The Test-Retest Reliability of Non-Navigated Transcranial Magnetic Stimulation (TMS) Measures of Corticospinal Pathway Excitability in a Neurologically Intact Adult Population

The test-retest reliability of Transcranial Magnetic Stimulation (TMS) measurements in healthy adults across the lifespan remains unclear. Determine the test-retest reliability and smallest detectable change (SDC) of motor evoked potential, (MEP), characteristics elicited by non-neuro-navigated Transcranial Magnetic Stimulation in neurologically intact adults. In two identical data collection sessions separated by five to seven days in a healthy adult sample was conducted. MEP characteristics assessed were motor threshold (MT) (rest and active conditions), amplitude (active), latency (MEP-L) (active conditions), silent period (SP) (active conditions), and recruitment curve (RC) (active conditions). Muscles investigated were bilateral biceps brachii (BB), extensor carpi radialis (ECR), and abductor pollicis brevis (APB). Test-retest reliability was calculated using the intra-class correlation coefficient (ICC) with corresponding 95% confidence intervals (CI) and limits of agreement (LOA), and the smallest detectable change was calculated. Acceptable reliability was set at a lower 95% CI of 0.70 or above for the ICC. In healthy adults (n = 51) none of the MEP characteristics were reliable. The lower end of the CI was below acceptable reliability (ICC < 0.7) for all MEP characteristics. Active MT of the non-dominant biceps was most reliable (e.g. ICC = 0.78[0.64–0.87]); whereas the RC demonstrated poor reliability for all muscles. The LOA had small mean differences between sessions with wide 95% LOA demonstrating measurement variability. The SDC were variable across muscles and MEP characteristics. In this study the findings indicate there is still limited evidence for acceptable reliability of TMS outcomes which are interpreted by the lower end of the 95% CI of the ICC.