O19 Abnormal interaction between somatosensory and the motor cortex in dystonia not responding to pallidal stimulation

Abstract

Objectives To analyse the influence of the primary somatosensory cortex (SI) on the motor cortex (MI) in dystonia in regards to the effectiveness of deep brain stimulation (DBS) of the globus pallidus interna (GPi). Methods We examined 21 patients (mean age 51 ± (SD)17 years) with dystonia treated by GPi DBS. The SI was modulated in DBS ON and OFF conditions by a 2-min series of paired associative stimulation (PAS) with 5 Hz frequency, consisting of electrical stimulation of the median nerve followed by 20 ms of TMS pulse. The excitability of the MI was tested by motor evoked potentials (MEP) applied before and after the PAS. The clinical effect (CE) was expressed as a change in the dystonic score between DBS ON condition and the preoperative state. Results The SI PAS caused a decrease of the MEP amplitude in responders ( N = 8, >50% CE) and in partial responders ( N = 5, 25–50% CE) during both conditions which was indistinguishable from controls. In non-responders ( N = 8, p Discussion Non-responders showed a quick suppression of an inhibitory effect of the SI on the MI after switching stimulation off than when compared with the group of responders and controls. Conclusion GPi DBS normalizes the excitability of MI probably due to strengthening of the sensorimotor interaction, suggesting a longer lasting cortical plasticity in the responders. Significance The SI PAS reduces the excitability of the MI in dystonia according to effectiveness of GPi DBS. Supported by the grants GACR 16-13323S and PROGRES Q27/LF1 .