Fast voluntary neck movements in patients with cervical dystonia: a kinematic study before and after therapy with botulinum toxin type A.

OBJECTIVE To study fast voluntary neck movements in patients with cervical dystonia (CD) before and after therapy with botulinum toxin type-A (BTX-A). METHODS A selected sample of 15 patients with CD (with prevalent torticollis) and 13 age-matched control subjects performed both right and left rotational, and flexion and extension neck movements as fast as possible. Movements were recorded with a motion analysis system (SMART, BTS). Movement time, angular amplitude, and peak angular velocity were analyzed. In patients, rotational neck movements were pooled as "pro-dystonic" (toward the dystonic side) and "anti-dystonic" (toward the non-dystonic side). Results obtained in patients before BTX-A treatment were compared with those of control subjects. The effect of BTX-A treatment was evaluated by comparing movement performance before and after treatment. RESULTS Before receiving BTX-A, patients performed pro- and anti-dystonic movements with lower peak angular velocity than control subjects. Pro-dystonic movements had a reduced angular amplitude. Anti-dystonic movements showed an abnormally long movement time. Flexion and extension movements required longer movement times, but the other kinematic variables were normal. After BTX-A injections, pro-dystonic movement amplitude and anti-dystonic movement peak angular velocity increased, whereas flexion and extension movements remained unchanged. CONCLUSIONS Before BTX-A injection patients with CD perform fast voluntary neck movements abnormally and BTX-A injections improved their peak velocity and amplitude. SIGNIFICANCE Kinematic studies can detect specific neck movement disturbance in patients with CD, and can quantify both the severity of clinical picture and the effect of BTX-A injections in these patients.