Abstracts

Rationale: Ictal-interictal continuum (IIC) patterns include periodic discharges and rhythmic delta activity, which represent hyperexcitable state of brain. Previous studies demonstrated metabolic derangement during this state using cerebral microdialysis. Since these are invasive procedures which cannot be done in all patients with IIC, we tried to demonstrate the metabolic derangement using the near-infrared spectroscopy (NIRS), which is a tool that can monitor brain oxygenation and hemodynamic state along with electroencephalography (EEG). There have been a number of studies that have analyzed EEG-NIRS on ictal discharge, but there are no studies in IIC. The purpose of this study is basically to test the feasibility of simultaneous EEG-NIRS long-term monitoring and to analyze changes in EEG-NIRS in periodic discharge or rhythmic discharge seen in patients with intractable epilepsy and status epilepticus (SE). Methods: We recruited patients with intractable epilepsy and SE who were evaluated with continuous 24-channel scalp EEG and synchronized NIRS. NIRS data were measured on 10 Hz sample rate and the distances between light sources and receivers are under 5cm. We tested whether the synchronization between two machines was acceptable and performed a visual analysis of EEG-NIRS waveforms while the periodic or rhythmic epileptiform discharge is presenting in the EEG. Epileptiform discharges for visual analysis were chosen when stable EEG was seen for 10 seconds before and after the epileptiform dischage. For comparison, we also selected stable segements without epileptiform discharge in the EEG of the same patient. Visual analysis was evaluated as positive when oxyhemoglobin (O2Hb), deoxyhemoglobin (HHb) and/or total hemoglobin (THb) were changed in NIRS and visual analysis was conducted by three epileptologists with blinded method. Results: Five patients, three with intractable seizure and two with status epilepticus, have successfully undergone multi-channel EEG-NIRS for up to 5 hours. The time error between EEG and NIRS was within 50ms/hr. We corrected this time error for further visual analyses. NIRS in all patients showed clear O2Hb pulsation which indicates a proper measurement of NIRS in our study. In two patients, one with intractable epilepsy due to Lennox-Gastaut syndrome and one with status epilepticus due to tuberculosis meningitis, generalized periodic discharges were observed and a visual analysis of EEG-NIRS was performed for a total of thirty segments including periodic discharges. Thirty segments of the comparative group were selected for each patient. Changes in NIRS were observed in 19 cases (63.3%) with periodic discharge, but no change in NIRS was observed in the comparative group. The main change was observed in O2Hb which increased during the period of periodic discharge. Conclusions: We demonstrated the feasibility of simultaneous EEG-NIRS monitoring in patients with intractable epilepsy and status epilepticus. We also revealed that NIRS changes significantly with periodic discharge in the EEG. Further studies are needed to characterize the hemodynamic responses of various types of epileptiform discharges in more patients. Funding: No funding