Quantitative Sensory Testing of Spinal Cord and Dorsal Root Ganglion Stimulation in Chronic Pain Patients.

BACKGROUND/OBJECTIVES: The physiological mechanisms underlying the pain-modulatory effects of clinical neurostimulation therapies, such as spinal cord stimulation (SCS) and dorsal root ganglion stimulation (DRGS), are only partially understood. In this pilot prospective study, we used patient-reported outcomes (PROs) and quantitative sensory testing (QST) to investigate the physiological effects and possible mechanisms of action of SCS and DRGS therapies. MATERIALS AND METHODS: We tested 16 chronic pain patients selected for SCS and DRGS therapy, before and after treatment. PROs included pain intensity, pain-related symptoms (e.g., pain interference, pain coping, sleep interference) and disability, and general health status. QST included assessments of vibration detection theshold (VDT), pressure pain threshold (PPT) and tolerance (PPToL), temporal summation (TS), and conditioned pain modulation (CPM), at the most painful site. RESULTS: Following treatment, all participants reported significant improvements in PROs (e.g., reduced pain intensity [p < 0.001], pain-related functional impairment [or pain interference] and disability [p = 0.001 for both]; better pain coping [p = 0.03], sleep [p = 0.002]), and overall health [p = 0.005]). QST showed a significant treatment-induced increase in PPT (p = 0.002) and PPToL (p = 0.011), and a significant reduction in TS (p = 0.033) at the most painful site, but showed no effects on VDT and CPM. We detected possible associations between a few QST measures and a few PROs. Notably, higher TS was associated with increased pain interference scores at pre-treatment (r = 0.772, p = 0.009), and a reduction in TS was associated with the reduction in pain interference (r = 0.669, p = 0.034) and pain disability (r = 0.690, p = 0.027) scores with treatment. CONCLUSIONS: Our preliminary findings suggest significant clinical and therapeutic benefits associated with SCS and DRGS therapies, and the possible ability of these therapies to modulate pain processing within the central nervous system. Replication of our pilot findings in future, larger studies is necessary to characterize the physiological mechanisms of SCS and DRGS therapies.

Objective Measures to Characterize the Physiological Effects of Spinal Cord Stimulation in Neuropathic Pain: A Literature Review.

OBJECTIVE: The physiological mechanisms behind the therapeutic effects of spinal cord stimulation (SCS) are only partially understood. Our aim was to perform a literature review of studies that used objective measures to characterize mechanisms of action of SCS in neuropathic pain patients. MATERIALS AND METHODS: We searched the PubMed data base to identify clinical studies that used objective measures to assess the effects of SCS in neuropathic pain. We extracted the study factors (e.g., type of measure, diagnoses, painful area[s], and SCS parameters) and outcomes from the included studies. RESULTS: We included 67 studies. Of these, 24 studies used neurophysiological measures, 14 studies used functional neuroimaging techniques, three studies used a combination of neurophysiological and functional neuroimaging techniques, 14 studies used quantitative sensory testing, and 12 studies used proteomic, vascular, and/or pedometric measures. Our findings suggest that SCS largely inhibits somatosensory processing and/or spinal nociceptive activity. Our findings also suggest that SCS modulates activity across specific regions of the central nervous system that play a prominent role in the sensory and emotional functions of pain. CONCLUSIONS: SCS appears to modulate pain via spinal and/or supraspinal mechanisms of action (e.g., pain gating, descending pain inhibition). However, to better understand the mechanisms of action of SCS, we believe that it is necessary to carry out systematic, controlled, and well-powered studies using objective patient measures. To optimize the clinical effectiveness of SCS for neuropathic pain, we also believe that it is necessary to develop and implement patient-specific approaches.

Restoring continuous finger function with temporarily paralyzed nonhuman primates using brain-machine interfaces.

Objective.Brain-machine interfaces (BMIs) have shown promise in extracting upper extremity movement intention from the thoughts of nonhuman primates and people with tetraplegia. Attempts to restore a user's own hand and arm function have employed functional electrical stimulation (FES), but most work has restored discrete grasps. Little is known about how well FES can control continuous finger movements. Here, we use a low-power brain-controlled functional electrical stimulation (BCFES) system to restore continuous volitional control of finger positions to a monkey with a temporarily paralyzed hand.Approach.We delivered a nerve block to the median, radial, and ulnar nerves just proximal to the elbow to simulate finger paralysis, then used a closed-loop BMI to predict finger movements the monkey was attempting to make in two tasks. The BCFES task was one-dimensional in which all fingers moved together, and we used the BMI's predictions to control FES of the monkey's finger muscles. The virtual two-finger task was two-dimensional in which the index finger moved simultaneously and independently from the middle, ring, and small fingers, and we used the BMI's predictions to control movements of virtual fingers, with no FES.Main results.In the BCFES task, the monkey improved his success rate to 83% (1.5 s median acquisition time) when using the BCFES system during temporary paralysis from 8.8% (9.5 s median acquisition time, equal to the trial timeout) when attempting to use his temporarily paralyzed hand. In one monkey performing the virtual two-finger task with no FES, we found BMI performance (task success rate and completion time) could be completely recovered following temporary paralysis by executing recalibrated feedback-intention training one time.Significance.These results suggest that BCFES can restore continuous finger function during temporary paralysis using existing low-power technologies and brain-control may not be the limiting factor in a BCFES neuroprosthesis.

Cervical spine trauma in children and adults: perioperative considerations.

A wide spectrum of cervical spine injuries, including stable and unstable injuries with and without neurologic compromise, account for a large percentage of emergency department visits. Effective treatment of the polytrauma patient with cervical spine injury requires knowledge of cervical spine anatomy and the pathophysiology of spinal cord injury, as well as techniques for cervical spine stabilization, intraoperative positioning, and airway management. The orthopaedic surgeon must oversee patient care and coordinate treatment with emergency department physicians and anesthesia services in both the acute and subacute settings. Children are particularly susceptible to substantial destabilizing cervical injuries and must be treated with a high degree of caution. The surgeon must understand the unique anatomic and biomechanical properties associated with the pediatric cervical spine as well as injury patterns and stabilization techniques specific to this patient population.

Intrathecal catheter for severe low back pain during deep brain stimulation placement: illustrative case.

BACKGROUND: Deep brain stimulation (DBS) is a U.S. Food and Drug Administration-approved therapy for medically refractory Parkinson's disease, essential tremor, and other neurological conditions. The procedure requires prolonged immobility and can result in significant patient discomfort, potentially limiting patient selection. In addition, surgical requirements necessitate avoidance of medications that may alter or suppress the patient's arousal or baseline tremor during macrostimulation testing. OBSERVATIONS: In this study, the authors describe the use of continuous spinal anesthesia with local anesthetic to manage a patient with severe back pain who was intolerant of semisupine position during stereotactic computed tomography and stage 1 of DBS placement. LESSONS: Continuous spinal anesthesia is an effective strategy to manage patients with severe back pain undergoing DBS surgery for upper extremity motor symptoms.

Transdermal power transfer for recharging implanted drug delivery devices via the refill port.

This paper describes a system for transferring power across a transdermal needle into a smart refill port for recharging implantable drug delivery systems. The device uses a modified 26 gauge (0.46 mm outer diameter) Huber needle with multiple conductive elements designed to couple with mechanical springs in the septum of the refill port of a drug delivery device to form an electrical connection that can sustain the current required to recharge a battery during a reservoir refill session. The needle is fabricated from stainless steel coated with Parylene, and the refill port septum is made from micromachined stainless steel contact springs and polydimethylsiloxane. The device properties were characterized with dry and wet ambient conditions. The needle and port pair had an average contact resistance of less than 2 Omega when mated in either environment. Electrical isolation between the system, the liquid in the needle lumen, and surrounding material has been demonstrated. The device was used to recharge a NiMH battery with currents up to 500 mA with less than 15 degrees C of resistive heating. The system was punctured 100 times to provide preliminary information with regard to device longevity, and exhibited about 1 Omega variation in contact resistance. The results suggest that this needle and refill port system can be used in an implant to enable battery recharging. This allows for smaller batteries to be used and ultimately increases the volume efficiency of an implantable drug delivery device.

A low power, microvalve regulated architecture for drug delivery systems.

This paper describes an actively-controlled architecture for drug delivery systems that offers high performance and volume efficiency through the use of micromachined components. The system uses a controlled valve to regulate dosing by throttling flow from a mechanically pressurized reservoir, thereby eliminating the need for a pump. To this end, the valve is fabricated from a glass wafer and silicon-on-insulator wafer for sensor integration. The valve draws a maximum power of 1.68 µW| (averaged over time); with the existing packaging scheme, it has a volume of 2.475 cm3. The reservoirs are assembled by compressing polyethylene terephthalate polymer balloons with metal springs. The metal springs are fabricated from Elgiloy® using photochemical etching. The springs pressurize the contents of 37 mLchambers up to 15 kPa. The system is integrated with batteries and a control circuit board within a 113 cm3 metal casing. This system has been evaluated in different control modes to mimic clinical applications. Bolus deliveries of1.5 mL have been regulated as well as continuous flows of 0.15 mL/day with accuracies of 3.22%. The results suggest that this device can be used in an implant to regulate intrathecal drug delivery

Recurrent cellulitis associated with long-term intrathecal opioid infusion therapy: a case report and review of the literature.

BACKGROUND: Lower-limb edema is recognized as an untoward side effect of intrathecal opioid therapy. Cellulitis, an acute, spreading pyogenic inflammation of the dermis and subcutaneous tissue, predisposed by persistent leg edema, can become problematic in patients on intraspinal opioid infusion therapy. OBJECTIVE: To present a case of recurrent cellulitis in an elderly lady with persistent leg edema associated with intrathecal morphine/hydromorphone infusion therapy. CASE REPORT: Sixty-one-year-old woman with intractable chronic low back pain and bilateral leg pain treated with an intrathecal infusion of morphine up to 5 mg/day over 3 months with satisfactory pain control developed progressive lower extremity edema, complicated by recurrent cellulitis, requiring repeated hospitalization and intravenous antibiotic treatment. Switching to intrathecal hydromorphone helped minimally. Intrathecal baclofen and clonidine infusion resulted in complete resolution of leg edema and pain relief over the following 12 months. CONCLUSION: Intrathecal Baclofen and Clonidine may be used as alternatives to provide spinally mediated antinociception when intraspinal opioid fails due to pharmacological side effects such as persistent edema.

Subdural hematoma following spinal cord stimulator implant.

Headache following interventional procedures is a diagnostic challenge due to the multitude of possible etiologies involved. Presentation can be simple (PDPH alone) or complex (exacerbation of pre-existing chronic headache along with PDPH) or headache associated with a new onset intracranial process. Subdural hematoma is a rare complication of cranio-spinal trauma. Cranial subdural hematoma may present in an acute, sub-acute, or chronic fashion. Diagnosis of a subdural hematoma in the wake of a PDPH is difficult, requiring a high level of suspicion. Delayed diagnosis of subdural hematoma is usually related to failure to consider it in the differential diagnosis. Thorough history, assessment of the evolution of symptoms, and imaging studies may identify the possible cause and help direct treatment. Change in the character of initial presenting symptoms may be a sign of resolution of the headache or the onset of a secondary process. We report a case of acute intracranial subdural hematoma secondary to unintentional dural puncture during placement of a permanent spinal cord stimulator lead for refractory angina. There is need for careful follow-up of patients with a known post-dural tear. Failure to identify uncommon adverse events in patients with complicated spinal cord stimulator implantation may lead to permanent injury.

Severe peripheral edema during an outpatient continuous epidural morphine infusion trial in a patient with failed back surgery syndrome.

BACKGROUND: Intraspinal drug delivery therapy has been increasingly used in patients with intractable, nonmalignant pain who fail to respond to conventional treatment or cannot tolerate systemic opioid therapy due to side effects. By infusing small amount of analgesics directly into the cerebrospinal fluid in close proximity to the receptor sites in the spinal cord, one is able to achieve the spinally mediated analgesia, sparing side effects due to systemic opioids. Prior to permanent intraspinal pump implantation, an intraspinal opioid screening trial is required to document the efficacy of intraspinal opioid for analgesia. Although there are a few approaches in conducting such screening trials, a patient controlled continuous epidural morphine infusion trial, performed in an outpatient setting, is widely accepted by many interventional pain specialists. The major advantage of conducting an outpatient trial is that it mimics what patients do in their daily living, therefore minimizing the false positive rate. OBJECTIVE: To report a case of severe peripheral edema observed during an outpatient continuous epidural morphine infusion trial. CASE REPORT: A 64-year-old female, with a 7-year history of severe low back pain and bilateral leg pain due to failed back surgery syndrome, was referred to our clinic for intraspinal drug delivery therapy after failing to respond to conservative treatment, including a previous history of 3 lumbosacral surgeries. Following a pre-implantation psychological evaluation confirming her candidacy, she underwent an outpatient patient-controlled continuous epidural morphine trial. A tunneled lumbar epidural catheter was placed at L2-L3 with catheter tip advanced to T12 under fluoroscopic guidance. Satisfactory catheter placement was confirmed by epidurogram. The proximal tip of the catheter was then tunneled, subcutaneously and connected to a Microject PCEA pump (Codman, Raynham, MA, USA) and reservoir bag containing preservative-free morphine 0.5 mg/mL. The pump was programmed to deliver a basal rate of 0.5 mL/hr. The bolus dose was 0.2 mL with 60 minute lock-out interval. The patient was instructed how to operate the infusion pump before discharging home. During the following 2 weeks, she reported more than 90% reduction of her low back and leg pain. She only had to use the on-demand bolus doses averaging 2 - 3 times a day. She was able to wean off her oral opioids completely. However, she developed bilateral leg edema and gained over 12 pounds during the 2-week infusion trial, despite wearing elastic stockings and keeping her legs elevated whenever possible. She did not experience any other significant side effects. Her edema finally resolved 2 days after termination of the epidural infusion. CONCLUSION: Peripheral edema may occur and persist during epidural morphine infusion. This report represents the first case report, to the best of our knowledge, describing severe peripheral edema in an otherwise healthy patient while on epidural morphine administration during an outpatient epidural morphine infusion trial. This case report shows that continuous epidural morphine infusion, even in small dose, may cause peripheral edema in some patients.

Pulsed radiofrequency of the median nerve under ultrasound guidance.

Neuropathy of the median nerve within the carpal tunnel (carpal tunnel syndrome) has an age adjusted incidence of 105 cases per 100,000 person years. Treatment of carpal tunnel syndrome ranges from conservative management with medication and exercise to surgical release of the median nerve. Conservative treatment accounts for a significant portion of resources utilized and includes splinting, nerve gliding, ultrasound, and carpal bone mobilization. Recurrent symptoms of carpal tunnel syndrome have been shown to occur in 0% to 19% of patients following carpal tunnel release, with up to 12% requiring re-exploration. Prognosis for re-exploration is not as good as for primary carpal tunnel release, with a high recurrence rate in some populations. Ultrasound has seen increasing use in regional anesthesia and has been shown to improve the quality of regional anesthetic blocks. Pulsed radiofrequency was developed with the goal of providing reduction in pain from the use of electrical fields in the absence of neural injury. The use of ultrasound guidance for positioning radiofrequency probes over peripheral nerves has not been reported. This case report describes the use of ultrasound guided pulsed radiofrequency in the treatment of recurrent carpal tunnel syndrome. Following revision carpal tunnel surgery, the patient in this report was unable to obtain relief of pain in either hand with medication therapy alone. After a successful diagnostic median nerve block at the cubital fossa, pulsed radiofrequency of the median nerve was performed on the left side at the cubital fossa, under ultrasound guidance. Radiofrequency probe adjustment around the nerve was conducted under live ultrasound guidance and multiple pulsed treatments were applied at anatomically distinct sites over the nerve. A 70% reduction in pain was reported over the follow up period of 12 weeks.

Priapism--a rare complication following continuous epidural morphine and bupivacaine infusion.

BACKGROUND: Intraspinal drug delivery (IDD) therapy has been increasingly used in patients with intractable, nonmalignant pain who fail to respond to conventional treatment or can not tolerate systemic opioid therapy due to side effects. By infusing a small amount of analgesics directly into the cerebrospinal fluid (CSF) in close proximity to the receptor sites in the spinal cord, one is able to achieve the spinally mediated analgesia, sparing side effects ffrom systemic opioids. Prior to permanent intraspinal pump implantation, an intraspinal opioid screening trial is required to document the efficacy of intraspinal opioid for analgesia. Although there are a few approaches in conducting such screening trials, a patient-controlled continuous epidural morphine infusion trial, performed in an outpatient setting, is widely accepted by many interventional pain specialists. The major advantage of conducting an outpatient functional opioid infusion trial versus an inpatient trial is that it more closely mimics what the patient does in his or her usual activities of daily living, therefore minimizing the false positive rate of the inpatient screening trial. OBJECTIVE: To describe a rare complication, priapism, observed during an outpatient continuous epidural morphine and bupivacaine infusion trial. CASE REPORT: A 49-year-old male with intractable, chronic low back pain due to diffuse lumbar degenerative disc disease, lumbar spondylosis referred to our clinic for consideration of IDD therapy, after failing to respond to multi-modality pain management including medications, physical therapy with modality, transcutaneous nerve stimulation (TENS), and various interventional procedures. Following a pre-implant psychological evaluation, he was scheduled for the outpatient epidural morphine and bupivacaine infusion trial. A tunneled lumbar epidural a catheter was placed at L3-L4 with the catheter tip advanced to L1 under fluoroscopic guidance. The proximal tip of the catheter was then tunneled, subcutaneously, and connected to a Microject PCEA pump (Codman, Raynham, MA, USA) and reservoir bag containing preservative-free morphine 0.4 mg/mL and bupivacaine 0.016%. The pump was programmed to deliver a basal rate of 0.5 mL/h. The bolus dose was 0.2 mL with a 60-minute lock out interval. The patient was instructed how to use the pump properly before discharging home. Two hours following the initiation of infusion trial, the patient started to experience penile erection. It was initially painless, but became progressively painful and intensified. The unremitting priapism lasted 8 hours, finally resolving 2 to 3 hours after discontinuing the infusion. The patient recovered fully without any sequelae. CONCLUSION: Priapism may occur as a rare complication following epidural morphine administration. This report represents the third case report thus far in the literature revealing priapism induced by epidural morphine administration, yet, it is the only report, to our knowledge, describing priapism occurring in a patient undergoing an outpatient epidural morphine and bupivacaine infusion trial. We believe that epidural morphine, rather than bupivacaine, is responsible for causing priapism in this patient, through a yet to be defined spinal mechanism.

Microstructural mechanisms of analgesia in percutaneous cervical cordotomy revealed by diffusion tensor imaging.

The purpose of this study is to demonstrate the potential of diffusion tensor imaging (DTI) to reveal structural mechanisms underlying spinal ablative procedures, including percutaneous radiofrequency cordotomy (PRFC). PRFC is a surgical procedure that produces analgesia through focal ablation of the lateral spinothalamic tract (STT), thereby interrupting the flow of pain information from the periphery to the brain. To date, studies regarding mechanisms of analgesia after PRFC have been limited to postmortem cadaveric dissection and histology. However, with recent advances in DTI, the opportunity has arisen to study the STT non-invasively in vivo. In this technical note, an individual with successful pain relief following unilateral STT PRFC was examined using DTI, with the contralateral STT serving as an internal control. PRFC substantially reduced rostrocaudal directional DTI signal in the STT from the lesion in the cervical spinal cord through the pons and mesencephalon. Our findings confirm that focal ablation and anterograde degeneration accompany the analgesic effects of PRFC. In vivo imaging of the STT with DTI may contribute to surgical targeting for PRFC procedures, better understanding of the therapeutic and untoward effects of PRFC, and a deeper understanding of spinothalamic contributions to nociception.

The effect of bench model fidelity on fluoroscopy-guided transforaminal epidural injection training: a randomized control study.

BACKGROUND AND OBJECTIVES: The purpose of this study was to determine whether high-fidelity simulators provide greater benefit than low-fidelity models in training fluoroscopy-guided transforaminal epidural injection. METHODS: This educational study was a single-center, prospective, randomized 3-arm pretest-posttest design with a control arm. Eighteen anesthesia and physical medicine and rehabilitation residents were instructed how to perform a fluoroscopy-guided transforaminal epidural injection and assessed by experts on a reusable injectable phantom cadaver. The high- and low-fidelity groups received 30 minutes of supervised hands-on practice according to group assignment, and the control group received 30 minutes of didactic instruction from an expert. RESULTS: We found no differences at posttest between the high- and low-fidelity groups on global ratings of performance (P = 0.17) or checklist scores (P = 0.81). Participants who received either form of hands-on training significantly outperformed the control group on both the global rating of performance (control vs low-fidelity, P = 0.0048; control vs high-fidelity, P = 0.0047) and the checklist (control vs low-fidelity, P = 0.0047; control vs high-fidelity, P = 0.0047). CONCLUSIONS: Training an epidural procedure using a low-fidelity model may be equally effective as training on a high-fidelity model. These results are consistent with previous research on a variety of interventional procedures and further demonstrate the potential impact of simple, low-fidelity training models.