Faculty Bibliography

BACKGROUND/UNASSIGNED:High intensity focused ultrasound (HiFU) is a relatively new incisionless intervention used for treatment of essential tremor and Parkinson's disease tremor. Understanding the indications, benefits, risks and limitations of HiFU, as well as how it compares to deep brain stimulation (DBS), is important in guiding appropriate recommendations for prospective patients. METHODS/UNASSIGNED:Current literature on efficacy and safety of HiFU in essential tremor and Parkinson's disease was reviewed. We additionally reviewed data on the patients who presented to our center for HiFU consultation, including outcomes of patients with low skull density ratios, and distances traveled for the procedure. RESULTS/DISCUSSION/UNASSIGNED:HiFU is an effective and generally well-tolerated treatment for tremor. Adverse events, especially gait instability, are typically temporary but should be discussed with patients. The risk of tremor recurrence in certain patients with Parkinson's disease is also of note. Identifying appropriate candidates for either intervention remains crucial and involves considering each patient's circumstances and preferences, potential adverse effects, and practical aspects like access to follow-up and expectations. Data on bilateral HiFU lesioning, use of HiFU in patients with low skull density ratios, and emerging targets like the pallidothalamic tract are discussed as well.

OBJECTIVES/OBJECTIVE:Spinal cord stimulation (SCS) therapy is an effective treatment for chronic pain, particularly in conditions such as postlaminectomy syndrome and complex regional pain syndrome (CRPS). Rare case reports described significant weight loss in patients who underwent dorsal column SCS therapy for chronic pain. Recently, neuromodulation for obesity has become a novel field for research. We aimed to investigate weight trends among patients treated with SCS for chronic pain. MATERIALS AND METHODS/METHODS:We conducted a retrospective chart review in 342 patients treated with SCS or dorsal root ganglion stimulators at our institution between 2010 and 2023. Patients had their weight recorded before SCS implantation and at least once within 12 months after surgery. We also conducted interviews with 28 patients who experienced significant weight loss or had revision procedures owing to weight loss. RESULTS:We found that 105 of 342 patients (30.7%) experienced weight loss of ≥5% within a year of implantation, and 32 of 105 (30.5%, 9.4% of all patients) experienced weight loss of ≥ 10%. A multivariate regression analysis revealed a modest increase in the likelihood of weight loss among patients with CRPS (odds ratio [OR] = 1.17, 95% CI [1.04, 1.30], p = 0.007) and in those who achieved pain relief after implantation (OR = 1.22, 95% CI [1.05,1.40], p = 0.008). Of the 28 patients with significant weight loss who were interviewed, 12 (43%) could not explain the reasons for their weight loss, whereas eight (29%) reported decreased appetite. Leads placed at higher thoracic levels were associated with increased rates of weight loss (37.2% at T6-T8 and 22.3% at T8-T10; p = 0.038). CONCLUSIONS:Our findings suggest that SCS therapy may affect weight in patients with chronic pain. Further studies are needed to investigate the potential role of SCS in weight modulation.

BACKGROUND AND OBJECTIVES/OBJECTIVE:Despite the well-established efficacy of deep brain stimulation (DBS) of the subthalamic nucleus (STN) for Parkinson's Disease (PD), there remains a subset of patients with only a moderate improvement in symptoms even with appropriate lead placement and optimal programming. In patients with persistent tremor or dyskinesias, one consideration is the addition of a second "rescue lead" to provide dual stimulation to primary and secondary targets to address the refractory component. This study aimed to assess all "rescue lead" cases from our institution and characterize the patients and their outcomes. METHODS:Records of all patients with PD treated at our institution between 2005 and 2023 were retrospectively reviewed. Clinical data of all patients treated with a second rescue lead to supplement a positive but inadequate initial DBS response were collected and reviewed. RESULTS:Of 670 patients with PD treated at our institution during the study period, 7 were managed with a rescue lead. All 7 were initially treated with STN DBS with a partial improvement in underlying symptoms, had confirmed appropriate lead placement, and underwent thorough programming. Four patients underwent rescue with a globus pallidus interna lead for persistent dyskinesias, all with subsequent improvement in their dyskinesias. Three patients had persistent tremors that were treated with a rescue ventrointermediate thalamus stimulation with subsequent improvement in tremor scores. There were no operative complications, and all patients tolerated dual stimulation. CONCLUSION/CONCLUSIONS:For a small subset of patients with PD with persistent dyskinesias or tremors after STN DBS despite optimized lead parameters and adequate lead placement, rescue lead placement offers an effective treatment option.

BACKGROUND AND OBJECTIVES/OBJECTIVE:Precise localization of the dentatorubrothalamic (DRT) tract can facilitate anatomic targeting in MRI-guided high-intensity focused ultrasound (HIFU) thalamotomy and thalamic deep brain stimulation for tremor. The anatomic segment of DRT fibers adjacent to the ventral intermediate nucleus of the thalamus (VIM), referred to as the rubral wing (RW), may be directly visualized on the fast gray matter acquisition T1 inversion recovery. We compared reproducibility, lesion overlap, and clinical outcomes when reconstructing the DRT tract using a novel anatomically defined RW region of interest, DRT-RW, to an existing tractography method based on the posterior subthalamic area region of interest (DRT-PSA). METHODS:We reviewed data of 23 patients with either essential tremor (n = 18) or tremor-predominant Parkinson's disease (n = 5) who underwent HIFU thalamotomy, targeting the VIM. DRT tractography, ipsilateral to the lesion, was created based on either DRT-PSA or DRT-RW. Volume sections of each tract were created and dice similarity coefficients were used to measure spatial overlap between the 2 tractographies. Post-HIFU lesion size and location (on postoperative T2 MRI) was correlated with tremor outcomes and side effects for both DRT tractography methods and the RW itself. RESULTS:DRT-PSA passed through the RW and DRT-RW intersected with the ROIs of the DRT-PSA in all 23 cases. A higher percentage of the RW was ablated in patients who achieved tremor control (18.9%, 95% CI 15.1, 22.7) vs those without tremor relief (6.7%, 95% CI% 0, 22.4, P = .017). In patients with tremor control 6 months postoperatively (n = 12), those with side effects (n = 6) had larger percentages of their tracts ablated in comparison with those without side effects in both DRT-PSA (44.8, 95% CI 31.8, 57.8 vs 24.2%, 95% CI 12.4, 36.1, P = .025) and DRT-RW (35.4%, 95% CI 21.5, 49.3 vs 21.7%, 95% CI 12.7, 30.8, P = .030). CONCLUSION/CONCLUSIONS:Tractography of the DRT could be reconstructed by direct anatomic visualization of the RW on fast gray matter acquisition T1 inversion recovery-MRI. Anatomic planning is expected to be quicker, more reproducible, and less operator-dependent.

INTRODUCTION/BACKGROUND: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/OBJECTIVE:We assessed DRG-S salvage therapy outcomes in patients who did not respond to SCS or had lost SCS efficacy. MATERIALS AND METHODS/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.

The efficacy of spinal cord stimulation for treating chronic pain has encouraged the development of a wide variety of different technologies for stimulation. In this review, the authors first discuss how parameters of stimulation determine the stimulation waveform. They then discuss new stimulation waveforms, including high frequency and burst stimulation, and the evidence supporting their use. Finally, the authors turn to emerging technologies and techniques including dorsal root ganglion stimulation, wireless stimulation, and closed-loop stimulation.

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.