An experimental study of viscero-visceral hyperalgesia using an ultrasound-based multimodal sensory testing approach

Electroacupuncture intervention of visceral hypersensitivity is involved in PAR-2-activation and CGRP-release in the spinal cord

Electroacupuncture (EA) relieves visceral hypersensitivity (VH) with underlying inflammatory bowel diseases. However, the mechanism by which EA treats ileitis-induced VH is not clearly known. To assess the effects of EA on ileitis-induced VH and confirm whether EA attenuates VH through spinal PAR-2 activation and CGRP release, goats received an injection of 2,4,6-trinitro-benzenesulfonic-acid (TNBS) solution into the ileal wall. TNBS-injected goats were allocated into VH, Sham acupuncture (Sham-A) and EA groups, while goats treated with saline instead of TNBS solution were used as the control. Goats in EA group received EA at bilateral Hou-San-Li acupoints for 0.5 h at 7 days and thereafter repeated every 3 days for 6 times. Goats in the Sham-A group were inserted with needles for 0.5 h at the aforementioned acupoints without any hand manipulation and electric stimulation. Visceromotor responses to colorectal distension, an indicator of VH, were recorded by electromyography. The terminal ileum and thoracic spinal cord (T₁₁) were sampled for evaluating ileitis at days 7 and 22, and distribution and expression-levels of PAR-2, CGRP and c-Fos on day 22. TNBS-treated-goats exhibited apparent transmural-ileitis on day 7, microscopically low-grade ileitis on day 22 and VH at days 7–22. Goats of Sham-A, VH or EA group showed higher (P < 0.01) VH at days 7–22 than the Control-goats. EA-treated goats exhibited lower (P < 0.01) VH as compared with Sham-A or VH group. Immunoreactive-cells and expression-levels of spinal PAR-2, CGRP and c-Fos in the EA group were greater (P < 0.01) than those in the Control group, but less (P < 0.01) than those in Sham-A and VH groups on day 22. Downregulation of spinal PAR-2 and CGRP levels by EA attenuates the ileitis and resultant VH.

Upper Gastrointestinal Sensitization And Symptom Generation

Functional gastrointestinal disorders (FGIDs) are a highly prevalent group of heterogeneous disorders, and their diagnostic criteria are symptom-based, with the absence of anatomical and biochemical abnormalities of the gastrointestinal tract. Chronic visceral symptoms are common both in patients with an identifiable organic disease but also in FGID patients. Patients suffering from upper gastrointestinal functional disorders typically present with various symptoms such as early satiety, postprandial fullness, bloating, nausea, vomiting, and epigastric pain. Considering their increasing prevalence, difficulties in diagnosis, and low quality of life, FGIDs have become an emerging problem in gastroenterology. We aimed to provide an updated summary of pathways involved in visceral sensitization. We examined the recent literature searching for evidence of the most important studies about the mechanisms underlying gastrointestinal symptom generation and sensitization.

Viscero-visceral hyperalgesia in dysmenorrhoea plus previous urinary calculosis: Role of myofascial trigger points and their injection treatment in the referred area

BACKGROUND

Women with dysmenorrhoea plus symptomatic urinary calculosis experience enhanced pain and referred muscle hyperalgesia from both conditions than women with one condition only (viscero-visceral hyperalgesia). The study aimed at verifying if enhanced dysmenorrhoea persists after urinary stone elimination in comorbid women and if local anaesthetic inactivation of myofascial trigger points (TrPs) in the lumbar area (of urinary pain referral) also relieves dysmenorrhoea.

METHODS

Thirty-one women with dysmenorrhoea plus previous urinary calculosis (Dys+PrCal) and lumbar TrPs, and 33 women with dysmenorrhoea without calculosis (Dys) underwent a 1-year assessment of menstrual pain and muscle hyperalgesia in the uterus-referred area (electrical pain threshold measurement in rectus abdominis, compared with thresholds of 33 healthy controls). At the end of the year, 16 comorbid patients underwent inactivation of TrPs through anaesthetic injections, whereas the remaining 12 received no TrP treatment. Both groups were monitored for another year at the end of which thresholds were re-measured.

RESULTS

In year1, Dys+PrCal presented significantly more painful menstrual cycles and lower abdominal thresholds than Dys, thresholds of both groups being significantly lower than normal (p < .001). Anaesthetic treatment versus no treatment of the lumbar TrP significantly reduced the number of painful cycles during year2 and significantly increased the abdominal thresholds (p < .0001).

CONCLUSION

Viscero-visceral hyperalgesia between uterus and urinary tract may persist after stone elimination due to nociceptive inputs from TrPs in the referred urinary area, since TrPs treatment effectively reverses the enhanced menstrual symptoms. The procedure could represent an integral part of the management protocol in these conditions.

SIGNIFICANCE

A past pain process from an internal organ can continue enhancing pain expression from a painful disease in another neuromerically connected organ (viscero-visceral hyperalgesia) if secondary myofascial trigger points (TrPs) developed in the referred area at the time of the previous visceral disease. Inactivation of these TrPs reverts the enhancement. Assessment and treatment of TrPs in referred areas from past visceral pain conditions should be systematically carried out to better control pain from current diseases in other viscera.

Opioid-Induced Constipation and Bowel Dysfunction: A Clinical Guideline

OBJECTIVE

To formulate timely evidence-based guidelines for the management of opioid-induced bowel dysfunction.

SETTING

Constipation is a major untoward effect of opioids. Increasing prescription of opioids has correlated to increased incidence of opioid-induced constipation. However, the inhibitory effects of opioids are not confined to the colon, but also affect higher segments of the gastrointestinal tract, leading to the coining of the term "opioid-induced bowel dysfunction."

METHODS

A literature search was conducted using Medline, EMBASE, and EMBASE Classic, and the Cochrane Central Register of Controlled Trials. Predefined search terms and inclusion/exclusion criteria were used to identify and categorize relevant papers. A series of statements were formulated and justified by a comment, then labeled with the degree of agreement and their level of evidence as judged by the Strength of Recommendation Taxonomy (SORT) system.

RESULTS

From a list of 10,832 potentially relevant studies, 33 citations were identified for review. Screening the reference lists of the pertinent papers identified additional publications. Current definitions, prevalence, and mechanism of opioid-induced bowel dysfunction were reviewed, and a treatment algorithm and statements regarding patient management were developed to provide guidance on clinical best practice in the management of patients with opioid-induced constipation and opioid-induced bowel dysfunction.

CONCLUSIONS

In recent years, more insight has been gained in the pathophysiology of this "entity"; new treatment approaches have been developed, but guidelines on clinical best practice are still lacking. Current knowledge is insufficient regarding management of the opioid side effects on the upper gastrointestinal tract, but recommendations can be derived from what we know at present.

The Role of Esophageal Hypersensitivity in Functional Esophageal Disorders

The Rome IV diagnostic criteria delineates 5 functional esophageal disorders which include functional chest pain, functional heartburn, reflux hypersensitivity, globus, and functional dysphagia. These are a heterogenous group of disorders which, despite having characteristic symptom profiles attributable to esophageal pathology, fail to demonstrate any structural, motility or inflammatory abnormalities on standard clinical testing. These disorders are associated with a marked reduction in patient quality of life, not least considerable healthcare resources. Furthermore, the pathophysiology of these disorders is incompletely understood. In this narrative review we provide the reader with an introductory primer to the structure and function of esophageal perception, including nociception that forms the basis of the putative mechanisms that may give rise to symptoms in functional esophageal disorders. We also discuss the provocative techniques and outcome measures by which esophageal hypersensitivity can be established.

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.

Systematic review: instruments to assess abdominal pain in irritable bowel syndrome

BACKGROUND

Consensus on standard methods to assess chronic abdominal pain in patients with irritable bowel syndrome (IBS) is currently lacking.

AIM

To systematically review the literature with respect to instruments of measurement of chronic abdominal pain in IBS patients.

METHODS

Systematic literature search was performed in PubMed/Medline databases for studies using pain measurement instruments in patients with IBS.

RESULTS

One hundred and ten publications were reviewed. A multitude of different instruments is currently used to assess chronic abdominal pain in IBS patients. The single-item methods, e.g. the validated 10-point numeric rating scale (NRS), and questionnaires assessing gastrointestinal symptoms severity, focus mostly on the assessment of only the intensity of abdominal pain. Of these questionnaires, the validated IBS-Symptom Severity Scale includes the broadest measurement of pain-related aspects. General pain questionnaires and electronic momentary symptom assessment tools have been used to study abdominal pain in IBS patients, but have not yet been validated for this purpose. The evidence for the use of provocation tests, e.g. the rectal barostat with balloon distention, for measurement of abdominal pain in IBS is weak, due to the poor correlation between visceral pain thresholds assessed by provocation tests and abdominal pain as assessed by retrospective questionnaires.

CONCLUSIONS

The multitude of different instruments to measure chronic abdominal pain in IBS makes it difficult to compare endpoints of published studies. There is need for validated instruments to assess chronic abdominal pain in IBS patients, that overcome the limitations of the currently available methods.

The effects of morphine and methylnaltrexone on gastrointestinal pain in healthy male participants

BACKGROUND

Opioid antagonists are increasingly used to abolish the gastrointestinal side effects of opioids. However, they can potentially interfere with local analgesia exerted via opioid receptors in the gut. Thus, in the current study we aimed to explore the effect of rectal morphine before and after blocking opioid receptors outside the central nervous system with methylnaltrexone (MNTX).

METHODS

In this randomized, placebo controlled, cross-over study 15 healthy male participants received the following drugs at three separate sessions: (i) placebo, (ii) 30 mg morphine administered per rectum, or (iii) 12 mg MNTX given subcutaneously before 30 mg rectal morphine. At baseline and after drug administration peripheral and central effects of the drugs were assessed by experimental pain to the skin, muscle, rectum and pupillometry.

KEY RESULTS

Compared to placebo there was no local effect of morphine on mechanical rectal distension. In contrast, an increase in tolerated volume was seen following MNTX/morphine administration (p < 0.001), starting 7 min after dosing. Both morphine and MNTX/morphine had a central effect manifested as an increase in mechanical muscle pressure thresholds (both p < 0.001) and a decrease in pupil diameter (both p < 0.001). These effects occurred 30 min after dosing.

CONCLUSIONS & INFERENCES

No peripheral analgesic effect of morphine was found. Methodological shortcomings may have contributed to the lack of peripheral analgesia and thus, a peripheral morphine effect on rectal pain cannot be excluded. On the other hand, the combination of MNTX and morphine exerted a local effect on rectal distensions and seems to improve analgesia.

Effect of nortriptyline on brain responses to painful esophageal acid infusion in patients with non-erosive reflux disease

BACKGROUND

Non-erosive reflux disease (NERD) patients generally present with heartburn as the main symptom. Antidepressants might help to relieve heartburn by acting on the esophagus-brain axis. We aimed to assess the effect of nortriptyline on behavioral and brain responses to painful esophageal acid infusion in NERD patients evaluated with functional magnetic resonance imaging (fMRI).

METHODS

In a randomized double-blind crossover design, 20 NERD patients off proton pump inhibitors (36.1 ± 9.3 years, 75% women) were assigned to 21 days of nortriptyline and placebo, in counterbalanced order, with a 21 days washout period in between both treatment periods. Changes in acid-induced brain response on fMRI and heartburn perception were assessed and at the end of each treatment.

KEY RESULTS

Nortriptyline significantly reduced the acid-induced brain response in prefrontal cortex (median [IQR]: -1.9 [-4.5 to -0.1] vs -0.3 [-2.5 to 2.3]; p = 0.050), caudate (-3.0 [-5.1 to -0.01] vs 0.48 [-1.9 to 3.1]; p = 0.029), insula (-2.4 [-4.8 to -0.6] vs -0.2 [-1.5 to 1.5]; p = 0.029), cingulate (-4.2 [-8.8 to -0.1] vs -0.6 [-1.8 to 3.0]; p = 0.017), and hippocampus (-2.7 [-6.0 to 0.5] vs -0.04 [-2.3 to 1.9]; p = 0.006) in comparison with placebo. However, there was no significant difference between nortriptyline and placebo in clinical outcomes and side effects.

CONCLUSIONS & INFERENCES

Nortriptyline decreased the brain response to esophageal acid infusion more markedly than placebo, but without clinical significance.

Overlap of functional heartburn and gastroesophageal reflux disease with irritable bowel syndrome

Several studies indicate a significant degree of overlap between irritable bowel syndrome (IBS) and gastroesophageal reflux disease (GERD). Likewise, both functional heartburn (FH) and IBS are functional digestive disorders that may occur in the same patients. However, data establishing a solid link between FH and IBS are lacking, mainly because the clinical definition of FH has undergone substantial changes over the years. The available literature on the overlap between GERD or FH and IBS highlights considerable heterogeneity in terms of the criteria and diagnostic procedures used to assess heartburn and IBS. In particular, several epidemiological studies included patients with concomitant IBS and GERD without any attempt to distinguish FH (as defined by the Rome III criteria) from GERD via pathophysiological investigations. Independent of these critical issues, there is preliminary evidence supporting a significant degree of FH-IBS overlap. This underscores the need for studies based on updated diagnostic criteria and accurate pathophysiological classifications, particularly to distinguish FH from GERD. This distinction would represent an essential starting point to achieving a better understanding of pathophysiology in the subclasses of patients with GERD and FH and properly assessing the different degrees of overlap between IBS and the subcategories of heartburn.The present review article intends to appraise and critically discuss current evidence supporting a possible concomitance of GERD or FH with IBS in the same patients and to highlight the pathophysiological relationships between these disorders.

Human experimental pain models for assessing the therapeutic efficacy of analgesic drugs

Pain models in animals have shown low predictivity for analgesic efficacy in humans, and clinical studies are often very confounded, blurring the evaluation. Human experimental pain models may therefore help to evaluate mechanisms and effect of analgesics and bridge findings from basic studies to the clinic. The present review outlines the concept and limitations of human experimental pain models and addresses analgesic efficacy in healthy volunteers and patients. Experimental models to evoke pain and hyperalgesia are available for most tissues. In healthy volunteers, the effect of acetaminophen is difficult to detect unless neurophysiological methods are used, whereas the effect of nonsteroidal anti-inflammatory drugs could be detected in most models. Anticonvulsants and antidepressants are sensitive in several models, particularly in models inducing hyperalgesia. For opioids, tonic pain with high intensity is attenuated more than short-lasting pain and nonpainful sensations. Fewer studies were performed in patients. In general, the sensitivity to analgesics is better in patients than in healthy volunteers, but the lower number of studies may bias the results. Experimental models have variable reliability, and validity shall be interpreted with caution. Models including deep, tonic pain and hyperalgesia are better to predict the effects of analgesics. Assessment with neurophysiologic methods and imaging is valuable as a supplement to psychophysical methods and can increase sensitivity. The models need to be designed with careful consideration of pharmacological mechanisms and pharmacokinetics of analgesics. Knowledge obtained from this review can help design experimental pain studies for new compounds entering phase I and II clinical trials.

Advances in research of esophageal visceral hypersensitivity

Gastroesophageal reflux disease (GERD) is a common disorder that is often associated with unpleasant symptoms requiring utilization of health care resource. Both animal and clinical studies suggest that a variety of receptors on afferent nerves sensitized upon exposure to acid increase afferent input to the spinal cord dorsal horn neurons and lead to a reduction in threshold of these neurons together with an increase in their receptive field. This increased sensitivity of primary afferent nerves is described as peripheral sensitization, whereas the consequent increase in sensitivity of the spinal dorsal horn neurons is described as central sensitization. Once these mechanisms have been established, they can cause a long-term increase in sensitivity of tissues to previously innocuous stimuli. Furthermore, psychological stress and mechanical stimulation both have been shown to increase DIS and may therefore facilitate peripheral sensitization. Currently peripheral and central sensitizations are considered to be important mechanisms of esophageal pain hypersensitivity and occurrence of symptoms to even physiological amounts of acid. In these patients treatments aimed at reducing neuronal sensitivity may be effective. This article mainly focuses on the recent advances in research of esophageal visceral hypersensitivity.

Sprouted innervation into uterine transplants contributes to the development of hyperalgesia in a rat model of endometriosis

Endometriosis is an enigmatic painful disorder whose pain symptoms remain difficult to alleviate in large part because the disorder is defined by extrauteral endometrial growths whose contribution to pain is poorly understood. A rat model (ENDO) involves autotransplanting on abdominal arteries uterine segments that grow into vascularized cysts that become innervated with sensory and sympathetic fibers. ENDO rats exhibit vaginal hyperalgesia. We used behavioral, physiological, and immunohistochemical methods to test the hypothesis that cyst innervation contributes to the development of this hyperalgesia after transplant. Rudimentary sensory and sympathetic innervation appeared in the cysts at two weeks, sprouted further and more densely into the cyst wall by four weeks, and matured by six weeks post-transplant. Sensory fibers became abnormally functionally active between two and three weeks post-transplant, remaining active thereafter. Vaginal hyperalgesia became significant between four and five weeks post-transplant, and stabilized after six to eight weeks. Removing cysts before they acquired functional innervation prevented vaginal hyperalgesia from developing, whereas sham cyst removal did not. Thus, abnormally-active innervation of ectopic growths occurs before hyperalgesia develops, supporting the hypothesis. These findings suggest that painful endometriosis can be classified as a mixed inflammatory/neuropathic pain condition, which opens new avenues for pain relief. The findings also have implications beyond endometriosis by suggesting that functionality of any transplanted tissue can be influenced by the innervation it acquires.

The pain system in oesophageal disorders: mechanisms, clinical characteristics, and treatment

Pain is common in gastroenterology. This review aims at giving an overview of pain mechanisms, clinical features, and treatment options in oesophageal disorders. The oesophagus has sensory receptors specific for different stimuli. Painful stimuli are encoded by nociceptors and communicated via afferent nerves to the central nervous system. The pain stimulus is further processed and modulated in specific pain centres in the brain, which may undergo plastic alterations. Hence, tissue inflammation and long-term exposure to pain can cause sensitisation and hypersensitivity. Oesophageal sensitivity can be evaluated ,for example, with the oesophageal multimodal probe. Treatment should target the cause of the patient's symptoms. In gastro-oesophageal reflux diseases, proton pump inhibitors are the primary treatment option, surgery being reserved for patients with severe disease resistant to drug therapy. Functional oesophageal disorders are treated with analgesics, antidepressants, and psychological therapy. Lifestyle changes are another option with less documentation.

The esophageal multimodal pain model: normal values and degree of sensitization in healthy young male volunteers

BACKGROUND

Sensory changes are thought to be involved in gastro-esophageal reflux disease (GERD). The esophageal multimodal pain model can be used to investigate sensations in response to distension, heat, electric current and acid.

AIMS

The aim of this study was to provide normal values for this model in the normal state and in the acid induced sensitized state.

METHODS

Fifty-three healthy men (20-38 years old) underwent esophageal stimulation with distension, heat and electrical current before and after sensitization with 0.1 N HCl acid. Stimulus intensities at painful and non-painful thresholds and referred pain areas were measured. The percentage of individual participants sensitized to each modality was calculated. In 22 subjects the pre-acid tests were repeated on three subsequent visits.

RESULTS

To reach moderate pain, subjects tolerated mean distension of 29.1 ± 11 mL, heat stimulation time of 141 ± 33 s, and mean current of 17.6 ± 6.4 mA. After acid exposure, significantly reduced thresholds were observed for mechanical (24%), heat (11%) and electrical (14%) stimulation (P values < 0.05). The percentage of subjects sensitized, defined as reductions in thresholds of ≥10% or ≥20% after acid perfusion, was as follows: for distension 77%/62%, for heat 48%/28%, and for current 58%/44%. The model showed good reliability (intra-class correlations >0.6).

CONCLUSIONS

Normal values for healthy young men are now provided for the normal and the sensitized state. The percentage of subjects sensitized after acid stimulation are thoroughly documented, and depends on stimulation type and the cut-off value chosen.

Rectal sensorimotor dysfunction in constipation

The pathophysiological mechanisms underlying chronic constipation in both adults and children remain to be unravelled. This is a not inconsiderable challenge, but is fundamental to improving management of such patients. Rectal sensorimotor function, which encompasses both sensation and motility, as well as biomechanical components (compliance, capacity), is now strongly implicated in the pathogenesis of constipation. Rectal hyposensitivity, rectal hypercompliance, increased rectal capacity, rectal motor dysfunction (phasic contractility and tone), and altered rectoanal reflex activity are all found in constipated patients, particularly in association with 'functional' disorders of defaecation (i.e. pelvic floor dyssynergia). This review covers contemporary understanding of how components of rectal sensorimotor function may contribute to symptom development in both adult and paediatric populations. The complex interaction between sensory/motor/biomechanical domains, and how best to measure these functions are addressed, and where data exist, the impact of sensorimotor dysfunction on therapeutic outcomes is highlighted.

Different effects of morphine and oxycodone in experimentally evoked hyperalgesia: a human translational study

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT * Previous studies using short-lasting experimental pain stimulations in healthy volunteers have shown differences in opioid effects regarding visceral pain stimulations. However, these differences can be more pronounced in patients due to a sensitized pain system. Therefore, the aim of the present study was to mimic the clinical situation by investigating opioid effects on experimental pain in healthy volunteers after experimentally evoked hyperalgesia. WHAT THIS STUDY ADDS? * We now know that morphine and oxycodone exerts different effects in the sensitized pain system as we found a greater analgesic effect of oxycodone in response to skin, muscle and oesophageal pain stimulation. This supports clinicians' experiences that oxycodone can be superior to morphine in the treatment of some pain conditions. The evoked hyperalgesia bridged findings from studies in healthy volunteers to patients, and new fundamental knowledge on different analgesic effects in hyperalgesia was found. AIM Similar analgesics may have different analgesic potencies especially in patients in whom the pain system is sensitized. The aim was to investigate different opioid effects on experimental pain after the sensitized pain system was mimicked evoking hyperalgesia in healthy volunteers. METHODS Twenty-four healthy volunteers were randomized to treatment with morphine (30 mg orally) and oxycodone (15 mg orally) or placebo in a double-blind crossover study. Hyperalgesia was induced by oesophageal perfusion with acid and capsaicin. Several exploratory endpoints were studied using skin heat, muscle pressure and oesophageal mechanical, heat and electrical stimulation. Effects on pain from deeper structures were considered most important. RESULTS Different analgesic potencies were found. Oxycodone had a greater analgesic effect than morphine attenuating pain from: (i) heat stimulation of skin (P= 0.016); difference between the means of 0.39 degrees C, 95% CI 0.22, 2.09. (ii) muscle pressure (P < 0.001); difference between the means of 11.93kPa, 95% CI 5.4, 18.5. (iii) oesophageal heat stimulation (P < 0.001); difference between the means of 38.54 cm(2), 95% CI 15.37, 61.71 and (iv) oesophageal electrical stimulation (P= 0.016); difference between the means of 6.69mA, 95% CI 1.23, 12.13. CONCLUSION After sensitization of the pain system different analgesic potencies of morphine and oxycodone were found in response to skin, muscle and oesophageal pain stimulation, in which oxycodone had a greater effect. As similar differential analgesic potencies of the two opioids have been found in patients with chronic pain, the experimental hyperalgesia model bridged findings from studies in healthy volunteers to patients.

Perception of gastro-oesophageal reflux

Gastro-oesophageal reflux disease (GORD) is common and often associated with unpleasant symptoms requiring utilisation of health care resource. While in the majority of patients symptom resolution occurs with acid suppressant therapy, in a proportion this treatment is ineffective in resolving symptoms. This is particularly the case in patients with non-erosive reflux disease (NERD) and functional heartburn (FH). It is increasingly being recognised that the presence of acid in the oesophagus can cause dilated intercellular spaces (DIS) which increases the exposure of the sub-epithelial nerves to the acid. Experimental studies in both animals and humans suggest that a variety of receptors on afferent nerves can be sensitised upon exposure to acid so that there is increased afferent input to the spinal cord dorsal horn neurons which leads to a reduction in threshold of these neurons together with an increase in their receptive field. This increased sensitivity of primary afferent nerves is described as peripheral sensitisation, whereas the consequent increase in sensitivity of the spinal dorsal horn neurons is described as central sensitisation. Once these mechanisms have been established they can cause a long term increase in sensitivity of tissues to previously innocuous stimuli. Furthermore, psychological stress has been shown to increase DIS and may therefore facilitate peripheral sensitisation. Currently peripheral and central sensitisations are considered to be important mechanisms of oesophageal pain hypersensitivity and occurrence of symptoms to even physiological amounts of acid. In these patients treatments aimed at reducing neuronal sensitivity may be effective in the management.

Descending inhibitory pain modulation is impaired in patients with chronic pancreatitis

BACKGROUND & AIMS

Pain is a prominent symptom in chronic pancreatitis (CP), but the underlying mechanisms are incompletely understood. We investigated the role of descending pain modulation from supraspinal structures as well as central nervous system sensitization in patients with pain from CP.

METHODS

Twenty-five patients with CP and 15 healthy volunteers were included. Descending pain modulation was investigated by diffuse noxious inhibitory control (a descending inhibitory response after conditioning stimulation). Central pain processing was investigated as the perceptual responses to multimodal (electrical, thermal, and mechanical) stimulations of the rectosigmoid and evoked brain potentials after electrical stimulation of the rectosigmoid.

RESULTS

Compared with healthy volunteers, the efficacy of diffuse noxious inhibitory control was reduced in patients with CP (13% +/- 21% vs 39% +/- 22%, respectively; F = 3.8; P = .01); central sensitization was indicated by remote hyperalgesia in the rectosigmoid to electrical stimulation (21 +/- 15 mA vs 27 +/- 15 mA; F = 6.2; P = .02) and heat stimulation (51 degrees C +/- 5 degrees C vs 53 degrees C +/- 4 degrees C; F = 5.9; P = .02). Compared with controls, patients with CP had increased latency of the early P1 peak to rectosigmoid stimulation (85 +/- 21 ms vs 108 +/- 28 ms, respectively; P = .02), possibly reflecting reorganization of central pain pathways.

CONCLUSIONS

Patients with CP have impairments in inhibitory pain modulation and evidence of central sensitization. Treatment of their pain therefore should focus not only on the pancreas, but also on descending pain modulation from supraspinal structures and central nervous system sensitization.

Viscero-visceral hyperalgesia: characterization in different clinical models

Co-existing algogenic conditions in two internal organs in the same patient may mutually enhance pain symptoms (viscero-visceral hyperalgesia). The present study assessed this phenomenon in different models of visceral interaction. In a prospective evaluation, patients with: (a) coronary artery disease (CAD)+gallstone (Gs) (common sensory projection: T5); (b) irritable bowel syndrome (IBS)+dysmenorrhea (Dys) (T10-L1); (c) dysmenorrhea/endometriosis+urinary calculosis (Cal)(T10-L1); and (d) gallstone+left urinary calculosis (Gs+LCal) (unknown common projection) were compared with patients with CAD, Gs, IBS, Dys or Cal only, for spontaneous symptoms (number/intensity of pain episodes) over comparable time periods and for referred symptoms (muscle hyperalgesia; pressure/electrical pain thresholds) from each visceral location. In patients' subgroups, symptoms were also re-assessed after treatment of each condition or after no treatment. (a) CAD+Gs presented more numerous/intense angina/biliary episodes and more referred muscle chest/abdominal hyperalgesia than CAD or Gs; cardiac revascularization or cholecystectomy also reduced biliary or cardiac symptoms, respectively (0.001<p<0.05). (b) IBS+Dys had more intestinal/menstrual pain and abdomino/pelvic muscle hyperalgesia than IBS or Dys; hormonal dysmenorrhea treatment also reduced IBS symptoms; IBS dietary treatment also improved dysmenorrhea (0.001<p<0.05) while no treatment of either conditions resulted in no improvement in time of symptoms from both. (c) Cal+Dys had more urinary/menstrual pain and referred lumbar/abdominal hyperalgesia than Cal or Dys; hormonal dysmenorrhea treatment/laser treatment for endometriosis also improved urinary symptoms; lithotripsy for urinary stone also reduced menstrual symptoms (0.001<p<0.05). (d) In Gs+LCal, cholecystectomy or urinary lithotripsy did not improve urinary or biliary symptoms, respectively. Mechanisms of viscero-visceral hyperalgesia between organs with documented partially common sensory projection probably involve sensitization of viscero-viscero-somatic convergent neurons.

Quantitative assessment and characterization of visceral hyperalgesia evoked by esophageal balloon distention and acid perfusion in patients with functional heartburn, nonerosive reflux disease, and erosive esophagitis

BACKGROUND AND OBJECTIVES

The role of esophageal hypersensitivity in functional heartburn (FH) with negative pH test, negative symptom index, and the proton pump inhibitor (PPI) failure has not been established. The aim of this study was to investigate the characterization of visceral hyperalgesia evoked by esophageal balloon distention and acid perfusion in patients with FH, nonerosive reflux disease, and erosive esophagitis and further characterize the pathophysiologic mechanism of FH.

METHODS

A total of 21 FH patients (with esophageal acid exposure <3.1% and a symptom index<50% and nonresponse to a therapeutic trial with proton pump inhibitors, 25 Nonerosive reflux disease (NERD) patients (with esophageal acid exposure>4%), 23 erosive esophagitis (EE) patients (LA grade B to D), and 18 healthy controls were recruited in the study. Mechanosensitivity including the initial perception threshold (IPT) and pain threshold (PT) was evaluated by using a Barostat with a double-random staircase distension protocol. Chemosensitivity was graded along a visual analog scale after perfusion of saline and 0.1 N HCl.

RESULTS

The baseline IPTs and PTs were all lower in patients with FH, NERD, and EE than in the controls (all P<0.01). In addition, the baseline PT in FH patients was significantly lower than those in NERD (P=0.015) and EE patients (P<0.001). After acid perfusion, the mean symptom intensity scores were significantly greater in patients with FH, NERD, and EE than those in the controls (all P<0.001). The postacid perfusion IPTs in patients with FH, NERD, and EE were all significantly lower than the corresponding baseline values (all P<0.01). The PTs in FH (P=0.026) and EE patients (P<0.001) were significantly lower than the corresponding baseline values. Moreover, the postacid perfusion PT was significantly lower in FH patients than in NERD patients (P<0.001).

CONCLUSIONS

FH patients are more sensitive to mechanical or chemical stimuli than NERD patients. Sensitization of esophageal acid-sensitive chemoreceptors may exert a significant influence on the pressure-sensitive mechanoreceptors, and there is the cooperative interaction in the process of esophageal visceral hyperalgesia.

Visceral organ cross-sensitization - an integrated perspective

Viscero-somatic referral and sensitization has been well documented clinically and widely investigated, whereas viscero-visceral referral and sensitization (termed cross-organ sensitization) has only recently received attention as important to visceral disease states. Because second order neurons in the CNS have been extensively shown to receive convergent input from different visceral organs, it has been assumed that cross-organ sensitization arises by the same convergence-projection mechanism as advanced for viscero-somatic referral and sensitization. However, increasing evidence also suggests participation of peripheral mechanisms to explain referral and sensitization. We briefly summarize behavioral, morphological and physiological support of and focus on potential mechanisms underlying cross-organ sensitization.

An endoscopic method for thermal and chemical stimulation of the human oesophagus

Previous methods for visceral thermal stimulation have lacked control of the temperature rate and visual inspection of the organ. The aims of this study was to develop a method for linear control of heat stimulation in the human oesophagus combined with endoscopy, to assess the reproducibility of this method and to investigate sensitivity to thermal stimulation of the distal oesophagus before and after acid perfusion. A probe with a 2.8 mm endoscope inside was constructed permitting heat and chemical stimulation. Three different temperature ramps were applied in the distal oesophagus in 12 healthy subjects by recirculation of heated water in a bag. Endoscopy of the oesophageal mucosa was performed prior to experimental stimulation. The temperature, the time of stimulation and the area under the temperature curve (AUC) were measured at the pain detection threshold. Thermal stimulation was repeated after perfusion of the oesophagus with acid. The method was tested on two subsequent days to assess reproducibility. All subjects had a normal endoscopic examination. Day-to-day reproducibility was good for the three temperature ramps (intra-class correlations >0.6). The subjects tolerated less heat stimulation, a decrease in AUC (P = 0.0003), a decrease in time to pain detection threshold (P = 0.005) and decreased temperature at pain detection threshold (P = 0.0001) after acid perfusion. The slow ramp was the most sensitive, showing a decrease in AUC of 29%. The present method was easily implemented and showed good reproducibility. It can potentially be used in basic experiments, drug and clinical studies as it provides a controllable thermal stimulus.

Evidence for oesophageal visceral hypersensitivity and aberrant symptom referral in patients with globus

We tested the hypotheses that globus patients demonstrate oesophageal visceral hypersensitivity and aberrant viscerosomatic referral of oesophageal stimuli. Oesophageal visceral perception was assessed by oesophageal balloon distension and electrical stimulation in nine patients with globus and compared with 11 healthy controls. Oesophageal perception and pain thresholds were determined. Subjects recorded the area of thoracic viscerosomatic referral on a body map in response to each stimulus. All the patients reported their first sensation at balloon volumes between 2 and 6 mL whereas controls reported their first sensation at volumes between 3 and 14 mL (P = 0.03). All the patients reported pain at balloon volumes between 5 and 12 mL whereas controls experienced pain at volumes between 8 and 20 mL (P = 0.001). In response to electrical stimulation to the oesophagus patients and controls demonstrated comparable sensory thresholds. In response to oesophageal balloon distension seven of nine patients, but no controls, referred the sensation to the region at or above the suprasternal notch (P = 0.001). Similarly, significant differences in viscerosomatic referral pattern were observed in response to oesophageal electrical stimulation (P = 0.03). Patients with globus demonstrate oesophageal visceral hypersensitivity to mechanical distension. The differential responses to stretch and electrical stimuli may indicate that the hypersensitivity is a peripheral, rather than central, phenomenon. The aberrant referral of oesophageal sensations in response to both mechanical and electrical stimulation supports the hypothesis that referral of symptoms to the neck might be a central phenomenon.

Rectal hyposensitivity: pathophysiological mechanisms

Rectal hyposensitivity (RH) relates to a diminished perception of rectal distension. It may occur due to afferent nerve dysfunction and/or secondary to abnormal structural or biomechanical properties of the rectum. The aim of this study was to determine the contribution of these underlying pathophysiological mechanisms by systematically evaluating rectal diameter, compliance and afferent nerve sensitivity in patients with RH, using methodology employed in clinical practice. The study population comprised 45 (33 women; median age 48, range 25-72 years) constipated patients (Rome II criteria) with RH and 20 with normal rectal sensitivity on balloon distension and 20 healthy volunteers. Rectal diameter was measured at minimum distending pressure during isobaric distension under fluoroscopic screening. Rectal compliance was assessed during phasic isobaric distension by measuring the slope of the pressure-volume curve. Electrical stimulation of the rectal mucosa was employed to determine afferent nerve function. Values were compared to normal ranges established in healthy volunteers. The upper limits of normal for rectal diameter, compliance and electrosensitivity were 6.3 cm, 17.9 mL mmHg(-1) and 21.3 mA respectively. Among patients with RH, rectal diameter, but not compliance, was increased above the normal range (megarectum) in seven patients (16%), two of whom had elevated electrosensitivity thresholds. Rectal diameter and compliance were elevated in 23 patients (51%), nine of whom had elevated electrosensitivity thresholds. The remaining 15 patients (33%) with RH had normal rectal compliance and diameter, all of whom had elevated electrosensitivity thresholds. Two-third of the patients with RH on simple balloon distension have elevated rectal compliance and/or diameter, suggesting that impaired perception of rectal distension is due to inadequate stimulation of the rectal afferent pathway. However, a proportion of such patients also appear to have impaired nerve function. In the remaining one-third of the patients, rectal diameter and compliance are normal, while electrosensitivity thresholds are elevated, suggestive of true impaired afferent nerve function. Identification of these subgroups of patients with RH may have implications regarding their management.

Sensory testing of the human gastrointestinal tract

The objective of this appraisal is to shed light on the various approaches to screen sensory information in the human gut. Understanding and characterization of sensory symptoms in gastrointestinal disorders is poor. Experimental methods allowing the investigator to control stimulus intensity and modality, as well as using validated methods for assessing sensory response have contributed to the understanding of pain mechanisms. Mechanical stimulation based on impedance planimetry allows direct recordings of luminal cross-sectional areas, and combined with ultrasound and magnetic resonance imaging, the contribution of different gut layers can be estimated. Electrical stimulation depolarizes free nerve endings non-selectively. Consequently, the stimulation paradigm (single, train, tetanic) influences the involved sensory nerves. Visual controlled electrical stimulation combines the probes with an endoscopic approach, which allows the investigator to inspect and obtain small biopsies from the stimulation site. Thermal stimulation (cold or warm) activates selectively mucosal receptors, and chemical substances such as acid and capsaicin (either alone or in combination) are used to evoke pain and sensitization. The possibility of multimodal (e.g. mechanical, electrical, thermal and chemical) stimulation in different gut segments has developed visceral pain research. The major advantage is involvement of distinctive receptors, various sensory nerves and different pain pathways mimicking clinical pain that favors investigation of central pain mechanisms involved in allodynia, hyperalgesia and referred pain. As impairment of descending control mechanisms partly underlies the pathogenesis in chronic pain, a cold pressor test that indirectly stimulates such control mechanisms can be added. Hence, the methods undoubtedly represent a major step forward in the future characterization and treatment of patients with various diseases of the gut, which provides knowledge to clinicians about the underlying symptoms and treatment of these patients.

Central neuronal mechanisms of gastric electrical stimulation in diabetic gastroparesis

OBJECTIVE

The mechanisms underlying symptom improvement in gastric electrical stimulation (GES) are not fully understood. Modulation of the central nervous system excitability may be involved. The objective of the study was to investigate the central effects of GES, including the possible modulation of the visceral sensory nervous system.

MATERIAL AND METHODS

A gastric electrical stimulator was implanted in seven diabetic patients with medically refractory gastroparesis. A double-blinded protocol was used to investigate the patients at baseline and one month after recovery with the stimulator turned on and off (1-month periods). The following assessments were carried out: mechanical, thermal and electrical stimulations with sensory recordings in the esophagus and duodenum, and standardized, self-administered, daily symptom questionnaires.

RESULTS

No difference was found between baseline and the on- and off periods in overall gut pain thresholds across all stimulus modalities in the esophagus (p=0.63), duodenum (p=0.19) or esophagus and duodenum combined (p=0.76). No difference in the sensory response to mechanical stimulation was found in the esophagus before (all p>0.31) and after (all p>0.43) smooth muscle relaxation with butylscopolamine. Similar findings were observed in the duodenum. No differences were found in thermal sensitivity (esophagus (p=0.67) and duodenum (p=0.17)), sensory response to electrical stimulation (esophagus (p=0.57) and duodenum (p=0.52)) or induced somatic referred pain areas (esophagus (p=0.75) and duodenum (p=0.51)). No difference was seen in the induced somatic referred pain areas or self-reported symptoms.

CONCLUSIONS

No evidence was found for GES-induced modulation of the visceral sensory system and central excitability. However, GES has been proven to modulate the central nervous system in animal studies, necessitating further human experiments in order unambiguously to establish the possible central effects of GES.

Multimodal sensory testing of the rectum and rectosigmoid: development and reproducibility of a new method

Evaluation of rectal and rectosigmoid sensation is important in basic, clinical and pharmacological studies. New methods to evoke and assess multimodal (electrical, thermal and mechanical) experimental pain of the upper gut activate distinct pathways and mimics clinical pain. The aims of the current study were to characterize the sensory response and reproducibility to multimodal stimulation of rectum and the rectosigmoid. A multimodal rectal probe was developed. Mucosal electrostimulation was delivered at the recto-sigmoid junction. In Rectum, impedance planimetry was used for measurement of cross-sectional area (CSA) during distension. Circulation of water within the bag at either 4 or 60 degrees C was applied for thermal stimulation. The method was tested in 12 healthy volunteers (six men mean age 32 years) on two subsequent days. Mechanical and sensory responses and referred pain areas were assessed. Stimulation with electrical, thermal and mechanical modalities resulted in different sensory perceptions. The relationship between stimulus intensity and sensory response was linear for all modalities. Sensory response to different modalities did not differ between investigation days (all P-values > 0.1). Approximately 75% of subjects felt referred pain in distinct skin locations. Between-days reproducibility was good for all modalities [intra-class correlation (ICC) > or = 0.6]. At sensory threshold, CSA showed best reproducibility (ICC > or = 0.9). At pain detection threshold stretch ratio, CSA and electrostimulation showed best reproducibility (ICC = 1.0; 0.9; 0.9). The present model was easily implemented, robust and showed good reproducibility. It can be used to study pathophysiology or pharmacological interventions in healthy controls and in patients with diseases involving the distal hindgut.

Oesophageal heat transfer properties indication of segmental blood flow changes during distension

The pain perception to distension of the oesophagus can be explained by activation of receptors responding to mechanical deformation or to distension-induced ischaemia. The aim of this study was to develop a new method for detection of changes in segmental blood flow during distension based on measurement of heat transfer. A bag was distended in the distal oesophagus of six healthy subjects followed by cooling or heating of the bag fluid to 5 or 60 degrees C. After equilibrium, the temperature was allowed to change back to body temperature. The temperature was recorded together with intraluminal ultrasound imaging, allowing assessment of the heat transfer properties at different bag volumes. The heat transfer constants were higher after heating the bag than after cooling the bag (Tukey, P < 0.05). The heat transfer constants after heating the bag decreased as function of bag volumes whereas the heat transfer during cooling was not affected by the bag volume (F = 0.9, P = 0.4). The findings indicate that segmental blood flow can be assessed indirectly by calculating the heat transfer properties. Distension induced a drop in regional blood flow. Hence, ischaemia may contribute to distension-induced pain. Furthermore, heat increased segmental blood flow and cold decreased segmental blood flow. This method may in the future be used to explore the mechanisms behind oesophageal pain.

Impaired contractility and remodeling of the upper gastrointestinal tract in diabetes mellitus type-1

AIM: To investigate that both the neuronal function of the contractile system and structural apparatus of the gastrointestinal tract are affected in patients with longstanding diabetes and auto mic neuropathy.

METHODS: The evoked esophageal and duodenal contractile activity to standardized bag distension was assessed using a specialized ultrasound-based probe. Twelve type-1 diabetic patients with autonomic neuropathy and severe gastrointestinal symptoms and 12 healthy controls were studied. The geometry and biomechanical parameters (strain, tension/stress, and stiffness) were assessed.

RESULTS: The diabetic patients had increased frequency of distension-induced contractions (6.0 ± 0.6 vs 3.3 ± 0.5, P < 0.001). This increased reactivity was correlated with the duration of the disease (P = 0.009). Impaired coordination of the contractile activity in diabetic patients was demonstrated as imbalance between the time required to evoke the first contraction at the distension site and proximal to it (1.5 ± 0.6 vs 0.5 ± 0.1, P = 0.03). The esophageal wall and especially the mucosa-submucosa layer had increased thickness in the patients (P < 0.001), and the longitudinal and radial compressive stretch was less in diabetics (P < 0.001). The esophageal and duodenal wall stiffness and circumferential deformation induced by the distensions were not affected in the patients (all P > 0.14).

CONCLUSION: The impaired contractile activity with an imbalance in the distension-induced contractions likely reflects neuronal abnormalities due to autonomic neuropathy. However, structural changes and remodeling of the gastrointestinal tract are also evident and may add to the neuronal changes. This may contribute to the pathophysiology of diabetic gut dysfunction and impact on future management of diabetic patients with gastrointestinal symptoms.

Assessment of experimental pain from skin, muscle, and esophagus in patients with chronic pancreatitis

OBJECTIVES

Comprehensive experimental methods are of major relevance assessing pain mechanisms in patients with chronic pain. Chronic pancreatitis is thought to involve the sensory response in other visceral organs and somatic tissue. We, therefore, aimed at exploring the pain mechanisms in chronic pancreatitis (CP) using a multimodal and multitissue stimulation approach.

METHODS

Ten patients (mean age, 50 years) with CP and 13 healthy controls (mean age, 35 years) participated. None of the patients took analgesics regularly. All were exposed to multimodal (mechanical, thermal, and electrical) experimental pain in the skin, muscles, and esophagus.

RESULTS

The patients were hyposensitive to mechanical stimulations of the skin (P = 0.001), but there were no differences in the pain to thermal and electrical stimulations. In the muscle and esophagus, no differences in pain thresholds were found. The difference between single and repeated stimulations reflecting the degree of central sensitization was 17% in controls and 36% in patients (P = 0.001). The referred pain area to electrical stimulation was 30.1 cm2 in the patients and 7.7 cm2 for the controls (P = 0.02).

CONCLUSIONS

The findings suggest that the balance among central hyperexcitability, neuroplastic changes, and descending pain-modulating pathways may explain the pain response to experimental multimodal stimulations in CP. This will likely also reflect the clinical pain mechanisms and may have important impact in selection of treatment, where drugs with potential effects on these mechanisms should be used.

Gut sensations in diabetic autonomic neuropathy

The pathogenesis of gastrointestinal symptoms in diabetes mellitus is complex and multi-factorial. Diabetes induced peripheral and central changes in the neuronal pain matrix may be of importance and were explored using a new multi-modal and multi-segmental sensory testing approach. The sensitivity to mechanical, thermal and electrical stimulations in the oesophagus and duodenum was assessed in 12 type-1 diabetic patients with proven autonomic neuropathy and severe gastrointestinal symptoms using a comprehensive stimulation device aiming to activate different gut nerves and pain mechanisms. Twelve healthy subjects served as controls. The sensory response and the somatic referred pain areas were recorded. In the diabetic patients an overall hyposensitivity to the combination of all stimulations was found in the oesophagus and duodenum (P=0.02). Post hoc analysis revealed hyposensitivity to mechanical stimulations in the oesophagus (P=0.006) and duodenum (P=0.002), and to thermal (P<0.001) and electrical (P=0.005) stimulations in the oesophagus and duodenum combined. The hyposensitivity in the gut was accompanied by a 46% increase in the somatic referred pain areas (P=0.04) indicating central neuronal changes. The multi-modal and multi-segmental sensory testing approach indicates that the sensory nerves are widely affected in the GI tract and generalized to nerves in all layers of the gut. Changes in the neuronal pain matrix including interactions between peripheral and central pain mechanisms may be involved in the pathogenesis of gastrointestinal symptoms in long-standing diabetes. Future targets in the treatment of gastrointestinal symptoms in diabetic patients with autonomic neuropathy could be based on modulation of the central nervous system excitability.

Dysmenorrhoea is associated with hypersensitivity in the sigmoid colon and rectum

Dysmenorrhoea patients experience intense visceral pain during menstruation. Recurrent and/or intense visceral pain can induce facilitation of somatic and visceral nociceptive processing which can lead to viscero-somatic (referred) and viscero-visceral hyperalgesia. Our aim was to study if dysmenorrhoea is associated with hypersensitivity in the referred somatic skin area or in the large bowel, i.e., viscero-visceral hyperalgesia. We measured skin sensitivity in the referred area of the sigmoid colon as well as stimulus-response relationships in the sigmoid colon and rectum. The latter were measured using mechanical (balloon) distension applied via a Barostat in 11 dysmenorrhoea patients without gastro-intestinal complaints and 10 healthy and age matched women, again without gastrointestinal complaints. We found no skin hypersensitivity in the colonic referred area. In contrast, significantly lower distension volumes were seen at each threshold in dysmenorrhoea patients, particularly in the sigmoid colon. The mean reduction in colonic distension volume thresholds for dysmenorrhoea patients vs. controls was 57% at the detection threshold and 39% at the pain threshold. There were no differences in compliance between the groups. These findings suggest that, despite the absence of overt gastro-intestinal symptoms or viscero-somatic sensitisation, dysmenorrhoea patients demonstrate intestinal hypersensitivity. This can be regarded as the result of centrally mediated viscero-visceral hyperalgesia due to recurrent intense menstrual pain.

Upper gastrointestinal sensory-motor dysfunction in diabetes mellitus

Gastrointestinal (GI) sensory-motor abnormalities are common in patients with diabetes mellitus and may involve any part of the GI tract. Abnormalities are frequently sub-clinical, and fortunately only rarely do severe and life-threatening problems occur. The pathogenesis of abnormal upper GI sensory-motor function in diabetes is incompletely understood and is most likely multi-factorial of origin. Diabetic autonomic neuropathy as well as acute suboptimal control of diabetes has been shown to impair GI motor and sensory function. Morphological and biomechanical remodeling of the GI wall develops during the duration of diabetes, and may contribute to motor and sensory dysfunction. In this review sensory and motility disorders of the upper GI tract in diabetes is discussed; and the morphological changes and biomechanical remodeling related to the sensory-motor dysfunction is also addressed.

Multimodal pain stimulation of the gastrointestinal tract

Understanding and characterization of pain and other sensory symptoms are among the most important issues in the diagnosis and assessment of patient with gastrointestinal disorders. Methods to evoke and assess experimental pain have recently developed into a new area with the possibility for multimodal stimulation (e.g., electrical, mechanical, thermal and chemical stimulation) of different nerves and pain pathways in the human gut. Such methods mimic to a high degree the pain experienced in the clinic. Multimodal pain methods have increased our basic understanding of different peripheral receptors in the gut in health and disease. Together with advanced muscle analysis, the methods have increased our understanding of receptors sensitive to mechanical, chemical and temperature stimuli in diseases, such as systemic sclerosis and diabetes. The methods can also be used to unravel central pain mechanisms, such as those involved in allodynia, hyperalgesia and referred pain. Abnormalities in central pain mechanisms are often seen in patients with chronic gut pain and hence methods relying on multimodal pain stimulation may help to understand the symptoms in these patients. Sex differences have been observed in several diseases of the gut, and differences in central pain processing between males and females have been hypothesized using multimodal pain stimulations. Finally, multimodal methods have recently been used to gain more insight into the effect of drugs against pain in the GI tract. Hence, the multimodal methods undoubtedly represents a major step forward in the future characterization and treatment of patients with various diseases of the gut.

Pain and mechanical properties of the rectum in patients with active ulcerative colitis

BACKGROUND

The pain, urgency, and incontinence in ulcerative colitis may be related to changes in viscoelastic properties of the gut wall or to alterations of the sensory pathways. In the present study, we used an advanced rectal probe to study the mechanosensory and smooth muscle properties in patients with active disease.

METHODS

Nine patients with ulcerative colitis (mean age 39.5 years) with exacerbation limited to the rectum and sigmoid colon and 17 age-matched healthy subjects were included. The rectum was distended before and after pharmacological relaxation of the smooth muscle until moderate pain was reported, and the cross-sectional area, volume, pressure, tension, and strain were computed. To investigate central integration of a tonic stimulus, the bag was finally distended to the pain threshold; then, the cross-sectional area was held constant for 2 min.

RESULTS

The patients were hypersensitive to mechanical stimuli as assessed by the cross-sectional area (F = 21.7; P < 0.001). There were no differences in compliance or stiffness between the 2 groups, but the hypersensitivity was abolished after muscle relaxation. Together with the muscle analysis, this finding demonstrated that the smooth muscles were tonically contracted in the inflamed rectum, resulting in a decreased rectal circumference. The tonic distensions did not evoke central integration of the pain response, indicating that hyperalgesia is more likely related to peripheral factors.

CONCLUSIONS

Patients with active ulcerative colitis have hypersensitivity and increased tone of the smooth muscles, which may explain the symptoms. Drugs that affect smooth muscle contraction may be helpful in difficult cases.