Focal ictal direct current shifts in human epilepsy as studied by subduraland scalp recording

In order to clarify further the characteristics of ictal direct current (DC ) shifts in human epilepsy, we investigated them by subdural and scalp reco rding in six and three patients, respectively, both having mainly neocortic al lobe epilepsy (five with frontal lobe epilepsy, two with parietal lobe e pilepsy 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 j ust one or two electrodes at which the conventional initial ictal EEG chang e was also observed, They were closely accompanied by the electrodecrementa l pattern in all patients except for one in whom 1 Hz rhythmic activity was superimposed on clear negative slow shifts, Seizure control after resectio n of the cortex, including the area showing DC shifts, was favourable irres pective of histological diagnosis, Scalp-recorded ictal slow shifts were ob served in 23% of all the recorded seizures (60 seizures) among the three pa tients, They were, like the subdurally recorded ones, mainly surface-negati ve in polarity, closely related to the electrodecremental pattern and consi stent in their location, It seems that scalp-recorded DC shifts were detect ed 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 co nfirm the conventional initial ictal EEG change, and that scalp-recorded ic tal slow shifts also have high specificity although their low sensitivity i s to be taken into account.