Abnormal movement-related suppression of sensory evoked potentials in upper limb dystonia

Gating of sensory evoked potentials (SEPs) around the onset of a voluntary movement is a physiological phenomenon with centripetal and central components, and may reflect sensorimotor integration required for normal movement control.

Our objective was the investigation of SEP suppression at the onset of movement and the interaction between SEP suppression and vibration of the limb.

Fourteen patients with primary focal/segmental dystonia and 17 age-matched healthy volunteers were studied. SEPs were elicited after electrical stimulation of the median nerve at the wrist. Electroencephalograms (EEGs) were recorded over the scalp at three sites according to the International 10-20 System (F3, C3 and P3). SEPs were recorded in four conditions: at rest, at the onset of movement (a self-paced abduction movement of the right thumb), both in the absence and in the presence of vibration of the limb.

Repeated measures anova revealed that there was a significant main effect of group [F(1, 11.1) = 0.471, P = 0.002]. Post hoc exploration of this effect revealed it to be due to an absence of SEP suppression at movement onset in patients (mean ratio SEP movement onset/rest 1.15 at F3, 1.13 at C3, 1.01 at P3) compared to controls, who had SEP suppression at movement onset (mean ratio SEP movement onset/rest 0.79 at F3, 0.78 at C3, 0.77 at P3). With vibration, SEP suppression reduced in both patients and controls to a similar extent.

These results demonstrate abnormal SEP suppression at the onset of movement in patients with primary dystonia, and in addition that vibration of the limb reduces SEP suppression in patients and controls.