Abnormal endogenous pain modulation is a shared characteristic of many chronic pain conditions

Exercise plasma improves traumatic brain injury outcomes in mice

Traumatic brain injury (TBI) is associated with pain and cognitive impairment although exercise may improve some adverse outcomes. We hypothesized that transfer of plasma derived from exercised mice would improve outcomes related to pain and memory after TBI. These studies used a concussive murine model of mild TBI. Plasma from sedentary or exercised mice was administered to TBI mice beginning 3 days after injuries. Mechanical nociceptive sensitization and descending control of nociception (DCN) were assessed. Object recognition memory and Y-maze were used to assess working memory. In addition, the spinal expression of Pdyn, Bdnf, Cxcl1 and Cxcl2 was measured 7 and 28 days after injuries. Levels of several candidate mediators of the exercise effects were measured in the transferred plasma. Mechanical allodynia following TBI recovered more quickly and DCN responses were partially preserved in animals receiving exercise plasma. Working memory was preserved in the same mice. The upregulation of spinal pain genes Pdyn and Bdnf was reduced by exercise plasma. Finally, exercise was associated with substantially higher plasma levels of TIMP2 and irisin. The present study suggests that developing therapies based on the administration of exercise plasma or its components may help reduce pain and cognitive loss after TBI.

Association Between Sedentary Behavior and Primary Dysmenorrhea in Young Korean Women: A Cross-Sectional Online Survey

BACKGROUND/OBJECTIVES

Sedentary behavior is an independent risk factor for various health conditions, but its association with dysmenorrhea has been little investigated. This study aimed to examine whether sedentary behavior is independently associated with primary dysmenorrhea in young women, controlling for moderate-to-vigorous physical activity and other known risk factors.

METHODS

An online survey was conducted in 603 young women in South Korea in 2023. Menstrual pain intensity was measured using a numeric rating scale, and symptoms were assessed with the Cox Menstrual Symptom Scale. Sedentary behavior and physical activity were assessed using the Global Physical Activity Questionnaire. Known risk factors for dysmenorrhea included menstrual and lifestyle characteristics, sleep quality, and stress.

RESULTS

Longer sedentary time (hours/day) was correlated with more frequent (r = 0.144; p < 0.001) and severe (r = 0.123; p < 0.01) menstrual symptoms but not with pain intensity. Multiple linear regression analysis showed that sedentary time was independently associated with the frequency (β = 0.10; p < 0.01) and severity (β = 0.09; p < 0.05) of menstrual symptoms after adjusting for physical activity and other risk factors for dysmenorrhea. Multiple logistic regression analysis showed that women with higher levels of sedentary time had 1.05 times greater odds (95% CI, 1.00-1.10; p < 0.05) of experiencing severe pain compared to those with less sedentary time, even after adjusting for physical activity and other risk factors.

CONCLUSIONS

Prolonged sedentary behavior in young women is associated with more frequent and severe menstrual symptoms, including more intense menstrual pain. These findings highlight the need for public health strategies that reduce sedentary behavior to alleviate dysmenorrhea.

The effect of mindfulness combined with exercise compared with a self-management guide on measures of nervous system sensitivity in individuals with chronic pain: a pilot randomised control trial

BACKGROUND

This study described a sensory profile of participants with chronic pain (CP) in a previously reported feasibility RCT, in terms of quantitative sensory testing (QST) measures and the Central Sensitisation Inventory (CSI).

AIMS

The study aimed to explore the changes in QST measures and the CSI in this sample following participation in a mindfulness and physical activity intervention compared to an online self-management guide.

METHODS

Participants were randomised into (i) a combined mindfulness and exercise online interactive group or (ii) an online self-management group. Pressure pain thresholds (PPT), temporal summation (TS), conditioned pain modulation (CPM) measures, and the CSI were completed with participants at baseline and post-intervention.

RESULTS

Baseline (n = 33) and post-intervention (n = 22) measurements were completed. High mean CSI scores (54.69, SD 23.85) were noted at baseline in participants, indicating the presence of central sensitisation [n = 33; 70% (n = 23) score > 40]. Mean baseline scores for TS were high (2.64, SD 1.60), indicating the presence of pain facilitation, and variable results were observed for baseline PPT and CPM measures. The combined intervention was not found to be superior to a self-management guide in this cohort in terms of changes in PPT, TS, and CPM measures and the CSI.

CONCLUSIONS

High baseline CSI and TS scores were identified in the cohort at baseline, with no notable trends identifiable with regard to changes in QST scores or the CSI post-intervention. Further studies are recommended with larger sample sizes in order to understand changes in QST measures following participation in interventions of this nature.

Quantitative sensory testing and exercise-induced hypoalgesia protocols in low back pain: A scoping review

A significant driver of pain in individuals with low back pain (LBP) is alterations to endogenous pain modulation (EPM). EPM can be measured using quantitative sensory testing (QST), however; there are inconsistencies in the way QST has been implemented across the low back pain literature. The objective of this scoping review was to summarize protocols used to assess EPM using QST (pain pressure threshold (PPT), temporal summation (TS), conditioned pain modulation (CPM)) or exercise-induced hypoalgesia (EIH) in LBP. Databases Medline, Embase, CINAHL and AMED were searched on June 15, 2023, for articles that used QST or EIH protocols in LBP populations. Data was extracted on participants, study design, setting and details on QST and EIH protocols. Of the 221 studies included in the review, 196 used PPT, 62 used TS and 60 used CPM; only 5 studies investigated EIH. For all QST, there was high variability in the type of equipment, timing, trials, and testing location with many studies not reporting this information. There were 4 testing modalities used for TS, and 7 different test stimuli, and 3 different conditioning stimuli used across the studies for CPM. For CPM and EIH, PPT was the most common testing modality. There were 4 types of exercises used across the 5 EIH studies. This scoping review provides a summary of QST and EIH protocols in LBP that may be used as a guide for assessment in future studies. These results demonstrate a need for the development of standardized protocols and reporting guidelines. PERSPECTIVE: This article presents a summary of measures used to assess EPM in LBP. The results show the wide variability of protocols used in the literature. Future research should focus on creating standardized protocols, reporting guidelines and providing more guidance for researchers in selecting appropriate tests for their research questions.

Noninvasive brain stimulation beyond the motor cortex: a systematic review and meta-analysis exploring effects on quantitative sensory testing in clinical pain

BACKGROUND

Noninvasive brain stimulation (NIBS) has been investigated increasingly as a means of treating pain. The effectiveness of NIBS in the treatment of pain has traditionally focused on protocols targeting the primary motor cortex (M1). However, over time, the effectiveness of M1 NIBS has been attributed to effects on interconnected cortical and subcortical sites rather than on M1 itself. Although previous reviews have demonstrated the effectiveness of non-M1 NIBS in improving subjective reports of pain intensity, the neurophysiological mechanisms underlying these effects remain incompletely understood. As chronic pain is associated with pain hypersensitivity and impaired endogenous descending pain modulation, it is plausible that non-M1 NIBS promotes analgesic effects by influencing these processes.

OBJECTIVE

The aim of this systematic review and meta-analysis was therefore to evaluate the effect of NIBS over non-M1 sites on quantitative sensory testing measures in clinical pain populations.

METHODS

A systematic search of electronic databases was conducted from inception to January 2024. Included articles (13 trials, n = 565 participants) were appraised with the Physiotherapy Evidence Database (PEDro) scale and Grading of Recommendations, Assessment, Development, and Evaluation (GRADE), and a random-effects model was used to meta-analyze outcomes where possible.

RESULTS

A small number of studies found that NIBS applied to the dorsolateral prefrontal cortex might improve pain modulation in patients with fibromyalgia and that stimulation of the posterior superior insula and prefrontal cortex could improve pain sensitivity in chronic neuropathic and osteoarthritic pain, respectively. However, findings varied among studies, and there remains a paucity of primary research.

CONCLUSION

This review indicates that current literature does not provide clear evidence that NIBS over non-M1 sites influences pain processing.

STUDY REGISTRATION

PROSPERO (CRD42020201076).

SCN10A gene polymorphism is associated with pain sensitivity and postoperative analgesic effects in patients undergoing gynecological laparoscopy

BACKGROUND

Postoperative pain intensity is influenced by various factors, including genetic variations. The SCN10A gene encodes the Nav1.8 sodium channel protein, which is crucial for pain signal transmission in peripheral sensory neurons.

OBJECTIVES

This study aims to investigate the relationship between genetic mutations in the SCN10A gene (rs6795970) and postoperative analgesic effects following gynecological laparoscopic surgery.

METHODS

Two hundred female patients undergoing gynecological laparoscopic surgery under general anesthesia were included. pain sensitivity was evaluated using the catastrophizing scale and pain sensitivity questionnaire (PSQ). Patients received patient-controlled intravenous analgesia with sufentanil and dexmedetomidine for 48 h post-surgery. Postoperative pain indicators, such as visual analog scale (VAS) scores, Ramsay scores, and side effects were recorded. SCN10A rs6795970 mutations were identified using MassARRAY SNP typing technology, and patients were categoried into homozygous mutant (AA), wild type (GG), and heterozygous mutation (GA) groups for analysis.

RESULTS

Patients in the AA group had higher scores on the pain Catastrophizing Scale, PSQ-total, PSQ-minor, and PSQ-moderate compared to GA and GG groups (P < 0.05). VAS scores at 4, 6, and 12 h post-operation were higher in the AA group than the GG group (P < 0.05). Ramsay scores were lower in AA patients at 2 and 4 h post-operation compared to GA and GG groups (P < 0.05). The AA group exhibited more self-control analgesic pump compressions within the first 24 h post-surgery, quicker depletion of analgesics in the pump, and lower patient satisfaction with pain relief compared to GA and GG groups (P < 0.05).

CONCLUSIONS

Female patients with homozygous SCN10A mutations may experience higher preoperative pain scores and increased sensitivity to postoperative pain following gynecological laparoscopic surgery with intravenous patient-controlled analgesia.

TRIAL REGISTRATION

www.chictr.org.cn , registration number: ChiCTR2200062425.

The effects of socioeconomic position on endogenous pain modulation: A quasi-experimental approach

Socioeconomic Position (SEP) is a multidimensional construct encompassing education, income, occupation, and neighborhood distress, influencing chronic pain severity, interference, and duration. However, its impact on placebo analgesia, where reduced pain perception occurs due to treatment belief, remains understudied. Using a quasi-experimental approach, we investigated SEP's influence on placebo analgesia in 401 participants with temporomandibular disorder (TMD) and 400 pain-free individuals. Using latent class analysis, we grouped participants into two SEP groups based on self-reported education, income, occupation, and neighborhood distress indices, including the area deprivation and distressed community indexes. Ancestry Informative Markers (AIMs) and self-reported race were included to account for genetic and demographic influences. Placebo analgesia was elicited using verbal suggestion and classical conditioning. Linear mixed models were employed to analyze SEP's impact, while multiple regression and ANCOVA assessed AIMs' and race's effects. Comparable placebo effects were observed between participants with TMD and pain-free individuals (F(1,4765.73) = 0.49, p = 0.48). A trend was noted in the main effect of SEP (F(1,4764.5) = 3.64, p = 0.056). Among TMD participants, those with distressed SEP exhibited lower placebo analgesia (F(1,4765.73) = 7.9, p = 0.005), while placebo response did not differ by SEP in pain-free participants (F(1,4765.73) = 0.27, p = 0.59). East Asian ancestry (β = 5.71, 95% CI [1.50, 9.92]) and self-reported Asian (mean = 24.20, sem = 1.52, p = 0.020) were associated with greater placebo analgesia. This study highlights the interplay of SEP, AIMs, and race in placebo analgesia and calls for tailored pain management interventions. PERSPECTIVE: SEP significantly contributes to pain disparities. This quasi-experimental study demonstrates analogous placebo analgesia between chronic pain and pain-free individuals but finds lower placebo analgesia only among individuals with chronic pain and distressed SEP. This highlights a link between chronic pain, SEP, and impaired placebo effects, suggesting new avenues for research.

Can Offset Analgesia Magnitude Provide Additional Information About Endogenous Pain Modulation in People With Knee Osteoarthritis?: An Experimental Study

OBJECTIVES

To investigate the relationship between offset analgesia magnitude and the responsiveness to conditioned pain modulation (CPM), temporal summation of (second) pain (TSP), and clinical pain severity in people with knee osteoarthritis (KOA).

METHODS

Electrical stimuli were applied to 88 participants with KOA to measure offset analgesia at the volar forearm of the dominant hand, and CPM and TSP at the most symptomatic knee and ipsilateral volar wrist. Clinical pain severity was assessed using the pain subscale of the Knee injury and Osteoarthritis Outcome Score (KOOS PAIN ). Linear mixed-effects models evaluated pain modulatory effects across all tests, and Spearman partial correlations assessed associations between offset analgesia, CPM, TSP, and KOOS PAIN while accounting for covariates of interest. Participants unable to validly finish all psychophysical tests were excluded from effect and correlation analyses but were evaluated for predictors of nonvalid completion using bivariate Stochastic Search Variable Selection.

RESULTS

Significant pain modulation was observed across all psychophysical tests ( P <0.05), and no meaningful predictors of nonvalid test completion were found. Offset analgesia magnitude did not significantly correlate with CPM, TSP, or KOOS PAIN ( P ≥0.05), with a maximum partial correlation coefficient of ρ =0.21.

DISCUSSION

Offset analgesia was not associated with CPM, TSP, or KOOS PAIN in people with KOA. Despite the lack of case-control studies comparing offset analgesia between people with KOA and healthy controls, these findings suggest that offset analgesia may provide information about endogenous pain modulation beyond CPM and TSP, though its clinical translation remains uncertain.

Altered Endogenous Pain-Inhibitory Function in Older Adults With Chronic Pain Is Associated With Disruptions in Functional Connectivity During Resting State

Increasing research points to a decline in the ability to internally regulate pain as a contributing factor to the increased pain susceptibility in aging. This study investigated the connection between pain regulation and resting-state functional connectivity (rsFC) in older adults with chronic pain. We compared functional magnetic resonance imaging rsFC of 30 older adults with chronic pain (69.5 ± 6.58 years, 14 males), 29 pain-free older (70.48 ± 4.60, 15 males), and 30 younger adults (20.0 ± 1.58, 15 males). Pain inhibition and facilitatory capabilities were assessed using conditioned pain modulation (CPM) and temporal summation. Older adults with chronic pain displayed lower pain inhibition during the CPM than pain-free older and younger adults. rsFC analysis showed that older adults with chronic pain, in comparison with younger participants, displayed an abnormal hyperconnectivity between right dorsolateral prefrontal cortex and left amygdala, which was significantly correlated with lower pain inhibition during the CPM. Older adults with chronic pain displayed higher connectivity between the primary somatosensory cortex and nucleus accumbens than pain-free older adults. Finally, both older adult groups displayed reduced connectivity between brain structures involved in pain inhibition and processing in comparison with younger adults. Altogether, our results suggest that suffering from pain during aging leads to a dysfunction of pain-inhibitory processes, which significantly surpass those caused by normal aging. Furthermore, our results point to a key role of emotional and motivational brain areas, and their interaction with executive and somatosensory areas, in the reduced inhibitory capacity and likely the maintenance of chronic pain in aging. PERSPECTIVE: This study examines the link between reduced pain-inhibition capacity and increased resting-state connectivity between affective, sensory, and executive brain structures in older adults with chronic pain. These findings could inform new pain assessment and treatment programs for this population.

Placebo effects in neuropathic pain conditions

Management of neuropathic pain is exceptionally challenging and development of new drugs and ways to optimize treatment effects in clinical practice are needed. Over the last decade, some of the mechanisms underlying placebo effects have been elucidated and some of the insights have the potential to improve the treatment for neuropathic pain. Research suggests that the increasing placebo responses observed in randomized controlled trials (RCTs) for neuropathic pain pose challenges for the development and availability of new effective pain medications. In neuropathic pain, these placebo responses are typically not controlled for the natural history of pain and other confounding factors. Thus, our knowledge about the magnitude and mechanisms of placebo effects in neuropathic pain is sparse. A few mechanistic studies investigating placebo effects by controlling for natural history of pain have found large placebo analgesia effects in neuropathic pain. Psychological factors such as expectations and emotions play a substantial role in inducing the placebo effects. Here, we review placebo effects and the psychological and neurobiological mechanisms contributing to the placebo effects. The knowledge obtained from studies of placebo mechanisms can help improve the information that can be obtained from RCTs and potentially improve development of new pain medications and optimize treatment of neuropathic pain in clinical practice.

Age-related differences in functional connectivity associated with pain modulation

Growing evidence suggests that aging is associated with impaired endogenous pain modulation, and that this likely underlies the increased transition from acute to chronic pain in older individuals. Resting-state functional connectivity (rsFC) offers a valuable tool to examine the neural mechanisms behind these age-related changes in pain modulation. RsFC studies generally observe decreased within-network connectivity due to aging, but its relevance for pain modulation remains unknown. We compared rsFC within a set of brain regions involved in pain modulation between young and older adults and explored the relationship with the efficacy of distraction from pain. This revealed several age-related increases and decreases in connectivity strength. Importantly, we found a significant association between lower pain relief and decreased strength of three connections in older adults, namely between the periaqueductal gray and right insula, between the anterior cingulate cortex (ACC) and right insula, and between the ACC and left amygdala. These findings suggest that the functional integrity of the pain control system is critical for effective pain modulation, and that its function is compromised by aging.

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.

Effect of dry needling on pain and central sensitization in women with chronic pelvic pain: A randomized parallel-group controlled clinical trial

Chronic pelvic pain (CPP) is a debilitating problem in women with clear evidence of myofascial dysfunction. It seems that Myofascial trigger points (MTrPs) contribute to the development of central sensitization (CS). This study aimed to investigate the effect of dry needling on pain and CS in women with CPP. Thirty-six women with CPP participated in this randomized controlled clinical trial and randomly assigned into three groups: dry needling group (DNG), placebo needling group (PNG) and control group (CG). The DNG received five sessions of DN using the "static needling", the PNG received non-penetrating method, and the CG did not receive any intervention. Assessment of outcomes including central sensitization inventory (CSI), short-form McGill pain questionnaire (SF-MPQ), electroencephalography (EEG), conditioned pain modulation (CPM), salivary cortisol concentration, 7-item general anxiety disorder scale (GAD-7), pain catastrophizing scale (PCS), and SF-36 questionnaire was performed pre-intervention, post-intervention, and three months post-intervention by a blind examiner. The result showed a significant group-by-time interaction for CSI, SF-MPQ, and PCS. There was a significant decrease in CSI score in post-intervention and three-months post-intervention compare to pre-intervention in the DNG and PNG. SF-MPQ-PPI score in DNG significantly decreased post-intervention. PCS-Total score decreased significantly post-intervention in DNG and PNG. No significant group-by-time interactions were observed for other variables. EEG results showed regional changes in the activity of frequency bands in both eye closed and eye open conditions. It seems that DN can affect central pain processing by removing the source of peripheral nociception. Trial registration: Iranian Registry of Clinical Trials (IRCT20211114053057N1, registered on: December 03, 2021. https://irct.behdasht.gov.ir/search/result?query=IRCT20211114053057N1).

Validity of central pain processing biomarkers for predicting the occurrence of oncological chronic pain: a study protocol

BACKGROUND

Despite recent improvements in cancer detection and survival rates, managing cancer-related pain remains a significant challenge. Compared to neuropathic and inflammatory pain conditions, cancer pain mechanisms are poorly understood, despite pain being one of the most feared symptoms by cancer patients and significantly impairing their quality of life, daily activities, and social interactions. The objective of this work was to select a panel of biomarkers of central pain processing and modulation and assess their ability to predict chronic pain in patients with cancer using predictive artificial intelligence (AI) algorithms.

METHODS

We will perform a prospective longitudinal cohort, multicentric study involving 450 patients with a recent cancer diagnosis. These patients will undergo an in-person assessment at three different time points: pretreatment, 6 months, and 12 months after the first visit. All patients will be assessed through demographic and clinical questionnaires and self-report measures, quantitative sensory testing (QST), and electroencephalography (EEG) evaluations. We will select the variables that best predict the future occurrence of pain using a comprehensive approach that includes clinical, psychosocial, and neurophysiological variables.

DISCUSSION

This study aimed to provide evidence regarding the links between poor pain modulation mechanisms at precancer treatment in patients who will later develop chronic pain and to clarify the role of treatment modality (modulated by age, sex and type of cancer) on pain. As a final output, we expect to develop a predictive tool based on AI that can contribute to the anticipation of the future occurrence of pain and help in therapeutic decision making.

Online Exercise Programs for Chronic Nonspecific Neck Pain: A Randomized Controlled Trial Reveals Comparable Effects of Global, Local, and Combined Approaches

OBJECTIVE

Specific neck exercises are recommended in the rehabilitation of chronic nonspecific neck pain (CNNP). They are unfortunately often accompanied by acute pain flare-ups. Global exercises might be a beneficial addition, as they activate endogenous analgesia without overloading painful structures. However, it is still unclear which type of exercise is most effective. This randomized controlled trial was done to evaluate the effect of an online blended program of global and specific neck exercises, compared to programs including only 1 of both types of exercise.

METHODS

Forty-eight patients with CNNP were randomized into 3 groups. Online questionnaires were collected at baseline, at midtreatment, immediately after treatment, and at the 3-month follow-up. Quantitative sensory testing and actigraphy were assessed at baseline and after treatment. Linear mixed-model analyses were performed to evaluate treatment effects within and between groups. Neck pain-related disability after treatment was considered the primary outcome.

RESULTS

No time × treatment interaction effects were found. All groups improved in neck pain-related disability, pain intensity, self-reported symptoms of central sensitization, local pain sensitivity, physical activity, and pain medication use. No effects were found on quality of life, sleep quality, depression, anxiety, stress, widespread pain sensitivity, health economics, or actigraphy measurements. A higher global perceived effect was reported after performing the blended program, compared to the other groups.

CONCLUSION

A blended exercise program was not superior to the stand-alone programs in reducing disability. Nevertheless, the global perceived effect of this type of exercise was higher. Future research necessitates larger sample sizes to adequately explore the optimal type of exercise for patients with CNNP.

IMPACT

Exercise therapy should be an important part of the rehabilitation of patients with CNNP, regardless of the type of exercise.

Influence of Transcutaneous Electrical Nerve Stimulation (TENS) on Pressure Pain Thresholds and Conditioned Pain Modulation in a Randomized Controlled Trial in Women With Fibromyalgia

Transcutaneous electrical nerve stimulation (TENS) effectively reduces pain in fibromyalgia (FM). The purpose of this study was to examine the influence of TENS use on pressure pain thresholds (PPT) and conditioned pain modulation (CPM) in individuals with FM using data from the Fibromyalgia Activity Study with TENS trial (NCT01888640). Individuals with FM were randomly assigned to receive active TENS, placebo TENS, or no TENS for 4 weeks. A total of 238 females satisfied the per-protocol analysis among the active TENS (n = 76), placebo TENS (n = 68), and no TENS (n = 94) groups. Following 4 weeks of group allocation, the active TENS group continued for an additional 4 weeks of active TENS totaling 8 weeks (n = 66), the placebo and no TENS groups transitioned to receive 4 weeks of active TENS (delayed TENS, n = 161). Assessment of resting pain, movement-evoked pain (MEP), PPT, and CPM occurred prior to and following active, placebo, or no TENS. There were no significant changes in PPT or CPM among the active TENS, placebo TENS, or no TENS groups after 4 weeks. Individuals who reported clinically relevant improvements in MEP (≥30% decrease) demonstrated increases in PPT (P < .001), but not CPM, when compared to MEP non-responders. There were no significant correlations among the change in PPT or CPM compared to MEP and resting pain following active TENS use (active TENS + delayed TENS). PPT and CPM may provide insight to underlying mechanisms contributing to pain; however, these measures may not relate to self-reported pain symptoms. PERSPECTIVE: Pressure pain threshold increased in individuals with clinically relevant improvement (≥30%) in MEP, indicating the clinical relevance of PPT for understanding mechanisms contributing to pain. CPM was not a reliable indicator of treatment response in MEP responders.

Duloxetine and cognitive behavioral therapy with phone-based support for the treatment of chronic musculoskeletal pain: study protocol of the PRECICE randomized control trial

BACKGROUND

Chronic musculoskeletal pain (CMP) is the most common, disabling, and costly of all pain conditions. While evidence exists for the efficacy of both duloxetine and web-based cognitive behavioral therapy (CBT) as monotherapy, there is a clear need to consider study of treatment components that may complement each other. In addition, given the reported association between patient's adherence and treatment outcomes, strategies are needed to enhance participant's motivation to adopt and maintain continued use of newly learned pain coping skills from CBT.

METHODS

Two hundred eighty participants will be recruited from the primary care clinics of a large academic health care system in North Carolina. Participants with CMP will be randomized to one of three treatment arms: (1) combination treatment (duloxetine + web-based self-guided CBT) with phone-based motivational interviewing (MI), (2) combination treatment without phone-based MI, and (3) duloxetine monotherapy. Participants will be in the study for 24 weeks and will be assessed at baseline, week 13, and week 25. The primary outcome is the Brief Pain Inventory (BPI)-Global Pain Severity score, which combines BPI pain severity and BPI pain interference. Secondary measures include between-group comparisons in mean BPI pain severity and BPI pain interference scores. Data collection and outcome assessment will be blinded to treatment group assignment.

DISCUSSION

This randomized controlled trial (RCT) will determine if combination treatment with duloxetine and web-based CBT is superior to duloxetine monotherapy for the management of CMP. Furthermore, this RCT will determine the effectiveness of phone-based motivational interviewing in promoting the continued practice of pain coping skills, thereby enhancing treatment outcomes.

TRIAL REGISTRATION

NCT04395001 ClinicalTrials.gov. Registered on May 15, 2020.

Duloxetine and Cognitive Behavioral Therapy with Phone-based Support for the Treatment of Chronic Musculoskeletal Pain: Study Protocol of the PRECICE Randomized Control Trial

Background

Chronic musculoskeletal pain (CMP) is the most common, disabling, and costly of all pain conditions. While evidence exists for the efficacy of both duloxetine and web-based cognitive behavioral therapy (CBT) as monotherapy, there is a clear need to consider study of treatment components that may complement each other. In addition, given the reported association between patient's adherence and treatment outcomes, strategies are needed to enhance participant's motivation to adopt and maintain continued use of newly learned pain coping skills from CBT.

Methods

Two hundred eighty participants will be recruited from the primary care clinics of a large academic health care system in North Carolina. Participants with CMP will be randomized to one of 3 treatment arms: (1) combination treatment (duloxetine + web-based self-guided CBT) with phone-based motivational interviewing (MI), (2) combination treatment without phone-based MI and (3) duloxetine monotherapy. Participants will be in the study for 24 weeks and will be assessed at baseline, week 13, and week 25. The primary outcome is the Brief Pain Inventory (BPI)-Global Pain Severity score, which combines BPI pain severity and BPI pain interference. Secondary measures include between-group comparisons in mean BPI pain severity and BPI pain interference scores. Data collection and outcome assessment will be blinded to treatment group assignment.

Discussion

This randomized controlled trial (RCT) will determine if combination treatment with duloxetine and web-based CBT is superior to duloxetine monotherapy for the management of CMP. Furthermore, this RCT will determine the effectiveness of phone-based motivational interviewing in promoting the continued practice of pain coping skills; thereby, enhancing treatment outcomes.

Trial Registration

NCT04395001. Registered in ClinicalTrials.gov on May 15, 2020.

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.

An investigation of neurological and/or biomechanical factors underpinning the effect of a thrust manipulation on chronic ankle symptoms: an observational study

BACKGROUND

Ankle sprains are a commonly occurring musculoskeletal injury potentially resulting in persistent pain and/or altered motion. Thrust manipulation may serve as an interventional strategy but limited evidence exists on the mechanism(s) by which a change to symptoms might occur.

OBJECTIVE

The study sought to quantify the immediate effect of a thrust manipulation to the ankle to determine a mechanism by which change to symptoms occurred.

METHODS

Eleven participants (6 m/5f, 26.09 ± 4.25 yrs) with a history of ankle sprain that occurred greater than three months ago with recurring pain and/or altered motion were recruited. Participants underwent neurophysiological testing to assess any pain alterations and instrumented gait analysis (IGA) for biomechanical assessment pre-post thrust manipulation to the ankle.

RESULTS

There were no significant differences in ankle dorsiflexion (DF) (p = 0.62), plantarflexion (PF) (p = 0.23), ground reaction force (GRF), or velocity (p = 0.63) following thrust manipulation compared to baseline; however, pre- and post-data did show differences in pain pressure threshold (p = 0.046). There were no significant differences in dynamic pain measurements.

CONCLUSIONS

Ankle sprains that result in persistent pain and/or altered motion can be impacted by a thrust manipulation which appears to act through neurophysiological mechanisms.

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.

Is conditioned pain modulation (CPM) affected by negative emotional state?

BACKGROUND

Conditioned pain modulation (CPM) is an experimental paradigm, which describes the inhibition of responses to a noxious or strong-innocuous stimulus, the test stimulus (TS), by the additional application of a second noxious or strong-innocuous stimulus, the conditioning stimulus (CS). As inadequate CPM efficiency has been assumed to be predisposing for clinical pain, the search for moderating factors explaining inter-individual variations in CPM is ongoing. Psychological factors have received credits in this context. However, research concerning associations between CPM and trait factors relating to negative emotions has yielded disappointing results. Yet, the influence of anxious or fearful states on CPM has not attracted much interest despite ample evidence that negative affective states enhance pain. Our study aimed at investigating the effect of fear induction by symbolic threat on CPM.

METHODS

Thirty-seven healthy participants completed two experimental blocks: one presenting aversive pictures showing burn wounds (high-threat block) and one presenting neutral pictures (low-threat block). Both blocks contained a CPM paradigm with contact heat as TS and hot water as CS; subjective numerical ratings as well as contact-heat evoked potentials (CHEPs) were assessed.

RESULTS

We detected an overall inhibitory CPM effect for CHEPs amplitudes but not for pain ratings. However, we found no evidence for a modulation of CPM by threat despite threat ratings indicating that our manipulation was successful.

DISCUSSION

These results suggest that heat/thermal CPM is resistant to this specific type of symbolic threat induction and further research is necessary to examine whether it is resistant to fearful states in general.

SIGNIFICANCE

The attempt of modulating heat conditioned pain modulation (CPM) by emotional threat (fear/anxiety state) failed. Thus, heat CPM inhibition again appeared resistant to emotional influences. Pain-related brain potentials proved to be more sensitive for CPM effects than subjective ratings.

The dual facilitatory and inhibitory effects of social pain on physical pain perception

Pain is a multi-dimensional phenomenon that encompasses both physical pain experienced physiologically and social pain experienced emotionally. The interactions between them are thought to lead to increased pain load. However, the effect of social pain on physical pain perception during interactions remains unclear. Four experiments were conducted merging physical and social pains to examine the behavioral pattern and neural mechanism of the effect of social pain on physical pain perception. Seemingly paradoxical effects of social pain were observed, which both facilitated and inhibited physical pain perception under different attention orientations. Brain imaging revealed that the posterior insula encoded the facilitatory effect, whereas the frontal pole engaged in the inhibitory effect. At a higher level, the thalamus further modulated both processes, playing a switch-like role under different concern statuses of social pain. These results provide direct evidence for the dual-pathway mechanism of the effect of social pain on physical pain.

The effectiveness of a combined exercise and psychological treatment programme on measures of nervous system sensitisation in adults with chronic musculoskeletal pain - a systematic review and meta-analysis

BACKGROUND

Quantitative sensory testing (QST) offers information regarding underlying mechanisms contributing to chronic pain (CP) in adults with musculoskeletal disorders. This review examined the use of QST measures in adults with CP following participation in a combined exercise and psychological intervention.

METHODS

The review was conducted in accordance with the PRISMA guidelines. Five databases were searched from inception to November 2022. All study designs which evaluated the effects of a combined exercise and psychological treatment on measures of nervous system sensitivity in adults with chronic musculoskeletal pain were included.

RESULTS

A total of 13 studies met the selection criteria, 10 of which were included in a meta-analysis. Local pressure pain thresholds were the most frequently used measure (n = 12 studies). Meta-analysis revealed statistically significantly improvements in favour of the combined exercise and psychological intervention group, compared to a control group, for local pressure pain threshold measures [SMD = 0.44, 95% CI 0.08-0.81, I2 = 84%], pain intensity scores [SMD=-0.89, 95% CI -1.66- -0.13, I2 = 94%] and the Central Sensitisation Inventory [SMD=-0.69, 95% CI -1.37- -0.02, I2 = 87%]. There were no significant differences found between groups for remote pressure pain thresholds, temporal summation or conditioned pain modulation.

CONCLUSIONS

The results suggest that a combined exercise and psychological intervention may lead to greater improvements in local pressure pain threshold, pain intensity and Central Sensitisation Inventory scores when compared to a control intervention in adults with CP, however these findings must be interpreted with caution as a large degree of heterogeneity was present in these results (I2: 84-94%). Further large, longitudinal studies are required using standardised QST measurement procedures and patient reported outcome measures to explore changes in nervous system sensitisation.

TRIAL REGISTRATION

This systematic review is registered with PROSPERO, ID Number CRD42022380464.

Physical activity and endogenous pain modulation in older people: a scoping review protocol

OBJECTIVE

This scoping review aims to provide an overview of the existing literature on physical activity and endogenous pain modulation (EPM), assessed using conditioned pain modulation (CPM), with a specific focus on older people with chronic pain.

INTRODUCTION

Approximately 20% of the European population reports chronic pain, highlighting the problem of chronic pain in the general population. This prevalence increases to 50% in older people. Physical activity is one of the most frequently used treatments for pain management and relief. A possible mechanism underlying the positive effects of physical activity on pain may be related to its influence on EPM. The review will map i) types of physical activity used to study its effect on EPM in older people; ii) intervention protocols investigating physical activity and EPM, measured using CPM, in older people experiencing pain; and iii) knowledge gaps requiring further research or interventions adapted to older people with pain.

INCLUSION CRITERIA

This review will consider studies of people aged 60 years or older, using CPM to examine the effect of physical activity on EPM. All types of care settings will be eligible.

METHODS

This review will be conducted in accordance with the JBI methodology for scoping reviews. The following databases will be searched: MEDLINE (Ovid), CINAHL (EBSCOhost), Embase, Cochrane Library, Web of Science, JBI Evidence Synthesis , PsycINFO, and PEDro.

REVIEW REGISTRATION

Open Science Framework https://osf.io/e7ndy/.

Altered resting-state brain functional activities and networks in Crohn's disease: a systematic review

Background

Crohn's disease (CD) is a non-specific chronic inflammatory disease of the gastrointestinal tract and is a phenotype of inflammatory bowel disease (IBD). The current study sought to compile the resting-state functional differences in the brain between CD patients and healthy controls.

Methods

The online databases PubMed, Web of Science Core, and EMBASE were used to find the published neuroimage studies. The search period was from the beginning through December 15, 2023. The predetermined inclusion and exclusion criteria allowed for the identification of the studies. The studies were assembled by two impartial reviewers, who also assessed their quality and bias.

Results

This review comprised 16 resting-state fMRI studies in total. The included studies generally had modest levels of bias. According to the research, emotional processing and pain processing were largely linked to increased or decreased brain activity in patients with CD. The DMN, CEN, and limbic systems may have abnormalities in patients with CD, according to research on brain networks. Several brain regions showed functional changes in the active CD group compared to the inactive CD group and the healthy control group, respectively. The abnormalities in brain areas were linked to changes in mood fluctuations (anxiety, melancholy) in patients with CD.

Conclusion

Functional neuroimaging helps provide a better understanding of the underlying neuropathological processes in patients with CD. In this review, we summarize as follows: First, these findings indicate alterations in brain function in patients with CD, specifically affecting brain regions associated with pain, emotion, cognition, and visceral sensation; second, disease activity may have an impact on brain functions in patients with CD; and third, psychological factors may be associated with altered brain functions in patients with CD.

Differential Effects of Thermal Stimuli in Eliciting Temporal Contrast Enhancement: A Psychophysical Study

Offset analgesia (OA) is observed when pain relief is disproportional to the reduction of noxious input and is based on temporal contrast enhancement (TCE). This phenomenon is believed to reflect the function of the inhibitory pain modulatory system. However, the mechanisms contributing to this phenomenon remain poorly understood, with previous research focusing primarily on painful stimuli and not generalizing to nonpainful stimuli. Therefore, the aim of this study was to investigate whether TCE can be induced by noxious as well as innocuous heat and cold stimuli. Asymptomatic subjects (n = 50) were recruited to participate in 2 consecutive experiments. In the first pilot study (n = 17), the parameters of noxious and innocuous heat and cold stimuli were investigated in order to implement them in the main study. In the second (main) experiment, subjects (n = 33) participated in TCE paradigms consisting of 4 different modalities, including noxious heat (NH), innocuous heat (IH), noxious cold (NC), and innocuous cold (IC). The intensity of the sensations of each thermal modality was assessed using an electronic visual analog scale. TCE was confirmed for NH (P < .001), NC (P = .034), and IC (P = .002). Conversely, TCE could not be shown for IH (P = 1.00). No significant correlation between TCE modalities was found (r < .3, P > .05). The results suggest that TCE can be induced by both painful and nonpainful thermal stimulation but not by innocuous warm temperature. The exact underlying mechanisms need to be clarified. However, among other potential mechanisms, this may be explained by a thermo-specific activation of C-fiber afferents by IH and of A-fiber afferents by IC, suggesting the involvement of A-fibers rather than C-fibers in TCE. More research is needed to confirm a peripheral influence. PERSPECTIVE: This psychophysical study presents the observation of temporal contrast enhancement during NH, NC, and innocuous cold stimuli but not during stimulation with innocuous warm temperatures in healthy volunteers. A better understanding of endogenous pain modulation mechanisms might be helpful in explaining the underlying aspects of pain disorders.

The Roles of Endogenous Opioids in Placebo and Nocebo Effects: From Pain to Performance to Prozac

Placebo and nocebo effects have been well documented for nearly two centuries. However, research has only relatively recently begun to explicate the neurobiological underpinnings of these phenomena. Similarly, research on the broader social implications of placebo/nocebo effects, especially within healthcare delivery settings, is in a nascent stage. Biological and psychosocial outcomes of placebo/nocebo effects are of equal relevance. A common pathway for such outcomes is the endogenous opioid system. This chapter describes the history of placebo/nocebo in medicine; delineates the current state of the literature related to placebo/nocebo in relation to pain modulation; summarizes research findings related to human performance in sports and exercise; discusses the implications of placebo/nocebo effects among diverse patient populations; and describes placebo/nocebo influences in research related to psychopharmacology, including the relevance of endogenous opioids to new lines of research on antidepressant pharmacotherapies.

Descending mechanism by which medial prefrontal cortex endocannabinoid signaling controls the development of neuropathic pain and neuronal activity of dorsal root ganglion

ABSTRACT

Although regulation of nociceptive processes in the dorsal horn by deep brain structures has long been established, the role of cortical networks in pain regulation is minimally explored. The medial prefrontal cortex (mPFC) is a key brain area in pain processing that receives ascending nociceptive input and exerts top-down control of pain sensation. We have shown critical changes in mPFC synaptic function during neuropathic pain, controlled by endocannabinoid (eCB) signaling. This study tests whether mPFC eCB signaling modulates neuropathic pain through descending control. Intra-mPFC injection of cannabinoid receptor type 1 (CB1R) agonist WIN-55,212-2 (WIN) in the chronic phase transiently alleviates the pain-like behaviors in spared nerve injury (SNI) rats. By contrast, intra-mPFC injection of CB1R antagonist AM4113 in the early phase of neuropathic pain reduces the development of pain-like behaviors in the chronic phase. Spared nerve injury reduced the mechanical threshold to induce action potential firing of dorsal horn wide-dynamic-range neurons, but this was reversed in rats by WIN in the chronic phase of SNI and by mPFC injection of AM4113 in the early phase of SNI. Elevated dorsal root ganglion neuronal activity after injury was also diminished in rats by mPFC injection of AM4113, potentially by reducing antidromic activity and subsequent neuronal inflammation. These findings suggest that depending on the phase of the pain condition, both blocking and activating CB1 receptors in the mPFC can regulate descending control of pain and affect both dorsal horn neurons and peripheral sensory neurons, contributing to changes in pain sensitivity.

Physical activity, sitting time, and thermal quantitative sensory testing responses in African Americans

Introduction

Prior research suggests that African Americans (AAs) have more frequent, intense, and debilitating pain and functional disability compared with non-Hispanic Whites (NHWs). Potential contributing factors to this disparity are physical activity and sedentary behavior, given that AAs are less physically active, and physical activity is associated with antinociception (whereas sedentary behavior is linked to pronociception). However, impact of these factors on pain processing has largely been unexplored in AAs, especially before chronic pain onset.

Objective

This study examined relationships between physical activity, sedentary behavior (sitting time), and laboratory measures of pain and pain modulation in adult AAs. These included heat pain threshold and tolerance, temporal summation of pain (TSP, a marker of central sensitization), and conditioned pain modulation (CPM, a marker of descending pain inhibition).

Methods

Multiple regressions were conducted to examine the effects of physical activity and sitting time on heat threshold and tolerance. Multilevel models were conducted to assess the relationship between physical activity, sitting time, and temporal summation of pain. Additional multilevel models were conducted to assess the relationship between physical activity, sitting time, and conditioned pain modulation.

Results

Higher level of physical activity, but not sitting time, was associated with reduced TSP slopes. Neither physical activity nor sitting time was associated with CPM slopes. No significant relationships between physical activity or sitting time and heat pain threshold or tolerance were detected.

Conclusions

These findings suggest that physical activity is associated with reduced TSP, an effect which may be driven by reduced spinal hyperexcitability in more active individuals. Thus, structural and individual interventions designed to increase physical activity in healthy, young AAs may be able to promote antinociceptive processes (ie, reduced TSP/reduced pain facilitation) potentially protective against chronic pain.

Mechanisms and treatments of chronic pain after traumatic brain injury

While pain after trauma generally resolves, some trauma patients experience pain for months to years after injury. An example, relevant to both combat and civilian settings, is chronic pain after traumatic brain injury (TBI). Headache as well as pain in the back and extremities are common locations for TBI-related chronic pain to be experienced. TBI-related pain can exist alone or can exacerbate pain from other injuries long after healing has occurred. Consequences of chronic pain in these settings include increased suffering, higher levels of disability, serious emotional problems, and worsened cognitive deficits. The current review will examine recent evidence regarding dysfunction of endogenous pain modulatory mechanisms, neuroplastic changes in the trigeminal circuitry and alterations in spinal nociceptive processing as contributors to TBI-related chronic pain. Key pain modulatory centers including the locus coeruleus, periaqueductal grey matter, and rostroventromedial medulla are vulnerable to TBI. Both the rationales and existing evidence for the use of monoamine reuptake inhibitors, CGRP antagonists, CXCR2 chemokine receptor antagonists, and interventional therapies will be presented. While consensus guidelines for the management of chronic post-traumatic TBI-related pain are lacking, several approaches to this clinically challenging situation deserve focused evaluation and may prove to be viable therapeutic options.

Neurophysiological oscillatory markers of hypoalgesia in conditioned pain modulation

Introduction

Conditioned pain modulation (CPM) is an experimental procedure that consists of an ongoing noxious stimulus attenuating the pain perception caused by another noxious stimulus. A combination of the CPM paradigm with concurrent electrophysiological recordings can establish whether an association exists between experimentally modified pain perception and modulations of neural oscillations.

Objectives

We aimed to characterize how CPM modifies pain perception and underlying neural oscillations. We also interrogated whether these perceptual and/or neurophysiological effects are distinct in patients affected by chronic pain.

Methods

We presented noxious electrical stimuli to the right ankle before, during, and after CPM induced by an ice pack placed on the left forearm. Seventeen patients with chronic pain and 17 control participants rated the electrical pain in each experimental condition. We used magnetoencephalography to examine the anatomy-specific effects of CPM on the neural oscillatory responses to the electrical pain.

Results

Regardless of the participant groups, CPM induced a reduction in subjective pain ratings and neural responses (beta-band [15-35 Hz] oscillations in the sensorimotor cortex) to electrical pain.

Conclusion

Our findings of pain-induced beta-band activity may be associated with top-down modulations of pain, as reported in other perceptual modalities. Therefore, the reduced beta-band responses during CPM may indicate changes in top-down pain modulations.

Adversity type and timing predict temporal summation of pain in African-American adults

African Americans are disproportionately exposed to adversity across the lifespan, which includes both stressful and traumatic events. Adversity, in turn, is associated with alterations in pain responsiveness. Racial differences in pain responsiveness among healthy adults are well established. However, the extent to which adversity type and timing are associated with alterations in pain responsiveness among healthy African-American adults is not well understood. The present study included 160 healthy African-American adults (98 women), ages 18 to 45. Outcome measures included pain tolerance and temporal summation of pain to evoked thermal pain. Composite scores were created for early-life adversity (childhood trauma, family adversity) and recent adversity (perceived stress, chronic stress burden). A measure of lifetime racial discrimination was also included. Higher levels of recent adversity were associated with higher temporal summation of pain, controlling for gender, age, and education. Neither early-life adversity nor lifetime racial discrimination were associated with temporal summation of pain. The present findings suggest that heightened temporal summation of pain among healthy African-American adults is associated with exposure to recent adversity events. Improved understanding of how recent adversity contributes to heightened temporal summation of pain in African Americans could help to mitigate racial disparities in pain experiences by identifying at-risk individuals who could benefit from early interventions.

Physical Activity to Prevent the Age-Related Decline of Endogenous Pain Modulation

As humans age, the capacity of the central nervous system to endogenously modulate pain significantly deteriorates, thereby increasing the risk for the development of chronic pain. Older adults are the least physically active cohort of all age groups. We hypothesize that a sedentary lifestyle and decreased physical activity may contribute to the decline of endogenous pain modulation associated with aging.

Effect of Voluntary Exercise on Endogenous Pain Control Systems and Post-traumatic Headache in Mice

Traumatic brain injury (TBI) can cause acute and chronic pain along with motor, cognitive, and emotional problems. Although the mechanisms are poorly understood, previous studies suggest disruptions in endogenous pain modulation may be involved. Voluntary exercise after a TBI has been shown to reduce some consequences of injury including cognitive impairment. We hypothesized, therefore, that voluntary exercise could augment endogenous pain control systems in a rodent model of TBI. For these studies, we used a closed-head impact procedure in male mice modeling mild TBI. We investigated the effect of voluntary exercise on TBI-induced hindpaw nociceptive sensitization, diffuse noxious inhibitory control failure, and periorbital sensitization after bright light stress, a model of post-traumatic headache. Furthermore, we investigated the effects of exercise on memory, circulating markers of brain injury, neuroinflammation, and spinal cord gene expression. We observed that exercise significantly reduced TBI-induced hindpaw allodynia and periorbital allodynia in the first week following TBI. We also showed that exercise improved the deficits associated with diffuse noxious inhibitory control and reduced bright light stress-induced allodynia up to 2 months after TBI. In addition, exercise preserved memory and reduced TBI-induced increases in spinal BDNF, CXCL1, CXCL2, and prodynorphin expression, all genes previously linked to TBI-induced nociceptive sensitization. Taken together, our observations suggest that voluntary exercise may reduce pain after TBI by reducing TBI-induced changes in nociceptive signaling and preserving endogenous pain control systems. PERSPECTIVE: This article evaluates the effects of exercise on pain-related behaviors in a preclinical model of traumatic brain injury (TBI). The findings show that exercise reduces nociceptive sensitization, loss of diffuse noxious inhibitory control, memory deficits, and spinal nociception-related gene expression after TBI. Exercise may reduce or prevent pain after TBI.

Sensory stimulations potentializing digital therapeutics pain control

For the past two decades, using Digital Therapeutics (DTx) to counter painful symptoms has emerged as a novel pain relief strategy. Several studies report that DTx significantly diminish pain while compensating for the limitations of pharmacological analgesics (e.g., addiction, side effects). Virtual reality (VR) is a major component of the most effective DTx for pain reduction. Notably, various stimuli (e.g., auditory, visual) appear to be frequently associated with VR in DTx. This review aims to compare the hypoalgesic power of specific stimuli with or without a VR environment. First, this review will briefly describe VR technology and known elements related to its hypoalgesic effect. Second, it will non-exhaustively list various stimuli known to have a hypoalgesic effect on pain independent of the immersive environment. Finally, this review will focus on studies that investigate a possible potentialized effect on pain reduction of these stimuli in a VR environment.

The relationship between musicianship and pain. Is chronic pain and its management a problem for student musicians only?

Introduction

The neuro-biological side of chronic pain research has presented reliable evidence of distinct cortical and spinal alteration compared to healthy individuals. Furthermore, research suggests that musicians are especially vulnerable to pain, and recent neurological investigations into musicians' brain plasticity support this hypothesis. However, chronic pain is not acute pain plus time, but a separate condition, and little is known about musicians' chronic pain-related emotions and behaviors. This knowledge, however, is a crucial step in understanding how chronic pain is processed by musicians.

Methods

This study investigated pain catastrophizing as a critical pain-related behavior and emotional concept alongside six complementary variables: anxiety, depression, depersonalisation, burnout, coping strategies and professional identity.

Results

103 under- and postgraduate students from various higher education institutions participated in an online survey. Students were allocated into three groups according to their main study subject and type of institution: music college musicians, university musicians and university non-musicians. A tree model confirmed the current chronic pain multifactorial model, suggesting a combination of several variables before catastrophizing pain. Group testing, however, showed that university non-musicians' pain catastrophizing was significantly worse especially when compared to music college musicians. Music college musicians and university musicians were less prone to maladaptive pain processes, despite perceiving pain for significantly longer.

Discussion

This novel finding indicates that chronic pain does not inevitably lead to dysfunctional pain processing for musicians and should be reflected accordingly to optimize pain-control. The biopsychosocio model of chronic pain provides a robust framework for future research in this population.

Heat of the night: sleep disturbance activates inflammatory mechanisms and induces pain in rheumatoid arthritis

Sleep has a homeostatic role in the regulation of the immune system and serves to constrain activation of inflammatory signalling and expression of cellular inflammation. In patients with rheumatoid arthritis (RA), a misaligned inflammatory profile induces a dysregulation of sleep-wake activity, which leads to excessive inflammation and the induction of increased sensitivity to pain. Given that multiple biological mechanisms contribute to sleep disturbances (such as insomnia), and that the central nervous system communicates with the innate immune system via neuroendocrine and neural effector pathways, potential exists to develop prevention opportunities to mitigate the risk of insomnia in RA. Furthermore, understanding these risk mechanisms might inform additional insomnia treatment strategies directed towards steering and reducing the magnitude of the inflammatory response, which together could influence outcomes of pain and disease activity in RA.

The Value of Pain Sensitivity Questionnaire in Predicting Postoperative Pain in Living Kidney Donors: A Prospective Observational Study

Purpose

This study aimed to investigate the value of the Pain Sensitivity Questionnaire (PSQ) for the prediction of postoperative pain and the relationship between pain sensitivity and postoperative pain in kidney donors undergoing living-related kidney transplantation.

Patients and Methods

A total of 148 kidney donors were selected and the preoperative pain sensitivity questionnaire was administered the day before surgery. Kidney donors were assigned to low PSQ group (PSQ < 6.5, n = 76) or high PSQ group (PSQ ≥ 6.5, n = 72). The primary endpoint was the number of patient-controlled analgesia (PCA). Other outcomes included: the incidence of acute pain, flurbiprofen axetil remediation rate, the incidence of chronic pain, neuropathic pain assessment scale (Douleur Neuropathique 4 Questions, DN4), visual analog scale (VAS) at rest after surgery as well as the correlation between PSQ and QST (Quantitative Sensory Testing).

Results

The low PSQ group had a significantly lower number of PCA than high PSQ group (P < 0.0001). The incidence of acute pain was 75% in low PSQ group and 100% in high PSQ group (P < 0.0001). Furthermore, flurbiprofen axetil remediation rate was lower in low PSQ group than that in high PSQ group (P = 0.042). The incidence of chronic pain was significantly lower in low PSQ group than in high PSQ group (6.6% vs 61.1%, P < 0.001). Moreover, DN4 was significantly lower in low PSQ group than that in high PSQ group (P < 0.001). The PSQ-mean was significantly negatively correlated with QST in kidney donors. VAS at rest for the low PSQ group were lower than those of the high PSQ group.

Conclusion

The PSQ was found to be associated with the intensity or postoperative pain and might be used to screen patients prior to living-kidney transplantation.

Relationship between Motor Corticospinal System, Endogenous Pain Modulation Mechanisms and Clinical Symptoms in Patients with Knee Osteoarthritis: New Perspectives on an Old Disease

Knee osteoarthritis (OA) is a painful condition characterized by joint and bone changes. A growing number of studies suggest that these changes only partially explain the pain experienced by individuals with OA. The purpose of the current study was to evaluate if corticospinal and bulbospinal projection measurements were interrelated in patients with knee OA, and to explore the relationship between these neurophysiological measures and temporal summation (excitatory mechanisms of pain) on one hand, and clinical symptoms on the other. Twenty-eight (28) patients with knee OA were recruited. Corticospinal projections were measured using transcranial magnetic stimulation, while bulbospinal projections were evaluated with a conditioned pain modulation (CPM) protocol using a counter-irritation paradigm. Validated questionnaires were used to document clinical and psychological manifestations. All participants suffered from moderate to severe pain. There was a positive association between corticospinal excitability and the effectiveness of the CPM (rs = 0.67, p = 0.01, n = 13). There was also a positive relationship between pain intensity and corticospinal excitability (rs = 0.45, p = 0.03, n = 23), and between pain intensity and temporal summation (rs = 0.58, p = 0.01, n = 18). The results of this study highlight some of the central nervous system changes that could be involved in knee OA and underline the importance of interindividual variability to better understand and explain the semiology and pathophysiology of knee OA.

Prolonged continuous theta burst stimulation increases motor corticospinal excitability and intracortical inhibition in patients with neuropathic pain: An exploratory, single-blinded, randomized controlled trial

OBJECTIVES

A new paradigm for Transcranial Magnetic Stimulation (TMS), referred to as prolonged continuous theta burst stimulation (pcTBS), has recently received attention in the literature because of its advantages over high frequency repetitive TMS (HF-rTMS). Clinical advantages include less time per intervention session and the effects appear to be more robust and reproducible than HF-rTMS to modulate cortical excitability. HF-rTMS targeted at the primary motor cortex (M1) has demonstrated analgesic effects in patients with neuropathic pain but their mechanisms of action are unclear and pcTBS has been studied in healthy subjects only. This study examined the neural mechanisms that have been proposed to play a role in explaining the effects of pcTBS targeted at the M1 and DLPFC brain regions in neuropathic pain (NP) patients with Type 2 diabetes.

METHODS

Forty-two patients with painful diabetic neuropathy were randomized to receive a single session of pcTBS targeted at the left M1 or left DLPFC. pcTBS stimulation consisted of 1,200 pulses delivered in 1 min and 44 s with a 35-45 min gap between sham and active pcTBS stimulation. Both the activity of the descending pain system which was examined using conditioned pain modulation and the activity of the ascending pain system which was assessed using temporal summation of pain were recorded using a handheld pressure algometer by measuring pressure pain thresholds. The amplitude of the motor evoked potential (MEP) was used to measure motor corticospinal excitability and GABA activity was assessed using short (SICI) and long intracortical inhibition (LICI). All these measurements were performed at baseline and post-pcTBS stimulation.

RESULTS

Following a single session of pcTBS targeted at M1 and DLPFC, there was no change in BPI-DN scores and on the activity of the descending (measured using conditioned pain modulation) and ascending pain systems (measured using temporal summation of pain) compared to baseline but there was a significant improvement of >13% in perception of acute pain intensity, increased motor corticospinal excitability (measured using MEP amplitude) and intracortical inhibition (measured using SICI and LICI).

CONCLUSION

In patients with NP, a single session of pcTBS targeted at the M1 and DLPFC modulated the neurophysiological mechanisms related to motor corticospinal excitability and neurochemical mechanisms linked to GABA activity, but it did not modulate the activity of the ascending and descending endogenous modulatory systems. In addition, although BPI-DN scores did not change, there was a 13% improvement in self-reported perception of acute pain intensity.

Alleviation of thermal nociception depends on heat-sensitive neurons and a TRP channel in the brain

Acute avoidance of dangerous temperatures is critical for animals to prevent or minimize injury. Therefore, surface receptors have evolved to endow neurons with the capacity to detect noxious heat so that animals can initiate escape behaviors. Animals including humans have evolved intrinsic pain-suppressing systems to attenuate nociception under some circumstances. Here, using Drosophila melanogaster, we uncovered a new mechanism through which thermal nociception is suppressed. We identified a single descending neuron in each brain hemisphere, which is the center for suppression of thermal nociception. These Epi neurons, for Epione-the goddess of soothing of pain-express a nociception-suppressing neuropeptide Allatostatin C (AstC), which is related to a mammalian anti-nociceptive peptide, somatostatin. Epi neurons are direct sensors for noxious heat, and when activated they release AstC, which diminishes nociception. We found that Epi neurons also express the heat-activated TRP channel, Painless (Pain), and thermal activation of Epi neurons and the subsequent suppression of thermal nociception depend on Pain. Thus, while TRP channels are well known to sense noxious temperatures to promote avoidance behavior, this work reveals the first role for a TRP channel for detecting noxious temperatures for the purpose of suppressing rather than enhancing nociception behavior in response to hot thermal stimuli.

Post-injury pain and behaviour: a control theory perspective

Injuries of various types occur commonly in the lives of humans and other animals and lead to a pattern of persistent pain and recuperative behaviour that allows safe and effective recovery. In this Perspective, we propose a control-theoretic framework to explain the adaptive processes in the brain that drive physiological post-injury behaviour. We set out an evolutionary and ethological view on how animals respond to injury, illustrating how the behavioural state associated with persistent pain and recuperation may be just as important as phasic pain in ensuring survival. Adopting a normative approach, we suggest that the brain implements a continuous optimal inference of the current state of injury from diverse sensory and physiological signals. This drives the various effector control mechanisms of behavioural homeostasis, which span the modulation of ongoing motivation and perception to drive rest and hyper-protective behaviours. However, an inherent problem with this is that these protective behaviours may partially obscure information about whether injury has resolved. Such information restriction may seed a tendency to aberrantly or persistently infer injury, and may thus promote the transition to pathological chronic pain states.

High intensity-transcutaneous electrical nerve stimulation does not inhibit temporal summation of the nociceptive flexion reflex

Pain facilitation contributes to chronic pain conditions. Transcutaneous electrical nerve stimulation (TENS) is used to alleviate pain. The effects of conventional TENS on chronic pain have been limited, and its effects on pain facilitation are controversial. Because the analgesic effects of TENS depend on the setting parameters (e.g., pulse intensities or treatment time), the optimal TENS settings to maximize analgesic effects under various pain conditions have been investigated. High-intensity TENS (HI-TENS), which involves tolerable-level pulse intensities for a short duration, is another conventional TENS method that used to alleviate pain. However, the effects of HI-TENS on pain facilitation remain unclear. The temporal summation of pain is widely used to evaluate pain facilitation, and the temporal summation-nociceptive flexion reflex (TS-NFR) is a neuropsychological parameter that can be used to evaluate pain facilitation. We aimed to investigate the effects of HI-TENS on the TS-NFR in healthy participants. Participants were randomly allocated into HI-TENS (n = 15) and control groups (n = 16). HI-TENS was administered at the left lateral lower leg for 1 min. The TS-NFR elicited by three noxious stimuluses at the left sural nerve was obtained from electromyography of the left biceps femoris. The nociceptive flexion reflex (NFR) was obtained by a single noxious stimulus. We measured the thresholds of the NFR and the TS-NFR at baseline and post-intervention. The application of HI-TENS significantly increased the NFR threshold (p = 0.013) but not the TS-NFR threshold (p > 0.05). These results suggest that HI-TENS does not inhibit pain facilitation.

Rat model of attention-deficit hyperactivity disorder exhibits delayed recovery from acute incisional pain due to impaired descending noradrenergic inhibition

Chronic pain and attention-deficit hyperactivity disorder (ADHD) frequently coexist. However, the common pathology is still unclear. Attenuated noradrenergic endogenous analgesia can produce acute pain chronification, and dysfunction of noradrenergic systems in the nervous system is relevant to ADHD symptoms. Noxious stimuli-induced analgesia (NSIA) is measured to estimate noradrenergic endogenous analgesia in spontaneously hypertensive rats (SHR) as an ADHD model and control. Recovery of pain-related behaviors after paw incision was assessed. Contributions of noradrenergic systems were examined by in vivo microdialysis and immunohistochemistry. The SHR showed attenuated NSIA and needed a more extended period for recovery from acute pain. These results suggest ADHD patients exhibit acute pain chronification due to pre-existing attenuated noradrenergic endogenous analgesia. Immunohistochemistry suggests abnormal noradrenaline turnover and downregulation of the target receptor (alpha2a adrenoceptor). Standard ADHD treatment with atomoxetine restored NSIA and shortened the duration of hypersensitivity after the surgery in the SHR. NSIA protocol activated the locus coeruleus, the origin of spinal noradrenaline, of both strains, but only the control exhibited an increase in spinal noradrenaline. This result suggests dysfunction in the noradrenaline-releasing process and can be recognized as a novel mechanism of attenuation of noradrenergic endogenous analgesia.

Thermal grill illusion of pain in patients with chronic pain: a clinical marker of central sensitization?

ABSTRACT

The thermal grill illusion of pain (TGIP) is a paradoxical burning pain sensation elicited by the simultaneous application of innocuous cutaneous warm and cold stimuli with a thermode ("thermal grill") consisting of interlaced heated and cooled bars. Its neurophysiological mechanisms are unclear, but TGIP may have some mechanisms in common with pathological pain, including central sensitization in particular, through the involvement of N-methyl- d -aspartate receptors. However, few studies have investigated TGIP in patients with chronic pain and its clinical relevance is uncertain. We hypothesized that the TGIP would be increased in comparison with controls in patients with fibromyalgia or irritable bowel syndrome, which are regarded as typical "nociplastic" primary pain syndromes related to changes in central pain processing. We compared the sensations elicited by a large range of combinations of temperature differentials between the warm and cold bars of a thermal grill applied to the hand between patients with fibromyalgia (n = 30) or irritable bowel syndrome (n= 30) and controls (n = 30). The percentage of TGIP responses and the intensity and unpleasantness of TGIP were significantly greater in patients than controls. Furthermore, positive correlations were found between TGIP intensity and clinical pain intensity and between TGIP intensity and the cold pain threshold measured on the hand. These results are consistent with our working hypothesis of shared mechanisms between TGIP and clinical pain mechanisms in patients with nociplastic chronic pain syndromes and suggest that TGIP might represent a clinical marker of central sensitization in these patients.

The Effects of Recovery Sleep on Experimental Pain

Recent research suggests that recovery sleep (RS) has the potential to restore pain sensitivity and modulation after hyperalgesia due to preceding sleep deprivation. However, it has not yet been systematically examined whether the restoration of these pain parameters is driven by sleep characteristics of RS. Thus, the present study assessed changes in experimental pain during RS after total sleep deprivation (TSD) to test whether RS parameters predicted the restoration of the pain system. Thirty healthy participants completed one night of habitual sleep, one night of TSD and a subsequent recovery night. At-home sleep during baseline and recovery was assessed using portable polysomnography and a questionnaire. Before and after each night pressure pain thresholds (PPTs), temporal pain summation (TSP) and conditioned pain modulation (CPM) were assessed. PPTs decreased after TSD and increased following RS, indicating a restoration of pain sensitivity after hyperalgesia. RS characteristics did not predict this restoration, suggesting other mechanisms (eg, changes in serotonergic activity) underlying the observed pain changes. TSP indicated a lack of effect of experimental sleep manipulations on excitatory processes whereas CPM lacked sufficient reliability to investigate inhibitory processes. Thus, results indicate moderate effects of sleep manipulations on pain sensitivity, but not on pain modulation. PERSPECTIVE: This article highlights the potential of recovery sleep to let pain thresholds return to normal following their decrease after a night of total sleep deprivation. In contrast, endogenous pain modulation (temporal pain summation, conditioned pain modulation) was not affected by sleep deprivation and recovery sleep.

Significant Analgesic Benefits of Perioperative Duloxetine in Patients Who Have Depressive Symptoms Undergoing Total Hip Arthroplasty: A Randomized Controlled Trial

BACKGROUND

Major symptoms of depression are commonly observed in patients requiring total hip arthroplasty (THA), and this is associated with increased pain scores and opioid consumption. We aimed to investigate the analgesic effect of duloxetine in these high-risk patients.

METHODS

Among 263 patients scheduled for primary unilateral THA, 67 patients who scored at least 8 on the 17-item Hamilton Depression Scale (HAMD) were enrolled in this study. Patients were randomized to the duloxetine group (60 mg daily, from the day of surgery to postoperative day 6) or the placebo group. The postoperative visual analog scale (VAS) score during walking, the VAS score during hip flexion, and resting VAS score was measured. Postoperative morphine consumption, hip range of motion (ROM), Harris hip score (HHS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) function, postoperative length of stay (LOS), and adverse events were recorded.

RESULTS

The duloxetine group had significantly lower VAS scores during walking and hip flexion from postoperative day 3 to week 3 than the placebo group. With regard to the resting VAS score, duloxetine showed a better analgesic effect from postoperative day 3 to week 2 than placebo. Patients in the duloxetine group had less consumption of morphine. The duloxetine group exhibited better hip function scores, including ROM, HHS, and WOMAC function scores than the placebo group. No significant difference was observed in LOS or adverse events between groups.

CONCLUSION

Perioperative short-term duloxetine provides advantages in decreasing pain, reducing morphine consumption, and increasing hip function in THA patients who have depressive symptoms.

Broad-spectrum cannabis oil ameliorates reserpine-induced fibromyalgia model in mice

Fibromyalgia (FM) is an idiopathic disorder characterized by generalized pain and associated symptoms such as depression and anxiety. Cannabis sativa shows different pharmacological activities, such as analgesic, anti-inflammatory, neuroprotective, and immunomodulatory. Associated with this, the use of an oil with low concentrations of THC can reduce the psychomimetic adverse effects of the plant. Therefore, the present study aimed to evaluate the analgesic effect of broad-spectrum cannabis oil with low THC concentration in an experimental model of FM. Mechanical hyperalgesia, thermal allodynia, depressive- and anxious-related behavior, and locomotor activity were evaluated after reserpine (0.25 mg/kg; injected subcutaneously (s.c.) once daily for three consecutive days) administration. Our results showed that oral administration of broad-spectrum cannabis oil (0.1, 1, and 3 mg/kg, p.o.) in a single dose on the 4th day inhibited mechanical hyperalgesia and thermal allodynia induced by reserpine. Relevantly, treatment during four days with broad-spectrum cannabis oil (0.1 mg/kg, p.o.) reduced mechanical hyperalgesia 1 h after reserpine administration. Intraplantar treatment with cannabis oil significantly reversed mechanical and heat thermal nociception induced by reserpine injection. Interestingly, spinal and supraspinal administration of broad-spectrum cannabis oil completely inhibited mechanical hyperalgesia and thermal sensitivity induced by reserpine. The repeated cannabis oil administration, given daily for 14 days, markedly mitigated the mechanical and thermal sensitivity during the FM model, and its reduced depressive-like behavior induced by reserpine. In summary, broad-spectrum cannabis oil is an effective alternative to reverse the reserpine-induced fibromyalgia model.