Douglas L. Beck, AuD, speaks with private practice co-owner and author, Bre Myers, about her new book that includes topics such as electronystagmography, videonystagmography, rotary chair testing, and more.
Academy: Hi, Bre. It’s a pleasure to meet you.
Myers: Hi, Doug. Thanks for the invitation.
Academy: Bre, to get us started, would you please give us a brief bio-sketch?
Myers: Sure. I earned my master’s from Bloomsburg University in Pennsylvania back in 2003, and then I earned my doctorate at what’s now called the George Osborne College of Audiology at Salus University. I’m in private practice with my colleague Mindy Brudereck, AuD, and we see the entire spectrum of amplification patients from pediatric to geriatric. We also offer auditory processing disorders diagnosis and treatment and, of course, vestibular diagnostics and rehabilitation.
Academy: Fantastic. And the name of your practice is?
Myers: Berks Hearing Professionals. Our Web site is http://berkshearing.com/
Academy: Excellent. Well it finally had to happen—I believe you’ve supplanted the excellent, pragmatic, and classic Stockwell-Barber Manual of Electronystagmography with an up-to-date, step-by-step vestibular manual! I think my original paperback copy is still somewhere in my office and I clearly recall yellow highlighting the most important passages, which meant the whole book was yellow-highlighted! The Stockwell-Barber Manual was so well written and so practical that it served as the primary ENG guidebook for many of us for some 30 years. Of course, so much has changed since that was written—and reading your 2011 book was interesting and actually revived my interest in vestibular issues.
Myers: Thanks, Doug. I know there are other excellent texts in vestibular science, but I wanted to create a relatively straightforward step-by-step manual. And so, Vestibular Learning Manual is kind of a “greatest hits” version of what professionals need to know and a “how-to-do-it” manual.
Academy: And I would like to mention for all the “vestibular wannabees” that the book is very brief. Some 70 pages are dedicated to basics such as; VNG, ENG, ocular-motor and gaze evaluation, positioning and positional evaluation, air and water calorics, as well as bedside and screening evaluations. And then another 60 pages are dedicated to “advanced” vestibular tests such as rotary chair, auto head rotation, CDP, dynamic visual acuity, VEMPS, and case studies. Okay, so the first thing I noticed in your book is the pipe cleaner model of the vestibular system.
Myers: Yes…well, that’s not the best illustration in the book, but it does emphasize the importance of understanding the relationship between the three pairs of semi-circular canals (SCCs) as well as their orientation, which matters a great deal for diagnostic and treatment purposes.
Academy: So I believe you’re referring to the fact that the left anterior SCC is paired with the right posterior SCC, the right anterior SCC is paired with the left posterior SCC, and the two horizontal SCCs work together as a pair?
Myers: That’s right. And as we discussed a few moments ago (off the air) the case can be made that there’s not much point to a vestibular diagnosis, unless there’s a treatment option, and again, the diagnosis and treatment options are well-founded and often based on the anatomic position of the three pairs of SCCs.
Academy: Right—and we’ll detail some vestibular rehabilitative options in the next interview this fall (2011), but for today, we’ll try to stay on the topic of diagnostics and the new book. So, Bre, what’s the difference between video-nystagmography (VNG) and electro-nystagmography (ENG)?
Myers: Well, ENG uses electrodes positioned around the eyes to measure the corneo-retinal potential (CRP), whereas VNG uses specialized video goggles (infra red or other) to measure and record the movement of the darkest part of the pupil. But the test batteries are the same, it’s just a matter of how we obtain the recording, and it can likely be assumed that the VNG offers a more accurate recording as it’s a more direct measure of nystagmus with less interference. And finally, just a quick reminder with regard to nystagmus, it’s named based on the fast phase and measured based on the slow phase!
Academy: Okay, that makes sense. And for those of us who studied this decades ago, can you please review the meaning and definitions of VOR and Ewald’s Law?
Myers: Sure. The vestibulo-ocular reflex (VOR) simply describes and refers to the reflexive relationship between the ear and the extraocular eye muscles (and consequent positioning of the eye) so as to allow us to maintain a steady gaze as we move about the world. In other words, the VOR allows us to maintain a stable visual image even though we may be walking, driving a car, riding a roller coaster or swinging on a tire-swing. With regard to Ewald’s Law, that’s the specific principle that states when your head quickly turns to the right, your eyes must rotate to the left to maintain the visual image.
Academy: Okay, that was simple! Tell me about otoconia, cupulolithiasis, and canalithiases?
Myers: Well, that becomes a lengthy discussion quickly, but benign paroxysmal positional vertigo (BPPV) is the most common diagnosis for patients with vestibular disorders. So with regard to BPPV, the reason BPPV happens is that tiny calcium-carbonate crystals (a.k.a. otoconia), which are usually lodged in the utricle become dislodged and they float around the SCCs. The displaced otoconia make the particular SCC unusually sensitive to gravitational and linear forces, thus creating the brief and intense sensation of vertigo. Finally, if the otoconia are “free-floating,” the term used to describe the situation is canalithiases, and if the otoconia are adherent to the cupula, it’s called cupulolithiasis.
Academy: And the particular SCC canal within which the otoconia winds up matters a great deal.
Myers: Absolutely. BPPV is most likely to occur in the posterior canals as they’re located inferior to (below) the utricle, but they can float into the horizontal or anterior canal.
Academy: And so when canalithiases happens in the anterior or posterior canals (i.e., the vertical canals) the patient experiences less than a minute of torsional nystagmus once the head is in the “provocative” position?
Myers: Right, and conversely, if you have cupulolithiasis in the vertical canals, the torsional nystagmus usually lasts longer than 60 seconds in response to a provocative position, such as the Dix-Hallpike maneuver.
Academy: And which ear do you recommend testing first with Dix-Hallpike?
Myers: Great question. For Dix-Hallpike, always test the suspect ear first. Of course, when you do the Dix-Hallpike, you’re stimulating both sides, but the posterior SCC is the usual suspect, and it usually responds robustly to the Dix-Hallpike and we want to make our recordings before the response fatigues…so if possible, you do want to target the “worst side” first…and as you know, Doug, often the patients will report to you which side is their bad side, so test that side first.
Academy: Good advice. And here’s a totally unrelated question from far-left field….what’s the purpose of positional evaluations?
Myers: Positional evaluations are used to identify nystagmus during specific head and body positions, which helps us know whether the nystagmus is peripheral, central, or iatrogenic. The rationale is based on the fact that peripheral and central nystagmus are often present with eyes closed, yet in general, only central nystagmus occurs with eyes open and fixed.
Academy: That makes total sense. And what can you tell me about diagnosing cervicogenic dizziness?
Myers: Well, that becomes tricky, but in general, the screening protocol for cervicogenic origin requires that the patient sits in a chair and the audiologist is seated in front of the patient and holds the patient’s head still. The patient is instructed to turn their body only (not their head) to the right and maintain that position for 30 seconds, and then the same on the left. If this movement creates symptoms or nystagmus, the patient may have cervicogenic vertigo and they probably need to be referred for cervical spinal imaging.
Academy: Bre, I know our time is running short, but I’ve got a few more questions, is that okay?
Myers: Sure. Go for it!
Academy: What about the differences in air and water calorics? I recall water irrigations are traditionally thought to give a more robust response, and I think water irrigations are more common?
Myers: Another good question. Actually, I think most bi-thermal calorics are now done with air, rather than water, because I believe most practitioners think it is easier. Although air requires less preparation and clean-up, you need to be absolutely sure you are hitting the tympanic membrane directly. Whereas with open flow water, you have a little more wiggle room. Regardless of which method you use, the most important thing to verify is that you have delivered equivalent stimuli to both ears. So long as the ear is healthy, and no perforations are present, water is still my gold standard!
Academy: And jumping around a little more…In the book, you offer a great discussion on rotational chair (RC) and the sinusoidal harmonic acceleration (SHA) and the benefits of these highly calibrated tests.
Myers: Exactly. I state in the book that SHA picks up where the caloric evaluation stops. So SHA can be measured at the frequencies that better approximate the patient’s world as they walk around. So it offers more information about their real-world invoked dizziness. And through the use of RC, we measure phase, gain, and symmetry.
Academy: And is it gain that compares the slow phase eye velocity to the chair velocity?
Myers: Yes, that’s right. As we mentioned earlier, when the head moves right, the eyes should move left, indicating the total responsiveness of the peripheral vestibular system. For example, reduced gain in the lows and normal gain in the mid-frequencies might indicate partial bilateral vestibular loss and reduced gain across all tested frequencies might indicate a complete bilateral vestibular loss. “Phase” measurements reflect the timing issues between peak eye velocity and peak chair velocity. For example, in low frequency testing (slow chair rotation), eye movement often leads chair movement, and when there are abnormally large phase leads (eye movement ahead of chair movement) this is often consistent with peripheral vestibular disorders. “Symmetry” refers to the differences between the maximal/peak right beating versus maximal/peak left beating nystagmus.
Academy: Okay, well, we’ve clearly run out of time…but I want to mention that the book also covers more sophisticated RC tests, auto-head rotation, computerized dynamic posturography, dynamic visual acuity, VEMPs, and many less sophisticated “bedside” screening tests such as Romberg/Tandem Romberg, Fukuda, Gait Assessment, and active/passive head shaking.
Myers: Yes, those are all mentioned and explained in the book.
Academy: Bre, this really has been fun. I think the Vestibular Learning Manual is excellent, efficient, simple, and comprehensive. I absolutely believe it will be a tremendous resource for anyone involved with the assessment and treatment of the dizzy patient as a practical learning manual, I give it my highest recommendation.
Myers: Thanks, Doug.
Bre Myers, AuD, is co-owner of a private practice in Birdsboro, PA. She is also the author of the Vestibular Learning Manual available at www.pluralpublishing.com.
Douglas L. Beck, AuD, Board Certified in Audiology, is the Web content editor for the American Academy of Audiology.