A resting-state functional MRI study on the effect of vagal nerve stimulation on spontaneous regional brain activity in drug-resistant epilepsy patients

Altered intrinsic brain activity in patients with neuropathic pain after brachial plexus avulsion

OBJECTIVE

This study aimed to investigate brain activity changes in patients suffering from neuropathic pain (NP) following brachial plexus avulsion (BPA).

METHODS

Fifteen patients with NP following BPA and eight healthy participants (HP) were recruited for this study. All participants underwent examination using resting-state functional MRI. The amplitude of low-frequency fluctuation (ALFF) and regional homogeneity (ReHo) were calculated and compared between the BPA group, left-BPA subgroup, right-BPA subgroup, and the HP group using independent samples t-tests.

RESULTS

In the BPA group, there were notable increases in ALFF/ReHo observed in the left rolandic operculum, insula, and supramarginal gyrus, while decreases were observed in the left paracentral lobule, fusiform gyrus, calcarine fissure and surrounding cortex, lingual gyrus, precuneus, as well as the bilateral anterior/median cingulate and paracingulate gyri, supplementary motor area, and cerebellum. In the left-BPA subgroup, elevated ALFF/ReHo levels were identified in the left middle/inferior frontal gyri, rolandic operculum, and supramarginal gyrus, with corresponding decreases in the left calcarine fissure and surrounding cortex, inferior occipital gyrus, fusiform gyrus, lingual gyrus, as well as the bilateral anterior/median cingulate and paracingulate gyri, postcentral gyri, supplementary motor area, paracentral lobules, and cerebellum. The right-BPA subgroup displayed increased ALFF/ReHo in the left frontal lobe, rolandic operculum, insula, fusiform gyrus, and lingual gyrus, as well as the right cerebellum. Conversely, decreases in ALFF/ReHo were observed in the bilateral anterior/median cingulate and paracingulate gyri, calcarine fissure and surrounding cortex, cuneus, and occipital lobes.

CONCLUSIONS

The NP after BPA caused spontaneous activity changes in brain regions associated with linguistic, visual, somatosensory, and motor coordination and processing function. The majority of these abnormal areas were situated in the left cerebral hemisphere, while the effect of cingulate gyri and cerebellum seemed to be bilateral.

Epilepsy Networks and Their Surgical Relevance

Surgical epilepsy is a rapidly evolved field. As the understanding and concepts of epilepsy shift towards a network disorder, surgical outcomes may shed light on numerous components of these systems. This review documents the evolution of the understanding of epilepsy networks and examines the data generated by resective, ablative, neuromodulation, and invasive monitoring surgeries in epilepsy patients. As these network tools are better integrated into epilepsy practice, they may eventually inform surgical decisions and improve clinical outcomes.

Altered local spontaneous brain activity pattern in children with right-eye amblyopia of varying degrees: evidence from fMRI

PURPOSE

To investigate the abnormal changes of local brain activity in children with right-eye amblyopia of varying degrees.

METHODS

Data of resting-state functional magnetic resonance imaging were collected from 16 children with severe amblyopia, 17 children with mild to moderate amblyopia, and 15 children with normal binocular vision. Local brain activity was analyzed using the amplitude of low-frequency fluctuations (ALFF) and regional homogeneity (ReHo).

RESULTS

There were extensive ALFF differences among the three groups in 10 brain regions. There were extensive differences in ReHo among the three groups in 11 brain regions. The ALFF and ReHo of the right orbital part of the middle frontal gyrus displayed a significantly positive correlation with the best-corrected visual acuity of the right eye, respectively. The ALFF value and ReHo value of the right orbital part of the middle frontal gyrus followed the pattern of normal control < mild to moderate amblyopia < severe amblyopia.

CONCLUSION

This study demonstrated that there were changes in specific patterns of ALFF and ReHo in children with right-eye amblyopia of different degrees in brain regions performing visual sensorimotor and attentional control functions.

Brain functional connectivity-based prediction of vagus nerve stimulation efficacy in pediatric pharmacoresistant epilepsy

OBJECTIVE

Although vagus nerve stimulation (VNS) is a common and widely used therapy for pharmacoresistant epilepsy, the reported efficacy of VNS in pediatric patients varies, so it is unclear which children will respond to VNS therapy. This study aimed to identify functional brain network features associated with VNS action to distinguish VNS responders from nonresponders using scalp electroencephalogram (EEG) data.

METHODS

Twenty-three children were included in this study, 16 in the discovery cohort and 7 in the test cohort. Using partial correlation value as a measure of whole-brain functional connectivity, we identified the differential edges between responders and nonresponders. Results derived from this were used as input to generate a support vector machine-learning classifier to predict VNS outcomes.

RESULTS

The postcentral gyrus in the left and right parietal lobe regions was identified as the most significant differential brain region between VNS responders and nonresponders (p < 0.001). The resultant classifier demonstrated a mean AUC value of 0.88, a mean sensitivity rate of 91.4%, and a mean specificity rate of 84.3% on fivefold cross-validation in the discovery cohort. In the testing cohort, our study demonstrated an AUC value of 0.91, a sensitivity rate of 86.6%, and a specificity rate of 79.3%. Furthermore, for prediction accuracy, our model can achieve 81.4% accuracy at the epoch level and 100% accuracy at the patient level.

SIGNIFICANCE

This study provides the first treatment response prediction model for VNS using scalp EEG data with ictal recordings and offers new insights into its mechanism of action. Our results suggest that brain functional connectivity features can help predict therapeutic response to VNS therapy. With further validation, our model could facilitate the selection of targeted pediatric patients and help avoid risky and costly procedures for patients who are unlikely to benefit from VNS therapy.

Advances in Image Processing for Epileptogenic Zone Detection with MRI

Focal epilepsy is a common and severe neurologic disorder. Neuroimaging aims to identify the epileptogenic zone (EZ), preferably as a macroscopic structural lesion. For approximately a third of patients with chronic drug-resistant focal epilepsy, the EZ cannot be precisely identified using standard 3.0-T MRI. This may be due to either the EZ being undetectable at imaging or the seizure activity being caused by a physiologic abnormality rather than a structural lesion. Computational image processing has recently been shown to aid radiologic assessments and increase the success rate of uncovering suspicious regions by enhancing their visual conspicuity. While structural image analysis is at the forefront of EZ detection, physiologic image analysis has also been shown to provide valuable information about EZ location. This narrative review summarizes and explains the current state-of-the-art computational approaches for image analysis and presents their potential for EZ detection. Current limitations of the methods and possible future directions to augment EZ detection are discussed.

Prediction of the Responsiveness to Vagus-Nerve Stimulation in Patients with Drug-Resistant Epilepsy via Directed-Transfer-Function Analysis of Their Perioperative Scalp EEGs

This study aims to compare directed transfer function (DTF), which is an effective connectivity analysis, derived from scalp EEGs between responder and nonresponder groups implanted with vagus-nerve stimulation (VNS). Twelve patients with drug-resistant epilepsy (six responders and six nonresponders) and ten controls were recruited. A good response to VNS was defined as a reduction of ≥50% in seizure frequency compared with the presurgical baseline. DTF was calculated in five frequency bands (delta, theta, alpha, beta, and broadband) and seven grouped electrode regions (left and right frontal, temporal, parieto-occipital, and midline) in three different states (presurgical, stimulation-on, and stimulation-off states). Responders showed presurgical nodal strength close to the control group in both inflow and outflow, whereas nonresponders exhibited increased inward and outward connectivity measures. Nonresponders also had increased inward and outward connectivity measures in the various brain regions and various frequency bands assessed compared with the control group when the stimulation was on or off. Our study demonstrated that the presurgical DTF profiles of responders were different from those of nonresponders. Moreover, a presurgical normal DTF profile may predict good responsiveness to VNS.

Vagus nerve stimulation for conservative therapy-refractive epilepsy and depression

Numerous studies confirm that the vagus nerve stimulation (VNS) is an efficient, indirect neuromodulatory therapy with electrically induced current for epilepsy that cannot be treated by epilepsy surgery and is therapy-refractory and for drug therapy-refractory depression. VNS is an established, evidence-based and in the long-term cost-effective therapy in an interdisciplinary overall concept.Long-term data on the safety and tolerance of the method are available despite the heterogeneity of the patient populations. Stimulation-related side effects like hoarseness, paresthesia, cough or dyspnea depend on the stimulation strength and often decrease with continuing therapy duration in the following years. Stimulation-related side effects of VNS can be well influenced by modifying the stimulation parameters. Overall, the invasive vagus nerve stimulation may be considered as a safe and well-tolerated therapy option.For invasive and transcutaneous vagus nerve stimulation, antiepileptic and antidepressant as well as positive cognitive effects could be proven. In contrast to drugs, VNS has no negative effect on cognition. In many cases, an improvement of the quality of life is possible.iVNS therapy has a low probability of complete seizure-freedom in cases of focal and genetically generalized epilepsy. It must be considered as palliative therapy, which means that it does not lead to healing and requires the continuation of specific medication. The functional principle is a general reduction of the neuronal excitability. This effect is achieved by a slow increase of the effectiveness sometimes over several years. Responders are those patients who experience a 50% reduction of the seizure incidence. Some studies even reveal seizure-freedom in 20% of the cases. Currently, it is not possible to differentiate between potential responders and non-responders before therapy/implantation.The current technical developments of the iVNS generators of the new generation like closed-loop system (cardiac-based seizure detection, CBSD) reduce also the risk for SUDEP (sudden unexpected death in epilepsy patients), a very rare, lethal complication of epilepsies, beside the seizure severity.iVNS may deteriorate an existing sleep apnea syndrome and therefore requires possible therapy interruption during nighttime (day-night programming or magnet use) beside the close cooperation with sleep physicians.The evaluation of the numerous iVNS trials of the past two decades showed multiple positive effects on other immunological, cardiological, and gastroenterological diseases so that additional therapy indications may be expected depending on future study results. Currently, the vagus nerve stimulation is in the focus of research in the disciplines of psychology, immunology, cardiology as well as pain and plasticity research with the desired potential of future medical application.Beside invasive vagus nerve stimulation with implantation of an IPG and an electrode, also devices for transdermal and thus non-invasive vagus nerve stimulation have been developed during the last years. According to the data that are currently available, they are less effective with regard to the reduction of the seizure severity and duration in cases of therapy-refractory epilepsy and slightly less effective regarding the improvement of depression symptoms. In this context, studies are missing that confirm high evidence of effectiveness. The same is true for the other indications that have been mentioned like tinnitus, cephalgia, gastrointestinal complaints etc. Another disadvantage of transcutaneous vagus nerve stimulation is that the stimulators have to be applied actively by the patients and are not permanently active, in contrast to implanted iVNS therapy systems. So they are only intermittently active; furthermore, the therapy adherence is uncertain.

Vagus nerve stimulation in brain diseases: Therapeutic applications and biological mechanisms

Brain diseases, including neurodegenerative, cerebrovascular and neuropsychiatric diseases, have posed a deleterious threat to human health and brought a great burden to society and the healthcare system. With the development of medical technology, vagus nerve stimulation (VNS) has been approved by the Food and Drug Administration (FDA) as an alternative treatment for refractory epilepsy, refractory depression, cluster headaches, and migraines. Furthermore, current evidence showed promising results towards the treatment of more brain diseases, such as Parkinson's disease (PD), autistic spectrum disorder (ASD), traumatic brain injury (TBI), and stroke. Nonetheless, the biological mechanisms underlying the beneficial effects of VNS in brain diseases remain only partially elucidated. This review aims to delve into the relevant preclinical and clinical studies and update the progress of VNS applications and its potential mechanisms underlying the biological effects in brain diseases.

A systematic review of magnetic resonance imaging in patients with an implanted vagus nerve stimulation system

Purpose

Vagus nerve stimulation (VNS) is an effective adjunctive treatment for drug-resistant epilepsy (DRE) and difficult-to-treat depression (DTD). More than 125.000 patients have been implanted with VNS Therapy® System (LivaNova PLC) since initial approval. Patients with DRE often require magnetic resonance imaging (MRI) of the brain during the course of their disease. VNS Therapy System devices are labeled to allow MRI under certain conditions; however, there are no published comprehensive articles about the real-world experience using MRI in patients with implanted VNS devices.

Methods

A systematic review in accordance with PRISMA statement was performed using PubMed database. Full-length articles reporting MRI (1.5 T or 3 T scanner) of patients with implanted VNS for DRE or DTD and published since 2000 were included. The primary endpoint was a positive outcome that was defined as a technically uneventful MRI scan performed in accordance with the VNS Therapy System manufacturer guidelines and completed according to the researchers’ planned scanning protocol without harm to the patient.

Results

Twenty-six articles were eligible with 25 articles referring to the VNS Therapy System, and 216 patients were included in the analysis. No serious adverse events or serious device-related adverse events were reported. MRI scan was prematurely terminated in one patient due to a panic attack.

Conclusion

This systematic review indicates that cranial MRI of patients with an implanted VNS Therapy System can be completed satisfactorily and is tolerable and safe using 1.5 T and 3 T MRI scanners when performed in adherence to the VNS manufacturer’s guidelines.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00234-021-02705-y.