Abstracts

Rationale: Sleep-related hypermotor epilepsy (SHE), formerly known as nocturnal frontal lobe epilepsy, is characterized by seizures of frontal lobe semiology occurring predominantly during sleep. However, the seizure onset zone (SOZ) in SHE is not always a frontal one. Our objectives were to contrast the clinical and electrophysiological features of frontal onset SHE with those of extra-frontal SHE and search for particular features in each subgroup that could increase diagnostic accuracy. Methods: From a database of 1433 patients who underwent epilepsy surgery in our center from October 1997 to July 2015, we identified 135 consecutive patients with a diagnosis of video-EEG documented SHE. All had a known post-operative histopathological etiology and a post-operative follow-up of at least 12 months. Based on SOZ, each patient was categorized as frontal, temporal, operculo-insular or posterior onset SHE. We then compared clinical characteristics and seizure semiology patterns between subgroups.  In patients with both stereo-EEG recordings and an Engel class I outcome, we also reviewed and compared seizure characteristics. Results: Of the 135 patients with SHE, 44 had an extra-frontal SOZ (33%). Seizure frequency was high in all groups with 64% experiencing daily seizures and 90% having at least one seizure per week. Other shared features included similar rates of MRI-identifiable lesion (64% vs. 68%), video-EEG abnormalities (79% vs. 89%) and etiology, focal cortical dysplasia type II being the most common (67%). Seizure semiology in frontal SHE followed a rostro-caudal distribution with an anterior SOZ producing more complex behavioral manifestations while a posterior frontal SOZ generated more elementary or unnatural hypermotor features. In temporal SHE, seizures were more likely to resemble anterior frontal semiology while operculo-insular and posterior SHE tended to resemble posterior frontal lobe features (p = 0.01). Epileptic auras were present in 70% of patients and some auras, i.e. cephalic, auditory, visual and painful somatosensory, had a useful localizing value. Temporal SHE presented a higher rate of post-ictal confusion compared to other groups (67% vs. 13-26%, p = 0.001). Seizure duration, both clinically and electrographically, were significantly shorter in frontal SHE (p < 0.001). Moreover, the time-lapse between the first video-detectable movement, usually an awakening, and the start of hypermotor semiology was very short in frontal compared to extra-frontal SHE (1.95 sec ± 2.20 vs. 11.29 ± 8.55, p < 0.001). Finally, the groups of frontal and temporal SHE achieved the best two-year post-operative outcome (Engel I in 84% and 92%, respectively). Conclusions: Our series confirm that frontal and extra-frontal SHE share many features and can thus be considered part of the same syndrome. Certain clinical features in SHE such as the type of hypermotor manifestations, auras, post-ictal confusion and seizure length can be helpful in distinguishing a frontal from an extra-frontal SOZ, even in MRI-negative cases. Funding: Fonds de Recherche du Québec en Santé - Research fellowship grant