Predictive factors for outcome of invasive video-EEG monitoring and subsequent resective surgery in patients with refractory epilepsy

Objective: This is a descriptive study of patients who underwent invasive video-EEG monitoring (IVEM) at Ghent University Hospital. The aim of the study is to identify predictive factors for outcome of IVEM and resective surgery (RS). These factors may optimize the patient flow following the non-invasive presurgical evaluation towards IVEM and RS or other treatments.

Patients and methods: Over the past 16 years, 68/710 refractory epilepsy patients included in the presurgical evaluation protocol (M/F 41/27, mean age 33 years) underwent IVEM at Ghent University Hospital. Patient features and follow-up data were collected from the patients' medical files and the electronic patient database at the neurology and neurosurgery department. Predictive factors for IVEM outcome were identified by comparing features of patients with a positive IVEM outcome (i.e. ictal onset zone identification) and patients with a negative IVEM outcome. Predictive factors for RS outcome were identified by comparing features of patients with Engel class I and patients with Engel class II-IV outcome.

Results: In 56/68 patients (82%) IVEM outcome was positive. The occurrence of a seizure-free interval in the patient's history and a non-localizing ictal scalp EEG in patients with a structural abnormality on MRI (p<0.05) were predictive factors for a negative IVEM outcome. 32/68 patients underwent RS. In 22/32 (70%) patients RS resulted in an Engel class I outcome. A structural abnormality on MRI was a predictive factor for a positive RS outcome in patients in whom a focal or regional focus was resected (p<0.05).

Conclusion: This study shows that IVEM identifies one or more ictal onset zone(s) in up to 80% of patients. The potential of IVEM to identify the ictal onset zone is unlikely in patients with a seizure-free interval in their medical history and a non-localizing ictal scalp EEG during the non-invasive presurgical evaluation. Half of these patients underwent RS with long-term seizure freedom in 70%. Patients with structural MRI lesions have the highest chance of seizure freedom. These findings may contribute to the optimization of patient management during both the invasive and non-invasive presurgical work-up.