Looking at Temporal Lobe Epilepsy as a Network Disorder

In the October 9, 2013, articles published ahead of print in the journal Neurology, Drs. Bonilha and colleagues from the Medical University of South Carolina present an interesting study looking at temporal lobe epilepsy from a different perspective, i.e., as a network problem or a connectome. Investigators sought to evaluate the actual network or connections of the area of epilepsy that is causing temporal lobe epilepsy to understand epilepsy from a network perspective. The purpose of the study was to evaluate whether the patients with surgically refractory medial temporal lobe epilepsy have a distinct pattern of structural network organization involving temporal lobe and non-temporal lobe areas.

The investigators studied 18 healthy controls and 20 patients with medication refractory unilateral mesial temporal lobe epilepsy who underwent temporal lobectomy for treatment of seizures and then assessed whether they became seizure free or not. They also then proceeded to evaluate connections based on a special MRI technique known as MRI diffusion tensor imaging from 83 defined regions of interest encompassing the entire brain and made notes about the differences in connectivity with regards to seizure freedom or not.

The investigators found:

• Patients with temporal lobe epilepsy had a decrease in connectivity involving the same side as the epilepsy location with regards to connections to the thalamus and a pathological increase in the same side mesial temporal lobe, insular and frontal connections.
• Among patients that were not seizure free, they had a higher connection between structures in the same side of the temporal lobe, both the middle and the lateral temporal lobe, ipsilateral, medial temporal, and parietal lobe, and contralateral temporal pole and parietal lobe.
• The patients who were not seizure free also had a lower sub-network within the ipsilateral temporal lobe with higher sub-network integration at the expense of segregation.

The authors concluded:

• Mesial temporal lobe epilepsy is associated with network rearrangement within, but not restricted to, the temporal lobe ipsilateral to the onset of seizures.
• Networks that involve key components of the medial temporal lobe and structures traditionally not removed during surgery may be associated with seizure control after treatment of mesial temporal lobe epilepsy.