VEMPS, Rotational Tests, and Platform Posturography: Interview with Devin L. McCaslin, PhD
Douglas L. Beck, AuD, spoke with Dr. McCaslin, an associate professor in the Department of Hearing and Speech Sciences, Communicative Disorders, Vanderbilt Bill Wilkerson Center at Vanderbilt University, about electronystagmography and videonystagmography, rotational chair, discontinuing dizziness medicines prior to testing, monothermal screenings versus bi-thermal tests, and more.
Academy: Good morning, Devin. Good to speak with you.
McCaslin:: Hi, Doug. Nice to speak with you, too.
Academy: Devin, I know you're as associate professor at Vanderbilt, and I have to think that's just about the busiest vestibular clinic in the United States? How long have you been there?
McCaslin:: Yes, well, we're pretty busy. I've been here for 10 years. I recall when I started we did about 250 balance exams annually and now we are approaching 1,500 per year. As a result, we have six of us doing balance assessments as our primary day-to-day clinical responsibility, including Gary Jacobson (director of the audiology division), Sarah Grantham, Lauren Tegel, Jill Gruenwald, Lindsay Danielle, and myself. Lindsay is running our satellite balance clinic, and the rest of us are here at Bill Wilkerson on the same floor as otolaryngology.
Academy: That's pretty substantial growth—and besides the raw numbers, there's also been growth into new areas, too?
McCaslin:: Yes, it's really changed over the years. The depth of the exams has increased substantially, and we're also seeing a lot more children. So the bottom line is we operate three complete vestibular labs, full time, every day.
Academy: Pretty amazing! So then, what is the "core" battery of vestibular tests?
McCaslin:: Great question! The core battery of tests has evolved over the years, and as you know, Doug, the diagnostic tests vary a bit based on the patient's situation, chief complaint, overall health, age and other factors. Nonetheless, the core test protocol includes cervical vestibular-evoked myogenic potentials (VEMP), ocular VEMPs, rotational testing, and ENG/VNG, and, again, based on the patient's signs and symptoms we may elect to do posturography and sometimes electrocochleography, too.
Academy: That's great, and I think it makes sense to include VEMPs up front. If you don't mind, I'd like to make a few observations about your new book and then I'll ask a few questions about balance testing in general.
McCaslin:: Sure thing.
Academy: Okay, well my first thought as I read through the book is that you have the clearest and most useful collection of vestibular illustrations I've ever seen all gathered in one place. Further, the appendix is brilliant. If I were in clinical practice there's a really good chance I'd be photocopying the multiple sections of the appendix and using them with just about every patient. The appendix includes a multipart dizziness questionnaire (characteristics of dizziness, associated ear symptoms, associated neurologic symptoms, history, time course, and aggravating factors), a patient's guide to BPPV, the Vanderbilt Balance Disorders patient brochure, a four page counseling brochure, a list of "alerting" tasks and a chart showing the reliability and localizing value of each sub-test. And, as long as I'm on a roll, I'll have to admit the actual text is very clear and well written, too!
McCaslin:: Thanks, Doug. You mentioned a few things that were really important to me as I embarked on the project. I'm a visual learner, and for me, it really was important to have the best illustrations relative to vestibular anatomy to "how-to" illustrations for anticipating and measuring nystagmus as well as how to do various procedures, such as Dix-Hallpike and repositioning maneuvers.
As far as the text, the book is written for the audiologist, and so that may also help separate it from the pack! The goal was to have everything you need to learn, understand, and implement regarding the evaluation of the dizzy patient, for new or newly interested audiologists, and to have it available all in one place.
Academy: Clearly, you've accomplished the goal. Let me ask you a couple of questions, which I believe will be beneficial for many of the readers.
McCaslin:: Okay, shoot.
Academy: First…tell me your thoughts about receiving first-hand historical information from the patient.
McCaslin:: Yes…well that's critically important. That is, although referrals and questionnaires all have their place and can obviously be very useful, I believe it's important to question the patient directly. That is, we should gather his or her first-hand description of the problem, rather than, or in addition to, the other paperwork surrounding the patient. Further, when we get the case history directly from the patient, it allows us to build trust and establish rapport, all of which matter a great deal as we go through the evaluation. We usually allow about two hours for the evaluation, and frankly, we use about 20 or 30 minutes of that for the case history, which helps us focus and fine-tune our test protocol for that individual patient.
Academy: What do you tell patients as far as discontinuing their medicines prior to their balance tests?
McCaslin:: Great issue! Well, we've gone all the way from discontinuing to maintaining all medicines. The issue is, when you tell them to discontinue their medications, they may accidentally discontinue something they should have stayed on, they may get confused, they may have a really bad day on the day of test because they didn't take medicines they were accustomed to—and one never knows the exact outcome that could happen if the patient gets confused or skips an important medicine. Bottom line…we do not tell them to discontinue their medications.
Our current approach is to test the patients on their medications and at the time of the appointment and document closely which they have taken and when. I will say that since we have adopted this policy, we have not observed any change in the number of patients presenting with bilateral caloric weaknesses or ocular motor impairments.
Academy: And I know this is highly controversial, but to me, and I mean this a little bit tongue in cheek (but not completely!)—if the vestibular and dizziness suppressants were actually working, they wouldn't be here!
McCaslin:: Of course, that's a fair point! But truly, when you tell the patient to discontinue meds, we just don't know what's going to happen, so we tell them take what your doctor has prescribed and bring a list of your medicines and we'll interpret the results accordingly. Let me also add, there's no study that I'm aware of that shows the patient cannot have caffeine on the morning of their test! Caffeine is fine and it's not likely to impact the test an hour or two later, but without caffeine, the patient may be very cranky and some may start to get a caffeine-withdrawal headache! So we absolutely let them have their coffee!
Academy: Okay, fair enough. I agree—your approach is rational and very likely causes the least confusion and allows us to verify their physiological response to the test battery with regard to their typical day-to-day (i.e., medicated) routine. Further, I've never seen a study that shows a control and an experimental group with and without their meds, in which there was a statistically significant outcome on the vestibular test battery.
My final point on this is if one were to discontinue their meds, it's hard to know how many hours or days ahead of time to do so, as the dosage and their body mass and their metabolism and resistance to the meds will all impact the meds "on board" at the time of test.
Okay then, moving on…what are your thoughts as to warm or cold (mono-thermal) screenings, as compared to bi-thermal testing?
McCaslin:: Well, I have to admit, some of us have been re-thinking this over the last few years. Here's what I think…if all other test results are normal, and specifically if there are no surprises or abnormal findings, monothermal screenings are okay. That is, you'll never get all the data from a screening that you're going to get from the entire test protocol, but in light of an otherwise normal set of earlier vestibular test results, a mono-thermal screening is likely to give you just about the same quality of information as the entire bi-thermal test battery. In fact, based on thousands of patients, previous work has shown that if the monothermal results are within 10 percent of each other, the chance of incurring a false negative test finding is 1 percent. So I'm pretty comfortable going with the screenings in the absence of other unusual or abnormal results.
Academy: Devin, it's really been a pleasure chatting with you. Thanks so much for your time and best of luck with the new book. If I were teaching a vestibular class right now, your book would be mandatory reading for the students.
McCaslin:: Thanks, Doug, I appreciate that!
Devin McCaslin, PhD, an associate professor in the Department of Hearing and Speech Sciences, Communicative Disorders, Vanderbilt Bill Wilkerson Center at Vanderbilt University.
Douglas L. Beck, AuD, Board Certified in Audiology, is the Web content editor for the American Academy of Audiology.
References and Recommended Readings
Murnane OD, Akin FW, Lynn S G, Cyr DG. (2009) Monothermal caloric screening test performance: a relative operating characteristic curve analysis. Ear and Hearing 30:313–329.
McCaslin: DL, Jacobson GP, Gruenwald JM. (2011) The predominant forms of vertigo in children and their associated findings on balance function testing. Otolaryngol Clin North Am 44(2):291-307.
McCaslin: DL, Jacobson GP, Grantham SL, Piker EG, Verghese S. (2011) The influence of unilateral saccular impairment on functional balance performance and self-report dizziness. Am Acad Audiol 22(8):542-9
McCaslin: DL (2012) Electronystagmography and Videonystagmography Core Clinical Concept Series: Plural Publishing.
McNerney K, Coad ML, Burkard R. (2012)Caffeine and Vestibular Function: Is Abstaining Really Necessary? Presented at the American Balance Society Meeting.