Pitfalls in Reading EEG for Temporal Lobe Epilepsy: The "Southern-hemisphere" Spike and Normal Variants Masaya Togo 1,2 , Kohei Morimoto 1 , Riki Matsumoto 1 1Division of Neurology, Kobe University Graduate School of Medicine 2Department of Neurology, Graduate School of Medicine Kyoto University Keyword: 単極導出法 , 双極導出法 , 平均電位基準法 , 発作時心静止 , referential montage , bipolar montage , average montage , ictal asystole pp.425-436
Published Date 2020/4/1
DOI https://doi.org/10.11477/mf.1416201541
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Electroencephalogram (EEG) reading in clinical settings commonly uses three montage types: referential montage, bipolar montage, and average montage. Since each montage type has its advantages and disadvantages, there is no single best montage. To correctly read EEG, it is essential 1) to use the montage appropriate for the focus and distribution of epileptic activity and 2) to correctly recognize  EEG waveforms that are often misdiagnosed as epileptic activity. In this article, we present the so-called “southern-hemisphere” epileptic activity, which is recognized as challenging to diagnose, along with two cases of temporal lobe epilepsy. Case 1 exhibited seizures that started with palpitations and epigastric discomfort, followed by loss of awareness and oral automatisms. Case 2 experienced recurrent episodes of syncope and was diagnosed with temporal lobe epilepsy based on EEG findings and the observed improvement with anti-epileptic medication. In both cases, the longitudinal bipolar montage (“double-banana montage”) failed to visualize the epileptic activity, while the referential montages (ear lobe reference or average reference) clearly showed maximal activity at the earlobe electrode. Additionally, we present the normal variants of normal EEG waveforms that are often misdiagnosed as epileptic activity.

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