Central sensitisation in chronic pain conditions: latest discoveries and their potential for precision medicine

Exercise-induced changes in central sensitization outcomes in individuals with chronic musculoskeletal pain: A systematic review with meta-analysis

BACKGROUND AND OBJECTIVE

Temporal summation of pain (TSP) and conditioned pain modulation (CPM) are the two most commonly used clinical measures of central sensitization (CS). However, the effectiveness of exercise on TSP and CPM has yet to be evaluated. This review aims to investigate the effect of exercise alone on CS outcomes in individuals with chronic musculoskeletal pain.

DATABASES AND DATA TREATMENT

This is a systematic review and meta-analysis. MEDLINE, EMBASE, CINAHL, PEDro and Cochrane databases were searched. Data were extracted based on the exercise modality and grouped into aerobic, resistance, isometric, or motor control modalities. Risk of bias was assessed using RoB2, RoB2 for crossover trials and ROBINS-I tools. Quality of evidence was assessed using GRADE. Random-effects meta-analyses were conducted, with subgroup analysis conducted for each exercise modality.

RESULTS

The meta-analyses included thirteen studies, consisting of eight non-randomized studies, three randomized controlled trials and three randomized crossover trials. Data were categorized into four subgroups for analyses based on exercise modality. No statistically significant effect existed for both TSP and conditioned pain modulation. However, motor control exercise was found to have a significant enhancing effect on conditioned pain modulation. No significant differences were found between the exercise subgroup for both TSP and conditioned pain modulation.

CONCLUSIONS

We did not find an overall effect of physical exercise on TSP and CPM. However, subgroup analysis shows favourable effects of motor control exercise in individuals with chronic neck pain. Future research should focus on exercise modality and dosage and their role in the mechanism involved in TSP and CPM in predefined populations.

SIGNIFICANCE STATEMENT

Results from this study found that motor control exercise has a significant enhancing effect on conditioned pain modulation, with subgroup analysis showing favourable effects of motor control exercise in individuals with chronic neck pain. This indicates that physical exercise may have a positive effect on central sensitisation in individual with chronic neck pain. However, differential effects may exist between different types of exercise. These findings will inform understanding of neurobiological effects underlying chronic neck pain and may guide the development of more effective, personalised treatments.

Shared and distinct aberrations in frontal-striatal system functional patterns among patients with irritable bowel syndrome and major depressive disorder

BACKGROUND

Considering the high comorbidity, shared risk factors, and genetic pathways between irritable bowel syndrome (IBS) and major depressive disorder (MDD), we hypothesized that there would be both shared and disorder-specific alterations in brain function.

METHODS

A total of 39 IBS patients, 39 MDD patients, and 40 healthy controls (HCs) were enrolled and matched for sex, age, and educational level. All subjects underwent resting-state functional MRI. The clinical variables of anxiety, depression, gastrointestinal symptoms and alexithymia were recorded. The 12 subregions of the striatum were employed as seeds to assess their functional connectivity (FC) with every voxel throughout the whole brain.

RESULTS

Compared to HC, IBS and MDD patients exhibited aberrant frontal-striatal circuitry. We observed a common decrease in FC between the dorsal striatum and regions of the hippocampus, sensorimotor cortex, and prefrontal cortex (PFC) in both IBS and MDD patients. Patients with IBS exhibited disorder-specific decreases in FC within the striatum, along with reduced connectivity between the ventral striatum and sensorimotor cortex. In contrast, MDD patients showed disorder-specific hyperconnectivity in the medial PFC-limbic system. Receiver operating characteristic curve analysis showed that frontal-striatal FC values could serve as transdiagnostic markers of IBS and MDD. Within the IBS group, striatal connectivity was not only negatively associated with weekly abdominal pain days but also negatively correlated with the levels of anxiety and alexithymia.

CONCLUSIONS

This exploratory analysis indicated that patients with IBS and MDD exhibited both shared and disorder-specific frontal-striatal circuit impairments, potentially explaining both comorbidity and distinct phenotypes.

Application of the IASP Grading System to Identify Underlying Pain Mechanisms in Patients With Knee Osteoarthritis: A Prospective Cohort Study

OBJECTIVES

This study aimed to apply the International Association for the Study of Pain (IASP) grading system for identifying nociplastic pain in knee osteoarthritis (KOA) awaiting total knee arthroplasty (TKA) and propose criteria to fine-tune decision-making. In addition, the study aimed to characterize a "probable" versus "no or possible" nociplastic pain mechanism using biopsychosocial variables and compare both groups in their 1-year post-TKA response.

METHODS

A secondary analysis of baseline data of a longitudinal prospective study involving 197 patients with KOA awaiting total TKA in Belgium and the Netherlands was performed. Two approaches, one considering 4 and the other 3 pain locations (step 2 of the grading system), were presented. Linear mixed model analyses were performed to compare the probable and no or possible nociplastic pain mechanism groups for several preoperative biopsychosocial-related variables and 1-year postoperative pain. Also, a sensitivity analysis, comparing 3 pain mechanism groups, was performed.

RESULTS

Thirty (15.22%-approach 4 pain locations) and 46 (23.35%-approach 3 pain locations) participants were categorized under probable nociplastic pain. Irrespective of the pain location approach or sensitivity analysis, the probable nociplastic pain group included more woman, was younger, exhibited worse results on various preoperative pain-related and psychological variables, and had more pain 1-year post-TKA compared with the other group.

DISCUSSION

This study proposed additional criteria to fine-tune the grading system for nociplastic pain (except for discrete/regional/multifocal/widespread pain) and characterized a subgroup of patients with KOA with probable nociplastic pain. Future research is warranted for further validation.

Novel neurophysiological evidence for preserved pain habituation across chronic pain conditions

OBJECTIVE

The present study aimed to investigate whether subjective and objective measures of pain habituation can be used as potential markers for central sensitization across various chronic pain patients.

METHODS

Two blocks of contact-heat stimuli were applied to a non-painful area in 93 chronic pain patients (low back pain, neuropathic pain, and complex regional pain syndrome) and 60 healthy controls (HC). Habituation of pain ratings, contact-heat evoked potentials (CHEP), and sympathetic skin responses (SSR) was measured.

RESULTS

There was no significant difference in any measure of pain habituation between patients and HC. Even patients with apparent clinical signs of central sensitization showed no reduced pain habituation. However, prolonged baseline CHEP and SSR latencies (stimulation block 1) were found in patients compared to HC (CHEP: Δ-latency = 23 ms, p = 0.012; SSR: Δ-latency = 100 ms, p = 0.022).

CONCLUSION

Given the performed multimodal neurophysiological testing protocol, we provide evidence indicating that pain habituation may be preserved in patients with chronic pain and thereby be of limited use as a sensitive marker for central sensitization. These results are discussed within the framework of the complex interactions between pro- and antinociceptive mechanism as well as methodological issues. The prolonged latencies of CHEP and SSR after stimulation in non-painful areas may indicate subclinical changes in the integrity of thermo-nociceptive afferents, or a shift towards antinociceptive activity. This shift could potentially affect the relay of ascending signals.

SIGNIFICANCE

Our findings challenge the prevailing views in the literature and may encourage further investigations into the peripheral and central components of pain habituation, using advanced multimodal neurophysiological techniques.

Central sensitization symptoms in vulvodynia: exploring the role of temperament, personality traits, childhood adverse events, defense mechanisms, and mental pain on quality of life

BACKGROUND

Vulvodynia is a chronic pain syndrome characterized by persistent vulvar pain, occurring without clinically identifiable disorders. Central sensitization (CS) is suggested to play a role in the pathophysiology of vulvodynia, as for other nociplastic pain conditions.

AIM

This study delves into the complex interplay between psychosocial factors and CS burden in women with vulvodynia, aiming to identify potential predictors (temperament, personality traits, childhood adverse events, defense mechanisms, and mental pain) and understand their impact on quality of life (QoL).

METHODS

A cohort-based cross-sectional web survey of 357 women with vulvodynia.

OUTCOMES

Outcomes included 8 self-report measures to assess the Central Sensitization Inventory (CSI) and psychological variables, including sensory processing sensitivity, traumatic experiences, personality traits, defense mechanisms, and mental pain.

RESULTS

Hierarchical multiple regression analyses were conducted in study 1, revealing that the following predicted higher CSI scores in women with vulvodynia: higher emotional overexcitability, decreased low sensory threshold, increased bodily threat experiences, elevated psychoticism, greater use of immature and neurotic defense mechanisms, and heightened mental pain. The final regression model identified the following as the strongest predictors of CS: low sensory threshold (β = 0.316), bodily threat experiences (β = 0.145), neurotic defenses (β = 0.210), and mental pain (β = 0.269). In study 2, the model presented interactions among these psychological factors in predicting CSI values explaining 48.9% of the variance in CS, 30.3% in psychological QoL, and 57.1% in physical QoL.

CLINICAL TRANSLATION

This model opens discussion for tailored psychological interventions aimed to improve overall QoL in women with vulvodynia.

STRENGTHS AND LIMITATIONS

Strengths of the study include innovative insights into the interplay between psychological variables and the construct of CS and quality of life. As a limitation, the research was conducted as a cross-sectional study with self-reported measures.

CONCLUSION

The study calls for comprehensive assessments that consider physical and mental aspects, paving the way for holistic health care approaches in the management of vulvodynia.

Effects of Executive Functions and Cognitive Variables in Experimentally Induced Acute Pain Perception during a Distraction Task: A Study on Asymptomatic Pain-Free Individuals

The aim of this study was to investigate the influence of executive functioning and cognitive performance on individual experimentally induced pain perception during distractor tasks in an asymptomatic pain-free population. A total of 59 healthy pain-free subjects (59.3% women, mean age: 46.5 ± 24.7 years) completed a battery test that assessed execution functions (cognitive flexibility, working memory, mental inhibition), attention level, and psychological aspects (anxiety/depressive levels-HADS, pain catastrophizing-PCS, pain anxiety symptoms-PASS 20, sleep quality-PSQI) before conducting two n-back distraction tasks. Pain was experimentally induced with a thermal stimulus that was able to induce moderate pain (70/100 points) and applied to the non-dominant forearm. The thermal stimulus was applied before and during both (one-back and two-back) distraction tasks. The analyses consisted of separated repeated-measures ANOVA that considered the functioning on each test (cognitive flexibility, working memory, mental inhibition, selective attention) and controlled for sociodemographic and psychological aspects by comparing the pain intensity at the baseline and during the one-back and two-back distractor tasks. All ANOVAs found a significant effect of the distraction task, which indicates that the perceived pain intensity scores were lower during the one-back and two-back tasks (p < 0.001) as compared with the baseline. No interaction effect between the distractor tasks and working memory (p = 0.546), mental inhibition (p = 0.16), cognitive flexibility (p = 0.069), or selective attention (p = 0.105) was identified. The current study found that a distraction task decreased the perceived intensity of experimentally induced pain in asymptomatic pain-free individuals and that this effect was not related to executive function or attention levels.

Immersive VR movement visualization in patients with hemophilic knee arthropathy: randomized, multicenter, single-blind clinical trial

PURPOSE

To evaluate the efficacy of an immersive movement visualization intervention in patients with hemophilia and hemophilic knee arthropathy.

MATERIALS AND METHODS

Randomized, single-blind clinical study. Twenty-eight patients with hemophilia were recruited. Patients were randomized to an experimental group (four weeks of immersive movement visualization) and a control group (no intervention). The intensity of pain, pressure pain threshold in the knee, tibialis anterior muscle, lower back level, conditioned pain modulation, range of knee motion, and lower limb functionality were evaluated.

RESULTS

There were statistically significant differences in the intergroup effect on knee pain intensity (F = 23.71; p < 0.001) and lower limb functionality (F = 7.11; p = 0.003). 42.86% of the patients in the experimental group exhibited changes greater than the minimum detectable change (MDC) in functionality. 39.29% of the patients subject to the intervention experienced changes greater than the MDC in the knee pressure pain threshold.

CONCLUSIONS

Immersive motion visualization can improve the intensity of joint pain and functionality in patients with hemophilic knee arthropathy. Functionality, pressure pain threshold, and pain intensity improved in those patients who conducted immersive movement visualization.Implications for rehabilitationImmersive visualization of movement significantly improves intensity of joint pain, functionality, pressure pain threshold, joint health, and conditioned pain modulation in patients with hemophilic knee arthropathy.The fact that it is a therapy without potential aversive stimuli makes it a possible access pathway for patients with high levels of kinesiophobia and/or catastrophism.This low-cost, home-based technology allows its use in patients far from hemophilia reference centers or with difficult access to physiotherapy treatments.The immersive visualization of movement influences the democratization of treatment, in accordance with the WHO's Sustainable Development Goal 3 (health and well-being for all).

Open-Label Placebo Injection for Chronic Back Pain With Functional Neuroimaging: A Randomized Clinical Trial

Importance

Chronic back pain (CBP) is a leading cause of disability. Placebo treatments often provide as much pain relief as bona fide treatments, such as steroid injections. Open-label (honestly prescribed) placebos (OLPs) may relieve CBP without deception, but OLP mechanisms remain poorly understood.

Objective

To investigate the long-term efficacy and neurobiological mechanisms of OLP for CBP.

Design, Setting, and Participants

A randomized clinical trial of CBP with longitudinal functional magnetic resonance imaging (MRI) comparing OLP with usual care, with 1-year follow-up, was conducted in a university research setting and a community orthopedic clinic. Participants were individuals aged 21 to 70 years with CBP. The trial was conducted from November 2017 to August 2018, with 1-year follow-up completed by November 2019. Data analysis was performed from April 2020 to May 2024. The primary analysis was conducted on an intention-to-treat sample.

Interventions

Participants randomized to OLP received a 1-time subcutaneous lumbar saline injection presented as placebo accompanied by information about the power of placebo to relieve pain, alongside their ongoing care. Usual care participants continued their ongoing care.

Main Outcomes and Measures

The primary outcome was pain intensity (0-10, with 0 indicating no pain and 10 the most intense) at 1 month posttreatment. Secondary outcomes included pain interference, depression, anxiety, anger, and sleep quality. Functional MRI was performed before and after treatment during evoked and spontaneous back pain.

Results

A total of 101 adults (52 [51.4%] females; mean [SD] age, 40.4 [15.4] years) with moderate severity CBP (mean [SD], 4.10 [1.25] intensity; duration, 9.7 [8.5] years) were enrolled. Compared with usual care, OLP reduced CBP intensity posttreatment (relative reduction, 0.61; Hedges g = 0.45; 95% CI, -0.89 to 0.04; P = .02). Through 1-year follow-up, pain relief did not persist, although significant benefits were observed for depression, anger, anxiety, and sleep disruption (Hedges g = 0.3-0.5; all P < .03). Brain responses to evoked back pain for OLP vs usual care increased in rostral anterior cingulate and ventromedial prefrontal cortex and decreased in somatomotor cortices and thalamus. During spontaneous pain, functional connectivity analyses identified OLP vs usual care increases in ventromedial prefrontal cortex connectivity to the rostral ventral medulla, a pain-modulatory brainstem nucleus. No adverse effects of treatment were reported by participants.

Conclusions and Relevance

In this randomized clinical trial of OLP vs usual care, a single nondeceptive placebo injection reduced CBP intensity for 1 month posttreatment and provided benefits lasting for at least 1 year posttreatment. Brain mechanisms of OLP in a clinical population overlap with those of deceptive placebos in healthy volunteers, including engagement of prefrontal-brainstem pain modulatory pathways.

Trial Registration

ClinicalTrials.gov Identifier: NCT03294148.

Linking Intra-Articular Inflammatory Biomarkers with Peripheral and Central Sensitization in Late-Stage Knee Osteoarthritis Pain: A Pilot Study

Background/Objectives: To investigate if intra-articular biomarkers relate to peripheral and central sensitization in patients with late-stage knee osteoarthritis (KOA). Methods: A total of 17 (6M, 11F) patients (aged 69 ± 10 years) were assessed for peripheral (pressure pain thresholds (PPT)) and central (temporal summation (TS) and conditioned pain modulation (CPM)) sensitization the day before total knee arthroplasty. Synovial fluid was collected during surgery and assayed for IL-6, IL-8, IL-10, TNF-α, CXCL-10, BDNF, NGF, CCL2, CCL5, VEGF, IL-1RI, MMP-1, MMP-7, IL-1β, and CXCL-9. Associations of biomarkers and their combinations reflecting chronic (CXCL-9) and acute ((CCL2×CXCL-10)/IL-10)) inflammation, cartilage degeneration (MMP-1×MMP-7), and neurotrophy (NGF×BDNF) with PPT, TS, and CPM were analyzed by bivariate correlations and by multiple linear regression analyses corrected for BMI, sex, and age. Results: The medial joint line and the superior medial joint region showed the lowest PPT. Higher acute inflammation related significantly to worse pressure tenderness at the superior medial joint region (R2 = 0.642; p = 0.010). Cartilage degeneration and chronic inflammation were associated with both absolute (R2 = 0.827; p = 0.001) and relative CPM (R2 = 0.882; p < 0.001). Acute inflammation and neurotrophy were related to relative TS at the m. tibialis anterior (R2 = 0.728; p = 0.02). Conclusions: This study demonstrates that increased levels of intra-articular biomarkers of acute inflammation are related to peripheral sensitization and that biomarkers of cartilage degeneration and chronic inflammation are associated with central sensitization. These results may be a stepping-stone toward a better understanding of the working mechanism of peripheral and central sensitization in KOA pain and the development of more targeted therapeutic interventions.

The Influence of Pain Hypersensitivity and Psychological Factors on Pain and Disability in the Transition From Acute to Chronic Low Back Pain: A Longitudinal Exploratory Investigation and Cluster Analysis

Pain hypersensitivity is present in some people with acute low back pain (LBP) and thought to be involved in the development of chronic LBP. Early evidence suggests that pain hypersensitivity in acute LBP precedes poor long-term outcome. We aimed to examine whether the presence of pain hypersensitivity in acute LBP influenced recovery status at 6 months and differentiated how pain and disability changed over time. Participants with acute nonspecific LBP (<6 weeks after pain onset, N = 118) were included in this longitudinal study. Quantitative sensory testing, including pressure and heat pain thresholds, and conditioned pain modulation and questionnaires were compared at baseline and longitudinally (at 3 and 6 months) between recovered and unrecovered participants. Using k-means clustering, we identified subgroups based on baseline sensory measures alone, and in combination with psychological factors, and compared pain and disability outcomes between subgroups. Sensory measures did not differ at baseline or longitudinally between recovered (N = 50) and unrecovered (N = 68) participants. Subgrouping based on baseline sensory measures alone did not differentiate pain or disability outcomes at any timepoint. Participants with high psychological distress at baseline (N = 19) had greater disability, but not pain, at all timepoints than those with low psychological distress, regardless of the degrees of pain sensitivity. Our findings suggest that pain hypersensitivity in acute LBP does not precede poor recovery at 6 months or differentiate how pain and disability change over time. High psychological distress during acute LBP is associated with unremitting and pronounced disability, while pain severity is unaffected. PERSPECTIVE: Pain hypersensitivity is thought to be involved in the transition to chronic LBP. Contradictory to prevailing hypothesis, our findings suggest pain hypersensitivity alone in acute LBP does not precede poor recovery. High psychological distress in acute LBP has a stronger influence than pain hypersensitivity on long-term disability, but not pain outcomes.

Evaluating Sensitization-associated, Neuropathic-like Symptoms and Psychological Factors in Patients With Interstitial Lung Disease

The aims of this study were to phenotype pain in patients with interstitial lung disease (ILD) by investigating the association between sensitization-associated symptoms with quality of life, anxiety/depression, pain catastrophizing, and kinesiophobia levels and identifying those risk factors explaining the variance of quality of life in individuals with ILD and pain. One hundred and thirty-two (38.6% women, mean age: 70, standard deviation: 10.5 years) patients with ILD completed clinical (age, sex, height, weight), psychological (Hospital Anxiety and Depression Scale [HADS] and the Pittsburgh Sleep Quality Index), and health-related quality of life (EQ-5D-5L) variables, as well as the Central Sensitization Inventory (CSI), the Self-Report Leeds Assessment of Neuropathic Symptoms (S-LANSS), Pain Catastrophizing Scale, and Tampa Scale for Kinesiophobia (TSK-11) questionnaires. The prevalence of sensitization-associated symptomatology (CSI), neuropathic-like features (S-LANSS), anxiety symptoms, depressive symptoms, or poor sleep was 20.5%, 23.5%, 23.6%, 22.9%, or 51.6%. Significant associations between CSI, S-LANSS, HADS-A, HADS-D, Pain Catastrophizing Scale, TSK-11, and EQ-5D-5L (.220 < r < .716) were found. The regression analysis revealed that CSI, TSK-11, and HADS-D explained 44.8% of the variance of EQ-5D-5L (r2 adjusted: .448). This study found the presence of sensitization-associated and neuropathic-like symptoms as well as other central nervous system-derived symptoms, such as anxiety, depression, poor sleep, pain catastrophizing, and kinesiophobia in 25% of ILD patients with pain. Sensitization-associated symptoms, depression, and kinesiophobia were associated with a worse quality of life. These findings would support that individuals with ILD can exhibit different pain phenotypes, including nociplastic-like pain phenotype based on self-reported measurements. PERSPECTIVE: Pain in patients with ILD can fulfill features of different phenotypes, including nociplastic pain, when sensory, emotional, and cognitive mechanisms are involved at the same time.

Reliability of Pressure Pain Threshold (PPT) and Conditioned Pain Modulation (CPM) in Participants with and without Chronic Shoulder Pain

The objectives of this study were to estimate the intra-rater and inter-rater reliability of the Pressure Pain Threshold (PPT) and Conditioned Pain Modulation (CPM) in healthy participants and patients with chronic shoulder pain. Additionally, the Standard Error of Measurement (SEM) and Smallest Detectable Change (SDC) were calculated. Thirty-one healthy volunteers and twenty patients with chronic shoulder pain were assessed using the PPT and CPM by two raters, with a 24 h interval between sessions. Excellent intra-rater reliability was demonstrated for PPT, with similar SEM and SDC when assessed by the same rater. The inter-rater reliability for PPTs in patients was moderate to good (ICC = 0.59-0.89) with higher SEM (73.83-121.98 kPa) and SDC (61.58-97.59) values than the asymptomatic group (ICC = 0.92-0.96, SEM = 49.61-103.12 kPa, SDC = 42.01-56.30) respectively. CPM's intra-rater reliability was good (ICC = 0.82) in the patients and moderate (ICC = 0.67) in the asymptomatic group, while inter-rater reliability was low for the asymptomatic group (ICC = 0.37) and extremely low (ICC = 0.074) for the patients, with comparable SEM and SDC outcomes in both groups. PPT and CPM measurements are highly reliable when conducted by the same rater on the same day. Patients had lower inter-rater PPT reliability but better intra-rater CPM reliability. Clinicians need to be mindful of potential variability when interpreting these test results.

Establishing central sensitization inventory cut-off values in Dutch-speaking patients with chronic low back pain by unsupervised machine learning

BACKGROUND

Human Assumed Central Sensitization (HACS) is involved in the development and maintenance of chronic low back pain (CLBP). The Central Sensitization Inventory (CSI) was developed to evaluate the presence of HACS, with a cut-off value of 40/100. However, various factors including pain conditions (e.g., CLBP), contexts, and gender may influence this cut-off value. Unsupervised clustering approaches can address these complexities by considering diverse factors and exploring possible HACS-related subgroups. Therefore, this study aimed to determine the cut-off values for a Dutch-speaking population with CLBP based on unsupervised machine learning.

METHODS

Questionnaire data covering pain, physical, and psychological aspects were collected from patients with CLBP and aged-matched healthy controls (HC). Four clustering approaches were applied to identify HACS-related subgroups based on the questionnaire data and gender. The clustering performance was assessed using internal and external indicators. Subsequently, receiver operating characteristic (ROC) analysis was conducted on the best clustering results to determine the optimal cut-off values.

RESULTS

The study included 63 HCs and 88 patients with CLBP. Hierarchical clustering yielded the best results, identifying three clusters: healthy group, CLBP with low HACS level, and CLBP with high HACS level groups. The cut-off value for the overall groups were 35 (sensitivity 0.76, specificity 0.76).

CONCLUSION

This study found distinct patient subgroups. An overall CSI cut-off value of 35 was suggested. This study may provide new insights into identifying HACS-related patterns and contributes to establishing accurate cut-off values.

Psychosocial Factors, Sleep, and Central Pain Processing for Making a Prognosis About Recovery of Pain, Function, and Quality of Life After Rotator Cuff Repair: An Exploratory Longitudinal Study

OBJECTIVE: To explore modifiable psychosocial factors, sleep-related variables, indices of central pain processing and patients' characteristics as potential prognostic factors for pain, shoulder function, and quality of life (QoL) 1 year after rotator cuff repair. DESIGN: This observational longitudinal study included 142 patients who were undergoing rotator cuff repair. All measures took place pre-rotator cuff repair (T0), and 12 weeks (T1) and 12 months (T2) after rotator cuff repair. METHODS: Mixed-effects linear regression modeled relationships between the Western Ontario Rotator Cuff Index (WORC, model A), the Subjective Shoulder Value (SSV, model B), and EuroQol's EQ-5D-5L for QoL (model C), and potential prognostic factors over time. Factors included psychosocial variables, sleep-related indices, and proxies of central pain processing. Patients' age, sex, and body mass index complemented the analyses. RESULTS: At follow-up (T2), data from 124 participants were available for analysis. Five prognostic factors were identified for the 1-year outcome. Better expectations for symptom reduction (P<.0001, -1.4 mm) and an increase in Douleur Neuropathique 4 score (P = .0481, -0.9 mm) affected the evolution of WORC over time (model A). An increase in injury perception subscale consequence (P = .0035, 0.04%) influenced the SSV trajectory (model B). In addition, when sleep quality (P = .0011, -0.13%) and sleep efficiency (P = .0002, 0.005%) improved, the EQ-5D-5L slope was affected (model C). CONCLUSION: Addressing cognitions, pain mechanisms and sleep behavior prior to rotator cuff repair can identify people who are at risk of a poor outcome after surgery. J Orthop Sports Phys Ther 2024;54(8):530-540. Epub 4 July 2024. doi:10.2519/jospt.2024.12398.

Epigenetic Landscapes of Pain: DNA Methylation Dynamics in Chronic Pain

Chronic pain is a prevalent condition with a multifaceted pathogenesis, where epigenetic modifications, particularly DNA methylation, might play an important role. This review delves into the intricate mechanisms by which DNA methylation and demethylation regulate genes associated with nociception and pain perception in nociceptive pathways. We explore the dynamic nature of these epigenetic processes, mediated by DNA methyltransferases (DNMTs) and ten-eleven translocation (TET) enzymes, which modulate the expression of pro- and anti-nociceptive genes. Aberrant DNA methylation profiles have been observed in patients with various chronic pain syndromes, correlating with hypersensitivity to painful stimuli, neuronal hyperexcitability, and inflammatory responses. Genome-wide analyses shed light on differentially methylated regions and genes that could serve as potential biomarkers for chronic pain in the epigenetic landscape. The transition from acute to chronic pain is marked by rapid DNA methylation reprogramming, suggesting its potential role in pain chronicity. This review highlights the importance of understanding the temporal dynamics of DNA methylation during this transition to develop targeted therapeutic interventions. Reversing pathological DNA methylation patterns through epigenetic therapies emerges as a promising strategy for pain management.

Chronic Musculoskeletal Pain and Central Sensitization-Related Symptoms in Chilean Victims of Political Violence During the 1973 to 1990 Dictatorship

People who suffer political violence (PV) are at risk of developing mental illness, chronic noncommunicable diseases, chronic pain, and decreased life expectancy. However, these indicators have been studied primarily in war veterans and refugees. The objective of this study was to estimate the prevalence of chronic musculoskeletal pain (CMP) and central sensitization-related symptoms (CSRS) in Chilean victims of PV during the 1973 to 1990 dictatorship. A cross-sectional observational multicenter study was conducted. Three hundred twenty-five people from six centers of a Ministry of Health of Chile program participated. The presence of CMP was determined by a history of pain ≥3 months, and CSRS was determined using the central sensitization inventory. About 69.23% of the sample had CMP (76.85% of females and 56.56% of males). About 60% of people with CMP showed a high level of CSRS severity (66.67% females and 44.93% males). Females presented significantly higher proportions of CMP (p < .001), and there was an association between CSRS severity and being female (p = .004). Chilean victims of PV during the 1973 to 1990 dictatorship presented a high prevalence of CMP and high-level CSRS severity. Both conditions affected females more than males. Future studies are needed to further delve into these variables' behavior and their influence on the quality of life in this population.

CPM-Related Mechanisms Could Play a Key Role in the Effects on Pain Sensitivity Induced by Manual Therapy: Three Crossover Trials Investigating the Effects of Manual Pressure

Objective: The aim of this study is to assess whether pain-inducing manual pressure (PIMP) leads to effects on pressure pain threshold (PPT) mediated by conditioned pain modulation (CPM) and whether these effects are influenced by the intensity and repetition of the stimulus. Additionally, the influence of psychological factors and physical activity on the response to PIMP was explored. Methods: A total of 72 pain-free students were randomly assigned to three crossover trials. Trial 1 compared the effects of PIMP with the cold pressor task and pain-inducing electrostimulation. Trial 2 compared the effects of manual pressure that elicited moderate pain, mild pain, and no pain. Trial 3 compared a single PIMP stimulation with four stimuli applied at the same site or at different sites. Results: PIMP produced a lower increase in PPT than cold pressor task and no difference with electrostimulation. Manual pressure that caused moderate pain led to a greater increase in PPT compared to mild pain and pain-free application. Repetition of PIMP stimulus, whether at the same or different sites, did not significantly increase PPT compared to a single stimulation. No association with psychological factors or physical activity was found. Conclusions: PIMP produces an increase in PPT, suggesting the involvement of CPM-related mechanisms.

Cross-sectional experimental assessment of pain modulation as part of multidimensional profiling of people with cervicogenic headache: protocol for a feasibility study

BACKGROUND

An endogenous pain modulation profile, reflecting antinociceptive and pronociceptive mechanisms, may help to direct management by targeting the involved pain mechanism. For individuals with cervicogenic headache (CeH), the characteristics of such profiles were never investigated. However, the individual nature of experiencing pain demands profiling within a multidimensional framework including psychosocial lifestyle characteristics. The objective of the current protocol is to assess the pain modulation profile, which includes psychosocial lifestyle characteristics among people with CeH.

METHODS AND ANALYSIS

A protocol is described to map pain modulation profiles in people with CeH. A cross-sectional non-randomised experimental design will be used to assess feasibility of mapping these profiles. The pain modulation profile is composed based on results on the Depression, Anxiety, Stress Scale, Pittsburgh Sleep Quality Index, Headache Impact Test and on responses to temporal summation of pain (pinprick), conditioned pain modulation and widespread hyperalgesia (mechanical pressure pain threshold and cuff algometry). Primary analyses will report results relating to outcomes on feasibility. Secondary analyses will involve an analysis of proportions (%) of the different psychosocial lifestyle profiles and pain profiles.

ETHICS AND DISSEMINATION

Ethical approval was granted by the Ethics Committee Research UZ/KU Leuven (Registration number B3222024001434) on 30 May 2024. Results will be published in peer-reviewed journals, at scientific conferences and, through press releases. Protocol V.3. protocol date: 3 June 2024.

Pain Neuroscience Education for Acute Pain

In musculoskeletal and sports medicine, pain has traditionally been linked to tissue injury, often assuming a linear correlation between tissue damage and pain intensity. However, modern pain science has illuminated the complexity of the human pain experience, incorporating psychosocial elements, nervous system sensitization, immune responses, and structural changes in the brain as factors. This contemporary understanding of pain has proven highly beneficial for both clinicians treating individuals in pain and those experiencing pain. Pain neuroscience education (PNE) provides individuals in pain with an understanding of the underlying neurobiology and neurophysiology of their pain experience, which has been shown to result in decreased self-reported pain, reduced disability, the alleviation of fear and fear-avoidance behaviors, diminished pain catastrophizing, and improved movement. Currently, research on PNE predominantly focuses on interventions with individuals with persistent or chronic pain conditions. However, those who experience acute, sub-acute, and perioperative pain also have the potential for elevated levels of fear, fear-avoidance, and pain catastrophizing, indicating potential benefits from PNE. This invited commentary seeks to inform readers about the latest advancements in pain science and propose a conceptual model for delivering PNE in acute pain experiences.

Level of Evidence

5.

Is the Central Sensitization Inventory (CSI) associated with quantitative sensory testing (QST)? A systematic review and meta-analysis

Central sensitization (CS) involves an amplification of neural processing within the central nervous system that can result in widespread pain patterns and hypersensitivity to stimuli. The Central Sensitization Inventory (CSI) and various quantitative sensory testing (QST) methods purport to assess clinical markers of CS. The purpose of this systematic review and meta-analysis was to summarize and quantify the associations between total CSI scores and QST measures from previous studies. A systematic search identified 39 unique studies that were deemed eligible for the systematic review and 33 studies for meta-analyses (with 3314 subjects and 154 effect sizes), including five QST modalities: conditioned pain modulation, temporal summation, pressure pain threshold, heat pain threshold, and cold pain threshold. The meta-analysis yielded statistically significant CSI-QST correlations in total subject samples for all five QST modalities. The strongest associations were identified between CSI scores and pain threshold testing, especially pressure pain threshold, in which 51% of effects sizes, from 29 studies and 3071 subjects, were determined to be in a medium to large range.

Effect of exposure-based vs traditional cognitive behavior therapy for fibromyalgia: a two-site single-blind randomized controlled trial

ABSTRACT

Fibromyalgia is a debilitating pain condition for which treatment effects are typically modest. The most evaluated psychological treatment is traditional cognitive behavior therapy (T-CBT), but promising effects have recently been seen in exposure-based cognitive behavior therapy (Exp-CBT). We investigated whether Exp-CBT was superior to T-CBT in a randomized controlled trial. Self-referred participants with fibromyalgia (N = 274) were randomized (1:1) to 10 weeks of Exp-CBT or T-CBT. Treatments were delivered online and presented as "CBT for fibromyalgia." Participants were assessed at baseline, weekly during treatment, posttreatment, and at 6- and 12-month follow-up. Primary outcome was the difference in reduction in fibromyalgia severity as measured using the Fibromyalgia Impact Questionnaire (FIQ) over 11 assessment points from baseline to posttreatment, modelled within an intention-to-treat framework using linear mixed effects models fitted on multiple imputed data. Approximately 91% of weekly FIQ scores were collected over the main phase. There was no significant difference between Exp-CBT and T-CBT in the mean reduction of fibromyalgia severity from pretreatment to posttreatment (b = 1.3, 95% CI -3.0 to 5.7, P = 0.544, d = -0.10). Minimal clinically important improvement was seen 60% in Exp-CBT vs 59% in T-CBT. Effects were sustained up to 12 months posttreatment. This well-powered randomized trial indicated that Exp-CBT was not superior to T-CBT for fibromyalgia. Both treatments were associated with a marked reduction in fibromyalgia severity, and the online treatment format might be of high clinical utility. T-CBT can still be regarded a reference standard treatment that remains clinically relevant when compared to novel treatment approaches.

Central sensitization: its prevalence and impact on quality of life among hemodialyzed patients

BACKGROUND/AIM

Data on the role of central sensitization in hemodialyzed patients are scarce. The aim was to identify the impact of central sensitization on quality of life and elucidate the risk factors for the development of central sensitization in patients receiving hemodialysis.

METHODS

Central sensitization, quality of life, psychological well-being, and sleep were assessed by the Central Sensitization Inventory (CSI), abbreviated version of the World Health Organization Quality of Life Instrument (WHOQOL-BREF), Hospital Anxiety and Depression Scale (HADS), and Jenkins Sleep Evaluation Scale (JSS), respectively. The effect of central sensitization on quality of life and the predictors of the development of central sensitization were assessed by regression analyses.

RESULTS

The frequency of central sensitization was 48% in the study population (n = 100). Patients with central sensitization had significantly higher pain intensity, worse sleep quality, and more impaired psychological status (p < 0.05 for all). The CSI score negatively affected all quality of life domains on its own (p < 0.001 for all, adjusted R2 ranged from 0.17 to 0.47). Dialysis vintage (OR, 0.8; 95% CI, 0.7 to 1.0), pain (OR, 1.5; 95% CI, 1.1 to 2.0), JSS (OR, 1.3; 95% CI, 1.1 to 1.5), and HADS-total (OR, 1.1; 95% CI, 1.0 to 1.2) were determined as the independent risk factors for central sensitization (p < 0.05 for all).

CONCLUSION

This study confirms that given the high frequency of central sensitization and its significant negative impact on quality of life, the presence of central sensitization should be investigated in patients undergoing hemodialysis.

Special Issue "Latest Research in Post-COVID (Long COVID): Pathological and Treatment Studies of Sequelae and Complications"

The Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) pathogen provoked the most unprecedented sanitary outbreak of the current century by causing coronavirus disease 2019 (COVID-19), which has led to approximately 775 million confirmed cases and more than 7 million deaths globally [...].

Phenotyping of chronic pain in breast cancer survivors: an original study using the cancer pain phenotyping (CANPPHE) Network multidisciplinary international guidelines

PURPOSE

The primary aim of this cross-sectional study is to examine the prevalence of pain phenotypes in breast cancer survivors (BCS). A secondary aim entails examining whether health related quality of life differs between the main pain phenotypes in BCS.

METHODS

BCS who experienced chronic pain were asked to complete the numeric pain rating scale for pain, Margolis pain diagram, and short form 36 (SF-36). Following administration of questionnaires and quantitative sensory examinations were applied. To determine the prevalence of the predominant type of pain, a recently proposed classification system by the Cancer Pain Phenotyping (CANPPHE) Network was used.

RESULTS

Of the 86 female participants, 19 (22.09%) had dominant neuropathic pain, 18 (20.93%) had dominant nociceptive pain and 14 (16.28%) had dominant nociplastic pain. 35 participants (40.70%) were classified as having mixed pain. One-way ANOVA revealed a significant difference between the four pain groups for the SF-36 general health (F = 3.205, p = 0.027), social functioning (F = 4.093, p = 0.009), and pain (F = 3.603, p = 0.017) subscale scores.

CONCLUSION

This study found that pain in BCS was mostly of mixed phenotype, followed by predominantly neuropathic and nociplastic pain. Furthermore, it was found that, compared to BCS with predominant neuropathic and nociceptive pain, BCS with predominant nociplastic pain have lower health related quality of life in the areas of bodily pain and social functioning.

Anatomo-physiological basis and applied techniques of electrical neuromodulation in chronic pain

Chronic pain, a complex and debilitating condition, poses a significant challenge to both patients and healthcare providers worldwide. Conventional pharmacological interventions often prove inadequate in delivering satisfactory relief while carrying the risks of addiction and adverse reactions. In recent years, electric neuromodulation emerged as a promising alternative in chronic pain management. This method entails the precise administration of electrical stimulation to specific nerves or regions within the central nervous system to regulate pain signals. Through mechanisms that include the alteration of neural activity and the release of endogenous pain-relieving substances, electric neuromodulation can effectively alleviate pain and improve patients' quality of life. Several modalities of electric neuromodulation, with a different grade of invasiveness, provide tailored strategies to tackle various forms and origins of chronic pain. Through an exploration of the anatomical and physiological pathways of chronic pain, encompassing neurotransmitter involvement, this narrative review offers insights into electrical therapies' mechanisms of action, clinical utility, and future perspectives in chronic pain management.

Retrospective review of the efficacy for sublingual ketamine in the treatment of chronic low back pain defined by a cause and central functional pain symptom focused clinical model

PURPOSE

Chronic low back pain is a leading cause of disability worldwide. A clinical model for its cause is lacking. Defining a cause based clinical model and a framework of understanding back pain in terms of peripheral structural and central functional pain is essential for optimal management.

MATERIALS AND METHODS

We describe the results of the largest published audit of 41 chronic low back pain patients, receiving outpatient sublingual ketamine therapy for defined central functional pain along with conventional peripheral structural pain management. Our clinical model assigns Movement Dysfunction as the primary cause for low back pain symptoms and restores it with Movement Therapy focused rehabilitation which is also defined. Patients were derived from a tertiary single neurosurgical specialist practice in Brisbane Australia over a three year period.

RESULTS

Severe pain and disability measurements more than halved and only 13% of patients ceased ketamine prematurely due to predominantly non-sinister side effects common to all pharmaceutical therapies. All other surveyed metrics of utility were highly favourable in this challenging cohort of chronic back pain patients biased to poor outcomes.

CONCLUSIONS

Outpatient ketamine maintains high efficacy and safety used in conjunction with a unique clinical model that describes chronic low back pain.

Assessment of Multisensory Sensitivity May Assist With the Management of Children With Chronic Pain

Chronic pain is a significant problem in adults; however, it can also be challenging to evaluate and manage effectively in pediatric and adolescent populations. Many theories implicate different factors that cause pain to become chronic, more severe, or more detrimental to function. There is emerging evidence for the role of generalized multisensory sensitivity (MSS) as a contributing factor to chronic pain in the adult population; however, similar evidence in the pediatric literature is lacking. Thus, the purpose of this case series is to highlight the clinical use of MSS assessment in children and adolescents with chronic pain to better phenotype and provide targeted treatment. In this case series, we reviewed 5 patients between 12 and 16 years of age who received evaluation for multifocal, chronic pain in a multidisciplinary pain clinic. During the initial consultations, we reviewed the medical records, completed a full medical history, performed a physical examination, and assessed for MSS. It is theorized that MSS is a marker of increased central nervous system sensitivity to sensory input that may also impact pain processing and, potentially, a poorer prognosis. Four patients with MSS appeared to benefit from the inclusion of additional therapies, such as desensitization and occupational therapy, which was in contrast to the patient without notable MSS. Based on anecdotal observation of these 5 cases, increased sensory hypersensitivity is 1 additional factor that may be used to delineate possible neurobiological mechanisms and aid in the treatment decision-making for this challenging population.

Complex regional pain syndrome: advances in epidemiology, pathophysiology, diagnosis, and treatment

Complex regional pain syndrome (CRPS) is a rare pain disorder that usually occurs in a limb after trauma. The features of this disorder include severe pain and sensory, autonomic, motor, and trophic abnormalities. Research from the past decade has offered new insights into CRPS epidemiology, pathophysiology, diagnosis, and treatment. Early identification of individuals at high risk of CRPS is improving, with several risk factors established and some others identified in prospective studies during the past 5 years. Better understanding of the pathophysiological mechanisms of CRPS has led to its classification as a chronic primary pain disorder, and subtypes of CRPS have been updated. Procedures for diagnosis have also been clarified. Although effective treatment of CRPS remains a challenge, evidence-based integrated management approaches provide new opportunities to improve patient care. Further advances in diagnosis and treatment of CRPS will require coordinated, international multicentre initiatives.

Current understanding of the molecular mechanisms of chemotherapy-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is the most common off-target adverse effects caused by various chemotherapeutic agents, such as cisplatin, oxaliplatin, paclitaxel, vincristine and bortezomib. CIPN is characterized by a substantial loss of primary afferent sensory axonal fibers leading to sensory disturbances in patients. An estimated of 19-85% of patients developed CIPN during the course of chemotherapy. The lack of preventive measures and limited treatment options often require a dose reduction or even early termination of life-saving chemotherapy, impacting treatment efficacy and patient survival. In this Review, we summarized the current understanding on the pathogenesis of CIPN. One prominent change induced by chemotherapeutic agents involves the disruption of neuronal cytoskeletal architecture and axonal transport dynamics largely influenced by the interference of microtubule stability in peripheral neurons. Due to an ineffective blood-nerve barrier in our peripheral nervous system, exposure to some chemotherapeutic agents causes mitochondrial swelling in peripheral nerves, which lead to the opening of mitochondrial permeability transition pore and cytochrome c release resulting in degeneration of primary afferent sensory fibers. The exacerbated nociceptive signaling and pain transmission in CIPN patients is often linked the increased neuronal excitability largely due to the elevated expression of various ion channels in the dorsal root ganglion neurons. Another important contributing factor of CIPN is the neuroinflammation caused by an increased infiltration of immune cells and production of inflammatory cytokines. In the central nervous system, chemotherapeutic agents also induce neuronal hyperexcitability in the spinal dorsal horn and anterior cingulate cortex leading to the development of central sensitization that causes CIPN. Emerging evidence suggests that the change in the composition and diversity of gut microbiota (dysbiosis) could have direct impact on the development and progression of CIPN. Collectively, all these aspects contribute to the pathogenesis of CIPN. Recent advances in RNA-sequencing offer solid platform for in silico drug screening which enable the identification of novel therapeutic agents or repurpose existing drugs to alleviate CIPN, holding immense promises for enhancing the quality of life for cancer patients who undergo chemotherapy and improve their overall treatment outcomes.

Sensitization-Associated Symptoms and Neuropathic-like Features in Patients with Cervical Dystonia and Pain

Background: This exploratory study evaluated the presence of sensitization-associated and neuropathic-like symptoms and identified their association with pressure sensitivity, pain, and disability in patients with cervical dystonia (CD). Methods: Thirty-one patients with CD (74.2% women, age: 61.2 years, SD 10.1) participated. Data collected included clinical variables, the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS), the Central Sensitization Inventory (CSI), the Self-administered Leeds Assessment of Neuropathic Symptoms and Signs (S-LANSS), the Hospital Anxiety and Depression Scale (HADS) and the Pittsburgh Sleep Quality Index (PSQI), as well as widespread pressure pain thresholds (PPTs). Results: Patients with CD with pain (n = 20, 64.5%) showed higher scores on the TWSTRS disability subscale and the CSI (p < 0.001), and lower PPTs (p < 0.05). Fifteen patients (15/31, 48%) showed sensitization-associated symptoms (CSI ≥ 40), whereas five of the patients with pain (5/20, 25%) exhibited neuropathic-like symptoms (S-LANSS ≥ 12). The CSI and S-LANSS were positively associated with the TWSTRS, HADS-A and HADS-D, and negatively associated with PPTs. HADS-D and S-LANSS explained 72.5% of the variance of the CSI (r2: 0.725), whereas CSI explained 42.3% of the variance of the S-LANSS (r2: 0.423). Conclusions: Pain is an important source of disability in CD, and may be a consequence of different mechanisms, including sensitization.

Prevalence, diagnostic delay and economic burden of endometriosis and its impact on quality of life: results from an Eastern Mediterranean population

BACKGROUND

There are limited data on endometriosis from the Eastern Mediterranean region. This study for the first time estimates the prevalence and impact of endometriosis on women in Northern Cyprus, an under-represented region in Europe.

METHODS

Cyprus Women's Health Research Initiative, a cross-sectional study recruited 7646 women aged 18-55 in Northern Cyprus between January 2018 and February 2020. Cases were identified using self-reported and ultrasound data and two control groups were defined, with (n = 2922) and without (n = 4314) pain. Standardized tools, including the 11-point Numerical Rating Scale and the Short Form 36 Health Survey version 2, were used to assess pain and quality of life, respectively.

RESULTS

Prevalence and median diagnostic delay of endometriosis were 5.4% [95% confidence interval (CI): 4.9-5.9%, n = 410] and 7 (interquartile range 15.5) years. Endometriosis cases experienced a higher prevalence of bladder pain compared with asymptomatic pain controls (6.3% vs. 1.0%, P < 0.001) and irritable bowel syndrome relating to pelvic pain compared with symptomatic (4.6% vs. 2.6%, P = 0.027) and asymptomatic (0.3%, P < 0.001) controls. The odds of endometriosis cases reporting an anxiety diagnosis was 1.56 (95% CI: 1.03-2.38) higher than the symptomatic and 1.95 (95% CI: 1.30-2.92) times higher than the asymptomatic controls. The physical component score of the health-related quality-of-life instrument suggested a significant difference between the endometriosis cases and the symptomatic controls (46.8 vs. 48.5, P = 0.034). Average annual economic cost of endometriosis cases was Int$9864 (95% CI: $8811-$10 917) including healthcare, costs relating to absence and loss of productivity at work.

CONCLUSION

Prevalence was lower than the global 10% estimate, and substantial proportion of women without endometriosis reported moderate/severe pelvic pain hinting at many undiagnosed cases within this population. Coupled with lower quality of life, significant economic burden and underutilized pain management options, the study highlights multiple opportunities to improve care for endometriosis patients and women with pelvic pain.

Trends in U.S. Medical Cannabis Registrations, Authorizing Clinicians, and Reasons for Use From 2020 to 2022

BACKGROUND

As medical cannabis availability increases, up-to-date trends in medical cannabis licensure can inform clinical policy and care.

OBJECTIVE

To describe current trends in medical cannabis licensure in the United States.

DESIGN

Ecological study with repeated measures.

SETTING

Publicly available state registry data from 2020 to 2022.

PARTICIPANTS

People with medical cannabis licenses and clinicians authorizing cannabis licenses in the United States.

MEASUREMENTS

Total patient volume and prevalence per 10 000 persons in the total population, symptoms or conditions qualifying patients for licensure (that is, patient-reported qualifying conditions), and number of authorizing clinicians.

RESULTS

In 2022, of 39 jurisdictions allowing medical cannabis use, 34 reported patient numbers, 19 reported patient-reported qualifying conditions, and 29 reported authorizing clinician numbers. Enrolled patients increased 33.3% from 2020 (3 099 096) to 2022 (4 132 098), with a corresponding 23.0% increase in the population prevalence of patients (175.0 per 10 000 in 2020 to 215.2 per 10 000 in 2022). However, 13 of 15 jurisdictions with nonmedical adult-use laws had decreased enrollment from 2020 to 2022. The proportion of patient-reported qualifying conditions with substantial or conclusive evidence of therapeutic value decreased from 70.4% (2020) to 53.8% (2022). Chronic pain was the most common patient-reported qualifying condition in 2022 (48.4%), followed by anxiety (14.2%) and posttraumatic stress disorder (13.0%). In 2022, the United States had 29 500 authorizing clinicians (7.7 per 1000 patients), 53.5% of whom were physicians. The most common specialties reported were internal or family medicine (63.4%), physical medicine and rehabilitation (9.1%), and anesthesia or pain (7.9%).

LIMITATION

Missing data (for example, from California), descriptive analysis, lack of information on individual use patterns, and changing evidence base.

CONCLUSION

Enrollment in medical cannabis programs increased overall but generally decreased in jurisdictions with nonmedical adult-use laws. Use for conditions or symptoms without a strong evidence basis continues to increase. Given these trends, more research is needed to better understand the risks and benefits of medical cannabis.

PRIMARY FUNDING SOURCE

National Institute on Drug Abuse of the National Institutes of Health.

Pain sensitisation and joint inflammation in patients with active rheumatoid arthritis

INTRODUCTION

Despite better therapies and strategies, many people with rheumatoid arthritis (RA) have persistent pain, often from abnormal pain processing, now termed nociplastic pain. However, RA patients with fibromyalgia (FM), a central nociplastic pain syndrome, also have power doppler ultrasound (PDUS+) joint inflammation. To understand the complex causes of pain, we performed clinical examination and patient-reported outcome measures (PROMs) plus comprehensive PDUS evaluation not previously combined.

METHODS

In a cross-sectional study of sequential RA patients with at least moderate DAS28 erythrocyte sedimentation rate disease activity, we assessed 66/68 joints for swelling and tenderness, respectively, FM American College of Rheumatology 2010 diagnostic criteria, completed PROMs for function, quality of life and mood, alongside PDUS examination of 44 joints. Statistical analysis included logistic regression modelling and regularised (lasso) logistic regression methods.

RESULTS

From 158 patients, 72 (46%) patients met FM criteria, with significantly worse tender joint counts and PROMs, but no differences in PDUS compared with the non-FM group. Categorising patients by PDUS+ joint presence and/or FM criteria, we identified four distinct groups: 43 (27.2%) patients with -FM-PD, 43 (27.2%) with -FM+PD, 42 (26.6%) with +FM-PD and 30 (19%) with +FM+PD. Both FM+ groups had worse PROMs for fatigue, mood and pain, compared with the FM- groups. We were unable to develop algorithms to identify different groups.

CONCLUSION

The unexpected group -FM-PD group may have peripheral nociplastic pain, not commonly recognised in rheumatology. Only 46% of patients demonstrated PDUS+ inflammation. However clinical examination and PROMs did not reliably differentiate groups, emphasising PDUS remains an important tool.

Towards a Real-Life Understanding of the Altered Functional Behaviour of the Default Mode and Salience Network in Chronic Pain: Are People with Chronic Pain Overthinking the Meaning of Their Pain?

Chronic pain is a source of substantial physical and psychological suffering, yet a clear understanding of the pathogenesis of chronic pain is lacking. Repeated studies have reported an altered behaviour of the salience network (SN) and default mode network (DMN) in people with chronic pain, and a majority of these studies report an altered behaviour of the dorsal ventromedial prefrontal cortex (vmPFC) within the anterior DMN. In this topical review, we therefore focus specifically on the role of the dorsal vmPFC in chronic pain to provide an updated perspective on the cortical mechanisms of chronic pain. We suggest that increased activity in the dorsal vmPFC may reflect maladaptive overthinking about the meaning of pain for oneself and one's actions. We also suggest that such overthinking, if negative, may increase the personal "threat" of a given context, as possibly reflected by increased activity in, and functional connectivity to, the anterior insular cortex within the SN.

Can we achieve pain stratification in musculoskeletal conditions? Implications for clinical practice

In the last few years there has been an increased appreciation that pain perception in rheumatic and musculoskeletal diseases (RMDs) has several mechanisms which include nociceptive, inflammatory, nociplastic and neuropathic components. Studies in specific patient groups have also demonstrated that the pain experienced by people with specific diagnoses can present with distinctive components over time. For example, the pain observed in rheumatoid arthritis has been widely accepted to be caused by the activation of nociceptors, potentiated by the release of inflammatory mediators, including prostaglandins, leukotrienes and cytokine networks in the joint environment. However, people with RA may also experience nociplastic and neuropathic pain components, particularly when treatments with disease modifying anti-rheumatic drugs (DMARDs) have been implemented and are insufficient to control pain symptoms. In other RMDs, the concept of pain sensitisation or nociplastic pain in driving ongoing pain symptoms e.g. osteoarthritis and fibromyalgia, is becoming increasingly recognised. In this review, we explore the hypothesis that pain has distinct modalities based on clinical, pathophysiological, imaging and genetic factors. The concept of pain stratification in RMD is explored and implications for future management are also discussed.

Application of a Clinical Approach to Diagnosing Primary Pain: Prevalence and Correlates of Primary Back and Neck Pain in a Community Physiatry Clinic

Chronic back or neck pain (CBNP) can be primary (nociplastic or neuroplastic; without clear peripheral etiology) or secondary (to nociceptive or neuropathic causes). Expanding on available models of nociplastic pain, we developed a clinic-ready approach to diagnose primary/nociplastic pain: first, a standard physical exam and review of imaging to rule out secondary pain; and second, a detailed history of symptom presentation to rule in primary pain. We trained a physician who evaluated 222 patients (73.9% female, age M = 59.6) with CBNP; patients separately completed pain and psychosocial questionnaires. We estimated the prevalence of primary CBNP and explored biomedical, imaging, and psychological correlates of primary CBNP. Although almost all patients (97.7%) had at least 1 spinal anomaly on imaging, the diagnostic approach estimated that 88.3% of patients had primary pain, 5.0% had secondary pain, and 6.8% had mixed pain. Patients with primary pain were more likely than the other 2 groups of patients (combined as "non-primary pain") to report certain functional conditions, central sensitization, and features such as sensitivity to light touch, spreading pain, and pain worsening with stress; however, no difference was detected in depression, anxiety, and pain catastrophizing between those with primary and nonprimary pain. These findings are consistent with prior estimates that 85 to 90% of CBNP is "nonspecific." Further research is needed to validate and perhaps refine this diagnostic approach, which holds the potential for better outcomes if patients are offered treatments targeted to primary pain, such as pain neuroscience education and several emerging psychological therapies. PERSPECTIVE: We developed an approach to diagnose chronic primary pain, which was applied in a physiatry clinic to 222 patients with CBNP. Most patients (88.3%) had primary pain, despite almost universal anomalies on spinal imaging. This diagnostic approach can guide educational and psychological treatments tailored for primary pain.

Mapping Brain Structure Variability in Chronic Pain: The Role of Widespreadness and Pain Type and Its Mediating Relationship With Suicide Attempt

BACKGROUND

Chronic pain affects nearly 20% of the U.S.

POPULATION

It is a leading cause of disability globally and is associated with a heightened risk for suicide. The role of the central nervous system in the perception and maintenance of chronic pain has recently been accepted, but specific brain circuitries involved have yet to be mapped across pain types in a large-scale study.

METHODS

We used data from the UK Biobank (N = 21,968) to investigate brain structural alterations in individuals reporting chronic pain compared with pain-free control participants and their mediating effect on history of suicide attempt.

RESULTS

Chronic pain and, more notably, chronic multisite pain was associated with, on average, lower surface area throughout the cortex after adjusting for demographic, clinical, and neuropsychiatric confounds. Only participants with abdominal pain showed lower subcortical volumes, including the amygdala and brainstem, and lower cerebellum volumes. Participants with chronic headaches showed a widespread thicker cortex compared with control participants. Mediation analyses revealed that precuneus thickness mediated the relationship of chronic multisite pain and history of suicide attempt. Mediating effects were also identified specific to localized pain, with the strongest effect being amygdala volume in individuals with chronic abdominal pain.

CONCLUSIONS

Results support a widespread effect of chronic pain on brain structure and distinct brain structures underlying chronic musculoskeletal pain, visceral pain, and headaches. Mediation effects of regions in the extended ventromedial prefrontal cortex subsystem suggest that exacerbated negative internal states, negative self-referencing, and impairments in future planning may underlie suicidal behaviors in individuals with chronic pain.

Blink rate during saccadic eye movements: insights from patients with chronic pain

Chronic pain (CP) significantly impacts quality of life and poses an increasing economic burden on healthcare systems worldwide. This study investigates the relationship between blink rate during saccadic eye movements and pain perception in patients with CP. Ninety-two patients with CP (24 men, 68 women) were assessed using eye-tracking technology during horizontal and vertical saccadic tasks. Pain perception was evaluated using the Central Sensitization Inventory - Part A and the McGill Pain Questionnaire, and anxiety levels were measured using the State-Trait Anxiety Inventory. The results revealed a significant correlation between blink rates in horizontal and vertical tasks (ρ = 0.668, P < 0.001). However, there was no correlation between blink rate and age, pain perception, or anxiety scores. Conversely, measures of pain perception were positively correlated with each other and with anxiety scores. These findings suggest that while blink rate may reflect oculomotor function, it is not directly influenced by pain perception or anxiety in patients with CP. The present study highlights the potential of eye tracking for the comprehensive assessment and management of patients with CP.

Nociceptive, neuropathic, or nociplastic low back pain? The low back pain phenotyping (BACPAP) consortium's international and multidisciplinary consensus recommendations

The potential to classify low back pain as being characterised by dominant nociceptive, neuropathic, or nociplastic mechanisms is a clinically relevant issue. Preliminary evidence suggests that these low back pain phenotypes might respond differently to treatments; however, more research must be done before making specific recommendations. Accordingly, the low back pain phenotyping (BACPAP) consortium was established as a group of 36 clinicians and researchers from 13 countries (five continents) and 29 institutions, to apply a modified Nominal Group Technique methodology to develop international and multidisciplinary consensus recommendations to provide guidance for identifying the dominant pain phenotype in patients with low back pain, and potentially adapt pain management strategies. The BACPAP consortium's recommendations are also intended to provide direction for future clinical research by building on the established clinical criteria for neuropathic and nociplastic pain. The BACPAP consortium's consensus recommendations are a necessary early step in the process to determine if personalised pain medicine based on pain phenotypes is feasible for low back pain management. Therefore, these recommendations are not ready to be implemented in clinical practice until additional evidence is generated that is specific to these low back pain phenotypes.

Eating habits and the desire to eat healthier among patients with chronic pain: a registry-based study

Healthcare professionals often meet pain patients with a poor nutritional status such as obesity, unhealthy dietary behaviors, and a suboptimal dietary intake. A poor nutritional status may play a significant role in the occurrence, development, and prognosis of chronic pain. This study investigated eating habits in a specialized pain rehabilitation center using data (N = 2152) from the Swedish quality registry for pain rehabilitation during the period 2016-2021. Patients answered a lifestyle questionnaire regarding their eating habits and desire to modify their lifestyle. The mean (SD) patient age was 46.1 (14.6) years, with 24.8% classified as obese. Suboptimal eating habits included irregular mealtimes (27.2%), weekly consumption of fast-food (20.3%) and nearly daily consumption of confectionery (33.3%). Approximately 20% (n = 426) reported a desire to eat healthier. Frequent confectionery intake (Odds ratio [OR] 1.23, 95% Confidence Interval (CI) 1.04-1.47) and fast-food consumption (OR 1.58, 95% CI 1.24-2.02) increased the likelihood to desire healthier eating. Younger patients (18-29 years), those classified as obese, and those with more extended spatial pain were more likely to express a desire to eat healthier. Eating habits should be addressed in pain management and interdisciplinary pain rehabilitation teams are encouraged to provide nutritional care tailored to the patient's needs.

Small fibre pathology, small fibre symptoms and pain in fibromyalgia syndrome

A proportion of people with fibromyalgia demonstrate small fibre pathology (SFP). However, it is unclear how SFP directly relates to pain phenomenology. Thirty-three individuals with FMS and ten healthy volunteers underwent assessment of SFP and sensory phenotyping using corneal confocal microscopy, validated questionnaires and quantitative sensory testing (QST). Corneal nerve fibre length was used to stratify participants with fibromyalgia into with SFP [SFP+] and without SFP [SFP-]. SFP was detected in 50% of the fibromyalgia cohort. Current pain score and QST parameters did not differ between SFP+ and SFP-. Mechanical pain sensitivity (MPS) demonstrated a significant gain-of-function in the SFP- cohort compared to healthy-volunteers (p = 0.014, F = 4.806, η2 = 0.22). Further stratification revealed a cohort without structural SFP but with symptoms compatible with small fibre neuropathy symptoms and a significant gain in function in MPS (p = 0.020 Chi-square). Additionally, this cohort reported higher scores for both depression (p = 0.039, H = 8.483, η2 = 0.312) and anxiety (p = 0.022, F = 3.587, η2 = 0.293). This study confirms that SFP is present in a proportion of people with fibromyalgia. We also show that in a proportion of people with fibromyalgia, small fibre neuropathy symptoms are present in the absence of structural SFP. Greater mechanical pain sensitivity, depression and anxiety are seen in these individuals.

Quality of Life and Treatment Modalities in Patients with Interstitial Cystitis: The Patients' Perspective

BACKGROUND

Quality of life (QoL)-based outcomes are hardly incorporated into interstitial cystitis/bladder pain syndrome (IC/BPS) guidelines, because studies are limited and outdated. Therefore, guidelines might not reflect the current clinical situation accurately. Secondly, guidelines suggest using a multimodal approach for BPS/IC management, but data on the patient-perceived efficacy of these therapies are limited. The aim of this study is to investigate the perception of IC/BPS patients of their QoL, to determine which treatments they have received, and to examine how they evaluate the efficacy of these various (alternative) therapies.

METHODS

A quantitative retrospective database evaluation was performed, with data from an existing IC/BPS patient survey (n = 217) that was conducted in 2021. This survey contained QoL data based on validated questionnaires such as EQ-5D 5L.

RESULTS

The QoL of patients is affected significantly by IC/BPS. This is evident from the various affected domains on the EQ-5D 5L. The symptom severity was negatively affected by a delay in diagnosis, and there were clear differences in QoL domains between females and males. Secondly, coagulation therapy and intravesical glycosaminoglycan (GAG) therapy were most appreciated by patients. Other (alternative) treatments were commonly utilized, although some had doubtful results and high discontinuation rates.

CONCLUSION

QoL is considerably impaired in IC/BPS patients. The diverse responses and adherence to various treatments warrant a personalized approach (phenotype-oriented therapy). To achieve QoL improvement, it is important to incorporate the patient's perspective in treatment guidelines.

Neuromodulation Techniques in Chronic Refractory Coccydynia: A Narrative Review

Refractory coccydynia is a condition characterized by severe coccygeal pain and poses a challenging management dilemma for clinicians. Advancements in neuromodulation (NM) technology have provided benefits to people experiencing chronic pain that is resistant to standard treatments. This review aims to summarize the spectrum of current NM techniques employed in the treatment of refractory coccydynia along with their effectiveness. A review of studies in the scientific literature from 2012 to 2023 was conducted, revealing a limited number of case reports. Although the available evidence at this time suggests significant pain relief with the utilization of NM techniques, the limited scope and nature of the studies reviewed emphasize the need for large-scale, rigorous, high-level research in this domain in order to establish a comprehensive understanding of the role of NM and its effectiveness in the management of intractable coccydynia.

Conditioned Pain Modulation and Temporal Summation of Pain in Patients With Traumatic and Non-Specific Neck Pain: A Systematic Review and Meta-Analysis

In patients with neck pain, it is unclear whether pain inhibition and facilitation endogenous pain mechanisms are altered. This systematic review and meta-analysis aimed to improve their understanding by assessing conditioned pain modulation (CPM) and temporal summation of pain (TSP) in patients with neck pain associated with whiplash-associated disorders (WAD) or of a nonspecific neck pain (NSNP) nature compared to pain-free controls. Very low certainty evidence suggests: impaired CPM when assessed remotely in chronic WAD patients (n = 7, 230 patients and 204 controls, standardized mean differences (SMD) = -.47 [-.89 to -.04]; P = .04) but not locally (n = 6, 155 patients and 150 controls; SMD = -.34 [-.68 to .01]; P = .05), impaired CPM in chronic NSNP patients when assessed locally (n = 5, 223 patients and 162 controls; SMD = -.55 [-1.04 to -.06]; P = .04) but not remotely (n = 3, 72 patients and 66 controls; SMD = -.33 [-.92 to .25]; P = .13), TSP not facilitated in either chronic WAD (local TSP: n = 4, 90 patients and 87 controls; SMD = .68 [-.62 to 1.99]) (remote TSP: n = 8, 254 patients and 214 controls; SMD = .18 [-.12 to .48]) or chronic NSNP (local TSP: n = 2, 139 patients and 92 controls; SMD = .21 [-1.00 to 1.41]), (remote TSP: n = 3; 91 patients and 352 controls; SMD = .60 [-1.33 to 2.52]). The evidence is very uncertain whether CPM is impaired and TSP facilitated in patients with WAD and NSNP. PERSPECTIVE: This review and meta-analysis present the current evidence on CPM and TSP in patients with WAD and NSNP. Standardization of measurement methodology is needed to draw clear conclusions. Subsequently, future studies should investigate the clinical relevance of these measurements as prognostic variables or predictors of treatment success.

Why most (but perhaps not all) DMARDs work equally well

Biological- or targeted-synthetic DMARD-responses reported in randomized clinical trials, placebo-controlled or head-to-head, in patients with rheumatoid arthritis, psoriatic arthritis or spondyloarthritis are unbelievably similar, when looking across trials performed in the same disease and applying the same primary outcome measures. The exception to this rule may be the response to Janus-kinase-inhibitors, which seem to work 10 % better in all trials (JAK-bonus) This article provides a potential explanation for this remarkable phenomenon, including an explanation for the JAK-bonus. It seems as if JAK-inhibitors exert some inflammation-independent effects on pain, fatigue and wellbeing, and that drug treatment of rheumatic diseases is more than the inhibition of inflammation alone.

An update on the pharmacotherapeutic options for complex regional pain syndrome

INTRODUCTION

Complex regional pain syndrome (CRPS) is a rare and painful condition that has a wide range of triggering factors, often traumatic, and can present various clinical manifestations. The lack of knowledge about the underlying mechanisms has led to numerous treatment approaches, both conservative and surgical, which work through different mechanisms of action.

AREAS COVERED

In this review, the authors explore the key aspects of CRPS, including definition, diagnostic criteria, pitfalls, pathogenic hypotheses, and treatment strategies with a focus on pharmacotherapy. The review was based on a comprehensive search of the literature using PubMed, while also considering international guidelines for managing CRPS.

EXPERT OPINION

Based on the available evidence, pharmacological interventions appear to be effective in treating CRPS, especially when they target peripheral mechanisms, specifically nociceptive inflammatory pain, and when administered early in the course of the disease. However, there is still a lack of reliable evidence regarding the effects of drugs on central mechanisms of chronic pain in CRPS. In our expert opinion, drug therapy should be initiated as soon as possible, particularly in warm CRPS patient clusters, to prevent significant functional limitations, psychological distress, and negative impacts on individuals' social and economic well-being.

Early Effects of a Pain-Informed Movement Program in Patients with Post-COVID-19 Condition Experiencing Persistent Pain: Protocol for a Randomized Controlled Trial

(1) Background: The COVID-19 pandemic has generated 771 million confirmed cases. Of these patients, 60% have developed persistent symptoms including pain. This pain is a complex symptom that needs comprehensive therapeutic strategies to address it holistically. The main objective of this study will be to evaluate the early impact of the Pain Informed Movement (PIM) program in patients with post-COVID-19 conditions experiencing new-onset persistent pain. (2) Methods: A randomized, single-blind clinical trial will be performed. Patients will be randomly assigned (1:1) to the experimental or control group. The experimental group will undergo a PIM program consisting of low-intensity functional exercises, pain neuroscience education, and relaxation techniques. The control group will receive no intervention. (3) Results: The results will be published as a peer-reviewed article. (4) Conclusions: This study will provide a basis for future research to support the implementation of comprehensive therapeutic approaches in the care of patients with post-COVID-19 persistent pain.