Early onset motor semiology in seizures triggered by cortical stimulation during SEEG

The objective of the study was to describe electroclinical patterns in habitual seizures with motor semiology at onset, triggered by diagnostic stimulation, in patients undergoing presurgical evaluation using stereoelectroencephalography (SEEG).

Seizure semiology, stimulation parameters, electroclinical data, and anatomical localization were evaluated in stimulated and spontaneous seizures.

From 120 habitual seizures triggered by 50-Hz train bipolar stimulation during SEEG, 20 presented initial motor semiology (elementary motor signs, complex motor behavior, or both). Two patterns occurred: long latency onset (7/20), where semiology occurred after the stimulation train, following visible cortical epileptic discharge similarly to spontaneous seizures; and short latency onset (13/20), in which typical semiological expression occurred during the stimulation train, preceding typical cortical discharge.

This novel observation shows that in some conditions, seizures with habitual motor semiology could be triggered early during stimulation, before typical cortical epileptic discharge became visible. The earliness of clinical onset with regard to visible cortical discharge, notably in comparison with clinically similar spontaneous seizures, suggests differences in electrophysiological mechanisms that require further investigation. These may involve preferential involvement of descending corticosubcortical connections within the same epileptogenic network for a given patient.