Objective: To investigate the influence of the cerebellum on the motor cortex in primary focal dystonia using cerebellar continuous theta-burst stimulation (cTBS) and to evaluate any relationship with movement abnormalities.

Background: The pathophysiology of focal dystonia is still not completely understood. Although dystonia has been historically considered a disorder of the basal ganglia, recent experimental evidence suggests that the cerebellum may be involved in this condition (Sadnika et al., 2012; Prudente et al., 2014).

Methods: Thirteen patients with focal hand dystonia, 13 patients with cervical dystonia and 13 healthy subjects underwent two experimental sessions: (i) cTBS over the cerebellar hemisphere (real cerebellar cTBS) and (ii) cTBS over the neck muscles (sham cerebellar cTBS). The two sessions were performed at least one week apart. The effects of real and sham cerebellar cTBS were quantified as excitability changes in the contralateral primary motor cortex, as well as possible changes in arm and neck movements in patients. Primary motor cortex excitability was assessed by recording the input/output curve of the motor-evoked potentials from the first dorsal interosseous muscle. Arm and neck movement analysis was performed using kinematic techniques.

Results: Real cerebellar cTBS reduced excitability in the contralateral primary motor cortex in healthy subjects and in patients with cervical dystonia, though not in patients with focal hand dystonia. There was no correlation between individual changes in M1 excitability and arm and neck movement kinematics in patients. Additionally, there were no significant changes in clinical scores or in arm and neck movements, as assessed by kinematic techniques, after either real or sham cerebellar cTBS in patients.

Conclusions: The functional influence of the cerebellum on the motor cortex assessed by cTBS may not be the same in different types of focal dystonia. The reduced cerebellar inhibitory modulation of M1 in dystonia may relate to the topography of the disorder as opposed to being a widespread pathophysiological abnormality of the disease.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/effects-of-cerebellar-theta-burst-stimulation-on-arm-and-neck-movement-kinematics-in-patients-with-focal-dystonia/