Computerized Dynamic Posturography (CDP) Sensory Test Scoring: VEST sensory analysis

Timothy C. Hain, MD • Page last modified: March 4, 2021Return to testing indexReturn to Sensory analysis page

In this page we are taking a deep dive into the method of scoring the Neurocom CDP sensory tests.

Typical Sensory Analysis

This is an example CDP sensory analysis, of an older unsteady person. This shows a large reduction of the "VEST" score, 3rd from the left.

Processed CDP scores
Score Formula Compared Apparent Intent
Vest 5/1 (V-F)/(V+E+F) Close eyes and distort feet Vestibular input

The "Vest" score divides a number derived from inverse sway elicited by having the individual balance themselves with eyes closed on a "teeter-totter" type support surface, by inverse sway on a stable platform with eyes open. The idea is to "take out" proprioception with the teeter-totter, and take out vision by closing the eyes, leaving them entirely dependent on their vestibular system. With this challenging arrangement where two senses of the usual 3 are gone, one would then expect the equilibrium score in practically anyone would be less than situations where just one sense is subtracted (i.e. VIS or SOM). This is the reason that the gray bar to identify the lower limit of normal above is lower for this sensory analysis than for SOM and VIS.

VEST scores with respect to age in a broad group of dizzy patients.

CDP Vest scores in dizzy patients
Vest scores r.e. age
The graph above shows mean Vest scores as a boxplot from almost 2000 dizzy patients tested at Chicago Dizziness and Hearing. Age is associated with a huge reduction in Vest scores. Graph made with "R". The large error bars show that Vest score is also very variable in a "Dizzy" population. Of course, these measurements are not from "normal" subjects, but rather a mixture of many subjects with individual conditions. So some of the variability is likely due to subject composition.

 

Discussion:

Posturography is insensitive to vestibular disorders in general , and normal posturography should not be considered indicative of normal vestibular function (Di Fabio, 1995). However, the implied question is poorly formed. The vestibular system is composed of 3 angular rotation sensors (the canals), and 2 linear acceleration sensors (the otoliths). It is irrational to think that posturography should be sensitive to, for example, lateral canal disease, as with the head upright the lateral canals have little to contribute to balance. The otoliths on the other hand would likely be more salient to posture. Thus criticizing posturography because it does not detect partial damage to the vestibular system may be a "straw man" question -- of course not.

Examples showing the CDP test is not a "complete" test: The author has had instances in which there is a severe disturbance of caloric testing and rotatory chair testing, accompanied by a normal CDP. CDP is therefore not an adequate test for vestibular disturbance of the canals , by itself. In addition to the false negative problem (lack of sensitivity), CDP also has false positives - -it suggests that there is a vestibular problem when none exists. The "vestibular" pattern on CDP is actually not specific for vestibular disorders -- it is positive in (for example) cerebellar disorders as well.

Liu et al (2017) studied the VEST score in particular. They found that "Regression model indicated that oVEMP, as an independent variable, exerted the greatest influence on VEST ratio, followed by age and cVEMP. "

The lack of general utility for the VEST indicator of vestibular dysfunction is shown by newer tests for vestibular (such as VHIT), that can be perfect even when the CDP is "vestibular". Some examples of false positives and negatives are shown here.

References (for all posturography pages)