vHIT for Vertigo

Good, But Not Sliced Bread Yet

This week’s post would fall under the heading of “unsolicited opinion.” I received my copy of the March/April edition of AudiologyToday, which is produced by the American Academy of Audiology.  I spotted a Letter to the Editor by Gary Jacobson and Devin McCaslin, both on the faculty at Vanderbilt University. Jacobson and McCaslin are well known as innovators, clinicians, teachers, and have the well deserved reputations of being amongst the best in our profession. Like the old E.F. Hutton commercial, when Jacobson and McCaslin speak, I listen.

The letter they submitted was in response to an article titled “A Streamlined Approach to Assessing Patients with Peripheral Vestibular Disorders”, that appeared in the Sep/Oct 2015 issue of the same periodical. Jacobson and McCaslin expressed concern that the article may have implied that the combination of VEMP and vHIT testing is a substitute for more traditional VNG testing, including caloric testing. I went back and read the article and came away with some of the same concerns.

One of the article’s co-authors, Wendy Crumley Welsh, followed up with a clarification better outlining the role of VEMP and vHIT. This was a great exchange between some very knowledgeable people, and a good example of the checks and balances that should exist between industry and the clinical/academic world, and a good example of how we advance as a profession. In that spirit, I will offer a couple of thoughts.

First, I think it is important to acknowledge that vHIT testing is not a replacement for existing vestibular testing such as caloric irrigation (CI) and rotational chair (RC). The Vestibular Ocular Reflex (VOR) functions across a wide range of head speeds in multiple planes. While it is true that CI and RC evaluate the horizontal canal only, they provide a lot of very sensitive information across much of that range. It is an important point that Jacobson and McCaslin make regarding the fact that many patients that have a low frequency VOR deficit will have normal high frequency function (such as that tested with vHIT). Unless you are in a clinical setting that performs CI, RC, and vHIT routinely, this fact may not be apparent. Making a judgment about the health or efficiency of the VOR based on the response to rapid impulsive head movements is risky. I think Ms. Crumley Welsh clarifies that point well in her follow up.

Second, there are a couple of clear factual errors in the article. While I agree that vHIT tests the VOR at head speeds “comparable to looking both ways before crossing the street”, those speeds are actually 4 to 5 HZ (not 4000 to 5000 HZ as stated in the article). Also, caloric testing is generally considered to stimulate the VOR analogous to a head movement around .003HZ (not .025HZ, which is about ten times faster).

So….this is an esoteric discussion that is mindnumbingly boring to most readers, but it is one that needs to happen. We need companies like GN Otometrics to bring new products forward and educate clinicians regarding their potential benefits, and we need people like Drs. Jacobson and McCaslin to step in and say “Hey! Wait a minute.”  And it was all done with mutual respect and a common goal of better patient care.  Our politicians could learn a thing or two from these folks.

 

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About Alan Desmond

Dr. Alan Desmond is the director of the Balance Disorders Program at Wake Forest Baptist Health Center, and holds an adjunct assistant professor faculty position at the Wake Forest School of Medicine. In 2015, he received the Presidents Award from the American Academy of Audiology.