Central sensitisation in visceral pain disorders

Advancing Pain Understanding and Drug Discovery: Insights from Preclinical Models and Recent Research Findings

Despite major advancements in our understanding of its fundamental causes, pain-both acute and chronic-remains a serious health concern. Various preclinical investigations utilizing diverse animal, cellular, and alternative models are required and frequently demanded by regulatory approval bodies to bridge the gap between the lab and the clinic. Investigating naturally occurring painful disorders can speed up medication development at the preclinical and clinical levels by illuminating molecular pathways. A wide range of animal models related to pain have been developed to elucidate pathophysiological mechanisms and aid in identifying novel targets for treatment. Pain sometimes drugs fail clinically, causing high translational costs due to poor selection and the use of preclinical tools and reporting. To improve the study of pain in a clinical context, researchers have been creating innovative models over the past few decades that better represent pathological pain conditions. In this paper, we provide a summary of traditional animal models, including rodents, cellular models, human volunteers, and alternative models, as well as the specific characteristics of pain diseases they model. However, a more rigorous approach to preclinical research and cutting-edge analgesic technologies may be necessary to successfully create novel analgesics. The research highlights from this review emphasize new opportunities to develop research that includes animals and non-animals using proven methods pertinent to comprehending and treating human suffering. This review highlights the value of using a variety of modern pain models in animals before human trials. These models can help us understand the different mechanisms behind various pain types. This will ultimately lead to the development of more effective pain medications.

Review of the Patient Burden and Therapeutic Landscape of Irritable Bowel Syndrome with Constipation in the United States

Irritable bowel syndrome (IBS) is a common disorder of the gut-brain axis. IBS with constipation (IBS-C) accounts for approximately one-third of IBS cases and is associated with substantial burden of illness and decreased quality of life. This narrative review provides an overview of the current and upcoming treatment options and disease management for IBS-C from a US perspective and discusses the importance of the relationship between patient and health care provider in diagnosis and treatment. A positive diagnostic strategy for IBS-C is recommended, based on clinical history, physical examination, and minimal laboratory tests. An effective communication strategy between patients and health care professionals is essential to ensure early diagnosis and reduce both health care costs and overall disease burden. Treatment typically begins with lifestyle interventions and nonpharmacologic options, such as dietary interventions, fiber supplements, and osmotic laxatives. In patients with inadequate response to these therapies, 4 currently available therapies (lubiprostone, linaclotide, plecanatide, and tenapanor) approved by the US Food and Drug Administration may relieve IBS-C symptoms. These agents are generally well tolerated and efficacious in improving IBS-C symptoms, including constipation and abdominal pain. In patients with persistent abdominal pain and/or psychological symptoms, brain-gut behavioral therapy or neuromodulator therapy may be beneficial.

Differential responses from the left postcentral gyrus, right middle frontal gyrus, and precuneus to meal ingestion in patients with functional dyspepsia

Background

Functional dyspepsia (FD) is most often a meal-induced syndrome. Studies using resting-state functional magnetic resonance imaging (rs-fMRI) reported abnormal connectivity in areas related to pain processing in FD. However, only a few studies have attempted to determine how meal ingestion affects the brain's working patterns. Through rs-fMRI, this study observed how meal ingestion affected brain regions related to visceral hypersensitivity and emotional response networks in FD patients.

Methods

A total of 30 FD patients and 32 healthy controls (HC) were enrolled and underwent clinical investigations. Rs-fMRI was performed twice after a 4-h fast and 50 min after a meal. The mean functional connectivity strength (FCS) values were extracted from brain regions with significant differences to show the trend of changes related to meal ingestion after FCS analyses.

Results

Depression, anxiety, sleep disturbances, and weight loss were more common in FD patients (P ≤ 0.001). Compared with HCs (corrected cluster P-value < 0.05), FD patients had significantly higher FCS in the right middle frontal gyrus before meals and higher meal-induced FCS in the left postcentral gyrus. HCs had greater meal-induced activation in the right precuneus and anterior cingulate cortex. FD patients had a decreasing trend in the right inferior frontal gyrus compared to the increasing trend in HCs. We only found anxiety to be negatively correlated with FCS in the right inferior frontal gyrus in FD (r = -0.459, p = 0.048, uncorrected).

Conclusions

In this study, we discovered that FD patients have different perceptual and emotional responses to food intake in defined brain areas, providing promising impetus for understanding pathogenic brain mechanisms in FD.

Sex differences in pain-related behaviors and clinical progression of disease in mouse models of colonic pain

ABSTRACT

Previous studies have reported sex differences in patients with irritable bowel syndrome and inflammatory bowel disease, including differences in visceral pain perception. Despite this, sex differences in behavioral manifestations of visceral pain and underlying pathology of the gastrointestinal tract have been largely understudied in preclinical research. In this study, we evaluated potential sex differences in spontaneous nociceptive responses, referred abdominal hypersensitivity, disease progression, and bowel pathology in mouse models of acute and persistent colon inflammation. Our experiments show that females exhibit more nociceptive responses and referred abdominal hypersensitivity than males in the context of acute but not persistent colon inflammation. We further demonstrate that, after acute and persistent colon inflammation, pain-related behavioral responses in females and males are distinct, with increases in licking of the abdomen only observed in females and increases in abdominal contractions only seen in males. During persistent colon inflammation, males exhibit worse disease progression than females, which is manifested as worse physical appearance and higher weight loss. However, no measurable sex differences were observed in persistent inflammation-induced bowel pathology, stool consistency, or fecal blood. Overall, our findings demonstrate sex differences in pain-related behaviors and disease progression in the context of acute and persistent colon inflammation, highlighting the importance of considering sex as a biological variable in future mechanistic studies of visceral pain as well as in the development of diagnostics and therapeutic options for chronic gastrointestinal diseases.

Nalbuphine May Be Superior to Sufentanil in Relieving Postcesarean Uterine Contraction Pain in Multiparas: A Retrospective Cohort Study

Purpose

Postcesarean pain remains a major complaint from puerperium women who have undergone cesarean section, especially uterine contraction induced visceral pain. The optimal opioid for pain relief after cesarean section (CS) is still unclear. The goal of this study was to compare the analgesic effect of Nalbuphine to Sufentanil in patients who underwent CS.

Patients and Methods

In this single-center retrospective cohort study, we included patients who received Nalbuphine or Sufentanil Patient-Controlled Intravenous Analgesia (PCIA) after CS between 1 January 2018 and 30 November 2020. Data on a Visual Analog Scale (VAS) at uterine contraction, at rest, and at movement, analgesic consumption, and side effects were collected. We performed logistic regression to identify predictors of severe uterine contraction pain.

Results

A total of 674 patients were identified in the unmatched cohort, and 612 patients in the matched one. Compared to the Sufentanil group, lower VAS-contraction was recorded in the Nalbuphine group in both the unmatched and matched cohorts, the mean difference (MD) on POD1 was 0.35 (95% CI: 0.17 to 0.54, p<0.001) and 0.28 (95% CI: 0.08 to 0.47, p<0.001), respectively, and the MD of POD2 was 0.12 (95% CI: 0.03 to 0.40, P=0.019) and 0.12 (95% CI: 0.03 to 0.41, P=0.026), respectively. On POD1 but not POD2, VAS-movement was lower in the Nalbuphine group as compared to the Sufentanil group. No difference was found between VAS-rest on POD1 and POD2 in both unmatched and matched cohorts. Less analgesic consumption, and side effects were recorded in the Nalbuphine group. Logistic regression indicated that multipara and analgesic consumption were risk factors for severe uterine contraction pain. In subgroup analysis, VAS-contraction was meaningfully reduced in the Nalbuphine group compared with the Sufentanil group in multipara patients, but not primiparas.

Conclusion

Compared to Sufentanil, Nalbuphine may provide better analgesia on uterine contraction pain. The superior analgesia may only exhibit in multiparas.

Involvement of Intestinal Enteroendocrine Cells in Neurological and Psychiatric Disorders

Neurological and psychiatric patients have increased dramatically in number in the past few decades. However, effective treatments for these diseases and disorders are limited due to heterogeneous and unclear pathogenic mechanisms. Therefore, further exploration of the biological aspects of the disease, and the identification of novel targets to develop alternative treatment strategies, is urgently required. Systems-level investigations have indicated the potential involvement of the brain–gut axis and intestinal microbiota in the pathogenesis and regulation of neurological and psychiatric disorders. While intestinal microbiota is crucial for maintaining host physiology, some important sensory and regulatory cells in the host should not be overlooked. Intestinal epithelial enteroendocrine cells (EECs) residing in the epithelium throughout intestine are the key regulators orchestrating the communication along the brain-gut-microbiota axis. On one hand, EECs sense changes in luminal microorganisms via microbial metabolites; on the other hand, they communicate with host body systems via neuroendocrine molecules. Therefore, EECs are believed to play important roles in neurological and psychiatric disorders. This review highlights the involvement of EECs and subtype cells, via secretion of endocrine molecules, in the development and regulation of neurological and psychiatric disorders, including Parkinson’s disease (PD), schizophrenia, visceral pain, neuropathic pain, and depression. Moreover, the current paper summarizes the potential mechanism of EECs in contributing to disease pathogenesis. Examination of these mechanisms may inspire and lead to the development of new aspects of treatment strategies for neurological and psychiatric disorders in the future.

Practical approach to irritable bowel syndrome-diarrhea beyond low-FODMAP diet

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by abdominal pain and altered defecation, usually accompanied by abdominal bloating or distension. The integrated model of bidirectional interaction between the central, autonomic, enteric nervous system, the microbiome, and the gut barrier allows a better understanding of the pathophysiology of IBS, as well as consideration of potential therapeutic strategies. IBS with predominant diarrhea (IBS-D) represents a therapeutic challenge. Dietary changes or restrictions are most commonly used by patients in an attempt at symptom control. Therefore, a number of diets, especially low-FODMAP diet, have increasingly gained interest as a therapy for IBS-D or mixed IBS. However, this kind of diet, while effective, is not exempt of problems. It is therefore necessary that other therapeutic options be considered while bearing pathophysiological mechanisms and general symptom management in mind.

Electroacupuncture Attenuates Post-Inflammatory IBS-Associated Visceral and Somatic Hypersensitivity and Correlates With the Regulatory Mechanism of Epac1-Piezo2 Axis

Electroacupuncture (EA) is considered to have a therapeutic effect in the relief of irritable bowel syndrome (IBS)-associated visceral hypersensitivity via the reduction of the level of 5-hydroxytryptamine (5-HT) and 5-HT₃ receptors (5-HT₃R). However, whether Epac1/Piezo2, as the upstream of 5-HT, is involved in this process remains unclear. We investigated whether EA at the ST36 and ST37 acupoints alleviated visceral and somatic hypersensitivity in a post-inflammatory IBS (PI-IBS) model mice via the Epac1-Piezo2 axis. In this study, we used 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced PI-IBS as a mouse model. Visceral sensitivity was assessed by the abdominal withdrawal reflex test. Somatic sensitivity was evaluated by the hind paw withdrawal threshold. Quantitative real-time PCR, immunofluorescence staining, ELISA, and Western blotting were performed to examine the expressions of Epac1, Piezo2, 5-HT, and 5-HT₃R from the mouse distal colon/L5-S2 dorsal root ganglia (DRG). Our results showed that EA improved the increased visceral sensation and peripheral mechanical hyperalgesia in PI-IBS model mice, and the effects of EA were superior to the sham EA. EA significantly decreased the protein and mRNA levels of Epac1 and Piezo2, and reduced 5-HT and 5-HT₃R expressions in the distal colon. Knockdown of colonic Piezo2 eliminated the effect of EA on somatic hypersensitivity. Combined knockdown of colonic Epac1 and Piezo2 synergized with EA in relieving visceral hypersensitivity and blocked the effect of EA on somatic hypersensitivity. Additionally, protein levels of Epac1 and Piezo2 were also found to be decreased in the L5-S2 DRGs after EA treatment. Taken together, our study suggested that EA at ST36 and ST37 can alleviate visceral and somatic hypersensitivity in PI-IBS model mice, which is closely related to the regulation of the Epac1-Piezo2 axis.

Oral and parenteral anti-neuropathic agents for the management of pain and discomfort in irritable bowel syndrome: A systematic review and meta-analysis

BACKGROUND

Irritable bowel syndrome (IBS) is a highly prevalent and economically burdensome condition; and pain is often the most unpleasant, disruptive, and difficult-to-treat symptom. Visceral hypersensitivity is a common feature driving pain in IBS, suggesting that neuropathic mechanisms may be implicated. We conducted a systematic review of available evidence to examine the role of anti-neuropathic medicines in the management of pain in IBS.

METHODS

We systematically searched scientific repositories for trials investigating conventional oral, and/or parenteral, pharmaceutical antineuropathic treatments in patients with IBS. We summarized key participant characteristics, outcomes related to pain (primary outcome), and selected secondary outcomes.

KEY RESULTS

We included 13 studies (n = 629 participants): six investigated amitriptyline, three duloxetine, three pregabalin, and one gabapentin. There was considerable methodological and statistical heterogeneity, so we performed a narrative synthesis and limited meta-analysis. Amitriptyline was most extensively studied, though only in diarrhea-predominant patients. In individual trials, amitriptyline, pregabalin and gabapentin generally appeared beneficial for pain outcomes. While duloxetine studies tended to report improvements in pain, all were un-controlled trials with high risk of bias. Meta-analysis of three studies (n = 278) yielded a pooled relative-risk of 0.50 (95%CI 0.38-0.66) for not improving with anti-neuropathic agent vs control. We did not identify any eligible studies investigating the role of parenteral anti-neuropathics.

CONCLUSIONS AND INFERENCES

Anti-neuropathic analgesics may improve pain in IBS, and deserve further, high-quality investigation, potentially considering parenteral administration and agents with minimal gastrointestinal motility effects. Investigation of amitriptyline's efficacy in non-diarrhea-predominant subtypes is currently lacking, and we recommend particular caution for its use in IBS-C.

Subcortical-Cortical Functional Connectivity as a Potential Biomarker for Identifying Patients with Functional Dyspepsia

The diagnosis of functional dyspepsia (FD) presently relies on the self-reported symptoms. This study aimed to determine the potential of functional brain network features as biomarkers for the identification of FD patients. Firstly, the functional brain Magnetic Resonance Imaging data were collected from 100 FD patients and 100 healthy subjects, and the functional brain network features were extracted by the independent component analysis. Then, a support vector machine classifier was established based on these functional brain network features to discriminate FD patients from healthy subjects. Features that contributed substantially to the classification were finally identified as the classifying features. The results demonstrated that the classifier performed pretty well in discriminating FD patients. Namely, the accuracy of classification was 0.84 ± 0.03 in cross-validation set and 0.80 ± 0.07 in independent test set, respectively. A total of 15 connections between the subcortical nucleus (the thalamus and caudate) and sensorimotor cortex, parahippocampus, orbitofrontal cortex were finally determined as the classifying features. Furthermore, the results of cross-brain atlas validation showed that these classifying features were quite robust in the identification of FD patients. In summary, the current findings suggested the potential of using machine learning method and functional brain network biomarkers to identify FD patients.

Efficacy of Linaclotide in Reducing Abdominal Symptoms of Bloating, Discomfort, and Pain: A Phase 3B Trial Using a Novel Abdominal Scoring System

INTRODUCTION

Linaclotide improves abdominal pain and constipation in patients with constipation-predominant irritable bowel syndrome (IBS-C). Patients report additional bothersome abdominal symptoms of bloating and discomfort. The intention of this study was to evaluate linaclotide's efficacy in relieving IBS-C-related abdominal symptoms (bloating, discomfort, and pain) using a novel multi-item Abdominal Score (AS).

METHODS

Patients with IBS-C with abdominal pain ≥3 (0-10 scale) were randomized to linaclotide 290 μg or placebo daily for 12 weeks. The AS, derived from the Diary for IBS Symptoms-Constipation, is the average of abdominal bloating, discomfort, and pain at their worst (0 = none, 10 = worst possible). The primary end point was overall change from baseline (CFB) in AS. Secondary end points included CFB in 12-week AS evaluated using cumulative distribution function and 6-week/12-week AS responder (AS improvement ≥2 points for ≥6-week/12-week).

RESULTS

Overall, 614 patients (mean age 46.7 years; 81% female) were randomized. All prespecified end points showed significant benefit of linaclotide vs placebo. The mean overall CFB AS reduction for linaclotide was -1.9 vs -1.2 for placebo (P < 0.0001); the 6-week/12-week AS responder rate was 40.5% for linaclotide vs 23.4% for placebo (odds ratio = 2.2 [95% confidence interval, 1.55-3.12; P < 0.0001]). Diarrhea was the most common treatment-emergent adverse event (linaclotide = 4.6%, placebo = 1.6%).

DISCUSSION

Linaclotide significantly reduced multiple abdominal symptoms important to patients with IBS-C (bloating, discomfort, and pain) compared with placebo, as measured by a novel multi-item AS. The AS, derived from the Diary for IBS Symptoms-Constipation, should be considered for use in future IBS-C clinical studies to measure clinically meaningful improvements beyond traditional end points.

Sensory Adaptation Training or Escitalopram for IBS With Constipation and Rectal Hypersensitivity: A Randomized Controlled Trial

INTRODUCTION

Rectal hypersensitivity is an important pathophysiological dysfunction in irritable bowel syndrome with predominant constipation (IBS-C), whose treatment remains challenging. In a randomized controlled trial, we compared the efficacy and safety of a novel sensori-behavioral treatment, sensory adaptation training (SAT) with escitalopram.

METHODS

Patients with IBS-C (Rome III) with rectal hypersensitivity received 6 biweekly sessions of SAT or escitalopram 10 mg daily for 3 months. SAT was performed by repetitive gradual distension of 10-cm long highly compliant rectal balloon above tolerability thresholds using barostat. Treatment effects on sensory thresholds and symptoms were compared. Coprimary outcome measures were those achieving improvements in rectal hypersensitivity (≥20% increase in ≥2/3 sensory thresholds) and pain (≥30% decrease).

RESULTS

We randomized 49 patients; 26 received SAT and 23 escitalopram. SAT significantly improved desire to defecate (Δ 13.5 ± 2.3 vs 2.2 ± 1.1 mm Hg, P = 0.0006) and maximum tolerability (Δ 14.8 ± 1.9 vs 1.6 ± 0.9 mm Hg, P < 0.0001) thresholds compared with escitalopram. There were significantly greater percentage of hypersensitivity responders with SAT than escitalopram (69% vs 17%, P < 0.001), but not pain responders (58% vs 44%, P = 0.4). Daily pain scores did not differ between groups (P = 0.8) or escitalopram (P = 0.06) but decreased with SAT (P = 0.0046) compared with baseline. SAT significantly increased rectal compliance (P < 0.019) and complete spontaneous bowel movements per week than escitalopram (P = 0.04). Five withdrew from adverse events with escitalopram and none with SAT.

DISCUSSION

SAT was significantly more efficacious in improving hypersensitivity and bowel symptoms in IBS-C than escitalopram. SAT is a promising novel treatment for IBS with rectal hypersensitivity.

Visceral pain, mechanisms, and implications in musculoskeletal clinical practice

The global impact of visceral pain is extremely high, representing a significant portion of all forms of chronic pain. In musculoskeletal practice, at least one-third of people with persistent noncancerous pain report recurrent abdominal, pelvic, or chest pain symptoms. Visceral pain can be felt in several different areas of the body and can migrate throughout a region, even though the site of origin does not appear to change. Traditionally, clinicians have examined musculoskeletal pain through a reductionist lens that ignores the influence of the visceral system on musculoskeletal pain. The hypothesis presented is that visceral pain has an important influence on developing and maintaining different types of musculoskeletal pain through processes within the peripheral or central nervous systems, as a result of a visceral nociceptive stimulus generated by pathoanatomical or functional alterations. The hypothesis predicts that a consideration of the function of the visceral system in musculoskeletal pain conditions will improve clinical outcomes, moving beyond a linear model and adopting a more holistic approach, especially in the more complex groups of patients.

Validation of the Leiden Visual Sensitivity Scale and Visual Discomfort Scale in Chronic Pain Conditions

Discomfort provoked by normally innocuous visual stimuli has been reported by people with chronic pain. Visual discomfort may be higher in pain conditions in which central sensitization is implicated, such as Complex Regional Pain Syndrome (CRPS) and fibromyalgia. In an online study, we validated the Leiden Visual Sensitivity Scale (L-VISS) and Visual Discomfort Scale (VDS) in people with CRPS (n = 57), fibromyalgia (n = 75), and general chronic pain (n = 53); investigated whether these groups and pain-free controls (n = 125) differed in visual discomfort; and evaluated the effect of age. The L-VISS and VDS had good internal consistency. Both scales were positively related with experimentally induced visual distortions for mid-spatial frequency striped patterns, suggesting good construct validity. The scales were positively related with each other, and dissociated between the pain and pain-free groups in similar ways, suggesting good construct validity. There was no relationship between age and L-VISS scores and a small negative relationship between age and VDS scores. Visual discomfort was highest in the fibromyalgia group, followed by the CRPS group. This research confirms the utility of the L-VISS and VDS for measuring visual sensitivity in chronic pain and adds to evidence that central sensitization is an important mechanism of visual discomfort.

The association between exposure to domestic abuse in women and the development of syndromes indicating central nervous system sensitization: A retrospective cohort study using UK primary care records

BACKGROUND

Domestic abuse is a global public health issue. The association between the development of central sensitivity syndromes (CSS) and previous exposure to domestic abuse has been poorly understood particularly within European populations.

METHODS

A retrospective cohort study using the 'The Health Improvement Network,' (UK primary care medical records) between 1st January 1995-31st December 2018. 22,604 adult women exposed to domestic abuse were age matched to 44,671 unexposed women. The average age at cohort entry was 36 years and the median follow-up was 2.5 years. The outcomes of interest were the development of a variety of syndromes which demonstrate central nervous system sensitization. Fibromyalgia, chronic fatigue syndrome and temporomandibular joint disorder outcomes have been reported previously. Outcomes were adjusted for the presence of mental ill health.

RESULTS

During the study period, women exposed to domestic abuse experienced an increased risk of developing chronic lower back pain (adjusted incidence rate ratio [aIRR] 2.28; 95% CI 1.85-2.80), chronic headaches (aIRR 3.15; 95% CI 1.07-9.23), irritable bowel syndrome (aIRR 1.41; 95% CI 1.25-1.60) and restless legs syndrome (aIRR 1.89; 95% CI 1.44-2.48). However, no positive association was seen with the development of interstitial cystitis (aIRR 0.52; 95% CI 0.14-1.93), vulvodynia (aIRR 0.42; 95% CI 0.14-1.25) and myofascial pain syndrome (aIRR 1.01; 95% CI 0.28-3.61).

CONCLUSION

This study demonstrates the need to consider a past history of domestic abuse in patients presenting with CSS; and also consider preventative approaches in mitigating the risk of developing CSS following exposure to domestic abuse.

SIGNIFICANCE

Domestic abuse is a global public health issue, with a poorly understood relationship with the development of complex pain syndromes. Using a large UK primary care database, we were able to conduct the first global cohort study to explore this further. We found a strong pain morbidity burden associated with domestic abuse, suggesting the need for urgent public health intervention to not only prevent domestic abuse but also the associated negative pain consequences.

The association between exposure to childhood maltreatment and the subsequent development of functional somatic and visceral pain syndromes

BACKGROUND

Childhood maltreatment is a global public health issue linked to a vast mortality and morbidity burden. This study builds on current literature to explore the risk of developing central sensitivity syndromes (CSS) (consisting of somatic and visceral pain syndromes) subsequent to childhood maltreatment exposure.

METHODS

A retrospective population based open cohort study using the UK primary care database, 'The Health Improvement Network,' between 1st January 1995-31st December 2018. 80,657 adult patients who had experienced childhood maltreatment or maltreatment related concerns (exposed patients) were matched to 161,314 unexposed patients by age and sex. Outcomes of interest were the development of CSS: either somatic (Fibromyalgia, chronic fatigue syndrome, temporomandibular joint disorder, chronic lower back pain, chronic headache, myofascial pain syndrome and restless leg syndrome) or visceral (Interstitial cystitis, vulvodynia, chronic prostatitis and irritable bowel syndrome) in nature. Effect sizes are presented as adjusted incidence rate ratios (aIRR) with confidence intervals (CI). Models were adjusted for the following covariates at cohort entry: age, sex, deprivation, anxiety, depression and serious mental ill health.

RESULTS

The average age at cohort entry was 23.4 years and the median follow was 2.2 years. There was an increased risk of developing fibromyalgia (aIRR 2.06; 95% CI 1.71-2.48), chronic fatigue syndrome (1.47; 1.08-2.00), chronic lower back pain (1.99; 1.68-2.35), restless leg syndrome (1.82; 1.41-2.35) and irritable bowel syndrome (1.15; 1.08-1.22) when compared to the unexposed group, whereas no statistical association was seen with the development of temporomandibular joint disorder (1.00; 0.88-1.13), chronic headache (1.04; 0.59-1.86), interstitial cystitis (1.19; 0.51-2.74), vulvodynia (0.65; 0.34-1.26), chronic prostatitis (0.34; 0.07-1.77) and myofascial pain syndrome (0.88; 0.36-2.14). Outcome numbers were low, most likely, due to the rarity of visceral conditions (aside from irritable bowel syndrome). The association between a history of childhood maltreatment and CSS were mainly observed in somatic CSS.

INTERPRETATION

The debilitating effects of CSS carry a substantial physical, psychological and economic burden to both the individuals who are diagnosed with them and the health services who serve them. Primary prevention approaches targeting childhood maltreatment as well as secondary preventative approaches should be considered to minimise the associated burden of CSS.

Hyperexcitability of the Central Nervous System in Children with Chronic Pain: A Systematic Review

Objective

Hyperexcitability of the central nervous system plays an important role in the development and maintenance of chronic pain in adults. This knowledge has led to improved treatment strategies within this population. In children, however, research on the presence of central hyperexcitability is scarce. To further investigate this topic in children with chronic pain, there is a need for a clear literature overview.

Design

Systematic review.

Methods

The literature search was performed using the electronic databases PubMed and Web of Science. An article was considered eligible if it included children (age two to 12 years) diagnosed with chronic pain. Articles had to report original research outcomes related to central hyperexcitability, and a comparison with a healthy control group was necessary. Characteristics of the study sample, the assessment, and conclusions regarding central hyperexcitability were extracted from each included article.

Results

Twelve case-control studies were included with moderate to good methodological quality (510 children with chronic pain and 670 healthy controls). After summarizing the articles' results on indices of central hyperexcitability, we concluded that secondary hyperalgesia might be present in children with recurrent abdominal pain, juvenile fibromyalgia, and juvenile idiopathic arthritis. Preliminary evidence exists for altered cortical nociceptive processing in children with migraine and recurrent abdominal pain.

Conclusion

Based on the results of this review, central hyperexcitability might be present in in several pediatric chronic pain conditions. Further research on other manifestations of central hyperexcitability (e.g., bottom-up and top-down mechanisms and nociceptive brain changes) is necessary to provide firm evidence about its presence in children with chronic pain.

The comorbidities of dysmenorrhea: a clinical survey comparing symptom profile in women with and without endometriosis

Purpose

Dysmenorrhea is a common disorder that substantially disrupts the lives of young women. The frequency of 14 associated symptoms both within and outside the pelvis was determined.

Patients and methods

Symptom questionnaires were completed by 168 women with dysmenorrhea, allocated to three groups based on their diagnostic status for endometriosis confirmed (Endo+), endometriosis excluded (Endo-), or endometriosis diagnosis unknown (No Lap). Those with endometriosis confirmed were further divided into current users (Endo+ Hx+) and non-users of hormonal treatments (Endo+ Hx-). Users of hormonal treatments were further divided into users (Endo+ Hx+ LIUCD+) and non-users (Endo+ Hx+ LIUCD-) of a levonorgestrel-releasing intra-uterine contraceptive device (LIUCD). The frequency and number of symptoms within groups and the effect of previous distressing sexual events were sought.

Results

Women with and without endometriosis lesions had similar symptom profiles, with a mean of 8.5 symptoms per woman. Only 0.6% of women reported dysmenorrhea alone. The presence of stabbing pelvic pains was associated with more severe dysmenorrhea (P=0.006), more days per month of dysmenorrhea (P=0.003), more days per month of pelvic pain (P=0.016), and a diagnosis of migraine (P=0.054). The symptom profiles of the Endo+ Hx+ and Endo+ Hx- groups were similar. A history of distressing sexual events was associated with an increased number of pain symptoms (P=0.003).

Conclusion

Additional symptoms are common in women with dysmenorrhea, and do not correlate with the presence or absence of endometriosis lesions. Our study supports the role of central sensitization in the pain of dysmenorrhea. The presence of stabbing pelvic pains was associated with increased severity of dysmenorrhea, days per month of dysmenorrhea, days per month of pelvic pain, and a diagnosis of migraine headache. A past history of distressing sexual events is associated with an increased number of pain symptoms.

Urology Consultation and Emergency Department Revisits for Children with Urinary Stone Disease

PURPOSE

We determined the association between urology consultation and emergency department revisits for children with urinary stones.

MATERIALS AND METHODS

This retrospective cohort study included patients 18 years old or younger who presented to an emergency department in South Carolina with a urinary stone from 1997 to 2015. The primary exposure was urology consultation during the index emergency department visit. The primary outcome was a stone related emergency department revisit occurring within 180 days of discharge from an index emergency department visit. Secondary outcomes included computerized tomography use, inpatient admission and emergent surgery.

RESULTS

Of 5,642 index emergency department visits for acute urinary stones 11% resulted in at least 1 stone related emergency department revisit within 180 days. Of revisits 59% occurred within 30 days of discharge and 39% were due to pain. The odds of emergency department revisit were highest within the first 48 hours of discharge home (OR 22.6, 95% CI 18.0 to 28.5) and rapidly decreased thereafter. Urology consultation was associated with a 37% lower adjusted odds of emergency department revisit (OR 0.63, 95% CI 0.44 to 0.90) and 68% lower odds of computerized tomography use across all emergency department visits (OR 0.32, 95% CI 0.15 to 0.69). Among patients who revisited the emergency department the frequency of pain complaints was 27% in those with a urological consultation at the index visit and 39% in those without.

CONCLUSIONS

Urology consultation was associated with decreased emergency department revisits and computerized tomography use in pediatric patients with urinary stones. Future studies should identify patients who benefit most from urology consultation and ascertain processes of care that decrease emergency department revisits among high risk patients.

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.

Fibromyalgia remains a significant burden in rheumatoid arthritis patients in Australia

AIM

High rates of fibromyalgia (FM) are reported in rheumatoid arthritis (RA) patients. Advances in RA management have occurred, but information regarding current significance of FM in RA is limited. This investigation estimated the prevalence and health effects of concomitant FM in Australian RA patients.

METHODS

Participants were recruited from Australian rheumatology clinics. Subjects were assessed using the 1990 and 2011 American College of Rheumatology (ACR) FM criteria and the polysymptomatic distress score (PDS) was calculated. A medical history and a clinical examination were recorded. RA Disease Activity Score of 28 joints - erythrocyte sedimentation rate (DAS-28 ESR), and the Short Form-36 survey (SF-36) were completed.

RESULTS

Of 117 RA patients, 33.3% (n = 39) met 1990 ACR FM criteria and 41.9% (n = 49) met 2011 ACR FM criteria. RA patients with comorbid FM had worse outcomes across all domains of health as defined by the SF-36 (P < 0.05). There was correlation between both physical and mental health outcomes and the PDS (P < 0.001). RA patients with FM on average took 1.18 extra ongoing prescribed medications (P < 0.05), despite comparable RA disease activity (DAS-28: 3.09 vs. 3.27, P = NS). Comorbid central sensitivity conditions were more common in patients with FM (P < 0.001).

CONCLUSION

FM continues to demonstrate a high prevalence in a population of RA patients. RA patients with FM have more symptoms of other chronic sensitivity syndromes in addition to FM. They have a lower quality of life outcome and higher medication use. This has important clinical implications in terms of diagnosis, response to therapy, prescribing choices and clinical outcomes.

Comparison of Rectal and Esophageal Sensitivity in Women With Functional Heartburn

This study tested the primary hypothesis that there is a correlation of maximum pain threshold (MPT) in the esophagus and rectum in persons with functional heartburn. Secondary aims evaluated correlations with initial perception threshold (IPT) and pain threshold (PT). This study explored objective sensory endpoints of IPT, PT, and MPT in the esophagus and rectum of 14 females with functional heartburn to determine whether visceral hypersensitivity is generalized or organ-specific. Data on volume and pressure measurements at IPT, PT, and MPT with esophageal and rectal barostat distention were collected. The relationship of sensation and pain to volume, pressure, and compliance was analyzed. Esophageal and rectal IPT balloon volume scores were highly and significantly correlated (r = .61, p = .02). Esophageal and rectal PT balloon volume scores were highly and significantly correlated (r = .6, p = .02). Esophageal and rectal MPT balloon volume scores were not correlated (r = .35, p = .26). The correlation of visceral sensitivity in the esophagus and rectum in persons with functional heartburn supports the hypothesis that visceral sensory changes in functional gastrointestinal disorders are not organ specific.

Functional neuroimaging studies in functional dyspepsia patients: a systematic review

BACKGROUND

There is increasing evidence in support of the presence of abnormal central changes (compared to healthy controls) in functional dyspepsia (FD) in addition to the peripheral changes in gastrointestinal tract.

PURPOSE

This systematic review aims to provide an integrative understanding of the abnormal functional brain activity, visceral sensation, dyspeptic symptoms, and psychological changes of FD. Electronic and hand searches were conducted to identify functional neuroimaging studies involving FD patients. Sixteen studies were selected and divided into three categories: 10 resting state studies, three visceral distention studies, and three acupuncture studies. Changes were reported in several brain areas in FD patients including the frontal cortex, somatosensory cortex, insula, anterior cingulate cortex, thalamus, hippocampus, and amygdala. These brain activity changes were associated with visceral hypersensitivity, dyspeptic symptoms, poorer quality of life, anxiety, and depression. The results show that FD is associated with functional abnormalities in sensory and pain modulation, emotion, saliency, and homeostatic processing regions. The diversity of conditions, heterogeneous results, poorly standardized diagnoses of FD, and various comorbidities may be responsible for the variability in the results.

Factors Predicting Outcomes After a Total Pancreatectomy and Islet Autotransplantation Lessons Learned From Over 500 Cases

OBJECTIVE

Our objective was to analyze factors predicting outcomes after a total pancreatectomy and islet autotransplantation (TP-IAT).

BACKGROUND

Chronic pancreatitis (CP) is increasingly treated by a TP-IAT. Postoperative outcomes are generally favorable, but a minority of patients fare poorly.

METHODS

In our single-centered study, we analyzed the records of 581 patients with CP who underwent a TP-IAT. Endpoints included persistent postoperative "pancreatic pain" similar to preoperative levels, narcotic use for any reason, and islet graft failure at 1 year.

RESULTS

In our patients, the duration (mean ± SD) of CP before their TP-IAT was 7.1 ± 0.3 years and narcotic usage of 3.3 ± 0.2 years. Pediatric patients had better postoperative outcomes. Among adult patients, the odds of narcotic use at 1 year were increased by previous endoscopic retrograde cholangiopancreatography (ERCP) and stent placement, and a high number of previous stents (>3). Independent risk factors for pancreatic pain at 1 year were pancreas divisum, previous body mass index >30, and a high number of previous stents (>3). The strongest independent risk factor for islet graft failure was a low islet yield-in islet equivalents (IEQ)-per kilogram of body weight. We noted a strong dose-response relationship between the lowest-yield category (<2000 IEQ) and the highest (≥5000 IEQ or more). Islet graft failure was 25-fold more likely in the lowest-yield category.

CONCLUSIONS

This article represents the largest study of factors predicting outcomes after a TP-IAT. Preoperatively, the patient subgroups we identified warrant further attention.

Behavioral and molecular processing of visceral pain in the brain of mice: impact of colitis and psychological stress

Gastrointestinal disorders with abdominal pain are associated with central sensitization and psychopathologies that are often exacerbated by stress. Here we investigated the impact of colitis induced by dextran sulfate sodium (DSS) and repeated water avoidance stress (WAS) on spontaneous and nociception-related behavior and molecular signaling in the mouse brain. DSS increased the mechanical pain sensitivity of the abdominal skin while both WAS and DSS enhanced the mechanical and thermal pain sensitivity of the plantar skin. These manifestations of central sensitization were associated with augmented c-Fos expression in spinal cord, thalamus, hypothalamus, amygdala and prefrontal cortex. While WAS stimulated phosphorylation of mitogen-activated protein kinase (MAPK) p42/44, DSS activated another signaling pathway, both of which converged on c-Fos. The DSS- and WAS-induced hyperalgesia in the abdominal and plantar skin and c-Fos expression in the brain disappeared when the mice were subjected to WAS+DSS treatment. Intrarectal allyl isothiocyanate (AITC) evoked aversive behavior (freezing, reduction of locomotion and exploration) in association with p42/44 MAPK and c-Fos activation in spinal cord and brain. These effects were inhibited by morphine, which attests to their relationship with nociception. DSS and WAS exerted opposite effects on AITC-evoked p42/44 MAPK and c-Fos activation, which indicates that these transduction pathways subserve different aspects of visceral pain processing in the brain. In summary, behavioral perturbations caused by colitis and psychological stress are associated with distinct alterations in cerebral signaling. These findings provide novel perspectives on central sensitization and the sensory and emotional processing of visceral pain stimuli in the brain.

Role of principal ionotropic and metabotropic receptors in visceral pain

Visceral pain is the most common form of pain caused by varied diseases and a major reason for patients to seek medical consultation. It also leads to a significant economic burden due to workdays lost and reduced productivity. Further, long-term use of non-specific medications is also associated with side effects affecting the quality of life. Despite years of extensive research and the availability of several therapeutic options, management of patients with chronic visceral pain is often inadequate, resulting in frustration for both patients and physicians. This is, most likely, because the mechanisms associated with chronic visceral pain are different from those of acute pain. Accumulating evidence from years of research implicates several receptors and ion channels in the induction and maintenance of central and peripheral sensitization during chronic pain states. Understanding the specific role of these receptors will facilitate to capitalize on their unique properties to augment the therapeutic efficacy while at the same time minimizing unwanted side effects. The aim of this review is to provide a concise review of the recent literature that reports on the role of principal ionotropic receptors and metabotropic receptors in the modulation visceral pain. We also include an overview of the possibility of these receptors as potential new targets for the treatment of chronic visceral pain conditions.

Neurobiological mechanisms of pelvic pain

Pelvic pain is a common condition which significantly deteriorates health-related quality of life. The most commonly identified causes of pain in the pelvic region are gynaecologic, urologic, gastrointestinal, neurological, and musculoskeletal. However, in up to 33% of patients the source of this symptom is not identified, frustrating both patients and health-care professionals. Pelvic pain may involve both the somatic and visceral systems, making the differential diagnosing challenging. This paper aimed to review the mechanisms involved in pelvic pain perception by analyzing the neural plasticity and molecules which are involved in these complex circuits.

Total pancreatectomy and islet autotransplantation in chronic pancreatitis: recommendations from PancreasFest

DESCRIPTION

Total pancreatectomy with islet autotransplantation (TPIAT) is a surgical procedure used to treat severe complications of chronic pancreatitis or very high risk of pancreatic cancer while reducing the risk of severe diabetes mellitus. However, clear guidance on indications, contraindications, evaluation, timing, and follow-up are lacking.

METHODS

A working group reviewed the medical, psychological, and surgical options and supporting literature related to TPIAT for a consensus meeting during PancreasFest.

RESULTS

Five major areas requiring clinical evaluation and management were addressed: These included: 1) indications for TPIAT; 2) contraindications for TPIAT; 3) optimal timing of the procedure; 4) need for a multi-disciplinary team and the roles of the members; 5) life-long management issues following TPIAP including diabetes monitoring and nutrition evaluation.

CONCLUSIONS

TPIAT is an effective method of managing the disabling complications of chronic pancreatitis and risk of pancreatic cancer in very high risk patients. Careful evaluation and long-term management of candidate patients by qualified multidisciplinary teams is required. Multiple recommendations for further research were also identified.

Visceral and somatic sensory function in functional dyspepsia

BACKGROUND

Visceral hypersensitivity is one of the proposed underlying mechanisms in functional dyspepsia (FD). It is not clear whether visceral hypersensitivity in FD is a manifestation of a central sensitization also encompassing somatic sensitization. Transient receptor potential vanilloid-1 (TRPV(1)) pathways are involved in gastric mechanosensory physiology and the TRPV(1) receptor agonist, capsaicin, has been used as a chemical stimulant.

METHODS

In this double-blind, randomized study we evaluated both visceral and somatic sensory function in 34 FD patients and 42 healthy controls using quantitative sensory testing. Visceral pain sensitivity was assessed using a validated gastric pain model with oral capsaicin capsule titration and somatic pain sensitivity was determined by foot heat and hand electric stimulation.

KEY RESULTS

The median capsaicin dose required to attain moderate pain was 0.5mg in FD and 1mg in controls (P = 0.03). At these doses, mean pain intensities on a 0-100 visual analog scale were greater for FD than controls [56.9 (95% confidence intervals, 52.2-61.5) vs 45.1 (41.6-48.6), resp.] (P = 0.005). Overall, mean somatic sensory and pain thresholds were similar in FD and control groups, but in a subgroup of FD pain hypersensitivity was seen on the hand and on the foot at different stimulation thresholds.

CONCLUSIONS & INFERENCES

A majority of patients with FD have visceral chemo-hypersensitivity involving TRPV(1) pathways. A substantial subgroup also has somatic hypersensitivity as evidence of central sensitization.

Need for a comprehensive medical approach to the neuro-immuno-gastroenterology of irritable bowel syndrome

Irritable bowel syndrome (IBS) is defined by the Rome III criteria as symptoms of recurrent abdominal pain or discomfort with the onset of a marked change in bowel habits with no evidence of an inflammatory, anatomic, metabolic, or neoplastic process. As such, many clinicians regard IBS as a central nervous system problem of altered pain perception. Here, we review the recent literature and discuss the evidence that supports an organic based model, which views IBS as a complex, heterogeneous, inter-dependent, and multi-variable inflammatory process along the neuronal-gut axis. We delineate the organic pathophysiology of IBS, demonstrate the role of inflammation in IBS, review the possible differences between adult and pediatric IBS, discuss the merits of a comprehensive treatment model as taught by the Institute of Functional Medicine, and describe the potential for future research for this syndrome.

Biopsychosocial assessment criteria for functional chronic visceral pain: a pilot review of concept and practice

Functional chronic visceral pain (FCVP) is one of the most common causes of morbidity in the general population. Pain perceived within the abdomen may occur due to a range of different mechanisms according to the organ and their afferent pathways. Advances in our understanding of the complexities of FCVP could lead to the exploitation of contemporary research in order to develop and utilize our understanding of neurobiological and psychobiological visceral mechanisms in a clinical setting. This progression, together with increasing amounts of epidemiological and gender based information concerning specific abdominal pain syndromes can allow us to develop assessment tools that go beyond disease only analysis and move toward a more comprehensive assessment model so that patients may have access to expert or multidisciplinary management sooner, rather than later. Based on current evidence, one must consider the main contributors to pain, whether it is nociceptive, neuropathic or psychosocial or as is common with FCVP, a combination of all three.

AIM

This comprehensive assessment model should encompass not only systematic evaluation for reliable communication, but should also progress toward idiographic diagnosis relating to the uniqueness of the patient. This model should be practical in a multidisciplinary setting, taking into account the multi-faceted nature of this presentation.

Pelvic girdle pain in pregnancy: the impact of parity

OBJECTIVE

The purpose of this study was to estimate the association of parity with pelvic girdle syndrome (PGS; pain in anterior and bilateral posterior pelvis).

STUDY DESIGN

We included 75,939 pregnant women in the Norwegian Mother and Child Cohort Study. Data were obtained by self-administered questionnaires.

RESULTS

By pregnancy week 30, 15% of the women had developed PGS. Among first-time mothers, 11% of the women reported PGS, compared with 18% of the women with 1 previous delivery and 21% of women with 2 previous deliveries. The odds ratios for PGS of having had 1 or 2 previous deliveries were 1.9 (95% confidence interval [CI], 1.9-2.0) and 2.4 (95% CI, 2.3-2.6), respectively, after adjustment for other study factors. For PGS with severe pain, the corresponding odds ratios were 2.6 (95% CI, 2.3-2.9) and 3.8 (95% CI, 3.3-4.3).

CONCLUSION

The risk of the development of PGS increased with number of previous deliveries, which suggests that parity-related factors play a causal role.

Functional abdominal pain in childhood and adolescence increases risk for chronic pain in adulthood

A few studies of long-term outcomes for pediatric functional abdominal pain (FAP) have assessed acute non-abdominal pain at follow-up, but none has assessed chronic pain. We followed a cohort of pediatric patients with FAP (n=155) and a well control group (n=45) prospectively for up to 15 years. Participants ranged in age from 18 to 32 years at a follow-up telephone interview. FAP patients were classified as Resolved (n=101) versus Unresolved (n=54) at follow-up, based on whether they reported symptoms consistent with the adult Rome III criteria for a functional gastrointestinal disorder. Headache symptoms and reports of chronic non-abdominal pain also were assessed at follow-up. In the Unresolved group, 48.1% reported one or more sites of chronic non-abdominal pain at follow-up, compared to 24.7% in the Resolved group and 13.3% in the control group, p<0.01. More than half (57.4%) of the Unresolved group endorsed symptoms consistent with International Headache Society criteria for headache, compared to 44.6% of the Resolved group and 31% of controls, p<0.05. One-third of the Unresolved group reported both headache and one or more sites of chronic non-abdominal pain at follow-up, compared to 17.8% of the Resolved group and 4.4% of controls. Youth with FAP that persists into adulthood may be at increased risk for chronic pain and headache. Examination of central mechanisms that are common across chronic pain disorders may enhance understanding of this subgroup of FAP.

Unexplained gastrointestinal symptoms and joint hypermobility: is connective tissue the missing link?

BACKGROUND Unexplained gastrointestinal (GI) symptoms and joint hypermobility (JHM) are common in the general population, the latter described as benign joint hypermobility syndrome (BJHS) when associated with musculo-skeletal symptoms. Despite overlapping clinical features, the prevalence of JHM or BJHS in patients with functional gastrointestinal disorders has not been examined. METHODS The incidence of JHM was evaluated in 129 new unselected tertiary referrals (97 female, age range 16-78 years) to a neurogastroenterology clinic using a validated 5-point questionnaire. A rheumatologist further evaluated 25 patients with JHM to determine the presence of BJHS. Groups with or without JHM were compared for presentation, symptoms and outcomes of relevant functional GI tests. KEY RESULTS Sixty-three (49%) patients had evidence of generalized JHM. An unknown aetiology for GI symptoms was significantly more frequent in patients with JHM than in those without (P < 0.0001). The rheumatologist confirmed the clinical impression of JHM in 23 of 25 patients, 17 (68%) of whom were diagnosed with BJHS. Patients with co-existent BJHS and GI symptoms experienced abdominal pain (81%), bloating (57%), nausea (57%), reflux symptoms (48%), vomiting (43%), constipation (38%) and diarrhoea (14%). Twelve of 17 patients presenting with upper GI symptoms had delayed gastric emptying. One case is described in detail. CONCLUSIONS & INFERENCES In a preliminary retrospective study, we have found a high incidence of JHM in patients referred to tertiary neurogastroenterology care with unexplained GI symptoms and in a proportion of these a diagnosis of BJHS is made. Symptoms and functional tests suggest GI dysmotility in a number of these patients. The possibility that a proportion of patients with unexplained GI symptoms and JHM may share a common pathophysiological disorder of connective tissue warrants further investigation.

Brain activation in response to visceral stimulation in rats with amygdala implants of corticosterone: an FMRI study

Background

Although visceral pain of gastrointestinal (GI) origin is the major complaint in patients with irritable bowel syndrome (IBS) it remains poorly understood. Brain imaging studies suggest a defect in brain-gut communication in IBS with a greater activation of central arousal circuits including the amygdala. Previously, we found that stereotaxic implantation of corticosterone (CORT) onto the amygdala in rats induced anxiety and colonic hypersensitivity. In the present study we used functional magnetic resonance imaging (fMRI) to identify specific brain sites activated in a rat model characterized by anxiety and colonic hypersensitivity.

Methodology/Principal Findings

Anesthetized male rats received micropellets (30 µg each) of either CORT or cholesterol (CHOL), to serve as a control, implanted stereotaxically on the dorsal margin of each amygdala. Seven days later, rats were anesthetized and placed in the fMRI magnet (7T). A series of isobaric colorectal balloon distensions (CRD - 90s ‘off’, 30s ‘on’, 8 replicates) at two pressures (40 and 60 mmHg) were performed in a standard block-design. Cross correlation statistical analysis was used to determine significant differences between distended and non-distended states in CORT and CHOL-treated animals. Analysis of the imaging data demonstrated greater overall brain activation in response to CRD in rats with CORT implants compared to CHOL controls. Additionally, CORT implants produced significant positive bilateral increases in MRI signal in response to CRD in specific nuclei known as integration sites important in anxiety and pain perception.

Conclusions and Significance

These data indicate that chronic exposure of the amygdala to elevated levels of CORT enhances overall brain activation in response to CRD, and identified other specific brain regions activated in response to mechanical distension of the colon. These results demonstrate the feasibility of performing fMRI imaging in a rodent model that supports clinical observations in IBS patients with enhanced amygdala activation and symptomatology of abdominal pain and anxiety.

Estrogen altered visceromotor reflex and P2X(3) mRNA expression in a rat model of colitis

P2X(3) and P2X(2/3) receptors are expressed in peripheral tissues and dorsal root ganglia (DRG) and participate in peripheral pain. However, the mechanisms underlying P2X receptor-mediated nociception at different ovarial hormone levels has not been examined. In this study, 24 female rats were randomly divided into sham-operated (sham), ovariectomized (OVX), estrogen-treated, and estrogen-progesterone-treated groups with colitis. In each group, the visceromotor reflex (VMR) to colorectal distension was tested and the DRG were harvested for a real-time PCR analysis of P2X(3) and P2X(2) receptor mRNA. In OVX rats with colitis we found that the VMR to colorectal distension and P2X(3) receptor mRNA in DRG were both significantly decreased. Estrogen replacement reversed the decrease. However, neither the VMR nor the P2X(3) mRNA level in DRG from OVX colitis rats was reversed by the complex of estrogen and progesterone. Patch-clamp recording showed that in colitis rats, estradiol rapidly potentiated the sustained and transient currents evoked by ATP to 336+/-49% and 122+/-12% of controls, respectively, in a subpopulation of DRG neurons, which were blocked by ICI 182, 780, an antagonist of the estrogen receptor. Whereas progesterone rapidly inhibited the transient currents induced by ATP to 67+/-10% of control and had no effect on the sustained currents evoked by the same agonist. These results indicate that P2X(3) receptors are likely to be an important contributor to the altered colonic functions in colitis rats, where the underlying mechanisms are closely related to endogenous estrogen modulation.

Neuropathic pain in dogs and cats: if only they could tell us if they hurt

Neuropathic pain is difficult to diagnose in veterinary patients because they are unable to verbalize their pain. By assuming that neuropathic pain may exist based on the history of events that each patient has experienced, a focused client history and neurologic examination may identify a lesion resulting in persistent or spontaneous pain. Once neuropathic pain is diagnosed, a trial analgesic or acupuncture session(s) should be prescribed with instructions for owners to observe behavior. Dosing of the analgesic can be titrated to the patient's needs while avoiding adverse effects. When a particular analgesic may be ineffectual, an alternate class should be tried. As research into the neurobiologic mechanisms of neuropathic pain continues, specific therapies for its management should eventually appear in the human clinical setting and subsequently be investigated for veterinary clinical use.

G protein-coupled receptor kinase 6 controls post-inflammatory visceral hyperalgesia

Post-inflammatory pain is a poorly understood phenomenon. G protein-coupled receptors are involved in regulating pain signaling in the context of inflammation. G protein-coupled receptor kinases (GRK) modulate signaling through these receptors. We investigated whether GRK6 contributes to post-inflammatory visceral hyperalgesia. Colitis was induced in female mice by 1% dextran sodium sulphate in drinking water for 7 days. Disease score, colon length, and colonic cytokines were determined. On day 49, when animals had recovered from colitis, we induced visceral pain by intracolonic capsaicin instillation. Behavioral responses to capsaicin were monitored for 20 min. Referred hyperalgesia was measured using von Frey hairs. Spinal cord c-Fos was visualized by immunohistochemistry. In contrast to our earlier observations in male GRK6-/- and wild type (WT) mice, we did not detect differences in the course of colitis or in expression of colonic cytokines between female GRK6-/- and WT mice. After recovery from colitis, capsaicin-induced behavioral pain responses and spinal cord c-Fos expression were more pronounced in female GRK6-/- than WT mice. Naive GRK6-/- and WT animals did not differ in pain and c-Fos responses to capsaicin. Capsaicin-induced referred hyperalgesia post-colitis was increased in GRK6-/- compared to WT mice. However, referred hyperalgesia post-colitis was not affected by ablation of GRK6. Furthermore, in vitro IL-1beta sensitized the capsaicin receptor TRPV1 and this process was inhibited by over-expression of GRK6. We describe the novel concept that GRK6 inhibits post-inflammatory visceral hyperalgesia but does not contribute to visceral pain in naive animals. We propose that GRK6 regulates inflammation-induced sensitization of TRPV1.

Relation between clinical symptoms and experimental visceral hypersensitivity in pediatric patients with functional abdominal pain

OBJECTIVE

The association between clinical symptoms and laboratory visceral sensitivity remains poorly defined and controversial. It has even been suggested that laboratory observations of visceral sensitivity are irrelevant to the clinical presentation of chronic visceral pain. To better understand this association, gastrointestinal and psychological features of pediatric patients' clinical presentation were examined in relation to a laboratory-based measure of visceral sensitivity.

PATIENTS AND METHODS

At the time of their medical evaluation, 101 patients with medically unexplained abdominal pain (ages 8-15 years) completed validated questionnaires assessing recent depressive symptoms, functional disability, pain efficacy beliefs, gastrointestinal (GI), and non-GI symptoms. These clinical features were examined in relation to visceral sensitivity assessed 2 months later in the laboratory. The measure of visceral sensitivity was based on increases in GI complaints in response to the water load symptom provocation task.

RESULTS

More severe GI symptoms and functional disability in the weeks before patients' clinical evaluation were associated with significantly greater increases in GI symptoms in the laboratory in response to the water load symptom provocation task (all P < 0.04). Patients believing that they had the ability to alleviate their pain (high problem-focused pain efficacy) had significantly lower laboratory visceral sensitivity (P < 0.01). Clinical depressive symptoms and non-GI symptoms were not associated with laboratory visceral sensitivity.

CONCLUSIONS

Clinical presentations of more severe GI symptoms and disability as well as low perceived pain efficacy are significant predictors of laboratory visceral sensitivity in children with functional abdominal pain. Depression does not account for the association between clinical presentation of GI symptoms and a laboratory measure of visceral sensitivity.

Somatic pain sensitivity in children with recurrent abdominal pain

OBJECTIVE

Evidence is accumulating that recurrent abdominal pain (RAP) in children is associated with visceral hyperalgesia. However, it is not known whether somatic sensitivity is altered as well. Therefore, the aim of our study was to assess somatic pain sensitivity in children with RAP and healthy controls at the abdomen and a distal site (thenar).

METHODS

We examined 20 children with RAP (age 8-14) and 23 healthy control children (age 9-14). Heat and mechanical pain thresholds as well as measures of perceptual sensitization in response to repetitive mechanical or tonic thermal noxious stimulation were assessed.

RESULTS

At the abdominal site, pain sensitivity in children with RAP did not differ significantly when compared to controls. At the thenar, pain thresholds of children in the RAP group were not significantly different from control children. However, children with RAP showed less perceptual sensitization in response to tonic heat and repetitive mechanical stimuli (ps <or= 0.05) than controls.

CONCLUSIONS

We found no evidence for somatic hyperalgesia in RAP arguing against generalized hyperalgesia in these children. Somatic hypoalgesia at the thenar might either be related to a dysregulation of sensory processing and/or attentional avoidance of pain-related stimuli.

The Role of Angina Pectoris in Chronic Pain After Coronary Artery Bypass Graft Surgery

Visceral nociception readily sensitizes the central nervous system, causing referred somatic pain and hyperalgesia via somato-visceral convergence. Hyperalgesia in the perioperative period may increase vulnerability to subsequent development of chronic pain. The study aim is to investigate the role of angina pectoris, an ischemic visceral pain, in long-term pain after coronary artery bypass surgery (CABG). We sent questionnaires to 369 patients who underwent CABG surgery in 2003. Questions were asked about angina pectoris and other pain in the period before surgery, the first week postoperatively (= acute pain), and the period after 3 months after surgery (= chronic pain). We obtained results from 256 patients (response rate = 69%). The point prevalence of chronic pain after CABG was 27% after a mean follow-up of 16 months (SD +/- 3 months). Patients with chronic pain after CABG had more angina pectoris than those without chronic pain: Before surgery (P = .07), early on postoperatively (P = .004), and more than 3 months after surgery (P = .000004). We found cumulative prevalences of chronic pain after CABG at 3 months of 39%, and of 32% after 6 months. Other predictive factors for chronic pain after CABG were acute postoperative pain (P = .00002) and younger age (P = .002). Angina pectoris is associated with chronic pain after CABG surgery. Other predictive factors include acute postoperative pain and younger age.

PERSPECTIVE

The influence of postoperative angina pectoris for chronic pain after CABG surgery has not been described in the literature to date. Visceral nociception may play an important role in the development of chronic pain after surgery and should be taken into account in future studies.

Cognitive behavioural model of irritable bowel syndrome

“All or nothing” behaviour in irritable bowel syndrome

Visceral and somatic hypersensitivity in a subset of rats following TNBS-induced colitis

BACKGROUND

Chronic abdominal pain is one of the most common gastrointestinal symptoms experienced by patients. Visceral hypersensitivity has been shown to be a biological marker in many patients with chronic visceral pain. We have previously shown that IBS patients with visceral hypersensitivity also have evidence of thermal hyperalgesia of the hand/foot.

OBJECTIVE

The objective of the current study was to develop an animal model of chronic visceral and somatic hypersensitivity in rats treated with intracolonic trinitrobenzene sulfonic acid.

DESIGN

Male Sprague-Dawley rats (200-250g) were treated with either 20mg/rat trinitrobenzene sulfonic acid (TNBS, Sigma Chemical Co.) in 50% ethanol (n=75), an equivalent volume of 50% ethanol (n=20) or an equivalent volume of saline (n=20). The agents were delivered with a 24-gauge catheter inserted into the lumen of the colon. Mechanical and thermal behavioral tests were performed using an automated von Frey and Hargreaves device to evaluate somatic hyperalgesia. Colonic distension was performed using an automated distension device to evaluate visceral pain thresholds. All animals were tested 16weeks after TNBS treatment following complete resolution of the colitis.

RESULTS

At 16weeks, 24% of the treated rats (18/75 rats) still exhibited evidence of visceral as well as somatic hypersensitivity compared to saline- and ethanol-treated rats.

CONCLUSION

Transient colonic inflammation leads to chronic visceral and somatic hypersensitivity in a subset of rats. These findings are similar to the subset of patients who develop chronic gastrointestinal symptoms following enteric infection.