Hearing Loss in Newborns and Infants: Deafness vs. Auditory Neuropathy

Charles I. Berlin, PhD

Audiologists can now identify different types of hearing loss objectively using a combination of screening tools in the newborn. If the screening tools suggest a hearing loss, then follow-up with complete testing should include both a diagnostic level Otoacoustic Emissions test and an Auditory Brainstem Response Test which will help confirm the hearing loss and point to management techniques.

Why should we screen for hearing loss?

The lack of hearing can keep a child from learning language and speaking normally. Language and speech are among the most important skills we need to impart to our children so that they can become literate self-sufficient citizens when they mature.

Who should be screened for hearing loss?

There are people who feel all newborns should be screened, and others who feel that we should start with children at high risk (for example, prematures, jaundiced babies, infants with family history of deafness, etc.) But everyone agrees that the earlier the diagnosis is made the better for the child. Dr. Christy Yoshinaga-Itano has recently shown that language develops for hearing impaired children treated before 6 months far earlier than for children who are not managed until after 1 year. In fact, some children managed early often show normal language development compared to normal hearing peers.

What do the screening tests do?

There are two commonly used screening tests:

1. An automated ABR which does a computer controlled screening ABR test and tells the operator whether or not to refer for full diagnostic work up. This evaluates the effectiveness of the inner ear and nerves in sending messages to the brain.
2. An automated otoacoustic emissions screening test which also alerts the diagnostician to whether or not additional testing is appropriate. This test measures sounds which come from certain hair cells in the inner ear; these sounds are only present when the hair cells are normal.

What should happen if a child fails a screening test?

A full diagnostic battery of Otoacoustic Emissions and Auditory Brainstem Response using 2 different sounds, one which starts with an inward push of the sound ( a positive polarity click ) and one which starts with an outward pull of the sound (a negative polarity click), then a bone conduction test and tone-specific tests should be performed by an Audiologist. Some organizations prefer the use of tone bursts instead of clicks to enhance accuracy.

What are the possible outcomes?

1. Normal: Both otoacoustic emissions and ABR are normal at very low levels of sound testing for all the different types of stimuli. These children will not have speech and language problems which can be helped by hearing aids.
2. Absent responses: No ABR and no emissions usually mean severe to profound hearing loss. These children can usually be helped with hearing aids and/or cochlear implants and special education by experts in hearing loss. An absent response to a click however does not mean total deafness.

Normal Emissions and Absent or mirror-image ABR: This is consistent with a so-called auditory neuropathy where the waves obtained through the two different polarity clicks are mirror images and really come from a part of the inner ear which does not respond to hearing aids. These patients require special attention from experienced diagnosticians, do not usually learn language through their hearing mechanism at first, and respond well to Cued Speech-Language (a method for teaching your native language with the aid of hand and mouth positions which is usually easy for normal hearing parents to learn and use.

Some children with jaundice in their backgrounds actually outgrow the hearing problem, others get worse and may respond to cochlear implants. This is a new area and many professionals disagree on management or are unfamiliar with the issues.

Can an audiologist tell a child is hearing impaired by just observing how they respond to sound?

Not always, although if you feel your child has a hearing problem trust your judgment and ask for some objective tests to evaluate your concerns. Most audiologists today rely on objective tests in addition to their own clinical observations. While any objective tests can be misinterpreted or poorly administered, they usually help solidify the behavioral observations which, in turn, can be done under highly controlled statistical and computer controlled conditions.

What are some of the danger signs of hearing loss?

If your child doesn't startle to loud noises or awaken from sleep by very loud noises in the house,,,

If your child is not babbling repetitively (ba-ba ba da da da etc.) by 8 to 10 months, or if your child doesn't turn to localize the source of your voice by 7 to 8 months, you should be wary. Ask for an objective set of tests by an audiologist.