Does stereoelectroencephalographic depth electrode insertion alter seizure frequency? A baseline versus endpoint...

The implantation effect refers to a transient reduction in seizure frequency following intracranial electrode insertion in patients with epilepsy, independent of therapeutic intervention. This retrospective study examined potential clinical and demographic predictors of the implantation effect in 51 patients who underwent stereoelectroencephalographic investigation between December 2018 and February 2020. Follow-up data were collected at 1, 3, 6, and 12 months postimplantation. A ≥50% reduction in seizure frequency defined responder status. Responder rates were 71.4% at 1 month, 35.0% at 3 months, 33.3% at 6 months, and 50.0% at 12 months. Complete seizure freedom was observed in 42.9% of patients at 1 month and 20.0% at 3 months. No significant associations were found between seizure reduction and age, sex, imaging findings, cortical stimulation, electrode count, or preimplantation antiseizure medication type or load. The lack of predictive variables, alongside seizure reduction in patients with previously uncontrolled epilepsy, supports the hypothesis that electrode-induced microlesions may transiently disrupt epileptogenic networks. The quantity of electrodes did not influence outcomes, suggesting that implantation location may be more important. The effects of antiseizure medications remain unclear due to limited tracking of dosage or regimen changes. Further prospective research is needed to clarify the mechanisms underlying the implantation effect.