What is Auditory Neuropathy Spectrum Disorder (ANSD)?
- the outer ear – the physical ear and ear canal;
- the middle ear – the ear drum, the middle ear cavity, three tiny ear bones;
- the inner ear – the cochlea containing inner and outer hair cells; and
- the auditory nerve pathways in the brain (including the connection between the nerve and the inner hair cells).
While a hearing loss occurring in one or more of the first three parts of the hearing system is well known and described, scientists recently discovered that in some children hearing loss is caused by a malfunction of the auditory nerve pathways.
In practical terms, this means that while a child may appear to have normal hearing when the first three parts of the hearing system is assessed, he or she may have difficulty hearing because of a deficit in the auditory nerve pathways.
In 2008, a group of experts met to develop a uniform definition of ANSD, its symptoms, diagnosis, and treatment. During this meeting, the following guidelines were developed to provide children with auditory neuropathy spectrum disorder with the best possible care:
The symptoms of individual children with ANSD vary considerably with one common thread that helps define the disorder – impaired speech perception abilities. In order words, children with ANSD have mild to considerable difficulty in understanding speech, even in the presence of normal hearing.
However, many children with ANSD have mild to severe hearing loss when assessed with standard hearing tests. Speech perception is frequently poorer than what might be expected from degree of hearing loss. An individual with ANSD may also have a fluctuating hearing loss, where the ability to hear comes and goes with time.
The symptoms of ANSD are highly variable amongst individual children – some seem to not be affected at all by their diagnosis, while others are severely impacted by the limitation in their speech perception abilities.
The diagnosis of ANSD depends on a highly sophisticated battery of tests. Specialized equipment is required to carry out these tests, focusing on different parts of the hearing system. The test battery includes an assessment of: health and development history, behavioral response to sound, response to speech sounds, middle ear function, inner ear function, and auditory nerve function. When the results of the middle- and inner-ear tests are normal and the auditory nerve function test results are abnormal, a diagnosis of ANSD is considered.
Treatment plans for children with ANSD is a highly individualized process, because the symptoms and functional implication of the disorder vary between affected children. A treatment strategy for a specific child can also change as the condition fluctuates in some children. For certain children, amplifying sounds with hearing aids are helpful, while others can be considered as candidates for cochlear implants (a surgical procedure where electrodes are inserted into the inner ear).
Visual aids to assist speech understanding can also be very helpful for children with ANSD. It is very important that the hearing of a child with ANSD be carefully monitored to notice any fluctuations in his or her ability to hear.
Much about ANSD is still unknown, and several longitudinal studies are underway to sharpen our understanding of this disorder. However, whatever science teaches us about ANSD, the teamwork between parents and knowledgeable and caring professionals is the essential cornerstone of providing children with ANSD with the care that they deserve.