STERNOCLEIDOMASTOID MUSCLE RESPONSES TO TRANSCRANIAL MAGNETIC STIMULATION IN PATIENTS WITH CERVICAL DYSTONIA

Ten cervical dystonia (CD) patients, with involuntary head rotation to one side and contralateral sternocleidomastoid muscle (SCM) hypertrop hy, were investigated with transcranial magnetic stimulation, and the results were compared to those of 10 healthy subjects. Monopolar needl e electrodes with isolated shafts were used for bilateral electromyogr aphic recordings in the SCMs of the motor evoked potentials (MEPs) eli cited by the magnetic stimulator. The latencies of ipsilateral SCM MEP s were shorter in the CD patients than in the control subjects (P < 0. 001). The latencies of SCM activity suppression by TMS were longer in the CD patients than in the control group when stimuli were given on t he contralateral side (P < 0.05). Both the clinically dystonic and the contralateral SCM of the CD patients exhibited significantly abnormal latencies of the ipsilateral SCM MEPs (P < 0.01) and of the SCM suppr ession (P < 0.05). Three CD patients also had consistent activity in t he SCM counteracting the direction of head rotation during the suppres sion experiments. The latencies of the suppression of this abnormal ac tivation were shorter (P < 0.05), than the latencies of the suppressio n in the SCM during normal voluntary activation by these CD patients ( i.e. rotation of the head in the contrary direction). The results sugg est bilaterally enhanced motoneuronal excitability and disturbed inhib itory regulation in patients with CD. (C) 1997 Elsevier Science Irelan d Ltd.