1. It's Not a Case of Selective Hearing
Auditory neuropathy, or auditory dysynchrony, is a complex, rare condition where auditory signals from the inner ear to the brain are not adequately transmitted. For all outward appearances, the person has normal hearing, or only mild hearing loss. But they do suffer from an impaired speech-perception capability. Thus, a person with auditory neuropathy can often hear and understand speech in a quiet setting, but not in a noisy environment. Sounds may have a tendency to be out of sync and fade in and out. This condition can affect anyone from infancy to adulthood.
2. What May Be Going Wrong Beyond Your Eardrum
Exactly what part or parts of the inner ear are affected due to auditory neuropathy is not clearly understood. It may be due to the inner hair cells (sensory cells) being unable to transmit sound signals through the nerves to the brain. There may be a problem between the inner hair cells and the nerve leading from the inner ear to the brain, or there could even be damage to the nerve itself. Some believe there may be a combination of these causes in at least some cases of auditory neuropathy. Outer hair cells seem to be healthy and do not play a role in people suffering from auditory neuropathy.
3. A Possible Link to Other Diseases and Disorders
Some infectious diseases such as mumps or autoimmune diseases may trigger auditory neuropathy (between 20 and 50 percent of AIDS patients are diagnosed with this condition). Inherited neurological diseases such as Charcot-Marie-Tooth disease (causing motor and sensory neuropathy) or Friedreich's Ataxia (a nervous system disease causing anything from weakened muscles to heart disease) are linked to auditory neuropathy. In infants, anoxia (lack of oxygen) at birth or hyperbilirubinemia (a condition wherein there is too much bilirubin in the blood, causing jaundice) that requires a blood transfusion are possible causes.
4. Two Tests, One Diagnosis
A combination of two tests is best to arrive at a conclusive diagnosis of auditory neuropathy. The tests are an auditory brainstem response (ABR), where electrodes attached to the head record activity from the inner ear nerve to the brain, and an otoacoustic emission test (OAE), involving the placement of a microphone into the ear canal to measure low-intensity sounds produced by stimulated outer hair cells. An abnormal ABR together with a normal OAE is usually indicative of auditory neuropathy.
5. Getting Back Your Fifth Sense
As an effective medical treatment for auditory neuropathy is still being researched, the only available options are hearing aids or cochlear implants (a small electronic device implanted into the inner ear to stimulate the auditory nerve). Many audiologists are of differing opinions regarding the benefits of hearing aids to treat auditory neuropathy, and cochlear implants, at one time not used often for this condition, are becoming the treatment of choice.
