Faculty Bibliography

INTRODUCTION/BACKGROUND:Dorsal root ganglion stimulation (DRG-S) is a relatively new neuromodulation modality. Therefore, data on long-term device explantation rates is limited. This investigation aimed to assess DRG-S device explantation rates at long-term follow-up. METHODS:We retrospectively reviewed individuals implanted with DRG-S in four pain centers from different continuous periods between April 2016 to September 2020. We recorded patient demographics, diagnoses, duration to explantation or last follow-up, treatment complications, and failure etiologies. RESULTS:A total of 249 patients with 756 leads and a mean 27-month follow-up were included. The mean age was 55 ± 15 years; 148 (63%) were female. Leading diagnoses were CRPS (n = 106, 43%), followed by FBSS (n = 64, 26%), and non-surgical low back pain (n = 23, 9%). The explantation rate was ~2% per year (n = 10 total). At explantation, the average time from implantation was 13 ± 10 months. Six patients were explanted for inadequate pain relief. Two patients were explanted due to device-related complications. One patient was explanted secondary to infection and subsequently reimplanted. Five explanted patients experienced a therapy-related complication before eventual explantation: one transient post-procedural neuritis and pocket site pain, one lead fracture, two lead migrations, and one experienced a fracture, a migration, and pocket site pain. DISCUSSION/CONCLUSIONS:This large retrospective study of DRG-S revealed a low therapy-termination rate. The rate of infection leading to explantation was objectively very low at 0.4%. The leading cause of explantation was inadequate pain relief. Explanted patients often had a therapy-related complication. Therefore, minimizing adverse treatment events may reduce ultimate explantation rates.

OBJECTIVE:The human myotome is fundamental to the diagnosis and treatment of neurological disorders. However, this map was largely constructed decades ago, and its breadth, variability, and reliability remain poorly described, limiting its practical use. METHODS:The authors used a novel method to reconstruct the myotome map in patients (n = 42) undergoing placement of dorsal root ganglion electrodes for the treatment of chronic pain. They electrically stimulated nerve roots (n = 79) in the intervertebral foramina at T12-S1 and measured triggered electromyography responses. RESULTS:L4 and L5 stimulation resulted in quadriceps muscle (62% and 33% of stimulations, respectively) and tibialis anterior (TA) muscle (25% and 67%, respectively) activation, while S1 stimulation resulted in gastrocnemius muscle activation (46%). However, L5 and S1 both resulted in abductor hallucis (AH) muscle activation (17% and 31%), L5 stimulation resulted in gastrocnemius muscle stimulation (42%), and S1 stimulation in TA muscle activation (38%). The authors also mapped the breadth of the myotome in individual patients, finding coactivation of adductor and quadriceps, quadriceps and TA, and TA and gastrocnemius muscles under L3, L4, and both L5 and S1 stimulation, respectively. While the AH muscle was commonly activated by S1 stimulation, this rarely occurred together with TA or gastrocnemius muscle activation. Other less common coactivations were also observed throughout T12-S1 stimulation. CONCLUSIONS:The muscular innervation of the lumbosacral nerve roots varies significantly from the classic myotome map and between patients. Furthermore, in individual patients, each nerve root may innervate a broader range of muscles than is commonly assumed. This finding is important to prevent misdiagnosis of radicular pathologies.

OBJECTIVES/OBJECTIVE:Allergic reactions are rare and poorly understood complications of neuromodulation device implantation. There are currently no guidelines for management of allergic reactions to these devices and their components. Here we review the published cases of allergic reactions to implanted neuromodulatory devices and leverage the experiences of other specialties that deal with similar complications to formulate recommendations for prevention and management. MATERIALS AND METHODS/METHODS:A review and assessment of the literature. RESULTS:Allergic reactions to a number of implantable devices have been observed and published. In dentistry and orthopedics, metals such as nickel are the most frequent cause of allergic reactions. In interventional cardiology, where devices closely resemble neuromodulatory devices, titanium, silicone, and polyurethanes are the most common causes of allergic reactions. In neurosurgery, allergic reactions to implantable neuromodulatory devices are rare, and we summarize 13 cases published to date. Such allergic reactions generally present as local dermatitis, erythema, and pruritus, which can be difficult to distinguish from surgical site infection. In one published case, symptoms resolved with corticosteroid treatment, but all other cases required explantation. The successful reimplantation with a modified device was reported in some cases. CONCLUSIONS:Patients should be screened for a personal history of contact allergy before implantation procedures. A multidisciplinary approach to suspected cases of postoperative allergic reactions involving collaboration between neurosurgeons and other implanting physicians, dermatologists or allergists, and device manufacturers is recommended. In cases where an allergic reaction is suspected, an infectious etiology should be ruled out first. Clinical suspicion can then be supported with the use of patch testing, interpreted by an experienced dermatologist or allergist. If patch testing supports an allergic etiology, the implanting physician and the device manufacturer can work together to modify the device for safe reimplantation.

INTRODUCTION/BACKGROUND:Dorsal root ganglion stimulation (DRG-S) is a neuromodulation technique introduced in the last decade with evolving implant methods. Initial prospective research found low incidences of lead migration and lead fracture with DRG-S. However, several recent studies have highlighted high lead migration and lead fracture rates with DRG-S. We investigated the influence of lead anchoring on migrations and fractures. METHODS:We performed a retrospective review between 2016 and 2020 of individuals implanted with DRG-S leads by 4 experienced implanters. The implanters independently changed their standard practice regarding lead anchoring over time, with opposing trends (no anchoring > anchoring, anchoring > no anchoring). We compared lead migration and lead fracture rates between anchored and unanchored DRG-S leads in the entire study cohort. Cox regression was performed on lead migration and fracture distributions. RESULTS:We included 756 leads (n = 565 anchored and n = 191 unanchored) from 249 patients. In unanchored leads, migration occurred in 16 leads (8.4%) from 13 patients (21.0%). In anchored leads, migration occurred in 8 leads (1.4%) from 5 patients (2.7%). Fracture in unanchored leads occurred in 6 leads (3.1%) from 6 patients (9.7%). Fractures in anchored leads occurred in 11 leads (1.9%) from 9 patients (4.8%). The migration survival distributions for the anchored and unanchored leads were statistically significantly different (p < 0.01) with decreased survival for unanchored leads (hazard ratio = 5.8, 95% confidence interval [CI] = 2.2-15.5). DISCUSSION/CONCLUSIONS:We found that anchoring DRG-S leads significantly reduces lead migration when compared to leads placed without an anchor. There was no significant difference in fracture rate between anchored and unanchored leads.

The subthalamic nucleus (STN) is theorized to globally suppress movement through connections with downstream basal ganglia structures. Current theories are supported by increased STN activity when subjects withhold an uninitiated action plan, but a critical test of these theories requires studying STN responses when an ongoing action is replaced with an alternative. We perform this test in subjects with Parkinson's disease using an extended reaching task where the movement trajectory changes mid-action. We show that STN activity decreases during action switches, contrary to prevalent theories. Furthermore, beta oscillations in the STN local field potential, which are associated with movement inhibition, do not show increased power or spiking entrainment during switches. We report an inhomogeneous population neural code in STN, with one sub-population encoding movement kinematics and direction and another encoding unexpected action switches. We suggest an elaborate neural code in STN that contributes to planning actions and changing the plans.

Background Magnetic resonance imaging (MRI)-guided laser interstitial thermal therapy (LITT) is a minimally invasive treatment modality that has been gaining traction in neuro-oncology. Laser ablation is a particularly appealing treatment option when eloquent neurologic function at the tumor location precludes conventional surgical excision. Although typically performed under general anesthesia, LITT in awake patients may help monitor and preserve critical neurologic functions. Objective To describe intraoperative workflow and clinical outcomes in patients undergoing awake laser ablation of brain tumors. Methods We present a cohort of six patients with tumors located in eloquent brain areas that were treated with awake LITT and report three different workflow paradigms involving diagnostic or intraoperative MRI. In all cases, we used NeuroBlate® (Monteris Medical, Plymouth, MN) fiberoptic laser probes for stereotactic laser ablation of tumors. The neurologic status of patients was intermittently assessed every few minutes during the ablation. Results The mean preoperative tumor volume that was targeted was 12.09 ± 3.20 cm³, and the estimated ablation volume was 12.06 ± 2.75 cm³. Performing the procedure in awake patients allowed us close monitoring of neurologic function intraoperatively. There were no surgical complications. The length of stay was one day for all patients except one. Three patients experienced acute or delayed worsening of pre-existing neurologic deficits that responded to corticosteroids. Conclusion We propose that awake LITT is a safe approach when tumors in eloquent brain areas are considered for laser ablation.

OBJECTIVE:To conduct a systematic literature review of brain neurostimulation for pain. DESIGN/METHODS:Grade the evidence for deep brain neurostimulation (DBS). METHODS:An international, interdisciplinary work group conducted a literature search for brain stimulation. Abstracts were reviewed to select studies for grading. Randomized controlled trials (RCTs) meeting inclusion/exclusion criteria were graded by two independent reviewers. General inclusion criteria were prospective trials (RCTs and observational) that were not part of a larger or previously reported group. Excluded studies were retrospective or existed only as abstracts. Studies were graded using the modified Interventional Pain Management Techniques-Quality Appraisal of Reliability and Risk of Bias Assessment, the Cochrane Collaborations Risk of Bias assessment, and the United States Preventative Services Task Force level-of-evidence criteria. RESULTS:Two high-quality RCTs and three observational trials supported DBS, resulting in Level II (moderate) evidence. CONCLUSION/CONCLUSIONS:Moderate evidence supports DBS to treat chronic pain. Additional Level I RCTs are needed to further the strength of the evidence in this important area of medicine, but the current evidence suggests that DBS should be considered as an option in treating complex pain cases.

The introduction of peripheral neuromodulation to treat headache and facial pain two decades ago opened up the field to non-neurosurgical practitioners, given the relatively low risk and technical ease of the procedure. These procedures, primarily occipital nerve stimulation (ONS) and trigeminal branch stimulation such as supra- and infraorbital nerve stimulation, are now established to be effective in a number of facial pain and headache syndromes, despite their lack of approval by regulatory agencies such as the US Food and Drug Administration (FDA). For that reason and others, dedicated hardware for these procedures has not yet been developed, thus relying on hardware designed for placement in the epidural space for spinal cord stimulation (SCS). This has led to a series of technical issues and device-related complications not traditionally seen with SCS. I will review the surgical technique of ONS and peripheral nerve stimulation of the head and face utilizing this equipment, and discuss methods learned by experienced practitioners over the years to minimize device-related complications.

Deep brain stimulation may be an effective therapy for select cases of severe, treatment-refractory Tourette syndrome; however, patient responses are variable, and there are no reliable methods to predict clinical outcomes. The objectives of this retrospective study were to identify the stimulation-dependent structural networks associated with improvements in tics and comorbid obsessive-compulsive behaviour, compare the networks across surgical targets, and determine if connectivity could be used to predict clinical outcomes. Volumes of tissue activated for a large multisite cohort of patients (n = 66) implanted bilaterally in globus pallidus internus (n = 34) or centromedial thalamus (n = 32) were used to generate probabilistic tractography to form a normative structural connectome. The tractography maps were used to identify networks that were correlated with improvement in tics or comorbid obsessive-compulsive behaviour and to predict clinical outcomes across the cohort. The correlated networks were then used to generate 'reverse' tractography to parcellate the total volume of stimulation across all patients to identify local regions to target or avoid. The results showed that for globus pallidus internus, connectivity to limbic networks, associative networks, caudate, thalamus, and cerebellum was positively correlated with improvement in tics; the model predicted clinical improvement scores (P = 0.003) and was robust to cross-validation. Regions near the anteromedial pallidum exhibited higher connectivity to the positively correlated networks than posteroventral pallidum, and volume of tissue activated overlap with this map was significantly correlated with tic improvement (P < 0.017). For centromedial thalamus, connectivity to sensorimotor networks, parietal-temporal-occipital networks, putamen, and cerebellum was positively correlated with tic improvement; the model predicted clinical improvement scores (P = 0.012) and was robust to cross-validation. Regions in the anterior/lateral centromedial thalamus exhibited higher connectivity to the positively correlated networks, but volume of tissue activated overlap with this map did not predict improvement (P > 0.23). For obsessive-compulsive behaviour, both targets showed that connectivity to the prefrontal cortex, orbitofrontal cortex, and cingulate cortex was positively correlated with improvement; however, only the centromedial thalamus maps predicted clinical outcomes across the cohort (P = 0.034), but the model was not robust to cross-validation. Collectively, the results demonstrate that the structural connectivity of the site of stimulation are likely important for mediating symptom improvement, and the networks involved in tic improvement may differ across surgical targets. These networks provide important insight on potential mechanisms and could be used to guide lead placement and stimulation parameter selection, as well as refine targets for neuromodulation therapies for Tourette syndrome.

OBJECTIVE:To conduct a systematic literature review of dorsal root ganglion (DRG) stimulation for pain. DESIGN/METHODS:Grade the evidence for DRG stimulation. METHODS:An international, interdisciplinary work group conducted a literature search for DRG stimulation. Abstracts were reviewed to select studies for grading. General inclusion criteria were prospective trials (randomized controlled trials and observational studies) that were not part of a larger or previously reported group. Excluded studies were retrospective, too small, or existed only as abstracts. Studies were graded using the modified Interventional Pain Management Techniques-Quality Appraisal of Reliability and Risk of Bias Assessment, the Cochrane Collaborations Risk of Bias assessment, and the US Preventative Services Task Force level-of-evidence criteria. RESULTS:DRG stimulation has Level II evidence (moderate) based upon one high-quality pivotal randomized controlled trial and two lower-quality studies. CONCLUSIONS:Moderate-level evidence supports DRG stimulation for treating chronic focal neuropathic pain and complex regional pain syndrome.