How Reproducible Are Transcranial Magnetic Stimulation-Induced MEPs in Subacute Stroke?

Purpose: Motor evoked potentials (MEPs) and total motor conduction time (TMCT) induced by transcranial magnetic stimulation (TMS) are used to make assumptions about the prognosis of motor outcome after stroke. Understanding the different sources of variability is fundamental to the concept of reliability. Reliability testing of TMS-MEPs and TMCTs within and between two independent examiners in healthy and stroke subjects is still an unexplored field in the clinical neurophysiology. Assessing the reproducibility of TMS measurements requires studies to investigate the test-retest reliability of TMS-induced MEPs and TMCT. The authors set out to test the reliability of these TMS measurements. Methods: Eighteen patients with stroke and 8 healthy volunteers were tested twice within a 1-week period by 2 examiners using TMS to determine MEPs and TMCT for the abductor pollicis brevis muscle of their affected and unaffected hands. Results: The authors found moderate to perfect reliability of TMS-induced MEPs in healthy volunteers, noninfarcted hemispheres (perfect agreement), and infarcted hemispheres (Kappa's = 0.45-0.87). Reliability of TMCT was good to excellent in the volunteers (intraclass correlation coefficients = 0.77-0.97), excellent in the noninfarcted hemispheres (intraclass correlation coefficients = 0.97-1.00), and poor to excellent in the infarcted hemispheres (intraclass correlation coefficients = 0.44-0.90). Conclusions: The reliability of TMS-induced MEPs and TMCT measurements in healthy volunteers and the noninfarcted hemisphere of patients with stroke with an upper paretic limb was good to excellent. In contrast, TMS measurements in the infarcted hemisphere were less consistent. Based on the lower reproducibility of TMCT measurements in the infarcted hemisphere, we recommend to repeat the TMCT measurements to improve the reliability of tests.