Suppression of action tremor by sensory electrical stimulation in patients with essential tremor

Essential tremor (ET) is the most common movement disorder that includes postural tremor and action tremor. This study investigates whether sensory electrical stimulation (SES) is effective on the action tremor in patients with ET. One task in the clinical testing of action tremor, "Archimedes spiral drawing", was performed in 18 patients for three sessions, which were named as pre-stimulation (PRE), stimulation on (ON), and 5min after stimulation (POST). SES (sub-motor threshold) was applied on the muscles of the elbow and wrist only at ON session. Three-dimensional (3D) angular velocities were measured on three segments (index finger, hand, and forearm) from which movements of metacarpophalangeal (MP) and wrist joints were derived. Average tremor intensity in each session was represented by root mean square of the vector sum of 3D angular velocities. Tremor intensities in ON session were smaller than in PRE session in one segment (finger) and two joints (MP and wrist) (p<0.05). Tremor intensities in POST session were even smaller than in ON session in all segments and one joint (wrist) (p<0.05). The results indicate that SES suppresses action tremor and the effect continues and even improves 5min after the termination of stimulation. The findings of this study may contribute to the improvement of the quality of life in patients with ET.