A case of pathological excitability located with navigated-TMS: presurgical evaluation of focal neocortical epilepsy.
OBJECTIVE
The quality of presurgical evaluation in focal extratemporal epilepsy surgery is highly dependent on precise structural and functional identification of the epileptic focus. Navigated transcranial magnetic stimulation (nTMS) is a tool that combines the spatial information of high-resolution magnetic resonance imaging (MRI) with the functionality of non-invasive cortical stimulation. The non-invasive character of nTMS suggests that it could be a promising tool for presurgical evaluation of cortical excitability.


METHODS
Presurgical nTMS evaluation was performed on an 8-year-old boy with left-sided intractable focal epilepsy, somatosensory auras and epilepsia partialis continua. In line with standardized procedures, motor evoked potentials were sought in both hemispheres over perirolandic cortex during simultaneous belly-tendon surface recordings of the first dorsal interosseus muscles.


RESULTS
One singular motor-evoked potential (MEP) could be elicited in the unaffected hemisphere. In contrast, in the affected hemisphere MEPs could be elicited over a large area of the cortex even after the stimulation strength was reduced by at least 44%. Latency stratification in the affected hemisphere differentiated a motor from a sensory region of interest. Stimulation over the sensory region induced a sensory aura. The sensory site was concordant with a previous transient diffusion restriction found in an MRI two years prior to nTMS.


CONCLUSIONS
NTMS can locate pathological excitability with high spatial precision. Future studies should compare nTMS with direct cortex stimulation, as well as the combination of nTMS with electroencephalography (EEG) in a larger patient-collective.
Schmidt
Sein
S
Department of Neurology, Charité Campus Mitte (CCM), Berlin, Germany.
Holst
Eric
E
Irlbacher
Kerstin
K
Oltmanns
Frank
F
Merschhemke
Martin
M
Brandt
Stephan A
SA
D002648:Child; D017036:Epilepsia Partialis Continua / Q000175:diagnosis / Q000473:pathology / Q000601:surgery; D004827:Epilepsy / Q000175:diagnosis* / Q000503:physiopathology* / Q000601:surgery; D019054:Evoked Potentials, Motor / Q000502:physiology; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D008297:Male; D019579:Neocortex / Q000473:pathology* / Q000601:surgery; D009431:Neural Conduction / Q000502:physiology; D038361:Neuronavigation / Q000379:methods; D011300:Preoperative Care / Q000379:methods*; D050781:Transcranial Magnetic Stimulation / Q000379:methods*