Where is my arm? Investigating the link between complex regional pain syndrome and poor localisation of the affected limb

Background

Anecdotally, people living with Complex Regional Pain Syndrome (CRPS) often report difficulties in localising their own affected limb when it is out of view. Experimental attempts to investigate this report have used explicit tasks and yielded varied results.

Methods

Here we used a limb localisation task that interrogates implicit mechanisms because we first induce a compelling illusion called the Disappearing Hand Trick (DHT). In the DHT, participants judge their hands to be close together when, in fact, they are far apart. Sixteen volunteers with unilateral upper limb CRPS (mean age 39 ± 12 years, four males), 15 volunteers with non-CRPS persistent hand pain (‘pain controls’; mean age 58 ± 13 years, two males) and 29 pain-free volunteers (‘pain-free controls’; mean age 36 ± 19 years, 10 males) performed a hand-localisation task after each of three conditions: the DHT illusion and two control conditions in which no illusion was performed. The conditions were repeated twice (one for each hand). We hypothesised that (1) participants with CRPS would perform worse at hand self-localisation than both the control samples; (2) participants with non-CRPS persistent hand pain would perform worse than pain-free controls; (3) participants in both persistent pain groups would perform worse with their affected hand than with their unaffected hand.

Results

Our first two hypotheses were not supported. Our third hypothesis was supported —when visually and proprioceptively encoded positions of the hands were incongruent (i.e. after the DHT), relocalisation performance was worse with the affected hand than it was with the unaffected hand. The similar results in hand localisation in the control and pain groups might suggest that, when implicit processes are required, people with CRPS’ ability to localise their limb is preserved.

Sensory Function and Psychological Factors in Children With Complex Regional Pain Syndrome Type 1

OBJECTIVE

To assess thermal-sensory thresholds and psychosocial factors in children with Complex Regional Pain Syndrome Type 1 (CRPS-I) compared to healthy children.

METHODS

We conducted quantitative sensory testing on 34 children with CRPS-I and 56 pain-free children. Warm, cool, heat, and cold stimuli were applied to the forearm. Children with CRPS-I had the protocol administered to the pain site and the contralateral-pain site. Participants completed the self-report Behavior Assessment System for Children.

RESULTS

Longer pain durations (>5.1 months) were associated with decreased sensitivity to cold pain on the pain site (P = .04). Higher pain-intensity ratings were associated with elevated anxiety scores (P = .03). Anxiety and social stress were associated with warmth sensitivity (both P < .05) on the contralateral-pain site.

CONCLUSIONS

Pain duration is an important factor in assessing pediatric CRPS-I. Hyposensitivity in the affected limb may emerge due to degeneration of nociceptive nerves. Anxiety may contribute to thermal-sensory perception in childhood CRPS-I.

Complex Regional Pain Syndrome: A Comprehensive Qualitative Research Study on Unmet Needs in the "Patient Journey"

Purpose

This qualitative research study aimed to characterize the "patient journey" for patients with complex regional pain syndrome (CRPS) and identify the unmet needs related to the management and treatment of the condition for healthcare providers (HCPs), patients, and their caregivers.

Materials and Methods

Multifaceted, dynamic methodology, iteratively gathering cognitive, emotional and social insights, was used to support and conduct in-depth, immersion interviews across the USA with 59 HCPs in-office and in roundtable discussions, and 20 patient-support partner dyads in-home.

Results

Patients were aged >18 years, primarily female, and all were diagnosed with CRPS (limited to type 1 in this patient cohort). Results show that the current state of CRPS treatment may fall short in multiple key areas. In some cases, poor awareness of CRPS causes delayed diagnoses impacting the opportunity for early treatment, resulting in long-term poor health outcomes. Consequently, the CRPS "patient journey" may be characterized by clinical frustration of physicians and disappointment for some patients. The poor treatment experiences and outcomes for some patients and HCPs may build the perception of a non-collaborative relationship. HCPs and patients agree that an effective treatment would be one that addresses CRPS rather than its symptoms, and the availability of such an option would transform the treatment experience.

Conclusion

CRPS leads to cognitive, social and emotional burdens for patients and their caregivers. There is an unmet need for improved CRPS disease awareness and successful therapeutic options to aid in earlier diagnoses, effective treatment and better outcomes for HCPs, patients, and their caregivers.

Attentional modulation of neural dynamics in tactile perception of complex regional pain syndrome patients

Body perceptual disturbances are an increasingly acknowledged set of symptoms and possible clinical markers of complex regional pain syndrome (CRPS), but the neurophysiological and neurocognitive changes that underlie them are still far from being clear. We adopted a multivariate and neurodynamical approach to the analysis of EEG modulations evoked by touch to highlight differences between patients and healthy controls, between affected and unaffected side of the body, and between "passive" (i.e., no task demands and equiprobable digit stimulation) and "active" tactile processing (i.e., where a digit discrimination task was administered and spatial probability manipulated). When correct identifications are considered, an early reduction in cortical decodability (28-56 ms) distinguishes CRPS patients from healthy volunteers. However, when error trials are included in the classifier's training, there is an unexpected increased decodability in the CRPS group compared with healthy volunteers (280-320 ms). These group differences in neural processing seemed to be driven by the affected rather than the unaffected side. We corroborated these findings with several exploratory analyses of neural representation dynamics and behavioural modelling, highlighting the need for single participant analyses. Although several limitations impacted the robustness and generalizability of these comparisons, the proposed analytical approach yielded promising insights (as well as possible biomarkers based on neural dynamics) into the relatively unexplored alterations of tactile decision-making and attentional control mechanisms in chronic CRPS.

Low mechano-afferent fibers reduce thermal pain but not pain intensity in CRPS

Background

Human hairy (not glabrous skin) is equipped with a subgroup of C-fibers, the C-tactile (CT) fibers. Those do not mediate pain but affective aspects of touch. CT-fiber-activation reduces experimental pain if they are intact. In this pilot study we investigated pain modulating capacities of CT-afferents in CRPS.

Methods

10 CRPS-patients (mean age 33 years, SEM 3.3) and 11 healthy controls (mean age 43.2 years, SEM 3.9) participated.

CT-targeted-touch (brush stroking, velocity: 3 cm/s) was applied on hairy and glabrous skin on the affected and contralateral limb. Patients rated pleasantness of CT-targeted-touch (anchors: 1 “not pleasant”—4 “very pleasant”) twice daily on 10 days. Pain intensity (NRS: 0 “no pain” – 10 “worst pain imaginable”) was assessed before, 0, 30, 60 and 120 min after each CT-stimulation. To assess sensory changes, quantitative-sensory-testing was performed at the beginning and the end of the trial period.

Results

CT-targeted-touch was felt more pleasant on the healthy compared to the affected limb on hairy (p < 0.001) and glabrous skin (p 0.002), independent of allodynia. In contrast to healthy controls patients felt no difference between stimulating glabrous and hairy skin on the affected limb. Thermal pain thresholds increased after CT-stimulation on the affected limb (cold-pain-threshold: p 0.016; heat-pain-threshold: p 0.033).

Conclusions

CT-stimulation normalizes thermal pain thresholds but has no effect on the overall pain in CRPS. Therefore, pain modulating properties of CT-fibers might be too weak to alter chronic pain in CRPS. Moreover, CT-fibers appear to lose their ability to mediate pleasant aspects of touch in CRPS.

Is trigeminal neuralgia the only definitive diagnosis for pain in a tooth extraction site?

Knowing the International Classification of Orofacial Pain helps pain specialists to differentiate types of orofacial pain. It is important to select the best treatment or intervention for the patients based on the diagnosis. As part of our study, we reviewed the article published in BMC Oral Health, titled “Clinical characteristics and associated factors of trigeminal neuralgia: Experience from Addis Ababa, Ethiopia” by Ayele et al. (Ethiopia BMC Oral Health 20(1):7, 2020). For patients suffering from Classical Trigeminal Neuralgia taking a suitable dose of Carbamazepine or Gasser Ganglion radiofrequency could be helpful. Patients complaining Trigeminal neuralgia who had a history of a dental extraction in the painful region should be categorized in other group as Complex Regional Pain Syndrome type 1, who need larger dose of carbamazepine with anticonvulsant or tricyclic agent drugs (e.g. pregabalin or doxepin) or intervention (PPG radiofrequency).

[Complex regional pain syndrome, CRPS]

Complex regional pain syndrome, CRPS, occurs with severe disabling pain, usually in the leg or hand, coupled with changes in pain perception, hyperesthesia and allodynia. There is as well, edema, changes in the color of the skin, trophic changes, and dystonia. The pain syndrome is often triggered by minor trauma. The pain perception is severe and out of context with the initial trauma. The syndrome is rare, occurring in a population-based study in the United States, with an incidence of only 5.5 per hundred thousand people per year. The incidence in Iceland, from the National Register of Diseases from the Directorate of Health, was 1.3 per annum, per hundred thousand people. The exact etiology of the disease is unknown. It is presumed that inflammation is the cause, often resulting from an autoimmune reaction. The term pain sensitization is also used to describe the pain mechanism, both in peripheral nerves and in the central nervous system. There are changes and displacement of the area of the neocortex that is coupled with pain perception. The criteria of the International Association for the Study of Pain (IASP) were the basis for the diagnosis. Interdisciplinary team management according to the biopsychosocial model is thought to be the preferred treatment approach. The members of the team are occupational therapists, physiotherapists, social workers, psychologists, nurses, and medical doctors, augmented by other disciplines as needed. One treatment option is mirror therapy, where the diseased extremity is held behind a mirror during the training and the patient observes movements of the healthy extremity. Initially treatment is aimed at treating the inflammation, often with NSAID drugs, or with steroids. Medical treatments are the same as apply for the treatment of neural pain, with drugs such as Gabapentin, or anti depressive agents as duloxetine or imipramine. There is an indication to use bisphosphonates such as alendronate, especially if there is osteoporosis. It is assumed that the function of the NMDA receptor has changed in the central nervous system and treatment with intravenous ketamine, is an option. Spinal cord stimulation of the dorsal horns of the spine has been effective as well. In majority of cases the syndrome resolves in the first two years, but for the rest the prognosis is dire, symptoms getting worse and persisting for years and even decades.

Assessing the Feasibility of an Open-Source Virtual Reality Mirror Visual Feedback Module for Complex Regional Pain Syndrome: Pilot Usability Study

BACKGROUND

Complex regional pain syndrome (CRPS) is a rare and severe chronic pain condition, with effective treatment options not established for many patients. The underlying pathophysiology remains unclear, but there is a growing appreciation for the role of central mechanisms which have formed the basis for brain-based therapies such as transcranial magnetic stimulation and mirror visual feedback (MVF). MVF has been deployed in the treatment of CRPS using both conventional mirrors and virtual reality (VR).

OBJECTIVE

The aim of this study was to further investigate the use of VR in the treatment of patients with unilateral upper limb CRPS. VR has the potential advantage of more flexible and more motivating tasks, as well as the option of tracking patient improvement through the use of movement data.

METHODS

We describe the development, acceptability, feasibility, and usability of an open-source VR program MVF module designed to be used with consumer VR systems for the treatment of CRPS. The development team was an interdisciplinary group of physical therapists, pain researchers, and VR researchers. Patients recruited from a pain clinic completed 3-5 visits each to trial the system and assessed their experiences in pre- and post-treatment questionnaires.

RESULTS

All 9 (100%) participants were able to use the system for 3, 4, or 5 trials each. None of the participants quit any trial due to cybersickness. All 9 (100%) participants reported interest in using the module in the future. Participants' reported average pain scores in the affected limb were not significantly different from baseline during treatment or after treatment (P=.16). We did not find a statistically significant effect on participants' self-reported average pain scores.

CONCLUSIONS

We propose that this module could be a useful starting point for modification and testing for other researchers. We share modifications to make this module usable with standalone headsets and finger tracking. Next steps include adapting this module for at-home use, or for use with participants with lower limb pain.

Truncal complex regional pain syndrome, myth or reality: Case report

Introduction

Complex regional pain syndrome (CRPS) is an under diagonised, chronic pain condition commonly described occurring in the extremities. Its occurrence in the trunk is rarely reported and is thought by some to be non existent.

Case presentation

We report an unusual case of trunkul CRPS post appendectomy which presented with debilitating pain and review relevant literature.

Discussion and conclusion

We recommend that subsequent descriptions and diagnostic criteria should include the trunk as a site of occurrence of CRPS and not just the extremities. This will help reduce under diagnosis of this important condition.

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CRPS can also occur in the trunk and not only limbs as previously thought.

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CRPS can also occur after appendicectomy and surgeons must be wary.

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Early diagnosis and treatment are essential for better outcome.

Intact tactile anisotropy despite altered hand perception in complex regional pain syndrome: rethinking the role of the primary sensory cortex in tactile and perceptual dysfunction

Complex Regional Pain Syndrome (CRPS) is characterised by pain, autonomic, sensory and motor abnormalities. It is associated with changes in the primary somatosensory cortex (S1 representation), reductions in tactile sensitivity (tested by two-point discrimination), and alterations in perceived hand size or shape (hand perception). The frequent co-occurrence of these three phenomena has led to the assumption that S1 changes underlie tactile sensitivity and perceptual disturbances. However, studies underpinning such a presumed relationship use tactile sensitivity paradigms that involve the processing of both non-spatial and spatial cues. Here, we used a task that evaluates anisotropy (i.e., orientation-dependency; a feature of peripheral and S1 representation) to interrogate spatial processing of tactile input in CRPS and its relation to hand perception. People with upper limb CRPS (n = 14) and controls with (n = 15) or without pain (n = 19) judged tactile distances between stimuli-pairs applied across and along the back of either hand to provide measures of tactile anisotropy. Hand perception was evaluated using a visual scaling task and questionnaires. Data were analysed with generalised estimating equations. Contrary to our hypotheses, tactile anisotropy was bilaterally preserved in CRPS, and the magnitude of anisotropic perception bias was comparable between groups. Hand perception was distorted in CRPS but not related to the magnitude of anisotropy or bias. Our results suggest against impairments in spatial processing of tactile input, and by implication S1 representation, as the cause of distorted hand perception in CRPS. Further work is warranted to elucidate the mechanisms of somatosensory dysfunction and distorted hand perception in CRPS.

Characterising sensorimotor adaptation in Complex Regional Pain Syndrome

It has been suggested that sensorimotor conflict contributes to the maintenance of some pathological pain conditions, implying that there are problems with the adaptation processes that normally resolve such conflict. We tested whether sensorimotor adaptation is impaired in people with Complex Regional Pain Syndrome (CRPS) by characterising their adaption to lateral prismatic shifts in vision. People with unilateral upper-limb CRPS Type I (n = 17), and pain-free individuals (n = 18; matched for age, sex, and handedness) completed prism adaptation with their affected/non-dominant and non-affected/dominant arms. We examined 1) the rate at which participants compensated for the optical shift during prism exposure (i.e., strategic recalibration), 2) endpoint errors made directly after prism adaptation (sensorimotor realignment) and the retention of these errors, and 3) kinematic markers associated with strategic control. Direct comparisons between people with CRPS and controls revealed no evidence of any differences in strategic recalibration, including no evidence for differences in a kinematic marker associated with trial-by-trial changes in movement plans during prism exposure. All participants made significant endpoint errors after prism adaptation exposure, indicative of sensorimotor realignment. Overall, the magnitude of this realignment did not differ between people with CRPS and pain-free controls. However, when endpoint errors were considered separately for each hand, people with CRPS made greater errors (indicating more rather than less realignment) when using their affected hand than their non-affected hand. No such difference was seen in controls. Taken together, these findings provide no evidence of impaired strategic control or sensorimotor realignment in people with CRPS. In contrast, they provide some indication that there could be a greater propensity for sensorimotor realignment in the CRPS-affected arm, consistent with more flexible representations of the body and peripersonal space. Our study challenges an implicit assumption of the theory that sensorimotor conflict might underlie some pathological pain conditions.

Patients Describe their Lived Experiences of Battling to Live with Complex Regional Pain Syndrome

Complex regional pain syndrome (CRPS) has never comprehensively been examined from a lived experience perspective. Patients generally have a poorer quality of life than people with other chronic pain conditions. This study aimed to understand the essence of living with CRPS. Data were collected from 17 patients via in-depth interviews. Hermeneutic discussions with four health professionals generated deeper insights. Internet blogs and a book containing patient stories were included for theme verification and triangulation. CRPS is seen as a war-like experience and five themes were identified within the battle: "dealing with the unknown enemy", "building an armoury against a moving target", "battles within the war", "developing battle plans with allies" and "warrior or prisoner of war". Patients live with a chronic pain condition and experience problems unique to CRPS such as fear of pain extending to other parts of their body. Use of the model generated by this research may assist patient/clinician interactions and guide therapeutic discussions. Support for people living with CRPS does not always exist, and some healthcare professionals require additional education about the condition. Better health outcomes are experienced by patients when their personal situation and experiences are heard and understood by health care professionals. PERSPECTIVE: This article presents the lived experience of CRPS. This information and the model generated can help clinicians to better understand their patients and deliver appropriate patient-centered care.

Temporal Contribution of Myeloid-Lineage TLR4 to the Transition to Chronic Pain: A Focus on Sex Differences

Complex regional pain syndrome (CRPS) is a chronic pain disorder with a clear acute-to-chronic transition. Preclinical studies demonstrate that toll-like receptor 4 (TLR4), expressed by myeloid-lineage cells, astrocytes, and neurons, mediates a sex-dependent transition to chronic pain; however, evidence is lacking on which exact TLR4-expressing cells are responsible. We used complementary pharmacologic and transgenic approaches in mice to more specifically manipulate myeloid-lineage TLR4 and outline its contribution to the transition from acute-to-chronic CRPS based on three key variables: location (peripheral vs central), timing (prevention vs treatment), and sex (male vs female). We demonstrate that systemic TLR4 antagonism is more effective at improving chronic allodynia trajectory when administered at the time of injury (early) in the tibial fracture model of CRPS in both sexes. In order to clarify the contribution of myeloid-lineage cells peripherally (macrophages) or centrally (microglia), we rigorously characterize a novel spatiotemporal transgenic mouse line, Cx3CR1-Cre^ERT2-eYFP;TLR4^fl/fl (TLR4 cKO) to specifically knock out TLR4 only in microglia and no other myeloid-lineage cells. Using this transgenic mouse, we find that early TLR4 cKO results in profound improvement in chronic, but not acute, allodynia in males, with a significant but less robust effect in females. In contrast, late TLR4 cKO results in partial improvement in allodynia in both sexes, suggesting that downstream cellular or molecular TLR4-independent events may have already been triggered. Overall, we find that the contribution of TLR4 is time- and microglia-dependent in both sexes; however, females also rely on peripheral myeloid-lineage (or other TLR4 expressing) cells to trigger chronic pain.SIGNIFICANCE STATEMENT The contribution of myeloid cell TLR4 to sex-specific pain progression remains controversial. We used complementary pharmacologic and transgenic approaches to specifically manipulate TLR4 based on three key variables: location (peripheral vs central), timing (prevention vs treatment), and sex (male vs female). We discovered that microglial TLR4 contributes to early pain progression in males, and to a lesser extent in females. We further found that maintenance of chronic pain likely occurs through myeloid TLR4-independent mechanisms in both sexes. Together, we define a more nuanced contribution of this receptor to the acute-to-chronic pain transition in a mouse model of complex regional pain syndrome.

Hyperbaric oxygen treatment in recurrent development of complex regional pain syndrome: A case report

A broad spectrum of conditions including neuropathic pain, complex regional pain syndrome (CRPS) and fibromyalgia, have been implicated as causes of chronic pain. There is a need for new and effective treatments that patients can tolerate without significant adverse effects. One potential intervention is hyperbaric oxygen treatment (HBOT). The case reported here is unique in describing repeated HBOT in a patient who developed recurrent post-traumatic CRPS of the lower as well as the upper limbs. In the first event, two months after distortion and abruption of the external right ankle, the patient suffered leg pain, oedema formation, mild hyperaemia, limited mobility of the ankle and CRPS Type 1. In the second event, the same patient suffered fracture-dislocation of the distal radius 1.5 years after the first injury. After the plaster cast was removed the patient developed pain, warmth, colour changes, oedema formation and limited wrist mobility with CRPS Type 1. Pharmacological treatment as well as HBOT were used with significant improvement of functional outcome in both cases. Some studies suggest that patients with a history of CRPS are more likely to develop secondary CRPS compared to the rates reported in the literature among the general population. Patients with a history of CRPS should be counselled that they may be at risk for developing secondary CRPS if they undergo surgery or sustain trauma to another extremity.

Prism adaptation effects in complex regional pain syndrome: A therapo-physiological single case experimental design exploratory report

Complex Regional Pain Syndrome (CRPS) is an invalidating chronic condition that can occur after an acute peripheral lesion. Prism adaptation therapy is regarded as a promising tool to improve chronic pain in this syndrome but the mechanisms which lead to pain amelioration remain unknown. In this exploratory report we performed a retrospective analysis of longitudinal data collected from a single, atypical patient, who showed hyper-attention toward her affected (left) hand. Repeated assessments of pain and spatial neglect made during the course of the prism adaptation treatment revealed differential contributions of the two hands to adaptation-induced pain reduction. Treatment response appeared to be associated with a relative modification of the spatial behaviour of the two hands. This case study provides a new example of pain relief following prismatic deviation away from the pathological side.

Functional pain disorders - more than nociplastic pain

BACKGROUND

Nociplastic pain has been recently introduced as a third mechanistic descriptor of pain arising primarily from alterations of neural processing, in contrast to pain due to tissue damage leading to nociceptor activation (nociceptive) or due to lesion or disease of the somatosensory nervous system (neuropathic). It is characterized by hyperalgesia and allodynia, inconsistency and reversibility, as well as dynamic cross-system interactions with biological and psychobehavioral factors. Along with this renewed understanding, functional pain disorders, also classified as chronic primary pain, are being reframed as biopsychosocial conditions that benefit from multimodal treatment.

OBJECTIVE

To summarize the current understanding of nociplastic pain and functional pain disorders, with a focus on conditions that are common in neurology practice.

METHODS

This was a narrative literature review.

RESULTS

Chronic back pain, fibromyalgia syndrome and complex regional pain syndrome are best understood within a biopsychosocial framework of pain perception that considers structural factors (predispositions and sequelae) and psychobehavioral mechanisms. Although pain is often the primary complaint, it should not be the only focus of treatment, as accompanying symptoms such as sleep or mood problems can significantly impact quality of life and offer useful leverage points for multimodal treatment. Analgesic pharmacotherapy is rarely helpful on its own, and should always be imbedded in a multidisciplinary setting.

Interventional Modalities to Treat Complex Regional Pain Syndrome

PURPOSE OF REVIEW

Complex regional pain syndrome (CRPS) is a debilitating pain condition that often requires a multidisciplinary approach including medication, physical therapy, occupational therapy, psychological therapy, and interventional procedures to restore the patient's quality of life. This article reviews the interventional treatments for pain resulting from CRPS.

RECENT FINDINGS

Sympathetic nerve blocks (stellate ganglion and lumbar sympathetic) are the first-line interventional treatment options for patients with CRPS of the upper and lower extremities, respectively. Fluoroscopic techniques for lumbar sympathetic blocks have not significantly changed throughout the years. However, both novel fluoroscopic and ultrasound approaches to stellate ganglion blockade have arisen. In addition, novel neuromodulation therapies to treat CRPS have been developed to include new waveforms with dorsal column stimulation and entirely new nerve targets such as dorsal root ganglion stimulation. This paper will review the latest interventional treatment options available for the treatment of CRPS.

Anesthetic Management of a Complex Regional Pain Syndrome (CRPS) Patient With Ketamine

Complex regional pain syndrome (CRPS) is a potentially debilitating form of neuropathic pain that may manifest following a traumatic injury or surgery. CRPS is also known as algodystrophy, causalgia, or reflex sympathetic dystrophy (RSD). Patients describe unbearable burning pain from nonnociceptive stimuli, such as when taking a shower or brushing against another object. Regular tactile stimuli encountered during routine dental procedures may not be well-tolerated by a patient with CRPS. Ketamine infusions have been reported to help alleviate acute exacerbations or "flare-ups" of CRPS symptoms. This case report provides a brief overview of CRPS pathophysiology and treatment including data supporting the use of ketamine infusions and a discussion regarding the anesthetic management of a patient with CRPS presenting for dental care under deep sedation utilizing high-dose intravenous ketamine.

Utilization of Intravenous Lidocaine Infusion for the Treatment of Refractory Chronic Pain

Context

Chronic pain accounts for one of the most common reasons patients seek medical care. The financial burden of chronic pain on health care is seen by direct financial cost and resource utilization. Many risk factors may contribute to chronic pain, but there is no definite risk. Managing chronic pain is a balance between maximally alleviating symptoms by utilizing a therapeutic regimen that is safe for long-term use. Currently, non-opioid analgesics, NSAIDs, and opioids are some of the medical treatment options, but these have numerous adverse effects and may not be the best option for long-term use. However, Lidocaine can achieve both central and peripheral analgesic effects with relatively few side effects, which may be an ideal compound for managing chronic pain.

Evidence Acquisition

This is a Narrative Review.

Results

Infusion of lidocaine (2-(diethylamino)-N-(2,6-dimethylphenyl)acetamide), an amino-amide compound, is emerging as a promising option to fill the therapeutic void for treatment of chronic pain. Numerous studies have outlined dosing protocols for lidocaine infusion for the management of perioperative pain, outlined below. While there are slight variations in these different protocols, they all center around a similar dosing regimen to administer a bolus to reach a rapid steady state, followed by infusion for up to 72 hours to maintain the therapeutic analgesic effects.

Conclusions

Lidocaine may be a promising pharmacologic solution with a low side effect profile that provides central and peripheral analgesia. Even though the multifaceted mechanism is not entirely understood yet, lidocaine may be a promising novel remedy in treating chronic pain in various conditions.

An Unusual Case of Periosteal Glomus Tumor at the Metacarpal Base Presenting as Type II CRPS: Case Report

Background: An unusual case involving a middle-aged male with a 9-year history of presumptive chronic regional pain syndrome (CRPS) and ulnar neuropathy was referred for failure in treatment. Methods: On presentation, the patient was requesting an amputation of his arm. However, work-up uncovered a periosteal extra-digital glomus tumor on the base of the small finger metacarpal. Results: Surgical excision of the lesion resulted in rapid resolution of his pain and normal hand function was ultimately restored. Conclusions: Glomus tumors account for up to 5% of all soft tissue tumors of the upper extremity, occurring most frequently within or adjacent to the nail bed. Time from onset of symptoms to correct diagnosis may not be established for many years, especially with atypical tumor locations. Although glomus tumors have been widely reported, atypical locations of these tumors should be included in the differential diagnosis for patients with unusual chronic pain or neuropathy. Furthermore, when evaluating a chronic pain patient, our findings support the opinion that assignment of the diagnosis of CRPS should only be a diagnosis of exclusion.

Drug-Nutraceutical Co-Crystal and Salts for Making New and Improved Bi-Functional Analgesics

The discovery and development of effective analgesics is greatly lagging behind the steadily rising prevalence of chronic pain. Currently prescribed analgesics for chronic pain are lacking in efficacy mainly due to their narrowly-targeted mechanism of action. Driving neuronal hyperexcitability that underlies symptoms of chronic pain are multiple non-neuronal processes, among which are tissue hypoxia and oxidative stress. Here we demonstrate the design, synthesis, and activity of new multi-component bi-functional analgesic crystalline solids, co-crystals, and salts, based on pairing of vasodilatory anti-hypoxic drugs pentoxifylline, clonidine and linsidomine with antioxidant nutraceuticals protocatechuic acid, α-lipoic acid, and caffeic acid. After validation, chemical and structural characterization of these novel salts and co-crystals, topical formulations of the products were tested in a rat model of complex regional pain syndrome. Analgesic effects achieved with the salts and co-crystal exceeded the efficacy and/or potency of constituent compounds indicating that more effective, advanced analgesics can readily be developed by careful pairing of compounds that simultaneously target multiple neural and non-neural processes driving chronic pain.

Use of anticonvulsants and antidepressants for treatment of complex regional pain syndrome: a literature review

Complex regional pain syndrome (CRPS) is characterized by pain accompanied by symptoms including skin changes, sensory, motor, trophic changes and autonomic dysfunction. Anticonvulsants and antidepressants are commonly prescribed for neuropathic pain conditions; however, evidence is sparse whether these drugs are effective in reducing CRPS-related pain. As such, Pubmed was searched for studies published from January 1990 through March 2020; 13 studies were included in this review. Overall, evidence is considered insufficient for use of gabapentinoids for CRPS-related pain. However, three randomized controlled trials (RCTs) did find gabapentin to result in significant improvement in pain whereas one RCT reported use of amitriptyline to be equally as effective as gabapentin. Multiple case reports discussing the efficacy of pregabalin in pediatric CRPS patients, with relatively short duration of disease and underlying psychiatric illness, have been reported, but these findings need to be validated with RCTs.

Outcome in young adults who were diagnosed with complex regional pain syndrome in childhood and adolescence

Supplemental Digital Content is Available in the Text.

Most patients with childhood-onset complex regional pain syndrome continue to have some complex regional pain syndrome–related pain into young adulthood and have a lower health-related quality of life.

Introduction:

Complex regional pain syndrome (CRPS) is a neuropathic pain condition of unknown etiology. Little is known of long-term outcomes of young adults who were diagnosed with CRPS as children.

Methods:

In this study, surveys were mailed to adults who were treated for childhood CRPS at the Lucile Packard Children's Hospital between 1994 and 2018. Completed surveys were analyzed for pain symptoms. Health-related quality-of-life surveys, the Optum SF-8, were analyzed based on norm-based scoring.

Results:

This study had a 50% response rate. Patients were treated with physical and occupational therapy, peripheral or sympathetic nerve blocks, medication for neuropathic pain, and psychotherapy. Sixty-eight percent of the subjects reported pain. Each 1-year increase in the patient's age at the time of CRPS diagnosis increased the odds of having at least mild pain as an adult by 61% (P = 0.005). Most patients had slightly lower quality-of-life scores than the US population average in both the mental component score (43.4, 95%, confidence interval 3.4) and the physical component score (44.4, 95%, confidence interval 3.3).

Conclusions:

Young adults in our sample had long-lasting pain symptoms. More than two-thirds of adult patients reported some degree of pain, and these patients had a lower quality of life. Encouraging was that the majority did not have CRPS spreading to other areas, and their pain did not warrant further treatment. Understanding long-term outcomes may lead to risk stratification earlier in the disease to improve future quality of life.

Regional vitamin C in Bier block reduces the incidence of CRPS-1 following distal radius fracture surgery

BACKGROUND

Systemic vitamin C supplementation after wrist fracture has been suggested to reduce the incidence of complex regional pain syndrome (CRPS). This study aimed to evaluate the effect of regional vitamin C in Bier block in the early phase of fracture on CRPS occurrence following surgery for distal radius fractures.

METHODS

Seventy-four patients with isolated extra-articular distal radius fracture with the plan of fixation under Bier block were enrolled. Patients were assigned randomly into two groups: receiving either 500 mg vitamin C or sterile water as a Bier block adjuvant. Both groups received 500 mg of oral vitamin C for six weeks. The patients were evaluated for CRPS signs and symptoms at 2, 4, 6, and 12 weeks post-surgery.

RESULTS

The overall incidence of CRPS 12 weeks after surgery in the vitamin C group was significantly less than the controls (22.9% vs 45.5%, p = 0.04). Logistic regression analysis showed that the only significant contribution in predicting the incidence of CRPS came from the intervention variable (OR 0.26, CI95% 0.08-0.85; P = 0.027).

CONCLUSIONS

The findings suggest that adding vitamin C 500 mg to the local anesthetic in Bier block significantly reduces the incidence of CRPS following distal radius fractures.