Congenital and Hereditary Disorders

Hearing Sense Recovery

Help For Hearing Loss Sufferers

Get Instant Access

Sensorineural hearing losses present at birth are congenital disorders. Some, but not all, of them, are hereditary, i.e., genetic, and the others are complications of pregnancy. Most are due to cochlear defects. There may be destruction of the vascular and membranous regions supporting the organ of Corti (Scheibe deformity) or loss of the neural elements, from the hair cells inward toward cranial nerve VIII (Mondini deformity).

It is important to discover congenital hearing loss as early as possible to promote rehabilitation and fit a hearing aid, if indicated. Speech awareness, the sooner the better, is critical for development of the auditory centers of the brain. An analogy with the eye exists: if a child with strabismus is not patched to train the nondominant eye, the visual cortex of the brain for that side does not develop. The auditory cortex is similar.

Congenital hearing losses are often suspected before 1 year of age. Unfortunately, many are not discovered until much later than this. Usually the mother another family member first notes a problem. It is then important for the clinician to heed the family's concerns and follow through with audiometric evaluation. An experienced audiologist can get a good idea about a potential loss with basic audiometric testing in very early infancy.

Excellent diagnostic information can be gained by ABR. This test measures auditory responses in the sedated infant, and characteristic curves can even pinpoint the problem to the middle ear, inner ear, or cranial nerve VIII. Also, otoacoustic emissions (OAE) tests are involuntary screening tests that identify spontaneous sound emissions from normally functioning cochlear hair cells. An increasingly large number of hospital neonatal units in the country screen all newborns using either ABR or OAE.

Predominant risk factors for congenital loss are:

1. Family history of hereditary loss.

2. Prematurity, with birth weight less than approximately 1.5 kg (3.5 lb).

3. Maternal rubella during pregnancy.

4. The presence of maxillofacial deformities.

5. Kernicterus, with bilirubin levels greater than 12mg/dl.

6. Neonatal sepsis, especially with meningitis.

7. Forceps delivery, with temporal bone injury.

Hereditary, or familial, hearing loss may be present at birth, but also can develop during childhood or young adulthood. About 20% are reported as autosomal dominant, and 80% as recessive. The age of onset, severity, and audiometric patterns of loss vary greatly because many gene sites are possible. One pattern seen often is the "cookie-bite" audiogram, with an abrupt downward dip in the middle frequencies (Fig. 7.3).

Most of these losses do not involve syndromes with other organ systems, but a few do. Notable is Waardenburg's syndrome, an autosomal dominant disorder associated with widely displaced inner canthi of the eyes and a white forelock of hair. Another is Usher's syndrome, a recessive disorder with an eye problem, retinitis pigmentosa, as well. The severity of hearing impairment in these two is variable. In most familial disorders, the loss is bilateral. Genetic testing can now even localize and typify the gene involved.

There are syndromes of congenital hearing loss that do not involve the cochlea, but rather, the auditory nerve and more central pathways. Auditory neuropathy refers to an inability of the auditory nerve to send a good synchronous signal into the brainstem. These children have intact cochleas with normal OAEs, but abnormal ABRs. They can hear sounds of all frequencies, but fail to understand and develop speech. Kernicterus is a cause

Frequency in Hertz 125 250 500 1K

Frequency in Hertz 125 250 500 1K

I I

I I

>—[(

I

1_1

\i

/

v.

\

/

\

-CC

) 1

I

1 1

I I

1 1

I I

1 1

I I

1 1

I I

1 1

I I

1 1

I I

1 1

Fig. 7.3 "Cookie-bite" pattern of hereditary hearing loss, right ear.

Fig. 7.3 "Cookie-bite" pattern of hereditary hearing loss, right ear.

of some, but not all, cases. A number of afflicted individuals have other peripheral neuropathies, and there are probably genetic factors.

Some children have trouble with central auditory processing, a dysfunction somewhere between the brainstem and cortex. In general, they hear all frequencies normally and have good speech discrimination in quiet testing situations, but do poorly in situations of background noise or distractions. Their problems are milder than those of children with auditory neuropathy and are usually discovered as learning disabilities in school. They are then verified by specialized audiometric testing.

Treatment Summary

Great emphasis must be placed on the early detection of congenital hearing loss. Increasingly, hospital neonatal units are performing routine OAE or ABR screenings on newborns. Nonetheless, the medical practitioner should take seriously any concerned family member who suspects a loss and proceed with an audiology and ENT workup. Treatments for the disorders discussed above are tailored to the type of loss. Most mild to severe cochlear losses are best treated with early hearing aid fitting. Central auditory processing problems respond well to FM listening devices in the learning situation. These involve a microphone on the instructor and receiver earpieces on the student, eliminating background noise. Auditory neuropathy is seldom helped by aids, but instead by visual cues (cued speech, speech reading, or sign language) and possibly the cochlear implant, an electronic device surgically implanted in the inner ear by a very specialized otologic surgeon. The patient with profound hearing loss also has these last two options available. These treatments involve dedicated teams of audiologists, speech pathologists, and possibly specialized surgeons. They are mentioned only briefly in this text; the interested reader may look elswhere for further information.

Was this article helpful?

0 0
Hearing Aids Inside Out

Hearing Aids Inside Out

Have you recently experienced hearing loss? Most probably you need hearing aids, but don't know much about them. To learn everything you need to know about hearing aids, read the eBook, Hearing Aids Inside Out. The book comprises 113 pages of excellent content utterly free of technical jargon, written in simple language, and in a flowing style that can easily be read and understood by all.

Get My Free Ebook


Responses

Post a comment