Restorative Neurology and Neuroscience 28 (2010) 379–385 379 DOI 10.3233/RNN-2010-0540 IOS Press A case of pathological excitability located with navigated-TMS: Presurgical evaluation of focal neocortical epilepsy Sein Schmidt a , Eric Holst a , Kerstin Irlbacher a , Frank Oltmanns b , Martin Merschhemke b and Stephan A. Brandt a,* a Department of Neurology, Charit´ e Campus Mitte (CCM), Berlin, Germany b Epilepsy Center Berlin-Brandenburg, Ev. Krankenhaus K ¨ onigin-Elisabeth-Herzberge, Berlin, Germany Abstract. Purpose: 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, somatosen- sory 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. Keywords: Focal epilepsy, preoperative evaluation, navigated brain stimulation, cortical excitability, motor evoked potential, transcranial magnetic stimulation 1. Introduction About 60% of patients with epilepsy exhibit focal epileptic syndromes, of which approximately 60% be- come manifest in childhood (Rossi, 1995; Kim et al., 2000). In the case of intractable focal epilepsy about * Corresponding author: Department of Neurology, Charit´ e Cam- pus Mitte (CCM), Charit´ eplatz 1, 10117, Berlin, Germany. Tel.: +49 30 450660111; Fax: +49 30 450560955; E-mail: stephan.brandt@ charite.de. 15% of these patients may benefit from epilepsy surgery (Wyllie, 2000; Rosenow and Luders, 2001; Knake et al., 2005). The goal of surgery is the removal or dis- connection of epileptogenic tissue (Rosenow and Lud- ers, 2001). The success of surgery is dependent on the concordance of a structural and a functional lesion. This concordance predicts a 31% outcome benefit with a 70% probability of complete resolution of seizures (Avanzini et al., 2001; Duncan, 2002). On the oth- er hand, many patients will have pathological findings in various functional imagining methods (e.g. positron 0922-6028/10/$27.50  2010 – IOS Press and the authors. All rights reserved