The reliability of topographic measurements from navigated transcranial magnetic stimulation in healthy volunteers and tumor patients

Background Navigated transcranial magnetic stimulation (nTMS) is increasingly being used for preoperative mapping of the motor cortex. Any new technology should undergo rigorous validation before being widely adopted in routine clinical practice. The aim of this experimental study was to assess the intraexaminer and interexaminer reliability of topographic mapping with nTMS. Methods nTMS mapping of the motor cortex for the first dorsal interosseous (FDI) muscle was performed by an expert and a novice examiner, twice in ten healthy volunteers and once in ten tumor patients. The distances between the centers-of-gravity and hotspots were calculated, as were coefficients of variation. This study also compared orthogonal versus variable orientation of the stimulation coil. Results The mean (range) distance between centers-of-gravity for the expert examiner in the test-retest protocol with healthy volunteers was 4.40 (1.86-7.68) mm. Themean (range) distance between centers-of-gravity for the expert vs. novice examiner was 4.89 (2.39-9.22) mm. There were no significant differences in this result between healthy volunteers and tumor patients. Conclusions nTMS is sufficiently reliable for clinical use, but examiners should make efforts to minimize sources of error. The reliability of nTMS in tumor patients appears comparable to healthy subjects.