Sudden Hearing Loss

Function of the Normal Ear


The ear is divided into three parts: the external ear, the middle ear, and the inner ear. Each part performs an important function in the process of hearing. Sound waves pass through the canal of the external ear and vibrate the ear drum which separates the external ear from the middle ear. The three small bones in the middle ear (hammer or malleus, anvil or incus, and stirrup or stapes) act as a transformer to transmit energy of the sound vibrations to the fluids of the inner ear.

Vibrations in this fluid stimulate the delicate nerve fibers. The hearing nerve then carries the sound impulses to the brain where they are interpreted as understandable sound. Each part performs an important function in the process of hearing. Sound waves pass through the canal of the external ear and vibrate the ear drum which separates the external ear from the middle ear. The three small bones in the middle ear (hammer or malleus, anvil or incus, and stirrup or stapes) act as a transformer to transmit energy of the sound vibrations to the fluids of the inner ear. Vibrations in this fluid stimulate the delicate nerve fibers. The hearing nerve then carries the sound impulses to the brain where they are interpreted as understandable sound.


Types of Hearing Impairment

The external ear and the middle ear conduct sound: the inner ear receives it. If there is some difficulty in the external or middle ear, a conductive hearing loss occurs. If the trouble lies in the inner ear, a sensorineural (SNHL) or nerve hearing loss is the result. When there is some difficulty in both the middle and inner ear, a combination of conductive and sensorineural impairment exists.

Conductive Hearing Losses

Any disease affecting the ear canal (external ear), ear drum, middle ear space or the three small ear bones may cause a conductive hearing loss by interfering with the transmission of sound to the inner ear. Such a conductive hearing impairment may be due to a perforation (hole) in the ear drum, partial destruction or fixation of one or all of the three little ear bones, or scar tissue around the ear bones or in the ear drum. Other causes of conductive hearing losses include wax in the ear canal, middle ear fluid or infection or any other process that would prevent sound from reaching the inner ear.

Sensorineural Hearing Loss (inner ear hearing loss)

As illustrated above, Sensorineural hearing loss is an inner ear hearing loss. The inner ear loss can occur in the cochlea, the cochlear or auditory nerve, the brainstem, or the auditory cortex. The auditory cortex is the region of the brain in which sound is heard. For most cases of sensorineural hearing loss, including sudden SNHL, it is felt that the abnormality is within the cochlea itself. For most case of SNHL, including sudden SNHL, the external ear canal and the middle ear are normal. This section will discuss the causes, treatments and expected outcomes of sudden SNHL.

Definition:

Sudden sensorineural hearing loss (SSNHL) is defined as a decline in hearing greater than or equal to 20 dB over 3 days or less without any identifiable cause.

What are the symptoms?

Very few symptoms are usually experienced in patients with sudden SNHL. Obviously hearing loss (the majority in one ear only) is the major symptom. Tinnitus or ringing in the ear may also be experienced. Occasionally, fullness in the involved ear is encountered. Pain is rarely associated. In some cases imbalance, or true spinning (vertigo) can be associated with sudden SNHL.

Is this common to suddenly lose your hearing?

Approximately 4,000 cases of sudden SNHL occur annually in the United States. Hearing loss from aging (presbycusis) and noise exposure are relatively common. There types of losses occur gradually over many years. Sudden hearing losses that are sensorineural in nature (inner ear) are relatively uncommon. Sudden losses of a conductive type (see above) are much more common than sudden inner ear losses. Examples of sudden conductive hearing losses include wax in the ear canal, fluid or infection in the middle ear space, chronic infections of the ear or middle ear bone abnormalities.

What is the cause of sudden SNHL?

By definition the exact cause of sudden SNHL is idiopathic (literally unknown cause ). Current research is underway to determine the cause of sudden hearing loss and therefore potential cures. Some of the proposed cause are listed below. The most commonly proposed causes of sudden SNHL include viral infection of the inner ear, blood flow abnormalities to the inner ear, and problems with the fluid mechanics of the inner ear which leads to tears in the fine membranes of the cochlea.

Viral Infection

Perhaps the most common theory to explain sudden hearing loss is a viral infection. Evidence of viral infections have been found by researchers in patients who have had sudden SNHL, leading to this being proposed cause. A viral infection can cause inflammation of the inner ear or auditory nerve. This inflammation of the inner ear structure and associated blood vessels can cause hearing loss. No pain, fever, muscle cramps or other signs of a viral illness are usually encountered. Occasionally, signs of an upper respiratory infection may precede the onset of sudden SNHL.

Cochlear Membrane Tears

The cochlea or inner ear is made of fine, delicate membranes that contain fluid-filled spaces. It is the movement of the fluid in these spaces that creates sound. Potentials are created by the ear by actively storing particular electrolytes in these fluid filled spaces. This active storage of electrolytes creates different charges (+ or -) in these fluid-filled spaces that are separated by the fine membranes. This charge difference or potential between the spaces allows for the generation of a nerve impulse much in the same way a battery with its positive and negative poles can induce electricity.

A tear in the fine delicate membranes can lead to a mixing of the fluid, a loss in the potential, and an inability to generate a nerve impulse. This inability to generate a nerve impulse leads to a hearing loss. Tears in the membrane can occur from pre-existing defects (probably hereditary) and from excessive fluid in the spaces such as Menieres disease (see Menieres disease section)

Blood Flow Abnormalities

Another potential cause for hearing loss is abnormal blood flow to the cochlea. Severe hypertension may lead to bleeding in the inner ear with resulting hearing loss. Poor blood flow from arteriosclerosis may lead to inadequate perfusion or flow of blood into the cochlea. These mechanisms may be described as a stroke of the inner ear. This cause is more commonly found in the elderly, but may also be associated with the use of birth control pills in the younger population.

Below is a list of potential causes that have been proposed as causes for sudden hearing loss.

Potential Causes of Sudden SNHL

Explanation/ Examples

Viral infection

Inner ear viral infection

Bacterial infection

Otitis media, syphilis

Vascular occlusion

Stroke

Vasculitis

Inflammation of the blood vessels

Menieres disease

Inner ear fluid build up

Labyrinthitis

Viral or bacterial inner ear infection

Meningitis

Viral or bacterial infection of brain lining

Medical disorders

Diabetes, hypo or hyperthyroidism

Hereditary disorders

Inner ear hereditary hearing loss. Ushers syndrome, Waardenburgs syndrome

Low levels of oxygen (hypoxia)

Stroke

Medications

Antibiotics, (termed ototoxic medications)

Malignant neoplasm (tumors)

Cancer of the ear

Benign neoplasms (tumors)

Acoustic neuroma, meningioma

Autoimmune hearing loss

Immune system disorder that can affect the inner ear as rheumatoid arthritis is an immune system disorder that affects the joints

Cholesteatoma

Chronic middle ear infection can also cause an inner ear loss in advanced cases

Otosclerosis

Fixation of hearing bones, can also cause an inner ear loss

Hypertension

May cause bleeding in the inner ear or brain

Intra-cochlear membrane tears

A tear in one of the fine membranes that makes up the inner ear. May be the cause of hearing loss in Menieres disease.

What types of diagnostic tests are obtained?

The standard evaluation of a patient who comes to the office with the complaint of a hearing loss is to obtain a formal hearing test. An extensive history and physical examination is performed to determine if a cause can be found and therefore direct the evaluation and therapy. The first test obtained is a formal hearing test to determine the type and degree of hearing loss. If a sensorineural loss is confirmed, it is likely that an

MRI scan of the head will be obtained. It is likely that this radiology test will be normal; the primary purpose of this study is to rule out other causes of sudden hearing loss (tumors, strokes)

Below is a list of some of the potential diagnostic tests. The history, symptoms, physical examination and physician preference will determine which tests are to be obtained. It is not uncommon to order none of the tests below except for a hearing test (audiogram) and an MRI of the head.

Diagnostic tests

Explanation/ Examples

Complete blood count

Abnormalities of the blood, i.e. leukemia

ANA

Autoimmune disorder associated with hearing loss

FTA-abs or MHA-TP

A test for syphilis

Lyme titers

Lyme disease may cause hearing loss

ESR

A test for inflammatory disorders

MRI with Gadolinium

A radiology test for the inner ear, inner ear nerve and the brain

CT temporal bone

Radiology test that looks more specifically at the ear and ear-related structures. A poor test to see the brain and auditory nerve.

HIV

AIDS

Cholesterol

Elevated cholesterol

Triglycerides

Elevated tryglyceridemia or fatty acids in the blood

Glucose

diabetes

Immunoglobulins IgA, IgG, IgM

Immune deficiency disorders

Audiogram

hearing test

Auditory brainstem response testing (ABR)

Specialized hearing test

Otoacoustic emissions test (OAE)

Specialized hearing test

Is the hearing loss treatable ?

Recovery rates range from 5% to 90%, but the overall accepted recovery is felt to be 60% (two-thirds of patients are expected to recover hearing to some degree). In some patients, the hearing loss will recover spontaneously without therapy.

How is it treated?

Just as there is a long list of proposed causes for hearing loss, there is a long list of proposed therapies again depending on the history, symptoms, physical examination and physician preference. The most common medications used are steroids (prednisone) which are powerful anti-inflammatory agents. The term shotgun therapy is used to describe treatment for sudden SNHL. This is because multiple medications may be given to treat the proposed causes over a short period of time. The earlier treatment is started, the better the potential for hearing improvement.

Proposed therapies for sudden SNHL

Steroids
Antiviral agents
Aspirin
Coumadin
Heparin
Carbogen inhalation
Anti-inflammatory agents
Diuretics
Hyperbaric oxygen
Dexamethasone perfusion
Methylprednisolone perfusion
Steroid pump infusion
Plasmaphoresis
Cytoxan
Methotrexate
Dextran
Histamine
Calcium channel blockers
Magnesium

Prednisone is the mainstay in the treatment of sudden SNHL. Prednisone is usually given over a 10-14 day period as a tapering (decreasing) dose. Like all medications, steroids have certain potential side effects that include mood elevation, insomnia, and stomach irritation.

Some more uncommon side effects are listed below:

Side effects/complications of steroids use

Sodium and fluid retention
Electrolyte disturbance
Insomnia
Osteoporosis
Aseptic necrosis of the femoral and humeral heads
Vertebral compression fractures
Congestive heart failure
Tendon rupture
Dermatologic disorders
Gastrointestinal disorders Peptic ulcer disease
Gastritis
Perforation of the large and small bowel
Esophagitis
Pancreatitis
Neurologic disorders
Irritability
Increased intracranial pressure with papilledema
Psychosis
Headache
Glaucoma
Exophthalmos
Posterior cataracts
Adrenal and pituitary unresponsiveness
Latent diabetes mellitus
Decreased carbohydrate tolerance
Increased insulin and oral hypoglycemic requirements in diabetics
Myocardial rupture
Thromboembolism
Increased appetite
Weight gain
Malaise

Steroid (Dexamethasone) perfusion

The dexamethasone perfusion is a relatively straightforward procedure performed in the office setting. Essentially a steroid solution is injected directly into the middle ear space through the eardrum of the affected ear. Initial studies have demonstrated that transtympanic therapy may have a positive role in treating patients with sudden hearing loss. The Otology Group physicians are currently studying the potential beneficial effect on steroid perfusion to restore hearing. The effect is currently unknown.

Depending on the degree of residual hearing loss, the patient with a persistent SNHL has several treatment options:

  • Do nothing further.
  • Place a hearing aid on the affected ear (see hearing aid section)
  • Place a CROS hearing aid. (see hearing aid section)
  • Place a bone-anchored hearing aid (BAHA) on the affected ear. (see BAHA section)
  • Place a cochlear implant in the event of a bilateral SNHL (see Cochlear implant section)