Descending inhibitory pain modulation is impaired in patients with chronic pancreatitis

Somatosensory profiling to differentiate distinct painful diseases of the pancreas-a quantitative sensory testing case-control study

ABSTRACT

Mechanisms of pancreatic pain are insufficiently understood, and quantitative sensory testing (QST) may help to identify the underlying mechanisms. Accordingly, this study assessed comprehensive somatosensory profiles encompassing nociceptive and nonnociceptive parameters in 70 patients with distinct pancreatic diseases, namely acute (n = 23), chronic (n = 20), or autoimmune pancreatitis (n = 10) and pancreatic cancer (n = 17) and compared it with 30 healthy control subjects by standardized QST (protocol of the German research network on neuropathic pain). Patients with pancreatic diseases presented significant somatosensory deficits in all thermal and tactile detection and pain thresholds in the pancreatic viscerotome (Th10), when compared with a remote control area (dermatome C5) or reference data of matched healthy controls (P < 0.05-P < 0.0001). Unaltered vibration detection emphasizes the strictly regional character of losses. Loss of sensitivity paralleled the occurrence of paradoxical heat sensation (Th10 vs C5; P < 0.05), an indicator of thermal integration deficit. Punctate hyperalgesia or pain to light touch, the hallmark signs of spinal central sensitization were mostly absent and pain summation remained unchanged (P > 0.05). Stratification of patients revealed that somatosensory deficits were significantly more pronounced in acute compared with chronic pancreatitis (eg, cold and warm detection thresholds: -2.19 ± 1.42 vs -1.10 ± 1.23 and -1.30 ± 1.68 vs -0.11 ± 1.80 z-values; P < 0.05 each). Notably, blunt pressure hyperalgesia, the only somatosensory parameter exhibiting significant gain compared with the patients' remote C5 segment, was a frequent finding only in acute, but not in chronic pancreatitis. The somatosensory phenotype of patients with distinct pancreatic disorders was characterized by a wide array of sensory losses being most severe in acute pancreatitis.

16. Pain in chronic pancreatitis

INTRODUCTION

Chronic pancreatitis is defined as a disease of the pancreas in which recurrent inflammatory episodes result in replacement of the pancreatic parenchyma by fibrous connective tissue in individuals with genetic, environmental, and other risk factors. Pain is one of the most important symptoms of chronic pancreatitis and, in many cases, has chronic visceral nociceptive, nociplastic, and even neuropathic components, with evidence of both central and peripheral sensitization, neuroplasticity, and neurogenic inflammation.

METHODS

The literature on the diagnosis and treatment of pain in chronic pancreatitis was reviewed and summarized.

RESULTS

Treatment of abdominal pain in chronic pancreatitis is guided by pancreatic morphology on imaging, although the correlation between pain symptoms and pathoanatomical changes is not always straightforward. Patients with pancreatic duct obstruction are initially offered endoscopic or surgical therapies, while non-obstructive disease is mostly managed medically. Lifestyle changes and psychological support are of particular importance for all chronic pancreatitis patients. Analgesic options range from non-opioid medications to opioids and adjuvant agents. Interventional pain management may consist of radiofrequency treatment of the splanchnic nerves and spinal cord stimulation. To date, there are no randomized trials supporting their efficacy in the treatment of chronic pancreatitis pain, and the recommendation to consider these treatment options is justified by evidence from observational studies. Possible opioid-sparing effects of interventional pain treatments are important to consider because opioid use and dependency are common in chronic pancreatitis patients and associated with worse outcomes. Celiac plexus block is not generally recommended for chronic pancreatitis due to the limited quality of evidence, overall short duration of effect, and invasiveness of the procedure. Central sensitization can impact the effectiveness of invasive treatments.

CONCLUSIONS

Managing pain in chronic pancreatitis is a complex task that requires a multidimensional and individualized approach. Due to the lack of randomized trials, treatment decisions are often guided by expert opinion. Integrating pharmacological and non-pharmacological interventions and collaborating with a multidisciplinary team are key components of effective chronic pancreatitis pain management.

Pathophysiology, Assessment, and Management of Pain Associated with Chronic Pancreatitis

Chronic pancreatitis (CP) is a fibroinflammatory disease, with pain as its most prominent symptom. This article provides a comprehensive review of the pathophysiology, assessment methodologies, and management strategies pertaining to pain in CP. Pathophysiological mechanisms include inflammatory and neuropathic components, including peripheral and central sensitization. Pain assessment can include unidimensional and multidimensional pain assessment scales, neurophysiological assessments, and advanced imaging techniques. Management strategies include a spectrum from lifestyle modifications, pharmacologic interventions, and interventional procedures to neuromodulatory techniques and other experimental treatments.

Individualized Pain Treatment in Chronic Pancreatitis (INPAIN): An International, Multicenter, Investigator-Initiated, Prospective, Cohort Study

OBJECTIVES

Pain is the foremost complication of chronic pancreatitis (CP), affecting about 70% of patients. However, the pathophysiological understanding and management of CP-related pain are complex, likely as patients have diverse "pain phenotypes" responding differently to treatment. This study aims to develop a bedside test panel to identify distinct pain phenotypes, investigate the temporal evolution, and determine whether they can be used to predict treatment response.

METHODS

The INPAIN study is an international, multicenter, observational, longitudinal cohort study consisted of 4 substudies. The studies will prospectively enroll 400 CP patients (50 without pain and 350 with pain) and 50 control subjects, conducting biannual observations for 4 years. The test panel is consisted of comprehensive subjective and objective assessment parameters. Statistical analysis strategies differ across the substudies. A model to predict treatment efficacy will be developed using various machine learning techniques, including an artificial intelligence approach, with internal cross-validation. Trajectories in pain parameters will be characterized by graphical analysis and mixed effect models.

DISCUSSION

The INPAIN study aims to comprehensively understand pain in CP through a test panel developed for routine clinical use. This tool has the potential to personalize treatments, improve clinical practice, enhance patient care, improve quality of life, and minimize treatment side effects.

The mechanism of transcutaneous gastric pacing treatment on gastrointestinal motility recovery and inflammation improvement in early-stage acute pancreatitis patients

PURPOSE

Acute pancreatitis (AP) is often accompanied by gastrointestinal motility disorders. The purpose of this study was to investigate the efficacy and possible mechanism of transcutaneous gastric pacing (TGP) in early-stage AP patients.

MATERIALS AND METHODS

Sixty-five AP patients were randomly divided into conventional treatment group and TGP group. The serum ghrelin and vasoactive intestinal peptide (VIP) were used to assess the possible gastrointestinal hormonal mechanism involved. The parameters of electrogastrogram (EGG) were used to evaluate the gastric motility in AP patients. The first defecation time was used to assess the recovery of intestinal motility. The heart rate variability (HRV) test was performed to assess autonomic nervous function.

RESULTS

Compared with the conventional treatment group, the TGP treatment significantly improved symptoms in early AP patients, and shortened the first defecation time (p < 0.05) and the hospital days (p < 0.05). The level of VIP (P < 0.05) was also decreased in TGP group. The percentage of normal gastric slow waves (GSWS) (p < 0.05) was increased. The interleukin (IL)-6 level was decreased (P < 0.05). Concurrently, the vagal activity (HF) was increased (p < 0.01), the sympathetic activity (LF) was decreased (p < 0.01), and the ratio of sympathetic vagal (LF/HF) was decreased (p < 0.01).

CONCLUSIONS

The TGP treatment significantly improves the clinical symptoms in early AP patients. It also increases the percentage of normal GSWS. The therapeutic effect of TGP may be caused by autonomic nervous function mechanisms.

Delayed-Onset Muscle Soreness Alters Mechanical Sensitivity, but Not Thermal Sensitivity or Pain Modulatory Function

Introduction

Many clinical musculoskeletal pain conditions are characterized by chronic inflammation that sensitizes nociceptors. An unresolved issue is whether inflammation affects all nociceptors in a similar manner. Exercise-induced muscle damage (EIMD) has been proposed as a model for simulating clinical inflammatory pain in healthy samples. We sought to test the effect of EIMD on various painful stimuli (pressure and thermal), central pain processing (via the nociceptive flexion reflex) and endogenous pain modulation via conditioned pain modulation and exercise-induced hypoalgesia.

Methods

Eighteen participants (9F, age: 24.6 ± 3.3) were recruited for repeated measures testing and each completed pain sensitivity testing prior to and 48 hours after an eccentric exercise protocol. The participants performed a minimum of 6 rounds of 10 eccentric knee extension exercises to induce muscle damage and localized inflammation in the right quadriceps. Force decrements, knee range-of-motion, and delayed onset muscle soreness (DOMS) were used to quantify EIMD.

Results

There was a significant main effect of time for pressure pain (%diff; -58.9 ± 23.1; p = 0.02, ηp2 = 0.28) but no significant main effect was observed for limb (%diff; -15.5 ± 23.9; p = 0.53, ηp2 = 0.02). In contrast, there was a significant interaction between time and limb (p < 0.001, ηp2 = 0.47) whereby participants had lower pressure pain sensitivity in the right leg only after the damage protocol (%diff; -105.9 ± 29.2; p = 0.002).

Discussion

Individuals with chronic inflammatory pain usually have an increased sensitivity to pressure, thermal, and electrical stimuli, however, our sample, following muscle damage to induce acute inflammation only had sensitivity to mechanical pain. Exercise induced inflammation may reflect a peripheral sensitivity localized to the damaged muscle rather than a global sensitivity like those with chronic pain display.

Sensory phenotypes in complex regional pain syndrome and chronic low back pain-indication of common underlying pathomechanisms

Introduction

First-line pain treatment is unsatisfactory in more than 50% of chronic pain patients, likely because of the heterogeneity of mechanisms underlying pain chronification.

Objectives

This cross-sectional study aimed to better understand pathomechanisms across different chronic pain cohorts, regardless of their diagnoses, by identifying distinct sensory phenotypes through a cluster analysis.

Methods

We recruited 81 chronic pain patients and 63 age-matched and sex-matched healthy controls (HC). Two distinct chronic pain cohorts were recruited, ie, complex regional pain syndrome (N = 20) and low back pain (N = 61). Quantitative sensory testing (QST) was performed in the most painful body area to investigate somatosensory changes related to clinical pain. Furthermore, QST was conducted in a pain-free area to identify remote sensory alterations, indicating more widespread changes in somatosensory processing.

Results

Two clusters were identified based on the QST measures in the painful area, which did not represent the 2 distinct pain diagnoses but contained patients from both cohorts. Cluster 1 showed increased pain sensitivities in the painful and control area, indicating central sensitization as a potential pathomechanism. Cluster 2 showed a similar sensory profile as HC in both tested areas. Hence, either QST was not sensitive enough and more objective measures are needed to detect sensitization within the nociceptive neuraxis or cluster 2 may not have pain primarily because of sensitization, but other factors such as psychosocial ones are involved.

Conclusion

These findings support the notion of shared pathomechanisms irrespective of the pain diagnosis. Conversely, different mechanisms might contribute to the pain of patients with the same diagnosis.

Body Composition does not influence Conditioned Pain Modulation and Exercise Induced Hyperalgesia in Healthy Males and Females

BACKGROUND

Obese individuals report a higher susceptibility to chronic pain. Females are more likely to have chronic pain and excess adipose tissue. Chronic pain is associated with dysfunctional pain modulatory mechanisms. Body composition differences may be associated with pain modulation differences in males and females. The purpose of this study was to investigate body composition (lean vs fat mass) differences and pain modulatory functioning in healthy males and females.

METHODS

Pressure pain thresholds (PPT) of 96 participants (47M; 49F) were assessed in both arms and legs before and after a double footed ice bath (2°C) for 1min and an isometric knee extension, time to failure task. The difference between post and pre measures was defined conditioned pain modulatory (CPM) response (ice bath) and exercise induced hypoalgesia (EIH) response. Whole body and site-specific fat and lean tissue were assessed via DXA scan.

RESULTS

Sex differences were found in whole body lean mass (61.5±6.7kg vs 41.2±5.4kg; P<0.001) but not fat mass amount (17.2±10.5kg vs 21.0±9.7kg; P=0.068). No effect of sex was found between limb CPM (P=0.237) and limb EIH (P=0.512). When controlling for lean mass there was no significant effect of sex on CPM (P=0.732) or EIH (P=0.474) response. Similar findings were found for fat mass.

CONCLUSION

The lack of difference suggests that males and females have similar modulatory functioning. It appears that in healthy adults free from chronic pain, neither fat mass nor lean mass has an influence on endogenous pain modulatory function.

Pain patterns in chronic pancreatitis and chronic primary pain

BACKGROUND

Abdominal pain is the most distressing symptom of chronic pancreatitis (CP), and current treatments show limited benefit. Pain phenotypes may be more useful than diagnostic categories when planning treatments, and the presence or absence of constant pain in CP may be a useful prognostic indicator.

AIMS

This cross-sectional study examined dimensions of pain in CP, compared pain in CP with chronic primary pain (CPP), and assessed whether constant pain in CP is associated with poorer outcomes.

METHODS

Patients with CP (N = 91) and CPP (N = 127) completed the Comprehensive Pancreatitis Assessment Tool. Differences in clinical characteristics and pain dimensions were assessed between a) CP and CPP and b) CP patients with constant versus intermittent pain. Latent class regression analysis was performed (N = 192) to group participants based on pain dimensions and clinical characteristics.

RESULTS

Compared to CPP, CP patients had higher quality of life (p < 0.001), lower pain severity (p < 0.001), and were more likely to use strong opioids (p < 0.001). Within CP, constant pain was associated with a stronger response to pain triggers (p < 0.05), greater pain spread (p < 0.01), greater pain severity, more features of central sensitization, greater pain catastrophising, and lower quality of life compared to intermittent pain (all p values ≤ 0.001). Latent class regression analysis identified three groups, that mapped onto the following patient groups 1) combined CPP and CP-constant, 2) majority CPP, and 3) majority CP-intermittent.

CONCLUSIONS

Within CP, constant pain may represent a pain phenotype that corresponds with poorer outcomes. CP patients with constant pain show similarities to some patients with CPP, potentially indicating shared mechanisms.

Simple Quantitative Sensory Testing Reveals Paradoxical Co-existence of Hypoesthesia and Hyperalgesia in Diabetes

Background: Diabetic neuropathy is characterized by the paradoxical co-existence of hypo- and hyperalgesia to sensory stimuli. The literature shows consistently sensory differences between healthy and participants with diabetes. We hypothesized that due to differences in pathophysiology, advanced quantitative sensory testing (QST) might reveal sensory discrepancies between type 1 (T1D) and type 2 diabetes (T2D). Furthermore, we investigated whether vibration detection thresholds (VDT) were associated with sensory response.

Method: Fifty-six adults with T1D [43 years (28–58)], 99 adults with T2D [65 years (57–71)], and 122 healthy individuals [51 years (34–64)] were included. VDT, pressure pain detection thresholds (pPDT) and tolerance (pPTT), tonic cold pain (hand-immersion in iced water), and central pain mechanisms (temporal summation and conditioned pain modulation) were tested and compared between T1D and T2D. VDT was categorized into normal (< 18 V), intermediary (18–25 V), or high (> 25 V).

Results: In comparison to healthy, analysis adjusted for age, BMI, and gender revealed hypoalgesia to tibial (pPDT): p = 0.01, hyperalgesia to tonic cold pain: p < 0.01, and diminished temporal summation (arm: p < 0.01; abdomen: p < 0.01). In comparison to participants with T2D, participants with T1D were hypoalgesic to tibial pPDT: p < 0.01 and pPTT: p < 0.01, and lower VDT: p = 0.02. VDT was not associated with QST responses.

Conclusion: Participants with T1D were more hypoalgesic to bone pPDT and pPTT independent of lower VDT, indicating neuronal health toward normalization. Improved understanding of differentiated sensory profiles in T1D and T2D may identify improved clinical endpoints in future trials.

Pancreatic QST Differentiates Chronic Pancreatitis Patients into Distinct Pain Phenotypes Independent of Psychiatric Comorbidities

BACKGROUND & AIMS

Quantitative sensory testing (QST) has been previously used to study pain in chronic pancreatitis (CP) but included methods that are not suitable for clinical purposes. The aims of this study were to determine if pancreatic QST (P-QST) can differentiate patients into distinct pain phenotypes and to determine the association of these with their clinical pain and psychiatric comorbidities.

METHODS

A multicenter cross-sectional study was conducted where patients completed validated questionnaires assessing quality of life (QoL), depression and anxiety scores as well as clinical pain symptoms followed by P-QST which included a cold pressor test, repetitive pinprick stimuli and pressure stimulation of the upper abdominal (T10) and control dermatomes. P-QST categorized patients into pain phenotypes based on a previously established nomogram. QoL, clinical pain and psychiatric assessment scores were compared across these groups.

RESULTS

A total of 179 patients were enrolled with a mean age of 54.1±13.6 years among whom 59% were males and 42% had an alcoholic etiology. P-QST showed no hyperalgesia in 91 (51%), segmental hyperalgesia in 50 (28%) and widespread hyperalgesia in 38 (21%) patients. Patients with widespread hyperalgesia had significantly higher pain intensity scores (P = .03) and rates of constant pain (P = .002) as well as decreased QoL (P < .001) and physical functioning (P =.03) in comparison with the other two pain phenotypes. In contrast, psychiatric comorbidities were similar across all groups.

CONCLUSIONS

P-QST may serve as a novel unbiased pain assessment tool in CP as it categorizes patients into distinct pain phenotypes independent of their psychiatric comorbidities.

Assessment of pain associated with chronic pancreatitis: An international consensus guideline

Pain is the most common symptom in chronic pancreatitis (CP) with a major impact on quality of life. Few validated questionnaires to assess pain in CP exist, and the lack of consensus negatively impacts clinical management, research and meta-analysis. This guideline aims to review generic pain questionnaires for their usability in CP, to outline how pain assessment can be modified by confounding factors and pain types, to assess the value of additional measures such as quality of life, mental health and quantitative sensory testing, and finally to review pain assessment questionnaires used specifically in CP. A systematic review was done to answer 27 questions that followed the PICO (Population; Intervention; Comparator; Outcome) template. Quality of evidence of the statements was judged by Grades of Recommendation, Assessment, Development and Evaluation (GRADE) criteria. The manuscript was sent for review to 36 experts from various disciplines and continents in a multi-stage Delphi process, and finally reviewed by patient representatives. Main findings were that generic pain instruments are valid in most settings, but aspects of pain are specific for CP (including in children), and instruments have to account for the wide phenotypic variability and development of sensitization of the central nervous system. Side effects to treatment and placebo effects shall also be considered. Some multidimensional questionnaires are validated for CP and are recommended together with assessment of quality of life and psychiatric co-morbidities. This guideline will result in more homogeneous and comprehensive pain assessment to potentially improve management of painful CP.

Patients with symptomatic permanent atrial fibrillation show quantitative signs of pain sensitisation

Objective

Most patients with atrial fibrillation (AF) report symptoms, while one-third are asymptomatic. We hypothesised that sensory processing, in particular pain, differs in patients with symptomatic and asymptomatic AF.

Methods

Thirty individuals with permanent AF (15 symptomatic and 15 asymptomatic) completed the Atrial Fibrillation 6 (AF6) and short form 36 Health Survey questionnaires and underwent quantitative pain sensitisation testing using pressure algometry at the sternum (referred pain area) and the tibialis anterior muscle (generalised pain area). The primary objective was to assess differences in pressure pain thresholds (PPT), temporal summation of pain (TSP) and conditioned pain modulation (CPM) in the two groups. The secondary objective was to determine association of demographic and clinical parameters to measures of pain sensitisation.

Results

The symptomatic group had lower PPTs at both tibialis (p=0.004) and sternum (p=0.01), and impaired CPM (p=0.025) and facilitated TSP (p=0.008) at the tibialis but not sternum, compared with the asymptomatic group. The AF6 sum score was negatively correlated to PPT on both tibialis (r=−0.50, p=0.005) and sternum (r=−0.42, p=0.02) and positively correlated to TSP on both tibialis (r=0.57, p=0.001) and sternum (r=0.45, p=0.01), but not to CPM. The physical component summary score was positively correlated to the PPT on both tibialis (r=0.52, p=0.003) and sternum (r=0.40, p=0.03) and negatively to TSP on the tibialis (r=−0.53, p=0.003) but not sternum.

Conclusions

Patients with symptomatic AF exhibit lower pain tolerance than patients with asymptomatic AF, as well as impaired pain inhibitory control and facilitated summation of pain, indicating that pain sensitisation may be of importance in symptomatic AF.

Trial registration number

NCT04649437.

Pain stickiness in pediatric complex regional pain syndrome: A role for the nucleus accumbens

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Pain nonresponders have decreased nucleus accumbens (NAc) grey matter density.

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Pain nonresponders have reduced functional connectivity between NAc and dlPFC.

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Connectivity strength between NAc and dlPFC correlates with changes in pain.

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Prediction estimate for pain improvement with grey matter and connectivity was 87%.

Some individuals with chronic pain experience improvement in their pain with treatment, whereas others do not. The neurobiological reason is unclear, but an understanding of brain structure and functional patterns may provide insights into pain’s responsivity to treatment. In this investigation, we used magnetic resonance imaging (MRI) techniques to determine grey matter density alterations on resting functional connectivity (RFC) strengths between pain responders and nonresponders in patients with complex regional pain syndrome. Brain metrics of pediatric patients at admission to an intensive pain rehabilitative treatment program were evaluated. Pain responders reported significant pain improvement at discharge and/or follow-up whereas nonresponders reported no improvements in pain, increases in pain, or emergence of new pain symptoms. The pain (responder/nonresponder) groups were compared with pain-free healthy controls to examine predictors of pain responder status via brain metrics. Our results show: (1) on admission, pain nonresponders had decreased grey matter density (GMD) within the nucleus accumbens (NAc) and reduced RFC strength between the NAc and the dorsolateral prefrontal cortex vs. responders; (2) Connectivity strength was positively correlated with change in pain intensity from admission to discharge; (3) Compared with pain-free controls, grey matter and RFC differences emerged only among pain nonresponders; and (4) Using a discriminative model, combining GMD and RFC strengths assessed at admission showed the highest prediction estimate (87%) on potential for pain improvement, warranting testing in a de novo sample. Taken together, these results support the idea that treatment responsiveness on pain is underpinned by concurrent brain structure and resting brain activity.

Patient and Disease Characteristics Associate With Sensory Testing Results in Chronic Pancreatitis

BACKGROUND

Abdominal pain is the most common symptom in chronic pancreatitis (CP) and has an extensive impact on patients' lives. Quantitative sensory testing (QST) provides information on sensitivity to pain and mechanisms that can help quantify pain and guide treatment. The aims of this study were (1) to explore sensitivity to pain in patients with CP using QST and (2) to associate patient and disease characteristics with QST results.

METHODS

Ninety-one patients with painful CP and 28 healthy control participants completed a QST paradigm using static tests (muscle pressure stimulation and electrical skin stimulations) to unravel segmental and widespread hyperalgesia as a consequence of visceral pain. A dynamic conditioned pain modulation (CPM) paradigm was used as a proxy of pain modulation from the brainstem to inhibit incoming nociceptive barrage, and questionnaires were used to gather information on pain experience and quality of life.

RESULTS

Patients had impaired CPM compared with controls (18.0±29.3% vs. 30.9±29.3%, P=0.04) and were hypersensitive to pressure stimulation, specifically in the pancreatic (Th10) dermatome (P<0.001). The capacity of CPM was associated with clinical pain intensity (P=0.01) and (in the univariate analysis only) the use of opioids was associated with hyperalgesia to pressure stimulation (P<0.05).

CONCLUSIONS

Sensitivity to pain in CP patients can be characterized by a simple bedside QST. Severe clinical pain in CP was associated with reduced CPM function and should be targeted in management.

Combined extracorporeal shock wave lithotripsy and endoscopic treatment for pain in chronic pancreatitis (SCHOKE trial): study protocol for a randomized, sham-controlled trial

Background

Pain is the primary symptom of chronic pancreatitis (CP) and remains a considerable therapeutic challenge. In patients with obstruction of the pancreatic duct, including stones and strictures, endoscopic treatment with or without preceding extracorporeal shock wave lithotripsy (ESWL) has been used for pancreatic duct decompression. The rationale for these procedures is based on the assumption that obstruction of the pancreatic duct leads to ductal hypertension and pain. However, clinical pain symptoms correlate poorly with pancreatic duct morphology, and the evidence for pancreatic duct decompression as an effective treatment for pain is based on case series and comparison between different procedures. No randomized, prospective, sham-controlled trials are currently available. The SCHOKE (Extracorporeal Shock Wave Lithotripsy and Endotherapy for Pain in Chronic Pancreatitis) trial is a randomized, sham-controlled trial designed to determine if pancreatic duct decompression is an effective treatment for pain in patients with CP.

Methods

The SCHOKE trial is a randomized, single-blind, parallel-group, sham-controlled trial designed to evaluate the effect of combined ESWL and endoscopic treatment for pain in patients with CP. In total, 106 adult patients with painful CP and pancreatic duct obstruction will be randomized to combined ESWL and subsequent endoscopic treatment or corresponding sham procedures. The primary outcome is pain relief during the 3-month postrandomization period as documented in a pain diary. Secondary outcomes include quality of life and functional scores, patient global impression of change, change in use of analgesics, frequency of hospitalization, and complications. Standard follow-up is at 3 and 6 months after randomization. In an experimental substudy, quantitative sensory testing obtained before and after intervention will be used to obtain information on central pain processing and to develop models for prediction of treatment outcome.

Discussion

The SCHOKE trial investigates if pancreatic duct decompression, obtained by combined ESWL and endoscopic treatment, is effective for pain treatment in patients with CP.

Trial registration

ClinicalTrials.gov, NCT03966781. Registered on May 25, 2019.

Protocol date and version identifier: March 1, 2020; version 3.0.

Sponsor: Rupjyoti Talukdar, Department of Medical Gastroenterology, Asian Institute of Gastroenterology, Hyderabad, Telangana, India.

Association of multiple patient and disease characteristics with the presence and type of pain in chronic pancreatitis

BACKGROUND AND AIM

Pain is the primary symptom of chronic pancreatitis (CP) and associates with a number of patient and disease characteristics. However, the complex interrelations of these parameters are incompletely understood, and pain treatment remains unsatisfactory in a large proportion of patients. The aim of this study is to investigate multiple pain risk factors in a large population of CP patients, with a special emphasis on patients' patterns of smoking and alcohol use.

METHODS

This was a multicenter, cross-sectional study including 1384 patients with CP. Patient demographics and disease characteristics, as well as current patterns of smoking and alcohol use, were compared for patients with pain (n = 801) versus without pain (n = 583). Multivariate logistic regression models were performed to assess the variables associated with the presence and type of pain (constant vs intermittent pain).

RESULTS

The mean age of participants was 52.1 ± 14.6 years, and 914 (66%) were men. Active smoking (odds ratio 1.6 [95% confidence interval 1.1-2.2], P = 0.005) and alcohol consumption (odds ratio 1.8 [95% confidence interval 1.1-3.0], P = 0.03) were independently associated with the presence of pain. In addition, patients' age at diagnosis, pancreatic duct pathology, and the presence of pseudocysts, duodenal stenosis, and exocrine pancreatic insufficiency were confirmed as pain risk factors (all P ≤ 0.01). Constant pain, as opposed to intermittent pain, was more frequently reported by smokers (P = 0.03), while alcohol consumption was associated with intermittent pain (P = 0.006).

CONCLUSION

Multiple patient and disease characteristics, including patterns of smoking and alcohol consumption, associate with the presence and type of pain in patients with CP.

Gastrointestinal pain

Gastrointestinal (GI) pain - a form of visceral pain - is common in some disorders, such as irritable bowel syndrome, Crohn's disease and pancreatitis. However, identifying the cause of GI pain frequently represents a diagnostic challenge as the clinical presentation is often blurred by concomitant autonomic and somatic symptoms. In addition, GI pain can be nociceptive, neuropathic and associated with cancer, but in many cases multiple aetiologies coexist in an individual patient. Mechanisms of GI pain are complex and include both peripheral and central sensitization and the involvement of the autonomic nervous system, which has a role in generating the symptoms that frequently accompany pain. Treatment of GI pain depends on the precise type of pain and the primary disorder in the patient but can include, for example, pharmacological therapy, cognitive behavioural therapies, invasive surgical procedures, endoscopic procedures and lifestyle alterations. Owing to the major differences between organ involvement, disease mechanisms and individual factors, treatment always needs to be personalized and some data suggest that phenotyping and subsequent individual management of GI pain might be options in the future.

Effects of chronic pain history on perceptual and cognitive inhibition

Measures of sensory and cognitive inhibition were obtained from university students with and without a history of chronic pain. The form of sensory inhibition measured was diffuse noxious inhibitory controls (DNIC), the capacity of a painful stimulus to reduce the subjective intensity of a second stimulus delivered to a remote body site. To measure cognitive inhibition, the Stroop effect was used. Participants with a history of chronic pain showed less DNIC (i.e., less sensory inhibition) than the healthy controls, but had a smaller Stroop effect (indicating greater cognitive inhibition). The fact that chronic pain history is associated with opposite changes in these two measures casts doubt on the view that the two inhibitory processes are related. Scores on each experimental measure were equivalent in pain-history subjects with ongoing chronic pain and those whose chronic pain had resolved. This equivalence suggests that chronic pain in childhood or adolescence may have lingering effects on sensory and cognitive inhibition.

A clinically feasible method for the assessment and characterization of pain in patients with chronic pancreatitis

BACKGROUND AND AIMS

Pain is the primary symptom of chronic pancreatitis (CP), but methods for sensory testing and pain characterization have not previously been validated for clinical use. We present a clinically feasible method for the assessment and characterization of pain mechanisms in patients with CP based on quantitative sensory testing (QST).

METHODS

This was a cross-sectional, multicenter study of 122 control subjects without pancreatic disease and another 60 patients with painful CP. All subjects underwent standardized QST assessments including a cold pressor test, a conditioned pain modulation paradigm, repetitive pin-prick stimuli (temporal summation) and pressure stimulation of the upper abdominal (pancreatic) and control dermatomes. The effects of age and gender on QST assessment parameters were investigated and normative reference values based on quartile regression were derived and implemented in algorithms to categorize patients according to their patterns of central pain processing (normal vs. segmental sensitization vs. widespread sensitization).

RESULTS

Absolute pressure thresholds were subject to clinically relevant gender effects (all p < 0.001), while the remainder of QST parameters were unaffected by age and gender. The algorithm with the best discriminatory capacity showed good separation between patients and controls (p < 0.001); 50% of patients had normal central pain processing, 23% had evidence of segmental sensitization and 27% had evidence of widespread sensitization.

CONCLUSION

We show normative reference values for a clinically feasible method for assessment and characterization of pain mechanisms in patients with CP. Application of this method streamlines the evaluation of pancreatic pain and may be used to inform treatment. CLINICALTRIALS.

GOV ID

NCT03434392.

Targeting nNOS ameliorates the severe neuropathic pain due to chronic pancreatitis

BACKGROUND

Pain due to pancreatic cancer/PCa or chronic pancreatitis/CP, is notoriously resistant to the strongest pain medications. Here, we aimed at deciphering the specific molecular mediators of pain at surgical-stage pancreatic disease and to discover novel translational targets.

METHODS

We performed a systematic, quantitative analysis of the neurotransmitter/neuroenzmye profile within intrapancreatic nerves of CP and PCa patients. Ex vivo neuronal cultures treated with human pancreatic extracts, conditional genetically engineered knockout mouse models of PCa and CP, and the cerulein-induced CP model were employed to explore the therapeutic potential of the identified targets.

FINDINGS

We identified a unique enrichment of neuronal nitric-oxide-synthase (nNOS) in the pancreatic nerves of CP patients with increasing pain severity. Employment of ex vivo neuronal cultures treated with pancreatic tissue extracts of CP patients, and brain-derived-neurotrophic-factor-deficient (BDNF^+/-) mice revealed neuronal enrichment of nNOS to be a consequence of BDNF loss in the progressively destroyed pancreatic tissue. Mechanistically, nNOS upregulation in sensory neurons was induced by tryptase secreted from perineural mast cells. In a head-to-head comparison of several genetically induced, painless mouse models of PCa (KPC, KC mice) or CP (Ptf1a-Cre;Atg5^fl/fl) against the hypersecretion/cerulein-induced, painful CP mouse model, we show that a similar nNOS enrichment is present in the painful cerulein-CP model, but absent in painless genetic models. Consequently, mice afflicted with painful cerulein-induced CP could be significantly relieved upon treatment with the specific nNOS inhibitor NPLA.

INTERPRETATION

We propose nNOS inhibition as a novel strategy to treat the unbearable pain in CP. FUND: Deutsche Forschungsgemeinschaft/DFG (DE2428/3-1 and 3-2).

Mechanism-based pain management in chronic pancreatitis - is it time for a paradigm shift?

INTRODUCTION

Pain is the most common symptom in chronic pancreatitis and treatment remains a challenge. Management of visceral pain, in general, is only sparsely documented, and treatment in the clinic is typically based on empirical knowledge from somatic pain conditions. This may be problematic, as many aspects of the neurobiology differ significantly from somatic pain, and organs such as the gut and liver play a major role in tolerability to analgesics. On the other hand, clinical awareness and new methods for quantitative assessment of pain mechanisms, will likely increase our understanding of the visceral pain system and guide more individualized pain management. Areas covered: This review includes an overview of known pain mechanisms in chronic pancreatitis and how to characterize them using quantitative sensory testing. The aim is to provide a mechanism-oriented approach to analgesic treatment, including treatment of psychological factors affecting pain perception and consideration of side effects in the management plan. Expert opinion: A mechanism-based examination and profiling of pain in chronic pancreatitis will enable investigators to provide a well-substantiated approach to effective management. This mechanism-based, individualized regime will pave the road to better pain relief and spare the patient from unnecessary trial-and-error approaches and unwanted side effects.

When pain gets stuck: the evolution of pain chronification and treatment resistance

It is well-recognized that, despite similar pain characteristics, some people with chronic pain recover, whereas others do not. In this review, we discuss possible contributions and interactions of biological, social, and psychological perturbations that underlie the evolution of treatment-resistant chronic pain. Behavior and brain are intimately implicated in the production and maintenance of perception. Our understandings of potential mechanisms that produce or exacerbate persistent pain remain relatively unclear. We provide an overview of these interactions and how differences in relative contribution of dimensions such as stress, age, genetics, environment, and immune responsivity may produce different risk profiles for disease development, pain severity, and chronicity. We propose the concept of "stickiness" as a soubriquet for capturing the multiple influences on the persistence of pain and pain behavior, and their stubborn resistance to therapeutic intervention. We then focus on the neurobiology of reward and aversion to address how alterations in synaptic complexity, neural networks, and systems (eg, opioidergic and dopaminergic) may contribute to pain stickiness. Finally, we propose an integration of the neurobiological with what is known about environmental and social demands on pain behavior and explore treatment approaches based on the nature of the individual's vulnerability to or protection from allostatic load.

The effects of propranolol on heart rate variability and quantitative, mechanistic, pain profiling: a randomized placebo-controlled crossover study

Background and aims

The autonomic nervous system (ANS) is capable of modulating pain. Aberrations in heart rate variability (HRV), reflective of ANS activity, are associated with experimental pain sensitivity, chronic pain, and more recently, pain modulatory mechanisms but the underlying mechanisms are still unclear. HRV is lowered during experimental pain as well as in chronic pain conditions and HRV can be increased by propranolol, which is a non-selective β-blocker. Sensitization of central pain pathways have been observed in several chronic pain conditions and human mechanistic pain biomarkers for these central pain pathways include temporal summation of pain (TSP) and conditioned pain modulation (CPM). The current study aimed to investigate the effect of the β-blocker propranolol, and subsequently assessing the response to standardized, quantitative, mechanistic pain biomarkers.

Methods

In this placebo-controlled, double-blinded, randomized crossover study, 25 healthy male volunteers (mean age 25.6 years) were randomized to receive 40 mg propranolol and 40 mg placebo. Heart rate, blood pressure, and HRV were assessed before and during experimental pain tests. Cuff pressure pain stimulation was used for assessment of pain detection (cPDTs) and pain tolerance (cPTTs) thresholds, TSP, and CPM. Offset analgesia (OA) was assessed using heat stimulation.

Results

Propranolol significantly reduced heart rate (p<0.001), blood pressure (p<0.02) and increased HRV (p<0.01) compared with placebo. No significant differences were found comparing cPDT (p>0.70), cPTT (p>0.93), TSP (p>0.70), OA-effect (p>0.87) or CPM (p>0.65) between propranolol and placebo.

Conclusions

The current study demonstrated that propranolol increased HRV, but did not affect pressure pain sensitivity or any pain facilitatory or modulatory outcomes.

Implications

Analgesic effects of propranolol have been reported in clinical pain populations and the results from the current study could indicate that increased HRV from propranolol is not associated with peripheral and central pain pathways in healthy male subjects.

Assessment and manifestation of central sensitisation across different chronic pain conditions

Different neuroplastic processes can occur along the nociceptive pathways and may be important in the transition from acute to chronic pain and for diagnosis and development of optimal management strategies. The neuroplastic processes may result in gain (sensitisation) or loss (desensitisation) of function in relation to the incoming nociceptive signals. Such processes play important roles in chronic pain, and although the clinical manifestations differ across condition processes, they share some common mechanistic features. The fundamental understanding and quantitative assessment of particularly some of the central sensitisation mechanisms can be translated from preclinical studies into the clinic. The clinical perspectives are implementation of such novel information into diagnostics, mechanistic phenotyping, prevention, personalised treatment, and drug development. The aims of this paper are to introduce and discuss (1) some common fundamental central pain mechanisms, (2) how they may translate into the clinical signs and symptoms across different chronic pain conditions, (3) how to evaluate gain and loss of function using quantitative pain assessment tools, and (4) the implications for optimising prevention and management of pain. The chronic pain conditions selected for the paper are neuropathic pain in general, musculoskeletal pain (chronic low back pain and osteoarthritic pain in particular), and visceral pain (irritable bowel syndrome in particular). The translational mechanisms addressed are local and widespread sensitisation, central summation, and descending pain modulation.

Significance

Central sensitisation is an important manifestation involved in many different chronic pain conditions. Central sensitisation can be different to assess and evaluate as the manifestations vary from pain condition to pain condition. Understanding central sensitisation may promote better profiling and diagnosis of pain patients and development of new regimes for mechanism based therapy. Some of the mechanisms underlying central sensitisation can be translated from animals to humans providing new options in development of therapies and profiling drugs under development.

Towards a neurobiological understanding of pain in chronic pancreatitis: mechanisms and implications for treatment

We summarize the evidence for a neurobiological understanding of pain in patients with chronic pancreatitis and discuss its potential impact on prevention and treatment.

Introduction:

Chronic pancreatitis (CP) is a disease characterized by inflammation of the pancreas resulting in replacement of the normal functioning parenchyma by fibrotic connective tissue. This process leads to progressively impairment of exocrine and endocrine function and many patients develop a chronic pain syndrome.

Objectives:

We aimed to characterize the neurobiological signature of pain associated with CP and to discuss its implications for treatment strategies.

Methods:

Relevant basic and clinical articles were selected for review following an extensive search of the literature.

Results:

Pathophysiological changes in the peripheral (pancreatic gland) and central nervous system characterize the pain syndrome associated with CP; involved mechanisms can be broken down to 3 main branches: (1) peripheral sensitization, (2) pancreatic neuropathy, and (3) neuroplastic changes in the central pain pathways. Disease flares (recurrent pancreatitis) may accelerate the pathophysiological process and further sensitize the pain system, which ultimately results in an autonomous and self-perpetuating pain state that may become independent of the peripheral nociceptive drive. These findings share many similarities with those observed in neuropathic pain disorders and have important implications for treatment; adjuvant analgesics are effective in a subset of patients, and neuromodulation and neuropsychological interventions may prove useful in the future.

Conclusion:

Chronic pancreatitis is associated with abnormal processing of pain at the peripheral and central level of the pain system. This neurobiological understanding of pain has important clinical implications for treatment and prevention of pain chronification.

Expression of aromatase in the rostral ventromedial medulla and its role in the regulation of visceral pain

AIMS

Estrogens are known to exert a wide spectrum of actions on brain functions including modulation of pain. Besides the circulating estrogens produced mainly by the ovaries, many brain regions are also capable of de novo synthesizing estrogens, which may exert important modulatory effects on neuronal functions. This study was aimed to test the hypothesis that aromatase, the enzyme that catalyzes the conversion of testosterone to estradiols, may be distributed in the rostral ventromedial medulla (RVM), where it may impact on visceral pain.

METHODS AND RESULTS

Adult female rats were treated with cyclophosphamide (CPM, 50 mg/kg, ip, once every 3 days) or saline. At approximately day 10 following the 3rd injection, CPM-treated rats exhibited colorectal hyperalgesia as they showed significantly greater abdominal withdrawal responses (AWR) to graded colorectal distension (CRD, 0-100 mm Hg) than the saline group. Immunofluorescent staining and Western blot assay revealed that CPM-induced colorectal hyperalgesia was associated with significantly increased expression of aromatase and phosphorylated μ-type opioid receptor (pMOR) and decreased expression of total MOR in the RVM. Intracisternal application of aromatase inhibitors, fadrozole, and letrozole reversed CPM-induced colorectal hyperalgesia and restored pMOR and MOR expression in the RVM.

CONCLUSIONS

Our observations confirmed the expression of aromatase in the RVM, a pivotal brain region in descending modulation of pain and opioid analgesia. The results support the hypothesis that locally produced estrogens in the RVM may be involved in the maintenance of chronic visceral hyperalgesia and the downstream signaling may involve phosphorylation of MOR.

Guidelines for the understanding and management of pain in chronic pancreatitis

Abdominal pain is the foremost complication of chronic pancreatitis (CP). Pain can be related to recurrent or chronic inflammation, local complications or neurogenic mechanisms with corresponding changes in the nervous systems. Both pain intensity and the frequency of pain attacks have been shown to reduce quality of life in patients with CP. Assessment of pain follows the guidelines for other types of chronic pain, where the multidimensional nature of symptom presentation is taken into consideration. Quantitative sensory testing may be used to characterize pain, but is currently used in a research setting in advanced laboratories. For pain relief, current guidelines recommend a simple stepwise escalation of analgesic drugs with increasing potency until pain relief is obtained. Abstinence from alcohol and smoking should be strongly advised. Pancreatic enzyme therapy and antioxidants may be helpful as initial treatment. Endoscopic treatment can be used in patients with evidence of ductal obstruction and may be combined with extracorporeal shock wave lithothripsy. The best candidates are those with distal obstruction of the main pancreatic duct and in early stage of disease. Behavioral interventions should be part of the multidisciplinary approach to chronic pain management particularly when psychological impact is experienced. Surgery should be considered early and after a maximum of five endoscopic interventions. The type of surgery depends on morphological changes of the pancreas. Long-term effects are variable, but high success rates have been reported in open studies and when compared with endoscopic treatment. Finally, neurolytical interventions and neuromodulation can be considered in difficult patients.

Acute physiological and electrical accentuation of vagal tone has no effect on pain or gastrointestinal motility in chronic pancreatitis

Background

The effective management of pain in chronic pancreatitis (CP) remains a therapeutic challenge. Analgesic drugs, such as opioids, and the underlying pathology can impair gut function. The autonomic nervous system influences hormone secretion and gut motility. In healthy volunteers, electrical (using noninvasive transcutaneous vagal nerve stimulation [t-VNS]) and physiological (using deep slow breathing [DSB]) modulation of parasympathetic tone results in pain attenuation and enhanced gut motility. Thus, the aims were to investigate whether t-VNS and DSB could enhance the parasympathetic tone, decrease pain sensitivity and improve gut motility in CP.

Patients and methods

A total of 20 patients (12 males, mean age=61 years, range: 50–78 years) with CP were randomized to short-term (60 minutes) t-VNS and DSB, or their placebo equivalent, in a crossover design. Cardiometrically derived parameters of autonomic tone, quantitative sensory testing of bone and muscle pain pressure, conditioned pain modulation (CPM) and assessments of gastroduodenal motility with ultrasound were performed.

Results

In comparison to sham, t-VNS and DSB increased cardiac vagal tone (CVT) (P<0.001). However, no changes in pain pressure thresholds for bone (P=0.95) or muscle (P=0.45) were seen. There was diminished CPM (P=0.04), and no changes in gastroduodenal motility were observed (P=0.3).

Conclusion

This explorative study demonstrated that t-VNS and DSB increased CVT in patients with CP. However, this short-lasting increase did not affect pain sensitivity to musculoskeletal pain or gastroduodenal motility. The chronic pain in CP patients is complex, and future trials optimizing neuromodulation for pain relief and improved motility are needed.

Acupuncture for Pain in Chronic Pancreatitis: A Single-Blinded Randomized Crossover Trial

OBJECTIVES

Many patients with painful chronic pancreatitis (CP) have insufficient effect of treatment, and the prevalence of adverse effects is high. Consequently, alternatives to conventional management are needed. We aimed to study the effect of acupuncture in painful CP.

METHODS

This was a prospective, single-blinded, randomized crossover trial. Fifteen patients with CP were assigned to a session of acupuncture followed by sham stimulation or vice versa. Patients rated clinical pain scores daily on a 0 to 10 visual analogue scale (VAS) and completed the Patient Global Impression of Change. For mechanistic linkage, resting state electroencephalograms were recorded and quantified by spectral power analysis to explore effects on central pain processing.

RESULTS

Acupuncture, compared with sham stimulation, caused more pain relief (2.0 ± 1.5 VAS vs 0.7 ± 0.8 VAS; P = 0.009). The effect, however, was short, and after 1-week follow-up, there was no difference in clinical pain scores between groups (P = 1.0) or the rating of Patient Global Impression of Change (P = 0.8). Electroencephalogram spectral power distributions between sham and acupuncture were comparable between groups (all P > 0.6).

CONCLUSIONS

The study presents proof-of-concept for the analgesic effect of acupuncture in pancreatic pain. Although the effect was short lasting, the framework may be used to conceptualize future trials of acupuncture in visceral pain.

A Framework for Understanding the Relationship between Descending Pain Modulation, Motor Corticospinal, and Neuroplasticity Regulation Systems in Chronic Myofascial Pain

Myofascial pain syndrome (MPS) is a leading cause of chronic musculoskeletal pain. However, its neurobiological mechanisms are not entirely elucidated. Given the complex interaction between the networks involved in pain process, our approach, to providing insights into the neural mechanisms of pain, was to investigate the relationship between neurophysiological, neurochemical and clinical outcomes such as corticospinal excitability. Recent evidence has demonstrated that three neural systems are affected in chronic pain: (i) motor corticospinal system; (ii) internal descending pain modulation system; and (iii) the system regulating neuroplasticity. In this cross-sectional study, we aimed to examine the relationship between these three central systems in patients with chronic MPS of whom do/do not respond to the Conditioned Pain Modulation Task (CPM-task). The CPM-task was to immerse her non-dominant hand in cold water (0-1°C) to produce a heterotopic nociceptive stimulus. Corticospinal excitability was the primary outcome; specifically, the motor evoked potential (MEP) and intracortical facilitation (ICF) as assessed by transcranial magnetic stimulation (TMS). Secondary outcomes were the cortical excitability parameters [current silent period (CSP) and short intracortical inhibition (SICI)], serum brain-derived neurotrophic factor (BDNF), heat pain threshold (HPT), and the disability related to pain (DRP). We included 33 women, (18-65 years old). The MANCOVA model using Bonferroni's Multiple Comparison Test revealed that non-responders (n = 10) compared to responders (n = 23) presented increased intracortical facilitation (ICF; mean ± SD) 1.43 (0.3) vs. 1.11 (0.12), greater motor-evoked potential amplitude (μV) 1.93 (0.54) vs. 1.40 (0.27), as well a higher serum BDNF (pg/Ml) 32.56 (9.95) vs. 25.59 (10.24), (P < 0.05 for all). Also, non-responders presented a higher level of DRP and decreased HPT (P < 0.05 for all). These findings suggest that the loss of net descending pain inhibition was associated with an increase in ICF, serum BDNF levels, and DRP. We propose a framework to explain the relationship and potential directionality of these factors. In this framework we hypothesize that increased central sensitization leads to a loss of descending pain inhibition that triggers compensatory mechanisms as shown by increased motor cortical excitability.

Management of chronic visceral pain

Despite marked differences in underlying pathophysiology, the current management of visceral pain largely follows the guidelines derived from the somatic pain literature. The effective management of patients with chronic visceral pain should be multifaceted, including both pharmacological and psychological interventions, thereby providing a mechanism-orientated approach to treatment. Patients can frequently become disenfranchised, and subsequently disengaged, with healthcare providers leading to repeated consultations. Thus, a key aspect of management is to break this cycle by validating patients' symptoms, adopting an empathic approach and taking time to educate patients. To optimize treatment and outcomes in chronic visceral pain we need to move away from approaches exclusively based on dealing with peripheral nociceptive input toward more holistic strategies, taking into account alterations in central pain processing.

Rectal Mechano-sensory Function in Patients with Carcinoid Diarrhea

BACKGROUND/AIMS

In patients with neuroendocrine tumors, excessive production of serotonin and other amines may cause the carcinoid syndrome,which is mainly characterized by diarrhea and flushing. Little is known about the pathophysiology of carcinoid diarrhea. In severalother groups of patients, diarrhea may be associated with rectal hypersensitivity and increased rectal tone. Therefore, the aim of thepresent study was to compare rectal sensitivity and compliance in patients with carcinoid diarrhea and in healthy subjects.

METHODS

Twelve patients (6 males, aged 54-78 years, median 65 years), with carcinoid diarrhea and 19 healthy subjects (7 males, aged 50-78 years, median 61 years) were included. Rectal mechanical and heat stimulation was used for assessment of rectal mechano-sensory properties.

RESULTS

Overall, 5.3% higher temperatures were needed to elicit sensory responses in patients with carcinoid diarrhea than in healthy subjects (P = 0.015). Posthoc analyses revealed that the sensory threshold to heat was 48.1 ± 3.1°C in patients vs 44.7 ± 4.7°C in healthy subjects (P = 0.041). In contrast, patients and healthy subjects showed no overall differences in rectal sensory response to mechanical distension (P = 0.731) or rectal compliance (P = 0.990).

CONCLUSIONS

Patients with carcinoid diarrhea have higher sensory thresholds to heat stimulation in comparison to healthy subjects, but normalrectal sensation to mechanical distension and normal compliance. Therefore, treatment of carcinoid diarrhea should aim at prolonging gastrointestinal transit and decreasing secretion, rather than modifying rectal mechano-sensory function.

Predictors of Post-Operative Pain Relief in Patients with Chronic Pancreatitis Undergoing the Frey or Whipple Procedure

BACKGROUND

Post-operative pain relief in chronic pancreatitis (CP) is variable. Our objective was to determine clinical imaging or histopathologic predictor(s) of post-operative pain relief in CP patients undergoing the Whipple or Frey procedure.

METHODS

All patients who underwent a Whipple (n = 30) or Frey procedure (n = 30) for painful CP between January 2003 and September 2013 were evaluated. A toxic etiology was defined as a history of alcohol use and/or smoking. The pre-operative abdominal CT was evaluated for calcification(s) and main pancreatic duct (MPD) dilation (≥5 mm). The post-operative histopathology was evaluated for severe fibrosis. Clinical imaging and histopathologic features were evaluated as predictors of post-operative pain relief using univariable and multivariable regression analysis.

RESULTS

A total of 60 patients (age 51.6 years, 53% males) were included in our study, of whom 42 (70%) reported post-operative pain relief over a mean follow-up of 1.1 years. There were 37 (62%) patients with toxic etiology, 36 (60%) each with calcification(s) and MPD dilation. A toxic etiology, calcifications, and severe fibrosis were associated with post-operative pain relief on univariable analysis (all p < 0.01). However, only a toxic etiology was an independent predictor of post-operative pain relief (OR 5.7, 95% CI 1.3, 24.5, p = 0.02).

CONCLUSION

Only a toxic etiology, and not imaging or histopathologic findings, independently predicts post-operative pain relief in CP patients undergoing the Whipple or Frey procedure.

Single dose delta-9-tetrahydrocannabinol in chronic pancreatitis patients: analgesic efficacy, pharmacokinetics and tolerability

AIM

We aimed to assess the analgesic efficacy, pharmacokinetics, tolerability and safety of a single dose of Δ9-THC in patients with chronic abdominal pain resulting from chronic pancreatitis (CP).

METHODS

This was a randomized, single dose, double-blinded, placebo-controlled, two way crossover study in patients suffering from abdominal pain as result of CP (n = 24), post hoc subdivided into opioid and non-opioid users. Δ9-THC (8 mg) or active placebo (5 mg/10 mg diazepam) was administered orally in a double dummy design.

RESULTS

No treatment effect was shown for delta VAS pain scores after Δ9-THC compared with diazepam. Δ9-THC was well absorbed with a mean tmax of 123 min. No significant differences were found between Δ9-THC vs. diazepam for alertness, mood, calmness or balance. Feeling anxious and heart rate were significantly increased after Δ9-THC compared with diazepam. The most frequently reported adverse events (AEs) after Δ9-THC administration were somnolence, dry mouth, dizziness and euphoric mood.

CONCLUSIONS

A single dose of Δ9-THC was not efficacious in reducing chronic pain resulting from CP, but was well tolerated with only mild or moderate AEs. The PK results in CP patients showed delayed absorption and an increased variability compared with healthy volunteers.

Neural plasticity in pancreatitis and pancreatic cancer

Pancreatic nerves undergo prominent alterations during the evolution and progression of human chronic pancreatitis and pancreatic cancer. Intrapancreatic nerves increase in size (neural hypertrophy) and number (increased neural density). The proportion of autonomic and sensory fibres (neural remodelling) is switched, and are infiltrated by perineural inflammatory cells (pancreatic neuritis) or invaded by pancreatic cancer cells (neural invasion). These neuropathic alterations also correlate with neuropathic pain. Instead of being mere histopathological manifestations of disease progression, pancreatic neural plasticity synergizes with the enhanced excitability of sensory neurons, with Schwann cell recruitment toward cancer and with central nervous system alterations. These alterations maintain a bidirectional interaction between nerves and non-neural pancreatic cells, as demonstrated by tissue and neural damage inducing neuropathic pain, and activated neurons releasing mediators that modulate inflammation and cancer growth. Owing to the prognostic effects of pain and neural invasion in pancreatic cancer, dissecting the mechanism of pancreatic neuroplasticity holds major translational relevance. However, current in vivo models of pancreatic cancer and chronic pancreatitis contain many discrepancies from human disease that overshadow their translational value. The present Review discusses novel possibilities for mechanistically uncovering the role of the nervous system in pancreatic disease progression.

Pancreatic pain

PURPOSE OF REVIEW

Pain is the most common symptom of chronic pancreatitis, with a profound socioeconomic impact. Historical management paradigms failed, as they did not adequately address the fundamental underlying mechanisms. The present article describes the neurobiology of pain and sensitization in this condition, in an effort to explain prior failings and provide future directions for managing pain in chronic pancreatitis.

RECENT FINDINGS

A number of recent advances have been made in understanding the neurobiology of pain for this condition. This has been coupled with clinical advances in assessing sensitization to pain in these patients, which has been shown to predict response to medical and surgical therapy.

SUMMARY

Pain in chronic pancreatitis is complex. Addressing the mechanical and morphological findings in chronic pancreatitis without addressing the underlying neurobiological mechanisms is destined to fail. New advances in our understanding of the neurobiology of pain in chronic pancreatitis helps to explain prior failings and provides future direction for managing pain in patients afflicted by this disease.

A Randomized Controlled Trial on the Effect of Tapentadol and Morphine on Conditioned Pain Modulation in Healthy Volunteers

BACKGROUND

Modulatory descending pathways, originating at supraspinal sites that converge at dorsal horn neurons, influence pain perception in humans. Defects in descending pain control are linked to chronic pain states and its restoration may be a valuable analgesic tool. Conditioned pain modulation (CPM) is a surrogate marker of descending inhibition that reduces the perception of pain from a primary test stimulus during application of a conditioning stimulus. Here the effects of the analgesics tapentadol, a combined mu-opioid receptor agonist and noradrenaline reuptake inhibitor, and morphine, a strong mu-opioid receptor agonist, were tested on CPM in a randomized, double-blind, placebo-controlled crossover trial in 12 healthy pain-free volunteers, to understand possible differences in mechanism of action between these opioids.

METHODS AND RESULTS

On three occasions CPM responses were obtained 60-90 and 120-150 min following intake of tapentadol (100 mg immediate release tablet), morphine (40 mg immediate release tablet) or placebo. At both time points, CPM was detectable after treatment with placebo and tapentadol (peak pain ratings reduced by 20-30% after application of the conditioning stimulus) but not after morphine. Compared to placebo morphine displayed significantly less CPM: mean treatment difference 18.2% (95% CI 3.4 to 32.9%) at 60-90 min after drug intake and 19.5% (95% CI 5.7 to 33.2%) at 120-150 min after drug intake (p = 0.001). No difference in CPM between placebo and tapentadol was detected: mean treatment difference 1.5% (95% CI -11.6 to 14.6%) at 60-90 min after drug intake and 1.5% (95% CI -16.0 to 18.9%) at 120-150 min after drug intake (p = 0.60).

CONCLUSIONS

Our data show that in volunteers morphine affects CPM, while tapentadol was without effect despite identical experimental conditions. These data confirm that tapentadol's main mechanism of action is distinct from that of morphine and likely related to the effect of adrenergic stimulation on descending controls.

TRIAL REGISTRATION

Netherlands Trial Register NTR2716.

Systematic mechanism-orientated approach to chronic pancreatitis pain

Pain in chronic pancreatitis (CP) shows similarities with other visceral pain syndromes (i.e., inflammatory bowel disease and esophagitis), which should thus be managed in a similar fashion. Typical causes of CP pain include increased intrapancreatic pressure, pancreatic inflammation and pancreatic/extrapancreatic complications. Unfortunately, CP pain continues to be a major clinical challenge. It is recognized that ongoing pain may induce altered central pain processing, e.g., central sensitization or pro-nociceptive pain modulation. When this is present conventional pain treatment targeting the nociceptive focus, e.g., opioid analgesia or surgical/endoscopic intervention, often fails even if technically successful. If central nervous system pain processing is altered, specific treatment targeting these changes should be instituted (e.g., gabapentinoids, ketamine or tricyclic antidepressants). Suitable tools are now available to make altered central processing visible, including quantitative sensory testing, electroencephalograpy and (functional) magnetic resonance imaging. These techniques are potentially clinically useful diagnostic tools to analyze central pain processing and thus define optimum management approaches for pain in CP and other visceral pain syndromes. The present review proposes a systematic mechanism-orientated approach to pain management in CP based on a holistic view of the mechanisms involved. Future research should address the circumstances under which central nervous system pain processing changes in CP, and how this is influenced by ongoing nociceptive input and therapies. Thus we hope to predict which patients are at risk for developing chronic pain or not responding to therapy, leading to improved treatment of chronic pain in CP and other visceral pain disorders.

Pain management in patients with inflammatory bowel disease: translational approaches from bench to bedside

Abdominal pain is a common symptom in patients with inflammatory bowel disease (IBD) that negatively affects quality of life and can lead to increased health-seeking behavior. Although abdominal pain has been traditionally attributed to inflammation, there is growing literature demonstrating the existence of functional abdominal pain in patients with IBD, of which there are a variety of potential causes. Thus, when approaching a patient with IBD who has abdominal pain, in addition to IBD-related complications (e.g., inflammation/stricture), it is important to screen for related contributors, including peripheral factors (visceral hypersensitivity, bacterial overgrowth, and bowel dysmotility) and centrally mediated neurobiological and psychosocial underpinnings. These central factors include psychological symptoms/diagnoses, sleep disturbance, and stress. Opioid-induced hyperalgesia (e.g., narcotic bowel syndrome) is also growing in recognition as a potential central source of abdominal pain. This review draws from clinical studies and animal models of colitis and abdominal pain to consider how knowledge of these potential etiologies can be used to individualize treatment of abdominal pain in patients with IBD, including consideration of potential novel treatment modalities for the future. Accurate assessment of the source(s) of pain in patients with IBD can help guide appropriate diagnostic workup and use of disease-modifying therapy.

Sacral nerve stimulation changes rectal sensitivity and biomechanical properties in patients with irritable bowel syndrome

BACKGROUND

Sacral nerve stimulation (SNS) has been demonstrated to alleviate symptoms and improve quality of life in selected patients with irritable bowel syndrome (IBS). The mechanisms of action, however, remain unknown. The aim of the study was to evaluate the effects of SNS on rectal sensitivity and biomechanical properties in patients with IBS.

METHODS

Twenty patients with diarrhea-predominant (n = 11) or mixed (n = 9) IBS were treated with SNS in a controlled, randomized crossover trial. They were randomized to either 1 month of SNS (ON) or placebo (OFF) with the opposite setting for the next month. Sensory and biomechanical parameters were assessed by multimodal rectal stimulation at the end of each period. IBS-specific symptoms were evaluated at baseline and at the end of each treatment period.

KEY RESULTS

Cold stimuli were better tolerated in the ON period (19.9 °C[± 0.6]) compared to the OFF period (21.8 °C[± 0.6]; p = 0.03). Significantly lower cross-sectional areas were needed to elicit sensory responses in the ON period (1545 mm(2) [± 95]) compared to the OFF period (1869 mm(2) [± 92]; p = 0.015). The association between reduced sensory threshold and improvement of constipation was of borderline significance (p = 0.05). Wall stiffness was significantly lower in the ON period (192 mmHg[± 10]) compared to the OFF period (234 mmHg[± 10]; p = 0.004). Reduced wall stiffness was significantly associated with improved overall GSRS-IBS symptom score (p = 0.01). Reduced sensory threshold to stretch (p = 0.02) and reduced wall stiffness (p < 0.001) were predictors of the GSRS-IBS symptom score.

CONCLUSIONS & INFERENCES

SNS for diarrhea-predominant and mixed IBS relaxes the rectal wall, while making it more sensitive to stretch and less sensitive to cold. Reduced wall stiffness and increased sensitivity to stretch are associated with improved GSRS-IBS symptom score.

Is the conditioned pain modulation paradigm reliable? A test-retest assessment using the nociceptive withdrawal reflex

The aim of this study was to determine the reliability of the conditioned pain modulation (CPM) paradigm assessed by an objective electrophysiological method, the nociceptive withdrawal reflex (NWR), and psychophysical measures, using hypothetical sample sizes for future studies as analytical goals. Thirty-four healthy volunteers participated in two identical experimental sessions, separated by 1 to 3 weeks. In each session, the cold pressor test (CPT) was used to induce CPM, and the NWR thresholds, electrical pain detection thresholds and pain intensity ratings after suprathreshold electrical stimulation were assessed before and during CPT. CPM was consistently detected by all methods, and the electrophysiological measures did not introduce additional variation to the assessment. In particular, 99% of the trials resulted in higher NWR thresholds during CPT, with an average increase of 3.4 mA (p<0.001). Similarly, 96% of the trials resulted in higher electrical pain detection thresholds during CPT, with an average increase of 2.2 mA (p<0.001). Pain intensity ratings after suprathreshold electrical stimulation were reduced during CPT in 84% of the trials, displaying an average decrease of 1.5 points in a numeric rating scale (p<0.001). Under these experimental conditions, CPM reliability was acceptable for all assessment methods in terms of sample sizes for potential experiments. The presented results are encouraging with regards to the use of the CPM as an assessment tool in experimental and clinical pain. Trial registration: Clinical Trials.gov NCT01636440.