„Silent event-related“ fMRI reveals sensorimotor dysfunction in laryngeal dystonia

Background: Laryngeal dystonia (LD) represents a focal dystonia localized in the larynx. Previous functional imaging work showed a dysorganization of sensorimotor cortices in other focal dystonias, idiopathic torsion dystonia and acquired dystonia. Using functional magnetic resonance imaging (fMRI) we aimed at studying the pattern of sensorimotor activation in patients with LD and its modulation by local treatment with botulinum toxin (BTX).

Methods: We included 12 patients with adductor LD and 12 healthy volunteers. Patients were scanned before (pre) and after (post) treatment with local injections of BTX. We studied sensorimotor activation during simple vocalization inducing dystonia in LD patients and during a whispering task where patients were clinically asymptomatic. To avoid movement artefacts when examining an oral motor-tasks we used a 'silent event-related' fMRI technique involving non-continuous MR sampling with no data acquisition during task performance. Online voice-recordings served for further detailed analysis of task performance and for quantitative voice analysis.

Results: Our results show reduced activation of primary sensorimotor as well as of premotor and sensory association cortices during vocalization in LD patients preBTX compared to controls. This was partly demonstrated also during the whispering task where patients were clinically asymptomatic. BTX treatment did not reverse reduced cortical activation in patients with LD. Quantitative analysis of the voice recordings showed no significant differences concerning performance parameters as well as fundamental voice frequencies and amplitudes in controls and patients pre and postBTX reflecting balanced voice/motor output during vocalization and thus assuring comparability of the imaging data. A significantly higher frequency variability in patients pre and postBTX compared to controls reflects hoarseness of voice in LD.

Conclusions: For the first time we report reduced signal in sensorimotor cortices associated with movement of the affected body part in LD. This extends previous functional imaging findings in other forms of dystonia and corroborates the dystonic basis of this voice disorder.