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

Mirogabalin and pregabalin alleviate nociplastic sensitization induced by chemogenetic activation of the central amygdala neurons in rodents

Nociplastic pain represents the third mechanistic descriptor of pain, alongside neuropathic and nociceptive pain, as proposed in 2017 by the International Association for the Study of Pain (IASP). It describes pain occurring in the absence of nociceptor activation, tissue damage, or neuropathy. The underlying brain mechanisms of nociplastic pain remain poorly understood. Despite the potentially large patient population with chronic pain of this class, effective pharmacological treatments for nociplastic pain are still limited, highlighting the urgent need for drug development using appropriate preclinical models. In this study, we investigated the anti-sensitization effects of two gabapentinoids-mirogabalin besylate (MGB) and pregabalin (PGB)-using a rodent model of nociplastic pain. This model involves experimental excitation of central amygdala neurons via designer receptors exclusively activated by designer drugs (DREADDs), causing widespread sensitization. Administration of an artificial ligand, deschloroclozapine (DCZ; 0.1 mg/kg, i.p.), significantly reduced the 50 %-paw withdrawal threshold, which was significantly elevated by MGB (10 mg/kg, i.p.) and PGB (30 mg/kg, i.p.), restoring it to levels not significantly different from the pre-DCZ baseline. We conclude that MGB and PGB alleviate widespread sensitization in this nociplastic pain model, likely through their action on α2δ-1 subunits within brain circuits that regulate pain sensitivity.

Characteristics of Children With Persistent Pain and Their Parents in a Tertiary Interdisciplinary Pain Clinic

Persistent Pain (PP) in children often has a high impact on their functioning. Knowledge about how to meet the needs is insufficient, especially regarding younger children, children with comorbid psychiatric health conditions, and within different national contexts. A specialized pediatric pain clinic for PP in Sweden offers assessment and interdisciplinary pain rehabilitation (IPR) and collects data on referred children and their parents in a registry. The aims of this study are to (i) describe clinically relevant aspects of children and parents at the first team assessment, (ii) investigate associations between symptoms of psychiatric comorbidity and functioning, (iii) investigate associations between symptoms of ADHD or symptoms of ASD and functioning, and (iv) describe the recommendations after the first team assessment and their rationale. A retrospective cohort study with a descriptive and exploratory design focusing on the characteristics of children (n = 510) and their parents at their first visit for specialized assessment at a tertiary pediatric pain clinic in Sweden between 2013 and 2021. Impairments and complexity appeared to increase with age, with high impact on daily and emotional functioning, especially in relation to symptoms of psychiatric comorbidity and ADHD or ASD. A majority of children and parents were uncertain about the cause of the pain. Only half of the children were recommended IPR, and numerous problems in functioning were found, not only related to pain. In agreement with previous studies describing characteristics of children with PP, there were more girls than boys and older than younger children at the first assessment. Both children and parents report several significant problems in physical, psychological, and social functioning, indicating a need for increased knowledge of PP and care in all kinds of pediatric health care and community settings. Tailored treatment interventions are recommended to improve functioning, including pain education, parental aspects, and addressing psychiatric comorbidities, with a special focus on ADHD or ASD symptoms. More thorough information to referring physicians about evaluations needed before referring to tertiary pain clinics could potentially help set the right expectations for further care and reduce the risk of diagnostic uncertainty.

Nociplastic pain among individuals with chronic ocular surface pain: One cause for "pain without stain"?

Chronic ocular surface pain (COSP) refers to interrelated symptoms such as burning, aching, and irritation and can occur as an isolated condition or comorbid with numerous ocular disorders, including dry eye syndrome Treatments for COSP are largely aimed at the ocular surface and modulating pain arising from damaged corneal nerves; however, the average impact of these treatments on COSP are low to absent. A potential explanation for this is that, in a subset of patients with COSP, individuals have amplified and/or dysregulated neural signaling and sensory processing within the central nervous system (CNS). As in other chronic pain conditions, this might be the pathogenic mechanism primarily responsible for maintaining pain - a phenomenon now referred to as nociplastic pain. The key clinical features of nociplastic pain include symptoms out of proportion to signs, regional or widespread pain, the presence of other chronic pain conditions, and non-pain CNS mediated symptoms (e.g., sleep disorders). We provide an overview for eye care clinicians of nociplastic pain and delineate the emerging evidence for the presence of nociplastic pain among some individuals with COSP. We highlight gaps in our current understanding of nociplastic pain in COSP and provide clinicians with specific tools that may aid in the assessment and management of nociplastic pain.

"Exploring The Nexus": Chronic musculoskeletal pain in diabetic vs non-diabetic population

Introduction

Diabetes-mellitus (DM) has transcended the boundaries and affected populations across globe, it predisposes individual to stiffness and musculoskeletal-pain due to accumulation of glycation-end-products. Musculoskeletal-pain is a common yet frequently neglected complication. Pain mechanisms have been categorized as nociceptive, neuropathic, nociplastic, and idiopathic. Four criteria were put by Kosek-et-al to identify nociplastic pain that affects the musculoskeletal-system. Study aimed to evaluate prevalence of chronic musculoskeletal (cMSK) pain and its association with diabetes and glycaemic control and to evaluate comorbid conditions of cMSK pain.

Methods and materials

A prospective case-control study was conducted at a level-1-tertiary-care-facility. Patients with type-2 DM above 30-years-age who visited outpatient department participated in the study (study group). Age-matched equal number of healthy individuals (control-cohort) were recruited in the study. We collected data from 300 participants in each group. Analysis was done based-on HbA1c-levels, random-blood-sugar (RBS),clinical-history, and comorbidities. Information regarding cMSK-pain was gathered using modified version of Nordic standard questionnaire.

Results

Overall prevalence of cMSK pain was 23.3 % (140 out of 600). Among Group-1/Diabetic group, it was 27.7 % and among group-2/Healthy Cohort it was 19 % and the odds ratio was 1.6. Most commonly reported region with cMSK among group-1 and group-2 was shoulder (32.5 %) and knee (36.8 %) respectively. We found a significant association between cMSK-pain and HbA1c levels (p < 0.005). and individuals with HbA1c levels of more than 12 reported involvements in multiple regions. We didn't find significant association between cMSK and DM, HTN, dyslipidemia, or hypothyroidism (P > 0.05).

Conclusion

Study highlights higher-prevalence and significant impact of cMSK pain in diabetic patients compared to non-diabetic individuals. Addressing musculoskeletal-pain is crucial for improving overall quality-of-life in diabetic patients. Clinicians should adopt a proactive and comprehensive approach to pain management in diabetics. Using a simple Nordic questionnaire during routine check-ups helps with screening of joint and surrounding soft tissue pathology, preventing future complications that could lead to disability.

[Chronic pain syndrome in musculoskeletal diseases-how different are fibromyalgia and long Covid?-Part 1]

Chronic pain is a common problem in rheumatology. Nociceptive pain is distinguished from neuropathic and nociplastic pain. Mechanistically, the former is explained by persistent inflammation, for example. Included in the second category is nerve damage of various causes. In contrast, nociplastic pain is not caused by tissue damage or a lesion in the somatosensory nerve system. It is caused by an altered sensation of pain through the modulation of stimulus processing. The concept of central sensitization, together with further neurobiological and psychosocial mechanisms, best explains such pain conditions. Fibromyalgia (FM) plays a big part in rheumatology - on the one hand, as a differential diagnosis, and on the other, because the management of inflammatory rheumatic conditions is made more difficult by the simultaneous occurrence of FM. In the context of the coronavirus pandemic, persistent pain syndromes with similarities to FM have been described after COVID-19 infection. There is an increasing scientific controversy whether the so-called long Covid syndrome is an actual entity or "only" a variant of FM. This discussion and the current state of knowledge on the problem are the subject of this review.

Nerve stimulation and neuromodulation for painful nerves: a narrative review

Nerve injury primarily leads to neuropathic pain but may also have overlapping elements of nociplastic pain or ongoing nociceptive pain. Electrical stimulation is particularly effective in the treatment of neuropathic pain and may be effective for nociplastic and nociceptive pain. While multiple mechanisms contribute to the analgesic effect of electrical stimulation, the most widely accepted theory for the predominant effect is that of Melzack and Wall's gate control theory. According to this theory, non-painful sensory input carried by low-threshold large-diameter Aβ fibres disrupt the transmission of pain signals in small pain fibers (Aδ and C fibres). This occurs through the activation of inhibitory interneurons in the dorsal horn, which ultimately blocks pain signal transmission.This theory has been employed for different forms of stimulation, including transcutaneous electrical nerve stimulation (TENS), percutaneous electrical nerve stimulation (PENS), and peripheral nerve stimulation (PNS). Each of these methods offers a different approach to localized stimulation and neuromodulation for the treatment of pain. TENS is a non-invasive technique, that delivers electrical currents via surface electrodes placed on the skin. PENS, in contrast, is a minimally invasive method that applies electrical currents through small needles inserted near a target muscle or neural structure. PNS involves the implantation of temporary or permanent electrodes to deliver electrical stimulation directly to peripheral nerves. These modalities are widely used to manage various pain conditions including non-malignant, chronic musculoskeletal and neuropathic pain, such as chronic low back pain, neck pain, neuropathic pain, myofascial pain, and post-operative pain. TENS is particularly notable as a non-invasive device that is affordable, over-the-counter, self-administered, and nonpharmacological option that does not pose the risk of toxicity or overdose. PENS stands out for its ability to integrate electrical stimulation therapy with electroacupuncture through a minimally invasive technique. PNS, on the other hand, is unique in its capacity to precisely target specific nerves and provide a range of stimulation options for extended treatment durations.This article provides a narrative overview of TENS, PENS and PNS with a particular focus on their application for neuropathic pain management and for athletes. We will review mechanisms of action, indications, diagnostic and treatment algorithms, as well as complications and limitations. The overview concludes with a complex case study demonstrating the use of various electrical stimulation therapies, ultimately to successful pain resolution for the patient.

Spinal hyperexcitability in patients with chronic musculoskeletal pain or headache as evidenced by alterations in the nociceptive withdrawal reflex: a systematic review and meta-analysis

ABSTRACT

The nociceptive withdrawal reflex (NWR) is a spinal withdrawal reflex induced by painful stimulation. It is a measure of spinal hyperexcitability, which is believed to contribute to chronic musculoskeletal pain (MSKP) and headache. Previous syntheses of the evidence for alterations in the NWR in patients with chronic MSKP and headache needed a comprehensive update. This systematic review and meta-analysis was performed after the Preferred Items for Systematic reviews and Meta-Analyses guidelines. Studies examining NWR-related outcome measures in patients with chronic MSKP and headache compared to pain-free controls were identified through electronic database searches and included after screening against predefined eligibility criteria. Standardized mean differences or mean differences and 95% confidence intervals (CI) were calculated. Thirty-one studies were included in the systematic review and 25 in the meta-analysis. Moderate-quality evidence was found indicating lower NWR threshold (-3.68; 95% CI, -4.56 to -2.80; P < 0.001), larger NWR area (standardized mean difference = 0.69; 95% CI, 0.37-1.01; P < 0.001), and shorter NWR latency (mean difference = -13.68; 95% CI, -22.69, -4.67; P = 0.003) in patients compared to controls. These findings remained robust when performing meta-regressions based on subgroups (ie, headache, fibromyalgia, whiplash-associated disorder, and osteoarthritis). Low-quality evidence demonstrated facilitated temporal summation of NWR threshold (-2.48; 95% CI, -3.13 to -1.83; P < 0.001) in patients compared to controls. Spinal hyperexcitability as evidenced by lowered NWR threshold values and temporal summation of the NWR is present in patients with chronic MSKP and headache. No evidence was found for alterations in NWR duration and NWR magnitude. Future research is needed to address the gap in research on NWR-related outcome measures other than NWR threshold.

The gut microbiota promotes pain in fibromyalgia

Fibromyalgia is a prevalent syndrome characterized by widespread pain in the absence of evident tissue injury or pathology, making it one of the most mysterious chronic pain conditions. The composition of the gut microbiota in individuals with fibromyalgia differs from that of healthy controls, but its functional role in the syndrome is unknown. Here, we show that fecal microbiota transplantation from fibromyalgia patients, but not from healthy controls, into germ-free mice induces pain and numerous molecular phenotypes that parallel known changes in fibromyalgia patients, including immune activation and metabolomic profile alterations. Replacing the fibromyalgia microbiota with a healthy microbiota substantially alleviated pain in mice. An open-label trial in women with fibromyalgia (Registry MOH_2021-11-04_010374) showed that transplantation of a healthy microbiota is associated with reduced pain and improved quality of life. We conclude that altered gut microbiota has a role in fibromyalgia pain, highlighting it as a promising target for therapeutic interventions.

Influence of chronic pain on regional brain volume reduction in a general older Japanese population: a longitudinal imaging analysis from the Hisayama Study

Longitudinal analyses of the influence of chronic pain on pain-related regional brain volumes in general populations are warranted. This prospective cohort study investigated the association between the presence of chronic pain at baseline and the subsequent changes in pain-related regional brain volumes among Japanese community-dwelling older residents. Participants aged 65 years or older who underwent brain magnetic resonance imaging (MRI) scans in both 2012 and 2017 were included. According to the presence or absence of chronic pain (defined as pain lasting for longer than 3 months) in 2012, participants were categorized into a 'chronic pain' group and 'no chronic pain' group. Region-of-interest analyses for the ventrolateral prefrontal cortex, dorsolateral prefrontal cortex, orbitofrontal cortex, postcentral gyrus, insular cortex, thalamus, anterior cingulate cortex, posterior cingulate cortex, amygdala and hippocampus were performed using FreeSurfer software. Whole-brain analysis was conducted by voxel-based morphometry. Rates of change in regional brain volume at 5 years after baseline were estimated using analysis of covariance. Among the 766 participants included in the FreeSurfer analysis, 444 (58%) were female and 287 (37%) were categorized into the chronic pain group. The results of FreeSurfer analysis showed that the chronic pain group had significantly greater decreases in regional volume in the postcentral gyrus (-2.187% in the chronic pain group versus -1.681% in the no chronic pain group, P = 0.01), thalamus (-4.400% versus -3.897%, P = 0.006), anterior cingulate cortex (-2.507% versus -1.941%, P = 0.004) and amygdala (-4.739% versus -4.022%, P = 0.03) compared to the no chronic pain group after adjusting for age, sex, education attainment, marital status, hypertension, diabetes, serum total cholesterol level, body mass index, current smoking, current drinking, regular exercise, cerebrovascular lesions on MRI, activities in daily living disability and depressive symptoms. Among the 730 participants included in the voxel-based morphometry analysis, 433 (59%) were female and 272 (37%) were categorized into the chronic pain group. The voxel-based morphometry analysis showed that the chronic pain group had a significantly greater regional volume decrease in the right anterior insula than the no chronic pain group. Our findings suggest that the presence of chronic pain at baseline is associated with a significantly greater decrease in the volume of pain-related brain regions at 5 years after baseline in community-dwelling older Japanese.

A systematic review and meta-analysis of pharmacological methods to manipulate experimentally induced secondary hypersensitivity

ABSTRACT

Understanding the physiology of specific clinical features of persistent pain, such as secondary hypersensitivity, is crucial for developing effective treatments. This systematic review and meta-analysis investigated the effects of pharmacological manipulations on the magnitude (primary outcome) and surface area (secondary outcome) of experimentally induced secondary hypersensitivity. Following Cochrane Collaboration guidelines and a published and registered protocol, we conducted an electronic search on February 7, 2024. After screening articles in duplicate, we included 117 articles, consisting of 222 datasets. Risk of bias assessments identified potential flaws in methodological quality. Datasets were pooled by the mechanism of action of the manipulation and by outcome. Effect sizes were estimated using standardised mean difference (SMD). Most datasets (207 of 222) had an unclear risk of performance and detection bias for inadequate reporting of blinding procedures. Thirteen different methods were used to induce, and 23 different drug classes were used to manipulate secondary hypersensitivity. The pooled SMDs [95% CI] suggested that alpha-2-delta subunit of voltage-gated calcium channel ligands reduced both the magnitude (-0.24 [-0.39; -0.08]) and surface area (-0.38 [-0.59; -0.18]) of secondary hypersensitivity, and that both N-methyl-D-aspartate receptor antagonists (-0.36 [-0.55; -0.17]) and voltage-gated sodium channel blockers (-1.02 [-1.63; -0.42]) reduced only the surface area of secondary hypersensitivity. These results suggest a need to understand and compare the physiological underpinnings of magnitude and area of secondary hypersensitivity, and to clarify the relative importance of magnitude vs anatomical spread (ie, surface area) of secondary hypersensitivity to people living with pain.

Methods to Discriminate Between Nociceptive, Neuropathic and Nociplastic in Children & Adolescents: A Systematic Review of Psychometric Properties and Feasibility

The aim of this systematic review was to identify and critically analyse the tools available for categorising pain as nociceptive, neuropathic and nociplastic pain in children and adolescents. Studies were included if they (i) included children and adolescents with a mean age of 0-24 years old, (ii) examined assessment tools that categorise pain as nociceptive, neuropathic or nociplastic, and (iii) examined the psychometric properties of the tools. Sensitive searches were conducted in five online databases in March 2024. Eligible studies were assessed for risk of bias and quality by two authors using COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) criteria. The search yielded 26 studies for 11 tools. No assessment tool had evidence for all nine recommended psychometric properties. Quantitative Sensory Testing, a tool used to identify signs and symptoms of nociplastic and neuropathic pain, was the most studied tool and had moderate evidence for construct validity, criterion validity and reliability. Three self-reported questionnaires, the Self-reported Leeds Assessment of Neuropathic Symptoms and Signs (S-LANSS), Central Sensitisation Inventory (CSI) and PainDETECT, had moderate evidence for construct validity and show promise as preliminary tools to identify possible neuropathic or nociplastic pain. However, they had low specificity when used in isolation. All assessment methods would benefit from further psychometric evaluation and validation in children and adolescents. PERSPECTIVE: This systematic review highlights the limited validation of pain assessment tools for children and adolescents. While Quantitative Sensory Testing and self-reported questionnaires show promise in identifying pain mechanisms, their applicability remains uncertain. Further psychometric validation is crucial to improve pain assessment and guide personalized treatment in young populations.

The concept of difficult-to-treat disease in rheumatology: where next?

New pathogenesis-based therapeutics and evidence-based consensus treatment recommendations, often with predefined treatment goals, have remarkably improved outcomes across many chronic diseases. However, a clinically significant subgroup of patients responds poorly to interventions and show a progressive decline in the disease trajectory, which poses an increasing health-care challenge. Difficult-to-treat approaches exist in several areas of medicine and the need for similar definitions has recently also emerged in rheumatology. The term difficult-to-treat refers not only to patients with pathology-driven, treatment-refractory disease, but also implicates multiple other factors that can contribute to patients being in this state, including having few treatment options, misdiagnosis, and coincident psychosocial factors. Therefore, the difficult-to-treat state requires a comprehensive, holistic, multidisciplinary approach that considers the specific characteristics of each disease and the personalised needs of the patient. In this Personal View, we provide an overview of the different aspects of the concept of difficult-to-treat disease, highlight its advantages, and propose the importance of incorporating this concept more widely in the design of rheumatological treatment strategies.

Sex, Neural Networks, and Behavioral Symptoms Among Adolescents With Multisite Pain

Importance

Multisite pain disproportionately affects females starting in adolescence and is associated with central nervous system dysregulation. Understanding the heterogeneity of underlying neural networks and behavioral symptoms is essential.

Objective

To characterize sex-related resting-state neural networks and co-occurring symptoms, including sleep and behavioral problems, in youth with multisite pain.

Design, Setting, and Participants

This cross-sectional analysis leverages the 2-year follow-up data from the Adolescent Brain and Cognitive Development Study. A total of 684 youth aged 11 to 12 years with multisite pain were compared with 1368 youth with no pain or with regional pain, matched by pubertal status, handedness, and race and ethnicity. Data were collected from July 2018 to February 2021 and released October 2021. Data were analyzed from June 2023 to July 2024.

Exposure

Youth-reported number of painful regions during the last month classified into multisite (≥3), regional (1-2), and no pain groups.

Main Outcomes and Measures

Sex-stratified group iterative multiple model estimation was used for sparse network estimation of regions from the salience network (SLN), sensorimotor network (SMN), and default mode network (DMN). Individual within-network and between-network densities were calculated. Symptoms were behavioral problems and sleep disturbances. Sex-stratified differences in network densities and symptoms were examined between groups. Associations between brain networks and co-occurring symptoms were explored.

Results

Of 2052 participants (1044 [50.88%] female), mean (SD) pubertal status was 2.23 (0.65) and mean (SD) age was 12.02 (0.66) years; 25 (1.22%) were Asian, 149 (7.26%) were Black, 361 (17.59%) were Hispanic, 1307 (63.69%) were White, and 210 (10.23%) were other race or ethnicity. A total of 1646 participants (80.21%) were right-handed, 100 (4.87%) were left-handed, and 306 (14.91%) were ambidextrous. Multisite pain was associated with lower within-SMN connectivity in male (F2,1005 = 61.40; η2 = 0.11; false discovery rate [FDR] P < .001) and female (F2,1041 = 13.38; η2 = 0.03; FDR P < .001) participants and was associated with greater behavioral problems in male (F2,918 = 28.12; η2 = 0.04; FDR P < .001) and female (F2,945 = 9.12; η2 = 0.02; FDR P < .001) participants compared with the subgroup with no pain. Male participants with multisite pain had heightened DMN-SMN connectivity (F2,1005 = 3.55; η2 = 0.007; FDR P = .04). Female participants with multisite pain had heightened sleep disturbances (F2,1039 = 10.64; η2 = 0.02; FDR P = .002), partially explained by reduced within-SMN connectivity (indirect effect estimate, 0.15; 95% CI, 0.03-0.34).

Conclusions and Relevance

In this cross-sectional study of 2052 adolescents, sex-related neurophysiological mechanisms were associated with multisite pain. Brain connectivity partially explained the sleep-pain association in female participants only. On replication and evidence of persistence, these findings suggest that female adolescents with pain may especially benefit from interventions targeting sleep disturbances.

Hidradenitis Suppurativa Symptom Relief: Pain and Itch

Hidradenitis suppurativa (HS) is a chronic inflammatory skin condition that may cause debilitating pain and itch. Given their physical and psychological burden, recognition and treatment of HS-associated symptoms are critical for supporting patients with HS. The complex nature of HS pain, encompassing acute and chronic timing as well as nociceptive, neuropathic, and nociplastic character, requires a tailored treatment approach. Itch in HS, although less studied, is also a prevalent and distressing symptom. The aim of this narrative review is to apply current knowledge of HS pain and pruritus to develop a practical approach for symptomatic management in the dermatology office.

"How Do You Live the Best Life You Can With This Pain?" A Qualitative Study of Adults Living With CF and Pain in the Modulator ERA

BACKGROUND

Despite pain's high prevalence and impact on quality of life and health outcomes, no studies have examined psychosocial approaches for treating pain in CF. We interviewed adults with CF and pain about their experiences to inform development of a CF-specific psychosocial pain management intervention.

METHODS

We partnered with CF Community Voice to recruit 14 adults with CF and pain for 1.5 h individual qualitative interviews and conducted a hybrid inductive-deductive thematic analysis (NVivo 14).

RESULTS

Participants' age ranged from 23 to 64 years; Seven were taking a modulator, 4 eligible/not taking, 3 ineligible. Pain sources included lung/chest, head/sinus, joint, bone, back, neuropathic, GI; 100% reported multiple sources. Pain experience: A major theme was the close interrelationship of pain and CF. Subthemes included pain being part of life with CF, having CF leads to high pain tolerance and effects of aging with CF. Participants described CFTR modulators effect pain experiences with 3 noting improvement and 4 worsening pain. Pain centralization was common: fatigue, difficulties with cognition/sleep, increased sensitivity to nonpainful stimuli. Pain impact: Pain has a widespread negative impact on quality of life and especially mental health. Resiliency was a theme: the need for coping strategies, support and strong self-advocacy. Advice for CF Care Teams: Participants endorsed a need for increased acknowledgment of pain experiences and co-development of a treatment plan.

CONCLUSIONS

Pain remains a prominent, burdensome symptom in the modulator era, necessitating a multi-component management approach. Results informed the development and pilot of a mind-body pain intervention for adults with CF.

Trends in Mixed Pain Research Over Three Decades (1993-2024): A Bibliometric Analysis

BACKGROUND

The term "mixed pain" is frequently used in clinical practice to describe the coexistence of nociceptive, neuropathic, and nociplastic pain mechanisms. However, its inconsistent use and lack of a formal definition warrant further investigation. This bibliometric analysis aims to explore publication trends, research networks, and key themes in mixed pain literature.

METHODS

A bibliometric analysis was conducted using the Web of Science Core Collection. The search was performed in February 2024, with journal rankings obtained from Journal Citation Reports™ 2022 (Clarivate Analytics). Extracted data included publication trends, citation analysis, co-authorship networks, and keyword mapping.

RESULTS

A total of 229 publications were identified, demonstrating an increasing trend in both publication volume and citations. Most studies were published in high-ranking Q1 journals as research (77%) and review articles (19%). The USA (21%), Italy (15%), and Germany (12%) were the leading contributors, yet global collaboration was weak, with limited co-authorship connections except within the USA. The keyword analysis revealed five major research clusters, with "neuropathic pain," "management," and "quality of life" emerging as central themes.

CONCLUSIONS

Despite the progressive increase in mixed pain articles in highly ranked journals, this bibliometric analysis highlighted the absence of a well-structured collaborative network among authors and a lack of clear connections between keywords. Given the critical clinical implications of mixed pain, further high-quality studies on this topic and enhanced international collaborations are recommended.

Discordance between preclinical and clinical testing of Na V 1.7-selective inhibitors for pain

ABSTRACT

The voltage-gated sodium channel Na V 1.7 plays an important role in pain processing according to genetic data. Those data made Na V 1.7 a popular drug target, especially since its relatively selective expression in nociceptors promised pain relief without the adverse effects associated with broader sodium channel blockade. Despite encouraging preclinical data in rodents, Na V 1.7-selective inhibitors have not yet proven effective in clinical trials. Discrepancies between preclinical and clinical results should raise alarms. We reviewed preclinical and clinical reports on the analgesic efficacy of Na V 1.7-selective inhibitors and found critical differences in several factors. Putting aside species differences, most preclinical studies tested young male rodents with limited genetic variability, inconsistent with the clinical population. Inflammatory pain was the most common preclinical chronic pain model whereas nearly all clinical trials focused on neuropathic pain despite some evidence suggesting Na V 1.7 channels are not essential for neuropathic pain. Preclinical studies almost exclusively measured evoked pain whereas most clinical trials assessed average pain intensity without distinguishing between evoked and spontaneous pain. Nearly all preclinical studies gave a single dose of drug unlike the repeat dosing used clinically, thus precluding preclinical data from demonstrating whether tolerance or other slow processes occur. In summary, preclinical testing of Na V 1.7-selective inhibitors aligned poorly with clinical testing. Beyond issues that have already garnered widespread attention in the pain literature, our results highlight the treatment regimen and choice of pain model as areas for improvement.

Prescription time trends in patients with high-impact chronic pain: A National Patient Registry Study

BACKGROUND

High-impact chronic pain (HICP), defined as chronic pain with a significant impact on daily function, affects approximately 8% of the Western population. In Denmark, HICP still remains to be described at the population level. Some patients with HICP are referred to the Danish pain centres, where they are registered with a procedural code. We conducted a nationwide registry-based study of all Danish patients registered with a visit to a pain centre from January 2005 to March 2022, to explore time trends in the prescription of analgesics and sedatives in this HICP subpopulation. Furthermore, data on socioeconomics and hospital diagnoses are reported.

METHODS

We used data from the Central Person Registry, the Danish National Patient Registry, the Danish National Prescription Registry, combined with data on socioeconomic information from Statistics Denmark. Data was collected on prescriptions 3 months before the first visit to a pain centre. Prescriptions were stratified into five calendar periods: before 2011, 2011-2013, 2014-2016, 2017-2019, and 2020-2022.

RESULTS

We identified 66,577 patients referred to a pain centre. Over 15 years, prescriptions before referral declined for opioids (from 53.2% to 31.7%), NSAIDs (from 28.3% to 23.5%), antidepressants (from 20.5% to 16.8%), anxiolytics (from 12.3% to 3.2%), and sleep medication (from 15.8% to 7.6%). In contrast, prescriptions increased for paracetamol (from 31.1% to 48.9%) and gabapentinoids (from 19.2% to 27.7%).

CONCLUSIONS

In patients with HICP visiting Danish pain centres, prescriptions before referral decreased for opioids over 15 years, with a simultaneously increased prescription of gabapentinoids (gabapentin and pregabalin).

SIGNIFICANCE STATEMENT

This nationwide study of 66,577 Danish patients with high-impact chronic pain reveals a significant decrease in filled opioid prescriptions over the past 15 years, with a simultaneous rise in gabapentinoid use before referral to pain centres. These findings suggest a shift in clinical practice towards alternative pain management strategies. The study underscores the need for continued research into the long-term effects of these changes and their impact on patient outcomes.

The Interplay Between Chronic Pelvic Pain and Pelvic Organ Prolapse

INTRODUCTION AND HYPOTHESIS

Chronic pelvic pain (CPP) affects approximately 26% of the world's female population and has various proposed etiologies. This manuscript aims to review concepts related to pelvic organ prolapse (POP) and CPP, encompassing its etiology, risk factors, clinical findings, and pain management.

METHODS

A narrative review was performed using MeSH terms and text words on PubMed, and the Cochrane Database of Systematic Reviews through May 2024. A total of 33 references were used to address the questions posed in this review.

RESULTS

Specific risk factors for CPP associated with POP include pain antedating POP onset, POP surgery duration, and extent of soft tissue trauma. Studies indicate that uterosacral ligament repair performed during surgical interventions for POP correction has alleviated CPP symptoms whether performed vaginally or laparoscopically. Women with preexisting CPP or central sensitization syndrome (CSS) undergoing pelvic reconstructive surgery for POP may experience less favorable postoperative outcomes compared to those without preexisting pain conditions. These outcomes include lower patient satisfaction, less resolution of discomfort, and poorer improvement in urinary symptoms.

CONCLUSIONS

On the basis of current evidence, surgeries for POP correction, especially those involving the uterosacral ligament, have shown a positive impact on reducing pelvic pain. However, untreated CPP is associated with lower satisfaction and less improvement in outcomes after POP surgery regarding pelvic symptoms and quality of life. Screening for and treating CPP conditions prior to POP surgery should be prioritized. Pain management of CPP should be addressed preoperatively, perioperatively, and postoperatively.

Antidepressants to Manage Osteoarthritic Pain: The Value of Pain Phenotyping

Osteoarthritis (OA) is a chronic condition in which pain significantly affects quality of life, often leading to reduced physical activity and disability. Globally, an estimated 595 million people are affected, with the numbers likely to increase owing to an aging population and rising obesity rates. Effective pain management is crucial, yet current treatments, such as nonsteroidal anti-inflammatory drugs (NSAIDs) and opioids, often provide limited relief and come with risks. One reason for this limited success is the insufficient recognition of the importance of psychosocial factors and heterogeneity of patients with OA (such as anxiety and depression), which can exacerbate pain and its impacts. The variability in patient pain experiences highlights the potential value of pain phenotyping, which involves a comprehensive assessment of pain characteristics to tailor treatments to individual needs. Antidepressants, particularly serotonin-norepinephrine reuptake inhibitors (SNRIs), show promise in alleviating both psychological symptoms and OA-related pain, but their effectiveness varies among individuals. Therefore, further research into standardized pain phenotyping methods and their integration into antidepressant treatment is needed to improve efficacy and minimize side effects through more personalized approaches.

The medico-legal pertinence of musculoskeletal nociplastic pain

Pain conditions can be challenging; nociplastic pain, defined as pain that cannot be sufficiently explained by structural/anatomical changes, is newly categorised as the third pain mechanism. Nociplastic pain complaints are subjective, often accompanied by symptoms of fatigue, sleep and mood disturbance and cognitive difficulties with no diagnostic biomarker or reliable measurement of severity. Medico-legal challenges include attribution of causation after an alleged triggering event, assessment of severity, and reported functional impairment. This review considers nociplastic pain in regard to the musculoskeletal system with focus on causation and temporality of the pain condition and impairment. We hope that this overview will provide a better understanding of these challenging pain conditions.

Characterisation of periorbital mechanical allodynia in the reserpine-induced fibromyalgia model in mice: The role of the Schwann cell TRPA1/NOX1 signalling pathway

Fibromyalgia (FM) is a complex and multifaceted condition characterized by a range of clinical symptoms, including widespread pain and a strong association with migraine headaches. Recent findings have underscored the role of oxidative stress and transient receptor potential ankyrin 1 (TRPA1) channel in migraine and FM. However, the precise mechanisms underlying the comorbidity between migraine and FM are unclear. Periorbital mechanical allodynia (PMA), which recapitulates one of the major symptoms of migraine, and the feed-forward mechanism driven by reactive oxygen species and TRPA1, were investigated in a reserpine-induced FM model in C57BL/6J mice, employing pharmacological interventions and genetic approaches. Reserpine-treated mice developed PMA (which was alleviated by antimigraine drugs) and increased endoneurial macrophages and oxidative stress markers in the trigeminal nerve tissues (neuroinflammation). These responses were absent upon macrophage depletion and by pharmacological inhibition or global genetic deletion of the TRPA1 channel. Furthermore, selective silencing of TRPA1 in Schwann cells attenuated both reserpine-induced PMA and neuroinflammation, while selective silencing of TRPA1 in sensory neurons reduced PMA but not neuroinflammation. In reserpine-treated mice, Schwann cell TRPA1 promoted NADPH oxidase 1-mediated reactive oxygen species generation and macrophage density increase in the mouse trigeminal nerve, which sustains PMA. Targeting TRPA1 channels in Schwann cells could offer a novel therapeutic strategy for FM-related headaches.

Engrams across diseases: Different pathologies - unifying mechanisms?

Memories are our reservoir of knowledge and thus, are crucial for guiding decisions and defining our self. The physical correlate of a memory in the brain is termed an engram and since decades helps researchers to elucidate the intricate nature of our imprinted experiences and knowledge. Given the importance that memories have for our lives, their impairment can present a tremendous burden. In this review we aim to discuss engram malfunctioning across diseases, covering dementia-associated pathologies, epilepsy, chronic pain and psychiatric disorders. Current neuroscientific tools allow to witness the emergence and fate of engram cells and enable their manipulation. We further suggest that specific mechanisms of mnemonic malfunction can be derived from engram cell readouts. While depicting the way diseases act on the mnemonic component - specifically, on the cellular engram - we emphasize a differentiation between forms of amnesia and hypermnesia. Finally, we highlight commonalities and distinctions of engram impairments on the cellular level across diseases independent of their pathogenic origins and discuss prospective therapeutic measures.

Innovative therapeutic strategies using ADHD medications tailored to the behavioral characteristics of patients with chronic pain

Chronic pain affects a significant portion of adults and is linked to psychosocial issues, cognitive dysfunction, and psychiatric disorders, complicating treatment. Attention deficit hyperactivity disorder (ADHD) is increasingly recognized as a contributing factor to chronic pain, particularly nociplastic pain, with a notable prevalence of comorbidity between ADHD and conditions like fibromyalgia and chronic low back pain. ADHD behaviors such as impulsivity and overactivity can exacerbate pain by leading patients to seek risky treatments or discontinue care prematurely. ADHD medications are expected to alleviate pain severity by improving associated cognitive dysfunction and addressing central sensitization, a fundamental mechanism in chronic pain. Brain abnormalities in ADHD contribute to increased spontaneous activity in the anterior cingulate cortex-posterior insular pathway due to neuroinflammation, alterations in action potential firing, and changes in transmission pathways in the spinal dorsal horn. Additionally, increased norepinephrine synthesis and reduced transmission efficiency amplify nociceptive information from the periphery and facilitate central sensitization in ADHD. Beyond typical ADHD medications like central stimulants, norepinephrine reuptake inhibitors, and alpha-2 receptor agonists, various antidepressants, mood stabilizers, antipsychotics, Parkinson's disease medications, and antidementia medications have proven effective in alleviating ADHD symptoms. These medications, effective for ADHD, may offer innovative solutions for managing chronic pain by targeting both the cognitive/behavioral dysfunction and central sensitization observed in chronic pain comorbid with ADHD. Further research into these mechanisms could lead to new, more effective pharmacological treatments for chronic pain with comorbid ADHD, a condition that is often overlooked.

Neuroinflammatory and Immunological Aspects of Fibromyalgia

Fibromyalgia is a common, high-impact condition of chronic widespread pain and sensory dysfunction associated with altered central and peripheral sensory processing. A growing body of evidence supports the role of neuroinflammation and immune changes in fibromyalgia, and a narrative review of this literature was undertaken. Published data suggest that the interactions between the neural pain networks and the immune system in fibromyalgia appear to be bidirectional and operate both centrally and peripherally. There is a growing focus on processes occurring in the dorsal root ganglia and the role of maladaptive microglial cell activation. Ongoing insight into neuroinflammatory mechanisms in fibromyalgia opens potential avenues for the development of mechanism-based therapies in what is, at present, a challenging-to-manage condition.

Applying Nociplastic Pain Criteria in Chronic Musculoskeletal Conditions: A Vignette Study

Background/Objectives: The International Association for the Study of Pain (IASP) recently introduced clinical criteria and a grading system to identify nociplastic pain, marking a pivotal step toward improving diagnostic accuracy. This study aimed to evaluate the reliability and validity of the IASP criteria using clinical vignettes, assessing their effectiveness in identifying nociplastic pain in clinical settings. Methods: A reliability and diagnostic accuracy study was conducted using 32 clinical vignettes based on the literature and pre-existing clinical data. The vignettes represented patients with and without the characteristics of nociplastic pain and were reviewed independently by two expert physiotherapists. Inter-rater and intra-rater reliability were evaluated with a 1-month interval between assessments. Criterion validity was analyzed by comparing the IASP criteria against the standardized vignettes as the reference standard. Sensitivity, specificity, and predictive values were calculated to assess diagnostic accuracy. Results: The IASP criteria demonstrated moderate-to-perfect intra-rater agreement (κ = 0.71-1.00, p < 0.05) and weak-to-perfect inter-rater agreement (κ = 0.52-1.00, p < 0.05). Criterion validity was moderate (κ = 0.68), with strong specificity (89.0%) and moderate sensitivity (69.0%). Positive and negative predictive values were high at 81.8% and 81.0%, respectively, supporting the criteria's accuracy in identifying and excluding nociplastic pain. Conclusions: The IASP criteria for nociplastic pain exhibited satisfactory reliability and criterion validity in this preliminary study, particularly after initial rater familiarization. Future research should evaluate their application in real-world clinical settings, explore concurrent and prognostic validity, and involve a broader range of raters to enhance generalizability.

Update on chronic pain management

Pain is a common presenting symptom to consultant physicians, both in the hospital and in the clinic or rooms. Biologically, pain serves as warning of tissue damage. But this is no longer the case when pain is present for months or years, especially when it has been fully investigated. There can be a substantial discrepancy between the magnitude of pain, disability and distress reported by a patient with chronic pain and the extent of tissue damage identified. From the 1990s until the mid-2010s, opioids were promoted as a safe and effective panacea for chronic non-cancer pain. This led to overprescribing with unfortunate consequences of misuse, abuse and overdose deaths. The response to the so-called 'opioid epidemic' has led to a renewed focus on how chronic pain should be managed. The aim of this article is to update fellows and trainees on the assessment and management of chronic pain in adult medical patients. In particular, we address the role of pharmacotherapy post-opioid epidemic (primarily antidepressants and anticonvulsants in neuropathic pain), the place of interventional procedures and the nature and effectiveness of pain self-management training in people with chronic pain, many of whom have had pain for a year or more and failed other treatments.

Rehabilitation Management of Neck Pain-Development of a Diagnostic Framework Based on the Pain and Disability Drivers Management Model

RATIONALE

Neck pain is a major cause of disability worldwide, and current rehabilitation strategies show limited effectiveness. Subgrouping patients by their primary pain and disability drivers can help tailor treatments. At this end, the Pain and Disability Drivers Management (PDDM) was developed and has demonstrated preliminary effectiveness in the management of low back pain. Nevertheless, the PDDM model was only validated for this population. Adapting this framework to patients with neck pain would provide a more global view of the patient's experience of pain and support a genuine biopsychosocial intervention.

AIMS AND OBJECTIVES

The aim of this study was to develop and validate the content of the PDDM model for patients living with neck pain.

METHODS

Through a modified DELPHI study design, participants with clinical and research expertize in rehabilitation of neck pain were invited to participate. A questionnaire was developed using literature reviews and endorsed by a steering committee. The relevance of each element of the newly adapted model was evaluated on a 4-point Likert scale. An item reached consensus if it obtained the predefined threshold of > 78% "relevant" and "very relevant." Participants left comments on terminology and recommended items to add in early rounds. Quantitative and qualitative analyses were performed.

RESULTS

An invitation was sent to 1650 potential participants, from which 155 accessed the survey, 64 completed the first round and 55 the second round. A total of 70 elements met consensus and were distributed across six domains: "Nociceptive pain drivers", "nociplastic pain drivers," "drivers associated with neuropathic pain", "comorbidity drivers", "cognitive-emotional drivers" and "environmental or lifestyle drivers, and social determinants of health."

CONCLUSION

Through a modified DELPHI study, the PDDM model was updated and adapted to people with neck pain. Subsequent steps include clinical integration and measures of efficacy when used for assessment/treatment.

Virally-initiated pain states: phenotypes, mechanisms, and future directions

The recent SARS-CoV-2 pandemic has underscored the significance of viral infections, affecting billions of lives and costing trillions of dollars globally. Even beyond SARS-CoV-2, common infections with viruses like influenza, HIV, and herpesviruses have profound impacts beyond their typical manifestations, often triggering acute and chronic pain syndromes that can be life-altering. These virally induced pain states can arise through direct viral replication within neurons, or indirectly, via immune responses to infection in both the contexts of afferent signaling in the dorsal root ganglion (DRG) or subsequent higher order integration in intracranial systems. Varicella-zoster virus (VZV), influenza virus, and SARS-CoV-2 each provide a unique lens through which to examine the interplay between viral activity and pain. This perspective paper is not meant to be an exhaustive review of virally-induced neuropathic pain states. It seeks to explore curated aspects of the complexities of these pain states, identify research gaps, and suggest solutions using nanoscale molecular understanding and psychoneuroimmunological and biopsychosocial frameworks. Each subheading is accompanied by a list of related issues for study which we think will lead to advances in our understanding of the vexing pain phenotype associated with viral infection.

Do Lumbar Paravertebral Muscle Properties Show Changes in Mothers with Moderate-Severity Low Back Pain Following a Cesarean Birth? A Case-Control Study

Background/Objectives: Cesarean birth (CB) is linked to nonspecific low back pain (NSLBP). Different properties of the muscular tissue, including contractile, biomechanical, and viscous properties, may reflect its physiological or pathological condition. This study aimed to measure these properties of lumbar paravertebral muscles (LPVMs) and their relationship with post-CB mothers with moderate-severity NSLBP and match their measurements to those of the controls. Methods: Sixty women were included in this case-control research. They were divided into two equal groups: Group (A) representing cases, consisted of 30 females who experienced CB and complained of moderate-severity NSLBP, and Group (B) representing controls, consisted of 30 healthy females who had never experienced pregnancy with no or mild-severity NSLBP. Results: The statistical analysis between the two groups yielded significant differences in the right and left LPVMs' tone (p = 0.002 and 0.015), relaxation time (p = 0.002 and 0.022), and creep (p = 0.013 and 0.008), respectively. On the other side, there were non-significant differences in the right and left LPVMs' stiffness (p = 0.055 and 0.367) and elasticity (p = 0.115 and 0.231), respectively. The regression analysis's final model indicated a strong overall performance (Nagelkerke: 1.00). Conclusions: The LPVMs of post-CB mothers with moderate-severity NSLBP showed remarkable changes in both contractile and viscous properties: muscle tone notably decreased, while viscosity increased. However, biomechanical properties like stiffness and elasticity showed negligible changes. This fitted regression analysis illustrated the holistic strong effect of LPVMs' properties as risk factors contributing to post-CB NSLBP, emphasizing their consideration in diagnosis and intervention strategies for such cases.

Sensory alterations and immunological changes during the chronification of postsurgical pain: a study protocol for a prospective observational cohort study

INTRODUCTION

Chronic postsurgical pain (CPSP) represents a widely underdiagnosed and often poorly treated medical problem, affecting 10-50% of all surgical patients, exhibiting neuropathic features in 35-60%. It is hypothesised that surgery-induced tissue damage and the subsequent immune response cause sensory alterations in the early postoperative period, ultimately leading to a chronic neuropathic or nociplastic pain state. The 'Sensory Changes and Immunological parameters in Postsurgical pain' study (SCIP-Pain study) was designed to test this hypothesis and identify sensory alterations and changes in the immunological response that are related to the development of CPSP with neuropathic features.

METHODS AND ANALYSIS

This protocol describes the SCIP-Pain study-an ongoing prospective observational cohort study involving 150 adult patients undergoing elective lower extremity orthopaedic surgery. Study participants complete questionnaires, undergo quantitative sensory testing (QST) and provide blood samples to assess the immunological response at various time points: before surgery, 2 weeks and 3 months after surgery. To reduce dimensionality, cluster analyses will be conducted on QST and immunological parameters. Cluster allocation, along with other preselected candidate predictors, will subsequently be used in a generalised mixed-effects model to predict CPSP with neuropathic features within 3 months after surgery as the primary outcome.

ETHICS AND DISSEMINATION

This study received approval from the Medical Ethics Committee NedMec (protocol NL77085.041.21), as well as from all participating centres. The study results are expected to be published in peer-reviewed journals and disseminated at international conferences.

Nociplastic pain: controversy of the concept

Classically, pain can be of a nociceptive or neuropathic nature, which refers to non-neural or neural tissue lesions, respectively. Chronic pain in conditions such as migraine, fibromyalgia, and complex regional pain syndrome (CRPS), is thought to perpetuate without a noxious input. Pain in such patients can be assigned neither to the nociceptive nor neuropathic category. Therefore, a third pain descriptor, named "nociplastic pain", has been adopted by the International Association for the Study of Pain. The current controversy-focused narrative review updates littledebated aspects of the new pain concept. The most disputable feature of nociplastic pain is its autonomous persistence, i.e., existence without causative tissue damage, presumably because of a malfunction of pain pathways and processing. This contradicts the fact that nociplastic pain is accompanied by persistent central sensitization that has been shown to require a continuing noxious input, e.g ., nerve injury. Even if sensitization occurs without a lesion, e.g ., in psychogenic and emotional pain, peripheral stimulus is necessary to produce pain. A logical weakness of the concept is that the word "plastic" in biology refers to adaptation rather than to maladaptation. The pathophysiologic mechanism of nociplastic pain may, in fact, be associated with background conditions that elude diagnosis because of the limitations of current diagnostic means. Misapplication of the nociplastic pain category may weaken diagnostic alertness toward occult causes of pain. Possible diagnostic errors could be avoided by understanding that nociplastic pain is a mechanism of pain rather than a diagnosis. Clinical use of this pain descriptor deserves a wider critical discussion.

Application of the grading system for "nociplastic pain" in chronic primary and chronic secondary pain conditions: a field study

ABSTRACT

The concept "nociplastic pain" has been developed for patients with features of nociceptive system sensitization that are not explained as nociceptive or neuropathic. Here, we tested how well the recently published grading system differentiates between chronic primary and secondary pain conditions. We recruited patients with fibromyalgia (FMS, n = 41), complex regional pain syndrome (CRPS, n = 11), osteoarthritis (OA, n = 21), or peripheral nerve injury (PNI, n = 8). We used clinical history, pain drawings, quantitative sensory testing (QST), and questionnaires to classify their pains as possibly or probably "nociplastic." All patients with chronic primary pain exhibited widespread/regional pain not explainable by either nociceptive or neuropathic mechanisms. Widespread pain occurred in 12 patients with OA but was identified as nociceptive in 11 of 12. Regional pain occurred in 4 patients with PNI but was identified as neuropathic in 3 of 4. At this step, the grading system had 100% sensitivity and 93% specificity. Clinical evidence for pain hypersensitivity by QST, and history of hypersensitivity and mental comorbidities did not differentiate between chronic primary pain (QST: 36/52 = 69%, history: 43/52 = 83%) and secondary pain conditions (QST: 20/29 = 69%, history: 24/29 83%). Based on these data, specificity remained excellent (93%), but sensitivity dropped substantially (60%) due to lacking evidence for pain hypersensitivity in many patients with FMS. This low sensitivity suggests that the published grading system is not suitable for screening purposes. We suggest structural and content modifications to improve sensitivity, including placement of patient history before clinical examination and addition of a high tender point count as evidence for widespread pain hypersensitivity.

["Mixed pain": Current conceptualization and approach for Primary Care]

Despite being referenced in the literature for over a decade, the term "mixed pain" has hardly been formally defined. The strict binary classification of pain as purely neuropathic or nociceptive left a good proportion of patients unclassified; even the introduction of the term "nociplastic pain" in the International Association for the Study of Pain terminology leaves out patients who clinically present with a substantial overlap of nociceptive, neuropathic, and nociplastic symptoms. For these patients the term "mixed pain" is becoming increasingly recognized and accepted by the scientific community. This narrative review summarizes the highlights of mixed pain and emphasizes the importance of recognizing this type of pain in clinical practice.

Using Natural Language Processing and Social Media Data to Understand the Lived Experience of People with Fibromyalgia

BACKGROUND AND OBJECTIVES

Fibromyalgia has many unmet needs relating to treatment, and the delivery of effective and evidence-based healthcare is lacking. We analyzed social media conversations to understand the patients' perspectives on the lived experience of fibromyalgia, factors reported to trigger flares of pain, and the treatments being discussed, identifying barriers and opportunities to improve healthcare delivery.

METHODS

A non-interventional retrospective analysis accessed detail-rich conversations about fibromyalgia patients' experiences with 714,000 documents, including a fibromyalgia language tag, which were curated between May 2019 and April 2021. Data were analyzed via qualitative and quantitative analyses.

RESULTS

Fibromyalgia conversations were found the most on Twitter and Reddit, and conversation trends remained stable over time. There were numerous environmental and modifiable triggers, ranging from the most frequent trigger of stress and anxiety to various foods. Arthritis and irritable bowel syndrome (IBS) were the most frequently associated comorbidities. Patients with fibromyalgia reported a wide range of symptoms, with pain being a cardinal feature. The massage, meditation and acupuncture domains were the most reported treatment modalities. Opportunities to improve healthcare delivered by medical providers were identified with current frustration relating to a lack of acknowledgement of their disease, minimization of symptoms and inadequately meeting their care needs.

CONCLUSIONS

We developed a comprehensive, large-scale study which emphasizes advanced natural language processing algorithm application in real-world research design. Through the extensive encapsulation of patient perspectives, we outlined the habitual symptoms, triggers and treatment modalities which provide a durable foundation for addressing gaps in healthcare provision.

Nociplastic Pain in Endometriosis: A Scoping Review

Endometriosis is an inflammatory chronic condition associated with nociceptive, neuropathic, and nociplastic pain. Central sensitization (CS) is the primary nociplastic pain mechanism. However, there are currently no standardized methods for detecting CS or nociplastic pain. This review aims to identify available tools for characterizing CS/nociplastic pain in endometriosis-related chronic pelvic pain. Following the PRISMA-P protocol, MEDLINE, Embase, Scopus, and PsychINFO databases were searched on 23 April 2024, for the terms "endometriosis", "central sensitization", "nociplastic pain", "widespread pain", and "assessment tools". Publications were selected if they mentioned tool(s) for detecting nociplastic pain or CS in endometriosis patients. Information was extracted on study demographics, assessment types, and the tools used for detection. Of the 379 citations retrieved, 30 papers met the inclusion criteria. When working to identify CS and nociplastic pain, fourteen studies exclusively used patient-reported questionnaires, six used quantitative sensory testing (QST), two used clinical assessments, and eight used multiple approaches combining patient-reported questionnaires and clinical assessment. This review illustrates the diversity of tools currently used to identify CS and nociplastic pain in endometriosis patients. Further research is needed to evaluate their validity and to standardize methods in order to improve the accuracy of nociplastic pain identification and guide treatment.

Same patient but different worlds: A state-of-the-art review translating best practice psychosocial care from musculoskeletal care to the orthopaedic context

BACKGROUND

Individuals with chronic musculoskeletal conditions experience persistent pain and disability that has deleterious impacts on physical function, psychological health, social engagement, relationships, and work participation. This impact is greater in people with psychosocial risk factors, and best practice musculoskeletal care recommends a biopsychosocial approach to management. Orthopaedic surgery is often an effective management approach for chronic musculoskeletal conditions, but research has only recently explored the links between differing patient outcomes after orthopaedic surgery and psychosocial risk factors. Implementing biopsychosocial approaches to musculoskeletal care has taken great strides in the primary care setting however, implementation of the biopsychosocial approach in orthopaedic surgery brings complexity as the context changes from primary care to hospital based secondary care. The aim of this review therefore is to explore implementation of psychosocial care in the elective orthopaedic surgery context, informed by evidence in musculoskeletal care.

ASSESSMENT AND MANAGEMENT OF PSYCHOSOCIAL FACTORS

Several composite screening tools for psychosocial factors or 'yellow flags' are recommended for use in primary care for musculoskeletal conditions alongside a comprehensive patient interview. However, in the orthopaedic surgery context, composite measures have focused on discharge destination, and there is not a universal approach to comprehensive patient interview incorporating a biopsychosocial approach. A range of biopsychosocial approaches to musculoskeletal conditions have been developed for the primary care setting, yet few have been explored in the context of orthopaedic surgery.

IMPLEMENTATION OF PSYCHOSOCIAL CARE

Implementing best practice psychosocial care into the orthopaedic context has enormous potential for all stakeholders, but several barriers exist at the level of the individual patient and practitioner, workforce, health service and society. We have discussed key considerations for implementation including workforce composition, patient-centred care and shared decision making, health literacy, continuity of care, and consideration of preferences for women and culturally diverse communities.

CONCLUSION

This review considers current literature exploring implementation of psychosocial care into the orthopaedic surgery context, informed by current research in musculoskeletal care. This presents a critical opportunity for orthopaedic surgery to provide optimised, equitable, high-value, patient-centred care.

Electroacupuncture Mitigates TRPV1 Overexpression in the Central Nervous System Associated with Fibromyalgia in Mice

BACKGROUND

Fibromyalgia (FM) is characterized by chronic pain, significantly affecting the quality of life and functional capabilities of patients. In addition to pain, patients may experience insomnia, chronic fatigue, depression, anxiety, and headaches, further complicating their overall well-being. The Transient Receptor Potential Vanilloid 1 (TRPV1) receptor responds to various noxious stimuli and plays a key role in regulating pain sensitivity and inflammation. Thus, targeting TRPV1 may provide analgesic and anti-inflammatory benefits. This study investigates the efficacy of electroacupuncture (EA) in alleviating chronic pain in FM through TRPV1 and its downstream molecules in the central nervous system (CNS).

METHODS

To model FM, we subjected mice to intermittent cold stress (ICS) for three days. The study comprised five rodent groups: Control (CON), ICS, ICS + EA, ICS + Sham EA, and ICS + KO (TRPV1 knockout mice).

RESULTS

Our findings revealed that ICS induced allodynia and hyperalgesia in mice by day four, persisting until day 21. EA at 2 Hz and TRPV1 KO significantly decreased both mechanical and thermal hypersensitivity (Withdrawal-Day 14: 2.43 ± 0.19 g; Day 21: 5.88 ± 0.47 g, n = 6, p < 0.05; Latency-Day 14: 2.77 ± 0.22 s; Day 21: 5.85 ± 0.41 s, n = 6, p < 0.05). In contrast, sham EA did not produce significant effects. Additionally, TRPV1 and several pain-related proteins were significantly elevated in the thalamus, somatosensory cortex (SSC), medial prefrontal cortex (mPFC), hippocampus, hypothalamus, cerebellum regions V (CB V), VI (CB VI) and VII (CB VII) after the ICS model. Both EA at the ST36 acupoint and TRPV1 KO mice showed diminished overexpression of pain-related proteins, with the sham EA group showing no significant changes compared to the ICS group.

CONCLUSIONS

Chronic widespread pain was reduced by EA and TRPV1 KO, with the effects of EA on the TRPV1 pain pathway clearly evident in the CNS after 21 days.

Is chronic pain caused by central sensitization? A review and critical point of view

Chronic pain causes disability and loss of health worldwide. Yet, a mechanistic explanation for it is still missing. Frequently, neural phenomena, and among them, Central Sensitization (CS), is presented as causing chronic pain. This narrative review explores the evidence substantiating the relationship between CS and chronic pain: four expert researchers were divided in two independent teams that reviewed the available evidence. Three criteria were established for a study to demonstrate a causal relationship: (1) confirm presence of CS, (2) study chronic pain, and (3) test sufficiency or necessity of CS over chronic pain symptoms. No study met those criteria, failing to demonstrate that CS can cause chronic pain. Also, no evidence reporting the occurrence of CS in humans was found. Worryingly, pain assessments are often confounded with CS measures in the literature, omitting that the latter is a neurophysiological and not a perceptual phenomenon. Future research should avoid this misconception to directly interrogate what is the causal contribution of CS to chronic pain to better comprehend this problematic condition.

TRPA1 Agonist-Responsive Afferents Contribute to Central Sensitization by Suppressing Spinal GABAergic Interneurons Through Somatostatin 2A Receptors

Altered nociception, a key feature of nociplastic pain, often involves central sensitization. We previously found that central sensitization underlying a nociplastic pain state in female mice depends on the ongoing activity of TRPA1 agonist-responsive afferents. Here, we investigated how the activity of these afferents induces and maintains central sensitization at the spinal level. We hypothesized that, in the superficial dorsal horn where somatostatin (SST) is expressed in excitatory interneurons and the SST2A receptor (SST2A-R) in GABAergic inhibitory interneurons (GABAn), TRPA1 agonist-responsive afferents stimulate SST-expressing excitatory interneurons (SSTn), leading to GABAn suppression through SST2A-R and resulting in altered nociception. We tested this hypothesis using ex vivo Ca2+ imaging of dorsal root-attached spinal cord slices expressing GCaMP6f in either SSTn or GABAn and in vivo assessment of mechanical hypersensitivity. The dorsal root was chemically (with allyl isothiocyanate [AITC]) and electrically stimulated to activate TRPA1-expressing nociceptors and all afferents, respectively. The stimulation of dorsal root with AITC excited SSTn. During activation of AITC-responsive afferents, a subset of SSTn showed potentiated responses to both low- and high-threshold afferent inputs, whereas a subset of GABAn showed suppressed responses to those afferents in an SST2A-R-dependent manner. Intrathecally administered SST2A-R antagonist inhibited the development of mechanical hypersensitivity by intraplantar AITC injection and alleviated persistent mechanical hypersensitivity in the murine model of nociplastic pain. These results suggest that the activity of TRPA1 agonist-responsive afferents induces and maintains central sensitization by activating dorsal horn SSTn and suppressing GABAn via SST2A-R, resulting in altered nociception that manifests as mechanical hypersensitivity. PERSPECTIVE: This article presents experimental evidence that TRPA1 agonist-responsive afferents induce and maintain central sensitization at the spinal level by activating SST-expressing excitatory interneurons and suppressing GABAergic inhibitory interneurons via SST2A-R. Spinal SST2A-R may represent a promising target for treating mechanical pain hypersensitivity due to central sensitization by TRPA1 agonist-responsive afferents.

The relationship between neuropathic pain and lower urinary tract symptom scores in patients with primary Sjögren's syndrome

OBJECTIVE

To evaluate the effect of neuropathic pain on lower urinary tract symptoms (LUTS) scores in patients with primary Sjögren's syndrome (pSS).

METHODS

Seventy-two patients diagnosed with pSS were included in the study. The patients with pSS were divided into two groups according to the presence/absence of neuropathic pain. The Leeds Assessment of Neuropathic Symptoms and Signs (LANSS) questionnaire was recorded assess neuropathic pain. LUTS was evaluated using the International Prostate Symptom Score (IPSS), International Incontinence Consultation Questionnaire Short Form (ICIQ-SF) and Overactive Bladder Questionnaire (OAB-V8).

RESULTS

The mean age of the patients was 52.4 ± 11.2 years. Neuropathic pain was recorded in 21 (29.2%) patients. Among the patients, the number of patients with mild symptoms was recorded as 41 (56.9%), moderate symptoms in 25 (34.7%), and severe symptoms in 6 (8.3%) according to IPSS. IPSS and IPSS voiding subscores were statistically significantly higher in patients with neuropathic pain than non-neuropathic pain group (p = 0.035; p = 0.001, respectively). Although ICIQ-SF, OAB-V8 and IPSS storage subscores were found to be higher in patients with neuropathic pain group, there was no statistically significant difference between the groups (p = 0.299; p = 0.283; p = 0.237, respectively).

CONCLUSION

Neuropathic pain concomitant with PSS patients may negatively affect bladder voiding functions.

Short- and medium-term effects of a single session of pain neuroscience education on pain and psychological factors in patients with chronic low back pain. A single-blind randomized clinical trial

INTRODUCTION

Biopsychosocial approach in patients suffering chronic low back pain (CLBP) promotes pain self-management strategies. Current evidence recommends high dose of Pain Neuroscience Education (PNE) for clinically significant differences. However, the workload and time constraints experienced by healthcare providers impede the application of the recommended treatment regimen. In fact, Back School with a biomechanical model is the main approach to manage CLBP in public systems.

OBJECTIVE

The objective of this study is to explore the effect of a 60 min single session of PNE as an adjunct to back school on pain intensity and psychological variables patients with CLBP.

METHODS

A double-blind, two-arm randomized controlled clinical trial was conducted in patients with CLBP who attended back school sessions held in a Spanish public hospital. A total of 121 patients were randomized into control group, who received the Back School program during 5 weeks, and intervention group, who additionally received a single session of PNE. Patient-reported outcomes were the Numerical Pain Rating Scale, Central Sensitization Inventory, Pain Catastrophizing Scale, and Tampa Scale of Kinesiophobia, with a 12-week follow-up.

RESULTS

A total of 113 patients were analysed. Intervention and control group presented similar effects on pain and kinesiophobia. At follow-up, intervention group exhibited reduced sensitization and catastrophism scores compared with control, including the subscales. Additionally, PNE reduced the percentage of participants classified as having central sensitization compared with control.

CONCLUSIONS

Adding a single PNE session in the back school program did not reduce pain but improved psychological factors as central sensitization and pain catastrophizing at medium-term. This study highlights the potential of PNE to optimize treatment strategies for CLBP, especially in public health centres where time resources are scarce.

SIGNIFICANCE STATEMENT

Adding a single PNE session in the back school program did not reduce pain but improved psychological factors as central sensitization and pain catastrophism at medium-term.

Sensitization-associated and neuropathic-associated symptoms in patients with unilateral lateral elbow tendinopathy: an exploratory study

OBJECTIVES

We evaluate the presence of sensitization-associated symptoms and neuropathic pain features and identify if there is an association between these symptoms and pressure pain sensitivity, pain, and related-disability in lateral elbow tendinopathy.

METHODS

Thirty-seven (43% women, age: 45.5 ± 9.5 years) patients with lateral elbow tendinopathy completed: demographic (i.e. age, height, and weight); clinical (i.e. pain history, pain intensity, and Disabilities of the Arm, Shoulder and Hand); and psychophysical (i.e. pressure pain thresholds at the elbow, cervical spine, hand, and leg) outcomes, and the Central Sensitization Inventory and Self-administered Leeds Assessment of Neuropathic Symptoms and Signs questionnaires. Step-wise multiple linear regression models were performed to identify predictors of sensitization- or neuropathic-associated symptoms.

RESULTS

Six (16%) patients exhibited sensitization-associated symptoms (mean: 46.5, SD: 6.1), whereas 13 (35%) patients showed neuropathic-associated symptoms (mean: 13.5; SD: 1.4). Sensitization-associated symptoms were positively associated with neuropathic-associated symptoms (r = 0.538, P = .001) and negatively associated with pressure pain thresholds at the leg (r = -0.378, P = .021). Neuropathic-associated symptoms were positively associated with related-disability (r = 0.479, P = .003) and negatively associated with pressure pain threshold at the elbow (r = -0.394, P = .017). Stepwise regression analyses revealed that neuropathic-like symptoms explained 26.8% of the variance of sensitization symptoms (r2: 0.268), whereas pressure pain threshold at the elbow explained an additional 6.6% to neuropathic-like symptoms (r2: 0.334).

CONCLUSION

This explorative study identified sensitization- and neuropathic-associated symptoms in 16% and 35% of the people with lateral elbow tendinopathy. Sensitization- and neuropathic-associated symptoms were associated. Pressure pain sensitivity at the elbow (peripheral sensitization) was associated with neuropathic -associated symptoms.

The concept of nociplastic pain-where to from here?

ABSTRACT

Nociplastic pain, a third mechanistic pain descriptor in addition to nociceptive and neuropathic pain, was adopted in 2017 by the International Association for the Study of Pain (IASP). It is defined as "pain that arises from altered nociception" not fully explained by nociceptive or neuropathic pain mechanisms. Peripheral and/or central sensitization, manifesting as allodynia and hyperalgesia, is typically present, although not specific for nociplastic pain. Criteria for possible nociplastic pain manifesting in the musculoskeletal system define a minimum of 4 conditions: (1) pain duration of more than 3 months; (2) regional, multifocal or widespread rather than discrete distribution of pain; (3) pain cannot entirely be explained by nociceptive or neuropathic mechanisms; and (4) clinical signs of pain hypersensitivity present in the region of pain. Educational endeavors and field testing of criteria are needed. Pharmacological treatment guidelines, based on the three pain types, need to be developed. Currently pharmacological treatments of nociplastic pain resemble those of neuropathic; however, opioids should be avoided. A major challenge is to unravel pathophysiological mechanisms driving altered nociception in patients suffering from nociplastic pain. Examples from fibromyalgia would include pathophysiology of the peripheral as well as central nervous system, such as autoreactive antibodies acting at the level of the dorsal root ganglia and aberrant cerebral pain processing, including altered brain network architecture. Understanding pathophysiological mechanisms and their interactions is a prerequisite for the development of diagnostic tests allowing for individualized treatments and development of new strategies for prevention and treatment.

An interdisciplinary perspective on peripheral drivers of pain in rheumatoid arthritis

Pain is one of the most debilitating symptoms of rheumatoid arthritis (RA), and yet remains poorly understood, especially when pain occurs in the absence of synovitis. Without active inflammation, experts most often attribute joint pain to central nervous system dysfunction. However, advances in the past 5 years in both immunology and neuroscience research suggest that chronic pain in RA is also driven by a variety of abnormal interactions between peripheral neurons and mediators produced by resident cells in the local joint environment. In this Review, we discuss these novel insights from an interdisciplinary neuro-immune perspective. We outline a potential working model for the peripheral drivers of pain in RA, which includes autoantibodies, resident immune and mesenchymal cells and their interactions with different subtypes of peripheral sensory neurons. We also offer suggestions for how future collaborative research could be designed to accelerate analgesic drug development.