Hearing Impairment Clinical Presentation

General presentation and age at detection

Before neonatal hearing screening was routine, deafness was diagnosed at a mean age of 2.5 years. Since the implementation of successful Universal Newborn Hearing Screening (UNHS) programs, this improved to a mean of 14 months, with 74% being diagnosed and receiving intervention by 6 months. Most recently, the average age of diagnosis has been reported to be just 2-3 months.^[17] The goal is universal screening, to detect hearing loss prior to 3 months, and intervention prior to 6 months, in accordance with the Newborn and Infant Hearing Loss: Detection and Intervention policy statement from the American Academy of Pediatrics (AAP).^[2]

In a screened population, the rate of referral for services before 6 months is 19 times higher than in an unscreened population. The rates for confirmation and management of hearing loss are 5 times and 8 times higher, respectively, for a screened population.

In the unscreened population or for those with progressive or acquired hearing loss, parents are the first to suspect hearing loss in almost two thirds of the patients. Pediatricians detect roughly 10% of cases, and other healthcare providers suspect it first in approximately 15% of patients. The mean time from the first suspicion of hearing loss to its diagnosis is 9 months.

High-risk criteria for hearing loss in neonates and infants

Prior to most states implementing UNHS programs, the high-risk criteria were an important tool in the early detection of hearing loss. However, the dissemination of high-risk criteria for neonates and infants in 1990 did not notably alter the mean age at diagnosis. About 50% of children with SNHL do not meet any of the criteria listed, and only 10% of neonates have 1 or more of the high-risk criteria that prompt an evaluation. These rates were among the reasons cited for the need for universal neonatal hearing screening. However, these criteria (especially for age 29 d to 2 y) serve as a reminder for those children for whom providers should have an increased level of suspicion and a decreased threshold to refer for testing for missed congenital, progressive, or acquired hearing loss.

High-risk criteria for neonates (birth to 28 d) are as follows:

• Family history of congenital or early SNHL
• Congenital infection known to be associated with SNHL
• Craniofacial anomalies
• Birth weight of more than 1500 g (< 3.3 lb)
• Hyperbilirubinemia over the exchange level
• Exposure to ototoxic medications
• Bacterial meningitis
• Low Apgar scores at birth
• Prolonged mechanical ventilation
• Findings of a syndrome associated with SNHL

High-risk criteria for infants (29 d to 2 y) are as follows:

• Concern about hearing, speech, language, and/or developmental delay
• Bacterial meningitis
• Neonatal risk factors associated with SNHL
• Head trauma, especially with fracture of the temporal bone
• Findings of a syndrome associated with SNHL
• Exposure to ototoxic medications
• Neurodegenerative disorders
• Infectious diseases associated with SNHL

Indications for a hearing evaluation and findings

Concern about a child's hearing loss expressed by a parent or caregiver always should prompt immediate evaluation. Hearing loss can be diagnosed at whatever age it is suspected, so delaying the diagnosis in the belief that a child is too young to be tested is unjustified. Other causes of language delay or behavioral problems should be considered as well, but hearing loss may be the cause of these problems. The results of referral for hearing loss are definitive, whereas evaluations for language or behavioral problems are more subjective and dependent on the skill of the person providing the evaluation.

Children with congenital or perinatally acquired profound SNHL (>90 dB) may present with loss of cooing by the age of 6-9 months and with frank language delay. Those with hearing loss less severe than this may present with minor speech impediments, language delay, behavioral problems, or school failure. The degree of hearing loss or loss of speech discrimination correlates with the patient's speech and language problems.

Behavioral problems may be major or minor, and they are probably best correlated with the child's personality and with how the parents deal with what they may consider a stubborn child. Before speech impediments, mental retardation, autism, attention deficit, or adjustment disorders are presumed, many children could benefit from a hearing evaluation.

Upon evaluation, a child who cannot hear normal speech can reproduce only what he or she hears. A child who cannot hear the teacher cannot learn. In addition, a child who is bored fidgets. A child who cannot understand and who is berated by caregivers for lack of cooperation may act out.

Healthcare providers should understand that normal speech volumes are 30-50 dB, whereas typical street traffic is about 60 dB. Standard phones ring and shouts register at approximately 80 dB, and lawnmowers are approximately 90 dB. Therefore, children with a 60-dB hearing loss hear their mother when she yells at them and startle when the telephone rings. However, they do not hear most conversational speech, and they may not always hear the teacher in a classroom, especially if they are not in the front and there is significant extraneous noise.

If children have poor speech discrimination, the diagnosis is usually made relatively early because they may mispronounce words or may be unable to understand what is being said. In children with good speech discrimination, hearing loss may go undetected because speech production and comprehension are less affected.

Children with mild hearing losses that begin prelingually or postlingually may present with difficulties late in childhood.

In general, children who lose their hearing postlingually present with a decline in language skills they had previously achieved. In children of this age group, clinically significant hearing loss is usually the result of an obvious medical event. Those who lose their hearing postlingually may be able to describe their loss. However, if the decline is gradual, they may not initially recognize the deficit.

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 be withdrawal from social activities and playing alone, or playing the television and music with increasingly loud volumes.

Carefully evaluate children with congenital hearing loss for any evidence of other physical stigmata or for possible associated syndromes (ie, a white forelock to suggest Waardenburg syndrome). For a partial list of syndromes related to deafness, see Causes. Because almost every organ system can potentially provide evidence of an associated syndrome, detailed physical examination is necessary.

For patients with acquired hearing loss an otolaryngologist should evaluate their ears by inspecting them for external defects or for obstructions that block sound conduction down the ear canal (eg, cerumen, foreign bodies). In addition, pneumatic otoscopy should be performed to detect any evidence of current or chronic infections, such as perforation or scarring of the tympanic membrane, cholesteatoma, abnormal landmarks, and fluid behind the tympanic membrane.

The remainder of the otolaryngology examination should be focused on the head and neck to carefully rule out other abnormalities that may lead to a diagnosis.

If children are old enough to cooperate, they should undergo tests of balance because dysfunction of the inner ear or vestibular nerve may also be present.

Genetic causes

Most sources cite genetic causes as accounting for at least 50% of hearing loss.^{[1, 14, 16, 18]} These can be divided into syndromic and nonsyndromic types. As with all genetic syndromes, genetic causes of hearing loss may be autosomal dominant (AD), autosomal recessive (AR), X-linked, mitochondrial, or sporadic.

Nonsyndromic deafness accounts for slightly more than two thirds of all cases of genetic deafness. It probably accounts for most cases classified as unknown. Children with nonsyndromic deafness are deaf or hard of hearing; however, they have no other physical abnormalities, no particular risk to other organ systems, and no increased risk of mental deficiency. Some children have a history of deafness in a close or distant family member. Others have new mutations or an AR gene with no known proband. The histories of subsequent siblings and progeny may help to distinguish a genetic cause from developmental arrest or a prenatal insult.

Exciting developments in genetic mapping have revealed approximately 2 dozen abnormal genes that lead to deafness. These genes have been classified according to their mode of inheritance: ADs (DFNA1 through DFNA48), ARs (DFNB1 through DFNB67), X-linked recessives (DFN1 through DFN8), or mitochondrial (at least 5 loci identified, including 12Sr RNA and tRNA-Ser UCN).

Mutations in these genes result in a functional or structural defect (eg, collagen in the basilar membrane; a structural defect in a membrane-gating protein, such as connexin 26).^[19] In some of these, one or more specific mutations in the DNA sequence have been identified. One such example is DFNA44, for which the problem is on gene CCDC50, which codes for Ymer, a cytoplasmic protein that inhibits the down-regulation of the epidermal growth factor receptor, affecting the normal development of the structural organization of the pillar cells of the inner ear.^{[20, 21]} Several of the genes exhibit variable penetrance, so the presence of the gene does not correlate directly with the degree of hearing loss.

Syndromic deafness accounts for the remaining cases of genetic deafness, with more than 300 syndromes described.^[2] Some syndromes have a particular inheritance pattern (eg, AD for Waardenburg syndrome and Gernet syndrome, AR for Jervell Lange-Nielson syndrome and Winter syndrome, X linked for Alport syndrome and Rosenberg syndrome). Others are sporadic (eg, cat-eye syndrome, Turner syndrome, Klinefelter syndrome). Physical findings usually help to indicate the presence of a particular syndrome; however, children with some syndromes develop the associated physical findings late in childhood. Other children present early in life with either deafness or the sequelae of a biochemical or metabolic derangement.

As noted above, syndromes may affect any single organ or several organ systems. Just as the genetics of nonsyndromic deafness have advanced, more is known about the genetics of syndromes associated with deafness. For example, Waardenburg syndrome type IV is caused by an abnormality of endothelin 3 (EDN3), which results in abnormalities of ligand molecules affecting striatal intermediate, GI, and pigment cells.^[22]

Syndromic associations

A small sample of syndromes associated with deafness is summarized below. A few may be familiar, although many are not; most are fairly uncommon. For many of these syndromes, good data about their actual prevalences are difficult to find.

The first few syndromes listed for each organ or system are most commonly known. They may be most widely recognized because their associated findings or illnesses may result in high morbidity or mortality rates, because the physical stigmata are classic and therefore make the syndrome easily identifiable, or because they are overrepresented in test questions on pediatric examinations.

Table. Some Syndromes Associated with Deafness (Open Table in a new window)

Prenatal causes

Prenatal causes lead to 5-10% of hearing losses. Congenital infections (eg, cytomegaloviral [CMV] infections, herpes, rubella, syphilis, toxoplasmosis, varicella) can result in SNHL.^[23] Fetal exposure to teratogens (eg, methyl mercury, retinoic acid, thalidomide, trimethadione) may also result in SNHL. Most of these perinatal insults result in physical abnormalities, which should prompt the clinician to recognize the diagnosis and perform a confirmatory evaluation.

However, the physical findings sometimes are subtle or are not apparent until the child ages (eg Hutchinson molars). In these cases, it may be the identification of hearing loss that leads to the evaluation leading to the diagnosis, or even the later appearance of developmental delays. Even if children with a known prenatal exposure pass the neonatal screen, careful follow-up of their hearing is necessary.

Perinatal causes

Perinatal causes are responsible for 5-15% of hearing losses. A history of prematurity, low birth weight, anoxia and/or low Apgar scores, hyperbilirubinemia, or sepsis should prompt an evaluation of hearing because these conditions may also result in SNHL.

Postnatal causes

About 10-20% of hearing loses are due to postnatal causes. Childhood infections, such as meningitis or mumps, may result in SNHL. Treatment with ototoxic medications, such as aminoglycosides or furosemide, also can lead to SNHL. Otitis media or major head injury may cause SNHL or CHL.

Unknown causes

About 20-30% of deaf children have no certain etiology. Their hearing losses likely result from a maldevelopment of the ear or neurologic system. Such an event may have been a developmental accident or the result of an undiagnosed infection or exposure to a teratogenic agent. However, many are likely due to an undiagnosed genetic defect that may represent a new mutation or a genetic recessive trait.