Do you always test both ears when conducting ABR testing in infants to estimate hearing sensitivity, or is there a protocol for estimating the opposite ear in certain cases?
Well that's a good question. I always evaluate both ears. Let’s say a child failed a hearing screening in one ear, and comes back to the clinic for a diagnostic assessment. A unilateral failure in the nursery means the other ear that passed the screening is at risk for hearing loss, and there is a lot of research to support that fact. We do not want to assume that just because the screening result was normal in one ear, that a diagnostic assessment of that ear is not in order.
In addition, sometimes you have a unilateral anomaly – such as unilateral atresia or unilateral microtia. Some audiologists would recommend performing ABR only on the ear with the anomaly. That makes no sense to me. If you perform ABR only on the ear with the anomaly, you are assuming that because one of the child’s ears is typical in appearance that there is normal hearing in that ear. If that were the case, we wouldn’t ever have to do hearing tests because we could assume everyone with a typical-looking pinna had normal hearing. Of course we know as audiologists, that you can have a profound hearing loss (or any degree of hearing loss) with a typical-looking outer ear.
In addition, when you have a concern about a conductive loss, whether it is based on an ear anomaly like microtia, based on a delayed wave I in the ABR, or based on an abnormal tympanometry result, always do air and bone conduction ABR on both sides. You may think that if there is aural atresia, you only need to do bone conduction to prove that the cochlea is normal. That's not a good idea. You can’t estimate the degree of conductive loss based on looking at somebody’s ear. I've evaluated hundreds of patients with aural atresia and you never know what to expect in terms of hearing. I've had cases with aural atresia in one ear, a perfectly normal looking other ear, but they had otitis media in that ear, which resulted in a bilateral conductive loss.
I would always test both ears, but not always do a bone conduction ABR unless there are some risk factors for conductive loss. Always test both ears and try to always use clicks and tone bursts unless you have some other compelling evidence that hearing sensitivity is normal, such as normal OAEs plus the ABR.
This Ask the Expert was taken from the Q & A session of the course, Update on Auditory Evoked Responses: Value of Chirp Stimuli in ABR/ASSR Measurment, which is available in both a recorded course and a text course format.