Otoacoustic Emissions, Mis-Match Negativity, and Hearing Screenings: Interview with Rebekah F. Cunningham, PhD
Douglas L. Beck, AuD, speaks with Dr. Cunningham about OAEs, transient OAEs, distortion product OAEs, auditory neuropathy spectrum disorders, and more.
Academy: Good morning, Rebekah. Nice to chat with you again.
Cunningham: Hi, Doug. Thanks for your time, too.
Academy: My pleasure. I believe your PhD was from the University of Cincinnati, but I cannot recall the year? Were you there during the reign of my good friend Bob Keith?
Cunningham: I received my PhD in 2000 and, yes, Bob Keith was my mentor. He’s the reason I went there.
Academy: I’m sure that’s true for many people! What was your dissertation on?
Cunningham: Mismatch negativity (MMN).
Academy: I’ve always found that to be fascinating, but I’ve never seen anyone apply it clinically. What did you find in your research?
Cunningham: Well, that’s a good observation. I did a pilot study and then the research study itself based on long duration tone bursts across about 25 children. We found that in general, the MMN is pretty difficult to obtain and even in our normal hearing children, the MMN was only present in about 70 percent of the group.
Academy: And so the task was to give a very tiny difference in stimuli, and to see if the child’s brain “registered” the difference (so to speak) without the child actually noticing the difference?
Cunningham: Yes, more or less, that was the idea.
Academy: And so MMN still seems to be “not ready for prime time” with regard to clinical use?
Cunningham: Right. As we cannot easily demonstrate or acquire MMNs consistently in normal hearing children, it doesn’t appear to lend itself to clinical utility.
Academy: Good enough. Let’s move on to otoacoustic emissions (OAEs). Please start by defining the two most common types.
Cunningham: Sure thing. Of course the two most common types are the distortion product OAEs (DPOAEs) and transient-evoked OAEs (TEOAEs), which refer to the specific stimuli used to evoke the OAE. Transients are evoked essentially by a very rapid, broad band click stimuli, and DPOAEs are evoked by two distinct pure tones and the distortion product is a third frequency produced by the original two pure tones. So basically with DPOAEs, we can measure more frequency specific information than we can using transients, because DPOAEs stimulate more specific areas along the basilar membrane, while TEOAEs are much more of a broad band response.
Academy: And, in the early days, most people primarily used TEOAEs for newborn screenings?
Cunningham: Yes, and that’s changed through time, experience, and knowledge. It seems to me that DPOAEs are being used quite a lot more today for screening purposes, and that makes a lot of sense to me. One thing that adds a little to the mix is that some people believe TEOAEs are faster to complete than are DPOAEs; however, in experienced hands, the two are just about the same with respect to test time—although again, you derive more information from DPOAEs.
Academy: And what if you could only screen with one tool, the OAE or the auditory brainstem response (ABR), which would you pick for newborns?
Cunningham: Well, this is a good and important question. I’ll start by saying that in the NeoNatal Intensive Care Units (NICU) that I work with, we use automated ABR (AABR) or a two-stage auditory screening, and in the well-baby clinics we use OAEs.
Academy: And how does that work with regard to identification of children with auditory neuropathy spectrum disorders (ANSDs)?
Cunningham: Well, with the AABR screenings in the NICU, we’ll likely do very well. However, I think your point is that if we only screen with OAEs in the well-baby clinics, there’s a chance we won’t identify some children with ANSD.
Academy: Yes, and that’s a pretty important issue. The most recent information I’ve seen is that some 10 percent of all children with severe-to-profound sensorineural hearing loss have ANSD.
Cunningham: Yes, I’ve been reading that, too, and it’s a staggering statistic. Frankly, I haven’t seen it at the 10 percent level, but I’m certainly seeing it more than I did 10 years ago. And of course nobody knows if we’re better at identifying it, or has it become more common, or a combination of those two things. However, the likelihood is that as our awareness has increased, we’ve looked for and identified more children with ANSD. Of course, there may be multiple etiologies, so we’re still learning about ANSD and there’s probably a lot to learn!
Academy: Yes, I agree. Seems to me back in the old days (20 years ago) as ANSD was a relatively new diagnosis and only a few children were reported in the world’s literature at that time, it appeared to be a lesser issue. But then OAEs arrived and AABR arrived and the more we looked, the more we found. So I’ll bet it was always there, but the key is we now have tools to identify it, and more importantly—we’re looking for it!
Cunningham: Absolutely. And this gets to the point of using AABR to screen and test for ANSD. If the dysfunction is between or along the synapses between the inner hair cells and the auditory nerve, you need to use ABR (or AABR) to identify neural dys-synchrony and that’s something OAEs cannot tell you.
Academy: And another thing that may cause difficulty is the presumed “gold standard” in diagnostics, such that when you have a normal OAE and an abnormal ABR many people will presume ANSD. Can you address that?
Cunningham: Sure. The thing to realize is that many of these babies who do have ANSD will eventually lose their OAEs. And so you cannot use the most common “normal OAE and abnormal ABR” as the only criteria. Yes, that is the “gold standard” and it should always raise eyebrows, but there are other diagnostic results that may be consistent with ANSD, such as “abnormal/absent OAE and abnormal/absent ABR.” And so what is more reliable in identifying ANSD is the outer hair cells activity as reflected via the cochlear microphonic, which as you know, Doug, comes from electrocochleography.
Academy: And the classic electrocochleography ANSD pattern would be a cochlear microphonic that flips with polarity reversal present with no other waveforms. Is that right?
Cunningham: Exactly. The cochlear microphonic (CM) response comes from the outer hair cells and so the presence or absence of the CM can be very important in identifying and diagnosing these children. The CM will flip with polarity reversal even in normals, but it is often bigger in children and those with ANSD. So when it is present with no other waveforms, and you see that robust flip, it is a sure sign of ANSD.
Academy: And for some readers, it would be useful to review Ferraro’s recent paper on ECOG (JAAA, Volume 21, Pages 145-152) to learn more about getting a consistent and well defined cochlear microphonic.
Cunningham: Yes, I agree.
Academy: Okay, thanks so much Rebekah! I appreciate your time and knowledge!
Cunningham: My pleasure. Thank you, too!
Rebekah F. Cunningham, PhD, is an assistant professor and clinical coordinator at A.T. Still University, Arizona School of Health Sciences.
Douglas L. Beck, AuD, Board Certified in Audiology, is the Web content editor for the American Academy of Audiology.