Associations among neurophysiology measures in irritable bowel syndrome (IBS) and their relevance for IBS symptoms

First description of a histopathologic grading system and relationship to outcomes after robotic median arcuate ligament release with celiac ganglionectomy and lymphadenectomy

BACKGROUND

Two dominating theories regarding median arcuate ligament syndrome include vascular and neurogenic etiologies from celiac artery and ganglion compression, respectively. Celiac ganglionectomy is not routine during surgery, and specimens are rarely excised; therefore, the extent of nerve involvement and histopathology are unknown. Our study aims to characterize histopathologic findings in median arcuate ligament syndrome, establish a histopathologic grading system, and correlate with clinical outcomes.

METHODS

Robotic median arcuate ligament release, celiac ganglionectomy, and lymphadenectomy were performed with specimens excised and stained using hematoxylin & eosin, trichrome, and S100. Neurofibrosis, adiposity, and reactive changes were described, a grading scale was developed, and results were analyzed with clinical outcomes.

RESULTS

Fifty-four patients were evaluated, of whom 36 met inclusion criteria (81% female, 34.9 [25.9-47.5] years, body mass index 23.5 [19.6-28.1] kg/m2). Histopathologic evaluation revealed fibrosis (hematoxylin & eosin and trichrome median score 1.5 [0-2.5]), reactive lymphadenopathy (89%), intraparenchymal nerves (31%), and lipogranulomas (31%). Greater fibrosis was associated with a lack of preoperative celiac plexus block relief (100% vs. 30%, P = .044) and lower postoperative celiac artery velocities (198 vs 323 cm/s, P = .02). Intraparenchymal nerves were associated with greater decreases in pre to postoperative velocities (161 vs 84 cm/s, P = .037). Symptoms improved in 28 patients (78%).

CONCLUSION

We developed the first histopathologic grading system and identified unique findings of intraparenchymal nerves and lipogranulomas. Histopathologic abnormalities were associated with objective improvement and symptomatic relief postoperatively. These findings support nerve compression and inflammation as predominant contributors to median arcuate ligament syndrome pain, celiac ganglia resection to treat symptoms, and continued histopathologic analysis to better elucidate median arcuate ligament syndrome etiology.

Not a general, symptom-unspecific, transdiagnostic marker for functional symptoms: sensorimotor processing of head control is intact in chronic pain

Introduction

Functional disorders are prevalent in all medical fields and pose a tremendous public health problem, with pain being one of the most common functional symptoms. Understanding the underlying, potentially unifying mechanism in functional (pain) disorders is instrumental in facilitating timely diagnosis, stigma reduction, and adequate treatment options. Neuroscientific models of perception suggest that functional symptoms arise due to dysregulated sensorimotor processing in the central nervous system, with brain-based predictions dominating the eventual percept. Experimental evidence for this transdiagnostic mechanism has been established in various functional symptoms. The goal of the current study was to investigate whether erroneous sensorimotor processing is an underlying transdiagnostic mechanism in chronic (functional) pain.

Method

A total of 13 patients with chronic (functional) pain [three patients with chronic (functional) pain disorder, F45.40, ICD-10; 10 patients with chronic pain disorder with somatic and psychological factors, F45.41, ICD-10]; and 15 healthy controls performed large combined eye-head gaze shifts toward visual targets, naturally and with increased head moment of inertia. We simultaneously measured participants' eye and head movements to assess head oscillations at the end of the gaze shift, which are an established indicator of (transdiagnostic) sensorimotor processing deficits of head control.

Results

Using a Bayesian analysis protocol, we found that patients with chronic (functional) pain and control participants stabilized their heads equally well (Bayes Factor 01 = 3.7, Bayes Factor exclusion = 5.23; corresponding to substantial evidence) during all sessions of the experiment.

Conclusion

Our results suggest that patients with chronic (functional) pain do not show measurable symptom-unspecific sensorimotor processing deficits. We discuss outcome parameter choice, organ system specificity, and selection of patient diagnoses as possible reasons for this result and recommend future avenues for research.

Contribution of sex and gender roles to the incidence of post-infectious irritable bowel syndrome in a prospective study

Post-infectious irritable bowel syndrome (PI-IBS) occurs in about 10% of cases following gastroenteritis. The incidence of IBS is higher in females. However, it is not clear whether this is due to biological or psychosocial factors. We aimed to investigate the influence of gender roles on the incidence of PI-IBS, alongside traditional risk factors. Our study included 231 patients diagnosed with gastroenteritis who were hospitalized and treated with antibiotics between 2018 and 2021. The Korean Sex Role Inventory-Short Form (KSRI-SF), based on the Bem Sex Role Inventory (BSRI) was used to categorize patients (androgynous, masculine, feminine, and undifferentiated types). Six months after treatment, we conducted a telephone survey to confirm the presence of PI-IBS using the ROME IV criteria. Among the patients, 43.3% were female, and the mean age was 43.67 ± 16.09 years. After 6 months, 34 patients developed PI-IBS. Univariate analysis revealed that younger age, female sex, KSRI-SF undifferentiated type, and longer duration of antibiotic use independently influenced the occurrence of PI-IBS. Multivariate analysis showed that PI-IBS was associated with the KSRI-SF undifferentiated type and higher C-reactive protein (CRP) levels. Our study showed that the KSRI-SF undifferentiated type and high CRP levels at initial infection were associated with PI-IBS.

Inhibition and Heart Rate Variability in Experimentally Induced Pain

Introduction

Pain is a complex experience that requires executive functions (EFs) to be processed. The autonomic outcome of the neural networks involved in the cognitive evaluation of pain is reflected by heart rate variability (HRV), an index of self-regulation abilities. Although some results suggest a relationship between HRV, EFs, and pain, studies focusing on this three-way relationship are still scarce.

Objective

This study aims to investigate the relationship between pain, cognitive, and autonomic mechanisms, hypothesizing an association between resting HRV and both cognitive and motor inhibition as indices of executive functioning. This relationship was investigated after an experimental-induced pain.

Methods

Seventy-six young adults were exposed to the Cold Pressure Arm Warp to induce experimental pain. HRV was collected, and cognitive tasks were administered to assess executive performance.

Results

The results showed that (1) HRV indices significantly increased during pain stimulation, (2) cognitive inhibition was positively correlated with vagal indices and with pain parameters, (3) both inhibition tasks significantly predicted pain threshold while the performance on the Stroop Task predicted pain tolerance.

Conclusion

Results suggest a three-way relationship. Further research would focus on the role of HRV and cognitive strategies in pain management in chronic pain conditions.

Multi-omics profiles of the intestinal microbiome in irritable bowel syndrome and its bowel habit subtypes

BACKGROUND

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder that is thought to involve alterations in the gut microbiome, but robust microbial signatures have been challenging to identify. As prior studies have primarily focused on composition, we hypothesized that multi-omics assessment of microbial function incorporating both metatranscriptomics and metabolomics would further delineate microbial profiles of IBS and its subtypes.

METHODS

Fecal samples were collected from a racially/ethnically diverse cohort of 495 subjects, including 318 IBS patients and 177 healthy controls, for analysis by 16S rRNA gene sequencing (n = 486), metatranscriptomics (n = 327), and untargeted metabolomics (n = 368). Differentially abundant microbes, predicted genes, transcripts, and metabolites in IBS were identified by multivariate models incorporating age, sex, race/ethnicity, BMI, diet, and HAD-Anxiety. Inter-omic functional relationships were assessed by transcript/gene ratios and microbial metabolic modeling. Differential features were used to construct random forests classifiers.

RESULTS

IBS was associated with global alterations in microbiome composition by 16S rRNA sequencing and metatranscriptomics, and in microbiome function by predicted metagenomics, metatranscriptomics, and metabolomics. After adjusting for age, sex, race/ethnicity, BMI, diet, and anxiety, IBS was associated with differential abundance of bacterial taxa such as Bacteroides dorei; metabolites including increased tyramine and decreased gentisate and hydrocinnamate; and transcripts related to fructooligosaccharide and polyol utilization. IBS further showed transcriptional upregulation of enzymes involved in fructose and glucan metabolism as well as the succinate pathway of carbohydrate fermentation. A multi-omics classifier for IBS had significantly higher accuracy (AUC 0.82) than classifiers using individual datasets. Diarrhea-predominant IBS (IBS-D) demonstrated shifts in the metatranscriptome and metabolome including increased bile acids, polyamines, succinate pathway intermediates (malate, fumarate), and transcripts involved in fructose, mannose, and polyol metabolism compared to constipation-predominant IBS (IBS-C). A classifier incorporating metabolites and gene-normalized transcripts differentiated IBS-D from IBS-C with high accuracy (AUC 0.86).

CONCLUSIONS

IBS is characterized by a multi-omics microbial signature indicating increased capacity to utilize fermentable carbohydrates-consistent with the clinical benefit of diets restricting this energy source-that also includes multiple previously unrecognized metabolites and metabolic pathways. These findings support the need for integrative assessment of microbial function to investigate the microbiome in IBS and identify novel microbiome-related therapeutic targets. Video Abstract.

Interactions between symptoms and psychological status in irritable bowel syndrome: An exploratory study of the impact of a probiotic combination

BACKGROUND

Stress is an exacerbator of irritable bowel syndrome (IBS) symptoms, and anxiety and depression are co-morbidities. Bifidobacterium longum strains 1714® and 35642® attenuate stress responses in healthy people and reduce symptoms in IBS, respectively. Here, we explore relationships between the psychological and visceral effects of the two strains (COMBO) in IBS subjects and biomarkers of stress and inflammation.

METHODS

We recruited 40 patients with IBS (Rome III) and mild to moderate anxiety (HADS-A) and/or depression (HADS-D) and 57 asymptomatic female controls with low or moderate stress. IBS patients were fed COMBO (1 × 10⁹ cfu/day) for 8 weeks with an 8-week washout. IBS symptoms, psychometric measures, salivary cortisol awakening response (CAR), and plasma inflammatory biomarkers were assessed every 4 weeks.

KEY RESULTS

Compared to healthy controls, IBS subjects had a blunted CAR. Treatment with COMBO restored CAR and improved IBS symptoms compared to baseline during the treatment phase. The COMBO reduced HADS-D, HADS-A score, and TNF-α, while sleep quality improved significantly from baseline to the end of the intervention. Surprisingly, these parameters improved further once treatment ended and maintained this improvement by Week 16.

CONCLUSIONS AND INFERENCES

These findings suggest that the stress response is a major driver of IBS symptoms. The time course of the beneficial effect of COMBO on IBS symptoms suggests that this is achieved through a restoration of the stress response. In contrast, the time course of the effects of COMBO on anxiety and depression in IBS paralleled an anti-inflammatory effect as indicated by a reduction in circulating levels of TNF-α.

Phase II Feasibility Study of the Efficacy, Tolerability, and Impact on the Gut Microbiome of a Low-Residue (Fiber) Diet in Adult Patients With Mitochondrial Disease

Background and Aims

Gastrointestinal (GI) dysmotility is a common and debilitating clinical manifestation in patients with mitochondrial DNA (mtDNA)-related disease with no curative and few effective symptomatic therapies. A low-residue diet (LRD) has been shown to be effective at reducing bowel urgency, pain, and distension in functional GI-related conditions. We assessed tolerability and effects of an LRD on bowel habits in patients with mtDNA-related disease.

Methods

This was a 12-week single-arm pilot study in patients with genetically determined primary mtDNA-related disease, meeting the ROME III constipation criteria. The co-primary outcomes were tolerability of an LRD (<10 g fiber per day) assessed by food diaries and changes in stool frequency and consistency. The secondary outcomes included GI symptoms, disease burden, laxatives, physical activity levels, colonic transit time using radiopaque markers, gut microbiome (patients and controls), and metabolomics. The gut microbiome of the mtDNA-related disease patients was compared against controls for observational purpose only.

Results

Twenty-eight patients were enrolled, and 24 completed the LRD intervention. The LRD was well tolerated with a mean fold change of -34% in dietary fiber (5.3 ± 10.4 grams) per day (P = .03, confidence interval = 0.7-9.9) with no adverse events. The proportion of stool samples with normal stool consistency increased from 36% to 49% (P = .01); GI symptoms and laxative use were reduced. However, the LRD did not change stool frequency, stool output, and colonic transit time. The gut microbiome was significantly different between patients and controls but was not modulated by the dietary intervention.

Conclusion

The LRD in patients with mtDNA-related mitochondrial disease and significant constipation is well tolerated and a promising treatment for alleviating GI symptoms. These positive findings should be confirmed in a randomized controlled trial.ClinicalTrials.gov Identifier: NCT03388528.

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.

Corticotropin-releasing factor receptor 1 (CRF-R1) antagonists: Promising agents to prevent visceral hypersensitivity in irritable bowel syndrome

Corticotropin-releasing factor (CRF) is a 41-amino acid polypeptide that coordinates the endocrine system, autonomic nervous system, immune system, and physiological behavior. CRF is a signaling regulator in the neuro-endocrine-immune (NEI) network that mediates visceral hypersensitivity. Rodent models to simulate changes in intestinal motility similar to those reported in the irritable bowel syndrome (IBS), demonstrate that the CRF receptor 1 (CRF-R1) mediates intestinal hypersensitivity under many conditions. However, the translation of preclinical studies into clinical trials has not been successful possibly due to the lack of sufficient understanding of the multiple variants of CRF-R1 and CRF-R1 antagonists. Investigating the sites of action of central and peripheral CRF is critical for accelerating the translation from preclinical to clinical studies.

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.

Dietary fibres and IBS: translating functional characteristics to clinical value in the era of personalised medicine

Clinical guidelines in the use of fibre supplementation for patients with IBS provide one-size-fits-all advice, which has limited value. This narrative review addresses data and concepts around the functional characteristics of fibre and subsequent physiological responses induced in patients with IBS with a view to exploring the application of such knowledge to the precision use of fibre supplements. The key findings are that first, individual fibres elicit highly distinct physiological responses that are associated with their functional characteristics rather than solubility. Second, the current evidence has focused on the use of fibres as a monotherapy for IBS symptoms overall without attempting to exploit these functional characteristics to elicit specific, symptom-targeted effects, or to use fibre types as adjunctive therapies. Personalisation of fibre therapies can therefore target several therapeutic goals. Proposed goals include achieving normalisation of bowel habit, modulation of gut microbiota function towards health and correction of microbial effects of other dietary therapies. To put into perspective, bulking fibres that are minimally fermented can offer utility in modulating indices of bowel habit; slowly fermented fibres may enhance the activities of the gut microbiota; and the combination of both fibres may potentially offer both benefits while optimising the activities of the microbiota throughout the different regions of the colon. In conclusion, understanding the GI responses to specific fibres, particularly in relation to the physiology of the individual, will be the future for personalising fibre therapy for enhancing the personalised management of patients with IBS.

Local Colonic Administration of a Serine Protease Inhibitor Improves Post-Inflammatory Visceral Hypersensitivity in Rats

Dysregulation of the protease–antiprotease balance in the gastrointestinal tract has been suggested as a mechanism underlying visceral hypersensitivity in conditions such as inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS). We aimed to study the potential therapeutic role of an intracolonically administered serine protease inhibitor for the treatment of abdominal pain in a post-inflammatory rat model for IBS. An enema containing 2,4,6-trinitrobenzene sulfonic acid (TNBS) was used to induce colitis in male Sprague–Dawley rats, whereas controls received a saline solution. Colonoscopies were performed to confirm colitis and follow-up mucosal healing. In the post-inflammatory phase, the serine protease inhibitor UAMC-00050 (0.1–5 mg/kg) or its vehicle alone (5% DMSO in H₂O) was administered in the colon. Thirty minutes later, visceral mechanosensitivity to colorectal distensions was quantified by visceromotor responses (VMRs) and local effects on colonic compliance and inflammatory parameters were assessed. Specific proteolytic activities in fecal and colonic samples were measured using fluorogenic substrates. Pharmacokinetic parameters were evaluated using bioanalytical measurements with liquid chromatography–tandem mass spectrometry. Post-inflammatory rats had increased trypsin-like activity in colonic tissue and elevated elastase-like activity in fecal samples compared to controls. Treatment with UAMC-00050 decreased trypsin-like activity in colonic tissue of post-colitis animals. Pharmacokinetic experiments revealed that UAMC-00050 acted locally, being taken up in the bloodstream only minimally after administration. Local administration of UAMC-00050 normalized visceral hypersensitivity. These results support the role of serine proteases in the pathophysiology of visceral pain and the potential of locally administered serine protease inhibitors as clinically relevant therapeutics for the treatment of IBS patients with abdominal pain.

Identifying threshold sizes for enlarged abdominal lymph nodes in different age ranges from about 200,000 individual's data

The threshold size for enlarged abdominal lymph nodes (E-ALNs), a common pediatric disorder, has yet to be standardized. According to the maximum short-axis diameter, this study divided ALNs into Grade A (≥ 10 mm), Grade B (8–10 mm), Grade C (5–8 mm), and Grade D (< 5 mm, normal). To identify the threshold size for E-ALNs, the prevalence of each grade was compared between asymptomatic individuals and symptomatic (e.g., abdominal pain) individuals without other diseases (e.g., appendicitis) that could explain the symptoms for different ages using data from > 200,000 individuals. The results showed the following: (1) For ages 1–3 years, the recommended threshold size is 8 mm, as the differences in the prevalence between the two groups were nonsignificant for Grade C but significant (p < 0.05) for both Grades A and B. (2) For ages 3–14 years, the recommended threshold size is 5 mm, as the differences between the two groups were significant (p < 0.05) for Grades A, B, and C. (3) The prevalence of Grades A, B, and C was very low for ages 0–1 years and high for ages 1–6 years. (4) The prevalence for males was generally higher than that for females for Grades A and B.

Adults living with irritable bowel syndrome (IBS): A qualitative systematic review

OBJECTIVE

To consolidate existing qualitative studies which examined the experiences and needs of adults living with IBS, and to gather a holistic insight for future directions and avenues to support these adults.

METHODS

A qualitative systematic review was conducted and six databases were searched for qualitative studies, beginning from each database's inception to July 2020. The qualitative data were meta-synthesised and thematic analysis was adopted. Any discrepancies that arose were discussed between the reviewers until a consensus was reached throughout the process of data screening, selection, critical appraisal and synthesis.

RESULTS

Seventeen studies with a total of 299 adults diagnosed with IBS were included. Four themes were identified: (1) physical, psychological, and social consequences; (2) impact of IBS on working adults; (3) dealing with IBS; and (4) sources of support and support needs.

CONCLUSION

Future research across geographically diverse locations are needed to gather a thorough perspective of the experiences and needs of adults living with IBS. The development and evaluation of technology-based, trained peer-led volunteers, and interventions that adopt mindfulness, active coping strategies, cognitive behavioural therapy and acceptance, and commitment therapy are needed. Ultimately, the collaboration between the relevant stakeholders is essential for standardised instruments and materials for accurate testing, diagnosis, assessment, treatment and management of IBS.