Vagus nerve stimulation for epilepsy: A narrative review of factors predictive of response

Abstract

Vagus nerve stimulation (VNS) is an established therapy for drug-resistant epilepsy. However, there is a lack of reliable predictors of VNS response in clinical use. The identification of factors predictive of VNS response is important for patient selection and stratification as well as tailored stimulation programming. We conducted a narrative review of the existing literature on prognostic markers for VNS response using clinical, demographic, biochemical, and modality-specific information such as from electroencephalography (EEG), magnetoencephalography, and magnetic resonance imaging (MRI). No individual marker demonstrated sufficient predictive power for individual patients, although several have been suggested, with some promising initial findings. Combining markers from underresearched modalities such as T1-weighted MRI morphometrics and EEG may provide better strategies for treatment optimization.

Keywords: EEG; MRI; VNS; Vagus nerve stimulation; prediction.

FIGURE 1

Differences in brain areas found using a variety of modalities point to the mechanistic reason for vagus nerve stimulation (VNS) response. Key areas indicated in response have been discussed within the literature. Abnormality between responders and non‐responders found in any of these areas could be key in identifying both the mechanism of VNS and differences between responders and non‐responders prospectively. This can potentially be done through diverse modalities, although each will relate to distinct underlying biological differences. DWI, diffusion‐weighted imaging; ECG, electrocardiography; EEG, electroencephalography; fMRI, functional MRI; MEG, magnetoencephalography; MRI, magnetic resonance imaging.

FIGURE 2

When is vagus nerve stimulation (VNS) effective? VNS effectiveness may be due to the varied abnormality between responders and non‐responders. Non‐responders show greater abnormality than responders across a variety of metrics., We hypothesize that there is point of maximum abnormality where individuals with epilepsy will no longer respond to VNS therapy.

FIGURE 3

Translating predictive models into clinical practice. A number of promising models from a range of different data have been described. However, for these markers to be used in clinical practice, their predictive power needs to be demonstrated prospectively and across sites globally. Work is still required to determine the most effective markers for each modality and the optimum use in combination to predict patient outcome. DWI, diffusion‐weighted imaging; EEG, electroencephalography; fMRI, functional MRI; MEG, magnetoencephalography; MRI, magnetic resonance imaging; T1w, T1‐weighted.