P065 Abnormally low intracortical inhibition in dystonia with poor response to pallidal stimulation

Abstract

Introduction Pallidal stimulation (GPi DBS) is an effective treatment of dystonic syndromes with a relatively high variability of clinical benefit. As patients with dystonia typically have a lower ability to suppress unwanted movements, we expected a decreased intracortical inhibition of motor cortex, which can be potentially reversed by GPi DBS. Objectives To distinguish between patients with dystonia according to the clinical outcome of GPi DBS using short-latency intracortical inhibition (SICI) of the motor cortex assessed by paired transcranial magnetic stimulation (TMS). Patients & methods We examined 22 patients (mean age 51 ± 17 years) with dystonia of various distribution and origin treated by GPi DBS in different time intervals from implantation. Paired TMS with subthreshold conditioning stimulus followed by a supratreshold testing stimulus 2.5 ms later were applied to the motor cortex to elicit SICI in GPi DBS ON and GPi DBS OFF condition two hours later. The clinical effect (CE) was expressed as a change in the dystonic score (Burke-Fahn-Marsden Dystonia rating Scale or Toronto Western Spasmodic Torticollis Scale) between actual GPi DBS ON condition and the preoperative state. Results The SICI was less effective in patients than in controls regardless of the ON and OFF conditions (p Download : Download high-res image (206KB) Download : Download full-size image ). Non-responders (n = 9; 50% CE, p Download : Download high-res image (225KB) Download : Download full-size image Fig. 2a) and in addition, the shortest MEP onset latency was observed in non-responders (p Conclusions Our results suggest that the best responders to GPi DBS treatment exhibited a similar level of SICI as in healthy controls. On the contrary, non-responders were unable to increase their reduced cortical inhibition and effectively suppressed dystonic symptoms. We speculate that decreased intracortical inhibition with abnormally fast transmission volley is underpinned by the poor complexity of the motor network. Supported by the grant IGA MZ CR NT12282-5/2011.