Brain, Vol. 122, No. 5, 827-838,
May 1999
© 1999 Oxford University Press
Focal ictal direct current shifts in humanepilepsy as studied by subdural and scalp recording
1 Departments of Brain Pathophysiology, 2 Neurosurgery and 3 Neurology, Kyoto University School of Medicine, Kyoto and 4 Department of Neurosurgery, Tottori University School of Medicine, Tottori, Japan
Correspondence to:
Akio Ikeda, MD, Department of Brain Pathophysiology, Kyoto University School of Medicine, Shogoin, Sakyo-ku, Kyoto, 606, Japan E-mail: akio{at}kuhp.kyoto-u.ac.jp
In order to clarify further the characteristics of ictal direct current (DC) shifts in human epilepsy, we investigated them by subdural and scalp recording in six and three patients, respectively, both having mainly neocortical lobe epilepsy (five with frontal lobe epilepsy, two with parietal lobe epilepsy and two with temporal lobe epilepsy). By using subdural electrodes made of platinum, ictal DC shifts were observed in 85% of all the recorded seizures (89 seizures) among the six patients, and they were localized to just one or two electrodes at which the conventional initial ictal EEG change was also observed. They were closely accompanied by the electrodecremental pattern in all patients except for one in whom 1 Hz rhythmic activity was superimposed on clear negative slow shifts. Seizure control after resection of the cortex, including the area showing DC shifts, was favourable irrespective of histological diagnosis. Scalp-recorded ictal slow shifts were observed in 23% of all the recorded seizures (60 seizures) among the three patients. They were, like the subdurally recorded ones, mainly surface-negative in polarity, closely related to the electrodecremental pattern and consistent in their location. It seems that scalp-recorded DC shifts were detected particularly when seizures were clinically intense, while no slow shifts were observed in small seizures. It is concluded that at least subdurally recorded ictal slow shifts are clinically useful before epilepsy surgery to delineate more specifically an epileptogenic area as well as to further confirm the conventional initial ictal EEG change, and that scalp-recorded ictal slow shifts also have high specificity although their low sensitivity is to be taken into account.
ictal DC shift; ictal EEG; subdural recording; scalp recording; epilepsy
DC = direct current; FLE = frontal lobe epilepsy; HFF = high frequency filter; LFF = low frequency filter; MTLE = mesial temporal lobe epilepsy; NLE = neocortical lobe epilepsy; PLE = parietal lobe epilepsy; SEP = somatosensory evoked potential; TLE = temporal lobe epilepsy
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