ear disease

▪ human

Introduction

      any of the diseases or disorders that affect the human ear and hearing.

      Impaired hearing (deafness) is, with rare exception, the result of disease or abnormality of the outer, middle, or inner ear. Serious impairment of hearing at birth almost always results from a dysfunction of the auditory nerve and cannot be improved by medical or surgical treatment. In early and late childhood the most frequent cause for impaired hearing is poor functioning of the eustachian tubes (eustachian tube) with the accumulation of a clear, pale yellowish fluid in the middle-ear cavity, a disorder called serous, or secretory, otitis media. In early and middle adult life the usual cause for progressive impairment of hearing is otosclerosis. The usual cause of hearing loss after the age of 60 is presbycusis, a disorder that results from the aging process.

      In most cases when loss of hearing is due to a problem with sound conduction, surgical restoration can correct the defect and restore hearing. When loss of hearing is the result of nerve damage, however, surgery is not of use. Medical treatment of auditory nerve damage is helpful only in rare cases—e.g., when the loss is due to syphilis or an early case of Ménière's disease or in some instances when zinc deficiency is the underlying cause.

      More important than a cure for auditory nerve damage is prevention. Cases of deafness in the newborn due to rubella (German measles) in the mother can be averted with the rubella vaccine. Nerve damage caused by exposure to excessive and prolonged noise is preventable by early detection. One approach is to give routine hearing tests to individuals who work in environments where excessive noise is unavoidable.

      The incidence of impaired hearing in the general population depends on the degree of hearing loss defined as impaired (see ear: The physiology of hearing: Hearing tests: Audiometry (ear, human)). According to U.S. statistics, by age 6, 0.2 percent of all children have impaired hearing in one or both ears that is sufficient to warrant consultation of an ear specialist. By age 18 the number of children with hearing loss sufficient to require diagnostic examination reaches 2.5 to 3 percent. By age 65 the number of adults with a recognizable hearing impairment reaches 5 percent. After age 65 the incidence of impaired hearing rises rapidly. About 30 to 35 percent of individuals between the ages of 65 and 75 and 40 percent of those older than 75 are affected by hearing loss.

      Comparable figures from Great Britain show that 1 in 6 persons is estimated to have some hearing difficulty, but only one-fourth of these have any real handicap, with one-third of this latter group needing hearing aids and 1 in 20 being deaf to all speech and beyond help with a hearing aid. Of British children, 1 in 1,000 is severely deaf, and as many as 7 per 1,000 are estimated to have a level of impairment that requires some form of help.

      The structure and function of the human auditory and vestibular systems are treated in the following sections from the ear article: Anatomy of the human ear (ear, human), The physiology of hearing (ear, human), and The physiology of balance (ear, human). This article deals with the more important diseases and disorders of the outer, middle, and inner ear.

Outer ear

      Diseases of the outer ear are those that afflict skin, cartilage, and the glands and hair follicles in the outer-ear canal. The sound-transmitting function of the outer ear is impaired when the ear canal becomes filled with tumour, infected material, or earwax (cerumen), so that sound cannot reach the tympanic membrane, or eardrum. The most common diseases of the outer ear are briefly described in the following paragraphs.

Infections and injuries

frostbite

      The exposed position of the outer ear makes it the part of the body most frequently affected by freezing, or frostbite. Humidity, duration of exposure, and, most of all, wind, in addition to degrees of temperature below freezing, predispose to the occurrence of frostbite. The frozen area begins along the upper and outer edge of the ear, which becomes yellow-white and waxy in appearance, cold and hard to the touch, and numb with loss of skin sensation.

      In treatment of frostbite the victim is placed as soon as possible in a warm room, but the frozen ear is kept cool by applying ice wrapped in a towel until the returning blood circulation gradually thaws the frozen part from within. Massage of the frozen ear is avoided, for it is likely to injure the skin. Heat applied to the frozen area before circulation is established can result in clotting of the blood in the blood vessels. This in turn can result in death of that part of the ear, which turns black and eventually falls off, a process called dry gangrene.

Hematoma

      Injury to the outer ear can cause bleeding between the cartilage and the skin, producing a smooth, rounded, nontender purplish swelling called hematoma. The accumulation of clotted blood is removed by a surgeon because, if it is left, it will become transformed into scar tissue and cause a permanent, irregular thickening of the outer ear commonly called cauliflower ear and seen in boxers and wrestlers whose ears receive much abuse.

perichondritis

      Infection of the cartilage of the outer ear, called perichondritis, is unusual but may occur from injury or from swimming in polluted water. It is due to a particular microorganism, Pseudomonas aeruginosa. There is a greenish or brownish, musty or foul-smelling discharge from the outer-ear canal, while the affected outer ear becomes tender, dusky red, and two to three times its normal thickness. Prompt antibiotic treatment is necessary to prevent permanent deformity of the outer ear.

External otitis (otitis externa)

      Infection of the outer-ear canal by molds or various microorganisms occurs especially in warm, humid climates and among swimmers. The ear canal itches and becomes tender; a small amount of thin, often foul-smelling material drains from it. If the canal becomes clogged by the swelling and drainage, hearing will be impaired. Careful and thorough cleaning of the outer-ear canal by a physician, application of antiseptic or antibiotic eardrops, and avoidance of swimming are indicated to clear up the infection.

boil in the ear (furuncle)

      Infection of a hair follicle anywhere on the body is known as a boil, or furuncle. This can occur in a hair follicle in the outer-ear canal, especially when there is infection of the skin of the canal. It always occurs because of a particular type of germ known as staphylococcus. Because the skin of the ear canal is closely attached to the underlying cartilage, a boil in the ear canal is especially painful, with swelling, redness, and tenderness but generally without fever. Heat applied to the outer ear by a hot-water bottle or electric pad helps the infection to come to a head and begin to drain. Treatment with a systemic and local antibiotic is required to prevent other hair follicles from becoming infected.

erysipelas of the outer ear

      Erysipelas is an infection in the skin caused by a particular type of streptococcus and characterized by a slowly advancing red, slightly tender thickening of the skin. It may begin at the ear and spread to the face and neck. Centuries ago erysipelas epidemics caused severe and often fatal infections. In AD 1089 one of the most severe erysipelas epidemics occurred. The disease was referred to as St. Anthony's fire because those who prayed to St. Anthony were said to recover; others, who did not, died. Today erysipelas is usually a mild and comparatively rare infection that clears up rapidly when treated with an antibiotic.

leprosy

      Leprosy, seen rarely outside the tropics today, was another scourge of ancient times that sometimes affected the outer ear. It is caused by the leprosy bacillus, Mycobacterium leprae, which causes a painless, slowly progressing thickening and distortion of the affected tissues. The diagnosis is made by examining a bit of the infected tissue under a microscope and finding the leprosy bacilli, which in appearance are not unlike the bacilli that cause tuberculosis. Fortunately, the antibiotics effective against tuberculosis are effective today in arresting the progression of the disease.

osteoma of the bony ear canal

      Osteoma of the bony ear canal is a bony knob that grows close to the tympanic membrane, especially in those who swim a great deal in cold water. It is not dangerous and does not need to be removed unless the bony overgrowth becomes large enough to block the ear canal.

cyst of the ear

      A cyst is a sac filled with liquid or semisolid material. A cyst of the ear is most often caused by a gland that lubricates the skin behind the earlobe, less often at the entrance of the ear canal. If the duct of this gland becomes stopped, the lubricating fatty material accumulates as a soft, rounded nodule in the skin. Infection of the cyst causes a tender abscess to form and drain. The cyst will re-form unless removed completely by surgery.

      Another type of cyst occurs above the ear canal, just in front of the outer ear or, rarely, in the neck behind and below the ear. This is a remnant of the primitive gill of the early embryo, a reminder of our ancient fishy ancestors. It may appear as a tiny pitlike depression that discharges a little moisture from time to time, or a cystic swelling may develop when the opening of the pit is closed, requiring surgical removal.

keloid of the ear

      In dark-skinned people, overgrowth of scar tissue from any skin incision or injury can cause a thickened elevation on the scar called a keloid. Having the earlobes pierced for earrings sometimes results in a large, painless nodular keloid enlargement of the earlobe, harmless but unsightly. Keloids are removed surgically (see also skin disease (integument)).

Deformities

Absence of the outer ear

      Congenital deformity or absence of the outer ear, usually on one side, sometimes on both, is often accompanied by absence of the outer-ear canal. This failure of the primitive gill structures to become properly transformed into the normal outer and middle ear is, in rare instances, hereditary. More often it occurs for no known reason. In some cases it can be traced to the damaging effects on the embryo of rubella in the mother during the first three months of her pregnancy. Since the inner ear and nerves of equilibrium and hearing come from the otic vesicle, separate from the gill structure, in most cases of deformed or absent outer ear the hearing nerve is normal. Surgical construction of a new ear canal and tympanic membrane can often improve the hearing, which has been impaired by the failure of sound conduction to reach the hearing nerve in the inner ear.

Lop ear

      Lop ear, excessive protrusion of the ear from the side of the head, is a more frequent but less serious deformity of the outer ear. Surgery may be performed to bring the ears back to a more normal and less conspicuous position.

Other ailments

Eczema (dermatitis)

      Eczema of the skin of the outer ear, like eczema elsewhere, is an itching, scaling redness, sometimes with weeping of the affected skin. It is often the result of an allergy to a food or substance such as hair spray that comes in contact with the skin. The best treatment is discovery and avoidance of the allergen. Cortisone ointment applied topically may temporarily relieve symptoms.

Impacted earwax

      The waxy substance produced by glands in the skin of the outer-ear canal normally is carried outward by slow migration to the outer layers of skin. When wax is produced too rapidly, it can accumulate, completely filling the outer-ear canal and blocking the passage of sound to the tympanic membrane, causing a painless impairment of hearing. Large plugs of earwax need to be removed by a physician. Smaller amounts may be softened by a a few drops of baby oil left in the ear overnight, then syringed out with warm water and a soft-rubber infant ear syringe.

cancer of the outer ear

      Cancer of the outer ear occurs chiefly in instances where the outer ear has been exposed for many years to direct sunlight. A small and at first painless ulcer, with a dry scab covering it, that slowly enlarges and deepens may be a skin cancer. It is diagnosed by removing a small bit of tissue from the edge and examining it under a microscope. The cancerous tissue must be completely eradicated, by either surgery or radiation, to effect a cure. Cancer that arises in the ear canal is more serious, for it may invade the bone before it is diagnosed. It is then more difficult to cure by removal. Cancers of the ear canal are rather rare, while cancers of the skin of the outer ear are more common, as well as more readily cured by removal.

Middle ear

      The air-filled middle-ear cavity and the air cells in the mastoid bone that extend backward from it are supplied with air by the eustachian tube that extends from the upper part of the pharynx to the middle-ear cavity. The brain cavity lies just above and behind the middle ear and mastoid air spaces, separated from them only by thin plates of bone. The nerve that supplies the muscles of expression in the face passes through the middle-ear cavity and mastoid bone; it, too, is separated from them by only a thin layer of bone. In some instances this bony covering is incomplete, so that the facial nerve lies directly against the mucous membrane that lines the middle ear and mastoid air cells. This mucous membrane, an extension of a similar mucus-producing membrane that lines the nose and upper part of the throat, extends all the way through the eustachian tube into the middle ear and mastoid. It is subject to the same allergic reactions and infections that afflict the nasal passages. Thus, an acute head cold or other infection of the nose and throat, such as measles or scarlet fever, may extend through the eustachian tube into the middle ear and mastoid air cells. The proximity of the brain cavity to the mastoid air cells is such that an infection, if severe and untreated, may lead to meningitis (inflammation of the covering of the brain) or brain abscess. The large vein that drains blood from the brain passes through the mastoid bone on its way to the jugular vein in the neck. Infection from the middle ear can extend to this vein, resulting in “blood poisoning” (infection of the bloodstream, also called septicemia). Paralysis of the facial nerve and infection extending from the middle ear to the labyrinth of the inner ear are other possible complications of middle-ear infection. All these possibilities spring from the particular location of the small but important middle-ear cavity.

Acute middle-ear infection

      Fortunately, acute middle-ear infections, called acute otitis media, are nearly always due to microorganisms that respond quickly to antibiotics. As a result, acute infection of the mastoid air cells resulting in a dangerous mastoid abscess with the possibility of meningitis, brain abscess, septicemia, infection of the labyrinth, or facial nerve paralysis, complicating an acute infection of the middle-ear cavity, has become rare. Abscess of the mastoid and the other complications of acute middle-ear infection are seen chiefly in remote regions and countries where the population lacks proper nutrition and adequate medical care.

      While serious and life-threatening acute infections of the middle ear and mastoid air cells have become rare, chronic infections, mentioned below, continue to occur, and another type of middle-ear disease, secretory otitis media, is frequent.

Secretory otitis media

      In secretory otitis media the middle-ear cavity becomes filled with a clear, pale yellowish, noninfected fluid. The disorder is the result of inadequate ventilation of the middle ear through the eustachian tube. The air in the middle ear, when it is no longer replenished through this tube, is gradually absorbed by the mucous membrane, and fluid takes its place. Eventually, the middle-ear cavity is completely filled with fluid instead of air. The fluid impedes the vibratory movements of the tympanic membrane and the ossicular chain, causing a painless impairment of hearing.

      The usual causes for secretory otitis media are an acute head cold with swelling of the membranes of the eustachian tube, an allergic reaction of the membranes in the eustachian tube, and an enlarged adenoid (nodule of lymphoid tissue) blocking the entrance to the eustachian tube. The condition is cured by finding and removing the cause and then removing the fluid from the middle-ear cavity, if it does not disappear by itself within a week or two. Removal of the fluid requires puncturing the tympanic membrane and forcing air through the eustachian tube to blow out the fluid. In the absence of fever and infection of the middle ear, antibiotics, which may impede the normal immune protection of the middle ear, are not necessary. In cases in which an allergic reaction is not the underlying cause of the condition, it may be necessary to insert a tiny plastic tube through the membrane to aid in reestablishing normal ventilation of the middle-ear cavity. After a time, when the middle ear and hearing have returned to normal, this plastic tube is removed. The small hole left in the tympanic membrane quickly heals.

Aero-otitis (ear squeeze) media

      Aero-otitis media is a painful type of hearing loss that can result from an inability to equalize the air pressure in the middle-ear cavity when a sudden change in altitude occurs, as may happen in a rapid descent in a poorly pressurized aircraft. Allergies or a preexisting head cold may inhibit an individual's ability to equalize, which is accomplished by yawning or swallowing to open the eustachian tube. The tympanic membrane becomes sharply retracted when the air pressure becomes less within than without, while the opening of the tube into the upper part of the throat becomes pressed tightly together by the increased air pressure in the throat, so that the tube cannot be opened by swallowing. A severe sense of pressure in the ear is accompanied by pain and a decrease in hearing. Sometimes the tympanic membrane ruptures because of the difference in pressure on its two sides. More often, the pain continues until the middle ear fills with fluid or the membrane is surgically punctured. Usually aero-otitis media produced during a flight is of a temporary nature and disappears of its own accord.

Chronic middle-ear infection

      Chronic infection of the middle ear occurs when there is a permanent perforation of the tympanic membrane that allows dust, water, and germs from the outer air to gain access to the middle-ear cavity. This results in a chronic drainage from the middle ear through the outer-ear canal. There are two distinct types of chronic middle-ear infection, one relatively harmless, the other caused by a dangerous bone-invading process that leads, when neglected, to serious complications.

      The harmless type of chronic middle-ear disease is recognized by a stringy, odourless, mucoid discharge that comes from the surface of the mucous membrane that lines the middle ear. Medical treatment with applications of boric acid powder will dry up the chronic drainage. The perforation in the membrane may then be closed, restoring the normal structure and function of the ear with recovery of hearing.

      The dangerous type of chronic middle-ear drainage is recognized by its foul-smelling discharge, often scanty in amount, coming from a bone-invading process beneath the mucous membrane. Such cases are usually caused by a condition known as cholesteatoma of the middle ear. This is an ingrowth of skin from the outer-ear canal that forms a cyst within the middle ear. An infected cholesteatoma cyst enlarges slowly but progressively, gradually eroding the bone until the cyst reaches the brain cavity, the nerve that supplies the muscles of the face, or a semicircular canal of the inner ear. The infected material within the cyst then produces a serious complication: meningitis or brain abscess, paralysis of the facial nerve, or infection of the labyrinth of the inner ear with vertigo, all of which may lead to total deafness.

      Fortunately, cholesteatoma of the middle ear is now rarely so neglected as to permit development of a serious complication. By careful examination of the tympanic membrane perforation and by X-ray studies, the bone-eroding cyst can be diagnosed; it can then be removed surgically before it has caused serious harm. This operation is known as a radical mastoid or a modified radical mastoid operation. If during the same procedure the perforation in the tympanic membrane is closed and the ossicular chain repaired, the operation is known as a tympanoplasty, or plastic reconstruction of the middle-ear cavity.

Ossicular interruption

      The ossicular chain of three tiny bones needed to carry sound vibrations from the tympanic membrane to the fluid that fills the inner ear may be disrupted by infection or by a jarring blow on the head. Most often the separation occurs at its weakest point, where the incus joins the stapes. If the separation is partial, there is a mild impairment of hearing; if it is complete, there is a severe hearing loss. In such a case, a hearing test demonstrates that the nerve of hearing in the inner ear is functioning normally but that sound fails to be conducted from the tympanic membrane to the inner ear. The defective ossicular chain can be surgically corrected through tympanoplasty, which allows sound to be conducted to the inner ear once again.

otosclerosis

      The commonest cause for progressive hearing loss in early and middle adult life is a disease of the hard shell of bone that surrounds the labyrinth of the inner ear. This disease of bone is known as otosclerosis, a name that is misleading, for in its early and actively expanding stage the nodule of diseased bone is softer than the ivory-hard bone that it replaces. The more appropriate name otospongiosis is sometimes used, but such is the tenacity of tradition that the older name, applied before the process was well understood, has persisted and is the term generally used.

      The cause for the occurrence of the nodule of softened otosclerotic bone is unknown. There is a certain familial tendency, half the cases occurring in families in which one or several relatives have the same condition. It is one-tenth as common among blacks as among whites and twice as common in women as in men. The nodule of softened otosclerotic bone first appears in late childhood or in early adult life. Fortunately, in most cases it remains quite small and harmless, producing no symptoms, and is discoverable only if the ear bones are removed after death and examined under a microscope. Such evidence indicates that approximately 1 in 10 white adult men and 1 in 5 white adult women will be found to have such a nodule of otosclerotic bone by middle adult life.

      In about 12 percent of otosclerosis cases the nodule of softened bone becomes large enough to reach the oval window containing the footplate of the stapes (stirrup). Increasing pressure caused by the expanding nodule begins to impede its vibratory movements in response to sound striking the tympanic membrane. Gradually and insidiously, affected persons begin to lose their sharpness of hearing. First they begin to lose the ability to hear faint sounds of low pitch, next they begin to have difficulty hearing the whispered voice, then they have difficulty in hearing conversation from a distance, and finally they can hear and understand the spoken voice only when it is quite loud or close to the ear. One of the characteristics of impaired hearing due to stirrup fixation by otosclerosis is retained ability to hear a telephone conversation by pressing the receiver against the head so that the sound is carried to the inner ear by bone conduction. Another characteristic of this type of impaired hearing is that hearing seems to improve while one is riding in an automobile, in a plane, or on a train. This is because the low-pitched roar of motors causes persons with normal hearing to unconsciously raise their voices, while the individual with stirrup fixation fails to hear the low-pitched roar and thus hears better and enjoys the raised voices around him.

      The diagnosis of stirrup fixation by otosclerosis is made on the basis of a history of a gradually increasing impairment of hearing with absence of any chronic infection of the middle ear or of perforation of the tympanic membrane and with hearing tests showing that the auditory nerve in the inner ear is functioning but that sound fails to be conducted properly to it. Hearing tests carried out with either a tuning fork or an audiometer demonstrate that the hearing by bone conduction is better than by air conduction.

      The final and conclusive diagnosis of otosclerosis is a finding made through surgical exploration—namely, that the stapes is fixed and unable to be moved because of a nodule of bone that has grown against it. An X ray of the ear using computed tomography (computerized axial tomography) may be made to demonstrate that the footplate of the stapes has been invaded by otosclerosis.

      Fixation of the stapes can be corrected surgically. In 1956 it was found that the fixed stapes could be removed and replaced by a plastic or wire substitute in cases in which it could not be mobilized. Today this operation, known as stapedectomy, is the one most often used to correct fixation of the stapes by otosclerosis.

      The otosclerotic bone disease in some cases expands as far as the cochlea of the inner ear, causing a gradual deterioration of the auditory nerve. This progressive nerve deafness may precede, accompany, or follow fixation of the stapes. In some cases it may occur without fixation of the stapes.

      While the exact cause of otosclerosis is not known, it may be associated in some cases with lack of fluoride in drinking water. There is evidence that increasing the intake of fluoride may promote hardening of the softened nodule of otosclerotic bone, thus arresting or retarding its expansion. In this way the gradual impairment of auditory nerve function that often occurs with fixation of the stapes may be retarded. Fluoridation of water supplies, which is carried out in many countries, has reduced the incidence of otosclerosis.

inner ear

      The labyrinth of the inner ear contains the nerve endings of the vestibular nerve—the nerve of equilibrium (proprioception)—and the auditory nerve, which are branches of the vestibulocochlear, or eighth cranial, nerve. The vestibular nerve ends supply the semicircular canals and the otolithic membranes in the vestibule. The auditory nerve supplies the cochlea. Diseases of the labyrinth of the inner ear may affect both the vestibular nerve and the auditory nerve, or they may affect only the auditory nerve, with loss of hearing, or the vestibular nerve, bringing on vertigo. The commoner inner-ear diseases are described in the following paragraphs.

Nerve deafness

Congenital nerve deafness

      Congenital nerve deafness, a defect of the auditory nerve in the cochlea, may be present at birth or acquired during or soon after birth. Usually both inner ears are affected to a similar degree, and as a rule there is a severe impairment of hearing, although in some cases of congenital nerve loss the impairment is moderate. Many cases of congenital nerve deafness have been caused by the rubella (German measles) virus in the mother during the first three months of her pregnancy, causing arrest of development of the vesicle of the embryo. This can happen during a rubella epidemic, even when the mother has no symptoms of the infection. In most cases the vestibular nerve is not affected or is affected to a lesser degree, and in most (but not all) cases the outer- and middle-ear structures are not affected. A vaccine against the rubella virus made available in 1969 has reduced the number of cases of congenital nerve deafness in developed countries.

      Congenital nerve deafness acquired at or soon after birth may result from insufficient oxygen (anoxia) during a difficult and prolonged delivery or from the condition known as kernicterus, in which the baby becomes jaundiced because of incompatibility between its blood and that of the mother. In a few cases congenital nerve deafness is an inherited failure of the cochlea to develop properly. When the hearing loss is severe, speech cannot be acquired without special training. Children so afflicted must attend special classes or schools for the severely deaf, where they can be taught lipreading, speech, and sign language. Electrical hearing aids (hearing aid) can be helpful, especially during classes, to use the remnants of hearing usually present in such cases. Another alternative, although controversial within the deaf community, is a cochlear implant, which is sometimes useful in cases of profound hearing loss or total absence of hearing when the nerve itself is present. In this operation an electrode is surgically implanted to directly stimulate the auditory nerve between the brain and the ear.

Viral nerve deafness

      Viral infections can cause severe degrees of sensorineural hearing loss in one ear, and sometimes in both, at any age. The mumps virus is one of the commonest causes of severe sensorineural hearing loss in one ear. The measles and influenza viruses are less-common causes. There is no effective medical or surgical treatment to restore hearing impaired by a virus.

Effects of injury and trauma

Ototoxic drugs

      Ototoxic (harmful to the ear) drugs can cause temporary and sometimes permanent impairment of auditory nerve function. Salicylates such as aspirin in large enough doses may cause ringing in the ears and then a temporary decrease in hearing that ceases when the person stops taking the drug. quinine can have a similar effect but with a permanent impairment of auditory nerve function in some cases. Certain antibiotics (antibiotic), such as streptomycin, dihydrostreptomycin, neomycin, and kanamycin, may cause permanent damage to auditory nerve function. Susceptibility to auditory nerve damage from ototoxic drugs varies greatly among individuals. In most cases, except when streptomycin is the drug taken, the more durable and less easily damaged vestibular nerve is not affected. Streptomycin affects the vestibular nerve more than it affects the auditory nerve.

skull fracture and concussion

      Skull fracture and concussion from a severe blow on the head can impair the functioning of the auditory and vestibular nerves in varying degrees. The greatest hearing loss arises when a fracture of the skull passes through the labyrinth of the inner ear, totally destroying its function.

Exposure to noise

      The effects of noise exposure on hearing depend on the intensity and duration of the noise. The effects may be temporary or permanent. A single exposure to an extremely intense sound, such as an explosion, may produce a severe and permanent loss of hearing. Repeated exposures to sounds in excess of 80 to 90 decibels (decibel) may cause gradual deterioration of hearing by destroying the hair cells of the inner ear, with possible subsequent degeneration of nerve fibres (see from the article ear, human ). The levels of noise produced by rock music bands frequently exceed 110 decibels. The noise generated by farm tractors, power mowers, and snowmobiles may reach 100 decibels. In the United States, legislation requires that workers exposed to sound levels greater than 90 decibels for an eight-hour day be provided some form of protection, such as earplugs or earmuffs.

      Individuals differ in their susceptibility to hearing loss from noise exposure. Because hearing loss typically begins at the higher frequencies of 4,000 to 6,000 hertz, the effects of noise exposure may go unnoticed until the hearing loss spreads to the lower frequencies of 1,000 to 2,000 hertz.

      Inhalation of carbogen, a mixture of 5 percent carbon dioxide and 95 percent oxygen, for 20 minutes will accelerate recovery of hearing if administered within a few hours after excessive noise exposure.

Inflammation and tumour

labyrinthitis

      Labyrinthitis, an inflammation of the labyrinth of the inner ear, happens when infection occurs as a result of meningitis, syphilis, acute otitis media and mastoiditis, or chronic otitis media and cholesteatoma. Loss of both equilibrium and hearing occurs in the affected ear. Prompt antibiotic treatment sometimes arrests the damage and allows for the possibility of partial recovery of the function of the inner ear.

acoustic neuroma

      An acoustic neuroma is a benign tumour that grows on the auditory nerve near the point where it enters the labyrinth of the inner ear. The tumour causes gradual and progressive loss of auditory and vestibular nerve function on one side. Eventually the tumour grows out into the brain cavity, causing headaches and paralysis. If it is not removed, blindness and death may result. Fortunately, acoustic neuroma usually can be diagnosed early by magnetic resonance imaging (MRI) and removed before it has serious consequences.

Ménière's disease

      Ménière's disease, also called endolymphatic hydrops (Ménière disease), is a fairly common disorder of the labyrinth of the inner ear that affects both the vestibular nerve, with resultant attacks of vertigo, and the auditory nerve, with impairment of hearing. It was first described in 1861 by a French physician, Prosper Ménière. It is now known that the symptoms are caused by an excess of endolymphatic fluid in the inner ear. The diagnosis is made from the recurring attacks of vertigo, often with nausea and vomiting, impairment of hearing with a distortion of sound in the affected ear that fluctuates in degree, and a sense of fullness or pressure in the ear. The cause of the excess of endolymphatic fluid is not always known, although in many cases it results from defective functioning of the endolymphatic duct and sac, the structures that normally resorb endolymphatic fluid from the inner ear. Allergic reactions to certain foods may also cause the disease. The treatment of Ménière's disease is directed toward finding the cause of the excess of endolymphatic fluid in order to control it. If medical treatment does not relieve the repeated attacks of vertigo, surgery may be necessary.

presbycusis

      Presbycusis is the gradual decline of hearing function that results from aging. It is similar to other aging processes because it occurs at different ages and at different rates among the population. As a person ages, there is a gradual loss of cochlear hair cells, beginning at the basal end of the organ of Corti, with the result that hearing is gradually reduced and eventually lost, first for the highest audible frequencies (around 20,000 hertz) and then progressively for sounds of lower frequency. Usually the slow diminishing of hearing does not begin until after age 60. The affected individual notices increasing difficulty in hearing sounds of high pitch and in understanding conversation. Correction of a nutritional deficiency of zinc, coenzyme Q₁₀, or possibly vitamin A may stabilize the progressive hearing loss. The physician must make certain that the individual does not have a correctable impairment, such as accumulated earwax, secretory otitis media, or stirrup fixation by otosclerosis, as part of the difficulty. An electrical hearing aid is of limited help to some, while others find that a hearing aid makes voices louder but less clear and therefore is of little help.

Rehabilitation

      The child born deaf or with a severe hearing impairment cannot acquire speech by the normal process but must attend special classes or a school for the deaf to be taught speech and lipreading. Most of these children have remnants of the sense of hearing that can be utilized in their schooling by the use of aids to amplify sound. The child with a moderate or mild hearing impairment is able to acquire speech independently but a little more slowly than the child with normal hearing, while speech-correction instruction is usually required to improve diction. Cochlear implants can be considered for children and adults with a total absence of hearing or hearing loss so profound that hearing aids (hearing aid) are not helpful. Implants make it possible for a deaf child to develop speech and allow a deaf adult to communicate more effectively.

      Advances in hearing-aid technology have served to increase the proportion of hearing-impaired individuals who can benefit substantially from amplification. Selection of an appropriate hearing aid for individuals with sensori-neural (or nerve-type) hearing loss may be difficult and time-consuming. Research has demonstrated repeatedly, however, that the ability of listeners with sensorineural hearing loss to understand speech at conversational levels often can be enhanced significantly by use of an appropriate hearing aid. For those individuals whose hearing loss causes severe distortion of speech, use of a hearing aid in combination with lipreading may increase the amount of speech the individual can understand through lipreading alone. On the other hand, selection of a hearing aid is often a simpler matter for listeners with hearing loss of the conductive type. Careful selection is necessary to ensure that maximum understanding of speech is obtainable in noisy environments. The hearing-impaired individual should consult with trained professionals such as audiologists, who are trained in evaluating the benefit derived from the use of a hearing aid.

      Lipreading, which actually entails attentive observation of the entire facial expression rather than the movements of the lips alone, is used even by persons with normal hearing who, in the presence of background noise, need these visual clues to supplement hearing. As hearing begins to be impaired, lipreading, which might better be termed speechreading, becomes increasingly valuable and important.

      The hearing-impaired individual who knows a spoken language can learn lipreading by careful observation of a speaker of that language. Formal instruction in lipreading by a teacher individually or in classes is necessary for those hearing-impaired persons who have not acquired knowledge of a spoken language. The greater the loss of hearing, the more essential lipreading becomes, for which good lighting is essential. The hearing-impaired may also be taught a sign language, such as American Sign Language, as a communications tool.

      Speech-correction instruction, needed for the young with serious degrees of impaired hearing, also becomes necessary for the adult who suddenly loses all hearing in both ears. Without the monitoring effect of hearing one's own voice, speech begins to deteriorate and to acquire the flat, toneless quality of the profoundly deaf.

George E. Shambaugh

Additional Reading

Ear diseases and hearing disorders are discussed in Michael E. Glasscock III, George E. Shambaugh, Jr., and Glenn D. Johnson (eds.), Surgery of the Ear, 4th ed. (1990), a well-illustrated text on diseases of the ear and their surgical correction; James Jerger (ed.), Hearing Disorders in Adults (1984); John Ballantyne, M.C. Martin, and Antony Martin (eds.), Deafness, 5th ed. (1993); Robert Thayer Sataloff and Joseph Sataloff, Hearing Loss, 3rd ed., rev. and expanded (1993); and David M. Vernick et al., The Hearing Loss Handbook (1993). George E. Shambaugh, “A Restudy of the Minute Anatomy of Structures in the Cochlea with Conclusions Bearing on the Solution of the Problem of Tone Perception,” The American Journal of Anatomy, 7(2):245–257 (Aug. 1, 1907), was the first detailed description of the hearing-nerve end organ in the cochlea, where sound waves are converted into nerve impulses depending upon the pitch of the tone. George E. Shambaugh, Jr., and Alexandre Petrovic, “Effects of Sodium Fluoride on Bone: Application to Otosclerosis and Other Decalcifying Bone Diseases,” JAMA, 204(11):969–973 (June 10, 1968), summarizes research on the arrest, by means of sodium fluoride, of progressive deafness caused by otosclerosis. Philip H. Beales, Noise, Hearing, and Deafness (1965), is a useful review in lay language of the problem of deafness and the adverse influence on hearing of excess noise exposure; a more recent text is Karl D. Kryter, The Handbook of Hearing and the Effects of Noise: Physiology, Psychology, and Public Health (1994). Brief reports by panels of experts assembled by the National Institutes of Health are issued as NIH Consensus Statements; several statements are of clinical concern in the field of hearing and deafness: “Noise and Hearing Loss,” 8(1):1–24 (Jan. 22–24, 1990), also available with the same title in JAMA, 263(23):3185–3190 (June 20, 1990), “Early Identification of Hearing Impairment in Infants and Young Children,” 11(1):1–24 (Mar. 1–3, 1993), and “Cochlear Implants in Adults and Children,” 13(2):1–30 (May 15–17, 1995), also available with the same title in JAMA, 274(24):1955–1961 (Dec. 27, 1995). More information on the success of cochlear implants is available in Jeffrey P. Harris, John P. Anderson, and Robert Novak, “An Outcomes Study of Cochlear Implants in Deaf Patients,” Archives of Otolaryngology—Head and Neck Surgery, 121(4):398–404 (April 1995).George E. Shambaugh

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