Rationale: Neurostimulation of thalamic nuclei has demonstrated efficacy in more than 50% of patients with refractory epilepsy as judged by 50% seizure reduction in seizure frequency at two year follow up (Fischer 2010). Most studies have investigated the efficacy of deep brain stimulation in the anterior nucleus of the thalamus (ANT) and the centromedian nucleus of the thalamus (CMT). Limited information is available on the electrographic signals generated by thalamic nuclei in the peri-ictal and ictal states (Wu 2023).
Methods: We studied electrographic patterns from stereo EEG (sEEG) electrode implantation in ANT, CMT, and Pulvinar nuclei in patients with medically refractory epilepsy with diffuse or non-focal scalp EEG findings. Five patients (aged 14-41) were evaluated by unilateral and bilateral implantation of one or two thalamic nuclei with concurrent sEEG monitoring of cortical areas.
We analyzed characteristics of the ictal behavior relating to the implanted thalamic nuclei, including time from seizure onset in neocortical contacts to thalamic spread, morphology of thalamic EEG seizure activity, and laterality of spread.
Results:
Case 1
Implantation: Right fronto-temporal implantation, with right ANT and right CM electrodes
Thalamic spread: Seizure onset to thalamic spread in 1-7 seconds (total 6 seizures). CM nucleus preceded ANT in all seizures by 1-20 sec, except one where onset in both nuclei was simultaneous.
Proposed plan: Right temporal resection
Case 2 - Figure A
Implantation: Left temporal implantation with left pulvinar electrode
Thalamic spread: Seizure onset to thalamic spread in 1-4 sec (total 7 seizures)
Proposed plan: Left mesial temporal laser ablation
Case 3
Implantation: Bilateral temporo-occipital implantation, with bilateral pulvinar electrodes
Thalamic spread: Seizure onset from right occipital region spread to contralateral pulvinar nucleus in 2-11 sec, with no involvement of ipsilateral pulvinar nucleus. With left occipital onset seizures, spread to left pulvinar nucleus occurred within 1-3 sec (total 10 seizures).
Proposed plan: Right occipital responsive neurostimulator (RNS)
Case 4
Implantation: Left temporoparietal and right temporal implantation with left pulvinar electrode
Thalamic spread: Left temporal onset seizures with spread to left pulvinar nucleus 10-90 sec after onset (total 8 seizures)
Proposed plan: Bitemporal RNS
Case 5
Implantation: Bitemporal implantation with bilateral pulvinar electrodes
Thalamic spread: Bilateral independent temporal onset seizures with spread to ipsilateral pulvinar nuclei in 5-12 sec, with no spread to contralateral nuclei (total 9 seizures)
Proposed plan: Bilateral temporal RNS
Conclusions: Thalamic recordings from five patients we evaluated showed initial patterns of ictal spread, and noted thalamic involvement prior to distal cortical spread. Our study paves the way for further study of ictal and peri-ictal patterns in thalamic nuclei, adding to our understanding of cortico-thalamic connections and providing further insight into the utility of thalamic deep brain stimulation for refractory epilepsy depending on the epileptogenic zone.
References:
(1) Epilepsia. 2010;51(5):899-908.
(2) Brain. 2023;10.1093
Funding: None