Muscle control in chronic tic disorders.
EMG was recorded in nine subjects suffering from chronic tic disorder. Six subjects suffered asymmetrical tics and three had symmetrical tics. EMG in tic-affected and contralateral nonaffected sites was recorded at rest, during a baseline period, and at postbiofeedback training. All subjects received 2-4 biofeedback training sessions aimed at enhancing their ability to control levels of muscle contraction in both affected and nonaffected sites. All nine subjects met the criterion of discriminating unaided between levels of 0, 25%, 50%, and 75% of their fullest contraction. Five of the six people with asymmetrical tics showed lower resting EMG on the affected side at baseline, but EMG significantly increased in tic-affected but not nonaffected muscles after exercises aimed at enhancing muscle control. Six subjects reported a clinically significant > or = 40% decrease in tic frequency. The reflexlike quality of tic muscles can modified by biofeedback training and this constitutes a useful and relatively quickly acquired aid to tic management.