Avoid falling into the depths of the insular trap

Recent data have demonstrated that insular seizures can mimic those encountered in temporal lobe epilepsy (TLE), as well as nocturnal hypermotor attacks suggestive of nocturnal frontal lobe epilepsy (NFLE). To illustrate some of the issues raised by these observations, we report our first two patients with suspected TLE and NFLE, respectively, in whom we originally demonstrated an insular ictal onset zone. Patient 1 suffered from daytime seizures characterised by a rising and distressing epigastric sensation rapidly followed by oro-alimentary automatisms, associated with right temporal scalp-EEG ictal discharge. Neuroimaging showed consistent right temporal abnormalities, including MRI signs of hippocampal sclerosis, anterior and mesial glucose hypometabolism, and mesial decrease of benzodiazepine receptors. Intra-cerebral EEG investigation was primarily performed because of several ictal signs and symptoms suggesting a rapid involvement of the perisylvian region, and showed that the patient suffered two types of seizure, one of which arose from the mesial temporal structures, the other was sleep-related and originated in the posterior-inferior portion of the insula. Anterior temporal lobectomy failed to control this second type of seizure. Patient 2 suffered from brief, nocturnal, hypermotor seizures characterised by an indefinable aura followed by agitation, body rolling, scream and pelvic thrust. Interictal and ictal scalp-EEG failed to detect epileptiform discharges, whereas neuroimaging showed left mesial frontal, glucose hypometabolism and decreased benzodiazepine receptors associated with a left fronto-basal arachnoidal cyst. Invasive EEG monitoring was performed with the aim of identifying an orbital or mesial frontal ictal onset, but eventually demonstrated that the seizure originated in the anterior-superior portion of the left insula. The patient did not undergo surgery and died of SUDEP two years later. We discuss the heterogeneity of insular seizure semiology according to functional anatomy, the clinical signs and symptoms that might suggest an insular ictal onset, the indications and types of invasive EEG monitoring that are needed to identify an insular epileptogenic zone definitively, as well as potential surgical treatment.