P045 The stability of hand cortical motor representations in writer’s cramp patients after repetitive transcranial magnetic stimulation

Abstract

Introduction Writer’s cramp (WC) is a rare type of focal dystonia. The treatment of WC is complicated due to the variations in the forces and angles of involved joints. Abnormal interactions within motor system units such as primary motor cortex, premotor cortex, basal ganglia is found to play role in WC pathogenesis. Repetitive transcranial magnetic stimulation (rTMS) can change cortical areas interactions and though could be a promising tool in treatment of WC. The most accepted rTMS protocol is low-frequency rTMS of premotor cortex (PMC) but according to the latest clinical guidelines it doesn’t provide a sufficient level of evidence to establish recommendations on the use it in WC patients. (Lefaucheur et al., 2014). Objectives The aim of our study was to evaluate the dynamics of motor cortical representations after rTMS in WC patients. Materials & methods Twelve patients (m/f – 6/6, mean age = 46.0, SD = 15.6), all right-handed and suffering writer’s cramp were enrolled in this study. nTMS with right Abductor pollicis brevis (ABP) muscle mapping was performed with NBS eXimia Nexstim device before and after 10 trains of low-frequency rTMS of PMC (1 Hz, 1200 stimuli/session, 110% of resting motor threshold (RMT). We assessed spatial distribution and location of right APB cortical representation including hot spot and center of gravity (stimulation point vectors sum weighted by MEPs amplitude) location before and after rTMS. We also assessed RMT changes. The cortical representation’s visualization was made with self-made software using spherical Voronoi tessellation. Results No significant changes in RMT was found (RMT before 46.6 ± 12.4%, RMT after 46.7 ± 12.4%). Two trends were observed comparing spatial distribution and location of right APB cortical representation: we observe quite stable representations and hot spot and center of gravity in four patients while in other patients the representation changed significantly (Fig. 1 Download : Download high-res image (291KB) Download : Download full-size image ). Conclusion We found two opposite directed trends in cortical representation dynamics. We’re planning further study if these trends could be predictors of clinical efficacy of rTMS.