Thermal hypersensitivity in a subset of irritable bowel syndrome patients

Subtyping irritable bowel syndrome using cluster analysis: a systematic review

BACKGROUND

Irritable bowel syndrome (IBS) is a common chronic functional gastrointestinal disorder associated with a wide range of clinical symptoms. Some researchers have used cluster analysis (CA), a group of non-supervised learning methods that identifies homogenous clusters within different entities based on their similarity.

OBJECTIVE AND METHODS

This literature review aims to identify published articles that apply CA to IBS patients. We searched relevant keywords in PubMed, Embase, Web of Science, and Scopus. We reviewed studies in terms of the selected variables, participants' characteristics, data collection, methodology, number of clusters, clusters' profiles, and results.

RESULTS

Among the 14 articles focused on the heterogeneity of IBS, eight of them utilized K-means Cluster Analysis (K-means CA), four employed Hierarchical Cluster Analysis, and only two studies utilized Latent Class Analysis. Seven studies focused on clinical symptoms, while four articles examined anocolorectal functions. Two studies were centered around immunological findings, and only one study explored microbial composition. The number of clusters obtained ranged from two to seven, showing variation across the studies. Males exhibited lower symptom severity and fewer psychological findings. The association between symptom severity and rectal perception suggests that altered rectal perception serves as a biological indicator of IBS. Ultra-slow waves observed in IBS patients are linked to increased activity of the anal sphincter, higher anal pressure, dystonia, and dyschezia.

CONCLUSION

IBS has different subgroups based on different factors. Most IBS patients have low clinical severity, good QoL, high rectal sensitivity, delayed left colon transit time, increased systemic cytokines, and changes in microbial composition, including increased Firmicutes-associated taxa and depleted Bacteroidetes-related taxa. However, the number of clusters is inconsistent across studies due to the methodological heterogeneity. CA, a valuable non-supervised learning method, is sensitive to hyperparameters like the number of clusters and random initialization of cluster centers. The random nature of these parameters leads to diverse outcomes even with the same algorithm. This has implications for future research and practical applications, necessitating further studies to improve our understanding of IBS and develop personalized treatments.

Somatosensory Profiles Differentiate Pain and Psychophysiological Symptoms Among Young Adults With Irritable Bowel Syndrome: A Cluster Analysis

OBJECTIVE

The aim of this study was to investigate if somatosensory profiles can differentiate pain and psychophysiological symptoms among young adults with irritable bowel syndrome (IBS).

METHODS

We performed a cluster analysis of data collected from a randomized clinical trial of 80 IBS patients and 21 age-matched healthy controls (HCs) to stratify pain and symptoms among young adults with IBS by their peripheral sensory profiles. Data of quantitative sensory testing and IBS-related pain and symptoms were collected at baseline and 6-week and 12-week follow-ups.

RESULTS

Using the K-means method, IBS patients were classified into 2 clusters, the "IBS normal threshold" (IBS-NT) and the "IBS increased threshold" (IBS-IT). The IBS-NT cluster had a similar pain threshold as the HCs, and the IBS-IT cluster had an increased threshold of somatic pain perception (lower cold pain threshold, higher heat pain threshold, and higher pressure pain threshold, all P<0.001) than HCs. Compared with the IBS-NT cluster, the IBS-IT cluster reported higher levels of IBS-related pain intensity, anxiety, fatigue, and sleep disturbance over the 3 visits (all P<0.05).

DISCUSSION

Young adults with IBS fell into 2 clusters, one with a similar sensory threshold as the HCs and another with an increased pain threshold, who reported higher pain intensity and more severe symptoms. Somatic sensory profiles should be integrated into further personalized self-management intervention among patients with IBS.

A neuropsychosocial signature predicts longitudinal symptom changes in women with irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common disorder of brain-gut interactions characterized by chronic abdominal pain, altered bowel movements, often accompanied by somatic and psychiatric comorbidities. We aimed to test the hypothesis that a baseline phenotype composed of multi-modal neuroimaging and clinical features predicts clinical improvement on the IBS Symptom Severity Scale (IBS-SSS) at 3 and 12 months without any targeted intervention. Female participants (N = 60) were identified as "improvers" (50-point decrease on IBS-SSS from baseline) or "non-improvers." Data integration analysis using latent components (DIABLO) was applied to a training and test dataset to determine whether a limited number of sets of multiple correlated baseline'omics data types, including brain morphometry, anatomical connectivity, resting-state functional connectivity, and clinical features could accurately predict improver status. The derived predictive models predicted improvement status at 3-months and 12-months with 91% and 83% accuracy, respectively. Across both time points, non-improvers were classified as having greater correlated morphometry, anatomical connectivity and resting-state functional connectivity characteristics within salience and sensorimotor networks associated with greater pain unpleasantness, but lower default mode network integrity and connectivity. This suggests that non-improvers have a greater engagement of attentional systems to perseverate on painful visceral stimuli, predicting IBS exacerbation. The ability of baseline multimodal brain-clinical signatures to predict symptom trajectories may have implications in guiding integrative treatment in the age of precision medicine, such as treatments targeted at changing attentional systems such as mindfulness or cognitive behavioral therapy.

Clusters of community-dwelling individuals empirically derived from stool diaries correspond with clinically meaningful outcomes

BACKGROUND

Functional gastrointestinal disorders (FGIDs) are diagnosed according to expert consensus criteria based on recall of symptoms over periods of 3 months or longer. Whether the expert opinion concords with underlying disease process and whether individual recall is accurate are both in doubt. This study aimed to identify naturally occurring clusters of individuals with respect to symptom pattern, evaluate their significance, compare cluster profiles with expert opinion and evaluate their temporal stability.

METHODS

As part of a random population study of FGID-related symptoms, we first explored the use of prospective stool and symptom diaries combined with empirical grouping of individuals into clusters using nonhierarchical cluster analysis.

RESULTS

The analysis identified two clusters of individuals, one of which was characterized by elevated scores on all domains of symptoms (26% of the sample) and one that was low to average on all domains (74% of the sample). Cluster membership was found to be stable over a long interval. Clusters were found to differ on most domains of quality-of-life (d = 0.46-0.74), self-rated health (d = -0.42) and depression (d = -0.42) but not anxiety. Prevalence of clinically diagnosed irritable bowel syndrome (IBS) was higher in the more impacted cluster (33%) compared with the healthy cluster (13%; P < 0.0001).

CONCLUSION

A naturalistic classification of individuals challenges consensus criteria in showing that some IBS individuals have a symptom experience not unlike health. The proposed approach has demonstrated temporal stability over time, unlike consensus criteria. A naturalistic disease classification system may have practical advantages over consensus criteria when supported by a decision-analytic system.

Supraspinal Mechanisms of Intestinal Hypersensitivity

Gut inflammation or injury causes intestinal hypersensitivity (IHS) and hyperalgesia, which can persist after the initiating pathology resolves, are often referred to somatic regions and exacerbated by psychological stress, anxiety or depression, suggesting the involvement of both the spinal cord and the brain. The supraspinal mechanisms of IHS remain to be fully elucidated, however, over the last decades the series of intestinal pathology-associated neuroplastic changes in the brain has been revealed, being potentially responsible for the phenomenon. This paper reviews current clinical and experimental data, including the authors' own findings, on these functional, structural, and neurochemical/molecular changes within cortical, subcortical and brainstem regions processing and modulating sensory signals from the gut. As concluded in the review, IHS can develop and maintain due to the bowel inflammation/injury-induced persistent hyperexcitability of viscerosensory brainstem and thalamic nuclei and sensitization of hypothalamic, amygdala, hippocampal, anterior insular, and anterior cingulate cortical areas implicated in the neuroendocrine, emotional and cognitive modulation of visceral sensation and pain. An additional contribution may come from the pathology-triggered dysfunction of the brainstem structures inhibiting nociception. The mechanism underlying IHS-associated regional hyperexcitability is enhanced NMDA-, AMPA- and group I metabotropic receptor-mediated glutamatergic neurotransmission in association with altered neuropeptide Y, corticotropin-releasing factor, and cannabinoid 1 receptor signaling. These alterations are at least partially mediated by brain microglia and local production of cytokines, especially tumor necrosis factor α. Studying the IHS-related brain neuroplasticity in greater depth may enable the development of new therapeutic approaches against chronic abdominal pain in inflammatory bowel disease.

The Potential Role of Sensory Testing, Skin Biopsy, and Functional Brain Imaging as Biomarkers in Chronic Pain Clinical Trials: IMMPACT Considerations

Valid and reliable biomarkers can play an important role in clinical trials as indicators of biological or pathogenic processes or as a signal of treatment response. Currently, there are no biomarkers for pain qualified by the U.S. Food and Drug Administration or the European Medicines Agency for use in clinical trials. This article summarizes an Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials meeting in which 3 potential biomarkers were discussed for use in the development of analgesic treatments: 1) sensory testing, 2) skin punch biopsy, and 3) brain imaging. The empirical evidence supporting the use of these tests is described within the context of the 4 categories of biomarkers: 1) diagnostic, 2) prognostic, 3) predictive, and 4) pharmacodynamic. Although sensory testing, skin punch biopsy, and brain imaging are promising tools for pain in clinical trials, additional evidence is needed to further support and standardize these tests for use as biomarkers in pain clinical trials.

PERSPECTIVE

The applicability of sensory testing, skin biopsy, and brain imaging as diagnostic, prognostic, predictive, and pharmacodynamic biomarkers for use in analgesic treatment trials is considered. Evidence in support of their use and outlining problems is presented, as well as a call for further standardization and demonstrations of validity and reliability.

Widespread hyperalgesia in adolescents with symptoms of irritable bowel syndrome: results from a large population-based study

Widespread hyperalgesia is well documented among adult patients with irritable bowel syndrome (IBS), but little is known about pain sensitivity among adolescents with IBS. We examined pain sensitivity in 961 adolescents from the general population (mean age 16.1 years), including pain threshold and tolerance measurements of heat (forearm) and pressure pain (fingernail and shoulder) and cold pressor tolerance (hand). Adolescents with IBS symptoms (Rome III criteria) had lower heat pain thresholds compared to controls after adjustments for sex, comorbid pain, and psychological distress (mean difference = -.8 °C; 95% confidence interval [CI] = -1.6 to -.04). Similar results were found for pressure pain threshold at the shoulder (mean difference = -46 kPa; 95% CI = -78 to -13) and fingernail (mean difference = -62 kPa; 95% CI = -109 to -15), and for an aggregate of all 3 threshold measures (z-score difference = -.4; 95% CI = -.6 to -.2), though pressure pain threshold differences were nonsignificant after the final adjustments for psychological distress. No difference of pain tolerance was found between the IBS cases and controls. Our results indicate that adolescents in the general population with IBS symptoms, like adults, have widespread hyperalgesia.

PERSPECTIVE

This is the first report of widespread hyperalgesia among adolescents with IBS symptoms in the general population, with lower pain thresholds found to be independent of sex and comorbid pain. Our results suggest that central pain sensitization mechanisms in IBS may contribute to triggering and maintaining chronic pain symptoms.

Characteristics of sensitization associated with chronic pain conditions

OBJECTIVES

To describe and understand varieties and characteristics of sensitization contributing to hyperalgesia in participants with chronic pain conditions.

METHODS

Thermal stimulation was delivered to the face, forearm, and calf of pain-free participants and individuals with irritable bowel syndrome, temporomandibular pain disorder (TMD), and fibromyalgia syndrome (FM). Three-second contacts by a preheated thermode occurred at 30-second intervals in ascending and then in descending series (0.7°C steps).

RESULTS

Thermal pain ratings during ascending series were greater at each site in individuals diagnosed with chronic pain. Intense pain at the time of testing further enhanced the ratings at all sites, but mild or moderate clinical pain did not have this effect. Thermal pain in all participants was greater during descending series compared with the ascending series of arm and leg stimulation. The hypersensitivity during the descending series was comparable in pain-free, FM and TMD participants but was increased in duration for arm or leg stimulation of FM participants.

DISCUSSION

The widespread sensitization for irritable bowel syndrome and TMD participants does not rely on mechanisms of spatial and temporal summation often invoked to explain widespread hyperalgesia associated with chronic pain. Increased sensitivity during descending series of stimulation of an arm or leg but not the face indicates a propensity for sensitization of nociceptive input to the spinal cord. Abnormally prolonged sensitization for FM participants reveals a unique influence of widespread chronic pain referred to deep somatic tissues.

Perception and pain thresholds for cutaneous heat and cold, and rectal distension: associations and disassociations

BACKGROUND

Hypersensitivity to somatic or visceral pain has been reported in numerous clinical conditions such as fibromyalgia or the irritable bowel syndrome, and general hypersensitivity has been proposed to be the underlying mechanism. However, cross-modal relationships especially between somatic and visceral pain have rarely been investigated even in healthy volunteers. Furthermore, psychological influences on pain have rarely been characterized across modalities.

METHODS

Sixty-one healthy participants underwent testing of perception and pain thresholds for cutaneous thermode heat and cold, as well as for rectal balloon distension. Psychological testing for anxiety, depression, and pain experience (including catastrophizing and coping) as well as cardiac interoception was performed. Measurement quality and the correlations between the different modalities were examined.

KEY RESULTS

Significant correlations existed between the perception thresholds for cold/heat (τB  = -0.28, p = 0.002) and cold/distension (τB  = -0.21, p = 0.03) and for the pain thresholds for cold/heat (r = -0.61, p < 0.001) and heat/distension (r = 0.33, p = 0.01). No association was found between pain thresholds and anxiety, depression, psychological experience with and processing of pain, or cardiac interoception. Retest reliabilities for pain measurements were satisfying after short intertrial intervals (all intraclass correlation coefficients >0.8), but less so after longer intervals. The individuals contributing to the respective correlations differ between measurements.

CONCLUSIONS & INFERENCES

Moderate associations were found for pain thresholds across modalities. The strength of the associations and their stability over time warrants further investigation and might serve to increase the understanding of conditions affecting multiple pain modalities.

Increased pain sensitivity among adults reporting irritable bowel syndrome symptoms in a large population-based study

The aim of this study was to examine whether irritable bowel syndrome (IBS) is associated with increased somatic pain sensitivity in a large population-based sample and to test whether this association was independent of sex, age, comorbid chronic pain, and psychological distress. Pain sensitivity tests included assessment of heat-pain threshold (N=4054) and pressure-pain threshold (N=4689) and of cold-pressor pain intensity and tolerance (N=10,487). Cox regression and analysis of variance (ANOVA) were used to assess the relationship between IBS and pain sensitivity in stepwise multivariate models. The prevalence of IBS symptoms meeting the ROME II criteria was 5.3%. Compared with control subjects, IBS cases had reduced cold-pressor tolerance (hazard ratio=1.4, P<.01), increased cold-pressor pain intensity ratings (z-score=+0.20, P<0.01), and lower heat-pain thresholds (z-score=-0.20, P<0.01), after adjusting for sex and age. These results were only slightly attenuated and remained significant when controlling for comorbid chronic pain and psychological distress. Results for pressure-pain threshold were not significant. Heat- and cold-pressor pain sensitivity was greatest for the IBS reporting severe chronic abdominal pain, indicating that hyperalgesia in IBS is related to degree of clinical pain rather than to the diagnosis per se. Because all pain tests were all carried out on the upper extremities, our findings indicate the presence of widespread hyperalgesia in IBS, which may be a contributing factor to the high rate of comorbid pain seen in this patient group.

A Mechanism-Based Approach to Prevention of and Therapy for Fibromyalgia

Fibromyalgia syndrome (FMS) is characterized by pain referred to deep tissues. Diagnosis and treatment of FMS are complicated by a variable coexistence with regional pain, fatigue, sleep disruption, difficulty with mentation, and depression. The widespread, deep pain of FMS can be a consequence of chronic psychological stress with autonomic dysregulation. Stress acts centrally to facilitate pain and acts peripherally, via sympathetic vasoconstriction, to establish painful muscular ischemia. FMS pain, with or without a coexistent regional pain condition, is stressful, setting up a vicious circle of reciprocal interaction. Also, stress interacts reciprocally with systems of control over depression, mentation, and sleep, establishing FMS as a multiple-system disorder. Thus, stress and the ischemic pain it generates are fundamental to the multiple disorders of FMS, and a therapeutic procedure that attenuates stress and peripheral vasoconstriction should be highly beneficial for FMS. Physical exercise has been shown to counteract peripheral vasoconstriction and to attenuate stress, depression, and fatigue and improve mentation and sleep quality. Thus, exercise can interrupt the reciprocal interactions between psychological stress and each of the multiple-system disorders of FMS. The large literature supporting these conclusions indicates that exercise should be considered strongly as a first-line approach to FMS therapy.

Lesioning of TRPV1 expressing primary afferent neurons prevents PAR-2 induced motility, but not mechanical hypersensitivity in the rat colon

BACKGROUND

Proteinase activated receptor 2 (PAR-2) is expressed by many neurons in the colon, including primary afferent neurons that co-express transient receptor potential vanilloid 1 (TRPV1). Activation of PAR-2 receptors was previously found to enhance colonic motility, increase secretion and produce hypersensitivity to mechanical stimuli. This study examined the functional role of TRPV1/PAR-2 expressing neurons that innervate the colon by lesioning TRPV1 bearing neurons with the highly selective and potent TRPV1 agonist resiniferatoxin.

METHODS

Colonic motility in response to PAR-2 activation was evaluated in vitro using isolated segments of descending colon and in vivo using manometry. Colonic mechanical nociceptive thresholds were measured using colorectal distension. Transient receptor potential vanilloid 1 expressing neurons were selectively lesioned with resiniferatoxin.

KEY RESULTS

In vitro, the PAR-2 agonists, trypsin and SLIGRL did not alter contractions of colon segments when applied alone, however, the agents enhanced acetylcholine stimulated contraction. In vivo, PAR-2 agonists administered intraluminally induced contractions of the colon and produced hypersensitivity to colorectal distention. The PAR-2 agonist enhancement of colonic contraction was eliminated when TRPV1 expressing neurons were lesioned with resiniferatoxin, but the PAR-2 agonist induced hypersensitivity remained in the lesioned animals.

CONCLUSIONS & INFERENCES

Our findings indicate that TRPV1/PAR-2 expressing primary afferent neurons mediate an extrinsic motor reflex pathway in the colon. These data, coupled with our previous studies, also indicate that the recently described colospinal afferent neurons are nociceptive, suggesting that these neurons may be useful targets for the pharmacological control of pain in diseases such as irritable bowel syndrome.

The effect of topical local anesthetics on thermal pain sensitivity in patients with irritable bowel syndrome

Generalized hypersensitivity that extends into somatic areas is common in patients with irritable bowel syndrome (IBS). The sensitized state, particularly assessed by experimental methods, is known to persist even during remissions of clinical pain. It was hypothesized that disease-related nociceptive activity in the gut maintains a systemic-sensitized state. The present study evaluated responses to prolonged thermal stimuli maintained at constant temperature or constant pain intensity during stimulation. The effect of topically applied rectal lidocaine on heat sensitivity was also evaluated. The question is whether silencing potential intestinal neural activity (which may not always lead to a conscious pain experience) with lidocaine attenuates sensitization of somatic areas. Tests were also performed where lidocaine was applied orally to control for systemic or placebo effects of the drug. The IBS subjects exhibited a greater sensitivity to somatic heat stimuli compared to controls; however, lidocaine had no discernible effect on sensitization in this sample of IBS patients, where most of the individuals did not have clinical pain on the day of testing.

Decreased pain inhibition in irritable bowel syndrome depends on altered descending modulation and higher-order brain processes

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder involving abdominal pain and bowel dysfunction. IBS pain symptoms have been hypothesized to depend on peripheral and central mechanisms, but the pathophysiology is still unclear. The aim of the present study was to assess the contribution of cerebral and cerebrospinal processes to pain inhibition deficits in IBS. Fourteen female patients with diarrhea-predominant IBS (IBS-D) and 14 healthy female volunteers were recruited. Acute pain and the nociceptive withdrawal reflex (RIII reflex) were evoked by transcutaneous electrical stimulation of the right sural nerve with modulation by hetero-segmental counter-irritation produced by sustained cold pain applied on the left forearm. Psychological symptoms were assessed by questionnaires. Shock pain decreased significantly during counter-irritation in the controls (P<0.001) but not in IBS patients (P=0.52). Similarly, RIII-reflex amplitude declined during counter-irritation in the controls (P=0.009) but not in IBS patients (P=0.11). Furthermore, pain-related anxiety increased during counter-irritation in IBS patients (P=0.003) but not in the controls (P=0.74). Interestingly, across all subjects, counter-irritation analgesia was positively correlated with RIII-reflex inhibition (r=0.39, P=0.04) and negatively with pain-related anxiety (r=-0.61, P<0.001). In addition, individual differences in counter-irritation analgesia were predicted independently by the modulation of RIII responses (P=0.03) and by pain catastrophizing (P=0.01), with the latter mediating the effect of pain-related anxiety. In conclusion, these results demonstrate that pain inhibition deficits in female IBS-D patients depend on two potentially separable mechanisms reflecting: (1) altered descending modulation and (2) higher-order brain processes underlying regulation of pain and affect.

Traditional thoughts on the pathophysiology of irritable bowel syndrome

The pathogenesis of symptoms in irritable bowel syndrome (IBS) is multifactorial and varies from patient to patient. Disturbances of motor function in the small intestine and colon and smooth-muscle dysfunction in other gut and extraintestinal regions are prominent. Abnormalities of sensory function in visceral and somatic structures are detected in most patients with IBS, which may relate to peripheral sensitization or altered central nervous system processing of afferent information. Contributions from psychosocial disturbances are observed in patients from tertiary centers and primary practice. Proof of causation of symptom genesis for most of these factors is limited.

Effects of the N-methyl-D-aspartate receptor on temporal summation of second pain (wind-up) in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder in which the pathophysiological mechanisms of the pain and hypersensitivity are not well understood. IBS patients frequently complain of pain in body regions somatotopically distinct from the gut, suggesting that central hyperalgesic mechanisms may be involved. In the current study, during the wind-up testing session, a series of 6 heat pulses were presented with an interstimulus interval (ISI) of 3 seconds. Following the 1st, 3rd, and 6th thermal stimuli, subjects were asked to rate the late thermal sensation or second pain. IBS patients who demonstrated temporal summation of pain (TSSP) then received dextromethorphan and placebo in a randomized, double-blind, fashion to block wind-up. The results showed: 1) a subset of IBS patients, but not controls, showed TSSP in response to a series of noxious heat pulses; and 2) TSSP was blocked by administration of dextromethorphan, an NMDA receptor antagonist. In summary, these findings further elucidate mechanisms of somatic hypersensitivity in a subset of IBS patients. Our results also support an etiologic basis for abnormal NMDA receptor mechanisms in some IBS patients. Future studies are needed to determine if NMDA receptor antagonists may be used to treat IBS patients.

PERSPECTIVE

This study evaluates temporal summation of second pain in a subset of IBS patients that is blocked by Dextromethorphan, an NMDA receptor antagonist. Theses results could lead to the use of an NMDA receptor antagonist in the treatment of pain in a subset of IBS patients.

Ischemic hypersensitivity in irritable bowel syndrome patients

OBJECTIVE

Mixed evidence exists regarding whether irritable bowel syndrome (IBS) patients show increased somatic pain perception compared with controls. The current study used a deep, tonic somatic pain stimulus (ischemic pain) to evaluate somatic hypersensitivity in IBS patients.

METHODS

A total of 27 diarrhea-predominant and 15 constipation-predominant IBS patients, and 29 controls participated in the study. The modified submaximal effort tourniquet procedure was performed to induce ischemic arm pain, and the time required to reach pain threshold and pain tolerance were recorded in seconds. All subjects completed the Functional Bowel Disease Severity Index (FBDSI) scale as well as several psychosocial instruments. Group differences for threshold and tolerance were determined using a series of one-way anova tests followed by Tukey comparisons.

RESULTS

IBS patients had a shorter time to ischemic threshold (F = 34.606, P < 0.001) and tolerance (F = 38.656, P < 0.001) compared with controls; however, the groups did not differ on ratings of pain at the time of tolerance. IBS patients had a higher rating on the FBDSI scale compared with controls (P < 0.001), and ischemic pain threshold was negatively correlated with the FBDSI score.

CONCLUSIONS

The results of this study suggest that a widespread alteration in central pain processing in IBS patients may be present as they display hypersensitivity to ischemic arm pain, and ischemic pain threshold was associated with clinical symptoms. These findings could reflect a dysfunction in inhibitory pain systems in IBS patients, as ischemic (deep) pain may be under tonic inhibitory control.

Relationships between Irritable Bowel Syndrome Pain, Skin Temperature Indices of Autonomic Dysregulation, and Sensitivity to Thermal Cutaneous Stimulation

This study evaluated relationships between irritable bowel syndrome (IBS) pain, sympathetic dysregulation, and thermal pain sensitivity. Eight female patients with diarrhea-predominant IBS and ten healthy female controls were tested for sensitivity to thermal stimulation of the left palm. A new method of response-dependent thermal stimulation was used to maintain pain intensity at a predetermined level (35%) by adjusting thermal stimulus intensity as a function of pain ratings. Clinical pain levels were assessed prior to each testing session. Skin temperatures were recorded before and after pain sensitivity testing. The temperature of palmar skin dropped (1.5°C) when the corresponding location on the opposite hand of control subjects was subjected to prolonged thermal stimulation, but this response was absent for IBS pain patients. The patients also required significantly lower stimulus temperatures than controls to maintain a 35% pain rating. Baseline skin temperatures of patients were significantly correlated with thermode temperatures required to maintain 35% pain ratings. IBS pain intensity was not significantly correlated with skin temperature or pain sensitivity. The method of response-dependent stimulation revealed thermal hyperalgesia and increased sympathetic tone for chronic pain patients, relative to controls. Similarly, a significant correlation between resting skin temperatures and thermal pain sensitivity for IBS but not control subjects indicates that tonic sympathetic activation and a thermal hyperalgesia were generated by the chronic presence of visceral pain. However, lack of a significant relationship between sympathetic tone and ratings of IBS pain casts doubt on propositions that the magnitude of IBS pain is determined by psychological stress.

Central and peripheral hypersensitivity in the irritable bowel syndrome

Previous investigations of somatic hypersensitivity in IBS patients have typically involved only a single stimulus modality, and little information exists regarding whether patterns of somatic pain perception vary across stimulus modalities within a group of patients with IBS. Therefore, the current study was designed to characterize differences in perceptual responses to a battery of noxious somatic stimuli in IBS patients compared to controls. A total of 78 diarrhea-predominant and 57 controls participated in the study. We evaluated pain threshold and tolerance and sensory and affective ratings of contact thermal, mechanical pressure, ischemic stimuli, and cold pressor stimuli. In addition to assessing perceptual responses, we also evaluated differences in neuroendocrine and cardiovascular responses to these experimental somatic pain stimuli. A subset of IBS patients demonstrated the presence of somatic hypersensitivity to thermal, ischemic, and cold pressor nociceptive stimuli. The somatic hypersensitivity in IBS patients was somatotopically organized in that the lower extremities that share viscerosomatic convergence with the colon demonstrate the greatest hypersensitivity. There were also changes in ACTH, cortisol, and systolic blood pressure in response to the ischemic pain testing in IBS patients when compared to controls. The results of this study suggest that a more widespread alteration in central pain processing in a subset of IBS patients may be present as they display hypersensitivity to heat, ischemic, and cold pressor stimuli.