Experimental pain in the stomach: a model based on electrical stimulation guided by gastroscopy

Assessment of pain associated with chronic pancreatitis: An international consensus guideline

Pain is the most common symptom in chronic pancreatitis (CP) with a major impact on quality of life. Few validated questionnaires to assess pain in CP exist, and the lack of consensus negatively impacts clinical management, research and meta-analysis. This guideline aims to review generic pain questionnaires for their usability in CP, to outline how pain assessment can be modified by confounding factors and pain types, to assess the value of additional measures such as quality of life, mental health and quantitative sensory testing, and finally to review pain assessment questionnaires used specifically in CP. A systematic review was done to answer 27 questions that followed the PICO (Population; Intervention; Comparator; Outcome) template. Quality of evidence of the statements was judged by Grades of Recommendation, Assessment, Development and Evaluation (GRADE) criteria. The manuscript was sent for review to 36 experts from various disciplines and continents in a multi-stage Delphi process, and finally reviewed by patient representatives. Main findings were that generic pain instruments are valid in most settings, but aspects of pain are specific for CP (including in children), and instruments have to account for the wide phenotypic variability and development of sensitization of the central nervous system. Side effects to treatment and placebo effects shall also be considered. Some multidimensional questionnaires are validated for CP and are recommended together with assessment of quality of life and psychiatric co-morbidities. This guideline will result in more homogeneous and comprehensive pain assessment to potentially improve management of painful CP.

Missed Diagnosis of Cholangiocarcinoma Presenting with Atypical Symptoms

We report a case of delayed diagnosis of cholangiocarcinoma. A 62-year-old man developed acute abdominal pain in multiple sites. As the distribution pattern of the abdominal pain was not correctly interpreted based on the mechanisms of visceral and referred pain, the patient was not investigated with the best diagnostic test at first presentation. Moreover, miscommunication between physicians in a clinic and separate hospital delayed diagnosis. For prompt diagnosis, physicians should be practice careful reasoning and focus on good communication with physicians outside their hospital.

LEARNING POINTS

Abdominal pain without jaundice can be an initial symptom in patients with cholangiocarcinoma.Cholangiocarcinoma in the lower common bile duct can present as lower abdominal pain referred through the 7th-11th thoracic nerves.Physicians can determine the origin of abdominal pain through correct interpretation of the distribution pattern of abdominal pain based on knowledge of pathophysiology.

Gastrointestinal pain

Gastrointestinal (GI) pain - a form of visceral pain - is common in some disorders, such as irritable bowel syndrome, Crohn's disease and pancreatitis. However, identifying the cause of GI pain frequently represents a diagnostic challenge as the clinical presentation is often blurred by concomitant autonomic and somatic symptoms. In addition, GI pain can be nociceptive, neuropathic and associated with cancer, but in many cases multiple aetiologies coexist in an individual patient. Mechanisms of GI pain are complex and include both peripheral and central sensitization and the involvement of the autonomic nervous system, which has a role in generating the symptoms that frequently accompany pain. Treatment of GI pain depends on the precise type of pain and the primary disorder in the patient but can include, for example, pharmacological therapy, cognitive behavioural therapies, invasive surgical procedures, endoscopic procedures and lifestyle alterations. Owing to the major differences between organ involvement, disease mechanisms and individual factors, treatment always needs to be personalized and some data suggest that phenotyping and subsequent individual management of GI pain might be options in the future.

Assessment and manifestation of central sensitisation across different chronic pain conditions

Different neuroplastic processes can occur along the nociceptive pathways and may be important in the transition from acute to chronic pain and for diagnosis and development of optimal management strategies. The neuroplastic processes may result in gain (sensitisation) or loss (desensitisation) of function in relation to the incoming nociceptive signals. Such processes play important roles in chronic pain, and although the clinical manifestations differ across condition processes, they share some common mechanistic features. The fundamental understanding and quantitative assessment of particularly some of the central sensitisation mechanisms can be translated from preclinical studies into the clinic. The clinical perspectives are implementation of such novel information into diagnostics, mechanistic phenotyping, prevention, personalised treatment, and drug development. The aims of this paper are to introduce and discuss (1) some common fundamental central pain mechanisms, (2) how they may translate into the clinical signs and symptoms across different chronic pain conditions, (3) how to evaluate gain and loss of function using quantitative pain assessment tools, and (4) the implications for optimising prevention and management of pain. The chronic pain conditions selected for the paper are neuropathic pain in general, musculoskeletal pain (chronic low back pain and osteoarthritic pain in particular), and visceral pain (irritable bowel syndrome in particular). The translational mechanisms addressed are local and widespread sensitisation, central summation, and descending pain modulation.

Significance

Central sensitisation is an important manifestation involved in many different chronic pain conditions. Central sensitisation can be different to assess and evaluate as the manifestations vary from pain condition to pain condition. Understanding central sensitisation may promote better profiling and diagnosis of pain patients and development of new regimes for mechanism based therapy. Some of the mechanisms underlying central sensitisation can be translated from animals to humans providing new options in development of therapies and profiling drugs under development.

Opioid-Induced Constipation and Bowel Dysfunction: A Clinical Guideline

OBJECTIVE

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

SETTING

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Multivariate analysis of single-sweep evoked brain potentials for pharmaco-electroencephalography

BACKGROUND AND AIMS

Current findings on altered evoked potentials (EPs) caused by morphine are based on common alterations for a group of subjects after drug administration. However, this ignores the analysis of individual responses, which may explain the clinical differences in efficacy. Therefore, we explored the individual responses to morphine in terms of the altered single-sweep characteristics in a placebo-controlled crossover study. To account for multifactorial mechanisms, several characteristics were assessed simultaneously by multivariate pattern analysis (MVPA).

METHODS

EPs were recorded from 62 channels and obtained before and after morphine and placebo administration during repeated electrical stimulations of the oesophagus in 12 healthy males. Additionally, the pain detection threshold was recorded to reflect the subjective analgesic effect in each subject. The characteristics of the sweeps were extracted by a multivariate matching pursuit algorithm with Gabor atoms implemented with a variable amplitude and constant phase across the sweeps. The single-sweep amplitudes were used as input to an MVPA algorithm to discriminate individual responses. The accuracy of the MVPA for each individual subject was used for correlation analysis of the analgesic effect.

RESULTS

The mean classification accuracy when discriminating pre- and posttreatment morphine responses was 72% (p = 0.01). The individual classification accuracy was positively correlated to the analgesic effect of morphine (p = 0.03). Furthermore, the 2 posttreatment responses were classified and validated by the classification of the 2 pretreatment responses (p = 0.001).

CONCLUSIONS

The alterations in the single-sweep EPs after morphine reflect the analgesic effect. The MVPA approach is a novel methodology for monitoring the individual efficacy of analgesics.

Neurophysiology of the esophagus

The following, from the 12th OESO World Conference: Cancers of the Esophagus, includes commentaries on the methods and characteristics of esophageal afferents in humans; the pitfalls in characterization of mechanosensitive afferents; the sensitization of esophageal afferents in human studies; the brain source modeling in the understanding of the esophagus-brain axis; the use of evoked brain potentials in the esophagus; and measuring descending inhibition in animal and human studies.

Translational pain biomarkers in the early development of new neurotherapeutics for pain management

Translation of the analgesic efficacy of investigational neurotherapeutics from pre-clinical pain models into clinical trial phases is associated with a high risk of failure. Application of human pain biomarkers in early stages of clinical trials can potentially enhance the rate of successful translation, which would eventually reduce both length and costs of drug development after the pre-clinical stage. Human pain biomarkers are based on the standardized activation of pain pathways followed by the assessment of ongoing and paroxysmal pain, plus evoked responses which can be applied to healthy individuals and patients prior to and after pharmacological interventions. This review discusses the rationality and feasibility of advanced human pain biomarkers in early phases of drug development for pain management which is still an unmet medical need.

Gastrointestinal sensitivity and gastroesophageal reflux disease

This paper reports on gastrointestinal sensitivity, including on the role of refluxate volume on the perception of reflux symptoms; experimental pain models that mimic mechanisms and symptoms of pain associated with esophageal diseases; the potential role of the acid receptor TRPV1 in the genesis of gastroesophageal reflux disease (GERD) symptoms; and roles for ATP and the purine and pyrimidine receptor subfamilies P1, P2X, and P2Y in the pathogenesis of GERD symptoms.

Gastric electrical stimulation for abdominal pain in patients with symptoms of gastroparesis

Abdominal pain physiology may be better understood studying electrophysiology, histology, and symptom scores in patients with the symptoms of gastroparesis (Gp) treated with gastric electrical stimulation (GES). Ninety-five Gp patients' symptoms were recorded at baseline and during temporary and permanent GES. Gastric-emptying times and cutaneous, mucosal, and serosal electrogastrograms were obtained. S100-stained, full-thickness gastric biopsies were compared with autopsy controls. Sixty-eight patients reported severe pain at baseline. Severe pain patients' mean pain scores decreased with temporary GES from 3.62 to 1.29 (P < 0.001) and nonsevere pain from 1.26 to 0.67 (P = 0.01). With permanent GES, severe mean pain scores fell to 2.30 (P < 0.001); nonsevere pain changed to 1.60 (P = 0.221). Mean follow-up was 275 days. Mean cutaneous, mucosal, and serosal frequencies and frequency-to-amplitude ratios were markedly higher than literature controls. For patients with Gp overall and subdivided by etiology and severity of pain, S-100 neuronal fibers were significantly reduced in both muscularis propria layers. GES improved severe pain associated with symptoms of Gp. This severe pain is associated with abnormal electrogastrographic activity and loss of S100 neuronal fibers in the stomach's inner and outer muscularis propria and, therefore, could be the result of gastric neuropathy.

Gastric Electrical Stimulation for Abdominal Pain in Patients with Symptoms of Gastroparesis

Abdominal pain physiology may be better understood studying electrophysiology, histology, and symptom scores in patients with the symptoms of gastroparesis (Gp) treated with gastric electrical stimulation (GES). Ninety-five Gp patients’ symptoms were recorded at baseline and during temporary and permanent GES. Gastric-emptying times and cutaneous, mucosal, and serosal electrogastrograms were obtained. S100-stained, full-thickness gastric biopsies were compared with autopsy controls. Sixty-eight patients reported severe pain at baseline. Severe pain patients’ mean pain scores decreased with temporary GES from 3.62 to 1.29 ( P < 0.001) and nonsevere pain from 1.26 to 0.67 ( P = 0.01). With permanent GES, severe mean pain scores fell to 2.30 ( P < 0.001); nonsevere pain changed to 1.60 ( P = 0.221). Mean follow-up was 275 days. Mean cutaneous, mucosal, and serosal frequencies and frequency-to-amplitude ratios were markedly higher than literature controls. For patients with Gp overall and subdivided by etiology and severity of pain, S-100 neuronal fibers were significantly reduced in both muscularis propria layers. GES improved severe pain associated with symptoms of Gp. This severe pain is associated with abnormal electrogastrographic activity and loss of S100 neuronal fibers in the stomach's inner and outer muscularis propria and, therefore, could be the result of gastric neuropathy.

Gastric electrical stimulation for the treatment of obesity: from entrainment to bezoars-a functional review. ISRN Gastroenterol. 2013;2013:434706. [PMID: 23476793 DOI: 10.1155/2013/434706]

GROWING WORLDWIDE OBESITY EPIDEMIC HAS PROMPTED THE DEVELOPMENT OF TWO MAIN TREATMENT STREAMS: (a) conservative approaches and (b) invasive techniques. However, only invasive surgical methods have delivered significant and sustainable benefits. Therefore, contemporary research exploration has focused on the development of minimally invasive gastric manipulation methods featuring a safe but reliable and long-term sustainable weight loss effect similar to the one delivered by bariatric surgeries. This antiobesity approach is based on placing external devices in the stomach ranging from electrodes for gastric electrical stimulation to temporary intraluminal bezoars for gastric volume displacement for a predetermined amount of time. The present paper examines the evolution of these techniques from invasively implantable units to completely noninvasive patient-controllable implements, from a functional, rather than from the traditional, parametric point of view. Comparative discussion over the available pilot and clinical studies related to gastric electrical stimulation outlines the promises and the fallacies of this concept as a reliable alternative anti-obesity strategy.

Sensory testing of the human gastrointestinal tract

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

Unexplained chest/epigastric pain in patients with normal endoscopy as a predictor for ischemic heart disease and mortality: a Danish 10-year cohort study

Background

Normal upper endoscopy may be a marker of ischemic heart disease in patients with unexplained chest/epigastric pain.

Methods

We examined the 10-year risk of ischemic heart disease and mortality in a cohort of 386 Danish patients with chest/epigastric pain, normal upper endoscopy, and no prior hospital discharge diagnosis of ischemic heart disease (defined as patients with unexplained chest/epigastric pain), compared with 3,793 population controls matched by age, gender, and residence. Outcome data were obtained from population-based health registries. Cox regression analysis was used to estimate the relative risk of hospitalization for ischemic heart disease and the adjusted mortality rate ratio (MRR).

Results

The 10-year relative risk of hospitalization for ischemic heart disease following a normal upper endoscopy among patients with unexplained chest/epigastric pain was 1.6 (95% CI, 1.1–2.2), compared with controls. The 10-year MRR was 1.1 (95% CI, 0.9–1.5). Within the first year after the upper endoscopy the MRR was 2.4 (95% CI, 1.3–4.5). The cause-specific MRR among patients with unexplained chest/epigastric pain compared with controls was up to threefold higher for deaths related to alcohol dependence, pneumonia, and lung cancer.

Conclusion

Unexplained chest/epigastric pain in patients with normal endoscopy is a strong marker for ischemic heart disease and increased mortality.

Is the pain in chronic pancreatitis of neuropathic origin? Support from EEG studies during experimental pain

AIM: To prove the hypothesis that patients with chronic pancreatitis would show increased theta activity during painful visceral stimulation.

METHODS: Eight patients and 12 healthy controls underwent an experiment where the esophagus was electrically stimulated at the pain threshold using a nasal endoscope. The electroencephalogram (EEG) was recorded from 64 surface electrodes and “topographic matching pursuit” was used to extract the EEG information in the early brain activation after stimulation.

RESULTS: A major difference between controls and patients were seen in delta and theta bands, whereas there were only minor differences in other frequency bands. In the theta band, the patients showed higher activity than controls persisting throughout the 450 ms of analysis with synchronous brain activation between the channels. The main theta components oscillated with 4.4 Hz in the patients and 5.5 Hz in the controls. The energy in the delta (0.5-3.5 Hz) band was higher in the controls, whereas the patients only showed scattered activity in this band.

CONCLUSION: The differences in the theta band indicate that neuropathic pain mechanisms are involved in chronic pancreatitis. This has important implications for the understanding and treatment of pain in these patients, which should be directed against drugs with effects on neuropathic pain disorders.

Risk of gastrointestinal cancer in patients with unexplained chest/epigastric pain and normal upper endoscopy: a Danish 10-year follow-up study

Unexplained chest/epigastric pain is a common symptom in the general population. However, it has not previously been studied whether such pain could be a marker of subsequent gastrointestinal cancer. We aimed to estimate the risk of gastrointestinal cancers in a Danish 10-year follow-up study among patients with chest/epigastric pain, normal upper endoscopy, and no prior discharge diagnosis of ischemic heart disease (N = 386), compared with population controls (N = 3860). The overall 10-year risk of gastrointestinal cancer (stomach, colorectal, liver, and pancreas) was 2.9% for patients with unexplained chest/epigastric pain vs. 1.5% for controls. The adjusted relative risks <1 year and > or =1 year after upper endoscopy were 8.4 (95% confidence interval [CI], 2.6-27.5) and 1.2 (95% CI, 0.5-2.9), respectively. We found that patients with unexplained chest/epigastric pain have an increased risk of gastrointestinal cancer within the first year after upper endoscopy. Consequently, unexplained chest/epigastric pain might be an early gastrointestinal cancer symptom.

Risk of peptic ulcer, oesophagitis, pancreatitis or gallstone in patients with unexplained chest/epigastric pain and normal upper endoscopy: a 10-year Danish cohort study

BACKGROUND

No studies have examined the risk of upper gastrointestinal diseases among patients with unexplained chest/epigastric pain (UCEP) and a normal upper endoscopy.

AIM

To examine the relative risk of peptic ulcer, oesophagitis, pancreatitis or gallstone in UCEP patients.

METHODS

This Danish 10-year cohort study focused on UCEP patients (n = 386), diagnosed in 1992-93. Ten age- and gender-matched controls were selected per patient from Denmark's Civil Registration System (n = 3860). Kaplan-Meier analysis and Cox's regression analysis was used to calculate the risk of hospitalization for peptic ulcer, oesophagitis, pancreatitis or gallstone.

RESULTS

Compared with controls, the adjusted relative risks among UCEP patients <1 and > or = 1 year after upper endoscopy were for peptic ulcer 2.0 [95% confidence interval (CI) 0.2-18.4] and 1.7 (95% CI 0.9-3.4), for oesophagitis 8.2 (95% CI 1.2-59.2) and 1.9 (95% CI 0.7-5.0), for pancreatitis 9.2 (95% CI 2.0-41.8) and 3.9 (95% CI 1.4-10.5), and for gallstone 14.1 (95% CI 5.4-37.2) and 3.3 (95% CI 1.9-5.8).

CONCLUSIONS

UCEP is positively associated with all study outcomes especially in the first year after upper endoscopy, indicating that peptic ulcer, oesophagitis, pancreatitis or gallstone could be underlying early UCEP symptoms. However, the long-term association remained strong for pancreatitis and gallstone, suggesting a genuine excess risk.

Pain in chronic pancreatitis: the role of reorganization in the central nervous system

BACKGROUND & AIMS

In various chronic pain conditions cortical reorganization seems to play a role in the manifestations. The aim of this study was to investigate cortical reorganization in patients with pain caused by chronic pancreatitis.

METHODS

Twelve healthy subjects and 10 patients with chronic pancreatitis were included. The esophagus, stomach, and duodenum were stimulated electrically at the pain threshold using a nasal endoscope. The electroencephalogram was recorded from 64 surface electrodes and event-related brain potentials (EPs) were obtained.

RESULTS

As compared with healthy subjects, the patient group showed decreased latencies of the early EP components (N1, P < .001; P1, P = .02), which is thought to reflect the exogenous brain pain processing specifically. Source analysis showed that the dipolar activities corresponding to the early EPs were located consistently in the bilateral insula, in the anterior cingulate gyrus, and in the bilateral secondary somatosensory area. The bilateral insular dipoles were localized more medial in the patient group than in the healthy subjects after stimulation of all 3 gut segments (P < .01). There also were changes in the cingulate cortex where the neuronal source was more posterior in patients than in controls to stimulation of the esophagus (P < .05).

CONCLUSIONS

The findings indicate that pain in chronic pancreatitis leads to changes in cortical projections of the nociceptive system. Such findings also have been described in somatic pain disorders, among them neuropathic pain. Taken together with the clinical data this suggests a neuropathic component in pancreatic pain, which may influence the approach to treatment.

Reversibility of central neuronal changes in patients recovering from gallbladder stones or acute cholecystitis

AIM: To investigate the referred pain area in patients 2-7 years after cholecystectomy in order to test the hypothesis that neuroplastic changes could give rise to post cholecystectomy pain.

METHODS: Forty patients were tested. Twenty five were cholecystectomized due to uncomplicated gallbladder stones and 15 because of acute cholecystitis. Sensitivity to pinprick, heat, cold, pressure and single and repeated electrical stimulation was studied both in the referred pain area and in the control area on the contra lateral side of the abdomen.

RESULTS: Five patients still intermittently suffered from pain. But in the objective test of the 40 patients, no statistical significant difference was found between the referred pain area and the control area.

CONCLUSION: This study does not support the hypothesis that de novo neuroplastic changes could develop several years after cholecys-tectomy.

Somatosensory changes in the referred pain area before and after cholecystectomy in patients with uncomplicated gallstone disease

OBJECTIVE

It is estimated that 25-40% of patients have continuing symptoms after cholecystectomy and that 5-10% have pain. The pain may be related to central neuroplastic changes of sensory pathways induced by the gallstone disease. Such neuronal hyperexcitability can be reflected in the somatic referred pain area sharing central pathways with the gallbladder. The aim of this study was to examine somatosensory changes in the referred pain area evoked by painful gallstone attacks before and after cholecystectomy in patients with uncomplicated gallstone disease.

MATERIAL AND METHODS

Thirty-seven patients with uncomplicated gallstone disease were included in the study. The sensations and pain thresholds to pinprick, pinching, pressure, thermal and electrical stimulation were studied before and 4-12 weeks after surgery in the area where the pain was referred to during the previous gallstone attacks. An area on the contralateral side of the abdomen served as the control.

RESULTS

Somatosensory hyperalgesia in the referred pain area was observed in 84% of the patients before surgery. After elective cholecystectomy, none of the patients had pain complaints, and the sensibility in the referred area was normalized.

CONCLUSIONS

Uncomplicated gallstone disease leads to significant hyperalgesia in the somatic referred pain area. At the time of the postoperative investigation none of the patients suffered from pain, which was reflected in the normal sensory findings in the previous referred pain area.

Experimental human pain models in gastro-esophageal reflux disease and unexplained chest pain

Methods related to experimental human pain research aim at activating different nociceptors, evoke pain from different organs and activate specific pathways and mechanisms. The different possibilities for using mechanical, electrical, thermal and chemical methods in visceral pain research are discussed with emphasis of combinations (e.g., the multimodal approach). The methods have been used widely in assessment of pain mechanisms in the esophagus and have contributed to our understanding of the symptoms reported in these patients. Hence abnormal activation and plastic changes of central pain pathways seem to play a major role in the symptoms in some patients with gastro-esophageal reflux disease and in patients with functional chest pain of esophageal origin. These findings may lead to an alternative approach for treatment in patients that does not respond to conventional medical or surgical therapy.

Cerebral processing of painful oesophageal stimulation: a study based on independent component analysis of the EEG

BACKGROUND AND AIMS

Independent component analysis (ICA) of the electroencephalogram (EEG) overcomes many of the classical problems in EEG analysis. We used ICA to determine the brain responses to painful stimulation of the oesophagus.

METHODS

Twelve subjects with a median age of 41 years were included. With a nasal endoscope, two series of 35 electrical stimuli at the pain threshold were given to the distal oesophagus and the EEG was subjected to ICA. The sessions were separated by 30 minutes. For each component head models, event related images, spectral perturbation, coherence analysis, and dipoles were extracted. The most valid components were found according to time/frequency information and reliability in both experiments.

RESULTS

Reliable components with the most valid dipoles were found in the thalamus, insula, cingulate gyrus, and sensory cortex. Time locked activities were consistent with upstream activation of these areas, and cross coherence analysis of the sources demonstrated dynamic links in the beta(14-25 Hz) and gamma(25-50 Hz) bands between the suggested networks of neurones. The thalamic components were time and phase locked intermittently, starting around 50 ms. In the cingulate gyrus, the posterior areas were always firstly activated, followed by the middle and anterior regions. Components with dipoles in the sensory cortex were localised in several regions of the somatosensory area.

CONCLUSIONS

The method gives new information relating to the localisation and dynamics between neuronal networks in the brain to pain evoked from the human oesophagus, and should be used to increase our understanding of clinical pain.

Somatosensory changes in the referred pain area in patients with cholecystolithiasis

BACKGROUND AND AIMS

Patients with abdominal pain provoked by acute cholecystitis increase the somatic sensitivity in the referred somatic pain area. Our aim in the present paper was to examine somatosensory changes in the referred pain area (previously evoked by painful attacks) in patients with uncomplicated gallstone disease and to evaluate the possible relation between referred pain patterns and clinical findings. Somatosensory changes in these areas may be important in the persistent pain after treatment and may help to develop treatment strategies for abdominal pain in the post-cholecystectomy syndrome.

SUBJECTS

Forty-two patients with symptomatic cholecystolithiasis, confirmed ultrasonographically, were studied in the pain-free period.

METHODS

Sensitivity and pain thresholds for standardized experimental sensory testing including different modalities: pinprick, pinching, heat, cold, pressure, and single and repeated electrical stimulation were studied in the area where the pain was referred to during the acute attacks, and in a control area on the contralateral side of the abdomen.

RESULTS

Patients with verified cholecystolithiasis showed hyperalgesia to pinprick (26% of subjects, P < 0.05) and cold stimuli (21% of subjects, P < 0.05) in the referred pain area. There was also a significant reduction in sensation/pain thresholds (indicating hyperalgesia) in the referred pain area to single (P = 0.007/P = 0.002) and repeated electrical (P = 0.017/P = 0.043) stimuli, as well as in pain threshold to pinching and mechanical stimuli (P = 0.049/P < 0.001). There were no significant relations between the hyperalgesia and the clinical findings.

CONCLUSION

Cholecystolithiasis leads to significant hyperalgesia in the somatic area, where pain was referred to during the acute attacks. This is explained by viscero-somatic convergence mechanisms in the central nervous system. Therefore, central neuroplastic changes may be significant in diseases related to the gallbladder such as the post-cholecystectomy syndrome.

Dipolar source modelling of brain potentials evoked by painful electrical stimulation of the human sigmoid colon

The aim of the study was to compare the cerebral generators following painful stimulation of the sigmoid colon and the abdominal skin in 11 healthy subjects. The evoked potentials (EPs) were recorded from 31 surface electrodes following painful electrical stimuli of the sigmoid colon, and of the referred pain area on the abdomen. Current dipole models estimating the EPs amplitude and topography were calculated. For colon stimulation, the earliest cortical activities were described by dipoles in the bilateral insula and in the anterior cingulate cortex, while both secondary somatosensory areas were activated later. When the skin was stimulated, early bilateral dipoles in the primary and secondary somatosensory areas were estimated, followed by a dipole in the frontal region. This suggests that painful cutaneous and visceral stimuli are processed differently in the brain.

Multi-modal induction and assessment of allodynia and hyperalgesia in the human oesophagus

BACKGROUND AND AIMS

Experimental pain models based on single stimuli have to some degree limited visceral pain studies in humans. Hence, the aim of this study was to investigate the effect of multi-modal visceral pain stimuli of the oesophagus in healthy subjects before and after induction of visceral hyperalgesia. We used a multi-modal psychophysical assessment regime and a neurophysiological method (nociceptive reflex) for the characterisation of the experimentally induced hyperalgesia.

METHODS

A probe for multi-modal (cold, warm, electrical, and mechanical) visceral stimulation was positioned in the lower part of the oesophagus in eleven healthy subjects. Mechanical stimuli were applied as distensions with a bag, which also had electrodes mounted for electrical stimulation. Thermal stimulation with temperatures from 0 to 60 degrees C was applied with re-circulating water in the bag. To assess the interaction between visceral and somatic pathways, the nociceptive withdrawal reflex to electrical stimuli at the ankle was measured with and without simultaneous mechanical oesophageal distension to painful levels. Finally, the oesophageal sensitisation was induced by perfusion with hydrochloric acid. Multimodal responses (pain threshold, stimulus response function, size of nociceptive reflex, and referred pain areas) were assessed before and after the induced hyperalgesia.

RESULTS

The multi-modal psychophysical responses and reflex sizes were assessed twice before sensitisation, and the parameters were reproducible. Sensitisation of the oesophagus resulted in hyperalgesia to electrical and mechanical stimuli (29 and 35% decrease in pain threshold) and allodynia to cold and warmth stimuli (11% increase in sensory rating). After sensitisation, the referred pain area to mechanical stimuli increased more than 300% with a change in the localisation of the referred pain to all stimuli, and the amplitude of nociceptive reflex increased 100%, all indicating the presence of central hyperexcitability.

CONCLUSIONS

Visceral hyperalgesia/allodynia can be induced experimentally and assessed quantitatively by the newly introduced multi-modal psychophysical assessment approach. The significant changes of the experimentally evoked referred pain patterns and of the nociceptive reflex evoked from a distant somatic structure indicate that even short-lasting visceral hyperalgesia can generate generalised sensitisation.

Short latency cerebral response evoked by painful electrical stimulation applied to the human sigmoid colon and to the convergent referred somatic pain area

Background. The brain-gut interaction is important for the understanding of pain mechanisms related to gastroenterological diseases. Unfortunately little is known about the early cerebral events related to the processing of gut-evoked pain. The aims of this human study were (1) to investigate the early-evoked brain potentials (EPs) to painful sigmoid colon stimulation and (2) to evaluate the EPs evoked from the convergent referred skin pain area after this area was induced by the painful gut stimulation. The background for the second aim was to evaluate whether the convergent input between somatic and visceral structures could induce detectable short-term cortical reorganization. Methods. Eleven subjects (nine men) participated; the mean age was 39.5+/-11.9 years. The gut-evoked EPs (recorded from 31 scalp sites) were evoked by electrical stimulation 30 cm from the anal verge by a modified biopsy forceps, inserted through a sigmoidoscope. The painful gut stimulation elicited a characteristic pain pattern referred to the abdomen. The short latency somatosensory evoked potentials were evoked from the skin inside and outside the referred pain area elicited by gut stimulation. A total of 750 electrical stimuli were delivered to the gut at slight painful stimulus intensity and 500 stimuli were delivered to the skin. Results. Short-latency EPs to electrical gut stimulation with an onset of 50-60 ms could be recorded. The gut EP topography revealed three consecutive positive peaks (P63, P101, P145) towards the frontal area. Centroparietal negativities (N128 and N222) were found, which were followed by two central positivities (P269 and P352). The somatic and gut evoked EPs differed in morphology and topography, but the EPs to skin stimulation inside and outside the gut-evoked referred pain area did not differ significantly. Conclusion. Short latency (50-60 ms) EPs to painful electrical sigmoid colon stimulation were demonstrated, reflecting an early cortical processing of sensory input from the sigmoid colon. The early cortical processing of somatic input from experimentally evoked visceral referred pain areas did not cause any detectable short-term cortical reorganization.

Gut pain and hyperalgesia induced by capsaicin: a human experimental model

Human experimental visceral pain models using chemical stimulation are needed for the study of visceral hyperexcitability. Our aim was to stimulate the human gut with chemical activators (capsaicin, glycerol) and measure quantitatively the induced hyperexcitability to painful mechanical gut distension. Ten otherwise healthy subjects with an ileostoma participated. Increasing volumes of capsaicin 50 microg/ml (0.25, 0.5, 0.75, 1.0, 1.5, 2.0, and 3 ml), glycerol (2.5, 5, and 10 ml) or saline (2.5, 5, and 10 ml) intermingled with sham stimuli were randomly applied to the ileum via the stomal opening at three occasions separated by a week. After each application, pain intensity, qualities, and referred pain area were assessed together with the pain threshold to distension of the proximal gut. 'Boring' and 'hot' pain were evoked in all subjects by low doses (median 0.5 ml) of capsaicin. The median pain onset, peak pain, and pain duration were 55, 85, and 420 s, respectively. Referred somatic pain developed around the stomal opening with a correlation between the pain area and pain intensity. After application of capsaicin, significant hyperalgesia was found to distension of the gut (a 28% reduction pressure in pain threshold). No significant manifestations were found after application of glycerol and saline. Application of capsaicin to the human ileum induces pain and mechanical hyperalgesia. Specific activation of nociceptors in the gut mucosa provides new possibilities to study clinical relevant visceral pain mechanisms.

Induction of non-painful and painful intestinal sensations by hypertonic saline: a new human experimental model

BACKGROUND AND AIMS

To develop a pain model for chemical stimulation of the human gut.

METHODS

In a double-blind experimental study 10 subjects with a previously performed sigmoidostomy were randomised to receive injections with either isotonic or hypertonic saline in the colonic mucosa. In the hypertonic experimental arm, 0.1 ml of 0.9%, 2%, 4%, and 6% and 0.2 ml of 2% and 4% saline were given. In the placebo arm, six 0.9% saline injections of the same quantities were given. In a separate experiment 0.8 ml 4% saline was infused into the mucosa by a pump over a period of 2min. The pain intensity was rated on a 0-10 visual analogue scale with 5 as the pain threshold.

RESULTS

The hypertonic saline injections resulted in local as well as referred non-painful and painful sensations in 9 out of the 10 subjects. The evoked sensations were mostly described as a smarting sensation with an intensity of median 1 (range 0-5.6) for 0.1 ml 2% saline to median 2.9 (range 0-6.2) for 0.2 ml 4% saline. Seven subjects reported referred sensations to the abdominal skin. Continuous infusion of 4% saline resulted in a consistent sensory response in all subjects, with a median intensity of 4.1 (range 2.1-8.1). This sensory intensity was reproducible in 70% in a retest experiment after median 7 weeks. In the placebo arm a total of 70 isotonic saline injections only resulted in inconsistent, short-lasting non-painful sensations in three subjects.

CONCLUSION

The model represents a safe method for direct chemical activation of the sensory endings in the human gut. The model may be used for pharmacological screening of analgesics and for basic investigations in patients suffering from gastrointestinal diseases.

Responses and afferent pathways of C(1)-C(2) spinal neurons to gastric distension in rats

Some evidence shows that the upper cervical spinal cord might play an important role in propriospinal processing as a sensory filter and modulator for visceral afferents. The aims of this study were to determine (1). the responses of C(1)-C(2) spinal neurons to gastric distension and (2). the relative contribution of vagal and spinal visceral afferent pathways for transmission of gastric input to the upper cervical spinal cord. Extracellular potentials of single C(1)-C(2) spinal neurons were recorded in pentobarbital anesthetized male rats. Graded gastric distension (20-80 mm Hg) was produced by air inflation of a latex balloon surgically placed in the stomach. Sixteen percent of the neurons (32/198) responded to gastric distension; 17 neurons were excited and 15 neurons were inhibited by gastric distension. Spontaneous activity of neurons with inhibitory responses was higher than those neurons with excitatory responses (18.1+/-2.7 vs. 3.8+/-1.7 impulses s(-1), p<0.001). Twenty-eight of thirty-two (87.5%) neurons responded to mechanical stimulation of somatic fields on head, neck, ears or shoulder. Most lesion sites of neurons with excitatory responses were found in laminae V, VII; however, neurons with inhibitory responses were in laminae III, IV. Bilateral cervical vagotomy abolished responses of 4/8 neurons tested. Spinal transection at C(6)-C(7) abolished responses of the other four neurons that still responded to gastric distension after bilateral vagotomy. Results of these data supported the concept that a group of C(1)-C(2) spinal neurons might play a role in processing sensory information from the stomach that travels in vagal and spinal visceral afferent fibers.

Sensory and biomechanical responses to ramp-controlled distension of the human duodenum

The aim of this study was to develop a new method for investigation of the relationship among the mechanical stimulus, the biomechanical properties, and the visceral perception evoked by volume/ramp-controlled distension in the human duodenum in vivo. An impedance planimetric probe for balloon distension was placed in the third part of the duodenum in seven healthy volunteers. Distension of the duodenum was done at infusion rates of 10, 25, and 50 ml/min. The pump was reversed when level 7 was reached on a visual analog scale ranging from 0 to 10. Distensions were done with and without the administration of the antimuscarinic drug butylscopolamine. The total circumferential tension (T(total)) and the passive circumferential tension (T(passive)) were determined from the distension tests without and with the administration of butylscopolamine, respectively. T(total) and T(passive) showed an exponential behavior as a function of strain (a measure of deformation). The active circumferential tension (T(active)) was computed as T(total)-T(passive) and showed a bell-shaped behavior as a function of strain. At low distension intensities, the intensity of sensation at 10 ml/min was significantly higher than that obtained at 25 and 50 ml/min. The coefficient of variation at the pain threshold for circumferential strain (average 4.34) was closer to zero compared with those for volume (8.72), pressure (31.22), and circumferential tension (31.55). This suggests that the mechanoreceptors in the gastrointestinal wall depend primarily on circumferential strain. The stimulus-response functions provided evidence for the existence of low- and high-threshold mechanoreceptors in the human duodenum. Furthermore, the data suggest that high-threshold receptors are nonadapting.

Somatosensory changes in the referred pain area following acute inflammation of the appendix

BACKGROUND AND AIMS

Abdominal pain provoked by acute gastrointestinal disease may increase the sensitivity in the referred somatic pain area. The aim of this study was to examine sensory changes in the referred pain area during acute appendicitis.

SUBJECTS

Twenty patients with clinical symptoms of appendicitis were included; 16 of these had appendicitis confirmed at operation. Ten healthy volunteers served as controls.

METHODS

In patients with symptoms of appendicitis, somatic sensitivity was assessed using different stimuli presented in the area of referred pain and in a comparable non-painful area at the contralateral site of the abdomen. In healthy control subjects, the same stimuli were presented to McBurney's point and at a similar area on the left abdomen. The rating to pinprick was determined using a Von Frey hair. The rating to thermal stimuli was tested by warm and cold metal rollers. A constant current stimulator was used to measure the sensation and pain-detection threshold to single and repeated electrical stimuli. The pressure pain threshold was determined by an electronic pressure algometer.

RESULTS

Patients (n = 16) with verified appendicitis showed increased ratings to pinprick (50%, P < 0.05) and thermal stimuli (56%, P < 0.05) in the referred pain area. There was a reduction in pain thresholds to single electrical (4.3 v. 8.4 mA, P = 0.001), repeated electrical (3.5 v. 4.6 mA, P = 0.005) and pressure (89 v. 243 kPa, P < 0.001) stimuli in the referred pain area versus the control area. In the control group, no difference was observed between the two areas. The pain thresholds for electrical and pressure stimuli were lower in the referred pain area in patients compared with the same area in controls (P < 0.001).

CONCLUSION

Somatosensory hyperalgesia to experimental stimuli was observed in acute appendicitis. We believe that viscerosomatic convergence mechanisms and central nervous system hyperexcitability explain these findings.

Sensory-motor responses to volume-controlled duodenal distension

Abstract Visceral perception and secondary peristalsis evoked by distension of the duodenum were studied in 10 healthy volunteers. An impedance planimetric probe for cross-sectional area (CSA) measurements inside a balloon and with three pressure channels was used. Balloon distensions were performed in the fed state with or without the administration of the antimuscarinic drug butylscopolamine. A modified questionnaire was used to assess the nonpainful and painful sensations. The total tension (T(total)) and the passive tension (T(passive)) were determined from the distensions without and with the administration of butylscopolamine, respectively. The active tension (T(active)) was T(total) - T(passive). The stepwise balloon distensions induced the first sensation at a volume of 33 +/- 3 mL. After administration of butylscopolamine the first sensation appeared at 42 +/- 1 mL. The perception score (PS) revealed an approximately linear increase as function of volume, CSA, pressure and tension after the first sensation. Butylscopolamine resulted in significant changes in PS score as function of volume, CSA and strain, but not as a function of pressure and tension. The frequency of the secondary peristalsis increased to the highest value (8.2 +/- 0.8 contractions min(-1)) at a volume of 21 mL. Butylscopolamine almost abolished the distension-evoked motility. T(total) and T(passive) increased nonlinearly as a function of volume, whereas T(active) increased up to a distension volume of 33 mL and then decreased at higher volumes. Hence, the conventional length-tension diagrams as known from studies of smooth muscle strips in vitro can be reproduced in the human duodenum in vivo. This new way of studying intestinal sensation and motility may prove to have both basic and clinical importance as both passive tissue structures and the sensorimotor function are tested.

Multimodal assessment of pain in the esophagus: a new experimental model

A new multimodal pain assessment model was developed integrating electrical, mechanical, cold, and warmth stimuli into the same device. The device, with a bag and electrodes for electrical stimulation, was positioned in the lower part of the esophagus in 11 healthy subjects. Mechanical stimuli were delivered with an impedance planimetric system. Thermal stimuli were performed by circulating water of different temperatures (5-50 degrees C) inside the bag. All subjects reported both nonpainful and painful local and referred sensations to all stimuli. Temporal summation to repeated electrical stimuli could be studied. For all stimuli, there was a relationship between stimulus intensity and pain intensity. The referred pain area increased with increasing intensity of the electrical and mechanical stimuli. There were several differences between the sensations evoked by the four stimulus modalities, indicating activation of different visceral nerve pathways. This model offers the possibility for controlled multimodal stimuli activating the superficial and deeper layers of the human gut and should be used in basic, clinical, and pharmacological pain studies.

Pain referral from the sternoclavicular joint: a study in normal volunteers

OBJECTIVE

The sternoclavicular joint (SCJ) is commonly affected by rheumatological conditions. Case reports suggest that it may refer pain to distant areas, potentially leading to delays in diagnosis and inappropriately targeted investigations. Therefore, we studied the patterns of pain referral from the SCJ of nine healthy volunteers.

METHODS

Hypertonic saline was injected into the SCJ of nine normal volunteers and the location of any resulting pain was noted, as was the effect of resisted shoulder abduction and flexion. Composite pain maps were then constructed from individual pain diagrams.

RESULTS

An unpleasant, deep aching pain was produced locally in eight subjects and referred to distant sites in all subjects. Tests of shoulder movement had varied and inconstant effects.

CONCLUSIONS

We demonstrated that the SCJ is capable of referring pain to areas distant from the joint. Knowledge of these referral patterns will enable the SCJ to be considered in patients with pain in these areas.

Pain produced by electric stimulation of the rectum in patients with irritable bowel syndrome: further evidence of visceral hyperalgesia

BACKGROUND

Visceral hyperalgesia is most likely a phenomenon of substantial clinical importance and may also play a role in the pathophysiology of the irritable bowel syndrome (IBS). We investigated the manifestation of visceral hyperalgesia in IBS patients by nociceptive electric stimulation of the rectosigmoid junction and rectum.

METHODS

Twelve IBS patients fulfilling the Rome criteria and 9 healthy controls were studied. Visceral single and repeated electric burst stimuli were applied with a bipolar electric stimulator inserted through the sigmoidoscope. The sensation (ST) and pain detection (PDT) thresholds were determined in response to single and repeated stimuli at the rectosigmoid junction, and PDT to repeated stimuli at four different positions in the rectum. Cutaneous single and repeated electric stimuli were applied to the lateral aspect of the foot, determining ST and PDT.

RESULTS

Cutaneous stimulation showed no significant differences for ST and PDT between patients and controls. The rectosigmoid junction showed significantly lower ST for single stimuli (P<0.01) and a significantly lower PDT for single and for repeated stimuli (P<0.05 and P<0.02) in IBS patients. In the rectum the IBS patients had a significantly lower PDT than controls (P<0.001).

CONCLUSIONS

For cutaneous electric stimulation no differences in the pain thresholds between the two groups were found, showing that there is no generalized hyperalgesia in IBS patients. The IBS patients had a specific decrease of the pain thresholds in the rectum and rectosigmoid junction, indicating visceral hyperalgesia. These results point to central visceral hyperexcitability as an important factor in the pathophysiology of IBS.

An experimental pain model based on electric stimulations of the colon mucosa

BACKGROUND

Pain intensity and distribution related to diseases of the gut are important diagnostic indicators in gastroenterology. Experimental pain models provide a unique possibility for standardized activation of the nociceptive system, but only few human models exist.

METHODS

An experimental pain model based on electric stimuli in the human colon was developed and applied. Eleven patients who were referred for surveillance colonoscopy due to earlier polyps in the colon were included. None had any abdominal pain complaints. The following areas were stimulated with 'single', 'repeated', or 'continuous' electric current: the cecum, the hepatic and splenic flexures, and the rectosigmoid junction.

RESULTS

All subjects felt deep, diffuse pain during the stimulation, with referral to localized somatic structures. The pain detection thresholds after repeated stimuli were similar in the four areas. The threshold for single stimulation was higher than the threshold for repeated stimulation. Most reported pain in the lower and left site of the abdominal wall during stimuli at the splenic flexure and rectosigmoid junction. Stimuli at the right colon, however, resulted mostly in pain at the contralateral site of the abdomen.

CONCLUSIONS

The presented model was robust and suitable for eliciting pain in different regions of the large intestine. The importance of temporal summation in visceral pain was shown. Mapping of the referred pain areas mimics clinical observations and has ontogenetic and anatomic consistency. The model may therefore improve the evaluation of pain in patients with diseases of the colon.

Recent and forgotten aspects of visceral pain

Progress in the field of visceral pain research has been particularly rapid in recent years. Some aspects of the symptom that had previously been neglected for some time have now received a great deal of attention in both clinical and experimental studies. This regards, in particular, phenomena of hyperalgesia: (a) of visceral structures, because of local inflammatory/sensitizing processes (visceral hyperalgesia); (b) of areas of referred pain from viscera (referred somatic hyperalgesia from viscera); and (c) of a visceral structure, because of an algogenic process of another visceral domain (viscero-visceral hyperalgesia). Clinical studies in patients have led to characterisation of subjective and objective symptoms of these phenomena. A number of studies in human volunteers (employing experimental procedures to stimulate and measure pain reactivity in both visceral structures and somatic areas of referral) have further increased the knowledge about modalities of generation of the various forms of hyperalgesia.Animal experiments have improved understanding of pathophysiological mechanisms, mostly those underlying the referred hyperalgesia, with a number of findings supporting the notion of central changes at the basis of the phenomenon. An important aspect of laboratory experiments in recent years has been the setting up of animal models of visceral pain conditions closely mimicking a number of clinical pain states in patients. As a result, the outcome of experimental studies (electrophysiological, pharmacological, etc.) appears more directly applicable to the interpretation of the clinical reality.Finally, in the context of laboratory studies, a novel trend of investigation is represented by genetic experiments, particularly those employing 'knock-out' mice. These experiments, by generating animals lacking specific genes responsible for the production of various receptors implicated in pain transmission, have further contributed to the understanding of the generation of visceral pain symptoms. Although studies in this field are in their early stage, they seem particularly promising for a better understanding of the pathophysiology of visceral pain, and thus the establishment of more satisfying therapies in the future. Copyright 1999 European Federation of Chapters of the International Association for the Study of Pain.