with mutations in the GJB2 gene accounts for 30% to 50% of all cases of nonsyndromic hearing loss. Genetic malformations of the ear pinnae or ossicles do occur but are the least common cause of hearing loss. Genetic mutations may result in different types of deafness with various presentations and outcomes, that is, hearing loss may be conductive, sensorineural, or mixed and may be static or progressive, with the initial presentation in infancy or later childhood.

Acquired environmental causes of hearing loss include prenatal, perinatal, or postnatal events and exposures, such as congenital infections, bacterial meningitis, hyperbilirubinemia, complications of prematurity, and exposure to ototoxic drugs. Cytomegalovirus (CMV) likely is the most frequently unrecognized congenital infection causing deafness. Even if an infant is asymptomatic from the CMV infection, a 10% to 15% chance exists that the infant will develop an SNHL. Other congenital infections, such as toxoplasmosis, measles, mumps, rubella, herpes simplex virus, HIV, and syphilis can also cause hearing loss. Hearing loss associated with bacterial meningitis accounts for as many as 20% of cases, with Streptococcus pneumoniae as the prevalent responsible organism. The incidence of S pneumoniae and Haemophilus influenza type b meningitis has decreased tremendously in young children following the advent of conjugate vaccine, and the prevalence of postmeningitic hearing loss has similarly declined. The role of steroids in the management of bacterial meningitis has also contributed to the decrease in SNHL in survivors.

With the recognition and treatment of hyperbilirubinemia in term newborns, hyperbilirubinemia as a cause of hearing loss is now rare in the United States and other developed countries. Preterm birth as a cause of hearing loss is, however, not uncommon. Because of associated complications, preterm newborns have higher rates of severe hearing loss than do term newborns. Some antibiotics (eg, aminoglycosides) and other medications (eg, loop diuretic agents) can be irreversibly ototoxic; other drugs may cause only transient effects.

Any head injury, especially if the injury damages the temporal bone, can cause deafness in children. Fractures through the cochlea and vestibule can result in severe to profound hearing loss, and damage to the TM and/or ossicles can result in a significant CHL. Acoustic trauma (ie, noise-induced hearing loss) from continuous or significant exposure to loud noise can also cause irreversible SNHL. With children’s use of personal listening devices, the prevalence of this cause of hearing loss is increasing.

Hearing loss caused by middle ear effusions is the most common cause of childhood hearing loss. It is often not discussed because it is usually considered benign and transient in nature. However, of all ears with resolved otitis media persistent fluid is exhibited in 40% at 1 month, 20% at 2 months, and 10% at 3 months after infection or after the conclusion of treatment. It is important to identify whether this effusion is affecting the child’s hearing. Speech development is greatest in the first 3 years after birth and can be affected if a child has chronic effusion that is causing hearing loss. Any concern for hearing loss warrants objective testing, and consultation with an otolaryngologist should be recommended.

Adapted with permission from Gifford KA, Holmes MG, Bernstein HH. Hearing loss in children. Pediatr Rev. 2009;30(6):207–216.

Differential Diagnosis

In addition to hearing loss, communication disorders should be considered in the infant or child with delayed speech and language development. These include problems with speech perception, language comprehension, formulation of language output, and speech production. Unrecognized conditions, such as intellectual disability or autism spectrum disorder, are responsible for some of these disorders. Other etiologies include specific central nervous system deficits as well as impairments of fine motor control of the oropharynx.

Evaluation

Newborn Hearing Screening

The earlier the diagnosis of hearing loss is made, the sooner interventions can be initiated to help the child develop. In 1994, the Joint Committee on Infant Hearing (JCIH), composed of representatives from several professional organizations, endorsed universal newborn hearing screening. The goal was the early identification of hearing loss in newborns and infants before age 3 months and the implementation of intervention services by age 6 months. As a result of these recommendations, states have implemented legislation mandating newborn hearing screening and intervention programs. A subsequent position statement was issued in 2000. The American Academy of Pediatrics endorsed this statement and promoted newborn hearing screening as well as periodic hearing assessment for every child. As a result, hearing screening has been established as an essential newborn evaluation; however, a significant need exists to improve infrastructure to ensure that physicians receive and process screening results. The JCIH policy statement was most recently updated in 2007 and includes more specific guidelines for diagnostic audiologic evaluation, medical evaluation, and surveillance screening in the medical home. Per the policy, all infants and children— regardless of hearing screening results—should undergo ongoing assessment of communication skills beginning at 2 months of age. Any child with evidence of hearing loss in 1 ear or both ears should be offered early intervention. In 2013, a supplement was published to the 2007 JCIH position statement describing principles and guidelines for early intervention after a child is diagnosed with hearing impairment.

History

Because the primary symptom of hearing impairment or deafness is failure to learn to speak at the appropriate age, the most important aspect of the history in the child with possible hearing loss is determining whether speech is developing normally. Even an infant with deafness may begin cooing and babbling in infancy, and these early attempts at verbalization are not useful milestones for assessment of hearing deficits. It helps to ask the parent or guardian whether that individual is at all suspicious or concerned about the child’s speech or hearing. Guidelines for assessing language development are found in Table 88.2 (also see Chapter 33). It is also important to assess for risk factors for deafness, such as a positive family history, infection during gestation, history of prematurity, hyperbilirubinemia, neonatal sepsis, and asphyxia (Box 88.3).

Adapted from Feldman HM. Evaluation and management of language and speech disorders in preschool children. Pediatr Rev. 2005;26(4):131–142.

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