Multiple: Hearing Loss

Definition
Description
Demographics
Causes and Symptoms
Diagnosis
Treatment
Prognosis
Prevention
The Future
For more information

Definition

Hearing loss is a disorder in which a person begins to lose the ability to hear in one or both ears. It may come on suddenly or develop slowly over a period of years; it may be temporary or permanent, and vary in severity from mild hearing loss to total deafness. There are many possible causes of hearing loss ranging from birth defects and ear infections (common causes in children) to exposure to high levels of noise in the workplace and the aging process (common causes in adults).

There are two major categories of hearing loss, defined by whether the loss results from problems in the structures of the outer or middle ear or whether it results from damage to the hair cells of the inner ear. The first type is called conductive hearing loss (CHL) and the second type is called sensorineural hearing loss (SNHL). CHL is often reversible while SNHL is not. People who have both CHL and SNHL are said to have mixed hearing loss.

Description

Conductive hearing loss occurs when sound waves cannot move through the structures of the outer and middle ear. Ordinarily, sound

waves are funneled into the ear by the pinna, the visible part of the outer ear. The sound waves then pass through the ear canal, where they cause the eardrum and three tiny bones called ossicles to vibrate. The vibrations of the ossicles cause the liquid inside a snail-shaped structure

called the cochlea to move. The movement of the liquid in turn causes hair cells inside the cochlea to respond. The hair cells convert movement into electrical signals that are then relayed to the brain via the auditory nerve. Conductive hearing loss can occur when the ear canal is blocked by wax or a foreign object, the ear drum is punctured, the ossicles are dislocated, or the ear canal is swollen shut due to infection.

Sensorineural hearing loss is caused by damage to the hair cells in the cochlea or to the nerves that conduct hearing signals to the brain. This damage can be caused by infections (measles, mumps, rubella, influenza, or mononucleosis); by trauma; by diabetes and other disorders that affect the circulatory system; by cancer drugs and some other medications; or by a tumor affecting the auditory nerve. SNHL is sometimes associated with such problems as tinnitus (ringing in the ears) or dizziness.

Demographics

Hearing loss is a common problem in the general American population, particularly in older adults. According to the Centers for Disease Control and Prevention (CDC), most people over the age of twenty begin to develop a mild hearing loss. A third of adults over the age of seventy have trouble hearing. Hearing loss is more common in older men than in older women.

About 24,000 children (three in every 1,000) are born with hearing loss in the United States each year. Causes include genetic disorders, infections before birth (particularly rubella), absence of ossicles or other abnormalities in the shape or inner structures of the ear, or low birth weight.

Did You Know?

Doctors have found that unprotected exposure to sounds above 85–90 decibels (dB) for long periods of time can harm a person's hearing. Here is a list of the decibel levels of various common sounds:

• Weakest sound that can be heard: 0 dB.
• Soft whisper: 30 dB.
• Normal conversation: 60–70 dB.
• Piano music: 60–70 dB.
• Telephone dial tone: 80 dB.
• Freeway traffic: 85–90 dB.
• Trombone or French horn music: 90– 110 dB.
• Subway train 200 feet away: 95–100 dB.
• Power saw: 110 dB.
• Rock music: 115–120 dB.
• Pneumatic drill: 125 dB. This is the level at which most people feel pain in the ear.
• Gun blast, jet engine: 140 dB. This is the loudest recommended noise level even with hearing protection. Even short-term exposure can cause permanent hearing loss.
• Loud rock concert: 150 dB.
• Death of nerve endings and other hearing-related tissues: 180 dB.
• Loudest possible sound: 194 dB.

Hearing loss is equally common in all racial and ethnic groups, as far as is known.

Causes and Symptoms

The most common causes of conductive hearing loss are infections, trauma to the outer or middle ear, a buildup of earwax in the ear canal, foreign bodies in the ear, or dislocation of the ossicles caused by a blow to the ear.

The causes of sensorineural hearing loss include noise-induced hearing loss (NIHL), which causes trauma to the acoustic nerve; changes in atmospheric pressure inside the ear during deep-sea diving; fracture of the bone at the side and base of the skull; drugs that damage the nerves involved in hearing (cancer drugs, some antibiotics, diuretics, and aspirin or ibuprofen); diabetes; tumors on the auditory nerve; infectious diseases (mumps, measles, syphilis, meningitis, mononucleosis, and herpes); and aging.

The symptoms of hearing loss depend partly on the person's age. A baby who has not yet learned to talk or a child with hearing problems may have the following symptoms:

• Not responding to cooing or conversation from the parents or other family members
• Does not react to sudden loud noises
• Has trouble with certain word sounds
• Does not repeat words or phrases used by others
• Uses gestures to communicate with others
• Seems to watch people's faces for clues to understanding what they are saying
• Has trouble paying attention in school
• Turns up the radio or television louder than other members of the family

In adults, the symptoms of hearing loss may include:

• Problems hearing over the telephone
• Having trouble following conversations, particularly if two or more people are talking
• Having to ask others to repeat what they have just said
• Having difficulty hearing higher-pitched sounds, such as the voices of women and children
• Failing to hear the doorbell or telephone ring
• Having difficulty telling the direction of a sound

Diagnosis

Diagnosing hearing problems in babies or toddlers is critical because the period from birth to three years of age is when children learn to use language. Hearing difficulties during this period can affect a child's ability to speak normally. To test hearing in infants and small children, an audiologist (hearing professional) can perform a variety of tests.

In adults, the doctor will examine the ear canal for signs of infection, a foreign object, or damage to the ear drum. A primary care doctor can test each ear separately with a tuning fork to check for conductive hearing loss, but the patient may be referred to an audiologist for more detailed measurement of the type and extent of hearing loss.

Treatment

Treatment for hearing loss depends on the cause. Infections of the outer and middle ear can be treated with medicated ear drops or oral antibiotics. Earwax and foreign bodies in the ear are removed by suction, forceps, or flushing the ear canal with water. If the earwax has hardened, the doctor may use special drops to soften it and have the patient return a few days later to have it removed. Hearing loss caused by medications is treated by discontinuing the medication.

A tumor of the auditory nerve will usually be removed by a neurosurgeon or an otolaryngologist (a doctor who specializes in ear, nose, and throat disorders). Patients with sensorineural hearing loss are also usually referred to ear, nose, and throat specialists for evaluation and treatment.

Patients whose hearing loss is caused by exposure to high levels of noise in their workplace will be advised to wear earplugs or other protective equipment. Well-fitted ear plugs can reduce noise level by about 25 dB. In extreme cases, the patient may be advised to switch jobs.

Conductive hearing loss can be treated by hearing aids, which are electronic devices that fit in or behind the ear and amplify sounds. A recent variation on traditional hearing aids is the bone-implanted hearing aid or BAHA. A BAHA is implanted in the patient's skull by a neurosurgeon. It consists of a titanium post that allows a sound processor to be attached outside the skull. The processor transmits sound waves to the titanium implant, which transfers the sound vibrations to the skull and inner ear. BAHAs are recommended for patients who cannot wear hearing aids inside the ear or for those with one-sided hearing loss.

Another newer treatment for severe sensorineural hearing loss is the cochlear implant. A cochlear implant is an electronic device that is inserted in the inner ear by a surgeon and connected to a device worn outside the ear. Unlike a traditional hearing aid, a cochlear implant does not make sounds louder or clearer. Instead it works by stimulating the auditory nerve directly and bypassing damaged hair cells in the cochlea. Cochlear implants can be used only in adults or children over the age of twelve.

Prognosis

The prognosis of hearing loss depends on the cause and type. CHL is often reversible; typically, patients who suffer conductive hearing loss as a result of a plug of earwax or a foreign body in the ear, an infection of the outer or middle ear, or a ruptured eardrum will find that their hearing returns to normal after treatment.

Hearing loss caused by a medication may or may not improve after the drug is stopped. There is no proven treatment that can restore hearing other than discontinuing the drug.

Hearing loss caused by meningitis, tumors of the auditory nerve, and aging is usually permanent.

Prevention

Hereditary hearing loss cannot be prevented, but there are ways that other people can lower their risk of hearing loss as they get older:

• Avoid using several noisy machines at the same time.
• Learn to enjoy music, television, or radio programs at a moderate sound level.
• Avoid going to loud rock concerts on a frequent basis. Listening to rock music is a common cause of sensorineural hearing loss in teenagers and young adults.
• Wear earplugs when operating noisy equipment or when exposed to loud background noise for long periods of time. Earplugs can mean the difference between a safe and a dangerous level of noise.
• If work or commuting involves exposure to high noise levels, choose quiet activities for recreation or leisure time.
• See a doctor if hearing is lost suddenly or if there is pain, dizziness, or ringing in the ears.

The Future

Hearing loss is a growing concern to public health doctors because there is evidence that it is a growing problem in the United States, particularly among younger adults. One study completed in 2008 estimated that as many as 29 million Americans have at least partial hearing loss.

SEE ALSO Brain tumors; Ear infection; Measles; Rubella

WORDS TO KNOW

Audiologist: A health care professional who is specially trained to evaluate hearing disorders.

Cochlea: A snail-shaped fluid-filled chamber in the inner ear.

Decibel (dB): A unit of measurement for expressing the relative intensity of sounds.

Hair cells: Special cells in the cochlea that convert the movement of the fluid inside the cochlea into electrical signals that travel to the brain via the auditory nerve.

Ossicles: A group of three small bones in the middle ear that transmit sound waves to the cochlea.

Pinna: The visible part of the outer ear.

Tinnitus: The medical term for ringing in the ears.

For more information

BOOKS

Olsen, Wayne, ed. Mayo Clinic on Hearing. Rochester, MN: Mayo Clinic, 2003.

Pryor, Kimberley Jane. Hearing. Philadelphia: Chelsea Clubhouse Books, 2004.

Waldman, Debby. Your Child's Hearing Loss: What Parents Need to Know. New York: Perigee Books, 2005.

PERIODICALS

“Aiding Hearing Loss.” New York Times, September 26, 2006. Available online at http://www.video.on.nytimes.com/index.jsp?fr_story=22877bf669006281649b8d4ccaeed977b66fa46b (accessed on August 18, 2008). This is a three-minute video about the technological advances in hearing aids since the 1990s.

WEB SITES

American Academy of Otolaryngology—Head and Neck Surgery. Hearing Loss. Available online at http://www.entnet.org/HealthInformation/Hearing-Loss.cfm (updated January 2008; accessed on August 18, 2008). This page includes a brief 15-item questionnaire to help readers evaluate their need for a professional hearing test.

Centers for Disease Control and Prevention (CDC). Hearing Loss. Available online at http://www.cdc.gov/ncbddd/dd/hi3.htm (updated October 29, 2004; accessed on August 18, 2008).

How Stuff Works. Hearing. Available online at http://www.howstuffworks.com/hearing.htm# (accessed on August 18, 2008). This is a short animation that describes the basic structures of the ear and how they work.

KidsHealth. What's Hearing Loss? Available online at http://www.kidshealth.org/kid/health_problems/sight/hearing_impairment.html (updated June 2006; accessed on August 18, 2008).

National Institute on Deafness and Other Communication Disorders (NIDCD). Noise-Induced Hearing Loss. Available online at http://www.nidcd.nih.gov/health/hearing/noise.asp (updated May 2007; accessed on August 18, 2008).

National Institutes of Health Senior Health. Hearing Loss. Available online at http://www.nihseniorhealth.gov/hearingloss/toc.html (updated March 13, 2007; accessed on August 18, 2008).