Alkawadri R, et al. - A retrospective medical record review and prospective analysis of a novel ictal rhythm analysis method was conducted to examine the utility and reliability of ictal magnetoencephalography (MEG) in the localization of the epileptogenic zone. The findings from the present study suggested that ictal MEG data could provide reliable localization, even in cases that were difficult to localize via other modalities, and supported the use of extended-source localization for seizures recorded during MEG.

Methods

• From March 2008 to February 2012, this research was performed at a tertiary epilepsy center with a wide base of referrals for epilepsy surgery evaluation and included consecutive cases of patients who experienced epileptic seizures during routine MEG studies.
• An aggregate of 377 studies screened, and from November 2011 to October 2015, data were analyzed.
• Researchers reviewed presurgical workup and interictal and ictal MEG data.
• Finally, they analyzed the localizing value of using extended-source localization of a narrow band identified visually at onset.

Results

• Out of 44 enlisted subjects, the mean (SD) age at the time of recording was 19.3 (14.9) years, and 25 (57%) were male.
• In 3 patients, seizures were provoked by known triggers and were otherwise spontaneous.
• It was observed that 25 subjects (57%) had 1 seizure, 6 (14%) had 2, and 13 (30%) had 3 or more.
• Findings revealed that magnetoencephalography single equivalent current dipole analysis was possible in 29 subjects (66%), of whom 8 (28%) had no clear interictal discharges.
• Between ictal and interictal dipoles, sublobar concordance was seen in 18 of 21 subjects (86%).
• They discovered that 3 patients (7%) exhibited clear ictal MEG patterns without electroencephalography changes.
• They found that ictal MEG dipoles associated with the lobe of onset in 7 of 8 patients (88%) who underwent intracranial electroencephalography evaluations.
• Diffuse or poor dipolar ictal patterns, no MEG changes, and movement artifact were the included reasons for failure to identify ictal dipoles.
• Resection of areas containing a minimum-norm estimate of a narrow band at onset, not single equivalent current dipole, was correlated with sustained seizure freedom.