P149 Reproducibility of the long intracortical inhibition curve in healthy subjects

• Published in: Clinical neurophysiology Vol. 128; no. 3; p. e88
• Main Authors: de Goede, A, Eertman, C, ter Braack, E, van Putten, M
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.03.2017
• Subjects: Neurology
• ISSN: 1388-2457; 1872-8952
• DOI: 10.1016/j.clinph.2016.10.270

Introduction Over the last decades, transcranial magnetic stimulation (TMS) has been used to assess cortical excitability in a variety of neuropsychiatric conditions, e.g. epilepsy, dementia and depression. To detect changes in excitability in longitudinal studies, it is important to validate the repeatability of TMS outcomes for the same subject between different sessions. Previous studies in healthy subjects found mixed degrees of reproducibility, ranging from poor to good agreement (Badawy et al., 2012; Du et al., 2014) . Especially, the long intracortical inhibition (LICI) curve showed a large variability across sessions (Du et al., 2014). Objective To evaluate the reproducibility of the LICI curve in healthy subjects using paired pulse TMS. Subjects & methods Twenty-seven healthy subjects were studied two times ( ± 1 week apart) with paired pulse TMS combined with electromyography. Both motor hot spots (abductor digiti minimi) were stimulated with 50 paired pulses (intensity 120% of resting motor threshold) at interstimulus intervals (ISIs): 100, 150, 200, 250 and 300 ms. In nineteen subjects a figure-of-eight coil was positioned and held in place manually during both sessions, while in eight subjects a robotic arm was used. The concordance correlation coefficient (rho-c) was used to estimate the agreement between repeated sessions (Lin, 1989). Results The average LICI curve among all subjects showed a close agreement between TMS sessions for manual (rho-c = 0.88) and robot-guided (rho-c = 0.95) positioning. However, the reproducibility decreased when individual LICI curves were compared; manual (rho-c = 0.66) and robot-guided (rho-c = 0.86). There was a large variation in reproducibility between subjects, ranging from poor to good levels of agreement. Additionally, moderate levels of agreement and a large variation was found for individual ISIs: manual (range rho-c: 0.42–0.55) versus robot-guided (range rho-c: 0.62–0.89). Conclusion Reproducibility of LICI curves was highly variable between healthy subjects. Good levels of agreement were found for analysis on group levels, but reproducibility decreased for the level of individual subjects or ISIs. Overall, reproducibility of the LICI curve was higher for robot-guided than for manual coil positioning.