Neuropediatrics 2008; 39 - P065
DOI: 10.1055/s-0029-1215834

Does navigated transcranial magnetic stimulation (TMS) decrease the variability of motor evoked potentials (MEP) and increase its reproducibility?

NH Jung 1, N Kuhnke 1, D Hauschke 2, S Stolle 1, I Delvendahl 1, V Mall 1
  • 1Univ.-Klinik für Kinder- und Jugendheilkunde Freiburg, Neuropädiatrie, Freiburg, Germany
  • 2Institut für Biometrie und Statistik, Freiburg, Germany

Introduction: One major attribute of transcranial magnetic stimulation (TMS) is the variability of the MEP amplitudes. The purpose of this study was to investigate the variability of MEP amplitudes with and without navigated TMS at one time point as well as the reproducibility between different time points.

Methods: We investigated n=8 healthy subjects (w: n=4, m: n=4; age: 22 to 25; mean age 23.8±1.24) at three different points in time with and without an optically tracked frameless navigational device. We recorded dose-recruitment curves (from +5% to +30% maximum stimulator output above resting motor threshold (rMT)) and MEP amplitudes of 1 mV (SI1mV) were recorded. Statistical characteristic of variability was the coefficient of variation (CV). Reproducibility between different sessions was assessed via the MEP amplitudes.

Results: CV of MEP amplitudes did not show a significant difference between navigated and not-navigated TMS in dose-recruitment curves, although differences in single points of investigation were observed. This was the case towards a reduced variability for navigated TMS as well as for not-navigated TMS. A clear trend towards a reduced variability in navigated TMS could not be observed. Also MEPs of SI1mV, as term for reproducibility, did not differ significantly between sessions with and without navigated TMS as well.

Discussion: Our results do not support the hypothesis that spatial accuracy reduces the variability and increases the reproducibility of MEP amplitudes. The results are in accordance with previous findings that accurate coil placement does not influence the variability of MEP amplitudes (Gugino et al., 2001). Additionally, navigated TMS does not increase the reproducibility of MEP amplitudes at different points of investigation. Other factors such as spinal desynchronisation (Rösler et al., 2008) might stronger contribute to the variability of MEP amplitudes.