補足運動野てんかんの外科治療―発作症状が決め手となった2例

Surgical Treatment of Non-lesional Supplementary Motor Area Epilepsy: Two Case Reports

Ⅰ．はじめに

　てんかんの局在診断では，画像診断や脳波よりも発作症状が決め手となる場合がある．MRIで明らかなてんかん原性病変があり，脳波異常の局在がはっきりしている場合は，一般に外科治療で良好な成績が期待できる．しかし，皮質形成異常の最終診断で外科治療に至る例の最大25％程度は，術前のMRIで病変が検出できないとされる⁹⁾．また，側頭葉内側部や半球間裂深部などのてんかん性異常活動を，頭皮上脳波で検出するのは，ときに困難である³⁾．

　今回われわれは，MRIで異常所見を認めず，頭皮脳波所見でも確定的な局在異常を認めなかったが，発作症状を最大の手掛かりとして外科治療に成功した2症例を経験したので報告する．

　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 fronto-parietal 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.