Abstract
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.
Highlights
Focal or isolated dystonia is a neurological disorder where involuntary muscle contractions cause intermittent or sustained abnormal postures of an isolated body part, such as the hand (Fahn, 1984; Albanese et al, 2013)
The average pen pressure in pascals (APP) during light cyclic drawing was higher in the dystonia than the control group (P = 0.037) but was no different for fast cyclic drawing or handwriting (Figure 1D)
In the current study we examined the effect of anodal, cathodal and sham transcranial direct current stimulation (tDCS) to the cerebellum on handwriting and circle drawing kinematics, and corticomotor excitability and cerebellar-brain inhibition (CBI) in people with Focal hand dystonia (FHD) and controls
Summary
Focal or isolated dystonia is a neurological disorder where involuntary muscle contractions cause intermittent or sustained abnormal postures of an isolated body part, such as the hand (Fahn, 1984; Albanese et al, 2013). The excitability of the cerebellar to primary motor cortex (M1) pathway can be probed in humans using paired-pulse transcranial magnetic stimulation (TMS), known as cerebellarbrain inhibition (CBI; Ugawa et al, 1995; Daskalakis et al, 2004; Koch et al, 2008). The cerebellum exercises tonic inhibition over M1 via the cerebellothalamocortical pathway for precise control of the hand during an active task (Kassavetis et al, 2011). It is possible that motor deficits experienced in neurological movement disorders such as dystonia, might partially arise from aberrant cerebellar modulation over M1. The impact of a reduction of CBI on motor function remains unclear and more studies are needed to clarify exactly how cerebellar dysfunction demonstrated by CBI impairs movement in neurological disorders
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