Explore this issue:January 2015
Assessing dizziness is a diagnostic challenge. There are multiple possible etiologies for dizziness—some rooted in the anatomy and physiology of the inner ear, some not—and until recently, clinician assessment of dizziness and the vestibular system was limited by a lack of diagnostic tools.
For nearly a century, the assessment of the vestibular system was been restricted to assessment of the semicircular canals. The caloric test assesses lateral semicircular canal function. Bedside head impulse testing (HIT) can assess the function of the vertical semicircular canals, but the test is not always easy to perform or interpret; bedside HIT relies on clinicians’ subjective evaluation of saccade. The otolith organs have largely been ignored because there was no way to assess them.
“We’ve been limited up until now because we’ve only been able to see a small fraction of the picture of what’s happening,” said Kristen Janky, AuD, PhD, director of the Clinical Vestibular Lab and coordinator of vestibular services at Boys Town National Research Hospital in Omaha, Neb. “We weren’t able to get a big picture of what’s going on in the balance center.”
The advent of video head impulse testing (vHIT) and vestibular evoked myogenic potential (VEMP) testing now allows researchers and clinicians to probe the function of all ten end organs, including the three semicircular canals and two otoliths on each side.
These tests open new possibilities to researchers, clinicians, and patients. They also invite debate and confusion as clinicians figure out how best to utilize these tools for the benefit of patients.
Begin with the Basics
A thorough history and physical is still the best way to begin assessing a patient’s dizziness. In fact, a thorough history is “the most crucial part in figuring out what might be causing someone’s dizziness,” said Meredith E. Adams, MD, assistant professor of otolaryngology at the University of Minnesota in Minneapolis. So take your time and ask patients specific questions to elicit details about their dizziness. Many patients are eager to discuss their current symptoms, but also ask them when, where, and how the dizziness first began.
The information you receive will help you determine what tests to order. Many patients will still require an audiogram and/or imaging study. And, despite the availability of newer tests, electronystamography (ENG) or videonystagmography (VNG) remain mainstays of vestibular assessment.
“Videonystagmography gives you ear-specific information,” Dr. Adams said. “We also have a lot of data on it in different clinical disease states, so we know the most about its results in different diseases.”