What is hearing loss?
Hearing loss is any amount of impairment in hearing, from temporary and slight hearing loss to profound hearing loss. Ear infections that produce fluid in the middle ear can cause temporary hearing loss that goes away when the fluid is removed.
Here are some other types of hearing loss:
Conductive hearing loss: sound waves which hit the ear drum are not properly transmitted from the ear drum into the inner ear where the hearing nerve resides.
Sensorineural hearing loss: sound waves reach the inner ear but a problem with the cochlea, nerve or brain is the cause for lack of hearing. About 40,000 newborns each year are diagnosed with hearing loss, with one in 1,000 experiencing significant hearing loss. Half of these kids' hearing loss is hereditary. Most of the time, the cause of hereditary hearing loss cannot be found.
Mixed hearing loss: a combination of conductive and sensorineural hearing loss. This cause of hearing loss is less common than other causes.
There are ten known risk factors for newborn hearing loss:
Family history of hearing loss,
In utero infection,
Hyperbilirubinemia requiring exchange transfusion,
Birth weight less than 1500 grams,
Apgar scores of 0 to 4 at one minute or 0 to 6 at five minutes,
Mechanical ventilation (greater than five days),
Physical appearance of known syndrome.
Of those children with hearing loss associated with a known syndrome, advancement in the fields of genetics and molecular biology have allowed us to identify many of these syndromes. Sixty to 70% of these children have autosomal recessive hearing impairment, making it the most common pattern of transmission. In these cases, the parents have normal hearing but carry the recessive gene, and there is a 25% chance of the children being affected. The three mode of transmission is autosomal dominant inheritance, which accounts for the other 20 - 30% of cases. In this instance, one parent usually has hearing impairment and carries the abnormal gene, and there is a 50% chance that their children will be affected. A small percentage of hereditary hearing impairment is due to x-linked abnormalities. Because girls have two x chromosomes and boys only have one, x-linked disorders are "carried" by girls and "show-up" in boys.
The terms hereditary and familial are sometimes confusing to many parents. When a disorder is hereditary, we mean to say that there is an identifiable genetic basis for the disorder. There is usually an inheritance pattern that is recognizable by examining family history and seeing a definite pattern. However, when a disorder appears to be more common in a certain family but shows no definitive pattern of inheritance, we call this familial. In hereditary disorders, a percentage of affected children can be predicted. In familial disorders, affected individuals appear randomly and cannot be predicted.
Common Types of Hereditary Hearing Impairment
neurofibromatosis type II
autosomal dominant delayed (late) progressive sensorineural hearing impairment.
Hereditary causes of hearing loss are suspected in all cases of hearing impairment. Two factors which increase levels of suspicion are U-shaped audiograms and consanguinity of the parents (parents related before marriage). In general, the younger the child upon diagnosis and the less apparent the alternative causes, the more likely the diagnosis is of hereditary hearing impairment. A hereditary cause, however, must be considered even in adolescents and young adults because hereditary hearing impairment can occur with delayed onset. When hereditary hearing impairment is suspected, parents and siblings of the affected patient should also have audiologic testing.
Testing for hearing loss
There are no blood tests which are available to diagnose specific type of hearing loss. Your physician will probably order a hearing assessment by audiogram or ABR (auditory brain stem response). In addition, vestibular testing (testing of the balance system) may also be recommended. Although no specific blood test may identify hearing loss, some testing may be suggested by your physician and may include urinalysis (Alport syndrome), thyroid function studies (Pendred syndrome), EKG (JLN syndrome), ophthalmologic exam (Usher syndrome), computerized tomography (CT scan) or magnetic resonance imaging (MRI).
Otosclerosis - Otosclerosis is an autosomal dominant inherited disorder. It is a relatively common progressive disease of the middle ear. It may first become apparent with conductive hearing loss due to stapes (stirrup bone) fixation, but may progress to include sensorineural hearing loss. Hearing can usually be restored by surgery.
Treacher-Collins syndrome - Treacher-Collins is an autosomal dominant disorder. There is a characteristic appearance in this syndrome, and usually one parent will closely resemble the child. Abnormalities of the ear may include a small external ear, ear tag or narrowing and/or complete absence of the external ear canal. Other findings may include malformed middle ear bones. Conductive hearing loss is the most common hearing problem.
Goldenhar syndrome - Physical findings in this case may be one sided and may include the jawbone, ear, palate and the voice box. Hearing loss is usually conductive in nature.
Waardenburg syndrome - This syndrome is an autosomal dominant disorder with some facial findings as well as hair hypopigmentation (white forelock or early graying of the hair). Hearing loss in Waardenburg syndrome may range from mild to profound and may be one sided or effects both ears. It is usually sensorineural in character.
Branchio-Oto-Renal syndrome - This syndrome is an autosomal dominant syndrome with association between ear deformity (40%), hearing impairment and renal dysplasia. Mixed hearing loss (nerve and conductive) is most common.
Usher syndrome - Usher syndrome is autosomal recessive. This disorder usually is characterized by fairly profound congenital deafness and may or may not have abnormal balance function. These patients may eventually also suffer severe visual impairment and suffer from rhinitis pigmentosa.
Pendred syndrome - Pendred syndrome an autosomal recessive disorder characterized by thyroid enlargement and sensorineural type hearing loss. In more than half the patients, hearing loss is severe to profound, progressive and involve both ears.
Jervell and Lang-Nielsen syndrome - In this syndrome which is also autosomal recessive, there may be a history of syncopal episodes in a congenitally deaf child. Associated abnormalities on an EKG would be diagnostic.
Alport syndrome - Alport syndrome is a x-link disorder that usually involves congenital sensorineural hearing impairment and nephritis. Because it is x-linked, mothers are usually carriers without the disease, and the syndrome is more severe in males. The diagnoses of these hereditary hearing loss syndromes as well as non-hereditary hearing loss involves careful history taking and physical examination as well as testing. Your physician will suggest selected laboratory and x-ray studies based on the physical examination and history involving your particular child. Only some of the laboratory or x-ray studies listed above will be done on your child as not all of these tests may be appropriate in your situation. Therefore, selection of these particular studies is best decided on an individual basis.