Disturbances of dynamic balance in phasic cervical dystonia

Objective-To quantitatively assess control of balance under static and dyna mic conditions in patients with tonic and phasic cervical dystonia. Methods-Ten patients with purely tonic cervical dystonia with fixed postura l deviation and 20 patients with cervical dystonia with phasic head movemen ts were investigated at least 3 months after botulinum toxin injections. Se venteen age matched volunteers served as controls. Static posturography was performed on a force platform; dynamic equilibrium was studied on a stabil ometer, 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. Results-Sway path values in static posturography were not significantly dif ferent between patients with cervical dystonia and controls. On dynamic pos turography, patients with phasic cervical dystonia showed significantly hig her platform measures (maximum amplitude and Linear displacement of the piv ot) with eyes open and closed By contrast, none of the dynamic platform mea sures differed significantly between patients with tonic cervical dystonia and controls. Conclusions-Normal measures of dynamic equilibrium in tonic cervical dyston ia argue against a primary abnormality of balance control in cervical dysto nia. Impaired dynamic equilibrium in phasic cervical dystonia is Likely to reflect a disruption of vestibular input due to repetitive, involuntary hea d oscillations.