Abstracts

Rationale: 35% of referral to EMU in Level 3/4 Epilepsy Center is believed non-epileptic seizure (NES). Ruling out NES from medically intractable seizure is important task in EMU. One of the traditional criteria to diagnose of NES is absence of seizure activity during ictal event in Video-EEG monitoring study. The diagnostic acuracy by this criteria may not be assertained because of low resolution of 10-20 system. Inter-electrode distance in 10-20 system is 7 to 8 cm. Dense array EEG (dEEG) recording with 128 electrodes has only 2.2 cm in average inter-electrode distance. If an epileptogenic generater falls in between the large gap, it may not be detected. It is our clinical concern that some of patients may not be identified as epileptic due to the vast wide inter-electrode distance in 10-20 system, and therefore utilization of dEEG may overcome the weakness.Methods: This is a clinical presentation of 3 cases in the Veterans Administrations Hospital. These 3 cases were identified as they had history of episodic alteration of consciousness but had no clinical history of epileptic syndrome. They underwent 128 channel dEEG recoridng using a cap system. The EEG record was interchangable between 10-20 system montage and 128 channel recording montage at the review station.Results: Case 1 is a 61 year old veteran who experienced intermittent episodes of psychosis. He previously did not have an abnormal EEG. However, with the dEEG it demonstrated 4 seconds long of beta range electrographic seizure with frequency-amplitude evolution preceded by clear infra-slow delta negativity (See the attached figure) maximum at electrode #84. Electrical field extension was noted to #85, 86, and 105, but it totally escaped detection in 10-20 system. Case 2 was a old Alzheimer veteran having episodic unresponsiveness. dEEG showed sustained rhythmic epileptic beta at electrode #56 next to T3. Case 3 was a veteran who has recurrence of episodic confusion, but previous 10-20 system EEG recordings were all normal. The diagnosis of epileptic syndrome was not done. dEEG Clearly demonstrated 3Hz rhythmic sharp discharges at electrode #18 which is immediate posteromedial to Fp1 electrode. It escaped from detection in 10-20 system.Conclusions: dEEG has been able to identify an electrographic seizure out of the coverage of 10-20 system for patients who believed to be NES. dEEG procedure may potentialy reidentify epilepsy patient out of intractable psychogenic seizures. The limitation of the study is this is not a prospective study and patient population is not unbiased. Nevertheless, dEEG demonstrated superior spacial resolution by shorter inter-electrode distance in detecting electorgraphic seizures in a smaller cortical area. It is expected that denser channel dEEG and even MEG could demonstrate similar findings. Further study is planned in less biased populations.