Transcranial magnetic stimulation and silent period in spasmodic torticollis

Objective: Our objective was to st to neck muscles in cervical dystonia. Ou r objective was to study the corticobulbar projections Design: We compared both the motor evoked potentials and the electromyograp hic silent period after transcranial magnetic stimulation from sternocleido mastoid and trapezius muscles in a group of 13 patients with spasmodic tort icollis with those of 20 healthy volunteers. Results: With the target muscle at rest, no changes of motor threshold, mot or evoked potentials latency, and amplitude were observed in dystonic patie nts. With facilitation, the mean amplitude of the motor evoked potentials w as increased in patients compared with controls, the significant difference being for the trapezius muscle, whereas the latency did not differ between groups. The cortical silent period was significantly shorter in dystonic p atients than in healthy subjects in both muscles. The duration of the corti cal silent period recorded from the sternocleidomastoid muscle showed a pos itive correlation with the degree of neurologic disability assessed by Tsui 's scale. No abnormalities of both nerve conduction velocity and peripheral silent period by stimulation of accessory nerve were found. Conclusions: These results indicate an impairment of the mechanisms of inhi bitory motor control in patients with spasmodic torticollis, which could be the result of a decrease of the basal ganglia inhibitory output over the m otor cortex.