Treatment of chronic pain: diffusion tensor imaging identification of the ventroposterolateral nucleus confirmed with successful deep brain stimulation

A Study of Diffusion Tensor Imaging in Central Post-Stroke Pain: Traveling Beyond the Pain Pathways

Introduction

Central post-stroke pain (CPSP), seen in the aftermath of a stroke, is an underdiagnosed entity but quite a disabling complication. All the postulated theories regarding the pathogenesis of CPSP point to its origin in the central pain pathways. However, this study attempts to demonstrate the role of other contributing areas in the generation of CPSP.

Materials and Methods

In this single-center tertiary care hospital-based study, 24 patients with both ischemic and hemorrhagic strokes of variable durations were recruited, and Magnetic Resonance Imaging (MRI) imaging with diffusion tensor imaging (DTI) acquisition was done. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values of the spinothalamic tract (STT), corticospinal tract (CST), superior thalamic radiation (STR), basal ganglia (BG), and primary somatosensory cortex (SSC) were compared between normal and abnormal sides and also in extrathalamic lesions separately.

Results

Significant differences with lower FA were noted in STT, CST, STR, and SSC and higher ADC values in BG, STR, CST, and SSC on comparison between the normal and lesion sides. On individual sub-analysis, ischemic stroke had significant changes in the FA value of CST and the ADC value of STR and CST, while hemorrhagic stroke had significant changes in the FA and ADC values of STR and SSC, as well as the FA value of STT. In the analysis of the extrathalamic strokes, significance persisted in all the studied parameters except the BG. The CST abnormalities were evident even in patients with clinical motor improvement. On multivariate analysis, visual analogue scale score severity was correlated with thalamic lesions.

Conclusion

Contrary to the belief that STT is solely responsible for CPSP, the role of CST, STR, BG, and SSC as contributing areas is evident from this study and may be more well established if studied in a larger population.

Up-regulation of HCN2 channels in a thalamocortical circuit mediates allodynia in mice

Chronic pain is a significant problem that afflicts individuals and society, and for which the current clinical treatment is inadequate. In addition, the neural circuit and molecular mechanisms subserving chronic pain remain largely uncharacterized. Herein we identified enhanced activity of a glutamatergic neuronal circuit that encompasses projections from the ventral posterolateral nucleus (VPL^Glu) to the glutamatergic neurons of the hindlimb primary somatosensory cortex (S1HL^Glu), driving allodynia in mouse models of chronic pain. Optogenetic inhibition of this VPL^Glu→S1HL^Glu circuit reversed allodynia, whereas the enhancement of its activity provoked hyperalgesia in control mice. In addition, we found that the expression and function of the HCN2 (hyperpolarization-activated cyclic nucleotide-gated channel 2) were increased in VPL^Glu neurons under conditions of chronic pain. Using in vivo calcium imaging, we demonstrated that downregulation of HCN2 channels in the VPL^Glu neurons abrogated the rise in S1HL^Glu neuronal activity while alleviating allodynia in mice with chronic pain. With these data, we propose that dysfunction in HCN2 channels in the VPL^Glu→S1HL^Glu thalamocortical circuit and their upregulation occupy essential roles in the development of chronic pain.

Clinical applications of magnetic resonance imaging based functional and structural connectivity

Advances in computational neuroimaging techniques have expanded the armamentarium of imaging tools available for clinical applications in clinical neuroscience. Non-invasive, in vivo brain MRI structural and functional network mapping has been used to identify therapeutic targets, define eloquent brain regions to preserve, and gain insight into pathological processes and treatments as well as prognostic biomarkers. These tools have the real potential to inform patient-specific treatment strategies. Nevertheless, a realistic appraisal of clinical utility is needed that balances the growing excitement and interest in the field with important limitations associated with these techniques. Quality of the raw data, minutiae of the processing methodology, and the statistical models applied can all impact on the results and their interpretation. A lack of standardization in data acquisition and processing has also resulted in issues with reproducibility. This limitation has had a direct impact on the reliability of these tools and ultimately, confidence in their clinical use. Advances in MRI technology and computational power as well as automation and standardization of processing methods, including machine learning approaches, may help address some of these issues and make these tools more reliable in clinical use. In this review, we will highlight the current clinical uses of MRI connectomics in the diagnosis and treatment of neurological disorders; balancing emerging applications and technologies with limitations of connectivity analytic approaches to present an encompassing and appropriate perspective.

Neuroimaging of Deep Brain Stimulation

Deep brain stimulation is the most advanced and effective neuromodulation therapy for Parkinson disease, essential tremor, and generalized dystonia. This article discusses how imaging improves surgical techniques and outcomes and widens possibilities in translational neuroscience in Parkinson disease, essential tremor, generalized dystonia, and epilepsy. In movement disorders diffusion tensor imaging allows anatomic segment of cortical areas and different functional subregions within deep-seated targets to understand the side effects of stimulation and gain more data to describe the therapeutic mechanism of action. The introduction of visualization of white matter tracks increases the safety of neurosurgical techniques in functional neurosurgery and neuro-oncology.

Sensory percepts induced by microwire array and DBS microstimulation in human sensory thalamus

BACKGROUND

Microstimulation in human sensory thalamus (ventrocaudal, VC) results in focal sensory percepts in the hand and arm which may provide an alternative target site (to somatosensory cortex) for the input of prosthetic sensory information. Sensory feedback to facilitate motor function may require simultaneous or timed responses across separate digits to recreate perceptions of slip as well as encoding of intensity variations in pressure or touch.

OBJECTIVES

To determine the feasibility of evoking sensory percepts on separate digits with variable intensity through either a microwire array or deep brain stimulation (DBS) electrode, recreating "natural" and scalable percepts relating to the arm and hand.

METHODS

We compared microstimulation within ventrocaudal sensory thalamus through either a 16-channel microwire array (∼400 kΩ per channel) or a 4-channel DBS electrode (∼1.2 kΩ per contact) for percept location, size, intensity, and quality sensation, during thalamic DBS electrode placement in patients with essential tremor.

RESULTS

Percepts in small hand or finger regions were evoked by microstimulation through individual microwires and in 5/6 patients sensation on different digits could be perceived from stimulation through separate microwires. Microstimulation through DBS electrode contacts evoked sensations over larger areas in 5/5 patients, and the apparent intensity of the perceived response could be modulated with stimulation amplitude. The perceived naturalness of the sensation depended both on the pattern of stimulation as well as intensity of the stimulation.

CONCLUSIONS

Producing consistent evoked perceptions across separate digits within sensory thalamus is a feasible concept and a compact alternative to somatosensory cortex microstimulation for prosthetic sensory feedback. This approach will require a multi-element low impedance electrode with a sufficient stimulation range to evoke variable intensities of perception and a predictable spread of contacts to engage separate digits.

Improving Surgical Outcome Using Diffusion Tensor Imaging Techniques in Deep Brain Stimulation

Introduction

Recent advances in surgical imaging include the use of diffusion tensor imaging (DTI) in deep brain stimulation (DBS) and provide a detailed view of the white matter tracts and their connections which are not seen with conventional magnetic resonance imaging. Given that the efficacy of DBS depends on the precise and accurate targeting of these circuits, better surgical planning using information obtained from DTI may lead to improved surgical outcome. We aim to review the available literature to evaluate the efficacy of such a strategy.

Methods

A search of PubMed was performed to identify all articles using the search terms “(diffusion tractography OR diffusion tensor imaging OR DTI) AND (deep brain stimulation OR DBS).” Studies were included if DTI was used and clinical outcomes were reported.

Results

We identified 35 studies where the use of DTI in DBS was evaluated. The most studied pathology was movement disorders (17 studies), psychiatric disorders (11 studies), and pain (7 studies). The overall responder rates for tremor reduction was 70.0% (SD = 26.1%) in 69 patients, 36.5% (SD = 19.1%) for obsessive–compulsive disorder in 9 patients, 48.3% (SD = 40.0%) for depression in 40 patients, and 49.7% (SD = 35.1%) for chronic pain in 23 patients.

Discussion

The studies reviewed show that the use of DTI for surgical planning is feasible, provide additional information over conventional targeting methods, and can improve surgical outcome. Patients in whom the DBS electrodes were within the DTI targets experienced better outcomes than those in whom the electrodes were not. Many current studies are limited by their small sample size or retrospective nature. The use of DTI in DBS planning appears underutilized and further studies are warranted given that surgical outcome can be optimized using this non-invasive technique.

Deep Brain Stimulation for the Treatment of Dejerine-Roussy Syndrome

BACKGROUND/AIMS

Patients who suffer from Dejerine-Roussy syndrome commonly experience severe poststroke hemibody pain which has historically been attributed to thalamic lesions. Despite pharmacological treatment, a significant proportion of the population is resistant to traditional therapy. Deep brain stimulation is often appropriate for the treatment of resistant populations. In this review we aim to summarize the targets that are used to treat Dejerine-Roussy syndrome and provide insight into their clinical efficacy.

METHODS

In reviewing the literature, we defined stimulation success as achievement of a minimum of 50% pain relief.

RESULTS

Contemporary targets for deep brain stimulation are the ventral posterior medial/ventral posterior lateral thalamic nuclei, periaqueductal/periventricular gray matter, the ventral striatum/anterior limb of the internal capsule, left centromedian thalamic nuclei, the nucleus ventrocaudalis parvocellularis internis, and the posterior limb of the internal capsule.

CONCLUSIONS

Due to technological advancements in deep brain stimulation, its therapeutic effects must be reevaluated. Despite a lack of controlled evidence, deep brain stimulation has been effectively used as a therapeutic in clinical pain management. Further clinical investigation is needed to definitively evaluate the therapeutic efficacy of deep brain stimulation in treating the drug-resistant patient population.

Diffusion Tensor Imaging-Based Thalamic Segmentation in Deep Brain Stimulation for Chronic Pain Conditions

BACKGROUND/AIMS

Thalamic deep brain stimulation (DBS) for the treatment of medically refractory pain has largely been abandoned on account of its inconsistent and oftentimes poor efficacy. Our aim here was to use diffusion tensor imaging (DTI)-based segmentation to assess the internal thalamic nuclei of patients who have undergone thalamic DBS for intractable pain and retrospectively correlate lead position with clinical outcome.

METHODS

DTI-based segmentation was performed on 5 patients who underwent sensory thalamus DBS for chronic pain. Postoperative computed tomography images obtained for electrode placement were fused with preoperative magnetic resonance images that had undergone DTI-based thalamic segmentation. Sensory thalamus maps of 4 patients were analyzed for lead positioning and interpatient variability.

RESULTS

Four patients who experienced significant pain relief following DBS demonstrated contact positions within the DTI-determined sensory thalamus or in its vicinity, whereas 1 patient who did not respond to stimulation did not. Only 4 voxels (2%) within the sensory thalamus were mutually shared among patients; 108 voxels (58%) were uniquely represented.

CONCLUSIONS

DTI-based segmentation of the thalamus can be used to confirm thalamic lead placement relative to the sensory thalamus and may serve as a useful tool to guide thalamic DBS electrode implantation in the future.

Anaesthesia for deep brain stimulation: a review

PURPOSE OF REVIEW

Deep brain stimulation (DBS) is a well tolerated and efficacious surgical treatment for movement disorders, chronic pain, psychiatric disorder, and a growing number of neurological disorders. Given that the brain targets are deep and small, accurate electrode placement is commonly accomplished by utilizing frame-based systems. DBS electrode placement is confirmed by microlectrode recordings and macrostimulation to optimize and verify target placement. With a reliance on electrophysiology, proper anaesthetic management is paramount to balance patient comfort without interfering with neurophysiology.

RECENT FINDINGS

To achieve optimal pain control, generous amounts of local anaesthesia are instilled into the planned incision. During the opening and closing states, conscious sedation is the prevailing method of anaesthesia. The preferred agents are dexmedetomidine, propofol, and remifentanil, as they affect neurocognitive testing the least, and shorter acting. All the agents are turned off 15-30 min prior to microelectrode recording. Dexmedetomidine has gained popularity in DBS procedures, but has some considerations at higher doses. The addition of ketamine is helpful for pediatric cases.

SUMMARY

DBS is a robust surgical treatment for a variety of neurological disorders. Appropriate anaesthetic agents that achieve patient comfort without interfering with electrophysiology are paramount.

Personalized mapping of the deep brain with a white matter attenuated inversion recovery (WAIR) sequence at 1.5-tesla: Experience based on a series of 156 patients

OBJECTIVE

Deep brain mapping has been proposed for direct targeting in stereotactic functional surgery, aiming to personalize electrode implantation according to individual MRI anatomy without atlas or statistical template. We report our clinical experience of direct targeting in a series of 156 patients operated on using a dedicated Inversion Recovery Turbo Spin Echo sequence at 1.5-tesla, called White Matter Attenuated Inversion Recovery (WAIR).

METHODS

After manual contouring of all pertinent structures and 3D planning of trajectories, 312 DBS electrodes were implanted. Detailed anatomy of close neighbouring structures, whether gray nuclei or white matter regions, was identified during each planning procedure. We gathered the experience of these 312 deep brain mappings and elaborated consistent procedures of anatomical MRI mapping for pallidal, subthalamic and ventral thalamic regions. We studied the number of times the central track anatomically optimized was selected for implantation of definitive electrodes.

RESULTS

WAIR sequence provided high-quality images of most common functional targets, successfully used for pure direct stereotactic targeting: the central track corresponding to the optimized primary anatomical trajectory was chosen for implantation of definitive electrodes in 90.38%.

CONCLUSION

WAIR sequence is anatomically reliable, enabling precise deep brain mapping and direct stereotactic targeting under routine clinical conditions.

Diffusion Tractography in Deep Brain Stimulation Surgery: A Review

Deep brain stimulation (DBS) is believed to exert its therapeutic effects through modulation of brain circuitry, yet conventional preoperative planning does not allow direct targeting or visualization of white matter pathways. Diffusion MRI tractography (DT) is virtually the only non-invasive method of visualizing structural connectivity in the brain, leading many to suggest its use to guide DBS targeting. DT-guided DBS not only has the potential to allow direct white matter targeting for established applications [e.g., Parkinson’s disease (PD), essential tremor (ET), dystonia], but may also aid in the discovery of new therapeutic targets for a variety of other neurologic and psychiatric diseases. Despite these exciting opportunities, DT lacks standardization and rigorous anatomic validation, raising significant concern for the use of such data in stereotactic brain surgery. This review covers the technical details, proposed methods, and initial clinical data for the use of DT in DBS surgery. Rather than focusing on specific disease applications, this review focuses on methods that can be applied to virtually any DBS target.

DBSproc: An open source process for DBS electrode localization and tractographic analysis

Deep brain stimulation (DBS) is an effective surgical treatment for movement disorders. Although stimulation sites for movement disorders such as Parkinson's disease are established, the therapeutic mechanisms of DBS remain controversial. Recent research suggests that specific white-matter tract and circuit activation mediates symptom relief. To investigate these questions, we have developed a patient-specific open-source software pipeline called 'DBSproc' for (1) localizing DBS electrodes and contacts from postoperative CT images, (2) processing structural and diffusion MRI data, (3) registering all images to a common space, (4) estimating DBS activation volume from patient-specific voltage and impedance, and (5) understanding the DBS contact-brain connectivity through probabilistic tractography. In this paper, we explain our methodology and provide validation with anatomical and tractographic data. This method can be used to help investigate mechanisms of action of DBS, inform surgical and clinical assessments, and define new therapeutic targets.