Case 1
A three week old male infant, born at full term with no complications and with good prenatal care, did not pass a two stage hearing screening, OAE (otoacoustic emission) and ABR (auditory brainstem response), in either ear. He came back for an outpatient rescreen two weeks later and an OAE screening was performed again. The OAE was absent in both ears. The hospital hearing screening program notified the Department of Health (DOH) Newborn Hearing Screening Program and the infant’s pediatrician. He was then referred to Children’s Medical Center for a comprehensive diagnostic evaluation. A pediatric audiologist performed a series of audiological tests which consisted of a case history, middle ear evaluation, outer hair cell evaluation using OAE and ABR testing to estimate his hearing thresholds in each ear and to determine the type and degree of hearing loss. His parents reported no family history of hearing loss. The test results concluded that he has a bilateral severe to profound sensorineural hearing loss. His parents were very devastated but determined to move on and find out what they should do next to communicate with him. His parents gave the audiologist permission to refer the infant to the DOH Early Intervention program and parent support group. His pediatrician initiated a referral to an otolaryngologist, geneticist and an ophthalmologist for vision testing as he will rely heavily on his vision due to his lack of hearing.
Case 2
A three month old male infant was seen for a routine audiological evaluation due to a complete cleft palate. He passed his newborn hearing screening prior to newborn discharge. His parents reported a reflux of food and fluid into the nasal cavity after every feeding. The audiologist performed tympanometric testing which resulted in a bilateral type B tympanograms (no eardrum mobility) with intact eardrums. Otoacoustic emissions testing was performed of which no emissions were observed. In view of his age, behavioral audiometric testing was not appropriate. Therefore, the degree of hearing loss was unclear. The audiologist referred him to a pediatric otolaryngologist for further evaluation and necessary management. His middle ear status was monitored using tympanometry and OAE testing. The infant developed recurrent acute otitis media and the otolaryngologist inserted a ventilation tubes during palatoplasty. Behavioral audiometric testing was performed at seven months of age.
Hearing loss is the most common developmental disorder identifiable at birth and its prevalence increases throughout school-age due to additional cases of late-onset, late identification, and acquired hearing loss (1). The discovery of the otoacoustic emission (OAE) phenomenon in laboratories at London’s Royal National Throat Nose and Ear Hospital by Dr. David Kemp (2) led to the development of an automated device which made screening newborns for hearing loss possible. In 1988, the Whipps Cross Hospital in London became the first hospital in the world to provide routine newborn hearing screening with OAEs. In 1989, a comprehensive study funded by the Maternal Child and Health Bureau was conducted in the United States. It resulted in the introduction of universal newborn hearing screening across the United States in the mid-to-late 1990s. Hawaii was the second state in the nation to implement newborn hearing screening under the guidance of Dr. Jean Johnson, director of the Hawaii Zero-to-Three project; Dr. Calvin Sia, with the Carnegie project and the Hawaii Chapter of the American Academy of Pediatrics; and Dr. Nancy Kuntz, director of the Family Health Service Division of Hawaii Department of Health (3).
In 2007, The Joint Committee on Infant Hearing (JCIH) comprised of representatives from the American Academy of Pediatrics, American Academy of Otolaryngology-Head and Neck Surgery, American Academy of Audiology, American Speech-Language-Hearing Association, Council of Education of the Deaf, and several other supporting agencies endorsed the early detection and intervention of infants with hearing loss. A national goal for Early Hearing Detection and Intervention (EHDI) was established as "1 – 3 – 6" where infants should be screened no later than 1 month of age, receive a comprehensive audiological evaluation no later than 3 months of age, and receive appropriate intervention at no later than 6 months of age (4). The primary EHDI goal is to maximize linguistic competence and literacy development for children who are deaf or hard of hearing. Any delays may result in lower educational and employment levels in adulthood.
SURVEILLANCE OF HEARING LOSS IN CHILDREN
The AAP in their position statement, "Recommendations for Preventive Pediatric Health Care," recognized that hearing loss can occur at any time in one’s life--prenatal, postnatal and throughout adulthood. Harlor and Bower (5) provided a complete resource for understanding risk factors of late onset and progressive hearing loss, when and how to assess hearing in a physician’s office, and whom children with hearing loss should be referred to.
The 2007 JCIH position statement listed conditions and circumstances related to the late development and progressive hearing loss as shown in the following table.
| Caregiver concern regarding hearing, speech, language, or developmental delay. |
| Family history of permanent childhood hearing loss. |
| Neonatal intensive care of > 5 days, or any of the following regardless of length of stay: ECMO (extracorporeal membrane oxygenation), assisted ventilation, exposure to ototoxic medications (gentamicin and tobramycin) or loop diuretics (furosemide), and hyperbilirubinemia requiring exchange transfusion. |
| In-utero infections, such as CMV (cytomegalovirus), herpes, rubella, syphilis, and toxoplasmosis. |
| Craniofacial anomalies, including those involving the pinna, ear canal, ear tags, ear pits, and temporal bone anomalies. |
| Physical findings, such as a white forelock, that is associated with Waardenburg syndrome which includes sensorineural or permanent conductive hearing loss. |
| Syndromes associated with hearing loss or progressive or late-onset hearing loss, such as neurofibromatosis, osteopetrosis, and Usher syndrome. Other frequently identified syndromes include Waardenburg, Alport, Pendred, and Jervell and Lange-Nielson. |
| Neurodegenerative disorders, such as Hunter syndrome, or sensory motor neuropathies, such as Friedreich ataxia and Charcot-Marie-Tooth syndrome. |
| Culture-positive postnatal infections associated with sensorineural hearing loss, including bacterial and viral (e.g., herpes simplex viruses and varicella) meningitis. |
| Head trauma, especially basilar and temporal skull fractures requiring hospitalization. |
| Chemotherapy. |
Case 3
A five year old healthy male, with normal development and without any history of ear infections or serious illnesses, did not pass his hearing screening in the left ear at his pediatrician’s office. His father reports that he passed his OAE newborn hearing screening because of the results noted on his immunization card. He was then referred to an otolaryngologist for further otological evaluation which was normal. The otolaryngologist referred him to a pediatric audiologist. The middle ear test results were consistent with type A tympanograms suggesting normal eardrum mobility and middle ear pressures. Otoacoustic emissions were very robust in the right ear but absent in the left ear. Play audiometric test results were repeated twice and the results were consistent with a left sided severe to profound sensorineural hearing loss. His parents noted that he always placed the telephone receiver on his right ear even if they initially placed it on his left ear. The audiologist recommended a natural rest ABR and the results confirmed a suspicion of unilateral auditory neuropathy spectrum disorder which was missed by the OAE newborn hearing screening.
In the pediatric health care office, children under three years of age can be screened using a developmental screen including speech and language, and a physical examination of the ear including pneumatic otoscopy and parental report. Children with a risk factor for late developing hearing loss should receive a formal audiological evaluation by a pediatric audiologist at least once in the first three years of life. Children receiving extracorporeal membrane oxygenation (ECMO) or having a cytomegalovirus (CMV) infection should be screened for hearing loss at least once a year prior to 36 months of age. Children older than three can be screened for hearing loss in their pediatrician’s office. The American Academy of Pediatrics has developed a comprehensive publication on this topic, "Hearing Assessment in Infants and Children: Recommendations Beyond Neonatal Screening" (5). In general, for this latter group, screening consists of a physical examination of the ear including pneumatic otoscopy, parental report of the child’s auditory behavior, and objective pure tone air conduction audiometric screening. The American Academy of Audiology Clinical Practice guidelines for childhood hearing screening provides several important points to follow when performing pure tone air conduction screening. These are the following: perform a biological check on the pure tone screening equipment prior to using the audiometer; screen at 1000, 2000, and 4000 Hz at a 20 dB HL intensity level; present a tone more than once but no more than 4 times if a child fails to respond; only screen in a quiet room where a normal hearing adult is able to hear 15 dB tones presented by the testing audiometer; fail the child for a lack of response at any frequency in either ear; rescreen immediately after failure by removing the headphones, reinstructing the child and repositioning the headphones. For school aged children, screen at least at preschool, kindergarten, and grades 1, 3, 5, and either 7 or 9. Some children are easily instructed to respond to the tones by raising their hand each time they hear the tone. Some children between ages three and five will understand better with a play method. In the play method, the tester leaves the headphones on the table, and demonstrates to the child (using 50 or 60 dB tones at 1000 Hz) how to stack a ring or drop a cube in a bucket when the tones are heard.
Automated hearing screening equipment is commercially available in the market. However, a single-channel portable manually operated audiometer with either circum-aural or insert earphones is the best choice because the audiometer can produce frequencies between 250 and 8000 Hz at intensity levels ranging from 0 to at least 90 dB HL. In addition, the manual operation allows greater flexibility in meeting the performance variability present in young children, especially ages 3-5 years. High frequency hearing screening is useful for children in grades 5, 7 and 9 to rule out noise-induced hearing loss. Audiometers should be calibrated annually to the current standards developed and adopted by the American National Standards Institute (ANSI 3.6-2004). Annual calibration is usually performed by a certified service technician. The audiometer distributor should be able to provide the name of the calibration company for every state.
AUDIOLOGICAL TESTING PROCEDURES
Commonly used audiological testing procedures are tympanometry, otoacoustic emissions, behavioral audiometry, acoustic reflex testing, eustachian tube function test, and auditory brainstem response (ABR) testing.
Tympanometry is a test to evaluate the status of the middle-ear transmission system. The outcome is displayed as a graph to depict the relationship of air pressure in the ear canal to the impedance (resistance to movement) of the ear drum and the middle ear system. The results are categorized into three shapes: type A (normal, looks like a symmetric tent or a mountain peak) where the middle ear system is moving according to the pressure applied, type B (flat) where there is no movement or restricted movement of the eardrum due to middle ear fluid or a perforated tympanic membrane, and type C (the peak pressure is in the negative area, so this looks slike an asymmetric peak) which is usually related to the dysfunction of the eustachian tube. There are variations of the type A named as type As (also known as A shallow; shallow mobility) and type Ad (also known as A deep; hypermobility).
Otoacoustic emissions can be a distortion product or transient (click) evoked. Dr. David Kemp summarized that otoacoustic emissions are sounds made by our inner ear as it works to extract information from sound to pass on to the brain. These biological sounds are a natural by-product of this energetic biological process and their existence provides us with a valuable "window" on the mechanism of hearing, allowing us to detect the first signs of deafness, even in newborn babies. Dr. Kemp (2) further described that, to record otoacoustic emissions, a probe is inserted into the ear canal. The probe closes the ear canal, keeping the OAEs in and any noise out. The probe both stimulates the ear with precisely defined sounds and records the sounds made by the ear via a tiny microphone. Separating the applied sound from the ear's own sound is a delicate process requiring a computer microprocessor. Click-evoked OAEs (also called transient evoked OAEs - TEOAEs) consist of a complex response waveform which can be broken down into different frequency bands (typically half octaves). Distortion product OAEs are evoked by a pair of tones (typically one-third-octave apart).
The third test to be discussed is behavioral audiometry. The goal in this type of audiometric testing is to determine the hearing thresholds for speech frequencies, which are 250 - 8000 Hz. Ultra high frequency audiometric testing is usually used to monitor ototoxicity. There are three forms of behavioral audiometry. The first form is visual reinforcement audiometry. This testing method is usually used for children between 7 months and 27 months adjusted age. The reinforcement can be animated toys or video images. The second form is play audiometry and tangible reinforcement audiometry. In this method, children are trained to perform a task when they hear the testing tones, for example, stacking a ring or pushing an object or marker to receive a small toy from a toy dispenser. The third form is conventional audiometry which was described earlier.
Acoustic reflex testing is very useful in narrowing the differential diagnoses of hearing loss since it separates auditory neuropathy or other retrocochlear disorders from cochlear hearing loss. High intensity sounds are used to elicit a contraction of the stapedius muscles. However, this test alone is not sufficient to be used for interpretation.
The eustachian tube function test is a special test to assess the mechanical integrity of the eustachian tube. It is one of the features available in the tympanometric testing equipment. Conventional tympanometry will give us some ideas about the status of the eustachian tube at the time of the testing but does not provide information about the chronic condition. The eustachian tube function test is only appropriate for older children and adults who are able to understand verbal instruction. Tympanograms are repeated several times and the patient is instructed to swallow water between tympanograms. In general, a shift in pressure between 15 to 20 daPa indicates normal eustachian function.
Lastly, auditory brainstem response (ABR) testing (also known as brainstem auditory evoked response, or BAER) has two useful application outcomes. One is to estimate hearing thresholds of infants below seven months of age or of an individual who otherwise is not able to undergo behavioral audiometric testing. The second outcome is to evaluate the integrity of the auditory brainstem system. ABR is highly reproducible and easily recorded in a restful or sleeping patient; however, it can be misinterpreted if signals are contaminated with physiological artifacts and extraneous interference due to a restless individual. For this reason, the patient has to be sleeping, fully rested, or sedated during the testing. At the present time, one ABR manufacturer is able to sell a commercial unit which is less sensitive to interference in non-sedated or sleeping infants. These advances in the recording parameters would provide major benefits to patients, audiologists, and hospitals.
TYPE AND DEGREE OF HEARING LOSS
There are several different types of hearing loss. In conductive hearing loss, there is insufficient conduction of sounds through the external ear canal and the middle ear system (tympanic membrane, ossicles and Eustachian tube). In sensorineural hearing loss, there is damage in the cochlea or in the nerve pathways. Mixed hearing loss can occur when there is a combination of these two. Another type is the auditory neuropathy spectrum disorder (ANSD). According to ANSD guidelines published by the Bill Daniels Center for Children’s Hearing in 2008 (6), ANSD is used to describe a disorder characterized by evidence of normal cochlear outer hair cell (sensory) function and abnormal auditory nerve function. The last type is central auditory processing disorder (CAPD). The American Speech-Language-Hearing Association (ASHA) working group on CAPD (7), broadly stated that CAPD refers to the efficiency and effectiveness by which the central nervous system (CNS) utilizes auditory information. The assessment and management of this disorder are very intricate and beyond the scope of a standard audiology practice.
There are several classification systems to describe the degree of hearing loss. The one commonly used for children is the ASHA classification (8) which is based on the impact of the hearing loss on the child’s speech and academic access. Flexer et al., described that: hearing loss is not a mere loss of loudness, rather, sounds are often smeared together causing them to be distorted. Speech, therefore, might be audible, but not intelligible (9).
The degree of hearing loss can be seen in the following table:
To better understand this classification, hearing professionals use the "speech banana" graphic representation to describe the area where consonants and vowels of human speech appear on an audiogram.
MANAGEMENT OF HEARING LOSS
For conductive hearing loss, any postnatally acquired hearing disorder usually responds well to medical intervention. Such disorders are otitis media, excessive cerumen, tympanosclerosis, cholesteatoma, and otitis externa. On the other hand, congenital conductive disorders caused by outer and middle ear structural anomalies either have to wait until the patient is older or they may remain too complex to be treated. Examples under this category would be ear atresia and deformities of the ossicles.
Children newly diagnosed with sensorineural hearing loss (SNHL) or auditory neuropathy spectrum disorder (ANSD) have to be referred to a pediatric otolaryngologist to obtain a complete evaluation and medical clearance for hearing amplification if appropriate and to an ophthalmologist. Also, parents with children having ANSD should be offered a referral to a geneticist and neurologist.
Air and bone conduction amplification are commonly used for patients with chronic conductive hearing loss and sensorineural hearing loss. Digital technology has been replacing the analog electronic system in hearing aids and has resulted in smaller devices and much improved speech perception. Researchers are continuously striving to improve signal processing strategies to reduce noise interference to speech, to enhance the clarity of speech, and to reduce the occlusion effect of the hearing aid.
Cochlear implantation is the last resort in providing an individual with proper access to speech and is usually reserved for individuals with severe to profound bilateral sensorineural hearing loss. Current FDA guidelines allow cochlear implantation at one year of age for children with congenital hearing loss.
Different from a cochlear inplant, a bone anchored hearing system (BAHS) uses an osseointegration principle in that sounds are transmitted via bone conduction to the inner ear. The device has three main components: a titanium implant surgically embedded in the skull, an external abutment which is exposed outside of the skin, and the external sound processor. This system is used for individuals with unilateral deafness, chronic otitis media that are unable to wear an air conduction hearing aid due to adverse effects, and atresia and craniofacial anomalies.
Lastly, some parents of children or individuals with severe to profound hearing loss may choose manual language and lip reading for their mode of communication.
In conclusion, hearing loss is a common problem that all pediatricians face, and screening is important to prevent problems such as speech delay. After screening, there are many diagnostic tests the audiologist can perform to further diagnose this problem that will help with management. The treatment of hearing loss is dependent on whether it is a conductive or sensorineural hearing loss. Cochlear implantation is a new technology for patients who have severe deafness; however, sign language and lip reading are important ways of communication for those who are hearing impaired.
Questions
1. True/False: Newborns who pass hearing screening prior to discharge from the hospital have a lifetime guarantee of good hearing.
2. True/False: Otoacoustic Emissions testing is a method to test one’s hearing.
3. True/False: Unilateral hearing loss has no significant bad consequences.
4. True/False: Auditory Brainstem Response testing is the only reliable and valid method for testing children under three years of age.
5. What are the common causes of an acquired sensorineural hearing loss?
6. If one of your patients is diagnosed with congenital sensorineural hearing loss, what type of medical evaluation is useful or sometimes necessary?
References
1. American Academy of Audiology Clinical Practice Guidelines. Childhood Hearing Screening. September 2011. http://www.audiology.org/resources/documentlibrary/Documents/ChildhoodScreeningGuidelines.pdf
2. Kemp DT. The OAE story, an illustrated history of OAE research and applications through the first 25 years. 2003, Otodynamics Ltd.
3. Johnson JL, et al: Newborn Hearing Screening in Hawaii. Hawaii Med J 1997; 56: 352-355.
4. Joint Committee on Infant Hearing. Year 2007 Position Statement: Principles and Guidelines for Early Hearing Detection and Intervention Programs. Pediatrics 2007; 120(4): 898-921.
5. Harlor ADB, Bower C: Hearing Assessment in Infants and Children: Recommendations Beyond Neonatal Screening. Pediatrics 2009; 124 (4): 1252-1263.
6. Bill Daniels Center for Children’s Hearing. Guidelines for Identification and Management of Infants and Young Children with Auditory Neuropathy Spectrum Disorder. 2008: Children’s Hospital Colorado.
7. (Central) Auditory Processing Disorders [Technical Report]. (2005) From American Speech-Language-Hearing Association. Retrieved from http://www.asha.org/policy.
8. American Speech-Language-Hearing Association. Retrieved July 7, 2013 from http://www.asha.org/uploadedFiles/AIS-Hearing-Loss-Types-Degree-Configuration.pdf.
9. Flexer C, Wray D, Leavitt R. How the student with hearing loss can succeed in college: A handbook for students, families and professionals. 1990, Washington D.C.: The Alexander Graham Bell Association for the Deaf.
Answers to questions
1. False. Although passing the newborn hearing screen, hearing problems can develop later in life.
2. False. Otoacoustic emissions (OAEs) are sounds produced by the healthy inner ear. The presence of an OAE shows that the sensory components of the cochlea are functioning. The patient could still have a central hearing loss. Absent or unidentifiable OAEs are caused by cochlear and conductive hearing losses, but also by contaminating noise. In other words, if we can record an OAE, the inner ear is working. If we cannot, it does not necessarily mean it is not working. A few people with normal hearing do not have recordable OAEs. Someone with hearing loss greater than 25–30 decibels (dB) also does not produce OAEs.
3. False. It is consequential. Acquired unilateral hearing loss is medically significant. Congenital unilateral hearing loss presents academic consequences.
4. False. Children at seven months adjusted age to 30 months of age can be successfully assessed using Visual Reinforcement Audiometry. ABR will no longer be an appropriate option for children older than seven months except for children with severe cognitive delay or behavioral issues. If ABR is needed for children older than 7 months, sedation is required because these children will no longer able to sleep naturally to participate in the testing.
5. Ototoxic medication, head injury, meningitis and encephalitis, ear infections, excessive noise exposure, and illnesses such as mumps and measles.
6. Otolaryngologist, ophthalmologist, and geneticist.