The value of epileptogenicity index in operation of epilepsy post viral encephalitis

Abstract

Objective To explore application value of epileptogenicity index (EI) in operation of epilepsy post viral encephalitis (VE). Methods From January 2014 to August 2017, we retrospectively identified 10 patients with epilepsy post VE undergoing surgery at Epilepsy Center of Yuquan Hospital Tsinghua University. All patients underwent comprehensive presurgical evaluation. SEEG (stereo-electroencephalograhy) was necessary in those patients whose noninvasive investigation results did not reveal clear identification of epileptogenic zone (EZ). Habitual seizures were recorded and EI was calculated. We set a cut-off EI value as EI>0.4 (positive). Meanwhile, we superimposed the EI value on the patient's MRI image to better clarify the starting range. Ten patients underwent epileptic focus resection or SEEG-guided radiofrequency thermocoagulation. The outcome was evaluated by using international Engel epilepsy surgery outcome scale after 21 to 43 months of follow-up. Results Ten patients were followed up from 21 to 43 months, Engel class Ⅰ was achieved in 3 patients, Engel class Ⅱ in 3, Engel class Ⅲ in 2 and Engel class Ⅳ in 2. The number of electrodes classified as epileptogenic revealed by SEEG was closely correlated with number of EI positive ones (Spearman′s correlation r=0.794, P=0.006). EI analysis was consistent with SEEG visual onset and no completely contradictory results were found. Patients with good surgical outcome(Engel class Ⅰ-Ⅱ) showed a high value restricted to focal area and those with poor surgical outcome(Engel class Ⅲ-Ⅳ)revealed a diffuse EI value which involved widely spread onset. Conclusions EI plays an important role in localization of seizure onset of patients with epilepsy after VE and thus could serve as a strong evidence and supplement for SEEG onset. EI could assist in identification of EZ and accurate surgical resection. Key words: Epilepsy; Encephalitis, viral; Neurosurgical procedures; Epileptogenicity index; Stereoelectroencephalography