Sleep related epilepsy in focal cortical dysplasia type 2: Insights from sleep recordings in presurgical evaluation

ObjectiveTo determine the relationship between seizure onset, sleep stage and focal cortical dysplasia type 2 (FCD2) location in sleep related epilepsy (SRE).MethodsWe reviewed scalp video-EEG data of 77 patients with SRE among 130 surgically treated patients with histologically confirmed FCD2. Seizure onset was classified as occurring during NREM, REM and after arousal.ResultsSleep recordings were available for 65 patients (37 males, 7–49 years old). FCD2 was located in frontal lobe in 46 (71%) and in extra-frontal regions in 19, including the temporal lobe in 6. MRI was negative/doubtful in 35 cases. Interictal rhythmic/pseudorhythmic spike rate increased from 31% during waking to 65% during sleep. Seizure onset occurred from NREM in 46 cases (71%), mostly from stage 2, and after arousal in 14 (22%). Seizures occurring from NREM/REM sleep were significantly more frequent in frontal (89%) compared to extra-frontal location (42%), whilst arousal preceded seizure onset more often in extra-frontal (58%) compared to frontal location (7%).ConclusionsNREM seizure onset is the most common ictal pattern in SRE due to frontal FCD2 whereas preceding arousal points to extra-frontal regions.SignificanceSleep recordings may help for FCD2 localisation and suggest topography dependent impact on sleep related epileptic networks.