Do we need a third mechanistic descriptor for chronic pain states?

Looking at fibromyalgia differently - An observational study of the meaning and consequences of fibromyalgia as a dimensional disorder

OBJECTIVE

Despite data showing that fibromyalgia can be represented as a dimensional disorder, almost all assessments treat fibromyalgia as a dichotomous categorial disorder; and research shows that agreement between community diagnosis of fibromyalgia and fibromyalgia criteria is poor. We investigated the validity of FM as a discrete disorder by exploring the relationships of categorical fibromyalgia, the polysymptomatic distress (PSD) scale, and clinical variables.

METHODS

In a databank of 33,972 rheumatic disease patients, we studied the categorical diagnosis of fibromyalgia, the PSD scale separately and divided into severity groups, measures of widespread pain, as well as somatic syndrome questionnaires like the Patient Health Questionnaire-15 (PHQ-15), and clinical pain, global, HAQ disability and quality of life scales (EQ-5D).

RESULTS

Clinical and demographic variables became more abnormal with increasing PSD score groups, indicating substantial increase in symptoms and pain. The changes across PSD categories were linear and large. When we compared FM- (PSD 8-11) with FM+ (PSD 12-18) patients we found considerable overlap in scores for pain, HAQ disability, patient global, PHQ-15, psychological status, and other variables. Somatic symptom scores were highly correlated with PSD (r=0.718). There was no evidence of a differential pain effect that was present in FM+ but not FM- subjects.

CONCLUSION

Fibromyalgia is more accurately considered a dimensional than a dichotomous disorder. There is vast variability among fibromyalgia positive and negative cases that is governed by the strong and linear relationships between the dimensional PSD scale and clinical variables. The PSD scale provides measurements of the fibromyalgia dimension that support and enlighten categorical fibromyalgia and are an effective tool to measure clinical status and changes. Whatever the mechanism of the pain and symptom increase in fibromyalgia, it appears to operate over the entire fibromyalgia symptom dimension, not just in those with categorical fibromyalgia.

Kinins and their B1 and B2 receptors as potential therapeutic targets for pain relief

Kinins are endogenous peptides that belong to the kallikrein-kinin system, which has been extensively studied for over a century. Their essential role in multiple physiological and pathological processes is demonstrated by activating two transmembrane G-protein-coupled receptors, the kinin B₁ and B₂ receptors. The attention is mainly given to the pathological role of kinins in pain transduction mechanisms. In the past years, a wide range of preclinical studies has amounted to the literature reinforcing the need for an updated review about the participation of kinins and their receptors in pain disorders. Here, we performed an extensive literature search since 2004, describing the historical progress and the current understanding of the kinin receptors' participation and its potential therapeutic in several acute and chronic painful conditions. These include inflammatory (mainly arthritis), neuropathic (caused by different aetiologies, such as cancer, multiple sclerosis, antineoplastic toxicity and diabetes) and nociplastic (mainly fibromyalgia) pain. Moreover, we highlighted the pharmacological actions and possible clinical applications of the kinin B₁ and B₂ receptor antagonists, kallikrein inhibitors or kallikrein-kinin system signalling pathways-target molecules in these different painful conditions. Notably, recent findings sought to elucidate mechanisms for guiding new and better drug design targeting kinin B₁ and B₂ receptors to treat a disease diversity. Since the kinin B₂ receptor antagonist, Icatibant, is clinically used and well-tolerated by patients with hereditary angioedema gives us hope kinin receptors antagonists could be more robustly tested for a possible clinical application in the treatment of pathological pains, which present limited pharmacology management.

Topical review - salivary biomarkers in chronic muscle pain

BACKGROUND AND AIMS

Muscle related temporomandibular disorders (myogenous TMD), one of the most common orofacial pain conditions, is characterized by facial pain and often accompanied by jaw movement limitations. Although the underlying biological mechanisms are still unclear, a cluster of proteins and peptides is assumed to be involved in the pathophysiology. These proteins and peptides may be measured in a simple non-invasive saliva sample. This work investigated whether saliva can be used to sample algogenic substances that can serve as molecular biomarkers for TMD myalgia.

METHODS

Saliva and blood samples were collected from healthy individuals (n=69) and patients diagnosed with TMD myalgia (n=39) according to the Diagnostic Criteria for TMD. Unstimulated and stimulated whole, parotid, and sublingual saliva were analysed. The protein profiles were investigated using two-dimensional gel electrophoresis followed by identification with liquid chromatography tandem mass spectrometry. Levels of nerve growth factor (NGF), calcitonin gene-related peptide (CGRP), and brain derived neuro-tropic factor (BDNF) were determined using western blotting based technology and multiplex electro-chemiluminescence assay panel. Glutamate, serotonin, and substance p (SP) were determined using commercially available methods.

RESULTS

Different saliva collection approaches resulted in significant differences in the protein profile as well as in the expression of NGF, BDNF, CGRP, SP, and glutamate. Stimulated whole saliva showed least variability in protein concentration (35%) and was correlated to plasma levels of glutamate. Unlike SP and glutamate, NGF and BDNF expressed a rhythmic variation in salivary expression with higher levels in the morning (p<0.05). Patients with a diagnosis of TMD myalgia had significantly higher levels of salivary glutamate but lower salivary NGF and BDNF compared to controls; in addition, the lower NGF and BDNF levels correlated to psychological dysfunction. The quantitative proteomics data revealed 20 proteins that were significantly altered in patients compared to controls. The identified proteins are involved in metabolic processes, immune response, and stress response. Dissimilarities in protein profile and clinical variables were observed between TMD myalgia and myofascial pain.

CONCLUSIONS

The work highlights the importance of consistency in saliva collection approaches, including the timing of the collection. It displayed significant changes in pain specific mediators and protein profile in TMD myalgia and furthermore dissimilarities between subclasses indicating different pathophysiology. After extensive validation, potential salivary biomarkers can be combined with clinical features to better understand and diagnose TMD myalgia.

Towards precision pain medicine for pain after cancer: the Cancer Pain Phenotyping Network multidisciplinary international guidelines for pain phenotyping using nociplastic pain criteria

Pain after cancer remains underestimated and undertreated. Precision medicine is a recent concept that refers to the ability to classify patients into subgroups that differ in their susceptibility to, biology, or prognosis of a particular disease, or in their response to a specific treatment, and thus to tailor treatment to the individual patient characteristics. Applying this to pain after cancer, the ability to classify post-cancer pain into the three major pain phenotypes (i.e. nociceptive, neuropathic, and nociplastic pain) and tailor pain treatment accordingly, is an emerging issue. This is especially relevant because available evidence suggests that nociplastic pain is present in an important subgroup of those patients experiencing post-cancer pain. The 2021 International Association for the Study of Pain (IASP) clinical criteria and grading system for nociplastic pain account for the need to identify and correctly classify patients according to the pain phenotype early in their treatment. These criteria are an important step towards precision pain medicine with great potential for the field of clinical oncology. Within this framework, the Cancer Pain Phenotyping (CANPPHE) Network, an international and interdisciplinary group of oncology clinicians and researchers from seven countries, applied the 2021 IASP clinical criteria for nociplastic pain to the growing population of those experiencing post-cancer pain. A manual is provided to allow clinicians to differentiate between predominant nociceptive, neuropathic, or nociplastic pain after cancer. A seven-step diagnostic approach is presented and illustrated using cases to enhance understanding and encourage effective implementation of this approach in clinical practice.

Endometriosis and Opioid Receptors: Are Opioids a Possible/Promising Treatment for Endometriosis?

Endometriosis (EM), defined as the presence of endometrial-like tissue with surrounding smooth muscle cells outside the uterus, is a disregarded gynecological disease reported to affect 6-10% of women of reproductive age, with 30-50% of them suffering from chronic pelvic pain and infertility. Since the exact pathogenic mechanisms of EM are still unclear, no curative therapy is available. As pain is an important factor in EM, optimal analgesia should be sought, which to date has been treated primarily with non-steroidal anti-inflammatory drugs (NSAIDs), metamizole or, in extreme cases, opioids. Here, we review the pain therapy options, the mechanisms of pain development in EM, the endogenous opioid system and pain, as well as the opioid receptors and EM-associated pain. We also explore the drug abuse and addiction to opioids and the possible use of NOP receptors in terms of analgesia and improved tolerability as a target for EM-associated pain treatment. Emerging evidence has shown a promising functional profile of bifunctional NOP/MOP partial agonists as safe and nonaddictive analgesics. However, until now, the role of NOP receptors in EM has not been investigated. This review offers a thought which still needs further investigation but may provide potential options for relieving EM-associated pain.

Association between Experimental Pain Measurements and the Central Sensitization Inventory in Patients at Least 3 Months after COVID-19 Infection: A Cross-Sectional Pilot Study

Fatigue, pain, headache, brain fog, anosmia, ageusia, mood symptoms, and sleep disorders are symptoms commonly experienced by people with post-COVID-19 condition. These symptoms could be considered as manifestations of central sensitization. The aim of this study is to evaluate whether there are indicators of central sensitization by using experimental pain measurements and to determine their association with patient-reported outcome measures (PROMs). A cross-sectional study including 42 patients after COVID-19 infection was conducted. The central sensitization inventory (CSI) was administered as a PROM to evaluate central-sensitization-associated symptoms. Pressure pain thresholds (PPT), temporal summation, and descending nociceptive pain inhibition (CPM) were assessed as experimental pain measurements. The median score on the CSI was 46.5 (Q1-Q3: 33-54). The presence of central-sensitization-associated symptoms was seen in 64.3% of patients based on the CSI (≥40/100 points). A deficient CPM was seen in 12% and 14% of patients when measured at the trapezius and rectus femoris, respectively. A negative correlation between pressure sensitivity on the rectus femoris and the CSI score (r = -0.36, 95%CI -0.13 to -0.65, p = 0.007) was observed. Central-sensitization-associated symptoms were present in up to 64.3% of patients post-COVID-19 infection, based on a PROM, i.e., the CSI. A more objective evaluation of nociceptive processing through experimental pain measurements was less suggestive of indicators of central sensitization. Only a small negative correlation between pressure sensitivity and the CSI was observed, thereby pointing towards the discrepancy between the CSI and experimental pain measurements and presumably the complementary need for both to evaluate potential indicators of central sensitization in this population.

The effects of a 15-week physical exercise intervention on pain modulation in fibromyalgia: Increased pain-related processing within the cortico-striatal- occipital networks, but no improvement of exercise-induced hypoalgesia

Dysfunctional top-down pain modulation is a hallmark of fibromyalgia (FM) and physical exercise is a cornerstone in FM treatment. The aim of this study was to explore the effects of a 15-week intervention of strengthening exercises, twice per week, supervised by a physiotherapist, on exercise-induced hypoalgesia (EIH) and cerebral pain processing in FM patients and healthy controls (HC). FM patients (n = 59) and HC (n = 39) who completed the exercise intervention as part of a multicenter study were examined at baseline and following the intervention. Following the exercise intervention, FM patients reported a reduction of pain intensity, fibromyalgia severity and depression. Reduced EIH was seen in FM patients compared to HC at baseline and no improvement of EIH was seen following the 15-week resistance exercise intervention in either group. Furthermore, a subsample (Stockholm site: FM n = 18; HC n = 19) was also examined with functional magnetic resonance imaging (fMRI) during subjectively calibrated thumbnail pressure pain stimulations at baseline and following intervention. A significant main effect of exercise (post > pre) was observed both in FM patients and HC, in pain-related brain activation within left dorsolateral prefrontal cortex and caudate, as well as increased functional connectivity between caudate and occipital lobe bordering cerebellum (driven by the FM patients). In conclusion, the results indicate that 15-week resistance exercise affect pain-related processing within the cortico-striatal-occipital networks (involved in motor control and cognition), rather than directly influencing top-down descending pain inhibition. In alignment with this, exercise-induced hypoalgesia remained unaltered.

Pain mechanisms in complex regional pain syndrome: a systematic review and meta-analysis of quantitative sensory testing outcomes

BACKGROUND

Complex regional pain syndrome (CRPS) is a chronic condition following inciting events such as fractures or surgeries with sensorimotor and autonomic manifestations and poor prognosis. This review aimed to provide conclusive evidence about the sensory phenotype of CRPS based on quantitative sensory testing (QST) to understand the underlying pain mechanisms and guide treatment strategies.

DATABASES

Eight databases were searched based on a previously published protocol. Forty studies comparing QST outcomes (thermal, mechanical, vibration, and electric detection thresholds, thermal, mechanical, pressure, and electric pain thresholds, wind-up ratio, mechanical pain sensitivity, allodynia, flare area, area after pinprick hyperalgesia, pleasantness after C-tactile stimulation, and pain ratings) in chronic CRPS (adults and children) versus healthy controls were included.

RESULTS

From 37 studies (14 of low quality, 22 of fair quality, and 1 of good quality), adults with CRPS showed: (i) significant loss of thermal, mechanical, and vibration sensations, significant gain of thermal and mechanical pain thresholds, significant elevation of pain ratings, and no difference in wind-up ratio; (ii) significant reduction of pleasantness levels and increased area of pinprick hyperalgesia, in the affected limb. From three fair-quality studies, adolescents and children with CRPS showed loss of cold detection with cold hyperalgesia in the affected limb. There was moderate to substantial overall heterogeneity.

CONCLUSION

Diffuse thermal and mechanical hypoesthesia with primary and secondary hyperalgesia, enhanced pain facilitation evidenced by increased area of pinprick hyperalgesia, and elevated pain ratings are dominant in adults with CRPS. Adolescents and children with CRPS showed less severe sensory abnormalities.

Contemporary management of pain in cirrhosis: Toward precision therapy for pain

Chronic pain is highly prevalent in patients with cirrhosis and is associated with poor health-related quality of life and poor functional status. However, there is limited guidance on appropriate pain management in this population, and pharmacologic treatment can be harmful, leading to adverse outcomes, such as gastrointestinal bleeding, renal injury, falls, and hepatic encephalopathy. Chronic pain can be categorized mechanistically into three pain types: nociceptive, neuropathic, and nociplastic, each responsive to different therapies. By discussing the identification, etiology, and treatment of these three mechanistic pain descriptors with a focus on specific challenges in patients with cirrhosis, we provide a framework for better tailoring treatments, including nonpharmacologic therapies, to patients' needs.

Pregabalin attenuates long-lasting post-inflammatory nociplastic mechanical sensitization in mice

Nociplastic pain, the most recently proposed mechanistic descriptor of chronic pain, is the pain resulting from an altered nociceptive system and network without clear evidence of nociceptor activation, injury or disease in the somatosensory system. As the pain-associated symptoms in many patients suffering from undiagnosed pain would result from the nociplastic mechanisms, it is an urgent issue to develop pharmaceutical therapies that would mitigate the aberrant nociception in nociplastic pain. We have recently reported that a single injection of formalin to the upper lip shows sustained sensitization lasting for more than 12 days at the bilateral hindpaws, where there is no injury or neuropathy in rats. Using the equivalent model in mice, we show that pregabalin (PGB), a drug used for treating neuropathic pain, significantly attenuates this formalin-induced widespread sensitization at the bilateral hindpaws, even on the 6 day after the initial single orofacial injection of formalin. On the 10th day after formalin injection, the hindlimb sensitization before PGB injection was no more significant in mice receiving daily PGB injections, unlike those receiving daily vehicle injections. This result suggests that PGB would act on the central pain mechanisms that undergo nociplastic changes triggered by initial inflammation and mitigate widespread sensitization resulting from the established changes.

Characteristics and Outcomes of Patients Receiving Physical Therapy for Low Back Pain with a Nociplastic Pain Presentation: A Secondary Analysis

Introduction

Individuals with low back pain (LBP) may be classified based on mechanistic descriptors, such as a nociplastic pain presentation (NPP). The purpose of this secondary analysis was to examine the frequency and characteristics of patients with a NPP referred to physical therapy with LBP. Additionally, we characterized patients with LBP meeting the criteria for NPP by demographic, clinical, psychological, and pain sensitivity variables. Finally, we examined short- and long-term clinical outcomes in patients with a NPP compared to those without a NPP.

Materials and Methods

Patients referred to physical therapy for LBP completed the Patient Self-report Survey for the Assessment of Fibromyalgia. Participants were categorized as "LBP with NPP" or "LBP without NPP" based on the threshold established in this measure. A rank sum test examined for differences in pain-related psychological factors and pressure-pain threshold between groups. Next, a Friedman test examined if LBP intensity and disability trajectories differed by groups at one and six months after initiation of physical therapy.

Results

22.2% of patients referred to physical therapy for LBP met the criteria for a NPP. Patients with a NPP reported significantly greater disability, pain catastrophizing, depression, anxiety, and somatization compared to individuals without a NPP (p < 0.05). Pressure-pain threshold did not differ between groups (p > 0.05). Individuals with LBP with a NPP demonstrated nonsignificant, small to medium reductions in pain and disability at one and six months. Individuals experiencing LBP without a NPP demonstrated significant reductions in pain and disability in the short- and long term.

Conclusion

Patients with LBP with a NPP displayed greater negative pain-related psychological factors but similar pain sensitivity compared to LBP without NPP.

Generalized sensory sensitivity is associated with comorbid pain symptoms: a replication study in women with dysmenorrhea

ABSTRACT

Dysmenorrhea is characterized by high rates of transition to chronic pain. In a previous study using structural equation modeling, we demonstrated that several symptom domains associated with the emerging concept of nociplastic pain can be described using 2 symptom groups: generalized sensory sensitivity (GSS; composed of widespread pain, interceptive sensitivity, and environmental sensitivity) and SPACE (composed of unrefreshing sleep, pain, affective disturbances, cognitive issues, and reduced energy). Here, we perform a secondary cross-sectional analysis examining the same symptoms groups in a cohort of patients with dysmenorrhea without a diagnosis of chronic pain. Our purpose is to determine if the same symptom patterns are apparent and if they are associated with the presence and severity of comorbid pain. Participants were 201 women with dysmenorrhea. We replicated the hypothesized 2-factor structure in this cohort (comparative fit index = 0.971 and root mean square error of approximation =0.055; 90% CI: 0.000-0.097). Generalized sensory sensitivity was associated with the severity of bladder, bowel, and overall pain in multivariable models including SPACE, patient age, and BMI (all β > 0.32, all P < 0.05). Sleep, pain, affective disturbances, cognitive issues, and reduced energy were associated with menstrual pain during nonsteroidal anti-inflammatory drug use, whereas GSS was associated with the same in the absence of nonsteroidal anti-inflammatory drug use (both P < 0.05). This 2-factor model of symptoms seems to be replicable and valid in a cohort of women at risk for developing chronic pain conditions. These symptom groups are promising potential markers of future pain chronification and may point to patients in need of earlier or more aggressive intervention.

Pain Widespreadedness, and Not Primary Pain Location, is Associated With Comorbid Symptoms in Children With Chronic Pain

OBJECTIVES

Pediatric chronic pain represents heterogeneous diagnoses; often, primary pain location informs research classifications and treatment. In contrast, recent research has highlighted the role of widespread pain and this perspective has been adopted in assessments in specialty pediatric pain clinics. The lack of direct comparison between these 2 methods of categorizing pediatric chronic pain may hinder the adoption of evidence-based practices across the spectrum of care. Therefore, this study aimed to compare whether primary pain location or pain widespreadedness is more informative for pain-related symptoms in pediatric chronic pain.

METHODS

Youth (n=223) between the ages of 8 to 23 years (M=15.93, SD=2.11, 83% female) completed surveys upon intake at the pediatric chronic pain clinic. Free-text entries of primary pain location were coded into categories: headache, abdominal pain, and musculoskeletal pain. Additional domains assessed included widespread pain, pain interference, kinesiophobia, catastrophizing, anxiety, depression, sleep, and fatigue.

RESULTS

Differences based on primary pain location only emerged for kinesiophobia, F(2150)=8.20, P<0.001, with the highest scores among those with musculoskeletal pain. In contrast, controlling for sex, age, and pain intensity, pain widespreadedness was associated with pain interference, pain catastrophizing, fatigue, anxiety, and depression (P<0.05).

DISCUSSION

Pain widespreadedness was more consistently associated with pain-related outcomes among pediatric chronic pain patients than primary pain location, and body maps may be useful in determining a nociplastic pain mechanism to inform treatment. Improved assessment of pediatric pain mechanisms may help advance more precise treatment delivery.

Persistent Idiopathic Dentoalveolar Pain: Is It a Central Pain Disorder?

The International Classification of Orofacial Pain (ICOP) describes idiopathic pain as "unilateral or bilateral intraoral or facial pain in the distribution(s) of one or more branches of the trigeminal nerve(s) for which the etiology is unknown. Pain is usually persistent, of moderate intensity, poorly localized and described as dull, pressing or of burning character." Several diagnoses are included in the ICOP Idiopathic pain section, burning mouth syndrome and persistent idiopathic facial and dentoalveolar pain. This article, with a representative case presentation, briefly discusses common features that may lead to a common central cause for a variety of peripheral complaints.

Association between nociplastic pain and premature endocrine therapy discontinuation in breast cancer patients

PURPOSE

At least 5 years of adjuvant endocrine therapy (ET) is recommended for patients with hormone receptor-positive invasive breast cancer to reduce cancer recurrence risk. Up to half of patients prematurely discontinue ET, often due to musculoskeletal pain. Nociplastic pain is abnormal central nervous system pain processing without evidence of tissue or neuronal damage. This study aimed to evaluate the relationship between baseline nociplastic pain and ET discontinuation.

METHODS

This was a retrospective, single center, cohort study. Included patients were female, had stage 0-III invasive breast cancer, did not receive neoadjuvant therapy, and completed quality of life questionnaires prior to breast surgery, including Fibromyalgia Survey for nociplastic pain. Clinical data including duration of ET were abstracted from the medical record. Patient characteristics were analyzed with t-tests and Chi-squared tests, as appropriate. Univariate and multivariable regressions were performed with Cox proportional hazard models.

RESULTS

Six hundred eighty-one patients diagnosed between 2012 and 2019 met inclusion criteria; 480 initiated ET and were included in the analysis. Of these 480 patients, 203 (42.3%) prematurely discontinued initial ET therapy. On univariate analysis, tamoxifen use (hazard ratio [HR] 0.70, p = 0.021) and premenopausal status (HR 0.73, p = 0.04) were inversely associated with ET discontinuation, while Fibromyalgia Score was positively associated (HR 1.04, p = 0.043). On multivariable analysis, baseline Fibromyalgia Score remained associated with ET discontinuation.

CONCLUSION

Nociplastic pain present prior to surgery was associated with premature ET discontinuation. Fibromyalgia Score screening may be useful for evaluating ET discontinuation risk. Treatments targeting nociplastic pain may be more effective for treating ET-emergent pain.

Spinal GABAergic disinhibition allows microglial activation mediating the development of nociplastic pain in male mice

Previously we developed a murine model in which postinjury stimulation of an injured area triggers a transition to a nociplastic pain state manifesting as persistent mechanical hypersensitivity outside of the previously injured area. This hypersensitivity was maintained by sex-specific mechanisms; specifically, activated spinal microglia maintained the hypersensitivity only in males. Here we investigated whether spinal microglia drive the transition from acute injury-induced pain to nociplastic pain in males, and if so, how they are activated by normally innocuous stimulation after peripheral injury. Using intraplantar capsaicin injection as an acute peripheral injury and vibration of the injured paw as postinjury stimulation, we found that inhibition of spinal microglia prevents the vibration-induced transition to a nociplastic pain state. The transition was mediated by the ATP-P2X4 pathway, but not BDNF-TrkB signaling. Intrathecally injected GABA receptor agonists after intraplantar capsaicin injection prevented the vibration-induced transition to a nociplastic pain state. Conversely, in the absence of intraplantar capsaicin injection, intrathecally injected GABA receptor antagonists allowed the vibration stimulation of a normal paw to trigger the transition to a spinal microglia-mediated nociplastic pain state only in males. At the spinal level, TNF-α, IL-1β, and IL-6, but not prostaglandins, contributed to the maintenance of the nociplastic pain state in males. These results demonstrate that in males, the transition from acute injury-induced pain to nociplastic pain is driven by spinal microglia causing neuroinflammation and that peripheral injury-induced spinal GABAergic disinhibition is pivotal for normally innocuous stimulation to activate spinal microglia.

Pain prevalence and characteristics in survivors of solid cancers: a systematic review and meta-analysis

PURPOSE

The latest systematic review on the prevalence of pain in cancer survivors was published 5 years ago. The current review aims to provide an extended overview on the prevalence of pain, pain mechanisms, pain characteristics, and assessment methods in cancer survivors.

METHODS

A systematic research was conducted on 17th of April 2020 using MEDLINE, Embase, Scopus, Web of Science, and Cochrane looking at studies from 2014 to 2020. Studies had to report pain prevalence rates in cancer survivors with a solid tumor who finished curative treatment at least 3 months ago. Methodological quality was assessed by two independent reviewers using the Joanna Briggs Institute quality appraisal tool. Characteristics of the included studies, participants and reported pain prevalence rates were extracted. The reported prevalence rates of the individual studies were pooled within a meta-analysis. Meta-regressions were performed to identify possible determinants of the pooled pain prevalence.

RESULTS

After deduplication, 7300 articles were screened, after which 38 were included in the meta-analysis. Risk of bias was rated low in 26 articles and moderate in 12 articles. The pooled pain prevalence was 47% (95%CI 39-55), with a heterogeneity of 98.99%.

CONCLUSION

This meta-analysis suggests that nearly half of cancer survivors report pain after completing curative treatment at least 3 months ago. However, substantial unexplained heterogeneity warrants cautious interpretation of these results. Meta-regression using cancer type, treatment location, pain measurement, and follow-up time as a covariate could not explain influencing factors explaining the high heterogeneity.

Plasma proteins from several components of the immune system differentiate chronic widespread pain patients from healthy controls - an exploratory case-control study combining targeted and non-targeted protein identification

Chronic widespread pain (CWP), including fibromyalgia (FM), is characterized by generalized musculoskeletal pain and hyperalgesia. Plasma proteins from proteomics (non-targeted) and from targeted inflammatory panels (cytokines/chemokines) differentiate CWP/FM from controls. The importance of proteins obtained from these two sources, the protein-protein association network, and the biological processes involved were investigated. Plasma proteins from women with CWP (n = 15) and CON (n = 23) were analyzed using two-dimensional gel electrophoresis analysis and a multiplex proximity extension assay for analysis of cytokines/chemokines. Associations between the proteins and group were multivarietly analyzed. The protein-protein association network and the biological processes according to the Gene Ontology were investigated. Proteins from both sources were important for group differentiation; the majority from the two-dimensional gel electrophoresis analysis. 58 proteins significantly differentiated the two groups (R2 = 0.83). A significantly enriched network was found; biological processes were acute phase response, complement activation, and innate immune response. As with other studies, this study shows that plasma proteins can differentiate CWP from healthy subjects. Focusing on cytokines/chemokines is not sufficient to grasp the peripheral biological processes that maintain CWP/FM since our results show that other components of the immune and inflammation systems are also highly significant.

Distinctive alterations in the functional anatomy of the cerebral cortex in pain-sensitized osteoarthritis and fibromyalgia patients

Background

Pain-sensitized osteoarthritis and fibromyalgia patients characteristically show nociceptive system augmented responsiveness as a common feature. However, sensitization can be originally related to the peripheral injury in osteoarthritis patients, whereas pain and bodily discomfort spontaneously occur in fibromyalgia with no apparent origin. We investigated the distinct functional repercussion of pain sensitization in the cerebral cortex in both conditions.

Methods

Thirty-one pain-sensitized knee osteoarthritis patients and 38 fibromyalgia patients were compared with matched control groups. And new samples of 34 sensitized knee osteoarthritis and 63 fibromyalgia patients were used to directly compare each condition. A combined measure of local functional connectivity was estimated to map functional alterations in the cerebral cortex at rest.

Results

In osteoarthritis, weaker local connectivity was identified in the insula, which is a cortical area processing important aspects of the brain response to painful stimulation. In contrast, fibromyalgia patients showed weaker connectivity in the sensorimotor cortex extensively affecting the cortical representation of the body.

Conclusions

In osteoarthritis, weaker insular cortex connectivity is compatible with reduced neural activity during metabolic recovery after repeated activation. In the fibromyalgia neurophysiological context, weaker connectivity may better express both reduced neural activity and increased excitability, particularly affecting the sensorimotor cortex in patients with spontaneous body pain. Such a combination is compatible with a central gain enhancement mechanism, where low sensory tolerance results from the over-amplification of central sensory reception to compensate a presumably weak sensory input. We propose that deficient proprioception could be a factor contributing to weak sensory input.

The OPRM1 gene and interactions with the 5-HT1a gene regulate conditioned pain modulation in fibromyalgia patients and healthy controls

Fibromyalgia (FM) patients have dysfunctional endogenous pain modulation, where opioid and serotonergic signaling is implicated. The aim of this study was to investigate whether genetic variants in the genes coding for major structures in the opioid and serotonergic systems can affect pain modulation in FM patients and healthy controls (HC). Conditioned pain modulation (CPM), evaluating the effects of ischemic pain on pressure pain sensitivity, was performed in 82 FM patients and 43 HC. All subjects were genotyped for relevant functional polymorphisms in the genes coding for the μ-opioid receptor (OPRM1, rs1799971), the serotonin transporter (5-HTT, 5-HTTLPR/rs25531) and the serotonin 1a receptor (5-HT1a, rs6295). Results showed the OPRM1 G-allele was associated with decreased CPM. A significant gene-to-gene interaction was found between the OPRM1 and the 5-HT1a gene. Reduced CPM scores were seen particularly in individuals with the OPRM1 G*/5-HT1a CC genotype, indicating that the 5-HT1a CC genotype seems to have an inhibiting effect on CPM if an individual has the OPRM1 G-genotype. Thus, regardless of pain phenotype, the OPRM1 G-allele independently as well as with an interaction with the 5-HT1a gene influenced pain modulation. FM patients had lower CPM than HC but no group differences were found regarding the genetic effects on CPM, indicating that the results reflect more general mechanisms influencing pain modulatory processes rather than underlying the dysfunction of CPM in FM. In conclusion, a genetic variant known to alter the expression of, and binding to, the my-opioid receptor reduced a subject’s ability to activate descending pain inhibition. Also, the results suggest a genetically inferred gene-to-gene interaction between the main opioid receptor and a serotonergic structure essential for 5-HT transmission to modulate pain inhibition. The results in this study highlight the importance of studying joint synergistic and antagonistic effects of neurotransmittor systems in regard to pain modulation.

CHOIRBM: An R package for exploratory data analysis and interactive visualization of pain patient body map data

Body maps are commonly used to capture the location of a patient's pain and thus reflect the extent of pain throughout the body. With increasing electronic capture body map information, there is an emerging need for clinic- and research-ready tools capable of visualizing this data on individual and mass scales. Here we propose CHOIRBM, an extensible and modular R package and companion web application built on the grammar of graphics system. CHOIRBM provides functions that simplify the process of analyzing and plotting patient body map data integrated from the CHOIR Body Map (CBM) at both individual patient and large-dataset levels. CHOIRBM is built on the popular R graphics package, ggplot2, which facilitates further development and addition of functionality by the open-source development community as future requirements arise. The CHOIRBM package is distributed under the terms of the MIT license and is available on CRAN. The development version of the package with the latest functions may be installed from GitHub. Example analysis using CHOIRBM demonstrates the functionality of the modular R package and highlights both the clinical and research utility of efficiently producing CBM visualizations.

Phenotyping Post-COVID Pain as a Nociceptive, Neuropathic, or Nociplastic Pain Condition

Pain after an acute Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection and coronavirus disease 2019 (COVID-19) condition (post-COVID pain) is becoming a new healthcare emergency. Precision medicine refers to an evidence-based method of grouping patients based on their diagnostic/symptom presentation and then tailoring specific treatments accordingly. Evidence suggests that post-COVID pain can be categorized as nociceptive (i.e., pain attributable to the activation of the peripheral receptive terminals of primary afferent neurons in response to noxious chemical, mechanical, or thermal stimuli), neuropathic (i.e., pain associated with a lesion or disease of the somatosensory nervous system and limited to a "neuroanatomically plausible" distribution of the system), nociplastic (i.e., pain arising from altered nociception despite no clear evidence of actual or threatened tissue damage causing the activation of peripheral nociceptors or evidence for disease or lesion of the somatosensory system causing the pain), or mixed type (when two pain phenotypes co-exist). Each of these pain phenotypes may require a different treatment approach to maximize treatment effectiveness. Accordingly, the ability to classify post-COVID pain patients into one of these phenotypes would likely be critical for producing successful treatment outcomes. The 2021 International Association for the Study of Pain (IASP) clinical criteria and grading system provide a framework for classifying pain within a precision pain medicine approach. Here we present data supporting the possibility of grouping patients with post-COVID pain into pain phenotypes, using the 2021 IASP classification criteria, with a specific focus on nociplastic pain, which is probably the primary mechanism involved in post-COVID pain. Nociplastic pain, which is usually associated with comorbid symptomology (e.g., poor sleep quality, fatigue, cognitive-emotional disturbances, etc.) and is considered to be more difficult to treat than other pain types, may require a more nuanced multimodal treatment approach to achieve better treatment outcomes.

Evaluation of children with severe neurological impairment admitted to hospital with pain and irritability

BACKGROUND

Pain is the most common symptom reported by caregivers of children with severe neurological impairment (SNI), a descriptive term for children with disorders affecting the neurological system across multiple domains. In SNI, cognition, communication, and motor skills are impaired and other organ systems are impacted. Pain is difficult to identify and treat in children with SNI because of communication impairment. When a clear cause of pain is not determined, the term "Pain and Irritability of Unknown Origin (PIUO)" is used to describe pain-like behaviours. This study explores the clinical care received by children with SNI admitted to hospital after presenting to the emergency department of a tertiary pediatric hospital with pain or irritability. Findings are compared to the approach suggested in the PIUO pathway, an integrated clinical pathway for identifying and treating underlying causes of pain and irritability in children with complex conditions and limited communication.

METHODS

Retrospective chart review of children (age 0 to 18 years inclusive) with diagnoses compatible with SNI presenting with pain, irritability, and/or unexplained crying that required hospitalization between January 1st, 2019 and December 31st, 2019. Descriptive statistics were used to analyze the clinical care received by children in whom a source of pain was identified or not. In children for whom no cause of pain was identified, investigations completed were compared to the PIUO pathway.

RESULTS

Eight hospital admissions of six unique children were included for data analysis. A cause for pain and irritability was identified and resolved in three patients. In children with PIUO, there were gaps in history taking, physical examination, and investigations that might have allowed a cause of pain and irritability to be found. Pain was assessed using the r-FLACC pain scale and varying medications for pain/irritability were given during each hospital admission.

CONCLUSION

Children with SNI admitted to a tertiary pediatric hospital did not undergo a standardized approach to identifying a cause of pain and irritability. Future efforts should explore the effectiveness of the PIUO pathway, a standardized approach to reducing and resolving pain in children with SNI.

Identifying and Quantifying the Role of Inflammation in Pain Reduction for Patients With Psoriatic Arthritis Treated With Tofacitinib: A Mediation Analysis

INTRODUCTION

Pain is a multidimensional factor and core domain of psoriatic arthritis (PsA). This analysis aimed to quantify the role of potential inflammation-associated outcomes on pain reduction in patients with PsA receiving tofacitinib, using mediation modeling.

METHODS

Pooled data were from two phase 3 studies (OPAL Broaden and OPAL Beyond) of patients with active PsA treated with tofacitinib 5 mg twice daily or placebo. Mediation modeling was utilized to quantify the indirect effects (via Itch Severity Item [ISI], C-reactive protein [CRP] levels, swollen joint count [SJC], Psoriasis Area and Severity Index [PASI], and enthesitis [using Leeds Enthesitis Index]) and direct effects (representing all other factors) of tofacitinib treatment on pain improvement.

RESULTS

The initial model showed that tofacitinib treatment affects pain, primarily indirectly, via ISI, CRP, SJC, PASI, and enthesitis (overall 84.0%; P = 0.0009), with 16.0% (P = 0.5274) attributable to the direct effect. The model was respecified to exclude SJC and PASI. Analysis of the final model revealed that 29.5% (P = 0.0579) of tofacitinib treatment effect on pain was attributable to the direct effect, and 70.5% (P < 0.0001) was attributable to the indirect effect. ISI, CRP, and enthesitis mediated 37.4% (P = 0.0002), 15.3% (P = 0.0107), and 17.8% (P = 0.0157) of the tofacitinib treatment effect on pain, respectively.

CONCLUSIONS

The majority of the effect of tofacitinib on pain was collectively mediated by itch, CRP, and enthesitis, with itch being the primary mediator of treatment effect.

TRIAL REGISTRATION

NCT01877668, NCT01882439. GRAPHICAL PLS.

Fibromyalgia-associated hyperalgesia is related to psychopathological alterations but not to gut microbiome changes

Fibromyalgia-syndrome (FMS) is a complex disease characterized by chronic widespread pain and additional symptoms including depression, cognitive dysfunction ("fibro-fog") and maldigestion. Our research team examined whether FMS-related pain parameters assessed by quantitative sensory testing (QST) and psychological disturbances are accompanied by alterations of the fecal microbiome. We recruited 25 patients with FMS and 26 age- and sex-matched healthy controls. Medical background, food habits, psychopathology and quality of life were assessed through questionnaires. Stool samples were analyzed by 16S rRNA gene amplification and sequencing. QST was performed according to the protocol of the German Network for Neuropathic Pain. QST showed that both lemniscal and spinothalamic afferent pathways are altered in FMS patients relative to healthy controls and that peripheral as well as central pain sensitization processes are manifest. Psychometric assessment revealed enhanced scores of depression, anxiety and stress. In contrast, neither the composition nor the alpha- and beta-diversity of the fecal microbiome was changed in FMS patients. FMS patients segregate from healthy controls in various parameters of QST and psychopathology, but not in terms of composition and diversity of the fecal microbiome. Despite consideration of several confounding factors, we conclude that the contribution of the gut microbiome to the pathophysiology of FMS is limited.

Systematic Review and Meta-analysis Seem to Indicate that Cannabinoids for Chronic Primary Pain Treatment Have Limited Benefit

INTRODUCTION

The IASP ICD-11 chronic primary pain (CPP) definition includes 19 different painful conditions. In recent years, interest in the potential role of cannabinoids in the management of CPP has increased, since they demonstrated a possible efficacy in treating pain, especially in secondary pain conditions. However, limited evidence is available for patients with CPP. The aim of this systematic review and meta-analysis is to evaluate the efficacy and safety of cannabinoid administration in CPP.

METHODS

PubMed, EMBASE, and Cochrane Library were searched form the beginning up to 31 October 2021 to retrieve published articles of randomized controlled trials (RCTs) or observational, retrospective or prospective, studies, investigating cannabinoids in CPP. The study screening process was completed during November 2021. The primary outcome was pain reduction by means of the visual analogue scale (VAS). Secondary outcomes were quality of life by means of the fibromyalgia impact questionnaire (FIQ) or other available scales, appetite, anxiety, depression, and sleep by means of any available scales. Safety was assessed with the reporting of serious adverse events (SAE) and discontinuation due to adverse events. Risk of bias was assessed. The weighted generic inverse variance method and Mantel-Haenszel method were used to estimate the mean difference (MD) and odds ratios (OR) with 95% confidence intervals (CI) for continuous and dichotomous outcomes, respectively. For outcome measures reported with different scales (pain, anxiety, depression), we used the standardized MD (SMD) as the effect measure and then converted it into units of the VAS scale for pain, the Beck Anxiety Inventory (BAI) for anxiety, and the Beck Depression Inventory (BDI) for depression. Summary of findings was produced using GRADEproGDT.

RESULTS

From 3007 identified records, we included eight articles reporting the results of eight different RCTs (four parallel and four crossover studies; seven compared to placebo and one to amitriptyline), with a total population of 240 patients. VAS pain reduction was non-significant for cannabinoids against placebo (MD = - 0.64; 95% CI - 1.30 to 0.02) or amitriptyline (MD = - 0.19; 95% CI - 0.58 to 0.19). More than 4 weeks cannabinoid treatment significantly reduced pain compared to placebo in parallel studies with more than 4 weeks of treatment duration (MD = - 1.28; 95% CI - 2.33 to - 0.22). Differences for the FIQ (MD = - 21.69; 95% CI - 46.20 to 2.82), BAI (MD = - 2.32; 95% CI - 7.99 to 3.08), and BDI (MD = 2.32; 95% CI - 1.71 to 6.35) were non-significant, likewise for discontinuation due to adverse events (OR = 2.15; 95% CI 0.44-10.65), when comparing cannabinoids to placebo. The quality of the evidence was generally low mainly as a result of imprecision and risk of bias.

CONCLUSION

Cannabinoid treatment in patients with CPP had limited benefit on pain relief; however, it might improve pain with long-term administration.

Sickle cell disease chronic joint pain: Clinical assessment based on maladaptive central nervous system plasticity

Chronic joint pain (CJP) is among the significant musculoskeletal comorbidities in sickle cell disease (SCD) individuals. However, many healthcare professionals have difficulties in understanding and evaluating it. In addition, most musculoskeletal evaluation procedures do not consider central nervous system (CNS) plasticity associated with CJP, which is frequently maladaptive. This review study highlights the potential mechanisms of CNS maladaptive plasticity related to CJP in SCD and proposes reliable instruments and methods for musculoskeletal assessment adapted to those patients. A review was carried out in the PubMed and SciELO databases, searching for information that could help in the understanding of the mechanisms of CNS maladaptive plasticity related to pain in SCD and that presented assessment instruments/methods that could be used in the clinical setting by healthcare professionals who manage chronic pain in SCD individuals. Some maladaptive CNS plasticity mechanisms seem important in CJP, including the impairment of pain endogenous control systems, central sensitization, motor cortex reorganization, motor control modification, and arthrogenic muscle inhibition. Understanding the link between maladaptive CNS plasticity and CJP mechanisms and its assessment through accurate instruments and methods may help healthcare professionals to increase the quality of treatment offered to SCD patients.

Normalization of Neuroinflammation: A New Strategy for Treatment of Persistent Pain and Memory/Emotional Deficits in Chronic Pain

Chronic pain, which affects around 1/3 of the world population and is often comorbid with memory deficit and mood depression, is a leading source of suffering and disability. Studies in past decades have shown that hyperexcitability of primary sensory neurons resulting from abnormal expression of ion channels and central sensitization mediated pathological synaptic plasticity, such as long-term potentiation in spinal dorsal horn, underlie the persistent pain. The memory/emotional deficits are associated with impaired synaptic connectivity in hippocampus. Dysregulation of numerous endogenous proteins including receptors and intracellular signaling molecules is involved in the pathological processes. However, increasing knowledge contributes little to clinical treatment. Emerging evidence has demonstrated that the neuroinflammation, characterized by overproduction of pro-inflammatory cytokines and glial activation, is reliably detected in humans and animals with chronic pain, and is sufficient to induce persistent pain and memory/emotional deficits. The abnormal expression of ion channels and pathological synaptic plasticity in spinal dorsal horn and in hippocampus are resulting from neuroinflammation. The neuroinflammation is initiated and maintained by the interactions of circulating monocytes, glial cells and neurons. Obviously, unlike infectious diseases and cancer, which are caused by pathogens or malignant cells, chronic pain is resulting from alterations of cells and molecules which have numerous physiological functions. Therefore, normalization (counterbalance) but not simple inhibition of the neuroinflammation is the right strategy for treating neuronal disorders. Currently, no such agent is available in clinic. While experimental studies have demonstrated that intracellular Mg²⁺ deficiency is a common feature of chronic pain in animal models and supplement Mg²⁺ are capable of normalizing the neuroinflammation, activation of upregulated proteins that promote recovery, such as translocator protein (18k Da) or liver X receptors, has a similar effect. In this article, relevant experimental and clinical evidence is reviewed and discussed.

Pain Characteristics in Patients with Inflammatory Bowel Disease: A Monocentric Cross-Sectional Study

BACKGROUND AND AIMS

The abdominal pain common in inflammatory bowel disease [IBD] patients is traditionally associated with inflammation but may persist during clinical remission. Central sensitization [CS] has not previously been explored in these patients. This study aimed to determine the epidemiology of pain in IBD patients and to specify pain characteristics with particular attention to CS.

METHODS

This cross-sectional study included 200 patients; 67% had Crohn's disease [CD]. Pain was assessed using the McGill questionnaire, using the Douleur Neuropathique 4 [DN4] questionnaire and by clinical examination. Its impacts on quality of life, depression and anxiety were also assessed.

RESULTS

Three-quarters of IBD patients complained of pain, including intermittent pain attacks, 62% reported abdominal pain and 17.5% had CS. The prevalence of pain [83.6% vs 59.1%; p < 0.001] and abdominal pain [68.7% vs 48.5%; p = 0.006] was higher in CD patients than in ulcerative colitis [UC] patients. Multivariate analysis confirmed that age [p = 0.02], sex [female] [p = 0.004] and CD [p = 0.005] were independent risk factors for pain. Pain intensity was greater in the case of CS (6 [5-3] vs 3 [1.5-5], p < 0.003) which significantly impaired quality of life [p < 0.003] compared with pain without CS.

CONCLUSIONS

The prevalence of pain was high in IBD patients [≈75%] and higher in CD patients. Significant impacts on quality of life were confirmed. More than 25% of patients with abdominal pain described CS as responsible for more severe pain and worsened quality of life.

TRIAL REGISTRATION REF

NCT04488146.

Circulating polyunsaturated fatty acids, pressure pain thresholds, and nociplastic pain conditions

OBJECTIVE

Polyunsaturated fatty acids (PUFAs) play a role in pain regulation. This study sought to determine whether free PUFAs found in red blood cells also play a role in nociceptive processing. We examined associations between circulating PUFAs and nociceptive thresholds to noxious mechanical stimuli. We also determined whether nociceptive thresholds were associated with nociplastic pain conditions.

METHODS

This cross-sectional study used stored red bloods cells and data from 605 adult participants in the OPPERA-2 study of chronic overlapping pain conditions. In OPPERA-2 adults completed quantitative sensory testing in which pressure algometry measured deep muscular tissue sensitivity at six anatomical sites. Standardized protocols classified adults for presence or absence of five nociplastic pain conditions: temporomandibular disorder, headache, low back pain, irritable bowel syndrome and fibromyalgia. Liquid chromatography tandem mass spectroscopy quantified erythrocyte PUFAs. We conducted three sets of analyses. First, a multivariable linear regression model assessed the association between n-6/n-3 PUFA ratio and the number of overlapping nociplastic pain conditions. Second, a series of 36 multivariable linear regression models assessed covariate-adjusted associations between PUFAs and nociceptive thresholds at each of six anatomical sites. Third, a series of 30 multivariable linear regression models assessed covariate-adjusted associations between nociceptive thresholds at six anatomical sites and each of five pain conditions.

RESULTS

In multiple linear regression, each unit increase in n-6/n-3 PUFA ratio was associated with more pain conditions (β = 0.30, 95% confidence limits: 0.07, 0.53, p = 0.012). Omega-6 linoleic acid and arachidonic acid were negatively associated with lower nociceptive thresholds at three and at five, respectively, anatomical sites. In contrast, omega-3 alpha-linolenic acid, eicosapentaenoic acid, docosahexaenoic acid and the n-6/n-3 PUFA ratio were not associated with nociceptive thresholds at any site. Pain cases had significantly lower nociceptive thresholds than non-case controls at all anatomical sites.

CONCLUSION

A higher n-6/n-3 PUFA ratio was associated with more pain conditions. Omega-6 PUFAs may promote a generalized upregulation of nociceptive processing.

Clinical Phenotyping for Pain Mechanisms in Urologic Chronic Pelvic Pain Syndromes: A MAPP Research Network Study

Three categories of pain mechanisms are recognized as contributing to pain perception: nociceptive, neuropathic, and nociplastic (ie, central nervous system augmented pain processing). We use validated questionnaires to identify pain mechanisms in Urologic Chronic Pelvic Pain Syndrome (UCCPS) patients (n = 568, female = 378, male = 190) taking part in the Symptom Patterns Study of the Multidisciplinary Approach to the study of chronic Pelvic Pain Research Network. A cutoff score of 12 on the painDETECT questionnaire (-1 to 38) was used to classify patients into the neuropathic category while the median score of 7 on the fibromyalgia survey criteria (0-31) was used to classify patients into the nociplastic category. Categories were compared on demographic, clinical, psychosocial, psychophysical and medication variables. At baseline, 43% of UCPPS patients were classified as nociceptive-only, 8% as neuropathic only, 27% as nociceptive+nociplastic, and 22% as neuropathic+nociplastic. Across outcomes nociceptive-only patients had the least severe symptoms and neuropathic+nociplastic patients the most severe. Neuropathic pain was associated with genital pain and/or sensitivity on pelvic exam, while nociplastic pain was associated with comorbid pain conditions, psychosocial difficulties, and increased pressure pain sensitivity outside the pelvis. A self-report method classifying individuals on pain mechanisms reveals clinical differences that could inform clinical trials and novel targets for treatment. PERSPECTIVE: This article presents differences in clinical characteristics based on a simple self-report method of classifying pain mechanisms for Urologic Chronic Pelvic Pain Syndrome patients. This method can be easily applied to other chronic pain conditions and may be useful for exploring pathophysiology in pain subtypes.

Features and methods to discriminate between mechanism-based categories of pain experienced in the musculoskeletal system: a Delphi expert consensus study

ABSTRACT

Classification of musculoskeletal pain based on underlying pain mechanisms (nociceptive, neuropathic, and nociplastic pain) is challenging. In the absence of a gold standard, verification of features that could aid in discrimination between these mechanisms in clinical practice and research depends on expert consensus. This Delphi expert consensus study aimed to: (1) identify features and assessment findings that are unique to a pain mechanism category or shared between no more than 2 categories and (2) develop a ranked list of candidate features that could potentially discriminate between pain mechanisms. A group of international experts were recruited based on their expertise in the field of pain. The Delphi process involved 2 rounds: round 1 assessed expert opinion on features that are unique to a pain mechanism category or shared between 2 (based on a 40% agreement threshold); and round 2 reviewed features that failed to reach consensus, evaluated additional features, and considered wording changes. Forty-nine international experts representing a wide range of disciplines participated. Consensus was reached for 196 of 292 features presented to the panel (clinical examination-134 features, quantitative sensory testing-34, imaging and diagnostic testing-14, and pain-type questionnaires-14). From the 196 features, consensus was reached for 76 features as unique to nociceptive (17), neuropathic (37), or nociplastic (22) pain mechanisms and 120 features as shared between pairs of pain mechanism categories (78 for neuropathic and nociplastic pain). This consensus study generated a list of potential candidate features that are likely to aid in discrimination between types of musculoskeletal pain.

A Systematic Review of the Variation in Pain Catastrophizing Scale Reference Scores Based on Language Version and Country in Patients with Chronic Primary (Non-specific) Pain

INTRODUCTION

This systematic review aimed to investigate variations of reference scores for the Pain Catastrophizing Scale (PCS) between language versions and between countries in patients with chronic primary pain (CPP) or chronic primary pain, not otherwise specified (CPP-NOS).

METHODS

Electronic searches of the Ovid/Embase, Ovid/MEDLINE, and Ovid/PsycINFO databases were conducted to retrieve studies assessing PCS scores in adults with CPP or CPP-NOS proposed by the International Classification of Diseases, Eleventh Revision for any country where the translated PCS was available. The protocol for this systematic review was prospectively registered on the International Prospective Register of Systematic Reviews 2018 (registration number: CRD 42018086719).

RESULTS

A total of 3634 articles were screened after removal of duplicates. From these, 241 articles reporting on 32,282 patients with chronic pain were included in the review. The mean (± standard deviation) weighted PCS score across all articles was 25.04 ± 12.87. Of the 12 language versions and 21 countries included in the review, the weighted mean PCS score in Asian languages or Asian countries was significantly higher than that in English, European, and other languages or Western and other countries. The highest mean score of the weighted PCS based on language was in Japanese (mean 33.55), and the lowest was in Russian (mean 20.32). The highest mean score of the weighted PCS based on country was from Japan (mean 33.55), and the lowest was from Australia (mean 19.80).

CONCLUSION

The weighted PCS scores for people with CPP or CPP-NOS were significantly higher in Asian language versions/Asian countries than in English, European and other language versions or Western and other countries.

Clarifying "chronic primary musculoskeletal pain"? The waters remain murky

Commentary on: Fitzcharles M-A, Cohen SP, Clauw DJ, Littlejohn G, Usui C, Häuser W. Chronic primary musculoskeletal pain: a new concept of non-structural regional pain. PAIN Reports 2022;7:e1024. See also: Treede R-D. Chronic musculoskeletal pain: traps and pitfalls in classification and management of a major global disease burden. PAIN Reports 2022;7:e1023.

Chronic musculoskeletal pain: traps and pitfalls in classification and management of a major global disease burden

Mary-Ann Fitzcharles et al. propose to introduce "regional fibromyalgia" as a new diagnosis. This commentary summarizes why this term is misleading but nonetheless the article may pave the way towards useful concepts for myofascial pains.

Knowledge Mapping of Acupuncture for Fibromyalgia from 1990 to 2022: A Bibliometric Analysis

Background

Fibromyalgia is a rheumatic disease with no specific laboratory markers and is insensitive to hormonal drugs and nonsteroidal anti-inflammatory drugs commonly used to treat rheumatism. Guidelines recommend that non-pharmacological therapy should be the first-line treatment for fibromyalgia. Since the publication of the first diagnostic criteria for fibromyalgia in 1990, studies on acupuncture for fibromyalgia have been reported periodically. This study aims to explore the intellectual landscape of acupuncture for fibromyalgia since 1990, and to identify research trends and fronts in this field.

Methods

The Web of Science Core Collection Database was searched for publications on acupuncture for fibromyalgia from 1990 to 2022. VOSviewer and CiteSpace were used to analyze the annual publication, countries, institutions, authors and cited authors, journals and cited journals, references and keywords.

Results

A total of 280 publications were retrieved, and the number of publications showed an overall upward trend. The United States was the most productive country. China Medical University was the institution with the most publications. Lin Yi-wen was the most prolific author, while Wolfe was the most cited author. Evidence-Based Complementary and Alternative Medicine was the journal in which most of the research was published, while Pain was the most cited journal. An article by Wolfe (1990) had the most citations, but an article by Crofford (2001) had the highest centrality. The four most frequently used keywords in the included articles were mechanism, spinal cord, activation and sensitivity.

Conclusion

Acupuncture can effectively relieve pain in patients with fibromyalgia and improve accompanying symptoms such as anxiety and depression. However, the design of clinical trials still needs to be optimized to better verify the efficacy of acupuncture on various clinical symptoms of fibromyalgia. Exploring the central analgesic mechanism of acupuncture on fibromyalgia is also the focus research direction now and future.

Gentle Touch Therapy, Pain Relief and Neuroplasticity at Baseline in Fibromyalgia Syndrome: A Randomized, Multicenter Trial with Six-Month Follow-Up

Background: Fibromyalgia (FM) is considered a stress-related disorder characterized mainly by chronic widespread pain. Its pathogenesis is unknown, but cumulative evidence points at dysfunctional transmitter systems and inflammatory biomarkers that may underlie the major symptoms of the condition. This study aimed to evaluate pain scores (primary outcome), quality of life, inflammatory biomarkers and neurotransmitter systems in women with FM (secondary outcomes) subjected to gentle touch therapy (GTT) or placebo. Methods: A total of 64 female patients with FM were randomly assigned to two groups, namely GTT (n = 32) or Placebo (n = 32). Clinical assessments were conducted at baseline and post-intervention with six-month follow-up. We measured serum catecholamines (dopamine), indolamines and intermediary metabolites (serotonin or 5-hydroxyindolacetic acid (5-HIAA)), as well as tetrahydrobiopterin (BH4), which is a cofactor for the synthesis of neurotransmitters and inflammatory biomarkers in women with FM. A group of healthy individuals with no intervention (control group) was used to compare biochemical measurements. Intervention effects were analyzed using repeated measures (RM) two-way ANOVA followed by Bonferroni post hoc test and mixed ANCOVA model with intention to treat. Results: Compared to placebo, the GTT group presented lower pain scores and brain-derived neurotrophic factor (BDNF) levels without altering the quality of life of women with FM. Changes in BDNF had a mediating role in pain. Higher baseline serum BDNF and 5-HIAA or those with a history of anxiety disorder showed a higher reduction in pain scores across time. However, women with higher serum dopamine levels at baseline showed a lower effect of the intervention across the observation period revealed by an ANCOVA mixed model. Conclusions: In conclusion, lower pain scores were observed in the GTT group compared to the placebo group without altering the quality of life in women with FM. Reductions in BDNF levels could be a mechanism of FM pain status improvement. In this sense, the present study encourages the use of these GTT techniques as an integrative and complementary treatment of FM.

Associations of Central Sensitization-Related Symptoms with Low Back Pain-Related Factors and Work Status in Caregivers

Low back pain (LBP) is associated with psychological factors and central sensitization-related symptoms (CSSs). The relationship between CSSs, LBP-related factors, and work status in caregivers remain unclear. This multicentre, collaborative, cross-sectional study aimed to determine the association between CSS severity, LBP-related factors, and work status in caregivers with LBP. We measured LBP intensity, pain duration, pain sites, CSSs (using the Central Sensitization Inventory-9: CSI-9), psychological factors (using the Pain Catastrophizing and Pain Self-Efficacy scales), and work status (interference, amount of assistance, frequency of assistance, and work environment) in 660 caregivers. CSS severity was categorised as no (CSI-9:0−9), mild (CSI-9:10−19), or moderate/severe (CSI-9:20−36). We further performed multiple comparison analyses and adjusted the residual chi-square to reveal differences between CSS severity groups. Caregivers with more severe CSSs tended to exhibit worse LBP intensity (p < 0.01), widespread pain (p < 0.01), catastrophic thinking (p < 0.01), and pain self-efficacy (p < 0.01), and they also tended to experience work interference (p < 0.01). Caregivers without CSSs tended to receive a smaller amount of assistance with a lower frequency (p < 0.05). The number of participants with an adequate environment and equipment was significantly less in the moderate/severe CSS group (p < 0.01). Thus, our findings may suggest that CSS severity is associated with LBP intensity, widespread pain, psychological factors, and work status in caregivers.

Understanding chronic ocular surface pain: An unmet need for targeted drug therapy

Chronic ocular surface pain (COSP) may be defined as a feeling of pain, perceived as originating from the ocular surface, that persists for >3 months. COSP is a complex multifactorial condition associated with several risk factors that may significantly interfere with an individual's daily activities, resulting in poor quality of life (QoL). COSP is also likely to have a high burden on patients with substantial implications on global healthcare costs. While patients may use varied terminology to describe symptoms of COSP, any ocular surface damage in the ocular sensory apparatus (nociceptive, neuropathic, inflammatory, or combination thereof) resulting in low tear production, chronic inflammation, or nerve abnormalities (functional and/or morphological), is typically associated with COSP. Considering the heterogeneity of this condition, it is highly recommended that advanced multimodal diagnostic tools are utilized to help discern the nociceptive and neuropathic pain pathways in order to provide targeted treatment and effective clinical management. The current article provides an overview of COSP, including its multifactorial pathophysiology, etiology, prevalence, clinical presentation, impact on QoL, diagnosis, current management, and unmet medical needs.

Symmetry Function: The Differences between Active and Non-Active Above-the-Knee Amputees

The number of patients with unilateral above-knee amputation (AKA) due to non-vascular causes has remained stable over the years, at 0.92 per 1000 people per year. Post-AKA individuals are at risk of experiencing a higher incidence of chronic pain. Post rehabilitation, it is estimated that between 16−62% of patients with musculoskeletal disabilities fail to meet the minimum criteria for physical activity in comparison to a healthy population. The current study included 14 participants (11 men and 3 women) with a mean age of 46.1 ± 14.2 years, body height of 1.76 ± 0.09 m, and weight of 79.6 ± 18.3 kg, who were all post-unilateral above-the-knee amputees. Patients in the study were divided into two groups: active (AC) and non-active (NAC). This study was conducted in a certified Laboratory of Biomechanical Analysis using the BTS Smart-E system (BTS Bioengineering). In order to investigate the symmetry function (SF) of gait, the only measurements included were the time series assessment of gait variables defining pelvic and lower limb joint motion and ground reaction forces (GRF). Both groups had an asymmetrical gait pattern with a different magnitude and relative position in the gait cycle, which was revealed by SF. The differences in terms of median, minimum, and maximum were statistically significant (p < 0.05), with SF ranging from −25 to 24% for the AC group and from 43 to 77% (59% on average) for the NAC group. The AC’s pattern was more symmetrical compared to the NAC’s pattern, especially in the case of pelvic and hip joint motion.

Targeting TRPV1 activity via high-dose capsaicin in patients with sickle cell disease

Evidence suggests neuropathic pain (NP) develops over time in sickle cell disease (SCD), contributing to a complex, difficult-to-treat phenotype, with management based on scant evidence. One characteristic of NP found is hyperalgesia caused by nervous system sensitization, but risk factors for this have not been identified within the SCD population, as exact mechanisms leading to its development are not well defined. The SPICE (Sickle cell Pain: Intervention with Capsaicin Exposure) trial was a pilot safety and feasibility trial of high-dose (8%) topical capsaicin for patients with SCD and recurrent/chronic pain with neuropathic features, aimed at exploring capsaicin's utility as a mechanistic probe and adjunctive pain treatment for this population. Ten participants identifying "target" sites of pain with NP-type qualities consented to treatment. The primary endpoint was safety/tolerability. The novel Localized Peripheral Hypersensitivity Relief score (LPHR) was developed to determine improvement in sensitivity attributable to TRPV1 neutralization. There were no severe treatment-related adverse events. Higher baseline pain sensitivity at a given body site was associated with self-reported history of more frequent localized vaso-occlusive pain episodes at that site. There was a statistically significant improvement in the mean LPHR, evidencing TRPV1's importance to the development of hypersensitivity and a potential therapeutic benefit of capsaicin for SCD.

Reported Outcomes in Interdisciplinary Pain Treatment: An Overview of Systematic Reviews and Meta-Analyses of Randomised Controlled Trials

Background

There is considerable diversity of outcome selections and methodologies for handling the multiple outcomes across all systematic reviews (SRs) of Interdisciplinary Pain Treatment (IPT) due to the complexity. This diversity presents difficulties for healthcare decision makers. Better recommendations about how to select outcomes in SRs (with or without meta-analysis) are needed to explicitly demonstrate the effectiveness of IPT.

Objective

This overview systematically collates the reported outcomes and measurements of IPT across published SRs and identifies the methodological characteristics. Additionally, we provide some suggestions on framing the selection of outcomes and on conducting SRs of IPT.

Methods

Three electronic databases (PubMed, Cochrane Library, and Epistemonikos) and the PROSPERO registry for ongoing SR were supplemented with hand-searching ending on 30 September 2021.

Results

We included 18 SRs with data on 49007 people from 356 primary randomised controlled trials (RCTs); eight were followed by meta-analysis and ten used narrative syntheses of data. For all the SRs, pain was the most common reported outcome (72%), followed by disability/functional status (61%) and working status (61%). Psychological well-being and quality of life were also reported in half of the included SR (50%). The core outcome domains according to VAPAIN, IMMPACT, and PROMIS were seldom met. The methodological quality varied from critically low to moderate according to AMSTAR2. The AMSTAR2 rating was negatively correlated to the number of outcome domains in PROMIS, and VAPAIN was positively correlated with IMMPACT and PROMIS, indicating the intercorrelations between the reported outcomes.

Conclusion

This systematic overview showed wide-ranging disparity in reported outcomes and applied outcome domains in SRs evaluating IPT interventions for chronic pain conditions. The intercorrelations between the reported outcomes should be appropriately handled in future research. Some approaches are discussed as well.

Fibromyalgia: Associations Between Fat Infiltration, Physical Capacity, and Clinical Variables

Background

Obesity is a risk factor for the development of fibromyalgia (FM) and generally most studies report increased Body Mass Index (BMI) in FM. Obesity in FM is associated with a worse clinical presentation. FM patients have low physical conditioning and obesity further exacerbates these aspects. Hitherto studies of FM have focused upon a surrogate for overall measure of fat content, ie, BMI. This study is motivated by that ectopic fat and adipose tissues are rarely investigated in FM including their relationships to physical capacity variables. Moreover, their relationships to clinical variables including are not known. Aims were to 1) compare body composition between FM and healthy controls and 2) investigate if significant associations exist between body composition and physical capacity aspects and important clinical variables.

Methods

FM patients (n = 32) and healthy controls (CON; n = 30) underwent a clinical examination that included pressure pain thresholds and physical tests. They completed a health questionnaire and participated in whole-body magnetic resonance imaging (MRI) to determine body composition aspects.

Results

Abdominal adipose tissues, muscle fat, and BMI were significantly higher in FM, whereas muscle volumes of quadriceps were smaller. Physical capacity variables correlated negatively with body composition variables in FM. Both body composition and physical capacity variables were significant regressors of group belonging; the physical capacity variables alone showed stronger relationships with group membership. A mix of body composition variables and physical capacity variables were significant regressors of pain intensity and impact in FM. Body composition variables were the strongest regressors of blood pressures, which were increased in FM.

Conclusion

Obesity has a negative influence on FM symptomatology and increases the risk for other serious conditions. Hence, obesity, dietary habits, and physical activity should be considered when developing clinical management plans for patients with FM.

Pain is Not a "thing": How That Error Affects Language and Logic in Pain Medicine

Effectiveness in academic and clinical communication depends upon agreement on what words and concepts denote and on the consequent ability to argue logically and accurately. In the pain medicine literature there are many examples of imprecision and confusion in this respect, including misnomers and fallacies in reasoning. This article firstly critically examines some of these misnomers. Identified themes include pain being conceptualised as a "thing," conflation between nociception and pain, and confusion between stimulus and response and between the perspectives of the experiencer and the observer of "pain." Secondly, fallacies in reasoning are identified that contribute to imprecision and confusion. These include reification of pain, attributing to the brain functions that belong to whole organisms, and the illusory truth effect. Thirdly, these themes are identified also in constructs that are shown to be based more on speculation than on fact. Taken together, these observations reveal a need to review and, where necessary, modify terminology and concepts used in Pain Medicine. PERSPECTIVE: This article examines a number of words and constructs commonly found in the pain literature from the perspective of accuracy in terms of their consistency of usage, concordance with fact, degree of speculation and logical argument. A common major theme is the error of considering pain as a "thing" that has agentive properties. A need to clarify much of the language used in Pain Medicine is identified.