Objective: To assess brain activation during simple movements of the right hand in patients with cervical dystonia (CD) by means of fMRI. To test the impact of bilateral cerebellar interference by transcranial magnetic stimulation (TMS) on cerebral activation and on clinical measures of CD.

Background: CD is a movement disorder leading to involuntary neck muscle contractions. While there is growing evidence indicating an involvement of the cerebellum (CRB) and cerebello-thalamocortical circuits in the pathophysiology of CD, the exact nature of this involvement remains unclear.

Methods: An inhibitory TMS protocol (continuous thetaburst-stimulation, cTBS) was used to induce bilateral transient virtual lesions at CRB in 8 right-handed CD patients and controls. cTBS at the left dorsal premotor cortex (PMd) was used as control condition. fMRI data were acquired during a simple tapping task of the right index finger and thumb before and after cTBS, analysis was carried out with the FMRIB Software Library. Clinical assessment comprised the CGI as judged by the patient as well as the motor subscale of the Tsui score and the TWSTRS-M as rated by a blinded investigator based on video sequences.

Results: At baseline, finger tapping was associated with increased activation in the right CRB in CD patients as compared to healthy controls. Following bilateral cerebellar cTBS, this increased activation was even more pronounced, along with an additional movement-related activation in the left primary motor region. PMd stimulation had no effect on fMRI patterns. Subjective symptom perception improved slightly following cTBS at bilateral CRB (CGI efficacy index 9.7±3.3) but not at PMd (11.7±2.6), while TWSTRS-M and Tsui scores remained stable.

Conclusions: In CD patients, hand movements – though clinically non-dystonic – are associated with increased cerebellar activation. This concurs with previous animal studies indicating increase (or distortion) rather than loss of cerebellar activity to underly dystonia, and may point to general motor disorganization in focal dystonia which remains subclinical in most body regions. The changes of tapping-related fMRI pattern in CD patients after cerebellar cTBS may indicate predominant disinhibitory effects of cTBS on cerebello-thalamocortical circuits – a notion which might explain the slight and solely subjective clinical improvement achieved by this intervention.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/finger-tapping-related-brain-activation-and-impact-of-cerebellar-theta-burst-stimulation-in-cervical-dystonia-patients/