Quantitative somatosensory assessments in patients with persistent pain following groin hernia repair: A systematic review with a meta-analytical approach.

OBJECTIVES: Quantitative sensory testing (QST) provides an assessment of cutaneous and deep tissue sensitivity and pain perception under normal and pathological settings. Approximately 2-4% of individuals undergoing groin hernia repair (GHR) develop severe persistent postsurgical pain (PPSP). The aims of this systematic review of PPSP-patients were (1) to retrieve and methodologically characterize the available QST literature and (2) to explore the role of QST in understanding mechanisms underlying PPSP following GHR. METHODS: A systematic literature search was conducted from JAN-1992 to SEP-2022 in PubMed, EMBASE, and Google Scholar. For inclusion, studies had to report at least one QST-modality in patients with PPSP. Risk of bias assessment of the studies was conducted utilizing the Newcastle Ottawa Scale and Cochrane's Risk of Bias assessment tool 2.0. The review provided both a qualitative and quantitative analysis of the results. A random effects model was used for meta-analysis. RESULTS: Twenty-five studies were included (5 randomized controlled trials, 20 non-randomized controlled trials). Overall, risk of bias was low. Compared with the contralateral side or controls, there were significant alterations in somatosensory function of the surgical site in PPSP-patients. Following thresholds were significantly increased: mechanical detection thresholds for punctate stimuli (mean difference (95% CI) 3.3 (1.6, 6.9) mN (P = 0.002)), warmth detection thresholds (3.2 (1.6, 4.7) °C (P = 0.0001)), cool detection thresholds (-3.2 (-4.9, -1.6) °C (P = 0.0001)), and heat pain thresholds (1.9 (1.1, 2.7) °C (P = 0.00001)). However, the pressure pain thresholds were significantly decreased (-76 (-123, -30) kPa (P = 0.001)). CONCLUSION: Our review demonstrates a plethora of methods used regarding outcome assessments, data processing, and data interpretation. From a pathophysiological perspective, the most consistent findings were postsurgical cutaneous deafferentation and development of a pain generator in deeper connective tissues. TRIAL REGISTRATION: CRD42022331750.

Somatosensory Outcomes Following Re-Surgery in Persistent Severe Pain After Groin Hernia Repair: A Prospective Observational Study.

Purpose: After groin hernia repair (globally more than 20 million/year) 2-4% will develop persistent severe pain (PSPG). Pain management is challenging and may require multimodal interventions, including re-surgery. Quantitative somatosensory testing (QST) is an investigational psychophysiological tool with the potential to uncover the pathophysiological mechanisms behind the pain, ie, revealing neuropathic or inflammatory components. The primary objective was to examine and describe the underlying pathophysiological changes in the groin areas by QST before and after re-surgery with mesh removal and selective neurectomy. Patients and Methods: Sixty patients with PSPG scheduled for re-surgery and with an inflammatory "component" indicated by blunt pressure algometry were examined in median (95% CI) 7.9 (5.8-11.5) months before and 4.0 (3.5-4.6) months after re-surgery. The QST-analyses included standardized assessments of cutaneous mechanical/thermal detection and pain thresholds. Suprathreshold heat stimuli were applied. Deep tissue sensitivity was tested by pressure algometry. Testing sites were the groin areas and the lower arm. Before/after QST data were z-transformed. Results: Re-surgery resulted in median changes in rest, average, and maximal pain intensity scores of -2.0, -2.5, and -2.0 NRS (0/10) units, respectively (P = 0.0001), and proportional increases in various standardized functional scores (P = 0.0001). Compared with the control sites, the cutaneous somatosensory detection thresholds of the painful groin were increased before re-surgery and increased further after re-surgery (median difference: 1.28 z-values; P = 0.001), indicating a successive post-surgical loss of nerve fiber function ("deafferentation"). Pressure algometry thresholds increased after re-surgery (median difference: 0.30 z-values; P = 0.001). Conclusion: In this subset of patients with PSPG who underwent re-surgery, the procedure was associated with improved pain and functional outcomes. While the increase in somatosensory detection thresholds mirrors the surgery-induced cutaneous deafferentation, the increase in pressure algometry thresholds mirrors the removal of the deep "pain generator". The QST-analyses are useful adjuncts in mechanism-based somatosensory research.

Analgesic efficacy of sleep-promoting pharmacotherapy in patients with chronic pain: a systematic review and meta-analysis.

Dysregulation of sleep heightens pain sensitivity and may contribute to pain chronification. Interventions which consolidate and lengthen sleep have the potential to improve pain control. The main objective of this systematic review was to examine the effects of sleep-promoting pharmacotherapy on pain intensity in patients with chronic pain. Multiple electronic databases were searched from inception to January 2022 to identify relevant randomized controlled trials (RCTs). Two independent reviewers screened titles, abstracts, and full-text articles; extracted data; and assessed risk of bias for each included study. The GRADE approach was used to determine the strength of evidence. The search identified 624 articles. After full-text screening, 10 RCTs (n = 574 randomized participants) involving 3 pharmacologic interventions (melatonin, zopiclone, and eszopiclone) and 7 different chronic pain populations were included. Minimum clinically significant pain reduction ≥30% was reported in 4 studies. There is low-quality evidence (downgraded due to inconsistency and imprecision) that 2 to 8 weeks treatment with a sleep-promoting medication alone or in combination with an analgesic (6 trials, n = 397) decreases pain intensity compared with placebo or the same analgesic treatment alone (SMD -0.58 [95% confidence interval -1.00, -0.17], P = 0.006). Analyses of associations between changes in sleep and pain outcomes were only provided in 2 articles, with inconsistent findings. Notably, pain-relieving effects were most consistent in melatonin trials. Only 3 studies implemented polysomnography to obtain objective sleep measures. Low-quality evidence indicates that pharmacologic sleep promotion may decrease pain intensity in chronic pain populations. More research is needed to fully understand the influence of sleep-targeting interventions on pain control.

Low-dose naltrexone for treatment of pain in patients with fibromyalgia: a randomized, double-blind, placebo-controlled, crossover study.

Introduction: Fibromyalgia (FM) is a chronic fluctuating, nociplastic pain condition. Naltrexone is a µ-opioid-receptor antagonist; preliminary studies have indicated a pain-relieving effect of low-dose naltrexone (LDN) in patients with FM. The impetus for studying LDN is the assumption of analgesic efficacy and thus reduction of adverse effects seen from conventional pharmacotherapy. Objectives: First, to examine if LDN is associated with analgesic efficacy compared with control in the treatment of patients with FM. Second, to ascertain the analgesic efficacy of LDN in an experimental pain model in patients with FM evaluating the competence of the descending inhibitory pathways compared with controls. Third, to examine the pharmacokinetics of LDN. Methods: The study used a randomized, double-blind, placebo-controlled, crossover design and had a 3-phase setup. The first phase included baseline assessment and a treatment period (days -3 to 21), the second phase a washout period (days 22-32), and the third phase a baseline assessment followed by a treatment period (days 33-56). Treatment was with either LDN 4.5 mg or an inactive placebo given orally once daily. The primary outcomes were Fibromyalgia Impact Questionnaire revised (FIQR) scores and summed pain intensity ratings (SPIR). Results: Fifty-eight patients with FM were randomized. The median difference (IQR) for FIQR scores between LDN and placebo treatment was -1.65 (18.55; effect size = 0.15; P = 0.3). The median difference for SPIR scores was -0.33 (6.33; effect size = 0.13; P = 0.4). Conclusion: Outcome data did not indicate any clinically relevant analgesic efficacy of the LDN treatment in patients with FM.

Detailed statistical analysis plan for the neurological complications in endoscopic versus open radial artery harvest (NEO) randomised clinical trial.

INTRODUCTION: Coronary artery bypass grafting can be conducted using the radial artery as a bypass graft. However, it remains unclear which harvesting method is superior, i.e. endoscopic or open radial artery, and which site for proximal anastomosis of the radial artery has the greatest benefits? METHODS: The NEO Trial is a single site randomised clinical trial with a 2 × 2 factorial design. The first comparison assesses endoscopic versus open radial artery harvest with a primary outcome of hand function and secondary outcomes of neurological deficits through clinical exams and neurophysiological studies. The primary outcome is postoperatively hand function at three months. We anticipate a mean difference of 3 points with a standard deviation of 8 points, a power of 90%, and a type I error of 5%, resulting in a required sample size of 300 participants randomised 1:1. Secondary outcomes are neurological deficits (based on nerve conduction measurements, algometry test and von Frey hair test), clinical neurological examination of cutaneous sensibility, and registration of complications in the donor arm (haematoma formation, wound dehiscence, and/or infection). The second comparison assesses two different proximal anastomotic sites, i.e. aorto-radial anastomosis versus mammario-radial anastomosis. The primary outcome is a composite of cerebrovascular events and the secondary outcome is graft patency evaluation by multi-slice computer tomography-scan. These outcomes will be assessed at 1 year postoperatively, and the results of this comparison will be exploratory only. Both comparisons will be analysed using intention-to-treat and intervention groups will be compared using linear regression, logistic regression, or Mann-Whitney U test depending on data type. Two independent statisticians will follow the present plan and conduct the analyses which will hereafter be fused into a final analysis based on consensus. CONCLUSION: This detailed analysis plan will increase the validity of the NEO trial results by predefining the statistical analysis in detail. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT01848886 . Registered 25 February 2013. Danish Ethics committee number: H-3-2012-116. Danish Data Protection Agency: 2007-58-0015/jr. n:30-0838.

The Harald Breivik lecture 2022. Pathophysiology in persistent severe pain after groin hernia repair.

The transition from a healthy to a persistent severe pain state following otherwise successful elective surgery is a feared complication. Groin hernia repair, previously considered minor surgery, is a standard surgical procedure annually performed on 2,000 individuals per one million residents. A trajectory into persistent severe pain is, unfortunately, seen in 2-4%, severely impeding physical and psychosocial daily functions.

Trajectories in severe persistent pain after groin hernia repair: a retrospective analysis.

OBJECTIVES: Severe persistent post-surgical pain (PPSP) remains a significant healthcare problem. In the third most common surgical procedure in the U.K., groin hernia repair, including 85,000 surgeries, estimated 1,500-3,000 patients will annually develop severe PPSP. While the trajectory of PPSP is generally considered a continuation of the acute post-surgery pain, recent data suggest the condition may develop with a delayed onset. This study evaluated pain-trajectories in a consecutive cohort referred from groin hernia repair-surgeons to a tertiary PPSP-center. Potential explanatory variables based on individual psychometric, sensory, and surgical profiles were analyzed. METHODS: Patients completed graphs on pain trajectories and questionnaires on neuropathic pain, pain-related functional assessments, and psychometrics. Surgical records and quantitative sensory testing profiles were obtained. Pain trajectories were normalized, and pre- and post-surgical segments were analyzed by a normalized area-under-the-curve (AUC) technique. Principal component analysis (PCA) was applied to the explanatory variables. Significant PCA-components were further examined using multiple logistic regression models. RESULTS: In 95 patients, the AUC identified groups of post-surgical pain trajectories (p<0.0001): group I (n=48), acute high-intensity pain progressing to PPSP; group II (n=28), delayed onset of PPSP; group III (n=7), repeat-surgery gradually inducing PPSP. Data from groups IV (n=3) and V (n=9) were not included in the statistical analysis due to small sample size and data heterogeneity, respectively. The PCA/logistic analyses indicated that neuropathic pain scores, composite pain scores, and pain-related functional assessments were explanatory variables for groups I and II. CONCLUSIONS: Pain trajectories in PPSP after groin hernia repair are heterogeneous but can be classified into meaningful groups. Examination of pain trajectories, mirroring the transition from acute to severe persistent post-surgical pain, has the potential of uncovering clinically relevant pathophysiological mechanisms.

Neuroplasticity induced by general anaesthesia: study protocol for a randomised cross-over clinical trial exploring the effects of sevoflurane and propofol on the brain - A 3-T magnetic resonance imaging study of healthy volunteers.

BACKGROUND: Although used extensively worldwide, the effects of general anaesthesia on the human brain remain largely elusive. Moreover, general anaesthesia may contribute to serious conditions or adverse events such as postoperative cognitive dysfunction and delirium. To understand the basic mechanisms of general anaesthesia, this project aims to study and compare possible de novo neuroplastic changes induced by two commonly used types of general anaesthesia, i.e. inhalation anaesthesia by sevoflurane and intravenously administered anaesthesia by propofol. In addition, we wish to to explore possible associations between neuroplastic changes, neuropsychological adverse effects and subjective changes in fatigue and well-being. METHODS: This is a randomised, participant- and assessor-blinded, cross-over clinical trial. Thirty healthy volunteers (male:female ratio 1:1) will be randomised to general anaesthesia by either sevoflurane or propofol. Multimodal magnetic resonance imaging (MRI) of the brain will be performed before and after general anaesthesia and repeated after 1 and 8 days. Each magnetic resonance imaging session will be accompanied by cognitive testing and questionnaires on fatigue and well-being. After a wash-out period of 4 weeks, the volunteers will receive the other type of anaesthetic (sevoflurane or propofol), followed by the same series of tests. Primary outcomes: changes in T1-weighted 3D anatomy and diffusion tensor imaging. SECONDARY OUTCOMES: changes in resting-state functional magnetic resonance imaging, fatigue, well-being, cognitive function, correlations between magnetic resonance imaging findings and the clinical outcomes (questionnaires and cognitive function). Exploratory outcomes: changes in cerebral perfusion and oxygen metabolism, lactate, and response to visual stimuli. DISCUSSION: To the best of our knowledge, this is the most extensive and advanced series of studies with head-to-head comparison of two widely used methods for general anaesthesia. Recruitment was initiated in September 2019. TRIAL REGISTRATION: Approved by the Research Ethics Committee in the Capital Region of Denmark, ref. H-18028925 (6 September 2018). EudraCT and Danish Medicines Agency: 2018-001252-35 (23 March 2018). www.clinicaltrials.gov , ID: NCT04125121 . Retrospectively registered on 10 October 2019.

A single session of hyperbaric oxygen therapy demonstrates acute and long-lasting neuroplasticity effects in humans: a replicated, randomized controlled clinical trial.

PURPOSE: Animal studies have demonstrated anti-inflammatory, and anti-nociceptive properties of hyperbaric oxygen therapy (HBOT). However, physiological data are scarce in humans. In a recent experimental study, the authors used the burn injury (BI) model observing a decrease in secondary hyperalgesia areas (SHA) in the HBOT-group compared to a control-group. Surprisingly, a long-lasting neuroplasticity effect mitigating the BI-induced SHA-response was seen in the HBOT-preconditioned group. The objective of the present study, therefore, was to confirm our previous findings using an examiner-blinded, block-randomized, controlled, crossover study design. PATIENTS AND METHODS: Nineteen healthy subjects attended two BI-sessions with an inter-session interval of ≥28 days. The BIs were induced on the lower legs by a contact thermode (12.5 cm2, 47C°, 420 s). The subjects were block-randomized to receive HBOT (2.4 ATA, 100% O2, 90 min) or ambient conditions ([AC]; 1 ATA, 21% O2), dividing cohorts equally into two sequence allocations: HBOT-AC or AC-HBOT. All sensory assessments performed during baseline, BI, and post-intervention phases were at homologous time points irrespective of sequence allocation. The primary outcome was SHA, comparing interventions and sequence allocations. RESULTS: Data are mean (95% CI). During HBOT-sessions a mitigating effect on SHA was demonstrated compared to AC-sessions, ie, 18.8 (10.5-27.0) cm2 vs 32.0 (20.1-43.9) cm2 (P=0.021), respectively. In subjects allocated to the sequence AC-HBOT a significantly larger mean difference in SHA in the AC-session vs the HBOT-session was seen 25.0 (5.4-44.7) cm2 (P=0.019). In subjects allocated to the reverse sequence, HBOT-AC, no difference in SHA between sessions was observed (P=0.55), confirming a preconditioning, long-lasting (≥28 days) effect of HBOT. CONCLUSION: Our data demonstrate that a single HBOT-session compared to control is associated with both acute and long-lasting mitigating effects on BI-induced SHA, confirming central anti-inflammatory, neuroplasticity effects of hyperbaric oxygen therapy.

A national center for persistent severe pain after groin hernia repair: Five-year prospective data.

Severe persistent pain after groin hernia repair impairs quality-of-life. Prospective, consecutive cohort study including patients with pain-related impairment of physical and social life. Relevant surgical records were obtained, and examinations were by standardized clinical and neurophysiological tests. Patients demonstrating pain sensitivity to pressure algometry in the operated groin underwent re-surgery, while patients with neuropathic pain received pharmacotherapy. Questionnaires at baseline (Q0) and at the 5-year time point (Q5Y) were used in outcome analyses of pain intensity (numeric rating scale [NRS] 0-10) and pain-related effect on the activity-of-daily-living (Activities Assessment Scale [AAS]). Data are mean (95% CI).Analyses were made in 172/204 (84%) eligible patients. In 54/172 (31%) patients re-surgery (meshectomy/selective neurectomy) was performed, while the remaining 118/172 (69%) patients received pharmacotherapy. In the re-surgery group, activity-related, and average NRS-scores at Q0 were 6.6 (5.6-7.9) and 5.9 (5.6-5.9), respectively. Correspondingly, NRS-scores at Q5Y was 4.1 (3.3-5.1) and 3.1 (2.3-4.0; Q0 vs. Q5Y: P < .0005), respectively. Although both groups experienced a significant improvement in AAS-scores comparing Q0 vs. Q5Y (re-surgery group: 28% (4-43%; P < .0001); pharmacotherapy group: 5% (0-11%; P = .005)) the improvement was significantly larger in the re-surgery group (P = .02).This 5-year cohort study in patients with severe persistent pain after groin hernia repair signals that selection to re-surgery or pharmacotherapy, based on examination of pain sensitivity, is associated with significant improvement in outcome. Analyzing composite endpoints, combining pain and physical function, are novel in exploring interventional effects.ClinicalTrials.gov Identifier NCT03713047.

Bilateral distribution of anterior cutaneous nerve entrapment syndrome (ACNES): are clinical features and outcomes comparable to unilateral ACNES?

BACKGROUND AND OBJECTIVES: Mirror-image pain may occur in the presence of a one-sided peripheral nerve lesion leading to a similar distribution of pain on the contralateral side of the body ("mirrored"). Anterior cutaneous nerve entrapment syndrome (ACNES) is a neuropathic pain syndrome due to entrapment of terminal branches of intercostal nerves T7-12 in the abdominal wall and sometimes presents bilaterally. This study aims to address specifics of bilateral ACNES and to determine potential differences in clinical presentation and treatment outcomes when compared with the unilateral form of ACNES. METHODS: Electronic patient files and questionnaires of a case series of patients who were evaluated for chronic abdominal wall pain in a single center were analyzed using standard statistical methods. RESULTS: Between June 1, 2011 and September 1, 2016, 1116 patients were diagnosed with ACNES, of which a total of 146 (13%) with bilateral ACNES were identified (female, n = 114, 78 %; median (range) age 36 (1181) years). Average NRS (Numeric Rating Scale; 0-10) scores were similar (median (range) NRS scores 6 (0-10) although peak NRS scores were significantly higher in the bilateral group (9 (5-10) vs 8 (2-10); p=0.02). After a median of 26 months (1-68), the proportion of patients with bilateral ACNES reporting treatment success was 61%. CONCLUSIONS: One in eight patients with ACNES has bilateral abdominal wall pain. Characteristics are similar to unilateral ACNES cases. Further studies aimed at underlying mechanisms in mirror image pain pathogenesis could provide a more targeted approach in the management of this neuropathic pain.

Simultaneous quantification of high-dose naloxone and naloxone-3-ß-d-glucuronide in human plasma by UHPLC-MS/MS.

Aim: High-dose administration of the µ-opioid receptor inverse agonist naloxone (NX), has previously been demonstrated to reinstate nocifensive behavior in the late phase of inflammatory injuries. However, no current analytical methods can provide pharmacokinetic insight into the pharmacodynamic response of high-dose administration of NX. Materials & methods: Based on protein precipitation using 50 µl human plasma, NX and naloxone-ß-d-glucuronide (NXG) was analysed by UHPLC-MS/MS with 6 min cycle time. Results: A method for quantification of high-dose administered NX and NXG was developed and validated with intra- and interday precision and accuracy within ≤8.5% relative standard deviation (RSD) and -1.2-5.5% relative error (RE) for NX and ≤9.6% RSD and 0.6-6.5% RE for NXG. The method show excellent internal standard corrected matrix effects. Conclusion: A rapid UHPLC-MS/MS method was developed for quantification of NX and NXG in human plasma within 10-4000 ng/ml.

Aδ and not C fibers mediate thermal hyperalgesia to short laser stimuli after burn injury in man.

It remains unclear which nerve fibers are responsible for mediating hyperalgesia after skin injury. Here, we examined the role of Aδ and C fibers in inflammatory hyperalgesia after a first-degree burn injury. A CO2 laser delivered ultrafast short constant-temperature heat pulses to the upper part of the lower leg to stimulate selectively the relatively fast-conducting thinly myelinated Aδ and the slowly conducting unmyelinated C fibers. Participants were asked to respond as fast as possible whenever they detected a thermal stimulus. Thresholds and reaction times to selective Aδ and C fiber activations were measured in the conditioned and the surrounding intact skin, at pre-injury, and 1 hour and 24 hours after injury. First-degree burn injury caused a significant decrease in Aδ fiber detection thresholds and a significant increase in the proportion of Aδ-fiber-mediated responses in the inflamed area 24 hours, but not 1 hour, after burn injury. No changes in heat perception were observed in the intact skin surrounding the injury. No group differences in C-fiber-mediated sensations were observed. Our findings indicate that quickly adapting Aδ fibers but not quickly adapting C fibers are sensitized when activated by short and ultrafast heat stimuli after skin burn injury. Our results further show that this change occurs between 1 hour and 24 hours after injury and that it does not extend to the skin surrounding the injury.