ИСТИНА

Purpose The study was focused on MEG high frequency oscillation (>50 Hz) (HFO) occurring before clinical manifestation of seizure. Methods Three 18-year-old patients (MV, OA, PM) with drug resistant epilepsy due to right parietal lesion (OA), right temporal lesion (PM), or unknown cause (MV) underwent MEG presurgical work-up. Two patients had resective epilepsy surgery with good outcomes (Engel class Ia, OA; IIb, MV). OA and MV had one typical seizure and PM had three seizures during MEG session. We analyzed MEG signals from 204 planar gradiometers during 10s period preceding seizure onset pattern and increase of electromyogram signal. Complex Morlet wavelets and envelope of signal absolute amplitude within 55-95Hz frequency band obtained after Hilbert transformation were used. Results Both wavelet and Hilbert transform analysis showed an abrupt increase of HFO (60-95Hz) several seconds before alpha-beta ictal onset pattern in two patients. In patient PM the rise of HFO repeatedly occurred during electrodecremental pattern, which characterized ictal onset in three seizures observed during MEG session. In all patients the sensors that detected pre-ictal HFO increase also registered ictal alpha-beta onset pattern and/or the major proportions of interictal epileptiform activity. In OA and MV the respective brain areas were defined as ictal onset zones and removed during the surgery. Conclusion MEG is able to detect high frequency oscillations that characterize the ictal onset zone activity initiating seizure. Given that pre-ictal HFO were unnoticeable during a routine MEG assessment, time-frequency analysis of MEG during seizure onset may be a helpful addition to a routine clinical MEG.