Positive epileptiform discharges in children with neuronal migration disorders

Most epileptiform abnormalities show a negative polarity on EEG. Focal positive spike waves have rarely been identified in seizure disorders and are generally associated with physiological and neurological impairment. Results of EEG, computed tomography, MRI, and pathologic studies of 15 children with focal neuronal migration disorders who underwent surgery for refractory localization-related epilepsy were compared to examine the association between positive discharges and other findings. Subjects were studied both ictally and interictally by scalp EEG with the International 10-20 system and zygomatic or sphenoidal electrodes, and video EEG telemetry. The 5 children with positive discharges were significantly more likely to develop hemiparesis during the preoperative period (P < or = .025). Correlations were observed between positive discharges and lesions apparent on MRI situated around the rolandic fissure (P < or = .025). Children with positive discharges had a significantly less favorable outcome after surgical treatment (P < or = .025). Positive epilepti-form discharges in children with neuronal migration disorders may signal a more dysfunctional cortex leading to a focal neurological deficit or a more extended lesion than is detected on MRI. This would explain the less favorable outcome of seizures after surgery, since the epileptogenic areas and neuronal migration lesions cannot be completely resected.