Neurophysiology during movement disorder surgery.

During stereotactic procedures for treating medically refractory movement disorders, intraoperative neurophysiology shifts its focus from simply monitoring the effects of surgery to an integral part of the surgical procedure. The small size, poor visualization, and physiologic nature of these deep brain targets compel the surgeon to rely on some form of physiologic for confirmation of proper anatomic targeting. Even given the newer reliance on imaging and asleep deep brain stimulator electrode placement, it is still a physiologic target and thus some form of intraoperative physiology is necessary.

Closed-Loop Systems in Neuromodulation: Electrophysiology and Wearables.

Most currently available neuromodulation techniques for pain work through an open-loop system. The distance between the epidural space and the target of the stimulation in a dynamic body can change because of physiologic conditions. The closed-loop system in spinal cord neuromodulation consists of an integrated system that records real-time electrophysiological activity in the form of evoked compound action potentials and uses it in a feedback mechanism to adjust stimulus output.

Neurophysiologic Intraoperative Monitoring for Spine Surgery: A Practical Guide From Past to Present.

Intraoperative neuromonitoring was introduced in the second half of the 20th century with the goal of preventing patient morbidity for patients undergoing complex operations of the central and peripheral nervous system. Since its early use for scoliosis surgery, the growth and utilization of IOM techniques expanded dramatically over the past 50 years to include spinal tumor resection and evaluation of cerebral ischemia. The importance of IOM has been broadly acknowledged, and in 1989, the American Academy of Neurology (AAN) released a statement that the use of SSEPs should be standard-of-care during spine surgery.

Fiber Threshold Accommodation as a Mechanism of Burst and High-Frequency Spinal Cord Stimulation.

Objectives: Burst and high-frequency spinal cord stimulation (SCS), in contrast to low-frequency stimulation (LFS, < 200 Hz), reduce neuropathic pain without the side effect of paresthesia, yet it is unknown whether these methods' mechanisms of action (MoA) overlap. We used empirically based computational models of fiber threshold accommodation to examine the three MoA.

Materials And Methods: Waveforms used in SCS are composed of cathodic, anodic, and rest phases.

Dynamic Computational Model of the Human Spinal Cord Connectome.

Connectomes abound, but few for the human spinal cord. Using anatomical data in the literature, we constructed a draft connectivity map of the human spinal cord connectome, providing a template for the many calibrations of specialized behavior to be overlaid on it and the basis for an initial computational model. A thorough literature review gleaned cell types, connectivity, and connection strength indications.

Neuromonitoring for Spinal Cord Stimulation Lead Placement Under General Anesthesia.

Spinal cord stimulation (SCS) is a common therapeutic technique for treating medically refractory neuropathic back and other limb pain syndromes. SCS has historically been performed using a sedative anesthetic technique where the patient is awakened at various times during a surgical procedure to evaluate the location of the stimulator lead. This technique has potential complications, and thus other methods that allow the use of a general anesthetic have been developed.

Theoretical Effect of DBS on Axonal Fibers of Passage: Firing Rates, Entropy, and Information Content.

Background: Deep brain stimulation (DBS) has effects on axons that originate and terminate outside the DBS target area.

Objective: We hypothesized that DBS generates action potentials (APs) in both directions in "axons of passage," altering their information content and that of all downstream cells and circuits, and sought to quantify the change in fiber information content.

Methods: We incorporated DBS parameters (fiber firing frequency and refractory time, and AP initiation location along the fiber and propagation velocity) in a filtering function determining the AP frequency reaching the postsynaptic cell.

Lumbar disk herniation during pregnancy: a review on general management and timing of surgery.

Study Design: Narrative review with case illustration.

Objective: Provide an overview of existing management strategies to suggest a guideline for surgical management of lumbar disk herniation in pregnant women based on time of presentation.

Methods: We performed a narrative review on the topic using the PubMed database.

Investigation of mechanisms of vagus nerve stimulation for seizure using finite element modeling.

Objective: While the efficacy of vagus nerve stimulation (VNS) to reduce seizures in pharmaco-resistant patients is clinically proven, its efficacy and side effects mechanisms are not fully understood. Our goals were 1) to use a finite element model (FEM) and axon models to examine different fiber activation and blocking thresholds and 2) examine fiber activation and blocking in three fiber groups likely to be responsible for efficacy and side effects.

Methods: Using FEM, we examined the field potential along axons within a vagus nerve model with fascicles.

High-Frequency Stimulation of Dorsal Column Axons: Potential Underlying Mechanism of Paresthesia-Free Neuropathic Pain Relief.

Objective: Spinal cord stimulation (SCS) treats neuropathic pain through retrograde stimulation of dorsal column axons and their inhibitory effects on wide dynamic range (WDR) neurons. Typical SCS uses frequencies from 50-100 Hz. Newer stimulation paradigms use high-frequency stimulation (HFS) up to 10 kHz and produce pain relief but without paresthesia.

Occipital Nerve Stimulation for the Treatment of Patients With Medically Refractory Occipital Neuralgia: Congress of Neurological Surgeons Systematic Review and Evidence-Based Guideline.

Background: Occipital neuralgia (ON) is a disorder characterized by sharp, electrical, paroxysmal pain, originating from the occiput and extending along the posterior scalp, in the distribution of the greater, lesser, and/or third occipital nerve. Occipital nerve stimulation (ONS) constitutes a promising therapy for medically refractory ON because it is reversible with minimal side effects and has shown continued efficacy with long-term follow-up.

Objective: To conduct a systematic literature review and provide treatment recommendations for the use of ONS for the treatment of patients with medically refractory ON.

Primary Extradural Tumors of the Spine - Case Review with Evidence-guided Management.

Background: Primary extradural tumors of the spine comprise only a small percentage of all spinal tumors. However, given their relative radioresistance and their typical malignant, invasive nature, surgery may be associated with fairly high morbidity and mortality rates. Furthermore, it may be especially difficult to achieve gross total resections with tumor-free margins.

Case series on variable presentation of ligamentum flavum stimulation following percutaneous cylindrical spinal cord stimulator lead implants.

Background: Stimulation-evoked discomfort secondary to ligamentum flavum stimulation (LFS) is a technological limitation of percutaneous spinal cord stimulator (SCS) lead implants. There is a paucity of literature describing the clinical presentation and time periods at which this side effect may present following insertion of cylindrical lead(s).

Objective: To describe a series of 5 patients who presented at varying time periods after SCS lead placement with LFS.

Mechanism of dorsal column stimulation to treat neuropathic but not nociceptive pain: analysis with a computational model.

Objective: Stimulation of axons within the dorsal columns of the human spinal cord has become a widely used therapy to treat refractory neuropathic pain. The mechanisms have yet to be fully elucidated and may even be contrary to standard "gate control theory." Our hypothesis is that a computational model provides a plausible description of the mechanism by which dorsal column stimulation (DCS) inhibits wide dynamic range (WDR) cell output in a neuropathic model but not in a nociceptive pain model.

Modeling effects of scar on patterns of dorsal column stimulation.

Objective: The purpose of this study was to examine how scar formation may affect electrical current distribution in the spinal cord when using paddle leads placed in the epidural space during treatment with spinal cord stimulation.

Materials And Methods: A finite element model of the spinal cord was used to examine changes in stimulation using a guarded cathode configuration with and without scar. Additionally, two potential "compensatory" programming patterns were examined in order to understand how the three-dimensional electrical field may be affected by scar.

Localized stimulation and recording in the spinal cord with microelectrode arrays.

The use of microelectrodes for both recording and stimulation of cortical tissue is a well-established technique in neuroscience. We demonstrate that the use of existing microelectrode arrays and instrumentation can be extended to studying the spinal cord. We show that microelectrode arrays can be used to perform stimulation and recording in the corticospinal tract of an animal model commonly used in spinal cord injury (SCI) research.

Heuristic map of myotomal innervation in humans using direct intraoperative nerve root stimulation.

Objective: Considerable overlap exists in nerve root innervation of various muscles. Knowledge of myotomal innervation is essential for the interpretation of neurological examination findings and neurosurgical decision-making. Previous studies relied on cadaveric dissections, animal studies, and cases with anomalous anatomy.

A novel solution to reduce the complications of distal shunt catheter displacement associated with obesity.

Despite the varied sources of hydrocephalus, all shunt-treated conditions involve redirection of CSF to the body, commonly the peritoneum. Migration of the distal catheter tip out of the peritoneal space can occur, leading to the need for reoperation. Although uncommon, the authors have recently had 3 such cases in obese patients involving distal tubing retropulsion in otherwise uncomplicated surgeries.

Successful bilateral deep brain stimulation of the globus pallidus internus for persistent status dystonicus and generalized chorea.

The authors report the cases of 2 young male patients (aged 16 and 26 years) with dystonic cerebral palsy of unknown origin, who developed status dystonicus, an acute and persistent combination of generalized dystonia and chorea. Both patients developed status dystonicus after undergoing general anesthesia, and in 1 case, after administration of metoclopramide. In attempting to control this acute hyperkinetic movement disorder, multiple medication trials failed in both cases and patients required prolonged intubation and sedation with propofol.