Neuropathic pain: quality-of-life impact, costs and cost effectiveness of therapy

Neuropathic pain's biopsychosocial effects

The aim of our study is to understand neuropathic pain's social, psychological, and biological effects on the patients. All of the patients who were diagnosed with neuropathic pain (NP) by a neurologist were invited to participate in the study. The diagnoses were made based on the patients' history and symptoms and the results of their neurological examinations. Demographic characteristics (age and pain duration), diagnoses, and medical histories of the patients were recorded. Average daily pain intensity was measured using a 100-mm visual analogue scale (VAS). Quality of life was measured with RAND 36-Item Health Survey 1.0. Pittsburgh Sleep Quality Index (PSQI) was used to examine the quality of sleep, and Beck Depression Scale was used to examine depression status of the patients. A total of 26 patients (14 male, 12 female) between 33 and 79 years of age participated in the study. There were no dropouts from the study. Eleven (42.3%) patients' mood was normal and the others (57.7%) had different levels of depression. Two patients' (7.7%) quality of sleep was normal, but 24 (92.3%) of the patients' quality of sleep was poor. The patients' pain intensity was at an important and high value (VAS: 6.88). The most important result of this clinical study was that the biopsychosocial approach would be appropriate to understand and treat NP. The biopsychosocial approach to pain addresses psychological, sociocultural factors, and biomedical/physiological aspects. We wanted to draw attention to NP's psychological, emotional and sociocultural characteristics to show that the NP treatment can be applied within this framework.

Bifunctional opioid/nociceptin hybrid KGNOP1 effectively attenuates pain-related behaviour in a rat model of neuropathy

A bifunctional peptide containing an opioid and nociceptin receptor-binding pharmacophore, H-Dmt-D-Arg-Aba-β-Ala-Arg-Tyr-Tyr-Arg-Ile-Lys-NH2 (KGNOP1), was tested for its analgesic properties when administered intrathecally in naïve and chronic constriction injury (CCI)-exposed rats with neuropathy-like symptoms. KGNOP1 significantly increased the acute pain threshold, as measured by the tail-flick test, and also increased the threshold of a painful reaction to mechanical and thermal stimuli in CCI-exposed rats. Both of the effects could be blocked by pre-administration of [Nphe1]-Nociceptin (1-13)-NH2 (NPhe) or naloxone, antagonists for nociceptin and opioid receptors, respectively. This led us to conclude that KGNOP1 acts as a dual opioid and nociceptin receptor agonist in vivo. The analgesic effect of KGNOP1 proved to be more powerful than clinical drugs such as morphine and buprenorphine. Repeated daily intrathecal injections of KGNOP1 led to the development of analgesic tolerance, with the antiallodynic action being completely abolished on day 6. Nevertheless, the development of tolerance to the antihyperalgesic effect was delayed in comparison to morphine, which lost its efficacy as measured by the cold plate test after 3days of daily intrathecal administration, whereas KGNOP1 was efficient up to day 6. A single intrathecal injection of morphine to KGNOP1-tolerant rats did not raise the pain threshold in any of the behavioural tests; in contrast, a single intrathecal dose of KGNOP1 significantly suppressed allodynia and hyperalgesia in morphine-tolerant rats.

Contribution of the Suppressor of Variegation 3-9 Homolog 1 in Dorsal Root Ganglia and Spinal Cord Dorsal Horn to Nerve Injury-induced Nociceptive Hypersensitivity

BACKGROUND

Peripheral nerve injury-induced gene alterations in the dorsal root ganglion (DRG) and spinal cord likely participate in neuropathic pain genesis. Histone methylation gates gene expression. Whether the suppressor of variegation 3-9 homolog 1 (SUV39H1), a histone methyltransferase, contributes to nerve injury-induced nociceptive hypersensitivity is unknown.

METHODS

Quantitative real-time reverse transcription polymerase chain reaction analysis, Western blot analysis, or immunohistochemistry were carried out to examine the expression of SUV39H1 mRNA and protein in rat DRG and dorsal horn and its colocalization with DRG μ-opioid receptor (MOR). The effects of a SUV39H1 inhibitor (chaetocin) or SUV39H1 siRNA on fifth lumbar spinal nerve ligation (SNL)-induced DRG MOR down-regulation and nociceptive hypersensitivity were examined.

RESULTS

SUV39H1 was detected in neuronal nuclei of the DRG and dorsal horn. It was distributed predominantly in small DRG neurons, in which it coexpressed with MOR. The level of SUV39H1 protein in both injured DRG and ipsilateral fifth lumbar dorsal horn was time dependently increased after SNL. SNL also produced an increase in the amount of SUV39H1 mRNA in the injured DRG (n = 6/time point). Intrathecal chaetocin or SUV39H1 siRNA as well as DRG or intraspinal microinjection of SUV39H1 siRNA impaired SNL-induced allodynia and hyperalgesia (n = 5/group/treatment). DRG microinjection of SUV39H1 siRNA also restored SNL-induced DRG MOR down-regulation (n = 6/group).

CONCLUSIONS

The findings of this study suggest that SUV39H1 contributes to nerve injury-induced allodynia and hyperalgesia through gating MOR expression in the injured DRG. SUV39H1 may be a potential target for the therapeutic treatment of nerve injury-induced nociceptive hypersensitivity.

Falls, Functioning, and Disability Among Women With Persistent Symptoms of Chemotherapy-Induced Peripheral Neuropathy

Purpose Chemotherapy-induced peripheral neuropathy (CIPN) may persist after treatment ends and may lead to functional decline and falls. This study compared objective and self-report measures of physical function, gait patterns, and falls between women cancer survivors with and without symptoms of CIPN to identify targets for functional rehabilitation. Methods A secondary data analysis of 512 women cancer survivors (age, 62 ± 6 years; time since diagnosis, 5.8 ± 4.1 years) categorized and compared women self-reporting symptoms of CIPN (CIPN+) with asymptomatic women (CIPN-) on the following: maximal leg strength, timed chair stand, physical function battery, gait characteristics (speed; step number, rate, and length; base of support), self-report physical function and disability, and falls in the past year. Results After an average of 6 years after treatment, 47% of women still reported symptoms of CIPN. CIPN+ had significantly worse self-report and objectively measured function than did CIPN-, with the exception of maximal leg strength and base of support during a usual walk. Gait was slower among CIPN+, with those women taking significantly more, but slower and shorter, steps than did CIPN- (all P < .05). CIPN+ reported significantly more disability and 1.8 times the risk of falls compared with CIPN- ( P < .0001). Increasing symptom severity was linearly associated with worsening function, increasing disability, and higher fall risk (all P < .05). Conclusion This work makes a significant contribution toward understanding the functional impact of CIPN symptoms on cancer survivors. Remarkably, 47% of women in our sample had CIPN symptoms many years after treatment, together with worse function, greater disability, and more falls. CIPN must be assessed earlier in the clinical pathway, and strategies to limit symptom progression and to improve function must be included in clinical and survivorship care plans.

Flow cytometry analysis of inflammatory cells isolated from the sciatic nerve and DRG after chronic constriction injury in mice

BACKGROUND

Cellular responses to nerve injury play a central role in the pathogenesis of neuropathic pain. However, the analysis of site specific cellular responses to nerve injury and neuropathic pain is limited to immunohistochemistry staining with numerous limitations.

NEW METHODS

We proposed to apply flow cytometry to overcome some of the limitations and developed two protocols for isolation of cells from small specimens of the sciatic nerve and dorsal root ganglion (DRG) in mice. RESULTS AND COMPARASION WITH EXISTING: methods We found that both the non-enzymatic and enzymatic approaches were highly effective in harvesting a sufficient number of cells for flow cytometry analysis in normal and pathological conditions. The total number of cells in the injury site of the sciatic and its DRGs increased significantly 14days after chronic constriction injury (CCI) of the sciatic nerve, compared to sham surgery control or the contralateral control. The enzymatic approach yielded a significantly higher total number of cells and CD45 negative cells, suggesting that this approach allows for harvest of more resident cells, compared to the non-enzymatic method. The percentage of CD45⁺/CD11b⁺ cells was significantly increased in the sciatic nerve but not in the DRG. These results were consistent with both protocols.

CONCLUSIONS

We thus offer two simple and effective protocols that allow for application of flow cytometry to the investigation of cellular and molecular mechanisms of neuropathic pain.

Does Neuropathic Pain Affect the Quality of Sleep?

OBJECTIVE

We aimed to evaluate the quality of sleep (QoS) in patients with neuropathic pain (NP) and to investigate the association between possible QoS impairment and NP characteristics.

MATERIALS AND METHODS

Patients with NP and controls were examined. Age, sex, NP duration, NP cause (central, peripheral, or mixed), and pain intensity (with a Likert-type scale and visual analog scale) were recorded. NP was screened with Douleur Neuropathique 4 questions (DN4), and QoS was evaluated using the Pittsburg Sleep Quality Index (PSQI). Mann-Whitney U test and regression analysis were performed to evaluate the data.

RESULTS

Seventy patients with NP and 30 age- and sex-matched controls were included. The mean age of the patients and controls were 45.04±10.21 years and 39.00±19.23 years, respectively. Significantly higher scores of sleep latency (p=0.002), sleep duration (p=0.003), sleep efficiency (p=0.002), sleep disturbance (p<0.000), daytime dysfunction (p=0.04), and PSQI total were observed in patients with NP than in controls (p<0.000). In addition, 80% of patients with NP and 37 % of controls were classified as having poor QoS (p<0.000). Female sex, pain intensity, and NP duration were found to be factors related to having poor QoS in patients with NP (p=0.026, p=0.006, and p<0.000, respectively).

CONCLUSION

In our study, 80% of patients with NP had poor QoS regardless of the NP cause. Female sex, pain severity, and NP duration were found to be factors correlated with poor QoS. Treatment strategies that target not only NP itself but also better QoS may contribute to the overall success of management.

Prevention of chronic post-surgical pain: the importance of early identification of risk factors

Chronic post-surgical pain (CPSP) is currently an inevitable surgical complication. Despite the advances in surgical techniques and the development of new modalities for pain management, CPSP can affect 15-60% of all surgical patients. The development of chronic pain represents a burden to both the patient and to the community. In order to have a meaningful impact on this debilitating condition it is essential to identify those at risk. Early identification of patients at risk will help to reduce the percentage of patients who go on to develop CPSP. Unfortunately, evidence about any effective actions to reduce this condition is limited. This review will focus on providing context to the challenging problem of CPSP. The possible role of both the surgeon and anesthesiologist in reducing the incidence of this problem will be explored.

Patient-reported neuropathic pain in adolescent and young adult cancer patients

BACKGROUND

Neuropathic pain, a known complication of cancer and its treatments, negatively impacts quality of life. There are limited data using screening tools to aid in the diagnosis of neuropathic pain in cancer patients. Our primary objective was to determine the proportion of adolescent and young adult cancer patients reporting neuropathic pain on a patient-completed, neuropathic pain screening tool.

PROCEDURES

This prospective, cohort study enrolled patients 14-39 years of age who were receiving therapy for primary cancer diagnosis, cancer relapse, or had recently completed treatment. The painDETECT, a patient-completed, neuropathic pain screening tool used down to age 14, was administered a maximum of three times in on-therapy patients and once in off-therapy patients. Provider documentation of neuropathic pain at the corresponding visit was abstracted from the medical record.

RESULTS

Seventy-eight patients participated. Median (interquartile range) age at study enrollment was 18.1 (16-19.4) years and 47% were female. Cancer diagnoses included 41% leukemia, 26% solid tumor, 23% lymphoma, and 10% central nervous system tumor. The proportion of patients reporting neuropathic pain was 26% (95% confidence interval [CI] 16-40%) in on-therapy patients and 11% (95% CI 3-27%) in off-therapy patients. In patients reporting neuropathic pain, only 26% had a clinical diagnosis of neuropathic pain documented in the medical record at the corresponding visit.

CONCLUSIONS

Neuropathic pain occurs in one in four adolescents and young adults receiving cancer therapy. Use of screening tools may increase the detection of neuropathic pain in adolescents and young adults receiving cancer therapy and could ultimately improve pain treatment.

Chronic Pain Features Relate to Quality of Life More than Physiopathology: A Cross-Sectional Evaluation in Pain Clinics

OBJECTIVE

To compare the impact of chronic pain physiopathology on health-related quality of life (HR-QoL), considering the influence of pain features and psychosocial adjustment (intensity, interference, psychological comorbidities, and sleep quality).

DESIGN

A cross-sectional study involving 1,025 noncancer patients with predominantly neuropathic, nociceptive, or mixed chronic pain conditions was conducted in 88 pain clinics within Spain. The EuroQol-5 Dimensions instrument (EQ-5D) was used to measure HR-QoL. The Brief Pain Inventory (BPI), Hospital Anxiety and Depression Scale (HADS), and sleep scale developed for the MOS study (MOS-SQ) were used to measure pain features and psychosocial adjustment. Multivariate analyses were used to model HR-QoL measures.

RESULTS

All patients reported very low HR-QoL. The mean EQ-5D index scores were 0.33, 0.36, and 0.37 in the mixed, neuropathic, and nociceptive pain groups, respectively. The differences did not reach statistical significance (P = 0.057). Patients with nociceptive pain had less pain (least pain intensity score: 4.7 vs. 5.2 in the other groups; P = 0.006), less interference with daily activities (BPI average interference score: 6.3 vs. 6.6 and 6.7 in the neuropathic and mixed pain groups, respectively; P = 0.013), less anxiety (HADS score: 8.5 vs. 9.6 and 9.7 in the same respective groups; P = 0.001), and fewer sleep problems (MOS-SQ sleep problems index: 46.8 vs. 52.2 and 50.2 in the same respective groups; P = 0.005). In the adjusted analyses, HR-QoL measures were explained by pain intensity, anxiety, and sleep quality, but not by physiopathological pain type.

CONCLUSIONS

Pain features, particularly intensity, have a greater impact than pain physiopathology on HR-QoL. Distinct physiopathological mechanisms give rise to different pain features that, in turn, may mediate the HR-QoL of patients with chronic pain. This could be used to improve pain management strategies.

Sinomenine attenuates chronic inflammatory pain in mice

Sinomenine, an alkaloid originally isolated from the roots of Sinomeniumacutum, is used as a traditional Chinese medicine for rheumatic arthritis. However, little is known about the neuronal mechanisms underlying the analgesic effects of sinomenine in animals with chronic inflammatory pain. In this study, we investigated the persistent inflammatory pain induced by hind paw injection of complete Freund's adjuvant (CFA) in mice, which was reversed by sinomenine administration. In the anterior cingulate cortex (ACC), a region highly associated with chronic pain processing, the upregulation of GluN2B-containing N-methyl-D-aspartate (NMDA) receptors and Ca²⁺/calmodulin-dependent protein kinase II, total levels of GluA1, and phosphorylation of GluA1 at Ser831 (p-GluA1-Ser831) were reversed by systemically administrating sinomenine. Furthermore, sinomenine treatment downregulated the mammalian target of rapamycin (mTOR) pathway. Increases in p-mTOR, p-p70S6k, p-S6, and p-4EBP, which were induced by chronic inflammation, were all changed. However, sinomenine did not affect the levels of GluN2A-containing NMDA receptors and p-GluA1-Ser845, as well as the total levels of mTOR, p70S6k, S6, and 4EBP. In conclusion, results indicated that sinomenine reduced the chronic inflammatory pain induced by CFA, at least partially by regulating the GluN2B receptors and mTOR signals in the ACC.

Evaluating the Measurement Properties of the Self-Assessment of Treatment Version II, Follow-Up Version, in Patients with Painful Diabetic Peripheral Neuropathy

Background. The Self-Assessment of Treatment version II (SAT II) measures treatment-related improvements in pain and impacts and impressions of treatment in neuropathic pain patients. The measure has baseline and follow-up versions. This study assesses the measurement properties of the SAT II. Methods. Data from 369 painful diabetic peripheral neuropathy (PDPN) patients from a phase III trial assessing capsaicin 8% patch (Qutenza®) efficacy and safety were used in these analyses. Reliability, convergent validity, known-groups validity, and responsiveness (using the Brief Pain Inventory-Diabetic Neuropathy [BPI-DN] and Patient Global Impression of Change [PGIC]) analyses were conducted, and minimally important differences (MID) were estimated. Results. Exploratory factor analysis supported a one-factor solution for the six impact items. The SAT II has good internal consistency (Cronbach's alpha: 0.96) and test-retest reliability (intraclass correlation coefficients: 0.62–0.88). Assessment of convergent validity showed moderate to strong correlations with change in other study endpoints. Scores varied significantly by level of pain intensity and sleep interference (p < 0.05) defined by the BPI-DN. Responsiveness was shown based on the PGIC. MID estimates ranged from 1.2 to 2.4 (pain improvement) and 1.0 to 2.0 (impact scores). Conclusions. The SAT II is a reliable and valid measure for assessing treatment improvement in PDPN patients.

Neuroinflammation-a co-occurring phenomenon linking chronic pain and opioid dependence

Chronic pain is a disease that encompasses both sensory and emotional elements. Opioids are highly effective analgesics because they target both of these elements, by inhibiting pain pathways and alleviating negative affect (including depression) by engaging reward or hedonic pathways. Unfortunately, chronic opioid use is limited by the development of unwanted side effects, such as tolerance, hyperalgesia, and abuse liability. Thus, the challenge of providing effective pain treatment while minimizing these unwanted side effects is an ongoing issue with significant clinical and societal impact. In this review, we posit that neuroinflammation within the central nervous system is a shared phenomenon between chronic pain and opioids that contributes to pain sensitization and negative affect. The implications for pain progression, addiction liability, and alternative treatment strategies are discussed.

G9a inhibits CREB-triggered expression of mu opioid receptor in primary sensory neurons following peripheral nerve injury

Neuropathic pain, a distressing and debilitating disorder, is still poorly managed in clinic. Opioids, like morphine, remain the mainstay of prescribed medications in the treatment of this disorder, but their analgesic effects are highly unsatisfactory in part due to nerve injury-induced reduction of opioid receptors in the first-order sensory neurons of dorsal root ganglia. G9a is a repressor of gene expression. We found that nerve injury-induced increases in G9a and its catalyzed repressive marker H3K9m2 are responsible for epigenetic silencing of Oprm1, Oprk1, and Oprd1 genes in the injured dorsal root ganglia. Blocking these increases rescued dorsal root ganglia Oprm1, Oprk1, and Oprd1 gene expression and morphine or loperamide analgesia and prevented the development of morphine or loperamide-induced analgesic tolerance under neuropathic pain conditions. Conversely, mimicking these increases reduced the expression of three opioid receptors and promoted the mu opioid receptor-gated release of primary afferent neurotransmitters. Mechanistically, nerve injury-induced increases in the binding activity of G9a and H3K9me2 to the Oprm1 gene were associated with the reduced binding of cyclic AMP response element binding protein to the Oprm1 gene. These findings suggest that G9a participates in the nerve injury-induced reduction of the Oprm1 gene likely through G9a-triggered blockage in the access of cyclic AMP response element binding protein to this gene.

Impact of Massage Therapy on Fatigue, Pain, and Spasticity in People with Multiple Sclerosis: a Pilot Study

BACKGROUND

Multiple sclerosis (MS) is a chronic, immune-mediated, inflammatory disease that leads to fatigue, pain, and spasticity, as well as other sensorimotor and cognitive changes. Often traditional medical approaches are ineffective in alleviating these disruptive symptoms. Although about one-third of surveyed individuals report they use massage therapy (MT) as an adjunct to medical treatment, there is little empirical evidence that MT is effective for symptom management in people with MS.

PURPOSE

To measure the effects of MT on fatigue, pain, spasticity, perception of health, and quality of life in people with MS.

SETTING

Not-for-profit long-term care facility.

PARTICIPANTS

Twenty-four of 28 enrolled individuals with MS (average age = 47.38, SD = 13.05; 22 female) completed all MT sessions and outcome assessments.

RESEARCH DESIGN

Nonrandomized, pre-post pilot study.

INTERVENTION

Standardized MT routine one time a week for six weeks.

MAIN OUTCOME MEASURES

Modified Fatigue Index Scale (MFIS), MOS Pain Effects Scale (MOS Pain), and Modified Ashworth Scale (MAS). Secondary outcome measures: Mental Health Inventory (MHI) and Health Status Questionnaire (HSQ).

RESULTS

There was a significant improvement in MFIS (p < .01), MOS Pain (p < .01), MHI (p < .01), and HSQ (p < .01), all with a large effect size (ES) (Cohen's d = -0.76, 1.25, 0.93, -1.01, respectively). There was a significant correlation between change scores on the MFIS and the MOS Pain (r = 0.532, p < .01), MHI (r = -0.647, p < .01), and subscales of the HSQ (ranging from r = -0.519, to -0.619, p < .01).

CONCLUSIONS

MT as delivered in this study is a safe and beneficial intervention for management of fatigue and pain in people with MS. Decreasing fatigue and pain appears to correlate with improvement in quality of life, which is meaningful for people with MS who have a chronic disease resulting in long-term health care needs.

Symptom-Based Treatment of Neuropathic Pain in Spinal Cord-Injured Patients: A Randomized Crossover Clinical Trial

OBJECTIVE

The objective of this study was to identify the differences in medication effect according to pain characteristics in spinal cord-injured patients.

METHODS

This study is a prospective, randomized, crossover study. Fifty-five patients and 66 locations of neuropathic pain were included. Pain was classified into four spontaneous characteristics and three evoked pain characteristics. Oxcarbazepine (Na channel blocker) and pregabalin (calcium channel α2-δ ligand medication) were tried. Patients were divided into two groups: evoked pain present and evoked pain absent. Overall average visual analog scale was obtained.

RESULTS

Oxcarbazepine was significantly more effective for patients without evoked pain than in those with it for electrical, burning, and pricking pain. The effect of pregabalin was not different regarding the presence or absence of evoked pain for all pain categories, except burning pain. In patients with evoked pain, pregabalin was shown to be significantly more effective for electrical pain, allodynia, and heat hyperalgesia than oxcarbazepine. In the evoked pain absent group, oxcarbazepine showed greater improvement than pregabalin but was not significant.

CONCLUSIONS

In summary, the phenotype of neuropathic pain was associated with the efficacy of different pharmacologic treatments. Symptom-based treatment, therefore, can lead to more efficient analgesia.

Adverse Event Reporting in Clinical Trials of Intravenous and Invasive Pain Treatments: An ACTTION Systematic Review

Thorough assessment and reporting of adverse events (AEs) facilitates a detailed understanding of a treatment's risk-benefit profile. Although the Consolidated Standards of Reporting Trials (CONSORT) 2004 statement provides recommendations regarding AE reporting, adherence to these standards is often inadequate. We investigated AE reporting in clinical trials of intravenous and invasive pain treatments published in 6 major anesthesiology and pain journals between 2000 to 2003 and 2006 to 2012. We examined whether AE reporting improved after publication of the 2004 CONSORT recommendations and also comprehensively reviewed AE assessment using the Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities, and Networks (ACTTION) AE reporting recommendations. No improvement was found overall in CONSORT harms reporting scores from pre- to postpublication of the CONSORT recommendations, with only 5 of 10 fulfilled on average. AE reporting assessed using the ACTTION coding manual was generally inadequate, and 8% of articles failed to report any AE information at all. Anesthesiology and pain journals were similar in AE reporting quality, although industry-sponsored trials reported more AE information than nonindustry sponsored trials. Improvement is needed in AE reporting in analgesic clinical trials. The CONSORT checklist and ACTTION AE recommendations can assist investigators and editors in improving clinical trial transparency and quality.

PERSPECTIVE

This systematic review of AE reporting in intravenous and invasive pain treatment trials shows that little improvement has been made since the 2004 CONSORT harms reporting guidelines. Better assessment and reporting of treatment AEs is necessary to understand the full clinical effect of intravenous and invasive treatments.

Association between Neuropathic Pain and Reported Disability after Total Knee Arthroplasty

PURPOSE

To determine whether reporting neuropathic pain (NP) at an average of 5 years after total knee arthroplasty (TKA) was related to patient age, sex, preoperative comorbidity, arthritis self-efficacy, or disability before surgery and at 1 year after surgery. The estimate of NP prevalence and cross-sectional group differences were explored at 5 years after surgery.

METHODS

A subsample of participants in a formal research study was contacted via mail approximately 5 years after undergoing surgery and were sent four questionnaires: the Western Ontario and McMaster Universities Osteoarthritis Index, the Patient Health Questionnaire, the Self-Administered Leeds Assessment of Neuropathic Signs and Symptoms (S-LANSS), and a satisfaction questionnaire. NP was defined as an S-LANSS score of 12 or more.

RESULTS

Of 89 patients who met the inclusion criteria, data for 63 (71%) patients (47 women; mean age 67 [SD 8] y) were used for analysis. Of these 63, 9 (14%) were identified as having NP. None had a report of failure of prosthesis or other surgical complications according to most recent medical records. There was no relationship between preoperative patient characteristics and development of NP. However, the NP group on average had a higher report of stiffness (p=0.020), physical dysfunction (p=0.019), and pain (p=0.050) at 1 year after surgery. Cross-sectional comparisons showed higher levels of pain (p=0.001), stiffness (p=0.008), physical dysfunction (p=0.003), and depression (p=0.005) and lower satisfaction (p=0.018) at the time of the survey than the patients without NP.

CONCLUSION

The estimated prevalence of NP was 14%. Patients with NP reported higher levels of disability as early as 1 year after surgery. They remained more disabled, with a higher level of depression and less satisfaction, at an average of 5 years after surgery.

Analgesic effectiveness and tolerability of oral oxycodone/naloxone and pregabalin in patients with lung cancer and neuropathic pain: an observational analysis

INTRODUCTION

Cancer-related pain has a severe negative impact on quality of life. Combination analgesic therapy with oxycodone and pregabalin is effective for treating neuropathic cancer pain. We investigated the efficacy and tolerability of a dose-escalation combination therapy with prolonged-release oxycodone/naloxone (OXN-PR) and pregabalin in patients with non-small-cell lung cancer and severe neuropathic pain.

METHODS

This was a 4-week, open-label, observational study. Patients were treated with OXN-PR and pregabalin. Average pain intensity ([API] measured on a 0-10 numerical rating scale) and neuropathic pain (Douleur Neuropathique 4) were assessed at study entry and at follow-up visits. The primary endpoint was response to treatment, defined as a reduction of API at T28 ≥30% from baseline. Secondary endpoints included other efficacy measures, as well as patient satisfaction and quality of life (Brief Pain Inventory Short Form), Hospital Anxiety and Depression Scale, and Symptom Distress Scale; bowel function was also assessed.

RESULTS

A total of 56 patients were enrolled. API at baseline was 8.0±0.9, and decreased after 4 weeks by 48% (4.2±1.9; P<0.0001 vs baseline); 46 (82.1%) patients responded to treatment. Significant improvements were also reported in number/severity of breakthrough cancer pain episodes (P=0.001), Brief Pain Inventory Short Form (P=0.0002), Symptom Distress Scale (P<0.0001), Hospital Anxiety and Depression Scale depression (P=0.0006) and anxiety (P<0.0001) subscales, and bowel function (P=0.0003). At study end, 37 (66.0%) patients were satisfied/very satisfied with the new analgesic treatment. Combination therapy had a good safety profile.

CONCLUSION

OXN-PR and pregabalin were safe and highly effective in a real-world setting of severe neuropathic cancer pain, with a high rate of satisfaction, without interference on bowel function.

Pharmacokinetics and pharmacodynamics of multiple doses of BG00010, a neurotrophic factor with anti-hyperalgesic effects, in patients with sciatica

AIMS

BG00010 is a protein in the glial cell line-derived neurotrophic factor (GDNF) family. It is a selective ligand for the GDNF family receptor alpha-3 (GFRα3) co-receptor that normalizes cellular changes resulting from damage or disease, and potentially alleviates neuropathic pain. The main objectives of this study were to evaluate the pharmacokinetic and safety profiles and to determine the effects on pain of ascending doses of intravenous injections of BG00010 in patients with sciatica.

METHODS

This was a randomized, blinded, placebo-controlled multiple-dose study in subjects with sciatica. In Part I (16 patients), four IV dose levels were examined (50, 150, 400, 800 μg kg(-1) ) and in Part II (12 patients), three dose levels were examined (400, 600 and 1200 μg kg(-1) ). Safety and efficacy assessments were used as endpoints.

RESULTS

The BG00010 concentration-time data indicated relatively low inter-patient variability and there was a dose-dependent (not dose-proportional) increase in serum exposure from 150 to 1200 μg kg(-1) . The effective half-life was between 40 and 60 h. The most frequently occurring adverse events (AEs) reported by patients receiving BG00010 were headache (67-83%), feeling hot (50-100%), and pruritus (42-67%). Most AEs were mild; no serious AEs or AEs leading to discontinuation occurred. Higher dose regimens of BG00010 resulted in greater pain reduction than placebo or lower dose regimens, although a clear dose-response relationship was not seen.

CONCLUSIONS

The pharmacokinetic profile of BG00010 was characterized by low intra-patient variability. These data from a small sample suggest that BG00010 may have a benefit for patients with sciatica.

A burden of illness study for neuropathic pain in Europe

PURPOSE

Neuropathic pain (NP) is often severe and represents a major humanistic and economic burden. This study aimed at providing insight on this burden across France, Germany, Italy, Spain, and the UK, considering direct and indirect costs, productivity loss, and humanistic impact on patients and their families.

METHODS

Physician questionnaires provided data on patients presenting with NP covering demographics, sick leave and retirement, number of consultations, drug treatments, and surgical procedures. Patients provided further demographic and disease-related data and completed the Work Productivity and Activity Impairment (WPAI), the EuroQol 5-Dimension (EQ-5D), and the Brief Pain Inventory (BPI) questionnaires. All health-related direct unitary costs were collected from relevant country-specific sources and adjusted to 2012 prices (€) where necessary. A subgroup analysis of costs based on diabetic peripheral neuropathy (n=894), fibromyalgia (n=300), and low back pain (n=963) was performed.

FINDINGS

About 413 physicians completed a total of 3,956 patient records forms. Total annual direct health-care costs per patient ranged from €1,939 (Italy) to €3,131 (Spain). Annual professional caregiver costs ranged from €393 (France) to €1,242 (UK), but this only represented a small proportion of total care because much care is provided by family or friends. Sick leave costs ranged from €5,492 (UK) to €7,098 (France), with 10%-32% patients prevented from working at some point by NP. Total cost (including direct and indirect costs) of NP per patient was €10,313 in France (69% of the total cost), €14,446 in Germany (78%), €9,305 in Italy (69%), €10,597 in Spain (67%), and €9,685 in the UK (57%). Indirect costs (ie, sick leave) constituted the majority of costs in all five countries: €7,098 in France, €11,232 in Germany, €6,382 in Italy, €7,066 in Spain, and €5,492 in the UK. In the subgroup analysis, total annual direct costs per patient were highest for neuropathic back pain and radiculopathy, and lowest for fibromyalgia. Mean WPAI score range was 34.4-56.1; BPI interference was 4.1-4.8; and EQ-5D was 0.57-0.74. The results suggest that a significant proportion of the patient's work time in the previous week was affected by NP, and these are relatively high compared with other diseases such as diabetes, respiratory conditions, and arthritis.

IMPLICATIONS

Despite differences in practice between countries, these findings suggest a high opportunity cost for society in terms of lost work and productivity due to NP. The wider costs appear significantly higher to patients, carers/families, and society as a whole than to the health system alone.

Efficacy of Duloxetine in Chronic Low Back Pain with a Neuropathic Component: A Randomized, Double-blind, Placebo-controlled Crossover Trial

BACKGROUND

Among patients with chronic low back pain (CLBP), approximately 37% show signs of a neuropathic pain component (radicular pain). Treatment of this condition remains challenging. Therefore, the current study aimed to investigate the efficacy of duloxetine in the treatment of CLBP patients with neuropathic leg pain.

METHODS

The study was conducted as a prospective, randomized, placebo-controlled, double-blind crossover trial. CLBP with a visual analog scale (VAS) score greater than 5 and a neuropathic component that was assessed clinically and by the painDETECT questionnaire (score > 12) were required for inclusion. Patients were randomly assigned to either duloxetine or placebo for 4 weeks followed by a 2-week washout period before they crossed over to the alternate phase that lasted another 4 weeks. Duloxetine was titrated up to 120 mg/day. The primary outcome parameter was mean VAS score during the last week of treatment in each phase (VAS(week4)).

RESULTS

Of 41 patients, 21 patients completed both treatment phases. In the intention-to-treat analysis (n = 25), VAS(week4) was significantly lower in the duloxetine phase compared with placebo (4.1 ± 2.9 vs. 6.0 ± 2.7; P = 0.001), corresponding to an average pain reduction of 32%. The painDETECT score at the end of each treatment phase was significantly lower in the duloxetine phase compared with placebo (17.7 ± 5.7 vs. 21.3 ± 3.6 points; P = 0.0023). Adverse events were distributed equally between the duloxetine (65%) and placebo phases (62%) (P = 0.5).

CONCLUSION

In this crossover study, duloxetine proved to be superior to placebo for the treatment of CLBP with a neuropathic leg pain.

The Relationship between Dyslipidemia and Acute Axonal Function in Type 2 Diabetes Mellitus In Vivo

Objectives

Diabetic peripheral neuropathy (DPN) is a common and debilitating complication of diabetes mellitus. Treatment largely consists of symptom alleviation and there is a need to identify therapeutic targets for prevention and treatment of DPN. The objective of this study was to utilise novel neurophysiological techniques to investigate axonal function in patients with type 2 diabetes and to prospectively determine their relationship to serum lipids in type 2 diabetic patients.

Methods

Seventy-one patients with type 2 diabetes were consecutively recruited and tested. All patients underwent thorough clinical neurological assessments including nerve conduction studies, and median motor axonal excitability studies. Studies were also undertaken in age matched normal control subjects(n = 42). Biochemical studies, including serum lipid levels were obtained in all patients. Patient excitability data was compared to control data and linear regression analysis was performed to determine the relationship between serum triglycerides and low density lipoproteins and excitability parameters typically abnormal in type 2 diabetic patients.

Results

Patient mean age was 64.2±2.3 years, mean glycosylated haemoglobin (HbA1c%) was 7.8±0.3%, mean triglyceride concentration was 1.6±0.1 mmol/L and mean cholesterol concentration was 4.1±0.2mmol/L. Compared to age matched controls, median motor axonal excitability studies indicated axonal dysfunction in type 2 diabetic patients as a whole (T2DM) and in a subgroup of the patients without DPN (T2DM-NN). These included reduced percentage threshold change during threshold electrotonus at 10–20ms depolarising currents (TEd10–20ms)(controls 68.4±0.8, T2DM63.9±0.8, T2DM-NN64.8±1.6%,P<0.05) and superexcitability during the recovery cycle (controls-22.5±0.9, T2DM-17.5±0.8, T2DM-NN-17.3±1.6%,P<0.05). Linear regression analysis revealed no associations between changes in axonal function and either serum triglyceride or low density lipoprotein concentration when adjusted for renal function, a separate risk factor for neuropathy development. Our findings indicate that acutely, serum lipids do not exert an acute effect on axonal function in type 2 diabetic patients: TEd(10–20ms)(1.2(-1.4,3.8);P = 0.4) and superexcitability (2.4(-0.05, 4.8);P = 0.06).

Conclusions

These findings suggest that serum triglyceride levels are not related to axonal function in type 2 diabetic patients. Additional pathogenic mechanisms may play a more substantial role in axonal dysfunction prior to DPN development.

Antinociceptive effects of gentiopicroside on neuropathic pain induced by chronic constriction injury in mice: a behavioral and electrophysiological study

Gentiopicroside (Gent) is promising as an important protective secoiridoid compound against pain. The present study was designed to investigate whether administration of Gent would alleviate the expression of nociceptive behaviors and whether it would cause the relevant electrophysiological changes in a chronic constriction injury (CCI) model of neuropathic pain in mice. Gent was administered from the seventh day after surgery for 8 consecutive days. Behavioral parameters and sciatic functional index were assessed immediately before surgery and on days 7, 8, 10, 12, and 14 post-CCI, and electrophysiological activities of sciatic nerve were recorded immediately after the behavioral test on the last day. The present study has shown that administration of Gent (at a dose of 50 and 100 mg/kg) increased behavioral parameters from day 8 compared with the CCI-NS group. Electrophysiological data indicated that CCI caused a significant reduction in nerve conduction velocities in the sciatic nerves and the amplitudes of compound action potential, while Gent at a dose of 50 or 100 mg/kg caused a significant recovery of electrophysiological changes induced by CCI. Our data indicated that Gent has antinociceptive effects on neuropathic pain induced by CCI.

Epidermal growth factor receptor-inhibition (EGFR-I) in the treatment of neuropathic pain

BACKGROUND

Neurobiological work has demonstrated that expression of mitogen-activated protein kinases (MAPK) is upregulated on neurones and glial cells after nerve damage. Furthermore, the epidermal growth factor receptor (EGFR) has been identified as having a key role in this process and subsequent interruption of this using EGFR-Inhibitors (EGFR-I), may improve neuropathic pain. The aim of this report was to explore if EGFR-I attenuated neuropathic pain in humans.

METHODS

A selection of patients with neuropathic pain were treated off-label with one of four EGFR-Is, approved for the treatment of cancer. All patients had chronic and severe neuropathic pain (as defined by diagnostic criteria). Pain intensity, interference with function, and adverse events were prospectively registered.

RESULTS

Twenty patients were treated. Eighteen patients experienced clinically significant pain relief after treatment with EGFR-I. Median observed pain reduction for all patients was 8.5 (IQR=5-9.5) points on a 0-10 numeric rating scale. Neuropathic pain spike duration and frequency also improved. Pain relief was most often achieved within 24 h and was more rapid in cases of i.v. than oral administration. All four EGFR-I that were tested were of equal efficacy. The duration of pain relief was consistent with the individual drugs' half-lives. No cases of drug-tolerance were observed. Side-effects were predominantly skin reactions. One grade 3 adverse event was registered. Median follow-up for responders was 7 months (Range 1-37).

CONCLUSIONS

EGFR-I improves neuropathic pain and this is in keeping with basic science work. Controlled clinical trials are now eagerly awaited to assess this further.

Pain and Poppies: The Good, the Bad, and the Ugly of Opioid Analgesics

Treating pain is one of the most difficult challenges in medicine and a key facet of disease management. The isolation of morphine by Friedrich Sertürner in 1804 added an essential pharmacological tool in the treatment of pain and spawned the discovery of a new class of drugs known collectively as opioid analgesics. Revered for their potent pain-relieving effects, even Morpheus the god of dreams could not have dreamt that his opium tincture would be both a gift and a burden to humankind. To date, morphine and other opioids remain essential analgesics for alleviating pain. However, their use is plagued by major side effects, such as analgesic tolerance (diminished pain-relieving effects), hyperalgesia (increased pain sensitivity), and drug dependence. This review highlights recent advances in understanding the key causes of these adverse effects and explores the effect of chronic pain on opioid reward.

SIGNIFICANCE STATEMENT

Chronic pain is pervasive and afflicts >100 million Americans. Treating pain in these individuals is notoriously difficult and often requires opioids, one of the most powerful and effective classes of drugs used for controlling pain. However, their use is plagued by major side effects, such as a loss of pain-relieving effects (analgesic tolerance), paradoxical pain (hyperalgesia), and addiction. Despite the potential side effects, opioids remain the pharmacological cornerstone of modern pain therapy. This review highlights recent breakthroughs in understanding the key causes of these adverse effects and explores the cellular control of opioid systems in reward and aversion. The findings will challenge traditional views of the good, the bad, and the ugly of opioids.

Selective repression of gene expression in neuropathic pain by the neuron-restrictive silencing factor/repressor element-1 silencing transcription (NRSF/REST)

Neuropathic pain often develops following nerve injury as a result of maladaptive changes that occur in the injured nerve and along the nociceptive pathways of the peripheral and central nervous systems. Multiple cellular and molecular mechanisms likely account for these changes; however, the exact nature of these mechanisms remain largely unknown. A growing number of studies suggest that alteration in gene expression is an important step in the progression from acute to chronic pain states and epigenetic regulation has been proposed to drive this change in gene expression. In this review, we discuss recent evidence that the DNA-binding protein neuron-restrictive silencing factor/repressor element-1 silencing transcription factor (NRSF/REST) is an important component in the development and maintenance of neuropathic pain through its role as a transcriptional regulator for a select subset of genes that it normally represses during development.

Modeling the predictive value of pain intensity on costs and resources utilization in patients with peripheral neuropathic pain

OBJECTIVE

The aim of the present analysis was to model the association and predictive value of pain intensity on cost and resource utilization in patients with chronic peripheral neuropathic pain (PNP) treated in routine clinical practice settings in Spain.

METHODS

We performed a secondary economic analysis based on data from a multicenter, observational, and prospective cost-of-illness study in patients with chronic PNP that is refractory to prior treatment. Pain intensity was measured using the Short-Form McGill Pain Questionnaire. Univariate and multivariate linear regression models were fitted to identify independent predictors of cost and health care/non-health care resource utilization.

RESULTS

A total of 1703 patients were included in the current analysis. Pain intensity was an independent predictor of total costs ([total costs]=35.6 [pain intensity]+214.5; coefficient of determination [R(2)]=0.19, P<0.001), direct costs ([direct costs]=10.8 [pain intensity]+257.7; R=0.06, P<0.001), and indirect costs ([indirect costs]=24.8 [pain intensity]-43.4; R(2)=0.20, P<0.001) related to chronic PNP in the univariate analysis. Pain intensity remains significantly associated with total costs, direct costs, and indirect costs after adjustment by other covariates in the multivariate analysis (P<0.001). None of the other variables considered in the multivariate analysis were predictors of resource utilization.

DISCUSSION

Pain intensity predicts the health care and non-health care resource utilization, and costs related to chronic PNP. Management of patients with drugs associated with a higher reduction of pain intensity may have a greater impact on the economic burden of that condition.

Chronic Pain and Cognitive Behavioral Therapy

Cognitive behavioral therapy (CBT) is often used to treat chronic pain; however, more information is needed about what are the most efficacious dose and delivery methods. The aims of this review were to determine (a) which CBT doses, delivery methods, strategies, and follow-up periods have been explored in recent intervention studies of individuals with chronic pain and (b) whether the outcomes described in the selected studies were consistent with recommendations by the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials. The CINAHL, EMBASE, PubMed, PsycInfo, and SCOPUS databases were searched for randomized controlled trials published from 2009 to 2015 testing CBT for adults with chronic pain. Thirty-five studies were included in this review. Results revealed that CBT reduced pain intensity in 43% of trials, the efficacy of online and in-person formats were comparable, and military veterans and individuals with cancer-related chronic pain were understudied.

Psychometric Validation of the Japanese Version of the Neuropathic Pain Symptom Inventory

OBJECTIVE

This study aimed to evaluate the validity and reliability of the Japanese version of the Neuropathic Pain Symptom Inventory (NPSI-J).

DESIGN

Cross-sectional study design.

SUBJECTS AND METHODS

The original Neuropathic Pain Symptom Inventory (NPSI) was translated into Japanese according to published guidelines. Subsequently, an observational study of 60 Japanese patients suffering from neuropathic pain was performed to evaluate the validity and reliability of the NPSI-J.

RESULTS

The NPSI-J exhibited a statistically significant correlation with pain intensity (Numerical Rating Scale). The Cronbach alpha value for Likert items was 0.86. Using the test-retest analysis method, the intraclass correlation coefficient between the two scores was 0.81. Factor analysis revealed that the main component of NPSI-J comprised three determinative factors.

CONCLUSIONS

The NPSI-J is a reliable and valid pain assessment tool.

Capsaicin 8% patch versus oral pregabalin in patients with peripheral neuropathic pain

BACKGROUND

Clinical trials have not yet compared the efficacy of capsaicin 8% patch with current standard therapy in peripheral neuropathic pain (PNP).

OBJECTIVES

Head-to-head efficacy and safety trial comparing the capsaicin patch with pregabalin in PNP.

METHODS

Open-label, randomized, multicentre, non-inferiority trial. Patients with PNP, aged 18-80 years, were randomly assigned to either the capsaicin 8% patch (n = 282) or an optimised dose of oral pregabalin (n = 277), and assessed for a ≥30% mean decrease in Numeric Pain Rating Scale (NPRS) score from baseline to Week 8. Secondary endpoints included optimal therapeutic effect (OTE), time-to-onset of pain relief and treatment satisfaction.

RESULTS

The capsaicin 8% patch was non-inferior to pregabalin in achievement of a ≥30% mean decrease in NPRS score from baseline to Week 8 (55.7% vs. 54.5%, respectively; Odds ratio: 1.03 [95% CI: 0.72, 1.50]). The proportion of patients achieving OTE at Week 8 was 52.1% for the capsaicin 8% patch versus 44.8% for pregabalin (difference: 7.3%; 95% CI: -0.9%, 15.6%). The median time-to-onset of pain relief was significantly shorter for capsaicin 8% patch versus pregabalin (7.5 vs. 36.0 days; Hazard ratio: 1.68 [95% CI: 1.35, 2.08]; p < 0.0001). Treatment satisfaction was also significantly greater with the capsaicin 8% patch versus pregabalin. TEAEs were mild-to-moderate in severity, and resulted in treatment discontinuation only with pregabalin (n = 24). Systemic adverse drug reactions ranged from 0 to 1.1% with capsaicin 8% patch and 2.5 to 18.4% with pregabalin.

CONCLUSIONS

The capsaicin 8% patch provided non-inferior pain relief to an optimized dose of pregabalin in PNP, with a faster onset of action, fewer systemic side effects and greater treatment satisfaction.

Selective melatonin MT2 receptor ligands relieve neuropathic pain through modulation of brainstem descending antinociceptive pathways

Neuropathic pain is an important public health problem for which only a few treatments are available. Preclinical studies show that melatonin (MLT), a neurohormone acting on MT1 and MT2 receptors, has analgesic properties, likely through MT2 receptors. Here, we determined the effects of the novel selective MLT MT2 receptor partial agonist N-{2-([3-bromophenyl]-4-fluorophenylamino)ethyl}acetamide (UCM924) in 2 neuropathic pain models in rats and examined its supraspinal mechanism of action. In rat L5-L6 spinal nerve ligation and spared nerve injury models, UCM924 (20-40 mg/kg, subcutaneously) produced a prolonged antinociceptive effect that is : (1) dose-dependent and blocked by the selective MT2 receptor antagonist 4-phenyl-2-propionamidotetralin, (2) superior to a high dose of MLT (150 mg/kg) and comparable with gabapentin (100 mg/kg), but (3) without noticeable motor coordination impairments in the rotarod test. Using double staining immunohistochemistry, we found that MT2 receptors are expressed by glutamatergic neurons in the rostral ventrolateral periaqueductal gray. Using in vivo electrophysiology combined with tail flick, we observed that microinjection of UCM924 into the ventrolateral periaqueductal gray decreased tail flick responses, depressed the firing activity of ON cells, and activated the firing of OFF cells; all effects were MT2 receptor-dependent. Altogether, these data demonstrate that selective MT2 receptor partial agonists have analgesic properties through modulation of brainstem descending antinociceptive pathways, and MT2 receptors may represent a novel target in the treatment of neuropathic pain.

Cross-cultural Adaptation and Linguistic Validation of the Korean Version of the Leeds Assessment of Neuropathic Symptoms and Signs Pain Scale

Distinction between neuropathic pain and nociceptive pain helps facilitate appropriate management of pain; however, diagnosis of neuropathic pain remains a challenge. The aim of this study was to develop a Korean version of the Leeds Assessment of Neuropathic Symptoms and Signs (LANSS) pain scale and assess its reliability and validity. The translation and cross-cultural adaptation of the original LANSS pain scale into Korean was established according to the published guidelines. The Korean version of the LANSS pain scale was applied to a total of 213 patients who were expertly diagnosed with neuropathic (n = 113) or nociceptive pain (n = 100). The Korean version of the scale had good reliability (Cronbach's α coefficient = 0.815, Guttman split-half coefficient = 0.800). The area under the receiver operating characteristic curve was 0.928 with a 95% confidence interval of 0.885-0.959 (P < 0.001), suggesting good discriminate value. With a cut-off score ≥ 12, sensitivity was 72.6%, specificity was 98.0%, and the positive and negative predictive values were 98% and 76%, respectively. The Korean version of the LANSS pain scale is a useful, reliable, and valid instrument for screening neuropathic pain from nociceptive pain.

Spinal cord oligodendrocyte-derived alarmin IL-33 mediates neuropathic pain

Neuropathic pain from injury to the peripheral and CNS represents a major health care issue. We have investigated the role of IL-33/IL-33 receptor (ST2) signaling in experimental models of neuropathic pain in mice. Chronic constriction injury (CCI) of the sciatic nerve induced IL-33 production in the spinal cord. IL-33/citrine reporter mice revealed that oligodendrocytes are the main cells expressing IL-33 within the spinal cord together with a minor expression by neurons, microglia. and astrocytes. CCI-induced mechanical hyperalgesia was reduced in IL-33R (ST2)(-/ -) mice compared with wild-type (WT) mice. Intrathecal treatment of WT mice with soluble IL-33 receptor (IL-33 decoy receptor) markedly reduced CCI-induced hyperalgesia. Consistent with these observations, intrathecal injection of IL-33 enhanced CCI hyperalgesia and induced hyperalgesia in naive mice. IL-33-mediated hyperalgesia during CCI was dependent on a reciprocal relationship with TNF-α and IL-1β. IL-33-induced hyperalgesia was markedly attenuated by inhibitors of PI3K, mammalian target of rapamycin, MAPKs (p38, ERK, and JNK), NF-κB, and also by the inhibitors of glial cells (microglia and astrocytes). Furthermore, targeting these signaling pathways and cells inhibited IL-33-induced TNF-α and IL-1β production in the spinal cord. Our study, therefore, reveals an important role of oligodendrocyte-derived IL-33 in neuropathic pain.

Possible involvement of TRPV1 and TRPV4 in nociceptive stimulation- induced nocifensive behavior and neuroendocrine response in mice

Members of the transient receptor potential (TRP) family of ion channels play important roles in inflammation and pain. Here, we showed that both TRPV1 and TRPV4 might contribute to biphasic nocifensive behavior and neuroendocrine response following a formalin test. We subcutaneously injected saline, formalin, or the TRPV4 agonist, 4α-phorbol 12,13-didecanoate (4α-PDD) into one hindpaw of wild-type (WT), TRPV1-deficient (Trpv1(-/-)), and TRPV4-deficient (Trpv4(-/-)) mice to investigate nocifensive behaviors (phase I [0-10 min] and phase II [10-60 min]) and Fos expression in the dorsal horn of the spinal cord and other brain regions related to pain, in the paraventricular nucleus (PVN), paraventricular nucleus of the thalamus, the medial habenular nucleus, the medial nucleus of the amygdala and capsular part of the central amygdala. Subcutaneous (s.c.) injection of formalin caused less nocifensive behavior in Trpv1(-/-) and Trpv4(-/-) mice than in WT mice during phase I. In phase II, however, formalin induced less nocifensive behavior only in the Trpv1(-/-) mice, but not in the Trpv4(-/-) mice, relative to WT mice. The number of Fos-like immunoreactive (LI) neurons in laminae I-II of the dorsal horn increased in all types of mice 90 min after s.c. injection of formalin; however, there was no difference in the other regions between saline- and formalin-treated mice. Furthermore, s.c. injection of 4α-PDD did not induce nociceptive behavior nor influence the number of Fos-LI neurons in the all above mentioned regions in any of the mice. These results suggest that TRPV4-mediated nociceptive information from the peripheral tissue excluding the spinal pathway might be involved the formalin behavioral response during phase I. Only TRPV1 might regulate the formalin behavioral response in peripheral neuron.

Burden of HIV-Related Neuropathic Pain in the United States

BACKGROUND

HIV-related neuropathic pain (HIV-NeP) is common; however, the burden of HIV-NeP is not well-understood.

METHODS

The cross-sectional study aimed to characterize the HIV-NeP burden. A total of 103 patients with HIV-NeP recruited during routine office visits completed a questionnaire to assess patient-reported outcomes, including pain severity, health status, sleep, mood, and lost productivity. Physicians completed a 6-month retrospective chart review.

RESULTS

The sample was predominantly male and not employed for pay. A majority (75.7%) of patients experienced moderate or severe pain. Pain interference, general health, physical health, and depression were worse among patients with more severe pain (all Ps < .006). Most (87.4%) patients were prescribed at least 1 medication for NeP. HIV-related neuropathic pain was associated with 36.1% work impairment. Adjusted annualized costs increased with increasing pain severity (P < .0001).

CONCLUSION

The impact of HIV-NeP on health status, physical function, and depression increases with severity, resulting in substantial clinical and economic burden.

Topical analgesics for neuropathic pain in the elderly: current and future prospects

Neuropathic pain (NeP) is a significant medical and socioeconomic burden with limited therapeutic options. Elderly patients exhibit a higher incidence of several NeP conditions and pose a particular challenge due to age-related pharmacokinetic and pharmacodynamic issues, comorbid conditions, and polypharmacy, as well as frailty and cognitive decline. Topical analgesics are of interest because of their comparable efficacy to oral agents, good tolerability and safety, and potential to be add-on therapies to oral treatments. In recent years, two topical formulations for NeP have been approved (5% lidocaine medicated plaster, 8% capsaicin patch) but are not available in all countries. There are controlled trials and a growing body of open-label reports on their use in clinical care. Some studies provide a post hoc analysis of data in relation to older age (≥65 years), which is useful. The body of evidence relating to topical investigational agents is growing and involves controlled trials as well as individual cases. The largest single body of information is for topical ketamine, administered either alone or combined with other agents (particularly amitriptyline), and some large randomized controlled trials report efficacy. Other large trials involve topical clonidine and further ketamine combinations. Compounding analgesics involves challenges, including uncertain composition (two to five ingredients are used) and concentrations (range 0.5-5%), as well as the heterogeneity of data that support choices. Nevertheless, case reports and acceptable response rates in larger cohorts are intriguing, and this area merits further investigation in controlled settings as well as continued documentation of clinical experiences.

Association between extracellular signal-regulated kinase expression and the anti-allodynic effect in rats with spared nerve injury by applying immediate pulsed radiofrequency

BACKGROUND

The application of pulsed radiofrequency (PRF) close to the dorsal root ganglia, or peripheral nerves, has been demonstrated to be effective for the treatment of chronic neuropathic pain conditions. The goal of this study was to investigate the analgesic effect of immediate PRF treatment after nerve injury and its possible cellular alterations in the dorsal horn of the spinal cord in rats with spared nerve injury (SNI).

METHODS

Neuropathic pain was achieved in a SNI neuropathic pain model by ligating and cutting the common peroneal and tibial branches of the left sciatic nerve, leaving the sural nerve intact. Wistar rats were divided into four groups that received different treatments, i.e., SNI and PRF for 6 min at 45 V (SNI + PRF-45 V), at 60 V (SNI + PRF-60 V), SNI alone, and sham groups. After the SNI surgery, each rat was immediately given the PRF treatment (500 kHz, rate of 2 Hz, 20 ms duration, temperature below 42 °C) on the left sciatic nerve 0.3-0.4 cm proximal to the injured site. The behavioral measurements included mechanical allodynia and cold allodynia of the ipsilateral hind paw and were performed during the 28 days that followed the SNI surgery and PRF treatment. Total extracellular signal-regulated kinase 1 and 2 (ERK1/2) and phospho-ERK1/2 were measured using Western blot in the ipsilateral spinal cord from animals in the different groups.

RESULTS

The three groups of rats with nerve injuries manifested a lower paw withdrawal threshold (PWT) in the behavioral measurement of mechanical allodynia and a shorter painful-behavior duration in the cold allodynia test over 28 days. Mechanical allodynia measurement showed that both the PRF-45 V and PRF-60 V treatment groups exhibited a more prominent antiallodynic effect than did the SNI group from days 1 to 28 after surgery. Similarly, in comparison with the SNI group, both the SNI + PRF-45 V and SNI + PRF-60 V groups had significant inhibition on the cold allodynia measurement from days 1 to 28 after surgery. Furthermore, the activation of the extracellular signal-regulated kinase 1 and 2 (ERK1/2) in the ipsilateral spinal dorsal horn of SNI rats was effectively inhibited in the SNI + PRF-45 V and SNI + PRF-60 V groups for 28 days after surgery.

CONCLUSIONS

Immediate PRF application on the proximal nerve injury site provided a significant inhibition of neuropathic pain formation, accompanied by the inhibition of ERK activation.

Behavior of neuropathic pain in mice following chronic constriction injury comparing silk and catgut ligatures

Introduction

Neuropathic pain is defined as pain arising as a direct consequence of a lesion or disease affecting the somatosensory system and is common after surgery. Neuropathic pain can persist without an obvious injury. In this study we aim to validate a murine chronic constriction injury model as a model for neuropathic pain research and determine if silk or catgut ligatures induced most stable neuropathic pain behavior.

Methods

In this study mice underwent chronic constriction or sham surgery. Mice were tested on cutaneous hyperalgesia with the cumulative reaction time in the acetone test, on allodynia with the cumulative reaction time and number of lifts in the cold plate test and the maximal force before withdrawal in von Frey test.

Results

In the acetone test neuropathic pain was seen in CCI mice, but not in sham mice. Hyperalgesia was present postoperatively in CCI mice compared with preoperatively. In the cold plate test cumulative reaction time and number of lifts were higher in the ipsilateral hind paw than in the contralateral hind paw and sham mice. Postoperative measurements were higher than preoperatively. In the von Frey test the postoperative measurements were lower in the ipsilateral hind paw than preoperatively, while the contralateral hind paw showed an increase in maximal force before withdrawal. The contralateral hind paw showed more difference with sham mice than the ipsilateral hind paw. Silk ligatures showed more stable neuropathic pain behavior. In the acetone test, the cold plate test and the von Frey test the mice scored higher on neuropathic pain having silk ligatures, compared with catgut ligatures.

Conclusion

In this study we validated a murine CCI model for neuropathic pain behavior. In the murine CCI model it appears that silk ligatures demonstrate more stable neuropathic pain behaviors than catgut ligatures in de CCI model.

Electronic supplementary material

The online version of this article (doi:10.1186/s40064-015-1009-4) contains supplementary material, which is available to authorized users.

Therapy using implanted organic bioelectronics

Many drugs provide their therapeutic action only at specific sites in the body, but are administered in ways that cause the drug's spread throughout the organism. This can lead to serious side effects. Local delivery from an implanted device may avoid these issues, especially if the delivery rate can be tuned according to the need of the patient. We turned to electronically and ionically conducting polymers to design a device that could be implanted and used for local electrically controlled delivery of therapeutics. The conducting polymers in our device allow electronic pulses to be transduced into biological signals, in the form of ionic and molecular fluxes, which provide a way of interfacing biology with electronics. Devices based on conducting polymers and polyelectrolytes have been demonstrated in controlled substance delivery to neural tissue, biosensing, and neural recording and stimulation. While providing proof of principle of bioelectronic integration, such demonstrations have been performed in vitro or in anesthetized animals. Here, we demonstrate the efficacy of an implantable organic electronic delivery device for the treatment of neuropathic pain in an animal model. Devices were implanted onto the spinal cord of rats, and 2 days after implantation, local delivery of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) was initiated. Highly localized delivery resulted in a significant decrease in pain response with low dosage and no observable side effects. This demonstration of organic bioelectronics-based therapy in awake animals illustrates a viable alternative to existing pain treatments, paving the way for future implantable bioelectronic therapeutics.

Protective Effect of Ethanol Extracts of Hericium erinaceus on Alloxan-Induced Diabetic Neuropathic Pain in Rats

We investigated the effects of Hericium erinaceus (HEE) on alloxan induced diabetic neuropathic pain in laboratory rats. Alloxan induced diabetic rats were administered orally HEE. After 6 weeks of treatments, treatment with HEE 40 mg/kg in diabetic animals showed significant increase in pain threshold and paw withdrawal threshold and significant decrease in serum glucose and urine glucose. We also observed a significant increase in lactate dehydrogenase (LDH), Lipid peroxidation (LPO), glutathione peroxidase (GPx) activity, glutathione reductase (GR) activity, catalase (CAT) activity, Na⁺K⁺ATPase activity, and glutathione S transferase (GST) activity along with significant decreased levels of glutathione (GSH) content in diabetic rats. The total antioxidant status (TAOS) in the HEE-treated groups was significantly lower than that in the alloxan-treated group. HEE can offer pain relief in diabetic neuropathic pain. The improvement in diabetic state after HEE treatment along with the antioxidant activity could be the probable way by which it had alleviated diabetic neuropathy.

Double-blind, placebo-controlled study of HGF gene therapy in diabetic neuropathy

OBJECTIVE

To evaluate the safety and efficacy of a plasmid (VM202) containing two human hepatocyte growth factor isoforms given by intramuscular injections in patients with painful diabetic neuropathy.

METHODS

In a double-blind, placebo-controlled study, patients were randomized to receive injections of 8 or 16 mg VM202 per leg or placebo. Divided doses were administered on Day 0 and Day 14. The prospective primary outcome was change in the mean pain score measured by a 7 day pain diary. Secondary outcomes included a responder analysis, quality of life and pain measures, and intraepidermal nerve fiber density.

RESULTS

There were no significant adverse events attributable to VM202. Eighty-four patients completed the study. Patients receiving 8 mg VM202 per leg improved the most in all efficacy measures including a significant (P = 0.03) reduction at 3 months in the mean pain score and continued but not statistically significant reductions in pain at 6 and 9 months. Of these patients, 48.4% experienced a ≥50% reduction in pain compared to 17.6% of placebo patients. There were also significant improvements in the brief pain inventory for patients with diabetic peripheral neuropathy and the questionnaire portion of the Michigan Neuropathy Screening Instrument. Patients not on pregabalin or gabapentin had the largest reductions in pain.

INTERPRETATION

VM202 was safe, well tolerated and effective indicating the feasibility of a nonviral gene therapy approach to painful diabetic neuropathy. Two days of treatment were sufficient to provide symptomatic relief with improvement in quality of life for 3 months. VM202 may be particularly beneficial for patients not taking gabapentin or pregabalin.

From guideline to patient: a review of recent recommendations for pharmacotherapy of painful diabetic neuropathy

Painful diabetic peripheral neuropathy (DPN) is a common complication of diabetes mellitus, affecting, by some estimates, up to one quarter of diabetic patients. Since 2010, no fewer than 5 major international treatment guidelines for painful DPN have been issued, and there are meaningful differences among them. Duloxetine, pregabalin, gabapentin, and tricyclic antidepressants are the mainstays of treatment, but the choice of which class or agent to use in any given patient should be informed by patient characteristics. This review seeks to describe the differences among the recently issued guidelines, to assess the evidence on which they are based, and to offer insight into the most appropriate treatment choices based on patient characteristics.