9. Clinical yield of electric source imaging in epilepsy

Abstract

Objective In patients with drug-resistant epilepsy who are candidate for surgery, non-invasive functional imaging methods are helpful in guiding surgical resections. Our main aim was to determine localisation precision of the epileptogenic focus with electric source imaging (ESI) and to compare it to other well-established imaging tools. Methods One hundred fifty-two pharmaco-resistant epileptic patients with more than 1 year post-operative follow-up were included. Sensitivity (defined as % of seizure free patients with focus localization within the resected zone) and specificity (defined as % of patients with focus localization outside the operated area) of different techniques was assessed: ESI, magnetic resonance imaging (MRI), positron emission tomography (PET) and single-photon emission-computed tomography (SPECT). Results A total of 43 patients underwent all examinations. High-resolution ESI (>64 electrodes) using individual MRI as a head model rendered the highest sensitivity (80%) and, principally, specificity rate (88%), followed by MRI (71.4% and 50%), PET (62.9% and 37.5%) and SPECT (54.3% but a higher specificity as compared to MRI and PET of 62.5%). The sensitivity of ESI was high in both temporal and extratemporal lobe epilepsy (91% and 75%, resp). The chance to become seizure-free if the focus source maximum is resected is 97%. Conclusion From a clinical point of view, ESI is a very attractive non-invasive technique with a high localization yield which provides superior temporal resolution in the millisecond range, as compared to methods based on changes in metabolic or vascular correlates of neural activity. From a practical perspective, this type of examination does not require sedation, it can be performed at patient’s bedside and it is suitable in the pediatric population and cognitively impaired patients.