Dorsal Root Ganglion Stimulation as a Salvage Therapy Following Failed Spinal Cord Stimulation.

INTRODUCTION: Spinal cord stimulation (SCS) can provide long-term pain relief for various chronic pain conditions, but some patients have no relief with trial stimulation or lose efficacy over time. To "salvage" relief in patients who do not respond or have lost efficacy, alternative stimulation paradigms or anatomical targets can be considered. Dorsal root ganglion stimulation (DRG-S) has a different mechanism of action and anatomical target than SCS. OBJECTIVES: We assessed DRG-S salvage therapy outcomes in patients who did not respond to SCS or had lost SCS efficacy. MATERIALS AND METHODS: We retrospectively included consecutive patients from 2016 to 2020 who were salvaged with DRG-S after failed SCS trials (<50% pain reduction) or who had lost efficacy after permanent SCS. We compared numerical rating scale (NRS) pain, Oswestry disability index (ODI), health-related quality of life (EuroQol five-dimensions five-level), and oral morphine equivalent (OME) opioid requirements before DRG-S salvage and at patients' last follow-up. RESULTS: A total of 60 patients who had failed SCS were salvaged with DRG-S. The mean age was 56 ± 12 years, and the most common diagnoses were complex regional pain syndrome (n = 24) and failed back surgery syndrome (n = 24). The most common failed modalities included tonic (n = 32), Burst (n = 18), and high-frequency (n = 10) SCS. The median follow-up duration of salvage DRG-S was 34 months. With DRG-S, NRS decreased (8.7 ± 1.2 to 3.8 ± 2.1), and OME declined (median 23 mg to median 15 mg), whereas EuroQol 5D scores increased (0.40 ± 0.15 to 0.71 ± 0.15), and ODI improved (64 ± 14% to 31 ± 18%) (all p < 0.05). CONCLUSIONS: DRG-S can be used in patients with chronic pain who have previously failed to receive persistent benefit from SCS.

A broad and variable lumbosacral myotome map uncovered by foraminal nerve root stimulation.

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.

Peripheral Nerve Stimulation for Facial Pain Using Conventional Devices: Technique and Complication Avoidance.

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.

Subthalamic Gamma Knife Radiosurgery in Parkinson's Disease: A Cautionary Tale.

INTRODUCTION: Deep brain stimulation (DBS) targeting the subthalamic nucleus (STN) has been shown to reliably improve several symptoms of Parkinson's disease (PD) in appropriately selected patients. Various factors may preclude patients from undergoing DBS and for them, non-invasive lesion-based therapies such as focused ultrasound and Gamma Knife (GK) radiosurgery may present a safer alternative. MATERIALS AND METHODS: Based on preliminary positive reports of STN GK for PD, we conducted a prospective, open-label, single-center, pilot study in PD patients deemed potential candidates for unilateral DBS based on their disease characteristics, but contraindicated due to age >74, an irreversible bleeding diathesis, or significant comorbid medical disease. Stereotactic MRI-guided GK radiosurgery was performed using a single 110- or 120-Gy dose targeting the STN contralateral to the more symptomatic extremity. Clinical follow-up and imaging assessed the safety and efficacy of the procedure over a 12-month period. RESULTS: Four PD patients with medication-refractory tremors and disabling dyskinesias underwent unilateral STN GK radiosurgery. Contraindications to DBS included high-risk comorbid cardiovas-cular disease in 3 patients and an irreversible bleeding diathesis in 1. There were no immediate post-procedural adverse events. One patient who underwent left STN GK radiosurgery developed right hemiparesis and dysarthria 7 months post-procedure followed by hospitalization at 9 months for bacterial endocarditis and liver failure from which he died. The remaining 3 patients were free of adverse events up to 12 months post-procedure and experienced a reduction in contralateral rigidity, bradykinesia, and tremor. Upon extended follow-up, 2 patients developed subacute worsening of gait. One died at 16 months due to complications of a fall whereas the other saw no change in gait up to 42 months post-procedure. All 3 patients with adverse events demonstrated a hyper-response in the targeted area on follow-up neuroimaging. DISCUSSION/CONCLUSION: Despite the potential for clinical improvement, our results suggest that unilateral STN GK radiosurgery should be approached cautiously in medically frail PD patients who may be at higher risk of GK hyper-response and neurologic complications.

Effect of deep brain simulation on arm, leg, and chin tremor in Parkinson disease.

OBJECTIVE: The efficacy of deep brain stimulation (DBS) of the subthalamic nucleus (STN) in the treatment of Parkinson disease (PD)-related tremor has been well established. However, the relative impact on arm, leg, and chin tremor has been less clearly elucidated. The authors evaluated the distribution of tremors in a PD cohort undergoing STN DBS and sought to evaluate the differential impact of DBS as a function of tremor location. METHODS: A retrospective study of patients with PD with tremor who underwent DBS surgery between 2012 and 2016 was performed to evaluate the impact of STN stimulation on overall and regional tremor scores. RESULTS: Across 66 patients the authors found an average of 78% overall reduction in tremor after 6 months. In this cohort, the authors found that tremor reduction was somewhat better for arm than for leg tremors, especially in instances of higher preoperative tremor (84% vs 71% reduction, respectively, for initial tremor scores ≥ 2). No significant difference in response was found between patients with medication-responsive versus medication-nonresponsive tremors. CONCLUSIONS: The authors found that although DBS improved tremor in all regions, the improvement was not uniform between chin, arm, and leg-even within the same patient. The reasons behind these differing responses are speculative but suggest that STN DBS may more reliably reduce arm tremors than leg tremors.

Efficacy and Safety of Deep Brain Stimulation in Tourette Syndrome: The International Tourette Syndrome Deep Brain Stimulation Public Database and Registry.

Importance: Collective evidence has strongly suggested that deep brain stimulation (DBS) is a promising therapy for Tourette syndrome. Objective: To assess the efficacy and safety of DBS in a multinational cohort of patients with Tourette syndrome. Design, Setting, and Participants: The prospective International Deep Brain Stimulation Database and Registry included 185 patients with medically refractory Tourette syndrome who underwent DBS implantation from January 1, 2012, to December 31, 2016, at 31 institutions in 10 countries worldwide. Exposures: Patients with medically refractory symptoms received DBS implantation in the centromedian thalamic region (93 of 163 [57.1%]), the anterior globus pallidus internus (41 of 163 [25.2%]), the posterior globus pallidus internus (25 of 163 [15.3%]), and the anterior limb of the internal capsule (4 of 163 [2.5%]). Main Outcomes and Measures: Scores on the Yale Global Tic Severity Scale and adverse events. Results: The International Deep Brain Stimulation Database and Registry enrolled 185 patients (of 171 with available data, 37 females and 134 males; mean [SD] age at surgery, 29.1 [10.8] years [range, 13-58 years]). Symptoms of obsessive-compulsive disorder were present in 97 of 151 patients (64.2%) and 32 of 148 (21.6%) had a history of self-injurious behavior. The mean (SD) total Yale Global Tic Severity Scale score improved from 75.01 (18.36) at baseline to 41.19 (20.00) at 1 year after DBS implantation (P < .001). The mean (SD) motor tic subscore improved from 21.00 (3.72) at baseline to 12.91 (5.78) after 1 year (P < .001), and the mean (SD) phonic tic subscore improved from 16.82 (6.56) at baseline to 9.63 (6.99) at 1 year (P < .001). The overall adverse event rate was 35.4% (56 of 158 patients), with intracranial hemorrhage occurring in 2 patients (1.3%), infection in 4 patients with 5 events (3.2%), and lead explantation in 1 patient (0.6%). The most common stimulation-induced adverse effects were dysarthria (10 [6.3%]) and paresthesia (13 [8.2%]). Conclusions and Relevance: Deep brain stimulation was associated with symptomatic improvement in patients with Tourette syndrome but also with important adverse events. A publicly available website on outcomes of DBS in patients with Tourette syndrome has been provided.

Subcallosal cingulate deep brain stimulation for treatment-resistant depression: a multisite, randomised, sham-controlled trial.

BACKGROUND: Deep brain stimulation (DBS) of the subcallosal cingulate white matter has shown promise as an intervention for patients with chronic, unremitting depression. To test the safety and efficacy of DBS for treatment-resistant depression, a prospective, randomised, sham-controlled trial was conducted. METHODS: Participants with treatment-resistant depression were implanted with a DBS system targeting bilateral subcallosal cingulate white matter and randomised to 6 months of active or sham DBS, followed by 6 months of open-label subcallosal cingulate DBS. Randomisation was computer generated with a block size of three at each site before the site started the study. The primary outcome was frequency of response (defined as a 40% or greater reduction in depression severity from baseline) averaged over months 4-6 of the double-blind phase. A futility analysis was performed when approximately half of the proposed sample received DBS implantation and completed the double-blind phase. At the conclusion of the 12-month study, a subset of patients were followed up for up to 24 months. The study is registered at ClinicalTrials.gov, number NCT00617162. FINDINGS: Before the futility analysis, 90 participants were randomly assigned to active (n=60) or sham (n=30) stimulation between April 10, 2008, and Nov 21, 2012. Both groups showed improvement, but there was no statistically significant difference in response during the double-blind, sham-controlled phase (12 [20%] patients in the stimulation group vs five [17%] patients in the control group). 28 patients experienced 40 serious adverse events; eight of these (in seven patients) were deemed to be related to the study device or surgery. INTERPRETATION: This study confirmed the safety and feasibility of subcallosal cingulate DBS as a treatment for treatment-resistant depression but did not show statistically significant antidepressant efficacy in a 6-month double-blind, sham-controlled trial. Future studies are needed to investigate factors such as clinical features or electrode placement that might improve efficacy. FUNDING: Abbott (previously St Jude Medical).

Intraparenchymal Cysts Following Deep Brain Stimulation: Variable Presentations and Clinical Courses.

BACKGROUND: The development of cysts at the electrode lead is a rare complication of deep brain stimulation (DBS), with only 3 cases reported in the literature. A better understanding of the variable clinical presentations and courses of these cysts may help increase awareness of this potentially life-threatening complication. OBJECTIVE: To review the clinical presentation of patients with intraparenchymal cysts following DBS implantations. METHODS: We report 3 patients who developed a cyst along the course of the DBS lead. These patients received DBS for different indications and in different brain locations. RESULTS: Clinical courses differed considerably with 1 asymptomatic patient followed conservatively, 1 mildly symptomatic patient who had the DBS hardware removed for insidious worsening over months, and 1 who had it emergently removed for acute development of hydrocephalus. Serial imaging revealed spontaneous reduction in cyst size over time in the asymptomatic patient, and following removal in 1 of the symptomatic patients. CONCLUSION: This report highlights the variable clinical presentation and course of patients who develop cysts along the DBS lead. It suggests that some cases can be followed clinically without removal of hardware but that ongoing vigilance is required given the potential for serious adverse events.

The International Deep Brain Stimulation Registry and Database for Gilles de la Tourette Syndrome: How Does It Work?

Tourette Syndrome (TS) is a neuropsychiatric disease characterized by a combination of motor and vocal tics. Deep brain stimulation (DBS), already widely utilized for Parkinson's disease and other movement disorders, is an emerging therapy for select and severe cases of TS that are resistant to medication and behavioral therapy. Over the last two decades, DBS has been used experimentally to manage severe TS cases. The results of case reports and small case series have been variable but in general positive. The reported interventions have, however, been variable, and there remain non-standardized selection criteria, various brain targets, differences in hardware, as well as variability in the programming parameters utilized. DBS centers perform only a handful of TS DBS cases each year, making large-scale outcomes difficult to study and to interpret. These limitations, coupled with the variable effect of surgery, and the overall small numbers of TS patients with DBS worldwide, have delayed regulatory agency approval (e.g., FDA and equivalent agencies around the world). The Tourette Association of America, in response to the worldwide need for a more organized and collaborative effort, launched an international TS DBS registry and database. The main goal of the project has been to share data, uncover best practices, improve outcomes, and to provide critical information to regulatory agencies. The international registry and database has improved the communication and collaboration among TS DBS centers worldwide. In this paper we will review some of the key operation details for the international TS DBS database and registry.

Lessons Learned from Open-label Deep Brain Stimulation for Tourette Syndrome: Eight Cases over 7 Years.

BACKGROUND: Deep brain stimulation (DBS) remains an experimental but promising treatment for patients with severe refractory Gilles de la Tourette syndrome (TS). Controversial issues include the selection of patients (age and clinical presentation), the choice of brain targets to obtain optimal patient-specific outcomes, and the risk of surgery- and stimulation-related serious adverse events. METHODS: This report describes our open-label experience with eight patients with severe refractory malignant TS treated with DBS. The electrodes were placed in the midline thalamic nuclei or globus pallidus, pars internus, or both. Tics were clinically assessed in all patients pre- and postoperatively using the Modified Rush Video Protocol and the Yale Global Tic Severity Scale (YGTSS). RESULTS: Although three patients had marked postoperative improvement in their tics (>50% improvement on the YGTSS), the majority did not reach this level of clinical improvement. Two patients had to have their DBS leads removed (one because of postoperative infection and another because of lack of benefit). DISCUSSION: Our clinical experience supports the urgent need for more data and refinements in interventions and outcome measurements for severe, malignant, and medication-refractory TS. Because TS is not an etiologically homogenous clinical entity, the inclusion criteria for DBS patients and the choice of brain targets will require more refinement.

Thoracic radiculopathy following spinal cord stimulator placement: case series.

OBJECTIVE: The clinical entity of thoracic radiculopathy following spinal cord stimulator (SCS) placement has not been previously described. MATERIALS AND METHODS: A retrospective review of prospectively acquired data on 172 patients, having undergone thoracic SCS placement at our institution, was performed. In addition, four patients were implanted at outside institutions, and were referred for revision. We examine our early experience with placement of thoracic SCS in surgically treated patients with chronic pain and 15 associated specific postoperative radicular pain complications along respective thoracic dermatomes. We postulate that preexisting thoracic spinal pathology affords less compliance in the placement of larger paddles, and subsequent radicular pain in a band-like abdominal fashion. RESULTS: A syndrome of thoracic radiculopathy, presenting as intractable lower thoracic or abdominal wall pain occurring in the immediate postoperative period, was identified in 15 patients. These patients subsequently underwent revision surgery, with either a more extensive laminectomy to further decompress the dorsal nerve roots or lead removal, both of which resulted in near immediate relief of symptoms. CONCLUSIONS: Thoracic radiculopathy may occur following SCS paddle lead placement. This clinical syndrome is characterized by its immediate postoperative development, band-like thoracic or abdominal pain pattern, severe pain that both overwhelms the incisional pain and is refractory to medications, and absence of motor deficit. The lateral placement of paddle leads increases the risk of radicular symptoms. Preoperative thoracic spine magnetic resonance imaging may be helpful in identifying patients who may be susceptible to this syndrome.

The use of intraoperative electrophysiology for the placement of spinal cord stimulator paddle leads under general anesthesia.

BACKGROUND: Placement of spinal cord stimulating paddle leads has traditionally been performed under local anesthesia with intravenous sedation to allow intraoperative confirmation of appropriate placement. It may be difficult to maintain appropriate sedation in certain patients because of medical comorbidities. Furthermore, patients undergoing lead revision frequently have extensive epidural scarring, requiring multilevel laminectomies to place the electrode appropriately. OBJECTIVE: To report our technique of neurophysiologic monitoring that allows these procedures to be performed under general anesthesia. METHODS: Data from 78 patients who underwent electromyography during laminectomy for paddle lead placement were retrospectively reviewed. Seventy patients presented for first-time permanent system placement after a successful trial, and 8 were referred for revision or replacement of previously functioning systems. Surgeries were performed under general anesthesia with fluoroscopic guidance. Electromyography was used to help define the physiological midline of the spinal cord and to guide appropriate lead placement. Somatosensory evoked potentials were used as an adjunct to minimize the possibility of neural injury. RESULTS: Immediately postoperatively, 75 of 78 patients reported that the paresthesia coverage was as good as (or better than) that of the spinal cord stimulation trial. At the long-term follow-up, 1 system was removed for infection, and 6 systems were explanted for lack of efficacy. A total of 64 of the 78 implanted patients reported continued pain relief with stimulator use. Revision surgery was performed in 9 patients. CONCLUSION: The use of intraoperative electrophysiology for the placement of spinal cord stimulation paddle leads under general anesthesia is a safe and efficacious alternative to awake surgery.

Using imaging to identify psychogenic parkinsonism before deep brain stimulation surgery. Report of 2 cases.

The frequency with which patients with atypical parkinsonism and advanced motor symptoms undergo deep brain stimulation (DBS) procedures is unknown. However, the potential exposure of these patients to unnecessary surgical risks makes their identification critical. As many as 15% of patients enrolled in recent early Parkinson disease (PD) trials have been found to lack evidence of a dopaminergic deficit following PET or SPECT imaging. This suggests that a number of patients with parkinsonism who are referred for DBS may not have idiopathic PD. The authors report on 2 patients with probable psychogenic parkinsonism who presented for DBS surgery. They found that both patients had normal caudate and putamen [(18)F]-fluorodopa uptake on PET imaging, along with normal expression of specific disease-related metabolic networks for PD and multiple system atrophy, a common form of atypical neurodegenerative parkinsonism. The clinical and PET findings in these patients highlight the role of functional imaging in assisting clinical decision making when the diagnosis is uncertain.

Occipital neuromodulation for refractory headache in the Chiari malformation population.

Chronic occipital and suboccipital headache is a common symptom in patients with Chiari I malformation (CMI). These headaches may persist despite appropriate surgical treatment of the underlying pathology via suboccipital decompression, duraplasty and related procedures. Occipital stimulation has been shown to be effective in the treatment of a variety of occipital headache/pain syndromes. We present our series of 18 patients with CMI and persistent occipital headaches who underwent occipital neurostimulator trials and, following successful trials, permanent stimulator placement. Seventy-two percent (13/18) of patients had a successful stimulator trial and proceeded to permanent implant. Of those implanted, 11/13 (85%) reported continued pain relief at a mean follow-up of 23 months. Device-related complications requiring additional surgeries occurred in 31% of patients. Occipital neuromodulation may provide significant long-term pain relief in selected CMI patients with persistent occipital pain. Larger and longer-term studies are needed to further define appropriate patient selection criteria as well as to refine the surgical technique to minimize device-related complications.

A technique of distal to proximal revision of peripheral neurostimulator leads: technical note.

BACKGROUND: Peripheral nerve stimulation for chronic pain states is a safe and efficacious technique, being used with increasing frequency. The incidence of hardware-related complications requiring revision remains high. OBJECTIVES: The authors describe a technique of distal to proximal neurostimulator lead revision, which does not require the changing of generators or extension leads, and thus presumably will minimize further device-related complications. METHODS: The authors present a case series of 3 patients where the distal to proximal neurostimulator lead revision technique was utilized. RESULTS: The technique was well tolerated in each instance and all patients reported >50% pain reduction at long-term follow-up. CONCLUSIONS: The distal to proximal neurostimulator lead revision technique quickly and safely adjusts lead position, including both lead depth and lead tip location, without a need for replacement of components or revision of the entire system.

Metabolic correlates of subthalamic nucleus activity in Parkinson's disease.

Overactivity of subthalamic nucleus (STN) neurons is a consistent feature of Parkinson's disease (PD) and is a target of therapy for this disorder. However, the relationship of STN firing rate to regional brain function is not known. We scanned 17 PD patients with (18)F-fluorodeoxyglucose (FDG) PET to measure resting glucose metabolism before the implantation of STN deep brain stimulation electrodes. Spontaneous STN firing rates were recorded during surgery and correlated with preoperative regional glucose metabolism on a voxel-by-voxel basis. We also examined the relationship between firing rate and the activity of metabolic brain networks associated with the motor and cognitive manifestations of the disease. Mean firing rates were 47.2 +/- 6.1 and 48.7 +/- 8.5 Hz for the left and right hemispheres, respectively. These measures correlated (P < 0.007) with glucose metabolism in the putamen and globus pallidus, which receive projections from this structure. Significant correlations (P < 0.0005) were also evident in the primary motor (BA4) and dorsolateral prefrontal (BA46/10) cortical areas. The activity of both the motor (P < 0.0001) and the cognitive (P < 0.006) PD-related metabolic networks was elevated in these patients. STN firing rates correlated with the activity of the former (P < 0.007) but not the latter network (P = 0.39). The findings suggest that the functional pathways associated with motor disability in PD are linked to the STN firing rate. These pathways are likely to mediate the clinical benefit that is seen following targeted STN interventions for this disease.

Safety and efficacy of stereotactic radiosurgery for tumors of the spine.

OBJECT: The extension of stereotactic radiosurgery treatment of tumors of the spine has the potential to benefit many patients. As in the early days of cranial stereotactic radiosurgery, however, dose-related efficacy and toxicity are not well understood. The authors report their initial experience with stereotactic radiosurgery of the spine with attention to dose, efficacy, and toxicity. METHODS: All patients who underwent stereotactic radiosurgery of the spine were treated using the Novalis unit at Westchester Medical Center between December 2001 and January 2004 are included in a database consisting of demographics on disease, dose, outcome, and complications. A total of 31 patients (12 men, 19 women; mean age 61 years, median age 63 years) received treatment for 35 tumors. Tumor types included 26 metastases (12 lung, nine breast, five other) and nine primary tumors (four intradural, five extradural). Thoracic tumors were most common (17 metastases and four primary) followed by lumbar tumors (four metastases and four primary). Lesions were treated to the 85 to 90% isodose line with spinal cord doses being less than 50%. The dose per fraction and total dose were selected on the basis of previous treatment (particularly radiation exposure), size of lesion, and proximity to critical structures. CONCLUSIONS: Rapid and significant pain relief was achieved after stereotactic radiosurgery in 32 of 34 treated tumors. In patients treated for metastases, pain was relieved within 72 hours and remained reduced 3 months later. Pain relief was achieved with a single dose as low as 500 cGy. Spinal cord isodoses were less than 50% in all patients except those with intradural tumors (mean single dose to spinal cord 268 cGy and mean total dose to spinal cord 689 cGy). Two patients experienced transient radiculitis (both with a biological equivalent dose (BED) > 60 Gy). One patient who suffered multiple recurrences of a conus ependymoma had permanent neurological deterioration after initial improvement. Pathological evaluation of this lesion at surgery revealed radiation necrosis with some residual/recurrent tumor. No patient experienced other organ toxicity. Stereotactic radiosurgery of the spine is safe at the doses used and provides effective pain relief. In this study, BEDs greater than 60 Gy were associated with an increased risk of radiculitis.

Subthalamic nucleus stimulation in patients with a prior pallidotomy.

OBJECT: A substantial number of patients with Parkinson disease (PD) who have undergone unilateral stereotactic pallidotomy ultimately develop symptom progression, becoming potential candidates for further surgical treatment. Bilateral subthalamic nucleus (STN) deep brain stimulation (DBS) has been shown to be effective in the treatment of a subset of patients with refractory PD. Microelectrode recording is performed to help localize the STN and guide final placement of the electrode. Potential alterations in physiological features of the STN after pallidotomy may complicate localization of this structure in this group of patients. METHODS: Bilateral STN DBS surgery guided by microelectrode recording was performed in six patients who had undergone previous unilateral pallidotomies. Physiologically obtained parameters of the STN, including trajectory length, mean firing rate, cell number, and cell density were calculated. These data were compared with those from the side without prior pallidotomy within each patient, as well as with those from our series of 49 subthalamic nuclei explored in 26 patients who had not undergone prior pallidotomy but who underwent bilateral STN stimulator placement. In all patients, analysis of STN cellular activity on the side ipsilateral to the pallidotomy demonstrated a lower mean firing frequency than on the contralateral, intact side. The physiological features on the intact side were not significantly different from those found in our series of patients who had not undergone prior pallidotomy. CONCLUSIONS: Physicians who perform STN surgery in patients with prior pallidotomy should be aware of the electrophysiological differences between the STN that had undergone pallidotomy and the one that had not, to avoid prolonging recording time to search for the typical STN. The implications of these findings for the current models of information processing in the basal ganglia are discussed.

Neurophysiological refinement of subthalamic nucleus targeting.

OBJECTIVE: Advances in image-guided stereotactic surgery, microelectrode recording techniques, and stimulation technology have been the driving forces behind a resurgence in the use of functional neurosurgery for the treatment of movement disorders. Despite the dramatic effects of deep brain stimulation (DBS) techniques in ameliorating the symptoms of Parkinson's disease, many critical questions related to the targeting, effects, and mechanisms of action of DBS remain unanswered. In this report, we describe the methods used to localize the subthalamic nucleus (STN) and we present the characteristics of encountered cells. METHODS: Twenty-six patients with idiopathic Parkinson's disease underwent simultaneous, bilateral, microelectrode-refined, DBS electrode implantation into the STN. Direct and indirect magnetic resonance imaging-based anatomic targeting was used. Cellular activity was analyzed for various neurophysiological parameters, including firing rates and interspike intervals. Physiological targeting confirmation was obtained by performing macrostimulation through the final DBS electrode. RESULTS: The average microelectrode recording time for each trajectory was 20 minutes, with a mean of 5.2 trajectories/patient. Typical trajectories passed through the anterior thalamus, zona incerta/fields of Forel, STN, and substantia nigra-pars reticulata. Each structure exhibited a characteristic firing pattern. In particular, recordings from the STN exhibited an increase in background activity and an irregular firing pattern, with a mean rate of 47 Hz. The mean cell density was 5.6 cells/mm, with an average maximal trajectory length of 5.3 mm. Macrostimulation via the DBS electrode yielded mean sensory and motor thresholds of 4.2 and 5.7 V, respectively. CONCLUSION: The principal objectives of microelectrode recording refinement of anatomic targeting are precise identification of the borders of the STN and thus determination of its maximal length. Microelectrode recording also allows identification of the longest and most lateral segment of the STN, which is our preferred target for STN DBS electrode implantation. Macrostimulation via the final DBS electrode is then used primarily to establish the side effect profile for postoperative stimulation. Microelectrode recording is a helpful targeting adjunct that will continue to facilitate our understanding of basal ganglion physiological features.