There is increasing evidence that the cerebellum has a role in the pathophysiology of primary
focal hand dystonia and might provide an intervention target for non-invasive brain stimulation to improve function of the affected hand. The primary objective of this study was to determine if cerebellar
transcranial direct current stimulation (
tDCS) improves handwriting and cyclic drawing kinematics in people with hand
dystonia, by reducing cerebellar-brain inhibition (CBI) evoked by
transcranial magnetic stimulation (TMS). Eight people with
dystonia (5 writer's
dystonia, 3
musician's dystonia) and eight age-matched controls completed the study and underwent cerebellar anodal, cathodal and
sham tDCS in separate sessions.
Dystonia severity was assessed using the
Writer's Cramp Rating Scale (WRCS) and the Arm
Dystonia Disability Scale (ADDS). The kinematic measures that differentiated the groups were; mean
stroke frequency during handwriting and fast cyclic drawing and average pen pressure during light cyclic drawing. TMS measures of cortical excitability were no different between people with
FHD and controls. There was a moderate, negative relationship between TMS-evoked CBI at baseline and the WRCS in
dystonia. Anodal cerebellar
tDCS reduced handwriting mean
stroke frequency and average pen pressure, and increased speed and reduced pen pressure during fast cyclic drawing. Kinematic measures were not associated with a decrease in CBI within an individual. In conclusion, cerebellar anodal
tDCS appeared to improve kinematics of handwriting and circle drawing tasks; but the underlying neurophysiological mechanism remains uncertain. A study in a larger homogeneous population is needed to further investigate the possible therapeutic benefit of cerebellar
tDCS in
dystonia.