Nolan's Newborn ABR: Questions

Reason # 1,056,078 why I love the John Tracy Clinic: when you have questions, you get explanations.

Obviously, getting news that contradicts years of information is always a tad difficult to accept and digest. So our wonderful JTC audiologist sat down with me to explain why she has concerns about Nolan's diagnosis. Since Nolan was found during the newborn hearing screening procedure, his first test was an ABR. Essentially, Nolan's ABR states (paraphrased):

Pure tone responses were obtained at 60dB for 500 and 1000Hz. A click response was obtained at 35dB for the high frequencies. OAE indicate reduced cochlear function from 500-2000Hz, with present OAE from 3000-8000Hz (indicating normal cochlear function). This is consistent with a mild/moderate sensorineural hearing loss rising to normal in the high frequencies.

This sounds like a nice, consistent picture. Unfortunately, there are a lot of questions regarding this information:

1. No bone conduction testing was performed. There is a way to get objective bone conduction scores, because you can run bone conduction during an ABR test. For children with a moderate loss at birth, a bone conduction should always be run to verify the type of hearing loss.

2. Nolan's best response in the high frequency range was 35dB. This means at some point in the higher frequencies, his best hearing was at 35dB. This is not "normal hearing" in the high frequencies. While ABR's have a correction factor for pure tone responses, there is no correction factor for a click. His hearing, therefore, was never "rising to normal." A high frequency sensorineural component was always present- this is important for other reasons (determining hearing loss progression, for example).

3. While I thought several behavioral bone conduction testing had been performed at BHSC on Nolan, it turns out there has only been one bone conduction audiogram ever performed. When Nolan was two-and-a-half. In other words, Nolan has displayed a hearing loss since birth, but no one bothered to run a bone conduction test for 2.5 years. The only reason bone conduction was finally performed at BHSC was because he had another "drop" in his hearing that was unexplained. This test showed a rising pattern, so that is still an inconsistency. Of course, if you have diagnosed a child with a rising sensorineural loss for three years, you might be more likely to interpret bone conduction scores in a certain manner.

4. The OAE presence/absence on Nolan's ABR report. This was my main sticking point. I figured that Nolan's hearing loss showed no OAE in the low frequencies and present OAE in the high frequencies, so that was consistent with a rising sensorineural loss. I have since been educated on the meaning of OAE, and when they can be present vs. not present. Essentially, the present OAE in the high frequencies do not necessarily indicate normal hearing. Present OAE can be found with mild hearing losses. Also, absent OAE do not necessarily indicate sensorineural hearing loss. While Nolan was missing his low frequency OAE, a conductive hearing loss could also cause a failure to obtain OAE responses. Essentially, the sound can't get through to the cochlea to generate the OAE (and presumably, the OAE responses would have a hard time finding their way back to the probe). If you can't conduct the sound through the middle ear, you aren't going to generate OAE. This means that his OAE responses at the time of his ABR were not sufficient to determine a conductive vs. sensorineural hearing loss- bone conduction was needed.

So what DO we know about Nolan's hearing loss?

1. It is most likely (mostly) conductive in the low and mid frequencies.
2. It is a typical sloping sensorineural hearing loss in the mid-high frequencies.
3. It is probably not a progressive loss.
4. It is a fluctuating loss.

I will talk about congenital, permanent conductive losses in another post (no, it can't be fixed).

Our picture is changing, which is always hard to accept. At least I have been given information to understand our son's initial testing (and what should be standard protocol for a child with a moderate loss at birth). When we return home, our next step will be to find an independent audiologist, hide all of Nolan's hearing test results, and get a third bone conduction test. If the independent test matches John Tracy's results, we will have a definite picture of Nolan's hearing loss configuration/type.