Treatment of intractable pain with topical large-dose capsaicin: preliminary report

Perspectives on the pharmacological management of complex regional pain syndrome

INTRODUCTION

Complex regional pain syndrome (CRPS) is a chronic pain condition that is notoriously difficult to treat. Therapies for CRPS include cognitive behavioral, physical, and occupational therapy, single or multidrug pharmacotherapy, and a variety of interventional techniques. Unfortunately, randomized clinical trials of these therapies are limited. The large number of potential pharmacologic options can be overwhelming for providers in their attempts to develop a treatment plan.

AREAS COVERED

This article will review the literature on the pharmacologic management of CRPS. It is based on a systematic search of PubMed using keywords, followed by evaluation of the bibliographies for relevant articles.

EXPERT OPINION

No single drug has amassed enough evidence to suggest clear efficacy, but a handful of agents with at least modest evidence are commonly used, including gabapentinoids, bisphosphonates, ketamine, and pulsed dose steroids. Meanwhile, other agents that lack significant evidence specifically in CRPS but have evidence in other neuropathic conditions are commonly prescribed, including tricyclic antidepressants (TCAs) and selective serotonin reuptake inhibitors (SNRIs). In our opinion, careful selection and prompt initiation of appropriate pharmacotherapy may optimize pain relief and improve functionality in patients burdened with this debilitating condition.

Primary Erythromelalgia Treated With 10% Capsaicin Cream: A Case Report and a 10-Year Follow-Up

In this case report, we describe the difficulty in finding a suitable treatment for a nine-year-old girl with erythromelalgia. Initially, she could only find pain relief through immersion of her hands and feet in buckets of cool water. Her pain did not respond to outpatient treatments, and she was ultimately admitted to the hospital for pain management. Many different medications and modalities were tried over the course of several weeks in the hospital. Finally, she received the most benefit from 10% compounded capsaicin cream administered under general anesthesia with regional analgesia for post-application pain. Over the course of several years, exacerbations of her pain were treated with additional applications of 10% capsaicin cream, with each application providing relief for an increased duration. Her severe pain flares eventually went into remission after several years. Today, after more than a decade following her initial presentation, she is a successful college student and is taking no medications for her erythromelalgia.

TRP Channels as Molecular Targets to Relieve Cancer Pain

Transient receptor potential (TRP) channels are critical receptors in the transduction of nociceptive stimuli. The microenvironment of diverse types of cancer releases substances, including growth factors, neurotransmitters, and inflammatory mediators, which modulate the activity of TRPs through the regulation of intracellular signaling pathways. The modulation of TRP channels is associated with the peripheral sensitization observed in patients with cancer, which results in mild noxious sensory stimuli being perceived as hyperalgesia and allodynia. Secondary metabolites derived from plant extracts can induce the activation, blocking, and desensitization of TRP channels. Thus, these compounds could act as potential therapeutic agents, as their antinociceptive properties could be beneficial in relieving cancer-derived pain. In this review, we will summarize the role of TRPV1 and TRPA1 in pain associated with cancer and discuss molecules that have been reported to modulate these channels, focusing particularly on the mechanisms of channel activation associated with molecules released in the tumor microenvironment.

Complex regional pain syndrome secondary to sacrococcygeal dislocation following trauma to the lumbosacral region. Case report

Introduction: The complex regional pain síndrome (CRPS) is a rare condition characterized by inflammatory, vasomotor and central nervous system (CNS) involvement. Its clinical presentation can be subacute, acute or chronic, and may have severe effects on the patient’s quality of life.Case description: 21-year-old female patient with trauma in the lumbosacral region associated with pain and functional limitation. Diagnostic imaging showed sacrococcygeal dislocation with subsequent inflammatory and acute and chronic autonomic symptoms that were treated medically and surgically. The patient responded to treatment with long-term improvement of the symptoms.Discussion: In this case, CRPS occurred after trauma and caused subacute symptoms that became even more acute until reaching a chronic presentation. Inflammation, vasomotor dysfunction and CNS involvement made this case a multidisciplinary diagnostic and therapeutic challenge.Conclusion: CRPS is a rare disease that is difficult to diagnose. However, diagnosis should be timely in order to initiate personalized treatment, since this disease considerably affects the patient’s quality of life.

Recovery from tachyphylaxis of TRPV1 coincides with recycling to the surface membrane

The transient receptor potential vanilloid-1 (TRPV1) ion channel is essential for sensation of thermal and chemical pain. TRPV1 activation is accompanied by Ca²⁺-dependent desensitization; acute desensitization reflects rapid reduction in channel activity during stimulation, whereas tachyphylaxis denotes the diminution in TRPV1 responses to repetitive stimulation. Acute desensitization has been attributed to conformational changes of the TRPV1 channel; however, the mechanisms underlying the establishment of tachyphylaxis remain to be defined. Here, we report that the degree of whole-cell TRPV1 tachyphylaxis is regulated by the strength of inducing stimulation. Using light-sheet microscopy and pH-sensitive sensor pHluorin to follow TRPV1 endocytosis and exocytosis trafficking, we provide real-time information that tachyphylaxis of different degrees concurs with TRPV1 recycling to the plasma membrane in a proportional manner. This process controls TRPV1 surface expression level thereby the whole-cell nociceptive response. We further show that activity-gated TRPV1 trafficking associates with intracellular Ca²⁺ signals of distinct kinetics, and recruits recycling routes mediated by synaptotagmin 1 and 7, respectively. These results suggest that activity-dependent TRPV1 recycling contributes to the establishment of tachyphylaxis.

The Role of Toxins in the Pursuit for Novel Analgesics

Chronic pain is a major medical issue which reduces the quality of life of millions and inflicts a significant burden on health authorities worldwide. Currently, management of chronic pain includes first-line pharmacological therapies that are inadequately effective, as in just a portion of patients pain relief is obtained. Furthermore, most analgesics in use produce severe or intolerable adverse effects that impose dose restrictions and reduce compliance. As the majority of analgesic agents act on the central nervous system (CNS), it is possible that blocking pain at its source by targeting nociceptors would prove more efficient with minimal CNS-related side effects. The development of such analgesics requires the identification of appropriate molecular targets and thorough understanding of their structural and functional features. To this end, plant and animal toxins can be employed as they affect ion channels with high potency and selectivity. Moreover, elucidation of the toxin-bound ion channel structure could generate pharmacophores for rational drug design while favorable safety and analgesic profiles could highlight toxins as leads or even as valuable therapeutic compounds themselves. Here, we discuss the use of plant and animal toxins in the characterization of peripherally expressed ion channels which are implicated in pain.

Acute effect of different concentrations of cayenne pepper cataplasm on sensory-motor functions and serum levels of inflammation-related biomarkers in healthy subjects

Physical medicine therapies are often used in treating widespread musculoskeletal disorders, such as neck and low back pain. Herbal cataplasms containing rubefacient substances, such as Cayenne pepper, or galenic preparations like Munari cataplasm are commonly used as natural medications to treat painful areas. In this paper we show the effects of a 20-min application of Cayenne pepper and kaolin powder cataplasm (CPC) on healthy subjects. Treatment effects were evaluated by cold/hot feeling on visual analogue scale, blood pressure, body temperature, skin light touch sensations, two-point discrimination, and pain threshold to a mechanical stimulus, before and immediately after, 15 min after and 30 min after different concentration of Cayenne pepper in CPC preparation on healthy subjects. Maximal voluntary trunk extension force and trunk extension submaximal force matching error were also measured. In addition, the resulting optimal CPC mixture was tested for its safety by measuring changes in circulating levels of inflammatory-related biomarkers after 20-min application. The results indicate that the 5% concentration of Cayenne pepper in the preparation of CPC is the best choice, since no additional effects can be obtained with the 10% concentration, and the effects are higher than those observed at the 2.5% concentration. Importantly, 5% CPC application did not induce a significant increase of inflammatory-related biomarkers, suggesting that 20-min application has no negative side effects at systemic levels. Further studies are needed to investigate the immediate and long-term effects of repeated CPC applications as well as to understand the intersecting underlying mechanisms activated by Capsaicin and other identified factors, in order to be more extensively used in the field of physical medicine therapies.

Exciting perspectives for Translational Myology in the Abstracts of the 2018Spring PaduaMuscleDays: Giovanni Salviati Memorial - Chapter IV - Abstracts of March 17, 2018

Myologists working in Padua (Italy) were able to continue a half-century tradition of studies of skeletal muscles, that started with a research on fever, specifically if and how skeletal muscle contribute to it by burning bacterial toxin. Beside main publications in high-impact-factor journals by Padua myologists, I hope to convince readers (and myself) of the relevance of the editing Basic and Applied Myology (BAM), retitled from 2010 European Journal of Translational Myology (EJTM), of the institution of the Interdepartmental Research Center of Myology of the University of Padova (CIR-Myo), and of a long series of International Conferences organized in Euganei Hills and Padova, that is, the PaduaMuscleDays. The 2018Spring PaduaMuscleDays (2018SpPMD), were held in Euganei Hills and Padua (Italy), in March 14-17, and were dedicated to Giovanni Salviati. The main event of the “Giovanni Salviati Memorial”, was held in the Aula Guariento, Accademia Galileiana di Scienze, Lettere ed Arti of Padua to honor a beloved friend and excellent scientist 20 years after his premature passing. Using the words of Prof. Nicola Rizzuto, we all share his believe that Giovanni “will be remembered not only for his talent and originality as a biochemist, but also for his unassuming and humanistic personality, a rare quality in highly successful people like Giovanni. The best way to remember such a person is to gather pupils and colleagues, who shared with him the same scientific interests and ask them to discuss recent advances in their own fields, just as Giovanni have liked to do”. Since Giovanni’s friends sent many abstracts still influenced by their previous collaboration with him, all the Sessions of the 2018SpPMD reflect both to the research aims of Giovanni Salviati and the traditional topics of the PaduaMuscleDays, that is, basics and applications of physical, molecular and cellular strategies to maintain or recover functions of skeletal muscles. The translational researches summarized in the 2018SpPMD Abstracts are at the appropriate high level to attract endorsement of Ethical Committees, the interest of International Granting Agencies and approval for publication in top quality international journals. The abstracts of the presentations of the March 16, 2018 Padua Muscle Day and those of the remaining Posters are listed in this chapter IV. The Author Index of the 2018Spring PaduaMuscleDays follows at page 78.

Mobility disorders and pain, interrelations that need new research concepts and advanced clinical commitments

This Perspective will discuss topics recently suggested by Prof. Helmut Kern, Vienna, Austria, to advance the research activities of his team, that is: Topic A, 10 years post RISE; Topic B, New research for new solutions on old research questions; Topic C, Working groups on nerve regeneration, training-parameters of seniors in different ages, muscle adaptation; and studies of connective tissue and cartilage. This Perspective summarizes some of the basic concepts and of the evidence-based tools for developing further translational research activities. Clinically relevant results will ask for continuous interests of Basic and Applied Myologists and for the support during the next five to ten years of public and private granting agencies. All together, they will end in protocols, devices and multidisciplinary managements for persons suffering with muscle denervation, neuromuscular-related or non-related pain and for the increasing population of old, older and oldest senior citizens in Europe and beyond.

Use of Capsaicin to Treat Pain: Mechanistic and Therapeutic Considerations

Capsaicin is the pungent ingredient of chili peppers and is approved as a topical treatment of neuropathic pain. The analgesia lasts for several months after a single treatment. Capsaicin selectively activates TRPV1, a Ca²⁺-permeable cationic ion channel that is enriched in the terminals of certain nociceptors. Activation is followed by a prolonged decreased response to noxious stimuli. Interest also exists in the use of injectable capsaicin as a treatment for focal pain conditions, such as arthritis and other musculoskeletal conditions. Recently injection of capsaicin showed therapeutic efficacy in patients with Morton’s neuroma, a painful foot condition associated with compression of one of the digital nerves. The relief of pain was associated with no change in tactile sensibility. Though injection evokes short term pain, the brief systemic exposure and potential to establish long term analgesia without other sensory changes creates an attractive clinical profile. Short-term and long-term effects arise from both functional and structural changes in nociceptive terminals. In this review, we discuss how local administration of capsaicin may induce ablation of nociceptive terminals and the clinical implications.

Harnessing the Therapeutic Potential of Capsaicin and Its Analogues in Pain and Other Diseases

Capsaicin is the most predominant and naturally occurring alkamide found in Capsicum fruits. Since its discovery in the 19th century, the therapeutic roles of capsaicin have been well characterized. The potential applications of capsaicin range from food flavorings to therapeutics. Indeed, capsaicin and few of its analogues have featured in clinical research covered by more than a thousand patents. Previous records suggest pleiotropic pharmacological activities of capsaicin such as an analgesic, anti-obesity, anti-pruritic, anti-inflammatory, anti-apoptotic, anti-cancer, anti-oxidant, and neuro-protective functions. Moreover, emerging data indicate its clinical significance in treating vascular-related diseases, metabolic syndrome, and gastro-protective effects. The dearth of potent drugs for management of such disorders necessitates the urge for further research into the pharmacological aspects of capsaicin. This review summarizes the historical background, source, structure and analogues of capsaicin, and capsaicin-triggered TRPV1 signaling and desensitization processes. In particular, we will focus on the therapeutic roles of capsaicin and its analogues in both normal and pathophysiological conditions.

Capsaicin: Current Understanding of Its Mechanisms and Therapy of Pain and Other Pre-Clinical and Clinical Uses

In this review, we discuss the importance of capsaicin to the current understanding of neuronal modulation of pain and explore the mechanisms of capsaicin-induced pain. We will focus on the analgesic effects of capsaicin and its clinical applicability in treating pain. Furthermore, we will draw attention to the rationale for other clinical therapeutic uses and implications of capsaicin in diseases such as obesity, diabetes, cardiovascular conditions, cancer, airway diseases, itch, gastric, and urological disorders.

Skin Matters: A Review of Topical Treatments for Chronic Pain. Part Two: Treatments and Applications

In Part One of this two-part series, we discussed skin physiology and anatomy as well as generalities concerning topical analgesics. This modality of therapy has lesser side effects and drug-drug interactions, and patients tolerate this form of therapy better than many oral options. Unfortunately, this modality is not used as often as it could be in chronic pain states, such as that from neuropathic pain. Part Two discusses specific therapies, local anesthetics, and other drugs, as well as how a clinician might use specific aspects of a patient's neuropathic pain presentation to help guide them in the selection of a topical agent.

An equine pain face

Objective

The objective of this study was to investigate the existence of an equine pain face and to describe this in detail.

Study design

Semi-randomized, controlled, crossover trial.

Animals

Six adult horses.

Methods

Pain was induced with two noxious stimuli, a tourniquet on the antebrachium and topical application of capsaicin. All horses participated in two control trials and received both noxious stimuli twice, once with and once without an observer present. During all sessions their pain state was scored. The horses were filmed and the close-up video recordings of the faces were analysed for alterations in behaviour and facial expressions. Still images from the trials were evaluated for the presence of each of the specific pain face features identified from the video analysis.

Results

Both noxious challenges were effective in producing a pain response resulting in significantly increased pain scores. Alterations in facial expressions were observed in all horses during all noxious stimulations. The number of pain face features present on the still images from the noxious challenges were significantly higher than for the control trial (p = 0.0001). Facial expressions representative for control and pain trials were condensed into explanatory illustrations. During pain sessions with an observer present, the horses increased their contact-seeking behavior.

Conclusions and clinical relevance

An equine pain face comprising ‘low’ and/or ‘asymmetrical’ ears, an angled appearance of the eyes, a withdrawn and/or tense stare, mediolaterally dilated nostrils and tension of the lips, chin and certain facial muscles can be recognized in horses during induced acute pain. This description of an equine pain face may be useful for improving tools for pain recognition in horses with mild to moderate pain.

Capsaicinoids in the treatment of neuropathic pain: a review

The treatment of neuropathic pain is difficult. Oral pharmaceuticals have significant side effects, and treatment efficacy tends to be modest. The use of topical analgesics reduces the potential for systemic side effects and allows direct application of medications to the area of pain. The natural spicy substance, capsaicin, has historically been known for its topical use. Capsaicin, once applied to the skin, causes a brief initial sensitization followed by a prolonged desensitization of the local pain nerves. This occurs through stimulation of the transient receptor potential vanilloid-1 (TRPV1) expressing pain nerve fibers. While low-dose capsaicin has not resulted in good efficacy, the larger dose 8% topical capsaicin has had some of the best data currently available in the treatment of post-herpetic neuralgia (PHN) and other neuropathic conditions. This paper discusses the data currently existing for capsaicin 8% in the treatment of PHN. It further reviews data for the low-dose capsaicin products and the current status in the development of other capsaicinoids, e.g. resiniferotoxin, and high-concentration liquid capsaicin.

Positive allosteric modulation of TRPV1 as a novel analgesic mechanism

Background

The prevalence of long-term opiate use in treating chronic non-cancer pain is increasing, and prescription opioid abuse and dependence are a major public health concern. To explore alternatives to opioid-based analgesia, the present study investigates a novel allosteric pharmacological approach operating through the cation channel TRPV1. This channel is highly expressed in subpopulations of primary afferent unmyelinated C- and lightly-myelinated Aδ-fibers that detect low and high rates of noxious heating, respectively, and it is also activated by vanilloid agonists and low pH. Sufficient doses of exogenous vanilloid agonists, such as capsaicin or resiniferatoxin, can inactivate/deactivate primary afferent endings due to calcium overload, and we hypothesized that positive allosteric modulation of agonist-activated TRPV1 could produce a selective, temporary inactivation of nociceptive nerve terminals in vivo. We previously identified MRS1477, a 1,4-dihydropyridine that potentiates vanilloid and pH activation of TRPV1 in vitro, but displays no detectable intrinsic agonist activity of its own. To study the in vivo effects of MRS1477, we injected the hind paws of rats with a non-deactivating dose of capsaicin, MRS1477, or the combination. An infrared diode laser was used to stimulate TRPV1-expressing nerve terminals and the latency and intensity of paw withdrawal responses were recorded. qRT-PCR and immunohistochemistry were performed on dorsal root ganglia to examine changes in gene expression and the cellular specificity of such changes following treatment.

Results

Withdrawal responses of the capsaicin-only or MRS1477-only treated paws were not significantly different from the untreated, contralateral paws. However, rats treated with the combination of capsaicin and MRS1477 exhibited increased withdrawal latency and decreased response intensity consistent with agonist potentiation and inactivation or lesion of TRPV1-containing nerve terminals. The loss of nerve endings was manifested by an increase in levels of axotomy markers assessed by qRT-PCR and colocalization of ATF3 in TRPV1⁺ cells visualized via immunohistochemistry.

Conclusions

The present observations suggest a novel, non-narcotic, selective, long-lasting TRPV1-based approach for analgesia that may be effective in acute, persistent, or chronic pain disorders.

Topical capsaicin (low concentration) for chronic neuropathic pain in adults

BACKGROUND

Topical creams with capsaicin are used to treat pain from a wide range of chronic conditions including neuropathic pain. Following application to the skin capsaicin causes enhanced sensitivity to noxious stimuli, followed by a period with reduced sensitivity and, after repeated applications, persistent desensitisation. There is uncertainty about the efficacy and tolerability of capsaicin for treating painful chronic neuropathies. This is an update of an earlier review of topical capsaicin for chronic neuropathic pain in adults that looked at all doses and formulations of capsaicin. The original review has now been split: here we consider only formulations using a low concentration of capsaicin (< 1%) applied several times daily over several weeks, while another review will consider a single application of capsaicin at a high concentration.

OBJECTIVES

To review the evidence from controlled trials on the efficacy and tolerability of topically applied low-concentration (< 1%) capsaicin in chronic neuropathic pain in adults.

SEARCH METHODS

Cochrane CENTRAL, MEDLINE, EMBASE and Oxford Pain Relief Database, searched to July 2012.

SELECTION CRITERIA

Randomised, double-blind, placebo-controlled studies of at least six weeks' duration, using low-concentration (< 1%) topical capsaicin to treat neuropathic pain.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed study quality and validity, and extracted data. Information was extracted on numbers of participants with pain relief (clinical improvement) after at least six weeks, and with local skin reactions, and used to calculate relative risk (or risk ratio, RR) and numbers needed to treat to benefit (NNT) and harm (NNH). Details of definition of pain relief and specific adverse events were sought.

MAIN RESULTS

No additional studies were identified for this update of low concentration capsaicin. Included studies were published before 1996. Six studies (389 participants in total) compared regular application of low dose (0.075%) capsaicin cream with placebo cream. There was substantial heterogeneity in results, probably as a result of the small number of studies each with small numbers of participants, as well as the different pain conditions studied and different definitions of "clinical success" reported. Only two studies reported data for the preferred primary outcome of at least 50% pain relief, and there were too few data for pooled analysis. Local skin reactions were more common with capsaicin, usually tolerable, and attenuated with time; the NNH for repeated low-dose application was 2.5 (95% confidence interval (CI) 2.1 to 3.1). All studies satisfied minimum criteria for quality and validity, but maintenance of blinding remains a potential problem.

AUTHORS' CONCLUSIONS

There were insufficient data to draw any conclusions about the efficacy of low-concentration capsaicin cream in the treatment of neuropathic pain. The information we have suggests that low-concentration topical capsaicin is without meaningful effect beyond that found in placebo creams; given the potential for bias from small study size, this makes it unlikely that low-concentration topical capsaicin has any meaningful use in clinical practice. Local skin irritation, which was often mild and transient but may lead to withdrawal, was common. Systemic adverse effects were rare.

Small molecule positive allosteric modulation of TRPV1 activation by vanilloids and acidic pH

Transient receptor potential cation channel subfamily V member 1 (TRPV1) is a high-conductance, nonselective cation channel strongly expressed in nociceptive primary afferent neurons of the peripheral nervous system and functions as a multimodal nociceptor gated by temperatures greater than 43°C, protons, and small-molecule vanilloid ligands such as capsaicin. The ability to respond to heat, low pH, vanilloids, and endovanilloids and altered sensitivity and expression in experimental inflammatory and neuropathic pain models made TRPV1 a major target for the development of novel, nonopioid analgesics and resulted in the discovery of potent antagonists. In human clinical trials, observations of hyperthermia and the potential for thermal damage by suppressing the ability to sense noxious heat suggested that full-scale blockade of TRPV1 function can be counterproductive and subtler pharmacological approaches are necessary. Here we show that the dihydropyridine derivative 4,5-diethyl-3-(2-methoxyethylthio)-2-methyl-6-phenyl-1,4-(±)-dihydropyridine-3,5-dicarboxylate (MRS1477) behaves as a positive allosteric modulator of both proton and vanilloid activation of TRPV1. Under inflammatory-mimetic conditions of low pH (6.0) and protein kinase C phosphorylation, addition of MRS1477 further increased sensitivity of already sensitized TPRV1 toward capsaicin. MRS1477 does not affect inhibition by capsazepine or ruthenium red and remains effective in potentiating activation by pH in the presence of an orthosteric vanilloid antagonist. These results indicate a distinct site on TRPV1 for positive allosteric modulation that may bind endogenous compounds or novel pharmacological agents. Positive modulation of TRPV1 sensitivity suggests that it may be possible to produce a selective analgesia through calcium overload restricted to highly active nociceptive nerve endings at sites of tissue damage and inflammation.

Topical capsaicin for pain management: therapeutic potential and mechanisms of action of the new high-concentration capsaicin 8% patch

Topical capsaicin formulations are used for pain management. Safety and modest efficacy of low-concentration capsaicin formulations, which require repeated daily self-administration, are supported by meta-analyses of numerous studies. A high-concentration capsaicin 8% patch (Qutenza™) was recently approved in the EU and USA. A single 60-min application in patients with neuropathic pain produced effective pain relief for up to 12 weeks. Advantages of the high-concentration capsaicin patch include longer duration of effect, patient compliance, and low risk for systemic effects or drug-drug interactions. The mechanism of action of topical capsaicin has been ascribed to depletion of substance P. However, experimental and clinical studies show that depletion of substance P from nociceptors is only a correlate of capsaicin treatment and has little, if any, causative role in pain relief. Rather, topical capsaicin acts in the skin to attenuate cutaneous hypersensitivity and reduce pain by a process best described as 'defunctionalization' of nociceptor fibres. Defunctionalization is due to a number of effects that include temporary loss of membrane potential, inability to transport neurotrophic factors leading to altered phenotype, and reversible retraction of epidermal and dermal nerve fibre terminals. Peripheral neuropathic hypersensitivity is mediated by diverse mechanisms, including altered expression of the capsaicin receptor TRPV1 or other key ion channels in affected or intact adjacent peripheral nociceptive nerve fibres, aberrant re-innervation, and collateral sprouting, all of which are defunctionalized by topical capsaicin. Evidence suggests that the utility of topical capsaicin may extend beyond painful peripheral neuropathies.

Evidence based guidelines for complex regional pain syndrome type 1

Background

Treatment of complex regional pain syndrome type I (CRPS-I) is subject to discussion. The purpose of this study was to develop multidisciplinary guidelines for treatment of CRPS-I.

Method

A multidisciplinary task force graded literature evaluating treatment effects for CRPS-I according to their strength of evidence, published between 1980 to June 2005. Treatment recommendations based on the literature findings were formulated and formally approved by all Dutch professional associations involved in CRPS-I treatment.

Results

For pain treatment, the WHO analgesic ladder is advised with the exception of strong opioids. For neuropathic pain, anticonvulsants and tricyclic antidepressants may be considered. For inflammatory symptoms, free-radical scavengers (dimethylsulphoxide or acetylcysteine) are advised. To promote peripheral blood flow, vasodilatory medication may be considered. Percutaneous sympathetic blockades may be used to increase blood flow in case vasodilatory medication has insufficient effect. To decrease functional limitations, standardised physiotherapy and occupational therapy are advised. To prevent the occurrence of CRPS-I after wrist fractures, vitamin C is recommended. Adequate perioperative analgesia, limitation of operating time, limited use of tourniquet, and use of regional anaesthetic techniques are recommended for secondary prevention of CRPS-I.

Conclusions

Based on the literature identified and the extent of evidence found for therapeutic interventions for CRPS-I, we conclude that further research is needed into each of the therapeutic modalities discussed in the guidelines.

Transient receptor potential channels in pain and inflammation: therapeutic opportunities

In ancient times, physicians had a limited number of therapies to provide pain relief. Not surprisingly, plant extracts applied topically often served as the primary analgesic plan. With the discovery of the capsaicin receptor (transient receptor potential cation channel, subfamily V, member 1 [TRPV1]), the search for "new" analgesics has returned to compounds used by physicians thousands of years ago. One such compound, capsaicin, couples the paradoxical action of nociceptor activation (burning pain) with subsequent analgesia following repeat or high-dose application. Investigating this "paradoxical" action of capsaicin has revealed several overlapping and complementary mechanisms to achieve analgesia including receptor desensitization, nociceptor dysfunction, neuropeptide depletion, and nerve terminal destruction. Moreover, the realization that TRPV1 is both sensitized and activated by endogenous products of inflammation, including bradykinin, H+, adenosine triphosphate, fatty acid derivatives, nerve growth factor, and trypsins, has renewed interest in TRPV1 as an important site of analgesia. Building on this foundation, a new series of preclinical and clinical studies targeting TRPV1 has been reported. These include trials using brief exposure to high-dose topical capsaicin in conjunction with prior application of a local anesthetic. Clinical use of resiniferatoxin, another ancient but potent TRPV1 agonist, is also being explored as a therapy for refractory pain. The development of orally administered high-affinity TRPV1 antagonists holds promise for pioneering a new generation of analgesics capable of blocking painful sensations at the site of inflammation and tissue injury. With the isolation of other members of the TRP channel family such as TRP cation channel, subfamily A, member 1, additional opportunities are emerging in the development of safe and effective analgesics.

Topical capsaicin for chronic neuropathic pain in adults

BACKGROUND

Topical creams with capsaicin are used to treat pain from a wide range of chronic conditions including neuropathic pain. Following application to the skin capsaicin causes enhanced sensitivity to noxious stimuli, followed by a period with reduced sensitivity and, after repeated applications, persistent desensitisation. There is uncertainty about the efficacy and tolerability of capsaicin for treating painful chronic neuropathies.

OBJECTIVES

To review the evidence from controlled trials on the efficacy and tolerability of topically applied capsaicin in chronic neuropathic pain in adults.

SEARCH STRATEGY

Cochrane CENTRAL, MEDLINE, EMBASE and Oxford Pain Relief Database, searched in May 2009.

SELECTION CRITERIA

Randomised, double blind, placebo controlled studies of at least six weeks' duration, using topical capsaicin to treat neuropathic pain.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality and validity, and extracted data. Information was extracted on numbers of participants with pain relief (clinical improvement) after at least six weeks, and with local skin reactions, and used to calculate relative risk and numbers needed to treat to benefit (NNT) and harm (NNH). Details of definition of pain relief and specific adverse events were sought.

MAIN RESULTS

Six studies (389 participants in total) compared regular application of low dose (0.075%) capsaicin cream with placebo cream; the NNT for any pain relief over six to eight weeks was 6.6 (4.1 to 17). Two studies (709 participants in total) compared a single application of high dose (8%) capsaicin patch with placebo patch; the NNT for >/= 30% pain relief over twelve weeks was 12 (6.4 to 70). Local skin reactions were more common with capsaicin, usually tolerable, and attenuated with time; the NNH for repeated low dose application was 2.5 (2.1 to 3.1). There were insufficient data to analyse either data set by condition or outcome definition. All studies satisfied minimum criteria for quality and validity, but maintenance of blinding remains a potential problem.

AUTHORS' CONCLUSIONS

Capsaicin, either as repeated application of a low dose (0.075%) cream, or a single application of a high dose (8%) patch may provide a degree of pain relief to some patients with painful neuropathic conditions. Local skin irritation, which is often mild and transient but may lead to withdrawal, is common. Systemic adverse effects are rare. Estimates of benefit and harm are not robust due to limited amounts of data for different neuropathic conditions and inconsistent outcome definition.

Pharmacologic therapies for complex regional pain syndrome

Complex regional pain syndrome (CRPS) remains a challenging condition to diagnose and treat. There are few large-scale, randomized trials of pharmacologic agents, and most published studies are small, uncontrolled, or presented only in abstract form at meetings. The most commonly used agents, such as anticonvulsants, antidepressants, and opiates, have been found to be useful for other neuropathic pain conditions in large-scale trials but have not been adequately studied in CRPS. Systemic steroids delivered by multiple routes continue to be used, with some good evidence for short-term administration. N-methyl-D-aspartate antagonists have recently gained in popularity, without evidence from well-controlled trials. Bisphosphonates have been well studied and offer promise. In addition, there has been interest in thalidomide; however, we are still awaiting well-controlled trials. This article presents an overview of the available data regarding pharmacologic therapies for CRPS. These agents should be used in conjunction with a comprehensive interdisciplinary approach aimed at functional restoration and improved quality of life.

Topical agents for the treatment of chronic pain

Unlike systemic analgesics, topical analgesics exert their analgesic activity locally and without significant systemic absorption. This is in contrast to transdermal analgesics, which require systemic absorption for clinical benefit. The mechanism of action of a particular topical analgesic is unique to the specific medication being used as a topical analgesic. Topical analgesics have been studied in an increasing number of painful clinical conditions, and the results of some of these studies are summarized in this article. The potential role of topical analgesics acting peripherally in affecting the central processing of pain as well as painful states considered to be "central," not "peripheral," also are reviewed.

Challenges in the development of novel treatment strategies for neuropathic pain

Neuropathic pain might best be considered as a collection of various pain states with a common feature, that being symptoms suggestive of dysfunction of peripheral nerves. The development of therapeutic options for the treatment of neuropathic pain is complicated significantly by several factors. Neuropathic pain may arise from widely diverse etiologies such as physical trauma, disease, infection, or chemotherapy. Symptoms indicative of neuropathic pain may also arise in individuals with no evidence of any type of nerve trauma (idiopathic). Although neuropathic pain is a substantial health care issue, it is relatively uncommon and only occurs in a small fraction (<10%) of individuals with these initiating factors. Moreover, the efficacy of treatment protocols, even against the same type of symptoms, differ depending on the underlying initiating cause of the neuropathy. Although these observations strongly suggest that there are predisposing factors that may impart susceptibility to the development of neuropathic pain, no common predisposing factors or genetic markers have been satisfactorily identified. Because of these vagaries, treatment of neuropathic pain has been based on trial and error. However, recent progress in the understanding of neurophysiologic changes that accompany peripheral nerve dysfunction indicate that regulation of ion channels that maintain membrane potentials or generate action potentials may provide an important therapeutic approach. Neuropathic pain is accompanied by increased activity of peripheral nociceptors, which is produced in part by changes in levels of specific calcium and sodium channels. The identification of sodium and/or calcium channels subtypes that are expressed almost exclusively on nociceptors may provide a way of regulating the activity of exaggerated nociceptor function without altering other sensory modalities. Thus, the selective targeting of ion channels may represent a viable therapeutic target for the management of the neuropathic pain state, regardless of etiology.

Targeted peripheral analgesics therapy for neuropathic pain

The term targeted peripheral analgesics has been suggested to describe analgesics with a mechanism of action that appears to be primarily through reducing pain transmission within the peripheral nervous system. Key differences between targeted peripheral (topical) and systemic analgesics and the difference between topical and transdermal analgesics are discussed in this article. A review of the clinical conditions, which have been reported to respond to targeted peripheral analgesics, also is described in detail.

Targeted topical peripheral analgesics in the management of pain

The term "targeted peripheral analgesics" has been developed to describe analgesics whose mechanism of action appears to be primarily through reducing pain transmission within the peripheral nervous system. Key differences between targeted peripheral and systemic analgesics and the difference between topical and transdermal analgesics are discussed. A review of the clinical conditions that have reportedly responded to targeted peripheral analgesics is described in detail in this article.