CHAPTER

Disorders of Hearing and Vestibular Function

55

Susan A. Fontana and Carol M. Porth

DISORDERS OF AUDITORY FUNCTION The External Ear Disorders of the External Ear The Middle Ear and Eustachian Tube Eustachian Tube Dysfunction Barotrauma Otitis Media Otosclerosis Disorders of the Inner Ear Neural Pathways Tinnitus Disorders of the Central Auditory Pathways Hearing Loss Conduction Hearing Loss Sensorineural Hearing Loss Diagnosis and Treatment Hearing Loss in Infants and Children Hearing Loss in the Elderly DISORDERS OF VESTIBULAR FUNCTION The Vestibular System and Vestibular Reflexes Peripheral Vestibular Apparatus Neural Pathways Nystagmus Postural Reflexes Vertigo Motion Sickness Disorders of Peripheral Vestibular Function Benign Paroxysmal Positional Vertigo Acute Vestibular Neuronitis Ménière’s Disease Disorders of Central Vestibular Function Diagnostic Tests of Vestibular Function Electronystagmography Caloric Stimulation Rotational Tests Romberg Test Treatment of Vestibular Disorders Pharmacologic Methods Vestibular Rehabilitation Exercises

T

he ears are paired organs consisting of an external and middle ear, which function in capturing, transmitting, and amplifying sound, and an inner ear that contains the receptive organs that are stimulated by sound waves (i.e., hearing) or head position and movement (i.e., vestibular function). Otitis media, or inflammation of the middle ear, is a common disorder of childhood. Hearing loss is one of the most common disabilities experienced by persons in the United States, particularly among the elderly. Vertigo, a disorder of vestibular function, is also a common cause of disability among the elderly. This chapter is divided into two parts: the first focuses on disorders of the ear and auditory function and the second on disorders of the inner ear and vestibular function.

Disorders of Auditory Function After completing this section of the chapter, you should be able to meet the following objectives:

✦ List the structures of the external, middle, and inner ear and cite their function

✦ Describe two common disorders of the outer ear ✦ Relate the functions of the eustachian tube to the devel-

✦

✦ ✦

✦ ✦

✦ ✦

opment of middle ear problems, including acute otitis media and otitis media with effusion Describe anatomic variations as well as risk factors that make infants and young children more prone to develop acute otitis media List three common symptoms of acute otitis media Describe the disease process associated with otosclerosis and relate it to the progressive conductive hearing loss that occurs Characterize tinnitus Differentiate between conductive, sensorineural, and mixed hearing loss and cite the more common causes of each Describe methods used in the diagnosis and treatment of hearing loss Define the term presbycusis and describe factors that contribute to its development

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✦ Characterize the causes of hearing loss in infants and children and describe the need for early diagnosis and treatment

THE EXTERNAL EAR The external ear consists of the auricle, which collects sound, and the external acoustic meatus or ear canal, which conducts the sound to the tympanic membrane1,2 (Fig. 55-1). The auricle, or pinna, is composed of elastic cartilage covered with thin skin, and an occasional hair. Its rim is somewhat thicker, and its fleshy earlobe lack surrounding cartilage. The funnel shape of the auricle concentrates high-frequency sound entering from the lateral-forward direction into the ear canal. This shape also helps to prevent front–back confusion of sound sources. The external acoustic meatus, or ear canal, is a short (2 to 3 cm in adults) S-shaped canal. A thin layer of skin containing fine hairs, sebaceous glands, and ceruminous glands lines the ear canal. Ceruminous glands secrete cerumen, or earwax, which has certain antimicrobial properties and is thought to serve a protective function. The anterior portion of the auricle and external part of the ear canal are innervated by branches of the trigeminal nerve (cranial nerve [CN] V). The posterior portions of the auricle and the wall of the ear canal are innervated by auricular branches of the facial (CN VII), glossopharyngeal (CN IX), and vagus (CN X) nerves. Because of the vagal innervation, the insertion of a speculum or an otoscope into the external ear canal can stimulate coughing or vomiting reflexes, particularly in young children.

Inner ear

Middle ear Tympanic membrane

Semicircular canals

The tympanic membrane, which separates the external ear from the middle ear, has three layers: an outer layer of thin skin continuous with the lining of the external ear canal, a middle layer of tough collagenous fibers mixed with fibrocytes and some elastic fibers, and an inner epithelial layer continuous with the lining of the middle ear. It is attached in a manner that allows it to vibrate freely when audible sound waves enter the external auditory canal. When viewed through an otoscope, the tympanic membrane appears as a shallow, almost circular cone pointing inward toward its apex, the umbo (Fig. 55-2). Light usually is reflected from the pars tensa at approximately the 4-o’clock position. Landmarks include the lightened stripe over the handle of the malleus; the umbo at the end of the handle; the pars tensa, which constitutes most of the drum; and the pars flaccida, the small area above the malleus attachment. The tympanic membrane is semitransparent, and a small, whitish cord, which traverses the middle ear from back to front, can be seen just under its upper edge. This is the chorda tympani, a branch of the intermedius component of the facial nerve (CN VII).

Disorders of the External Ear The function of the external ear is disturbed when sound transmission is obstructed by impacted cerumen, inflammation (i.e., otitis externa), or drainage from the external ear (otorrhea).

Impacted Cerumen. Cerumen, or earwax, is a protective secretion produced by the ceruminous glands of the skin that lines the ear canal. Although the ear normally is selfcleaning, the cerumen can accumulate and narrow the

Cranial nerve VIII

Cochlear portion Vestibular portion

Incus

Cochlea Eustachian tube Malleus Auricle

External acoustic meatus

Stapes

Pharynx FIGURE 55-1 External, middle, and internal subdivisions of the ear.

CHAPTER 55 Disorders of Hearing and Vestibular Function Pars flaccida Short process of malleus

Posterior fold

Anterior fold

Pars tensa

Handle of malleus

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Treatment usually includes the use of ear drops containing an appropriate antimicrobial agent in combination with a corticosteroid to reduce inflammation. An antifungal agent may also be used. Protection of the ear from additional moisture and avoidance of trauma from scratching are important. Preventing recurrences is important, particularly in persons who swim frequently. Instillation of a dilute alcohol, acetic acid, or Burow’s otic solution (available in over-the-counter ear drops) immediately after swimming usually is an effective prophylaxis.

Umbo Cone of light Posterior

Anterior

FIGURE 55-2 Right eardrum.

canal. Impaction is a common cause of reversible hearing loss.3 Impacted cerumen usually produces no symptoms until the canal becomes completely occluded, at which point the person experiences a feeling of fullness, loss of hearing, tinnitus (i.e., ringing in the ears), or coughing because of vagal stimulation. In most cases, cerumen can be removed by gentle irrigation using a bulb syringe and warm tap water. Warm water is used to avoid inducing a feeling of disequilibrium owing to the vestibular caloric response. The ear canal should be dried thoroughly after irrigation to avoid introducing an infection. Irrigation should be avoided in an only-hearing ear or one that is postsurgical, prone to infection, or suspect for perforation of the tympanic membrane. Alternatively, health care professionals may remove cerumen using an otoscope and a wire loop or blunt cerumen curette. Cerumen that has become hardened or impacted can be softened by instillation of a few drops of a ceruminolytic agent available commercially (e.g., dilute hydrogen peroxide solution) or by prescription. Typically, these agents are instilled in the affected ear one or two times daily for up to 4 days before irrigation. Ceruminolytic agents should not be used in ears that may have a perforated tympanic membrane.

Otitis Externa. Otitis externa is an inflammation of the external ear that can vary in severity from a mild eczematoid dermatitis to severe cellulitis. It can be caused by infectious agents, irritation (e.g., wearing earphones), or allergic reactions. Predisposing factors include moisture in the ear canal after swimming (i.e., swimmer’s ear) or bathing and trauma resulting from scratching or attempts to clean the ear. Most infections are caused by gram-negative bacteria (e.g., Pseudomonas, Proteus) or fungi that grow in the presence of excess moisture.4 Otitis externa commonly occurs in the summer and is manifested by itching, redness, tenderness, and narrowing of the ear canal because of swelling. Inflammation of the pinna or canal makes movement of the ear painful. There may be watery or purulent drainage and intermittent hearing loss.

THE MIDDLE EAR AND EUSTACHIAN TUBE The middle ear, or tympanic cavity, is a small, mucosalined cavity within the petrous portion of the temporal bone (Fig. 55-3). It is bounded laterally by the tympanic membrane and medially by a bony wall with two openings, the superior oval (vestibular window) and the round (cochlear window). The middle ear is connected anteriorly with the nasopharynx by the eustachian tube, also called the pharyngotympanic tube. Posteriorly, it is connected with small air pockets in the temporal bone called mastoid air spaces or cells. Three tiny bones, the auditory ossicles, are suspended from the roof of the middle ear cavity and connect the tympanic membrane with the oval window (see Fig. 55-3). They are connected by synovial joints and are covered with the epithelial lining of the cavity.1,2 The malleus (“hammer”) has its handle firmly fixed to the upper portion of the tympanic membrane. The head of the malleus articulates with the incus (“anvil”), which articulates with the stapes (“stirrup”), which is inserted and sealed into the oval window by an annular ligament. Arrangement of the ear ossicles is such that their lever movements transmit vibrations from the tympanic membrane to the oval window and from there to the fluid in the inner ear. Two tissue-covered openings in the medial wall, the oval and the round windows, provide

Petreous portion of the temporal bone

Incus Malleus

Base (footplate) of stapes occupying oval window Stapes Tympanic cavity

Eustachian tube External acoustic meatus

Tympanic membrane

FIGURE 55-3 Anterior view of the ossicles in the middle ear.

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is opened by the action of the trigeminal (CN V)–innervated tensor veli palatini muscles (Fig. 55-5). Opening of the eustachian tube, which normally occurs with swallowing and yawning reflexes, provides the mechanism for equalizing the pressure of the middle ear with that of the atmosphere. This equalization ensures that the pressures on both sides of the tympanic membrane are the same, so that sound transmission is not reduced and rupture does not result from sudden changes in external pressure, as occurs during plane travel. The eustachian tube is lined with a mucous membrane that is continuous with the pharynx and the mastoid air cells. Infections from the nasopharynx can travel from the nasopharynx along the mucous membrane of the eustachian tube to the middle ear, causing acute otitis media. Toward the nasopharynx, the eustachian tube becomes lined by columnar epithelium with mucus-secreting cells. Hypertrophy of the mucus-secreting cells is thought to contribute to the mucoid secretions that develop during certain types of otitis media. Abnormalities in eustachian tube function are important factors in the pathogenesis of middle ear infections. There are two important types of eustachian tube dysfunction: abnormal patency and obstruction (see Fig. 55-5). The abnormally patent tube does not close or does not close completely. In infants and children with an abnormally patent tube, air and secretions often are pumped into the eustachian tube during crying and nose blowing. Obstruction can be functional or mechanical. Functional obstruction results from the persistent collapse of the eustachian tube due to a lack of tubal stiffness or poor function of the tensor veli palatini muscle that controls the opening of the eustachian tube. It is common in infants and young children because the amount and stiffness of the cartilage supporting the eustachian tube are less than in older children and adults. Changes in the craniofacial base also render the tensor muscle less efficient for opening the eustachian tube in this age group. In addition, craniofacial disorders, such as a cleft palate, alter the

DISORDERS OF THE MIDDLE EAR ➤ The middle ear is a small, air-filled compartment in the temporal bone. It is separated from the outer ear by the tympanic membrane; communication between the nasopharynx and the middle ear occurs through the eustachian tube; and tiny bony ossicles that span the middle ear transmit sound to the sensory receptors in the inner ear. ➤ Otitis media (OM) refers to inflammation of the middle ear, usually associated with an acute infection (acute OM) or an accumulation of fluid (OME). It commonly is associated with disorders of eustachian tube function. ➤ The function of the middle ear is to conduct sound waves from the external to the inner ear. Impaired conduction of sound waves and hearing loss occur when the tympanic membrane has been perforated; air in the middle ear has been replaced with fluid (OME); or the function of the bony ossicles has been impaired (otosclerosis).

for the transmission of sound waves between the air-filled middle ear and the fluid-filled inner ear. It is the piston-like action of the stapes footplate that sets up compression waves in the inner ear fluid.

Eustachian Tube Dysfunction The eustachian tube, which connects the nasopharynx with the middle ear, is located in a gap in the bone between the anterior and medial walls of the middle ear (Fig. 55-4). The eustachian tube serves three basic functions: (1) ventilation of the middle ear, along with equalization of middle ear and ambient pressures; (2) protection of the middle ear from unwanted nasopharyngeal sound waves and secretions; and (3) drainage of middle ear secretions into the nasopharynx.4,5 The nasopharyngeal entrance to the eustachian tube, which usually is closed,

Nasopharynx

Nose

Mastoid Middle ear

Eustachian tube

Palate

FIGURE 55-4 Nasopharynx–eustachian tube–mastoid air cell system. (Bluestone C.D. [1981]. Recent advances in pathogenesis, diagnosis, and management of otitis media. Pediatric Clinics of North America 28[4], 36. Reproduced with permission)

CHAPTER 55 Disorders of Hearing and Vestibular Function

Normal patency

TVP

Functional obstruction Floppy tube Poor TVP function Mechanical obstruction

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izes air pressure in the middle ear. Intranasal (e.g., phenylephrine HCl) or systemic decongestants may be used to prevent symptoms. Acute negative middle ear pressure that persists on the ground is treated with decongestants and attempts at autoinflation. More severe hearing loss or discomfort may require that the person consult an otolaryngologist. Myringotomy (i.e., surgical incision in the tympanic membrane) provides immediate relief and may be used in cases of acute otalgia and hearing loss. Placement of ventilation tubes may be considered for persons with repeated episodes of barotrauma related to frequent air travel.

Otitis Media

Intrinsic Inflammation

Extrinsic Tumor or adenoids FIGURE 55-5 Pathophysiology of the eustachian tube. TVP, tensor veli palatini. (Bluestone C.D. [1981]. Recent advances in the pathogenesis, diagnosis, and management of otitis media. Pediatric Clinics of North America 28[4], 737. With permission from Elsevier Science)

attachment of the tensor muscles, producing functional obstruction of the eustachian tube. Mechanical obstruction results from internal obstruction or external compression of the eustachian tube. Ethnic differences in the structure of the palate may increase the likelihood of obstruction. The most common internal obstruction is caused by swelling and secretions resulting from allergy and viral respiratory infections. External compression by prominent or enlarged adenoidal tissue surrounding the opening of the eustachian tube may make drainage less effective. Tumors also may obstruct drainage. With obstruction, air in the middle ear is absorbed, causing a negative pressure and the transudation of serous capillary fluid into the middle ear.

Barotrauma Barotrauma represents injury resulting from the inability to equalize the barometric stress on the middle ear imposed by air travel or, less commonly, by underwater diving. It occurs most often during air travel when there is a sudden change in atmospheric pressure. The pressure in the middle ear parallels atmospheric pressure; it decreases at high altitudes and increases at lower altitudes. The problem occurs during rapid airplane descent, when the negative pressure in the middle ear tends to cause the eustachian tube to collapse. If air cannot pass back through the eustachian tube, hearing loss and discomfort develop. This most often occurs in persons who travel while suffering from an upper respiratory tract infection. Autoinflation measures such as yawning, swallowing, and chewing gum facilitate opening of the eustachian tube, which equal-

Otitis media (OM) is an infection of the middle ear that is associated with a collection of fluid. Although OM may occur in any age group, it is the most common diagnosis made by health care providers who care for children.6–10 Infants and young children are at highest risk for OM, with the peak occurrence between 6 and 20 months of age.11 The occurrence of the disease tends to decrease as a function of age, with a marked decline after 6 years of age. The incidence is higher in boys, non–breast-fed infants, those who use pacifiers beyond infancy, children in large day care settings, children exposed to tobacco smoke, those with siblings or parents with a significant history of OM, those with allergic rhinitis, and children with congenital or acquired immune deficiencies (e.g., acquired immunodeficiency syndrome). The incidence of OM also is higher among children with craniofacial anomalies (e.g., cleft palate, Down syndrome) and among Canadian and Alaskan Eskimos and Native Americans. It is more common during the winter months, reflecting the seasonal patterns of upper respiratory tract infections. There are two reasons for the increased risk for OM in infants and young children: the eustachian tube is shorter, more horizontal, and wider in this age group than in older children and adults; and infection can spread more easily through the eustachian canal of infants who spend most of their day lying supine. Bottle-fed infants have a higher incidence of OM than breast-fed infants, probably because they are held in a more horizontal position during feeding, and swallowing while in the horizontal position facilitates the reflux of milk into the middle ear. Breast-feeding also provides for the transfer of protective maternal antibodies to the infant. Otitis media may present as acute otitis media (AOM), recurrent OM, or OM with effusion (OME) or fluid in the middle ear.

Acute Otitis Media. Acute OM is characterized by the presence of fluid in the middle ear in combination with signs and symptoms of an acute or systemic infection. Acute otitis media can fail to resolve despite antibiotic treatment (persistent OM), or it may resolve and then recur (recurrent OM). It is estimated that AOM resolves spontaneously without treatment in approximately 60% of children.11 Most cases of AOM follow an upper respiratory tract infection that has been present for several days. The mucosal

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lining of the middle ear is continuous with the eustachian tube and nasopharynx, and most middle ear infections enter through the eustachian tube (see Fig. 55-4). AOM may be of either bacterial or viral origin. Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis are the three major bacterial pathogens isolated from the middle ear in children with AOM.7–12 There may be more than one type of bacteria present in some children. S. pneumoniae causes the largest proportion (40% to 50%) of cases generated by a single organism, and it is the least likely to resolve without treatment.8,11 Emergence of a multidrugresistant strain of S. pneumoniae (DRSP) has led to increased numbers of treatment failures.13 Children may be considered as at either high or low risk for DRSP. Children who are at high risk for DRSP include those younger than 2 years of age, those who attend day care, and those who have received antibiotics in the past 3 months.8,11 The role of viruses as etiologic agents in AOM is controversial. Viruses have been identified as a single pathogen in only a few middle ear aspirates obtained from children with AOM. Viruses may promote bacterial infection by impairing eustachian tube function and other host defenses.11 The respiratory syncytial virus is the virus most frequently associated with AOM. Parainfluenza and influenza viruses are other common viral pathogens in AOM. As with bacterial infections, more than one type of respiratory virus may be present in the middle ear fluid of children with AOM.14

Manifestations. Acute OM is characterized by otalgia (earache), fever (temperature up to 104°F), and hearing loss. Children older than 3 years of age may have rhinorrhea or running nose, vomiting, and diarrhea. In contrast, younger children often have nonspecific signs and symptoms that manifest as ear tugging, irritability, nighttime awakening, and poor feeding. Ear pain usually increases as the effusion accumulates behind the tympanic membrane. Perforation of the tympanic membrane may occur acutely, allowing purulent material from the eustachian tube to drain into the external auditory canal. This may prevent spread of the infection into the temporal bone or intracranial cavity. Spontaneous perforation with discharge occurs most frequently in children of high-risk ethnic groups.

Diagnosis. Diagnosis of AOM is made by associated signs and symptoms and otoscopic examination. In persons with AOM, a bulging yellow or red tympanic membrane with subsequent obliteration of the bony landmarks and cone of light is observed. Gentle movement of the pinna can help to differentiate OM from otitis externa. This maneuver does not produce pain in AOM but causes severe discomfort in otitis externa. Although diagnosis of AOM often can be made by otoscopic examination alone, pneumatic otoscopy usually is performed to document middle ear effusion and immobility of the tympanic membrane.15 The use of the pneumatic otoscope permits the introduction of air into the ear canal for the purpose of determin-

ing tympanic membrane flexibility. The movement of the tympanic membrane is decreased in some cases of AOM and absent in chronic middle ear infection. The diagnosis of AOM can be confirmed using tympanometry or acoustic reflectometry. Tympanometry is helpful in detecting effusion in the middle ear or high negative middle ear pressure. A tympanogram is obtained by inserting a small probe into the external auditory canal; a tone of fixed characteristics is then presented through the probe, and the mobility of the tympanic membrane is measured electronically while the external canal pressure is artificially varied. The tympanogram provides a determination of the degree of negative pressure present in the middle ear. It detects disease when present but is less reliable when disease is absent. Acoustic reflectometry is used to reflect sound waves from the middle ear and provides information as to whether an effusion is absent or present. Increased reflected sound correlates with an increased likelihood of effusion. This technique is most useful in children older than 3 months, and its success depends on user technique. Tympanocentesis may be done to relieve pain from an effusion or to obtain an organism for culture and sensitivity testing. The procedure involves the insertion of a needle through the inferior part of the tympanic membrane. Because of the cost, effort, and lack of availability, it is not routinely used in management of AOM.12 In selected cases of refractory or recurrent middle ear disease, tympanocentesis can serve to improve diagnostic accuracy, guide treatment, and avoid unnecessary medical or surgical interventions. In instances in which the tympanic membrane has perforated with resultant drainage into the external ear, a culture c an be made and microbiologic studies done to identify a microorganism.

Treatment. The treatment of AOM includes the judicious use of antibiotic therapy in high-risk children, especially those younger than 2 years of age who are at increased risk for intracranial complications and speech and language impairment.8,11 The dramatic emergence of DRSP in the United States has led to increased treatment failures for AOM. Current recommendations suggest that if there is a lack of improvement in symptoms by day 3 of the initial antibiotic therapy, a switch to an antibiotic that targets resistant pathogens is recommended.16 Older children who have no fever or a low-grade fever usually do not require antibiotic treatment provided follow-up evaluation of symptoms occurs within 1 to 3 days. Regardless of whether antibiotic therapy is indicated, supportive therapy that includes analgesics, antipyretics, and local heat often is helpful. If the tympanic membrane is bulging and painful because of the accumulation of purulent drainage, a myringotomy may be done to relieve the pressure, thus reducing pain and hearing loss. In addition, this procedure prevents the ragged opening that can follow spontaneous rupture of the tympanic membrane. Residual middle ear effusions are part of the continuum of AOM and persist regardless of whether antibiotics have been used. The effusion usually clears spontaneously within 1 to 3 months and does not require further treatment unless it persists beyond this period.

CHAPTER 55 Disorders of Hearing and Vestibular Function

Recurrent Otitis Media. Recurrent OM is defined as three new AOM episodes within 6 months or four episodes in 1 year that occur with almost every upper respiratory tract infection. Reinforcement of environmental controls, such as avoidance of passive tobacco smoke, is important. Children with recurrent OM should be evaluated to rule out any anatomic variations (e.g., enlarged adenoids) and immunologic abnormalities. Children with immunoglobulin G subclass deficiencies (see Chapter 21) and poor responses to polysaccharide vaccines are more likely to develop recurrent OM.11 Traditionally, prophylactic antibiotics or antibiotics given at one half the therapeutic dose may be given once daily for up to 6 months during winter and spring. Although children with recurrent OM respond well to such treatment, increasing concern regarding the emergence of bacterial resistance has emerged as a rationale for more judicious use of prophylactic antibiotics. Another approach to prevent recurrent OM is immunization with pneumococcal and influenza vaccines. Referral for placement of tympanostomy tubes is another alternative, particularly for children who have experienced five or more OM episodes within a 12-month period. Otitis Media With Effusion. Otitis media with effusion is a condition in which the tympanic membrane is intact and there is an accumulation of fluid in the middle ear without signs or symptoms of infection. The type of effusion often is described as serous, nonsuppurative, or secretory, but these terms may not be correct in all cases. The duration of the effusion may range from less than 3 weeks to more than 3 months. The similarity between OME and AOM is that hearing loss may be present in both conditions. The major distinction is that signs and symptoms of infection are lacking in OME, although some children may complain of a feeling of ear fullness. Distinguishing between OME and AOM often is difficult because of the variability and overlap of symptoms, particularly in young children. Diagnosis is based on otoscopic examination, which frequently reveals opacification of the tympanic membrane, making it difficult to visualize the effusion and, thus, characterize the type. If the tympanic membrane is translucent, a yellow or bluish fluid may be seen, as may an air–fluid level or bubbles, or both. Pneumatic otoscopy often reveals decreased mobility of the tympanic membrane, with a shape that is either retracted or convex. Alternatively, fullness or bulging may be noted. Most cases of persistent middle ear effusion resolve spontaneously within a 3-week to 3-month period. The management options for this duration include observation only, antibiotic therapy, or combination antibiotic and corticosteroid therapy. Topical and systemic decongestants usually are of little value in clearing middle ear effusion. Because there is concern over hearing loss and its effect on learning and speech, a hearing evaluation may be indicated and usually is done after 6 weeks. If the effusion persists for 3 months or longer and is accompanied by hearing loss of 20 decibels (dB) or greater in children of normal development, tympanostomy tube placement may be indicated.11 The tubes usually are placed

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under general anesthesia. The ears of children with tubes must be kept out of water. Spontaneous extrusion of tubes usually occurs after 5.5 to 7 months.17 Complications of tube placement include recurrent otorrhea; persistent perforation, scarring, and atrophy of the tympanic membrane; and cholesteatoma.

Complications. Since the advent of antimicrobial therapy, the intracranial suppurative complications of OM have been uncommon. However, extratemporal complications, including those affecting the middle ear, mastoid, and adjacent structures of the temporal bone, continue to occur. Hearing loss, which is a common complication of OM, usually is conductive and temporary based on the duration of the effusion. Hearing loss that is associated with fluid collection usually resolves when the effusion clears. Permanent hearing loss may occur as the result of damage to the tympanic membrane or other middle ear structures. Cases of sensorineural hearing loss are rare. Persistent and episodic conductive hearing loss in children may impair their cognitive, linguistic, and emotional development.8,9 Children younger than 3 years of age with recurrent OME are at increased risk for impaired language development.8 Additional studies indicate that before 3 years of age, time spent with middle ear effusion correlates with decreased cognitive development as measured by standardized inventories.18 However, the degree and duration of hearing loss required to produce such effects are unknown. Perforation of the tympanic membrane can occur spontaneously or result from surgical interventions. Temporary perforations are created for surgical treatment of AOM (myringotomy) or for tube placement. Usually, the perforations heal spontaneously. Antimicrobial treatment for AOM with acute perforation is the same as for AOM without perforation.13 When chronic drainage is present, cultures usually are performed and the antimicrobial regimen adjusted accordingly. Otic drops also may be instilled in the external ear to prevent or treat an external canal infection.13 Healing of the tympanic membrane usually follows resolution of the middle ear infection. Adhesive OM involves an abnormal healing reaction in an inflamed middle ear. It produces irreversible thickening of the mucous membranes and may cause impaired movement of the ossicles and possibly conductive hearing loss. Tympanosclerosis involves the formation of whitish plaques and nodular deposits on the submucosal surface of the tympanic membrane, with possible adherence of the ossicles and conductive hearing loss. A cholesteatoma is a saclike mass containing silverywhite debris of keratin, which is shed by the squamous epithelial lining of the tympanic membrane.19 As the lining of the epithelium sheds and desquamates, the lesion expands and erodes the surrounding tissues. The lesion, which is associated with chronic middle ear infection, is insidiously progressive, and erosion may involve the temporal bone, causing intracranial complications. Although often thought of as a complication of otitis media, a cholesteatoma may also occur as a congenital condition. Symptoms commonly include painless drainage from the ear

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and hearing loss. Treatment involves microsurgical techniques to remove the cholesteatomatous material. The mastoid antrum and air cells constitute a portion of the temporal bone and may become inflamed as an extension of acute or chronic OM. The disorder causes necrosis of the mastoid process and destruction of the bony intercellular matrix, which are visible by radiologic examination. Mastoid tenderness and drainage of exudate through a perforated tympanic membrane can occur. Chronic mastoiditis can develop as the result of chronic middle ear infection. The usefulness of antibiotics for this condition is limited. Mastoid or middle ear surgery, along with other medical treatment, may be indicated. The incidence of mastoiditis has markedly decreased compared with the preantimicrobial era. It remains uncertain whether this decrease is due to antimicrobial treatment, changes in the natural history of OM, changes in organism virulence, or increased host resistance.20 Intracranial complications, although rare, can develop if the infection spreads through vascular channels, by direct extension, or through preformed pathways such as the round window. These complications are seen more often with chronic suppurative OM and mastoiditis. They include meningitis, focal encephalitis, brain abscess, lateral sinus thrombophlebitis or thrombosis, labyrinthitis, and facial nerve paralysis. Any child who develops persistent headache, tinnitus, stiff neck, or visual or other neurologic symptoms should be investigated for possible intracranial complications.

Otosclerosis Otosclerosis refers to the formation of new spongy bone around the stapes and oval window, which results in progressive deafness21 (see Fig. 55-3). In most cases, the condition is familial and follows an autosomal dominant pattern with variable penetrance. Otosclerosis may begin at any time in life but usually does not appear until after puberty, most frequently between the ages of 20 and 30 years. The disease process accelerates during pregnancy. Otosclerosis begins with resorption of bone in one or more foci. During active bone resorption, the bone structure appears spongy and softer than normal (i.e., osteospongiosis). The resorbed bone is replaced by an overgrowth of new, hard, sclerotic bone. The process is slowly progressive, involving more areas of the temporal bone, especially in front of and posterior to the stapes footplate. As it invades the footplate, the pathologic bone increasingly immobilizes the stapes, reducing the transmission of sound. Pressure from the otosclerotic bone on inner ear structures or the vestibulocochlear nerve (CN VIII) may contribute to the development of tinnitus, sensorineural hearing loss, and vertigo. The symptoms of otosclerosis involve an insidious hearing loss. Initially, the affected person is unable to hear a whisper or someone speaking at a distance. In the earliest stages, the bone conduction by which the person’s own voice is heard remains relatively unaffected. At this point, the person’s own voice sounds unusually loud, and the sound of chewing becomes intensified. Because of bone conduction, most of these persons can hear fairly well on

the telephone, which provides an amplified signal. Many are able to hear better in a noisy environment, probably because the masking effect of background noise causes other persons to speak louder. The treatment of otosclerosis can be medical or surgical. A carefully selected, well-fitting hearing aid may allow a person with conductive deafness to lead a normal life. Sodium fluoride has been used with some success in the medical treatment of osteospongiosis. Because much of the conductive hearing loss associated with otosclerosis is caused by stapedial fixation, surgical treatment involves stapedectomy with stapedial reconstruction using the patient’s own stapes or a stapedial prosthesis. The argon laser may be used in the surgical procedure.

DISORDERS OF THE INNER EAR The inner ear contains the receptors for hearing.1,2,22 It contains a labyrinth or system of intercommunicating channels and the receptors for hearing and position sense. Structurally, it consists of an outer bony labyrinth located in the temporal bone and an inner, fluid-filled membranous labyrinth (Fig. 55-6). Two separate fluids are found in the inner ear. The perilymph or periotic fluid separates the bony labyrinth from the membranous labyrinth, and the endolymph or otic fluid fills the membranous labyrinth. The composition of the perilymph is similar to that of the CSF, and a tubular perilymphatic duct connects the perilymph with the CSF in the arachnoid space of the posterior fossa. The endolymph has a potassium content that is similar to that of intracellular fluid. A small-diameter tubular extension, the endolymphatic sac, connects this system with the subdural space near the jugular foramen, providing an exit for the slowly circulating endolymph. The bony labyrinth occupies a volume with a diameter less than the size of a dime. It is divided into a series of perilymph-filled interconnected cavities: the cochlea, the semicircular canals, the utricle, and the saccule. The receptors for hearing are contained in the cochlea, and those for head position sense are contained in the semicircular canals, the utricle, and the saccule. The vestibule is the central egg-shaped cavity of the bony labyrinth that lies posterior to the cochlea and anterior to the semicircular canals. The oval window that connects the inner ear with the middle ear is located in its lateral wall. The cochlea is enclosed in a bony tube shaped like a snail shell that winds around a central bone column called the modiolus. A membranous triangular cochlear duct stretches across the cochlea, separating it into two parallel tubes, each containing perilymph: the scala vestibuli and the scala tympani (Fig. 55-7). One side of the cochlear duct, the basilar membrane, stretches under tension laterally from the modiolus to an elastic spiral ligament. A second side, the vestibular membrane (i.e., Reissner’s membrane), is a delicate double layer of squamous epithelial cells. The third side consists of a well-vascularized epithelium, the stria vascularis, which is the source of the endolymph. The cochlear duct separates the scala vestibuli and the scala tympani from the base of the cochlea throughout its two and one-half spiral turns to its apex. An opening at the

CHAPTER 55 Disorders of Hearing and Vestibular Function

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Semicircular canals Common limb Vestibular ganglion

Anterior Semicircular ducts

Posterior Lateral

Vestibular nerve Cochlear nerve

Vestibulocochlear nerve (CN VIII)

Spiral ganglion Cochlea Ampullae of semicircular ducts

Utricle

Saccule Basal turn of cochlea

Spiral canal site of spiral organ (of Corti)

FIGURE 55-6 Schematic lateral view of the bony and membranous labyrinths showing the membranous labyrinth in a closed system of ducts and chambers filled with endolymph and bathed in perilymph with the bony labyrinth. Observe the parts of membranous labyrinth: the cochlear duct, the saccule and utricle within the vestibule, and the semicircular ducts within the semicircular canals. (From Moore K.L., Dalley A.F. [1999]. Clinically oriented anatomy [4th ed., p. 1102]. Philadelphia: Lippincott Williams & Wilkins)

Scala vestibuli (perilymph) Oval window Vestibular membrane Cochlear duct (endolymph) Tectorial membrane Organ of Corti Basilar membrane Middle ear Round window Scala tympani (perilymph)

Cochlear nerve Spiral ganglion

A

Inner hair cell

Outer hair cell

Tectorial membrane

FIGURE 55-7 (A) Path taken by sound waves reaching the inner ear. (B) Spiral organ of Corti has been removed from the cochlear duct and greatly enlarged to show the inner and outer hair cells, the basilar membrane, and cochlear nerve fibers.

Cochlear nerve fibers B

Basilar membrane

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apex, called the helicotrema, permits fluid waves to move between the two scalae. Unlike light, which can be transmitted through a vacuum such as outer space, sound is a pressure disturbance originating from a vibrating object and propagated by the molecules of an elastic medium. Sound waves, delivered by the stapes footplate to the perilymph, travel throughout the fluid of the inner ear, including up the scala vestibuli, to the apex of the cochlea. Because fluids are incompressible, each time the fluid adjacent to the oval window is forced medially by the stapes, the membrane in the round window bulges out into the middle ear and acts as a pressure valve. As the pressure wave descends through the flexible vestibular membrane, it sets the entire basilar membrane into vibrations. The basilar membrane becomes progressively more massive from base to its distal apex and resonates to higher frequencies near the base and to lower frequencies toward the apex as the fluid pressure wave travels up the cochlear spiral. This “tuned” aspect of the basilar membrane results in increased amplitude of displacement at the resonant locations, responding to a particular sound frequency and greater firing of cochlear neurons innervating this region. This mechanism provides the major basis for the discrimination of sound frequency. Perched on the basilar membrane and extending along its entire length is an elaborate arrangement of columnar epithelium called the organ of Corti (see Fig. 55-7). Continuous rows of hair cells separated into inner and outer rows can be found within the columnar arrangement. The cells have hairlike cilia that protrude through openings in an overlying supporting reticular membrane into the endolymph of the cochlear duct. A gelatinous mass, the tectorial membrane, extends from the medial side of the duct to enclose the cilia of the outer hair cells. The traveling compression waves moving from base to apex through the periotic fluid distort the organ of Corti, causing the hairs to bend against the less flexible tectorial membrane. Each inner hair cell is innervated by several nerve fibers and the outer hair cells, by many cochlear afferent neuron terminals. Selective destruction of hair cells in a particular segment of the cochlea can lead to hearing loss of particular tones. The outer rows of hair cells appear to provide the signals on which the experience of loudness, a correlate of the sound’s physical intensity, is based.

Neural Pathways Afferent fibers from the organ of Corti have their cell bodies in the spiral ganglion in the central portion of the cochlea. Nerve fibers from the spiral ganglion (i.e., vestibulocochlear or auditory nerve [CN VIII]) travel to the cochlear nuclei in the caudal pons. Many secondary nerve fibers from the cochlear nuclei pass to the opposite side of the pons. These secondary fibers may project to such cell groups as the trapezoid or the superior olivary nucleus, or rostrally toward the inferior colliculus of the midbrain. Ipsilateral (same side) projections and interconnections between the nuclei of the two sides occur throughout the

central auditory system. Consequently, impulses from either ear are transmitted through the auditory pathways to both sides of the brain stem. From the inferior colliculus, the auditory pathway passes to the medial geniculate nucleus of the thalamus, where all the fibers synapse. Considerable evidence supports the capability of this level of organization to provide crude auditory experience, including crude tone and intensity discrimination and the directionality of a sound source. From the medial geniculate nucleus, the auditory tract spreads through the auditory radiation to the primary auditory cortex (area 41), located mainly in the superior temporal gyrus and insula (see Chapter 49, Fig. 49-24). This area and its corresponding higher-order thalamic nucleus are required for high-acuity loudness discrimination and precise discrimination of pitch. The auditory association cortex (areas 42 and 22) borders the primary cortex on the superior temporal gyrus. This area and its associated higherorder thalamic nuclei are necessary for auditory gnosis, or the meaningfulness of sound, to occur. Experience and the precise analysis of momentary auditory information are integrated during this process.

Tinnitus Tinnitus (from the Latin tinniere, meaning “to ring”) is the perception of abnormal ear or head noises, not produced by an external stimulus.23–25 Although it often is described as “ringing of the ears,” it may also assume a hissing, roaring, buzzing, or humming sound. Tinnitus may be constant, intermittent, and unilateral or bilateral. It has been estimated that 37 million people in the United States have the disorder. Nearly 10 million of these are estimated to have severe or troubling tinnitus.24 The condition affects males and females equally, is most prevalent between 40 and 70 years of age, and occasionally affects children.23 Although tinnitus is subjective, for clinical purposes it is subdivided into objective and subjective tinnitus. Objective tinnitus refers to those rare cases in which the sound is detected or potentially detectable by another observer. Typical causes of objective tinnitus include vascular abnormalities or neuromuscular disorders. In some vascular disorders, for example, sounds generated by turbulent blood flow (e.g., arterial bruits or venous hums) are conducted to the auditory system. Vascular disorders typically produce a pulsatile form of tinnitus. Subjective tinnitus refers to noise perception when there is no noise stimulation of the cochlea. A number of causes and conditions have been associated with subjective tinnitus. Intermittent periods of mild, high-pitched tinnitus lasting for several minutes are common in normal-hearing persons. Impacted cerumen is a benign cause of tinnitus, which resolves after the earwax is removed. Medications such as aspirin and stimulants such as nicotine and caffeine can cause transient tinnitus. Conditions associated with more persistent tinnitus include noise-induced hearing loss, presbycusis (sensorimotor hearing loss that occurs with aging), hypertension, atherosclerosis, head injury, and cochlear or labyrinthine infection or inflammation.

CHAPTER 55 Disorders of Hearing and Vestibular Function

The physiologic mechanism underlying subjective tinnitus is largely unknown. It seems likely that there are several mechanisms, including abnormal firing of auditory receptors, dysfunction of cochlear neurotransmitter function or ionic balance, damage to the auditory nerve, or alterations in central processing of the signal. Because tinnitus is a symptom, the diagnosis relies heavily on the person’s description of the problem, including onset, frequency, description, and location of the tinnitus; perceived cause; and extent to which the person is bothered by the problem.26 A history of medication or stimulant use and dietary factors that may cause tinnitus should be obtained. Tinnitus often accompanies hearing disorders, and tests of auditory function usually are done. Causes of objective tinnitus, such as serious vascular abnormalities, should be ruled out. Treatment measures are designed to treat the symptoms rather than effect a cure.23–25 They include elimination of drugs or other substances such as caffeine, some cheeses, red wine, and foods containing monosodium glutamate that are suspected of causing tinnitus. The use of an externally produced sound (noise generators or tinnitusmasking devices) may be used to mask or inhibit the tinnitus. Medications, including antihistamines, anticonvulsant drugs, calcium channel blockers, benzodiazepines, and antidepressants, have been used for tinnitus alleviation, but most are not effective, and many produce undesirable side effects. For persistent tinnitus, psychological interventions may be needed to help the person deal with the stress and distraction associated with the condition. Tinnitus retraining therapy, which includes directive counseling and extended use of low-noise generators to facilitate auditory adaptation to the tinnitus, has met with considerable success. Surgical intervention (i.e., cochlear nerve section, vascular decompression) is a last resort for persons in which all other interventions have failed and in whom the disorder is disabling.

DISORDERS OF THE CENTRAL AUDITORY PATHWAYS The auditory pathways in the brain involve communication between the two sides of the brain at many levels. As a result, strokes, tumors, abscesses, and other focal abnormalities seldom produce more than a mild reduction in auditory acuity on the side opposite the lesion. For intelligibility of auditory language, lateral dominance becomes important. On the dominant side, usually the left side, the more medial and dorsal portion of the auditory association cortex is of crucial importance. This area is called Wernicke’s area, and damage to it is associated with auditory receptive aphasia (and agnosia of speech). Persons with damage to this area of the brain can speak intelligibly and read normally but are unable to understand the meaning of major aspects of audible speech. Irritative foci that affect the auditory radiation or the primary auditory cortex can produce roaring or clicking

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sounds, which appear to come from the auditory environment of the opposite side (i.e., auditory hallucinations). Focal seizures that originate in or near the auditory cortex often are immediately preceded by the perception of ringing or other sounds preceded by a prodrome (i.e., aura). Damage to the auditory association cortex, especially if bilateral, results in deficiencies of sound recognition and memory (i.e., auditory agnosia). If the damage is in the dominant hemisphere, speech recognition can be affected (i.e., sensory or receptive aphasia).

HEARING LOSS Nearly 30 million Americans have hearing loss.27,28 It affects persons of all age groups. One of every 1000 infants born in the United States is completely deaf, and more than 3 million children have hearing loss. Between 25% and 40% of people older than 65 years of age have hearing loss.29 Hearing is a specialized sense that provides the ability to perceive vibration of sound waves. Functions of the ear include receiving sound waves, distinguishing their frequency, translating this information into nerve impulses, and transmitting these impulses to the CNS. The compression waves that produce sound have frequency and intensity. Frequency indicates the number of waves per unit time (reported in cycles per second [cps] or hertz [Hz]). The human ear is most sensitive to waves in the frequency range of 1000 to 3000 Hz. Most persons cannot hear compression waves that have a frequency higher than 20,000 Hz. Waves of higher frequency are called ultrasonic waves, meaning that they are above the audible range. In the audible frequency range, the subjective experience correlated with sonic frequency is the pitch of a

HEARING LOSS ➤ Hearing is a special sensory function that incorporates the sound-transmitting properties of the external ear canal, the eardrum that separates the external and middle ear, the bony ossicles of the middle ear, the sensory receptors of the cochlea in the inner ear, the neural pathways of the vestibulocochlear or auditory nerve, and the primary auditory and auditory association cortices. ➤ Hearing loss represents impairment of the ability to detect and perceive sound. ➤ It can range from mild, affecting sounds of different tones and intensities, to moderate or profound. ➤ Hearing loss can be caused by conductive disorders, in which auditory stimuli are not transmitted through the structures of the outer and middle ears to the sensory receptors in the inner ear; by sensorineural disorders that affect the inner ear, auditory nerve, or auditory pathways; or by a combination of conductive and sensorineural disorders.

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sound. Waves below 20 to 30 Hz are experienced as a rattle or drum beat rather than a tone. Wave intensity is represented by amplitude or units of sound pressure. By convention, the intensity (in power units, or ergs per square centimeter) of a sound is expressed as the ratio of intensities between the sound and a reference value. A 10-fold increase in sound pressure is called a bel, after Alexander Graham Bell. Because this representation is too crude to be of use, the decibel (dB), or one tenth of a bel, is used. For purposes of hearing evaluation, the threshold for perception of sound at a given frequency in persons with normal hearing is set at 0 dB.30 Hearing loss is qualified as mild, moderate, severe, or profound. “Hard of hearing” is defined as hearing loss greater than 20 to 25 dB in adults and greater than 15 dB in children. Profound deafness is defined as hearing loss greater than 100 dB31 or 70 dB in children.32 There are many causes of hearing loss or deafness. Most fit into the categories of conductive, sensorineural, or mixed deficiencies that involve a combination of conductive and sensorineural function deficiencies of the same ear.30 Chart 55-1 summarizes common causes of hearing loss. Hearing loss may be genetic or nongenetic, sudden or progressive, unilateral or bilateral, partial or complete, reversible or irreversible. Age and suddenness of onset provide important clues as to the cause of hearing loss.

Conductive Hearing Loss Conductive hearing loss occurs when auditory stimuli are not adequately transmitted through the auditory canal, tympanic membrane, middle ear, or ossicle chain to the inner ear. Temporary hearing loss can occur as the result of impacted cerumen in the outer ear or fluid in the middle ear. Foreign bodies, including pieces of cotton and insects, may impair hearing. More permanent causes of hearing loss are thickening or damage of the tympanic membrane or involvement of the bony structures (ossicles and oval window) of the middle ear due to otosclerosis or Paget’s disease (see Chapter 58).

CHART 55-1 Common Causes of Conductive and Sensorineural Hearing Loss Conductive Hearing Loss • External ear conditions • Impacted earwax or foreign body • Otitis externa Middle ear conditions • • Trauma • Otitis media (acute and with effusion) • Otosclerosis • Tumors Sensorineural Hearing Loss • Trauma • Head injury • Noise • Central nervous system infections (e.g., meningitis) • Degenerative conditions • Presbycusis • Vascular • Atherosclerosis • Sudden deafness • Ototoxic drugs (e.g., aminoglycosides, salicylates, loop diuretics) • Tumors • Vestibular schwannoma (acoustic neuroma) • Meningioma • Metastatic tumors • Idiopathic • Ménière’s disease Mixed Conductive and Sensorineural Hearing Loss • Middle ear conditions • Barotrauma • Cholesteatoma • Otosclerosis Temporal bone fractures •

Sensorineural Hearing Loss Sensorineural, or perceptive, hearing loss occurs with disorders that affect the inner ear, auditory nerve, or auditory pathways of the brain. With this type of deafness, sound waves are conducted to the inner ear, but abnormalities of the cochlear apparatus or auditory nerve decrease or distort the transfer of information to the brain. Tinnitus often accompanies cochlear nerve irritation. Abnormal function resulting from damage or malformation of the central auditory pathways and circuitry is included in this category. Sensorineural hearing loss may have a genetic cause or may result from intrauterine infections such as maternal rubella, or developmental malformations of the inner ear. Genetic hearing loss may result from mutation in a single gene (monogenetic) or from a combination of mutations in different genes and environmental factors (multifactorial). It has been estimated that 50% of profound deafness in children has a monogenetic basis.30,31 The inheritance pat-

tern for monogenetic hearing loss is autosomal recessive in approximately 75% of cases.32 Hearing loss may begin before development of speech (prelingual) or after speech development (postlingual). Most prelingual forms are present at birth. Genetic forms of hearing loss also can be classified as being part of a syndrome in which other abnormalities are present, or as nonsyndromic, in which deafness is the only abnormality. Sensorineural hearing loss also can result from trauma to the inner ear, tumors that encroach on the inner ear or sensory neurons, vascular disorders with hemorrhage, or thrombosis of vessels that supply the inner ear. Other causes of sensorineural deafness are infections and drugs. Sudden sensorineural hearing loss represents an abrupt loss of hearing that occurs instantaneously or on awakening. It most commonly is caused by viral infections, circulatory disorders, or rupture of the labyrinth membrane that can occur during tympanotomy.33

CHAPTER 55 Disorders of Hearing and Vestibular Function

Environmentally induced deafness can occur through direct exposure to excessively intense sound, as in the workplace or at a concert. This is a particular problem in older adults who were working in noisy environments before the mid-1960s, when there were no laws mandating use of devices for protective hearing. This type of deafness was once called boilermaker’s deafness because of the intense reverberating sound to which riveters were exposed when putting together boiler tanks. Sustained or repeated exposure to noise pollution at sound intensities greater than 100 to 120 dB can cause corresponding mechanical damage to the organ of Corti on the “tuned” basilar membrane. If damage is severe, permanent sensorineural deafness to the offending sound frequencies results. Wearing earplugs or ear protection is important under many industrial conditions and for musicians and music listeners exposed to high sound amplification. Noise pollution often is characterized by high-intensity sounds of a specific frequency that cause corresponding damage to the organ of Corti. Temporary threshold shift is a reversible hearing loss that occurs in individuals who attend loud concerts and hear ringing sounds after the event. A number of infections can cause hearing loss. Deafness or some degree of hearing impairment is the most common serious complication of bacterial meningitis in infants and children, reportedly resulting in sensorineural hearing loss in 5% to 35% of persons who survive the infection.30 The mechanism causing hearing impairment seems to be a suppurative labyrinthitis or neuritis resulting in the loss of hair cells and damage to the auditory nerve. Untreated suppurative OM also can extend into the inner ear and cause sensorineural hearing loss through the same mechanisms. Congenital and acquired syphilis can cause unilateral or bilateral sensorineural hearing loss. Hypothyroidism is a potential cause of sensorineural hearing loss in older persons. Among the neoplasms that impair hearing are acoustic neuromas. Acoustic neuromas are benign Schwann cell tumors affecting CN VIII. These tumors usually are unilateral and cause hearing loss by compressing the cochlear nerve or interfering with blood supply to the nerve and cochlea. Other neoplasms that can affect hearing include meningiomas and metastatic brain tumors. The temporal bone is a common site of metastases. Breast cancer may metastasize to the middle ear and invade the cochlea. Drugs that damage inner ear structures are labeled ototoxic. Vestibular symptoms of ototoxicity include lightheadedness, giddiness, and dizziness; if toxicity is severe, cochlear symptoms consisting of tinnitus or hearing loss occur. Hearing loss is sensorineural and may be bilateral or unilateral, transient or permanent. Several classes of drugs have been identified as having ototoxic potential, including the aminoglycoside antibiotics and some other basic antibiotics, antimalarial drugs, some chemotherapeutic drugs, loop diuretics, and salicylates (e.g., aspirin). The symptoms of drug-induced hearing loss may be transient, as often is the case with salicylates and diuretics, or they may be permanent. The risk for ototoxicity depends on the total dose of the drug and its concentration in the bloodstream. It is increased in persons with impaired kid-

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ney functioning and in those previously or currently treated with another potentially ototoxic drug.

Diagnosis and Treatment Although approximately 10% of Americans have some degree of hearing loss, including one third of persons older than 65 years of age, hearing loss often is underdiagnosed. While visual impairments are readily accepted and vigorously treated, loss of hearing often is denied, minimized, or ignored. In a society that favors youth, glasses and contact lens are considered normal and even fashionable, whereas hearing aids often are regarded as a sign of “graceless aging.”31 Diagnosis of hearing loss is aided by careful history of associated otologic factors such as otalgia, otorrhea, tinnitus, and self-described hearing difficulties; physical examination to detect the presence of conditions such as otorrhea, impacted cerumen, or injury to the tympanic membrane; and hearing tests.28,29 A history of occupational and noise exposure is important, as is the use of medications with ototoxic potential. Testing for hearing loss includes a number of methods, including a person’s reported ability to hear an observer’s voice, use of a tuning fork to test air and bone conduction, audioscopes, and auditory brain stem evoked responses (ABRs). Tuning forks are used to differentiate conductive and sensorineural hearing loss. A 512-Hz or higher-frequency tuning fork is used because frequencies below this level elicit a tactile response. The Weber test evaluates conductive hearing loss by lateralization of sound. It is done by placing the lightly vibrating tuning fork on the forehead or vertex of the head. In persons with conductive losses, the sound is louder on the side with the hearing loss, but in persons with sensorineural loss, it radiates to the side with the better hearing. The Rinne test compares air and bone conduction. The test is done by alternately placing the tuning fork on the mastoid bone and in front of the ear canal. In conductive losses, bone conduction exceeds air conduction; in sensorineural losses, the opposite occurs. Audioscopes can be used to assess a person’s ability to hear pure tones at 1000 to 2000 Hz (usual speech frequencies). If a person cannot hear these tones, referral for a full audiogram should be done. The audiogram is an important method of analyzing a person’s hearing and is generally considered the gold standard for diagnosis of hearing loss. It is done by an audiologist and requires highly specialized sound production and control equipment. Pure tones of controlled intensity are delivered, usually to one ear at a time, and the minimum intensity needed for hearing to be experienced is plotted as a function of frequency. The ABR is a noninvasive method that permits functional evaluation of certain defined parts of the central auditory pathways. Electroencephalographic (EEG) electrodes and high-gain amplifiers are required to produce a record of the brain wave activity elicited during repeated acoustic stimulations of either or both ears. ABR recording involves subjecting the ear to loud clicks and using a computer to pick up nerve impulses as they are processed in the midbrain. With this method, certain of the early waves that come from discrete portions of the pons and midbrain

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auditory pathways can be correlated with specific sensorineural abnormalities. Imaging studies such as computed tomography scans and magnetic resonance imaging can be done to determine the site of a lesion and the extent of damage.27

Treatment. Untreated hearing loss can have many consequences. Social isolation and depressive disorders are common in hearing-impaired elderly. Hearing-impaired people may avoid social situations in which background noise makes conversation difficult to hear. Safety issues, both in and out of the home, may become significant. Treatment of hearing loss ranges from simple removal of impacted cerumen in the external auditory canal to surgical procedures such as those used to reconstruct the tympanic membrane. For other people, particularly the frail elderly, hearing aids remain an option. Cochlear implants also are an option for some people. Hearing aids remain the mainstay of treatment for many persons with conductive and sensorineural hearing loss. With the advent of microcircuitry, hearing aids are now being designed with computer chips that allow multiple programs to be placed in a single hearing aid. The various programs allow the user to select a specific setting for different listening situations. The development of microcircuitry has also made it possible for hearing aids to be miniaturized to the point that, in many cases, they can be placed deep in the ear where they take advantage of the normal shape of the external ear and ear canal. Although modern hearing aids have improved greatly, they cannot replicate the hearing person’s ability to hear both soft and loud noises. They also fail to filter out distorted or background noise consistently. Many persons who are fitted with hearing aids use them inconsistently, often because of social embarrassment, increase in background noise, or the sound of their own voice being transmitted through the hearing aid.34 Other aids for the hearing impaired include alert and signal devices, assistedlistening devices from telephone companies, and dogs trained to respond to various sounds. Most important, hearing impairment produces a loss of the important communicative function of auditory language, leading to social isolation. Although many assistance devices are available to persons with hearing loss, understanding on the part of family and friends is perhaps the most important.31 The interpretation of speech involves both visual and auditory clues. It is important that people speaking to persons with hearing impairment face the person and articulate so that lip reading cues can be used. Adequate lighting is important. Distractions such as background noise can make communication difficult and should be avoided when possible. Surgically implantable cochlear prostheses for the profoundly deaf have been developed and are available for use in adults and children 2 years of age or older.35 These prostheses are inserted into the scala tympani of the cochlea and work by providing direct stimulation to the auditory nerve, bypassing the stimulation that typically is provided by transducer cells but that is absent or nonfunctional in a deaf cochlea. For the implant to work, the auditory nerve

must be functional. Whereas early implants used a single electrode, current implants use multielectrode placement, enhancing speech perception. Much of the progress in implant performance has been achieved through improvements in the speech processors that convert sound into electrical stimuli. Advances in the development of the multichannel implant have improved performance such that cochlear implants have been established as an effective option for adults and children with profound hearing impairment.36,37 Most persons who are deafened after learning speech derive substantial benefit when cochlear implants are used in conjunction with lip reading; some are able to understand selected types of speech without lip reading; and some are able to communicate by telephone.

Hearing Loss in Infants and Children Even mild or unilateral hearing loss can have a detrimental effect on the language development and hearingassociated learning of the young child. Although estimates vary dependent on the group surveyed and testing methods used, from 1 to 2 per 1000 newborns have moderate (30 to 50 dB), severe (50 to 70 db), or profound (≥70 dB) sensorineural hearing loss.11 An additional 1 to 2 per 1000 may have milder or unilateral impairments. When considering less severe or transient conductive hearing loss that is commonly associated with middle ear disease in young children, the numbers are even greater. The cause of hearing impairment in children depends on whether the hearing loss is conductive or sensorineural. Most cases of conductive hearing loss is caused by middle ear infections. Causes of sensorineural hearing impairment include genetic, infectious, traumatic, and ototoxic factors. Genetic causes are probably responsible for as many as 50% of sensorineural hearing loss in children. The most common infectious cause of congenital sensorineural hearing loss is cytomegalovirus (CMV), which infects 1 in 100 newborns in the United States each year; of these, about 1200 to 2000 have sensorineural hearing loss.11 Of particular concern is the fact that congenital CMV can cause both symptomatic and asymptomatic hearing loss in the newborn. Some children with congenital CMV infection, who were asymptomatic as newborns, have suddenly lost residual hearing at 4 to 5 years of age.11 Postnatal causes of sensorineural hearing loss include β streptococcal sepsis in the newborn and bacterial meningitis. Streptococcus pneumoniae is the most common cause of bacterial meningitis that results in sensorineural hearing loss after the neonatal period; this cause may become less frequent with the routine administration of the conjugate pneumococcal vaccine. Other causes of sensorineural hearing loss are toxins and trauma. Early in pregnancy, the embryo is particularly sensitive to toxic substances, including ototoxic drugs such as the aminoglycosides and loop diuretics. Trauma, particularly head trauma, may cause sensorineural hearing loss. Because hearing impairment can have a major impact on the development of a child, early identification through screening programs is strongly advocated. The American Academy of Pediatricians (AAP) and the Joint Commission on Infant Hearing (JCIH) recently published a position

CHAPTER 55 Disorders of Hearing and Vestibular Function

paper calling for universal screening of all infants by physiologic measurements before 3 months of age, with proper intervention no later than 6 months of age.37,38 Many states have now enacted legislation supporting the position paper; as result, newborn hearing screening programs have been implemented in newborn nurseries throughout the United States.39 The currently recommended screening techniques are either the evoked otoacoustic emissions (EOAE) or the ABR. Both methodologies are noninvasive, relatively quick (