Neuroimaging of functional and structural alterations in Juvenile Myoclonic Epilepsy and Frontal Lobe Epilepsy

Epilepsy is the commonest neurological disorder and has profound effects on patients, who suffer from epileptic seizures and also from cognitive impairment. The exact mechanisms of cognitive impairment remain unclear. Aim of this study was to analyse in more detail the functional and structural alterations in two different patient groups, juvenile myoclonic epilepsy (JME) and frontal lobe epilepsy (FLE). We recruited and investigated 26 healthy controls, 30 patients with JME and 67 patients with FLE. All participants underwent magnetic resonance imaging (MRI), including structural imaging, five functional MRI paradigms and diffusion tensor imaging (DTI) as well as neuropsychological assessment. In patients with JME we could show motor cortex hyperactivity and an increased functional connectivity between the pre-frontal cognitive cortex and the motor system. This correlated with increased structural connectivity, measured by DTI and also with disease severity: patients with more active epilepsy showed a stronger hyperconnectivity. In FLE, we could show extensive reorganization of cognitive functions, and we could show, that functional MRI can be used as a new diagnostic method, to identify dysfunctional areas, indicative of the seizure onset zone. This is particularly important in patients with nonlesional FLE, where epilepsy surgery may be advisable but is challenged by the absence of a visible surgical target. The study has provided new insights into pathophysiological mechanisms in JME, specifically explaining the characteristic effect of motor seizures triggered by cognitive effort. It has contributed strong evidence that the observed imaging alterations are the cause and not a consequence of JME, by documenting marked structural changes in seizure free patients. For patients with FLE the study showed highly individual effects of chronic epilepsy on cognitive processing in the frontal lobe. These alterations are clinically relevant for both, avoiding complications from surgery, but also to identify pathological alterations not visible in conventional MRI.