Hearing loss
Hearing loss results from a mechanical or nervous impediment to the transmission of sound waves. The major forms of hearing loss are classified as conductive loss (interrupted passage of sound from the external ear to the junction of the stapes and oval window), sensorineural loss (impaired cochlea or acoustic [eighth cranial] nerve dysfunction, causing failure of transmission of sound impulses within the inner ear or brain), or mixed loss (combined dysfunction of conduction and sensorineural transmission). Hearing loss may be partial or total and is calculated from this American Medical Association formula: Hearing is 1.5% impaired for every decibel that the pure tone average exceeds 25 dB.
Causes and incidence
Congenital hearing loss may be transmitted as a dominant, autosomal dominant, autosomal recessive, or sex-linked recessive trait. Hearing loss in neonates may also result from trauma, toxicity, or infection during pregnancy or delivery. Predisposing factors include a family history of hearing loss or known hereditary disorders (otosclerosis, for example), maternal exposure to rubella or syphilis during pregnancy, use of ototoxic drugs during pregnancy, prolonged fetal anoxia during delivery, and congenital abnormalities of the ears, nose, or throat. Premature or low-birth-weight neonates are most likely to have structural or functional hearing impairment; those with serum bilirubin levels above 20 mg/dl also risk hearing impairment from the toxic effect of high serum bilirubin levels on the brain. In addition, trauma during delivery may cause intracranial hemorrhage and may damage the cochlea or the acoustic nerve.
Sudden deafness refers to sudden hearing loss in a person with no prior hearing impairment. This condition is considered a medical emergency because prompt treatment may restore full hearing. Its causes and predisposing factors may include:
❑ acute infections, especially mumps (most common cause of unilateral sensorineural hearing loss in children), and other bacterial and viral infections, such as rubella, rubeola, influenza, herpes zoster, and infectious mononucleosis; and mycoplasma infections
❑ blood dyscrasias (leukemia, hypercoagulation)
❑ head trauma or brain tumors
❑ metabolic disorders (diabetes mellitus, hypothyroidism, hyperlipoproteinemia)
❑ neurologic disorders (multiple sclerosis, neurosyphilis)
❑ ototoxic drugs (tobramycin, streptomycin, quinine, gentamicin, furosemide, ethacrynic acid)
❑ vascular disorders (hypertension, arteriosclerosis).
Noise-induced hearing loss, which may be transient or permanent, may follow prolonged exposure to loud noise (85 to 90 dB) or brief exposure to extremely loud noise (greater than 90 dB). Such hearing loss is common in workers subjected to constant industrial noise and in military personnel, hunters, and rock musicians.
Presbycusis, an otologic effect of aging, results from a loss of hair cells in the organ of Corti. This disorder causes progressive, symmetrical, bilateral sensorineural hearing loss, usually of high-frequency tones.
Minor decreases in hearing are common after age 20. Some deafness due to nerve damage occurs in one of every five people by age 55.
Signs and symptoms
Although congenital hearing loss may produce no obvious signs of hearing impairment at birth, a deficient response to auditory stimuli generally becomes apparent within 2 to 3 days. As the child grows older, hearing loss impairs speech development.
Sudden deafness may be conductive, sensorineural, or mixed, depending on etiology. Associated clinical features depend on the underlying cause.
Noise-induced hearing loss causes sensorineural damage, the extent of which depends on the duration and intensity of the noise. Initially, the patient loses perception of certain frequencies (around 4,000 Hz) but, with continued exposure, eventually loses perception of all frequencies.
Presbycusis usually produces tinnitus and the inability to understand the spoken word.
PEDIATRIC TIP The behavior of an infant who’s deaf may appear normal and mislead the parents as well as the professional, especially if the infant has autosomal recessive deafness and is the first child of carrier parents.
Diagnosis
CONFIRMING DIAGNOSIS Patient, family, and occupational histories and a complete audiologic examination usually provide ample evidence of hearing loss and suggest possible causes or predisposing factors.
The Weber, Rinne, and specialized audiologic tests differentiate between conductive and sensorineural hearing loss.
Treatment
After the underlying cause is identified, therapy for congenital hearing loss refractory to surgery consists of developing the patient’s ability to communicate through sign language, speech reading, or other effective means. Measures to prevent congenital hearing loss include aggressively immunizing children against rubella to reduce the risk of maternal exposure during pregnancy; educating pregnant women about the dangers of exposure to drugs, chemicals, or infection; and careful monitoring during labor and delivery to prevent fetal anoxia.
Treatment for sudden deafness requires prompt identification of the underlying cause. Prevention necessitates educating patients and health care professionals about the many causes of sudden deafness and the ways to recognize and treat them.
Hyperbilirubinemia can be controlled by phototherapy and exchange transfusions. Children need the appropriate immunizations. Medications that may be ototoxic should be used judiciously in children and monitored closely. Reduction of exposure to loud noises generally prevents high-frequency hearing loss.
In people with noise-induced hearing loss, overnight rest usually restores normal hearing in those who have been exposed to noise levels greater than 90 dB for several hours; but not in those who have been exposed to such noise repeatedly. As hearing deteriorates, treatment must include speech and hearing rehabilitation, because hearing aids are seldom helpful. Prevention of noise-induced hearing loss requires public recognition of the dangers of noise exposure and insistence on the use, as mandated by law, of protective devices such as earplugs during occupational exposure to noise.
Amplifying sound, as with a hearing aid, helps some patients with presbycusis, but many patients have an intolerance to loud noise and wouldn’t be helped by a hearing aid.
Special considerations
❑ When speaking to a patient with hearing loss who can read lips, stand directly in front of him, with the light on your face, and speak slowly and distinctly. If possible, speak to him at eye level. Approach the patient within his visual range, and elicit his attention by raising your arm or waving; touching him may be unnecessarily startling.
❑ Make other staff members and facility personnel aware of the patient’s disability and his established method of communication. Carefully explain diagnostic tests and facility procedures in a way the patient understands.
❑ Make sure the patient with a hearing loss is in an area where he can observe unit activities and people approaching because such a patient depends totally on visual clues.
❑ When addressing an older patient, speak slowly and distinctly in a low tone; avoid shouting.
❑ Provide emotional support and encouragement to the patient learning to use a hearing aid. Teach him how the aid works and how to maintain it.
❑ Refer children with suspected hearing loss to an audiologist or otolaryngologist for further evaluation. Any child who fails a language screening examination should be referred to a speech pathologist for language evaluation. The child with a mild language delay may be involved with a home language-enrichment program.
❑ To help prevent hearing loss, watch for signs of hearing impairment in the patient receiving ototoxic drugs. Emphasize the danger of excessive exposure to noise; stress the danger to pregnant women of exposure to drugs, chemicals, and infection (especially rubella); and encourage the use of protective devices in a noisy environment.
Book Source Details
- Book Title: Professional Guide to Diseases (Eighth Edition)
- Author(s): Springhouse
- Year of Publication: 2005
- Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2005 Lippincott Williams & Wilkins.
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Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2008 Williams & Wilkins.
More About Causes of Ear symptoms
» Next page: Benign tumors of the ear canal (Professional Guide to Diseases (Eighth Edition))
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