Disturbances of dynamic balance in phasic cervical dystonia

To quantitatively assess control of balance under static and dynamic conditions in patients with tonic and phasic cervical dystonia.

Ten patients with purely tonic cervical dystonia with fixed postural deviation and 20 patients with cervical dystonia with phasic head movements were investigated at least 3 months after botulinum toxin injections. Seventeen age matched volunteers served as controls. Static posturography was performed on a force platform; dynamic equilibrium was studied on a stabilometer, which requires the subject to continuously adapt upright posture to an unstable tilting surface. Measurements of maximum amplitude and linear displacement of the pivot were taken with open and closed eyes.

Sway path values in static posturography were not significantly different between patients with cervical dystonia and controls. On dynamic posturography, patients with phasic cervical dystonia showed significantly higher platform measures (maximum amplitude and linear displacement of the pivot) with eyes open and closed By contrast, none of the dynamic platform measures differed significantly between patients with tonic cervical dystonia and controls.

Normal measures of dynamic equilibrium in tonic cervical dystonia argue against a primary abnormality of balance control in cervical dystonia. Impaired dynamic equilibrium in phasic cervical dystonia is likely to reflect a disruption of vestibular input due to repetitive, involuntary head oscillations.