LAUSR

Introduction Dense array EEG (dEEG) covers entire scalp surface by 128 or 256 leads, with shorter inter-electrode distance, making a better spatial resolution. It has been utilized only in selected cases for intractable seizure and a part of the presurgical evaluation. It is time-consuming to analyze EEG because of exceeding number of channels beyond the space of LCD monitor. There was no study that dEEG was applied for routine outpatient EEG evaluation. This result may be compared with routine outpatient EEG by 10–20 recording. Methods We utilized dense array EEG system (dEEG) for patients visiting neurology clinic for mental status change in recent past 2 years. Electrodes were applied by the cap system. EEG was recorded using high-impedance DC amplification system by EGI (Eugene, OR, USA), 128 channels with a sampling frequency of 1000 Hz. We developed “double-banana” based convenient montage so that all relevant leads information can be seen by one monitor size without moving the EEG images up and down, that enabled us to review a large number of dEEG quickly. A recording sensitivity was 7 uV/mm, HFF 120 Hz, LFF 1.0 Hz. Recording duration was 30 min for all the patients. Results 788 dEEG recordings were accumulated in our outpatient clinic. Among them, diffuse background slowing was seen in 117 cases (14.8%), focal slowing in 197 (25%), interictal epileptiform discharges were seen in 285 (36.1%). Among the IID cases, 157 (55.1% of IID cases: 19.9% of total) were electrographic seizure pattern. Moreover, scalp permeating HFO (frequency 50–120 Hz) were seen in 46 (5.8%) Infra-slow delta (Defined as frequency Conclusion 128 channel dEEG is sufficiently increased the special resolution and higher yield of inter-ictal abnormalities including IID and focal slowing. Moreover, it would increase the detecting yield of focal abnormalities, i.e., electrographic rhythmic pattern, Infra-slow delta activities, and scalp permeating HFO. Routine outpatient utilization of dEEG may potentially be more efficient in detection of abnormality than routine 10–20 system recording.