AAN 2022 | Multicenter study of laser interstitial thermal therapy for mesial temporal lobe epilepsy

Just for some background, patients with epilepsy who fail two or more adequate medication trials are considered drug resistant and have a low probability of seizure freedom with continued pharmacotherapy, and so guidelines recommend referral for surgical evaluation. Now, for select patients with temporal lobe epilepsy, anterior temporal lobectomy, an open surgical resection is the gold standard surgical treatment, with level one evidence. 60 to 80% rates of seizure freedom. Yet, epilepsy surgery is heavily underutilized, owing in part to concerns about the risks and invasiveness. And so this is where laser ablation, or more specifically MRI guided laser interstitial thermal therapy, has emerged and is growing in popularity as a minimally invasive first line alternative to open surgical resection.

And so the most common indication of laser ablation so far has been mesial temporal lobe epilepsy in which the small fiber is inserted to the target, in this case, the mesial temporal lobe structures, the amygdala, hippocampus, parts of the parahippocampal gyrus. And then these are that ablated while the temperature is monitored in real time with MR thermometry to prevent overheating and to minimize the risk of injury to surrounding structures.

And so this has been very appealing to patients and surgeons alike, it’s a less than once centimeter incision, patients are able to go home the next day. But so far, most of the data on the procedure has come from single center studies with one to two year follow up. So the reported rates of seizure freedom have been highly variable, the long term durability is largely unknown. And so that’s where we set out to do a multi-center retrospective cohort study, and we included 268 patients treated consecutively at one of 11 centers for mesial temporal laser ablation for drug resistant epilepsy. And this was done between 2012 and 2018, making it the largest study to date and with longer and more complete follow up.

So the key finding was that at median follow up of over four years, we found that approximately half of patients remained seizure free. And then, as well, we also found that about two thirds of patients had a favorable outcome, so an angle one seizure free outcome, or an angle two outcome of rarer disabling seizures. This with a relatively favorable safety profile, so few permanent serious complications and most patients being discharged home post-operative day one.

So while this rate of seizure freedom is not quite as good as the 60 to 80% that we see with ATL, I think we also need to compare it to the roughly 3% of patients that would be seizure free with continued medication alone, because many patients do prefer the minimally invasive procedure, including some patients who are simply unwilling to undergo open surgery. So laser ablation may be an option for these patients and reduce barriers to patients undergoing surgery.

I would also add that one of the key findings that we found in addition is that patients who choose laser ablation first may still be candidates for open surgery if they fail. So in that sense, laser ablation doesn’t burn any bridges. We saw 21 patients who went on to have anterior temporal lobectomy after laser ablation, an additional two thirds of these patients achieve seizure freedom without any unusual rate of complications.

So in terms of who would be the ideal candidate for mesial temporal laser ablation, our study did include the early experience and fairly heterogeneous populations from each of the sites. So that included patients with and without mesial temporal sclerosis, patients with discordant EEG and PET findings. So we did find that certain preoperative characteristics were associated with earlier seizure recurrence. These were things like discordant PET findings, focal to bilateral tonic-clonic seizures, as opposed to just focal seizures, were associated with earlier seizure recurrence, which is all to say that with improved patient selection, based on some of this data and additional findings, we may see outcomes that improve and get above that 50% seizure freedom rate.

So I would say that if a patient wants the best chance at seizure freedom upfront from a single procedure, they should probably go with an anterior temporal lobectomy, particularly if there’s any suggestion of involvement of the lateral temporal neocortex. But if evidence points to mesial temporal lobe epilepsy and patient is not willing to undergo that operation, or wants a minimally invasive option to try first, then LIT has a pretty good chance of treating the seizures in well selected patients. And again, open surgery remains an option for them in the future.

So in summary, I would just say that laser ablation is a viable first line treatment for patients with mesial temporal lobe epilepsy where evaluated at a comprehensive epilepsy center. Anterior temporal lobectomy remains a safe and effective treatment option for well selected patients who fail laser ablation. These results reflect the early experience of each center and a heterogeneous population of mesial temporal lobe epilepsy patients, so outcomes may improve with modifications in technique and patient selection. And of course, there’s still a need for prospective long term seizure outcomes and neuropsychological outcomes.