EP 113. Increased coherence to the midline in interictal EEG predicts generalized seizures in focal epilepsy

• Published in: Clinical neurophysiology 2016-09, Vol.127 (9), p.e288-e289
• Main Authors: Ernst, K, Hartl, E, Goc, J, Noachtar, S, Vollmar, C
• Format: Article
• Language: English
• Subjects: Neurology
• ISSN: 1388-2457; 1872-8952
• DOI: 10.1016/j.clinph.2016.05.156

Background Presurgical evaluation of patients with focal epilepsy relies strongly on EEG. Usually, interictal EEG is analyzed for spikes and regional slowing, providing localizing information, and ictal EEG allows to localize electrical activity during a seizure, including seizure onset and secondary propagation. EEG coherence analyses allow to make inferences on the synchronization between different brain regions, but are rarely used in epilepsy. Here we evaluate the clinical value of interictal EEG coherence analyses to contribute clinically relevant information during the presurgical evaluation of epilepsy patients. Methods Nineteen patients with focal epilepsy were included in this study. To avoid effects from major structural lesions on the EEG, we included only patients with no structural lesion ( n = 10) or small lesions, less than 2 cm diameter ( n = 9). All patients had continuous video EEG monitoring for 5–12 days, where 40 channel EEG was recorded with a sampling rate of 512 Hz. We have selected 5 epochs of awake, artifact free, interictal EEG, with a duration of 4–10 min for each patient. EEG coherence was analyzed using Matlab and fieldtrip software. Coherence was calculated between all possible pairs of electrodes, for five different frequency bands. Coherence values between neighboring pairs of electrodes were averaged for a total of 17 anatomical brain regions (7 left, 7 right, 3 midline) and were analyzed for asymmetries between the left and right hemisphere. Coherence data was correlated with clinical information from the video EEG monitoring. Results Regional coherence changes were seen in 17 of 19 patients (89%). Two different patterns were observed: In 10 patients (53%) we saw an increased coherence between the epileptogenic region and the midline regions, and 7 of these 10 showed a reduced coherence within the hemisphere ipsilateral to the epileptogenic zone. In the other 7 patients (37%) there was increased coherence within the epileptogenic hemisphere and 5 of these 7 showed decreased coherence between the epileptogenic region and the midline regions. Nine of the 10 patients with increased coherence between the epileptogenic region and the midline regions had clinical signs of fast propagation, such as predominant bilateral seizure pattern in EEG, or frequent and fast clinical evolution to generalized tonic clonic seizures. On the other hand, none of the patients with decreased coherence to the midline had contralateral spikes, bila