Postural responses to continuous unilateral neck muscle vibration in standing patients with cervical dystonia.

Several observations support the notion that integration
of neck proprioceptive input is impaired in cervical dystonia
(CD). An example is the inconsistent or opposite to
normal effect of lateral neck muscle vibration on body rotation
during stepping. We hypothesized that lateral neck vibration
produces abnormal responses also in a static task. Normal
subjects and patients with CD stood quietly with eyes closed,
without or with vibration applied to the sternocleidomastoid
muscle, and center of foot pressure and body sway were recorded
by a dynamometric platform. Patients had a larger than
normal sway under control condition. They showed little or no
postural responses to vibration. When body tilt occurred, it was
rarely in the frontal plane as in normal subjects, but in the
sagittal plane. No relationship existed between vibration-induced
tilt during stance and body rotation during stepping.
Therefore, in CD, proprioceptive neck input is less used for the
construction of the postural vertical during quiet stance than it
is used for the definition of the subjective straight ahead during
a dynamic task.