Characterization of cortical activity in juvenile myoclonic epilepsy by gradient magnetic field topography

Gradient magnetic field topography (GMFT) illustrates the magnetic field gradients of epileptic spike or polyspikes (S/PS) activities on a volume-rendered brain surface. The purpose is to characterize cortical activation in juvenile myoclonic epilepsy (JME).

We compared interictal S/PS activities in 10 patients with JME to five patients with Lennox-Gastaut syndrome (LGS). We defined areas with gradients exceeding 300fT/cm as activated zones (AZs) on GMFT. We defined the hemisphere where an AZ initially appeared as the "preceding hemisphere". We localized the foci where AZs arose and evaluated their spatiotemporal changes.

In JME, the localization of S/PS in the preceding hemisphere was frontal in 18 activities (28%), parietal in 10 (15%), and frontal/parietal in 33 (51%), and in the contralateral hemisphere it was frontal in 14 (32%), parietal in 6 (14%), and frontal/parietal in 19 (43%). In LGS, AZs arose in every lobe of the brain. The median interhemispheric time difference was 7 ms (range: 0-20) in JME, which was significantly shorter than the 19 ms (1-50) observed among patients with LGS (p < 0.0001).

AZs are localized within the bilateral frontal and parietal regions. AZs arose serially from foci with small time differences.

These results are consistent with regional network involvement in JME.