The first thing Dad did when Meredith was born was to check out the little details. Fingers, toes, eyes, ears, lips—everything perfect. So he and Mom were both shocked when Merrie did not pass her newborn hearing screening the next day. The nurse told them that it may mean nothing at all, but she advised them that Merrie needed further testing. After a series of tests Merrie’s ear specialist told Mom and Dad that their perfect child had a nerve-type hearing loss. It would most likely be permanent and could possibly get worse. This was Dad’s worst fear because hearing loss ran in his side of the family.
Hearing loss is the most common birth defect in the United States, affecting one to three of every thousand newborns. Some 25 percent of children who are born with impaired hearing will have severe to profound loss, enough to prevent normal language acquisition and intellectual, emotional, and social development. Figure 6.1 shows the relative incidence of the most common birth defects. Notice that hearing loss is by far the most common.
The impact of untreated congenital deafness is high, averaging well over $1 million per profoundly hearing impaired child. This figure includes direct costs such as education (a third of total cost) and loss of earning potential (two-thirds of total cost).
Causes of Congenital Hearing Loss
Congenital means that the hearing loss is either present at birth or the genes that will cause deafness later are present at birth. For example, in genetic deafness from Alport syndrome (kidney failure and hearing loss), the abnormal Alport gene is present at birth but hearing loss may not be noticeable until adolescence. Non-genetic congenital deafness can be caused by viral infections, bacterial meningitis, newborn jaundice, low birth weight, low oxygen levels, some life-saving antibiotics, and other causes (see figure 6.2).
Figure 6.1
Incidence of birth defects per thousand births in the United States. Hearing loss is the most common birth defect in the United States. It occurs more than twice as frequently as any other birth defect.
Genetic Hearing Loss
Inherited deafness is complex and the following explanations are just the basics. Genetic abnormalities are responsible for about 60 percent of congenital hearing loss in children. Over a hundred different gene mutations causing deafness have been identified. Everyone has about twenty-four thousand genes that are grouped together on chromosomes. Half of our forty-six chromosomes come from each parent. As described below some forms of deafness only occur when the infant inherits abnormal hearing genes from both parents (recessive deafness) and other forms require only an abnormal hearing gene from one parent (dominant).
Figure 6.2
Causes of congenital sensorineural hearing loss. The majority of worldwide hearing loss in newborns is caused by genetic inheritance.
Syndromic vs. Non-Syndromic Deafness
The term syndromic indicates that deafness is associated with other clinical abnormalities. Examples include renal failure with deafness (Alport syndrome); widely spaced, different colored eyes and a streak of gray hair with deafness (Waardenberg syndrome); goiter with deafness (Pendred syndrome); and heart problems with deafness (Jervell and Lang-Nielson syndrome). In all, about 20 percent of congenital hearing loss is syndromic and over four hundred syndromes have been identified.
Conversely, children with non-syndromic deafness have no other abnormalities. Non-syndromic deafness is much more common, accounting for about 80 percent of congenital hearing loss.
Dominant vs. Recessive Hearing Loss
Genes are categorized as dominant (20 percent) or recessive (80 percent). Dominant genes can be thought of as being so powerful that only one (from one parent) is required to cause hearing loss. Most syndromic hearing loss is associated with dominant genes. On the other hand, two recessive genes (one from each parent) are required to cause recessive hearing loss.
For a child to be born deaf, he or she must inherit at least one dominant deafness gene (from one parent) or two recessive deafness genes (one from each parent). If one parent has a dominant deafness gene, that parent will be deaf and has a 50 percent chance of producing a deaf child. If both parents are dominant, they have a 75 percent chance of producing a deaf child.
In the most common situation, both parents are hearing but each carries one recessive deafness gene. Parents who have a single recessive gene have normal hearing and are called carriers.
It may be difficult to trace deafness from one generation to the next in families with recessive genes. If both parents are carriers (one recessive gene each), the chance of having a child who is hearing impaired is 25 percent; the chance of having a child who is a carrier is 50 percent; and the chance of having a child with no recessive deafness gene is 25 percent. Over 90 percent of deaf children are born to two normally hearing parents and over 95 percent are born to at least one hearing parent.
Rare Forms of Inheritance: X-linked and Mitochondrial
These two types of inheritance are transmitted solely by the mother. X-linked deafness affects predominantly males and mitochondrial deafness affects both males and females. But a male with mitochondrial deafness cannot pass it on. Together these two rare forms account for only about 2 percent of genetic deafness.
Genetic Counseling and Testing
Genetic testing is just one part of the process of genetic counseling, in which potential parents or parents concerned with inherited deafness are advised about the cause of their hearing loss or the chances of developing or transmitting it. The information is complex and may have a large impact on family life, so the counseling aspect is as important as the actual test results.
Although blood tests can identify over a hundred genes that have been associated with hearing loss, many of those tests are limited to research laboratories. However, the most prevalent gene abnormalities are GJB2 and GJB6. Clinically this is often referred to as connexin-related deafness and readily available testing for these two genes identifies the cause of 50 percent of childhood deafness.
Acquired (Non-Genetic) Congenital Deafness
Infections
Most congenital infections are viral and cause an estimated 10 percent of congenital deafness. Infection can be transmitted by the mother before birth through the placenta, during birth from infected vaginal secretions, after birth from breast milk, or from airborne germs transmitted by coughing and sneezing. The severity of the infection and the amount of hearing loss caused are related to the type of virus as well as the stage of maturity of the child at the time of infection. A viral infection in the first trimester may cause more damage than the same virus would cause in the third trimester.
The most frequent viral infections include cytomegalovirus (CMV), rubella (German measles), and herpes simplex. Mothers can also transmit toxoplasmosis (a parasite) and syphilis (a spiral bacterium) that cause hearing loss. You may come across the acronym TORCH. This is a group of blood tests that screen for infections in newborns. The screening detects toxoplasmosis, rubella, cytomegalovirus, herpes simplex, HIV, and syphilis infections.
Congenital syphilis may cause deafness, saddle-nose, and deformed teeth, fingers, and toes. It may also result in miscarriage, prematurity, and stillbirth. Adult-onset deafness and eye inflammation may also occur from a delayed form of congenital syphilis.
Malformations of the Inner Ear
Up to 20 percent of children with congenital hearing loss have a cochlear malformation. Abnormal genes causing some malformations have been identified. Inner ear malformations are associated with a risk of meningitis.
The most common inner ear malformation is called enlarged vestibular aqueduct (EVA), which can cause a progressive loss of hearing during childhood and adolescence. The progressive loss usually occurs in steps that may follow mild head bumps. Some ear specialists recommend that children with EVA avoid contact sports and rough play. The vestibular aqueduct is a bony channel that contains inner ear fluid and it is enlarged in up to 5 percent of children.
Mondini malformation is an enlarged vestibular aqueduct plus incomplete inner walls (partitions) of the cochlea. Both enlarged vestibular aqueduct and Mondini deformities may be associated with a genetic abnormality that also causes Pendred syndrome (deafness and goiter).
Ototoxic Drugs
Sometimes life-saving antibiotics are required for pregnant mothers or infants even though side effects include hearing loss. Infectious disease specialists, obstetricians, and pediatricians use these drugs only as a last resort. They monitor blood levels to minimize chances for damage, and they communicate the possible risks to families. The most common medications to cause hearing loss are a family of antibiotics known as aminoglycosides. This family includes gentamicin, tobramycin, kanamycin, and streptomycin. There is a genetically determined high risk in some families. Tests are available in such cases.
Diuretics (“water pills” used to treat high blood pressure or fluid retention) can also be ototoxic. The loop diuretic ethacrynic acid is ototoxic and is used only when a similar drug, furosemide, cannot be prescribed because of a sulfur allergy. Ototoxicity is more likely when aminoglycosides are used in combination with loop diuretics.
Hearing loss can also be produced by cancer chemotherapy. The most likely drugs to cause hearing loss are cisplatin, carboplatin, and oxaplatin. Good hydration, slow administration, and use of lower dosage can all play a role in reducing toxicity. Vincristine can cause reversible hearing loss and is less toxic but often less effective. Both oral and in-the-ear steroids have been used to reduce ototoxicity. Other ototoxic medications include high-dose aspirin and other NSAIDs (nonsteroidal anti-inflammatory drugs) and quinine (all reversible when medication is discontinued). In addition, mercury and lead poisoning are associated with hearing loss. (See chapter 24for more detail on ototoxic medications.)
Newborn Jaundice
Hyperbilirubinemia, or too much bilirubin, is a common condition of infants that often requires medical treatment. It is caused by an excessive buildup of bilirubin, a blood chemical that occurs when the body replaces old blood cells with new ones. Jaundice (yellowness of the skin, eyes, and other tissues) is a result of the pigment of the bilirubin.
When abnormal levels reach about 13 mg/dL, treatment is required with phototherapy (exposure to blue fluorescent light reduces unconjugated bilirubin). Jaundice that requires phototherapy is severe enough to cause hearing loss. The wavelength of this light has the property of breaking down bilirubin so that it can be excreted in urine or stool. In severe cases of hyperbilirubinemia, exchange transfusions (replacing much of the newborn’s blood with donor blood) are necessary.
Temporary Causes of Congenital Conductive Hearing Loss
Some newborn hearing loss is caused by temporary conditions that resolve spontaneously or with treatment. Newborns have tiny outer ear canals that tend to collapse during hearing testing. Collapse can lead to false positive test results. The canals can also be filled with vernix, the white, creamy covering of fetal skin that has antibiotic and moisturizing properties. Both conditions can cause a temporary hearing loss that tends to resolve in the first weeks of life. Amniotic fluid may also be swallowed by the fetus and end up in the middle ear. Acute otitis media is an infection of the middle ear that may rarely occur soon after birth. It causes fluid to build up in the middle ear and blocks sound waves from entering.
Identification of Hearing Loss in Infants
Early identification of newborn hearing loss is essential to allow treatment that can reduce the linguistic, intellectual, social, and emotional deficits caused by deafness. Two common methods of early identification include universal newborn hearing screening and identification of high-risk factors for hearing loss. Best results occur when both methods are applied.
Universal Newborn Hearing Screening
Newborn hearing screening is a public health program designed to identify infants with hearing loss and enhance timely referral to hearing health care professionals. According to the CDC, in 2011, 98 percent of American newborns underwent hearing screening in the first few months of life.
Ideally newborns should be screened before they leave the hospital but no later than one month of age. There are two methods of screening: the auditory brainstem response test (ABR) and the otoacoustic emission test(OAE). Both tests are very sensitive and are structured to identify problems. But they are not highly specific, falsely identifying hearing loss when there is none in up to 30 percent of infants. As a result children with normal hearing are too often referred for unnecessary and expensive batteries of diagnostic testing.
The ABR test measures the electrical hearing signals that run from the cochlea to the mid-brain. The signals are picked up by electrodes taped to the head. The stimulus is a click that is presented through headphones at a loud level and soft level. Testing takes about five minutes if the child is sleeping (longer if the child is not lying still) and may be performed by a health professional or trained lay volunteer.
The OAE test measures sound waves that are created in the cochlea during the process of hearing. These emissions travel back out to the ear canal where they are picked up by a tiny microphone. Unfortunately, this test does not identify problems with the nerve of hearing or the hearing areas of the brainstem. It is also more likely to be affected by temporary fluid in the middle ear and ear canal causing more unnecessary trips for testing after discharge from the hospital.
High-Risk Factors for Newborn Hearing Loss
A high-risk register (HRR) identifies infants who are at risk to have hearing loss. These risk factors are presented in table 6.1. High-risk registers are not as sensitive as universal newborn screening and will miss about 50 percent of infants who have hearing loss. On the other hand, certain types of congenital hearing loss have a delayed onset and cannot be identified with hospital-based screening tests. If either the screening test or HRR show abnormality, the infant is referred for definitive evaluation by a team that consists of an audiologist and physician.
Table 6.1
High-Risk Factors for Newborn Hearing Loss
• Admission to newborn ICU for more than five days
• Prematurity (gestation of less than thirty-seven weeks)
• Maternal infection
• Abnormal appearance (head, face, ears, neck, eyes, fingers)
• Ototoxic drugs given to mother or child
• Yellow skin or eyes (hyperbilirubinemia)
• Identification of known deafness syndrome
When high-risk factors are identified, the child should be referred for complete evaluation of hearing even if he or she passes newborn hearing screening tests. Ideally the complete evaluation would be performed at a facility that offers a team approach to hearing loss including an otolaryngologist, audiologists, and a language specialist.
Since hearing loss may not be present until later in life, ongoing evaluation throughout childhood is important. One method is surveillance of milestones by physicians and patients of communication development between two months and two years of age. Children who do not meet these milestones should be referred for hearing and language evaluations.
Table 6.2
Normal Hearing and Language Milestones
0–3 months
Startles to loud sounds
Quiets when spoken to
Changes sucking behavior in response to sound
3–6 months
Identifies direction of sound with eyes
Listens to music
6–12 months
Turns head toward sound
Recognizes first words
Begins canonical babbling (rhythmic, repetitive)
12 months
Says first words
24 months
Follows one-stage commands (“Find Daddy.”)
Speaks in short phrases (“Mommy come.”)
Knows dozens of words
Current strategies to identify hearing loss that does not begin until children are older include awareness training for parents and teachers and periodic testing. Hearing is routinely tested through public schools or physician offices at ages four, six, ten, and eighteen. Classroom teachers are also trained to recognize hearing loss and to discuss this with parents and the school audiologist.
Evaluation of Hearing Loss in Infants
If your newborn is found to have a hearing loss, the next step is an evaluation by an ear specialist. Your physician will conduct a thorough history and physical examination. Questions focus on birth history (such as: During pregnancy, did the mother have a fever or rash, take any medications, have high blood pressure?) and family history (for example: Does hearing loss run in the family?). During the physical examination the specialist is looking for any abnormalities: Are the ears, head, face, fingers, and toes well formed? Is there anything obstructing the ear canal? Is there fluid or infection of the middle ear? Are the eyes, nose, and throat normal? Testing follows and is guided by the findings of the history and physical examination.
Testing
This evaluation includes hearing tests and may include blood tests, urinalysis, and imaging (CT scan or MRI) of the ear and brain. Certain eye, kidney, and heart abnormalities may occur in conjunction with deafness. For this reason an eye examination by a pediatric ophthalmologist, urine testing, and EKG may all be indicated.
While hearing screening tests are designed to be fast and inexpensive, diagnostic hearing testing is time consuming and expensive because it is more detailed and accurate. Diagnostic testing can show the type and degree of hearing loss and help lead to a specific diagnosis and treatment plan.
Hearing testing is best performed by an audiologist working as part of a team. Typical hearing tests in the first six months of life include immittance, auditory brainstem responses (ABR), and otoacoustic emissions (OAE) (see chapter 26).
Interacting with the Doctor
Your ear specialist team must be sensitive to the family when providing the critical answers to question like: Is my baby deaf? Whose fault is it? How severe is it? What caused it? Will it be permanent? What can be done? It may take several visits to fully understand the diagnosis and to work with your team to form a treatment plan.
The first things you will learn are the extent of hearing loss and what that means to your child and family. Further evaluation will be necessary to pin down the cause. If your child has significant hearing loss, a hearing aid evaluation (see chapter 8) will be recommended. Remember, time is of the essence. Do not delay. Early intervention may make a huge difference in your child’s future. Your team can provide this service.
If your child has severe to profound loss of hearing, you will have the options of using sign language, using a hearing aid, or, if a hearing aid is not sufficient, using a cochlear implant (see chapter 9). Most parents like to have the chance to meet and talk to other parents who have been in similar positions and had to make difficult decisions. Your team can help arrange this.