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Testing for hearing loss in children.

Hearing impairment is the number one birth defect. The prevalence of hearing loss in the general population of infants and young children ranges from one in 750 to one in 2000. In the "at-risk" population that figure is 30 to 60 times higher than in the general population. "At-risk" children are those who have other identifiable disabilities or who may be susceptible due to premature birth.

The appearance of hearing loss in the majority of cases is a surprise. Greater than half of the children with hearing loss have NO risk factors for the disorder.

The period of development from birth to three years of age is a critical period for the development of normal speech and language (although the period actually extends to age 12!). It is ideal to assess hearing as early as possible, within days of birth if possible, and critical to rapid intervention. However, it is more realistic to establish a goal of hearing assessment within the first three months and intervention within six months of birth.

Even mild hearing loss in one ear can affect the course of speech and language development. Research has shown that once the critical period is passed it is difficult for a child to "catch up" even with intervention.

Infants with hearing loss can be fitted with amplification devices as early as six weeks of age. With amplification and appropriate intervention the likelihood of more normal speech and language development is greater.

Approximately 75 to 80 percent of genetic hearing loss involving a single gene mutation is "autosomal recessive." This means that when this type of hearing loss exists, neither parent expresses the disorder. The disorder may not even be known in the family and it usually takes a careful genetic search to locate it. Children with these syndromes are usually profoundly hearing impaired at birth, the hearing loss is non-progressive and most often low-frequency hearing is unaffected. Examples of autosomal recessive syndromes are Usher's, Jervell and Lange-Nielsen, and Pendred syndromes.

Autosomal dominant syndromes account for approximately 20 percent of genetic hearing loss. These syndromes include Waardenburg, Alport, Treacher Collins and Crouzan syndromes. With these syndromes, there is hearing loss at birth but it is progressive and affects all frequencies. Approximately two percent of genetic hearing loss is sex-linked. These syndromes include otopalatal-digital and Hunter syndromes. In these syndromes, the hearing loss is usually conductive or mixed conductive and sensorineural.

Chromosomal abnormalities are seen in about one percent of the newborn population. Children with Down and Cri-du-Chat syndrome are examples of syndromes which can display conductive, sensorineural or mixed-type hearing losses.

Types of Hearing Loss

Sensorineural hearing loss may be either sensory (due to sensory or hair cell dysfunction in the inner ear) or neural (related to the auditory nerve carrying information from the inner ear to the brain). These are often difficult to distinguish but with recent technology, audiologists are better able to evaluate whether the loss is sensory or neural.

Conductive hearing loss represents a sound conduction problem. Dysfunction of the tympanic membrane, ossicular chain, middle ear space and eustachian tube result in a failure of sound to conduct properly to the inner ear. Cerumen (earwax) accumulation in the ear canal or atresia (or closure) of the canal are also causes of conductive hearing loss

"Mixed" hearing losses have both a conductive and a sensorineural component. Sensorineural hearing loss requires auditory rehabilitation such as: learning lip reading, speech reading, and methods of manual communication. In almost all cases, conductive hearing loss can be improved by medication or surgery.

Degrees of Hearing Loss

Hearing loss can range from slight to profound. When the frequencies or tones most important for hearing speech, 500, 1000, and 2000 Hertz (Hz), are involved, the degree of involvement can be used to classify the extent of the problem. Mild hearing losses, measured in degrees of loudness ranging from 20 to 40 decibels (dB), can result in difficulties only with soft speech. Moderate losses (from 40 to 60 dB) can cause frequent difficulties understanding normal level speech. Severe losses (60 to 90 dB) result in difficulty understanding all but very loud or amplified speech. Profound hearing losses (90 dB +) usually result in an inability to understand even amplified speech.

Audiograms

An audiogram is a chart of hearing across frequency (250 to 8000 Hz). It indicates the hearing thresholds (softest detectable sounds) at each frequency. Speech information above threshold is audible, information below threshold cannot be heard. The ability to hear across the frequency range between 0 and 40 dB is critical for the development of normal speech and language.

Testing the Hearing of Infants and Young Children

Testing infants and young children requires diligence, creativity, and imagination in addition to audiological expertise. Getting frequency-specific information using regular pure tone audiometric protocol is difficult if not impossible with infants, some young children and exceptional children. Pediatric audiology can be considered a subspecialty of audiology. The pediatric audiologist must have a broad clinical knowledge and the technical expertise to get accurate and meaningful results.

Evelyn Cherow, director of audiology policy for the American Speech-Language Hearing Association (ASHA), states, "ASHA and three federal agencies have been working for several years to support universal newborn hearing screening programs. ASHA continues to support a number of state and federal legislative proposals. The federal legislation (H.R. 2923), introduced by U.S. Rep. James Walsh (R-NY) will provide grant support to the states to establish and implement statewide programs for early detection, diagnosis, and intervention for newborns and infants with hearing loss."

The audiological evaluation for infants and young children includes behavioral testing, Auditory Brainstem Response, Otoacoustic Emissions, and Impedance measures.

According to ASHA, eight states currently mandate universal screening and 18 have a legislative mandate to screen high risk new born infants. The majority of the rest have programs other than those mandated by the state, operating to screen new born infants.

Behavioral Tests

Arousal testing using a high frequency band of noise at 90 to 100 dB has been used to elicit a response (i.e. eye blink, eye widening or arousal from sleep). Using a variety of noisemakers, expected responses from infants and young children are;

BIRTH TO SIX WEEKS: eye widening, startle, blink, arousal from sleep.

SIX WEEKS TO FOUR MONTHS: eye shift, blink, quieting, head turn to sound.

FOUR TO NINE MONTHS: head turn to sound, direct localization of sounds to the side.

NINE TO 24 MONTHS: direct localization to sound to the side, above and below.

Visual Reinforcement Audiometry (VRA)

This involves the presentation of a visual stimulus following an appropriate localization response. This results in the enhancement of the response behavior which leads to a more accurate clinical assessment of hearing. This technique is used with children age two or older.

Tangible (or Visual) Reinforcement Operant Conditioning Audiometry (TROCA or VROCA)

TROCA, VROCA and conventional (handraising) audiometry is used with children from ages two to five. These highly structured procedures utilize candy or trinkets (reinforcers) dispensed automatically if the child presses a button when a tone is perceived. In the case of VROCA, a visual reinforcement is presented in place of a tangible reinforcement. The child receives no reinforcer if an inappropriate response is made. This technique uses earphones in a sound treated environment TROCA and VROCA have been used with exceptional children with success in assessing hearing thresholds.

Auditory Brainstem Response (ABR)

This is the electrical response of the auditory system. Simply, it is the auditory portion of the EEG, extracted by signal averaging, in response to click stimuli delivered to the ear. Although not a true test of hearing, it verifies the integrity of onset sensitive neural units in the afferent (when a sensory nerve carries a message toward the brain), auditory pathway from the cochlea to the highest points in the auditory brain-stem. This does not require voluntary responses from the child.

Otoacoustic Emissions (OAE o DPOAE)

This test identifies the presence or absence of nonlinear and active processes involving the outer hair cells in the inner ear. While not a test of hearing, the emissions offer frequency-specific information relating to the function of the inner ear. This is the only test which specifically tests the inner ear. Behavioral tests and the ABR depend on the status of the central auditory nervous system. OAE's can be rapidly obtained even from sleeping infants and young children.

Impedance Measures

Simply stated, the tympanogram is obtained by presenting a tone into the ear canal and recording the movement of the ear drum and the middle ear bones. A minor amount of pressure is applied and then removed. The instrument tracks how the ear absorbs and reflects the tone under all the conditions of pressure. A curve is created which translates to the compliance (flexability) of the middle ear. These measures are differentially diagnostic for fluid in the middle ear space, eustachian tube dysfunction, tympanic membrane integrity and other middle ear pathologies.

The future in a voice from the past

Marion Downs is often considered the "Mother of Pediatric Audiology." She worked tirelessly for over 50 years to establish a policy of universal detection of hearing loss in infants and young children. She said, "....the goal is all. Not just the children with parents who can afford testing and monitoring; not just those who happen to fall into a category that places them at risk for deafness; not just the ones who happen to be in the right place at the right time to be screened, but all children. They are all entitled to be touched by the screening hand of modern technology."

RELATED ARTICLE: Common Signs of Childhood Hearing Loss

BIRTH TO 6 MONTHS

* Does startle, cry or react to unexpected loud noise

* Does not arouse from sleep to loud noise

* Does not try to imitate sound

* Cannot be soothed by parent's voice

* Does not turn head toward voice

6 TO 12 MONTHS

* Does not point to familiar people or objects when asked

* No evidence of babbling

* At 1 year of age does not seem to understand "wave bye-bye" or "clap hands" by listening alone

13 MONTHS TO 2 YEARS

* Does not turn head to soft speech

* Does not respond on the first call

* Is unaware of environmental sounds

* Does not imitate simple words

* Does not appear to use the same sounds as children with normal speech

* Listen to TV at loud level

* Sits very close to TV

* Unresponsive to voices on the telephone

* Changes hands constantly when listening on the telephone

* Surprised look when the child realizes someone is speaking to them

The single most important sign of hearing loss is lack of or delayed development of speech and language!

RELATED ARTICLE: Risk Factors

FAMILY

* History of hereditary childhood sensorineural hearing loss.

PREGNANCY

* Mother used drugs or alcohol

* Mother had flu, rubella, or a viral infection.

BIRTH TO 28 DAYS

* Birth weight less than 3.5 pounds

* Craniofacial deformities

* Hyperbilirubinemia

* Apgar score of 0-4 at 1 minute, 0-6 at five minutes

* Meningitis

* Received antibiotics intravenously

29 DAYS TO 2 YEARS

* Communication or developmental delay

* Meningitis

* Head trauma associated with skull fracture

* Ototoxic medications

Gary Hilt holds a master of science in audiology and speech pathology and works as an audiologist with the Kessler Rehabilitation Institute in Saddle Brook, NJ, as well as in conjunction with other eye, ear nose and throat specialist. He also has his own private practice, the EARLAB, Inc. Amplification Laboratory, in Fairlawn, NJ.

For more information on hearing loss and legislation for new born screening, contact:

American Speech, Language, Hearing Association 10801 Rockville Pke Rockville, MD 20852 Telephone: (301) 897-5700.
COPYRIGHT 1998 EP Global Communications, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1998 Gale, Cengage Learning. All rights reserved.

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Author:Hilt, Gary
Publication:The Exceptional Parent
Date:May 1, 1998
Words:1931
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