Abstracts

Rationale:
Radiofrequency Thermocoagulation (RFTC) is considered to be a low risk primary treatment during SEEG recordings of patients with intractable focal epilepsiesRFTC provides the unique opportunity to record SEEG directly from the brain prior and after deactivating proposed epileptic foci. Recently, relevant changes in the amount of electrographic seizures and number of recorded epileptic spikes have been reported in around 30% of treated patients. In this context, the effect of RFTC on HFO (ripples: 80-200Hz, fast ripples (FR): 200-500Hz) which are promising new biomarkers for epileptic tissue, has not yet been examined. This study aims to investigate the effect of RFTC on HFO and interictal epileptic spikes (IES) generation on local epileptic networks and possible effects on neighbouring and remote brain areas.
Method:
We reviewed the medical charts, video‐SEEG recordings and outcomes of patients who underwent RFTC interventions in the Epilepsy Unit of University Grenoble Alpes since 2017. Coagulations were performed with 40–50V, 75–110mA current for 10–60s on SEEG contacts within the epileptogenic region. Of these, 8 patients met the inclusion criteria with an EEG sample rate of 2048 kHz and periods of at least 1hour of interictal sleep EEG before and after the intervention. In each patient, three types of SEEG contacts were selected: 1.RFTC channels, 2.contacts with high epileptogenicity index (EI). 3.“Remote contacts” with low EI. The automatic detector of Lachner-Piza was used to identify 7 event subtypes (see fig.1)
Results:
After minimum 3 months follow-up after the RFTC intervention, seizure reduction was seen in 5 from 8 patients (good outcome) with an average seizure reduction of 57%. In 3 patients seizure frequency remained unchanged (bad outcome). Overall, ripple rates were significantly reduced in RFTC channels, consistent in HighEI-contacts and increased in remote contacts. FR were significantly increased and IES significantly reduced in all 3 types of contacts. In more detail, figure 1 shows the 7 subtypes in RFTC contacts. Analysing on the individual patient level , significant ripple reduction and FR increase in RFTC channels was seen in 4 of the 5 patients with good outcome but only in one patient with bad outcome (see fig. 2)
Conclusion:
RFTC intervention proved partially successful in our cohort concerning seizure reduction. RFTC reduced ripples and IES, but interestingly increased FR rates. The pattern of reduced ripples and increased FR could be a correlate for a good post-RFTC-outcome.  Network changes in contacts with high epileptic activity or “healthy” remote contacts were not explicitly seen. As expected most effects of RFTC on HFO were found locally, but in some patients even remote effects were seen. Surprisingly successful RFTC did not result in a uniform decrease of all epileptic activity. Ripples and IES showed a different response to RFTC than FR and this observation might indicate distinct generating mechanisms and modulation by RFTC for the events. Our posttreatment seizure observation is currently limited and needs more data but there might be an indication that successful suppression of ripples and spikes indicates better response to RFTC.
Funding:
:This project is supported by grant JA 1725/4-1 of the German Research Foundation