In the present study with a large cohort, we aimed to characterize intracerebral seizure onset patterns (SOP) of mesial temporal lobe epilepsy (mTLE), with or without hippocampal sclerosis (HS) as identified via magnetic resonance imaging (MRI).

We retrospectively analyzed 255 seizures of 76 consecutive patients with mTLE explored by stereoelectroencephalography (SEEG), including HS-mTLE (n = 52) and non-HS- mTLE (n = 24). Relevant results were obtained by a combination of spectral analysis and manual review. High-frequency oscillations (HFO) were quantified across different SOP by an automatic detection method.

We identified six SOP according to previous work by Lagarde et al.: (1) Low-voltage fast activity (LVFA); (2) Rhythmic spikes followed by LVFA; (3) Burst of spikes followed by LVFA; (4) Periodic spikes or spike-wave followed by LVFA; (5) Rhythmic spike or spike-wave; (6) Theta or alpha sharp activity. Notably, Periodic spikes or spike-wave followed by LVFA had a high prevalence in all seizures (37 %). A significant association was established between Periodic spike followed by LVFA and HS-mTLE (  < 0.05). Furthermore, the counts of ripples and fast ripples were significantly higher in SOP displaying LVFA compared to those that did not (P < 0.05). Rhythmic spikes followed by LVFA had the best prognosis (92 % seizure-free), while Burst of spikes followed by LVFA were linked to poorest prognosis (67 % SF).

HS-mTLE and non-HS-mTLE exhibit distinct SOP characteristics, which can offer valuable prognostic insights with a more informative interpretation of ictal iEEG for clinical guidance.