The current status of presurgical diagnosis for epilepsy surgery in Japan

Abstract

Epilepsy surgery has become one alternative in treating medically irremediable epilepsies. This was achieved partially due to the development of diagnostic techniques for foci. To establish some standard guide lines, we studied the current status of the presurgical focus diagnostic protocol in the Japanese institutes where specialized epilepsy surgeries are performed. Since 2001 till 2005, the annual number of epilepsy surgeries was counted as 489, 620, 600, 553, and 595, respectively. In 2005, three institutes recorded more than 60 surgeries each. The distribution of foci was as Follows ; medial temporal 46%, lateral temporal 11%, and frontal 23%. Interictal SPECT was carried out in more than 80% of thge cases. MEG was performed in about 50% of the cases, whereas this rate was more than 80% for parietal and occipital foci. Ictal SPECT was performed in about 50% of neocortical cases but in only 10% of MTLE cases. This reflects the difficuty of this method in practice. Ictal EEG was considered to be a gold standard for focus diagnosis and it was performed in more than 80% of all cases. In contrast, intracranial EEG was used in about 40% of MTL cases and about 80% of neocortical foci cases. This implies that many "skip" cases were found in MTLE because focus the diagnosis is easier here than in other locations. Subdural electrodes were used in most of the neocortical foci cases, because of the need for focus diagnosis and functional mapping using electrical stimulation at the same time. Postsurgical outcome was good (Class I + II : 90%) for medial temporal foci cases, whereas it was less than 80% for neocortical foci cases. These results are considered to be comparable to those reported in the US. Several representative cases were demonstrated to delinate the methodologies used.