Test-retest reliability of navigated transcranial magnetic stimulation of the motor cortex

Because navigated transcranial magnetic stimulation (nTMS) is increasingly used in neurosurgical research, interpretation of its results is of utmost importance.

To evaluate the test-retest reliability of nTMS.

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.

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.

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.