Laryngeal Muscle-Evoked Potential Recording as an Indicator of Vagal Nerve Fiber Activation

Charlotte Bouckaert; Robrecht Raedt; Lars Emil Larsen; Riëm El Tahry; Stefanie Gadeyne; Evelien Carrette; Silke Proesmans; Frank Dewaele; Jean Delbeke; Veerle De Herdt; Alfred Meurs; Ann Mertens; Paul Boon; Kristl Vonck

doi:10.1016/j.neurom.2022.01.014

Laryngeal Muscle-Evoked Potential Recording as an Indicator of Vagal Nerve Fiber Activation

Neuromodulation. 2022 Apr;25(3):461-470. doi: 10.1016/j.neurom.2022.01.014. Epub 2022 Feb 15.

Affiliations

¹ 4Brain, Department of Neurology, Department of Head and Skin, Ghent University, Ghent, Belgium.
² Centre for Refractory Epilepsy, Department of Neurology, Cliniques Universitaires Saint-Luc, Brussels, Belgium.
³ Department of Neurosurgery, Ghent University Hospital, Ghent, Belgium.
⁴ 4Brain, Department of Neurology, Department of Head and Skin, Ghent University, Ghent, Belgium. Electronic address: kristl.vonck@ugent.be.

PMID: 35177376
DOI: 10.1016/j.neurom.2022.01.014

Abstract

Background: Vagus nerve stimulation (VNS) is an adjunctive therapy for drug-resistant epilepsy. Noninvasive evoked potential recordings in laryngeal muscles (LMEPs) innervated by vagal branches may provide a marker to assess effective vagal nerve fiber activation. We investigated VNS-induced LMEPs in patients with epilepsy in acute and chronic settings.

Materials and methods: A total of 17 of 25 patients underwent LMEP recordings at initiation of therapy (acute group); 15 of 25 patients after one year of VNS (chronic group); and 7 of 25 patients were tested at both time points (acute + chronic group). VNS-induced LMEPs were recorded following different pulse widths and output currents using six surface laryngeal EMG electrodes to calculate input/output curves and estimate LMEP latency, threshold current for minimal (I_threshold), half-maximal (I₅₀), and 95% of maximal (I₉₅) response induction and amplitude of maximal response (V_max). These were compared with the acute + chronic group and between responders and nonresponders in the acute and chronic group.

Results: VNS-induced LMEPs were present in all patients. I_threshold and I₉₅ values ranged from 0.25 to 1.00 mA and from 0.42 to 1.77 mA, respectively. Estimated mean LMEP latencies were 10 ± 0.1 milliseconds. No significant differences between responders and nonresponders were observed. In the acute + chronic group, I_threshold values remained stable over time. However, at the individual level in this group, V_max was lower in all patients after one year compared with baseline.

Conclusions: Noninvasive VNS-induced LMEP recording is feasible both at initiation of VNS therapy and after one year. Low output currents (0.25-1.00 mA) may be sufficient to activate vagal Aα-motor fibers. Maximal LMEP amplitudes seemed to decrease after chronic VNS therapy in patients.

Keywords: Biomarkers; epilepsy; laryngeal muscle-evoked potentials; response; vagus nerve stimulation.

MeSH terms

Epilepsy* / therapy
Evoked Potentials
Humans
Laryngeal Muscles / innervation
Laryngeal Muscles / physiology
Nerve Fibers
Vagus Nerve / physiology
Vagus Nerve Stimulation* / adverse effects