P157 Reliability of threshold tracking technique for short interval intracortical inhibition. Issue 3 (March 2017)

• Record Type: Journal Article
• Authors: Samusyte, G.; Bostock, H.; Rothwell, J.; Koltzenburg, M.
• Is Part Of: Clinical neurophysiology. Volume 128:Issue 3(2017:Mar.)
• Page Start: e93
• Publication Date: 2017-03
• Subjects: Neurophysiology -- Periodicals; Electroencephalography -- Periodicals; Electromyography -- Periodicals; Neurology -- Periodicals; 612.8
• DOI: 10.1016/j.clinph.2016.10.278
• Languages: English
• ISSNs: 1388-2457

Abstract

Abstract : Introduction: In threshold-tracking TMS, stimulation intensity is adjusted online to maintain a predefined target MEP response, thus allowing monitoring and controlling for the naturally occurring fluctuations in corticospinal excitability as well as technical errors. Although it is emerging as a useful clinical tool, little is known about its reliability and comparability with conventional techniques. Objectives: To evaluate the reproducibility of the threshold-tracking (constant response ) TMS technique for short interval intracortical inhibition (SICI) and compare it with standard (constant stimulus ) measurements. Methods: SICI was measured in 12 healthy volunteers (6 males, 31 ± 7.6 years) from the right FDI muscle using an automated stimulation protocol incorporating (i) conventional, fixed-intensity (A-SICI) and (ii) threshold tracking (T-SICI) methods at conditioning stimuli (CS) of 50–80% resting motor threshold (RMT) and interstimulus interval of 2.5 ms. RMT was defined as a stimulation intensity required to evoke a response of 0.2 mV and was determined by threshold tracking. Measurements were repeated on the same day and at least a week later by a single operator. Results: No significant differences in mean RMT, A-SICI and T-SICI were observed between sessions. RMT and TS, measured by threshold-tracking technique, showed excellent intra- and adequate interday reproducibility. At 50% RMT CS both types of SICI had poor reproducibility. At all other CS intensities, T-SICI had excellent intraday (intraclass correlation coefficient, ICC 0.81–0.92) and adequate-to-excellent interday (ICC 0.61–0.88) reproducibility, while A-SICI showed poor intraday and poor-to-adequate interday reproducibility (ICC 0.29–0.37 and 0.37–0.51, respectively). Conclusion: SICI measured by threshold tracking shows good intra- and interday reproducibility. Automation of the procedure and allowance for naturally occurring fluctuations in cortical excitability by threshold tracking may increase the reproducibility of SICI.