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![[SYMPOSIUM]](../../../graphics/sym_logo.gif){kind=logo} Hearing loss: The invisible disabilityHelping patients overcome a stigma of old ageJack A. Shohet, MD; Thomas Bent, MD VOL 104 / NO 3 / SEPTEMBER 1998 / POSTGRADUATE MEDICINE This page is best viewed with a browser that supports tables This is the third of four articles on common ENT problems Preview: Loss of hearing is a national health problem with significant physical and psychological repercussions. Although there is no cure for certain forms of hearing loss, many patients can be helped, especially when the problem is recognized early. The authors discuss the important role of primary care physicians in early identification, management, and counseling of hearing-impaired patients. Hearing loss ranks with arthritis, hypertension, and heart disease as one of the most common physical disorders in the United States. After low back pain, hearing loss is the second most common physical disability in this country. About 10% of the US population has some degree of hearing loss, including one third of Americans over 65 years of age. However, the significance of hearing loss and the impact on the health and productivity of those affected by it often go unrecognized. Although loss of vision is readily acknowledged and vigorously treated, loss of hearing is often denied, minimized, or ignored. In a society that glorifies youth, eyeglasses are considered normal and even fashionable, but hearing aids are a stigma of graceless aging.
Untreated hearing loss can have multiple consequences. Social isolation and depressive disorders are very common in the elderly, and the communication barrier that hearing loss presents can cause or exacerbate such problems. Patients may avoid social situations where background noise makes normal conversation difficult to understand. As hearing loss Primary care physicians can play an important role in addressing these issues. Routine screening and counseling should be an integral part of a complete physical examination, especially in people with significant noise exposures and anyone over age 65. Most cases of hearing loss are correctable; thus, hearing-impaired patients should be counseled on available treatment options. The patience and support of family and friends should also be enlisted to circumvent frustration, depression, and social isolation. Anatomy and physiology of hearingThe level of sound is referenced to hearing level, where 0 dB is the threshold for perception of sound at a given frequency in persons with normal hearing. A tenfold increase in the sound pressure level from 0 dB is measured as 20 dB. Normal conversation levels are about 45 to 60 dB, whereas the pain threshold is about 140 dB (table 1).
The hearing mechanism consists of three components: the external ear, middle ear, and inner ear. Each is designed to augment the sound delivered to the cochlea.
External and middle ear The middle ear transforms acoustic energy from the air to the fluid of the inner ear in an impedance-matching system, which ensures that energy is not lost. Sound reaches the tympanic membrane, causing it to vibrate and set into motion the three middle ear ossicles: malleus, incus, and stapes. The stapes interfaces with the fluid-filled inner ear at the oval window, which is found just deep to the stapes footplate. The ratio of the vibrating portion of the tympanic membrane to that of the stapes footplate creates a 17:1 increase in sound energy delivered to the inner ear. Additionally, the handle of the malleus is about 1.3 times longer than the incus, creating a type of lever system that increases the force received at the stapes. Thus, the structures of a healthy middle ear effectively magnify the sound pressure level presented to them.
Inner ear Nerve impulses are transmitted through the spiral ganglion cells within the cochlea to the modiolus, where the fibers form the cochlear branch of cranial nerve VIII. The fibers pass to the cochlear nucleus in the brain stem, where they undergo a complex array of synapses within the central pathway.
Types of hearing lossThe three types of hearing loss are conductive, sensorineural, and mixed. Common causes of hearing loss are listed in table 2.
Conductive
Sensorineural Presbycusis (age-related hearing loss) is by far the most common cause of sensorineural hearing loss. There are many possible audiologic patterns in presbycusis; however, the most common is a sloping high-frequency hearing loss that affects a patient's ability to discriminate sounds in environments with background noise. Presbycusis may be associated with tinnitus, which is often perceived as growing louder as hearing loss progresses. Retrocochlear hearing loss occurs at the level of cranial nerve VIII or the brain. Tumors, multiple sclerosis, and stroke are important causes of retrocochlear loss; thus, recognition of these disorders is essential. Certain audiologic characteristics, such as asymmetry in the pure tone averages, speech discrimination scores, or abnormalities in advanced audiologic tests, suggest the presence of a retrocochlear lesion.
Mixed
HistoryA thorough history, including past history, may uncover diseases that predispose a patient to hearing loss. Family history is also critical, because many hearing disorders, both congenital and acquired, are familial. Age at onset helps determine whether the cause of hearing loss is congenital or acquired. For example, the cause of unilateral hearing loss present since birth is most likely congenital, whereas adult-onset unilateral hearing loss should raise suspicion of a tumor. Sudden onset of hearing loss implies a disorder (eg, viral infection, perilymphatic fluid leak from the inner ear, vascular embolism) that requires further tests and treatment. Gradual onset is more consistent with presbycusis or noise-induced hearing loss. Acoustic neuromas, autoimmune disorders, and ototoxicity are usually gradual in onset but may occasionally present as a sudden hearing loss. A progressive hearing loss is characteristic of an ongoing disorder and requires careful diagnostic evaluation and follow-up. Diagnosis is aided by the presence of associated otologic factors, such as otalgia, otorrhea, tinnitus, fluctuation, or vertigo. Otalgia and otorrhea may indicate an infectious or neoplastic process, which may be either an independent or a causative factor. Tinnitus is more characteristic of noise-induced hearing loss, ototoxicity, presbycusis, or Meniere's disease. However, otosclerosis, a conductive hearing loss disorder, can present as tinnitus. Fluctuation in hearing is very characteristic of endolymphatic hydrops or Meniere's disease. Vertigo is rarely seen with presbycusis and noise-induced hearing loss; however, it is commonly seen with acoustic neuromas and autoimmune hearing loss and is almost always seen with Meniere's disease or a perilymphatic fistula. Any history of trauma to the ear or head should be noted. Trauma ranges from a cotton swab in the ear canal to a strenuous cough. Mechanical trauma, such as a blow to the head, can cause a temporal bone fracture, resulting in hearing loss from a hemotympanum (blood behind the tympanic membrane), deafness from a labyrinthine fracture, or perforation of the tympanic membrane. Laceration of the external auditory canal, resulting in bleeding or subsequent infection, can cause conductive hearing loss. Hearing loss after barotrauma from, for example, sneezing, coughing, scuba diving, or strenuous bowel movement signals a probable perilymphatic fistula. Hearing loss is often attributed to occupational or recreational noise exposure. Patients who work in such settings as factories or automotive garages commonly complain of hearing loss at a young age. The audiometric pattern typically seen in noise-induced hearing loss slopes precipitously in the 3,000- to 6,000-Hz range, with some recovery at 8,000 Hz, giving a notched appearance in the high-frequency scores. Hearing loss caused by noise exposure is irreversible, but use of hearing protection can minimize further damage. The Occupational Safety and Health Administration's guidelines limit the amount of time employees may work at a certain noise level. Generally, 8 hours is the maximum amount of exposure allowed at 90 dB; this time is halved for every 5-dB increase and doubled for every 5-dB decrease. Some hobbies, such as motor vehicle racing, carpentry, and target practice, expose patients to a great deal of noise and are common causes of hearing loss. For example, firearm discharge may cause unilateral hearing loss on the side of the predominant firing hand. Current and past medications should be reviewed, because many agents (eg, loop diuretics, salicylates) have been shown to be ototoxic. Aminoglycosides are most commonly implicated in drug-induced hearing loss, although the chemotherapeutic agent cisplatin (Platinol-AQ) has been shown to have greater ototoxicity. Renal failure potentiates the ototoxicity of most of these medications. Most ototoxic substances affect the cochlea by damaging the auditory hair cells and stria vascularis ductus cochlearis (an epithelial organ that controls the homeostasis of fluids and electrolytes).
Physical examinationStarting with the auricle, the ear should be carefully examined. Minor disfigurement suggests a potential congenital conductive hearing loss, because the development of the auricle, external auditory canal, and middle ear structures is closely related. An atresia or any other obstruction of the external auditory canal (eg, impacted cerumen, foreign body) will prevent sound from being conducted through the air to the middle ear. Generally, however, only a complete obstruction of the cross-sectional area of the external auditory canal causes this type of conductive hearing loss. The tympanic membrane and its architecture should be examined. Perforations, tympanosclerosis, cholesteatoma, effusion, and infection are usually readily identifiable causes of hearing loss. Otoinsufflation using a tightly fitting speculum to test the mobility of the tympanic membrane can uncover middle ear pathology. Tuning fork tests, such as Weber's test and the Rinne test, are also used to qualitatively test hearing. They work on the principle that bone-conduction hearing is augmented in patients with conductive hearing loss. Both tests use a 512-Hz tuning fork to minimize the amount of vibratory stimulus. Weber's test is performed by placing a vibrating tuning fork to the midline of the forehead and asking the patient to indicate which ear perceives the sound. In conductive hearing loss, the sound is louder in the affected ear (or in the worse ear in bilateral hearing loss); in sensorineural hearing loss, the tone is louder in the unaffected ear. The Rinne test is performed by first placing the stem of a vibrating tuning fork on the mastoid process (stimulating bone conduction) and then suspending the fork adjacent to the ear canal (stimulating air conduction). The patient is asked to determine in which position the sound is louder. Normally, air conduction is greater than bone conduction, so sound would be louder with the tuning fork placed in front of the ear. However, patients with significant conductive hearing loss perceive sound louder with the fork placed behind the ear. Generally, a difference (air-bone gap) of about 25 dB is necessary for the test to indicate greater bone conduction than air conduction. Although referral for complete audiologic testing is necessary to determine the extent of hearing loss, physicians can easily identify hearing loss and gauge its severity during a routine office visit. Patients with slight hearing loss have difficulty understanding a normal speaking voice from more than 12 ft away. Those with moderate hearing loss have trouble hearing normal speech from more than 3 ft away. Severe hearing loss excludes all normal speech, and a speaker must use a raised voice directly into the patient's ear. Cranial nerve testing is important for any head or neck complaint. Particular attention should be paid to facial nerve function, because cranial nerves VII and VIII are closely associated at the brain stem and in the temporal bone. Several pathologic conditions affect both nerves and consequently provide qualitative and site-of-lesion information about the cause of the hearing loss. The trigeminal and lower cranial nerves (IX through XII) can also be affected by a lesion at the brain stem, such as acoustic neuroma presenting as hearing loss.
Hearing testsA formal audiogram consisting of pure tone thresholds for both air and bone conduction is essential to diagnose and quantify hearing loss, which in turn helps to determine treatment options. Asymmetry in the bone conduction lines (sensorineural hearing) signals a potential retrocochlear process that usually requires further follow-up. The speech-discrimination score is also important in evaluating nerve function and determining the advisability of a hearing aid. The patient is presented with and repeats a list of phonetically balanced, one-syllable words; a score of less than 50% makes a hearing aid a less viable option, because the patient may be able to perceive a sound but not comprehend it. A tympanogram is often part of routine audiologic testing. It provides a measure of tympanic membrane compliance that can assist in the diagnosis of tympanic membrane perforation, middle ear effusion, ossicular fixation, disruption, and other causes of hearing loss. Auditory brain stem response is tested by placing electrodes on the scalp overlying the auditory cortex and measuring the conduction of sound from the cochlea to the brain using a probe placed in the ear canal. A slowing in conduction between ears may indicate retrocochlear pathology, such as an acoustic neuroma. Although this test is often used to screen patients with uncomplicated, asymmetric hearing loss or tinnitus, it has only 70% and 90% sensitivity; thus, careful follow-up is required. Computed tomographic (CT) scanning of the temporal bones (without contrast) and magnetic resonance imaging (MRI) of the head and internal auditory canals (with gadolinium contrast) are the radiologic tests of choice in diagnosis of hearing loss. A CT scan is used to examine bony detail in patients with suspected malformation of the external auditory canal, middle ear, or inner ear and to delineate bone erosion secondary to infection, cholesteatoma, or tumor. MRI is the "gold standard" in diagnosis of a retrocochlear lesion and is often used when results of the auditory brain stem response are abnormal or when history and clinical findings suggest a possible neoplasm in the internal auditory canal or brain.
ManagementSimple removal of impacted cerumen within the external auditory canal may correct conductive hearing loss. In most cases, surgical procedures (eg, tympanoplasty to reconstruct the tympanic membrane, ossiculoplasty to repair the ossicular chain, stapedectomy to restore hearing in otosclerosis) are quite successful. The chances of significant restoration of hearing have been increased with refinements in otologic surgical techniques and advances in the biocompatibility of the materials used in such procedures. Of course, hearing aids remain an option for conductive hearing loss, especially in frail patients who are not surgical candidates. There are medically and surgically treatable forms of sensorineural hearing loss. Antibiotic therapy can be used to treat tertiary syphilis, which can cause profound, bilateral hearing loss. In many cases, corticosteroids can be used to effectively treat immune-related or viral hearing loss. Surgical intervention, such as repairing a perilymphatic fistula or early detection and removal of an acoustic neuroma, can often halt the progression of associated hearing loss. Ear protection helps to prevent noise-induced hearing loss by reducing the level of exposure to loud sounds. Earmuffs, custom-fitted earplugs, and disposable earplugs provide 20 to 40 dB of sound attenuation and should be recommended to patients who are exposed to high noise levels. Hearing aids are the most common treatment option for patients with sensorineural hearing loss. Such devices vary in size from large, behind-the-ear models to invisible, in-the-canal models that are placed deep inside the external auditory canal. Recent advances in microelectronics have expanded the function of hearing aids beyond simple amplification; many units are programmable, allowing patients to adjust the output to match the listening environment. Assistive devices, such as amplified telephones and televisions, as well as clock radios or fire alarms that flash or vibrate the bed, are among the many important adjuncts to hearing aids. Although many assistive devices are available to patients with hearing loss, the most powerful medicine is the patience and understanding of family and friends. Remember that interpretation of speech involves both visual and auditory clues. A speaker should directly face the patient and articulate so that lip reading cues can be used; adequate lighting is helpful. If there are multiple distractions, especially background noise, moving to a quieter, more private setting can greatly improve communication. Hearing-impaired patients should be encouraged to request these courtesies without embarrassment.
ConclusionHearing loss is a common disability that affects people of all ages, particularly the elderly. Conductive hearing loss can often be surgically corrected, while sensorineural loss usually requires careful follow-up and hearing-amplification devices. Findings that should prompt further follow-up include asymmetric, sensorineural hearing loss or tinnitus, coexisting otalgia, otorrhea, vertigo, or other neurologic deficits. Universal screening for patients over 65 years of age should be seriously considered, because this population is especially vulnerable to social isolation and depressive disorders caused by hearing loss (2). References
Information about hearing lossAmerican Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS)One Prince St Alexandria, VA 22314-3357 703-836-4444 http://www.entnet.org/patient World's largest organization of physicians dedicated to care of the ear, nose, and throat. Web site has information sheets on a variety of topics.
Better Hearing Institute
Ear, Nose, and Throat Information Center
Hear Now
Self-Help for Hard-of-Hearing People
Dr Shohet is assistant clinical professor and director of neurotology, department of otolaryngology-head and neck surgery, and Dr Bent is associate clinical professor, department of family medicine, University of California, Irvine, College of Medicine. Correspondence: Jack A. Shohet, MD, Department of Otolaryngology-Head and Neck Surgery, UCI Medical Center, 101 The City Dr S, Bldg 25, Orange, CA 92868. E-mail: jshohet@uci.edu. Symposium Index
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