Hain (2011) reports that approximately 15 percent of the U.S. population experiences significant dizziness every year and most causes of dizziness are indeed, non-vestibular. Hain notes that there are five dizziness sensors in each ear: the three semicircular canals—(1 )anterior, (2) posterior, and (3) horizontal—and two otolithic organs, (1) saccule and (2) utricle. Of note, although current (typical) test protocols can test the horizontal canal (ENG/VNG), the horizontal canal and the saccule (rotary chair tests) and the saccule (vestibular-evoked myogenic potential, VEMP), at present there are no (typical) utricular tests, and no specific test for the anterior and posterior semi circular canals. Therefore, he cautions, current (typical) vestibular test protocols cannot absolutely exclude vestibular damage. That is “normal” results do not necessarily mandate or fully describe a normal inner ear.
Hain reports that VEMPS are easy and quick to evaluate. The primary parameters evaluated are the size and symmetry of the response. VEMPS tend to decline with age and are rarely present in individuals over 70 years of age. Superior canal dehiscence is often correlated with larger VEMPs. If the VEMP responses are large from both ears and if there is substantial asymmetry, Hain says the possibility of superior canal dehiscence should be noted.
Hain reports videonystagmography (VNG) is superior to electronystagmography (ENG) due to higher resolution, better stability and increased ability to observe/capture/record torsion. ENG and VNG address two categories of tests: (1) vestibular function (spontaneous nystagmus, positional nystagmus, and calorics tests) and (2) oculomotor function (calibration, pursuit, and optokinetics). Oculomotor tests are almost always normal, and abnormalities found are generally due to “overly enthusiastic attribution” of test results to central nervous system disorders.
For More Information, References, and Recommendations
Hain T. (2011) Vestibular Function—Making the Right Interpretation with the Right Test. Hearing Journal 64(12):26-30.