PEDIATRIC HEARING LOSS

University of Kansas Grand Rounds, 1998

by Joseph Edmonds, MD

It is estimated that 1.5-6 children for every 1000 live births have some hearing impairment. Impairments of 30 dB and greater, in the 500-4000 Hz frequency range, will definitely lead to impaired speech and language development. Many would add that even smaller hearing deficits can also lead developmental delay. If these developmental delays are to be minimized it is ideal to identify the child’s impairment prior to three months of age. These facts have made hearing loss in the pediatric population an issue which has captured the interest of pediatricians, audiologists, speech therapists, parents and lawmakers. However, it is the Otolaryngologist who is looked to as the expert. Therefore, it is imperative that the Otolaryngologist be knowledgeable about existing and evolving technologies for diagnosis and the debate regarding their implementation. The Otolaryngologist should be aware of existing federal legislation regarding the subject. The Otolaryngologist should also posses a broad based fund of knowledge of the many reasons children have poor or no hearing, and develop an orderly approach to this potentially confusing subject.

A entity was founded in 1969 to address this complicated matter with a unified voice to the medical community and the nation. It is called The Joint Committee on Infant Hearing. The body is now comprised of the American Speech-Language-Hearing Association, the American Academy of Otolaryngology-Head and Neck Surgery, the American Academy of Audiology, the American Academy of Pediatrics, and the Directors of Speech and Hearing Programs in State and Welfare Agencies. Their first position statement published in 1974 pointed to careful history and physical examinations to identify the population at risk. In 1982 a follow up statement was published which recommended identification of infants at risk for hearing loss in terms of specific risk factors. It also emphasized follow-up audiologic evaluation until accurate assessment could be made. In 1990 the position statement was modified to expand the list of risk factors and recommended a specific hearing screening protocol. The position statement of 1994 endorses the goal of universal detection of infants with hearing loss. The statement does not specifically recommend how this should be done. The statement does recognize ABR and OAE as the two best options. It says that the decision to use one or the other be up to the local team of health care professionals implementing the universal screening program. The statement recommends the screening take place in the nursery prior to discharge for logistical ease. Children born outside the hospital should be tested within three months of birth. The position statement maintains the role risk factors as important evaluation tools, especially until the goal of universal screening is fully implemented. The list of risk factors has been modified from the previous list in 1990. The revised list is as follows:

A. Neonates (birth-28 days)

1. family history of hereditary childhood SNHL

2. in utero infection (CMV, rubella, syphilis, toxoplasmosis)

3. craniofacial abnormalities, including those of the EAC and pinna

4. birth weight less than 1,500 gm

5. hyperbilirubinemia requiring exchange transfusion

6. ototoxic medications

7. bacterial meningitis8. apgars 0-4 at 1 minute or 0-6 at 5 minutes

9. mechanical ventilation for 5 days or greater

10. stigmata associated with a syndrome associated with CHL OR SNHL

B. Infants (29 days-2 years)

1. parent /caregiver concern

2. bacterial meningitis

3. head trauma associated with loss of consciousness or skull fracture

4. stigmata associated with a syndrome associated with CHL OR SNHL

5. ototoxic medications

6. recurrent or persistent OM with effusion for at least 3 months

C. Infants (29 days-2 years) who require periodic monitoring of hearing. Some newborns and infants may pass initial screening but require periodic monitoring of hearing to detect delayed onset SNHL or CHL. These children should be monitored every six months until age three, and appropriately thereafter.

1. Delayed onset SNHL

a. family history of hereditary childhood hearing loss.

b. in utero infection (CMV, rubella, syphilis, toxoplasmosis)

c. neurofibromatosis type II and neurodegenerative disorders

2. Delayed onset CHL

a. recurrent or persistent OM with effusion

b. anatomic deformities and other disorders that affect Eustachian tube function

c. neurodegenerative disorders

The federal government has responded to the issue of infant hearing loss as well. Several pieces of federal legislation have been enacted recently which apply to children with hearing deficits. Part H of the Education for All Handicapped Children Act (public law 102-119), passed in 1986, provides early intervention services, including language and speech development for disabled children from birth to age three. Part B of the Individuals with Disabilities Education Act (IDEA), passed in 1990, provides the disabled, ages 3 to 21 years, a free and appropriate public education. The Americans with Disabilities Act of 1990 has broadened the obligations of society to the disabled to include equal accommodations for the disabled in any public place (which includes a physician’s office or any other place of business).

As a clinician, evaluating a child with hearing loss can be difficult and somewhat overwhelming unless one is prepared for these tasks prior to meeting the child in the clinic situation. This preparation requires a preconceived systematic approach to the problem along with a basic understanding of the many different causes of hearing loss. There are many ways to approach and deal with the problem of hearing loss. It is not important which way you choose but important to have a method. The following outline is a proposed method to approach a patient. It is organized into five main categories all beginning with the letter C, to facilitate their memory. The categories are confirm, core, characterize, complete examination, and care.

I. Confirm the diagnosis of hearing loss. Is hearing loss present? The method of confirmation is age dependent. The neonate and infant will require special testing. The tests described above for screening, ABR and OAE, are also the tests used to confirm the diagnosis of hearing loss in these age groups. They supply similar information. They share the weakness of giving poor low frequency hearing information. The preschool aged child (2-5 years), the school aged child (5-10 years), and the preadolescent child (10-14 years) are usually all testable by audiometry. Special conditioning may be necessary in the younger children.

II. Core information. It is essential to collect core historical facts as they relate to the child’s hearing. It is said that 60% of diagnosis can be made by careful history taking and this is especially true of hearing loss. Also critical to understand is that taking a complete history is just that, it must be taken, it is never given. This is especially true of hearing loss. Many view hearing loss in the family as embarrassing or find it uncomfortable to discuss and will not offer information willingly about it. Others are unaware that there is hearing loss in the family. Questions about hearing aid use, or speech abnormalities are sometimes helpful to elicit the history. The risk factors as enumerated by the Joint Committee are the end point to a good history. Arriving at that endpoint requires the examiner to consider the gestational history, the perinatal history, and the family history.

A. Gestational History The human embryo is most susceptible to factors that can cause major morphologic abnormalities from three weeks through ten weeks. Many women may be unaware of pregnancy during this early period. Therefore, it is important to question the mother about infection and drug use during and also “just prior” to discovering the pregnancy. Prenatal infections, such as rubella, toxoplasmosis, influenza, CMV, and syphilis, can cause changes in the developing embryo that will lead to functional hearing impairment. Subclinical rubella infection in the mother can lead to rubella embryopathy. This can occur even if the mother has had the rubella infection in the past, as immunity is not necessarily permanent. Many medications taken during gestation are implicated as ototoxic. A partial list includes streptomycin, quinine, and chloroquine phosphate. These ingestions often lead to SNHL. Thalidomide embryopathy cause widespread deformation of the auditory apparatus, leading to mixed hearing loss. Endocrine disorders such as psedohypoparathyroidism and diabetes mellitus in the mother have been implicated in the development of hearing loss in the child.

B. Perinatal History Intrapartum asphyxia and anoxia may lead to hearing loss through toxic damage to the cochlear neurons, which are sensitive to oxygen deprivation. Kernicturus may also cause damage to the cochlear nuclei or other central auditory pathways. Intrauterine hemorrhage, placenta previa, prolonged labor, instrument delivery, and cesarean section birth have all been implicated in damage to the auditory system. Emperic evidence also has demonstrated that premature birth is associated with hearing loss.

C. Family History As alluded to earlier this may be difficult to obtain. However a carefully obtained family history may give clues to the type of hearing loss. Half of all deafness discovered in children is thought to be of genetic origin. At least three fourths of these cases, and perhaps ninety percent, are recessively inherited. Recessively inherited hearing loss is characterized by stable SNHL. The loss may be discovered at different ages, but if diagnosed early would show little change with time. The hearing loss in family members will have been stable, if there are other family members with hearing loss. When two or more siblings are affected but the parents and other relatives are not, AR inheritance may be assumed. When the parents are consanguineous, no matter how many children are affected AR can be assumed.

The inherited autosomal dominant hearing loss, by contrast, is progressive. In general unilateral and mild bilateral progressive SNHL is more suggestive of AD mode of transmission. When one or more siblings are affected along with other relatives (parents, aunts, uncles, cousins) it may be difficult in estimating the type of inheritance, based on family history alone, as this may be the case with AR or AD loss.

There are no known conductive AR deafness syndromes. Therefore familial conductive hearing loss can be assumed to be AD (rarely X linked). The most common example is otosclerosis. This often does not affect young children.

There are still other clues to pay attention to when investigating the family history. Are males and females equally affected? If only males are affected an X-linked mode of transmission is likely.

Despite the fact that over 50 inherited syndromes exist with hearing loss as a component, and that most of the space in a standard text is devoted to these syndromes, the vast majority of cases of inherited hearing loss are clinically undifferentiated.

III. CHARACTERIZE the hearing loss. There are many modifiers which you can use, based on the information already gathered which will help you as you proceed to the examination. Remember the “TOE”, for Type, Onset, and Etiology.

A. Type of loss present can usually be characterized as CHL, SNHL, mixed, or fluctuating. The standard audiogram will differentiate these easily. It is necessary to be aware that an audiogram can be used in children as young as the preschool age group, and sometimes even in younger children. Success depends on the child ‘s ability to cooperate and the skill of the audiologist. A child develops the ability to localize sound at the age of one, and this enables the use of visual reinforcement audiometery. The results in this setting (sound field audiometry), gives no information about the type of hearing loss.

Careful interpretation of an ABR does give information regarding the type of loss. Delayed appearance of wave one with normal inter-wave latencies may be indicative of CHL. Elevated thresholds without a delay in the appearance of wave one, with normal inter-wave latencies indicates SNHL is most probable. When inter-wave latencies are abnormal a more central process is probably involved.

OAE is a response to sound by the outer hair cells. It is either present or absent at various decreasing levels to threshold. Abnormal OAE threshold or unobtainable emissions says nothing of the type of loss, but does reliably demonstrate abnormal hearing. Tympanometery can also be helpful in deciding the type of hearing loss present. The boney architecture of the tympanic ring is developed by one year of age. This rigidity makes the results of the tympanometry meaningful, and often gives important information about the middle ear and indirectly the probable type of loss.

It is also important to remember that CHL, does not preclude concomitant SNHL. The maximum CHL is around 60 dB. These tests used individually, or obtained in some complementary grouping, must be correlated with the physical exam in the young child to successfully infer the type of hearing loss.

Another type of hearing loss is fluctuating hearing loss. Fluctuating hearing loss in children is rarely encountered. Sudden onset of fluctuating hearing loss in conjunction with ataxia is suspicious for a perilymph fistula. Usually these children will have a history of barotrauma, blunt head trauma, or a predisposing condition such as a widely patent cochlear aqueduct or anomaly of the temporal bone.

B. Onset of the hearing loss can be either congenital or postnatal. Congenital hearing loss simply implies the hearing loss was present at birth. If it develops later, refer to it as postnatal. Often this is difficult to determine. As universal screening becomes more commonplace determination of the onset will become more objective, and less reliant on historical questioning. Speech patterns are probably the most important historical items to focus on when having to make a determination regarding onset without objective information. Often a child, hearing or deaf, will coo and babble. If this ceases, usually around eight months of age, be highly suspicious of severe congenital loss. If it is impossible to determine, simply document the onset is indeterminate.

C. Etiology. The cause of the hearing loss can be an inherited , genetic disorder or the hearing loss can be acquired through some sort of injury. This can be an extremely difficult task, as can be determining onset. In the work up of SNHL, one must determine if there is some reason to suspect injury to a genetically normally coded apparatus. That is, is there a history of birth injury, ototoxic medication, kernicterus, meningitis, or other incident to suspect a reason other than an inherited genetic cause. If there is not such a history, the loss is most likely the result of an inherited deficiency.

CHL is obviously more common than SNHL, thanks to the most common culprit of all hearing impairment in the pediatric population, OM with effusion. This type of hearing loss can be categorized as an infectious injury to a normal hearing ear. Some other causes of CHL involving deformity of the EAC or pinna are generally genetic malformations. Otosclerosis, as previously discussed, is an inherited form of CHL.

Categorizing lesions as genetic or acquired is important to be able to properly counsel the parents regarding future risk to additional children. The help of a geneticist may be sought at the parents request. Determination of inherited hearing loss can engender serious feelings of guilt in the parents. One must be incredibly sensitive to this fact. Determining a loss was the result of an injury or insult can have medical-legal implications, and documentation should be precise and careful. Documenting an undetermined etiology is sometimes helpful in this regard, unless the cause seems quite clear.

IV. Complete Exam. The complete examination requires a focused physical examination, necessary lab, radiologic testing in specific situations and occasionally specialty consultation.

A. Physical examination. Significant abnormalities detected during physical examination may indicate that an observed hearing loss is part of a syndrome. An organized evaluation of abnormalities associated with syndromes may greatly facilitate diagnosis of one of the many syndromes. For example, Table One is an excellent organized sheet to use in beginning the physical exam. Another adjunct to the general exam is Table Two. This table organizes the syndromes by other (in addition to hearing loss) associated abnormalities which fulfill the diagnosis of a recognized syndrome. Either or both of these aids will make the occasional examiner of the pediatric patient with hearing loss faster , more confidant and more complete.

Regarding the otologic examination, it is necessary to clean the EAC and examine it and the tympanic membrane with a microscope. It is best to do this with a pneumotoscope to asses the TM mobility. Don’t forget the forks ! The tuning fork examination can confirm the results of the audiogram, tympanogram and the physical examination. Furthermore, they can be important pieces of information when trying to differentiate a SNHL from a CHL.

B. Laboratory Examination. There is no defined battery of laboratory examinations used for diagnosis. Rather, lab tests in this setting are best used to confirm or negate items in the differential diagnosis. Available lab tests that may be helpful in this capacity are the “TORCHES” antibody panel, FTA-ABS, thyroid function tests, and urinalysis. TORCHES is an acronym to describe antibody assays for toxoplasmosis, other, rubella, CMV, herpes, hepatitis B, and syphilis. Serial sera from both the mother and the infant are required. In the mother a rising specific IgG and/or the presence of IgM indicates active infection. Active infection in the neonate is indicated by IgG antibody levels that are unchanged ( in the normal situation levels should fall) or increase in serial sera over several months. The presence of IgM in the infant indicates active disease. In congenital rubella, the virus can be cultured up to three years after birth. Cultures may be taken from urine, the nasopharynx, and the throat. Cultures can be important because although elevated IgM titers may be highly suggestive of infection, normal titers do not exclude it.

When congenital syphilis is suspected FTA-ABS is required. VDRL often does not demonstrate a positive result in children , therefore is not used in this setting.

Thyroid function tests are indicated if Pendred’s syndrome (congenital defective binding if iodine by the thyroid gland with goiter, and SNHL) is suspected.

Protein found in the urine during routine urinalysis should alert one to the possibility if Alport’s (hereditary nephritis and progressive SNHL) or Muckle-Wells syndrome (nephritis with urticaria and deafness). Urinary examination can also be helpful if metabolic or mucopolysaccharide abnormality is suspected. Dermatan sulfate and heparan sulfate are detected in Hunter’s and Hurler’s syndromes.

C. Radiologic Examination. CT examination does not play a significant role in the examination of children under six years of age with stable SNHL in the absence of other findings.

CT examination is probably most useful in the following situations: progression (or sudden deterioration) of SNHL; presence of vertigo; family history or suspicion of Neurofibromatosis Type II (although MRI is now considered superior in the evaluation of acoustic neuroma); or suspicion of perilymphatic fistula. If perilymph fistula is suspected CT may be helpful to demonstrate abnormalities within the otic capsule or a widely patent cochlear aqueduct, both of which are known to be associated with perilymph fistula.

CT examination of the mastoids can be helpful in determining whether or not a cholesteatoma is present and in assessing the extent of bone erosion involving the lateral wall of the epitympanum(scutum) and of the ossicles. CT is also essential in evaluating EAC atresia to determine the status of the ossicular chain and in assessing the suitability of the given ear for reconstructive surgery.

D. Referrals or special testing.1. ECG. Prolonged Qt interval when associated with syncopal episodes and congenital SNHL is indicative of Jervell and Lange -Neilson syndrome. Routine ECG is probably not warranted in the absence of history of syncopal episodes.

2. Ophthalmology consult. Usher’s syndrome is characterized by a multitude of progressive sensory defects including retinitis pigmintosa (RP) and congenital SNHL. A test for RP is electroretinography. It may be difficult to perform in young children. An ophalmologist skilled in examining young children should be able to make the diagnosis with or without the ERG results. Suspicion of the diagnosis warrants a consultation. Early treatment is essential in minimizing morbidity. Routine ophthalmologic consultation is not necessary.

3. Vestibular testing. It is advisable to test vestibular function in children with SNHL who have difficulty walking, or have difficulty maintaining their equilibrium. Many syndromes have been associated with aberrations in vestibular tests, and therefore aberrations are not specific. Testing is used to localize the cause of the symptoms to the vestibular system. Tests of vestibular function appropriate for children include: caloric tests, torsional swing, rotational chair, electroposturography and ENG. ENG can be performed on children younger than six.

V. CARE A multitude of treatment options exist for the multitude of problems that exist under this very broad heading. What can be summarized of all situations is that a long term treatment plan must be constructed and followed, if morbidity is to be minimized.