Test-retest Reliability of Navigated Transcranial Magnetic Stimulation of the Motor Cortex

BACKGROUND: Because navigated transcranial magnetic stimulation (nTMS) is increasingly used in neurosurgical research, interpretation of its results is of utmost importance. OBJECTIVE: To evaluate the test-retest reliability of nTMS. METHODS: Twelve healthy participants underwent nTMS at 2 different sessions separated by 10.3 +/- 9.6 days. Investigated parameters included resting motor thresholds, hotspots, and centers of gravity calculated for the first dorsal interosseous, abductor pollicis brevis, extensor digitorum, tibial anterior, and abductor hallucis muscles. RESULTS: Excellent reliability of resting motor thresholds was observed. Hotspots and centers of gravity showed moderate to excellent repeatability along the anteroposterior axis (intraclass correlation coefficient, 0.54-0.89), whereas the x coordinate presented mainly poor to moderate stability (intraclass correlation coefficient, 0.11-0.89). Movement of centers of gravity over sessions was 0.57 +/- 0.32 cm, and hotspots laid 0.79 +/- 0.47 cm apart. Calculation of coefficient of variation revealed high reliability of investigated parameters in upper extremities; in lower extremity muscles, high variation across sessions was observed. CONCLUSION: nTMS can be considered a reliable tool, thus opening new fields of noninvasive investigations in neurosurgery. The results presented here should be considered in the interpretation of individual nTMS results.