Multimodal approaches to the management of neuropathic pain: the role of topical analgesia

Evaluation of the analgesic potential and safety of Cinnamomum camphora chvar. Borneol essential oil

Cinnamomum camphora chvar. Borneol essential oil (BEO, 18.2% v/v borneol) is a by-product of steam distillation to produce natural crystalline borneol (NCB, 98.4% v/v borneol). Given the known medicinal properties of borneol, the analgesic function and safety were studied. Horn’s method and the Draize test revealed a gender difference in mice regarding acute oral LD₅₀, i.e., low-toxicity to female mice (2749 mg/kg), but practically nontoxic to male mice (5081 mg/kg). There was no acute and skin or eye irritation when BEO was applied directly, if the BEO concentration was less than 50%. The analgesic effect of BEO was evaluated by the glacial acetic acid-induced writhing pain model. Continuous topical application of BEO to the abdomen of mice for 6 d, significantly reduced observed writhing in mice (p < 0.001) with a strong dose-response relationship (r = −0.9006). Concomitantly, the levels of the serum pain-related mediators, prostaglandin E₂ (PGE₂) and transient receptor potential melastatin-8 (TRPM8) were significantly reduced (p < 0.001), and the latter showed a strong dose-response relationship (r = −0.9427). Therefore, BEO had similar analgesic functions to borneol and was demonstrated to be safe for medicinal use.

Topical Treatments and Their Molecular/Cellular Mechanisms in Patients with Peripheral Neuropathic Pain-Narrative Review

Neuropathic pain in humans results from an injury or disease of the somatosensory nervous system at the peripheral or central level. Despite the considerable progress in pain management methods made to date, peripheral neuropathic pain significantly impacts patients' quality of life, as pharmacological and non-pharmacological methods often fail or induce side effects. Topical treatments are gaining popularity in the management of peripheral neuropathic pain, due to excellent safety profiles and preferences. Moreover, topical treatments applied locally may target the underlying mechanisms of peripheral sensitization and pain. Recent studies showed that peripheral sensitization results from interactions between neuronal and non-neuronal cells, with numerous signaling molecules and molecular/cellular targets involved. This narrative review discusses the molecular/cellular mechanisms of drugs available in topical formulations utilized in clinical practice and their effectiveness in clinical studies in patients with peripheral neuropathic pain. We searched PubMed for papers published from 1 January 1995 to 30 November 2020. The key search phrases for identifying potentially relevant articles were "topical AND pain", "topical AND neuropathic", "topical AND treatment", "topical AND mechanism", "peripheral neuropathic", and "mechanism". The result of our search was 23 randomized controlled trials (RCT), 9 open-label studies, 16 retrospective studies, 20 case (series) reports, 8 systematic reviews, 66 narrative reviews, and 140 experimental studies. The data from preclinical studies revealed that active compounds of topical treatments exert multiple mechanisms of action, directly or indirectly modulating ion channels, receptors, proteins, and enzymes expressed by neuronal and non-neuronal cells, and thus contributing to antinociception. However, which mechanisms and the extent to which the mechanisms contribute to pain relief observed in humans remain unclear. The evidence from RCTs and reviews supports 5% lidocaine patches, 8% capsaicin patches, and botulinum toxin A injections as effective treatments in patients with peripheral neuropathic pain. In turn, single RCTs support evidence of doxepin, funapide, diclofenac, baclofen, clonidine, loperamide, and cannabidiol in neuropathic pain states. Topical administration of phenytoin, ambroxol, and prazosin is supported by observational clinical studies. For topical amitriptyline, menthol, and gabapentin, evidence comes from case reports and case series. For topical ketamine and baclofen, data supporting their effectiveness are provided by both single RCTs and case series. The discussed data from clinical studies and observations support the usefulness of topical treatments in neuropathic pain management. This review may help clinicians in making decisions regarding whether and which topical treatment may be a beneficial option, particularly in frail patients not tolerating systemic pharmacotherapy.

Peripheral Mechanisms of Neuropathic Pain-the Role of Neuronal and Non-Neuronal Interactions and Their Implications for Topical Treatment of Neuropathic Pain

Neuropathic pain in humans arises as a consequence of injury or disease of somatosensory nervous system at peripheral or central level. Peripheral neuropathic pain is more common than central neuropathic pain, and is supposed to result from peripheral mechanisms, following nerve injury. The animal models of neuropathic pain show extensive functional and structural changes occurring in neuronal and non-neuronal cells in response to peripheral nerve injury. These pathological changes following damage lead to peripheral sensitization development, and subsequently to central sensitization initiation with spinal and supraspinal mechanism involved. The aim of this narrative review paper is to discuss the mechanisms engaged in peripheral neuropathic pain generation and maintenance, with special focus on the role of glial, immune, and epithelial cells in peripheral nociception. Based on the preclinical and clinical studies, interactions between neuronal and non-neuronal cells have been described, pointing out at the molecular/cellular underlying mechanisms of neuropathic pain, which might be potentially targeted by topical treatments in clinical practice. The modulation of the complex neuro-immuno-cutaneous interactions in the periphery represents a strategy for the development of new topical analgesics and their utilization in clinical settings.

The use of antineuropathic medications for the treatment of chronic pain

Chronic pain syndromes cost the US healthcare system over $600 billion per year. A subtype of chronic pain is neuropathic pain (NP), which is defined as "pain caused by a lesion or disease of the somatosensory system," according to the International Association for the Study of Pain (IASP). The pathophysiology of neuropathic pain is very complex, and more research needs to be done to find the exact mechanism. Patients that have preexisting conditions such as cancer and diabetes are at high-risk of developing NP. Many NP patients are misdiagnosed and receive delayed treatment due to a lack of a standardized classification system that allows clinicians to identify, understand, and utilize pain management in these patients. Medications like tricyclic antidepressants, serotonin-norepinephrine reuptake Inhibitor (SNRIs), and gabapentinoids are first-line treatments followed by opioids, cannabinoids, and other drugs. There are limited studies on the treatment of NP.

Topical Treatment of Localized Neuropathic Pain in the Elderly

The prevalence of neuropathic pain in the older population has been reported to be very high and is most commonly localized to a circumscribed area. Treatment failure is frequent in neuropathic pain and is accompanied by central side effects with recommended oral drugs acting on the central nervous system. A number of topical pharmaceuticals are available on prescription and also sold over the counter. This review in persons aged older than 60 years shows the efficacy of lidocaine 5% and capsaicin 8% for localized neuropathic pain while results with other pharmaceuticals are rather inconsistent. Local application of drugs has a very limited systemic effect and the pharmacological advantages of local over systemic treatment are particularly interesting in older persons who often have comorbidities and take multiple medications. However, more information is needed on the efficacy and safety of lidocaine 5% and capsaicin 8% in older old persons and on the long-term effects of these pharmaceuticals. These studies should also pave the way for research and development in the field of topical analgesics with a satisfactory level of evidence-based medicine.

Risk factors predicting less favorable outcomes in endoscopic lumbar discectomies

Background

Endoscopic lumbar discectomy was among the first minimally invasive spine procedures commonly performed. As such, all the benefits of minimal invasion were seen, including less pain, less soft tissue destruction, and faster recovery. While outcomes compare favorably to micro and open discectomy, not all patients fare equally well. This paper examines independent risk factors to assess their correlation to suboptimal outcomes after endoscopic lumbar discectomy.

Methods

Retrospective analysis of clinical outcomes of 55 consecutive patients treated with endoscopic discectomy between June 2018 and March 2019 by the author. Primary outcome measures were postoperative reductions of visual analog score (VAS) for back and leg pain modified MacNab criteria as well as time to narcotic independence. Risk factors examined included smoking, facet disease, adjacent segments disc degeneration, obesity, alcohol abuse, and psychiatric illness.

Results

There were 31 males and 24 females with a mean age of 41.76±12.53. Most patients suffered from contained herniations (49.1%) followed by extruded herniations (18.2%). Follow-up ranged from 6-18 months. The most common surgical levels were L5-S1 level (30.9%), L4-S1 (29.1%), and L4-5 (25.5%). The mean return to work (RTW) was 23.83±26.01 weeks. The average body mass index (BMI) was 29.11±4.75. The average time for narcotic independence was 9.64±7.29 days. MacNab outcomes showed that 47.3% (26/55) had excellent, 36.4% good (20/55), 12.7% fair (7/55), and 3.6% had poor (2/55), respectively. The VAS scores for the back (7.69 to 2.65) and leg (6.78 to 2.65) pain reduced significantly (P<0.0001). Smoking (P=0.048), psychiatric disease (P=0.029), disc herniations larger than 10 mm, facet disease, obesity (BMI >30), diabetes, and alcohol abuse was associated with fair and poor MacNab outcomes.

Conclusions

Endoscopic lumbar discectomy safely and reliably reduces axial pain and radiculopathy from lumbar disc herniations. Risk factors associated with incomplete pain relief are large herniations, obesity, instability, smoking, advanced facet degeneration, and decreased ability to cope with the surgery.

A clinical and mechanistic study of topical borneol-induced analgesia

Bingpian is a time‐honored herb in traditional Chinese medicine (TCM). It is an almost pure chemical with a chemical composition of (+)‐borneol and has been historically used as a topical analgesic for millennia. However, the clinical efficacy of topical borneol lacks stringent evidence‐based clinical studies and verifiable scientific mechanism. We examined the analgesic efficacy of topical borneol in a randomized, double‐blind, placebo‐controlled clinical study involving 122 patients with postoperative pain. Topical application of borneol led to significantly greater pain relief than placebo did. Using mouse models of pain, we identified the TRPM8 channel as a molecular target of borneol and showed that topical borneol‐induced analgesia was almost exclusively mediated by TRPM8, and involved a downstream glutamatergic mechanism in the spinal cord. Investigation of the actions of topical borneol and menthol revealed mechanistic differences between borneol‐ and menthol‐induced analgesia and indicated that borneol exhibits advantages over menthol as a topical analgesic. Our work demonstrates that borneol, which is currently approved by the US FDA to be used only as a flavoring substance or adjuvant in food, is an effective topical pain reliever in humans and reveals a key part of the molecular mechanism underlying its analgesic effect.

Cytotoxicity and cellular response mechanisms of water-soluble platinum(II) complexes of lidocaine and phenylcyanamide derivatives

Three new platinum(II) complexes of lidocaine and phenylcyanamide derivative ligands of formula K[Pt(3,5-(NO₂)₂pcyd)₂(LC)], 1, K[Pt(3,5-(CF₃)₂pcyd)₂(LC)], 2, K[Pt(3,5-Cl₂pcyd)₂(LC)], 3 (LC: lidocaine, 3,5-(NO₂)₂pcyd: 3,5-dinitro phenylcyanamide, 3,5-(CF₃)₂pcyd: 3,5-bis(trifluoromethyl) phenylcyanamide, 3,5-Cl₂pcyd: 3,5-dichloro phenylcyanamide) have been synthesized and fully characterized. Cellular uptake, DNA platination and cytotoxicity against a panel of human tumor cell lines were evaluated. The complexes 1-3 revealed a significant in vitro antiproliferative activity against human ovarian carcinoma (A2780), colorectal adenocarcinoma (HT29), breast (MCF-7), liver hepatocellular carcinoma (HepG-2) and lung adenocarcinoma (A549) cancer cell lines. All the complexes are more active than cisplatin and follow the trend 1 > 2 > 3. Mechanistic studies showed that the trend in cytotoxicity of the Pt(II) complexes is mainly consistent with their ability to accumulate into cancer cells and to increase intracellular basal reactive oxygen species levels, which consequently results in the loss of mitochondrial membrane potential and apoptosis induction. The complex 1 caused to approximately 80-fold higher DNA platination level with respect to cisplatin. The complexes 1-3 can considerably stimulate the production of hydrogen peroxide in a time-dependent manner. Also, the complexes 1-3 induced an increase in reactive oxygen species (ROS) production that was superior to that induced by antimycin. The complex 1 had the most effect on ROS production in comparison with other complexes.

Skin matters! The role of keratinocytes in nociception: a rational argument for the development of topical analgesics

Treatment of neuropathic pain using topical formulations is still in its infancy. Only few topical analgesic formulations have become available for clinical use, and among these, analgesic creams are still rare. This is unfortunate because analgesic creams offer a number of advantages over patches, such as convenience, ease of adapting the frequency of application, and dose, and “rubbing cream where it hurts” involves the patient much more in the therapeutic process compared to patches and other localized treatment modalities. Although the literature supporting the efficacy and safety of analgesic creams (mostly compounded) is growing since the last decade, most pain physicians have not yet noticed and appreciated the therapeutic potential and clinical value of these creams. This is most probably due to a prejudice that topical application should need to act transdermally, more or less as a slow-release formulation, such as in patches delivering opioids. We will discuss this prejudice and show that there are multiple important targets in the skin to be reached by topical analgesic or anti-inflammatory compounds, and that the keratinocyte is one of those targets. By specifically targeting the keratinocyte, analgesia seems possible, effective, and safe, and thus topical analgesic creams may hold promise as a novel treatment modality for neuropathic pain.

Advances in topical analgesics

PURPOSE OF REVIEW

The recent increase in opioid consumption in the modern world prompted pain physicians to find new and improved solutions to tackle chronic, refractory pain syndromes. Topical analgesics are emerging as a valued multimodal analgesic arm in the fight against chronic pain.

RECENT FINDINGS

New and improved topical formulations have emerged as effective tools to treat chronic refractory pain. In addition to formulations manufactured by the pharmaceutical industry, there has been a recent interest in mixed topical products by local, regional and national compounding pharmacies. This review will focus on advances in topical analgesics, especially their role as an effective analgesic in nociceptive and neuropathic refractory pain states. We will explore topical analgesics' mechanisms of action and their efficacy as opioid-sparing formulations.

SUMMARY

This review will allow physicians to understand the role of topical agents in the treatment of intractable pain syndromes. Increasing medical providers' familiarity with these agents will allow their incorporation as part of a complex analgesic regimen for an improved pain management plan benefiting the patient population at large.

Pain in cancer survivors

Cancer and its treatment exert a heavy psychological and physical toll. Of the myriad symptoms which result, pain is common, encountered in between 30% and 60% of cancer survivors. Pain in cancer survivors is a major and growing problem, impeding the recovery and rehabilitation of patients who have beaten cancer and negatively impacting on cancer patients' quality of life, work prospects and mental health. Persistent pain in cancer survivors remains challenging to treat successfully. Pain can arise both due to the underlying disease and the various treatments the patient has been subjected to. Chemotherapy causes painful chemotherapy-induced peripheral neuropathy (CIPN), radiotherapy can produce late effect radiation toxicity and surgery may lead to the development of persistent post-surgical pain syndromes. This review explores a selection of the common causes of persistent pain in cancer survivors, detailing our current understanding of the pathophysiology and outlining both the clinical manifestations of individual pain states and the treatment options available.

Topical treatment in pain medicine: from ancient remedies to modern usage

Over several millennia, substances have been applied to the skin for treatment of pain. Some ingredients are in current use; others have been discontinued. Mechanisms of action include interactions with nociceptive neural networks and inflammatory processes. Substances must penetrate the stratum corneum barrier and vehicles that enhance penetration have been developed. Topical drugs with links to the past include menthol, capsaicin, some opioids, local anesthetic agents and NSAIDs. Mandragora is also described as an example of a herbal remedy that has been discontinued due to its toxicity. The future for topical drugs is promising, with the advent of new drugs tailored for specific pain mechanisms and the development of both penetration enhancers and sterile preparation methods.

The conformational stability, solvation and the assignments of the experimental infrared, Raman, (1)H and (13)C NMR spectra of the local anesthetic drug lidocaine

The structure, vibrational and (1)H and (13)C NMR spectra of the local anesthetic drug lidocaine were investigated by the B3LYP/6-311G(∗∗) calculations. The molecule was predicted to have the non-planar cis (NCCN∼0°) structures being about 2-6kcal/mol lower in energy than the corresponding trans (NCCN∼180°) forms. The calculated NCCN (9.6°) and CNCC (-132.2°) torsional angles were in a good qualitative agreement with the reported X-ray angles (3.1 and 13.0°, -102.67 and -77.9°, respectively, for H-bonded dimers). The Gibbs energy of solution of lidocaine in formamide, water, dimethylsulfoxide, acetonitrile, methanol, ethanol and chloroform solutions was estimated at the B3LYP level. The predicted affinity of lidocaine toward the alcohols, acetonitrile and chloroform solutions was in excellent agreement with the reported experimental solubility of the drug in organic solvents. The analysis of the observed vibrational spectra is consistent with the presence of lidocaine in only one conformation at room temperature. The (1)H and (13)C NMR spectra of lidocaine were interpreted by experimental and DFT calculated chemical shifts of the drug. The RMSD between experimental and theoretical (1)H and (13)C chemical shifts for lidocaine is 0.47 and 8.26ppm, respectively.

Topical NSAID formulations

OBJECTIVE

This article reviews topical nonsteroidal anti-inflammatory drug (NSAID) formulations available in the United States, including advantages and disadvantages, therapeutic usefulness, adverse effects, and formulation considerations.

RESULTS

In the United States, several topical NSAID products are approved to treat painful conditions including diclofenac sodium 1% gel (Voltaren Gel®; Endo Pharmaceuticals), diclofenac sodium topical solution 1.5% w/w in 45.5% dimethyl sulfoxide (PENNSAID®; Mallinckrodt, Inc.), and diclofenac epolamine 1.3% (Flector Patch®; Alpharma Pharmaceuticals LLC, a subsidiary of Pfizer, Inc.). Recent studies suggest topical diclofenac preparations are effective for osteoarthritis pain and suggest the efficacy of topical formulations is similar to that achieved with oral NSAID formulations. All NSAID formulations contain the same boxed warnings regarding cardiovascular and renal toxicity; however, topical NSAIDs are proposed to have a more favorable safety profile than oral NSAIDs due to the low serum concentrations achieved with topical NSAID formulations.

CONCLUSIONS

Topical NSAIDs have been shown to be beneficial from both a therapeutics and adverse effect perspective, and are increasingly recommended in treatment guidelines.

[Pain management in patients with liver cirrhosis]

Pain management in patients with liver cirrhosis is a real challenge and is often inadequate due to a lack of therapeutic efficacy or the high incidence of adverse effects. The focus of treatment differs depending on whether the pain is acute or chronic and involves understanding the causative pathophysiological mechanism. Analgesics should be started with the minimum effective dose and should be titrated slowly with avoidance of polypharmacy. Adverse effects must be monitored, especially sedation and constipation, which predispose the patient to the development of hepatic encephalopathy. The first-line drug is paracetamol, which is safe at doses of 2-3g/day. Non-steroidal anti-inflammatory agents are contraindicated because they can cause acute renal failure and/or gastrointestinal bleeding. Tramadol is a safe option for moderate-severe pain. The opioids with the best safety profile are fentanyl and hydromorphone, with methadone as an alternative. Topical treatment can reduce oral drug consumption. In neuropathic pain the first-line therapeutic option is gabapentin. The use of antidepressants such as amitriptyline can be considered in some patients. Interventional techniques are a valuable tool in moderate to severe pain, since they allow a reduction in drug therapy and consequently its adverse effects. Psychological treatment, physical therapy and rehabilitation should be considered as part of multimodality therapy in the management of chronic pain.

Topical analgesics

BACKGROUND AND OBJECTIVES

Pain treatment involves the usage of common and opioid analgesics, nonsteroidal anti-inflammatory drugs (NSAIDs) and adjuvant analgesics. Traditionally, these drugs are administered systemically or into the neuraxis. However, when analgesics are applied through these pathways, they are associated with significant side effects, which can hinder its use. Topical administration of analgesics is an alternative. The objective of this paper is to discuss topical analgesics, the mechanisms of action and clinical efficacy.

CONTENT

This is a review paper addressing the usage of the topical local anesthetics: capsaicin, clonidine, tricyclic antidepressants, ketamine, opioids and cannabinoids, discussing mechanism of action and effectiveness.

CONCLUSIONS

Topical analgesics are promising as a strategy for pain treatment, as they are associated with lower incidence of side effects. The benefit of local anesthetics, NSAID's and capsaicin is well established. However, the efficacy of clonidine, tricyclic antidepressants, ketamine, opioids and cannabinoids is still questionable. Studies have shown that the multimodal approach is an alternative, but studies are needed to confirm this hypothesis.

Central neuropathic pain in a patient with multiple sclerosis treated successfully with topical amitriptyline

Central neuropathic pain in patients with multiple sclerosis (MS) is a common debilitating symptom, which is mostly treated with tricyclic antidepressants or antiepileptics. Unfortunately, the use of these drugs is often limited due to adverse events. We investigated the analgesic effect of topical amitriptyline 5% and 10% cream in a patient with central neuropathic pain due to MS. The analgesic effect of topical amitriptyline cream on neuropathic pain was dose related. To evaluate whether this analgesic effect is due to the active compound or placebo, we conducted a double-blind placebo-controlled n-of-1 study with amitriptyline 5% cream and placebo. The instruction was to alternate the creams every week following the pattern ABAB, with an escape possibility of amitriptyline 10% cream. The result was a complete pain reduction after application of cream B, while most of the time cream A did not reduce the pain. The patient could correctly unblind both creams, determining B as active. She noted that in the week of using the active cream no allodynia was present, with a carryover effect of one day.

Use of 5% lidocaine medicated plaster to treat localized neuropathic pain secondary to traumatic injury of peripheral nerves

OBJECTIVE

The efficacy of 5% lidocaine medicated plaster (LMP) has previously been demonstrated in post-traumatic localized neuropathic pain. This study evaluated the use of LMP in localized neuropathic pain secondary to traumatic peripheral nerve injury.

PATIENTS AND METHODS

This prospective observational study enrolled patients with traumatic injuries to peripheral nerves that were accompanied by localized neuropathic pain of more than 3 months duration. Demographic variables, pain intensity (measured using the numeric rating scale; NRS), answers to the Douleur Neuropathique 4 (DN4) questionnaire, and the size of the painful area were recorded.

RESULTS

Nineteen patients were included, aged (mean ± standard deviation) 41.4 ± 15.7 years. Nerve injuries affected the upper (eight patients) or lower (11 patients) limbs. The mean duration of pain before starting treatment with LMP was 22.6 ± 43.5 months (median 8 months). Mean baseline values included: NRS 6.7 ± 1.6, painful area 17.8 ± 10.4 cm(2) (median 18 cm(2)), and DN4 score 6.7 ± 1.4. The mean duration of treatment with LMP was 19.5 ± 10.0 weeks (median 17.4 weeks). Mean values after treatment were: NRS 2.8 ± 1.5 (≥3 point reduction in 79% of patients, ≥50% reduction in 57.9% of patients) and painful area 2.1 ± 2.3 cm(2) (median 1 cm(2), ≥50% reduction in 94.7% of patients). Functional improvement after treatment was observed in 14/19 patients (73.7%).

CONCLUSION

LMP effectively treated traumatic injuries of peripheral nerves which presented with chronic localized neuropathic pain, reducing both pain intensity and the size of the painful area.

Transdermal lidocaine and ketamine for neuropathic pain: a study of effectiveness and tolerability

Background:

Acute neuropathic pain is a common disorder. Transdermal cream could be an alternative to oral medications.

Objective:

To evaluate the effectiveness and tolerability of transdermal Lidocaine and Ketamine for acute neuropathic pain.

Study Design:

Retrospective chart review

Setting:

University-affiliated outpatient Physiatry clinic

Methods:

articipants: neuropathic pain with a prescription of a transdermal cream containing Lidocaine and Ketamine. Ef-fectiveness was evaluated by the number of patients with improvement divided by the total number of patients who re-ceived a prescription of the cream.

Results:

A total of 854 patient charts were reviewed. Twenty-one patients with symptoms, signs, and/or a documented di-agnosis of neuropathic pain and had been given a prescription of a transdermal preparation containing Lidocaine and Ketamine. Four groups were identified: those with a clearly stated diagnosis of neuropathic pain and prescribed a transdermal compound containing Lidocaine and Ketamine with follow-up (Group A) or without follow-up (Group B), and those with a suggested diagnosis of neuropathic pain with (Group C) or without follow-up (Group D). Effectiveness of the cream was seven out of eight (87%) for Group A and one out of three (33%) for Group C. In total, eight out of 11 patients (73%) benefited from a cream containing Lidocaine and Ketamine. Two patients experienced skin reactions that led to discontin-uation of treatment.

Limitations:

This is a retrospective chart review without control group.

Conclusion:

Transdermal cream containing Ketamine and Lidocaine was effective in 73% of patients with acute neuro-pathic pain and may be a good alternative to oral medications.

What is localized neuropathic pain? A first proposal to characterize and define a widely used term

SUMMARY According to several guidelines, topical agents should be considered for the pharmacological management of localized neuropathic pain. As a definition for the term ‘localized neuropathic pain’ that might facilitate easier identification of patients who are putatively responsive to topical treatments could not be found in the literature, six pain specialists met in 2010 to address this challenging issue. The following nucleus of a definition that is based on the International Association for the Study of Pain (IASP) definition of neuropathic pain, is the most detailed that can currently be proposed: ‘Localized neuropathic pain is a type of neuropathic pain that is characterized by consistent and circumscribed area(s) of maximum pain’. An extended version of this core definition and the difficulties in covering all aspects of localized neuropathic pain are presented, and discussions within the scientific community are encouraged to develop a definition that might help to identify patients who could benefit most from topical treatment.

Treatment of localized post-traumatic neuropathic pain in scars with 5% lidocaine medicated plaster

OBJECTIVE

To evaluate the use of 5% lidocaine medicated plaster (LMP) for treating painful scars resulting from burns or skin degloving.

PATIENTS AND METHODS

This was a prospective, observational case series study in individuals with painful scars <70 cm(2) in area, caused by burns or skin degloving. The study included a structured questionnaire incorporating demographic variables, pain evaluation using the numeric rating scale (NRS), the DN4 questionnaire, and measurement of the painful surface area. Patients with open wounds in the painful skin or with severe psychiatric disease were excluded.

RESULTS

Twenty-one men and eight women were studied, aged (mean + standard deviation) 41.4 ± 11.0 years, with painful scars located in the upper extremity (n = 9), lower extremity (n = 19), or trunk (n = 1). Eleven patients (37.9%) had an associated peripheral nerve lesion. The scars were caused by burns (n = 13), degloving (n = 7), and/or orthopedic surgery (n = 9). The duration of pain before starting treatment with lidocaine plaster was 9.7 ± 10.0 (median 6) months. The initial NRS was 6.66 ± 1.84 points, average painful area 23.0 ± 18.6 (median 15) cm(2), and DN4 score 4.7 ± 2.3 points. The duration of treatment with LMP was 13.9 ± 10.2 (median 11) weeks. After treatment, the NRS was reduced by 58.2% ± 27.8% to 2.72 ± 1.65. The average painful area was reduced by 72.4% ± 24.7% to 6.5 ± 8.6 (median 5) cm(2). Nineteen patients (69%) showed functional improvement following treatment.

CONCLUSION

LMP was useful for treating painful scars with a neuropathic component, producing meaningful reductions in the intensity of pain and painful surface area. This is the first time that a decrease in the painful area has been demonstrated in neuropathic pain using topical therapy, and may reflect the disease-modifying potential of LMP.

Guidelines for the diagnosis and management of neuropathic pain: consensus of a group of Latin American experts

These consensus guidelines have been developed by a group of Latin American experts in pain management, to point out patterns and make practical recommendations to guide the diagnosis, identify warning signs (yellow and red flags), and establish comprehensive medical management (pharmacologic and nonpharmacologic treatment) and monitoring plans for patients enduring neuropathic pain. From the viewpoint of pharmacologic management, drugs are classified into groups according to efficacy, availability/accessibility, and safety criteria. Drugs are recommended for use depending on the disease and particular circumstances of each patient, with an approach that favors multimodal treatment while taking into consideration the idiosyncrasies of medical practice in Latin America.

Chronic pain management in older adults: special considerations

The rising prevalence of neuropathic pain and the multifaceted sequelae of pain particularly within older adults are part of the increasing challenges in providing good geriatric pain management. Aging can lead to a higher sensitivity to pain within older adults, whereas physiological changes modify the absorption, bioavailability, and transit time of pharmaceutical agents. Ultimately, these differences within older adults require clinicians treating them to provide individually tailored analgesic approaches. Progressive age increases the variance in physiology among people; thus, the management approach should reflect an individual's unique requirements and limitations based on findings at the time of assessment.

NGX-4010, a high-concentration capsaicin patch, for the treatment of postherpetic neuralgia: a randomised, double-blind study

BACKGROUND

The limitations of current treatments for postherpetic neuralgia (PHN) have led to the investigation of localised, non-systemic alternatives. NGX-4010, a high-concentration (8%) capsaicin dermal patch, was developed to treat patients with neuropathic pain. We report the results of a randomised, double blind, 12-week study of the efficacy and safety of one application of NGX-4010 in patients with PHN.

METHODS

In this multicentre, double-blind, parallel-group trial, 402 patients were randomly assigned to one 60-min application of NGX-4010 (640 microg/cm(2) [8% capsaicin]) or a low-concentration capsaicin control patch (3.2 microg/cm(2) [0.04% capsaicin]). Patients were aged 18-90 years, had had postherpetic neuralgia for at least 6 months, and had an average baseline numeric pain rating scale (NPRS) score of 3 to 9. The primary efficacy endpoint was percentage change in NPRS score from baseline to weeks two to eight. Analysis was by intention to treat. This trial is registered with ClinicalTrials.gov, number NCT00115310.

FINDINGS

Patients who were randomly assigned to NGX-4010 (n=206) had a significantly greater reduction in pain during weeks two to eight than did patients who had the control patch (n=196). The mean changes in NPRS score were -29.6%vs -19.9% (difference -9.7%, 95% CI -15.47 to -3.95; p=0.001). 87 (42%) patients who received NGX-4010 and 63 (32%) controls had a 30% or greater reduction in mean NPRS score (odds ratio [OR] 1.56, 95% CI 1.03 to 2.37; p=0.03). The patients who had NGX-4010 had significant improvements in pain during weeks two to 12 (mean change in NPRS score -29.9%vs -20.4%, difference -9.5, -15.39 to -3.61; p=0.002). Transient blood pressure changes associated with changes in pain level were recorded on the day of treatment, and short-lasting erythema and pain at the site of application were common, self-limited, and generally mild to moderate in the NGX-4010 group and less frequent and severe in the controls.

INTERPRETATION

One 60-min application of NGX-4010 provided rapid and sustained pain relief in patients with postherpetic neuralgia. No adverse events were associated with treatment except for local reactions at the site of application and those related to treatment-associated pain.

Current developments in opioid therapy for management of cancer pain

Pain remains a highly prevalent problem for patients with cancer and typically falls into one of 3 types: visceral, somatic, and neuropathic. A mechanistic, pathophysiologic approach to pain management involves a good assessment of the type of pain, followed by tailoring of the treatment based on the diagnosis. This pain management strategy can provide rapid pain control with a lower incidence of complications and side effects than other methods. Furthermore, pharmacogenetics may play an important role in individualizing therapies in the future, but for now this type of data offers explanations for phenomena commonly observed in clinical practice, such as (1) differences in individual analgesic and side-effect responses to various opioid agents, (2) incomplete cross-tolerance seen when switching between mu opioid analgesics, and (3) why opioid rotation can be beneficial for patients after an opioid therapy loses efficacy or becomes associated with intolerable side effects. Especially for difficult-to-manage pain patients, additions to the opioid analgesic armamentarium can potentially better individualize pain management, and provide another option to be used for opioid rotation. Among the most recent Food and Drug Administration-approved opioid analgesics for acute pain and persistent pain are oral immediate-release and extended-release formulations of oxymorphone, whereas for breakthrough pain, the ultrarapid-acting opioid, fentanyl effervescent buccal tablets, has newly been developed and indicated within the United States.