Authors :
Presenting Author: Erafat Rehim, MD – Emory University
Michelle Calmet, MD – University of Pittsburgh Medical Center
Golbarg Saber, MD – University of Pittsburgh Medical Center
Thandar Aung, MD,MS – University of Pittsburgh Medical School
Jorge González-Martínez, MD,PhD – University of Pittsburgh Medical School
Alexandra Urban, MD – University of Pittsburgh Medical Center
Rationale:
The implantation effect (IE) refers to a transient reduction in seizure frequency following implantation of neuromodulation devices, as observed in the sham group of neuromodulation trials. The clinical significance of IE remains unexplored. This study examines whether the presence and duration of IE in patients undergoing responsive neurostimulation (RNS) predicts long-term seizure outcome.
Methods:
We conducted a retrospective study of patients who underwent RNS implantation at our center between 2015 and 2024. Clinical, surgical and seizure outcome data were extracted from medical records. IE was defined as a spontaneous ≥50% seizure reduction following device implantation but prior to stimulation activation. The duration of IE was calculated from the implant date to the first programmed stimulation date. One-year seizure outcomes were classified using Engel classification (EC), dichotomized into favorable (EC I and II) and unfavorable (EC III and IV) outcomes.
Results:
A total of 61 patients were included. The median age at implantation was 36 years (IQR 28.0 – 44.0); 62% were women. Most had focal epilepsy (75.4%), a minority had generalized epilepsy (18.0%), and 4 patients had mixed generalized and focal epilepsy (6.6%). Ten patients had previous resective surgery, and 15 patients had current or prior vagal nerve stimulation. The median epilepsy duration was 17.0 years (IQR 12.0 – 29.0), and patients had tried a median of 5 antiseizure medications (IQR 4.0–7.0) before RNS implantation. Cortical leads were implanted in 38 patients (62.3%), bilateral thalamic leads in 21 (34.4%), and corticosubcortical leads in 2 (3.3%).
Seventeen patients (27.9%) experienced IE[Table 1]. At one-year follow-up, 13 patients (21.3%) achieved a favorable outcome, of whom 10 were in the IE group. IE was associated with significantly greater odds of favorable outcome (OR 19.52, 95% CI 4.27–89.17, p < 0.001), particularly when IE lasted longer than 3 months (OR 26.83, 95% CI 4.49 – 160.24, p < 0.001). Among the 21 patients with bilateral thalamic implants, 6 (27.3%) experienced IE, and 4 achieved favorable outcome at 1 year. In this subgroup, IE was also significantly associated with favorable outcome (OR 13.00, 95% CI 1.36–124.30, p = 0.031), and all patients (n = 4) with IE > 3 months achieved favorable outcome in this subgroup.
Conclusions:
A small but measurable portion of patients demonstrated IE following RNS implantation. Despite the limited sample size, IE was significantly associated with seizure freedom or near seizure freedom at one year, especially when the effect persisted beyond 3 months. Recognizing IE may help identify potential super-responders to RNS therapy. These findings warrants further investigation in larger cohorts.
Funding: None