Sensorimotor overactivity as a pathophysiologic trait of embouchure dystonia.

BACKGROUND: Embouchure dystonia is a focal task-specific dystonia affecting the complex interplay of lower facial, jaw, and tongue muscles in musicians playing brass or woodwind instruments. Although it is highly disabling for affected patients, little is known about the pathophysiologic basis of this rare movement disorder. METHODS: We therefore studied sensorimotor activation patterns during 2 orofacial motor tasks in brass players with embouchure dystonia by using fMRI. A "dystonia-specific" task involved buzzing at an instrument-specific, fully functional mouthpiece. A "neutral" task involved simply blowing into a tube. RESULTS: Compared with healthy brass players, patients with embouchure dystonia showed significantly increased activation of somatotopic face representations within the bilateral primary sensorimotor cortex and of the bilateral premotor cortex during buzzing at the mouthpiece. Interestingly, a similar activation pattern was present during the neutral task when patients were clinically asymptomatic. CONCLUSION: Sensorimotor overactivity could reflect deficient subcortical and intracortical inhibition as well as abnormal sensorimotor integration and reorganization in musicians with embouchure dystonia. Because this overactivity was also found during the neutral task, it could be a crucial pathophysiologic factor predisposing for the development of orofacial dystonia rather than a mere correlate of dystonic motor output.

"Silent event-related" fMRI reveals reduced sensorimotor activation in laryngeal dystonia.

OBJECTIVE: To study with fMRI the pattern of sensorimotor activation in patients with spasmodic dysphonia (laryngeal dystonia) compared to healthy controls. METHODS: The authors performed fMRI measurements during vocal motor tasks in 12 patients with laryngeal dystonia and compared them with those of 12 healthy volunteers. Patients were scanned before (pre) and after (post) treatment with local injections of botulinum toxin (BTX). They examined two different motor tasks: simple vocalization inducing dystonia and whispering without appearance of dystonic symptoms. To avoid movement artifacts with oral motor tasks, the authors used a silent event-related fMRI approach involving noncontinuous sampling with no data acquisition during task performance. RESULTS: They found reduced activation of primary sensorimotor as well as of premotor and sensory association cortices during vocalization in patients with laryngeal dystonia pre-BTX. This was partly observed also during the asymptomatic whispering task. BTX treatment did not result in reversal of reduced cortical activation. CONCLUSION: fMRI signal is reduced in sensorimotor cortices associated with movement of the affected body part in laryngeal dystonia, supporting a dystonic basis for this voice disorder.