Abstracts

Rationale: Felbamate is an inhibitor of glutamate receptor of NMDA type and a very effective anticonvulsant for intractable complex partial seizure. It is estimated that approximately 70,000 patients have had it prescribed for seizure control. However, there is no previous report of chronic felbamate effect on electroencephalogram. Relation between AED withdrawal and high-frequency activity was suggested by some studies, but clinical implication of an individual drug has not been discussed. Knowing that scalp EEG may detect high-frequency oscillation (HFO) during sleep state in the frequency range up to 140 Hz (Kobayashi, Epilepsia 2010), this presentation speculates three steady seizure-free cases of chronic felbamate therapy that demonstrated findings of enhanced high-frequency oscillation in scalp EEG. Methods: Three patients (patient #1, #2, and #3) were referred to the Bronson Epilepsy Outpatient Clinic with a history of intractable complex partial seizure disorder but seizure free for more than 10 years by established felbamate monotherapy, and had recent EEG studies with hope of drug termination. These EEGs were routine 10-20 system scalp recording in awake and sleep state with a sampling frequency of 1000 Hz using Nicolet system. Results: A common feature of the EEGs, of the three seizure-free patients with felbamate, was sustained gamma ripple with bilateral frontotemporal distribution during the sleep state. The patient #1: 27 year old man with history of hydrocephalus and shunt placement in the right hemisphere. He has been on felbamate (2800 mg/day) since it was released in 1994. EEG showed 80-150 Hz bi-frontotemporal ripple sustained during sleep state. The patient #2: 41 year old man with history of intractable seizure, treated with felbamate (400mg bid) for 12 years and no seizure in the past 10 years. EEG showed intermittent 125-150 Hz bilateral frontotemporal ripple with left side preponderance. Interictal discharges were seen in the right posterior temporal lead. The patient #3: 56 year old man with frontal lobe seizure originating from the right frontal neocortex with felbamate (600 mg bid). EEG showed 80-100 Hz bilateral frontotemporal ripples. Conclusions: Scalp recording has limitation of recordable frequency range up to 140 Hz as ripple. Enhanced bilateral frontotemporal high-frequency ripples were the common finding in the sleep state EEGs of these three patients who have received steady dose of felbamate and had seizure-free state. The distribution of these ripples was bilateral frontotemporal regardless of lateralization of a primary epileptogenic focus. The findings may suggest that chronic use of felbamate maintains high-frequency oscillation (HFO) in the frontotemporal neocortex. In previous studies (Staba, et.al., 2007), it was suggested that high frequency ripple discharges may represent protective activity of the synchronous GABA inhibitory mechanism. Felbamate inhibitory mechanism may have parallel features of chronic NMDA receptor inhibition and GABA receptor accentuation. The limitation of the study is small number of seizure-free steady state cases by felbamate.