Epilepsy
Transcutaneous Vagus Nerve Stimulation Jens Ellrich
Professor of Medical Physiology, Department of Health Science and Technology, Medical Faculty, Aalborg University and Chief Medical Officer, Medical Department, cerbomed GmbH
Abstract
Invasive vagus nerve stimulation (VNS) is an approved treatment for drug-resistant epilepsy. Besides its recognised clinical efficacy, there are major drawbacks, such as invasiveness and a great many side effects. Therefore there is a medical demand for transcutaneous VNS (t-VNS®), which combines selective, non-invasive access to vagus nerve afferents with a low risk profile. Both treatments excite thick myelinated fibres of vagus nerve branches that project to the nucleus of the solitary tract in the brainstem. Preclinical data emphasise the equivalent anticonvulsive effects of both methods. Based upon the common mode of action and the first clinical data, the t-VNS device received Conformité Européenne (CE) approval. Besides the approved intended use for drug-resistant epilepsy and depression, a future clinical trial will address the efficacy of t-VNS in chronic pain.
Keywords Anticonvulsive, brainstem, concha, depression, drug-resistant, ear, epilepsy, neuromodulation, non-invasive, pain, vagus nerve
Disclosure: Jens Ellrich is Chief Medical Officer at cerbomed GmbH. Received: 10 August 2011 Accepted: 23 September 2011 Citation: European Neurological Review, 2011;6(4):254–6 Correspondence: Jens Ellrich, Chief Medical Officer, Medical Department, cerbomed GmbH, Medical Valley Centre, Henkestrasse 91, D-91052 Erlangen, Germany. E:
jens.ellrich@cerbomed.com
Support: The publication of this article was funded by cerbomed GmbH.
Alternative treatment options are resective neurosurgery, deep brain stimulation and invasive vagus nerve stimulation (VNS).2 Invasive stimulation of the cervical branch of the vagus nerve has been shown to be highly effective in clinical trials, with a responder rate of approximately 60 %.3,4
Drug-resistant epilepsy accounts for more than 30 % of epileptic patients.1
Surgically and technically induced complications
include electrode fractures, deep wound infections, transient vocal cord palsy, cardiac arrhythmia under test stimulation, electrode malfunction and post-traumatic dysfunction of the stimulator.5 Frequent side effects of chronic invasive VNS, such as hoarseness, cough, dyspnoea and pain, are mainly due to bidirectional stimulation of efferent and afferent fibres within the mixed cervical branch of the vagus nerve.
Besides the recognised clinical efficacy of invasive VNS, there are major drawbacks, such as invasiveness, and a great many side effects, due to electrical stimulation of a mixed peripheral nerve. Therefore there is a medical demand for an alternative medical device that combines selective, non-invasive access to vagus nerve afferents with a low risk profile.6
This article assesses the new neuromodulatory technique of transcutaneous VNS (t-VNS®) on the basis of the following requirements for effective VNS therapy inferred from recent concepts of the mechanisms of action:3,4,7
•
unidirectional stimulation of thick myelinated afferent vagus nerve fibres;
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• access to the nucleus of the solitary tract (NTS) in the brainstem; and •
elicitation of a typical cerebral activation pattern.
Site of Transcutaneous Vagus Nerve Stimulation t-VNS targets the cutaneous receptive field of the auricular branch of the vagus nerve (ABVN) at the outer ear. Several lines of evidence from anatomical and clinical studies reveal the topographical anatomy and the functional impact of the ABVN on the autonomic nervous system.
Nerve Supply of the Outer Ear The human outer ear (see Figure 1A) is supplied by three sensory nerves, namely the auriculotemporal nerve, the great auricular nerve and the ABVN.8
On 14 human ears the complete
course of nerve supply was exposed and each branch was defined by identifying its origin. In 73 % of cases the ABVN, and in 18 % the great auricular nerve, were found on the antihelix solely and 9 % showed a double innervation. In 9 % of specimens the ABVN provided ramification for the crura antihelices, in 45 % for the cavity of conchae and in 100 % for the cymba conchae. In 55 % the ABVN and the great auricular nerve were found on the cavity of conchae. No region with triple innervation was found. Thus, in all specimens the ABVN was found to significantly supply the cavity of conchae and exclusively supply the cymba conchae.
Intracranial Section of the Vagus Nerve A patient with tongue cancer suffered from severe pain in the outer ear. This refractory pain was treated by intracranial section
© TOUCH BRIEFINGS 2011
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