Hidden Error in Optical Stereotactic Navigation Systems and Strategy to Maximize Accuracy.

BACKGROUND: Optical neuronavigation has been established as a reliable and effective adjunct to many neurosurgical procedures. Operations such as asleep deep brain stimulation (aDBS) benefit from the potential increase in accuracy that these systems offer. Built into these technologies is a degree of tolerated error that may exceed the presumed accuracy resulting in suboptimal outcomes. OBJECTIVE: The objective of this study was to identify an underlying source of error in neuronavigation and determine strategies to maximize accuracy. METHODS: A Medtronic Stealth system (Stealth Station 7 hardware, S8 software, version 3.1.1) was used to simulate an aDBS procedure with the Medtronic Nexframe system. Multiple configurations and orientations of the Nexframe-Nexprobe system components were examined to determine potential sources of, and to quantify navigational error, in the optical navigation system. Virtual entry point and target variations were recorded and analyzed. Finally, off-plan error was recorded with the AxiEM system and visual observation on a phantom head. RESULTS: The most significant source of error was found to be the orientation of the reference marker plate configurations to the camera system, with the presentation of the markers perpendicular to the camera line of site being the most accurate position. Entry point errors ranged between 0.134 ± 0.048 and 1.271 ± 0.0986 mm in a complex, reproducible pattern dependent on the orientation of the Nexprobe reference plate. Target errors ranged between 0.311 ± 0.094 and 2.159 ± 0.190 mm with a similarly complex, repeatable pattern. Representative configurations were tested for physical error at target with errors ranging from 1.2 mm to 1.4 mm. Throughout data acquisition, no orientation was indicated as outside the acceptable tolerance by the Stealth software. CONCLUSIONS: Use of optical neuronavigation is expected to increase in frequency and variety of indications. Successful implementation of this technology depends on understanding the tolerances built into the system. In situations that depend on extremely high precision, surgeons should familiarize themselves with potential sources of error so that systems may be optimized beyond the manufacturer's built-in tolerances. We recommend that surgeons align the navigation reference plate and any optical instrument's reference plate spheres in the plane perpendicular to the line of site of the camera to maximize accuracy.

Verification of the Deep Brain Stimulation Electrode Position Using Intraoperative Electromagnetic Localization.

BACKGROUND: Electromagnetic (EM) localization has typically been used to direct shunt catheters into the ventricle. The objective of this study was to determine if this method of EM tracking could be used in a deep brain stimulation (DBS) electrode cannula to accurately predict the eventual location of the electrode contacts. METHODS: The Medtronic AxiEMTM system was used to generate the cannula tip location directed to the planned target site. Prior to clinical testing, a series of phantom modelling observations were made. RESULTS: Phantom trials (n = 23) demonstrated that the cannula tip could be accurately located at the target site with an error of between 0.331 ± 0.144 and 0.6 ± 0.245 mm, depending on the orientation of the delivery system to the axis of the phantom head. Intraoperative EM localization of the DBS cannula was performed in 84 trajectories in 48 patients. The average difference between the planned target and the EM stylet location at the cannula tip was 1.036 ± 0.543 mm. The average error between the planned target coordinates and the actual target electrode location (by CT) was 1.431 ± 0.607 and 1.145 ± 0.636 mm for the EM stylet location in the cannula (p = 0.00312), indicating that EM localization reflected the position of the target electrode more accurately than the planned target. CONCLUSIONS: EM localization can be used to verify the position of DBS electrodes intraoperatively with a high accuracy.

Preoptic area cooling increases the sympathetic outflow to brown adipose tissue and brown adipose tissue thermogenesis.

Modest cold exposures are likely to activate autonomic thermogenic mechanisms due to activation of cutaneous thermal afferents, whereas central thermosensitive neurons set the background tone on which this afferent input is effective. In addition, more prolonged or severe cold exposures that overwhelm cold defense mechanisms would directly activate thermosensitive neurons within the central nervous system. Here, we examined the involvement of the canonical brown adipose tissue (BAT) sympathoexcitatory efferent pathway in the response to direct local cooling of the preoptic area (POA) in urethane-chloralose-anesthetized rats. With skin temperature and core body temperature maintained between 36 and 39°C, cooling POA temperature by ~1-4°C evoked increases in BAT sympathetic nerve activity (SNA), BAT temperature, expired CO2, and heart rate. POA cooling-evoked responses were inhibited by nanoinjections of ionotropic glutamate receptor antagonists or the GABAA receptor agonist muscimol into the median POA or by nanoinjections of ionotropic glutamate receptor antagonists into the dorsomedial hypothalamic nucleus (bilaterally) or into the raphe pallidus nucleus. These results demonstrate that direct cooling of the POA can increase BAT SNA and thermogenesis via the canonical BAT sympathoexcitatory efferent pathway, even in the face of warm thermal input from the skin and body core.

Asleep Deep Brain Stimulation Reduces Incidence of Intracranial Air during Electrode Implantation.

BACKGROUND: Asleep deep brain stimulation (aDBS) implantation replaces microelectrode recording for image-guided implantation, shortening the operative time and reducing cerebrospinal fluid egress. This may decrease pneumocephalus, thus decreasing brain shift during implantation. OBJECTIVE: To compare the incidence and volume of pneumocephalus during awake (wkDBS) and aDBS procedures. METHODS: A retrospective review of bilateral DBS cases performed at Oregon Health & Science University from 2009 to 2017 was undertaken. Postimplantation imaging was reviewed to determine the presence and volume of intracranial air and measure cortical brain shift. RESULTS: Among 371 patients, pneumocephalus was noted in 66% of wkDBS and 15.6% of aDBS. The average volume of air was significantly higher in wkDBS than aDBS (8.0 vs. 1.8 mL). Volumes of air greater than 7 mL, which have previously been linked to brain shift, occurred significantly more frequently in wkDBS than aDBS (34 vs 5.6%). wkDBS resulted in significantly larger cortical brain shifts (5.8 vs. 1.2 mm). CONCLUSIONS: We show that aDBS reduces the incidence of intracranial air, larger air volumes, and cortical brain shift. Large volumes of intracranial air have been correlated to shifting of brain structures during DBS procedures, a variable that could impact accuracy of electrode placement.

Factors Affecting Stereotactic Accuracy in Image-Guided Deep Brain Stimulator Electrode Placement.

BACKGROUND/AIMS: Intraoperative imaging allows near-real-time assessment of stereotactic accuracy during implantation of deep brain stimulation (DBS) electrodes. Such technology can be used to examine factors impacting stereotactic error. METHODS: Intraoperative CT imaging was reviewed in patients undergoing DBS placement at Oregon Health and Sciences University. Coordinates of the target electrode were compared to the operative plan to characterize the magnitude and direction of stereotactic error with respect to side of implantation, target, and electrode approach angles. RESULTS: One hundred sixty-nine leads in 94 patients were examined. Targets were GPi (n = 86), STN (n = 31), and Vim (n = 52). The average Euclidean error was 1.63 mm (SD 0.87). The error magnitude was higher for Vim (1.95 mm) than for GPi (1.44 mm), while STN (1.65 mm) did not differ from either Vim or GPi (ANOVA: F = 6.15, p = 0.003). Electrodes targeting Vim and STN were significantly more likely to deviate medially compared to those targeting GPi (ANOVA: F = 9.13, p < 0.001). The coronal approach angle affected the error when targeting Vim (ρ = 0.338, p = 0.01). These findings were confirmed during multivariate analyses. CONCLUSIONS: This study shows a significant effect of target on the accuracy of electrode placement for DBS. Targeting Vim results in a greater Euclidean error and a greater medial deviation off target. These systematic deviations should be taken into account during electrode implantation.

Effect of Subthalamic Nucleus Stimulation on Pedunculopontine Nucleus Neural Activity.

BACKGROUND: The pedunculopontine nucleus has recently been proposed as an alternative target for deep brain stimulation for the treatment of medically intractable Parkinson's disease. The suggested indication for pedunculopontine nucleus deep brain stimulation is severe and medically intractable axial symptoms such as gait and postural impairment. OBJECTIVE: Our goal in this study was to describe the effects of subthalamic nucleus stimulation on pedunculopontine nucleus electrophysiological activity. METHODS: Fourteen male Wistar rats were divided into a sham stimulation group and an experimental group. In both groups, electrodes were implanted bilaterally into the subthalamic nucleus and into the right pedunculopontine nucleus. Microelectrode recordings were carried out in both groups prior to and during subthalamic nucleus stimulation. RESULTS: Subthalamic nucleus stimulation produced no clear inhibition of neuronal firing in the pedunculopontine nucleus. However, we found that stimulation of the subthalamic nucleus at 60 Hz produces some entrainment of pedunculopontine nucleus neuronal firing and a shift of subthalamic nucleus firing patterns to more tonic and random patterns. These results are consistent with the effects of deep brain stimulation on neuronal activity in the subthalamic nucleus and globus pallidus internus. CONCLUSION: The result of this study provides additional evidence to improve our understanding of the mechanism of subthalamic nucleus-deep brain stimulation, and its physiological consequences.

The effect of deep brain stimulation randomized by site on balance in Parkinson's disease.

BACKGROUND: The effect of the surgical site of DBS on balance and gait in Parkinson's Disease (PD) is uncertain. This is the first double-blind study of subjects randomized to either the STN (N = 14) or GPi (N = 14) who were assessed on a range of clinical balance measures. METHODS: Balance testing occurred before and 6 months postsurgery. A control PD group was tested over the same period without surgery (N = 9). All subjects were tested on and off medication and DBS subjects were also tested on and off DBS. The Postural Instability and Gait Disability items of the UPDRS and additional functional tests, which we call the Balance and Gait scale, were assessed. Activities of Balance Confidence and Activities of Daily Living questionnaires were also recorded. RESULTS: Balance was not different between the best-treated states before and after DBS surgery for both sites. Switching DBS on improved balance scores, and scores further improved with medication, compared to the off state. The GPi group showed improved performance in the postsurgery off state and better ratings of balance confidence after surgery, compared to the STN group. CONCLUSIONS: Clinical measures of balance function for both the STN and GPi sites showed that balance did not improve beyond the best medically treated state before surgery. Both clinical balance testing in the off/off state and self-reported balance confidence after surgery showed better performance in the GPi than the STN group.

Use of an artificial neural network for diagnosis of facial pain syndromes: an update.

BACKGROUND: Based on a classification scheme for facial pain syndromes and a binomial (yes/no) facial pain questionnaire, we previously reported on the ability of an artificial neural network (ANN) to recognize and correctly diagnose patients with different facial pain syndromes. OBJECTIVES: We now report on an updated questionnaire, the development of a secure web-based neural network application and details of ANNs trained to diagnose patients with different facial pain syndromes. METHODS: Online facial pain questionnaire responses collected from 607 facial pain patients (395 female, 65%, ratio F/M 1.86/1) over 5 years and 7 months were used for ANN training. RESULTS: Sensitivity and specificity of the currently running ANN for trigeminal neuralgia type 1 and trigeminal neuralgia type 2 are 92.4 and 62.5% and 87.8 and 96.4%, respectively. Sensitivity and specificity are 86.7 and 95.2% for trigeminal neuropathic pain, 0 and 100% for trigeminal deafferentation pain and 100% for symptomatic trigeminal neuralgia and postherpetic neuralgia. Sensitivity is 50% for nervus intermedius neuralgia (NIN) and 0% for atypical facial pain (AFP), glossopharyngeal neuralgia (GPN) and temporomandibular joint disorder (TMJ). Specificity for AFP, NIN and TMJ is 99% and for GPN, 100%. CONCLUSIONS: We demonstrate the utilization of question-based historical self-assessment responses used as inputs to design an ANN for the purpose of diagnosing facial pain syndromes (outputs) with high accuracy.

A Well-Being Well-Check for Neurosurgery: Evidence-Based Suggestions for Our Specialty Based on a Systematic Review.

BACKGROUND: The path through neurosurgery is rigorous. Many neurosurgeons may experience burnout, depression, or suicide throughout training and practice. We review the literature to help foster a culture of awareness and self-care and arm trainees with coping skills to reduce burnout and, thus, suicidality during all phases of their medical careers. METHODS: A systematic search was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines using 4 databases. 7 studies were included. RESULTS: Overlying themes of interventions were to increase balance, mindfulness, and physical fitness. The most common interventions included in programs were educational and physical activity. We suggest a comprehensive wellness program emphasizing interventions from 4 wellness dimensions-physical, spiritual, mental, and emotional. CONCLUSIONS: Many neurosurgeons experience burnout, leading to a lack of satisfaction and early retirement; this necessitates a discipline-wide acknowledgment of endemic burnout among neurosurgeons. Systemic changes are needed to refine the training process and prioritize physician well-being- this cannot be left to chance.

Deep brain stimulation entrains local neuronal firing in human globus pallidus internus.

Deep brain stimulation (DBS) in the internal segment of the globus pallidus (GPi) relieves the motor symptoms of Parkinson's disease, yet the mechanism of action remains uncertain. To address the question of how therapeutic stimulation changes neuronal firing in the human brain, we studied the effects of GPi stimulation on local neurons in unanesthetized patients. Eleven patients with idiopathic Parkinson's disease consented to participate in neuronal recordings during stimulator implantation surgery. A recording microelectrode and a DBS macroelectrode were advanced through the GPi in parallel until a single neuron was isolated. After a baseline period, stimulation was initiated with varying voltages and different stimulation sites. The intra-operative stimulation parameters (1-8 V, 88-180 Hz, 0.1-ms pulses) were comparable with the postoperative DBS settings. Stimulation in the GPi did not silence local neuronal activity uniformly, but instead loosely entrained firing and decreased net activity in a voltage-dependent fashion. Most neurons had decreased activity during stimulation, although some increased or did not change firing rate. Thirty-three of 45 neurons displayed complex patterns of entrainment during stimulation, and burst-firing was decreased consistently after stimulation. Recorded spike trains from patients were used as input into a model of a thalamocortical relay neuron. Only spike trains that occurred during therapeutically relevant voltages significantly reduced transmission error, an effect attributable to changes in firing patterns. These data indicate that DBS in the human GPi does not silence neuronal activity, but instead disrupts the pathological firing patterns through loose entrainment of neuronal activity.

Pallidal versus subthalamic deep-brain stimulation for Parkinson's disease.

BACKGROUND: Deep-brain stimulation is the surgical procedure of choice for patients with advanced Parkinson's disease. The globus pallidus interna and the subthalamic nucleus are accepted targets for this procedure. We compared 24-month outcomes for patients who had undergone bilateral stimulation of the globus pallidus interna (pallidal stimulation) or subthalamic nucleus (subthalamic stimulation). METHODS: At seven Veterans Affairs and six university hospitals, we randomly assigned 299 patients with idiopathic Parkinson's disease to undergo either pallidal stimulation (152 patients) or subthalamic stimulation (147 patients). The primary outcome was the change in motor function, as blindly assessed on the Unified Parkinson's Disease Rating Scale, part III (UPDRS-III), while patients were receiving stimulation but not receiving antiparkinsonian medication. Secondary outcomes included self-reported function, quality of life, neurocognitive function, and adverse events. RESULTS: Mean changes in the primary outcome did not differ significantly between the two study groups (P=0.50). There was also no significant difference in self-reported function. Patients undergoing subthalamic stimulation required a lower dose of dopaminergic agents than did those undergoing pallidal stimulation (P=0.02). One component of processing speed (visuomotor) declined more after subthalamic stimulation than after pallidal stimulation (P=0.03). The level of depression worsened after subthalamic stimulation and improved after pallidal stimulation (P=0.02). Serious adverse events occurred in 51% of patients undergoing pallidal stimulation and in 56% of those undergoing subthalamic stimulation, with no significant between-group differences at 24 months. CONCLUSIONS: Patients with Parkinson's disease had similar improvement in motor function after either pallidal or subthalamic stimulation. Nonmotor factors may reasonably be included in the selection of surgical target for deep-brain stimulation. (ClinicalTrials.gov numbers, NCT00056563 and NCT01076452.)

Thalamotomy as a treatment option for tremor after ineffective deep brain stimulation.

BACKGROUND: As the number of deep brain stimulation (DBS) surgeries increases, complications from malpositioned electrodes, tolerance to stimulation and loss of efficacy have also increased. Our objective was to assess thalamotomy as a salvage treatment option after ineffective DBS. METHODS: A retrospective chart analysis of patients who underwent ipsilateral stereotactic thalamotomy after an ineffective ventrointermediate nucleus DBS procedure was undertaken. Patient outcome was based on follow-up visit chart notes, and a nonvalidated patient telephone questionnaire to assess patients' perception of tremor and functional ability after thalamotomy. RESULTS: Six patients with essential tremor and 1 with tremor-predominant Parkinson's disease met our inclusion criteria. Thalamotomies were undertaken for ineffective DBS due to dysarthria and paresthesias with programming in 2 patients, tremor that failed to respond to increased DBS despite a lack of side effects in 2 patients, malpositioned electrode in 2 patients, and sudden loss of DBS efficacy following eye surgery in 1 patient. Following thalamotomy, 3 patients reported improvement in symptoms and function, 3 patients reported improvement in symptoms that were not reflected in functional improvement, and 1 patient reported no improvement in symptoms or function. CONCLUSION: Thalamotomy may provide a viable salvage solution in patients who fail to respond to DBS due to complications such as malpositioned electrodes, tolerance to stimulation or loss of efficacy.

Percutaneous trigeminal tractotomy-nucleotomy with use of intraoperative computed tomography and general anesthesia: report of 2 cases.

For confirming the correct location of the radiofrequency electrode before creation of a lesion, percutaneous CT-guided trigeminal tractotomy-nucleotomy is most commonly performed with the patient prone and awake. However, for patients whose facial pain and hypersensitivity are so severe that the patients are unable to rest their face on a support (as required with prone positioning), awake CT-guided tractotomy-nucleotomy might not be feasible. The authors describe 2 such patients, for whom percutaneous intraoperative CT-guided tractotomy-nucleotomy under general anesthesia was successful. One patient was a 79-year-old man with profound left facial postherpetic neuralgia, who was unable to tolerate awake CT-guided tractotomy-nucleotomy, and the other was a 45-year-old woman with intractable hemicranial pain that developed after a right frontal lesionectomy for epilepsy. Each patient underwent a percutaneous intraoperative CT-guided tractotomy-nucleotomy under general anesthesia. No complications occurred, and each patient reported excellent pain relief for up to 6 and 3 months after surgery, respectively. Percutaneous intraoperative CT-guided tractotomy-nucleotomy performed on anesthetized patients is effective for facial postherpetic neuralgia and postoperative hemicranial neuralgia.

Acute deep brain stimulation of the paraventricular nucleus of the hypothalamus increases brown adipose tissue thermogenesis in rats.

Brown adipose tissue (BAT) activity is controlled by the sympathetic nervous system. Activation of BAT has shown significant promise in preclinical studies to elicit weight loss. Since the hypothalamic paraventricular nucleus (PVN) contributes to the regulation of BAT thermogenic activity, we sought to determine the effects of electrical stimulation of the PVN as a model of deep brain stimulation (DBS) for increasing BAT sympathetic nerve activity (SNA). The rostral raphe pallidus area (rRPa) was also chosen as a target for DBS since it contains the sympathetic premotor neurons for BAT. Electrical stimulation (100 µA, 100 µs, 100 Hz, for 5 min at a 50 % duty cycle) of the PVN increased BAT SNA and BAT thermogenesis. These effects were prevented by a local nanoinjection of bicuculline, a GABAA receptor antagonist. We suggest that electrical stimulation of the PVN elicited local release of GABA, which inhibited BAT sympathoinhibitory neurons in PVN, thereby releasing a restraint on BAT SNA. Electrical stimulation of the rRPa inhibited BAT thermogenesis and this was prevented by a local nanoinjection of bicuculline, suggesting that local release of GABA suppressed BAT SNA. Electrical stimulation of the PVN activates BAT metabolism via a mechanism that may include activation of local GABAA receptors. These findings contribute to our understanding of the mechanisms underlying the effects of DBS in the regulation of fat metabolism and provide a foundation for further DBS studies targeting hypothalamic circuits regulating BAT thermogenesis as a therapy for obesity.

Deep Brain Stimulation for the Treatment of Hemichorea: Case Series and Literature Review.

Background: Hemichorea (HC) and its severe form hemiballismus (HB) are rare movement disorders which can be medically refractory to treatments and may need surgical intervention. Case Report: We report 3 patients with HC-HB who had meaningful clinical improvement with unilateral deep brain stimulation (DBS) of the globus pallidus interna (GPi). We identified 8 prior cases of HC-HB treated with GPi-DBS, and a majority of these patients experienced significant improvement in their symptoms. Discussion: GPi-DBS can be considered in medically refractory HC-HB in carefully selected patients. However, data is limited to small case series and further studies are needed.

Identifying the therapeutic zone in globus pallidus deep brain stimulation for Parkinson's disease.

OBJECTIVE: The globus pallidus internus (GPI) has been demonstrated to be an effective surgical target for deep brain stimulation (DBS) treatment in patients with medication-refractory Parkinson's disease (PD). The ability of neurosurgeons to define the area of greatest therapeutic benefit within the globus pallidus (GP) may improve clinical outcomes in these patients. The objective of this study was to determine the best DBS therapeutic implantation site within the GP for effective treatment in PD patients. METHODS: The authors performed a retrospective review of 56 patients who underwent bilateral GP DBS implantation at their institution during the period from January 2015 to January 2020. Each implanted contact was anatomically localized. Patients were followed for stimulation programming for at least 6 months. The authors reviewed preoperative and 6-month postsurgery clinical outcomes based on data from the Unified Parkinson's Disease Rating Scale Part III (UPDRS III), dyskinesia scores, and levodopa equivalent daily dose (LEDD). RESULTS: Of the 112 leads implanted, the therapeutic cathode was most frequently located in the lamina between the GPI external segment (GPIe) and the GP externus (GPE) (n = 40). Other common locations included the GPE (n = 24), the GPIe (n = 15), and the lamina between the GPI internal segment (GPIi) and the GPIe (n = 14). In the majority of patients (73%) a monopolar programming configuration was used. At 6 months postsurgery, UPDRS III off medications (OFF) and on stimulation (ON) scores significantly improved (z = -4.02, p < 0.001), as did postsurgery dyskinesia ON scores (z = -4.08, p < 0.001) and postsurgery LEDD (z = -4.7, p < 0.001). CONCLUSIONS: Though the ventral GP (pallidotomy target) has been a commonly used target for GP DBS, a more dorsolateral target may be more effective for neuromodulation strategies. The assessment of therapeutic contact locations performed in this study showed that the lamina between GPI and GPE used in most patients is the optimal central stimulation target. This information should improve preoperative GP targeting.

Lesioning and stimulation in tremor-predominant movement disorder patients: an institutional case series and patient-reported outcome.

BACKGROUND: In certain movement disorder cases, a combined stimulation and lesioning approach in the same patient could be the ideal beneficial option. OBJECTIVES: The object of this study was to retrospectively examine the indications, outcome and complications in patients who had undergone both a lesioning (thalamotomy) and deep brain stimulation (DBS) procedure (bilateral or unilateral) for a tremor-predominant movement disorder performed by a single surgeon at one institution over a 15-year period. METHODS: A retrospective review of patient records was undertaken. Patient outcome was based on follow-up visit chart notes and on a non-validated patient telephone questionnaire. RESULTS: Thirty patients required a combined stimulation and lesioning approach to control tremor. Twelve patients had either unilateral or bilateral DBS as the first procedure followed by thalamotomy; two patients required a third procedure. Eighteen patients had thalamotomy as the first procedure followed by contralateral DBS either as the second or the third procedure. Eight patients required three procedures, which included either a repeat thalamotomy or a repeat DBS. We were able to contact 22 of 30 (15 male and 15 female, average age 70.7 ± 15.4 years) tremor-predominant movement disorder patients, retrospectively. Patient-reported outcome as assessed by a non-validated telephone questionnaire was: improvement in both symptoms and function in 59%, symptom but not function improvement in 32% and no improvement in either symptom or function or worsening in 9%. In comparison, based on retrospective chart review, 77% of patients had improved symptoms and functions, 20% of patients had improved symptoms with no effect on function and 3% of patients had no improvements of symptoms or functions. CONCLUSIONS: Lesioning, which has to a great extent fallen out of favor, still has a valuable role to play in the treatment of tremor-predominant movement disorders; it can still be applied in combination with stimulation with outcome results similar to that of bilateral stimulation.

The Long-Term Outcome of Radiofrequency Ablation in Multiple Sclerosis-Related Symptomatic Trigeminal Neuralgia.

BACKGROUND: Radiofrequency lesioning (RFL) is used to surgically manage trigeminal neuralgia (TN) secondary to multiple sclerosis (MS). However, the long-term outcome of RFL has not been established. OBJECTIVE: To investigate the long-term clinical outcome of RFL in MS-related TN (symptomatic trigeminal neuralgia [STN]). METHODS: During a 23-yr period, institutional data were available for 51 patients with STN who underwent at least one RFL procedure to treat facial pain. Patient outcome was evaluated at a mean follow-up of 69 mo (95% confidence interval; range 52-86 mo). No pain with no medication (NPNM) was the primary long-term outcome measure. RESULTS: After an initial RFL procedure, immediate pain relief was achieved in 50 patients (98%), and NPNM as assessed at 1, 3, and 6 yr was 86%, 52%, and 22%, respectively. At the last clinical visit after an initial RFL, 23 patients (45%) with pain recurrence underwent repeat RFL; NPNM at 1, 3, and 6 yr after a repeat RFL was 85%, 58%, and 32%, respectively. There was no difference in pain outcome after an initial and repeat RFL ( P = .77). Ten patients with pain recurrence underwent additional RFL procedures. Two patients developed mastication muscle weakness, one patient experienced a corneal abrasion, which resolved with early ophthalmological interventions, and one patient experienced bothersome numbness. CONCLUSION: RFL achieves NPNM status in STN and can be repeated with similar efficacy.