Differences in somatic perception in female patients with irritable bowel syndrome with and without fibromyalgia

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.

Intestinal membrane permeability and hypersensitivity in the irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder in which the underlying pathophysiology is poorly understood; however, increased intestinal permeability in diarrhea-predominant IBS patients has been reported. Here we demonstrate that diarrhea-predominant IBS (D-IBS) patients display increased intestinal permeability. We have also found that increased intestinal membrane permeability is associated with visceral and thermal hypersensitivity in this subset of D-IBS patients. We evaluated 54 D-IBS patients and 22 controls for intestinal membrane permeability using the lactulose/mannitol method. All subjects ingested 5g of lactulose and 2g of mannitol in 100ml of water after which their urine was collected. We also evaluated the mean mechanical visual analogue scale (M-VAS) pain rating to nociceptive thermal and visceral stimulation in all subjects. All study participants also completed the FBDSI scale. Approximately 39% of diarrhea-predominant IBS patients had increased intestinal membrane permeability as measured by the lactulose/mannitol ratio. These IBS patients also demonstrated higher M-VAS pain intensity reading scale. Interestingly, the IBS patients with hypersensitivity and increased intestinal permeability had a higher FBDSI score (100.8 + or - 5.4) than IBS patients with normal membrane permeability and sensitivity (51.6 + or - 12.7) and controls (6.1 + or - 5.6) (p<0.001). A subset of D-IBS patients had increased intestinal membrane permeability that was associated with an increased FBDSI score and increased hypersensitivity to visceral and thermal nociceptive pain stimuli. Thus, increased intestinal membrane permeability in D-IBS patients may lead to more severe IBS symptoms and hypersensitivity to somatic and visceral stimuli.

Widespread hypersensitivity is related to altered pain inhibition processes in irritable bowel syndrome

The mechanisms of chronic pain in irritable bowel syndrome (IBS) have been widely investigated but remain unclear. The present study investigated the relation between visceral hypersensitivity, cutaneous thermal sensitivity, and central pain mechanisms. Rectal sensitivity was assessed with a barostat, and forearm and calf sensitivity with a contact thermode. Central mechanisms were assessed by counterirritation using sustained cold-pain to the hand and painful electric shocks to the ankle. Psychological symptoms were also assessed, using questionnaires. Female volunteers with diarrhea-predominant IBS (n=27) and healthy controls (n=25) participated in the study. IBS patients had lower rectal and calf pain thresholds compared to controls (p's<0.05). IBS patients also reported more pain than controls for rectal distensions, and heat pain on the calf and forearm (all p's<0.001). Cold-pain inhibited shock-pain in controls but not IBS patients (controls: -13.5+/-5.3 vs IBS: +1.9+/-10.5; p<0.01). In addition, visceral hypersensitivity was significantly correlated to cutaneous thermal hypersensitivity and pain inhibition deficits, although effects were only weak and moderate, respectively. Furthermore, covariance analyses indicated that psychological factors accounted for group differences in visceral hypersensitivity and pain inhibition deficits. In conclusion, this study confirms the relation between altered pain inhibition processes and widespread hypersensitivity in IBS. The present results also suggests that psychological symptoms and altered pain processing in IBS patients may reflect at least in part, common underlying mechanisms.

Subjective theories of illness and clinical and psychological outcomes in patients with irritable bowel syndrome

OBJECTIVES

Patients' ideas about the nature, cause, and treatment of their illnesses are part of the complex process of coping with illness. To date, limited research on subjective theories of illness in patients with irritable bowel syndrome (IBS) has been performed. The aim of the study was to investigate patients' subjective theories of illness and how these are related to clinical and psychological outcome criteria, in particular IBS symptom severity and quality of life.

METHODS

Eighty-eight patients with IBS, as defined by Rome III criteria, were administered a battery of questionnaires to collect the following data: sociodemographic variables, subjective theories of illness (Subjektive Krankheitstheorien, Cause Questionnaire), anxiety (Hospital Anxiety and Depression Scale), depression (Beck Depression Inventory), quality of life (SF-12), and IBS symptoms (Questionnaire for Gastrointestinal Symptoms).

RESULTS

Almost all patients reported theories of illness reflecting their subjective causal assumptions. The most frequently mentioned causal factors were physical illness, intrapsychic factors, and stress. Patients with mainly somatic attributions had higher IBS symptoms scores (P<.05) and reduced physical quality of life. Intrapsychic attributions were associated with reduced mental quality of life and enhanced physical quality of life (P<.01). All correlations were independent of gender, age, and irritable bowel subgroups.

CONCLUSIONS

Subjective theories of illness can have significant implications for IBS symptom severity, as well as for physical and mental quality of life.

Thermal hypersensitivity in a subset of irritable bowel syndrome patients

AIM: To characterize thermal hypersensitivity in patients with constipation- and diarrhea-predominant irritable bowel syndrome (IBS).

METHODS: Thermal pain sensitivity was tested among patients with diarrhea-predominant IBS (D-IBS) and constipation-predominant IBS (C-IBS) compared to healthy subjects. A total of 42 patients (29 female and 13 male; mean age 27.0 ± 6.4 years) with D-IBS; 24 patients (16 female and eight male; mean age 32.5 ± 8.8 years) with C-IBS; and 52 control subjects (34 female and 18 male; mean age 27.3 ± 8.0 years) participated in the study. Thermal stimuli were delivered using a Medoc Thermal Sensory Analyzer with a 3 cm × 3 cm surface area. Heat pain threshold (HPTh) and heat pain tolerance (HPTo) were assessed on the left ventral forearm and left calf using an ascending method of limits. The Functional Bowel Disease Severity Index (FBDSI) was also obtained for all subjects.

RESULTS: Controls were less sensitive than C-IBS and D-IBS (both at P < 0.001) with no differences between C-IBS and D-IBS for HPTh and HPTo. Thermal hyperalgesia was present in both groups of IBS patients relative to controls, with IBS patients reporting significantly lower pain threshold and pain tolerance at both test sites. Cluster analysis revealed the presence of subgroups of IBS patients based on thermal hyperalgesia. One cluster (17% of the sample) showed a profile of heat pain sensitivity very similar to that of healthy controls; a second cluster (47% of the sample) showed moderate heat pain sensitivity; and a third cluster (36% of the sample) showed a very high degree of thermal hyperalgesia.

CONCLUSION: A subset of IBS patients had thermal hypersensitivity compared to controls, who reported significantly lower HPTh and HPTo. All IBS patients had a higher score on the FBDSI than controls. Interestingly, the subset of IBS patients with high thermal sensitivity (36%) had the highest FBDSI score compared to the other two groups of IBS patients.

Role of anxiety in the pathophysiology of irritable bowel syndrome: importance of the amygdala

A common characteristic of irritable bowel syndrome (IBS) is that symptoms, including abdominal pain and abnormal bowel habits, are often triggered or exacerbated during periods of stress and anxiety. However, the impact of anxiety and affective disorders on the gastrointestinal (GI) tract is poorly understood and may in part explain the lack of effective therapeutic approaches to treat IBS. The amygdala is an important structure for regulating anxiety with the central nucleus of the amygdala facilitating the activation of the hypothalamic-pituitary-adrenal axis and the autonomic nervous system in response to stress. Moreover, chronic stress enhances function of the amygdala and promotes neural plasticity throughout the amygdaloid complex. This review outlines the latest findings obtained from human studies and animal models related to the role of the emotional brain in the regulation of enteric function, specifically how increasing the gain of the amygdala to induce anxiety-like behavior using corticosterone or chronic stress increases responsiveness to both visceral and somatic stimuli in rodents. A focus of the review is the relative importance of mineralocorticoid receptor and glucocorticoid receptor-mediated mechanisms within the amygdala in the regulation of anxiety and nociceptive behaviors that are characteristic features of IBS. This review also discusses several outstanding questions important for future research on the role of the amygdala in the generation of abnormal GI function that may lead to potential targets for new therapies to treat functional bowel disorders such as IBS.

Widespread hyperalgesia in irritable bowel syndrome is dynamically maintained by tonic visceral impulse input and placebo/nocebo factors: evidence from human psychophysics, animal models, and neuroimaging

Irritable bowel syndrome (IBS) is a highly prevalent gastrointestinal disorder that is often accompanied by both visceral and somatic hyperalgesia (enhanced pain from colorectal and somatic stimuli). Neural mechanisms of both types of hyperalgesia have been analyzed by neuroimaging studies of IBS patients and animal analog studies of "IBS-like" rats with delayed rectal and somatic hypersensitivity. Results from these studies suggest that pains associated with both visceral and widespread secondary cutaneous hyperalgesia are dynamically maintained by tonic impulse input from the non-inflamed colon and/or rectum and by brain-to-spinal cord facilitation. Enhanced visceral and somatic pains are accompanied by enhanced pain-related brain activity in IBS patients as compared to normal control subjects; placebos can normalize both their hyperalgesia and enhanced brain activity. That pain in IBS which is likely to be at least partly maintained by peripheral impulse input from the colon/rectum is supported by results showing that local rectal-colonic anesthesia normalizes visceral and somatic hyperalgesia in IBS patients and visceral and somatic hypersensitivity in "IBS-like" rats. Yet these forms of hyperalgesia are also highly modifiable by placebo and nocebo factors (e.g., expectations of relief or distress, respectively). Our working hypothesis is that synergistic interactions occur between placebo/nocebo factors and enhanced afferent processing so as to enhance, maintain, or reduce hyperalgesia in IBS. This explanatory model may be relevant to other persistent pain conditions.

Prevalence of functional gastrointestinal disorders in patients with fibromyalgia and the role of psychologic distress

BACKGROUND & AIMS

Fibromyalgia is a rheumatologic disorder associated with somatic and psychologic conditions. Although fibromyalgia is associated with irritable bowel syndrome, its relationship with other functional gastrointestinal disorders (FGID) is unclear. We evaluated the prevalence of FGID in patients with fibromyalgia and the role of psychologic factors in this relationship.

METHODS

From a Spanish population, 100 patients with fibromyalgia and 100 matched controls completed the Rome II Integrative Questionnaire to assess the prevalence of FGID and the Symptom Checklist-90 Revised (SCL-90R) to evaluate psychologic distress. Patients completed the Fibromyalgia Impact Questionnaire to evaluate the overall impact of fibromyalgia and controls filled out the Chronic Widespread Pain Questionnaire to detect potential cases of fibromyalgia.

RESULTS

Ninety-three percent of the total study population was female, with a mean age of 50 years. We identified 6 cases of widespread pain among controls. The average Fibromyalgia Impact Questionnaire score for patients was 67.28 +/- 14.25. All gastrointestinal symptoms except for vomiting were more frequent in patients. Ninety-eight percent of patients with fibromyalgia had at least one FGID, compared with only 39% of controls. Fibromyalgia was correlated most highly with irritable bowel syndrome. Patients presented with significantly higher scores of psychologic distress than controls, especially those with fecal incontinence.

CONCLUSIONS

There is a prevalence of FGID in patients with fibromyalgia and a wider distribution of such symptoms along the gastrointestinal tract compared with controls. We propose that an increased degree of psychologic distress in these patients predisposes them to FGID, especially significant for anorectal syndromes.

Increased startle responses in interstitial cystitis: evidence for central hyperresponsiveness to visceral related threat

PURPOSE

Hypersensitivity to visceral stimuli in interstitial cystitis/painful bladder syndrome may result from enhanced responsiveness of affective circuits (including the amygdala complex) and associated central pain amplification. Potentiation of the eyeblink startle reflex under threat is mediated by output from the amygdala complex and, therefore, represents a noninvasive marker to study group differences in responsiveness in this brain circuit.

MATERIALS AND METHODS

Acoustic startle responses were examined in female patients with interstitial cystitis/painful bladder syndrome (13) and healthy controls (16) during context threat (application of muscle stimulation electrodes to the lower abdomen overlying the bladder), and cued conditions for safety (no stimulation possible), anticipation and imminent threat of aversive abdominal stimulation over the bladder.

RESULTS

Patients showed significantly greater startle responses during nonimminent threat conditions (baseline, safe and anticipation periods) while both groups showed similar robust startle potentiation during the imminent threat condition. Higher rates of anxiety and depression symptoms in the patient group did not account for the group differences in startle reflex magnitude.

CONCLUSIONS

Compared to controls, female patients with interstitial cystitis/painful bladder syndrome showed increased activation of a defensive emotional circuit in the context of a threat of abdominal pain. This pattern is similar to that previously reported in patients with anxiety disorders as well as those with irritable bowel syndrome. Since these circuits have an important role in central pain amplification related to affective and cognitive processes, these results support the hypothesis that the observed abnormality may be involved in the enhanced perception of bladder signals associated with interstitial cystitis/painful bladder syndrome.

Psychiatric disorder, irritable bowel syndrome, and extra-intestinal symptoms in a population-based sample of twins

OBJECTIVES

To determine, in a population-based sample of twin pairs, if extra-intestinal symptoms (EIS) are closely associated with both irritable bowel syndrome (IBS) and psychiatric disorders and whether such associations are explained on a genetic basis.

METHODS

A random sample of twins between the ages of 44 and 64 years enrolled in the Minnesota Twins Registry completed the Modified Mayo Clinic Bowel Disease Questionnaire, a questionnaire on extra-intestinal symptoms, and the Psychiatric Diagnostic Screening Questionnaire.

RESULTS

Of the 3,048 participants (51% response rate), 371 (12.2%) fulfilled Rome II criteria for IBS; 61 (16.4%) had a psychiatric disorder compared with 7.6% (n=204) of those without IBS (P<0.001). In regression analysis both IBS and psychiatric disorders were independently associated with the number of extra-intestinal symptoms (P<0.0005). Concordance rates for high EIS score were 30.0% for monozygote (MZ) twins and 16.7% in dizygote (DZ) twins (P=0.020) and the OR for concordance remained substantially higher for MZ than DZ twins after adjustment for psychiatric disorder and presence of IBS (6.82 (95% CI 4.45-10.45) and 2.71 (95% CI 1.69-4.37)). In MZ twins discordant for IBS, EIS and IBS were significantly associated (P=0.004) and psychiatric disorder and EIS were significantly associated (P=0.001).

CONCLUSIONS

Extra-intestinal symptoms are independently associated with both IBS and psychiatric disorders. There is evidence that there is a genetic basis to EIS, but the association with IBS and psychiatric disorders is not primarily explained by genetic influences.

Increased acoustic startle responses in IBS patients during abdominal and nonabdominal threat

BACKGROUND AND AIMS

Visceral hypersensitivity and symptom severity in Irritable Bowel Syndrome (IBS) are both exacerbated by stress. The eye-blink startle response represents a noninvasive measure of central defensive responding. Evidence for central hyperexcitability was studied in IBS patients by examining potentiation of the startle reflex to a nociceptive threat.

METHODS

Acoustic startle responses were examined in female IBS patients (n = 42) and healthy controls (n = 22) during cued periods in which an aversive abdominal or biceps stimulation was impossible (safe), possible (imminent threat) or anticipated (period just before the imminent threat), and during a threatening context (muscle stimulation pads attached but no cues for stimulation).

RESULTS

Both groups showed potentiation of startle responses during the imminent threat condition compared with both the anticipation and safe conditions. Compared with controls, IBS subjects showed significantly larger startle responses during anticipation and imminent threat conditions after receiving an initial aversive stimulation. There were no group differences during the context threat manipulation. Moreover, in IBS patients but not controls, higher neuroticism was associated with larger startle responses during safe and anticipation conditions but not imminent threat, whereas anxiety symptoms were negatively associated with startle magnitude during imminent threat.

CONCLUSIONS

Female IBS patients show increased startle responses to threat of aversive stimulation at both abdominal and nonabdominal sites compared with controls. The data represent the first demonstration of altered threat potentiated startle in a functional pain condition and provide support for the use of these paradigms in further evaluation of affective mechanisms in these disorders.

Review article: the psychoneuroimmunology of irritable bowel syndrome--an exploration of interactions between psychological, neurological and immunological observations

BACKGROUND

The pathogenesis of irritable bowel syndrome (IBS) is founded on interactive mechanisms. Disentangling these processes is a prerequisite for the development of effective drug therapy.

AIM

To identify the interaction between the various factors implicated in IBS.

METHODS

Articles pertaining to IBS pathogenesis focusing on psychoneuroimmunology were identified using following search terms: IBS, animal models, microbiota, probiotics, immunology, visceral hypersensitivity, imaging, psychology and visceral pain.

RESULTS

Cerebral imaging using MRI and proton emission tomography scanning has revealed differential regional cerebral activation, whereas stimuli induced activation has been captured by both MRI and cortical evoked potentials. At the peripheral neurological level, the concept of visceral hypersensitivity has been challenged as perhaps representing psychological traits with symptom over-reporting or hyper-vigilance. Gut mucosal immunology is thought to be relevant with immunological changes reflected as peripheral blood cytokine level changes. Molecular technology advances suggest a role for microbiota by activating the gut immunological system. These interactions have been examined in IBS animal models.

CONCLUSIONS

Translation of animal model findings to humans is needed to link the various psychological, neurological and immunological changes noted in IBS. This analysis may identify patient sub-groups, which will ultimately be critical for drug testing to be focused accordingly.

Complementary and alternative medicine for IBS in adults: mind-body interventions

Standard treatment for IBS focuses on the management or alleviation of the predominant gastrointestinal presenting symptoms, such as diarrhea or constipation, often using pharmacological therapy. For many patients, this approach is unsatisfactory, and patients frequently seek the advice of complementary and alternative medicine (CAM) practitioners in order to explore other treatment options. CAM practices include a broad range of modalities, and mind-body interventions hold particular promise as treatment modalities for IBS because psychological factors could have an important role in IBS symptomatology and quality of life. Psychological stressors are postulated to result in gastrointestinal symptoms through alteration of intestinal function mediated by the autonomic nervous system, hypothalamic-pituitary-adrenal axis and immune system. Hypnotherapy has the strongest supportive evidence as a beneficial mind-body intervention for IBS. Clinical studies of hypnotherapy have uniformly shown improvement of gastrointestinal symptoms, anxiety, depression and quality of life in patients with IBS. Mindfulness meditation remains unstudied for IBS, but is theoretically attractive as a stress-reduction technique. There is a suggestion that relaxation therapy or multimodal therapy (a combination of relaxation therapy, education and psychotherapy) is beneficial for IBS. The most generally accepted psychological mind-body intervention is cognitive behavioral therapy, and clinical trials support the beneficial effects of cognitive behavioral therapy in patients with IBS.

Biology and therapy of fibromyalgia. Evidence-based biomarkers for fibromyalgia syndrome

Researchers studying fibromyalgia strive to identify objective, measurable biomarkers that may identify susceptible individuals, may facilitate diagnosis, or that parallel activity of the disease. Candidate objective measures range from sophisticated functional neuroimaging to office-ready measures of the pressure pain threshold. A systematic literature review was completed to assess highly investigated, objective measures used in fibromyalgia studies. To date, only experimental pain testing has been shown to coincide with improvements in clinical status in a longitudinal study. Concerted efforts to systematically evaluate additional objective measures in research trials will be vital for ongoing progress in outcome research and translation into clinical practice.

Psychophysiology of visceral pain in IBS and health

The psychophysiology of visceral pain as it relates to gastrointestinal motility, visceral sensitivity, and putative mechanisms of the processing of visceral stimuli by the central and peripheral nervous systems are discussed. Peripheral mechanisms may include low-grade mucosal inflammation, and it is likely that central nervous mechanisms such as neuronal plasticity at the level of the spinal cord and attentional bias at the cortical level are relevant for the chronification of visceral pain. From a psychophysiological perspective, visceral pain therefore remains a complex symptom because behavioral variables, such as the way an individual deals with stress, may be as important for the etiology of visceral pain as, for example, a history of inflammation.

Brain imaging of visceral functions in healthy volunteers and IBS patients

From experience, most people know about a link between psychological processes and gastrointestinal sensory and motor functions. Cognitive processes (e.g., attention) as well as affective processes (e.g., fear) play a role in gastrointestinal sensations in healthy controls and patients with irritable bowel syndrome (IBS) alike. However, the exact nature of this relationship has not been completely understood yet. Brain imaging techniques allow for the study of brain-gut interactions in vivo. Accordingly, positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have been widely used to study neural mechanisms underlying visceral sensations. This article will summarize the results of functional brain imaging studies in healthy controls and selected studies assessing the influence of psychological processes on gastrointestinal functions. Subsequently, this article will deal with those brain areas activated by visceral stimulation in IBS patients. Special attention will be paid to recently published studies concerning psychological factors and novel research questions.

Somatic comorbidities of irritable bowel syndrome: a systematic analysis

OBJECTIVE

A large number of irritable bowel syndrome (IBS) patients are additionally afflicted with other somatic intestinal and/or extraintestinal comorbidities. The occurrence of one or more comorbidities is correlated with enhanced medical help seeking, worse prognosis, and higher rates of anxiety and depression-all resulting in a reduced quality of life. The aims of this study were, firstly, to review the literature on comorbidities of IBS and to assess gastrointestinal and extraintestinal comorbidities, and, secondly, to evaluate explanatory hypotheses and possible common pathophysiological mechanisms.

METHODS

We systematically reviewed the scientific literature in the past 25 years, as cited in MEDLINE.

RESULTS

IBS patients present with a twofold increase in somatic comorbidities compared to controls, possibly caused by common pathophysiological mechanisms. Nevertheless, to date, there has been no convincing evidence for a consolidated underlying pathophysiology or somatization. Gastrointestinal disorders, such as functional dyspepsia, gastroesophageal reflux disease, functional constipation, and anal incontinence, occur in almost half of the patients. In a broad variety of extraintestinal comorbidities, fibromyalgia, chronic fatigue syndrome, and chronic pelvic pain are best documented and appear in up to 65%.

CONCLUSION

The knowledge and structured assessment of comorbid somatic symptoms might allow to identify subgroups of IBS patients with special characteristics and lead to adaptation of the therapeutic concept.

Somatic pain sensitivity in children with recurrent abdominal pain

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Reversal of visceral and somatic hypersensitivity in a subset of hypersensitive rats by intracolonic lidocaine

Chronic abdominal pain is a common gastrointestinal symptom experienced by patients. We have previously shown that IBS patients with visceral hypersensitivity also have evidence of thermal hypersensitivity of the hand and foot that is reversed by rectal lidocaine jelly. We have also recently developed an animal model of chronic visceral and somatic hypersensitivity in rats treated with intracolonic trinitrobenzene sulfonic acid (TNBS). The objective of the current study was to determine the effects of intracolonic lidocaine on visceral/somatic hypersensitivity in TNBS-treated rats. A total of 20 hypersensitive rats received either 20mg intracolonic lidocaine (n=10) or saline jelly (n=10). In comparison to saline jelly, intracolonic lidocaine jelly reduced responses to nociceptive visceral/somatic stimuli in hypersensitive rats. The effects were present within 5-30 min after administration of lidocaine and lasted for 6h. Lidocaine had no effects on recovered rats or control rats that had originally been treated with intracolonic saline instead of TNBS. Local anesthetic blockade of peripheral impulse input from the colon reduces both visceral and somatic hypersensitivity in TNBS-treated rats, similar to results in IBS patients. The results provide further evidence that visceral and secondary somatic hypersensitivity in a subset of TNBS-treated rats reflect central sensitization mechanisms maintained by tonic impulse input from the colon. This study evaluates the reversal of visceral/somatic hypersensitivity in a subset of TNBS-treated rats with intracolonic lidocaine. This animal model may be used in the future to study the mechanisms of local anesthetic agents applied to the gut to reduce visceral pain.

Visceral and somatic hypersensitivity in TNBS-induced colitis in rats

Inflammation of visceral structures in rats has been shown to produce visceral/somatic hyperalgesia. Our objectives were to determine if trinitrobenzene sulfonic acid (TNBS) induced colitis in rats leads to visceral/somatic hypersensitivity. Male Sprague-Dawley rats (200-250 g) were treated with 20 mg of TNBS in 50% ethanol (n = 40) or an equivalent volume of ethanol (n = 40) or saline (n = 25) via the colon. Colonic distension, Von Frey, Hargreaves, and tail reflex tests were used to evaluate for visceral, mechanical, and thermal sensitivity. The rats demonstrated visceral hypersensitivity at 2-28 days following TNBS administration (P < 0.0001). The ethanol-treated rats also demonstrated visceral hypersensitivity that resolved after day 14. TNBS-treated rats demonstrated somatic hypersensitivity at days 14-28 (P < 0.0001) in response to somatic stimuli of the hind paw. TNBS colitis is associated with visceral and somatic hypersensitivity in areas of somatotopic overlap. This model of colitis should allow further investigation into the mechanisms of visceral and somatic hypersensitivity.

NMDA Receptors and Colitis: Basic Science and Clinical Implications

During the last decade, research focusing primarily on alterations in the peripheral and central nervous system has improved our understanding of the pathophysiological mechanisms of chronic visceral pain. These studies have demonstrated significant physiological changes following injury to the viscera in the firing patterns of both primary afferent neurons that transmit nociceptive information from the viscera and in central neurons that process the nociceptive information. A number of receptors, neurotransmitters, cytokines, and second messenger systems in these neurons have been implicated in the enhancement of visceral nociception. N-methyl-d-aspartic acid (NMDA) receptors play an important role in chronic visceral pain and hypersensitivity that is present in the setting of colonic inflammation. NMDA receptors are found in the peripheral nervous system as well as the central terminal of primary afferent neurons and have been shown to play an important role in regulating the release of nociceptive neurotransmitters. Recent work has demonstrated the presence of NMDA receptors in the enteric nervous system. In this article, we will discuss more recent evidence of the role of NMDA receptors in visceral pain associated with colitis.

Abnormal endogenous pain modulation and somatic and visceral hypersensitivity in female patients with irritable bowel syndrome

AIM: To investigate the role of endogenous pain modulatory mechanisms in the central sensitization implicated by the visceral hypersensitivity demonstrated in patients with irritable bowel syndrome (IBS). Dysfunction of modulatory mechanisms would be expected to also result in changes of somatic sensory function.

METHODS: Endogenous pain modulatory mechanisms were assessed using heterotopic stimulation and somatic and visceral sensory testing in IBS. Pain intensities (visual analogue scale, VAS 0-100) during suprathreshold rectal distension with a barostat, cold pressor stimulation of the foot and during both stimuli simultaneously (heterotopic stimulation) were recorded in 40 female patients with IBS and 20 female healthy controls.

RESULTS: Rectal hypersensitivity (defined by 95% CI of controls) was seen in 21 (53%), somatic hypersensitivity in 22 (55%) and both rectal and somatic hypersensitivity in 14 of these IBS patients. Heterotopic stimulation decreased rectal pain intensity by 6 (-11 to -1) in controls, but increased rectal pain by 2 (-3 to +6) in all IBS patients (P < 0.05) and by 8 (-2 to +19) in IBS patients with somatic and visceral hypersensitivity (P < 0.02).

CONCLUSION: A majority of IBS patients had abnormal endogenous pain modulation and somatic hypersensitivity as evidence of central sensitization.

Thermal and visceral hypersensitivity in irritable bowel syndrome patients with and without fibromyalgia

BACKGROUND

Irritable bowel syndrome (IBS) is a chronic gastrointestinal disorder characterized by both visceral and somatic hyperalgesia, producing a similar effect seen with the central hypersensitivity mechanism in fibromyalgia (FM).

OBJECTIVES

The aim of the current study was to compare magnitudes of visceral and thermal hypersensitivity in IBS patients and FM patients with IBS (FM+IBS) compared with healthy controls.

METHODS

Female patients with IBS (n=12), FM+IBS (n=12), and control participants (n=13) rated pain intensity to hot water immersion (45 and 47 degrees C) of the hand/foot and to phasic distension of the rectum (35, 55 mm Hg) on a Mechanical Visual Analog Scale. The data were analyzed with 3 separate 1-way analyses of variance with post hoc Tukey tests.

RESULTS

For both thermal and visceral stimuli, the control group had lower pain ratings than either the IBS or FM+IBS groups (P<0.001). IBS patients rated rectal distension as more painful than the FM+IBS group (P=0.005). During hot water immersion of the foot, the FM+IBS group had higher pain ratings than the IBS group (P<0.001). During hand immersion, FM+IBS and IBS patients did not significantly differ in their pain intensity ratings (P=0.4).

CONCLUSIONS

FM+IBS patients show greater thermal hypersensitivity compared with IBS patients. However, IBS patients exhibit higher pain ratings to rectal distension compared with FM+IBS patients. This data suggests that regions of primary and secondary hyperalgesia are dependent on the primary pain complaint.

Functional brain imaging of gastrointestinal sensation in health and disease

It has since long been known, from everyday experience as well as from animal and human studies, that psychological processes-both affective and cognitive-exert an influence on gastrointestinal sensorimotor function. More specifically, a link between psychological factors and visceral hypersensitivity has been suggested, mainly based on research in functional gastrointestinal disorder patients. However, until recently, the exact nature of this putative relationship remained unclear, mainly due to a lack of non-invasive methods to study the (neurobiological) mechanisms underlying this relationship in non-sleeping humans. As functional brain imaging, introduced in visceral sensory neuroscience some 10 years ago, does provide a method for in vivo study of brain-gut interactions, insight into the neurobiological mechanisms underlying visceral sensation in general and the influence of psychological factors more particularly, has rapidly grown. In this article, an overview of brain imaging evidence on gastrointestinal sensation will be given, with special emphasis on the brain mechanisms underlying the interaction between affective & cognitive processes and visceral sensation. First, the reciprocal neural pathways between the brain and the gut (brain-gut axis) will be briefly outlined, including brain imaging evidence in healthy volunteers. Second, functional brain imaging studies assessing the influence of psychological factors on brain processing of visceral sensation in healthy humans will be discussed in more detail. Finally, brain imaging work investigating differences in brain responses to visceral distension between healthy volunteers and functional gastrointestinal disorder patients will be highlighted.

Low dose ketamine: a therapeutic and research tool to explore N-methyl-D-aspartate (NMDA) receptor-mediated plasticity in pain pathways

Ketamine is a dissociative anaesthetic that has been used in the clinic for many years. At low, sub-anaesthetic doses, it is a relatively selective and potent antagonist of the N-methyl-D-aspartate (NMDA) receptor. It belongs to the class of uncompetitive antagonists and blocks the receptor by binding to a specific site within the NMDA receptor channel when it is open. Like other compounds of this class, ketamine can cause hallucinations or other untoward central effects which limit its use in the clinic. Nevertheless, because of the evidence on the importance of NMDA receptor-mediated pLasticity in chronic pain, low doses of ketamine have been explored in a wide range of pain conditions. The majority of studies with ketamine have shown efficacy; however, it has not been possible to separate safely the pain relief from the side effects of the drug. Hence, clinical use of ketamine as a pain treatment is very limited. Nevertheless, ketamine has served as a useful tool to provide a compelling rationale for developing other NMDA antagonists. Some of the new compounds of this class, particularly those acting at the NR2B subtype of the NMDA receptor, have shown promise in preclinical and clinical studies.

Protease-activated receptors: potential therapeutic targets in irritable bowel syndrome?

Protease-activated receptors (PARs) are a family of four G-protein-coupled receptors (PAR-1 to PAR-4) activated by the proteolytic cleavage of their N-terminal extracellular domain. This activation first involves the recognition of the extracellular domain by proteases, such as thrombin, but also trypsin or tryptase which are particularly abundant in the gastrointestinal tract, both under physiological circumstances and in several digestive diseases. Activation of PARs, particularly of PAR-1 and -2, modulates intestinal functions, such as gastrointestinal motility, visceral nociception, mucosal inflammatory response, and epithelial functions (intestinal secretion and permeability). As these physiological properties have been shown to be altered in various extents and combinations in different clinical presentations of irritable bowel syndrome, PARs appear as putative targets for future therapeutic intervention in these patients.

Mechanisms of hypersensitivity in IBS and functional disorders

General introduction The concept of visceral hypersensitivity is accepted as being germane to several functional gastrointestinal disorders (FGIDs). The causes or risk factors associated with this hypersensitivity are unclear. This article addresses the proposed mechanisms leading to hypersensitivity: from genetic to inflammatory disorders, from central to peripheral alterations of function. However, in order to place visceral hypersensitivity in a more global perspective as an aetiological factor for FGIDs, it also provides a review of recent evidence regarding the role of other peripheral mechanisms (the intraluminal milieu), as also genetic factors in the pathophysiology of these disorders. The article has been divided into five independent sections. The first three sections summarize the evidence of visceral hypersensitivity as a biological marker of functional gut disorders, the peripheral and central mechanisms involved, and the role of inflammation on hypersensitivity. In opposition to visceral hypersensitivity as an isolated phenomenon in functional gut disorders, the last two sections focus on the importance of peripheral mechanisms, like motor disturbances, specifically those resulting on altered transport of intestinal gas, and alterations of the intraluminal milieu and genetics.

Sensitivity disturbances in patients with irritable bowel syndrome and fibromyalgia

BACKGROUND

Although visceral hypersensitivity is a common feature among patients with irritable bowel syndrome (IBS), studies on somatic sensitivity have given controversial results.

AIM

To assess visceral sensitivity in response to isotonic rectal distensions and somatic sensitivity at different layers of the body wall (skin, subcutis, and muscle) in patients with IBS and fibromyalgia (FM), within and outside the area of abdominal pain referral.

MATERIALS AND METHODS

We studied 10 patients with IBS, 5 patients with FM, 9 patients with IBS+FM, and 9 healthy controls. Rectal distensions were performed by increasing tension at 4 g steps up to 64 g or discomfort. Pain thresholds to electrical stimulation were measured within and outside the areas of abdominal pain referral.

RESULTS

Patients with IBS and IBS+FM demonstrated rectal hypersensitivity in comparison to controls. The threshold of discomfort was 44 +/- 5 g in IBS and 36 +/- 5 in IBS+FM patients, while patients with FM and healthy controls tolerated all distensions without discomfort. In the areas of pain referral, pain thresholds of all three tissues of the body wall were lower than normal in all patients groups (p < 0.001). In control areas, the pain thresholds were normal in skin, and lower than normal in subcutis and muscle in IBS (p < 0.001). FM and IBS+FM demonstrated somatic hypersensitivity at all sites (p < 0.001 vs healthy).

CONCLUSION

Our observations seem to indicate that, although sharing a common hypersensitivity background, multiple mechanisms may modulate perceptual somatic and visceral responses in patients with IBS and FM.

[Considerations on alterations in brain activity in patients with fibromyalgia]

Fibromyalgia is a chronic musculoskeletal pain disorder of unknown etiology, characterized by widespread pain. Clinical and experimental research has demonstrated that patients with fibromyalgia may have enhanced pain sensitivity at several points of the body, together with neuroendocrine abnormalities, and abnormal activation of pain-related brain regions. Recent data have also shown that affective and cognitive processing of pain-related information could also be disturbed in fibromyalgia. In our opinion, all these findings suggest the existence of abnormal central pain processing, which could be responsible for the persistence of chronic pain in these patients.

Functional findings in irritable bowel syndrome

The pathophysiology of IBS is complex and still incompletely known. Both central and peripheral factors, including psychosocial factors, abnormal GI motility and secretion, and visceral hypersensitivity, are thought to contribute to the symptoms of IBS. Several studies have demonstrated altered GI motor function in IBS patients and the pattern differs between IBS subgroups based on the predominant bowel pattern. Few studies have so far addressed GI secretion in IBS, but there are some evidence supporting altered secretion in the small intestine of IBS patients. Visceral hypersensitivity is currently considered to be perhaps the most important pathophysiological factor in IBS. Importantly, several external and internal factors can modulate visceral sensitivity, as well as GI motility, and enhanced responsiveness within the GI tract to for instance stress and nutrients has been demonstrated in IBS patients. Today IBS is viewed upon as a disorder of dysregulation of the so-called brain-gut axis, involving abnormal function in the enteric, autonomic and/or central nervous systems, with peripheral alterations probably dominating in some patients and disturbed central processing of signals from the periphery in others.

Somatic pain sensitivity during formation and healing of acetic acid-induced gastric ulcers in conscious rats

A classical feature of visceral pain is its referring to somatic locations. Gastric ulcer is a source of visceral pain. In the present study we investigated whether gastric ulcers may trigger the changes in somatic nociception. For this aim somatic pain sensitivity was estimated under conditions of gastric ulcer development and healing. Gastric ulcers were induced by luminal application of 60% acetic acid under surgical conditions. Control rats were subjected to the same surgical procedure, but with the application of saline instead of the acid. Somatic pain sensitivity (tail flick latency), plasma corticosterone level, adrenal and thymus weight were investigated under conditions of the formation and the healing of gastric ulcers. The application of the acid resulted in the formation of kissing gastric ulcers, the increase of somatic pain sensitivity (the decrease of tail flick latency) as well as the appearance of typical signs of chronic stress: long-lasting increase of plasma corticosterone level, adrenal gland hypertrophy and thymus gland involution. Natural healing of gastric ulcers was accompanied by restoration of pain sensitivity as well as attenuation of the signs of chronic stress. Delay of ulcer healing by the daily indomethacin administration (2 mg/kg, s.c.) prevented the restoration of somatic pain sensitivity. The results suggest that chronic gastric ulcers may trigger somatic hypersensitivity.

Perception of electrocutaneous stimuli in irritable bowel syndrome

BACKGROUND AND AIM

Irritable bowel syndrome (IBS) and fibromyalgia syndrome (FMS) are common conditions with some similarities, but different perceptual responses to somatic and visceral stimuli. The purpose of this study was to assess in a large group of IBS patients the somatic perception by transcutaneous electrical nerve stimulation (TENS) and its relation to the level of severity and presence of FMS.

METHODS

In 99 patients grouped by the validated functional bowel disorder severity index (FBDSI) in mild, moderate, and severe IBS and in 33 healthy controls (HC), we studied discomfort thresholds and perception of somatic stimuli at control (hands and elbows) and active (trapezius) sites by TENS and by using a specific questionnaire.

RESULTS

The use of TENS showed that IBS showed significant higher thresholds and lower perception cumulative score compared to HC. The severity of IBS is significantly associated with age and mean control site values for discomfort and borderline associated with gender in the ordinal model constructed for the ascending series protocol. The severity of IBS is also significantly associated with the active cumulative perception score in the long stimulus protocol. Due to limited sample size of IBS men with FMS, analyses of discomfort thresholds and cumulative perception score by FMS were done only for women. IBS women without FMS had significantly higher mean control site values for discomfort and significantly lower active cumulative perception score than HC. IBS women with FMS had significantly lower mean active site values for discomfort thresholds than IBS women without FMS (Dunn's test p < 0.05).

CONCLUSIONS

IBS patients showed somatic hypoalgesia to electrical stimuli. The severity of IBS and the presence of FMS influence the perception of somatic stimuli induced by TENS.

Experimental colitis in mice and sensitization of converging visceral and somatic afferent pathways

Chronic pain syndromes affecting different organs often coexist. We hypothesized that sensitization of one afferent pathway may affect converging input from other areas of the body. We induced colitis in mice with 2,4,6-trinitrobenzenesulfonic acid (TNBS); control animals were treated with equal volumes of vehicle (50% ethanol) only. Visceromotor responses to graded colorectal distension, cystometrograms, and response thresholds to mechanical and thermal stimulation of both hind paws were determined on days 7 and 14. Inflammation of colon and bladder was assessed with validated histological markers and scores. TNBS caused significant colitis on day 7 that resolved by day 14; there was no evidence of bladder inflammation. There was a significant hypersensitivity to colorectal distension on day 7, which returned to normal on day 14. This was associated with bladder overactivity, as demonstrated by early onset of micturition and more frequent micturition on day 7 after TNBS administration. Colitis also significantly altered responses to mechanical and thermal stimulation of both hind paws on day 7 but not day 14. We conclude that cross talk between afferent visceral and somatic pathways may contribute to the coexistence of pain syndromes.

Visceral hypersensitivity in irritable bowel syndrome: a summary review

We examined published reports from 1970 to the present to evaluate the theory that abnormal visceral sensitivity characterizes the irritable bowel syndrome. Evidence to support claims that abnormal visceral sensitivity defines the irritable bowel syndrome falls short because of cognitive deficits in gastrointestinal neurobiology, limitations in experimental design and execution, and the interpretation of results.

Brain-gut connections in functional GI disorders: anatomic and physiologic relationships

Understanding the neural regulation of gut function and sensation makes it easier to understand the interrelatedness of emotionality, symptom-attentive behavior or hypervigilance, gut function and pain. The gut and the brain are highly integrated and communicate in a bidirectional fashion largely through the ANS and HPA axis. Within the CNS, the locus of gut control is chiefly within the limbic system, a region of the mammalian brain responsible for both the internal and external homeostasis of the organism. The limbic system also plays a central role in emotionality, which is a nonverbal system that facilitates survival and threat avoidance, social interaction and learning. The generation of emotion and associated physiologic changes are the work of the limbic system and, from a neuroanatomic perspective, the 'mind-body interaction' may largely arise in this region. Finally, the limbic system is also involved in the 'top down' modulation of visceral pain transmission as well as visceral perception. A better understanding of the interactions of the CNS, ENS and enteric immune system will significantly improve our understanding of 'functional' disorders and allow for a more pathophysiologic definition of categories of patients currently lumped under the broad umbrella of FGID.

Functional gastrointestinal disorders and mood disorders in patients with inactive inflammatory bowel disease: prevalence and impact on health

BACKGROUND

Symptoms of functional gastrointestinal disorders (FGID) associated with mood disorders (MD), such as depression and anxiety, occur in some patients with quiescent inflammatory bowel disease (IBD) and could be caused by changes in gut motility, visceral hypersensitivity, or psychological dysfunction. We assessed the prevalence of FGID symptoms and mood disorders in ambulatory patients with quiescent IBD and examined their impact on health-related quality of life (HRQOL) and use of health resources.

METHODS

Consecutive ambulatory patients with IBD completed a survey of Rome II criteria for FGID, the Hospital Anxiety and Depression Survey, HRQOL indices, and health resource utilization. Logistic and linear regression analyses tested for predictors of FGID and HRQOL.

RESULTS

Of 361 patients surveyed, 149 (44 ulcerative colitis [UC] and 105 Crohn's disease [CD]) had inactive IBD during the previous 12 months. Symptoms of at least 1 FGID occurred in 81.9%. Functional anorectal disorders were the most prevalent (53.7%) followed by functional bowel disorders (51.7%), and both were of greater prevalence than in the Canadian population (41.6% and 22.6%, respectively). Irritable bowel syndrome symptoms were more common in inactive CD than in UC (26% versus 9.1%, P = .01) and functional constipation was more common in inactive UC than in CD (26.2% versus 5.8%, P < .01). MD occurred in 27.3% of UC and 31.3% of CD patients. Age > or =40 years and anxiety independently predicted an FGID. Both FGID symptoms and MD were associated with impaired HRQOL and increased use of health services.

CONCLUSIONS

Many patients with inactive IBD have symptoms compatible with FGID. Both FGID-like symptoms and MD are associated with impaired HRQOL and increased health resource utilization. Recognition and treatment of FGID and MD could potentially improve daily functioning of IBD patients.

New insights into the pathophysiology of irritable bowel syndrome: implications for future treatments

Irritable bowel syndrome (IBS) is a multifactorial disorder characterized by abdominal pain and altered bowel habits. Chronic symptoms may occur due to changes in gastrointestinal motor function, enhanced perception of gut stimuli, and psychosocial factors. Recent data suggest that abnormal processing of afferent signals occurs in IBS patients. A newly recognized causative factor in a subset of IBS patients is post-infectious IBS. Altered transport of intestinal gas and bowel distention may contribute to abdominal discomfort, pain, and bloating. Changes in gut microflora have also been reported, but data remain scant. Advances have been made in our understanding of serotonin signaling and metabolism in IBS patients, in part due to the introduction of specific receptor agonists and antagonists. Finally, exciting data are emerging on genetic alterations that may contribute to the pathophysiology and treatment of IBS. Increasingly novel mechanisms are being identified that should aid in better understanding of the complex pathophysiology of IBS and developing new therapies.

Symptom overlap and comorbidity of irritable bowel syndrome with other conditions

Irritable bowel syndrome (IBS) is one of several highly prevalent, multi-symptom gastrointestinal motility disorders that have a wide clinical spectrum and are associated with symptoms of gastrointestinal dysmotility and visceral hypersensitivity. Symptom overlap and comorbidity between IBS and other gastrointestinal motility disorders (eg, chronic constipation, functional dyspepsia, gastroesophageal reflux disease), with gastrointestinal disorders that are not related to motility (eg, celiac disease, lactose intolerance), and with somatic conditions (eg, fibromyalgia, chronic fatigue syndrome), are frequent. The clinical associations and pathophysiologic links between IBS and these disorders continue to be explored. This review discusses overlapping symptoms and comorbidity of IBS with select gastrointestinal and non-gastrointestinal disorders and attempts to identify commonalities among these conditions.

Cross-organ sensitization of lumbosacral spinal neurons receiving urinary bladder input in rats with inflamed colon

BACKGROUND & AIMS

Clinical studies show that patients with irritable bowel syndrome and colonic diseases frequently experience sensory and motor dysfunctions of the urinary bladder. The aim of this study was to investigate the spinal neuronal mechanisms responsible for potential cross talk between these visceral organs.

METHODS

Colonic inflammation was induced by dextran sulfate sodium (5%) in drinking water for 7-12 days (n = 12); another group of rats without dextran sulfate sodium (n = 12) was used as control. Extracellular potentials of single L6 to S2 spinal neurons were recorded in pentobarbital-anesthetized and paralyzed rats with dextran sulfate sodium-induced colitis or normal colon. Urinary bladder distention (0.5-2.0 mL; 20 seconds) was produced with saline inflation, and colorectal distention was induced by inflation of an air balloon (80 mm Hg; 20 seconds).

RESULTS

A total of 58 of 153 (38%) and 55 of 152 (36%) spinal neurons responded to urinary bladder distention in dextran sulfate sodium-treated and control animals, respectively. The mean background activity of neurons excited by urinary bladder distention in rats with dextran sulfate sodium-induced colitis was significantly higher than in the control group. The threshold volume for excitatory responses to urinary bladder distention in rats with inflamed colon (0.024 +/- 0.09 mL; n = 30) was significantly lower than for control rats (0.062 +/- 0.016 mL; n = 31; P < .05). The stimulus-response curves of excitatory responses to graded urinary bladder distention were significantly increased for both viscerovisceral (urinary bladder distention and colorectal distention) convergent neurons and urinary bladder distention-receptive neurons in rats with colitis compared with control animals.

CONCLUSIONS

Acute colitis sensitized lumbosacral spinal neurons receiving input from the urinary bladder. Thus, spinal neuronal hyperexcitability may be involved in central cross-organ sensitization of visceral nociception between the colon and urinary bladder.

Pain perception in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by chronic abdominal discomfort or pain in the absence of detectable organic disease. IBS is common and is associated with a significant impairment in health-related quality of life. Enhanced perception of visceral stimuli ("visceral hypersensitivity") appears to be an important pathophysiological mechanism. Early IBS studies using functional brain imaging techniques suggest an alteration in central pain modulation circuits, rather than an increased sensitivity of peripheral visceral pain pathways. The frequent comorbidity with psychiatric disorders suggests the possibility of shared pathophysiological mechanisms and etiologic factors.

Psychophysical evidence of hypersensitivity in subjects with interstitial cystitis

PURPOSE

We quantified differences in somatic and visceral sensation in healthy subjects and subjects with interstitial cystitis (IC).

MATERIALS AND METHODS

A total of 13 subjects with IC and 13 healthy subjects answered psychological questionnaires and underwent psychophysical testing of thermal and pressure thresholds for sensation as well as the ischemic forearm test of pain tolerance. A subset of subjects also underwent bladder sensory testing with the determination of 3 consecutive cystometrograms. Ratings of intensity and unpleasantness were determined.

RESULTS

Subjects with IC were significantly more sensitive to deep tissue measures of sensation related to pressure, ischemia and bladder than healthy subjects. Cutaneous thermal pain measures were similar in the 2 groups. Psychological measures indicated higher reactivity in subjects with IC.

CONCLUSIONS

Similar to other visceral pain disorders, such as irritable bowel syndrome, hypersensitivity to somatic stimuli was noted in subjects with IC. This suggests altered central mechanisms in the processing of sensory events from the bladder.

Brain responses to visceral and somatic stimuli in irritable bowel syndrome: a central nervous system disorder?

In healthy subjects, the brain regions most consistently activated in visceral and somatic pain are the key regions in the central pain matrix,including the mid/anterior insula, subregions of the ACC, PFC, thalamus,and in some cases, pontine regions such as the dorsal pons and PAG. Functional neuroimaging studies have demonstrated evidence of altered regional brain activation responses during visceral and somatic stimuli in IBS that have been associated with perceptual differences. Although perceptual studies have shown increased sensitivity to rectosigmoid distension in IBS, most somatic pain studies have demonstrated normal or decreased sensitivity compared with controls; however, a recent study showed increased sensitivity to thermal heat. Altered brain responses in IBS,particularly to visceral stimuli, include activation of regions concerned with attentional processes and response selection, corticolimbic regions concerned with emotional and autonomic responses to stimuli, and subcortical regions receiving cortical projections from the latter and afferent input from the soma and viscera. Altered activations of these regions also may be present in the absence of a noxious visceral stimulus. Changes in rCBF of some of these regions have been associated with treatment response in IBS. With regard to differences in cortical processing of visceral versus somatic stimuli in IBS, there have been only two studies. Greater activations of the dorsal ACC, thalamus, and PFC have been shown with visceral stimuli compared with somatic stimuli in IBS. A plausible hypothesis for the observations from brain imaging studies is that IBS patients demonstrate a compromised activation of pain inhibition circuits including those of the cortico-pontine circuit but increased activation of limbic and paralimbic circuits that may be related to pain facilitation.