Combining three-phase EEG pattern and ipsilateral isolated eye deviation to predict seizure focus in the frontal interhemispheric fissure

Objective

Identification of seizure focus on the interhemispheric fissure (IHF) is often challenging at the step of scalp video-EEG monitoring on preoperative evaluations. We previously reported ictal three-phase EEG patterns (3Ph-EEG) and isolated eye deviation (isolated ED) to side of the seizure focus during seizures, each of which is available for identifying the seizure focus for frontal IHF (F-IHF). This study aimed to evaluate the accuracy of predicting the F-IHF focus using a combination of 3Ph-EEG and isolated ED in patients with frontal lobe epilepsy and the accuracy of predicting lateralization of the F-IHF focus using the predominance of findings.

Methods

We collected 15 patients diagnosed with frontal lobe epilepsy showing clinical seizures arising only from the frontal lobe, from 131 patients with intracranial video-EEG performed between January 2012 and December 2019. All 15 patients were classified into the IHF group (n = 7) and the extra-IHF group (n = 8) based on intracranial video-EEG. We statistically evaluated the accuracies of predicting F-IHF onset using combinations of 3Ph-EEG and isolated ED on scalp-EEG: 1) 3Ph-EEG (+); 2) isolated ED (+); 3) 3Ph-EEG (+) and/or isolated ED (+); and 4) 3Ph-EEG (+) and isolated ED (+). We also evaluated the accuracy of predicting focus lateralization using 3Ph-EEG and isolated ED.

Results

Both 3Ph-EEG (+) and isolated ED (+) demonstrated good accuracy for identifying F-IHF foci. They showed identical sensitivities of 71.4 %, with odds ratios of 7.5 for 3Ph-EEG (+) and 17.5 for isolated ED (+), respectively. Only the combination of 3Ph-EEG (+) and/or isolated ED (+) showed significant associations (p = 0.007). This combination demonstrated the highest sensitivity (100 %) and modified odds ratio (39.0), indicating that all patients in the IHF group exhibited at least one of the following: 3Ph-EEG or isolated ED. The combination of 3Ph-EEG (+) and isolated ED (+) offered one of the highest specificities, at 87.5 %. To predict lateralization with the F-IHF focus, both the predominant side for the third phase of 3Ph-EEG (n = 5) and the direction of isolated ED (n = 5) were perfectly concordant with the F-IHF focus side (100 % for both).

Conclusion

The combination of 3Ph-EEG and isolated ED can detect the IHF seizure focus with higher sensitivity in patients with frontal lobe epilepsy compared with using each method individually. Moreover, the absence of these two features eliminated the possibility of an F-IHF focus. Based on 3Ph-EEG and the direction of isolated ED, the focus side could presume lateralization of the F-IHF focus. Combining 3Ph-EEG and ipsilateral isolated ED at presurgical evaluation may help in designating locations for intracranial EEG electrodes.