Muscle activity changes in spasmodic torticollis after botulinum toxin treatment

We assessed electromyographic (EMG) activity in neck muscles before and after botulinum toxin injections in 28 patients with spasmodic torticollis (ST) to investigate possible changes in muscle activation after treatment. A six-channel EMG with surface electrodes was used to record activity of sternocleiodomastoid, trapezius and splenius capitis bilaterally. Objective benefit (>25% reduction in Tsui's score) occurred in 22 patients (78%). Of the 168 muscles studied before botulinum toxin injections, 90 presented EMG activity. Sixty-eight of these muscles were injected and a decrease in EMG activity occurred in 44 (65%) of them. A decrease in EMG activity was also detected in 15 (68%) of those which were not injected. On the other hand, 70 of the 78 muscles without pre-botulinum toxin EMG activity were not injected. However, after treatment, EMG activity increased in 37 (52%) of these muscles. These changes involved 18 patients and occurred without concomitant change in the main direction of head deviation despite the improvement observed in most cases. These results suggest that in ST head turning results from an abnormal central motor program which results in non-specific neck muscle activation.