[Surgical treatment of non-lesional supplementary motor area epilepsy: two case reports]

A 37-year-old male and a 12-year-old female presented with non-lesional epilepsy arising from the supplementary motor area in the medial frontal cortex, manifesting as daily brief tonic seizures involving the bilateral extremities, which were intractable to multiple antiepileptic medications. During the seizure, there was no impairment of awareness, and the tonus was always higher in the limbs contralateral to the epileptogenic hemisphere in both patients. Scalp EEG detected midline epileptiform discharges. Three-tesla MR imaging using the FLAIR and short tau inversion recovery sequences, interictal IMP-SPECT, IMZ-SPECT, and FDG-PET detected no focal abnormalities in either patient. Invasive intracranial EEG evaluation was performed using chronically implanted subdural electrodes on the interhemispheric frontoparietal cortices, based mainly on the seizure semiology and the associated EEG findings. Intracranial EEG successfully identified the location of the seizure onset in the supplementary motor area in the medial frontal cortex. Focal cortical resection including the area of seizure onset resulted in freedom from seizures and significant improvement in both patients. Histological study revealed focal cortical dysplasia in both patients. Recognition of the typical seizure semiology is very important in the correct diagnosis and surgical treatment of supplementary motor area epilepsy, especially in the absence of MR imaging lesions.