Postural Responses to Continuous Unilateral Neck Muscle Vibration in Standing Patients with Cervical Dystonia Marco Bove, MD, 1 * Giampaolo Brichetto, MD, 2 Giovanni Abbruzzese, MD, 2 Roberta Marchese, MD, 2 and Marco Schieppati, MD 3,4 1 Department of Experimental Medicine, Section of Human Physiology, University of Genoa, Genoa, Italy 2 Department of Neurological Sciences, Movement Disorder Unit, University of Genoa, Genoa, Italy 3 Department of Experimental Medicine, Section of Human Physiology, University of Pavia, Pavia, Italy 4 Human Movement Laboratory (CSAM), Fondazione Salvatore Maugeri (IRCCS), Scientific Institute of Pavia, Pavia, Italy Abstract: Several observations support the notion that integra- tion of neck proprioceptive input is impaired in cervical dys- tonia (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 re- corded 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-in- duced 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. © 2007 Movement Disorder Society Key words: cervical dystonia; neck proprioception; vibra- tion; spatial orientation; static and dynamic posture. Idiopathic cervical dystonia (CD) is the most common adult-onset focal dystonia and is characterized by abnor- mal head posture associated to involuntary neck muscle contraction. The existence of a pathogenetic role of sen- sory feedback processing in dystonia has been dis- cussed. 1–3 Impaired processing of neck proprioceptive input could lead to abnormal head posture, either directly or through distortion of spatial orientation. 4,5 Muscle vibration is an adequate stimulus for eliciting la spindle firing 6 and has been extensively used for evaluating sensori-motor integration. 7 In healthy sub- jects, vibration of the lateral aspect of the neck induces body tilt during quiet stance and body rotation during stepping-in-place toward the side opposite to the vibrated muscle. 8,9 In patients with CD, the effects of lateral neck muscle vibration on spatial orientation during stepping- in-place are different. 10 Depending on the patient, when vibration is applied to lateral neck (sternocleidomastoid muscle, SCM) the induced body rotation is inconsistent: it can be normal (but never so from both sides), or absent or opposite to normal. Does lateral vibration produce abnormal postural re- sponses during quiet stance, a task in which control of dynamic equilibrium is not required? Is there any rela- tionship in these patients between the effects of lateral vibration on stepping-in-place and on stance? Answer to these questions would help understanding whether the motor task type is responsible for abnormal integration of proprioceptive neck input in patients with CD. SUBJECTS AND METHODS Subjects Sixteen patients with CD (4 males and 12 females, age range 33– 82, mean 60.2  14 SD), with disease duration 8.8 years (range: 2–21 years) and 12 normal subjects (7 *Correspondence to: Marco Bove, Department of Experimental Medicine, Section of Human Physiology, University of Genoa, Viale Benedetto XV, 3, Genoa I-16132, Italy. E-mail: bove@dibe.unige.it Received 9 September 2006; Accepted 10 September 2006 Published online 16 January 2007 in Wiley InterScience (www. interscience.wiley.com). DOI: 10.1002/mds.21357 Movement Disorders Vol. 22, No. 4, 2007, pp. 498 –503 © 2007 Movement Disorder Society 498