Abstracts

Rationale: Hemimegalencephaly is well known to be epileptic encephalopathy from neonates in most of cases. In neonatal EEGs, interictal epileptiform discharges of spike and slow waves are rarely noticed. Ictal fast oscillations (FOs) are recognized on intracranial video EEG and during epileptic spasms on scalp EEG. Our aims of this study are to analyze epileptogenic FO and patterns of interictal epileptiform discharges in neonates and infants with hemimegalencephaly. Methods: We collected seven patients with total hemimegalencephaly (5) and partial hemimegalencephaly (2). We retrospectively analyzed EEGs (sampling rate 200Hz or 500Hz) between 3 days and 23 months of age before surgery. We applied multiple band frequency analysis (MBFA) to analyze maximum frequency and power of FO (3-60Hz for 200Hz sampling, 3-150Hz for 500Hz sampling) in selected interictal periods.Results: Maximum interictal FO ranged between 20 and 55Hz in seven patients with suppression-burst (55Hz at 3 day old, 32Hz at 8 week, 53Hz at 8 week), continuous high amplitude slow waves with spikes (36Hz at 3 day old), and frequent high amplitude spike and slow waves (20Hz 11 week old, 34Hz at 4 month, 33Hz at 5 month) over the hemimegalencephaly side. Four patients had consecutive EEG recordings before surgery (11 week old – 35 month old). Interictal EEG expression changed from suppression-burst to continuous spike and slow waves in two patients, the opposite way in two patients. Slow wave components of epileptiform discharges became high amplitude and long duration in both burst and continuous discharge along with aging. The interictal FO superimposed with burst or spikes did not change from the initial recorded frequency in all four patients.Conclusions: We confirmed interictal epileptogenic FO in neonatal and infantile EEGs of patients with hemimegalencephaly. The EEG expressions altered during maturation and course, however, interictal FO established from the beginning and remained similar range within the different interictal discharges until infants. The rising slow waves of the epileptiform discharges in infants with hemimegalencephaly might indicate the development of inhibitory function.