Right-sided vagus nerve stimulation for drug-resistant epilepsy: A systematic review of the literature and perspectives.

BACKGROUND: Right-sided vagus nerve stimulation (RS-VNS) is indicated when the procedure was deemed not technically feasible or too risky on the indicated left side. OBJECTIVE: The present study aims to systematically review the literature on RS-VNS, assessing its effectiveness and safety. METHODS: A systematic review following PRISMA guidelines was conducted: Pubmed/MEDLINE, The Cochrane Library, Scopus, Embase and Web of science databases were searched from inception to August 13th,2023. Gray literature was searched in two libraries. Eligible studies included all studies reporting, at least, one single case of RS-VNS in patients for the treatment of drug-resistant epilepsy. RESULTS: Out of 2333 initial results, 415 studies were screened by abstract. Only four were included in the final analysis comprising seven patients with RS-VNS for a drug-resistant epilepsy. One patient experienced nocturnal asymptomatic bradycardia whereas the other six patients did not display any cardiac symptom. RS-VNS was discontinued in one case due to exercise-induced airway disease exacerbation. Decrease of epileptic seizure frequency after RS-VNS ranged from 25 % to 100 % in six cases. In the remaining case, VNS effectiveness was unclear. In one case, RS-VNS was more efficient than left-sided VNS (69 % vs 50 %, respectively) whereas in another case, RS-VNS was less efficient (50 % vs 95 %, respectively). CONCLUSION: Literature on the present topic is limited. In six out of seven patients, RS-VNS for drug-resistant epilepsy displayed reasonable effectiveness with a low complication rate. Further research, including prospective studies, is necessary to assess safety and effectiveness of RS-VNS for drug-resistant epilepsy patients.

Towards a better identification of ictal semiology patterns in insular epilepsies: A stereo-EEG study.

OBJECTIVE: To describe pure insular ictal semiology and patterns of extra-insular spread demonstrated by stereoelectroencephalography (SEEG) according to a classification based on the insular cytoarchitecture. METHODS: We investigated the ictal semiology in 17 patients undergoing SEEG for insular epilepsy. The insular cortex was divided into three regions roughly overlapping with the agranular, dysgranular and granular regions. Ictal semiology was described accordingly: anterior insula (AI, short anterior and middle gyri), middle insula (MI, short posterior and long anterior gyri) and posterior insula (PI, long posterior gyrus). RESULTS: Awareness impairment occurred secondarily to extra-insular ictal spread. Subjective manifestations were constant. AI seizures (n = 3) presented with autonomic (increased heart rate [HR], respiratory changes), oropharyngeal (mainly throat sensations), emotional (fear, anguish) semiology and the "hand-to-throat" sign followed by frontal-like semiology. MI seizures (n = 8) presented with mainly non-painful paresthesia, some autonomic (respiratory, increased HR), oropharyngeal or thermic symptoms and early motor features with spread to the opercular cortex. PI seizures (n = 6) were characterized by somatosensory semiology, mainly paresthesia potentially painful, and cephalic sensations. CONCLUSIONS: Cytoarchitectonic-based classification and the corresponding ictal features support the antero-posterior grading of insular seizures and highlight specific ictal symptoms. SIGNIFICANCE: This refinement of insular semiology can help optimize the planning of SEEG for presumed insular epilepsy.

The Ictal Signature of Thalamus and Basal Ganglia in Focal Epilepsy: A SEEG Study.

OBJECTIVE: To determine the involvement of subcortical regions in human epilepsy by analyzing direct recordings from these regions during epileptic seizures using stereo-EEG (SEEG). METHODS: We studied the SEEG recordings of a large series of patients (74 patients, 157 seizures) with an electrode sampling the thalamus and in some cases also the basal ganglia (caudate nucleus, 22 patients; and putamen, 4 patients). We applied visual analysis and signal quantification methods (Epileptogenicity Index [EI]) to their ictal recordings and compared electrophysiologic with clinical data. RESULTS: We found that in 86% of patients, thalamus was involved during seizures (visual analysis) and 20% showed high values of epileptogenicity (EI >0.3). Basal ganglia may also disclose high values of epileptogenicity (9% in caudate nucleus) but to a lesser degree than thalamus (p < 0.01). We observed different seizure onset patterns including low voltage high frequency activities. We found high values of thalamic epileptogenicity in different epilepsy localizations, including opercular and motor epilepsies. We found no difference between epilepsy etiologies (cryptogenic vs malformation of cortical development, p = 0.77). Thalamic epileptogenicity was correlated with the extension of epileptogenic networks (p = 0.02, ρ 0.32). We found a significant effect (p < 0.05) of thalamic epileptogenicity regarding the postsurgical outcome (higher thalamic EI corresponding to higher probability of surgical failure). CONCLUSIONS: Thalamic involvement during seizures is common in different seizure types. The degree of thalamic epileptogenicity is a possible marker of the epileptogenic network extension and of postsurgical prognosis.

The effect of medial pulvinar stimulation on temporal lobe seizures.

We investigated the effect of electrical stimulation of the medial pulvinar (PuM) in terms of its effect on temporal lobe seizures. Eight patients with drug-resistant temporal lobe epilepsy undergoing stereoelectroencephalographic exploration were included. All had at least one electrode exploring the PuM. High-frequency (50 Hz) stimulations of the PuM were well tolerated in the majority of them. During diagnostic stimulation to confirm the epileptogenic zone, 19 seizures were triggered by stimulating the hippocampus. During some of these seizures, ipsilateral pulvinar stimulation was applied (130 Hz, pulse width = 450 microseconds, duration = 3-7 seconds, 1-2 mA). Compared to non-PuM-stimulated seizures, five of eight patients experienced clinically less severe seizures, particularly in terms of degree of alteration of consciousness. On the electrical level, seizures were more rapidly clonic with a shorter tonic phase. This proof of concept study is the first to suggest that PuM stimulation could be a well-tolerated and effective means of therapeutic deep brain stimulation in drug-resistant epilepsies.