Abstracts

Rationale: Lateralization of motor innervation was studied with Transcranial Magnetic Stimulation (TMS) and functional Magnetic Resonance Imaging (fMRI) in children with intractable focal epilepsy. To evaluate preoperative lateralization and localization of cerebral motor function, non-invasive methods such as TMS and fMRI may prove valuable alternatives for invasive methods as WADA testing. Methods: 34 children with intractable focal epilepsy were studied. Motor function of each hand was qualified as good or poor. Cerebral lesions were classified as as early or late. Motor cortices of both hemispheres were stimulated and Motor Evoked Potentials (MEPs) recorded from both hands seperately. Lateralization of motor innervation was classified as no response, contralateral, ipsilateral or bilateral representation. When feasible, patients additionally underwent fMRI using a motor task of the hands. Results: All patients with a good function of the hand opposite the affected hemisphere had exclusive contralateral motor innervation of this hand. In 83% of the children with poor function of the affected hand, TMS revealed ipsilateral or bilateral innervation of the paretic hand. Lateralization of motor innervation was significantly correlated with quality of motor function (p = 0.001). Fourteen patients in whom no MEP was elicitable were signifantly younger than the remaining 20 with a motore response to TMS (3.3 vs. 11.4 years, p < 0.001). FMRI could be succesfully performed in 5 patients and results on lateralization of motor innervation were consistent with TMS findings in 4 out of 5 patients. Conclusions: Poor function of the paretic hand is strongly associated with motor innervation from the ipsilateral hemisphere. Reorganization in the contralateral hemisphere is probably the only efficient mode of plasticity for motor function of the contralesional hand. Accurate clinical examination of the quality of hand function combined with TMS (and fMRI) is helpful in defining the pattern of motor innervation prior to epilepsy surgery.