Epileptogenic networks in seizures arising from motor systems

Classification of seizures arising from the cortical motor system classically distinguishes between primary motor seizures and supplementary motor area (SMA) seizures. With the aim of better characterizing the underlying networks of motor seizures, we quantitatively studied the “epileptogenicity” of brain structures in 28 patients investigated by intracerebral recordings (stereoelectroencephalography, SEEG). Epileptogenicity of various motor regions (rolandic, SMA, pre-SMA, cingulate motor area (CMA), lateral area 6) as well as prefrontal and parietal areas, was calculated according to the “epileptogenicity index” (EI), a technique that allows mathematical quantification of rapid discharges at seizure onset. According to the maximal value of EI five groups of patients were identified: precentral, premotor/precentral, mesial premotor, lateral premotor and mesio-lateral premotor groups. Most patients disclosed a complex pattern of motor/premotor involvement, while pure mesial premotor seizures (“SMA seizures”) were rare. A positive correlation between the number of structures exhibiting high EI and epilepsy duration was found, as well as a relationship between high EI values in rolandic cortex and poorer surgical outcome. Seizures arising from the motor system appear to be organized in complex electrophysiological patterns that often involve both lateral and mesial aspects of premotor areas together with precentral cortex.