Systematic review with meta-analysis: conditioned pain modulation in patients with the irritable bowel syndrome

The impact of transcutaneous electrical acustimulation (TEA) on rectal distension-induced pain in patients with irritable bowel syndrome (IBS)-A study to determine the optimal TEA delivery modalities and effects on rectal sensation and autonomic function

BACKGROUND

Treatment options for abdominal pain in IBS are inadequate. TEA was reported effective treatment of disorders of gut-brain interaction but its mechanism of action and optimal delivery method for treating pain in IBS are unknown. This study aims to determine the most effective TEA parameter and location to treat abdominal pain in patients with IBS-Constipation and delineate the effect of TEA on rectal sensation and autonomic function.

METHODS

Nineteen IBS-C patients underwent TEA at acupoints ST36 (leg), PC6 (wrist), or sham-acupoint. Each patient was studied in five randomized sessions on separate days: (1) TEA/ST36-100 Hz; (2) TEA/ST36-25 Hz; (3) TEA/PC6-100 Hz; (4) TEA/PC6-25 Hz; (5) TEA/Sham-25 Hz. In each session, barostat-guided rectal distention (RD) was performed before and after TEA. Patients graded the RD-induced pain and recorded three rectal sensation thresholds. A heart rate variability (HRV) signal was derived from the electrocardiogram for autonomic function assessment.

KEY RESULTS

Studied patients were predominantly female, young, and Caucasian. Compared with baseline, patients treated with TEA/ST36-100 Hz had significantly decreased pain scores at RD pressure-points 20-50 mmHg (p < 0.04). The average pain reduction was 40%. Post-treatment scores did not change significantly with other TEA modalities except with sham-TEA (lesser degree compared to ST36-100 Hz, p = 0.04). TEA/ST36-100, but not other modalities, increased the rectal sensation threshold (first sensation: p = 0.007; urge to defecate: p < 0.026). TEA/ST36-100 Hz was the only treatment that significantly decreased sympathetic activity and increased parasympathetic activity with and without RD (p < 0.04).

CONCLUSIONS & INFERENCES

TEA at ST36-100 Hz is superior stimulation point/parameter, compared to TEA at PC-6/sham-TEA, to reduce rectal distension-induced pain in IBS-C patients. This therapeutic effect appears to be mediated through rectal hypersensitivity reduction and autonomic function modulation.

Gastrointestinal pain: A systematic review of temporal summation of pain paradigms and outcomes

BACKGROUND AND OBJECTIVE

Since targeted treatment for gastrointestinal pain is elusive, identifying the mechanistic underpinning of this pain type is important. Facilitation of spinal neuronal responses underpins certain pain types, and the psychophysical temporal summation of pain (TSP) paradigm provides a proxy measure of spinal facilitatory processes. Our aim was to systematically review whether facilitated TSP is a feature of gastrointestinal pain in patients with, or pain-free people experiencing experimentally induced, gastrointestinal pain.

DATABASES AND DATA TREATMENT

EMBASE, MEDLINE, PsychInfo, CINAHL, and Web of Science were systematically searched, from inception to July 2023, for human studies reporting TSP paradigm outcomes in the context of gastrointestinal pain. The Appraisal tool for Cross-Sectional studies was used for quality assessment and applied independently by two researchers.

RESULTS

Fifteen papers consisting of cross-sectional (n = 6), case-control (n = 8), and retrospective cohort (n = 1) studies, were included. Thirteen studies investigated TSP in people with gastrointestinal pain with (n = 5) or without (n = 8) defined pathology. Two studies evoked TSP by repetitive gut stimulation in people undergoing abdominal medical procedures. Preliminary evidence showed that facilitated TSP correlated with the presence of functional gastrointestinal pain in women, and those with a history of trauma. No effect was observed in people with inflammatory bowel disease, although it was often unclear if they experienced pain.

CONCLUSIONS

It is not possible to conclude whether facilitated TSP is a feature of gastrointestinal pain. We recommend that subgroup findings are corroborated and that TSP paradigms are standardized in order that direct comparisons between studies may be made.

SIGNIFICANCE STATEMENT

Evidence indicated that pain facilitatory processes, as evidenced by a facilitated TSP outcome, contribute to functional gastrointestinal pain in women and those with a history of trauma. However, heterogeneity of study populations and paradigms precluded statistical synthesis and findings would need be corroborated. Studies exploring facilitatory processes in people with inflammatory bowel diseases did not report significant results, but pain is not a given in these conditions and, conversely, may be driven by peripheral inflammation during active disease. This should be taken in consideration in future explorations.

REGISTRATION REVIEW

PROSPERO CRD42022341845.

Aetiological Understanding of Fibromyalgia, Irritable Bowel Syndrome, Chronic Fatigue Syndrome and Classificatory Analogues: A Systematic Umbrella Review

Background

This umbrella review systematically assesses the variety and relative dominance of current aetiological views within the scientific literature for the three most investigated symptom-defined functional somatic syndromes (FSS) and their classificatory analogues within psychiatry and psychology.

Method

An umbrella review of narrative and systematic reviews with and without meta-analyses based on a search of electronic databases (PubMed, Web of Science, Embase, PsychINFO) was conducted. Eligible reviews were published in English, focused on research of any kind of aetiological factors in adults diagnosed with fibromyalgia syndrome (FMS), irritable bowel syndrome (IBS), chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME), and somatic symptom disorder (SSD)/somatoform disorder (SFD).

Results

We included 452 reviews (132 systematic reviews including meta-analyses, 133 systematic reviews, 197 narrative reviews), of which 132 (29%) focused on two or more of the investigated health conditions simultaneously. Across diagnoses, biological factors were addressed in 90% (k = 405), psychological in 33% (k = 150), social in 12% (k = 54), and healthcare factors in 5% (k = 23) of the reviews. The methodological quality of the included systematic reviews (k = 255) was low (low/critically low: 41% [k = 104]; moderate: 49% [k = 126]; high quality: 10% [k = 25]). The high-quality systematic reviews suggest that deficient conditioned pain modulation, genetic factors, changes in the immune, endocrinological, gastrointestinal, cardiovascular, and nervous system, and psychosocial factors such as sexual abuse and pain catastrophizing increase the risk for FSS.

Conclusion

Only very few systematic reviews have used comprehensive, biopsychosocial disease models to guide the selection of aetiological factors in FSS research. Future research should strive for higher scientific standards and broaden its perspective on these health conditions.

Factors influencing rectal hypersensitivity in irritable bowel syndrome: A systematic review and meta-analysis

BACKGROUND

A frequent, although not universal, feature of irritable bowel syndrome (IBS) is heightened sensitivity to mechanical stimulation of the rectum, termed rectal hypersensitivity (RH). Differences in RH-based on sex, IBS subtype, IBS diagnostic criteria and age of population studied are incompletely understood. We aimed to determine whether IBS population had lower pain thresholds than healthy controls.

METHODS

We searched MEDLINE and EMBASE databases (1970-2021). Prospective studies that compared pain/discomfort thresholds to mechanical rectal stimuli in IBS and healthy controls were included. Data were pooled for meta-analyses and effect sizes were calculated with 95% confidence interval (CIs).

RESULTS

Our search strategy identified 809 studies of which 32 studies met the inclusion criteria. Reduced rectal pain thresholds was more common in IBS patients compared to healthy controls with an effect size of 1.00 95% CIs (0.77-1.24) (p < 0.0001) (I²  = 78.6%). The pediatric IBS population had lower pain thresholds than adult IBS populations (p = 0.05) but no difference based on IBS diagnostic criteria, subtype or sex.

CONCLUSION & INFERENCES

The results suggest that reduced rectal pain threshold to experimental stimulation is far more common in IBS patients than healthy controls. Further research is required to understand the pathophysiological and therapeutic implications of rectal sensitivity such as its role in measuring response to treatment and prognosis in IBS.

Efficiency of pain inhibition and facilitation of fibromyalgia patients is not different from healthy controls: Relevance of sensitivity-adjusted test stimuli

Background

Pain is a dynamic phenomenon dependent on the balance of endogenous excitatory and inhibitory systems, which can be characterized by quantitative sensory testing. Many previous studies of pain modulatory capacity of patients with fibromyalgia syndrome (FM) have reported decreased pain inhibition or increased pain facilitation. This is the first study to assess pain modulation, including conditioned pain modulation (CPM) and temporal pain summation, in the same healthy control (HC) and FM participants.

Methods

Only sensitivity-adjusted stimuli were utilized for testing of conditioned pain modulation (CPM) and temporal pain summation in 23 FM patients and 28 HC. All subjects received sensitivity-adjusted ramp-hold (sRH) during testing of pain facilitation (temporal summation) and pain inhibition (CPM). CPM efficacy was evaluated with test stimuli applied either concurrently or after application of the conditioning stimulus. Finally, the effects of CPM on pressure pain thresholds were tested.

Results

FM subjects required significantly less intense test and conditioning stimuli than HC participants to achieve standardized pain ratings of 50 ± 10 numerical rating scale (NRS) (p = 0.03). Using such stimuli, FM subjects' temporal pain summation and CPM efficacy was not significantly different from HC (all p > 0.05), suggesting similar pain facilitation and inhibition. Furthermore, the CPM efficacy of FM and HC participants was similar regardless of whether the test stimuli were applied during or after the conditioning stimulus (p > 0.05).

Conclusion

Similar to previous studies, FM participants demonstrated hyperalgesia to heat, cold, and mechanical stimuli. However, using only sensitivity-adjusted stimuli during CPM and temporal summation testing, FM patients demonstrated similarly effective pain inhibition and facilitation than HC, suggesting that their pain modulation is not abnormal.

Bladder Pain Sensitivity Is a Potential Risk Factor for Irritable Bowel Syndrome

BACKGROUND

Although dysmenorrhea is a highly prevalent risk factor for irritable bowel syndrome (IBS), the factors underlying this risk are not fully understood. Prior studies support a hypothesis that repeated distressing menstrual pain promotes cross-organ pelvic sensitization with heightened visceral sensitivity.

AIMS

To further explore cross-organ pelvic sensitization we examined the association of dysmenorrhea, provoked bladder pain, and other putative factors with self-reported IBS-domain pain frequency and new onset after 1-year follow up.

METHODS

We measured visceral pain sensitivity with a noninvasive provoked bladder pain test in a cohort of reproductive-aged women, enriched for those reporting moderate-to-severe menstrual pain intensity but without any prior IBS diagnosis (n = 190). We analyzed the relationship between menstrual pain, provoked bladder pain, pain catastrophizing, anxiety, and depression with primary outcomes: (1) frequency of self-reported IBS-domain pain and (2) new onset of IBS-domain pain after 1-year follow up.

RESULTS

All hypothesized factors correlated with the frequency of IBS-domain pain (p's ≤ 0.038). In a cross-sectional model, only menstrual pain (standardized adjusted odds ratio 2.07), provoked bladder pain (1.49), and anxiety (1.90) were independently associated with IBS-domain pain ≥ 2 days/month (C statistic = 0.79). One year later, provoked bladder pain (3.12) was the only significant predictor of new onset IBS-domain pain (C statistic = 0.87).

CONCLUSION

Increased visceral sensitivity among women with dysmenorrhea could lead to IBS. Because provoked bladder pain predicted subsequent IBS, prospective studies should be performed to see if the early treatment of visceral hypersensitivity mitigates IBS.

Somatosensory assessments in patients with inflammatory bowel disease: a cross-sectional study examining pain processing pathways and the role of multiple patient factors

BACKGROUND

Pain affects the majority of patients with inflammatory bowel disease (IBD), where pain experiences may be influenced by multiple patient factors and changes within central pain processing pathways, termed central sensitization. The current study aimed to investigate pain processing pathways in patients with IBD through somatosensory testing and associations with multiple patient factors.

METHODS

A cross-sectional study of adults with IBD. Assessments included: somatosensory tests [i.e. pressure pain thresholds (PPT), temporal summation (TS), conditioned pain modulation (CPM)], and patient factors (i.e. demographics, comorbidity, sleep quality, psychological, pain severity and interference, and IBD features). Multiple regression analyses explored associations between somatosensory tests and multiple patient factors.

RESULTS

Decreased CPM in participants (N = 51) was associated with worse abdominal pain severity and use of biologic therapies (R2 = 0.30, F(5,44) = 5.18, P = 0.001). Increased TS was associated with biologic use (R2 = 0.11, F(1,49) = 6.13, P = 0.017). Decreased PPT at the low back (R2 = 0.29, F(2,48) = 11.21, P < 0.001) and Tibialis anterior (R2 = 0.41, F(2,48) = 18.26, P < 0.001) were associated with female sex and the absence of a stoma.

CONCLUSION

Study results demonstrated associations between multiple patient factors and somatosensory tests in patients with IBD. The absence of a stoma and female sex was associated with greater sensitivity to pressure in two remote body regions, suggestive of widespread hyperalgesia. Worse abdominal pain severity and biologic use were associated with decreased pain inhibition, and biologic use was also associated with increased pain facilitation. These findings suggest the presence of altered pain processing and mechanisms of central sensitization in patients with IBD.

Quantitative Sensory Testing Across Chronic Pain Conditions and Use in Special Populations

Chronic pain imposes a significant burden to the healthcare system and adversely affects patients' quality of life. Traditional subjective assessments, however, do not adequately capture the complex phenomenon of pain, which is influenced by a multitude of factors including environmental, developmental, genetic, and psychological. Quantitative sensory testing (QST), established as a protocol to examine thermal and mechanical sensory function, offers insight on potential mechanisms contributing to an individual's experience of pain, by assessing their perceived response to standardized delivery of stimuli. Although the use of QST as a research methodology has been described in the literature in reference to specific pain populations, this manuscript details application of QST across a variety of chronic pain conditions. Specific conditions include lower extremity chronic pain, knee osteoarthritis, chronic low back pain, temporomandibular joint disorder, and irritable bowel syndrome. Furthermore, we describe the use of QST in placebo/nocebo research, and discuss the use of QST in vulnerable populations such as those with dementia. We illustrate how the evaluation of peripheral sensory nerve function holds clinical promise in targeting interventions, and how using QST can enhance patient education regarding prognostic outcomes with particular treatments. Incorporation of QST methodology in research investigations may facilitate the identification of common mechanisms underlying chronic pain conditions, guide the development of non-pharmacological behavioral interventions to reduce pain and pain-related morbidity, and enhance our efforts toward reducing the burden of chronic pain.

Review article: current and future treatment approaches for pain in IBS

BACKGROUND

Abdominal pain is a core symptom of IBS and a primary driver of care seeking. Visceral hypersensitivity is a key pathophysiological mechanism and therapeutic target for pain in IBS, with components of peripheral and central sensitisation and psychological factors.

AIM

To review current and future treatment approaches specifically for the pain component of IBS.

METHODS

Pubmed search terms included combinations of irritable bowel, pain, visceral hypersensitivity, novel, new, emerging, future and advances.

RESULTS

Established non-pharmacological treatments for IBS pain include the low FODMAP diet, probiotics and psychological interventions, especially hypnotherapy. Tricyclics remain the best evidenced pharmacological approach with GCC agonists, tenapanor, lubiprostone, eluxadoline and 5HT3 antagonists second line according to patient characteristics and availability. Less well-evidenced current options include anti-spasmodics, peppermint oil, SSRIs, SNRIs, alpha 2 delta ligands, melatonin and histamine antagonists. Patients are vulnerable to iatrogenesis and harmful approaches to be avoided include opioids and unwarranted surgical interventions. For severe pain, the concept of augmentation with combined gut-brain neuromodulators and psychotherapy in a multi-disciplinary setting is considered. A plethora of molecular targets and ligands are emerging from pre-clinical studies, together with early clinical evidence for a range of pharmacological, dietary, neurostimulation and novel psychological treatment delivery methods which are reviewed. The history of such emerging approaches, however, merits both caution and optimism in equal measure.

CONCLUSIONS

Despite good in-roads and emerging options, the management of abdominal pain remains one of the biggest challenges and research priorities for patients with IBS.

Central sensitization and severity of gastrointestinal symptoms in irritable bowel syndrome, chronic pain syndromes, and inflammatory bowel disease

BACKGROUND

Central sensitization has been suggested as an explanation of the wide range of gastrointestinal and extraintestinal symptoms commonly seen in irritable bowel syndrome (IBS). In this study, the presence and level of central sensitization, and its association to gastrointestinal (GI) symptoms were explored in IBS in comparison with control groups.

METHODS

We investigated patients with IBS (n = 215), chronic pain disorders (n = 36), and inflammatory bowel disease (IBD) (n = 40) and volunteers without chronic diseases (n = 112). The Central Sensitization Inventory (CSI) was translated and validated in Swedish and used together with the Highly Sensitive Person (HSP) scale to measure the presence and level of central sensitization. Furthermore, severity of GI symptoms (GSRS-IBS and IBS-SSS), and anxiety and depression (HAD) were determined.

KEY RESULTS

The Swedish translation of CSI demonstrated excellent validity. Central sensitization, defined by validated cut-off levels for CSI and HSP, was common in the whole cohort (40% and 28%) and in IBS (57% and 35%). Study participants with central sensitization had more severe GI symptoms, anxiety and depression, than participants without central sensitization. Strong associations were seen between CSI and GI symptom severity in the whole cohort (GSRS-IBS: partial η²  = 0.455, p < 0.001; IBS-SSS: partial η²  = 0.408, p < 0.001), with decreasing strength in patients with chronic pain, IBD, IBS, and volunteers.

CONCLUSION AND INFERENCES

Central sensitization was common in IBS and associated with GI symptom severity, but with stronger associations in chronic pain disorders and IBD. This implies that other mechanisms may be of equal or greater importance for GI symptom severity in IBS.

Conditioned pain modulation and pain sensitivity in functional somatic disorders: The DanFunD study

Background

Disrupted pain regulation has been proposed as a component in functional somatic disorders (FSD). The objective of this study was to examine a general population sample, encompassing three delimitations of FSD while assessing pain sensitivity and conditioning pain modulation (CPM).

Methods

Pressure pain thresholds (PPTs) at the tibialis and trapezius muscles were recorded at baseline. During cold pressor stimulation of the hand, the tibialis PPTs were re‐assessed and the difference from baseline measures defined the CPM effect. Participants (n = 2,198, 53% females) were randomly selected from the adult Danish population. FSD was established by self‐reported symptom questionnaires.

Results

With a few exceptions, only weak associations were seen between PPTs and CPM in cases with FSD (p > .1). A high PPT was associated with lower odds of having multi‐organ bodily distress syndrome (OR^{PPT trapezius}: 0.66, 95% CI: 0.49–0.88, p = .005), with the symptom profile characterized by all symptoms (OR^{PPT trapezius}: 0.72, 95% CI: 0.58–0.90, p = .003 and OR^{PPT tibialis}: 0.75, 95% CI: 0.62–0.91, p = .004), and with multiple chemical sensitivity (OR^{PPT trapezius}: 0.81, 95% CI: 0.67–0.97, p = .022). High CPM was associated with high odds of having irritable bowel (OR^{CPM relative}: 1.22, 95% CI: 1.04–1.43, p = .013 and OR^{CPM absolute} = 2.66, 95% CI: 1.07–6.45, p = .033).

Conclusion

However, only PPT measured over the trapezius muscle were still significant after correction for multiple testing for the symptom profile characterized by all symptoms. Findings from this study do not support altered pain regulation in questionnaire‐based FSD which is in contrast with the existing presumption. Further epidemiological studies in this field are needed.

Significance

Disrupted pain regulation as measured by abnormal pain thresholds has been hypothesized as a central mechanism in Functional Somatic Disorders (FSD). The hypothesis has been raised in clinical setting where patients presented subjective and objective features of hypersensitivity. The present population‐based study does not support this notion. This points to the importance of further studies into the underlying pathophysiology mechanisms of FSD.

Rectal Hypersensitivity in Inflammatory Bowel Disease: A Systematic Review and Meta-analysis

Abdominal pain is a key symptom of inflammatory bowel disease (IBD), particularly in active IBD, but also occurs in patients with quiescent disease suggesting that mechanisms other than active inflammation may be responsible. Putative hypothesis to explain chronic abdominal pain in patients with quiescent IBD includes crossover with irritable bowel syndrome where rectal hypersensitivity is common and has pathophysiological implications. In contrast, in IBD, the role of rectal hypersensitivity has not been established. We aimed to determine if rectal hypersensitivity was more common in IBD compared to a healthy control population. We searched MEDLINE and EMBASE databases (1970-2018). Prospective studies that measured pain/discomfort thresholds to mechanical rectal stimuli in IBD and healthy controls were included. Data were pooled for meta-analysis and effect sizes were calculated with 95% confidence intervals (CIs). Our search strategy identified 222 citations of which 8 met the inclusion criteria, covering 133 individuals with IBD (67 men), aged between 10 and 77 compared to 99 healthy controls (55 men), aged between 10 and 67. The prevalence of rectal hypersensitivity in IBD compared to healthy controls was similar with an effect size of 0.59 (95% CIs: -0.27 to 1.44, P = .16, I ² = 87.3%). Subgroup analysis did show a significant effect size for patients compared to healthy controls with active disease (1.32) but not for quiescent disease (-0.02). These results suggest that reduced rectal pain thresholds to experimental stimulation are not seen in IBD populations except during active flares of the disease. Further research is required to understand the pathophysiology of chronic abdominal pain in quiescent IBD populations with and without chronic abdominal pain to identify appropriate management strategies.

Dysmenorrhea subtypes exhibit differential quantitative sensory assessment profiles

Women who develop bladder pain syndrome (BPS), irritable bowel syndrome, or dyspareunia frequently have an antecedent history of dysmenorrhea. Despite the high prevalence of menstrual pain, its role in chronic pelvic pain emergence remains understudied. We systematically characterized bladder, body, and vaginal mechanical sensitivity with quantitative sensory testing in women with dysmenorrhea (DYS, n = 147), healthy controls (HCs) (n = 37), and women with BPS (n = 25). Previously, we have shown that a noninvasive, bladder-filling task identified a subset of women with both dysmenorrhea and silent bladder pain hypersensitivity, and we repeated this to subtype dysmenorrhea sufferers in this study (DYSB; n = 49). DYS, DYSB, and BPS participants had lower vaginal mechanical thresholds and reported more pain to a cold stimulus during a conditioned pain modulation task and greater pelvic examination after-pain than HCs (P's < 0.05). DYSB participants also had reduced body mechanical thresholds and less conditioned pain modulation compared to HCs and DYS participants (P's < 0.05). Comparing quantitative sensory testing results among the DYS and HC groups only, provoked bladder pain was the only significant predictor of self-reported menstrual pain (r = 0.26), bladder pain (r = 0.57), dyspareunia (r = 0.39), and bowel pain (r = 0.45). Our findings of widespread sensory sensitivity in women with dysmenorrhea and provoked bladder pain, much like that observed in chronic pain, suggest a need to study the trajectory of altered mechanisms of pain processing in preclinical silent visceral pain phenotypes to understand which features convey inexorable vs modifiable risk.

Enhanced Pronociceptive and Disrupted Antinociceptive Mechanisms in Nonspecific Chronic Neck Pain

OBJECTIVE

Evidence suggests altered pronociceptive and antinociceptive mechanisms in many chronic pain conditions. Knowledge about these mechanisms in nonspecific chronic neck pain (NSNP) would improve understanding of the causes and the design of more effective treatments. Pressure pain threshold (PPT) is often used to assess presence of altered nociceptive processing in NSNP; however, its usefulness to detect this is yet to be established. The purpose of this study was to determine the functional status of temporal summation of second pain (TSSP) and conditioned pain modulation (CPM) in NSNP and to characterize the association of both measures with PPT and clinical features of NSNP.

METHODS

Thirty-two participants with NSNP (mean [SD] age = 44 [11] years; 27 female) and 32 age- and sex-matched healthy controls were recruited. TSSP was assessed using an electrical stimulus at the dorsum of the hand, and CPM was evaluated with the Cold Pressor Test. PPT was assessed bilaterally at the neck and tibialis anterior muscles.

RESULTS

Participants with NSNP showed greater TSPP (mean difference = 0.23; 95% CI = 0.46-0.01; Cohen d = 0.51) and lower CPM (mean difference = 19.44; 95% CI = 10.42-28.46; Cohen d = 1.09). Pooled data from all participants showed lower PPTs at the neck than the tibialis anterior. However, PPT measures did not differ between groups at either location. PPT measures were not correlated with CPM and TSP.

CONCLUSION

NSNP is associated with enhanced pronociceptive and impaired antinociceptive mechanisms, which may explain long-lasting pain and failure of some treatments to resolve symptoms. However, due to the observational nature of this study, a clear cause-effect relationship cannot be established. Normal PPT values in the clinic should not be interpreted as absence of altered nociceptive processing.

IMPACT

This study fills in some gaps in knowledge. Changes in central nociceptive processing may explain persistent and recurrent symptoms in NSNP and failure of treatments to obtain long-lasting relief. Further research is required to ascertain if TSSP and CPM assessment in the clinic may help predict physical therapy treatment outcome. Whether symptomatic relief with physical therapy is mediated by an improvement in TSSP and CPM should also be explored. PPTs were unaltered in participants with NSNP despite evidence of impairment in the central pain modulatory systems. Normal PPTs should not be interpreted as evidence of unaltered central pain-related processing.

Pain Severity Correlates With Biopsy-Mediated Colonic Afferent Activation But Not Psychological Scores in Patients With IBS-D

INTRODUCTION

Despite heterogeneity, an increased prevalence of psychological comorbidity and an altered pronociceptive gut microenvironment have repeatedly emerged as causative pathophysiology in patients with irritable bowel syndrome (IBS). Our aim was to study these phenomena by comparing gut-related symptoms, psychological scores, and biopsy samples generated from a detailed diarrhea-predominant IBS patient (IBS-D) cohort before their entry into a previously reported clinical trial.

METHODS

Data were generated from 42 patients with IBS-D who completed a daily 2-week bowel symptom diary, the Hospital Anxiety and Depression score, and the Patient Health Questionnaire-12 Somatic Symptom score and underwent unprepared flexible sigmoidoscopy. Sigmoid mucosal biopsies were separately evaluated using immunohistochemistry and culture supernatants to determine cellularity, mediator levels, and ability to stimulate colonic afferent activity.

RESULTS

Pain severity scores significantly correlated with the daily duration of pain (r = 0.67, P < 0.00001), urgency (r = 0.57, P < 0.0005), and bloating (r = 0.39, P < 0.05), but not with psychological symptom scores for anxiety, depression, or somatization. Furthermore, pain severity scores from individual patients with IBS-D were significantly correlated (r = 0.40, P < 0.008) with stimulation of colonic afferent activation mediated by their biopsy supernatant, but not with biopsy cell counts nor measured mediator levels.

DISCUSSION

Peripheral pronociceptive changes in the bowel seem more important than psychological factors in determining pain severity within a tightly phenotyped cohort of patients with IBS-D. No individual mediator was identified as the cause of this pronociceptive change, suggesting that nerve targeting therapeutic approaches may be more successful than mediator-driven approaches for the treatment of pain in IBS-D.

Conditioned pain modulation-A comprehensive review

Conditioned pain modulation (CPM) is a centrally processed measure of the net effect of the descending pain pathway. This comprises both the facilitatory as well as the inhibitory effect. In the past, CPM or similar effects have been previously described using different terminologies such as diffuse noxious inhibitory control (DNIC), heterotopic noxious conditioning stimulation (HNCS) or endogenous analgesia (EA). A variety of patient-related factors such as age, gender, hormones, race, genetic and psychological factors have been thought to influence the CPM paradigms. CPM paradigms have also been associated with a wide range of methodological variables including the mode of application of the 'test' as well as the 'conditioning' stimuli. Despite all these variabilities, CPM seems to reliably lend itself to the pain modulation profile concept and could in future become one of the phenotypic biomarkers for pain and also a guide for mechanism-based treatment in chronic pain. Future research should focus on establishing consistent methodologies for measuring CPM and thereby enhancing the robustness of this emerging biomarker for pain.

Electrophysiological investigation of the contribution of attention to altered pain inhibition processes in patients with irritable bowel syndrome

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder associated with chronic abdominal pain and altered pain processing. The aim of this study was to examine whether attentional processes contribute to altered pain inhibition processes in patients with IBS. Nine female patients with IBS and nine age-/sex-matched controls were included in a pain inhibition paradigm using counter-stimulation and distraction with electroencephalography. Patients with IBS showed no inhibition of pain-related brain activity by heterotopic noxious counter-stimulation (HNCS) or selective attention. In the control group, HNCS and selective attention decreased the N100, P260 and high-gamma oscillation power. In addition, pain-related high-gamma power in sensorimotor, anterior cingulate and left dorsolateral prefrontal cortex was decreased by HNCS and selective attention in the control group, but not in patients with IBS. These results indicate that the central pain inhibition deficit in IBS reflects interactions between several brain processes related to pain and attention.

Extragastrointestinal Symptoms and Sensory Responses During Breath Tests Distinguish Patients With Functional Gastrointestinal Disorders

INTRODUCTION

Patients with functional gastrointestinal disorders (FGIDs) are classified based on their gastrointestinal (GI) symptoms, without considering their frequent extra-GI symptoms. This study defined subgroups of patients using both GI and extra-GI symptoms and examined underlying mechanisms with fructose and lactose breath tests.

METHODS

Latent class analysis defined distinct clusters of patients with FGID based on their long-term GI and extra-GI symptoms. Sensory and breath gas responses after fructose and lactose ingestion were compared across symptom clusters to investigate differences in sensory function and fermentation by intestinal microbiota.

RESULTS

Six symptom clusters were identified in 2,083 patients with FGID. Clusters were characterized mainly by GI fermentation-type (cluster 1), allergy-like (cluster 2), intense pain-accentuated GI symptoms (cluster 3), central nervous system (cluster 4), musculoskeletal (cluster 5), and generalized extra-GI (cluster 6) symptoms. In the 68% of patients with complete breath tests, the areas under the curve of GI and central nervous system symptoms after fructose and lactose ingestion differed across the clusters (P < 0.001). The clusters with extensive long-term extra-GI symptoms had greater symptoms after the sugars and were predominantly women, with family or childhood allergy histories. Importantly, the areas under the curves of hydrogen and methane breath concentrations were similar (P > 0.05) across all symptom clusters. Rome III criteria did not distinguish between the symptom clusters.

DISCUSSION

Patients with FGID fall into clusters defined extensively by extra-GI symptoms. Greater extra-GI symptoms are associated with evidence of generalized sensory hypersensitivity to sugar ingestion, unrelated to intestinal gas production. Possible underlying mechanisms include metabolites originating from the intestinal microbiota and somatization.

A novel clinical applicable bed-side tool for assessing conditioning pain modulation: proof-of-concept

Background and aims

In recent years, focus on assessing descending pain modulation or conditioning pain modulation (CPM) has emerged in patients with chronic pain. This requires reliable and simple to use bed-side tools to be applied in the clinic. The aim of the present pilot study was to develop and provide proof-of-concept of a simple clinically applicable bed-side tool for assessing CPM.

Methods

A group of 26 healthy volunteers participated in the experiment. Pressure pain thresholds (PPT) were assessed as test stimuli from the lower leg before, during and 5 min after delivering the conditioning tonic painful pressure stimulation. The tonic stimulus was delivered for 2 min by a custom-made spring-loaded finger pressure device applying a fixed pressure (2.2 kg) to the index finger nail. The pain intensity provoked by the tonic stimulus was continuously recorded on a 0–10 cm Visual Analog Scale (VAS).

Results

The median tonic pain stimulus intensity was 6.7 cm (interquartile range: 4.6–8.4 cm) on the 10 cm VAS. The mean PPT increased significantly (P = 0.034) by 55 ± 126 kPa from 518 ± 173 kPa before to 573 ± 228 kPa during conditioning stimulation. When analyzing the individual CPM responses (increases in PPT), a distribution of positive and negative CPM responders was observed with 69% of the individuals classified as positive CPM responders (increased PPTs = anti-nociceptive) and the rest as negative CPM responders (no or decreased PPTs = Pro-nociceptive). This particular responder distribution explains the large variation in the averaged CPM responses observed in many CPM studies. The strongest positive CPM response was an increase of 418 kPa and the strongest negative CPM response was a decrease of 140 kPa.

Conclusions

The present newly developed conditioning pain stimulator provides a simple, applicable tool for routine CPM assessment in clinical practice. Further, reporting averaged CPM effects should be replaced by categorizing volunteers/patients into anti-nociceptive and pro-nociceptive CPM groups.

Implications

The finger pressure device provided moderate-to-high pain intensities and was useful for inducing conditioning stimuli. Therefore, the finger pressure device could be a useful bed-side method for measuring CPM in clinical settings with limited time available. Future bed-side studies involving patient populations are warranted to determine the usefulness of the method.

Risk of irritable bowel syndrome in patients who underwent appendectomy: A nationwide population-based cohort study

BACKGROUND

Appendectomy is one of the most common surgical procedures; however, the possible long-term consequences have not been fully explored. The appendix has been associated with microflora of the gut and immune functions. However, literature examining the relationship between prior appendectomy and the risk of irritable bowel syndrome (IBS) is lacking. The aim of this study was to evaluate the risk of irritable bowel syndrome for patients who underwent appendectomy by using a nationwide longitudinal population-based cohort.

METHODS

Data from this study was collected from Taiwan's National Health Insurance Research Database (NHIRD), a population-based database. We identified 12,760 patients who underwent appendectomy between January 1, 2000 and December 31, 2012. A total of 9236 patients who had appendectomy (case group) were randomly matched with 9236 patients who had not undergone appendectomy (control group) in a ratio of 1:1 by means of propensity scores. The hazard ratio (HR) of IBS was calculated by multiple Cox regression. Furthermore, sensitivity test and stratified analysis were performed.

FINDINGS

The incidence rate of IBS was 51.30 per 10,000 person-years in patients having appendectomy, more than the 35.28 per 10,000 person-years in patients not having appendectomy. Patients who underwent appendectomy had 1.46-fold risk of IBS compared to patients not having appendectomy (HR, 1.46; 95% CI, 1.24-1.72). Stratified analysis revealed that the higher HR of 1.55 (95% CI, 1.18-2.04) in patients <40 years old, and particularly within the first 5 years follow-up period of undergoing appendectomy. In addition, patients diagnosed with fibromyalgia had a greater risk of suffering IBS after appendectomy (HR, 1.41; 95% CI, 1.04-1.92).

INTERPRETATION

Patients with appendectomy have a higher incidental risk of IBS than the control population. The risk is higher for patients under 40 years old and those who received appendectomy within 5 years. Physicians could take this into consideration for treatment plans of patients who have underwent this surgery. Further research on the pathogenesis of this association is required.

FUNDING

This work was supported by grants from the Ministry of Health and Welfare, Taiwan (MOHW108-TDU-B-212-133004), China Medical University Hospital, Academia Sinica Stroke Biosignature Project (BM10701010021), MOST Clinical Trial Consortium for Stroke (MOST 108-2321-B-039-003-), Tseng-Lien Lin Foundation, Taichung, Taiwan, and Katsuzo and Kiyo Aoshima Memorial Funds, Japan.

Microbiota-neuroimmune cross talk in stress-induced visceral hypersensitivity of the bowel

Visceral hypersensitivity of the lower gastrointestinal tract, defined as an increased response to colorectal distension, frequently prompts episodes of debilitating abdominal pain in irritable bowel syndrome (IBS). Although the pathophysiology of IBS is not yet fully elucidated, it is well known that stress is a major risk factor for development and acts as a trigger of pain sensation. Stress modulates both immune responses as well as the gut microbiota and vice versa. Additionally, either microbes themselves or through involvement of the immune system, activate or sensitize afferent nociceptors. In this paper, we review current knowledge on the influence of stress along the gut-brain-microbiota axis and exemplify relevant neuroimmune cross talk mechanisms in visceral hypersensitivity, working toward understanding how gut microbiota-neuroimmune cross talk contributes to visceral pain sensation in IBS patients.

A study of cortical and brainstem mechanisms of diffuse noxious inhibitory controls in anaesthetised normal and neuropathic rats

Diffuse noxious inhibitory controls (DNIC) are a mechanism of endogenous descending pain modulation and are deficient in a large proportion of chronic pain patients. However, the pathways involved remain only partially determined with several cortical and brainstem structures implicated. This study examined the role of the dorsal reticular nucleus (DRt) and infralimbic (ILC) region of the medial prefrontal cortex in DNIC. In vivo electrophysiology was performed to record from dorsal horn lamina V/VI wide dynamic range neurones with left hind paw receptive fields in anaesthetised sham‐operated and L5/L6 spinal nerve‐ligated (SNL) rats. Evoked neuronal responses were quantified in the presence and absence of a conditioning stimulus (left ear clamp). In sham rats, DNIC were reproducibly recruited by a heterotopically applied conditioning stimulus, an effect that was absent in neuropathic rats. Intra‐DRt naloxone had no effect on spinal neuronal responses to dynamic brush, punctate mechanical, evaporative cooling and heat stimuli in sham and SNL rats. In addition, intra‐DRt naloxone blocked DNIC in sham rats, but had no effect in SNL rats. Intra‐ILC lidocaine had no effect on spinal neuronal responses to dynamic brush, punctate mechanical, evaporative cooling and heat stimuli in sham and SNL rats. However, differential effects were observed in relation to the expression of DNIC; intra‐ILC lidocaine blocked activation of DNIC in sham rats but restored DNIC in SNL rats. These data suggest that the ILC is not directly involved in mediating DNIC but can modulate its activation and that DRt involvement in DNIC requires opioidergic signalling.

Conditioned Pain Modulation (CPM) is Reduced in Irritable Bowel Syndrome: A Systematic Review and Meta-Analysis of CPM and the Role of Psychological Factors

This systematic review summarises evidence assessing endogenous pain inhibition in people with irritable bowel syndrome (IBS) compared with healthy controls using conditioned pain modulation (CPM) and offset analgesia (OA). Evidence regarding the role of psychological variables is also examined. The review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. Four electronic databases were searched to retrieve studies assessing CPM or OA in adults diagnosed with IBS according to the ROME II/III criteria. Standardized mean differences were calculated for each study and a random effects model was used for meta-analysis. Eleven studies were included, 5 of which reported results on the relationship between CPM and psychological variables. None of the studies assessed OA. The risk of bias assessment found a lack of assessor blinding in all studies. The pooled effect estimate was 0.90 (95% CI, 0.40-1.40) indicating a significantly lower CPM effect in people with IBS compared with controls. This effect was reduced to 0.51 when 1 outlier was excluded from the analysis. In addition, reduced CPM responses were significantly correlated with higher anxiety (r=0.17 to 0.64), stress (r=0.63), and pain catastrophizing (r=0.38) in people with IBS; however, the evidence available was limited and the strength of these associations variable. Depression was not found to be associated with CPM in these IBS cohorts. The results of this review suggest that people with IBS, as a group, demonstrate reduced pain inhibition measured by CPM. The preliminary evidence about the association between psychological factors and CPM warrants further investigations.