Transcranial direct current stimulation and retraining in musician's hand dystonia

Musician's dystonia (MD) is a task-specific movement disorder with a loss of voluntary motor control in highly trained movements. Defective inhibition on different levels of the central nervous system is discussed to be involved in the pathophysiology. Transcranial direct current stimulation (tDCS) modulates cortical excitability of the motor cortex. Cathodal tDCS may increase cortical inhibition, whereas anodal tDCS enhances excitability.

DC-Stimulation of musicians suffering from MD was expected to (a) increase inhibition through cathodal tDCS and (b) facilitate learning of non-dystonic movement patterns through anodal tDCS.

Methods: In two experiments tDCS (2mA) was applied for 20min on the primary motor cortex contralateral to the affected hand.

1) Professional guitarists (n=10) with MD played guitar exercises before, directly and 60min after singular cathodal tDCS. Movements were video-documented and symptoms were evaluated by three independent raters.

2) In a double-blind single case study, tDCS was combined with retraining on the piano. The patient (professional pianist) was treated with three stimulation protocols consecutively, with a minimum of 5 weeks between treatment sessions: anodal tDCS, cathodal tDCS and placebo stimulation (3×5 days). During stimulation, the patient practiced slow, non-dystonic movement patterns on the piano. Fine motor control was assessed by an objective MIDI-based method.

Results: 1) No beneficial effects of single session cathodal tDCS were found. Fine motor control of one guitarist improved after stimulation. This patient suffered from arm dystonia, while the other guitarists suffered from focal hand dystonia.

2) In the pianist, improvement of fine motor control after retraining and tDCS was found in all three conditions. Cathodal tDCS produced a prolonged after-effect of retraining.

Discussion: 1) Singular cathodal tDCS without retraining did not facilitate fine motor control in guitarists with MD.

2) Fine motor control was significantly improved after 20min of retraining both in the placebo condition and active conditions. Cathodal tDCS resulted in prolonged motor improvement. This effect might alternatively be explained by cumulative retraining effects in the third study week (cathodal week).

Daily repeated retraining seems to be a promising tool with a high therapeutic potential in MD. This is in agreement with previous reports. Therapeutic potential of repeated tDCS has to be further illuminated in future studies.