The methodology of experimentally induced diffuse noxious inhibitory control (DNIC)-like effect in humans

Biopsychosocial contributors to irritability in individuals with shoulder or low back pain

OBJECTIVES

Irritability is a foundational clinical reasoning concept in rehabilitation to evaluate reactivity of the examination and treatment. While originally theorized to reflect tissue damage, a large body of evidence supports pain is a biopsychosocial experience impacted by pain sensitivity and psychological factors. Therefore, the purpose of this study was to examine biopsychosocial contributors to irritability.

METHODS

40 patients with shoulder (n = 20) and low back (n = 20) pain underwent Quantitative Sensory Testing (QST) (Pressure Pain Threshold, Heat Pain Threshold, Conditioned Pain Modulation, Temporal Summation), completed pain-related psychological questionnaires, an Exercise-Induced Hypoalgesia protocol, and standardized irritability assessment based on Clinical Practice Guidelines. Participants were then categorized as irritable or not irritable based on Maitland's criteria and by irritability level based on Clinical Practice Guidelines. An independent samples t-test examined for differences in QST and psychological factors by irritability category. A MANOVA examined for differences in QST and psychological factors by irritability level (high, moderate, low).

RESULTS

Significantly lower heat and pressure pain thresholds at multiple locations (p < 0.05), as well as less efficient conditioned pain modulation (p = 0.02), were demonstrated in individuals categorized as irritable. Heat and pressure pain thresholds were also significantly lower in patients with high irritability compared to other levels. Significantly higher depression and anger, as well as lower self-efficacy, were reported in individuals with an irritable presentation.

DISCUSSION/CONCLUSION

Biopsychosocial factors, including widespread hyperalgesia and elevated psychological factors, may contribute to an irritable presentation.

The association between conditioned pain modulation and psychological factors in people with chronic spinal pain: A systematic review

Chronic spinal pain has negative effects on physical and mental well-being. Psychological factors can influence pain tolerance. However, whether these factors influence descending modulatory control mechanisms measured by conditioned pain modulation (CPM) in people with chronic spinal pain is unclear. This systematic review investigated the association between CPM response and psychological factors in people with chronic spinal pain. Published and unpublished literature databases were searched from inception to 23rd October 2023 included MEDLINE, EMBASE, CINAHL, and PubMed. Studies assessing the association between CPM response and psychological factors in people with chronic spinal pain were eligible. Data were pooled through meta-analysis. Methodological quality was assessed using the AXIS tool and the certainty of evidence measured through GRADE. From 2172 records, seven studies (n = 598) were eligible. Quality of included studies was moderate. There was very low certainty of evidence that depression (r = 0.01 [95% CI -0.10 to 0.12], I2 = 0%), and anxiety (r = -0.20 [95% CI -0.56 to 0.16], I2 = 84%), fear avoidance (r = -0.10 [95% CI -0.30 to 0.10], I2 = 70%) had no statistical associations with CPM responder status. Higher pain catastrophising was associated with CPM non-responder status (r = -0.19; 95% CI: -0.37 to -0.02; n = 545; I2: 76%) based on a very low certainty of evidence measured by GRADE. There is currently limited available evidence demonstrating an association between CPM response and psychological factors for people with chronic pain. Managing an individual's chronic pain symptoms irrespective of comorbid psychological distress, should continue until evidence offer insights that more targeted interventions are needed.

Physical activity is predictive of conditioned pain modulation in healthy individuals: a cross-sectional study

Even in healthy populations, conditioned pain modulation (CPM) magnitude varies. This may be accounted for by (non-)modifiable factors, including physical activity. Yet, little research has thoroughly examined physical activity and its relation with CPM magnitude in a representative sample. Therefore, the present study investigated the predictive effect of physical activity on CPM magnitude in 105 healthy adults. Physical activity was assessed during seven consecutive days by self-report using the International Physical Activity Questionnaire and by monitored-based accelerometry. CPM was examined using a heterotopic noxious conditioning stimulation protocol during which the effect of a hot water conditioning stimulus on pressure pain thresholds was evaluated. Comparative, correlation, and hierarchical linear regression analyses were performed. Report-based walking predicts 4.8% of variance in pain modulatory capacity, moderate physical activity predicts 10.2% of variance in pain modulatory capacity, and report-based time spent on total physical activity predicts 7.0% of variance in pain modulatory capacity. More MET-minutes/week spent on total physical activity, including walking and moderate physical activity is associated with greater pain modulatory capacity. The findings of this study add to the limited evidence on the predictive effect of physical activity on CPM. It urges to consider physical activity a confounding factor when examining CPM. The current study provides evidence that a physically active lifestyle benefits endogenous pain modulation in healthy adults. Given its potential, walking and moderate-intensity physical activity might be achievable treatment strategies for pain patients known to have impaired CPM. PERSPECTIVE: The results of this article show that a physically active lifestyle including larger amounts of walking and moderate activity predict greater pain modulatory capacity. TRIAL REGISTRATION: This study has not been preregistered.

A sham-controlled, randomized trial of spinal cord stimulation for the treatment of pain in chronic pancreatitis

BACKGROUND

Spinal cord stimulation (SCS) has emerged as a treatment option for patients with chronic pancreatitis (CP) who experience pain that does not respond to standard interventions. However, there is a lack of sham-controlled trials to support its efficacy.

METHODS

This randomized, double-blinded, sham-controlled, cross-over trial enrolled 16 CP patients with insufficient pain relief from standard therapies. Patients underwent high-frequency (1000 Hz) paraesthesia-free SCS or sham for two 10-day stimulation periods, separated by a 3-day washout period. The primary outcome was daily pain intensity registered in a pain diary based on a numeric rating scale (NRS). Secondary outcomes included various questionnaires. Quantitative sensory testing was used to probe the pain system before and after interventions.

RESULTS

The average daily pain score on the NRS at baseline was 5.2 ± 1.9. After SCS, the pain score was 4.2 ± 2.1 compared to 4.3 ± 2.1 in the sham group (mean difference -0.1, 95% CI [-1.4 to 1.1]; P = 0.81). Similarly, no differences were observed between groups for the maximal daily pain score, secondary outcomes or quantitative sensory testing parameters. During an open-label, non-sham-controlled and non-blinded extension of the study, the average daily NRS was 5.2 ± 1.7 at baseline, 3.2 ± 1.8 at 3 months, 2.9 ± 1.9 at 6 months and 3.4 ± 2.2 at 12 months of follow-up (P = 0.001).

CONCLUSION

In this first sham-controlled trial of SCS in painful CP, we did not find evidence of short-term pain relief with paraesthesia-free high-frequency (1000 Hz) stimulation. However, evaluation of the long-term effect by larger sham-controlled trials with long-term follow-up is warranted.

SIGNIFICANCE STATEMENT

In this first sham-controlled trial to apply high-frequency (1000 Hz) spinal cord stimulation in patients with visceral pain due to chronic pancreatitis, we did not find evidence for clinically relevant pain relief. Taken together with potential procedure-related complications, adverse effects and costs associated with spinal cord stimulation, our findings question its use for management of visceral pain.

Optimizing pediatric periprocedural pain management part II-Adjunct therapies to support the use of infiltrative anesthetics

Pediatric procedure-related pain management is often incompletely understood, inadequately addressed, and critical in influencing a child's lifelong relationship with the larger healthcare community. We present a comprehensive review of infiltrative anesthetics, including a comparison of their mechanisms of action and relative safety and efficacy data to help guide clinical selection. We also describe the multimodal utilization of adjunct therapies-in series and in parallel-to support the optimization of pediatric periprocedural pain management, enhance the patient experience, and provide alternatives to sedation medication and general anesthesia.

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).

Exercise induced hypoalgesia during different intensities of a dynamic resistance exercise: A randomized controlled trial

INTRODUCTION

Exercise produces an immediate lessening of pain sensitivity (Exercise-Induced Hypoalgesia (EIH)) in healthy individuals at local and distant sites, possibly through a shared mechanism with conditioned pain modulation (CPM). Dynamic resistance exercise is a recommended type of exercise to reduce pain, yet limited research has examined the effects of intensity on EIH during this type of exercise. Therefore, the primary purpose of this study is to compare changes in PPT at a local and distant site during a leg extension exercise at a high intensity, a low intensity, or a quiet rest condition. A secondary purpose is to examine if CPM changes after each intervention. The final purpose is to examine if baseline pain sensitivity measures are correlated with response to each intervention.

METHODS

In a randomized controlled trial of 60 healthy participants, participants completed baseline pain sensitivity testing (heat pain threshold, temporal summation, a cold pressor test as measure of CPM) and were randomly assigned to complete a knee extension exercise at: 1) high intensity (75% of a 1 Repetition Maximum (RM), 2) low intensity (30% 1RM), or 3) Quiet Rest. PPT was measured between each set at a local (quadriceps) and distant (trapezius) site during the intervention. CPM was then repeated after the intervention. To test the first purpose of the study, a three-way ANOVA examined for time x site x intervention interaction effects. To examine for changes in CPM by group, a mixed-model ANOVA was performed. Finally, a Pearson Correlation examined the association between baseline pain sensitivity and response to each intervention.

RESULTS

Time x site x intervention interaction effects were not significant (F(5.3, 150.97) = 0.87, p = 0.51, partial eta2 = 0.03). CPM did not significantly change after the interventions (time x intervention F(1,38) = 0.81, p = 0.37, partial eta2 = 0.02. EIH effects at the quadriceps displayed a significant, positive moderate association with baseline HPT applied over the trapezius (r = 0.61, p<0.01) and TS (r = 0.46, p = 0.04).

DISCUSSION

In healthy participants, PPT and CPM did not significantly differ after a leg extension exercise performed at a high intensity, low intensity, or quiet rest condition. It is possible pre-intervention CPM testing with a noxious stimuli may have impaired inhibitory effects frequently observed during exercise but future research would need to examine this hypothesis.

Effect of Low-Intensity Bloodflow Restriction Training on Nontraumatic Knee Joint Conditions: A Systematic Review and Meta-analysis

CONTEXT

Nontraumatic knee conditions are common in clinical practice. Existing pharmaceutical and immobilization approaches provide limited pain relief and functional enhancement. Low-intensity bloodflow restriction training (LI-BFRT) is being investigated as a nonpharmacological alternative; however, its efficacy is uncertain.

OBJECTIVE

To assess the effectiveness of LI-BFRT for nontraumatic knee conditions and compare it with high-intensity resistance training (HI-RT) and low-intensity resistance training (LI-RT).

DATA SOURCES

PubMed, EBSCO, Science Direct, Cochrane Library, China Knowledge Infrastructure, Wanfang Data, and VIP databases were searched until May 30, 2023.

STUDY SELECTION

Original randomized controlled trials involving nontraumatic knee joint conditions with interventions consisting mainly of LI-BFRT, HI-RT, or LI-RT. The results assessed mainly pain and muscle performance.

STUDY DESIGN

Systematic review and meta-analysis.

LEVEL OF EVIDENCE

Level 1.

DATA EXTRACTION

Sample characteristics, study design, country, disease, groups, evaluation time, duration, and outcomes were extracted.

RESULTS

A total of 13 randomized controlled trials were included in the systematic review. Compared with pretreatment, LI-BFRT significantly alleviated pain (weighted standardized mean difference [SMD], -1.33; 95% CI, -1.62 to -1.05), with better additional effects on hip muscle training (SMD, -3.14; 95% CI, -4.07 to -2.75). Compared with LI-RT, LI-BFRT significantly relieved pain in male patients (SMD, -1.47; 95% CI, -1.92 to -1.01). LI-BFRT significantly increased quadriceps cross-sectional area (SMD, 0.53; 95% CI, 0.27-0.78), knee extension strength (SMD, 0.84; 95% CI, 0.48-1.2), and leg press strength (SMD, 0.64; 95% CI, 0.34-0.94) compared with pretreatment. Its effects were superior to those of LI-RT and similar to those of HI-RT. However, sex differences in muscle strength improvement were observed.

CONCLUSION

In patients with nontraumatic knee joint conditions, LI-BFRT effectively alleviated pain, increased muscle cross-sectional area, and enhanced muscle strength. LI-BFRT showed pain relief comparable with that of LI-RT while surpassing LI-RT in muscle growth and strength improvement.

Conditioned pain modulation, kinesiophobia, and pain catastrophizing as prognostic factors for chronicity in a population with acute low back pain: An exploratory prospective study

BACKGROUND

Psychosocial factors and alteration of the somatosensory functions have been associated with persistent low back pain (LBP). A decreased capacity of the central nervous system to modulate pain has been suggested as a potential contributor to the persistence of pain.

OBJECTIVE

To investigate whether conditioned pain modulation (CPM), initial symptoms/disability, kinesiophobia, and pain catastrophizing is associated with the transition from acute to chronic LBP.

DESIGN

Prospective cohort study.

METHOD

Fifty participants presenting with acute LBP (<6 weeks) took part in three evaluation sessions (baseline, 3 and 6 months). At baseline and 3-month evaluations, all participants completed self-administered questionnaires (Oswestry Disability Index [ODI], Short Form of Brief Pain Inventory [BPI-SF], Tampa Scale of Kinesiophobia [TSK] and Pain Catastrophizing Scale [PCS]) and CPM was assessed. At the 6-month evaluation, questionnaires were readministered, and participants were dichotomized according to their status (Non-chronic LBP [NCLBP] or chronic LBP [CLBP]). Univariate tests were used to compare baseline variables between NCLBP and CLBP.

RESULTS

No significant baseline difference was found for TSK (p = 0.48), PCS (p = 0.78), CPM (p = 0.82), ODI (p = 0.78), BPI-SF severity (p = 0.50), and interference subscales (p = 0.54) between those categorized as NCLBP or CLBP at 6 months.

CONCLUSIONS

This exploratory study failed to support the hypothesis that inefficient CPM mechanisms and the presence of psychological factors could be factors associated with the transition to chronic pain in individuals with acute LBP.

Exploring Interactions Between Sex, Pain Characteristics, Disability, and Quality of Life in People With Chronic Spinal Pain: A Structural Equation Model

In people with nonspecific chronic spinal pain (nCSP), disability and quality of life are associated with clinical, cognitive, psychophysical, and demographic variables. However, evidence regarding the interactions between these variables is only limited to this population. Therefore, this study aims to explore path models explaining the multivariate contributions of such variables to disability and quality of life in people with nCSP. This secondary analysis uses baseline data from a randomized controlled trial including 120 participants with nCSP. Structural equation modeling was used to explore path models for the Pain Disability Index (PDI), the Short Form 36-item physical (SF-36 PC), and mental (SF-36 MC) component scores. All models included sex, pain catastrophizing, kinesiophobia, hypervigilance, and pain intensity. Additionally, the PDI and SF-36 PC models included pressure pain thresholds (PPTs) at the dominant pain site (ie, neck or low back). Significant associations were found between sex, pain cognitions, pain intensity, and PPTs. Only pain catastrophizing significantly directly influenced the PDI (P ≤ .001) and SF-36 MC (P = .014), while the direct effects on the SF-36 PC from kinesiophobia (P = .008) and pain intensity (P = .006) were also significant. However, only the combined effect of all pain cognitions on the SF-36 PC was mediated by pain intensity (P = .019). Our findings indicate that patients' pain-related cognitions have an adverse effect on their physical health-related quality of life via a negative influence on their pain intensity in people with nCSP. PERSPECTIVE: This secondary analysis details a network analysis confirming significant interactions between sex, pain cognitions, pain intensity, and PPTs in relation to disability and health-related quality of life in people with chronic spinal pain. Moreover, its findings establish the importance of pain cognitions and pain intensity for these outcomes. TRIALS REGISTRATION: Clinicaltrials.gov (NCT02098005).

An overview of systematic reviews examining the quantitative sensory testing-derived hypoalgesic effects of manual therapy for musculoskeletal pain

BACKGROUND

Changes in quantitative sensory testing (QST) after manual therapy can provide insight into pain relief mechanisms. Prior systematic reviews have evaluated manual-therapy-induced QST change. This overview of systematic reviews aims to consolidate this body of literature and critically review evidence on the hypoalgesic effects of manual therapy in clinical populations.

METHODS

A comprehensive search was conducted on PubMed, CINAHL, PsycInfo, and Embase. Peer-reviewed systematic reviews with or without meta-analysis were eligible if the reviews examined the effect of manual therapy compared to non-manual therapy interventions on QST outcomes in clinical populations. Methodological quality was assessed with the AMSTAR 2 tool. Meta-analysis results and qualitative (non-meta-analysis) interpretations were summarized by type of manual therapy. Overlap of studies was examined with the corrected covered area (CCA) index.

RESULTS

Thirty systematic reviews, including 11 meta-analyses, met inclusion. There was a slight overlap in studies (CCA of 1.72% for all reviews and 1.69% for meta-analyses). Methodological quality was predominantly low to critically low. Eight (27%) reviews examined studies with a range of manual therapy types, 13 (43%) reviews focused on joint-biased manual therapy, 7 (23%) reviews focused on muscle-biased manual therapy, and 2 (7%) reviews focused on nerve-biased manual therapy. Twenty-nine (97%) reviews reported on pressure pain threshold (PPT). Meta-analytic results demonstrated conflicting evidence that manual therapy results in greater hypoalgesic effects compared to other interventions or controls.

CONCLUSION

Our overview of QST effects, which has relevance to mechanisms underlying hypoalgesia, shows conflicting evidence from mostly low to critically low systematic reviews.

Concurrent validity of dynamic bedside quantitative sensory testing paradigms in breast cancer survivors with persistent pain

BACKGROUND

Studies on the concurrent validity of clinically applicable testing protocols for conditioned pain modulation (CPM) and temporal summation of pain (TSP) in breast cancer survivors (BCS) with persistent pain are lacking.

OBJECTIVES

This study investigated the concurrent validity of two bedside protocols for CPM and TSP in comparison to a respective reference protocol. The participants' preferences for bedside CPM and TSP protocols were assessed.

METHODS

Thirty BCS experiencing persistent pain were included in this study. Each participant underwent a reference test along with two bedside alternatives for assessing both TSP and CPM. For CPM, a cold pressor test (CPT) and blood pressure cuff (BPC) were used as conditioning stimulus. The test stimulus was elicited in parallel by pressure pain threshold after 45 and 90 s of conditioning at the lower limb. The CPM reference test consisted of parallel heat stimuli at the forearms using a two-thermode system. TSP was elicited using a von Frey monofilament (256 mN) and an algometer (98 kPa) at the affected site and opposite lower limb. The TSP reference test consisted of heat stimuli at the affected site and opposite lower limb. Participants' testing preference was examined using a purpose-designed questionnaire. Spearman's rank test examined the correlation between protocols.

RESULTS

The two bedside CPM protocols were strongly correlated (r = 0.787-0.939, p < 0.005). A strong correlation was found between the BPC protocol and reference test using the relative effect magnitude (r = 0.541-0.555, p < 0.005). The bedside TSP protocols were moderately correlated with each other only at the lower limb using absolute change scores (r = 0.455, p = 0.012). No significant correlation was found between the bedside and reference TSP protocols.

CONCLUSION

The significantly moderate to very strong correlations between the bedside protocols validate their interchangeability. Researchers and clinicians should be able to choose which bedside protocol they utilize; however, participants favored the use of a BPC and algometer for the evaluation of CPM and TSP, respectively.

Conditioned Pain Modulation Does Not Differ Between People With Lower-Limb Tendinopathy and Nontendinopathy Controls: A Systematic Review With Individual Participant Data Meta-analysis

OBJECTIVE: To explore whether people with lower-limb tendinopathy have reduced relative conditioned pain modulation (CPM) when compared to nontendinopathy controls. DESIGN: Systematic review with individual participant data (IPD) meta-analysis. LITERATURE SEARCH: Eight databases were searched until August 29, 2022. STUDY SELECTION CRITERIA: Cross-sectional studies comparing the magnitude of the CPM effect in people with lower-limb tendinopathy to nontendinopathy controls in a case-control design. DATA SYNTHESIS: Included studies provided IPD, which was reported using descriptive statistics. Generalized estimating equations (GEEs) determined between-group differences in the relative CPM effect, when adjusting for co-variables. Study quality was assessed using a Joanna Briggs Institute checklist, and certainty of the evidence was assessed using the Grading of Recommendations Assessment, Development, and Evaluations. RESULTS: Five records were included, IPD were provided for 4 studies (n = 219 with tendinopathy, n = 226 controls). The principal GEE (model 1) found no significant relative CPM effects for tendinopathy versus controls (B = -1.73, P = .481). Sex (B = 4.11, P = .160), age (B = -0.20, P = .109), and body mass index (B = 0.28, P = .442) did not influence relative CPM effect. The Achilles region had a reduced CPM effect (B = -22.01, P = .009). In model 2 (adjusting for temperature), temperature (B = -2.86, P = .035) and female sex (B = 21.01, P = .047) were associated with the size of the relative CPM effect. All studies were low-quality, and the certainty of the evidence was moderate. CONCLUSION: There were no between-group differences in the magnitude of the CPM effect, suggesting clinicians should manage lower-limb tendinopathy using interventions appropriate for peripherally dominant pain (eg, tendon loading exercises such as heavy slow resistance). Based on the "moderate"-certainty evidence, future studies are unlikely to substantially change these findings. J Orthop Sports Phys Ther 2023;54(1):1-10. Epub 19 October 2023. doi:10.2519/jospt.2023.11940.

Harnessing the conditioned pain modulation response in migraine diagnosis, outcome prediction, and treatment-A narrative review

OBJECTIVE

To present the potential use and relevance of the conditioned pain modulation (CPM) response to migraine diagnosis, outcome prediction, and treatment.

BACKGROUND

The CPM response is a widely used laboratory test to examine inhibitory pain modulation capabilities.

METHODS

This narrative review summarizes and synthesizes the findings on the CPM response in patients with migraine.

RESULTS

For diagnosis, we summarized the studies comparing CPM responses between patients with migraine and individuals without migraine or with other headache syndromes, as well as between patients with subtypes of migraine. For prediction, we summarized the studies utilizing the CPM response to predict migraine outcome, such as response to interventions. For treatment, we described a device that utilizes the CPM response for acute and preventative migraine treatment. In addition, we suggest the requirements needed for the CPM response to be used for migraine diagnosis, outcome prediction, and treatment.

CONCLUSIONS

Although more research is needed, the CPM response could be a useful tool for improving migraine management.

Psychophysics of Pain: A Methodological Introduction

For over 100 years, psychophysics ..÷ the scientific study between physical stimuli and sensation ... has been successfully employed in numerous scientific and healthcare disciplines, as an objective measure of sensory phenomena. This manuscript provides an overview of fundamental psychophysical concepts, emphasizing pain and research application..÷defining common terms, methods, and procedures.Psychophysics can provide systematic and objective measures of sensory perception that can be used by nursing scientists to explore complex, subjective phenomena..÷such as pain perception. While there needs to be improved standardization of terms and techniques, psychophysical approaches are diverse and may be tailored to address or augment current research paradigms. The interdisciplinary nature of psychophysics..÷like nursing..÷provides a unique lens for understanding how our perceptions are influenced by measurable sensations. While the quest to understand human perception is far from complete, nursing science has an opportunity to contribute to pain research by using the techniques and methods available through psychophysical procedures.

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.

Corticospinal excitability and reflex modulation in a contralateral non-stretched muscle following unilateral stretching

PURPOSE

Muscle stretching effect on the range of motion (ROM) and force deficit in non-stretched muscle, and the underlying mechanisms, is an ongoing issue. This study aimed to investigate crossover stretching effects and mechanisms on the plantar flexor muscles.

METHODS

Fourteen recreationally active females (n = 5) and males (n = 9) performed six sets of 45-s static stretching (SS) (15-s recovery) to the point of discomfort of the dominant leg (DL) plantar flexors or control (345-s rest). Participants were tested for a single 5-s pre- and post-test maximal voluntary isometric contraction (MVIC) with each plantar flexor muscle and were tested for DL and non-DL ROM. They were tested pre- and post-test (immediate, 10-s, 30-s) for the Hoffman (H)-reflex and motor-evoked potentials (MEP) from transcranial magnetic stimulation in the contralateral, non-stretched muscle.

RESULTS

Both the DL and non-DL-MVIC force had large magnitude, significant (↓10.87%, p = 0.027, pƞ2 = 0.4) and non-significant (↓9.53%, p = 0.15, pƞ2 = 0.19) decreases respectively with SS. The SS also significantly improved the DL (6.5%, p < 0.001) and non-DL (5.35%, p = 0.002) ROM. The non-DL MEP/MMax and HMax/MMax ratio did not change significantly.

CONCLUSION

Prolonged static stretching improved the stretched muscle's ROM. However, the stretched limb's force was negatively affected following the stretching protocol. The ROM improvement and large magnitude force impairment (statistically non-significant) were transferred to the contralateral muscles. The lack of significant changes in spinal and corticospinal excitability confirms that the afferent excitability of the spinal motoneurons and corticospinal excitability may not play a substantial role in non-local muscle's ROM or force output responses.

Factors predicting the transition from acute to persistent pain in people with 'sciatica': the FORECAST longitudinal prognostic factor cohort study protocol

INTRODUCTION

Sciatica is a common condition and is associated with higher levels of pain, disability, poorer quality of life, and increased use of health resources compared with low back pain alone. Although many patients recover, a third develop persistent sciatica symptoms. It remains unclear, why some patients develop persistent sciatica as none of the traditionally considered clinical parameters (eg, symptom severity, routine MRI) are consistent prognostic factors.The FORECAST study (factors predicting the transition from acute to persistent pain in people with 'sciatica') will take a different approach by exploring mechanism-based subgroups in patients with sciatica and investigate whether a mechanism-based approach can identify factors that predict pain persistence in patients with sciatica.

METHODS AND ANALYSIS

We will perform a prospective longitudinal cohort study including 180 people with acute/subacute sciatica. N=168 healthy participants will provide normative data. A detailed set of variables will be assessed within 3 months after sciatica onset. This will include self-reported sensory and psychosocial profiles, quantitative sensory testing, blood inflammatory markers and advanced neuroimaging. We will determine outcome with the Sciatica Bothersomeness Index and a Numerical Pain Rating Scale for leg pain severity at 3 and 12 months.We will use principal component analysis followed by clustering methods to identify subgroups. Univariate associations and machine learning methods optimised for high dimensional small data sets will be used to identify the most powerful predictors and model selection/accuracy.The results will provide crucial information about the pathophysiological drivers of sciatica symptoms and may identify prognostic factors of pain persistence.

ETHICS AND DISSEMINATION

The FORECAST study has received ethical approval (South Central Oxford C, 18/SC/0263). The dissemination strategy will be guided by our patient and public engagement activities and will include peer-reviewed publications, conference presentations, social media and podcasts.

TRIAL REGISTRATION NUMBER

ISRCTN18170726; Pre-results.

Efficiency of pain inhibition and facilitation of fibromyalgia patients is not different from healthy controls: Relevance of sensitivity-adjusted test stimuli

Background

Pain is a dynamic phenomenon dependent on the balance of endogenous excitatory and inhibitory systems, which can be characterized by quantitative sensory testing. Many previous studies of pain modulatory capacity of patients with fibromyalgia syndrome (FM) have reported decreased pain inhibition or increased pain facilitation. This is the first study to assess pain modulation, including conditioned pain modulation (CPM) and temporal pain summation, in the same healthy control (HC) and FM participants.

Methods

Only sensitivity-adjusted stimuli were utilized for testing of conditioned pain modulation (CPM) and temporal pain summation in 23 FM patients and 28 HC. All subjects received sensitivity-adjusted ramp-hold (sRH) during testing of pain facilitation (temporal summation) and pain inhibition (CPM). CPM efficacy was evaluated with test stimuli applied either concurrently or after application of the conditioning stimulus. Finally, the effects of CPM on pressure pain thresholds were tested.

Results

FM subjects required significantly less intense test and conditioning stimuli than HC participants to achieve standardized pain ratings of 50 ± 10 numerical rating scale (NRS) (p = 0.03). Using such stimuli, FM subjects' temporal pain summation and CPM efficacy was not significantly different from HC (all p > 0.05), suggesting similar pain facilitation and inhibition. Furthermore, the CPM efficacy of FM and HC participants was similar regardless of whether the test stimuli were applied during or after the conditioning stimulus (p > 0.05).

Conclusion

Similar to previous studies, FM participants demonstrated hyperalgesia to heat, cold, and mechanical stimuli. However, using only sensitivity-adjusted stimuli during CPM and temporal summation testing, FM patients demonstrated similarly effective pain inhibition and facilitation than HC, suggesting that their pain modulation is not abnormal.

The association between adverse childhood experiences and peripartal pain experience

ABSTRACT

Adverse childhood experiences (ACEs) are associated with altered ongoing and evoked pain experiences, which have scarcely been studied for the peripartum period. We aimed to investigate how ACEs affect pain experience in pregnancy and labor. For this noninterventional trial with a short-term follow-up, pregnant women were divided into a trauma group (TG) with ACEs (n = 84) and a control group (CG) without ACEs (n = 107) according to the Childhood Trauma Questionnaire. Pain experience in pregnancy and labor was recorded by self-report and the German Pain Perception Scale. Pain sensitivity prepartum and postpartum was assessed by Quantitative Sensory Testing and a paradigm of conditioned pain modulation (CPM), using pressure pain thresholds (PPTs) and a cold pressor test. The TG showed higher affective and sensory scores for back pain and a more than doubled prevalence of preexisting back pain. Pelvic pain differences were nonsignificant. The TG also exhibited increased affective scores (1.71 ± 0.15 vs 1.33 ± 0.11), but not sensory scores for labor pain during spontaneous delivery. There were no group differences in prepartum pain sensitivity. While PPTs increased through delivery in the CG (clinical CPM), and this PPT change was positively correlated with the experimental CPM (r = 0.55), this was not the case in the TG. The association of ACEs with increased peripartal pain affect and heightened risk for preexisting back pain suggest that such women deserve special care. The dissociation of impaired clinical CPM in women with ACEs and normal prepartum experimental CPM implies at least partly different mechanisms of these 2 manifestations of endogenous pain controls.

Exploring the sex differences in conditioned pain modulation and its biobehavioral determinants in healthy adults

BACKGROUND

Females are at greater risk of chronic pain, and exhibit higher pain sensitivity compared to males. However, sex differences in conditioned pain modulation (CPM), a neurophysiological risk factor of chronic pain, are unclear. CPM is influenced by many factors, some of which are sex-dependent. This study explored the sex differences in CPM and its biobehavioral determinants, such as blood pressure responses, physical activity levels, pain catastrophizing scores, and conditioning stimulus intensity, in young, healthy, physically active males and females.

METHODS

Twenty-six males and 24 females completed the CPM test using an electrical pain stimulus and a cold pain stimulus induced via 2 min of cold pressor test. Blood pressure was assessed at baseline and during cold pressor test, whereas cold pain ratings were obtained during cold pressor test to monitor the conditioning stimulus intensity. Physical activity was evaluated via questionnaires and accelerometer, whereas pain catastrophizing was evaluated via a questionnaire.

RESULTS

Both males and females exhibited CPM, without sex differences in the magnitude of CPM. The males showed higher resting blood pressure, higher physical activity levels, and lower pain catastrophizing scores than the females, without sex differences observed in cold pain ratings and proportion of those who met the physical activity guidelines. No correlations were observed between CPM and its determinants.

CONCLUSIONS

The results suggest the complexity of mechanisms underlying the sex differences in CPM. The sex differences in CPM, along with its determinants, may need to be examined in individuals with some risk factors for chronic pain.

Association between systemic inflammation and experimental pain sensitivity in subjects with pain and painless neuropathy after traumatic nerve injuries

OBJECTIVES

Peripheral neuropathies that occur secondary to nerve injuries may be painful or painless, and including a low-grade inflammation and pro-inflammatory cytokines associated with both regeneration and damage of peripheral nerve cells and fibers. Currently, there are no validated methods that can distinguished between neuropathic pain and painless neuropathy. The aim of this study was to search for proinflammatory and anti-inflammatory proteins associated with pain and experimental pain sensitivity in subjects with surgeon-verified nerve injuries in the upper extremities.

METHODS

One hundred and thirty-one subjects [69 with neuropathic pain, NP; 62 with painless neuropathy, nP] underwent a conditioned pain modulation (CPM) test that included a cold pressor task (CPT) conducted with the non-injured hand submerged in cold water (4 °C) until pain was intolerable. CPM was assessed by pain ratings to pressure stimuli before and after applying the CPT. Efficient CPM effect was defined as the ability of the individual's CS to inhibit at least 29% of pain (eCPM). The subjects were assigned to one of two subgroups: pain sensitive (PS) and pain tolerant (PT) after the time they could tolerate their hand in cold water (PS<40 s and PT=60 s) . Plasma samples were analyzed for 92 proteins incorporated in the inflammation panel using multiplex Protein Extension Array Technology (PEA). Differentially expressed proteins were investigated using both univariate and multivariate analysis (principal component analysis-PCA and orthogonal partial least-squares discriminant analysis-OPLS-DA).

RESULTS

Significant differences in all protein levels were found between PS and PT subgroups (CV-ANOVA p<0.001), but not between NP and nP groups (p=0.09) or between inefficient CPM (iCPM) and eCPM (p=0.53) subgroups. Several top proteins associated with NP could be detected using multivariate regression analysis such as stromelysin 2 (MMPs), interleukin-2 receptor subunit beta (IL2RB), chemokine (C-X-C motif) ligand 3 (CXCL3), fibroblast growth factor 5 (FGF5), chemokine (C-C motif) ligand 28 (CCL28), CCL25, CCL11, hepatocyte growth factor (HGF), interleukin 4 (IL4), IL13. After adjusting for multiple testing, none of these proteins correlated significantly with pain. Higher levels of CCL20 (p=0.049) and CUB domain-containing protein (CDCP-1; p=0.047) were found to correlate significantly with cold pain sensitivity. CDCP-1 was highly associated with both PS and iCPM (p=0.042).

CONCLUSIONS

No significant alterations in systemic proteins were found comparing subjects with neuropathic pain and painless neuropathy. An expression of predominant proinflammatory proteins was associated with experimental cold pain sensitivity in both subjects with pain and painless neuropathy. One these proteins, CDC-1 acted as "molecular fingerprint" overlapping both CPM and CPT. This observation might have implications for the study of pain in general and should be addressed in more detail in future experiments.

Conditioned pain modulation is not associated with thermal pain illusion

OBJECTIVES

Paradoxical sensations, known as thermal pain illusions, can be evoked by painful cold-heat pulse stimulation. They may provide diagnostic value; however, the possible interaction between conditioned pain modulation and thermal pain illusions has not been explored. The present study examined: (1) whether conditioned pain modulation could be induced by alternating tonic painful cold-heat pulse stimulation; and (2) whether the presence of thermal pain illusions during the conditioning stimulus influences the degree of conditioned pain modulation.

METHODS

This study was approved by the Ethics Committee of Meikai University (A1507). Conditioned pain modulation was provoked using alternating painful cold-heat pulses delivered at 20-s intervals applied to the forearm. Thermal pain illusions were qualitatively evaluated, and conditioned pain modulation was assessed quantitatively using the pressure pain threshold as a test stimulus. Differences in the conditioned pain modulation effect between the participants who experienced thermal pain illusions and those who did not were analysed using Student's t-test.

RESULTS

A significant positive conditioned pain modulation effect (51.0 ± 4.7%, overall effect) was detected. There was no significant difference in conditioned pain modulation between the participants who experienced thermal pain illusions and those who did not (44.3 ± 6.0% and 55.5 ± 6.8%, respectively; p = 0.255).

CONCLUSIONS

Conditioned pain modulation induced by alternating painful conditioning cold-heat pulse stimulation was identical during the conditioning stimulation in volunteers with and without thermal pain illusions. Conditioning cold-heat pulse stimulation is useful to evaluate conditioned pain modulation. Moreover, conditioned pain modulation is not influenced by the presence of thermal pain illusions, indicating partially different underlying supraspinal, neuronal networks.

Hyperbaric oxygen therapy compared to pharmacological intervention in fibromyalgia patients following traumatic brain injury: A randomized, controlled trial

Fibromyalgia is a chronic pain syndrome with unsatisfactory response to current treatments. Physical trauma, including traumatic brain Injury (TBI) is among the etiological triggers. Hyperbaric Oxygen therapy (HBOT) is an intervention that combines 100% oxygen with elevated atmospheric pressure. HBOT has been applied as a neuro-modulatory treatment in central nervous system-related conditions. The current study investigated the utility of HBOT for TBI-related fibromyalgia. Fibromyalgia patients with a history of TBI were randomized to either HBOT or pharmacological intervention. HBOT protocol comprised 60 daily sessions, breathing 100% oxygen by mask at 2 absolute atmospheres (ATA) for 90 minutes. Pharmacological treatment included Pregabalin or Duloxetine. The primary outcome was subjective pain intensity on visual analogue scale (VAS); Secondary endpoints included questionnaires assessing fibromyalgia symptoms as well as Tc-99m-ECD SPECT brain imaging. Pain threshold and conditioned pain modulation (CPM) were also assessed. Results demonstrated a significant group-by-time interaction in pain intensity post-HBOT compared to the medication group (p = 0.001), with a large net effect size (d = -0.95) in pain intensity reduction following HBOT compared to medications. Fibromyalgia related symptoms and pain questionnaires demonstrated significant improvements induced by HBOT as well as improvements in quality of life and increase in pain thresholds and CPM. SPECT demonstrated significant group-by-time interactions between HBOT and medication groups in the left frontal and the right temporal cortex. In conclusion, HBOT can improve pain symptoms, quality of life, emotional and social function of patients suffering from FMS triggered by TBI. The beneficial clinical effect is correlated with increased brain activity in frontal and parietal regions, associated with executive function and emotional processing.

Inter-subject variability of pleasant pain relief using a data-driven approach in healthy volunteers

Background

The offset of a painful and unpleasant sensation can elicit pleasure. This phenomenon, namely pleasant pain relief (PPR), is attracting growing interest in research. While the cold pressor test (CPT) has been frequently used to study the inhibition of pain by the administration of another painful stimulation (inhibitory conditioned pain modulation; ICPM), a preliminary study from our research team has shown that CPT can also elicit a robust and long-lasting PPR. However, its effects on pain relief and inhibition vary greatly between subjects. Although substantial research has been carried out on inter-individual variability in the case of ICPM, the same cannot be said of PPR. Therefore, the current study sought to identify clusters of healthy volunteers with similar dynamic pain responses during the CPT, using a data-driven approach, and to investigate the inter-subject variability for PPR and ICPM.

Methods

One hundred and twenty-two healthy volunteers were recruited. A sequential ICPM paradigm was carried out with CPT (water at 10°C) and a Peltier Thermode to evaluate pain intensity and unpleasantness. Moreover, PPR was measured for four minutes at CPT offset. Statistical analyses were performed using group-based trajectory modelling.

Results

Four trajectories (groups) were identified for CPT pain intensity and unpleasantness ratings with varying levels of tonic pain and pain sensitization (e.g., temporal summation). PPR scores were correlated with both pain ratings trajectories (p &lt; 0.001). On the other hand, no differences were found between groups regarding ICPM efficacy (percentage pain inhibition).

Discussion

This study has provided a first step into the investigation of PPR and ICPM interindividual variability. Using a data-driven approach, it was shown that PPR at CPT offset differs between clusters of participants identified based on dynamic pain intensity and unpleasantness responses from CPT. Thus, it was brought to light that both the levels of tonic pain and pain sensitization underlie individual differences in PPR. The lack of correlation between CPT pain trajectories and ICPM efficacy may be explained by the hypotheses that eliciting ICPM requires only a certain threshold of stimulation which doesn’t need to be noxious. In the future, studies on the inter-subject variability of PPR in large samples of chronic pain patients are warranted.

Sex-related differences in experimental pain sensitivity in subjects with painful or painless neuropathy after surgical repair of traumatic nerve injuries

Higher pain intensities at all experimental stimuli but a tendency to faster recovery after cold conditioning stimuli were seen in women with neuropathy in comparison with men.

Introduction:

Sex-related influences represent a contributor to greater pain sensitivity and have a higher prevalence of many chronic pain conditions, including neuropathic pain (NP), among women.

Objectives:

The aim was to analyze how differences in ongoing pain, experimental pain intensity, and conditioned pain modulation (CPM) relate to sex in subjects with neuropathy after traumatic nerve injuries.

Methods:

Endogenous pain modulation was compared between male (n = 77) and female (n = 55) subjects and between subjects with NP (female = 31, male = 39) and pain-free subjects with posttraumatic neuropathy (female = 24, male = 38). Conditioned pain modulation was assessed by pain ratings to pressure stimuli before and after a noxious conditioning stimulus (CS) conducted with one arm submerged in cold water (4°C) for 1 minute. Time of recovery (Time off) of pain intensity from peak VAS_maxc after CS was recorded and compared between male and female patients.

Results:

Greater ongoing pain intensity was found among female patients compared with male patients and more experimental pain after pressure and cold induced pain. Summing all groups together, women had 0.8 times higher odds (20%) of recovering sooner than men after CS (95% CI = 0.65–2.9). No differences in CPM, time off, and psychosocial variables were seen between female and male patients (P < 0.05).

Conclusion:

Our hypothesis for sex differences in endogenous pain modulation was only supported by a shorter after-sensation time after cold CS in female patients. No sex differences in the magnitude of CPM effect were identified. Increased pain intensity for experimental pain, in both neuropathic pain and neuropathy without pain, was found in female patients.

The effects of cannabidiol and analgesic expectancies on experimental pain reactivity in healthy adults: A balanced placebo design trial

Despite its frequent use for pain relief, no experimental pain research has tested the analgesic effects of cannabidiol (CBD) in humans. The goal of this study was to experimentally test the effects of CBD and expectancies for receiving CBD on human pain reactivity. Using a crossover, 2 × 2 factorial balanced placebo design, drug administration (given inactive substance or given active CBD) and verbal instruction sets (told inactive substance or told active CBD) were experimentally manipulated. Fifteen healthy adults each completed four separate experimental sessions. Participants were randomly assigned to different counterbalanced manipulation conditions at each session: control (told inactive-given inactive); expectancy (told active CBD-given inactive); drug (told inactive-given active CBD); and expectancy + drug (told active CBD-given active CBD). Primary outcomes were pain threshold, tolerance, intensity, unpleasantness, conditioned pain modulation (CPM), and offset analgesia (OA). There was a significant main effect of instructions on OA, such that the OA response was significantly larger when participants were told that they received CBD, regardless of drug content. Pain unpleasantness was significantly reduced in the drug, expectancy, and expectancy + drug conditions, relative to the control condition. The drug and expectancy conditions separately improved CPM, whereas the expectancy + drug and control conditions produced the lowest CPM change scores. We did not detect significant effects for pain threshold, tolerance, or intensity. Our results indicated that separate pain outcomes can be differentially affected by CBD and/or expectancies for receiving CBD. Future investigations of the psychological and pharmacological mechanisms underlying CBD analgesia are warranted. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Effects of psychosocial stress and performance feedback on pain processing and its correlation with subjective and neuroendocrine parameters

OBJECTIVES

Previous research on stress-induced pain modulation suggests that moderate psychological stress usually leads to hyperalgesia while more severe threat results in hypoalgesia. However, existing studies often lack suitable control conditions imperative to identify mere stress effects. Similarly, research mainly focused on pure anticipation of a social threat, not taking into consideration actual experiences of social evaluation. Therefore, we set out to investigate actual social up- and downgrading combined with a standardized stress paradigm to evaluate short-term and prolonged changes in pain perception and their potential association with neuroendocrine and subjective stress parameters.

METHODS

We allocated 177 healthy women to four experimental conditions, either the standard version of the Trier Social Stress Test (TSST) followed by positive, negative or no performance feedback, or a well-matched but less demanding placebo version of the TSST. Stress responses were assessed with ratings, salivary alpha-amylase, and salivary cortisol. To capture putative effects of stress on pain, heat pain threshold, ratings of phasic heat pain stimuli, and conditioned pain modulation were measured.

RESULTS

Despite a largely successful stress induction, results do not support a reliable influence of experimentally induced social stress-with or without subsequent performance feedback-on pain in women. Further, we found no clear association of pain modulation and changes in neuroendocrine or subjective stress responses.

CONCLUSIONS

Our results contrast previous studies, which repeatedly demonstrated stress-induced hypo- or hyperalgesia. This might be due to methodological reasons as former research was often characterized by high heterogeneity regarding the applied stressors, low sample sizes, and lacking or inconclusive control conditions. Thus, our results raise the question whether pain modulation in women by experimental psychosocial stress might have been overestimated in the past. Future research is necessary, which should employ parametric stress induction methods including well-matched control tasks, taking into consideration the participants' gender/sex and the time course of the stress response relative to pain assessment. The study is registered as DRKS00026946 at 'Deutsches Register Klinischer Studien' (DRKS) and can be also found at the World Health Organization's search portal.

Sex and gender differences in pain

Chronic pain affects 20% of adults and is one of the leading causes of disability worldwide. Women and girls are disproportionally affected by chronic pain. About half of chronic pain conditions are more common in women, with only 20% having a higher prevalence in men. There are also sex and gender differences in acute pain sensitivity. Pain is a subjective experience made up of sensory, cognitive, and emotional components. Consequently, there are multiple dimensions through which sex and gender can influence the pain experience. Historically, most preclinical pain research was conducted exclusively in male animals. However, recent studies that included females have revealed significant sex differences in the physiological mechanisms underlying pain, including sex specific involvement of different genes and proteins as well as distinct interactions between hormones and the immune system that influence the transmission of pain signals. Human neuroimaging has revealed sex and gender differences in the neural circuitry associated with pain, including sex specific brain alterations in chronic pain conditions. Clinical pain research suggests that gender can affect how an individual contextualizes and copes with pain. Gender may also influence the susceptibility to develop chronic pain. Sex and gender biases can impact how pain is perceived and treated clinically. Furthermore, the efficacy and side effects associated with different pain treatments can vary according to sex and gender. Therefore, preclinical and clinical research must include sex and gender analyses to understand basic mechanisms of pain and its relief, and to develop personalized pain treatment.

Symptomatic but not Asymptomatic COVID-19 Impairs Conditioned Pain Modulation in Young Adults

Pain is a common symptom reported in COVID-19 patients. Impaired endogenous pain-modulatory mechanisms such as conditioned pain modulation (CPM), and exercise-induced hypoalgesia (EIH) have been found in chronic pain conditions but is often overlooked in acute conditions that evoke painful symptoms, such as COVID-19. The purpose was to compare pressure-pain sensitivity, CPM, and EIH function among individuals who previously had COVID-19, both symptomatically and asymptomatically, and a healthy control group. Pressure pain thresholds of 59 participants were assessed in the forearm and leg using a pressure algometer before and after 1) submersion of their dominant foot in cold water (2°C) for 1min; and 2) isometric knee extension performed to task-failure at 25% of their maximal contraction. The CPM response was attenuated in individuals who were infected with symptomatic COVID-19 (N = 26) compared to asymptomatic COVID-19 (N = 13) in arm (-1.0% ± 20.3 vs 33.3% ± 26.2; P < .001) and leg (12.8% ± 22.0 vs 33.8% ± 28.2; P = .014) and compared to controls (N = 20) in arm only (-1.0% ± 26.2 vs 23.4% ± 28.2; P = .004). The EIH response was not different between groups. CPM was impaired in individuals who had symptomatic COVID-19, which may have long-term implications on pain modulation.

Perspective

This study reveals that CPM was impaired in individuals who had symptomatic COVID-19 during the first wave of COVID-19, pre vaccine. These findings present a preliminary motive to study the long-term implications of COVID-19 and its effects on pain modulation.

Questionnaire-based somatosensory profiling in breast cancer survivors: are we there yet? Associations between questionnaires and quantitative sensory testing

PURPOSE

Pain and sensory disturbances are common side effects of breast cancer treatment. Differential somatosensory functioning may reflect distinct pathophysiological backgrounds and therapeutic needs. Aim was to examine whether questionnaires evaluating signs and symptoms related to somatosensory functioning correlate sufficiently with quantitative sensory testing (QST) in breast cancer survivors to warrant consideration for somatosensory profiling in clinical practice.

METHODS

One year after breast cancer surgery, 147 women underwent QST and completed following questionnaires: Douleur Neuropathique en 4 questions (DN4), Central Sensitization Inventory, Margolis Pain Diagram and Visual Analog Scales (VAS). Associations between the questionnaires and QST were evaluated using Spearman correlation coefficients (rs).

RESULTS

Significant but weak (rs < 0.30) correlations were found between total DN4 score and QST results at the inner upper arm for detection of sharp stimuli (rs = 0.227), cold stimuli (rs = -0.186), and painful heat stimuli (rs = 0.179), as well as between QST evaluating conditioned pain modulation and the Margolis Pain Diagram on one hand (rs = 0.176) and minimum-maximum pain intensity differences (VAS) on the other (rs = -0.170).

CONCLUSION

Questionnaires evaluating signs and symptoms related to somatosensory functioning are insufficient for somatosensory profiling. Although somatosensory profiling may be valuable in a mechanism-based management, more research on the most appropriate clinical tools is needed.IMPLICATIONS FOR REHABILITATIONClinicians should be able to recognize that patients with persistent pain or sensory disturbances following breast cancer surgery may have a component of altered somatosensory processing as a significant contributor to their complaint in order to address it appropriately.Somatosensory profiling has yet to be implemented into clinical practice.No evidence-based recommendations can be made on the use of self-reported questionnaires to assess somatosensory processing in a breast cancer population based on the findings of this study.It is suggested to combine information on how individuals process and experience somatosensory stimulation with information from the patient interview or questionnaires to consider which biological, psychological and/or social factors may drive or sustain these neurophysiological processes.

Preoperative dynamic quantitative sensory testing in remote pain-free areas is associated with axial pain after posterior cervical spinal surgeries

BACKGROUND

Postoperative axial pain (PAP), characterized by pain and/or stiffness around the posterior neck, periscapular areas and/or shoulder region, is a vexing complication affecting 5-60% of patients undergoing posterior cervical decompression. Given its relatively high frequency and negative impact on patients' physical and mental status, efforts preoperatively to confirm patients at risk of developing PAP to offer more efficient pain management to minimize this complication have a high priority. The aim of this study is to investigate the role of preoperative dynamic quantitative sensory testing (QST) in predicting the PAP after posterior cervical decompression.

METHODS

This longitudinal observational study included 122 patients with degenerative cervical myelopathy undergoing laminoplasty or laminectomy. Preoperatively, all patients underwent the assessment of pressure pain thresholds (PPTs) at local and remote pain-free areas and both temporal summation (TS) and conditioned pain modulation (CPM) at remote pain free-areas. These patients underwent further pain-related, psychosocial and clinical function assessments before and/or after operation.

RESULTS

In the present study, 21 patients (21/122, 17.2%) developed PAP, and the 6-month postoperative follow-up demonstrated that 8 of these 21 patients developed chronic PAP (CPAP). All preoperative covariates with significant differences between the PAP and non-PAP groups were subjected to multivariate logistic regression, and the presence of preoperative axial pain, surgical plan including C2 decompression, total international physical activity questionnaire score (cutoff value [CV]: 2205.5, sensitivity: 82.4%; specificity: 61.1%) and TS value (CV: 2.5, sensitivity: 42.9%; specificity: 83.2%) were independently associated with PAP (P < 0.05). Logistic regression further revealed that the presence of preoperative axial pain, TS value (CV: 2.5, sensitivity: 62.5%; specificity: 83.2%) and CPM value (CV: 0.65, sensitivity: 87.5%; specificity: 61.4%) were significant predictors of CPAP (P < 0.05).

CONCLUSIONS

The findings of this study support the hypothesis that preoperative endogenous pain modulation efficiency may be associated with axial pain after posterior cervical decompression. Clinically, preoperative estimation of both TS and CPM in remote pain-free areas may provide additional useful information for identifying patients who may be at risk of developing both PAP and CPAP, which may be beneficial in enabling stratification in the perioperative period of patients based on individual vulnerabilities to avoid/reduce this complication.

Conditioned pain modulation is more efficient in patients with painful diabetic polyneuropathy than those with nonpainful diabetic polyneuropathy

ABSTRACT

Endogenous pain modulation, as tested by the conditioned pain modulation (CPM) protocol, is typically less efficient in patients with chronic pain compared with healthy controls. We aimed to assess whether CPM is less efficient in patients with painful diabetic polyneuropathy (DPN) compared with those with nonpainful DPN. Characterization of the differences in central pain processing between these 2 groups might provide a central nervous system explanation to the presence or absence of pain in diabetic neuropathy in addition to the peripheral one. Two hundred seventy-one patients with DPN underwent CPM testing and clinical assessment, including quantitative sensory testing. Two modalities of the test stimuli (heat and pressure) conditioned to cold noxious water were assessed and compared between patients with painful and nonpainful DPN. No significant difference was found between the groups for pressure pain CPM; however, patients with painful DPN demonstrated unexpectedly more efficient CPMHEAT (-7.4 ± 1.0 vs -2.3 ± 1.6; P = 0.008). Efficient CPMHEAT was associated with higher clinical pain experienced in the 24 hours before testing (r = -0.15; P = 0.029) and greater loss of mechanical sensation (r = -0.135; P = 0.042). Moreover, patients who had mechanical hypoesthesia demonstrated more efficient CPMHEAT (P = 0.005). More efficient CPM among patients with painful DPN might result from not only central changes in pain modulation but also from altered sensory messages coming from tested affected body sites. This calls for the use of intact sites for proper assessment of pain modulation in patients with neuropathy.

The Potential Clinical Utility of Pressure-Based vs. Heat-Based Paradigms to Measure Conditioned Pain Modulation in Healthy Individuals and Those With Chronic Pain

Conditioned pain modulation (CPM) is a physiological measure thought to reflect an individual's endogenous pain modulation system. CPM varies across individuals and provides insight into chronic pain pathophysiology. There is growing evidence that CPM may help predict individual pain treatment outcome. However, paradigm variabilities and practical issues have impeded widespread clinical adoption of CPM assessment. This study aimed to compare two CPM paradigms in people with chronic pain and healthy individuals. A total of 30 individuals (12 chronic pain, 18 healthy) underwent two CPM paradigms. The heat CPM paradigm acquired pain intensity ratings evoked by a test stimulus (TS) applied before and during the conditioning stimulus (CS). The pressure CPM paradigm acquired continuous pain intensity ratings of a gradually increasing TS, before and during CS. Pain intensity was rated from 0 (no pain) to 100 (worst pain imaginable); Pain50 is the stimulus level for a response rated 50. Heat and pressure CPM were calculated as a change in TS pain intensity ratings at Pain50, where negative CPM scores indicate pain inhibition. We also determined CPM in the pressure paradigm as change in pressure pain detection threshold (PDT). We found that in healthy individuals the CPM effect was significantly more inhibitory using the pressure paradigm than the heat paradigm. The pressure CPM effect was also significantly more inhibitory when based on changes at Pain50 than at PDT. However, in individuals with chronic pain there was no significant difference in pressure CPM compared to heat or PDT CPM. There was no significant correlation between clinical pain measures (painDETECT and Brief Pain Inventory) and paradigm type (heat vs. pressure), although heat-based CPM and painDETECT scores showed a trend. Importantly, the pressure paradigm could be administered in less time than the heat paradigm. Thus, our study indicates that in healthy individuals, interpretation of CPM findings should consider potential modality-dependent effects. However, in individuals with chronic pain, either heat or pressure paradigms can similarly be used to assess CPM. Given the practical advantages of the pressure paradigm (e.g., short test time, ease of use), we propose this approach to be well-suited for clinical adoption.

Exploring the relationship between meaningful conditioned pain modulation and stress system reactivity in healthy adults following exposure to the cold pressor task

BACKGROUND

The sympathetic nervous system (SNS) and hypothalamic-pituitary-adrenal (HPA) axis have been implicated in conditioned pain modulation (CPM). As there has recently been a push to identify meaningful CPM responses based on ± 2 SEM of the test stimulus, we sought to evaluate if meaningful CPM had relationships with both SNS and HPA axis reactivity.

METHODS

50 university-aged healthy participants (25 males, 25 females) underwent evaluation of pressure pain detection threshold (PPDT), conditioned pain modulation (CPM), galvanic skin response (GSR) and salivary cortisol before and after a cold pressor test (CPT). Meaningful CPM was evaluated based on change ±2 SEM of baseline PPDT to classify participants as experiencing inhibition of pain, facilitation, or non-response.

RESULTS

As a group, there were no significant changes in PPDT or salivary cortisol after exposure to noxious cold. GSR was significantly elevated from baseline values during the CPT, and 10 min after (p < 0.001). When meaningful CPM was assessed, only 30% of participants experienced inhibitory CPM. Within this group, there was a large positive correlation ranging from r = 0.63 to 0.69 (p < 0.01) between CPM and the absolute change in GSR from baseline to immersion, and the immediate 5 min after immersion.

CONCLUSIONS

This work continues to support the growing body of literature suggesting that CPM is not universally experienced. Inhibitory CPM may be associated with an increase in SNS activity for healthy participants in reaction to noxious cold. Future work is required to ascertain individual characteristics (e.g., age, sex) that relate to CPM responses.

No relevant differences in conditioned pain modulation effects between parallel and sequential test design. A cross-sectional observational study

Background

Conditioned pain modulation (CPM) is measured by comparing pain induced by a test stimulus with pain induced by the same test stimulus, either during (parallel design) or after (sequential design) the conditioning stimulus. Whether design, conditioning stimulus intensity and test stimulus selection affect CPM remains unclear.

Methods

CPM effects were evaluated in healthy participants (N = 89) at the neck, forearm and lower leg using the cold pressor test as the conditioning stimulus. In three separate experiments, we compared the impact of (1) design (sequential versus parallel), (2) conditioning stimulus intensity (VAS 40/100 versus VAS 60/100), and (3) test stimulus selection (single versus dual, i.e., mechanical and thermal). Statistical analyses of the main effect of design (adjusted for order) and experiment were conducted using linear mixed models with random intercepts.

Results

No significant differences were identified in absolute CPM data. In relative CPM data, a sequential design resulted in a slightly lower CPM effect compared to a parallel design, and only with a mechanical test stimulus at the neck (−6.1%; 95% CI [−10.1 to −2.1]) and lower leg (−5.9%; 95% CI [−11.7 to −0.1]) but not forearm (−4.5%; 95% CI [−9.0 to 0.1]). Conditioning stimulus intensity and test stimulus selection did not influence the CPM effect nor the difference in CPM effects derived from parallel versus sequential designs.

Conclusions

Differences in CPM effects between protocols were minimal or absent. A parallel design may lead to a minimally higher relative CPM effect when using a mechanical test stimulus. The conditioning stimulus intensities assessed in this study and performing two test stimuli did not substantially influence the differences between designs nor the magnitude of the CPM effect.

Combined Evaluation of Nociceptive Detection Thresholds and Evoked Potentials during Conditioned Pain Modulation: A Feasibility Study

Deficient top-down inhibitory control via diffuse noxious inhibitory control (DNIC) is a mechanism known to be responsible for the maintenance and development in several chronic pain syndromes. Experimentally, DNIC is often induced by conditioned pain modulation (CPM) paradigms such as a Cold Pressor Test (CPT). Recently, a method called the NDT-EP method has been developed with the aim to evaluate the nociceptive function, which it does via simultaneous tracking of nociceptive detection thresholds (NDT) and evoked potentials (EP). It remains to be investigated whether we can evaluate DNIC via the NDT-EP method. In this study, we take the first step to investigate this by evaluating the feasibility to combine the NDT-EP method with a 7 minutes CPT. In total 20 participants of a wide age-range were measured before, during, and after a CPT. All except 1 participant were able to complete the protocol, and enough stimulus-response pairs could be obtained for psychophysical as well as electrophysiological evaluation. Preliminary analysis of the NDT's and EP's showed results in line with earlier research such as a higher threshold for nociceptive stimuli and a lower EP amplitudes. Several NDT's of mostly elderly people (59±16 years), however, exceeded the maximum applicable stimulus strength during (7/20) or after (9/20) CPT and consequently had to be excluded from the analysis. To what extent this is a consequence of the CPT or other factors such as strong habituation associated more with elderly people, is subject to further investigation. In conclusion, the results of this study show that with the present protocol, it is feasible to combine the NDT-EP method with a CPM paradigm in almost all subjects, but that the NDT data of mostly older subjects could not be properly analyzed. Further directions for research and improvements are outlined.

Development of a novel brief quantitative sensory testing protocol that integrates static and dynamic pain assessments: Test-retest performance in healthy adults

OBJECTIVE

Quantitative sensory testing is an expanding pain research domain with numerous clinical and research applications. There is a recognized need for brief reliable quantitative sensory testing protocols that enhance assessment feasibility. This study aimed to integrate static (pain threshold, tolerance, suprathreshold) and dynamic (conditioned pain modulation, offset analgesia, temporal summation) pain reactivity measures into a brief 20-minute protocol that uses a single portable device. The test-retest performance of this optimized protocol was evaluated.

DESIGN

Using a test-retest design, the brief quantitative sensory testing assessment was administered to participants on two occasions separated by exactly 7 days.

SETTING

A clinical psychology research laboratory at Syracuse University.

SUBJECTS

Participants were 33 healthy adults recruited from Syracuse University's online research participation pool.

METHODS

A portable computerized quantitative sensory testing device delivered contact-heat pain to assess static and dynamic pain measures in participants. Dynamic responses were continuously recorded using a computerized visual analog scale.

RESULTS

Pain threshold, tolerance, and suprathreshold exhibited excellent reliability (intraclass correlations ranged from 0.80 to 0.83). Conditioned pain modulation, offset analgesia, temporal summation yielded reliability in the good to excellent range (intraclass correlations ranged from 0.66 to 0.71).

CONCLUSIONS

Findings suggested that this brief integrated QST protocol may reliably monitor human pain reactivity over brief periods. This protocol may enhance quantitative sensory testing feasibility in clinical and research settings.

Inter-Individual Differences Explain More Variance in Conditioned Pain Modulation Than Age, Sex and Conditioning Stimulus Intensity Combined

Conditioned pain modulation (CPM) describes the reduction in pain evoked by a test stimulus (TS) when presented together with a heterotopic painful conditioning stimulus (CS). CPM has been proposed to reflect inter-individual differences in endogenous pain modulation, which may predict susceptibility for acute and chronic pain. Here, we aimed to estimate the relative variance in CPM explained by inter-individual differences compared to age, sex, and CS physical and pain intensity. We constructed linear and mixed effect models on pooled data from 171 participants of several studies, of which 97 had repeated measures. Cross-sectional analyses showed no significant effect of age, sex or CS intensity. Repeated measures analyses revealed a significant effect of CS physical intensity (p = 0.002) but not CS pain intensity (p = 0.159). Variance decomposition showed that inter-individual differences accounted for 24% to 34% of the variance in CPM while age, sex, and CS intensity together explained <3% to 12%. In conclusion, the variance in CPM explained by inter-individual differences largely exceeds that of commonly considered factors such as age, sex and CS intensity. This may explain why predictive capability of these factors has had conflicting results and suggests that future models investigating them should account for inter-individual differences.

Analgesia induced by anodal tDCS and high-frequency tRNS over the motor cortex: Immediate and sustained effects on pain perception

BACKGROUND

Many studies have shown effects of anodal transcranial direct current stimulation (a-tDCS) and high-frequency transcranial random noise stimulation (tRNS) on elevating cortical excitability. Moreover, tRNS with a direct current (DC)-offset is more likely to lead to increases in cortical excitability than solely tRNS. While a-tDCS over primary motor cortex (M1) has been shown to attenuate pain perception, tRNS + DC-offset may prove as an effective means for pain relief.

OBJECTIVE

This study aimed to examine effects of a-tDCS and high-frequency tRNS + DC-offset over M1 on pain expectation and perception, and assess whether these effects could be influenced by the certainty of pain expectation.

METHODS

Using a double-blinded and sham-controlled design, 150 healthy participants were recruited to receive a single-session a-tDCS, high-frequency tRNS + DC-offset, or sham stimulation over M1. The expectation and perception of electrical stimulation in certain and uncertain contexts were assessed at baseline, immediately after, and 30 min after stimulation.

RESULTS

Compared with sham stimulation, a-tDCS induced immediate analgesic effects that were greater when the stimulation outcome was expected with uncertainty; tRNS induced immediate and sustained analgesic effects that were mediated by decreasing pain expectation. Nevertheless, we found no strong evidence for tRNS being more effective for attenuating pain than a-tDCS.

CONCLUSIONS

The analgesic effects of a-tDCS and tRNS showed different temporal courses, which could be related to the more sustained effectiveness of high-frequency tRNS + DC-offset in elevating cortical excitability. Moreover, expectations of pain intensity should be taken into consideration to maximize the benefits of neuromodulation.

Endogenous Modulation of Pain: The Role of Exercise, Stress, and Cognitions in Humans

BACKGROUND

Pain is a complex and highly subjective phenomenon that can be modulated by several factors. On the basis of results from experimental and clinical studies, the existence of endogenous pain modulatory mechanisms that can increase or diminish the experience of pain is now accepted.

METHODS

In this narrative review, the pain modulatory effects of exercise, stress, and cognitions in humans are assessed.

RESULTS

Experimental studies on the effect of exercise have revealed that pain-free participants show a hypoalgesic response after exercise. However, in some patients with chronic pain, this response is reduced or even hyperalgesic in nature. These findings will be discussed from a mechanistic point of view. Stress is another modulator of the pain experience. Although acute stress may induce hypoalgesia, ongoing clinical stress has detrimental effects on pain in many patients with chronic pain conditions, which have implications for the understanding, assessment, and treatment of stress in patients with pain. Finally, cognitive strategies play differing roles in pain inhibition. Two intuitive strategies, thought suppression and focused distraction, will be reviewed as regards experimental, acute, and chronic pain.

CONCLUSION

On the basis of current knowledge on the role of exercise, stress, and cognitive pain control strategies on the modulation of pain, implications for treatment will be discussed.

Test-retest reliability of pressure pain threshold and heat pain threshold as test stimuli for evaluation of conditioned pain modulation

OBJECTIVES

There is growing interest in conditioned pain modulation (CPM) protocols for evaluating the function of the descending pain-modulatory system in clinical settings. The aim of this study was to evaluate test-retest reliability of a CPM protocol with contact heat as a conditioning stimulus (CS) and two test stimuli (pressure pain threshold (PPT) and heat pain threshold (HPT)), all applied within one session. In addition, gender and age differences were evaluated.

METHODS

The study included 87 healthy subjects (average age 37.95 ± 12.02 years, 57.5% females). The magnitude of the results of the CPM test was calculated as the difference between subject-reported pain thresholds before and after application of the CS. To assess the reliability of the protocol, a subgroup of 66 subjects underwent re-test after 14±1 days. In order to investigate the influence of age on the CPM magnitude, subjects were divided into subgroups (20-29, 30-39, 40-49, 50-59 years).

RESULTS

The pain thresholds for both test stimuli (TS) were significantly higher following the application of the CS (p < 0.001). Values of the interclass correlation coefficient (ICC) for the CPM with PPT as the TS indicated good reliability (ICC=0.631, 95% CI:0.365-0.782), while those for the HPT indicated poor reliability (ICC=0.328, 95% CI:-0.067-0.582). Significant differences in CPM between genders were found for both TS. Significant CPM differences were not detected among the four age subgroups for either TS.

CONCLUSIONS

CPM effects can be successfully induced with both PPT and HPT as a TS, but PPT showed significantly higher reliability.

Local hyperalgesia, normal endogenous modulation with pain report beyond its origin: a pilot study prompting further exploration into plantar fasciopathy

Background and aims Persistent tendinopathies were previously considered solely as peripheral conditions affecting the local tendinous tissue until quantitative sensory testing identified involvement of altered pain processing. In similar fashion, pain in patients with persistent plantar fasciopathy may also involve more than local tissue. The aim of this pilot study was to investigate potential differences in conditioned pain modulation and pressure and thermal pain thresholds, between individuals with PF and healthy pain-free controls, as a precursor to a larger-scale study. Methods We assessed 16 individuals with plantar fasciopathy and 11 pain-free controls. Plantar fasciopathy diagnosis was: palpation pain of the medial calcaneal tubercle or the proximal plantar fascia, duration ≥3 months, pain intensity ≥2/10, and ultrasound-measured plantar fascia thickness ≥4 mm. Quantitative sensory tests were performed locally at the plantar heel and remotely on the ipsilateral elbow. Assessments included pain thresholds for pressure, heat and cold, and conditioned pain modulation measured as change in local resting pressure pain threshold with cold water hand immersion. Participants rated pain intensity at pain threshold. Additionally, the area and distribution of plantar fasciopathy pain was drawn on a digital body chart of the lower limbs. Descriptive analyses were performed and between-group differences/effects expressed as standardised mean differences (d). Results There was no conditioned pain modulation difference between participants with plantar fasciopathy and controls (d = 0.1). Largest effects were on local pressure pain threshold and reported pain intensity on pressure pain threshold (d > 1.8) followed by pain intensity for heat and cold pain thresholds (d = 0.3-1.5). According to the digital body chart, pain area extended beyond the plantar heel. Conclusions The unlikelihood of a difference in conditioned pain modulation yet a pain area extending beyond the plantar heel provide a basis for exploring altered pain processing in a larger-scale study. Implications This was the first study to investigate the presence of altered pain processing in individuals with plantar fasciopathy using a conditioned pain modulation paradigm and thermal pain thresholds. We found no indication of an altered pain processing based on these measures, however, patients rated pain higher on thresholds compared to controls which may be important to clinical practice and warrants further exploration in the future.

Pain referral area is reduced by remote pain

BACKGROUND

Endogenous pain inhibitory mechanisms are known to reduce pain intensity, but whether they influence the size and distribution of pain referral is unclear. This study aimed to determine if referred pain is reduced by applying a remote, conditioning painful stimulus.

METHODS

Twenty-four healthy men participated in this randomized, crossover study with a control and conditioning session. Referred pain was induced from the infraspinatus muscle (dominant side) by a painful pressure for 60 s. When applying pressure, the intensity was adjusted to a local pain intensity of 7/10 on a numerical rating scale. In the conditioning session, tonic painful pressure was simultaneously applied to the non-dominant leg during induction of referred pain. The area of referred pain was drawn onto a digital body chart and size extracted for data analysis.

RESULTS

For the total group and in a subgroup with distinct patterns of referred pain (n = 15/24), the pain area perceived in the back and front+back was smaller during the conditioning compared with the control (p < 0.05). No significant difference was found between sessions in a subgroup only demonstrating local pain (n = 9/24).

CONCLUSIONS

Engaging the descending noxious inhibitory control reduced the size of pain areas predominately when distinct pain referral was present. Assuming a conditioning effect of descending inhibitory control acting on dorsal horn neurons, these findings may indicate that mechanisms underlying pain referral can be modulated by endogenous control. The findings may indicate that referred pain may be a useful proxy to evaluate sensitivity of central pain mechanisms as previously suggested.

SIGNIFICANCE

The current results indicate a link between endogenous inhibition and pain referral. Descending inhibitory control effects on pain referral support a spinal mechanism involved in pain referral. Future studies should investigate whether the spatial characteristics of referred pain (e.g. size, frequency of affected body regions and distribution away from the primary nociceptive stimulus) can useful to evaluate the efficiency of endogenous pain modulation.

Strength Exercise Has Different Effects on Pressure Pain Thresholds in Women with Endometriosis-Related Symptoms and Healthy Controls: A Quasi-experimental Study

OBJECTIVE

To evaluate the influence of strength exercises on remote pain sensitivity in women with endometriosis-related symptoms.

DESIGN

A quasi-experimental study.

SETTING

University Hospital, a tertiary health unit.

SUBJECTS

Twenty-one women with endometriosis-related symptoms and 21 healthy women provided written informed consent.

METHODS

The participants performed weekly exercise sessions on an extensor chair for four consecutive weeks. An electronic algometer was used to measure the pressure pain thresholds on the nondominant forearm. Heart rate and blood pressure were measured using a digital device. All measurements were taken before, immediately after, and 10 and 20 minutes after the exercise series.

RESULTS

Women with endometriosis-related symptoms had lower pain thresholds. Pressure pain thresholds increased immediately after exercise in healthy women, returning to baseline level 20 minutes after exercise. Women with endometriosis-related symptoms did not present significant pressure pain threshold alterations after exercise. However, they had a higher heart rate and systolic, diastolic, and average blood pressure than healthy women at all the timepoints. There were no consistent correlations between pressure pain thresholds and heart rate or blood pressure.

CONCLUSIONS

The strength exercise regimen used in this study increased pain thresholds in healthy women but not in women with endometriosis-related painful symptoms. The maintenance or even worsening of pain perception after exercise in women with persistent pain, such as those with endometriosis, may limit their adherence to a physical training program, which in turn could prevent them from experiencing the long-term beneficial effects of exercise.

Brain-Derived Neurotrophic Factor Modulates the Effect of Sex on the Descending Pain Modulatory System in Healthy Volunteers

OBJECTIVES

We investigated sex differences and the influence of brain-derived neurotrophic factor (BDNF) in the descending pain modulatory system (DPMS), as measured by change on the numerical pain scale (NPS; 0-10) during conditioned pain modulation (CPM task; primary outcome) and by function of the corticospinal motor pathway and heat pain thresholds (HPTs; secondary outcomes).

METHODS

This cross-sectional study included healthy volunteers ranging in age from 18 to 45 years (32 male and 24 female). Assessment included serum BDNF, HPT, change on the NPS (0-10) during the CPM task, and motor-evoked potential (MEP) using transcranial magnetic stimulation (TMS).

RESULTS

The MEP (Mv) amplitude was larger in male participants compared with female participants (mean [SE] = 1.55 [0.34] vs mean [SE] = 1.27 [0.27], respectively, P = 0.001). The mean NPS (0-10) during CPM task changed more substantially for female compared with male participants (mean [SE] = -3.25 [2.01] vs mean [SE] = -2.29 [1.34], respectively, P = 0.040). In addition, a higher serum BDNF (adjusted index for age) was associated with a larger decrease of the NPS during CPM task (P = 0.003), although further regression analyses by sex showed that this was only significant for females (P = 0.010).

CONCLUSIONS

Significant sex differences were identified in DPMS function and corticospinal motor pathway integrity. Nevertheless, BDNF was associated with the function of the DPMS in female but not male participants, indicating that sex and neuroplasticity state are crucial factors for pain perception in healthy subjects.