Scalp EEG Could Record Both Ictal Direct Current Shift and High-Frequency Oscillation Together Even With a Time Constant of 2 Seconds.

Herein, the authors report for the first time, scalp-recorded (1) focal ictal direct current (DC) shifts (active DC shifts; that precede conventional pattern) from the chronic focus of focal epilepsy and (2) ictal high-frequency oscillation after ictal DC shifts (passive DC shifts; that follow both conventional and high-frequency oscillation ictal patterns) from the acute focus of acute symptomatic seizures (Szs) in a 77-year-old man. Sixteen episodes of clinical Szs were recorded by scalp EEG with a 2-seconds time constant. Among the 16 recorded episodes of Sz, four EEG Sz patterns originated from the left posterior temporal area (chronic focus), and all patterns (100%) exhibited active DC shifts preceding the conventional pattern by 12 seconds. Twelve EEG Sz patterns originated from the right parietal area (acute focus), and the high-frequency oscillations (five Szs) (41.6%) and DC shifts (six Szs) (50%) occurred first, followed by the conventional pattern 8 seconds later. Because both the active and the passive DC shifts were recorded with a time constant of 2 seconds, which was smaller than that reported previously for ictal DC shifts (e.g., time constant of 10 seconds), clinically useful ictal DC shifts could be routinely inspected with a time constant of 2 seconds.