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Hearing Loss Medical Foundations of Workers’ Compensation Hearing Loss Objective: This section will introduce the student to the topic of hearing loss, the types, causes, and symptoms of hearing loss, and how to test for it. Hearing Loss Overview Anatomy Types of Hearing Loss Causes of Hearing Loss Symptoms Exams and Tests Preventing Hearing Loss Treating Hearing Loss Hearing Loss Definitions General Definitions Testing Terminology Conductive Hearing Loss Presbycusis (Age related hearing loss) Sensorineural Hearing Loss Tinnitus Links to Review Ear Diagram Ear Diagram Quiz (Test Yourself) Audiogram 1 Medical Foundations of Workers’ Compensation Hearing Loss Hearing Loss Overview Hearing loss is a common problem that affects people of all ages. It is especially common in older adults: Among those between the ages of 65 and 75, 30% to 35% have reduced hearing. Hearing loss may be mild or severe, temporary or permanent, depending on the cause. In adults, noise-induced hearing loss and age-related hearing loss are the most common types of hearing loss. Whatever the cause, detection and treatment of hearing loss are important. Undiagnosed and untreated hearing loss can contribute to depression, social isolation, and loss of independence, especially in older adults. It can impact a person's personal safety and his or her productivity in the workplace and at home. Evaluation of a hearing loss is also important because hearing loss is sometimes reversible. Even if a hearing loss can't be reversed, hearing aids and other devices can help the person get the most out of any remaining hearing and make communication, social interaction, and work and leisure activities easier and more enjoyable. Anatomy There are four major sections of the ear: Nerves (consists of 30,000 fibers) take information to the brain. Inner Ear (cochlea) receptors for hearing and balance. Contains chambers, each of which are broken down into 3 more chambers. Each of the 3 chambers has their own job. Middle Ear (transformer). Three bones serve the transformer function – malleus (hammer), incus (anvil) and stapes (stirrup). The stapes (stirrup) moves by vibratory action. External ear (only seen in mammals). It serves as a scoop and as a place to hang earrings. The sections all play important roles in how we hear. A problem with any of them can cause a hearing loss. Types of Hearing Loss There are three basic types of hearing loss: A conductive hearing loss occurs when the normal physical movement (conduction) of sound waves through the external ear canal or the middle ear is blocked or misdirected. Anything that disrupts the passage of sound through the external and middle ear—such as hardened earwax, a foreign object, abnormal bone growth, swelling, or a tumor—can cause this type of hearing loss. Conductive hearing loss usually can be reversed by treating the underlying cause. A sensorineural hearing loss occurs when sound reaches the inner ear normally 2 but a problem in the inner ear, the cochlear (auditory) nerve, or, rarely, the brain itself prevents proper hearing. Damage to the tiny hair cells in the cochlea, resulting from age-related changes or repeated noise exposure, is the most common cause of sensorineural hearing loss. Conditions such as stroke, multiple sclerosis, or a tumor also may result in a sensorineural hearing loss by causing nerve damage. Sensorineural hearing loss often cannot be reversed. A mixed hearing loss, in which both the conductive and sensorineural systems are affected, can also occur. Causes of Hearing Loss Hearing loss can have many possible causes. In adults, the most common causes of hearing loss are: Noise. Noise-induced hearing loss can affect people of all ages and most often develops gradually over many years. In most cases, damage to the inner ear caused by exposure to harmful noise results in a permanent sensorineural hearing loss. Though extremely common, noise-induced hearing loss is almost always preventable. Age. In age-related hearing loss, or presbycusis, changes in the nerve tissue and cells of the inner ear that occur as a person grows older, cause a gradual but steady sensorineural hearing loss. The loss may be mild or severe, but it is always permanent. Other causes of hearing loss include: Earwax or an object in the ear. Earwax is an especially common and easily treatable cause of temporary hearing loss. Ototoxic medications and other substances (such as aspirin, arsenic, mercury, tin, lead, and manganese) that can damage the ear. Injury to the ear. Head injuries can also damage the structures in the ear and cause a sudden hearing loss. Ear infection. Otosclerosis (a condition affecting the bones of the middle ear). Acoustic neuroma (a benign tumor on the cochlear, or auditory, nerve). Ménière's disease (a disorder of the inner ear that can affect hearing and balance. It is characterized by episodes of dizziness and tinnitus and progressive hearing loss, usually in one ear. It is caused by an increase in volume and pressure of the endolymph of the inner ear). Symptoms People who have a hearing loss are sometimes not aware of it, especially when the loss has developed gradually. Family members or friends often notice signs that the person is having trouble hearing before the person realizes it. Symptoms of hearing loss include: Muffled hearing. Not being able to understand what is being said, especially when there are competing voices or background noise. (Being able to hear someone speaking, but 3 not able to distinguish the specific words.) Listening to the television or radio at higher volume than in the past. Avoiding conversation and social interaction. Social situations can be tiring and stressful for a person who does not hear well. Some people may increasingly avoid those situations as hearing becomes more difficult. This may also contribute to (or be mistaken for) depression, especially when it occurs in older people. Other symptoms that may occur with hearing loss include: Ringing, roaring, hissing, or buzzing in the ear (tinnitus). Ear pain. Pus or fluid discharge from the ear. This may result from an injury or infection that is causing hearing loss. The feeling that you or your surroundings are spinning or whirling when neither you nor the surroundings are actually moving (vertigo). This may occur with Ménière's disease, acoustic neuroma, or certain other conditions. Sudden hearing loss may be a medical emergency, especially when it follows a head or ear injury. Exams and Tests Hearing loss can often be detected during a routine visit to a health professional. If a patient reports symptoms of hearing loss or the doctor detects a possible hearing problem, he or she may ask the patient about recent or long-term exposure to loud noise, any medications being taken (some may be ototoxic, meaning they have a deleterious effect upon the eighth nerve or on the organs of hearing and balance), physical symptoms (such as muffled hearing, ringing in the ears, or vertigo), and other factors. The patient’s answers to these questions may sometimes suggest the cause of the hearing loss. Evaluation of a possible hearing problem also includes a physical examination of the ears, during which the doctor looks inside each ear using a lighted instrument called an otoscope. A physical exam of the ear can detect problems in the ear canal, eardrum, and middle ear, such as hardened earwax, an object or obstruction in the ear canal, infection or fluid in the ear, injury to the eardrum, and other problems that may contribute to hearing loss. The inner ear cannot be viewed through an otoscope. If a patient’s symptoms, exam, or history suggests a hearing problem may be present, the doctor may do one or two simple tests to screen for hearing loss. These may include the “whisper” test as well as tuning fork tests. Whisper test: a simple screening test that assesses a person’s ability to hear whispered speech across a short distance. Tuning fork test: the examiner strikes a two-pronged metal device (tuning fork) to produce a tone. The base of the tuning fork may then be placed on the patient’s forehead or the bone behind the ear or may be moved around in the area near the ear. These quick, easy tests can provide valuable information about the type of hearing loss that may be present. 4 If the initial screening tests suggest or reveal a hearing loss, a more thorough hearing evaluation may be needed to assess whether there is a hearing loss, how severe the loss is, and what part of the ear is affected. A standard hearing evaluation includes the following tests: Pure tone audiometry: an audiometer is used to produce tones that the patient listens for through earphones (air conduction) and via a bone conduction oscillator (bone conduction). Comparisons are made of the air and bone conduction thresholds to determine the nature of the hearing loss (conductive, sensorineural, or mixed). Speech reception and word recognition tests: measure the patient’s ability to hear and understand speech. Acoustic immitance tests (tympanometry and acoustic reflex tests): measure the amount of sound energy that is reflected back from the eardrum (tympanic membrane) and the bones of the middle ear instead of being conducted on to the inner ear. These tests help evaluate the function of the middle ear. Depending on the suspected cause of hearing loss, other tests may also be done. Imaging tests: such as computed tomography (CT) or magnetic resonance imaging (MRI) scanning might be done when an injury or tumor is suspected as the cause of the hearing loss. Auditory brainstem evoked potential testing: may be used to evaluate the function of certain nerve pathways in the brain if acoustic neuroma or another nerve problem is suspected as the cause of hearing loss.
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