What does the mechanism of spinal cord stimulation tell us about complex regional pain syndrome?

Analgesic Treatment Approach for Postherpetic Neuralgia: A Narrative Review

Post-herpetic neuralgia (PHN) is an entity derived from peripheral nerve damage that occurs during the reactivation of the Varicella Zoster Virus (VZV), which manifests itself through pain with neuropathic characteristics. This can prove to be very difficult to manage in the chronic stages of disease reappearance. There currently exists a multitude of treatment alternatives for PHN, however, prevention through the early initiation of antiviral regimens is vital. There are various pharmacological options available, but it is important to individualize each patient to maximize efficacy and minimize adverse effects. Interventional procedures have become a cornerstone in difficult-to-manage cases, and have shown promising outcomes when used in a multimodal approach by experienced specialists. It is necessary to make an objective diagnosis of PHN and start early treatment. Additionally there is current evidence that vouches for interventional therapies as well as individualization, with a clear establishment of therapeutic objectives according to the needs of each patient.

Allodynia, Hyperalgesia, (Quantitative) Sensory Testing and Conditioned Pain Modulation in Patients With Complex Regional Pain Syndrome Before and After Spinal Cord Stimulation Therapy

OBJECTIVES

Complex regional pain syndrome (CRPS) is a chronic debilitating disease characterized by sensory abnormalities. Spinal cord stimulation (SCS) is an effective therapy for CRPS, but few studies have investigated the effects of SCS therapy on sensory characteristics. Therefore, this study investigated the effect of SCS on allodynia, hyperalgesia, electrical quantitative sensory testing (QST) parameters, and conditioned pain modulation (CPM) effect.

MATERIALS AND METHODS

This study is part of a multicenter randomized controlled trial (ISRCTN 36655259). Patients with CRPS in one extremity and eligible for SCS were included. The outcome parameters allodynia (symptom and sign), hyperalgesia (symptom), sensory thresholds with QST, CPM effect, and pain scores were tested before and after three months of SCS (40-Hz tonic SCS). Both the CRPS-affected extremity and the contralateral, clinically unaffected extremity were used to test three sensory thresholds with electrical QST: current perception threshold (CPT), pain perception threshold (PPT), and pain tolerance threshold (PTT). The PTT also was used as a test stimulus for the CPM paradigm both before and after the conditioning ice-water test. Nonparametric testing was used for all statistical analyses.

RESULTS

In total, 31 patients were included for analysis. Pain, allodynia (sign and symptom), and hyperalgesia (symptom) were all significantly reduced after SCS therapy. On the unaffected side, none of the QST thresholds (CPT, PPT, and PTT) was significantly altered after SCS therapy. However, the CPT on the CRPS-affected side was significantly increased after SCS therapy. A CPM effect was present both before and after SCS.

CONCLUSIONS

Standard 40-Hz tonic SCS significantly reduces pain, hyperalgesia, and allodynia in patients with CRPS. These findings suggest that SCS therapy should not be withheld from patients who suffer from allodynia and hyperalgesia, which contradicts previous findings derived from retrospective analysis and animal research. ISRCTN Registry: The ISRCTN registration number for the study is ISRCTN 36655259.

Whole Body Vibration: A Valid Alternative Strategy to Exercise?

Several studies agree that mechanical vibration can induce physiological changes at different levels, improving neuromuscular function through postural control strategies, muscle tuning mechanisms and tonic vibration reflexes. Whole-body vibration has also been reported to increase bone mineral density and muscle mass and strength, as well as to relieve pain and modulate proprioceptive function in patients with osteoarthritis or lower back pain. Furthermore, vibratory training was found to be an effective strategy for improving the physical performance of healthy athletes in terms of muscle strength, agility, flexibility, and vertical jump height. Notably, several benefits have also been observed at the brain level, proving to be an important factor in protecting and/or preventing the development of age-related cognitive disorders. Although research in this field is still debated, certain molecular mechanisms responsible for the response to whole-body vibration also appear to be involved in physiological adaptations to exercise, suggesting the possibility of using it as an alternative or reinforcing strategy to canonical training. Understanding these mechanisms is crucial for the development of whole body vibration protocols appropriately designed based on individual needs to optimize these effects. Therefore, we performed a narrative review of the literature, consulting the bibliographic databases MEDLINE and Google Scholar, to i) summarize the most recent scientific evidence on the effects of whole-body vibration and the molecular mechanisms proposed so far to provide a useful state of the art and ii) assess the potential of whole-body vibration as a form of passive training in place of or in association with exercise.

Perioperative Management of Spinal Cord Stimulators and Intrathecal Pain Pumps

Spinal cord stimulators (SCSs) and intrathecal pain pumps (IPPs) are implantable devices used in the management of chronic pain or spasticity. Complications, such as infection, lead migration/failure, cerebrospinal fluid leak, neurologic injury, and other medical complications, can occur after placement and may require surgical intervention. Orthopaedic surgeons may encounter patients with these devices and should have a basic understanding of their function. In addition, they should be aware that patients may have residual stenosis or deformity contributing to their symptoms; thus, spine surgery referral may be indicated. If a patient with a SCS or IPP is undergoing revision spinal surgery, a preoperative discussion regarding retention versus removal of the device is imperative because indications for device retention, revision, and removal are complex. This review summarizes potential complications and intraoperative considerations concerning the proper perioperative management of SCSs/IPPs and will provide evidence-based data regarding management strategies for these devices.

The Central Nervous System and Psychosocial Factors in Primary Microvascular Angina

Patients diagnosed with ischemia without obstructive coronary artery disease (INOCA) comprise the group of patients with primary microvascular angina (MVA). The pathophysiology underlying ischemia and angina is multifaceted. Differences in vascular tone, collateralization, environmental and psychosocial factors, pain thresholds, and cardiac innervation seem to contribute to clinical manifestations. There is evidence suggesting potential interactions between the clinical manifestations of MVA and non-cardiac conditions such as abnormal function of the central autonomic network (CAN) in the central nervous system (CNS), pain modulation pathways, and psychological, psychiatric, and social conditions. A few unconventional non-pharmacological and pharmacological techniques targeting these psychosocial conditions and modulating the CNS pathways have been proposed to improve symptoms and quality of life. Most of these unconventional approaches have shown encouraging results. However, these results are overall characterized by low levels of evidence both in observational studies and interventional trials. Awareness of the importance of microvascular dysfunction and MVA is gradually growing in the scientific community. Nonetheless, therapeutic success remains frustratingly low in clinical practice so far. This should promote basic and clinical research in this relevant cardiovascular field investigating, both pharmacological and non-pharmacological interventions. Standardization of definitions, clear pathophysiological-directed inclusion criteria, crossover design, adequate sample size, and mid-term follow-up through multicenter randomized trials are mandatory for future study in this field.

Son of a Lesser God: The Case of Cell Therapy for Refractory Angina

In the last decades, various non-pharmacological solutions have been tested on top of medical therapy for the treatment of patients affected by refractory angina (RA). Among these therapeutics, neuromodulation, external counter-pulsation and coronary sinus constriction have been recently introduced in the guidelines for the management of RA in United States and Europe. Notably and paradoxically, although a consistent body of evidence has proposed cell-based therapies (CT) as safe and salutary for RA outcome, CT has not been conversely incorporated into current international guidelines yet. As a matter of fact, published randomized controlled trials (RCT) and meta-analyses (MTA) cumulatively indicated that CT can effectively increase perfusion, physical function and well-being, thus reducing angina symptoms and drug assumption in RA patients. In this review, we (i) provide an updated overview of novel non-pharmacological therapeutics included in current guidelines for the management of patients with RA, (ii) discuss the Level of Evidence stemmed from available clinical trials for each recommended treatment, and (iii) focus on evidence-based CT application for the management of RA.

Whole-body vibration mediates mechanical hypersensitivity through Aβ-fiber and C-fiber thermal sensation in a chronic pain model

Whole-body vibration (WBV), which is widely used as a type of exercise, involves the use of vibratory stimuli and it is used for rehabilitation and sports performance programmes. This study aimed to investigate the effect of WBV treatment in a chronic pain model after 10 WBV sessions. An animal model (chronic pain) was applied in 60 male Wistar rats (±180 g, 12 weeks old) and the animals were treated with low intensity exercise (treadmill), WBV (vibrating platform), and a combined treatment involving both. The controls on the platform were set to a frequency of 42 Hz with 2 mm peak-to-peak displacement, g ≈ 7, in a spiral mode. Before and after the vibration exposure, sensitivity was determined. Aβ-fibers-mediated mechanical sensitivity thresholds (touch-pressure) were measured using a pressure meter. C-fibers-mediated thermal perception thresholds (hot pain) were measured with a hot plate. After each session, WBV influenced the discharge of skin touch-pressure receptors, reducing mechanical sensitivity in the WBV groups (P < 0.05). Comparing the conditions "before vs. after", thermal perception thresholds (hot pain) started to decrease significantly after the third WBV session (P < 0.05). WBV decreases mechanical hyperalgesia after all sessions and thermal sensitivity after the third session with the use of WBV.

Successful Spinal Cord Stimulation for Necrotizing Raynaud's Phenomenon in COVID-19 Affected Patient: The Nightmare Comes Back

Necrotizing Raynaud’s phenomenon is a vascular clinical syndrome characterized by vasospasm of distal resistance vessels, usually triggered by cold temperatures or by psychological conditions such as anxiety and stress. Pain is the first reported symptom, related to insufficient oxygen delivery to the extremities that leads to ischemia of the peripheral tissues. The initial treatment is conservative, but if the symptoms persist, necrosis and distal amputation can occur. In selected patients, neuromodulation with spinal cord stimulation (SCS) can be an effective treatment by reducing pain and amputation rate. Recent evidence suggests that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can cause endotheliopathy with microvascular and macrovascular thrombotic events and can present as a systemic inflammatory vascular disease.

We present a case of a severe necrotizing Raynaud’s phenomenon successfully treated and controlled with SCS that abruptly reappeared during SARS-CoV-2 infection.

The report of this case is suggestive for potential treatment in case of peripheral ischemia consequent to COVID-19 vasculopathy. The interaction between SCS and SARS-CoV-2-related endotheliopathy is unknown and would deserve further studies.

Refractory Angina-Unsolved Problem

The article discusses pharmacologic and interventional therapeutic options for patients with refractory angina. Refractory angina refers to long-lasting symptoms (≥3 months) due to established reversible ischemia in the presence of obstructive coronary artery disease, which cannot be controlled by escalating medical therapy with second-line and third-line pharmacologic agents, bypass grafting, or stenting. Due to an aging population, increased number of comorbidities, and advances in coronary artery disease treatment, incidence of refractory angina is growing. Although the number of therapeutic options is increasing, there is a lack of randomized clinical trials that could help create recommendations for this group of patients.

The Quasi-uniform assumption for Spinal Cord Stimulation translational research

BACKGROUND

Quasi-uniform assumption is a general theory that postulates local electric field predicts neuronal activation. Computational current flow model of spinal cord stimulation (SCS) of humans and animal models inform how the quasi-uniform assumption can support scaling neuromodulation dose between humans and translational animal.

NEW METHOD

Here we developed finite element models of cat and rat SCS, and brain slice, alongside SCS models. Boundary conditions related to species specific electrode dimensions applied, and electric fields per unit current (mA) predicted.

RESULTS

Clinically and across animal, electric fields change abruptly over small distance compared to the neuronal morphology, such that each neuron is exposed to multiple electric fields. Per unit current, electric fields generally decrease with body mass, but not necessarily and proportionally across tissues. Peak electric field in dorsal column rat and cat were ∼17x and ∼1x of clinical values, for scaled electrodes and equal current. Within the spinal cord, the electric field for rat, cat, and human decreased to 50% of peak value caudo-rostrally (C5-C6) at 0.48 mm, 3.2 mm, and 8 mm, and mediolaterally at 0.14 mm, 2.3 mm, and 3.1 mm. Because these space constants are different, electric field across species cannot be matched without selecting a region of interest (ROI).

COMPARISON WITH EXISTING METHOD

This is the first computational model to support scaling neuromodulation dose between humans and translational animal.

CONCLUSIONS

Inter-species reproduction of the electric field profile across the entire surface of neuron populations is intractable. Approximating quasi-uniform electric field in a ROI is a rational step to translational scaling.

[The effect of spinal card stimulation on quality of life in patients with critical lower limb ischemia]

Today, there are insufficient data on the dynamics of quality of life (QoL) in patients with critical lower limb ischemia after spinal cord stimulation.

OBJECTIVE

To study the dynamics of QoL in patients with critical lower limb ischemia one year after spinal cord stimulation.

MATERIAL AND METHODS

QoL analysis was performed in 43 patients with critical lower limb ischemia using the SF-36 questionnaire before and one year after spinal cord stimulation.

RESULTS

At baseline, we detected reduced QoL parameters corresponding to the physical function (≤30 points). The parameters of mental health corresponded to the moderate level (the score ranged between 42 and 59 points). The total score of physical well-being was reduced: 22.8 (20.2-29.3); the mean score of mental well-being was 41 (32.8-49.2) (p<0.001). One year after spinal cord stimulation, the level of all QoL parameters was increased but the total score of physical well-being remained low 33.2 (24-44.1). The mean score of mental well-being corresponded to the moderate level of QoL 56.5 (49-60.4) (p<0.001). Multivariate regression analysis showed that the physical parameters of QoL after spinal cord stimulation are adversely affected by such factors as age, the history of stroke, the ankle-brachial index (ABI), the presence of type 2 diabetes mellitus (DM), and ischemic heart disease (IHD) in combination with stenosis of brachiocephalic arteries (BCA). The mental health is affected by age and the presence of stenosis of brachiocephalic arteries.

CONCLUSION

When selecting patients with critical lower limb ischemia for spinal cord stimulation, such factors as the baseline clinical status (comorbidities), age, history of stroke, and the severity of peripheral artery ischemia need to be taken into account to improve treatment effectiveness and QoL.

Unilateral L4-dorsal root ganglion stimulation evokes pain relief in chronic neuropathic postsurgical knee pain and changes of inflammatory markers: part II whole transcriptome profiling

Background

In our recent clinical trial, increased peripheral concentrations of pro-inflammatory molecular mediators were determined in complex regional pain syndrome (CRPS) patients. After 3 months adjunctive unilateral, selective L4 dorsal root ganglion stimulation (L4-DRG_STIM), significantly decreased serum IL-10 and increased saliva oxytocin levels were assessed along with an improved pain and functional state. The current study extended molecular profiling towards gene expression analysis of genes known to be involved in the gonadotropin releasing hormone receptor and neuroinflammatory (cytokines/chemokines) signaling pathways.

Methods

Blood samples were collected from 12 CRPS patients for whole-transcriptome profiling in order to assay 18,845 inflammation-associated genes from frozen blood at baseline and after 3 months L4-DRG_STIM using PANTHER™ pathway enrichment analysis tool.

Results

Pathway enrichment analyses tools (GOrilla™ and PANTHER™) showed predominant involvement of inflammation mediated by chemokines/cytokines and gonadotropin releasing hormone receptor pathways. Further, screening of differentially regulated genes showed changes in innate immune response related genes. Transcriptomic analysis showed that 21 genes (predominantly immunoinflammatory) were significantly changed after L4-DRG_STIM. Seven genes including TLR1, FFAR2, IL1RAP, ILRN, C5, PKB and IL18 were down regulated and fourteen genes including CXCL2, CCL11, IL36G, CRP, SCGB1A1, IL-17F, TNFRSF4, PLA2G2A, CREB3L3, ADAMTS12, IL1F10, NOX1, CHIA and BDKRB1 were upregulated.

Conclusions

In our sub-group analysis of L4-DRG_STIM treated CRPS patients, we found either upregulated or downregulated genes involved in immunoinflammatory circuits relevant for the pathophysiology of CRPS indicating a possible relation. However, large biobank-based approaches are recommended to establish genetic phenotyping as a quantitative outcome measure in CRPS patients.

Trial registration The study protocol was registered at the 15.11.2016 on German Register for Clinical Trials (DRKS ID 00011267). https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00011267

Molecular, Cellular and Circuit Basis of Cholinergic Modulation of Pain

In addition to being a key component of the autonomic nervous system, acetylcholine acts as a prominent neurotransmitter and neuromodulator upon release from key groups of cholinergic projection neurons and interneurons distributed across the central nervous system. It has been more than forty years since it was discovered that cholinergic transmission profoundly modifies the perception of pain. Directly activating cholinergic receptors or extending the action of endogenous acetylcholine via pharmacological blockade of acetylcholine esterase reduces pain in rodents as well as humans; conversely, inhibition of muscarinic cholinergic receptors induces nociceptive hypersensitivity. Here, we aim to review the considerable progress in our understanding of peripheral, spinal and brain contributions to cholinergic modulation of pain. We discuss the distribution of cholinergic neurons, muscarinic and nicotinic receptors over the central nervous system and the synaptic and circuit-level modulation by cholinergic signaling. AchRs profoundly regulate nociceptive transmission at the level of the spinal cord via pre- as well as postsynaptic mechanisms. Moreover, we attempt to provide an overview of how some of the salient regions in the pain network spanning the brain, such as the primary somatosensory cortex, insular cortex, anterior cingulate cortex, the medial prefrontal cortex and descending modulatory systems are influenced by cholinergic modulation. Finally, we critically discuss the clinical relevance of cholinergic signaling to pain therapy. Cholinergic mechanisms contribute to several both conventional as well as unorthodox forms of pain treatments, and reciprocal interactions between cholinergic and opioidergic modulation impact on the function and efficacy of both opioids and cholinomimetic drugs.

Neuronal NOS Activates Spinal NADPH Oxidase 2 Contributing to Central Sigma-1 Receptor-Induced Pain Hypersensitivity in Mice

We recently demonstrated that activation of spinal sigma-1 receptors (Sig-1Rs) induces pain hypersensitivity via the activation of neuronal nitric oxide synthase (nNOS) and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 2 (Nox2). However, the potential direct interaction between nNOS-derived nitric oxide (NO) and Nox2-derived reactive oxygen species (ROS) is poorly understood, particularly with respect to the potentiation of N-methyl-D-aspartate (NMDA) receptor activity in the spinal cord associated with the development of central sensitization. Thus, the main purpose of this study was to investigate whether Sig-1R-induced and nNOS-derived NO modulates spinal Nox2 activation leading to an increase in ROS production and ultimately to the potentiation of NMDA receptor activity and pain hypersensitivity. Intrathecal pretreatment with the nNOS inhibitor, 7-nitroindazole or with the Nox inhibitor, apocynin significantly inhibited the mechanical and thermal hypersensitivity induced by intrathecal administration of the Sig-1R agonist, 2-(4-morpholinethyl) 1-phenylcyclohexanecarboxylate hydrochloride (PRE084). Conversely, pretreatment with 5,10,15,20-tetrakis-(4-sulphonatophenyl)-porphyrinato iron(III) (FeTPPS; a scavenger of peroxynitrite, a toxic reaction product of NO and superoxide) had no effect on the PRE084-induced pain hypersensitivity. Pretreatment with 7-nitroindazole significantly reduced the PRE084-induced increase in Nox2 activity and concomitant ROS production in the lumbar spinal cord dorsal horn, whereas apocynin did not alter the PRE084-induced changes in nNOS phosphorylation. On the other hand pretreatment with apocynin suppressed the PRE084-induced increase in the protein kinase C (PKC)-dependent phosphorylation of NMDA receptor GluN1 subunit (pGluN1) at Ser896 site in the dorsal horn. These findings demonstrate that spinal Sig-1R-induced pain hypersensitivity is mediated by nNOS activation, which leads to an increase in Nox2 activity ultimately resulting in a ROS-induced increase in PKC-dependent pGluN1 expression.

A Comprehensive Outcome-Specific Review of the Use of Spinal Cord Stimulation for Complex Regional Pain Syndrome

BACKGROUND

Complex regional pain syndrome (CRPS) is a painful, debilitating affliction that is often difficult to treat. It has become common international practice to use spinal cord stimulation (SCS) for the treatment of CRPS as other therapies fail to provide adequate relief, quality of life, or improvement in function. This comprehensive outcome-specific systematic review of the use of SCS for CRPS was performed to elucidate the available evidence with focus on clinically relevant patient-specific outcomes.

METHODS

A systematic review of the literature was conducted to evaluate the effects of SCS on patients with CRPS for the following outcomes and provide summary levels of evidence in regard to each outcome: perceived pain relief, pain score, resolution of CRPS signs, functional status, quality of life, psychological impact, sleep hygiene, analgesic medication utilization, and patient satisfaction with SCS therapy. Search terms included "complex regional pain syndrome," "spinal cord stimulation," and "reflex sympathetic dystrophy," without restriction of language, date, or type of publication, albeit only original data were included in analyses. Of 30 studies selected, seven systematic reviews were excluded, as were four studies reporting combination therapy that included SCS and other therapies (ie, concurrent peripheral nerve stimulation, intrathecal therapy) without clear delineation to the effect of SCS alone on outcomes. A total of 19 manuscripts were evaluated.

RESULTS

Perceived pain relief, pain score improvement, quality of life, and satisfaction with SCS were all rated 1B+, reflecting positive high-level (randomized controlled trial) evidence favoring SCS use for the treatment of CRPS. Evidence for functional status improvements and psychological effects of SCS was inconclusive, albeit emanating from a randomized controlled trial (evidence level 2B±), and outcomes evidence for both sleep hygiene and resolution of CRPS signs was either nonexistent or of too low quality from which to draw conclusions (evidence level 0). An analgesic sparing effect was observed in nonrandomized reports, reflecting an evidence level of 2C+.

CONCLUSIONS

Spinal cord stimulation remains a favorable and effective modality for treating CRPS with high-level evidence (1B+) supporting its role in improving CRPS patients' perceived pain relief, pain score, and quality of life. A paucity of evidence for functional improvements, resolution of CRPS signs, sleep hygiene, psychological impact, and analgesic sparing effects mandate further investigation before conclusions can be drawn for these specific outcomes.

Management of Refractory Angina Pectoris

With improvements in survival from coronary artery disease (CAD) and an ageing population, refractory angina (RA) is becoming an increasingly common clinical problem facing clinicians in routine clinical practice. These patients experience chronic symptoms in the context of CAD, characterised by angina-type pain, which is uncontrolled despite optimal pharmacological, interventional and surgical therapy. Although mortality rates are no worse in this cohort, patients experience a significantly impaired quality of life with disproportionately high utilisation of healthcare services. It has been increasingly recognised that the needs of RA patients are multifactorial and best provided by specialist multi-disciplinary units. In this review, we consider the variety of therapies available to clinicians in the management of RA and discuss the promise of novel treatments.

Spinal cord stimulation for intractable visceral pain due to sphincter of oddi dysfunction

Sphincter of Oddi dysfunction (SOD) is a syndrome of chronic biliary pain or recurrent pancreatitis due to the functional obstruction of the pancreaticobiliary flow. We report a case of spinal cord stimulation (SCS) for chronic abdominal pain due to SOD. The patient had a history of cholecystectomy and had suffered from chronic right upper quadrant abdominal pain. The patient had been diagnosed as having SOD. The patient was treated with opioid analgesics and nerve blocks, including a splanchnic nerve block. However, two years later, the pain became intractable. We implanted percutaneous SCS at the T5-7 level for this patient. Visual analog scale (VAS) scores for pain and the amount of opioid intake decreased. The patient was tracked for more than six months without significant complications. From our clinical case, SCS is an effective and alternative treatment option for SOD. Further studies and long-term follow-up are necessary to understand the effectiveness and the limitations of SCS on SOD.

Spinal cord stimulation for complex regional pain syndrome type 1 with dystonia: a case report and discussion of the literature

Background: Complex Regional Pain Syndrome type 1 (CRPS-1) is a debilitating chronic pain disorder, the physiopathology of which can lead to dystonia associated with changes in the autonomic, central and peripheral nervous system. An interdisciplinary approach (pharmacological, interventional and psychological therapies in conjunction with a rehabilitation pathway) is central to progress towards pain reduction and restoration of function.Aim: This case report aims to stimulate reflection and development of mechanism-based therapeutic strategies concerning CRPS associated with dystonia.Case description: A 31 year old female CRPS-1 patient presented with dystonia of the right foot following ligamentoplasty for chronic ankle instability. She did not have a satisfactory response to the usual therapies. Multiple anesthetic blocks (popliteal, epidural and intrathecal) were not associated with significant anesthesia and analgesia. Mobilization of the foot by a physiotherapist was not possible. A multidisciplinary approach with psychological support, physiotherapy and spinal cord stimulation (SCS) brought pain relief, rehabilitation and improvement in the quality of life.Conclusion: The present case report demonstrates the occurrence of multilevel (peripheral and central) pathological modifications in the nervous system of a CRPS-1 patient with dystonia. This conclusion is based on the patient’s pain being resistant to anesthetic blocks at different levels and the favourable, at least initially, response to SCS. The importance of the bio-psycho-social model is also suggested, permitting behavioural change.

Mechanism of dorsal column stimulation to treat neuropathic but not nociceptive pain: analysis with a computational model

OBJECTIVE

Stimulation of axons within the dorsal columns of the human spinal cord has become a widely used therapy to treat refractory neuropathic pain. The mechanisms have yet to be fully elucidated and may even be contrary to standard "gate control theory." Our hypothesis is that a computational model provides a plausible description of the mechanism by which dorsal column stimulation (DCS) inhibits wide dynamic range (WDR) cell output in a neuropathic model but not in a nociceptive pain model.

MATERIALS AND METHODS

We created a computational model of the human spinal cord involving approximately 360,000 individual neurons and dendritic processing of some 60 million synapses--the most elaborate dynamic computational model of the human spinal cord to date. Neuropathic and nociceptive "pain" signals were created by activating topographically isolated regions of excitatory interneurons and high-threshold nociceptive fiber inputs, driving analogous regions of WDR neurons. Dorsal column fiber activity was then added at clinically relevant levels (e.g., Aβ firing rate between 0 and 110 Hz by using a 210-μsec pulse width, 50-150 Hz frequency, at 1-3 V amplitude).

RESULTS

Analysis of the nociceptive pain, neuropathic pain, and modulated circuits shows that, in contradiction to gate control theory, 1) nociceptive and neuropathic pain signaling must be distinct, and 2) DCS neuromodulation predominantly affects the neuropathic signal only, inhibiting centrally sensitized pathological neuron groups and ultimately the WDR pain transmission cells.

CONCLUSION

We offer a different set of necessary premises than gate control theory to explain neuropathic pain inhibition and the relative lack of nociceptive pain inhibition by using retrograde DCS. Hypotheses regarding not only the pain relief mechanisms of DCS were made but also regarding the circuitry of pain itself, both nociceptive and neuropathic. These hypotheses and further use of the model may lead to novel stimulation paradigms.

Stimulation of dorsal root ganglia for the management of complex regional pain syndrome: a prospective case series

BACKGROUND

Complex regional pain syndrome (CRPS) is a chronic and progressive pain condition usually involving the extremities and characterized by sensorimotor, vascular, and trophic changes. Spinal cord stimulation (SCS) is an effective intervention for this condition, but is hampered by the technical challenges associated with precisely directing stimulation to distal extremities. Dorsal root ganglia (DRG) may be more effective as a physiological target for electrical modulation due to recruitment of the primary sensory neurons that innervate the painful distal anatomical regions.

METHODS

Eleven subjects diagnosed with uni- or bilateral lower-extremity CRPS were recruited as part of a larger study involving chronic pain of heterogeneous etiologies. Quadripolar epidural leads of a newly developed neurostimulation system were placed near lumbar DRGs using conventional percutaneous techniques. The neurostimulators were trialed; 8 were successful and permanently implanted and programed to achieve optimal pain-paresthesia overlap.

RESULTS

All 8 subjects experienced some degree of pain relief and subjective improvement in function, as measured by multiple metrics. One month after implantation of the neurostimulator, there was significant reduction in average self-reported pain to 62% relative to baseline values. Pain relief persisted through 12 months in most subjects. In some subjects, edema and trophic skin changes associated with CRPS were also mitigated and function improved. Neuromodulation of the DRG was able to provide excellent pain-paresthesia concordance in locations that are typically hard to target with traditional SCS, and the stimulation reduced the area of pain distributions.

CONCLUSIONS

Neuromodulation of the DRG appears to be a promising option for relieving chronic pain and other symptoms associated with CRPS. The capture of discrete painful areas such as the feet, combined with stable paresthesia intensities independent of body position, suggests this stimulation modality may allow more selective and consistent targeting of painful areas than traditional SCS.

Interventions for treating pain and disability in adults with complex regional pain syndrome

BACKGROUND

There is currently no strong consensus regarding the optimal management of complex regional pain syndrome although a multitude of interventions have been described and are commonly used.

OBJECTIVES

To summarise the evidence from Cochrane and non-Cochrane systematic reviews of the effectiveness of any therapeutic intervention used to reduce pain, disability or both in adults with complex regional pain syndrome (CRPS).

METHODS

We identified Cochrane reviews and non-Cochrane reviews through a systematic search of the following databases: Cochrane Database of Systematic Reviews, Database of Abstracts of Reviews of Effects (DARE), Ovid MEDLINE, Ovid EMBASE, CINAHL, LILACS and PEDro. We included non-Cochrane systematic reviews where they contained evidence not covered by identified Cochrane reviews. The methodological quality of reviews was assessed using the AMSTAR tool.We extracted data for the primary outcomes pain, disability and adverse events, and the secondary outcomes of quality of life, emotional well being and participants' ratings of satisfaction or improvement. Only evidence arising from randomised controlled trials was considered. We used the GRADE system to assess the quality of evidence.

MAIN RESULTS

We included six Cochrane reviews and 13 non-Cochrane systematic reviews. Cochrane reviews demonstrated better methodological quality than non-Cochrane reviews. Trials were typically small and the quality variable.There is moderate quality evidence that intravenous regional blockade with guanethidine is not effective in CRPS and that the procedure appears to be associated with the risk of significant adverse events.There is low quality evidence that bisphosphonates, calcitonin or a daily course of intravenous ketamine may be effective for pain when compared with placebo; graded motor imagery may be effective for pain and function when compared with usual care; and that mirror therapy may be effective for pain in post-stroke CRPS compared with a 'covered mirror' control. This evidence should be interpreted with caution. There is low quality evidence that local anaesthetic sympathetic blockade is not effective. Low quality evidence suggests that physiotherapy or occupational therapy are associated with small positive effects that are unlikely to be clinically important at one year follow up when compared with a social work passive attention control.For a wide range of other interventions, there is either no evidence or very low quality evidence available from which no conclusions should be drawn.

AUTHORS' CONCLUSIONS

There is a critical lack of high quality evidence for the effectiveness of most therapies for CRPS. Until further larger trials are undertaken, formulating an evidence-based approach to managing CRPS will remain difficult.

Interventions for treating pain and disability in adults with complex regional pain syndrome

BACKGROUND

There is currently no strong consensus regarding the optimal management of complex regional pain syndrome although a multitude of interventions have been described and are commonly used.

OBJECTIVES

To summarise the evidence from Cochrane and non-Cochrane systematic reviews of the effectiveness of any therapeutic intervention used to reduce pain, disability or both in adults with complex regional pain syndrome (CRPS).

METHODS

We identified Cochrane reviews and non-Cochrane reviews through a systematic search of the following databases: Cochrane Database of Systematic Reviews, Database of Abstracts of Reviews of Effects (DARE), Ovid MEDLINE, Ovid EMBASE, CINAHL, LILACS and PEDro. We included non-Cochrane systematic reviews where they contained evidence not covered by identified Cochrane reviews. The methodological quality of reviews was assessed using the AMSTAR tool.We extracted data for the primary outcomes pain, disability and adverse events, and the secondary outcomes of quality of life, emotional well being and participants' ratings of satisfaction or improvement. Only evidence arising from randomised controlled trials was considered. We used the GRADE system to assess the quality of evidence.

MAIN RESULTS

We included six Cochrane reviews and 13 non-Cochrane systematic reviews. Cochrane reviews demonstrated better methodological quality than non-Cochrane reviews. Trials were typically small and the quality variable.There is moderate quality evidence that intravenous regional blockade with guanethidine is not effective in CRPS and that the procedure appears to be associated with the risk of significant adverse events.There is low quality evidence that bisphosphonates, calcitonin or a daily course of intravenous ketamine may be effective for pain when compared with placebo; graded motor imagery may be effective for pain and function when compared with usual care; and that mirror therapy may be effective for pain in post-stroke CRPS compared with a 'covered mirror' control. This evidence should be interpreted with caution. There is low quality evidence that local anaesthetic sympathetic blockade is not effective. Low quality evidence suggests that physiotherapy or occupational therapy are associated with small positive effects that are unlikely to be clinically important at one year follow up when compared with a social work passive attention control.For a wide range of other interventions, there is either no evidence or very low quality evidence available from which no conclusions should be drawn.

AUTHORS' CONCLUSIONS

There is a critical lack of high quality evidence for the effectiveness of most therapies for CRPS. Until further larger trials are undertaken, formulating an evidence-based approach to managing CRPS will remain difficult.

Dorsal column stimulator applications

Background:

Spinal cord stimulation (SCS) has been used to treat neuropathic pain since 1967. Following that, technological progress, among other advances, helped SCS become an effective tool to reduce pain.

Methods:

This article is a non-systematic review of the mechanism of action, indications, results, programming parameters, complications, and cost-effectiveness of SCS.

Results:

In spite of the existence of several studies that try to prove the mechanism of action of SCS, it still remains unknown. The mechanism of action of SCS would be based on the antidromic activation of the dorsal column fibers, which activate the inhibitory interneurons within the dorsal horn. At present, the indications of SCS are being revised constantly, while new applications are being proposed and researched worldwide. Failed back surgery syndrome (FBSS) is the most common indication for SCS, whereas, the complex regional pain syndrome (CRPS) is the second one. Also, this technique is useful in patients with refractory angina and critical limb ischemia, in whom surgical or endovascular treatment cannot be performed. Further indications may be phantom limb pain, chronic intractable pain located in the head, face, neck, or upper extremities, spinal lumbar stenosis in patients who are not surgical candidates, and others.

Conclusion:

Spinal cord stimulation is a useful tool for neuromodulation, if an accurate patient selection is carried out prior, which should include a trial period. Undoubtedly, this proper selection and a better knowledge of its underlying mechanisms of action, will allow this cutting edge technique to be more acceptable among pain physicians.

Contemporary insights into painful diabetic neuropathy and treatment with spinal cord stimulation

A substantial body of literature is available on the natural history of diabetes, but much less is understood of the natural history of painful diabetic peripheral neuropathy (PDPN), a pervasive and costly complication of diabetes mellitus. Multiple mechanisms have been proposed, including polyol pathway activation, advanced glycosylation end-product formation, and vasculopathic changes. Nevertheless, specific treatment modalities addressing these basic issues are still lacking. The mainstay of treatment includes pharmacological management with antidepressants, anticonvulsants, and opioids, but these drugs are often limited by unfavorable side-effect profiles. For over 30 years, spinal cord stimulation (SCS) has been used extensively for the management of various chronic neuropathic pain states. In the past decade, interest in the use of SCS for treatment of PDPN has increased. This article reviews pathophysiological mechanisms of PDPN, proposed mechanisms of SCS, and the role of SCS for the treatment of PDPN.

Modulation of somatosensory profiles by spinal cord stimulation in primary Raynaud's syndrome

BACKGROUND AND GOAL

 Spinal cord stimulation (SCS) is an effective antinociceptive treatment for various neuropathic pain syndromes. Apart from antinociceptive action, it may modulate overall somatosensory perception. This case report targets the question of whether SCS may alter quantitative sensory testing (QST) in a patient with primary Raynaud's syndrome.

MATERIALS AND METHODS

 We report on a 44-year-old female patient with primary Raynaud's syndrome who had SCS via cervical and lumbar electrodes. QST was performed in a standardized manner assessing cold detection threshold (CDT) and warm detection threshold (WDT), cold pain threshold (CPT) and heat pain threshold (HPT), mechanical detection threshold (MDT) and mechanical pain threshold (MPT) thresholds, and vibration detection threshold (VDT) and pressure pain thresholds (PPT). We tested at the dorsum of the right/left hand of the patient with engaged and disengaged SCS. Test results were compared with a control group of 80 subjects.

RESULTS

 Without SCS, the patient showed a sensory decrease in CDT, MDT, MPT, and VDT. SCS influenced the perception of cold, warm, and tactile detection thresholds, whereby CDT, WDT, and VDT were impaired and MDT was improved.

CONCLUSION

 SCS significantly modulated the somatosensory profile in a patient with primary Raynaud's syndrome. These effects were pronounced in qualities involving Aβ, C, and A∂ nerve fibers. Further investigations may help to understand the mechanisms of action of SCS.