NeuPSIG guidelines on neuropathic pain assessment

A large animal neuropathic pain model in sheep: a strategy for improving the predictability of preclinical models for therapeutic development

Background

Evaluation of analgesics in large animals is a necessary step in the development of better pain medications or gene therapy prior to clinical trials. However, chronic neuropathic pain models in large animals are limited. To address this deficiency, we developed a neuropathic pain model in sheep, which shares many anatomical similarities in spine dimensions and cerebrospinal fluid volume as humans.

Methods

A neuropathic pain state was induced in sheep by tight ligation and axotomy of the common peroneal nerve. The analgesic effect of intrathecal (IT) morphine was investigated. Interspecies comparison was conducted by analyzing the ceiling doses of IT morphine for humans, sheep, and rats.

Results

Peroneal nerve injury (PNI) produced an 86% decrease in von-Frey filament-evoked withdrawal threshold on postsurgery day 3 and the decrease lasted for the 8-week test period. Compared to the pre-injury, sham, and contralateral hindlimb, the IT morphine dose that produces 50% of maximum analgesia (ED₅₀) for injured PNI hindlimb was 1.8-fold larger and E_max, the dose that produces maximal analgesia, was 6.1-fold lower. The sheep model closely predicts human IT morphine ceiling dose by allometric scaling. This is in contrast to the approximately 10-fold lower morphine ceiling dose predicted by the rat spinal nerve ligated or spared nerve injury models.

Conclusion

PNI sheep model has a fast onset and shows stable and long-lasting pain behavioral characteristics. Since the antinociceptive properties of IT morphine are similar to those observed in humans, the PNI sheep model will be a useful tool for the development of analgesics. Its large size and consistent chronic pain behavior will facilitate the development and evaluation of surgical intervention and gene therapy. The PNI sheep pain model provides us with the opportunity for multi-species testing, which will improve the success of clinical trials.

Nutmeg extracts for painful diabetic neuropathy: a randomized, double-blind, controlled study

OBJECTIVES

Current treatment strategies for painful diabetic neuropathy (PDN) include oral medications, which are costly and may have adverse effects. Topical therapies have been used for PDN with some benefit. Nutmeg has certain properties that may be effective in ameliorating neuropathic pain. The purpose of this study was to determine whether topical nutmeg extracts can reduce pain or improve the quality of life in PDN sufferers.

DESIGN

This study was a randomized, double-blind, placebo-controlled trial.

SETTINGS/LOCATION

It was conducted at a primary care center in Trinidad, Caribbean.

SUBJECTS

Seventy-four (74) diabetic subjects who met criteria for painful neuropathy were recruited.

INTERVENTIONS

Participants were randomized to receive either topical nutmeg extracts (NEMM; mace oil [2%], nutmeg oil [14%], methyl salicylate [6%], menthol [6%], and coconut oil) or placebo (MM; methyl salicylate [6%], menthol [6%], coconut oil, and alcohol).

OUTCOME MEASURES

Outcome measures of pain and quality of life were assessed using the Brief Pain Inventory for Diabetic Painful Neuropathy and Neuropathic Pain Symptom Inventory.

RESULTS

An intention-to-treat analysis was done for 24 male and 50 female subjects (30-85 years) with an average duration of diabetes of 11 years. Significant reductions in worst and average pain scores were seen within each group (p ≤ 0.001). Similarly significant reductions were also noted for interference with walking, sleep, and mood scores as well as burning, pins and needles, and tingling scores within each group (p<0.05). There were no statistically significant differences between both groups after 4 weeks for any outcome measure.

CONCLUSIONS

In this trial topical, nutmeg extracts did not add to the improvements observed in PDN symptoms during 4 weeks treatment with preparations containing menthol and methyl salicylate. Further research designed to test the individual components of the topical therapies used in this study may clarify their benefit.

Epidemiology of neuropathic pain and its impact on quality of life

Epidemiology is an important clinical tool in designing and evaluating management and prevention strategies, and is particularly relevant to neuropathic pain. However, there is a relative lack of accurate information available. In one sense, neuropathic pain describes a symptom or a mechanism, rather than a specific disease; on the other hand, there are sufficient similarities in the effects and response to treatment between different causes to make it worthwhile to consider neuropathic pain as a distinct condition. However, there are important specific disease-based factors that need to be considered separately. Estimates of prevalence that are based on specific causes of neuropathic pain tend to be lower (1-2%) than those that are based on reports of the classic symptoms (6-8%), and further methodological research is needed. All neuropathic pain is associated with poor general health, comparable with other severe chronic diseases. The importance of newly proposed risk factors, including genetic factors, still needs to be assessed at a population level.

Central poststroke pain: somatosensory abnormalities and the presence of associated myofascial pain syndrome

Background

Central post-stroke pain (CPSP) is a neuropathic pain syndrome associated with somatosensory abnormalities due to central nervous system lesion following a cerebrovascular insult. Post-stroke pain (PSP) refers to a broader range of clinical conditions leading to pain after stroke, but not restricted to CPSP, including other types of pain such as myofascial pain syndrome (MPS), painful shoulder, lumbar and dorsal pain, complex regional pain syndrome, and spasticity-related pain. Despite its recognition as part of the general PSP diagnostic possibilities, the prevalence of MPS has never been characterized in patients with CPSP patients. We performed a cross-sectional standardized clinical and radiological evaluation of patients with definite CPSP in order to assess the presence of other non-neuropathic pain syndromes, and in particular, the role of myofascial pain syndrome in these patients.

Methods

CPSP patients underwent a standardized sensory and motor neurological evaluation, and were classified according to stroke mechanism, neurological deficits, presence and profile of MPS. The Visual Analogic Scale (VAS), McGill Pain Questionnaire (MPQ), and Beck Depression Scale (BDS) were filled out by all participants.

Results

Forty CPSP patients were included. Thirty-six (90.0%) had one single ischemic stroke. Pain presented during the first three months after stroke in 75.0%. Median pain intensity was 10 (5 to 10). There was no difference in pain intensity among the different lesion site groups. Neuropathic pain was continuous-ongoing in 34 (85.0%) patients and intermittent in the remainder. Burning was the most common descriptor (70%). Main aggravating factors were contact to cold (62.5%). Thermo-sensory abnormalities were universal. MPS was diagnosed in 27 (67.5%) patients and was more common in the supratentorial extra-thalamic group (P <0.001). No significant differences were observed among the different stroke location groups and pain questionnaires and scales scores. Importantly, CPSP patients with and without MPS did not differ in pain intensity (VAS), MPQ or BDS scores.

Conclusions

The presence of MPS is not an exception after stroke and may present in association with CPSP as a common comorbid condition. Further studies are necessary to clarify the role of MPS in CPSP.

Quantitative sensory testing somatosensory profiles in patients with cervical radiculopathy are distinct from those in patients with nonspecific neck-arm pain

The aim of this study was to establish the somatosensory profiles of patients with cervical radiculopathy and patients with nonspecific neck-arm pain associated with heightened nerve mechanosensitivity (NSNAP). Sensory profiles were compared to healthy control (HC) subjects and a positive control group comprising patients with fibromyalgia (FM). Quantitative sensory testing (QST) of thermal and mechanical detection and pain thresholds, pain sensitivity and responsiveness to repetitive noxious mechanical stimulation was performed in the maximal pain area, the corresponding dermatome and foot of 23 patients with painful C6 or C7 cervical radiculopathy, 8 patients with NSNAP in a C6/7 dermatomal pain distribution, 31 HC and 22 patients with FM. For both neck-arm pain groups, all QST parameters were within the 95% confidence interval of HC data. Patients with cervical radiculopathy were characterised by localised loss of function (thermal, mechanical, vibration detection P<.009) in the maximal pain area and dermatome (thermal detection, vibration detection, pressure pain sensitivity P<.04), consistent with peripheral neuronal damage. Both neck-arm pain groups demonstrated increased cold sensitivity in their maximal pain area (P<.03) and the foot (P<.009), and this was also the dominant sensory characteristic in patients with NSNAP. Both neck-arm pain groups differed from patients with FM, the latter characterised by a widespread gain of function in most nociceptive parameters (thermal, pressure, mechanical pain sensitivity P<.027). Despite commonalities in pain characteristics between the 2 neck-arm pain groups, distinct sensory profiles were demonstrated for each group.

Prevalence, characteristics, and factors associated with chronic pain with and without neuropathic characteristics in São Luís, Brazil

CONTEXT

Chronic pain (CP) with and without neuropathic characteristics is a public health problem. This is the first population-based study in South America, and the third in the world, to use the Douleur Neuropathique 4 Questions (DN4) tool in epidemiologic studies.

OBJECTIVES

The objectives were to estimate the prevalence and associated factors of CP with and without neuropathic characteristics in São Luís, Brazil.

METHODS

We surveyed 1597 people. The DN4 questionnaire was applied. Poisson regression was used to analyze the risk factors.

RESULTS

The prevalence of CP was 42%, and 10% had CP with neuropathic characteristics (CPNC). The results showed that female sex and age ≥30 years were associated with an increased prevalence of CP (P<0.001) and education ≥12 years with a reduction in the prevalence of CP. The sensations listed in the DN4 were more common in people with CPNC and most frequent were pins and needles (87.9%). The cephalic region (36%) and limbs (51%) were the locations most affected. Most respondents felt pain between six months and four years (51.6%), with daily frequency (45%). Pain intensity, the impediments caused by pain, and sadness were more prevalent in people who had CPNC (P<0.001). Health status was regular for most, 50.9% did not know the cause of their pain, 64.1% used drugs, and only 7% had consulted with a pain specialist. Dissatisfaction with treatment was reported by 55%.

CONCLUSION

CP with and without neuropathic characteristics is a public health problem in Brazil, with high prevalence and great influence on people's daily lives.

Chronic preoperative pain and psychological robustness predict acute postoperative pain outcomes after surgery for breast cancer

Background:

Few epidemiological studies have prospectively investigated preoperative and surgical risk factors for acute postoperative pain after surgery for breast cancer. We investigated demographic, psychological, pain-related and surgical risk factors in women undergoing resectional surgery for breast cancer.

Methods:

Primary outcomes were pain severity, at rest (PAR) and movement-evoked pain (MEP), in the first postoperative week.

Results:

In 338 women undergoing surgery, those with chronic preoperative pain were three times more likely to report moderate to severe MEP after breast cancer surgery (OR 3.18, 95% CI 1.45–6.99). Increased psychological ‘robustness’, a composite variable representing positive affect and dispositional optimism, was associated with lower intensity acute postoperative PAR (OR 0.63, 95% CI 0.48–0.82) and MEP (OR 0.71, 95% CI 0.54–0.93). Sentinel lymph node biopsy (SLNB) and intraoperative nerve division were associated with reduced postoperative pain. No relationship was found between preoperative neuropathic pain and acute pain outcomes; altered sensations and numbness postoperatively were more common after axillary sample or clearance compared with SLNB.

Conclusion:

Chronic preoperative pain, axillary surgery and psychological robustness significantly predicted acute pain outcomes after surgery for breast cancer. Preoperative identification and targeted intervention of subgroups at risk could enhance the recovery trajectory in cancer survivors.

Prevalence, causes, and treatment of neuropathic pain in Dutch nursing home residents: a retrospective chart review

OBJECTIVES

To identify the prevalence and causes of neuropathic pain in Dutch nursing home residents; to establish the prevalence of painful and nonpainful diabetic polyneuropathy in a subsample of individuals with diabetes mellitus and central poststroke pain (CPSP) in a subsample of individuals who had a stroke; and to study the prescription of antineuropathic drugs.

DESIGN

A descriptive, retrospective, cross-sectional study conducted by analyzing medical records.

SETTING

Data were collected in 12 Dutch nursing homes.

PARTICIPANTS

The data were derived from the medical records of 497 residents of chronic long-term stay and rehabilitation nursing home units.

MEASUREMENTS

Four groups were defined: actual (at some time in the previous year) neuropathic pain (ANP), possible neuropathic pain (PNP), neuropathic pain in the past (NPP), and no signs of neuropathic pain (NoNP).

RESULTS

The prevalence of ANP was 10.9% (95% confidence interval (CI) = 8.4-13.8%) and of PNP was 5.6% (95% CI = 3.9-7.9%). The most common causes were CPSP and phantom limb pain. In the subgroup with diabetes mellitus, 6.3% had nonpainful diabetic polyneuropathy, 0.7% had painful diabetic polyneuropathy, and 0.7% had possible painful diabetic polyneuropathy. In the poststroke subsample, 4.7% were identified as having CPSP, and 5.2% were identified as possibly having CPSP. Within the ANP group, 68.5% of the residents received antineuropathic drugs on the day the medical records were examined; 48.1% used anticonvulsants.

CONCLUSION

Dutch nursing home residents frequently experience neuropathic pain; therefore, neuropathic pain should receive more attention in frail elderly adults.

Meteorin reverses hypersensitivity in rat models of neuropathic pain

Neuropathic pain is caused by a lesion or disease to the somatosensory nervous system and current treatment merely reduces symptoms. Here, we investigate the potential therapeutic effect of the neurotrophic factor Meteorin on multiple signs of neuropathic pain in two distinct rat models. In a first study, two weeks of intermittent systemic administration of recombinant Meteorin led to a dose-dependent reversal of established mechanical and cold hypersensitivity in rats after photochemically-induced sciatic nerve injury. Moreover, analgesic efficacy lasted for at least one week after treatment cessation. In rats with a chronic constriction injury (CCI) of the sciatic nerve, five systemic injections of Meteorin over 9 days dose-dependently reversed established mechanical and thermal hypersensitivity as well as weight bearing deficits taken as a surrogate marker of spontaneous pain. The beneficial effects of systemic Meteorin were sustained for at least three weeks after treatment ended and no adverse side effects were observed. Pharmacokinetic analysis indicated that plasma Meteorin exposure correlated well with dosing and was no longer detectable after 24 hours. This pharmacokinetic profile combined with a delayed time of onset and prolonged duration of analgesic efficacy on multiple parameters suggests a disease-modifying mechanism rather than symptomatic pain relief. In sciatic nerve lesioned rats, delivery of recombinant Meteorin by intrathecal injection was also efficacious in reversing mechanical and cold hypersensitivity. Together, these data demonstrate that Meteorin represents a novel treatment strategy for the effective and long lasting relief from the debilitating consequences of neuropathic pain.

Prevalence of neuropathic features of back pain in clinical populations: implications for the diagnostic triage paradigm

SUMMARY Contemporary clinical assessment of back pain is based on the diagnostic triage paradigm. The most common diagnostic classification is nonspecific back pain, considered to be of nociceptive etiology. A small proportion are diagnosed with radicular pain, of neuropathic origin. In this study we review the body of literature on the prevalence of neuropathic features of back pain, revealing that the point prevalence is 17% in primary care, 34% in mixed clinical settings and 53% in tertiary care. There is evidence that neuropathic features of back pain are not restricted to typical clinical radicular pain phenotypes and may be under-recognized, particularly in primary care. The consequence of this is that in the clinic, diagnostic triage may erroneously classify patients with nonspecific back pain or radicular pain. A promising alternative is the development of mechanism-based pain phenotyping in patients with back pain. Timely identification of contributory pain mechanisms may enable greater opportunity to select appropriate therapeutic targets and improve patient outcomes.

Review of the history and current status of cell-transplant approaches for the management of neuropathic pain

Treatment of sensory neuropathies, whether inherited or caused by trauma, the progress of diabetes, or other disease states, are among the most difficult problems in modern clinical practice. Cell therapy to release antinociceptive agents near the injured spinal cord would be the logical next step in the development of treatment modalities. But few clinical trials, especially for chronic pain, have tested the transplant of cells or a cell line to treat human disease. The history of the research and development of useful cell-transplant-based approaches offers an understanding of the advantages and problems associated with these technologies, but as an adjuvant or replacement for current pharmacological treatments, cell therapy is a likely near future clinical tool for improved health care.

Measuring health-related quality of life in diabetic peripheral neuropathy: a systematic review

We undertook a systematic review of disease-specific measures of health-related quality of life (HRQL) in diabetic peripheral neuropathy (DPN) to appraise the scientific (psychometric) evidence and make recommendations about the best instrument(s) to use. DPN is a common complication of diabetes mellitus. A need to consider the broad impact of DPN, rather than just pain and the increasingly recognised need to assess patient-reported outcomes such as HRQL in evaluating healthcare has led to a demand for rigorous outcome measures. To identify appropriate disease-specific measures, we searched four databases: PubMed, Embase, PsycINFO and CINAHL Plus. Data were extracted from each article using a standard data extraction form and the psychometric properties of each HRQL measure were reviewed. We identified three DPN-specific measures of HRQL: PN-QOL-97, Norfolk QOL-DN, NeuroQoL. All three measures satisfy at least one criterion for both reliability and validity, though all also have some disadvantages. Where there is no requirement for multi-language versions, the PN-QOL-97 is a useful instrument. Studies that involve multiple languages would need to use the shorter QOL-DN but would also need to incorporate complementary instruments to address the psychological and emotional impact of DPN.

Towards a definition of refractory neuropathic pain for epidemiological research. An international Delphi survey of experts

Background

Best current estimates of neuropathic pain (NeuP) prevalence come from studies using various screening detecting pain with probable neuropathic features; the proportion experiencing significant, long-term NeuP, and the proportion not responding to standard treatment are unknown. These “refractory” cases are the most clinically important to detect, being the most severe, requiring specialist treatment.

Methods

We report an international Delphi survey of experts in NeuP, aiming for consensus on the features required to define, for epidemiological research: (1) neuropathic pain; and (2) when NeuP is “refractory”. A web-based questionnaire was developed and data collected from three rounds of questionnaires from nineteen experts.

Results

There was good consensus on essential inclusion of six items to identify NeuP (“prickling, tingling, pins & needles”, “pain evoked by light touch”, “electric shocks or shooting pain”, “hot or burning” pain, “brush allodynia on self-examination”, and “relevant history”) and on some items that were non-essential. Consensus was also reached on components of a “refractory NeuP” definition: minimum duration (one year); number of trials of drugs of known effectiveness (four); adequate duration of these trials (three months / maximum tolerated); outcomes of treatment (pain severity, quality of life). Further work needs to validate these proposed criteria in general population research.

Conclusions

This paper presents an international consensus on measuring the epidemiology of refractory neuropathic pain. This will be valuable in reaching an agreed estimate of the prevalence of neuropathic pain, and the first estimate of refractory neuropathic pain prevalence.

Cutaneous innervation and trigeminal pathway function in a patient with facial pain associated with Parry-Romberg syndrome

Parry-Romberg syndrome (PRS) is a rare condition manifesting with progressive hemifacial atrophy. Although reported PRS clinical disturbances include facial pain and recent studies raised the possibility that PRS-related pain is a neuropathic pain condition due to the trigeminal nerve damage, no studies have directly investigated cutaneous innervation and trigeminal pathway function in patients with this rare condition. In a 50-year-old woman presenting with a 10-year history of slowly progressive hemifacial atrophy and facial pain, we investigated large myelinated fibres with masticatory muscle electromyography and trigeminal reflexes, and tested small myelinated and unmyelinated fibres with laser-evoked potentials. We also investigated cutaneous innervation by measuring the intraepidermal nerve fibre (IENF) density after skin biopsy of the supraorbital regions. We found that neurophysiological data and IENF density came within normal ranges, with no differences between normal and affected side. Our study showing that the standard reference techniques for assessing cutaneous innervation and trigeminal pathway function disclosed no abnormalities in this patient with PRS suggest that this rare and disabling condition is not associated with trigeminal system damage. These findings indicate that in this patient PRS-related pain is not a neuropathic pain condition, rather it probably arises from the musculoskeletal abnormalities.

Bilateral sensory abnormalities in patients with unilateral neuropathic pain; a quantitative sensory testing (QST) study

In patients who experience unilateral chronic pain, abnormal sensory perception at the non-painful side has been reported. Contralateral sensory changes in these patients have been given little attention, possibly because they are regarded as clinically irrelevant. Still, bilateral sensory changes in these patients could become clinically relevant if they challenge the correct identification of their sensory dysfunction in terms of hyperalgesia and allodynia. Therefore, we have used the standardized quantitative sensory testing (QST) protocol of the German Research Network on Neuropathic Pain (DFNS) to investigate somatosensory function at the painful side and the corresponding non-painful side in unilateral neuropathic pain patients using gender- and age-matched healthy volunteers as a reference cohort. Sensory abnormalities were observed across all QST parameters at the painful side, but also, to a lesser extent, at the contralateral, non-painful side. Similar relative distributions regarding sensory loss/gain for non-nociceptive and nociceptive stimuli were found for both sides. Once a sensory abnormality for a QST parameter at the affected side was observed, the prevalence of an abnormality for the same parameter at the non-affected side was as high as 57% (for Pressure Pain Threshold). Our results show that bilateral sensory dysfunction in patients with unilateral neuropathic pain is more rule than exception. Therefore, this phenomenon should be taken into account for appropriate diagnostic evaluation in clinical practice. This is particularly true for mechanical stimuli where the 95% Confidence Interval for the prevalence of sensory abnormalities at the non-painful side ranges between 33% and 50%.

The validity of upper-limb neurodynamic tests for detecting peripheral neuropathic pain

The validity of upper-limb neurodynamic tests (ULNTs) for detecting peripheral neuropathic pain (PNP) was assessed by reviewing the evidence on plausibility, the definition of a positive test, reliability, and concurrent validity. Evidence was identified by a structured search for peer-reviewed articles published in English before May 2011. The quality of concurrent validity studies was assessed with the Quality Assessment of Diagnostic Accuracy Studies tool, where appropriate. Biomechanical and experimental pain data support the plausibility of ULNTs. Evidence suggests that a positive ULNT should at least partially reproduce the patient's symptoms and that structural differentiation should change these symptoms. Data indicate that this definition of a positive ULNT is reliable when used clinically. Limited evidence suggests that the median nerve test, but not the radial nerve test, helps determine whether a patient has cervical radiculopathy. The median nerve test does not help diagnose carpal tunnel syndrome. These findings should be interpreted cautiously, because diagnostic accuracy might have been distorted by the investigators' definitions of a positive ULNT. Furthermore, patients with PNP who presented with increased nerve mechanosensitivity rather than conduction loss might have been incorrectly classified by electrophysiological reference standards as not having PNP. The only evidence for concurrent validity of the ulnar nerve test was a case study on cubital tunnel syndrome. We recommend that researchers develop more comprehensive reference standards for PNP to accurately assess the concurrent validity of ULNTs and continue investigating the predictive validity of ULNTs for prognosis or treatment response.

Breakthrough pain in patients referred to pain clinics: the Italian pain network retrospective study

INTRODUCTION

Despite breakthrough pain (BTP) being one of the most severe forms of pain, there are no definitive data on its prevalence.

METHODS

The authors performed a retrospective survey of the prevalence of BTP in consecutive patients in four Italian pain clinics, subsequent to application of an Italian law mandating detailed clinical records on pain characteristics, treatment, and results. Mean pain intensity was assessed with a numerical rating scale from 0 to 10.

RESULTS

The authors analyzed records of 1,401 patients (58% women, 33.1% patients with cancer). Transient episodes of severe pain or BTP were referred by 790 patients (56.4%), including 58.2% of the men (342 of 588) and 55.1% of the women (448 of 813). Among the 464 patients with cancer, 70.3% reported daily exacerbation of pain. The mean BTP intensity was 8.31 ± 1.58 and 31.1% of patients reported experiencing three episodes per day.

CONCLUSION

Despite some limitations of the study, the authors show that transient episodes of severe pain or BTP are significantly present both in cancer and other diseases, and that many patients are not yet receiving appropriate opioid therapy. The authors need validated tools at international level for the diagnosis and treatment of BTP in patients with cancer and for transitory and patients with severe non-cancer pain. A survey at national level is needed to estimate the prevalence of BTP in different settings, to plan specific medical education.

Conditioned pain modulation predicts duloxetine efficacy in painful diabetic neuropathy

This study aims to individualize the selection of drugs for neuropathic pain by examining the potential coupling of a given drug's mechanism of action with the patient's pain modulation pattern. The latter is assessed by the conditioned pain modulation (CPM) and temporal summation (TS) protocols. We hypothesized that patients with a malfunctioning pain modulation pattern, such as less efficient CPM, would benefit more from drugs augmenting descending inhibitory pain control than would patients with a normal modulation pattern of efficient CPM. Thirty patients with painful diabetic neuropathy received 1 week of placebo, 1 week of 30 mg/d duloxetine, and 4 weeks of 60 mg/d duloxetine. Pain modulation was assessed psychophysically, both before and at the end of treatment. Patient assessment of drug efficacy, assessed weekly, was the study's primary outcome. Baseline CPM was found to be correlated with duloxetine efficacy (r=0.628, P<.001, efficient CPM is marked negative), such that less efficient CPM predicted efficacious use of duloxetine. Regression analysis (R(2)=0.673; P=.012) showed that drug efficacy was predicted only by CPM (P=.001) and not by pretreatment pain levels, neuropathy severity, depression level, or patient assessment of improvement by placebo. Furthermore, beyond its predictive value, the treatment-induced improvement in CPM was correlated with drug efficacy (r=-0.411, P=.033). However, this improvement occurred only in patients with less efficient CPM (16.8±16.0 to -1.1±15.5, P<.050). No predictive role was found for TS. In conclusion, the coupling of CPM and duloxetine efficacy highlights the importance of pain pathophysiology in the clinical decision-making process. This evaluative approach promotes personalized pain therapy.

A randomized, double-blind, controlled study of NGX-4010, a capsaicin 8% dermal patch, for the treatment of painful HIV-associated distal sensory polyneuropathy

INTRODUCTION

Effective treatment of HIV-associated distal sensory polyneuropathy remains a significant unmet therapeutic need.

METHODS

In this randomized, double-blind, controlled study, patients with pain due to HIV-associated distal sensory polyneuropathy received a single 30-minute or 60-minute application of NGX-4010--a capsaicin 8% patch (n = 332)--or a low-dose capsaicin (0.04%) control patch (n = 162). The primary endpoint was the mean percent change from baseline in Numeric Pain Rating Scale score to weeks 2-12. Secondary endpoints included patient global impression of change at week 12.

RESULTS

Pain reduction was not significantly different between the total NGX-4010 group (-29.5%) and the total control group (-24.5%; P = 0.097). Greater pain reduction in the 60-minute (-30.0%) versus the 30-minute control group (-19.1%) prevented intended pooling of the control groups to test individual NGX-4010 treatment groups. No significant pain reduction was observed for the 30-minute NGX-4010 group compared with 30-minute control (-26.2% vs.-19.1%, respectively, P = 0.103). Pain reductions in the 60-minute NGX-4010 and control groups were comparable (-32.8% vs. -30.0%, respectively; P = 0.488). Posthoc nonparametric testing demonstrated significant differences favoring the total (P = 0.044) and 30-minute NGX-4010 groups (P = 0.035). Significantly, more patients in the total and 30-minute NGX-4010 group felt improved on the patient global impression of change versus control (67% vs. 55%, P = 0.011 and 65% vs. 45%, P = 0.006, respectively). Mild to moderate transient application site pain and erythema were the most common adverse events.

CONCLUSIONS

Although the primary endpoint analyses were not significant, trends toward pain improvement were observed after a single 30-minute NGX-4010 treatment.

How close are we in utilizing functional neuroimaging in routine clinical diagnosis of neuropathic pain?

As with many disorders affecting the central nervous system, treatment of chronic pain is fraught with difficulties related to specific diagnosis and measures of treatment efficacy. Given the recent advances that brain-imaging techniques have contributed to our understanding of how chronic pain affects multiple aspects of brain function (including sensory, emotional, cognitive, and modulatory), opportunities to use these approaches in the clinic are clearly a focus of research laboratories around the world. The routine application of brain imaging as a clinical marker of disease state or therapeutic (drug) efficacy would significantly enhance the clinical process by providing objective measures for clinicians and patients.

Vatalanib decrease the positive interaction of VEGF receptor-2 and P2X2/3 receptor in chronic constriction injury rats

Neuropathic pain can arise from a lesion affecting the peripheral nervous system. Selective P2X(3) and P2X(2/3) receptors' antagonists effectively reduce neuropathic pain. VEGF inhibitors are effective for pain relief. The present study investigated the effects of Vatalanib (VEGF receptor-2 (VEGFR-2) inhibitor) on the neuropathic pain to address the interaction of VEGFR-2 and P2X(2/3) receptor in dorsal root ganglia of chronic constriction injury (CCI) rats. Neuropathic pain symptoms following CCI are similar to most peripheral lesions as assessed by the Neuropathic Pain Symptom Inventory. Sprague-Dawley rats were randomly divided into sham group, CCI group and CCI rats treated with Vatalanib group. Mechanical withdrawal threshold and thermal withdrawal latency were measured. Co-expression of VEGFR-2 and P2X(2) or P2X(3) in L4-6 dorsal root ganglia (DRG) was detected by double-label immunofluorescence. The modulation effect of VEGF on P2X(2/3) receptor agonist-activated currents in freshly isolated DRG neurons of rats both of sham and CCI rats was recorded by whole-cell patch-clamp technique. The mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) in CCI group were lower than those in sham group (p<0.05). MWT and TWL in CCI rats treated with Vatalanib group were increased compared with those in CCI group (p<0.05). VEGFR-2 and P2X(2) or P2X(3) receptors were co-expressed in the cytoplasm and surface membranes of DRG. The co-expression of VEGFR-2 and P2X(2) or P2X(3) receptor in CCI group exhibited more intense staining than those in sham group and CCI rats treated with Vatalanib group, respectively. VEGF enhanced the amplitude of ATP and α,β-meATP -activated currents of both sham and CCI rats. Increment effects of VEGF on ATP and α,β-meATP -activated currents in CCI rats were higher than those in sham rats. Both ATP (100 μM) and α,β-meATP (10 μM)- activated currents enhanced by VEGF ( 1nM) were significantly blocked by Vatalanib (1 μM, an inhibitor of VEGF receptors). The stain values of VEGFR-2, P2X(2) and P2X(3) protein expression in L4/5 DRG of CCI treated with Vatalanib group were significantly decreased compared with those in CCI group (p<0.01). Vatalanib can alleviate chronic neuropathic pain by decreasing the activation of VEGF on VEGFR-2 and the positive interaction between the up-regulated VEGFR-2 and P2X(2/3) receptors in the neuropathic pain signaling.

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.

Accelerating the development of improved analgesic treatments: the ACTION public-private partnership

There has been considerable progress identifying pathophysiologic mechanisms of neuropathic pain, but analgesic medications with improved efficacy, safety, and tolerability still represent an unmet public health need. Numerous treatments examined in recent randomized clinical trials (RCTs) have failed to show efficacy for neuropathic pain, including treatments that had previously demonstrated efficacy. This suggests that at least some negative results reflect limited assay sensitivity of RCTs to distinguish efficacious treatments from placebo. Patient characteristics, clinical trial research designs and methods, outcome measures, approaches to data analysis, and statistical power may all play a role in accounting for difficulties in demonstrating the benefits of efficacious analgesic treatments vs placebo. The identification of specific clinical trial characteristics associated with assay sensitivity in existing data has the potential to provide an evidence-based approach to the design of analgesic clinical trials. The US Food and Drug Administration recently launched the Analgesic Clinical Trial Innovations, Opportunities, and Networks (ACTION) public-private partnership, which is designed to facilitate the discovery and development of analgesics with improved efficacy, safety, and tolerability for acute and chronic pain conditions. ACTION will establish a collaborative effort to prioritize research objectives, develop a standardized analgesic database platform, and conduct methodologically focused studies to increase the assay sensitivity and efficiency of analgesic clinical trials. The results of these activities have the potential to inform and accelerate the development of improved pain management interventions of all types, not just pharmacologic treatments.

Neurological diseases and pain

Chronic pain is a frequent component of many neurological disorders, affecting 20-40% of patients for many primary neurological diseases. These diseases result from a wide range of pathophysiologies including traumatic injury to the central nervous system, neurodegeneration and neuroinflammation, and exploring the aetiology of pain in these disorders is an opportunity to achieve new insight into pain processing. Whether pain originates in the central or peripheral nervous system, it frequently becomes centralized through maladaptive responses within the central nervous system that can profoundly alter brain systems and thereby behaviour (e.g. depression). Chronic pain should thus be considered a brain disease in which alterations in neural networks affect multiple aspects of brain function, structure and chemistry. The study and treatment of this disease is greatly complicated by the lack of objective measures for either the symptoms or the underlying mechanisms of chronic pain. In pain associated with neurological disease, it is sometimes difficult to obtain even a subjective evaluation of pain, as is the case for patients in a vegetative state or end-stage Alzheimer's disease. It is critical that neurologists become more involved in chronic pain treatment and research (already significant in the fields of migraine and peripheral neuropathies). To achieve this goal, greater efforts are needed to enhance training for neurologists in pain treatment and promote greater interest in the field. This review describes examples of pain in different neurological diseases including primary neurological pain conditions, discusses the therapeutic potential of brain-targeted therapies and highlights the need for objective measures of pain.

The specific disease burden of neuropathic pain: results of a French nationwide survey

We report the first nationwide survey of the impact of neuropathic pain, as opposed to nonneuropathic pain, on quality of life and health care utilization in the French general population. A postal questionnaire was sent to a representative sample of 4554 respondents from an initial nationwide survey of 30,155 subjects with or without chronic pain. It included pain characteristics (Neuropathic Pain Symptom Inventory, DN4), quality of life (Medical Outcomes Short Form 12, SF-12), sleep, anxiety/depressive symptoms (Hospital Anxiety and Depression Scale) and health care utilization. In total, 3899 (85.6%) questionnaires were returned, 3816 (97.9%) could be assessed and 3165 subjects (82.9%) confirmed their pain status. Subjects reporting pain and neuropathic characteristics based on the DN4 displayed a higher degree of impairment of all dimensions relating to quality of life and sleep and had higher anxiety/depression scores than those reporting pain without neuropathic characteristics and those without pain (P<.01). They also made greater use of health care facilities, particularly as concerned neurological treatments and visits to neurologists (21% vs 9%; P<.01). Multivariate analyses showed that the neuropathic characteristics of pain made an independent contribution to quality-of-life impairment (P<.0001 and P=.0005 for the physical and mental scores of the SF-12 respectively). Our study indicates that the disease burden of chronic pain depends on the nature of the pain, independently of its intensity and duration.

Transcutaneous electrical nerve stimulation for the management of painful conditions: focus on neuropathic pain

The management of neuropathic pain is challenging, with medication being the first-line treatment. Transcutaneous electrical nerve stimulation (TENS) is an inexpensive, noninvasive, self-administered technique that is used as an adjunct to medication. Clinical experience suggests that TENS is beneficial providing it is administered at a sufficiently strong intensity, close to the site of pain. At present, there are too few randomized controlled trials on TENS for neuropathic pain to judge effectiveness. The findings of systematic reviews of TENS for other pain syndromes are inconclusive because trials have a low fidelity associated with inadequate TENS technique and infrequent treatments of insufficient duration. The use of electrode arrays to spatially target stimulation more precisely may improve the efficacy of TENS in the future.