What is sensory hearing loss?
There are two major types of hearing loss: conductive, which is caused by anything (e.g., earwax) that prevents sound waves from entering the inner ear, and sensory/ neural, which is caused by an interference with the inner ear's ability to process sound normally.
Under normal conditions, sound waves are generated by vibrations created in the air. The waves pass through the outer and middle portions of the ear into the inner chamber, where tiny, hairlike cells that line the cochlea (the bony, snail-shaped structure where hearing takes place) transform the vibrations into impulses along the auditory nerve. The auditory nerve then passes these impulses on to the brain for interpretation.
Most sensory hearing loss is caused by damage to the hairs or nerve fibers that are contained in the cochlea. The
- Decreasing ability to hear the radio or television at volumes that are comfortable to others.
- Decreasing ability to hear specific sounds and discriminate between certain words, such as "thin" and "fin."
- An unconscious tendency to speak loudly.
most common example is gradual hearing loss due to aging, which results from damage to the tiny cochlear hair cells.
Determining the source of neural or sensory hearing loss is often complex, but there are important distinguishing features. Neural hearing loss usually relates to damage to the so-called eighth nerve, and is likely to result from a brain tumor or other serious neurologic disorder. In contrast, sensory hearing loss results from local damage in the cochlea rather than an underlying disease. In addition, sensory hearing loss due to cochlear problems is characterized by mild to moderate loss of discrimination for speech. The ability to discriminate sounds increases with intensity; even small increases in intensity improve hearing.
What causes sensory hearing loss?
The most common causes of sensory hearing loss are:
- Viral labyrinthitis, an infection in the inner ear.
- Medications that damage the delicate inner-ear structures. Aspirin, antibiotics, and quinine are the most common examples.
- Excessive noise, such as chronic exposure to loud music or other sounds, or short-term exposure to an extremely loud noise.
- Meniere's disease, which causes dizziness and tinnitus (ringing in the ears).
How is sensory hearing loss diagnosed and treated?
Careful examination and testing are needed to differentiate sensory from neural hearing loss. Tests can measure such factors as hearing discrimination, the ability to differentiate phonetically balanced words, and sensitivity to small increments in sound intensity.
If neural hearing loss is suspected, tests are conducted to measure auditory responses. In general, these tests require that the patient sit in a soundproof room and wear special earphones. He or she can see the tester through a glass window and is instructed to signal when a sound is heard. The person being tested also repeats the sounds or words as they are heard.
What can I do myself?
Protect the ears from excessive noise. Hearing loss due to noise cannot be restored, but further deterioration can be slowed or prevented by protecting the ears. Avoid loud music. If a job involves exposure to loud noise, protective earphones should be worn.
If there is difficulty hearing what others say, the person should assume a position that allows him or her to read lips and see other visual clues that can improve understanding of what is being said.
When should I see my doctor?
Any signs of hearing loss should prompt a person to consult a physician.
What will the doctor do?
The first step is to identify the type of hearing loss. Treatment depends on the underlying cause. Nothing can be done to restore hearing loss caused by loud noise. In such instances, the best approach is to prevent further loss and to wear a hearing aid to maximize the remaining sense of sound.
If the hearing loss is due to a drug that is toxic to the ear's delicate structures, the drug should be stopped or the dosage modified.
If hearing loss is total but the auditory nerve is still intact, the patient may be able to benefit from a cochlear implant in the inner ear. Such an implant cannot restore normal hearing, but it enables a person to hear certain sounds, such as a horn, doorbell, or siren.
The course of sensory hearing loss
The extent and progress of sensory hearing loss depends upon the underlying cause and whether or not it can be treated effectively. Sometimes the hearing loss is temporary, as in the case of some viral infections.
If the hearing loss is due to a drug reaction, normal hearing usually returns when the drug is discontinued or the dosage reduced. However, some drugs can cause permanent hearing loss.
If the hearing loss is caused by Meniere's disease, the level of hearing usually fluctuates. Although it usually gets progressively worse, Meniere's typically affects only one ear and thus does not cause total hearing loss.
Is sensory hearing loss dangerous?
Sensory hearing loss usually is not a threat to health. But the inability to hear warning sounds, such as a siren or fire alarm, can put a person in a dangerous situation. Loss of hearing can also be frustrating and even disabling.
What can I do to avoid sensory hearing loss?
- Avoid overuse of aspirin.
- Avoid excessive noise. If a hobby or job requires noise exposure, use appropriate hearing protection.
- Discourage children from listening to extremely loud music, especially through earphones.
- If an earache or ear infection develops, seek prompt treatment.