Long-term prognostic value of early post-operative electroencephalogram in patients with drug-resistant temporal lobe epilepsy associated with hippocampal sclerosis.
PURPOSE Surgery is the treatment of choice for drug-resistant temporal lobe epilepsy (TLE) associated with hippocampal sclerosis (HS). We assessed whether interictal epileptiform discharges (IEDs) on early postoperative EEG predicted seizure outcome after surgery. METHODS We retrospectively included consecutive patients aged >16 years who underwent surgery for drug-resistant TLE with pathologically confirmed HS at Pitié-Salpêtrière Hospital, Paris, between 2003 and 2023. Eligible patients had at least 1 year of follow-up and an early postoperative EEG performed within 1 month after surgery. IED frequency was classified as high frequency (≥1/min) or low frequency (<1/min). Favourable 1-year outcome was defined as ILAE class 1. Long-term worsening was defined as any increase in ILAE class after the 1-year visit. RESULTS Among 168 patients, 131 (78.0%) were ILAE class 1 at 1 year. EEG was performed a median of 7 days after surgery. IEDs were present in 81 patients (48.2%), including 48 with low-frequency and 33 with high-frequency IEDs. EEG features, including IED presence and frequency, did not differ between patients with and without ILAE class 1 outcome at 1 year. During longer follow-up, high-frequency IEDs were associated with worsening compared with no IEDs in the whole cohort (HR 2.25, 95% CI 1.01-4.98; p=0.046) and among patients seizure-free at 1 year (HR 2.59, 95% CI 1.10-6.11; p=0.03). Low-frequency IEDs were not associated with worsening. CONCLUSION High-frequency IEDs on early postoperative EEG may identify patients at increased risk of long-term deterioration after surgery for HS-related TLE. Prospective studies are needed before modifying routine follow-up strategies.