大脳磁気刺激法による運動野の興奮性の評価

Motor cortex excitability in patients with intractable epilepsy：a transcranial magnetic stimulation study

機能的半球離断術（functional hemispherotomy：FHS），または運動野に対し軟膜下皮質多切術（multiple subpial transection：MST）を行った患者の術前後において，経頭蓋的大脳磁気刺激法を用いて，一次運動野の機能を評価した。対象はFHS施行例3名とMST施行例4名。術前および術後1～5カ月後に磁気刺激を行い，上肢筋から運動誘発電位（MEP）を記録した。FHS 3例においては，健側運動野刺激にて全例とも対側性MEPのみならず同側性MEPが記録された。FHS後，対側性・同側性MEPの振幅は増大し，脳梁離断に伴う脱抑制による結果と考えられた。MST 4例においては，1例の前腕筋において，術前に運動野興奮性の増大と，MEP波形の異常がみられ，術後に正常化した。その他の症例においては，術後に運動野興奮性は著明に低下した。大脳磁気刺激法は，てんかん患者の術前後の運動機能の評価に極めて有用である。

We investigated motor cortex excitability in patients with intractable epilepsy who underwent functional hemispherotomy（FHS；3 patients）or multiple subpial transection（MST；4 patients）over the primary motor cortex, using a trancranial magnetic stimulation technique. Transcranial magnetic stimulation was performed before and 1 to 5 months after the operation, and motor evoked potentials（MEP）were recorded from the upper extremity muscles. In 3patients with FHS, magnetic stimulation on the motor cortex of the intact hemisphere evoked not only contralateral MEPs but also ipsilateral MEPs in both the biceps brachii and first dorsal interosseous muscles. After FHS, the amplitudes of both the contralateral and ipsilateral MEPs were increased, which was presumably attributable to disinihibition of the motor cortex after the callosotomy. Among the patients who underwent MST, one patient showed abnormal polyphasic MEPs with long duration in his forearm muscle and exaggerated excitability of the affected motor cortex, both of which was normalized after the operation. In the other patients, the motor cortex excitability for the hand muscle was markedly decreased after MST. Transcranial magnetic stimulation was safe and extremely useful for evaluation of the motor cortex function before and after the surgical intervention in patients with intractable epilepsy.