Interview with Charles Berlin, PhD:
Auditory Neuropathy Spectrum Disorder, OAEs, ABR, and More
Douglas L. Beck, AuD, spoke with Dr. Berlin about amplification, hearing aids, cochlear implants, middle ear reflexes, audiograms, hearing in noise, and more.
Academy: Good morning, Chuck. Always a pleasure to speak with you.
Berlin: Thanks, Doug. Always fun chatting with you, too.
Academy: Chuck, I want to focus this entire interview on the key points for audiologists with regard to auditory neuropathy spectrum disorder (ANSD).
Berlin: Okay, that sounds great.
Academy: Okay, let's start with the operational definition. What is ANSD and what causes it?
Berlin: ANSD is a condition in which the ABR is desynchronized and the OAEs are (or once were) present and normal, and the middle ear muscle reflexes are elevated or absent. The most common cause of ANSD is compromised or damaged inner hair cells. The second most common cause is damaged auditory nerve fibers and the third most common cause is damage to both the inner hair cells and the auditory nerve. (Ref: Gibson, et al., Sydney Cochlear Implant Centre)
Academy: Very good…and let's spend a few seconds on the importance of the acoustic reflex when evaluating a patient for ANSD. I generally recommend people not search for middle ear reflexes above 100 dB. First of all, the presentation level above 100 dB is too loud, and delivering a tone at 105 or 110 dB can cause traumatic damage to an otherwise healthy ear. And further, it just doesn't matter if there is a reflex at 105 or 110, it's absence or elevated presence supports the same hypothesis. Would you agree with that?
Berlin: That's an interesting point, and, yes, in general I would have to agree, especially if the emissions are still present and/or the audiogram is at 70 dB HL or less.
Academy: I know you've previously stated that when you suspect ANSD, and even when you don't, the audiologist should ALWAYS perform a core battery of clinical tests to present a quick and easy foundation of neurophysiologic status including reflexes, tympanometry and OAEs.
Berlin: Right. And I want to underscore we need to do this on every patient, because then we have the data to justify further in-depth testing or not. And let's face it, there are a lot of people walking around with ANSD that have never been suspected of having it and they've never been tested for ANSD.
Academy: That's an excellent point. My recollection of the contemporary literature is that some 10 percent of all people with severe-to-profound hearing loss likely have ANSD. Would you agree with that number?
Berlin: No. I believe it's closer to 15 percent of the general hearing impaired population and as you note, in the severe and profound hearing loss population, it's likely higher.
Academy: And it's important to note that we cannot find what we don't look for. Specifically, until some 25 years ago, nobody heard of, looked for or diagnosed ANSD. Then some 23 years ago the first case was reported, a year later there were two or three more, and now there are thousands…but the point is, ANSD has always been out there, we just didn't know to look for it, and now that we look for it, we find it!
Berlin: Exactly, and that's why we need to do reflexes, tympanometry, and OAEs on everyone. When people developed screening batteries decades ago, we didn't know about OAEs, and so we didn't include reflexes and tympanometry in screening batteries, but we know about ANSD now, and so we have adapt our clinical protocols and guidelines to allow us to screen for ANSD. Of note, I know there are many people with normal hearing thresholds and difficulty hearing in noise. In general, if the person is a child, they may be tested for an APD, and they may test positive on APD tests, but for many, the true problem is they have ANSD, masquerading as an APD.
Academy: I agree. I know you and your colleagues at USF conducted a study in which you investigated 200 + veterans who were matched with regard to their audiograms, and the only difference in their test results was the issue of reflexes being absent or elevated in one group and present within normal limits in the other group. Please tell me about that?
Berlin: Yes. The work was done by Erin Emery, Terry Chisolm, Rachel McCardle, and Benjamn Russelll. They examined data on more than 200 subjects who had tymps, reflexes, and emissions done. They exacted subgroups with the same mild-to-moderate high frequency loss across all of whom performed the same on word recognition in quiet. However, of enormous importance, their ability to accurately perceive speech in noise was very different. Patients with normal middle ear reflexes did fine, and those without reflexes fell apart in noise—they were clearly different groups. And so when the middle ear reflexes are absent or elevated, this presents a critically important factor to the patient and their ability to perceive speech sounds accurately in noise, and we as audiologists should look at this issue in every patient, young or old.
Academy: In my presentations across the United States, I try to always make the point that virtually every patient we see in the office is there because he or she is having a hearing or listening problem. And of course, as we all know, the number one major complaint is "the inability to understand speech in noise." And yet the majority of clinicians don't include speech-in-noise tests, which is terrifically unfortunate. If we don't test speech-in-noise ability, we're not testing or documenting the most important complaint, which brought the patient in, and if we're not testing in noise after fitting the patient with amplification (hearing aids, FM, cochlear implants, etc.) then we haven't documented an improvement in the same arena as the original complaint.
Berlin: Exactly, and so speech in noise tests are critically important, and I agree, they need to be done on every patient for a multiplicity of reasons, including ruling out or raising the suspicion of ANSD. And as you know, Doug, the audiologists generally focus on audiograms because the audiogram has become the "gold standard" of hearing ability, but the real "gold standard" may actually be their speech-in-noise results. And further, it's important to understand that when someone has ANSD, it often does not impact their audiogram. That is, you cannot tell whether someone has or does not have ANSD simply by looking at their audiogram.
Academy: Right, makes perfect sense. Tell me about the myth that "some people are born without a stapedius muscle and so they don't have a middle ear reflex."
Berlin: That is simply not true. When I was a post-doc at Johns Hopkins I studied some 780 temporal bones and I didn't see one temporal bone without a stapedial muscle. It's just that simple….this concept of the missing stapedial muscle is crazy and I've never seen evidence to support it. So to me, it appears to be a wide spread and common urban audiology myth. If you have a patient with absent reflexes, you can test for the presence of the muscle by simply putting the probe in the ear under question and putting a puff of air on the patient's eye. If the muscle is there, you will see it contract on the impedance bridge.
Academy: Yes, and when you think about it, there are lots of patients who come to the audiology office and complain about speech-in-noise perception at cocktail parties. At that point, they get a pure tone test and if the pure tone hearing is within normal limits, that's often the end of the testing and we counsel the patient that the good news is their hearing is normal and that everyone does poorly in noise. However, if we had tested their middle ear reflexes and found them to absent or elevated, that should lead to an OAE and an ABR test and hopefully a speech-in-noise test, and I'll wager many of those patients with normal hearing and a complaint about speech perception in noise might eventually prove to have ANSD.
Berlin: Well, that's right. And again, the index of suspicion index is raised very high when reflexes are elevated or absent, and the test is easy and inexpensive and takes less than a minute, and it's of enormous practical importance.
Academy: Okay, point well made. And before I let you run, tell me your experience and thoughts on auditory rehabilitation for people with ANSD, with regard to amplification options.
Berlin: Well, this is a really interesting subject and one that generally doesn't lend itself to brevity. Nonetheless, most of these ANSD patients (such as children with normal hearing) likely should not be considered audiology patients, given that they have normal hearing. That is, they actually should be considered speech and language patients. So we need a baseline of their performance on speech and language measures and then they need to be monitored over time.
In our experience (Linda Hood, Thierry Morlet, and myself) of some 500 patients, about 7 percent are progressing well with regard to speech and language acquisition, and so they don't need additional audiology management, these children need ongoing speech and language training. Of course, if no one checks their reflexes, some of these same children will be misdiagnosed with APD. Additionally, some 10 percent (or so) of the children with ANSD will eventually do okay with hearing aids, but the vast majority will need cochlear implants.
Academy: And is it true that most of the children with ANSD who are fitted with hearing aids go on to eventually acquire a cochlear implant?
Berlin: Well, I'm not sure about that, although it seems to be true. However, one major issue is the length of the hearing aid trial period and the fact that some hearing aid trials for children with ANSD can last a year or two, while very little (or no) progress is being observed, and time is ticking away during these critical language developmental periods.
Academy: Right. Well, that's an important issue and certainly worthy of consideration. Chuck, it's always an interesting and educational experience and I am very appreciative of your friendship, knowledge, and time!
Berlin: Thanks, Doug. I appreciate your thoughts and interest in ANSD, too
Chuck Berlin, PhD, is a research professor of otolaryngology and head and neck surgery and communication sciences and disorders, at the University of South Florida.
Douglas L. Beck, AuD, Board Certified in Audiology, is the Web content editor for the American Academy of Audiology.