Semiology in spontaneous versus cortical stimulation-induced seizures during SEEG: A within-patient comparison study

We aimed to study the concordance of seizure semiology in direct electrical stimulation-induced seizures (SIS) compared to spontaneous seizures during stereoelectroencephalography (SEEG) and to report on patient-level variables associated with habitual and atypical SIS.

We retrospectively studied consecutive SEEG cases, performing a within-patient comparison of semiology in spontaneous seizures versus SIS. We classified each patient's SIS as "habitual" or "atypical" using a new electroclinical definition. We then classified patients by maximum clinical expression of habitual SIS: "Aura," "Fragment" (objective fragment ± aura), or "Full." Patient groups with/without SIS and with/without atypical seizures were analyzed regarding demographics, clinical and SEEG characteristics. Reported patient-level variables were categorically expressed as percentages or continuous.

Of the 67 patients undergoing SEEG, all underwent 50 Hz stimulation. Prevalence of patients with SIS was 48/67 (71.6%); most patients had 1-2 SIS. Of 97 SIS, 91/97 (93.8%) were semiologically concordant with habitual spontaneous seizures. Patients' maximum clinical expression of habitual SIS was "Aura" in 14/47 (25.5%), "Fragment" in 16/47 (38.3%), and "Full" in 17/47 (36.2%). Patients presenting any atypical SIS (5/67) accounted for 7.5%; only 1 patient had atypical SIS as the sole SIS. Patients presenting atypical SIS had a tendency to a more widespread epileptogenic zone (EZ) (>1 lobe); none proceeded to surgery following SEEG. There was also a tendency toward female predominance. Rarely, patients with habitual SIS could report "old" habitual semiology triggered during stimulation.

This within-patient comparison of semiology of spontaneous versus cortical stimulation-induced seizures (SIS), with semiologic stratification and a proposed electroclinical definition of atypical SIS, shows overall high semiologic concordance and a fairly low proportion (7.5%) of patients presenting atypical SIS at 50 Hz. Atypical seizures may occur in conditions where there is an altered stimulation threshold. No correlation was seen between dominant SIS semiologic subtype and surgical outcome.

This study reports on semiology (clinical symptoms and signs of seizures) in people with epilepsy undergoing in-depth brain exploration for presurgical evaluation. It compares the semiology in seizures occurring spontaneously with the semiology in seizures triggered by direct cortical stimulation. Semiologic similarity was high between spontaneous and stimulation-induced seizures. Atypical seizures triggered by stimulation were fairly rare. Atypical seizures may occur in conditions of altered stimulation threshold. Some patients experienced past seizure semiology reactivated by cortical stimulation.