Differential diagnosis of proprioceptive and vestibular deficits using dynamic support-surface posturography

The objective of this study was to evaluate how effective dynamic support-surface posturography could be as a diagnostic tool in patients with balance disorders (proprioceptive or vestibular deficits). Specifically, we studied whether measures of trunk control and simple toe-up rotational perturbations, selected using statistical techniques, could provide a better diagnostic yield than either the analysis of lower-body movements or use of a "nulled" ankle input paradigm. The test subjects were 15 control subjects, five patients with bilateral peripheral vestibular loss (VL) and five patients with selective bilateral, lower-leg proprioceptive loss (PL). Amplitudes and onset latencies of bursts of EMG activity in upper and lower-leg muscles, paraspinals and trapezius muscles, concurrent changes in ankle torque, and peak amplitudes of upper-leg, lower-leg, and trunk angular-velocities were measured. Stimuli included three different types of sudden movements of the support surface, a "nulled" ankle input paradigm, a simple toe-up rotation paradigm, and a combined toe-up rotation and backwards translation of the support surface. All stimuli were tested under eyes-open and eyes-closed conditions. For each type of movement and condition the diagnostic classification accuracy (i.e. the overall sensitivity and specificity) was calculated based on those posturography measures providing the highest diagnostic separation between the three populations. Both patient groups showed increased trunk sway, changed support-surface reaction forces and muscle amplitudes compared with controls for toe-up and "nulled" test conditions. Measures providing the greatest diagnostic utility were the amplitude of trunk-angular velocity (increased in VL subjects, less so in PL), the amplitude of balance-correcting paraspinal responses (increased in VL subjects, decreased in PL subjects), the amplitude of trapezius stabilising responses (increased in both patient groups) for simple toe-up rotations under eyes-closed conditions. We conclude, that diagnosis of balance disorders using dynamic posturography is best achieved using measures of trunk control following pure toe-up rotational perturbations tested under eyes-closed conditions.