Abstracts

Rationale: Brain-responsive neurostimulation with the RNS® System provides treatment by means of a neurostimulator that detects epileptiform activity including  ictal onset patterns and subsequently  triggers  a small stimulus directly to the seizure focus though intracranially placed leads.  Localizing the epileptogenic region , is achieved by means of short term intracranial electrode studies (phase II).  When seizure onsets fall within functional cortex making complete  resection impossible , RNS offers a creative treatment option.  Thus, we explore the contribution of  Phase II studies to optimal event detection by the RNS and the predictive value of phase II for  successful clinical outcomes. Methods: Seven consecutive patients in whom seizure onset zone fell within an area of eloquent cortex were treated with the RNS System at University of California, Los Angeles (UCLA); two of these had concomitant surgical resections and two had a history of previously failed resection.  For these seven patients we analyzed whether phase II was successful in capturing seizure onset, whether RNS detection patterns correlated electrographically with electrographic findings from the phase II and whether successful seizure onset zone determination guided clinical outcomes. We also compared outcomes between patients who were implanted only with RNS to those who also had surgical resection. Results: Our data indicates that in those patients in whom seizure onset zone was clearly captured during phase II, RNS implantation led to quick reduction in seizure frequency if RNS device was able to capture the seizure onset pattern similar to those seen during phase II. In those patients in whom seizure onset was missed but propagation patterns were seen during phase II, RNS implantation still led to self reports of improved quality of life through reduction of seizure severity (shorter duration and briefer post ictal state) . The onset of this effect was delayed as has been previously described with other neurostimulation modalities.  In addition, patients with RNS alone had improvements similar to those with partial  resection plus RNS suggesting that in some cases a  limited resection may not further  improve  the seizure outcome. Conclusions: Our findings suggest that  intracranial studies play an important role in determining RNS placement in patients with neocortical seizures. Accurate knowledge of seizure onset zone predicts quicker RNS response. Even if the seizure focus is not clear, clinical improvement is likely as long as seizure propagation  network is captured. RNS provides an excellent therapeutic alternative for patients in whom resection of the entire epileptogenic region  is not possible.  Partial resection without RNS  may not reduce seizure frequency. Funding: none