The effects of MEP counts on intra- and intersession reliability of single-pulse TMS-induced MEPs in the wrist extensor muscle of healthy individuals

Abstract

Background

Motor evoked potentials (MEPs) exhibit high intra-individual variability, which can compromise reliability. One suggested approach to reduce this variability is averaging multiple MEPs. However, there is no evidence regarding the optimal number of MEPs required to obtain the most reliable amplitude and latency measurements from the extensor carpi radialis (ECR) muscle.

New method

Healthy participants attended two sessions. In the first session, two sets of TMS-induced MEPs were recorded with a 20-minute interval to evaluate intra-session reliability. The second session was conducted after at least 48 h to assess inter-session reliability. Reliability was quantified using intraclass correlation coefficients (ICCs), one-way ANOVA, and Bland–Altman analysis.

Results

For MEP amplitude, both intra- and inter-session ICC values were excellent across all MEP block sizes, with reliability improving as the number of MEPs per block increased. For MEP latency, 10 MEPs were sufficient to achieve excellent intra-session reliability, whereas inter-session reliability ranged from good to excellent, with larger blocks (16–25 MEPs) providing the highest ICC values.

Comparison with existing methods

This study is the first to examine MEP reliability in the ECR muscle. Compared with previous methods, including monophasic TMS in other muscles, our protocol shows that MEP latency in the ECR requires larger MEP blocks to achieve high inter-session reliability.

Conclusions

This study suggests that averaging MEPs from the ECR yields highly reproducible amplitude measurements with few blocks, whereas MEP latency requires more blocks to achieve high inter-session reliability.