Persistent postsurgical pain: evidence from breast cancer surgery, groin hernia repair, and lung cancer surgery

New, long-term opioid use after lung cancer surgery is associated with reduced 2-year survival: a retrospective population-based cohort study in South Korea

INTRODUCTION

We aimed to investigate the proportion and associated factors for new long-term opioid use and its long-term effects after lung cancer surgery.

METHODS

The South Korean National Health Insurance Database was used as a nationwide registration data source. All patients undergoing lung cancer surgery between 2011 and 2018 were included, and patients who were preoperative opioid users were excluded from the analysis. New long-term opioid use was defined as an active opioid prescription at 6 months postoperatively.

RESULTS

In total, 54 509 patients were included in the final analysis. At 6 months postoperatively, 3325 (6.1%) patients who were newly prescribed opioids comprised the new long-term opioid user group. Older age, male sex, wider surgical extent, open thoracotomy, increased Charlson Comorbidity Index score, neoadjuvant or adjuvant chemotherapy, preoperative anxiety disorder and insomnia disorder were associated with a higher rate of new long-term opioid use. The new long-term opioid user group showed a 40% (HR, 1.40; 95% CI 1.29 to 1.53; p<0.001) higher risk of 2-year all-cause mortality. Moreover, the new long-term potent opioid user and less potent opioid user groups showed a 92% (HR, 1.92; 95% CI 1.67 to 2.21; p<0.001) and 22% (HR, 1.22; 95% CI 1.10 to 1.36; p<0.001) higher risk of 2-year all-cause mortality, respectively.

CONCLUSIONS

Among preoperative opioid-naive patients in South Korea, 6.1% became new long-term opioid users after lung cancer surgery. Certain factors are potential risk factors for new long-term opioid use, which could be associated with poorer long-term survival outcomes.

[Nociception monitoring : Method for intraoperative opioid control?]

The intraoperative dosing of opioids is a challenge in routine anesthesia as the potential effects of intraoperative overdosing and underdosing are not completely understood. In recent years an increasing number of monitors were approved, which were developed for the detection of intraoperative nociception and therefore should enable a better control of opioid titration. The nociception monitoring devices use either continuous hemodynamic, galvanic or thermal biosignals reflecting the balance between parasympathetic and sympathetic activity, measure the pupil dilatation reflex or the nociceptive flexor reflex as a reflexive response to application of standardized nociceptive stimulation. This review article presents the currently available nociception monitors. Most of these monitoring devices detect nociceptive stimulations with higher sensitivity and specificity than changes in heart rate, blood pressure or sedation depth monitoring devices. There are only few studies on the effect of opioid titration guided by nociception monitoring and the possible postoperative benefits of these devices. All nociception monitoring techniques are subject to specific limitations either due to perioperative confounders (e.g. hypovolemia) or special accompanying medical conditions (e.g. muscle relaxation). There is an ongoing discussion about the clinical relevance of nociceptive stimulation in general anesthesia and the effect on patient outcome. Initial results for individual monitor systems show a reduction in opioid consumption and in postoperative pain level. Nevertheless, current evidence does not enable the routine use of nociception monitoring devices to be recommended as a clear beneficial effect on long-term outcome has not yet been proven.

Depression and Anxiety Are Associated With Increased Health Care Costs and Opioid Use for Patients With Femoroacetabular Impingement Undergoing Hip Arthroscopy: Analysis of a Claims Database

PURPOSE

To determine if opioid use and health care costs in the year before and following hip arthroscopy for femoroacetabular impingement (FAI) differ between those with or without depression or anxiety.

METHODS

Using the Truven Health Marketscan database, FAI patients who underwent hip arthroscopy between October 2010 and December 2015 were identified (Current Procedural Terminology codes 29914 [femoroplasty], 29915 [acetabuloplasty], and/or 29916 [labral repair]). Patients were excluded if they had incomplete coverage for 1 year either before or following surgery. The number of patients with 1 or more claims related to depression or anxiety during the year before surgery was quantified (International Statistical Classification Diseases and Related Health-9 codes 296, 298, 300, 309, 311). Health care costs in the year before and following hip arthroscopy were compared between those with or without depression or anxiety. We also compared the number of patients in each group who filled a narcotic pain prescription within 180 days before surgery as well as >60 or >90 days after hip arthroscopy.

RESULTS

Depression or anxiety claims were seen in 5,208/14,830 patients (35.1%) before surgery. A significantly greater proportion of those with preoperative depression or anxiety filled opioid-related prescriptions in the 6 months before surgery (36.2% vs 25.6%, P < .0001) and both >60 days (31.3% vs 24.7%, P < .0001) and >90 days after surgery (29.5% vs 23.4%, P < .0001). The group with preoperative depression or anxiety had significantly greater health care costs both before ($8,775 vs $5,674, P < .0001) and following surgery ($5,287 vs $3,908, P < .0001).

CONCLUSIONS

Both before and following hip arthroscopy, opioid use and health care costs were significantly greater for FAI patients with comorbid depression or anxiety.

LEVEL OF EVIDENCE

Level III, retrospective comparative therapeutic study.

Quality of life, pain, and psychological factors in patients undergoing surgery for primary tumors of the spine

PURPOSE

Knowledge about quality of life (QOL), pain, and psychological factors in patients with primary tumors of the spine is limited, but is important in planning rehabilitation after surgery. Aims of this study were to assess the preoperative levels and improvement after surgery of these factors, and to identify the predictors of postoperative pain and QOL.

METHODS

Patients with primary tumors undergoing spine surgery were matched for sex and age with patients with metastatic tumors. QOL was measured at baseline and three months after surgery with the physical (PCS) and mental (MCS) components SF-12 subscales, pain intensity with a numeric rating scale (NRS), depression with the Beck Depression Inventory (BDI). Preoperative SF-12, NRS, and BDI levels and differences in follow-up improvement in SF-12 and NRS were compared across samples. LASSO regressions were performed to find predictors of follow-up SF-12 and NRS.

RESULTS

Patients with primary tumors showed better PCS and NRS, and similar BDI and MCS than patients with metastatic tumors. At follow-up, they showed stronger improvement in the MCS and no improvement in the PCS. All QOL scores were below those of the general population. Follow-up PCS was predicted by baseline PCS and BDI; MCS by baseline MCS; pain intensity by baseline pain intensity and BDI.

CONCLUSION

Patients with primary tumors of the spine suffer from moderate levels of physical and mental impairment. Depression influences surgical outcomes.

Prediction of Acute Postoperative Pain from Assessment of Pain Associated With Venous Cannulation

BACKGROUND

It has previously been reported that venous cannulation-induced pain (VCP) can be used to predict acute postoperative pain after laparoscopic cholecystectomy. Patients rating VCP at ≥2.0 VAS units had 3.4 times higher risk for moderate or severe pain. The purpose of this study was to evaluate if VCP scores of ≥2.0 VAS units are associated with higher risk for acute postoperative pain after various common surgical procedures.

METHODS

In a prospective clinical observational study, 600 male and female 18- to 80-year-old patients scheduled for elective surgery were included. The primary outcome measure was the difference in maximum postoperative pain intensity between low responders (VCP < 2.0) and high responders (VCP ≥ 2.0) to VCP. Secondary outcome measures were the difference in proportion of patients with moderate or severe postoperative pain between low and high responders, and potential influence of age, gender, and preoperative habitual pain.

RESULTS

Patients scoring VCP ≥2.0 VAS units reported higher acute postoperative pain intensity levels than those scoring VCP <2.0 VAS units (median 3.0 [interquartile range 0.0 to 5.0] vs. 0.2 [interquartile range 0.0 to 4.0], P = 0.001), and also had 1.7 times higher risk for moderate or severe postoperative pain (P = 0.005). Moderate or severe postoperative pain was reported by 38% of patients with VCP scores of ≥2.0 VAS units and by 26% with VCP scores of <2.0 VAS units (P = 0.005).

CONCLUSION

Scoring of VCP intensity before surgery, requiring no specific equipment or training, is useful to predict individual risks for moderate or severe postoperative pain, regardless of patient age or gender, in a setting involving different kinds of surgery.

International guidelines for groin hernia management

INTRODUCTION

Worldwide, more than 20 million patients undergo groin hernia repair annually. The many different approaches, treatment indications and a significant array of techniques for groin hernia repair warrant guidelines to standardize care, minimize complications, and improve results. The main goal of these guidelines is to improve patient outcomes, specifically to decrease recurrence rates and reduce chronic pain, the most frequent problems following groin hernia repair. They have been endorsed by all five continental hernia societies, the International Endo Hernia Society and the European Association for Endoscopic Surgery.

METHODS

An expert group of international surgeons (the HerniaSurge Group) and one anesthesiologist pain expert was formed. The group consisted of members from all continents with specific experience in hernia-related research. Care was taken to include surgeons who perform different types of repair and had preferably performed research on groin hernia surgery. During the Group's first meeting, evidence-based medicine (EBM) training occurred and 166 key questions (KQ) were formulated. EBM rules were followed in complete literature searches (including a complete search by The Dutch Cochrane database) to January 1, 2015 and to July 1, 2015 for level 1 publications. The articles were scored by teams of two or three according to Oxford, SIGN and Grade methodologies. During five 2-day meetings, results were discussed with the working group members leading to 136 statements and 88 recommendations. Recommendations were graded as "strong" (recommendations) or "weak" (suggestions) and by consensus in some cases upgraded. In the Results and summary section below, the term "should" refers to a recommendation. The AGREE II instrument was used to validate the guidelines. An external review was performed by three international experts. They recommended the guidelines with high scores. The risk factors for inguinal hernia (IH) include: family history, previous contra-lateral hernia, male gender, age, abnormal collagen metabolism, prostatectomy, and low body mass index. Peri-operative risk factors for recurrence include poor surgical techniques, low surgical volumes, surgical inexperience and local anesthesia. These should be considered when treating IH patients. IH diagnosis can be confirmed by physical examination alone in the vast majority of patients with appropriate signs and symptoms. Rarely, ultrasound is necessary. Less commonly still, a dynamic MRI or CT scan or herniography may be needed. The EHS classification system is suggested to stratify IH patients for tailored treatment, research and audit. Symptomatic groin hernias should be treated surgically. Asymptomatic or minimally symptomatic male IH patients may be managed with "watchful waiting" since their risk of hernia-related emergencies is low. The majority of these individuals will eventually require surgery; therefore, surgical risks and the watchful waiting strategy should be discussed with patients. Surgical treatment should be tailored to the surgeon's expertise, patient- and hernia-related characteristics and local/national resources. Furthermore, patient health-related, life style and social factors should all influence the shared decision-making process leading up to hernia management. Mesh repair is recommended as first choice, either by an open procedure or a laparo-endoscopic repair technique. One standard repair technique for all groin hernias does not exist. It is recommended that surgeons/surgical services provide both anterior and posterior approach options. Lichtenstein and laparo-endoscopic repair are best evaluated. Many other techniques need further evaluation. Provided that resources and expertise are available, laparo-endoscopic techniques have faster recovery times, lower chronic pain risk and are cost effective. There is discussion concerning laparo-endoscopic management of potential bilateral hernias (occult hernia issue). After patient consent, during TAPP, the contra-lateral side should be inspected. This is not suggested during unilateral TEP repair. After appropriate discussions with patients concerning results tissue repair (first choice is the Shouldice technique) can be offered. Day surgery is recommended for the majority of groin hernia repair provided aftercare is organized. Surgeons should be aware of the intrinsic characteristics of the meshes they use. Use of so-called low-weight mesh may have slight short-term benefits like reduced postoperative pain and shorter convalescence, but are not associated with better longer-term outcomes like recurrence and chronic pain. Mesh selection on weight alone is not recommended. The incidence of erosion seems higher with plug versus flat mesh. It is suggested not to use plug repair techniques. The use of other implants to replace the standard flat mesh in the Lichtenstein technique is currently not recommended. In almost all cases, mesh fixation in TEP is unnecessary. In both TEP and TAPP it is recommended to fix mesh in M3 hernias (large medial) to reduce recurrence risk. Antibiotic prophylaxis in average-risk patients in low-risk environments is not recommended in open surgery. In laparo-endoscopic repair it is never recommended. Local anesthesia in open repair has many advantages, and its use is recommended provided the surgeon is experienced in this technique. General anesthesia is suggested over regional in patients aged 65 and older as it might be associated with fewer complications like myocardial infarction, pneumonia and thromboembolism. Perioperative field blocks and/or subfascial/subcutaneous infiltrations are recommended in all cases of open repair. Patients are recommended to resume normal activities without restrictions as soon as they feel comfortable. Provided expertise is available, it is suggested that women with groin hernias undergo laparo-endoscopic repair in order to decrease the risk of chronic pain and avoid missing a femoral hernia. Watchful waiting is suggested in pregnant women as groin swelling most often consists of self-limited round ligament varicosities. Timely mesh repair by a laparo-endoscopic approach is suggested for femoral hernias provided expertise is available. All complications of groin hernia management are discussed in an extensive chapter on the topic. Overall, the incidence of clinically significant chronic pain is in the 10-12% range, decreasing over time. Debilitating chronic pain affecting normal daily activities or work ranges from 0.5 to 6%. Chronic postoperative inguinal pain (CPIP) is defined as bothersome moderate pain impacting daily activities lasting at least 3 months postoperatively and decreasing over time. CPIP risk factors include: young age, female gender, high preoperative pain, early high postoperative pain, recurrent hernia and open repair. For CPIP the focus should be on nerve recognition in open surgery and, in selected cases, prophylactic pragmatic nerve resection (planned resection is not suggested). It is suggested that CPIP management be performed by multi-disciplinary teams. It is also suggested that CPIP be managed by a combination of pharmacological and interventional measures and, if this is unsuccessful, followed by, in selected cases (triple) neurectomy and (in selected cases) mesh removal. For recurrent hernia after anterior repair, posterior repair is recommended. If recurrence occurs after a posterior repair, an anterior repair is recommended. After a failed anterior and posterior approach, management by a specialist hernia surgeon is recommended. Risk factors for hernia incarceration/strangulation include: female gender, femoral hernia and a history of hospitalization related to groin hernia. It is suggested that treatment of emergencies be tailored according to patient- and hernia-related factors, local expertise and resources. Learning curves vary between different techniques. Probably about 100 supervised laparo-endoscopic repairs are needed to achieve the same results as open mesh surgery like Lichtenstein. It is suggested that case load per surgeon is more important than center volume. It is recommended that minimum requirements be developed to certify individuals as expert hernia surgeon. The same is true for the designation "Hernia Center". From a cost-effectiveness perspective, day-case laparoscopic IH repair with minimal use of disposables is recommended. The development and implementation of national groin hernia registries in every country (or region, in the case of small country populations) is suggested. They should include patient follow-up data and account for local healthcare structures. A dissemination and implementation plan of the guidelines will be developed by global (HerniaSurge), regional (international societies) and local (national chapters) initiatives through internet websites, social media and smartphone apps. An overarching plan to improve access to safe IH surgery in low-resource settings (LRSs) is needed. It is suggested that this plan contains simple guidelines and a sustainability strategy, independent of international aid. It is suggested that in LRSs the focus be on performing high-volume Lichtenstein repair under local anesthesia using low-cost mesh. Three chapters discuss future research, guidelines for general practitioners and guidelines for patients.

CONCLUSIONS

The HerniaSurge Group has developed these extensive and inclusive guidelines for the management of adult groin hernia patients. It is hoped that they will lead to better outcomes for groin hernia patients wherever they live. More knowledge, better training, national audit and specialization in groin hernia management will standardize care for these patients, lead to more effective and efficient healthcare and provide direction for future research.

Membrane protein Nav1.7 contributes to the persistent post-surgical pain regulated by p-p65 in dorsal root ganglion (DRG) of SMIR rats model

Background

Persistent post-surgical pain is a difficult clinical problem. In this study, we intend to explore the mechanism underlying the persistent post-surgical pain in SMIR (skin/muscle incision and retraction) rats.

Methods

First of all, the expression of membrane protein Nav1.7 and p-p65 (Phosphorylation of p65) were detected in ipsilateral L4–6 DRGs of SMIR rats by western-blot and immunostaining. Then with ProTx-II (Nav1.7 blocker) or PDTC (p65 inhibitor) were intrathecally injected while the change of Nav1.7 expression and mechanical withdrawal threshold were detected. Finally chromatin immunoprecipitation assay method was used to detect whether could p-p65 bind in the Nav1.7 gene promoter region directly.

Results

The results shows that mechanical hyperalgesia occurs following SMIR model, from 5 day (d) and lasted more than 20d after surgery. Meanwhile, the expression of Nav1.7 was up-regulated at 10d, 15d and 20d after surgery compared with naïve group. The expression of p-p65 was up-regulated at 10d and 15d compared with incision group. The mechanical hyperalgesia induced by SMIR was reversed after blocking Nav1.7 or inhibiting p65. Furthermore, Nav1.7 expression was down-regulated when p-p65 was inhibited and p-p65 could combine with the Nav1.7 gene promoter region directly.

Conclusion

Membrane protein Nav1.7 could participate in the peripheral sensitization of persistent post-surgical pain, which may be regulated by p-p65.

Patient-Reported Symptom Interference as a Measure of Postsurgery Functional Recovery in Lung Cancer

CONTEXT

Few empirical studies have combined the patient's perspective (patient-reported outcomes [PROs]) with clinical outcomes (risk for complications, length of hospital stay, return to planned treatment) to assess the effectiveness of treatment after thoracic surgery for early-stage non-small cell lung cancer (NSCLC).

OBJECTIVES

Quantitatively measure PROs to assess functional recovery postsurgery.

METHODS

Treatment-naïve patients (N = 72) with NSCLC who underwent either open thoracotomy or video-assisted thoracoscopic surgery (VATS) used the MD Anderson Symptom Inventory (MDASI) to report symptom interference with general activity, work, walking, mood, relations with others, and enjoyment of life for three months after surgery. Functional recovery was defined as interference scores returning to presurgery levels. The MDASI's sensitivity to change in functional recovery over time was evaluated via its ability to distinguish between surgical techniques.

RESULTS

Interference scores increased sharply by Day 3 after surgery (all P < 0.001), then returned to baseline levels via different trajectories. Patients who had unscheduled clinic visits during the study period reported higher scores on all six MDASI interference items (all P < 0.05). Compared with the open-thoracotomy group, the VATS group returned more quickly to baseline interference levels for walking (18 vs. 43 days), mood (8 vs. 19 days), relations with others (4 vs. 16 days), and enjoyment of life (15 vs. 41 days) (all P < 0.05).

CONCLUSION

Repeated measurement of MDASI interference characterized functional recovery after thoracic surgery for NSCLC and was sensitive to VATS' ability to enhance postoperative recovery. Further study of the clinical applicability of measuring recovery outcomes using PRO-based functional assessment is warranted.

Effects of target-controlled infusion of high-dose naloxone on pain and hyperalgesia in a human thermal injury model: a study protocol: A randomized, double-blind, placebo-controlled, crossover trial with an enriched design

Mu-opioid-receptor antagonists have been extensively studied in experimental research as pharmacological tools uncovering mechanisms of pain modulation by the endogenous opioid system. In rodents, administration of high doses of mu-opioid-receptor antagonists after the resolution of an inflammatory injury has demonstrated reinstatement of nociceptive hypersensitivity indicating unmasking of latent sensitization. In a recent human study, pain hypersensitivity assessed as secondary hyperalgesia area (SHA), was reinstated 7 days after a mild thermal injury, in 4 out of 12 subjects after a naloxone infusion.The aims of the present study are first, to replicate our previous findings in a larger-sized study; second, to examine if high sensitizers (subjects presenting with large SHA after a thermal injury) develop a higher degree of hypersensitivity after naloxone challenge than low sensitizers (subjects presenting with restricted SHA after a thermal injury); and third to examine a dose-response relationship between 3 stable naloxone concentrations controlled by target-controlled infusion, and the unmasking of latent sensitization.Healthy participants (n = 80) underwent a screening day (day 0) with induction of a thermal skin injury (47°C, 420 seconds, 12.5 cm). Assessment of SHA was performed 1 and 2 hours after the injury. Using an enriched design, only participants belonging to the upper quartile of SHA (Q4, high sensitizers; n = 20) and the lower quartile of SHA (Q1, low sensitizers; n = 20) continued the study, comprising 4 consecutive days-days 1 to 4. Thermal skin injuries were repeated on day 1 and day 3, whereas day 2 and day 4 (7 days after day 1 and day 3, respectively) were target-controlled infusion days in which the subjects were randomly allocated to receive either naloxone (3.25 mg/kg, 4 mg/mL) or placebo (normal saline) intravenous. The primary outcome was SHA assessed by weighted-pin instrument (128 mN) 0, 1, 2, and 165 to 169 hours after the thermal injury (day 1-4). The secondary outcomes were pin-prick pain thresholds assessed by weighted-pin instrument (8-512 mN) at primary and secondary hyperalgesia areas (days 1-4).The naloxone-induced unmasking of latent sensitization is an interesting model for exploring the transition from acute to chronic pain. The results from the present study may provide valuable information regarding future research in persistent postsurgical pain states.

A retrospective study of open thoracotomies versus thoracoscopic surgeries for persistent postthoracotomy pain

OBJECTIVE

Persistent thoracotomy pain syndrome (PTPS) is a recognized complication and is considered to be less after video-assisted thoracoscopic surgery (VATS) compared with open thoracic surgery (OTS). The primary objective was to compare the incidence of PTPS at 6 months. Secondary objectives were to compare the incidence of neuropathic pain between VATS and OTS and to report perioperative factors associated with the development of PTPS.

METHODS

This historical cohort study involved patient contact by a questionnaire regarding the presence of PTPS and its type. Patient, surgical, and analgesia factors were collected from health records, acute pain, and thoracic surgery databases. The data were analyzed using a multivariable logistic regression analysis, with results reported as adjusted odds ratio (OR) (95% confidence interval; P value).

RESULTS

Of 308 patients, 130 returned their questionnaire, and 106 responses were analyzed. The incidence of PTPS was 35% and 54% with VATS and OTS respectively, with an adjusted OR, 0.33 (95% confidence interval, 0.13-0.86), P= .024. The percentage of neuropathic pain was 18% and 48%, with VATS and OTS respectively, with an adjusted OR, 0.18 (0.04-0.85), P= .031. The diagnosis of cancer and previous chronic pain history were observed to be significantly associated with PTPS.

CONCLUSIONS

Our study indicates that PTPS is significantly more common and has a higher chance of being neuropathic with OTS. Despite being relatively less traumatic, VATS still carries a significant potential for PTPS. A diagnosis of cancer and history of previous pain are highly predictive of its development.

Tools for the assessment of the recovery process following discharge from day surgery: a literature review

This literature review provides an overview of ten studies which assessed the patient's general recovery after discharge from hospital following elective surgery and anaesthesia. Ten multi-dimensional tools were identified and these included six common domain assessments: pain, physiological function, activities of daily living (ADL), emotions, nausea/vomiting and nutrition/elimination. Most of the tools assessed the recovery process by using patient-subjective reported outcomes on visual analogue (VAS) or pre-graded scales.

Protease-activated receptor 2 activation is sufficient to induce the transition to a chronic pain state

Protease-activated receptor type 2 (PAR2) is known to play an important role in inflammatory, visceral, and cancer-evoked pain based on studies using PAR2 knockout (PAR2(-/-)) mice. We have tested the hypothesis that specific activation of PAR2 is sufficient to induce a chronic pain state through extracellular signal-regulated kinase (ERK) signaling to protein synthesis machinery. We have further tested whether the maintenance of this chronic pain state involves a brain-derived neurotrophic factor (BDNF)/tropomyosin-related kinase B (trkB)/atypical protein kinase C (aPKC) signaling axis. We observed that intraplantar injection of the novel highly specific PAR2 agonist, 2-aminothiazol-4-yl-LIGRL-NH2 (2-at), evokes a long-lasting acute mechanical hypersensitivity (median effective dose ∼12 pmoles), facial grimacing, and causes robust hyperalgesic priming as revealed by a subsequent mechanical hypersensitivity and facial grimacing to prostaglandin E2 (PGE2) injection. The promechanical hypersensitivity effect of 2-at is completely absent in PAR2(-/-) mice as is hyperalgesic priming. Intraplantar injection of the upstream ERK inhibitor, U0126, and the eukaryotic initiation factor (eIF) 4F complex inhibitor, 4EGI-1, prevented the development of acute mechanical hypersensitivity and hyperalgesic priming after 2-at injection. Systemic injection of the trkB antagonist ANA-12 similarly inhibited PAR2-mediated mechanical hypersensitivity, grimacing, and hyperalgesic priming. Inhibition of aPKC (intrathecal delivery of ZIP) or trkB (systemic administration of ANA-12) after the resolution of 2-at-induced mechanical hypersensitivity reversed the maintenance of hyperalgesic priming. Hence, PAR2 activation is sufficient to induce neuronal plasticity leading to a chronic pain state, the maintenance of which is dependent on a BDNF/trkB/aPKC signaling axis.

Effect of a high-dose target-controlled naloxone infusion on pain and hyperalgesia in patients following groin hernia repair: study protocol for a randomized controlled trial

Background

Central sensitization is modulated by the endogenous opioid system and plays a major role in the development and maintenance of pain. Recent animal studies performed following resolution of inflammatory pain showed reinstatement of tactile hypersensitivity induced by administration of a mu-opioid-antagonist, suggesting latent sensitization is mediated by endogenous opioids. In a recent crossover study in healthy volunteers, following resolution of a first-degree burn, 4 out of 12 volunteers developed large secondary areas of hyperalgesia areas after a naloxone infusion, while no volunteer developed significant secondary hyperalgesia after the placebo infusion. In order to consistently demonstrate latent sensitization in humans, a pain model inducing deep tissue inflammation, as used in animal studies, might be necessary. The aim of the present study is to examine whether a high-dose target-controlled naloxone infusion can reinstate pain and hyperalgesia following recovery from open groin hernia repair and thus consistently demonstrate opioid-mediated latent sensitization in humans.

Methods/Design

Patients submitted to unilateral, primary, open groin hernia repair will be included in this randomized, placebo-controlled, double-blind, crossover study. The experimental days take place 6–8 weeks after surgery, time-points at which patients are expected to be almost pain- free. Prior to administration of naloxone or placebo, the primary outcome (a summated measure of pain: at rest, during transition from supine to standing position, and evoked by pressure algometry) and the secondary outcomes (secondary hyperalgesia/allodynia, pressure pain thresholds, assessed at the surgical site and at the mirror-site in the contralateral groin, and, opioid withdrawal symptoms) will be assessed. These assessments will be repeated at each step of the target-controlled infusion of placebo or naloxone at estimated median (95 % CI) plasma concentrations of 344 ng/ml (130;567), 1059 ng/ml (400;1752) and 3196 ng/ml (1205;5276).

Discussion

We aim to demonstrate opioid-mediated latent sensitization in a post-surgical setting, using pain as a clinical relevant variable. Impairment of the protective endogenous opioid system may play an important role in the transition from acute to chronic pain. In order to sufficiently block the endogenous opioid system, a high-dose target-controlled naloxone-infusion is used, in accordance with recent findings in animal studies.

Trial registration number

EUDRACT: 2015-000793-36 (Registration date: 16 February 2015)

Clinicaltrials.gov: NCT01992146 (Registration date: 12 December 2014)

Lost but making progress--Where will new analgesic drugs come from?

There is a critical need for effective new pharmacotherapies for pain. The paucity of new drugs successfully reaching the clinic calls for a reassessment of current analgesic drug discovery approaches. Many points early in the discovery process present significant hurdles, making it critical to exploit advances in pain neurobiology to increase the probability of success. In this review, we highlight approaches that are being pursued vigorously by the pain community for drug discovery, including innovative preclinical pain models, insights from genetics, mechanistic phenotyping of pain patients, development of biomarkers, and emerging insights into chronic pain as a disorder of both the periphery and the brain. Collaborative efforts between pharmaceutical, academic, and public entities to advance research in these areas promise to de-risk potential targets, stimulate investment, and speed evaluation and development of better pain therapies.

Persistent breast pain following breast cancer surgery is associated with persistent sensory changes, pain interference, and functional impairments

Interindividual variability exists in persistent breast pain following breast cancer surgery. Recently, we used growth mixture modeling to identify 3 subgroups of women (N = 398) with distinct persistent breast pain trajectories (ie, mild, moderate, severe) over 6 months following surgery. The purposes of this study were to identify demographic and clinical characteristics that differed among the breast pain classes and, using linear mixed effects modeling, to examine how changes over time and in sensitivity in the breast scar area, pain qualities, pain interference, and hand and arm function differed among these classes. Several demographic and clinical characteristics differentiated the breast pain classes. Of note, 60 to 80% of breast scar sites tested were much less sensitive than the unaffected breast. Significant group effects were observed for pain qualities and interference scores, such that, on average, women in the severe pain class reported higher scores than women in the moderate pain class. In addition, women in the moderate pain class reported higher scores than women in the mild pain class. Compared to women in the mild pain class, women in the severe pain class had significantly impaired grip strength, and women in the moderate and severe pain classes had impaired flexion and abduction.

PERSPECTIVE

Subgroups of women with persistent postsurgical breast pain differed primarily with respect to the severity rather than the nature or underlying mechanisms of breast pain. Pervasive sensory loss and the association between persistent breast pain and sustained interference with function suggest the need for long-term clinical follow-up.