| Research Abstract |
Ictal direct current (DC) potentials represent sustained paroxysmal depolarization shifts (PDSs) occurring in epileptic neurons, and thus reflect the nature of the neurons and adjacent glial cells in the epileptogenic area. In human epilepsy, scalp-recorded show negative shifts were demonstrated in association with spikes and wave complexes in patients with petit mal, but little clinical application has been done so far. When subdurally recorded in patients with intractable partial epilepsy, negative shifts were observed by currently available equipment : platinum electrodes using AC amplifier with a very high input impedance (>50Mohm) and opened low frequency filter (<0.016Hz).
In order to further clarify characteristics of ictal DC shifts in human epilepsy, we investigated them by subdural and scalp recording in 6 and 3 patients, respectively, both having mainly neocortical lobe epilepsy (5 with frontal lobe epilepsy, 2 with parietal lobe epilepsy and 2 with temporal lobe epilepsy). B
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y using subdural electrodes made of platinum, ictal DC shifts were observed in 85% of all the recorded seizures (89 seizures) among the 6 patients, and they were localized to just 1 or 2 electrodes at which the conventional initial EEG change was also observed. They were closely accompanied by the eletrodecremental pattern in all patients except for 1 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 favorable irrespective of histological diagnosis.
Scalp-recorded ictal slow shifts were observed in 23% of all the recorded seizures (60 seizures) among the 3 patients. They were, like the subdurally recorded ones, mainly surface-negative in polarity, closely related to the electrodecremental pattern, and consistent in their location. 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 sensitivity is to be taken into account. Less
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