Matthew was diagnosed as having hearing loss while still in the hospital, one day after he was born. It later proved to be a profound, permanent (nerve) type of hearing loss.
Shanika passed the hearing screening test done at the hospital two days after birth. The parents left the hospital feeling that everything was fine with their baby. Gradually she became less responsive to sounds. She was not startled by loud noises, nor did she turn her head in the direction of voices or sounds.
These children are not alone. A certain percentage of children pass the screening test, yet experience a gradual worsening of their hearing months or years after leaving the hospital because of acquired or progressive loss of hearing. Other newborns fail the hearing test, which later proved to be a permanent loss.
Two to four out of every thousand newborn children have some hearing loss. Three million children have some hearing impairment under the age of 18 in the United States. (1) These children are at risk for learning disabilities, development delays, social and emotional problems.
How did this happen?
Ninety two per cent of children born with permanent hearing loss are born to two hearing parents. (2) Some of the causes are: a viral infection of the mother that infects neonates in the womb or shortly after birth, a history of hearing loss in the family, and at times - no good explanation.
Less frequently, a permanent hearing loss develops over time in spite of the newborn initially passing the hearing test in the hospital. Other causes that might develop over time are wax in the outer ear, fluid or infections in the middle ear, and progressive sensorineural (nerve) loss.
How hearing works
Air Conduction
With air conduction, sounds pass through the outer ear canal, strike the eardrum causing it to vibrate. This vibration puts in motion the three tiny bones in the middle ear. One of them, the stapes, moves in and out of the inner ear kind of like a piston, which causes the fluid to move the inner ear hair cells. These hair cells move somewhat like weeds in water responding to the tune of the water current.
The hair cells change this movement (mechanical energy) into electrical impulses which are sent through the hearing nerve to the brain for interpretation. When everything is working well, your child hears normally.
Bone Conduction
Bone conduction is the transmission of sound into the inner ear through the bones in your head. When you click your teeth, or a tuning fork is placed on bone behind your ear, the transmission of sound is by bone conduction. Some hearing aids use bone conduction hearing systems.
Classification of hearing loss
Sensorineural hearing loss involves damage to the delicate hair cells of the inner ear and/or the auditory (hearing) nerve. Medications, head trauma and a family history of hearing loss are some causes of loss of hearing in children. Ordinarily, medication cannot reverse this type of permanent nerve loss.
A Conductive hearing loss can be the result of wax or foreign objects in the ear canal, fluid in the middle ear, a perforation of the eardrum and birth defects. These are some of the causes of temporary hearing loss in children that can be treated with an office visit (e.g. wax removal), medication or outpatient surgery.
A Mixed hearing loss is a combination of the above two types of hearing loss.
Hearing screening of newborns and infants
All fifty states in the U.S. have established programs to develop and operate newborn hearing screening programs. The federal government has issued ‘guidelines’ that all neonates be screened for loss of hearing before they are one month old. Those that failed the screening test have a complete audiological evaluation by three months of age.
It’s recommended that neonates diagnosed with permanent hearing loss receive medical/surgical, educational, audiological, speech and language support by the age of six months. The above is sometimes referred to as the “1-3-6” plan.
How will my child’s hearing be tested?
Trained personnel perform non-invasive, painless, objective hearing tests usually done while your child is asleep or lying still. Two computerized tests are commonly used for neonatal hearing screening.
Otoacoustic Emission Test (OAE)
OAE is a non-invasive, objective test that helps determine whether or not a hearing loss is present. It evaluates the function of the outer hair cells of the cochlear (inner ear).
A tiny probe is placed in the newborn’s ear canal that produces a sound causing the inner ear to emit ‘echo’ sounds that pass back through the middle ear so they can be recorded via a special microphone. If no sound is detected, the child may have a severe or profound hearing loss; or at times, it may be a false alarm. Careful follow-up and the “1-3-6” plan are essential for these children.
Auditory Brainstem Response (ABR)
This non-invasive, objective, diagnostic test evaluates the simultaneous action of the hearing system. The sound has to be loud enough for the inner ear to transmit it by way of the hearing (auditory) nerve to the brain. As a result, this test can be used to gain information about hearing sensitivity and evaluate auditory nerve function.
It’s important for the child to remain still during this procedure and, not infrequently, sedation is given. Tiny earphones are placed in the ear, electrodes are placed on the child’s head – like the electrocardiogram’s sticky electrodes – and clicking sounds are presented through the earphones. When used as screening tool, the child either passes or fails the test.
Hearing testing for older children
Conditioned Play Audiometry (CPA)
With CPA, children between two and five years of age are conditioned to a play activity, such as putting a block in a bucket or a ring over a peg when they hear a sound. A sound is introduced and the child associates the sound with a play activity. The audiologist may ask older children to raise their hand or press a button when the sound is presented to them.
With the advances in technology and availability of medical information, parents are becoming more empowered in the care of their children.
A future article will discuss a checklist guide for hearing and what parents can do to monitor their child’s hearing development.
References
- American Academy of Otolaryngology
- (Mitchell & Karchmer 2004)