In this retrospective study, prolonged video-EEG monitoring records of consecutive patients of medically refractory focal epilepsy, were reviewed and analysed. Those with  psychogenic events, generalized epilepsy and those with unidentifiable single epileptiform focus, were excluded. Based on clinical, video-EEG and neuroimaging data, all included patients were categorized into temporal lobe epilepsy (TLE) and extratemporal lobe epilepsy (ETLE) groups. Sleep scoring was carried out for studies in which sleep related seizures were recorded with precision to arousal, and onset of ictal rhythms.

A total of 1282 seizures were analyzed from studies of 171 patients. Among these, 331 were sleep related seizures in a subset of 89 patients (58 males, median age 21 [range 18-52]), with 68 in the TLE group and 21 in the ETLE group. We found a significantly higher percentage of sleep seizures in the ETLE group [32 out of 46 (69.5%)] to be preceded by an arousal, compared to 87 out of 225 seizures (38%) in the TLE group (p<0.001). However, the arousal-ictal -EEG-onset interval was significantly lower (mean 9 + 17 seconds) in the ETLE group, than in the TLE group (mean 27 + 28 seconds).

Majority of focal onset sleep related seizures are preceded by arousals, more so in patients with extratemporal lobe epilepsy. The implications of these findings in terms of interaction between arousal mechanisms, sleep and epileptic networks are discussed.