SHORT REPORT Disturbances of dynamic balance in phasic cervical dystonia

Objective—To quantitatively assess con-trol of balance under static and dynamic conditions in patients with tonic and pha-sic cervical dystonia. Methods—Ten patients with purely tonic cervical dystonia with fixed postural de-viation 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. Results—Sway path values in static pos-turography were not significantly diVer-ent between patients with cervical dystonia and controls. On dynamic pos-turography, patients with phasic cervical dystonia showed significantly higher plat-form measures (maximum amplitude and linear displacement of the pivot) with eyes open and closed By contrast, none of the dynamic platform measures diVered sig-nificantly between patients with tonic cer-vical dystonia and controls. Conclusions—Normal measures of dy-namic equilibrium in tonic cervical dysto-nia 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