Magnetoencephalographic Analysis of Gelastic Seizures in a Patient with Tuberous Sclerosis

Abstract

Purpose: The ictal EEG and magnetoencephalogram (MEG) for gelastic seizures were recorded in a 4‐year‐old girl with tuberous sclerosis. The sites of origin for the seizure activities were investigated by using an equivalent current dipole (ECD) with the MEG. Methods: EEG and MEG were recorded simultaneously under the administration of diazepam (DZP). The MEG recording was performed on a system consisting of an array of 64 sensors uniformly distributed over the patient's whole head (CTF, Canada), and the estimated ECDs were superimposed on the magnetic resonance imaging (MRI) images (Siemens, 1.5 Tesla). Results: Two laughing attacks lasting 5 s each were documented. The ictal EEG showed gradually increasing 11–Hz rhythmic α activities with dominance over the frontocentral areas bilaterally, followed by irregular spike‐and‐wave discharges. The ictal MEG detected bilateral frontal rhythmic sharp waves before the appearance of the activities on the EEG. The estimated ECDs were localized in the deep white matter of the right frontal lobe on the MRI. However, those dipoles did not coincide with the locations of her cortical tubers. Conclusions: Although gelastic seizures accompanied with hypothalamic hamartomas are well known, several reports have suggested a temporal or frontal lobe origin for gelastic seizures. In this patient, the ECD indicated that the seizures originated in the frontal lobe, although ictal scalp EEG recordings could not determine the precise focus. Thus, in cases in which the use of ictal scalp EEG fails to show the sites of origin for the seizures, it is recommended that the origins be estimated by using the non‐invasive method of ictal MEG analysis.