Use of surface electromyography to assess and select patients with idiopathic dystonia for bilateral pallidal stimulation

Object. The object of this study was to identify a preoperative physiological index by using surface electromyography (EMG) signals that would correlate with clinical outcome in dystonic patients following bilateral pallidal stimulation. Methods. In 14 patients with spasmodic torticollis, generalized dystonia, and myoclonic dystonia, surface EMG signals were recorded from the most affected muscle groups. Although the dystonia affected different body segments, the EMG signals in all patients could be decomposed into bursting and sustained components. Subsequently, a ratio of the EMG amplitude was calculated between the two components and then correlated with clinical outcome. Patients who experienced rapid improvement following bilateral pallidal stimulation had a significantly higher EMG ratio compared with those who did not. Furthermore, a significant correlation was found between the EMG ratio and clinical improvement during the 12-month period following pallidal stimulation. Conclusions. The authors concluded that surface EMG studies could be used to predict the clinical outcome of and to select patients for pallidal stimulation for dystonia.