Spasticity and dystonia differentiated via the equilibrium point hypothesis

Is the Equilibrium Point Hypothesis (EPH) able to explain the different motor behavior in subjects with Cerebral Palsy (CP) experiencing spasticity and/or dystonia? Can the Virtual trajectory of the EPH provide a plausible distinction between the two different neurological disorder characteristics? These questions and others will be discussed in this paper. Stimulation of the otolith organ is provided in this study as explained in previous work [8_New]. The data presented in this study belong to six children with CP (4 females and 2 males) and the pendulum knee drop (PKD) test was administered to evaluate their disorder. We anticipated improvement in spasticity due to the vestibular stimulation among all subjects with changes in the three optimized parameters that indicate a reduction of muscle tone. Contrary to expectations, the vestibular stimulation was very effective in some subjects and nearly completely ineffective in others. Further analysis showed that those subjects for whom the intervention was successful had a very different appearance in their pendulum knee trajectory that the subjects who did not respond. Un-blinding of the clinical diagnoses confirmed that the stimulation benefitted those diagnosed with spasticity only, while the stimulation had little to no effect on subjects diagnosed with dystonia or a combination of dystonia and spasticity. These preliminary findings suggest an objective differentiation between spasticity and dystonia may, for the first time be possible.