Computerized Dynamic Posturography (CDP) Sensory Analysis

Timothy C. Hain, MD • Page last modified: February 19, 2022Return to testing index •CompositeVISSOM, •VESTPREF

From the work of Sailing et al, 1991, one might expect a differential effect of sensory conditions according to the cause of imbalance. These authors stated "In patients with a vestibular lesion the authors observed more frequent elevated values in a lateral direction, a marked destabilization of the posture on the foam rubber and effective use of the added visual feedback. Cerebellar patients were unable to use effectively the visual biofeedback for stabilization of posture. They were characterized by an obvious increase of stabilometric parameters in both directions and under all circumstances. So in other words, there should be a strong sensitivity to vision in vestibular patients (a visual dependence), and no impact of vision (bad with or without eyes open), in cerebellar patients. This makes sense given that one might substitute another sense for a sensory disorder like vestibular loss, but for a central balance disturbance (cerebellar), sensory input might not be very effective.

An attempt to tease out the contributions of vision, somatosensation, and vestibular sensory input is reflected in the "sensory analysis" section of the report. This involves dividing one linear combination of scores by another, and then replotting them as shown above. There are four sensory analysis scores (as shown above), which are considered one by one in subpages indexed below. . These 6 sensory scores are processed in an attempt to provide something clinically useful. The following table provides the formulae, and the intended purpose of the scores. We examine how well these formulae work for clinical situations in the links.

Typical Sensory Analysis

This is an example CDP sensory analysis, of an older unsteady person. The red bars are below norms from manufacturor data. The green bars are above the norms.

Processed CDP scores (sensory analysis)
Score Formula Compared Apparent Intent
Composite 1+2+3*(3+4+5+6)/3 weighted sum Weighted average Average
Vis 4/1 (V+E-F)/(V+E+F) Take out feet Vision
Vest 5/1 (V-F)/(V+E+F) Take out eyes and feet Vest
Som 2/1 (V+F)/(V+E+F) Take out eyes Feet
Pref (3+6)/(2+5) (SR-Vis)/(Stable-Vis) Distort Vision Distortion

 

Discussion and overview:

Aside from the Composite, The sensory analysis scores (VIS, SOM, VEST, PREF) are generally not helpful for diagnosis. This is probably a reflection of the "GIGO" principle -- garbage in garbage out. The equilibrium scores are noisy things with noisy inputs and noisy outputs, and when you divide noisy things by each other, you end up with even more noise. The "Cevette" scoring system, sometimes used to detect malingering, is more generally useful. One would expect that other processed scoring systems might also add utility.

To look more closely at the strategy scores, click on the links above with the table.

References: