Consistency of evoked responses to dual-stimulator, single-pulse transcranial magnetic stimulation in the lower limb of people with multiple sclerosis

The purpose of this study was to explore the within session and test–retest consistency of motor evoked potentials (MEP) elicited by transcranial magnetic stimulation (TMS) from the resting tibialis anterior (TA) muscle of 10 patients (two men, eight women) with clinically definite multiple sclerosis (MS). Dual stimulators were configured to produce a single pulse (DS/SP) through a hand-held coil. MEP were recorded in five blocks of five trials with a repeat test occurring 7–14 days later. Analysis of a trial sequence revealed the area of the first MEP trial of each block to be significantly different to subsequent trials (trials 2–5; p < 0.05). We therefore discarded T1 from further analysis. Thereafter, repeated measures of analysis of variance of MEP characteristics and blocks of MEP (average of four trials) revealed no significant differences (p > 0.05). The results of the repeat session revealed no significant differences in motor thresholds, MEP latency, MEP amplitude or MEP area between sessions (p > 0.05). Test–retest intra-class coefficients of correlation and their 95% confidence intervals indicated high reliability (>0.80). Our results show that consistent, repeatable TMS measures can be obtained from the resting TA of MS patients using the DS/SP method.