Describe the key steps to early diagnosis of childhood hearing loss. Introduction. The prevalence of congenital ..... Turner syndrome. Progressive Hearing Loss ...
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otolaryngology
Pediatric Audiology: Ryan B. Gregg, AuD,* Lori S. Wiorek, MA,† Joan C. Arvedson, PhD‡
Objectives
A Review
After completing this article, readers should be able to:
1. Know at what age a child’s hearing can be tested accurately. 2. Recognize when a child should be referred for audiologic testing. 3. Discuss the importance of early diagnosis and management of children who have hearing loss. 4. Describe the key steps to early diagnosis of childhood hearing loss.
Introduction The prevalence of congenital deafness in the United States is estimated to be approximately 1:1,000 or 0.1%. Approximately 3:1,000 well babies have hearing loss of varying degrees. Approximately 6:1,000 combined well and at-risk babies have some degree of hearing loss (HL). Prior to the onset of Universal Newborn Hearing Screening (UNHS), there was an inverse relationship between degree of HL and average age of identification. In other words, mild HLs were identified much later than were severe HLs. Prior to UNHS, many children who had bilateral profound HL were not identified until 18 to 24 months of age. In some instances, children who had mild HL were not identified until 4 years of age or older. The single best predictor of school success is a child’s speech and language skills. HL has a significant negative impact on a child’s speech and language development. If a child is unable to hear sounds across the speech spectrum (250 through 4 kHz) at an appropriate level, it is unlikely that the child will be able to produce those speech sounds correctly. Furthermore, most speech and language learning takes place from birth to about 3 years of age. Even a borderline-to-mild HL that is not detected can affect a child during that critical Abbreviations period. The longer the time spent with a HL and the more time within the critical period that the child goes without appropriate AD: auditory dyssynchrony management, the poorer the long-term prognosis becomes AN: auditory neuropathy with regard to speech and language development. This is why BOA: behavioral observation audiometry early identification and UNHS are essential. BTE: behind the ear BAER: CI: CHL: dB HL: FM: HL: OAE: PTA SNHL: SRT: UNHS: VRA:
brainstem auditory evoked response cochlear implant conductive hearing loss decibels of hearing level frequency modulated hearing loss otoacoustic emissions pure tone average sensorineural hearing loss speech recognition threshold Universal Newborn Hearing Screening visual reinforcement audiometry
Degree of HL The degree of HL is highly variable and is measured in decibels of hearing level (dB HL) and plotted on an audiogram, which is a chart of an individual’s hearing sensitivity (Fig. 1). Intensity or loudness is on the y-axis of the audiogram. Frequency or pitch is on the x-axis. The degree of HL can be classified in terms of one absolute figure, such as the pure tone average (PTA) of air conduction thresholds measured at 500, 1,000, and 2,000 Hz. That number determines the severity of the loss. For example, a PTA of 71 dB HL is considered to be a severe HL. The degree of
*Senior Pediatric Audiologist. † Pediatric Audiologist. ‡ Program Coordinator, Feeding and Swallowing Services, Children’s Hospital of Wisconsin; Professor, Department of Pediatrics, Medical College of Wisconsin, Milwaukee, WI. 224 Pediatrics in Review Vol.25 No.7 July 2004
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Conductive HL
Figure 1. Recording forms used in audiometric testing. A) Audiogram (dB HL) that
visually describes degrees of hearing loss based on decibel levels. B) Speech testing, including speech detection threshold (SDT), speech recognition threshold (SRT), and speech discrimination ability.
A conductive HL (CHL) occurs in either the outer or middle ear. CHL impedes the air conduction pathway from the pinna and external auditory meatus to the tympanic membrane and ossicles in the middle ear. As seen in Figure 2B, the inner ear or cochlea is otherwise fully functional, and bone conduction thresholds usually are within normal limits. CHL varies widely in degree and may be congenital or acquired. Examples of congenital forms of CHL are aural stenosis and atresia, which can affect the outer as well as the middle ear structures. Various ossicular chain malformations and abnormalities may occur, including stapes fixation. Examples of acquired CHL include, but are not limited to, foreign bodies in the ear canal, cerumen impaction, otitis externa, otitis media with or without effusion, tympanic membrane perforation, cholesteatoma, ossicular discontinuity, collapsing ear canals, otosclerosis, and tympanosclerosis. The degree of CHL can vary between 20 and 60 dB HL, depending on the cause. Further, many CHLs are medically or surgically treatable.
Sensorineural HL HL also can be described in terms of configuration. For example, a loss may be described as mild falling to moderate in degree, or a loss may be described as a moderate rising to mild in degree. This technique of degree classification tends to be a more accurate description of the HL than is the use of PTA.
Types of HL Different types of HLs can be present in infants and children of all ages. Most HLs are peripheral, which for the purposes of this article means that they are relegated to the outer, middle, or inner ear or the auditory nerve. The three primary types of peripheral HL are conductive, sensorineural, and mixed (Fig 2). The remainder of the HLes are central in origin.
A sensorineural HL (SNHL) affects the inner ear (cochlea) or auditory nerve (eighth cranial nerve). Most SNHLs are sensory and restricted to the cochlea and do not result from an abnormality to the auditory nerve. Routine audiometric testing does not differentiate between a sensory loss and a neural loss. Electrophysiologic measures (brainstem auditory evoked response [BAER] and otoacoustic emissions [OAE]) must be used to differentiate between sensory and neural causes. A SNHL cannot be identified on routine physical otoscopic examination. In SNHL, the outer and middle ears generally appear unremarkable on physical examination. Bone conduction thresholds are within 10 dB of air conduction thresholds (Fig. 2C). In rare instances, an SNHL can be neural, which means that the deficit is at the level of the auditory nerve. These HLs typically are Pediatrics in Review Vol.25 No.7 July 2004 225
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Mixed HL Mixed HL occurs when an individual has a CHL overlying a SNHL. With a mixed HL, abnormalities are identified in the outer or middle ear as well as the inner ear. Mixed HL varies in degree. The air conduction thresholds exceed bone conduction thresholds by more than 10 dB, and the bone conduction thresholds are outside of the normal range (ie, ⬎15 to 20 dB HL) (Fig. 2D). However, the gap between the air conduction thresholds and the bone conduction thresholds (ie, air-bone gap) cannot exceed 60 dB. In some cases, the conductive component of the mixed HL can be medically/surgically treated, which would result in the individual being classified as having an SNHL.
Auditory Processing Disorders Although outside the scope of this article, some children exhibit auditory processing disorders or central auditory processing disorders that have a central nervous system cause. Generally, the lesion is beyond the level of the cochlear nucleus where the auditory nerve enters the brainstem. In other words, the peripheral auditory mechanism is intact, and hearing sensitivity is within Figure 2. Examples of a normal audiogram (A) and each of the three major hearing loss normal limits. The signal becomes types described in the text: (B) conductive, (C) sensorineural, (D) mixed. Results are shown degraded when the auditory stimufor the right ear only. lus reaches the level of the brainstem and beyond. Therefore, manlabeled auditory neuropathy (AN) or auditory dyssynagement of these disorders differs from that for a chrony (AD). Behavioral responses of AN/AD range peripheral HL. from normal detection of sounds with difficulty hearing in a noisy environment to total lack of auditory awareCauses of HL in Infants and Children ness. In addition, children who have AN/AD generally HL in children can result from multiple causes and can be do not respond well to traditional forms of audiologic present at birth (congenital HL) or acquired later. management, such as hearing aids. Preliminary case reports indicate positive outcomes with cochlear implants. Congenital SNHL, just like CHL, can be congenital or acquired. Congenital HL results about equally from environmental SNHL can vary in degree from borderline normal to a factors and genetic factors. Approximately 50% of conprofound HL. Causes of SNHL are discussed at greater genital HL is caused by environmental factors, including, length later. but not limited to, congenital perinatal infections (eg, 226 Pediatrics in Review Vol.25 No.7 July 2004
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TORCH complex), pre/perinatal asphyxia, and prenatal ototoxicity. Approximately 70% of genetic-based congenital HL appears to be nonsyndromic, and the other 30% is syndromic. The inheritance pattern in the nonsyndromic group is estimated to be 75% autosomal recessive and 25% autosomal dominant. In addition, a small number of genetic, nonsyndromic HLs are either X-linked or mitochondrial-based (Table 1).
Acquired HL can develop during infancy or childhood (progressive or delayed-onset HL). In 1972, the Joint Committee on Infant Hearing developed a list of risk indicators for HL in infants and children. This statement was updated several times, with the most recent published in 2000 (Table 2), and advocates for UNHS and the need to identify all infants who have HL. Risk indicators are divided into two categories. The first is used with neonates (0 to 28 d of age) where UNHS is not yet available. These risk indicators place the infant at higher risk for HL than an infant who does not have the risk indicators. The second category lists indicators that place a neonate (0 to 28 d of age) or infant (29 d through 2 y of age) at risk for progressive or delayed-onset SNHL or CHL. Due to the risk of delayed-onset HL, an infant who has any one of these risk indicators should receive audiologic testing every 6 months until 3 years of age. Once a child fails a UNHS or is identified as having a high-risk indicator, he or she is referred to an audiologist for audiologic testing.
Audiologic Testing Procedures Every child who is not responding to sounds or is not developing appropriate speech and language skills needs a hearing evaluation, which can be completed at any age. In most states in the United States, hearing tests on newborns are completed before they are discharged from the hospital. Several behavioral and electrophysiologic tests are available to obtain hearing thresholds for children. The child’s chronologic age and developmental age determine the test method (Table 3).
sides. The audiologist looks for changes in the child’s behavior that would indicate that the child heard the stimuli (eg, cessation of movement, widening of eyes, cessation of pacifier sucking, or attempts to look for a source of the sounds). BOA can assist in excluding a severe-to-profound HL, but it does not exclude HL or confirm normal hearing. In addition, threshold and earspecific information cannot be obtained. VISUAL REINFORCEMENT AUDIOMETRY (VRA) Typically, VRA is used with children whose developmental ages are 6 months to 3 years. The child is placed on a parent’s lap between two speakers (headphones are not used). Most children have strong localization skills. When the stimuli are presented, the child looks for the sounds. When the child looks for the sound, an animated toy is turned on to reinforce that behavior. Most children like the animated toy and continue to look for the sounds to see the toy. Thresholds can be obtained by this method. However, because speakers are used rather than headphones, ear-specific information is not obtained. The results are referred to as “the better ear results.” Because the results are not ear-specific, the test may not detect an HL in one ear. CONDITIONED PLAY AUDIOMETRY Children from ages 3 to 5 years usually participate in this activity. They wear headphones that provide ear-specific information. In addition, bone conduction thresholds can be obtained. The latter results differentiate between CHL and SNHL. The child wears headphones for air conduction testing or a bone oscillator for bone conduction testing and is conditioned to complete a task in response to an auditory stimulus (eg, drop a block in a bucket). In addition, speech testing can be completed at this stage. A speech recognition threshold (SRT) is the lowest intensity at which a child can repeat two-syllable words and should correspond with PTA. Speech discrimination ability is the percentage of one-syllable words that the child can repeat correctly at a comfortable listening level, which typically is 40 dB louder than the SRT.
Behavioral Procedures Behavioral testing is completed in a sound booth and requires the child to respond definitively to auditory stimuli. Four behavioral tests are in common use. BEHAVIORAL OBSERVATION AUDIOMETRY (BOA) BOA is used for children whose skill level is younger than 6 months developmental age. The child is placed on a parent’s lap. Stimuli are presented through two external speakers, which are located to the child’s right and left
CONVENTIONAL AUDIOMETRY Children older than 5 years of age usually can be tested by conventional audiometry. The procedure is the same as conditioned play audiometry, except that the child raises a hand or presses a button in response to the auditory stimuli rather than completing a play task. Earspecific and bone conduction thresholds are obtained. Speech testing for SRT and discrimination also can be completed. Pediatrics in Review Vol.25 No.7 July 2004 227
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Classification of Hereditary Deafness Table 1.
Table 1. ●
Congenital Sensorineural Hearing Loss Disorders ●
●
●
●
● ●
●
Craniofacial and Skeletal Disorders — Absence of tibia — Cleidocranial dysostosis — Diastrophic dwarfism — Hand-hearing syndrome — Klippel-Feil — Saddle nose and myopia — Split-hand and foot Integumentary and Pigmentary Disorders — Albinism with blue irides — Congenital atopic dermatitis — Ectodermal dysplasia — Keratopachyderma — Lentigines — Onychodystrophy — Partial albinism — Piebaldness — Pili torti — Waardenburg syndrome Eye Disorders — Hallgren — Laurence-Moon-Biedl-Bardet Nervous System Disorders — Cerebral palsy — Muscular dystrophy — Myoclonic epilepsy — Optococochleodentate degeneration — Richards-Rundel Cardiovascular System Disorders — Jervell and Lange-Nielsen Endocrine and Metabolic Disorders — Goiter — Hyperprolinemia I — Iminoglycinuria — Pendred Miscellaneous Somatic Disorders — Trisomy 13 through 15 — Trisomy 18
● ●
●
● ● ●
Craniofacial and Skeletal Disorders — Achondroplasia — Crouzon syndrome — Marfan syndrome — Pierre Robin — Pyle disease Integumentary and Pigmentary Disorders — Knuckle pads and leukonychia Eye Disorders — Mo¨bius syndrome Miscellaneous Somatic Disorders — Turner syndrome
Progressive Hearing Loss Disorders ●
Craniofacial and Skeletal Disorders — Apert syndrome — Fanconi anemia syndrome — Goldenhar syndrome — Madelung deformity — Malformed, low-set ears — Mohr syndrome — Otopalatodigital — Preauricular appendages — Proximal symphalangism — Thickened ears — Treacher Collins Integumentary and Pigmentary Disorders — Forney syndrome Eye Disorders — Cryptophthalmos — Duane syndrome
●
●
(Continued)
228 Pediatrics in Review Vol.25 No.7 July 2004
Renal Disorders — Nephrosis, urinary tract malformations — Renal-genital syndrome — Taylor syndrome
Disorders of Congenital Sensorineural or Conductive Hearing Loss
Congenital Conductive Hearing Loss Disorders ●
Continued
Sensorineural Progressive Hearing Loss of Later Onset — Craniofacial and Skeletal Disorders y Roaf syndrome y Van Buchem syndrome — Eye Disorders y Alstrom syndrome y Cockayne syndrome y Fahr corneal dystrophy y Flynn-Aird y Norrie syndrome y Optic atrophy and diabetes mellitus y Refsum syndrome — Nervous System Disorders y Acoustic neuromas y Friedreich ataxia y Hermann syndrome y Myoclonic seizures y Sensory radicular neuropathy y Severe infantile muscular dystrophy — Endocrine and Metabolic Disorders y Alport syndrome y Amyloidosis, nephritis, and urticaria y Hyperprolinemia II y Hyperuricemia y Primary testicular insufficiency Sensorineural or Conductive Progressive Hearing Loss — Craniofacial and Skeletal Disorders y Albers-Scho¨nberg disease y Engelmann syndrome y Osteogenesis imperfecta y Paget disease — Endocrine and Metabolic Disorders y Hunter syndrome y Hurler syndrome Progressive Conductive or Mixed Hearing Loss — Otosclerosis
Reprinted with permission from Northern J, Downs M. Hearing in Children. 4th ed. Baltimore, Md: Williams & Wilkens; 1991
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High-Risk Indicators for Hearing Loss*
Table 2.
Birth to 28 Days-Universal Hearing Screening Not Available: — Neonatal intensive care unit admission >48 h — Stigmata or features associated with a syndrome known to include SNHL or CHL — Family history of permanent childhood SNHL — Craniofacial anomalies — In utero infection, such as cytomegalovirus, herpes, Toxoplasma, or rubella Birth to 2 Years-Risk for Progressive/Delayed Onset SNHL and/or CHL: — Parental or caregiver concern regarding hearing, speech, language, and/or developmental delay — Family history of permanent childhood hearing loss — Stigmata or features associated with a syndrome known to include SNHL, CHL, or eustachian tube dysfunction — Postnatal infections associated with SNHL, including bacterial meningitis — In utero infections such as cytomegalovirus, herpes, rubella, syphilis, and toxoplasmosis — Neonatal indicators, specifically hyperbilirubinemia requiring exchange transfusion, persistent pulmonary hypertension of the newborn associated with mechanical ventilation, and conditions requiring the use of extracorporeal membrane oxygenation — Syndromes associated with progressive hearing loss, such as neurofibromatosis, osteopetrosis, and Usher syndrome — Neurodegenerative disorders, such as Hunter syndrome, or sensorimotor neuropathies, such as Friedreich ataxia and Charcot-Marie-Tooth syndrome — Head trauma — Recurrent or persistent otitis media with effusion for at least 3 months SNHL⫽sensorineural hearing loss; CHL⫽conductive hearing loss. *Adapted from the Joint Committee on Infant Hearing. Year 2000 position statement: principles and guidelines for early hearing detection and intervention programs. Am J Audiol. 2000;9:9 –29
Electrophysiologic Procedures Electrophysiologic procedures are used for children who cannot complete behavioral testing or to assess the function of a portion of the auditory system (eg, tympanometry to assess middle ear function). The need may be dictated by the child’s age, developmental abilities, or lack of cooperation. These procedures do not require the child to respond to auditory stimuli. The child sits quietly or sleeps during the procedures.
TYMPANOMETRY Tympanometry is not a hearing test; hearing thresholds are not measured. Tympanometry evaluates the function of the middle ear, which provides information about the health of the middle ear, such as the presence of middle ear fluid, tympanic membrane perforation, and excessive cerumen. Knowledge about the health of the middle ear helps determine whether an HL may be temporary or permanent. A probe is placed firmly against the external ear canal opening to create a seal. The pressure within the ear canal is changed from negative to positive. The measurements obtained are tympanic membrane compliance and ear canal volume. A normal healthy tympanic membrane should have peak compliance when pressure is equal on both sides of the tympanic membrane. A child’s normal ear canal volume is considered to be 0.5 mL to 1.0 mL. Findings for common disorders are shown in Table 4. OTOACOUSTIC EMISSIONS (OAE) OAE test outer hair cell function of the cochlea. OAE testing can be completed with children at any age. A quiet, cooperative child is required, but no specific behavioral response is necessary. Noise from the environment or the child interferes with the test, and a reliable result cannot be obtained. Two types of OAE testing can be used: 1) transient evoked OAE and 2) distortion product OAE. A probe is placed in the child’s ear canal, and stimuli are presented from the probe into the ear. Normal outer hair cells create an emission in response to the tone. The probe in the child’s ear has a microphone that measures the emission. Presence of the emission is consistent with normal outer hair cell function. When outer hair cell function is normal, the child’s ear is interpreted as functioning normally. This is a quick test. However, some children become fearful of the probe being placed in the ear canal, which precludes the measurement of reliable OAE. The child who accepts the probe does not have to respond to the stimulus. Therefore, a measurement of cochlear function can be obtained and inferences drawn regarding a child’s hearing when a child cannot complete behavioral testing. Limitations of the test include lack of threshold information. When the emission is absent, the degree of HL cannot be delineated. The emission is absent in the presence of middle ear abnormalities, so permanent hearing ability cannot be determined. OAE testing misses auditory abnormalities that occur beyond the cochlea, such as auditory neuropathy. Pediatrics in Review Vol.25 No.7 July 2004 229
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Table 3.
Audiologic Testing Procedures
Test
Age
Advantages
Disadvantages
Behavioral Observation Audiometry (BOA)
