Abstracts

Rationale: High frequency oscillations (HFOs) on EEG are a biomarker of the epileptogenesis. The detection of epileptogenic HFOs, however, has been often recorded by intracranial electrodes. Kobayashi et al., reported HFOs on scalp EEGs in infantile spasm patients and Yamazaki et al., found fast activities in young children with hemimegarencephaly. We recorded ictal HFOs on scalp EEG in patients with periodic spasms (PSs), who underwent epilepsy surgery to analyze the epileptogenicity of the ictal HFO during PSs. Methods: We studied three patients with PSs. All three patients underwent preoperative MRI, Magnetoencephalography (MEG), and scalp video-EEG using sampling rate of 1000Hz. We performed multiple band frequency analysis (MBFA) to analyze frequency and power of ictal HFOs.Results: Case 1: Two month-old boy presented with PSs from the birth. MRI showed cortical dysplasia in left perisylvian region. Interictal EEG showed diffuse spikes or polyspike bursts followed by attenuation. MBFA showed ictal 70-80 Hz HFOs around left centro-temporo-parietal regions consistently at 200-400ms before each spasm. The spasms completely disappeared after the focal resection. Pathology was reported cortical dysplasia type 2a. Case 2: Four month-old girl presented with PSs from one month of age, secondary to tuberous sclerosis complex with TSC1 gene mutation. MRI showed right frontal cortical tuber and calcification on the left parietal lobe. Interictal EEG showed diffuse spikes or polyspike and slow waves with right hemispheric predominance. MEG showed a cluster of spike dipoles in the right fronto-temporal lobe around cortical tuber. MBFA detected ictal 70-90 Hz HFOs over the right centro-parieto-occipital regions. Although PSs disappeared after the resection of the right frontal tuber, brief tonic seizures appeared. Postoperative EEG showed interictal spikes in right centro-parietal and left temporal regions independently. MEG showed diffuse spike dipoles over bilateral temporo-parietal resions. Case 3: Five month-old girl presented with PSs from two months of age. MRI showed slightly high signal intensity in the left parieto-occipital cortex. MEG showed diffuse spike dipoles over the bilateral temporo-parieto-occipital regions. Interictal EEG showed continuous spike and waves over bilateral occipital regions, without hypsarrhythmia. MBFA showed ictal 80-100Hz HFOs over the left temporo-occipital regions. Corpus callosotomy was performed for lateralization of epileptogenic hemisphere. The interictal spikes remained over the left temporo-occipital regions on EEG and MEG. Her PSs remained postoperatively but disappeared after adjunct valproic acid at one month follow-up. Conclusions: We captured ictal HFOs during PSs in three infants with malformations of cortical development. The resection of the lesion including the area of HFOs stopped PSs in one patient. The incomplete resection of area of ictal HFOs in the other 2 patients remained seizures. The area of ictal HFOs on scalp EEG during PS represented the epileptogenic zone in infants to be resected for control of PSs.