A Simple Specific Functional Test for SCD: VEMPs to High Frequency (4,000Hz) Stimuli—Their Origin and Explanation
Ian S. Curthoys, Leonardo Manzari
Abstract
We fully agree with the statement by Noij et al. ( It is highly specific for the detection of SCD and may be used to guide decision-making regarding the need for subsequent CT imaging" (1). The ideal is a very fast, innocuous test rather than extended and uncomfortable tests such as determining the threshold for VEMPs. Patients with a dehiscence show larger VEMPs and lower VEMP thresholds to air conducted sound (ACS) and bone conducted vibration (BCV). Standard VEMP stimuli (e.g., 500 Hz short tone bursts) are not optimal for such testing as Noij and Rauch reported. However, we wish to make clear that Manzari et al. (2) were the first to show that for clinical diagnosis of SCD a stimulus of 4,000 Hz is such a very simple very fast test with excellent specificity. We reported a (very short) Brief Communication in Otolaryngology and Head Neck Surgery showing the ocular VEMP to high frequency tone burst stimuli (either ACS or BCV) (2) to 4,000 Hz stimuli constituted a fast, simple innocuous functional test with a 100% success in showing SCD in 22 patients with CT verified SCD and the absence of VEMPs in 22 healthy control subjects. The test consisted of 50 presentations of brief (7 ms) tone bursts of high frequency (4,000 Hz) stimuli at a rate of 4/s instead of the standard VEMP test frequency of 500 Hz. Thus, the 4,000 Hz test is very short-a total of only 50 stimulus presentations were given at 4/s so the whole test is complete in 13 s. The sensitivity and specificity of the test was 1.0 and thus, diagnostic accuracy of 100%. In other words, if a patient had an oVEMP response to 4,000 Hz then they had a CT verified SCD. In that group of 22 healthy subjects, none had an oVEMP to 4,000 Hz stimulation. Leonardo Manzari discovered this very simple test at his clinic in Cassino, Italy and validated it on his patients with CT verified SCD and healthy controls. Others have followed his example with minor changes.