Epileptiform discharge propagation: Analyzing spikes from the onset to the peak

OBJECTIVE: To investigate how often discharge propagation occurs within the spikes recorded in patients evaluated for epilepsy surgery, and to assess its impact on the accuracy of source imaging.

METHODS: Data were analyzed from 50 consecutive patients who had presurgical workup. Discharge propagation was analyzed using sequential voltage-maps of the averaged spikes, and principal components analysis. When propagation was detected, sources were modeled both at onset and peak.

RESULTS: Propagation occurred in half of the patients. The median time of propagation between onset and peak was 17 ms. In 60% of the cases with propagation (15/25 patients) this remained in the same sub-lobar area where onset occurred. The accuracy of source imaging in cases of propagating spikes was 67% when only analyzing onset or peak. This was lower as compared to cases without propagation (79%). Combining source imaging at onset and at peak increased the accuracy to 83% for the propagating spikes.

CONCLUSIONS: Propagation occurs often in patients with focal epilepsy, evaluated for surgery. In 40% of the propagating cases, the source of onset and peak were in different sub-lobar regions.

SIGNIFICANCE: For optimal clinical utility, sources should be modeled both at onset and at peak epochs of the spikes.