Single-pulse electrical stimulation (SPES) was evaluated in 35 children who underwent intracranial subdural electroencephalographic (EEG) monitoring at Great Ormond Street Hospital for Children and King’s College Hospital, London, UK. Median age was 14 yrs 2 mos (range 9 mos to 17 yrs 7 mos). Using a series of 10 or more single, brief (1 ms) electrical stimuli, the cortical responses were examined for associations between response type, ictal onset zone, lesion boundary, and seizure outcome. Studies were conducted during interictal periods, while the patient was awake, and in parallel with video-EEG. Subdural grids (in 25 patients), subdural strips (in 30 patients), or depth electrodes (9 patients) covered a number of areas in each patient. The median number of electrodes in each patient was 54 (range 17-78). Abnormal responses to SPES indicative of epileptic cortical excitability were present in 54% of cases, and were “delayed”(DR) or “repetitive”(RR) in type. The DR is a sharp wave or spike, occurring later than 100 ms after stimulus, and corresponding with the area of seizure onset. The RR has the form of a successive repetition of an early response (ER), a sharp wave followed by a slow wave, typically lasting for a second or longer. Removal of the entire area responsible for abnormal responses to SPES was associated with good outcomes. [1]

COMMENT. Cortical responses to SPES in children are similar to those observed in adults. Abnormal SPES responses (DRs and RRs) correlate with epileptogenic cortex, and are useful in the presurgical evaluation and positioning of electrodes. The method may be used with or without anesthesia (Valentin et al, King’s College Hospital, unpublished observation).