Assessment of mechanisms in localized and widespread musculoskeletal pain

Modeling Masticatory Myalgia to Headache-like Referred Pain Triggers Local Gene Plasticity at Referred Pain Sites

Patients with myofascial pain in the head and neck area report widespread and referred pain, including headache. Existing preclinical models fail to replicate this clinical phenotype; therefore, we aimed to develop animal models mimicking referred pain phenomenon and investigate whether referred pain leads to gene plasticity at the referred sites. We modeled masticatory myalgia by stimulation of either the masseter (MM) or temporal muscle (TM) in mice. MM and TM were stimulated with a single high-dose injection of Collagenase-type II (Col), repetitive low-dose Col injections, repetitive gentle MM stimulation, or single or repetitive forceful mouth opening. Referred pain was assessed by measuring mechanical hypersensitivity in the periorbital area (representing headache-like behavior) and another masticatory muscle. Stimulation of the MM, whether through single or repetitive Col injections or mouth opening, produced inconsistent, short-lasting (1-2 days) headache-like behavior in both males and females. In contrast, stimulation of the TM, using different paradigms, triggered mechanical hypersensitivity in both the MM and the periorbital area. Referred headache-like behavior lasted longer in females compared to males, while referred myalgia in the MM was pronouncer in males. The referred pain in the MM and periorbital areas triggered by TM stimulation was associated with significant gene plasticity in the MM and dura mater. Transcriptional changes in the MM following Col injection into the TM resembled those observed after direct MM injections. Presented data imply that referred pain modeled by TM stimulation could be accounted by nociceptive signaling from multiple local sites involved in this referred pain network.

Effectiveness of motivational interviewing on pain-related outcomes in patients with musculoskeletal pain: a systematic review and meta-analysis

PURPOSE

To determine the effectiveness of motivational interviewing (MI) in the treatment of adult patients with musculoskeletal (MSK) pain.

MATERIALS AND METHODS

A comprehensive search strategy without date or language restrictions was performed in five scientific databases. Manual searches and reference tracking were also carried out. Two reviewers independently performed title and abstract as well as full-text screening, data extraction, assessment of risk of bias, and evaluation of overall certainty with the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) approach. Where possible, a meta-analysis was performed to identify effects across multiple studies.

RESULTS

Ten studies reported in 16 manuscripts met the previously defined eligibility criteria. Many outcomes could be extracted and analyzed. Nine of the ten studies were considered to have a high risk of bias according to the revised Cochrane RoB 2.0. The majority of comparisons were based on low to very low overall certainty of the evidence.

CONCLUSIONS

The existing literature did not allow a reliable statement about the effectiveness of MI on pain-related outcomes in people with MSK pain. Only tendencies towards a positive influence of MI were recognisable. However, this must be confirmed by high-quality randomized controlled trials in the future.IMPLICATIONS FOR REHABILITATIONMotivational interviewing appears to be an option for patients with chronic musculoskeletal pain which presumably has few to no adverse effects.Motivational interviewing could represent an opportunity, particularly for patients for whom other treatment strategies have been ineffective so far.Motivational interviewing can safely be combined with other forms of treatment such as an active exercise therapy.

Pain profiles and variability in temporal summation of pain and conditioned pain modulation in pain-free individuals and patients with low back pain, osteoarthritis, and fibromyalgia

BACKGROUND

Pain profiles (e.g. pro- and anti-nociceptive) can be developed using quantitative sensory testing (QST) but substantial variability exists. This study describes the variability in temporal summation of pain (TSP) and conditioned pain modulation (CPM) in chronic musculoskeletal pain patients, proposes cut-off values, and explores the association with clinical pain intensity.

METHODS

This is a secondary analysis in which TSP and CPM were assessed using cuff algometry in pain-free subjects (n = 69), and patients with chronic low back pain (cLBP, n = 267), osteoarthritis (n = 134), and fibromyalgia (n = 101). Using TSP and CPM from the pain-free subjects as a reference, four distinct pain profiles TSP (low/high) and CPM (low/high) were created, and differences in clinical pain between pain profiles were explored.

RESULTS

Individual data revealed large inter-person variability. High TSP and low CPM were found in fibromyalgia (p < 0.01) and osteoarthritis (p < 0.01) but not cLBP when compared to pain-free subjects. The proportion of patients classified into the distinct pain profiles was significantly different (p < 0.001) with the largest proportion in the high TSP and low CPM group in fibromyalgia (52.5%) and osteoarthritis (41.4%). Clinical pain was not significantly different comparing the pain profiles, and no significant correlations were observed between clinical pain and TSP or CPM.

CONCLUSION

These results demonstrated substantial inter-person variability in TSP and CPM in patients with different chronic pain conditions and pain-free subjects. The proportion of patients with a pro-nociceptive profile appears larger in fibromyalgia and osteoarthritis, but we found no association to clinical pain.

SIGNIFICANT STATEMENT

This analysis shows that there is variability when assessing TSP and CPM in both pain-free subjects and patients with chronic pain. A cut-off for determining when a person is pain-sensitive is proposed, and data based on this cut-off approach suggest that significantly more patients with osteoarthritis and fibromyalgia are pain-sensitive (i.e. higher TSP and lower CPM) compared to pain-free subjects. This analysis does not find an association between pain sensitivity and clinical pain.

Association between central sensitization and multisite pain in the general population: A cross-sectional analysis of The Wakayama Health Promotion Study

BACKGROUND

Central sensitization (CS), which is characterized by amplified nociceptive processing within the central nervous system, is a key mechanism underlying chronic pain disorders. Chronic pain is a significant global health issue; however, the relationship between CS and pain distribution in the general population remains unclear. This study aimed to investigate the association between CS and the number of locations of body pain in a representative sample of the general population.

METHODS

This cross-sectional study included 739 participants (340 men, 399 women) from the Wakayama Health Promotion Study. CS was assessed using the Japanese version of the Central Sensitization Inventory (CSI-J), with scores of ≥30 indicating CS. Participants reported pain at 13 locations. Statistical analyses, including chi-square tests, Student's t-tests, and multiple regression analyses, were performed to determine the associations between Central Sensitization Inventory (CSI) scores and pain locations.

RESULTS

Among the participants, 9.5 % were diagnosed with CS. Females had significantly higher CSI scores than males. Lower back pain (20.6 %) and shoulder pain (15.0 %) were most common in men, whereas shoulder pain (20.6 %), knee pain (20.1 %), and lower back pain (19.5 %) were most common in women. Multivariate analysis revealed that sex, headache, neck pain, shoulder pain, arm pain, lower back pain, hip pain, thigh pain, and knee pain were significantly associated with CSI scores. Participants with ≥3 locations were 14.4 times more likely to have CS.

CONCLUSIONS

This study highlights the significant prevalence of CS in the general population, with a higher prevalence in females. Specific locations of pain, particularly those close to the trunk, are strongly associated with CS. These findings underscore the importance of assessing CS in individuals with multisite pain for targeted management and treatment strategies.

The role and treatment potential of the complement pathway in chronic pain

The role of the complement system in pain syndromes has garnered attention on the back of preclinical and clinical evidence supporting its potential as a target for new analgesic pharmacotherapies. Of the components that make up the complement system, component 5a (C5a) and component 3a (C3a) are most strongly and consistently associated with pain. Receptors for C5a are widely found in immune resident cells (microglia, astrocytes, sensory neuron-associated macrophages (sNAMs)) in the central nervous system (CNS) as well as hematogenous immune cells (mast cells, macrophages, T-lymphocytes, etc.). When active, as is often observed in chronic pain conditions, these cells produce various inflammatory mediators including pro-inflammatory cytokines. These events can trigger nervous tissue inflammation (neuroinflammation) which coexists with and potentially maintains peripheral and central sensitization. C5a has a likely critical role in initiating this process highlighting its potential as a promising non-opioid target for treating pain. This review summarizes the most up-to-date research on the role of the complement system in pain with emphasis on the C5 pathway in peripheral tissue, dorsal root ganglia (DRG) and the CNS, and explores advances in complement-targeted drug development and sex differences. A perspective on the optimal application of different C5a inhibitors for different types (e.g., neuropathic, post-surgical and chemotherapy-induced pain, osteoarthritis pain) and stages (e.g., acute, subacute, chronic) of pain is also provided to help guide future clinical trials. PERSPECTIVE: This review highlights the role and mechanisms of complement components and their receptors in physiological and pathological pain. The potential of complement-targeted therapeutics for the treatment of chronic pain is also explored with a focus on C5a inhibitors to help guide future clinical trials.

Evidence for spinal disinhibition as a pain-generating mechanism in fibromyalgia syndrome

Introduction

Pain phenomenology in patients with fibromyalgia syndrome (FMS) shows considerable overlap with neuropathic pain. Altered neural processing leading to symptoms of neuropathic pain can occur at the level of the spinal cord, and 1 potential mechanism is spinal disinhibition. A biomarker of spinal disinhibition is impaired H-reflex rate-dependent depression (HRDD).

Objectives

This study investigated whether patients with FMS exhibit evidence of spinal disinhibition.

Methods

Thirty-one individuals with FMS and 20 healthy volunteers underwent testing of Hoffman reflex including HRDD, along with assessment of clinical signs and symptoms, pressure pain thresholds, temporal summation of pain (wind-up), and conditioned pain modulation (CPM). Small nerve fibre structure was quantified using intraepidermal nerve fibre density and corneal confocal microscopy.

Results

Patients with FMS had significantly impaired HRDD at 1 Hz (P = 0.026) and 3 Hz (P = 0.011) and greater wind-up ratio (P = 0.008) compared with healthy controls. Patients with the most impaired HRDD also had the most inefficient CPM but HRDD was not associated with wind-up. Both HRDD and CPM were most impaired in patients with a shorter duration of disease.

Conclusion

We demonstrate for the first time that people with FMS show evidence of spinal disinhibition, which is most dominant in shorter duration of disease and may represent a putative mechanism of pain generation in FMS. Identifying people with impairment of central pain processing at an early stage may provide opportunities for targeted mechanistically directed interventions. Longitudinal studies are warranted to tease out the precise contribution of these mechanisms.

Rapid weight loss and combat athletes: a study on psychological resilience and mechanical hyperalgesia

Introduction

The study investigates the effects of Rapid Weight Loss (RWL) on the levels of psychological resilience and mechanical pain sensitivity in elite kickboxers. The primary aim was to examine changes in psychological resilience subdimensions and pressure pain threshold (PPT) values in the thoracolumbar region before and after a one-month RWL period leading up to competition. Hypotheses included expectations of significant reductions in PPT values due to biomechanical and physiological changes during RWL, along with improvements in psychological resilience subdimensions due to structured routines and social support.

Methods

Thirty-seven elite male athletes (age: 22.94 ± 1.98) participated in the study. Psychological resilience was assessed using the Psychological Resilience Scale for Adults, and mechanical pain sensitivity was evaluated through Pressure Pain Threshold (PPT) measurements. Measurements were conducted before and after the RWL period, spanning one month prior to competition.

Results

The results revealed significant PPT values across all thoracolumbar segments after RWL (p < 0.001). Cohen's d values indicated large effect sizes for these changes (d = 2.10-2.36). The L5 segment exhibited the largest PPT decrease (t = -10.45, d = 2.36), while the Th1 segment showed the smallest decrease (t = -8.23, d = 2.10). Measurements taken at 4 cm from the spine midline also demonstrated significant PPT reductions (p < 0.001), with the highest change recorded in the L5 segment (t = -9.78, d = 2.30). Psychological resilience subdimensions, including "structured style," "social competence," "future orientation," and "social resources," improved significantly after RWL (p < 0.05), while "family cohesion" and "personal strength" did not show significant changes. Athletes who previously ranked in tournaments exhibited higher psychological resilience, potentially due to enhanced self-confidence.

Discussion

These findings align with literature suggesting that competitive success and optimism play crucial roles in resilience development. Personality traits and perceived social support further contributed to the observed resilience levels. This study highlights the multidimensional impact of RWL, emphasizing its detrimental effects on pain sensitivity and its mixed outcomes on psychological resilience. RWL-associated increases in mechanical hyperalgesia, especially in the lumbar region, were attributed to biomechanical and neurophysiological factors. Enhanced psychological resilience observed in certain subdimensions underscores the importance of structured and social support systems in mitigating RWL-induced stress. Future research should explore interventions to optimize resilience and manage pain during RWL periods, focusing on individualized support strategies for athletes. These findings contribute to understanding the interplay between psychological and physiological factors during RWL, practical insights for athletic training.

Pain sensitization in fibromyalgia. Cross-sectional associations between quantitative sensory testing of pain sensitization and fibromyalgia disease burden

BACKGROUND

Whether fibromyalgia burden is related to measures of sensitization, assessed by quantitative sensory testing (QST), is not clear. We examine the associations between sensitization and fibromyalgia disease burden as measured by the polysymptomatic sistress scale (PDS) and the fibromyalgia impact questionnaire (FIQ) (range 0-100).

MATERIALS AND METHODS

Participants were recruited from referrals to a rheumatology outpatient clinic and the fibromyalgia diagnosis was verified by a rheumatologist. They completed the PDS and FIQ and underwent QST of pressure pain threshold (PPT) at five sites, temporal summation (TS), and conditioned pain modulation (CPM) estimated as post-stimuli/pre-stimuli PPT. The associations between QST and disease burden were analysed in linear regression models adjusted for age, sex, and body mass index.

RESULTS

A total of 78 individuals with clinically verified fibromyalgia (90% women, mean age 40.9 years (SD 7.3)) were recruited. Overall mean PPT was associated with the FIQ total score (β-2.1, 95% CI-4.3, -0.0) and the function component (β-2.1, (-4.3, -0.0)). When examining the associations between PPT at individual sites and fibromyalgia disease severity, PPTs at the distal interphalangeal joint and tibialis anterior muscle were associated with both FIQ total score and the FIQ fatigue component. All associations were weak and insignificant after Bonferroni corrections.

CONCLUSION

In this cohort of individuals with fibromyalgia, sensitization was not significantly associated with self-reported disease burden. Our results point to the multifactorial nature of fibromyalgia disease severity.

SIGNIFICANCE

In patients with fibromyalgia, commonly used measures of sensitization do not explain the symptom burden or the functional impact.

The impact of central sensitization-related symptoms on subacromial steroid injection outcomes in patients with subacromial impingement syndrome: an observational study

Background

Evidence indicates that central sensitization (CS) plays a role in subacromial impingement syndrome (SIS). Reduced treatment response has been associated with pretreatment pain sensitization features, such as CSrelated symptoms.

Methods

Patients who received subacromial steroid injection were evaluated before the injection, at the first and third months. CS-related symptoms were investigated through the central sensitization inventory (CSI), and pain hypersensitivity was investigated by pressure pain threshold (PPT). Patients were evaluated using the visual analog scale (VAS), Quick Disabilities of the Arm, Shoulder, and Hand, Hospital Anxiety and Depression Scale, and Short Form-36.

Results

With the injection, all participants had a significant reduction in shoulder pain (P < 0.05). In all follow-ups, VAS values did not differ significantly between the groups, and patients with CSI ≥ 40 had higher levels of disability, anxiety, depression, and worse quality of life before treatment (P < 0.05). Post-injection disability decreased significantly in the CS group and reached similar levels in both groups at the third month (P > 0.05). Although both groups' PPT values were comparable pre-treatment and at the third month, the CS group's affected shoulder showed a notable PPT decline at the first month (P < 0.05).

Conclusions

Pre-treatment CS-related symptoms had no effect on SIS patients' responsiveness to steroid injections.

Affective and Clinical Outcomes Related to Pain After Graded Motor Imagery in Patients With Chronic Shoulder Pain: A Pre-Post-Single-Group Study

Objective: The aim of this study was to assess at 6-month and 1-year follow-up the effect of graded motor imagery (GMI) in addition to usual care on the affective and clinical outcomes in patients with chronic shoulder pain. Methods: A pre-post-intervention single-group study was conducted. One hundred forty-eight patients with chronic shoulder pain were included. All participants received a 6-week GMI program in addition to usual care. The primary outcome assessed was pain intensity using visual analog scale (VAS), the secondary outcomes were fear of movement with the Tampa Scale of Kinesiophobia (TSK), catastrophization with the pain catastrophization scale (PCS), shoulder flexion active range of motion (AROM) with a goniometer, and central sensitization with the central sensitization inventory (CSI). All outcomes were assessed at baseline and 6-month and 1-year follow-up. Results: At 6 months, GMI showed to be statistically significant for all outcomes assessed (p < 0.001). At 1-year follow-up, the VAS showed a decrease of 3.3 cm (p < 0.001), TSK showed a decrease of 16.1 points (p < 0.001), PCS showed a decrease of 17.4 points (p < 0.001), AROM showed an increase of 29.9° (p < 0.001), and CSI showed a decrease of 17.9 (p < 0.001). Conclusions: At medium- and long-term follow-up, the individuals who received the GMI program in addition to usual care showed a clinically and statistically significant change for all outcomes assessed. Further studies, including clinical trials, are needed to confirm our findings.

Persistent postsurgical pain in hip fracture patients. A prospective longitudinal study with multifaceted assessment

Background

Some patients with postoperative hip fractures (HF) experience persistent severe pain. In this longitudinal study, we examined the characteristics of patients with persistent pain after HF surgery, and the factors influencing pain intensity.

Methods

We conducted an 8-week prospective study in patients with postsurgical HF. Verbal rating scale (VRS), and multifaceted outcomes, including pressure pain threshold (PPT) (affected site and biceps), were evaluated at 2, 4, and 8 weeks postoperatively. Patients were divided into mild (VRS ≤1) and severe (VRS ≥2) groups according to pain intensity at 8 weeks postoperatively. Statistical analyses were performed using two-way ANOVA and decision-tree analysis.

Results

VRS, PPT at the affected site and biceps, and physical activity (PA) time were significantly lower in the severe group than in the mild group 2 weeks postoperatively. VRS, PPT at the affected site, pain catastrophizing (PCS)-13, and the Tampa Scale for Kineshiophobia (TSK)-11 did not show significant improvements in the severe group. Decision tree analysis revealed that the VRS and PCS-13 at 4 weeks, PA time at 2 weeks, and TSK-11 change between 4 weeks and 2 weeks were factors influencing severe pain intensity at 8 weeks after HF surgery.

Conclusion

Persistent severe pain after HF surgery was characterised by high peripheral and central sensitisation, pain catastrophizing, and reduced PA at 2 weeks after HF surgery. In addition, early pain intensity, pain catastrophizing, and PA may be hierarchically influential factors for persistent pain 8 weeks after HF surgery.

Trajectories of obesity indices and their association with pain in community-dwelling older adults: Findings from the English longitudinal study of ageing

BACKGROUND

The prevalence of pain has increased with the increase of obesity, and finding indicators to predict pain risk has become an urgent need. BMI, WC, and WHtR have the potential to be excellent predictors. However, the association of these obesity indicators with various pains remains unclear.

METHODS

This longitudinal cohort study included 2155 pain-free participants (mean age = 68.5 years, standard deviation [SD] = 8.6) from the English Longitudinal Study of Ageing (ELSA). BMI, WC, and WHtR were measured during nurse visits at waves 0, 2, and 4. The Group-Based Trajectory Model (GBTM) was used to identify optimal trajectories for BMI, WC, and WHtR. Self-reported pain at four anatomical sites (lower back, hip, knee and total pain) was assessed at Waves 4 to 9. Cox proportional hazards models were employed to estimate hazard ratios (HR) and 95% confidence intervals (CI) for the association between obesity indices and pain risk.

RESULTS

Over a median follow-up period of 7.49 years, we observed 1,059 incident cases of all-cause pain. After adjusting for confounders, participants in the High-Stable WC group had a 30% higher risk of experiencing pain (HR: 1.30, 95 % CI: 1.05-1.60, P = 0.014), while those in the High-Stable WHtR group had a 29% higher risk (HR: 1.29, 95% CI: 1.06-1.56, P = 0.010) compared to the Low-Stable group. High-stable trajectories for BMI, WC, and WHtR were also associated with an elevated risk of back, hip, and knee pain.

CONCLUSION

This study identifies long-term obesity indices as significant predictors of pain, suggesting the importance of monitoring these measures for effective clinical risk assessments. Further research is needed to explore the underlying mechanisms of these associations.

Amitriptyline and duloxetine attenuate activities of superficial dorsal horn neurons in a rat reserpine-induced fibromyalgia model

Fibromyalgia (FM) is an intractable disease with a chief complaint of chronic widespread pain. Amitriptyline (AMI) and duloxetine (DLX), which are antidepressant drugs, have been reported to ameliorate pain in patients with FM and pain-related behaviors in several rodent models of FM. However, the mechanisms of action of AMI and DLX are not yet fully understood. Here, we examined the effects of these drugs on the responsiveness of superficial dorsal horn (SDH) neurons in the spinal cord, using a rat FM model developed by injecting a biogenic amine depleter (reserpine). Extracellular recordings of SDH neurons in vivo demonstrated that bath application of AMI and DLX at concentrations of 0.1-1.0 mM on the dorsal surface of the spinal cord markedly suppressed spontaneous discharge and von Frey filament-evoked mechanical firing in SDH neurons. The suppression induced by the drugs was noted in a concentration-dependent manner and the suppressive effects resolved after washing the spinal cord surface. These results show that SDH neurons are the site of action for AMI and DLX in a rat reserpine-induced FM model. Spinal mechanisms may underlie the therapeutic effects of these drugs in patients with FM.

Do measures of central sensitization relate to movement-evoked pain in people with chronic low back pain? A longitudinal prospective study

BACKGROUND

One of the most frequent complaints among people with musculoskeletal pain is pain during physical activity, commonly referred to as movement-evoked pain. It is suggested to be associated with quantitative sensory testing measures of central pain process in individuals with musculoskeletal pain.

OBJECTIVE

To investigate the predictive association between movement-evoked pain scores and measures of central sensitization in patients with chronic nonspecific low back pain. The secondary aim was to determine whether changes in movement-evoked pain scores are associated with changes in measures of central sensitization.

METHODS

In this longitudinal prospective study, 50 participants with chronic low back pain were included. Pain pressure thresholds, temporal summation of pain, descending pain modulation, and the central sensitization index were assessed as measures of central sensitization. Movement-evoked pain was evaluated using the Back Performance Scale and a 5-minute walk test.

RESULTS

Measures of central sensitization, specifically pressure pain thresholds and temporal summation, demonstrated predictive associations with movement-evoked pain measures. In response to treatment, improvements in movement-evoked pain were associated with improvements in measures of central sensitization (i.e., pressure pain thresholds and temporal summation) and improved pressure pain thresholds in the plantar toe significantly predict movement-evoked pain measures experienced during the 5-minute walk test.

CONCLUSIONS

These results imply that movement-evoked pain is related to processes related to central modulation of pain in patients with nonspecific chronic low back pain.

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.

Development of a novel technique to insert intramuscular electromyography electrodes into the deep intrinsic foot muscles via the dorsum of the foot

This study aimed to develop an insertion technique for intramuscular EMG recording of the oblique head of adductor hallucis (AddH) and first dorsal interosseous (FDI) muscles in humans via the dorsum of the foot, and report feasibility of intramuscular EMG data acquisition during walking in shoes. In eight individuals without musculoskeletal pain or injury (5 males; 32 ± 8 years), intramuscular electrodes were inserted into AddH (oblique head) and FDI through the right foot's dorsum (between metatarsals I-II) with ultrasound guidance. The ultrasound transducer was positioned on the plantar surface. Intramuscular EMG was also recorded from abductor hallucis, tibialis posterior, flexor digitorum longus and peroneus longus. Participants performed six overground walking trials wearing modified shoes, and rated pain associated with the intramuscular electrodes during walking (numerical rating scale, 0-10). High-quality EMG recordings were obtained from intrinsic and extrinsic foot muscles. Analyses of power spectral densities indicated that movement artefacts commonly observed during gait were removed by filtering. Pain associated with AddH/FDI electrodes during walking was low (median[IQR] 1[2]; range 0-4) and similar to other sites. Findings demonstrate that intramuscular EMG recording from AddH (oblique head) and FDI using this insertion technique is feasible and associated with minimal pain when walking in shoes.

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.

Preoperative pain sensitivity and its correlation with postoperative acute and chronic pain: a systematic review and meta-analysis

BACKGROUND

Preoperative pain sensitivity (PPS) can be associated with postsurgical pain. However, estimates of this association are scarce. Confirming this correlation is essential to identifying patients at high risk for severe postoperative pain and for developing analgesic strategy. This systematic review and meta-analysis summarises PPS and assessed its correlation with postoperative pain.

METHODS

PubMed, Scopus, Cochrane Library, and PsycINFO were searched up to October 1, 2023, for studies reporting the association between PPS and postsurgical pain. Two authors abstracted estimates of the effect of each method independently. A random-effects model was used to combine data. Subgroup analyses were performed to investigate the effect of pain types and surgical procedures on outcomes.

RESULTS

A total of 70 prospective observational studies were included. A meta-analysis of 50 studies was performed. Postoperative pain was negatively associated with pressure pain threshold (PPT; r=-0.15, 95% confidence interval [CI] -0.23 to -0.07]) and electrical pain threshold (EPT; r=-0.28, 95% CI -0.42 to -0.14), but positively correlated with temporal summation of pain (TSP; r=0.21, 95% CI 0.12-0.30) and Pain Sensitivity Questionnaire (PSQ; r=0.25, 95% CI 0.13-0.37). Subgroup analysis showed that only TSP was associated with acute and chronic postoperative pain, whereas PPT, EPT, and PSQ were only associated with acute pain. A multilevel (three-level) meta-analysis showed that PSQ was not associated with postoperative pain.

CONCLUSIONS

Lower PPT and EPT, and higher TSP are associated with acute postoperative pain while only TSP is associated with chronic postoperative pain. Patients with abnormal preoperative pain sensitivity should be identified by clinicians to adopt early interventions for effective analgesia.

SYSTEMATIC REVIEW PROTOCOL

PROSPERO (CRD42023465727).

Laryngeal and Global Somatosensation in Primary Muscle Tension Dysphonia

INTRODUCTION

Primary muscle tension dysphonia (pMTD) is a functional voice disorder that reduces communicative abilities and adversely impacts occupational productivity and quality of life. Patients with pMTD report increased vocal effort, fatigue, discomfort, and odynophonia. Although laryngeal and paralaryngeal muscle tension and hyperfunction are the most commonly proposed mechanisms underlying these symptoms, recent studies suggest pMTD may have more to do with the somatosensory system. However, relationships between voice symptoms and somatosensory mechanisms are poorly understood, creating challenges for mechanistic-based pMTD management. The first objective was to compare laryngeal, paralaryngeal, and global somatosensation between subjects with and without pMTD. The second was to determine relationships between pMTD symptoms and somatosensation.

METHODS

Fifty-two (20 pMTD and 32 control) subjects underwent laryngeal sensory testing with aesthesiometers, as well as peripheral mechanosensory and dynamic temporal summation testing to paralaryngeal and limb regions. Voice symptom severities (vocal effort, fatigue, discomfort, and odynophonia) were collected on 100-mm visual analog scales before and after laryngeal sensory testing. Participants also completed the Central Sensitization Inventory.

RESULTS

Patients with pMTD reported significantly higher laryngeal sensations (P = 0.0072) and voice symptom severities (P < 0.001) compared with the control group, and had significantly more vocal tract discomfort postlaryngeal sensory testing compared with the prelaryngeal sensory testing timepoint (P = 0.0023). However, there were no significant group differences in laryngeal airway protection responses suggestive of peripheral laryngeal hypersensitivities (P = 0.444). There were also no significant group differences on paralaryngeal or global sensitivities (P > 0.05), and no correlations between severity of voice symptoms and perceptual laryngeal sensations or hypersensitivities (P > 0.05).

CONCLUSION

Patients with pMTD perceive more sensitivities in the larynx and feel more sensations related to the voice (vocal effort, fatigue, discomfort, and pain). However, in general, patients with pMTD do not have abnormal peripheral laryngeal hypersensitivities, increased global somatosensation, or heightened central sensitivity. The lack of significant correlations between peripheral laryngeal hypersensitivities and voice symptom severity ratings suggests these outcome variables target distinct mechanistic constructs.

Indication for spinal sensitization in chronic low back pain: mechanical hyperalgesia adjacent to but not within the most painful body area

Introduction

In 85% of patients with chronic low back pain (CLBP), no specific pathoanatomical cause can be identified. Besides primary peripheral drivers within the lower back, spinal or supraspinal sensitization processes might contribute to the patients' pain.

Objectives

The present study conceptualized the most painful area (MP) of patients with nonspecific CLBP as primarily affected area and assessed signs of peripheral, spinal, and supraspinal sensitization using quantitative sensory testing (QST) in MP, a pain-free area adjacent to MP (AD), and a remote, pain-free control area (CON).

Methods

Fifty-nine patients with CLBP (51 years, SD = 16.6, 22 female patients) and 35 pain-free control participants individually matched for age, sex, and testing areas (49 years, SD = 17.5, 19 female participants) underwent a full QST protocol in MP and a reduced QST protocol assessing sensory gain in AD and CON. Quantitative sensory testing measures, except paradoxical heat sensations and dynamic mechanical allodynia (DMA), were Z-transformed to the matched control participants and tested for significance using Z-tests (α = 0.001). Paradoxical heat sensations and DMA occurrence were compared between cohorts using Fisher's exact tests (α = 0.05). The same analyses were performed with a high-pain and a low-pain CLBP subsample (50% quantile).

Results

Patients showed cold and vibration hypoesthesia in MP (all Ps < 0.001) and mechanical hyperalgesia (P < 0.001) and more frequent DMA (P = 0.044) in AD. The results were mainly driven by the high-pain CLBP subsample. In CON, no sensory alterations were observed.

Conclusion

Mechanical hyperalgesia and DMA adjacent to but not within MP, the supposedly primarily affected area, might reflect secondary hyperalgesia originating from spinal sensitization in patients with CLBP.

Does the distribution of musculoskeletal pain shape the fate of long-term sick leave? A prospective cohort study with register follow-up

ABSTRACT

Although multisite pain can markedly reduce work ability, the relevance of the bodily pain distribution as a predictor of long-term sick leave is still unknown. This study aimed to investigate the association between musculoskeletal pain distributions and long-term sick leave in the general working population of Denmark and included 66,177 currently employed wage earners without long-term sick leave during the prior 52 weeks. Participants reported whether they had pain in the lower extremity (hips/knees), upper extremity (neck/shoulders), or the low back. The analysis controlled for age, sex, year of survey reply, educational level, occupational group, psychosocial work factors, body max index, smoking, leisure-time physical activity, and mental health confounders. The results demonstrated that the risk of long-term sick leave increased with the number of pain sites. Compared with no pain, localized pain in any body region increased the risk/hazard by 25% to 29% (HR [95% CI]: 1.29 [1.07-1.54] for pain only in the low back), whereas pain in 2 regions increased the risk by 39% to 44% (HR [95% CI]: 1.41 [1.18-1.69] for pain in the low back + hips/knees). Workers reporting pain in all 3 regions experienced a 72% increased risk (HR [95% CI]: 1.72 [1.55-1.91]). Thus, the number of pain regions seems to matter more than the exact pain location. The spatial extension of musculoskeletal pain in workers functions as a gradient system, where pain spread throughout the body is an independent indicator of the high risk of long-term sick leave.

Movement-evoked pain is not associated with pain at rest or physical function in knee osteoarthritis

INTRODUCTION

Knee Osteoarthritis (KOA) is mainly characterized by pain. The assessment of KOA-related pain frequently focuses on different constructs subject to sources of bias or drawbacks, as the classical Pain at Rest (PAR). Movement-evoked pain (MEP), recently defined as 'pain during walking', emerges as a differential concept, since PAR and MEP are driven by different underlying mechanisms. Given the novelty of the MEP approach, its association with PAR or with different performance-based tests has not been studied in KOA yet.

MATERIALS AND METHODS

A cross sectional study was conducted. PAR was measured, alongside the performance of four mobility tests and their corresponding MEP: Timed Up and Go Test, 10-metre Walk Test, 2-Minute Walk Test, and 6-Minute Walk Test. Association and agreement were explored for MEP versus PAR, while the correlation of the tests versus each corresponding MEP-measure was assessed.

RESULTS

Neither association nor agreement were found in the duality MEP versus PAR. Also, the lack of association between the performance of a mobility test and the perceived level of pain during the development of the test was stated.

CONCLUSION

Movement-evoked pain is neither related to pain at rest nor to functional performance in subjects affected by knee osteoarthritis. The results from our study suggest that MEP and pain at rest measure and refer to different constructs in knee osteoarthritis. The implementation of MEP as an outcome in exercise-therapy could enhance the tracking of results, as well as the development of tailored interventions under different conditions.

SIGNIFICANCE

This research elucidates the relevance of MEP, recently defined as 'pain during walking', through the analysis of its association with PAR and with functional performance (measured through four mobility tests) in knee osteoarthritis. The results from our study highlight the absence of either association or agreement between MEP and PAR, fact that supports and endorses the idea that both concepts measure and refer to different constructs in knee osteoarthritis.

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.

The role of endogenous opioids in mindfulness and sham mindfulness-meditation for the direct alleviation of evoked chronic low back pain: a randomized clinical trial

Chronic low back pain (cLBP) is the most prevalent chronic pain condition. There are no treatments that haven been found to directly assuage evoked cLBP. To this extent, mindfulness-meditation is a promising pain therapy. Yet, it is unclear if meditation can be utilized to directly attenuate evoked chronic pain through endogenous opioids. A double-blind, randomized, and placebo-controlled clinical trial with a drug crossover design examined if mindfulness-meditation, as compared to sham mindfulness-meditation, attenuated straight leg-raise test evoked chronic pain during intravenous (0.15 mg/kg bolus + 0.15 mg/kg/hour maintenance) naloxone (opioid antagonist) and placebo-saline infusion. Fifty-nine individuals with cLBP (mean age = 46 years; 30 females) completed all study procedures. After the pre-intervention pain testing session, patients were randomized to a four-session (20-min/session) mindfulness (n = 30) or sham mindfulness-meditation (n = 29) intervention. After the interventions, mindfulness and sham mindfulness-meditation were associated with significant reductions in back pain during saline and naloxone infusion when compared to rest (non-meditation) in response to the cLBP-evoking straight leg-raise test. These results indicate that meditation directly reduces evoked chronic pain through non-opioidergic processes. Importantly, after the interventions, the mindfulness group reported significantly lower straight leg-raise induced pain than the sham mindfulness-meditation group during rest (non-meditation) and meditation. Mindfulness and sham mindfulness-meditation training was also associated with significantly lower Brief Pain Inventory severity and interference scores. The pain-relieving effects of mindfulness meditation were more pronounced than a robust sham-mindfulness meditation intervention, suggesting that non-reactive appraisal processes may be uniquely associated with improvements in chronic low-back pain.Trial Registration: ClinicalTrials.gov identifier: NCT04034004.

Conditioned pain modulation (CPM) paradigm type affects its sensitivity as a biomarker of fibromyalgia

Fibromyalgia (FM) is a widespread chronic pain syndrome, possibly associated with the presence of central dysfunction in descending pain inhibition pathways. Conditioned Pain Modulation (CPM) has been proposed as a biomarker of FM. Nonetheless, the wide variety of methods used to measure CPM has hampered robust conclusions being reached. To clarify the validity of CPM as a biomarker of FM, we tested two CPM paradigms (parallel and sequential) in a sample of 23 female patients and 23 healthy women by applying test (mechanical) stimuli and conditioning (pressure cuff) stimuli. We evaluated whether CPM indices could correctly classify patients and controls, and we also determined the correlations between the indices and clinical variables such as symptomatology, disease impact, depression, quality of life, pain intensity, pain interference, fatigue and numbness. In addition, we compared the clinical status of CPM responders (efficient pain inhibitory mechanism) and non-responders. We observed that only parallel CPM testing correctly classified about 70% of patients with FM. In addition, more than 80% of healthy participants were found to be responders, while the rate was about 50% in the FM patients. The sequential CPM test was not as sensitive, with a decrease of up to 40% in the response rate for both groups. On the other hand, we did not observe any correlation between CPM measures and clinical symptoms. In summary, our findings demonstrate the influence of the CPM paradigm used and confirm that CPM may be a useful marker to complement FM diagnosis. However, the findings also cast doubts on the sensitivity of CPM as a marker of pain severity in FM.

Effects of virtual reality on psychophysical measures of pain: superiority to imagination and nonimmersive conditions

ABSTRACT

Virtual reality (VR) has been shown to be effective in pain management. However, to date, little is known about the mechanisms by which immersive experiences influence pain processing. The aim of this study was to investigate the direct effects of an immersive VR environment on the perception of experimental pain in individuals with chronic pain and pain-free controls. The immersion in a VR landscape was compared with mental imagery and a nonimmersive control condition. Using a randomized within-crossover design, pressure pain detection and tolerance thresholds, spatial and temporal summation (SSP, TSP), and conditioned pain modulation (CPM) were measured in 28 individuals with chronic pain and 31 pain-free controls using phasic cuff pressure on the legs. Direct comparison between the groups showed that although individuals with pain had significantly lower pain thresholds, reduced CPM effects, and increased TSP, the VR condition had the same pain-inhibitory effect on pain thresholds as in pain-free controls. Conditioned pain modulation effects were reduced by all conditions compared with baseline. There were no significant differences between conditions and baseline for TSP and SSP. Overall, pain modulatory effects were largest for VR and smallest for imagery. These results demonstrate that immersion in a VR environment has an increasing effect on pain thresholds, reduces pain inhibition in a CPM paradigm, and has no effects on TSP. This applies for participants with chronic pain and pain-free controls. These VR effects exceeded the effects of mental imagery on the nonimmersive control condition. This indicates that VR effectively modulates pain perception in both patients and controls irrespective of differences in pain perception.

Pain mechanisms for the practicing rheumatologist

Pain in rheumatic diseases transcends the traditional nociceptive paradigm, incorporating complex interactions between nociceptive, neuropathic, and nociplastic mechanisms, as well as significant psychosocial factors. Advances in understanding chronic pain highlight the role of peripheral and central sensitization, and the emergence of nociplastic pain-a result of altered central nervous system processing. This modern perspective acknowledges the influence of mood disorders, environmental stressors, and cognitive patterns like catastrophizing, revealing the intricate interplay between biological, psychological, and social determinants of pain. Research emphasizes the brain's pivotal role in pain perception, underscoring the importance of comprehensive approaches that integrate medical, psychological, and social interventions to address the multifaceted nature of chronic pain in rheumatic diseases effectively.

Subgrouping of facilitatory or inhibitory conditioned pain modulation responses in patients with chronic knee pain. Explorative analysis from a multicentre trial

BACKGROUND

Facilitatory and inhibitory conditioned pain modulation (CPM) responses are observed in healthy volunteers and chronic pain patients, but the clinical implications for phenotyping are unknown. This study aimed to subgroup and compare chronic knee pain patients according to their CPM responses.

METHODS

This explorative, cross-sectional study included 127 patients with chronic knee pain (osteoarthritis or following total knee arthroplasty). Individual CPM responses were categorized as facilitatory (test stimuli pain intensity increased when conditioning stimuli were applied), as inhibitory (test stimuli pain intensity decreased) or as no change (defined as less than 5.3% change in pain intensity). Outcomes were clinical pain intensities, temporal summation, widespread pain, self-reported physical function, PainDETECT questionnaire and Pain Quality Assessment Scale. Data were analysed as comparisons between the inhibitory and the facilitatory groups and using multivariate linear regression models.

RESULTS

Fifty-four patients had facilitatory CPM responses, 49 had inhibitory CPM responses, and 24 showed no change in CPM response. A between-group difference was observed for self-reported physical function, with the facilitatory CPM group reporting better function (54.4 vs. 46.0, p = 0.028) and the facilitatory CPM group reported more deep pain sensations (3.2 vs. 2.0, p = 0.021). The remaining outcomes showed no between-group differences. Higher clinical pain intensity and facilitated temporal summation were associated in the facilitated CPM group but not in the inhibitory CPM group.

CONCLUSION

These explorative findings indicated that quantitative clinical and experimental differences exist between facilitatory or inhibitory CPM responses in a chronic knee pain patient population. Differences in patients' CPM responses should be further investigated to unravel possible clinical importance.

SIGNIFICANCE

Our findings confirm that conditioned pain modulation consist of inhibitory and facilitatory responders among a patient population with chronic knee pain. This explorative study indicates that patients with either facilitatory or inhibitory conditioned pain modulation could exhibit differences in pain outcomes. Subgrouping of chronic pain patients depending on individual conditioned pain modulation responses could be considered in phenotyping patients prior to inclusion in clinical trials or used for personalizing the management regime.

Personalized Multimodal Lifestyle Intervention as the Best-Evidenced Treatment for Chronic Pain: State-of-the-Art Clinical Perspective

Chronic pain is the most prevalent disease worldwide, leading to substantial disability and socioeconomic burden. Therefore, it can be regarded as a public health disease and major challenge to scientists, clinicians and affected individuals. Behavioral lifestyle factors, such as, physical (in)activity, stress, poor sleep and an unhealthy diet are increasingly recognized as perpetuating factors for chronic pain. Yet, current management options for patients with chronic pain often do not address lifestyle factors in a personalized multimodal fashion. This state-of-the-art clinical perspective aims to address this gap by discussing how clinicians can simultaneously incorporate various lifestyle factors into a personalized multimodal lifestyle intervention for individuals with chronic pain. To do so the available evidence on (multimodal) lifestyle interventions targeting physical (in)activity, stress, sleep and nutritional factors, specifically, was reviewed and synthetized from a clinical point of view. First, advise is provided on how to design a personalized multimodal lifestyle approach for a specific patient. Subsequently, best-evidence recommendations on how to integrate physical (in)activity, stress, sleep and nutritional factors as treatment targets into a personalized multimodal lifestyle approach are outlined. Evidence supporting such a personalized multimodal lifestyle approach is growing, but further studies are needed.

Treating persistent pain after breast cancer: practice gaps and future directions

This paper discusses the growing problem of persisting pain after successful treatment of breast cancer and presents recommendations for improving pain-related outcomes for this group. We discuss the dominant treatment approach for persisting pain post-breast cancer treatment and draw contrasts with contemporary treatment approaches to persistent pain in non-cancer-related populations. We discuss modern application of the biopsychosocial model of pain and the notion of variable sensitivity within the pain system, moment by moment and over time. We present the implications of increasing sensitivity over time for treatment selection and implementation. By drawing on transformative changes in treatment approaches to persistent non-cancer-related pain, we describe the potentially powerful role that an intervention called pain science education, which is now recommended in clinical guidelines for musculoskeletal pain, may play in improving pain and disability outcomes after successful breast cancer treatment. Finally, we present several research recommendations that centre around adaptation of the content and delivery models of contemporary pain science education, to the post-breast cancer context.

Long-lasting decreased pain threshold negatively affects functional recovery after arthroscopic rotator cuff repair

PURPOSE

The relationship between sensitization and postoperative function in patients undergoing arthroscopic rotator cuff repair (ARCR). The purpose of this study was to evaluate the effect of pre-and postoperative reductions in the pressure pain threshold (PPT) on postoperative clinical outcomes in patients with ARCR and investigate changes in PPT and clinical outcomes resulting from postoperative administration of weak opioids activating the central inhibitory system.

METHODS

This retrospective study included patients who underwent primary ARCR, categorized into Group A (excellent/good Constant scores) and B (fair/poor Constant scores). In a complementary study, patients were randomized to the Control or Tramadol groups. Both studies evaluated the PPT, visual analog scale, active range of motion (ROM), Constant score, and retear rates pre-and postoperatively.

RESULTS

In the primary study with 158 patients, those with poor clinical outcomes exhibited significantly lower PPT at the affected shoulder preoperatively at 3 months postoperatively compared to those with good outcomes. The PPT of the affected side was lower than that of the uninvolved side not only at 1 and 3 months but also preoperatively and at 6 months in the poor outcome group. In the secondary study involving 96 patients, weak opioid administration was associated with increased PPT for 3 months, improved ROM at 3 months postoperatively, and reduced postoperative pain 1 year postoperatively.

CONCLUSION

Patients experiencing poor postoperative clinical outcomes exhibited prolonged lowered PPT. Lowered PPT due to sensitization may adversely affect functional recovery and pain perception. Elevating PPT using weak opioids improved clinical outcomes during the acute perioperative period after ARCR.

LEVEL OF EVIDENCE

III.

Effects of conditioned pain modulation on Capsaicin-induced spreading muscle hyperalgesia in humans

OBJECTIVES

Muscle pain can be associated with hyperalgesia that may spread outside the area of primary injury due to both peripheral and central sensitization. However, the influence of endogenous pain inhibition is yet unknown. This study investigated how endogenous pain inhibition might influence spreading hyperalgesia in experimental muscle pain.

METHODS

Conditioned pain modulation (CPM) was assessed in 30 male volunteers by cold pressor test at the non-dominant hand as conditioning and pressure pain thresholds (PPT) at the dominant 2nd toe as test stimuli. Subjects were classified as having inhibitory or facilitating CPM based on published reference values. Subsequently, muscle pain and hyperalgesia were induced by capsaicin injection into the non-dominant supraspinatus muscle. Before and 5, 10, 15, 20, 30, 40, 50 and 60 min later, PPTs were recorded at the supraspinatus, infraspinatus and deltoid muscle, ring finger and toe.

RESULTS

Compared to baseline, PPTs decreased at the supraspinatus, infraspinatus and deltoid muscle (p≤0.03), and increased at the finger and toe (p<0.001). In facilitating CPM (n=10), hyperalgesia occurred at 5, 10, 15, 20 and 40 min (p≤0.026). In inhibitory CPM (n=20), hyperalgesia only occurred after 10 and 15 min (p≤0.03). At the infraspinatus muscle, groups differed after 5 and 40 min (p≤0.008).

CONCLUSIONS

The results suggest that facilitating CPM is associated with more spreading hyperalgesia than inhibitory CPM. This implies that poor endogenous pain modulation may predispose to muscle pain and spreading hyperalgesia after injury, and suggest that strategies to enhance endogenous pain modulation may provide clinical benefits.

The Efficacy and Feasibility of an Interoceptive Exposure Technique for Preventing the Transition From Subacute to Chronic Back Pain by Altering the Emotional Response to Pain: Protocol for a Pilot Randomized Controlled Trial

BACKGROUND

Psychological factors such as stress, anxiety, mood, emotions, cognitive functioning, and pain behavior are relevant to the onset of pain and its continuation in the transition to chronic conditions. Subacute low back pain (LBP), a precursor to chronic LBP, is particularly poorly understood, and its relationships with psychological factors are understudied.

OBJECTIVE

We will conduct a study aiming to prevent the chronicity of subacute LBP by altering the emotional response to pain using an interoceptive exposure technique (IET). Considering the recent increase in knowledge about psychological risk factors, as well as recent findings in cognitive neuroscience regarding emotional and cognitive background factors in the LBP chronicity process, efforts should be made to discover effective preventive methods.

METHODS

We present a novel method aiming to prevent the transition from subacute to chronic back pain by altering the emotional response to pain using an IET. In this pilot randomized controlled trial, participants who are at a higher risk of LBP chronification due to the presence of a biomarker (ie, functional connectivity between the medial prefrontal cortex and nucleus accumbens) will be randomly assigned to the IET intervention group or control group A (treatment as usual). Participants who do not present with the biomarker will be assigned to control group B (treatment as usual) to assess how well this biomarker predicts the chronification of subacute LBP in this study population. Questionnaires measuring the pain experience and psychological distress will be used before the intervention, after the intervention (at 3 months), and at the 12-month follow-up.

RESULTS

This research project will combine 2 novel methods: a biomarker as the inclusion criterion and an IET as the intervention. The comparative study design enables evaluation of the efficacy of the IET, as well as replication of the biomarker's validity as a possible clinical screening method.

CONCLUSIONS

If found to be useful, the IET would offer a cost-effective and reasonable way to develop treatment for acute and subacute back pain conditions. Potential benefits include increased pain management and quality of life for the individual patient with the addition of a potentially useful functional pain management method at the societal level.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05450263; https://clinicaltrials.gov/ct2/show/NCT05450263.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

PRR1-10.2196/45701.

How Can Experimental Endotoxemia Contribute to Our Understanding of Pain? A Narrative Review

The immune system and the central nervous system exchange information continuously. This communication is a prerequisite for adaptive responses to physiological and psychological stressors. While the implicate relationship between inflammation and pain is increasingly recognized in clinical cohorts, the underlying mechanisms and the possibilities for pharmacological and psychological approaches aimed at neuro-immune communication in pain are not fully understood yet. This calls for preclinical models which build a bridge from clinical research to laboratory research. Experimental models of systemic inflammation (experimental endotoxemia) in humans have been increasingly recognized as an approach to study the direct and causal effects of inflammation on pain perception. This narrative review provides an overview of what experimental endotoxemia studies on pain have been able to clarify so far. We report that experimental endotoxemia results in a reproducible increase in pain sensitivity, particularly for pressure and visceral pain (deep pain), which is reflected in responses of brain areas involved in pain processing. Increased levels of blood inflammatory cytokines are required for this effect, but cytokine levels do not always predict pain intensity. We address sex-dependent differences in immunological responses to endotoxin and discuss why these differences do not necessarily translate to differences in behavioral measures. We summarize psychological and cognitive factors that may moderate pain sensitization driven by immune activation. Together, studying the immune-driven changes in pain during endotoxemia offers a deeper mechanistic understanding of the role of inflammation in chronic pain. Experimental endotoxemia models can specifically help to tease out inflammatory mechanisms underlying individual differences, vulnerabilities, and comorbid psychological problems in pain syndromes. The model offers the opportunity to test the efficacy of interventions, increasing their translational applicability for personalized medical approaches.

Referred sensations in the orofacial region are associated with a decreased descending pain inhibition and modulated by remote noxious stimuli and local anesthesia

ABSTRACT

Referred sensation (RS) as a specific clinical phenomenon has been known for a long time, although the underlying mechanisms remain unclear. The aims of this study were to assess if (1) healthy individuals who experienced RS had a less active endogenous pain system when compared with those who did not; (2) activation of descending pain inhibition mechanisms can modulate RS parameters; and finally, (3) a transient decrease in peripheral afferent input because of a local anesthetic (LA) block in the masseter muscle can modulate RS parameters. To assess these, 50 healthy participants were assessed in 3 different sessions. In the first session, conditioned pain modulation (CPM) as well as mechanical sensitivity and RS at the masseter muscle were assessed. In the same session, participants who experienced RS had their mechanical sensitivity and RS assessed again while undergoing a CPM protocol. In the second and third sessions, participants had their mechanical sensitivity and RS assessed before and after receiving an injection of 2 mL of LA and isotonic saline into the masseter muscle. The main findings of this study were (1) participants who experienced RS during standardized palpation exhibited increased mechanical sensitivity ( P < 0.05, Tukey post hoc test) and decreased CPM ( P < 0.05, Tukey post hoc test) when compared with those who did not; RS incidence ( P < 0.05, Cochran Q test), frequency ( P < 0.05; Friedman test), intensity ( P < 0.05, Tukey post hoc test), and area ( P < 0.05, Tukey post hoc test) were all significantly reduced when assessed (2) during a painful conditioning stimulus and (3) after LA block. These novel findings highlight that RS in the orofacial region are strongly modified by both peripheral and central nervous system factors.

Personalized medicine: Somatosensory phenotyping in musculoskeletal pain conditions

BACKGROUND

Current clinical phenotyping of musculoskeletal pain provides very limited evidence- based support to personalized medicine. This paper discusses the potential of somatosensory phenotyping to contribute to personalized medicine for prognosis and prediction of treatment effects.

METHODS

Highlight of definitions and regulatory requirements for phenotypes and biomarkers. Appraisal of the literature on somatosensory phenotyping in musculoskeletal pain.

RESULTS

Somatosensory phenotyping can identify clinical conditions and manifestations that may affect treatment decisions. However, studies have shown inconsistent associations of phenotyping measures with clinical outcomes, and the strength of association is mostly weak. Most somatosensory measures have been developed for research, are too demanding to find large acceptance in clinical settings, and have uncertain clinical usefulness.

CONCLUSIONS

Current somatosensory measures will unlikely be validated as strong prognostic or predictive biomarkers. However, they still have the potential to support personalized medicine. Including somatosensory measures in biomarker signatures, that is, a set of measures that are collectively associated with outcomes, is potentially more useful than aiming to the identification of single biomarkers. Furthermore, somatosensory phenotyping may be introduced as part of patient's evaluation to contribute to better-informed and personalized treatment decisions. To this purpose, a change in the way research currently approaches somatosensory phenotyping is warranted. A pathway is proposed that involves: (1) the identification of clinically applicable measures that are specific to clinical conditions; (2) the association of somatosensory phenotypes with outcomes; (3) multi-site replication; and (4) the determination of clinical benefits in randomized controlled trials.

SIGNIFICANCE

Somatosensory phenotyping has the potential to support personalized medicine. However, current measures do not seem to meet the criteria for being strong prognostic or predictive biomarkers, most of them are too demanding to find large acceptance in clinical settings, and their clinical usefulness has not been proven. The value of somatosensory phenotyping can be more realistically determined by re-orienting research to the development of simplified testing protocols, applicable to large-scale clinical practice, and tested for clinical usefulness in randomized controlled trials.

Are clinical outcomes associated with baseline sensory profiles in people with musculoskeletal shoulder pain? Protocol for a prospective longitudinal observational study

BACKGROUND

Musculoskeletal shoulder pain is a common problem and its symptoms often become persistent. The experience of pain is multidimensional, and therefore, a range of patient characteristics may influence treatment response. An altered sensory processing has been associated with persistent musculoskeletal pain states and may contribute to outcomes in patients with musculoskeletal shoulder pain. The presence and potential impact of altered sensory processing in this patient cohort is not currently known. The aim of this prospective longitudinal cohort study is to investigate if baseline sensory characteristics are associated with clinical outcomes in patients presenting to a tertiary hospital with persistent musculoskeletal shoulder pain. If found, a relationship between sensory characteristics and outcome may lead to the creation of more effective treatment strategies and improvements in risk adjustment and prognosis.

METHODS

This is a single-centre prospective cohort study with 6-, 12- and 24-month follow-up. A total of 120 participants aged ≥18 years with persistent musculoskeletal shoulder pain (≥3 months) will be recruited from an Australian public tertiary hospital orthopaedic department. Baseline assessments, including quantitative sensory tests and a standardised physical examination, will be performed. In addition, information will be obtained from patient interviews, self-report questionnaires and medical records. Follow-up outcome measures will comprise information from the Shoulder Pain and Disability Index and a six-point Global Rating of Change scale.

ANALYSIS

Descriptive statistics will be used to report baseline characteristics and outcome measures over time. Change in outcome measures at the primary endpoint of six months from baseline will be calculated using paired t-tests. Associations between baseline characteristics and outcomes at a 6-month follow-up will be reported using multivariable linear and logistic regression models.

DISCUSSION

Understanding the relationship between sensory profile and the variable response to treatment in people with persistent musculoskeletal shoulder pain may enhance our understanding of the mechanisms contributing to the presentation. In addition, through better understanding of the contributing factors, the results of this study may contribute to the development of an individualised, patient-centred approach to treatment for people with this highly prevalent and debilitating condition.

Relationship Between Chronic Pain Types (Nociceptive and Neuropathic-Like Symptoms) and Frailty in Community-Dwelling Japanese Older Adults: A Cross-Sectional Study

Purpose

Chronic pain may accelerate the development of frailty in older adults through a variety of mechanisms. There are no published investigations of the influence of neuropathic-like symptoms on physical frailty. We investigated the association between chronic pain types (nociceptive and neuropathic-like symptoms) and frailty in community-dwelling Japanese older adults.

Participants and Methods

This was a population-based cross-sectional study conducted in 2017 in the city of Itoshima, Japan of 917 participants aged 65-75 years, not in need of long-term care, who had completed the physical function tests and questionnaires administered at measurement sessions held at community centers at three sites over a 1- to 2-month period. Their chronic pain types were classified as no-chronic pain, nociceptive pain, and neuropathic-like symptoms according to their painDETECT scores. Frailty phenotypes were defined by the following five components: unintentional weight loss, low grip strength, exhaustion, slow gait speed, and low physical activity. A logistic regression model was used to compute the odds ratios (ORs) and 95% confidence interval (CIs) for frailty status outcomes.

Results

The prevalence of pre-frailty was 51.9%, and that of frailty was 5.1%. In multinomial logistic regression analyses, compared to the no-chronic pain group, the OR for the presence of pre-frailty among the participants with nociceptive pain was 1.54 (95% CI: 1.04-2.30, p=0.03), and the OR for the presence of frailty among the participants with neuropathic-like symptoms was 4.37 (95% CI: 1.10-17.37, p=0.04). The neuropathic sensory symptoms of burning, tingling/prickling, and numbness were each associated with frailty, but not with the risk of pre-frailty.

Conclusion

Neuropathic-like symptoms were significantly associated with the presence of frailty in community-dwelling Japanese older adults. Chronic pain types might have different effects on frailty status.

The history of Danish neuroscience

The history of Danish neuroscience starts with an account of impressive contributions made at the 17th century. Thomas Bartholin was the first Danish neuroscientist, and his disciple Nicolaus Steno became internationally one of the most prominent neuroscientists in this period. From the start, Danish neuroscience was linked to clinical disciplines. This continued in the 19th and first half of the 20th centuries with new initiatives linking basic neuroscience to clinical neurology and psychiatry in the same scientific environment. Subsequently, from the middle of the 20th century, basic neuroscience was developing rapidly within the preclinical university sector. Clinical neuroscience continued and was even reinforced during this period with important translational research and a close co-operation between basic and clinical neuroscience. To distinguish 'history' from 'present time' is not easy, as many historical events continue in present time. Therefore, we decided to consider 'History' as new major scientific developments in Denmark, which were launched before the end of the 20th century. With this aim, scientists mentioned will have been born, with a few exceptions, no later than the early 1960s. However, we often refer to more recent publications in documenting the developments of initiatives launched before the end of the last century. In addition, several scientists have moved to Denmark after the beginning of the present century, and they certainly are contributing to the present status of Danish neuroscience-but, again, this is not the History of Danish neuroscience.

Migraine patients with and without neck pain: Differences in clinical characteristics, sensitization, musculoskeletal impairments, and psychological burden

AIMS

This study aims to assess differences in clinical characteristics across healthy controls and migraine patients with (MNP) and without (MwoNP) neck pain.

METHOD

This study assessed: headache frequency; headache disability index (HDI); central sensitization inventory (CSI); Hospital Anxiety (HADS-A) and Depression (HADS-D) scale; active range of motion (AROM); flexion rotation test (FRT); activation pressure score (APS); number of active/latent myofascial trigger points (MTrPs) in head/neck muscles; number of positive cervical vertebral segments (C1/C2) who reproduce migraine pain; wind-up ratio (WUR); mechanical pain threshold (MPT) and static pressure pain threshold (sPPT) over the trigeminal area; sPPT and dynamic PPT (dPPT) over the cervical area; sPPTs and MPT over the hand.

RESULTS

Compared to controls, MNP had: worse CSI, HADS-A, and HADS-D (all, p < 0.002); reduced AROM (flexion, extension, left lateral-flexion, and right-rotation), FRT, APS, and a higher number of MTrPs and positive cervical vertebral segments (all, p < 0.020); reduced trigeminal MPT and sPPT, cervical sPPT and dPPT, hand MPT and sPPT (all, p < 0.006). Compared to controls, MwoNP had: worse CSI, and HADS-A (all, p < 0.002); reduced AROM (flexion, and left lateral-flexion), FRT, APS, and a higher number of MTrPs and positive cervical vertebral segments (all, p < 0.017); reduced trigeminal MPT and cervical dPPT (all, p < 0.007). Compared to MwoNP, MNP had higher headache frequency, worse HDI and CSI (all, p < 0.006); reduced AROM (flexion, and right rotation) (all, p < 0.037); reduced cervical dPPT (all, p < 0.002).

CONCLUSION

MNP had worse headache characteristics, more pronounced cervical musculoskeletal impairments, enhanced signs and symptoms related to sensitization, and worse psychological burden compared to MwoNP.

Validity of the Central Sensitization Inventory to Address Human Assumed Central Sensitization: Newly Proposed Clinically Relevant Values and Associations

Central sensitization cannot be directly demonstrated in humans and thus a gold standard is missing. Therefore, we used human assumed central sensitization (HACS) when associated with humans. The central sensitization inventory (CSI) is a screening questionnaire for addressing symptoms that are associated with HACS. This cross-sectional study compared patients with chronic pain and at least one central sensitivity syndrome with healthy, pain-free controls via ROC analyses. Analyses were performed for all participants together and for each sex separately. Regression analyses were performed on patients with chronic pain with and without central sensitivity syndromes. Based on 1730 patients and 250 healthy controls, cutoff values for the CSI for the total group were established at 30 points: women: 33 points; men: 25 points. Univariate and multivariate regression analyses were used to identify possible predictors for the CSI score in 2890 patients with chronic pain. The CSI score is associated with all independent factors and has a low association with pain severity in women and a low association with pain severity, age, and body mass index in men. The newly established CSI cutoff values are lower than in previous studies and different per sex, which might be of clinical relevance in daily practice and importance in research.

Change in Pain During Physical Activity Following Total Knee Arthroplasty: Associations With Improved Physical Function and Decreased Situational Pain Catastrophizing

Background and Objectives

Knee osteoarthritis is one of the primary causes of chronic pain among older adults and because of the aging population, the number of total knee arthroplasties (TKAs) performed is exponentially increasing. While pain reduction is a goal of TKA, movement-evoked pain is rarely assessed pre- and post-TKA. We characterized the distributions of change in pain, function, and situational catastrophizing in patients from presurgery to 3 months postsurgery and explored associations among these pre-post changes.

Research Design and Methods

This prospective study longitudinally assessed movement-evoked pain, function, and situational catastrophizing in patients with knee osteoarthritis (N = 92) using in-person performance-based tests (6-min walk test [6MWT], stair-climb test [SCT]) prior to and 3 months after TKA. Patients also completed the Western Ontario McMaster Universities Scales (WOMAC) pain and function subscales, and Pain Catastrophizing Scale, presurgery and 3- and 6-months postsurgery.

Results

Movement-evoked pain and function on performance tests significantly improved from pre- to post-TKA. Improved SCT function was associated with reduced SCT pain and catastrophizing. Similarly, reduced pain during the SCT was associated with reduced catastrophizing during the SCT. However, 6MWT function was not associated with 6MWT pain or catastrophizing; yet reduced pain during the 6MWT was associated with reduced catastrophizing during the 6MWT. Reduced movement-evoked pain during both performance tests was consistently associated with improved WOMAC function and pain, whereas improved function on performance tests was inconsistently associated with WOMAC function and pain. Notably, greater movement-evoked pain on both performance tests at 3-month post-TKA was associated with worse WOMAC function and pain at 6 months, whereas better function on performance tests at 3 months was associated with better WOMAC function, but not related to WOMAC pain at 6 months.

Discussion and Implications

Findings highlight the importance of situation-specific and in vivo assessments of pain and catastrophizing during physical activity.

Quantitative sensory testing as an assessment tool to predict the response to standard pain treatment in knee osteoarthritis: a systematic review and meta-analysis

Emerging evidence suggest that quantitative sensory testing (QST) may predict the treatment response to pain-relieving therapies. This systematic review and meta-analysis focus on the predictive value of QST for pain management of knee osteoarthritis (OA). MEDLINE and EMBASE were systematically searched for all studies from year 2000 to 2023 on pretreatment QST and treatment of OA including surgical, pharmaceutical, and nonsurgical and nonpharmaceutical therapies. Preclinical studies and reviews were excluded. The systematic review followed the PRISMA guidelines and was pre-registered on the Open Science Framework website (link: https://osf.io/4FETK/, Identifier: DOI 10.17605/OSF.IO/4FETK). Meta-analysis were conducted to demonstrate the strength of the pre-treatment QST predictions on pain outcomes after OA treatments. Sixteen surgical (all on total knee arthroplasty [TKA], N = 1967), 5 pharmaceutical (4 on non-steroidal anti-inflammatory drugs [NSAIDs], N = 271), and 4 exercise-based therapy studies (N = 232) were identified. Pretreatment QST parameters predicted pain-relieving treatment outcomes in 81% of surgical, 100% of pharmaceutical, and 50% of exercise-based therapy studies. Meta-analyses found pretreatment QST profiles to predicted pain outcomes after TKA (random effects: 0.309, 95% confidence interval [CI]: 0.206-0.405, P < 0.001), NSAIDs (random effects: 0.323, 95% CI: 0.194-0.441, P < 0.001), and exercise-based therapies (random effects: 0.417, 95% CI: 0.138-0.635, P = 0.004). The overall risk of bias for the included studies was low to moderate. This systematic review and meta-analysis demonstrate weak-to-moderate associations between pretreatment QST and pain outcomes after standard OA pain treatments. Based on this work, it is hypothesized that a subset of specific pain sensitive patients with OA exist and that these patients do not respond adequately to standard OA pain treatments.

Test-retest reliability of movement-evoked pain and sensitivity to movement-evoked pain in patients with rotator cuff-related shoulder pain

BACKGROUND

The number of researchers and clinicians using movement-evoked pain and sensitivity to movement-evoked pain to assess shoulder pain has increased. However, the intrarater test-retest reliability of movement-evoked pain and sensitivity to movement-evoked pain in people with rotator cuff-related shoulder pain (RCRSP) is still unknown.

OBJECTIVE

We examined the intrarater test-retest reliability of movement-evoked pain and sensitivity to movement-evoked pain in participants with RCRSP.

METHODS

Seventy-four participants with RCRSP performed five trials of active shoulder abduction to elicit pain under two experimental conditions: active shoulder abduction to the onset of pain and maximum range of motion (ROM). The primary outcome measures were pain intensity and ROM. Test-retest reliability of movement-evoked pain and sensitivity to movement-evoked pain was examined using intraclass correlation coefficient (ICC3,1) and minimal detectable change (MDC90).

RESULTS

The reliability of movement-evoked pain under both experimental conditions was good to excellent (ICC: 0.81 to 0.95), while the reliability of sensitivity to movement-evoked pain was poor in both conditions (ICC≤0.45). The MDC90 for pain intensity was 1.6 and 1.8 during shoulder abduction to the onset of pain and maximum ROM, respectively. The MDC90 for ROM was 17.5° and 11.2° during shoulder abduction to the onset of pain and maximum ROM condition, respectively.

CONCLUSION

This study confirms movement-evoked pain testing during active shoulder abduction to the onset of pain or maximum ROM condition is reliable to assess pain associated with movement in patients with RCRSP. The minimal detectable change score of movement-evoked pain can guide clinicians and researchers on how to interpret changes in these outcomes.

Neuromuscular adaptations to experimentally induced pain in the lumbar region: systematic review and meta-analysis

ABSTRACT

Experimental pain models are frequently used to understand the influence of pain on the control of human movement. In this systematic review, we assessed the effects of experimentally induced pain in the lumbar region of healthy individuals on trunk muscle activity and spine kinematics. Databases were searched from inception up to January 31, 2022. In total, 26 studies using either hypertonic saline injection (n = 19), heat thermal stimulation (n = 3), nociceptive electrical stimulation (n = 3), or capsaicin (n = 1) were included. The identified adaptations were task dependent, and their heterogeneity was partially explained by the experimental pain model adopted. Meta-analyses revealed an increase of erector spinae activity (standardized mean difference = 0.71, 95% confidence interval [CI] = 0.22-1.19) during full trunk flexion and delayed onset of transversus abdominis to postural perturbation tasks (mean difference = 25.2 ms, 95% CI = 4.09-46.30) in the presence of pain. Low quality of evidence supported an increase in the activity of the superficial lumbar muscles during locomotion and during voluntary trunk movements during painful conditions. By contrast, activity of erector spinae, deep multifidus, and transversus abdominis was reduced during postural perturbation tasks. Reduced range of motion of the lumbar spine in the presence of pain was supported by low quality of evidence. Given the agreement between our findings and the adaptations observed in clinical populations, the use of experimental pain models may help to better understand the mechanisms underlying motor adaptations to low back pain.

Pain Mechanisms Associated With Disease Activity in Patients With Rheumatoid Arthritis Treated With Disease-Modifying Antirheumatic Drugs: A Regression Tree Analysis

OBJECTIVE

Although pain affects the assessment of disease activity in patients with rheumatoid arthritis (RA), pain is not always directly related to peripheral joint inflammation. Peripheral and central nervous system regulatory mechanisms also affect pain perception. We used regression tree methodology to identify mechanisms most predictive of disease activity after disease-modifying antirheumatic drug (DMARD) treatment.

METHODS

Disease activity was evaluated using the Disease Activity Score in 28 joints (DAS28) in 176 patients with RA, before and after starting a DMARD. Quantitative sensory testing (QST), including pressure pain thresholds (PPTs), temporal summation, and conditioned pain modulation (CPM), were used to assess pain mechanisms. Regression tree methodology was used to determine the QST modalities most predictive of DAS28 after DMARD treatment.

RESULTS

This analysis identified 4 groups defined by baseline DAS28 category and either knee PPT (a combined measure of peripheral and central nervous system dysregulation) or CPM (a measure of descending pain inhibition). Among patients starting with low/moderate disease activity, lower knee PPT (PPT ≤ 4.65 kgf) most strongly predicted higher posttreatment disease activity (group 1 mean DAS28 2.8 [SD 1.0] vs group 2 mean DAS28 3.5 [SD 1.0]). Among patients starting with high baseline disease activity, less efficient descending pain modulation (CPM ≤ 1.55) most strongly predicted higher posttreatment disease activity (group 3 mean DAS28 3.4 [SD 1.4] vs group 4 mean DAS28 4.6 [SD 1.1]).

CONCLUSION

These results highlight the importance of identifying and treating aberrant peripheral and central pain regulation in patients with RA starting or switching DMARD therapy.

Effects of interdisciplinary pain rehabilitation programs on neuropathic and non-neuropathic chronic pain conditions - a registry-based cohort study from Swedish Quality Registry for Pain Rehabilitation (SQRP)

BACKGROUND AND AIM

Neuropathic pain arises as a direct consequence of a lesion or disease affecting the somatosensory system. Pharmacological treatments for neuropathic pain often fail despite following guidelines. Interdisciplinary Pain Rehabilitation Programs (IPRP) are an effective intervention for chronic pain conditions. Little research has investigated whether IPRP can benefit patients with chronic neuropathic pain compared to other chronic pain conditions. This study assesses the real-world effects of IPRP on patients with chronic neuropathic pain compared to non-neuropathic patients using Patient-Reported Outcome Measures (PROMs) available in the Swedish Quality Registry for Pain Rehabilitation (SQRP).

METHODS

A neuropathic group of patients (n = 1,654) were identified in two steps. This group was compared to a non-neuropathic group (n = 14,355) composed of common diagnoses (low back pain, fibromyalgia, whiplash associated disorders, and Ehlers-Danlos Syndrome) in relation to background variables, three overall outcome variables, and mandatory outcome variables (pain intensity, psychological distress symptoms, activity/participation aspects and health-related quality of life variables). Of these patients 43-44% participated in IPRP.

RESULTS

At assessment, the neuropathic group reported significantly (with small effect sizes (ES)) more physician visits the previous year, older age, shorter pain durations, and less spatial extent of the pain (moderate ES). Moreover, for the 22 mandatory outcome variables, we found only clinically insignificant differences according to ESs between the groups. For patients participating in IPRP, the neuropathic group displayed equal or in some cases slightly superior results compared to the non-neuropathic group.

DISCUSSION AND CONCLUSION

After assessing the real-world effects of IPRP, this large study found that neuropathic pain patients can benefit from the IPRP intervention. Both registry studies and RCTs are needed to better understand which patients with neuropathic pain are most suitable for IPRP and to what extent special considerations need to be made for these patients within the framework of IPRP.

Pain Sensitization as a Potential Mediator of the Relationship Between Sleep Disturbance and Subsequent Pain in Rheumatoid Arthritis

OBJECTIVE

Many patients with rheumatoid arthritis (RA) experience sleep disturbances, commonly attributed to joint pain. Sleep disturbances could also influence pain. One mechanism may be through dysregulated pain processing, manifested by enhanced pain sensitivity. The present study was undertaken to examine the role of pain sensitization, measured by quantitative sensory testing (QST), as a mediator in the pathway of sleep disturbance leading to subsequent pain.

METHODS

We used longitudinal data from 221 patients with active RA who were followed for 12 weeks after initiating a disease-modifying antirheumatic drug. Baseline QST included pressure pain thresholds at articular (wrists, knees) and nonarticular (trapezius, thumbnails) sites, temporal summation (TS) at the wrist and forearm, and conditioned pain modulation (CPM). Baseline sleep disturbance and subsequent pain intensity were assessed using the Patient-Reported Outcomes Measurement Information System (PROMIS). We evaluated correlations between sleep disturbance, QSTs, and subsequent pain intensity. Mediation analyses separately assessed each QST as a mediator, adjusting for baseline confounding factors.

RESULTS

Sleep disturbance was correlated with all QST measures except wrist TS and CPM. Sleep disturbance significantly predicted subsequent pain (coefficient for a meaningful increase of 5 units in sleep disturbance = 0.32 (95% confidence interval 0.11, 0.50) in multiple regression. QST mediated 10-19% of this effect.

CONCLUSION

Pain sensitization may be one mechanism through which sleep disturbance contributes to pain. The small magnitude of association indicates that unmeasured pathways may contribute to this relationship. Intervention studies are needed to establish causality and determine whether improving sleep can improve pain in patients with RA.

Diagnosing nociplastic pain in cancer survivors: a major step forward

Nociplastic pain syndromes include particular fibromyalgia, irritable bowel syndrome, headache, complex regional pain syndrome, and idiopathic orofacial pain. Several mechanisms have been proposed to account for nociplastic pain including central sensitisation, alterations of pain modulatory controls, epigenetic changes, and peripheral mechanisms. Importantly, nociplastic pain might also be present in patients with cancer pain, particularly those with pain related to complications of cancer treatment. Increased awareness of nociplastic pain associated with cancer should have important implications for monitoring and managing such patients.

Investigation of pain sensitivity following 3 nights of disrupted sleep in healthy individuals

BACKGROUND

Poor quality sleep is a common complaint among people with chronic pain. The co-occurrence of poor sleep quality and chronic pain often comes with increased pain intensity, more disability and a higher cost of healthcare. Poor sleep has been suggested to affect measures of peripheral and central pain mechanisms. To date, sleep provocations are the only models proven to affect measures of central pain mechanisms in healthy subjects. However, there are limited studies investigating the effect of several nights of sleep disruption on measures of central pain mechanisms.

METHODS

The current study implemented three nights of sleep disruption with three planned awakenings per night in 30 healthy subjects sleeping at home. Pain testing was conducted at the same time of day at baseline and follow-up for each subject. Pressure pain thresholds were assessed bilaterally on the infraspinatus and gastrocnemius muscles. Using handheld pressure algometry, suprathreshold pressure pain sensitivity and area were also investigated on the dominant infraspinatus muscle. Cuff-pressure pain detection and tolerance thresholds, temporal summation of pain and conditioned pain modulation were investigated using cuff-pressure algometry.

RESULTS

Temporal summation of pain was significantly facilitated (p = 0.022), suprathreshold pain areas (p = 0.005) and intensities (p < 0.05) were significantly increased, and all pressure pain thresholds were decreased (p < 0.005) after sleep disruption compared to baseline.

CONCLUSIONS

The current study found that three consecutive nights of sleep disruption at home induced pressure hyperalgesia and increased measures of pain facilitation in healthy subjects, which is consistent with previous findings.

SIGNIFICANCE

Poor quality of sleep is often experienced by patients with chronic pain, with the most common complaint being nightly awakenings. This exploratory study is the first to investigate changes in measures of central and peripheral pain sensitivity in healthy subjects after sleep disruptions for three consecutive nights without any restrictions on total sleep time. The findings suggest that disruptions to sleep continuity in healthy individuals can induce increased sensitivity to measures of central and peripheral pain sensitization.