Reproducibility of transcranial magnetic stimulation metrics in the study of proximal upper limb muscles

Abstract

Objective Reproducibility of transcranial magnetic stimulation (TMS) metrics is essential in accurately tracking recovery and disease. However, majority of evidence pertains to reproducibility of metrics for distal upper limb muscles. We investigate for the first time, reliability of corticospinal physiology for a large proximal muscle-the biceps brachii and relate how varying statistical analyses can influence interpretations. Methods 14 young right-handed healthy participants completed two sessions assessing resting motor threshold (RMT), motor evoked potentials (MEPs), motor map and intra-cortical inhibition (ICI) from the left biceps brachii. Analyses included paired t-tests, Pearson's, intra-class (ICC) and concordance correlation coefficients (CCC) and Bland-Altman plots. Results Unlike paired t-tests, ICC, CCC and Pearson's were >0.6 indicating good reliability for RMTs, MEP intensities and locations of map; however values were <0.3 for MEP responses and ICI. Conclusions Corticospinal physiology, defining excitability and output in terms of intensity of the TMS device, and spatial loci are the most reliable metrics for the biceps. MEPs and variables based on MEPs are less reliable since biceps receives fewer cortico-motor-neuronal projections. Statistical tests of agreement and associations are more powerful reliability indices than inferential tests. Significance Reliable metrics of proximal muscles when translated to a larger number of participants would serve to sensitively track and prognosticate function in neurological disorders such as stroke where proximal recovery precedes distal.

Reliability of TMS metrics in patients with chronic incomplete spinal cord injury

“…CCC builds on the SCC analysis, as it is able to take into account the differences in mean and variance between test 1 and test 2. 38 Significance of the CCC was determined based on guidelines established by Lin et al 37,39 Specifically, the strength of association between parameters collected over tests 1 and 2 was deemed as small (0 to 0.6), substantial (0.6 to 0.8) or near-perfect (0.8 to 1) based on the value of the CCC coefficient.…”

“…TMS metrics for proximal muscles are poorly reliable even in the healthy. 38 This is because representations of proximal muscles occupy a smaller region of the Figure 6 Between-muscle analysis of test-retest reliability in patients with iSCI. In general, we noted that higher MRC grade muscles and less affected sides of the body showed more test-retest reliability across patients with iSCI.…”

Test–Retest Reliability of the Effects of Continuous Theta-Burst Stimulation

“…Only two published studies have assessed the reproducibility of cTBS aftereffects (Vernet et al, 2014; Vallence et al, 2015). The first (Vernet et al, 2014) used a relatively small sample size ( n = 10) and did not report reliability coefficients of cTBS aftereffects, which can be compared with the reliability coefficients of other TMS measures (Carroll et al, 2001; Kimiskidis et al, 2004; Christie et al, 2007; Livingston and Ingersoll, 2008; Bastani and Jaberzadeh, 2012; Ngomo et al, 2012; Hinder et al, 2014; Liu and Au-Yeung, 2014; Sankarasubramanian et al, 2015; Schambra et al, 2015; Hermsen et al, 2016; Fried et al, 2017). The second study (Vallence et al, 2015) used an input–output curve approach that allowed assessment of cTBS aftereffects elicited over a range of stimulation intensities, but at the cost of fewer time-points.…”

TMSmap – Software for Quantitative Analysis of TMS Mapping Results

“…Standardizing the procedure of map construction and their parameters would lead to an easier comparison of results, thus, being particularly relevant for studying reorganization in the course of a disease, rehabilitation or training. Indeed, until now in order to investigate TMS motor maps, the changes were analyzed either by visual assessment (Mäkelä et al, 2013 ) or using parameters such as areas of the representations, CoGs location and a few other characteristics alternating from study to study (Littmann et al, 2013 ; Ruit et al, 2014 ; Sankarasubramanian et al, 2015 ; Kraus and Gharabaghi, 2016 ). Multi-parametric assessment of the TMS motor maps including standard and novel parameters accessible in TMSmap may reveal more subtle changes in cortical organization.…”