On the nature of interictal epileptiform discharges

The Sub-Regional Functional Organization of Neocortical Irritative Epileptic Networks in Pediatric Epilepsy

Between seizures, irritative network generates frequent brief synchronous activity, which manifests on the EEG as interictal epileptiform discharges (IEDs). Recent insights into the mechanism of IEDs at the microscopic level have demonstrated a high variance in the recruitment of neuronal populations generating IEDs and a high variability in the trajectories through which IEDs propagate across the brain. These phenomena represent one of the major constraints for precise characterization of network organization and for the utilization of IEDs during presurgical evaluations. We have developed a new approach to dissect human neocortical irritative networks and quantify their properties. We have demonstrated that irritative network has modular nature and it is composed of multiple independent sub-regions, each with specific IED propagation trajectories and differing in the extent of IED activity generated. The global activity of the irritative network is determined by long-term and circadian fluctuations in sub-region spatiotemporal properties. Also, the most active sub-region co-localizes with the seizure onset zone in 12/14 cases. This study demonstrates that principles of recruitment variability and propagation are conserved at the macroscopic level and that they determine irritative network properties in humans. Functional stratification of the irritative network increases the diagnostic yield of intracranial investigations with the potential to improve the outcomes of surgical treatment of neocortical epilepsy.

The relationship between seizures, interictal spikes and antiepileptic drugs

OBJECTIVE

A considerable decrease in spike rate accompanies antiepileptic drug (AED) taper during intracranial EEG (icEEG) monitoring. Since spike rate during icEEG monitoring can be influenced by surgery to place intracranial electrodes, we studied spike rate during long-term scalp EEG monitoring to further test this observation.

METHODS

We analyzed spike rate, seizure occurrence and AED taper in 130 consecutive patients over an average of 8.9days (range 5-17days).

RESULTS

We observed a significant relationship between time to the first seizure, spike rate, AED taper and seizure occurrence (F (3,126)=19.77, p<0.0001). A high spike rate was related to a longer time to the first seizure. Further, in a subset of 79 patients who experienced seizures on or after day 4 of monitoring, spike rate decreased initially from an on- to off-AEDs epoch (from 505.0 to 382.3 spikes per hour, p<0.00001), and increased thereafter with the occurrence of seizures.

CONCLUSIONS

There is an interplay between seizures, spikes and AEDs such that spike rate decreases with AED taper and increases after seizure occurrence.

SIGNIFICANCE

The direct relationship between spike rate and AEDs and between spike rate and time to the first seizure suggests that spikes are a marker of inhibition rather than excitation.

Evaluation of levetiracetam and valproic acid as low-dose monotherapies for children with typical benign childhood epilepsy with centrotemporal spikes (BECTS)

PURPOSE

This study aimed to compare the monotherapeutic efficacies of levetiracetam (LEV) and valproic acid (VPA) in a cohort of newly diagnosed children with typical benign childhood epilepsy with centrotemporal spikes (BECTS).

METHODS

A total of 56 children with typical BECTS were retrospectively reviewed in the analyses. Thirty-three children received LEV and 23 received VPA as initial monotherapy, and the treatments lasted for at least 18 months.

RESULTS

The average dosage of LEV was 22.7 ± 4.7 mg/kg/day, and that of VPA was 18.7 ± 5.7 mg/kg/day. The seizure-freedom rates were not significantly different between the two groups at 6 (57.5% vs. 60.9%), 12 (81.8% vs. 73.9%) or 18 months (100% vs. 100%). However, a greater number of the children taking VPA achieved Electroencephalography (EEG) normalization compared to those taking LEV both at 12 (78.3% vs. 45.5%) and 18 months (95.7% vs. 72.7%; p<0.05). No children discontinued therapy due to adverse effects during the follow-up. Only one child (4.7%) in the VPA group exhibited mild weight gain (BMI increase of 2 at the end of follow-up) but did not withdraw from treatment.

CONCLUSION

Low-dosage VPA and LEV monotherapies are equally effective in controlling seizures, but VPA exhibited better efficacy than LEV in improving the electrophysiological abnormalities of children with BECTS. None of the patients discontinued therapy, which was likely due to the administration of low dosages.