Pathophysiology of visceral pain

Pain Recognition in Ferrets

Recognition and accurate assessment of the severity of pain can be challenging in ferrets as they are unable to verbally communicate, and often hide their pain. Pain assessment relies on the assessment of behavioral, physiologic, and other clinical parameters that serve as indirect indicators of pain. Assessment of physiologic and clinical parameters requires handling, which results in changes in these parameters. Behavioral parameters can be assessed less invasively by observing the patient. Due to their nonspecificity, correct interpretation may be challenging. Just as in other species, a grimace scale seems to be the most helpful tool in recognizing pain in ferrets.

Influence of Butorphanol, Buprenorphine and Levomethadone on Sedation Quality and Postoperative Analgesia in Horses Undergoing Cheek Tooth Extraction

The aim of this prospective clinical trial was to compare the influence of butorphanol, buprenorphine and levomethadone on sedation quality and postoperative analgesia in horses undergoing cheek tooth extraction. Fifty horses were assigned to three groups prior to oral cheek tooth extraction. Horses were treated with acepromazine, followed by a detomidine bolus, one of the three opioids and both a nerve block and gingival anaesthesia. During the surgery, sedation was maintained with a detomidine constant rate infusion. After surgery, the quality of sedation, surgical conditions and severity of the extraction were assessed with a numerical rating scale. To evaluate differences in the quality of analgesia between the three treatments, postoperative pain was estimated with the Equine Utrecht University Scale for Facial Assessment of Pain. Additionally, several parameters that are associated with dental pain were added to this validated pain score, and blood samples were taken to measure serum cortisol. Our analysis showed lower pain scores and a greater analgesic effect with levomethadone and buprenorphine compared with butorphanol, with increased locomotor activity induced by buprenorphine. While cortisol values demonstrated higher response in horses treated with levomethadone and buprenorphine compared to butorphanol, these values could be biased by unrelated stressors.

Lateralization and Bodily Patterns of Segmental Signs and Spontaneous Pain in Acute Visceral Disease: Observational Study

Background

The differential diagnosis of acute visceral diseases is a challenging clinical problem. Older literature suggests that patients with acute visceral problems show segmental signs such as hyperalgesia, skin resistance, or muscular defense as manifestations of referred visceral pain in somatic or visceral tissues with overlapping segmental innervation. According to these sources, the lateralization and segmental distribution of such signs may be used for differential diagnosis. Segmental signs and symptoms may be accompanied by spontaneous (visceral) pain, which, however, shows a nonsegmental distribution.

Objective

This study aimed to investigate the lateralization (ie, localization on one side of the body, in preference to the other) and segmental distribution (ie, surface ratio of the affected segments) of spontaneous pain and (referred) segmental signs in acute visceral diseases using digital pain drawing technology.

Methods

We recruited 208 emergency room patients that were presenting for acute medical problems considered by triage as related to internal organ disease. All patients underwent a structured 10-minute bodily examination to test for various segmental signs and spontaneous visceral pain. They were further asked their segmental symptoms such as nausea, meteorism, and urinary retention. We collected spontaneous pain and segmental signs as digital drawings and segmental symptoms as binary values on a tablet PC. After the final diagnosis, patients were divided into groups according to the organ affected. Using statistical image analysis, we calculated mean distributions of pain and segmental signs for the heart, lungs, stomach, liver/gallbladder, and kidneys/ureters, analyzing the segmental distribution of these signs and the lateralization.

Results

Of the 208 recruited patients, 110 (52.9%) were later diagnosed with a single-organ problem. These recruited patients had a mean age of 57.3 (SD 17.2) years, and 40.9% (85/208) were female. Of these 110 patients, 85 (77.3%) reported spontaneous visceral pain. Of the 110, 81 (73.6%) had at least 1 segmental sign, and the most frequent signs were hyperalgesia (46/81, 57%), and muscle resistance (39/81, 48%). While pain was distributed along the body midline, segmental signs for the heart, stomach, and liver/gallbladder appeared mostly ipsilateral to the affected organ. An unexpectedly high number of patients (37/110, 33.6%) further showed ipsilateral mydriasis.

Conclusions

This study underlines the usefulness of including digitally recorded segmental signs in bodily examinations of patients with acute medical problems.

Chronic Abdominal Pain After Previous Bariatric Surgery: Consider the Abdominal Wall

BACKGROUND

Up to 30% of patients who undergo bariatric surgery experience recurrent abdominal pain within 3 years after the operation. Although some causes for persisting discomfort are well known, a small portion of patients may suffer from an abdominal wall pain associated with Anterior Cutaneous Nerve Entrapment Syndrome (ACNES). Aim of the present study is to discuss incidence, clinical presentation, and treatment outcome in patients with ACNES after bariatric surgery.

METHODS

This retrospective observational cohort study analyzed electronically stored data of patients with ACNES having a history of bariatric surgery. All were treated for ACNES between 2011 and 2017 in a Dutch center of excellence for abdominal wall and groin pain. Success after treatment was defined as a minimal 50% drop in pain level using a Numeric Rating Scale.

RESULTS

A total of 49 patients (female n = 44, median age 45 (25-63) years) were identified. Four (8%) experienced long-term pain relief after just one abdominal wall infiltration with lidocaine. Ten additional patients reported success after 2-5 injections. A total of 35 unresponsive patients chose to undergo a neurectomy that was successful in 27. Therefore, this step-up approach conferred an 84% success rate. Occurrence of ACNES after bariatric surgery was estimated at 1 in 100 patients.

CONCLUSION

ACNES should be considered in the differential diagnosis of ongoing pain following previous bariatric surgery. A treatment regimen including abdominal wall infiltrations using an anesthetic agent or a neurectomy is successful in a vast majority of these patients.

Pathophysiology and Management of Abdominal Myofascial Pain Syndrome (AMPS): A Three-Year Prospective Audit of a Management Pathway in 120 Patients

Background

Chronic abdominal wall pain arising from the myofascial structures is termed abdominal myofascial pain syndrome and is an important cause of refractory abdominal pain that utilizes significant health care costs. The current literature is vague on its management.

Design

The author presents a prospective audit of a structured management pathway and discusses the pathophysiology of abdominal myofascial pain syndrome. The objective was to identify an effective and durable treatment for the individual patient and evaluate patient satisfaction with the management pathway.

Methods

Over a three-year period, 120 patients diagnosed with abdominal myofascial pain syndrome were included in a structured management pathway and were prospectively audited at a tertiary care university hospital.

Results

Patient satisfaction with the pathway was high. Trigger point injection with local anesthetic was useful in diagnosis but ineffective in providing durable relief. Trigger point injection with steroids and pulsed radiofrequency treatment of trigger point(s) were effective therapeutic interventions, providing durable relief lasting six months in 32% and 60%, respectively. There was improvement reported in pain intensity scores, quality of life, anxiety, and depression scores following the interventional management of abdominal myofascial pain syndrome.

Conclusions

Abdominal myofascial pain syndrome is often unrecognized, especially in patients with a history of visceral inflammation. The suggested pathway may be an option in its management. Trigger point injection with steroids may have a role in the differential diagnosis of chronic abdominal pain.

Splanchnic block at T11 provides a longer relief than celiac plexus block from nonmalignant, chronic abdominal pain

Aim: Neural blockade at the celiac plexus is less specific compared with splanchnic nerve block. This retrospective study compares duration and potency of celiac versus splanchnic block. Patients & methods: Analyzed were data of 16 consecutive patients with visceral abdominal nonmalignant pain treated using both celiac plexus and T11 splanchnic block. Results: Improvement in pain scores was from 7.24 ± 1.0 to 4.1 ± 2.1 for celiac, and 7.8 ± 0.8 to 2.9 ± 2.1 for splanchnic at 4 weeks. Duration of the splanchnic nerve block was superior, median of 56 days versus only 21 days for celiac plexus block. Conclusion: T11 bilateral splanchnic block provided significantly longer relief from chronic nonmalignant abdominal pain, than celiac plexus block (p = 0.001). Reduction in pain severity was more with splanchnic compared with celiac block (p = 0.029).

The appropriate use of neurostimulation of the spinal cord and peripheral nervous system for the treatment of chronic pain and ischemic diseases: the Neuromodulation Appropriateness Consensus Committee

INTRODUCTION

The Neuromodulation Appropriateness Consensus Committee (NACC) of the International Neuromodulation Society (INS) evaluated evidence regarding the safety and efficacy of neurostimulation to treat chronic pain, chronic critical limb ischemia, and refractory angina and recommended appropriate clinical applications.

METHODS

The NACC used literature reviews, expert opinion, clinical experience, and individual research. Authors consulted the Practice Parameters for the Use of Spinal Cord Stimulation in the Treatment of Neuropathic Pain (2006), systematic reviews (1984 to 2013), and prospective and randomized controlled trials (2005 to 2013) identified through PubMed, EMBASE, and Google Scholar.

RESULTS

Neurostimulation is relatively safe because of its minimally invasive and reversible characteristics. Comparison with medical management is difficult, as patients considered for neurostimulation have failed conservative management. Unlike alternative therapies, neurostimulation is not associated with medication-related side effects and has enduring effect. Device-related complications are not uncommon; however, the incidence is becoming less frequent as technology progresses and surgical skills improve. Randomized controlled studies support the efficacy of spinal cord stimulation in treating failed back surgery syndrome and complex regional pain syndrome. Similar studies of neurostimulation for peripheral neuropathic pain, postamputation pain, postherpetic neuralgia, and other causes of nerve injury are needed. International guidelines recommend spinal cord stimulation to treat refractory angina; other indications, such as congestive heart failure, are being investigated.

CONCLUSIONS

Appropriate neurostimulation is safe and effective in some chronic pain conditions. Technological refinements and clinical evidence will continue to expand its use. The NACC seeks to facilitate the efficacy and safety of neurostimulation.

Biopsychosocial assessment criteria for functional chronic visceral pain: a pilot review of concept and practice

Functional chronic visceral pain (FCVP) is one of the most common causes of morbidity in the general population. Pain perceived within the abdomen may occur due to a range of different mechanisms according to the organ and their afferent pathways. Advances in our understanding of the complexities of FCVP could lead to the exploitation of contemporary research in order to develop and utilize our understanding of neurobiological and psychobiological visceral mechanisms in a clinical setting. This progression, together with increasing amounts of epidemiological and gender based information concerning specific abdominal pain syndromes can allow us to develop assessment tools that go beyond disease only analysis and move toward a more comprehensive assessment model so that patients may have access to expert or multidisciplinary management sooner, rather than later. Based on current evidence, one must consider the main contributors to pain, whether it is nociceptive, neuropathic or psychosocial or as is common with FCVP, a combination of all three.

AIM

This comprehensive assessment model should encompass not only systematic evaluation for reliable communication, but should also progress toward idiographic diagnosis relating to the uniqueness of the patient. This model should be practical in a multidisciplinary setting, taking into account the multi-faceted nature of this presentation.

Medical Screening for Red Flags in the Diagnosis and Management of Musculoskeletal Spine Pain

When a patient presents with pain in the different regions of the spine, the clinician executes a region-appropriate basic examination that includes appropriate historical cues and specific physical examination tests that can be used to identify red flags. The clinical tests include a specific examination of the sensory and motor systems. Test outcomes are best interpreted in context with the entire examination profile, where the sensitivity and specificity of these tests can influence their utility in uncovering red flags. These red flags can be categorized based on the nature and severity or the specific elements of the patient's presentation. Many general red flags can be observed in any region of the spine, while specific red flags must be categorized and discussed for each spinal region. This categorization can guide the clinician in the direction of management, whether that management is aimed at redirecting the patient's care to another specialist, reconsidering the presentation and observing for clusters of findings that may suggest red flags, or managing the patient within the clinician's specialty in context with the severity of the patient's presentation.

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.

Diagnosis and Management of the Painful Shoulder. Part 2: Examination, Interpretation, and Management

Diagnosis, interpretation and subsequent management of shoulder pathology can be challenging to clinicians. Because of its proximal location in the schlerotome and the extensive convergence of afferent signals from this region to the dorsal horn of the spinal cord, pain reference patterns can be broadly distributed to the deltoid, trapezius, and or the posterior scapular regions. This pain behavior can make diagnosis difficult in the shoulder region, as the location of symptoms may or may not correspond to the proximity of the pain generator. Therefore, a thorough history and reliable physical examination should rest at the center of the diagnostic process. Effective management of the painful shoulder is closely linked to a tissue-specific clinical examination. Painful shoulder conditions can present with or without limitations in passive and or active motion. Limits in passive motion can be classified as either capsular or noncapsular patterns. Conversely, patients can present with shoulder pain that demonstrates no limitation of motion. Bursitis, tendopathy and rotator cuff tears can produce shoulder pain that is challenging to diagnose, especially when they are the consequence of impingement and or instability. Numerous nonsurgical measures can be implemented in treating the painful shoulder, reserving surgical interventions for those patients who are resistant to conservative care.

A comparison of modality-specific somatosensory changes during menstruation in dysmenorrheic and nondysmenorrheic women

OBJECTIVE

The objective was to evaluate somatosensory thresholds to a multimodality stimulation regimen applied both within and outside areas of referred menstrual pain in dysmenorrheic women, over four phases of confirmed ovulatory cycles, and to compare them with thresholds in nondysmenorrheic women during menstruation.

DESIGN

Twenty dysmenorrheic women with menstrual pain scoring 5.45 +/- 0.39 cm (mean +/- standard error of mean) on a visual analog scale (10 cm) participated. Fifteen nondysmenorrheic women with a menstrual pain score of 0.4 +/- 0.2 cm participated as controls. Ovulation was confirmed by an enzyme-multiplied immunoassay technique. Menstrual pain was described with the McGill Pain Questionnaire. Areas within menstrual pain referral were two abdominal sites and the midline of the low back, and the arm and thigh were the control areas. The pressure pain threshold (PPT) and pinch pain threshold were determined by a hand-held electronic pressure algometer, the heat pain threshold (HPT) by a contact thermode, and the tactile threshold with von Frey hairs.

RESULTS

In dysmenorrheic women the McGill Pain Questionnaire showed a larger sensory and affective component of pain than the evaluative and miscellaneous groups. The HPT and PPT were lower in the menstrual phase than in the ovulatory, luteal, and premenstrual phases, both within and outside areas of referred menstrual pain (p <0.01), with a more pronounced decrease at the referral pain areas. The pinch pain threshold was lower in the menstrual phase than in the ovulatory phase (p <0.02), and the tactile threshold did not differ significantly across the menstrual phases or within any site. Dysmenorrheic women had a lower HPT at the control sites and a lower PPT at the abdomen, back, and control sites, than in those of nondysmenorrheic women in the menstrual phase.

CONCLUSIONS

The results show reduced somatosensory pain thresholds during menstruation to heat and pressure stimulation, both within and outside areas of referred menstrual pain in dysmenorrheic women. Dysmenorrheic women showed a lower HPT at the control sites and a lower PPT at all the sites than those for nondysmenorrheic women in the menstrual phase. The altered somatosensory thresholds may be dependent on a spinal mechanism of central hyperexcitability, induced by recurrent moderate to severe menstrual pain.

Sensory changes during the ovulatory phase of the menstrual cycle in healthy women

This study compared the pain sensitivity in healthy women at the abdomen and lower back (presumed referral areas of menstrual pain), thigh and arm (control areas), in the menstrual, ovulatory, luteal and premenstrual phases of confirmed ovulatory cycles, with that of males. The pressure pain threshold (PPT) and pinch pain threshold (PiPT) was determined by an electronic pressure algometer, heat pain threshold (HPT) by a contact thermode and tactile threshold (TT) with von Frey hairs. The abdominal PPT was significantly lower in females in all menstrual phases as compared to the control sites ( p<0.0007). The abdominal and lower back HPT was significantly lower in females in all menstrual phases compared with control areas, and to the sites in males ( p<0.002). The TT was significantly reduced in females compared with males ( p< 0.013). There was no difference in the PiPT between females and males. In males, the HPT, PPT and TT were not different within any site. During the ovulatory phase, the HPT was significantly reduced at the abdomen and the PPT at the back compared with the menstrual, luteal and premenstrual phases (p<0.0002). There were no within-menstrual phase variations in the PiPT and TT at any site, or for the HPT and PPT at the control areas. The reduced thresholds in menstruating women may be due to the presence of latent uterine algogenic stimuli, and the increased levels of oestrogen and leuteinizing hormone at ovulation may enhance nociception by acting both at the peripheral and central level, resulting in the hypersensitivity changes at the abdomen and lower back areas.

Referred Muscle Pain: Clinical and Pathophysiologic Aspects

Referred pain, that is, pain perceived in an area other than that in which the noxious stimulation takes place, is very frequent in the clinical setting. There are various forms of referred muscle pain from viscera and from somatic structures. Examples of the latter are referred pain from one muscle to another muscle (as in myofascial pain syndromes) and referred pain from joints (as in osteoarthritis of the knee). Whatever the origin of the symptom, a condition of secondary hyperalgesia very often takes place in the referred zones, together with trophic tissue changes. Referred muscle pain from viscera without hyperalgesia is explained on the basis of the convergence of visceral and somatic afferent fibers on the same central neurons. Referred muscle pain from viscera with hyperalgesia is not completely understood; it is hypothesized that it is due to both central (sensitization process) and peripheral (intervention of reflex arcs) mechanisms. Referred muscle pain from other muscles or from joints is not easily explained by the mechanism of "central convergence" in its original form, because in dorsal horn neurons there is little convergence from deep tissues. It has been proposed that convergent connections from deep tissues to dorsal horn neurons are not present from the beginning but are opened by nociceptive input from skeletal muscle, and referral to myotomes outside the lesion is due to a spread of central sensitization to adjacent spinal segments.

Neurophysiology of cancer pain

BACKGROUND

Recent basic science research has greatly added to our knowledge of pain mechanisms. Application of this knowledge to cancer pain syndromes has led to new and innovative approaches to cancer pain management.

METHODS

The mechanisms involved in the three main cancer pain syndromes (somatic, visceral, and neuropathic) are reviewed, and various therapeutic options are discussed.

RESULTS

Advances in knowledge in neurophysiology, neuroanatomy, and pharmacology have allowed a greater understanding of the peripheral and central mechanisms of pain. New drugs and interventional techniques based on this knowledge have improved the control of cancer pain.

CONCLUSIONS

Understanding the neurophysiology of cancer pain promotes use of the most appropriate palliative measures for pain control.

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.