السبت، 11 يونيو 2011

ـ Hearing Loss in Children ـ


Hearing Loss in Children
a risk factor for speech and language impairment
Hearing loss in children is a frequent contributing factor in speech and language impairment. A hearing loss can cause a speech or language disorder in some cases, or it can worsen an already existing speech or language disorder. For this reason, a hearing test is usually a part of a full speech-language evaluation.
If you think about it, it makes sense. To be capable of good language output, you have to have adequate input, and for most languages (sign languages being the obvious exception), the input has to travel through the ears to get to the brain. Hearing loss in children results in limited access to the speech sounds, vocabulary, and grammatical structures of their language; if their hearing loss goes undiagnosed and untreated during the first few years of life, it can have a lasting negative effect on their speech and language development.
What do I know, anyway?
In this section, as in the rest of my site, I am speaking out of my training and experience as a speech-language pathologist. As such, I have some basic training in audiology, but not to the extent that an audiologist would have. In my capacity as a speech-language pathologist, I do not perform full audiological evaluations or make recommendations regarding hearing aids or other amplification devices. I do perform hearing screenings, which are a simple pass-fail measure; if a child fails a screening, I refer the parents to an audiologist for further testing. If a child is diagnosed with a hearing loss, a speech-language pathologist often provides audiological rehabilitation to strengthen listening and auditory processing skills.
I am also speaking here as the father of a child with a unilateral hearing loss. My daughter was diagnosed with a moderately severe mixed hearing loss in the left ear at about age three. I'll talk more about her on my page about unilateral hearing loss.
All hearing losses are not created equal
The first thing to remember about hearing loss in children is that it can come in many different forms.
Before I get into that, though, I want to offer a few definitions:

  • The decibel scale is what we use to measure the loudness (a.k.a. intensity, amplitude) of sounds. The higher the number of decibels (dB), the louder the sound. The decibel scale is a bit tricky in that it is logarithmic instead of linear. Every increase of 10 dB is ten times louder (20dB is 10 times louder than 10 dB; 30 dB is 10 times louder than 20 dB, and 100 times louder than 10 dB, and so on). Also, keep in mind that zero decibels (0dB) is not a complete absence of sound; it is the quietest level at which the average healthy, young ear can hear sound. Some people can hear sounds at -5dB or even -10dB. Although most of us cannot hear sounds quieter than that, complete absence of sound can only exist in a vacuum, where there is no material for sound waves to travel through.
  • Hearing threshold is the quietest level at which a person can hear a sound. Thresholds between 0dB and 20dB are usually considered to be in the normal range. Lower thresholds indicate better hearing; people with thresholds above 20 dB are considered to have a hearing loss. A person may have a different threshold in the left ear than in the right. It's also common for thresholds to vary according to the frequency (pitch) of a sound. Hunters (especially those who don't wear hearing protection) sometimes have elevated thresholds for high frequencies corresponding to the those produced by gun blasts, but normal thresholds for lower-frequency sounds.
  • Frequency is the way we measure the pitch of a sound--how high or low it is. We measure frequency in cycles per second (CPS), also called Hertz (Hz). Sound is caused by vibrations, and the faster something vibrates (i.e., more cycles per second), the higher the sound will be. A typical adult speaking voice ranges from 100 Hz to 220 Hz on average; male voices tend to be at the lower end of that range, and female voices are usually toward the upper end. However, as we speak, we also produce higher frequencies, called harmonics or overtones, and it is these frequencies that change as we produce speech sounds. We need to be able to hear frequencies up to around 3000 Hz to be able to hear vowel sounds clearly, and to hear the difference between /s/ and /sh/ we need to hear up to between 7000 and 8000 Hz. Some types of hearing loss affect our ability to hear all frequencies equally, while others will affect some frequencies more than others. For example, noise-induced hearing loss often affects the higher frequencies more than the lower ones.

Degrees of hearing loss in children
Hearing losses range from mild to profound. A person with a mild hearing loss (hearing thresholds at 20-40 dB) may experience occasional difficulty hearing whispered words or very quiet sounds, or hearing what people are saying in settings with a lot of background noise. A lot of people with mild hearing loss are unaware that they even have a hearing loss. However, even this level of hearing loss in children can affect speech and language development, as well as success in school.
People with a moderate hearing loss (hearing thresholds at 40-70 dB) have difficulty hearing a normal conversation in a quiet room. Unstressed syllables, and words at the ends of sentences where the voice trails off, will be especially troublesome. School children with moderate hearing loss can benefit from a combination of amplification (hearing aids, FM system) and compensatory strategies (sitting close to the teacher, being positioned where they can see the teacher's face clearly).
Many professionals include a category called moderately severe hearing loss, which is typically the upper end of what others call "moderate": hearing thresholds between 55 and 70 dB. This is a helpful category to have, since there is actually a huge difference between 40 dB and 70 dB. Remember that the decibel scale is logarithmic, so a sound at 70 dB is 1,000 times louder than a 40 dB sound. People whose hearing is in this range often cannot hear people's voices at normal conversational levels, although they may be able to hear you if you raise your voice, especially if there is no background noise. Children with moderately severe hearing loss have a hard time learning effectively in a classroom setting unless they are using amplification and compensatory strategies.
A person with a severe hearing loss (hearing thresholds at 70-90 dB) cannot hear conversations held at normal levels. Only a loud voice close to the ear is audible. Severe hearing loss in children is associated with high risk for speech and language deficits. This risk can be reduced through the use of amplification or sign language in addition to compensatory strategies. There are people with this level of hearing loss who consider themselves deaf and use sign language as their primary mode of communication, and there are others who consider themselves hard-of-hearing and rely on amplification and oral communication.
A person with a profound hearing loss (hearing thresholds above 90 dB) is unable to hear any but the loudest noises, if that. Ninety decibels is about the level of a gas lawn mower. Even with hearing aids, most people with this level of hearing loss cannot hear spoken conversation. Children with profound hearing loss often do not benefit from hearing aids. Some parents of children with profound hearing loss elect to enroll their kids in special schools or programs for the deaf, while others choose cochlear implants for their children.
Different types of hearing loss in children
Conductive hearing loss. Plug your ears with your fingers. Are they plugged? Congratulations, you just gave yourself a conductive hearing loss. Fortunately, it's temporary (take your fingers out now--and go wash them before you touch the keyboard again!). A conductive hearing loss occurs due to blockage or structural damage in the ear canal or middle ear. All frequencies are affected equally, so this type of hearing loss can be easily corrected with amplification (hearing aids). In some cases, surgery can repair the damage or remove the blockage, restoring normal hearing. There is no such thing as a good hearing loss, but if you must have one, this is the kind to hope for.
Sensorineural hearing loss results from damage to the inner ear or the auditory nerve, which takes sound impulses from the inner ear to the brain. This type of hearing loss is irreversable and cannot be corrected with surgery. Also, the sensitivity to a given frequency depends on the site of the damage. In other words, you may be able to hear lower frequencies reasonably well, but have trouble with higher frequencies. When this happens, it is difficult, or even impossible, to distinguish among sounds like /s/, /sh/, and /f/. Correction for sensorineural hearing loss usually involves a digital hearing aid, which can be programmed to amplify the specific frequencies the wearer needs.
Mixed hearing loss occurs when there are elements of both conductive and sensorineural factors. Generally, there is damage to the middle ear and the inner ear, as a result of injury, illness, or congenital deformities. In some cases, surgery can correct the conductive issues, but the sensorineural component is irreversible.
In the case of a central auditory processing disorder (CAPD), the outer and inner ear and the auditory nerve are intact, but the brain has difficulty processing the sounds it receives. Areas of particular difficulty for children with CAPD include: listening in the presence of background noise; understanding and remembering directions, lists, and sequences; distinguishing between sounds in words (e.g., hearing bee when someone says key); maintaining attention to listening tasks; and higher-level listening tasks like drawing conclusions, making inferences, or interpreting math "story problems". Only an audiologist can diagnose CAPD, but treatment is usually done by a speech-language pathologist. This is a higher-level processing disorder, so a child with CAPD will be able to pass the kind of hearing screen the public schools provide (the beeps are easier to process than speech). For this reason, plus the fact that a lot of parents and teachers do not really know about CAPD, the approximately 5% of school-aged children who have it are often mis-diagnosed as having attention deficit disorder (ADD). In some very unfortunate cases, they are simply labeled "lazy" or "uncooperative", or accused of "selective hearing".
A bilateral hearing loss affects both ears, but it is possible that the degree or type of hearing loss may not be the same in both ears. For example, one ear may have a moderate conductive loss while the other may have a severe sensorineural loss. This is known as an asymmetrical hearing loss; a symmetrical loss is one in which the degree and type are the same in both ears.
A unilateral hearing loss, as the name suggests, occurs in just one ear; the other ear has normal hearing. A lot of people make the mistake of assuming that a unilateral hearing loss is "no big deal" because the person "can hear just fine" with the unaffected ear. Research has shown, however, that unilateral hearing loss in children is associated with increased risk for speech and language impairments and for difficulty in school. An additional factor with unilateral hearing loss is that it affects a person's ability to localize sound (tell which direction the sound is coming from).

Causes and prevention of hearing loss in children
Causes of hearing loss in children include a variety of genetic and environmental factors. About 50% of hearing losses are due to genetic factors. Some of these are recessive, so it is possible for a child of two parents with normal hearing to be born with a genetic hearing loss. Some environmental factors can cause hearing loss in children before birth (for example, the mother contracts rubella or cytomegalovirus during pregnancy), while others, like otitis media (middle ear infections), ototoxic medications, or noise exposure may cause hearing loss in children after birth.
Because so many cases of hearing loss are caused by environmental factors, education about hearing loss prevention can have a powerful effect on reducing the prevalence of hearing loss in children. Advances in medical diagnosis and treatment have reduced the incidence of illnesses that can cause hearing loss; at the same time, public education efforts have raised awareness of the dangers of noise exposure and the importance of hearing protection in noisy environments.
A fluctuating hearing loss may be caused by recurring bouts of otitis media. Fluid builds up in the middle ear and causes a conductive hearing loss. When the infection goes away, the fluid is re-absorbed (or drains out through a ruptured eardrum) and hearing returns to normal; however, the risk is always there that a viral infection could spread to the inner ear and result in a permanent hearing loss.
A temporary hearing loss may also result from an ear infection. Another possible cause is a build-up of ear wax, or cerumen, in the ear canal. Some people produce more cerumen than average and their ears become blocked as a result, unless they are proactive about managing the build-up. Ear wax buildup rarely causes hearing loss in children, however. Far more common is self-inflicted (or parent-inflicted) blockage of ear wax through the use of cotton swabs (Q-tips) to "clean" the ears. What many people do not realize is that swabs only remove a small amount of ear wax, and actually push most of it farther into the canal, where it hardens and eventually blocks the canal. Always consult a doctor before attempting to remove ear wax from your own ear or from your child's.
Diagnosing hearing loss in children
Until not too long ago, hearing loss in children tended to go undetected until a parent or other family member (usually the mother) noticed that something did not seem right. In the case of a severe hearing loss or deafness, the child might have been between one and two years in age when the parents noticed an absence of response to sound, such as turning toward a parent's voice, waking or startling at loud noises, and so on. Because children with less severe hearing loss, or a loss in just one ear, do respond to sound, these cases were often discovered even later, sometimes not until the child was in school. This is unfortunate, because the first years of a child's life are so important for speech and language development. Hearing losses that go undetected during this time can cause serious setbacks to speech, language, literacy, social interaction, and academic success.
Today, many industrialized nations require universal newborn screening for all babies born in hospitals. Newborns who fail the initial screening are re-screened, and if they fail the second screen, they are referred to an audiologist for a more thorough examination.
If the only kind of hearing test you have ever experienced is the one where you wear a headset and raise your hand when you hear a 'beep', you may be wondering how on earth one would test a newborn's hearing. The answer is that there are several passive tests to check how different parts of the auditory system are working. One type of test measures otoacoustic emissions (OAE), which are 'echoes' produced by the inner ear in response to sound. An earplug with both a speaker and a microphone are placed in the ear canal; the speaker emits a sound, and the microphone detects the echo. Another test detects auditory brainstem responses (ABR), or brainwaves produced in response to sound. Electrodes placed on the scalp detect activity in the brainstem following presentation of a tone through an earplug. For both of these tests, it is unnecessary for the child to raise a hand or indicate in any other way whether he heard the sound. In fact, the quieter and less active the child is, the better, and for ABR testing, it's best for the child to be asleep during the procedure.
It is important for parents, teachers, and others who work with children to be aware of the symptoms of hearing loss in children. There are two main reasons for this. First, I've never heard of a child going to his parent or teacher and saying, "You know, I think I may have a hearing loss. Maybe I should get tested." Children with a hearing loss are often unaware that anything is wrong with their hearing. They may notice that the grown-ups and other kids around them mumble a lot and then get upset with them when they don't understand, but it does not occur to them that this is due to their ears not working properly. Reason number two is that, when children miss something you say, they do not generally cup a hand behind their ear and say, "Eh? Speak up, sonny, I can't hear you!" In fact, if you ask them directly whether they heard you, children (with or without hearing disorders) will often answer "yes", because this is what they think you want to hear. The signs and symptoms of hearing loss in children are much more subtle, and adults who do not have hearing loss on their mind may easily mistake them for something else, like attention deficit disorder, a learning disability, autism, or just plain willfulness.
Symptoms of hearing loss in children will vary in their obviousness depending on the type and severity of the hearing loss. Common warning signs include:

  • not responding to a parent's voice at normal speaking level
  • absent startle response to loud sounds (with some types of hearing loss, however, loud sounds are amplified, even painful, and the child does startle.
  • inability to localize the source (tell where a sound is coming from)
  • difficulty following instructions or requests, despite appearing to listen attentively
  • reduced or absent responses to environmental noises (car horns, approaching footsteps, sirens outside, telephone ringing, doors opening or closing etc.)
  • consistently setting the volume at an unusually high level when watching television or listening to the radio.
  • enjoyment of rhythmic clapping games while appearing uninterested in music
  • immature speech-language development
  • social withdrawal
  • fatigue, frustration, and acting out


Treating hearing loss in children
Some types of conductive hearing loss can be corrected with surgery, or by removal of impacted ear wax. However, most hearing losses are not curable. Treatment usually focuses on some combination of the following elements:

  • amplification, including some combination of analog or digital hearing aids, cochlear implants, or FM transmitter systems.
  • compensatory strategies, such as lip reading, signing, cued speech, optimal seating/positioning, elimination of background noise.
  • prevention of further loss through education on environmental risk factors, such as loud noises, ototoxic medications, and exposure to diseases that can damage the auditory system.
  • cochlear implants, which use electrical impulses to stimulate the auditory nerve directly, bypassing the hearing organs

Hearing loss in children is a huge topic and one could build an entire web site devoted to it. The information I've provided is a good start, but it barely scratches the surface of all there is to know about hearing loss. If you suspect your child has a hearing loss, you should definitely ask your doctor for a referral to an audiologist. Hearing loss does not have to be a barrier to education or to a happy, fulfilling life--if you are proactive about it.

http://www.speech-language-development.com/hearing-loss-in-children.html

ليست هناك تعليقات:

إرسال تعليق