In this article, the author discusses the diagnosis and treatment of infants and children with hearing loss, including newborn hearing screening, audiologic testing and work-up, a brief discussion on the genetics of hearing loss, and the goals for early diagnosis and treatment.
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• Congenital hearing loss is the most common congenital sensory impairment and the most prevalent health problem screened for at birth.
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• Early diagnosis and intervention for hearing loss is essential to maximize speech, language, and cognitive development.
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• Binaural hearing is critical for speech perception and communication, and the consequences of unilateral hearing loss on several performance factors can be significant in the developing child.
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• Many types of tests, physiologic and behavioral, are available for diagnosing hearing loss and obtaining information about the auditory system.
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• When hearing loss is confirmed, further diagnostic and genetic testing can often help identify the cause of hearing loss, with implications for prognosis and family health.
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• Management options depend on the type and degree of hearing loss, and can include early intervention, speech therapy, sign language education, hearing aids, and surgical therapies such as tympanostomy tube insertion, cochlear implantation, and auditory brainstem implantation.
Historical note and terminology
Historical context. Hearing loss identification in infants and children has undergone a period of tremendous change over the past 20 years. The single most influential reason for this change is the advent of universal newborn hearing screening. With implementation of this program, hearing loss is being identified and managed at earlier ages. Along with improved technology and services for children with hearing loss, these measures have improved language and cognitive development in children with hearing loss.
Early hearing loss detection and intervention has been a goal for over 40 years. Prior to the initiation of newborn testing, risk-factor screening was the only means available for identifying infants at risk for hearing loss. A 1971 statement by the Joint Committee on Infant Hearing delineated the first high-risk factors for hearing loss and recommended screening infants using the following factors: a family history of hereditary childhood hearing impairment; congenital infection such as rubella, cytomegalovirus, syphilis, and herpes; craniofacial anomalies; birth weight less than 1500 grams; and a bilirubin level greater than 20. In 1982, bacterial meningitis and severe asphyxia were cited, with additional risk indicators added between 1982 and 1994 (05). Although this list was expanded in subsequent years, risk indicator screening is still only able to identify less than half of the children who have or will go on to develop childhood hearing loss.
In the early 1990s, the National Institutes of Health's Consensus Development Conference on Early Identification of Hearing Loss concluded that all infants should be screened for hearing impairment, preferably prior to hospital discharge. In 1999, the United States Congress passed into law a bill supporting a national program to develop and support universal newborn hearing screening, and in October 2017, a bill was passed, further extending funding for this important program. The latest position statement by the Joint Committee on Infant Hearing recommends that all newborns be screened for hearing loss by 1 month of age (06). If the child fails the screening process, an audiological diagnostic evaluation should occur before 3 months of age. When a hearing loss is confirmed, the child should be enrolled in early intervention before 6 months of age. These are referred to as the Early Hearing Detection and Intervention (EHDI) guidelines, and have been widely adopted by such organizations as the National Institutes of Health/National Institute of Deafness and other Communication Disorders, American Speech-Language Hearing Association, American Academy of Pediatrics, and the American Academy of Otolaryngology-Head and Neck Surgery.
Every state and territory in the United States has established an EHDI program (National Center for Hearing Assessment and Management). It is estimated that over 95% of children born in the United States currently receive newborn hearing screening (117). This figure is impressive and has led to the decrease in age of identification of hearing loss from about 2.5 years to less than 2 to 3 months. This earlier age of identification of hearing loss has led to earlier intervention, including amplification (eg, hearing aids) and enrollment into programs such as early intervention to facilitate language learning. Studies show that early identification and remediation of hearing loss leads to improvements in language development that are apparent even into the second decade of life (14; 80).
Type of hearing loss. There are many different ways to describe and characterize hearing loss. The most basic distinction is between conductive hearing loss, which results from blockage of transmission of sound from the environment to the cochlea, and sensorineural hearing loss, which results from dysfunction of the cochlea or auditory nerve. Distinguishing between these types is critical for diagnosis and management. Conductive hearing loss arises from a variety of causes, many of which are correctable with medical or surgical treatment. Most of this article deals with sensorineural hearing loss, which can fluctuate, but tends to be permanent. An individual may also have mixed hearing loss with a combination of the above.
Within sensorineural hearing loss, several other distinctions help classify the type, onset, and cause, which are useful for prognosis and treatment. Hearing loss can be congenital (present at birth) or acquired (onset after the first days to weeks of life). This can sometimes be difficult to distinguish, but there are several known causes of congenital hearing loss, and special attention should be paid to adequate screening and audiologic testing for these children. The age of onset of hearing loss can also affect speech and language acquisition. The first 36 months of life have been proven to be crucial for the development of linguistic and cognitive skills (38). For this reason, prelingual hearing loss (hearing loss prior to development of speech and language) can have greater effects on acquiring speech and language than postlingual hearing loss (hearing loss after the development of speech and language).
Hearing loss can be genetic (hereditary) or nongenetic. Some genetic hearing loss occurs in isolation (nonsyndromic), and other clinical features are sometimes associated (syndromic). It is estimated that approximately 70% of genetic hearing loss is nonsyndromic and 30% is syndromic.
Degree of hearing loss. Hearing is measured in decibels (dB), with a reference of 0 dB set as the value at which young adults with normal hearing detect a tone of a given intensity and frequency half of the time (103). “Hearing loss” is defined as the ability to hear at a threshold of 25 dB or higher in the frequencies important for understanding speech in one or both ears (Early Hearing Detection and Intervention (EHDI) Phase II State Model Legislation 2013). The classification for children is more stringent because of the effects of hearing loss on the development of speech and language and potential negative educational impact if left undetected. The American Speech-Language-Hearing Association classifies hearing loss in children as follows (04):
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• Normal range (10 to 15 dB): A child will hear all speech sounds.
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• Slight hearing loss (16 to 25 dB): A child will hear vowel sounds clearly, but might miss some consonant sounds.
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• Mild hearing loss (26 to 40 dB): A child will hear only some of the speech sounds.
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• Moderate hearing loss (41 to 55 dB): A child will hear almost no speech sounds at a normal speaking level.
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• Moderate-severe hearing loss (56 to 70 dB): A child will hear no speech sounds at a normal speaking level.
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• Severe hearing loss (70 to 90 dB): A child will hear no speech and almost no other sounds.
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• Profound hearing loss (91+ dB): A child will hear no speech and few other sounds.
Children who have bilateral hearing loss in the severe to profound range may be candidates for cochlear implantation. There have been an increasing number of children with severe to profound unilateral hearing loss who have undergone cochlear implantation, and this is an active area of research (110; 118). In July 2019, significant unilateral hearing loss was approved as an FDA indication for cochlear implantation for both children and adults.
Configuration of hearing loss. The configuration of the hearing loss describes the frequencies affected by the loss. Individuals can have high-frequency loss or low-frequency loss, with normal hearing in the rest of the spectrum. Some may have a flat configuration, where hearing is affected relatively equally across the frequency range. Descriptors such as “sloping” or “rising” can also describe the hearing loss as it changes across the frequency range. The configuration of the hearing loss can help providers predict the impact it will have on speech recognition and the possible benefit amplification will provide. Hearing loss can also be unilateral or bilateral, depending on whether 1 or both ears are affected, and can be symmetric or asymmetric in nature if the hearing loss is bilateral. Children can have stable hearing losses or hearing losses that progress with time, or their hearing can fluctuate over time.