Altered microstructural connectivity in juvenile myoclonic epilepsy: the missing link

Juvenile myoclonic epilepsy (JME) is characterized by myoclonic jerks of the upper limbs, often triggered by cognitive stressors. Here we aim to reconcile this particular seizure phenotype with the known frontal lobe type neuropsychological profile, photosensitivity, hyperexcitable motor cortex, and recent advanced imaging studies that identified abnormal functional connectivity of the motor cortex and supplementary motor area (SMA).

We acquired fMRI and diffusion tensor imaging (DTI) in a cohort of 29 patients with JME and 28 healthy control subjects. We used fMRI to determine functional connectivity and DTI-based region parcellation and voxel-wise comparison of probabilistic tractography data to assess the structural connectivity profiles of the mesial frontal lobe.

Patients with JME showed alterations of mesial frontal connectivity with increased structural connectivity between the prefrontal cognitive cortex and motor cortex. We found a positive correlation between DTI and fMRI-based measures of structural and functional connectivity: the greater the structural connectivity between these 2 regions, the greater the observed functional connectivity of corresponding areas. Furthermore, connectivity was reduced between prefrontal and frontopolar regions and increased between the occipital cortex and the SMA.

The observed alterations in microstructural connectivity of the mesial frontal region may represent the anatomic basis for cognitive triggering of motor seizures in JME. Changes in the mesial frontal connectivity profile provide an explanatory framework for several other clinical observations in JME and may be the link between seizure semiology, neurophysiology, neuropsychology, and imaging findings in JME.