Alterations in pronociceptive and antinociceptive mechanisms in patients with low back pain: a systematic review with meta-analysis

Sex and Sleep Quality Effects on the Relationship Between Sleep Disruption and Pain Sensitivity

BACKGROUND

Chronic pain affects around 20% of the global population and is influenced by various factors, including sleep quality. Studies indicate that sleep disruption can enhance pain sensitivity; however, it is unclear how sex and baseline sleep quality impact these findings. This study examines how sex and baseline sleep quality impact the effects of three nights of sleep disruption on pain sensitivity in healthy individuals.

METHODS

Fifty-nine participants (30 females) underwent two laboratory sessions, separated by three nights of sleep disruption. Pain sensitivity was measured using cuff and handheld algometry, and participants completed a battery of questionnaires on sleep quality, positive and negative affect, and pain catastrophising. Sleep patterns were collected through wrist actigraphy and self-reported sleep diaries.

RESULTS

Temporal summation of pain was significantly facilitated in males (p < 0.01), and pain during suprathreshold stimulation was increased for females (p < 0.01) after the experimental sleep disruption. No differences in any QST parameters were found when comparing participants with good or poor sleep at baseline, but those with good baseline sleep rated the suprathreshold stimulation as more painful (p < 0.05) after the experimental sleep disruption. Finally, having good or poor sleep quality at baseline was associated with a significant reduction in self-reported sleep quality and level of rest after the experimental sleep disruption (p < 0.05).

CONCLUSION

This study indicates that sleep disruption might impact sexes differently and indicates that prior sleep quality is less likely to impact this.

SIGNIFICANCE

Sleep disruption protocols can mimic the sleep problems experienced by patients with chronic pain. The current study explains how different sexes respond to a 3-night sleep disruption protocol and explains how sleep quality at baseline might impact these results.

Trends in Celecoxib Prescribing: A Single Institution 16-Month Review

Background/Objectives: Celecoxib, a COX-2 selective nonsteroidal anti-inflammatory drug (NSAID), is widely prescribed for pain management due to its efficacy and improved gastrointestinal safety profile compared to traditional NSAIDs. Understanding prescription trends and their comparison to other NSAIDs provides valuable insight into prescribing behaviors in clinical settings. Methods: This retrospective study analyzed celecoxib prescriptions written by three pain management physicians in a single institution over a 16-month period from 1 January 2023 to 30 April 2024. Prescription data were collected and grouped into four 4-month intervals to assess temporal trends. Additionally, we compared celecoxib prescriptions to other commonly prescribed NSAIDs, including ibuprofen, meloxicam, naproxen, and diclofenac. Results: A total of 143 celecoxib prescriptions were identified during the study period, with a steady increase observed across consecutive intervals: 8 prescriptions from January-April 2023, 22 from May-August 2023, 46 from September-December 2023, and 67 from January-April 2024. In comparison, a total of 165 prescriptions were written for other NSAIDs over the same period, with 26 prescriptions from January-April 2023, 41 from May-August 2023, 45 from September-December 2023, and 53 from January-April 2024. While prescriptions for both celecoxib and other NSAIDs increased over time, the rate of celecoxib prescriptions showed a steeper rise. Conclusions: The findings demonstrate a notable increase in celecoxib prescriptions in this pain management clinic, outpacing the growth of other NSAIDs. This trend may reflect increasing provider preference for COX-2 selective inhibitors due to their favorable safety profile and efficacy. Further research is warranted to explore the underlying factors driving these prescribing patterns.

C-fiber-related brain responses evoked by laser heat pulses applied to the back

The aim of the present study was to examine C-fiber-related brain responses evoked by laser heat stimuli applied to the lumbar area, and to determine the stimulation protocol that produces the most reliable responses. Thirty healthy volunteers completed the study. Combinations of different stimuli (single pulses or trains of three pulses) with different pulse durations (7 or 14 ms) were used to compare C-fiber-related brain responses between protocols. The four protocols elicited comparable C-fiber-related brain responses to laser heat pulses. However, pulse trains of 7 ms pulses at 0.67 Hz elicited C-LEPs in the greatest proportion of participants (86.7 %). C-LEPs occurred within a 500 ms to 1500 ms post-stimulus time window, consistent with the perception associated with C-fiber activation. These results provide novel data on C-fiber-related brain responses to painful stimuli and a reliable stimulation protocol for future studies on low back pain.

Differential pain perception among females with or without nonspecific chronic low back pain and comorbid insomnia: a quantitative sensory testing analysis

ABSTRACT

Sleep disturbance is a prevalent condition in individuals with chronic low back pain (CLBP). Despite a strong association between the 2 conditions, the potential mechanisms underlying the role of sleep disturbance in CLBP remain unclear. This case-control study aimed to examine pain perception among females with or without nonspecific CLBP and comorbid insomnia. One hundred females were recruited (mean age: 34.3 ± 11.4 years), with 25 individuals with concomitant CLBP and insomnia (CLBP+I), 25 with CLBP (CLBP+), 25 with insomnia (Insomnia+), and 25 healthy controls. All participants completed self-report questionnaires and quantitative sensory testing (QST). Our study found that CLBP+I exhibited lower mechanical pain and pressure pain thresholds (PPT) in both painful and nonpainful areas and impaired conditioned pain modulation (CPM) as compared to healthy controls. Similar findings were found in PPT at the back and CPM when compared to CLBP+. However, no significant differences were noted in thermal pain thresholds and temporal summation of pain across the 4 groups. Furthermore, CLBP+I and Insomnia+ displayed higher levels of functional disability, maladaptive beliefs, and negative mood than CLBP+ or healthy controls. There were significant increases in pain sensitivity to pressure stimuli, decreases in descending pain inhibitory effects, and higher levels of maladaptive psychological status in CLBP+I compared to CLBP+. These findings underscore the importance of incorporating sleep assessments as a routine practice in treating CLBP cases. Future studies are warranted to validate our findings in males, establish the diagnostic and prognostic value of QST, and probe the neurophysiological mechanisms in comorbid conditions.

Thermal temporal summation has good reliability in the lumbar region

OBJECTIVES

Temporal summation (TS) via a thermal stimulus is a form of dynamic quantitative sensory testing that is often used as an indirect measure of central sensitization. While TS is frequently used as an outcome measure to assess the effectiveness of various interventions, the reliability of this measure has yet to be fully assessed in the lumbar spine. Therefore, the primary purpose of this study was to determine the test-retest reliability of TS using a thermal stimulus at the lumbar spine (LS). The secondary purpose was to compare the thermal TS values in the LS to that of the tibialis anterior (TA) and the thenar eminence (TE).

METHODS

Adults with no activity limiting pain conditions between the ages of 18 and 40 were recruited to participate in this study. TS was measured following a series of heat-pulses administered by the Medoc Thermal Sensory Analyzer-II system. After undergoing an optimization session, TS was taken at the LS, the muscle belly of the TA, and the TE, all on the right side. A second thermal TS measurement was taken once again a week later.

RESULTS

A total of 25 (n = 11 female) individuals participated in this study. ICC values in the lumbar spine ranged from moderate to good (0.591 to 0.836) depending on the calculation method. This compared to the TA with ICC values ranging from 0.621 to 0.772 and the TE with values ranging from 0.572 to 0.751. Correlations of the thermal TS values were high between the LS and the TA (r = 0.745), moderate between the TA and the TE (r = 0.631), and weak between the LS and the TE (r = 0.443).

DISCUSSION/CONCLUSION

Thermal TS taken at the LS is a reliable measure with ICC values that are comparable to ICC values found at the TA and the TE.

A Parallel Human and Rat Investigation of the Interaction Between Descending and Spinal Modulatory Mechanisms

BACKGROUND

Healthy individuals demonstrate considerable heterogeneity upon dynamic quantitative sensory testing assessment of endogenous pain modulatory mechanisms. For those who stratify into a 'pro-nociceptive profile' cohort, consisting of inefficient conditioned pain modulation (CPM) and elevated temporal summation of pain (TSP), the optimal approach for balancing the net output of pain modulatory processes towards anti-nociception remains unresolved. In this translational healthy human and rat study, we examined whether descending modulation countered spinal amplification during concurrent application of a CPM and TSP paradigm alongside pupillometry since pontine activity was previously linked to functionality of endogenous pain modulatory mechanisms and pupil dilation.

METHODS

Perceptual (quantitative sensory testing) and spinal neuronal (in vivo electrophysiology) assessment was performed in healthy humans and rats respectively upon application of parallel CPM/diffuse noxious inhibitory controls (cuff algometry) and TSP/wind-up (pinprick) paradigms alongside pupillometry.

RESULTS

In humans, repetitive pinprick stimulation produced TSP while concurrent application of a noxious conditioning stimulus did not affect pain ratings to a single pinprick stimulus, repetitive stimulation or the wind-up ratio. In rats, repetitive pinprick produced neuronal wind-up while concurrent application of a noxious conditioning stimulus inhibited neuronal responses to a single stimulus and repetitive stimulation but not the wind-up ratio. For pupillometry experiments, dilatory responses did not increase during application of a TSP or CPM paradigm in humans, while reliable rat responses were not obtained.

CONCLUSIONS

Under the conditions of our study, spinal amplification mechanisms surpassed descending inhibitory controls while pupillometry did not offer a reliable indicator of endogenous pain modulatory mechanism function.

SIGNIFICANCE

In this translational healthy human and rat study, activity in descending inhibitory controls did not counter spinal amplification processes underpinned by wind up. Despite pupil dilation being previously linked to modulatory mechanisms, dilatory responses did not offer a reliable indicator of functionality. For pro-nociceptive individuals exhibiting inefficient conditioned pain modulation and/or high temporal summation of pain, dampening faciliatory mechanisms rather than augmenting top-down inhibitory processes may be a more effective pain-relief strategy.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

SIGNIFICANT STATEMENT

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

Can physical and psychological factors predict pain recurrence or an exacerbation of persistent non-specific low back pain? A protocol for a systematic review and meta-analysis

INTRODUCTION

Low back pain (LBP) is a global health concern. Approximately two-thirds of those who recover from LBP experience a relapse within a year, with many chronic cases encountering acute flare-ups (exacerbation). This systematic review will synthesise and analyse whether physical and/or psychological features can predict recurrent episodes of LBP or exacerbation of pain.

METHODS AND ANALYSIS

This systematic review protocol follows the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols guidelines. Comprehensive literature searches will be conducted in MEDLINE, EMBASE, APA PsycInfo, PubMed, CINAHL Plus, Web of Science, Scopus and ZETOC, spanning from each database's inception through to January 2025. Google Scholar and grey literature sources, including OpenGrey, will also be searched to ensure comprehensive coverage. Two independent reviewers will screen titles, abstracts and full texts, assessing the risk of bias with a modified Quality in Prognosis Studies tool. The overall certainty of evidence will be evaluated using an adapted Grading of Recommendations Assessment, Development and Evaluation approach. If sufficient data homogeneity is present, a meta-analysis will be performed; otherwise, findings will be synthesised narratively. The results will identify the ability of physical and/or psychological factors to predict pain recurrence or acute exacerbation in case of persistent non-specific LBP.

ETHICS AND DISSEMINATION

This study protocol does not present any ethical concerns. The findings from the systematic review will be submitted for publication in a peer-reviewed journal and will also be presented at relevant conferences.

PROSPERO REGISTRATION NUMBER

CRD42024599514.

Effectiveness of mobilization with movement on conditioned pain modulation, mechanical hyperalgesia, and pain intensity in adults with chronic low back pain: A randomized controlled trial

BACKGROUND

Chronic low back pain is associated with dysfunctions in endogenous analgesia mechanisms, as evaluated through conditioned pain modulation paradigms. Although mobilization with movement has demonstrated enhancements in conditioned pain modulation among patients with conditions such as knee osteoarthritis, its efficacy in chronic low back pain patients has yet to be established.

OBJECTIVES

To investigate the effects of mobilization with movement compared to sham mobilization in conditioned pain modulation, mechanical hyperalgesia, and pain intensity in chronic low back pain patients.

DESIGN

Randomized controlled trial following CONSORT and TIDieR guidelines.

METHOD

Fifty-eight patients with chronic low back pain (mean age 48.77 ± 13.92 years) were randomized into the experimental group, which received real mobilization with movement (n = 29), or the sham mobilization with movement group (n = 29). Only one intervention was performed. Patients were assessed before and after intervention. Conditioned pain modulation, mechanical hyperalgesia and pain intensity were assessed.

RESULTS

Mobilization with movement resulted in no statistically significant differences compared to sham mobilization for conditioned pain modulation (post-treatment difference: 0.023 [-0.299, 0.345], p = 0.158), mechanical hyperalgesia (post-treatment difference: -0.198 [-0.505, 0.109], p = 0.207), or movement-related pain intensity (post-treatment difference: 0.548 [-0.068, 1.236], p = 0.079) improvements post-intervention. Effect sizes were small for conditioned pain modulation (r = 0.126), mechanical hyperalgesia (r = 0.101), and pain intensity (r = 0.208).

CONCLUSIONS

Mobilization with movement resulted in no significant differences compared to sham mobilization with movement after one intervention for conditioned pain modulation, mechanical hyperalgesia or pain intensity, with small effect sizes. However, the findings should be interpreted with caution due to absence of screening for appropriately eligible patients.

Comparisons of the effects of psychologically-informed and usual physiotherapy on pain sensitivity in chronic low back pain: an exploratory randomized controlled trial

Introduction

The presence of altered central pain processing and modulation, as well as negative psychological factors, have been suggested to impede recovery in chronic low back pain (CLBP). Psychologically-informed physiotherapy (PiP) aims to specifically address the latter factors-in addition to physical factors-to improve treatment effects. This study aims to determine if the effect of PiP is superior to usual physiotherapy (UP) on pain sensitivity and modulation in participants with CLBP and if changes in these variables were associated with changes in clinical outcomes.

Methods

Forty participants with CLBP were randomly allocated to PiP or UP. Seven physiotherapy sessions over 6 weeks plus a booster session at an 11-week follow-up were delivered. Pressure pain threshold (PPT), temporal summation of pain (TSP), and exercise-induced hypoalgesia were assessed on lumbar, upper, and lower limb sites at baseline and after 6 weeks. Linear mixed models tested if PiP was superior to UP on pain sensitivity/modulation. Linear regressions tested if pain sensitivity/modulation changes were associated with changes in clinical outcomes (pain intensity, physical functioning, symptoms of central sensitization).

Results

PiP was not superior to UP to modulate pain sensitivity/modulation variables. All PPTs increased after 6 weeks regardless of the approach. Lumbar PPT and lumbar and lower limb TSP changes were associated with physical functioning changes.

Conclusion

Although our study suggests that neither approach has a superiority to impact on pain sensitivity, both approaches elicited widespread hypoalgesia. Future powered trials should verify if pain sensitivity can be a mediator of physical functioning improvement, as suggested by our results.

Conditioned Pain Modulation (CPM) Paradigms: Reliability and Relationship With Individual Characteristics

PURPOSE

Conditioned Pain Modulation (CPM) is a useful tool for testing the functionality of endogenous pain modulation. However, inconsistent results have been obtained in clinical populations, possibly due to the wide variety of CPM protocols used and the influence of demographic and psychological characteristics of the individuals assessed.

METHODS

We tested the sensitivity and reliability of four commonly used CPM paradigms in a sample of 58 healthy participants. We also checked how these measures were related to Temporal Summation of Second Pain (TSSP), sociodemographic (age and sex) and psychological variables (anxiety and stress).

RESULTS

CPM results were influenced by the test stimulus used, with tests using pain pressure threshold (PPT) obtaining a greater number of responders (over 65%) and being the most sensitive (higher size effect: Cohen's d > 0.5). However, all measures showed excellent intrasession reliability, with strong agreement between the CPM magnitudes. CPM indices were not correlated with TSSP, age or sex, and the psychological scales did not differentiate CPM responders and non-responders.

CONCLUSIONS

Although the CPM indices showed good reliability, construction of a large database with standardized values for healthy individuals seems necessary for the use of CPM in clinical settings.

Tonic Cold Pain Temporal Summation and Translesional Cold Pressor Test-Induced Pronociception in Spinal Cord Injury: Association with Spontaneous and Below-Level Neuropathic Pain

Background/Objectives: Although increased nociceptive excitability and deficient endogenous pain modulation are considered key features of pronociception and central sensitization, their contribution to neuropathic pain (NP) characteristics in SCI is unclear. The aim of this study was to characterize tonic cold perception and endogenous pain modulation in individuals with and without SCI-NP, considering the stage and severity of SCI and, secondarily, NP phenotype. Methods: Temporal summation of pain (TSP) and neuropathic features were assessed using the numerical rating scale (NRS) and Douleur Neuropathique 4 screening questionnaire (DN4) during the tonic cold pressor test (CPT, 12 °C 60 s) applied to the dominant hand and foot. CPT-induced pronociception was assessed as change in algometer pressure pain thresholds (PPTs) measured at the V2, C6, and L4 dermatomes. Results: A total of 72 individuals were recruited (age-sex-matched noninjured, n = 24; SCI-NP, n = 24; SCI-noNP, n = 24 [AIS A: n = 12, AIS B-D: n = 12; subacute SCI: n = 12, chronic SCI: n = 12]). TSP in response to the foot CPT was higher in subacute compared to chronic incomplete SCI-NP, while TSP to the hand CPT was significantly higher in chronic compared to the subacute complete SCI-NP group. Evoked pain intensity during the hand CPT correlated with duration of below-level SCI-NP. The hand CPT induced widespread pronociception (lower PPT), which correlated with 7-day non-evoked (spontaneous) pain intensity in individuals with incomplete SCI-NP. Individuals with below-level NP, but not at-level NP, showed higher TSP during the foot CPT and greater hand CPT-induced L4 dermatome pronociception. Conclusions: Collectively, measurements of above and below-level temporal summation of pain and translesional-induced pronociception in the SCI-NP group highlight the role of these mechanisms in widespread central sensitization, spontaneous pain intensity, and spinothalamic tract hyperexcitability, especially in individuals diagnosed with below-level NP.

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

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

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.

Deciphering nociplastic pain: clinical features, risk factors and potential mechanisms

Nociplastic pain is a mechanistic term used to describe pain that arises or is sustained by altered nociception, despite the absence of tissue damage. Although nociplastic pain has distinct pathophysiology from nociceptive and neuropathic pain, these pain mechanisms often coincide within individuals, which contributes to the intractability of chronic pain. Key symptoms of nociplastic pain include pain in multiple body regions, fatigue, sleep disturbances, cognitive dysfunction, depression and anxiety. Individuals with nociplastic pain are often diffusely tender - indicative of hyperalgesia and/or allodynia - and are often more sensitive than others to non-painful sensory stimuli such as lights, odours and noises. This Review summarizes the risk factors, clinical presentation and treatment of nociplastic pain, and describes how alterations in brain function and structure, immune processing and peripheral factors might contribute to the nociplastic pain phenotype. This article concludes with a discussion of two proposed subtypes of nociplastic pain that reflect distinct neurobiological features and treatment responsivity.

Night time heart rate predicts next-day pain in fibromyalgia and primary back pain

Introduction

Primary chronic pain is pain that persists for over 3 months without associated measurable tissue damage. One of the most consistent findings in primary chronic pain is its association with autonomic hyperactivation. Yet whether the autonomic hyperactivation causes the pain or results from it is still unclear. It is also unclear to what extent autonomic hyperactivation is related to experienced pain intensity in different subtypes or primary chronic pain.

Objectives

Our first aim was to test lagged relationships between the markers of autonomic activation (heart rate) and pain intensity to determine its directionality. The main question here was whether autonomic biomarkers predict pain intensity or whether pain intensity predicts autonomic biomarkers. The second aim was to test whether this relationship is different between people with primary back pain and people with fibromyalgia.

Methods

Sixty-six patients with chronic pain were observed over an average of 81 days. Sleep heart rate and heart rate variability were measured with a wearable sensor, and pain intensity was assessed from daily subjective reports.

Results

The results showed a predictive relationship between sleep heart rate and next-day pain intensity (P < 0.05), but not between daily pain intensity and next night heart rate. There was no interaction with the type of chronic pain.

Conclusions

These findings suggest that autonomic hyperactivation, whether stress-driven or arising from other causes, precedes increases in primary chronic pain. Moreover, the present results suggest that autonomic hyperactivation is a common mechanism underlying the pain experience in fibromyalgia and chronic back pain.

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

ABSTRACT

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

Conditioned pain modulation and psychological factors in young adults with recurrent or chronic neck pain

BACKGROUND

Controversy exists with the presence of alterations in descending pain inhibition mechanisms in patients with non-specific neck pain (NSNP). The aim of the present study was to evaluate the status of conditioned pain modulation CPM, remote pressure pain thresholds (PPT), and psychological factors in a specific subgroup of patients with NSNP such as young adult students. In addition, possible associations between CPM, psychological factors, and pain characteristics were analyzed.

METHODS

Thirty students with recurrent or chronic NSNP and 30 pain-free students were included in this cross-sectional study. The following measures were assessed: CPM, remote PPT, psychological factors (depression, anxiety, pain catastrophizing, and kinesiophobia), pain characteristics (duration, intensity, severity of chronic pain, interference with daily life), and central sensitization inventory (CSI).

RESULTS

No significant differences were found in the efficacy of CPM between students with chronic or recurrent NSNP and pain-free students (β coefficient = -0.67; 95% CI = -1.54, 0.20). However, students with pain showed a significantly higher remote PPT (mean difference = -1.94; 95% CI = -2.71, -1.18). and a greater presence of anxious (mean difference = 6; 95% CI = 2, 9) and depressive symptoms (mean difference = 8.57; 95% CI = 3.97, 13.16). In addition, significant moderate or strong correlations were found between CPM and pain intensity (partial r = 0.41), pain catastrophizing and mean pain intensity (r = 0.37), grade (r = 0.50), and interference of pain (r = 0.57), kinesiophobia and disability (r = 0.38), and depression and CSI (r = 0.39).

CONCLUSIONS

Young adult students with chronic or recurrent NSNP present remote hyperalgesia and symptoms of depression and anxiety but not dysfunctional CPM.

Pain Science in Practice (Part 7): How Is Descending Modulation of Pain Measured?

SYNOPSIS: Understanding the descending pain modulatory system allows for a neuroscientific explanation of naturally occurring pain relief. Evidence from basic science and clinical studies on the effectiveness of drugs in certain patient groups led to pharmacological manipulation of the descending pain modulatory system for analgesia. Understanding mechanisms and theories helps clinicians make sense of chronic musculoskeletal pain. This editorial explains how test paradigms, including conditioned pain modulation, offset analgesia, and stress-induced analgesia work, provide an overview of a placebo analgesia circuitry, and discusses how evoking activity in the descending pain modulatory system using specific paradigms can give new insights into how specific treatments work to reduce pain. J Orthop Sports Phys Ther 2024;54(2):1-6. doi:10.2519/jospt.2024.12113.

Body-site effect on CPM efficiency in healthy subjects: Central vs. peripheral stimulation

Structural changes in the peripheral nerve system in neuropathic states alter sensory capacity of the affected area, thus biasing results of conditioned pain modulation (CPM) responses. The aim of this study was to evaluate CPM efficiency of central (i.e. trunk) vs. peripheral (i.e. limb) application of 'test' and 'conditioning' stimuli. Methods: Healthy volunteers (ages 18-73 yrs) underwent two CPM protocols: 'CPM Limb' and 'CPM Trunk'. Each included two types of test stimuli (Ts) (pressure pain threshold: PPT; and contact heat) conditioned either to hand immersion in cold noxious water (CPM limb), or to noxious contact heat applied on lower back (CPM trunk). Results: Both protocols generated efficient pain inhibition for each of the applied Ts; the PPT-based protocol induced more efficient CPM when the conditioned stimulus was applied on the trunk (p = 0.016). Moreover, the PPT-based CPM responses were significantly correlated (ρ = 0.349; p = 0.007). Conclusions: An efficient CPM induced by both central and peripheral stimulation, along with significant correlation between PPT-based responses, advances using the central 'CPM Trunk' protocol in patients with peripheral neuropathy.

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.

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

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

Central Sensitization and Pain: Pathophysiologic and Clinical Insights

Central sensitization is an increased responsiveness of nociceptive neurons in the central nervous system to their normal or subthreshold afferent input.

AIM

To explain how the notion of central sensitization has changed our understanding of pain conditions, discuss how this knowledge can be used to improve the management of pain, and highlight knowledge gaps that future research needs to address.

METHODS

Overview of definitions, assessment methods, and clinical implications.

RESULTS

Human pain models, and functional and molecular imaging have provided converging evidence that central sensitization occurs and is clinically relevant. Measures to assess central sensitization in patients are available; however, their ability to discriminate sensitization of central from peripheral neurons is unclear. Treatments that attenuate central sensitization are available, but the limited understanding of molecular and functional mechanisms hampers the development of target-specific treatments. The origin of central sensitization in human pain conditions that are not associated with tissue damage remains unclear.

CONCLUSION

The knowledge of central sensitization has revolutionized our neurobiological understanding of pain. Despite the limitations of clinical assessment in identifying central sensitization, it is appropriate to use the available tools to guide clinical decisions towards treatments that attenuate central sensitization. Future research that elucidates the causes, molecular and functional mechanisms of central sensitization would provide crucial progress towards the development of treatments that target specific mechanisms of central sensitization.

Lifestyle factors and psychological factors are associated with central pain processing in service members with persistent low-back pain: A cross-sectional exploratory study

Persistent low-back pain (LBP) is highly prevalent in the military. Altered central pain processing is one of the mechanisms found to underlie persistent LBP. Our aim was to explore which factors are associated with altered pain processing in Dutch service members with persistent LBP. This knowledge may guide clinicians in what factors to address in the treatment of dysfunctional pain processing in service members with persistent LBP. Twenty-one service members with persistent LBP (mean age 34.0 years, 18 males) were included in this cross-sectional exploratory study. Participants completed questionnaires regarding lifestyle and psychological factors. Altered central pain processing was measured by temporal summation of pain to examine the function of the pain facilitatory system and by conditioned pain modulation to examine the pain inhibitory function. Univariable and multivariable linear regression analyses were performed. A higher local temporal summation of pain was associated with a longer sitting time, a higher level of physical activity and a higher level of pain catastrophizing. A higher local conditioned pain modulation was associated with a higher level of pain catastrophizing, anxiety and depression symptoms, and with a lower sleep quality. A higher remote conditioned pain modulation effect was associated with a higher level of physical activity, a higher body mass index and a shorter sitting time. This study succeeded in identifying lifestyle and psychological factors associated with altered pain processing in service members with persistent LBP. Prospective studies are needed to examine causality in these relationships.

The potential effect of walking on quantitative sensory testing, pain catastrophizing, and perceived stress: an exploratory study

OBJECTIVES

Studies suggest that a range of pain mechanisms, such as poor quality of sleep, perceived stress, pain catastrophizing or pain sensitivity, are likely to enhance clinical pain. Animal studies suggest that these pain mechanisms can be modulated by increasing physical activity, but human data are needed to support this hypothesis. This exploratory study aimed to investigate the changes in pain mechanisms after a simple self-directed walking program of 8-weeks. Additionally, this exploratory study investigated the interaction between changes over time in assessments of poor quality of sleep, perceived stress, pain catastrophizing or pain sensitivity and how these changes interacted with each other.

METHODS

This prospective cohort study included 30 healthy subjects who were assessed at baseline and 4- and 8-weeks after initiating the walking program (30 min walking/day for 8 weeks). Self-report outcomes included: Pain Catastrophizing Scale (PCS), the Perceived Stress Scale (PSS) and Pittsburgh Sleep Quality Index. Pressure pain thresholds, temporal summation of pain and conditioned pain modulation (CPM) were assessed using cuff algometry.

RESULTS

Twenty-four subjects completed all the visits (age: 42.2, SD: 14.9, 16 females). PCS and PSS significantly decreased at the 8-week's visit compared to baseline (p<0.05). No significant differences were seen for an improvement in quality of sleep (p=0.071) and pain sensitivity (p>0.075) when comparing the 8-week's visit to the baseline visit. Changes in pain mechanisms comparing baseline and 8-weeks data were calculated and regression analyses found that an improvement in PCS was associated with an improvement in CPM (R2=0.197, p=0.017) and that a higher adherence to the walking program was associated with a larger improvement in PCS (R2=0.216, p=0.013).

CONCLUSIONS

The current exploratory study indicates that a simple self-directed walking program of 8-weeks can improve pain catastrophizing thoughts, perceived stress. Higher adherence to the walking program were associated with an improvement in pain catastrophizing and an improvement in pain catastrophizing was associated with an increase in conditioned pain modulation.

Intrinsic brain connectivity alterations despite intact pain inhibition in subjects with neuropathic pain after spinal cord injury: a pilot study

Endogenous pain modulation in humans is frequently investigated with conditioned pain modulation (CPM). Deficient pain inhibition is a proposed mechanism that contributes to neuropathic pain (NP) after spinal cord injury (SCI). Recent studies have combined CPM testing and neuroimaging to reveal neural correlates of CPM efficiency in chronic pain. This study investigated differences in CPM efficiency in relation to resting-state functional connectivity (rsFC) between 12 SCI-NP subjects and 13 age- and sex-matched healthy controls (HC). Twelve and 11 SCI-NP subjects were included in psychophysical and rsFC analyses, respectively. All HC were included in the final analyses. Psychophysical readouts were analysed to determine CPM efficiency within and between cohorts. Group differences of rsFC, in relation to CPM efficiency, were explored with seed-to-voxel rsFC analyses with pain modulatory regions, e.g. ventrolateral periaqueductal gray (vlPAG) and amygdala. Overall, pain inhibition was not deficient in SCI-NP subjects and was greater in those with more intense NP. Greater pain inhibition was associated with weaker rsFC between the vlPAG and amygdala with the visual and frontal cortex, respectively, in SCI-NP subjects but with stronger rsFC in HC. Taken together, SCI-NP subjects present with intact pain inhibition, but can be differentiated from HC by an inverse relationship between CPM efficiency and intrinsic connectivity of supraspinal regions. Future studies with larger cohorts are necessary to consolidate the findings in this study.

Pain-related cognitions and emotional distress are not associated with conditioned pain modulation: an explorative analysis of 1142 participants with acute, subacute, and chronic pain

ABSTRACT

Reduced conditioned pain modulation (CPM) and psychological distress co-occur frequently in many pain conditions. This study explored whether common negative pain cognitions and emotional factors were related to lower CPM in individuals across the spectrum from acute to chronic pain. Previously collected data on the CPM effect, pain-related cognitions (fear of movement, pain catastrophizing), and emotional distress (depression, anxiety) through questionnaires from 1142 individuals with acute, subacute, or chronic pain were used. The presence of negative psychological factors was dichotomized according to cutoff values for questionnaires. Associations between the presence of each negative psychological factor and the amplitude of pain reduction in the CPM paradigm was explored with Generalized Linear Models adjusted for sex, age, body mass index, and pain duration. A secondary analysis explored the cumulative effect of psychological factors on CPM. When dichotomized according to cutoff scores, 20% of participants were classified with anxiety, 19% with depression, 36% with pain catastrophizing, and 48% with fear of movement. The presence of any negative psychological factor or the cumulative sum of negative psychological factors was associated with lower CPM (individual factor: β between -0.15 and 0.11, P ≥ 0.08; total: β between -0.27 and -0.12, P ≥ 0.06). Despite the common observation of psychological factors and reduced CPM in musculoskeletal pain, these data challenge the assumption of a linear relationship between these variables across individuals with acute, subacute, and chronic pain. Arguably, there was a nonsignificant tendency for associations in nonexpected directions, which should be studied in a more homogenous population.

Motor corticospinal excitability abnormalities differ between distinct chronic low back pain syndromes

OBJECTIVES

It is not known whether cortical plastic changes reported in low-back pain (LBP) are present in all etiologies of LBP. Here we report on the assessment of patients with three LBP conditions: non-specific-LBP (ns-LBP), failed back surgery syndrome (FBSS), and sciatica (Sc).

METHODS

Patients underwent a standardized assessment of clinical pain, conditioned pain modulation (CPM), and measures of motor evoked potential (MEPs)-based motor corticospinal excitability (CE) by transcranial magnetic stimulation, including short interval intracortical inhibition (SICI), and intracortical facilitation (ICF). Comparisons were also made with normative data from sex- and age-matched healthy volunteers.

RESULTS

60 patients (42 women, 55.1±9.1 years old) with LBP were included (20 in each group). Pain intensity was higher in patients with neuropathic pain [FBSS (6.8±1.3), and Sc (6.4±1.4)] than in those with ns-LBP (4.7±1.0, P<0.001). The same was shown for pain interference (5.9±2.0, 5.9±1.8, 3.2±1.9, P<0.001), disability (16.4±3.3, 16.3±4.3, 10.4±4.3, P<0.001), and catastrophism (31.1±12.3, 33.0±10.4, 17.4±10.7, P<0.001) scores for FBSS, Sc, and ns-LBP groups, respectively. Patients with neuropathic pain (FBSS, Sc) had lower CPM (-14.8±1.9, -14.1±16.7, respectively) compared to ns-LBP (-25.4±16.6; P<0.02). 80.0% of the FBSS group had defective ICF compared to the other two groups (52.5% for ns-LBP, P=0.025 and 52.5% for Sc, P=0.046). MEPs (140%-rest motor threshold) were low in 50.0% of patients in the FBSS group compared to 20.0% of ns-LBP (P=0.018) and 15.0% of Sc (P=0.001) groups. Higher MEPs were correlated with mood scores (r=0.489), and with lower neuropathic pain symptom scores(r=-0.415) in FBSS.

CONCLUSIONS

Different types of LBP were associated with different clinical, CPM and CE profiles, which were not uniquely related to the presence of neuropathic pain. These results highlight the need to further characterize patients with LBP in psychophysics and cortical neurophysiology studies.

Within-Session Test-Retest Reliability of Pressure Pain Threshold and Mechanical Temporal Summation in Chronic Low Back Pain

OBJECTIVES

To determine the absolute and relative within-session test-retest reliability of pressure pain threshold (PPT) and temporal summation of pain (TSP) at the low back and the forearm in individuals with chronic low back pain (CLBP) and to test the impact of different sequences of measurements on reliability metrics.

MATERIALS AND METHODS

Twenty-eight adults with CLBP were recruited. Relative (intraclass correlation coefficient [ICC] and coefficient of variation) and absolute reliability (standard error of measurement and minimal detectable changes) were quantified at 4 sites (back: sacrum and lumbar erector spinae; wrist: hand dorsum and wrist flexors) for PPT and 2 sites (hand and low back) for TSP, for various sequences of measurements.

RESULTS

Systematic differences were found between within test and retest for most PPT sequences at the lumbar erector spinae site and 1 TSP sequence (1-2-3) at back and hand sites, precluding reliability analyses for these data. Within-session PPT relative reliability was excellent at low back (ICC = 0.83 to 0.94) and wrist (ICC = 0.88 to 0.97) sites, whereas TSP showed good to excellent reliability at hand (ICC = 0.80 to 0.90) and low back (ICC = 0.73 to 0.89). In general, 2 and 3 measurements optimized absolute and relative reliability for TSP and PPT, respectively.

DISCUSSION

Within-session reliability was generally excellent for PPT and TSP at the low back and hand sites among individuals with CLBP. We recommend using 3 measurements for PPT and 2 for TSP to optimize reliability. Caution is recommended when testing PPT of the painful lower back area since a systematic difference was present between the test and retest.

Responders and nonresponders to topical capsaicin display distinct temporal summation of pain profiles

Introduction

Topical application of capsaicin can produce an ongoing pain state in healthy participants. However, approximately one-third report no pain response (ie, nonresponders), and the reasons for this are poorly understood.

Objectives

In this study, we investigated temporal summation of pain (TSP) profiles, pain ratings and secondary hyperalgesia responses in responders and nonresponders to 1% topical capsaicin cream.

Methods

Assessments were made at baseline and then during an early (ie, 15 minutes) and late (ie, 45 minutes) time points post-capsaicin in 37 healthy participants.

Results

Participants reporting a visual analogue scale (VAS) rating of >50 were defined as responders (n = 24) and those with <50 VAS rating were defined as nonresponders (n = 13). There was a facilitation of TSP during the transition from an early to the late time point post-capsaicin (P<0.001) and the development of secondary hyperalgesia (P<0.05) in the responder group. Nonresponders showed no changes in TSP or secondary hyperalgesia during the early and late time points. There was an association between baseline TSP scores and the later development of a responder or nonresponder phenotype (r = 0.36; P = 0.03). Receiver operating characteristic analysis revealed that baseline TSP works as a good response predictor at an individual level (area under the curve = 0.75).

Conclusion

These data suggest that responders and nonresponders have different facilitatory pain mechanisms. The assessment of TSP may help to identify participants with stronger endogenous pain facilitation who may be more likely to respond to topical capsaicin.

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.

Human assumed central sensitization in people with acute non-specific low back pain: A cross-sectional study of the association with brain-derived neurotrophic factor, clinical, psychological and demographic factors

BACKGROUND

Early evidence suggests human assumed central sensitization (HACS) is present in some people with acute low back pain (LBP). Factors influencing individual variation in HACS during acute LBP have not been fully explored. We aimed to examine the evidence for HACS in acute LBP and the contribution of brain-derived neurotrophic factor (BDNF), clinical, psychological and demographic factors to HACS.

METHODS

Participants with acute LBP (<6 weeks after pain onset, N = 118) and pain-free controls (N = 57) from a longitudinal trial were included. Quantitative sensory testing including pressure and heat pain thresholds and conditioned pain modulation, BDNF serum concentration and genotype and questionnaires were assessed.

RESULTS

There were no signs of HACS during acute LBP at group level when compared with controls. Sensory measures did not differ when compared between controls and LBP participants with different BDNF genotypes. Two LBP subgroups with distinct sensory profiles were identified. Although one subgroup (N = 60) demonstrated features of HACS including pressure/heat pain hypersensitivity at a remote site and deficient conditioned pain modulation, pain severity and disability did not differ between the two subgroups. Variation in sensory measures (~33%) was partially explained by BDNF genotype, sex, age and psychological factors.

CONCLUSIONS

This study confirms that HACS is present in some people with acute LBP, but this was not associated with pain or disability. Further, no relationship was observed between BDNF and HACS in acute LBP. More research is needed to understand factors contributing to individual variation in sensory measures in LBP.

SIGNIFICANCE

Human assumed central sensitization (HACS) is present in acute low back pain (LBP) but factors contributing to individual variation are not fully explored. This study investigated the relationship between factors such as brain derived neurotrophic factor (BDNF) and HACS in acute LBP. Our findings indicate that HACS was present in specific LBP subgroups but BDNF was unrelated to HACS. Combinations of BDNF genotype, demographic and psychological factors explained a small proportion of the variation in sensory measures during acute LBP.

Spinal neurovascular coupling is preserved despite time-dependent alterations of spinal cord blood flow responses in a rat model of chronic back pain: implications for functional spinal cord imaging

ABSTRACT

Functional magnetic resonance imaging has been used to investigate nociceptive processes in patients with chronic pain. However, the results may be confounded with changes in neurovascular coupling induced by chronic pain. The objective of this study was to examine spinal neurovascular coupling in a rat model of chronic back pain induced by muscle inflammation. Rats received 150 µL intramuscular injections of either complete Freund adjuvant (CFA: n = 18) or saline (control [CTL]: n = 18) in L5-L6 paravertebral muscles. Under 1.2% isoflurane anesthesia, spinal cord blood flow (SCBF) and local field potentials evoked by electrical stimulation of the sciatic nerve were recorded simultaneously in the lumbar enlargement of the spinal cord, 14 or 28 days after the injections. Mechanical hypersensitivity was observed in CFA rats compared with CTL rats for the back ( P < 0.001) and hind paws ( P < 0.01). Spinal cord blood flow response amplitude and local field potential amplitude were not significantly different between groups (day 14: P > 0.5; day 28: P > 0.6). However, the time course of SCBF responses was different between groups on day 14 ( P < 0.001) and day 28 ( P < 0.001). Nevertheless, neurovascular coupling was comparable between groups on days 14 and 28, whether neurovascular coupling was calculated with the amplitude or the area under the curve of SCBF responses (all P > 0.2). These results indicate that spinal hemodynamic changes reflect neuronal activity in this animal model, although the time course of SCBF responses is affected by chronic inflammatory back pain. This warrants a careful use of spinal functional magnetic resonance imaging in animal models and patients with chronic back pain.

Optimizing and Accelerating the Development of Precision Pain Treatments for Chronic Pain: IMMPACT Review and Recommendations

Large variability in the individual response to even the most-efficacious pain treatments is observed clinically, which has led to calls for a more personalized, tailored approach to treating patients with pain (ie, "precision pain medicine"). Precision pain medicine, currently an aspirational goal, would consist of empirically based algorithms that determine the optimal treatments, or treatment combinations, for specific patients (ie, targeting the right treatment, in the right dose, to the right patient, at the right time). Answering this question of "what works for whom" will certainly improve the clinical care of patients with pain. It may also support the success of novel drug development in pain, making it easier to identify novel treatments that work for certain patients and more accurately identify the magnitude of the treatment effect for those subgroups. Significant preliminary work has been done in this area, and analgesic trials are beginning to utilize precision pain medicine approaches such as stratified allocation on the basis of prespecified patient phenotypes using assessment methodologies such as quantitative sensory testing. Current major challenges within the field include: 1) identifying optimal measurement approaches to assessing patient characteristics that are most robustly and consistently predictive of inter-patient variation in specific analgesic treatment outcomes, 2) designing clinical trials that can identify treatment-by-phenotype interactions, and 3) selecting the most promising therapeutics to be tested in this way. This review surveys the current state of precision pain medicine, with a focus on drug treatments (which have been most-studied in a precision pain medicine context). It further presents a set of evidence-based recommendations for accelerating the application of precision pain methods in chronic pain research. PERSPECTIVE: Given the considerable variability in treatment outcomes for chronic pain, progress in precision pain treatment is critical for the field. An array of phenotypes and mechanisms contribute to chronic pain; this review summarizes current knowledge regarding which treatments are most effective for patients with specific biopsychosocial characteristics.

Experimental Pain Measurements Do Not Relate to Pain Intensity and Pain Cognitions in People Scheduled for Surgery for Lumbar Radiculopathy

OBJECTIVE

The present cross-sectional study aims to unravel associations of pain intensity and cognitions with quantitative sensory testing in people scheduled for surgery for lumbar radiculopathy. Additionally, insight will be provided into the presence of dysfunctional nociceptive processing and maladaptive pain cognitions in this population.

DESIGN

Cross-sectional study.

SETTING

Data from three hospitals in Belgium.

SUBJECTS

The final sample comprised 120 participants with lumbar radiculopathy scheduled for surgery, included between March 2016 and April 2019.

METHODS

Self-reported pain intensity was assessed on a visual analog scale, and pain cognitions were assessed with self-reported questionnaires (Pain Catastrophizing Scale, Tampa Scale for Kinesiophobia, and Pain Vigilance and Awareness Questionnaire). Quantitative sensory testing (detection thresholds, pain thresholds, temporal summation, and conditioned pain modulation) was evaluated, as well.

RESULTS

Evidence was found for the presence of an impaired inhibitory response to nociceptive stimuli and maladaptive pain cognitions in this population. Kinesiophobia was found to be present to a maladaptive degree in the majority of the patients (n = 106 [88%]). Significant, but weak, associations between electrical pain thresholds at the sural nerves and leg pain intensity (sural nerve symptomatic side: r = -0.23; P = 0.01; non-symptomatic side: r = -0.22; P = 0.02) and kinesiophobia levels (sural nerve non-symptomatic side: r = -0.26; P = 0.006) were identified.

CONCLUSIONS

Electrical detection thresholds and correlates for endogenous nociceptive facilitation and inhibition were not found to be related to any of the pain cognitions or to pain intensity in people scheduled to undergo surgery for lumbar radiculopathy.

Increased Clinical Pain Locations and Pain Sensitivity in Women After Breast Cancer Surgery: Influence of Aromatase Inhibitor Therapy

OBJECTIVES

Aromatase inhibitors (AIs), which potently inhibit estrogen biosynthesis, are a standard treatment for hormone sensitive early-stage breast cancer. AIs have been associated with substantial joint pain and muscle stiffness (aromatase inhibitor-associated musculoskeletal syndrome). However, the link between AIs and number of clinical pain locations and pain sensitivity are less well understood. The aim of this study was to compare longitudinal changes in clinical pain and quantitative pain sensitivity between women who did or did not receive AI therapy.

METHODS

Women with early-stage breast cancer were prospectively enrolled and assessed for clinical pain in surgical and nonsurgical body areas using the Brief Pain Inventory and Breast Cancer Pain Questionnaire, and for pain sensitivity using quantitative sensory testing preoperatively and at 1 year postoperatively. Pain outcomes between participants who did and did not begin adjuvant AI therapy were compared using Wilcoxon Signed-Ranks and generalized estimating equation linear regression analyses.

RESULTS

Clinical pain and pain sensitivity were comparable between AI (n=49) and no-AI (n=106) groups preoperatively. After adjusting for body mass index, AI therapy was associated with a greater increase in the number of painful nonsurgical body sites (significant time by treatment interaction, P =0.024). Pain location was most frequent in knees (28%), lower back (26%), and ankles/feet (17%). Quantitative sensory testing revealed a significant decrease in pain sensitivity (increased pressure pain threshold) in the no-AI group over time, but not in the AI group.

CONCLUSIONS

AI therapy was associated with increased diffuse joint-related pain and greater post-treatment pain sensitivity, potentially implicating central sensitization as a contributing pain mechanism of aromatase inhibitor-associated musculoskeletal syndrome worthy of future investigation.

The Effects of Combined Respiratory-Gated Auricular Vagal Afferent Nerve Stimulation and Mindfulness Meditation for Chronic Low Back Pain: A Pilot Study

OBJECTIVE

Respiratory-gated Auricular Vagal Afferent Nerve stimulation (RAVANS) is a safe nonpharmacological approach to managing chronic pain. The purpose of the current study was to examine (1) the feasibility and acceptability of RAVANS, combined with mindful meditation (MM) for chronic low back pain (CLBP), (2) the potential synergy of MM+RAVANS on improving pain, and (3) possible moderators of the influence of MM+RAVANS on pain.

DESIGN

Pilot feasibility and acceptability study.

SETTING

Pain management center at large academic medical center.

SUBJECTS

Nineteen adults with CLBP and previous MM training.

METHODS

Participants attended two sessions during which they completed quantitative sensory testing (QST), rated pain severity, and completed a MM+stimulation session. Participants received RAVANS during one visit and sham stimulation during the other, randomized in order. Following intervention, participants repeated QST.

RESULTS

MM+RAVANS was well tolerated, acceptable, and feasible to provide relief for CLBP. Both MM+stimulation sessions resulted in improved back pain severity, punctate pain ratings, and pressure pain threshold. Individuals with greater negative affect showed greater back pain improvement from MM+RAVANS while those with greater mindfulness showed greater back pain improvement from MM+sham.

CONCLUSIONS

Results suggest that for CLBP patients with prior MM training, the analgesic effects of MM may have overshadowed effects of RAVANS given the brief single session MM+RAVANS intervention. However, those with greater negative affect may benefit from combined MM+RAVANS.

Experimental Pain Phenotype Profiles in Community-dwelling Older Adults

OBJECTIVES

Pain sensitivity and the brain structure are critical in modulating pain and may contribute to the maintenance of pain in older adults. However, a paucity of evidence exists investigating the link between pain sensitivity and brain morphometry in older adults. The purpose of the study was to identify pain sensitivity profiles in healthy, community-dwelling older adults using a multimodal quantitative sensory testing protocol and to differentiate profiles based on brain morphometry.

MATERIALS AND METHODS

This study was a secondary analysis of the Neuromodulatory Examination of Pain and Mobility Across the Lifespan (NEPAL) study. Participants completed demographic and psychological questionnaires, quantitative sensory testing, and a neuroimaging session. A Principal Component Analysis with Varimax rotation followed by hierarchical cluster analysis identified 4 pain sensitivity clusters (the "pain clusters").

RESULTS

Sixty-two older adults ranging from 60 to 94 years old without a specific pain condition (mean [SD] age=71.44 [6.69] y, 66.1% female) were analyzed. Four pain clusters were identified characterized by (1) thermal pain insensitivity; (2) high pinprick pain ratings and pressure pain insensitivity; (3) high thermal pain ratings and high temporal summation; and (4) thermal pain sensitivity, low thermal pain ratings, and low mechanical temporal summation. Sex differences were observed between pain clusters. Pain clusters 2 and 4 were distinguished by differences in the brain cortical volume in the parieto-occipital region.

DISCUSSION

While sufficient evidence exists demonstrating pain sensitivity profiles in younger individuals and in those with chronic pain conditions, the finding that subgroups of experimental pain sensitivity also exist in healthy older adults is novel. Identifying these factors in older adults may help differentiate the underlying mechanisms contributing to pain and aging.

Differences in Quantitative Sensory Testing Outcomes Between Patients With Low Back Pain in Primary Care and Pain-free Controls

OBJECTIVES

Quantitative Sensory Testing (QST) is used to test somatosensory functioning in on people with chronic LBP in secondary/tertiary health care facilities. Studies using QST-testing on LBP populations in primary care are scarce. Central Sensitization Inventory (CSI) measures central sensitization (CS)-related symptoms and studies investigating the differences between QST-testing and participants with LBP with a positive and negative score on the CSI questionnaire are also rare. This case-control study investigates differences of an extensive QST-measurement between patients with acute, chronic LBP, and pain-free controls (PFCs) in primary care. Secondary aim is to investigate differences of an extensive QST-measurement between "CS" and "no-CS" group.

MATERIALS AND METHODS

Participants with LBP were recruited from November 2016 to October 2019. Demographic and clinical information was collected and a standardized QST protocol was taken. Data analysis involved determining differences between groups.

RESULTS

Data of 100 participants with LBP and 50 PFCs were analyzed. Heat pain thresholds, pressure pain threshold, and conditioned pain modulation local and remote were significantly moderately to relatively strongly affected by acute, chronic LBP and PFCs (P<0.001 to 0.001). Lumbar temporal summation was significantly moderately affected by acute, chronic LBP, and PFCs (P=0.001). Only pressure pain threshold showed significant difference between "CS" and "no-CS" group (P=0.001 to 0.002).

DISCUSSION

Signs of enhanced nociceptive processing and disturbed top-down nociceptive modulation are apparent in people with acute and chronic LBP in primary care. Results indicate existence of central mechanisms in LBP in primary care.

Mechanism Underlying Painful Radiculopathy in Patients with Lumbar Disc Herniation

BACKGROUND

Painful lumbar radiculopathy is a neuropathic pain condition, commonly attributed to nerve root inflammation/compression by disc herniation. The present exploratory study searched for associations between pain intensity and inflammatory markers, herniated disc size, infection, psychological factors and pain modulation in patients with confirmed painful lumbar radiculopathy scheduled for spine surgery.

METHODS

Prior to surgery, 53 patients underwent the following evaluation: pain intensity measured on a 0-10 numeric rating scale (NRS) and the Short-Form McGill Pain Questionnaire; sensory testing (modified DFNS protocol); pain processing including temporal summation and conditioned pain modulation (CPM); neurological examination; psychological assessment including Spielberger's Anxiety Inventory, Pain Sensitivity Questionnaire and the Pain Catastrophizing Scale. Pro-inflammatory cytokine levels (IL-1b, IL-6, IL-8, IL-17, TNFα, IFNg) and microbial infection (ELISA and rt-PCR) in blood and disc samples obtained during surgery. MRI scans assessments for disc herniation size/volume (MSU classification/ three-dimensional volumetric analysis).

RESULTS

Complete data was available from 40 (75%) patients (15 female) aged 44.8±16.3 years. Pain intensity (NRS) positively correlated with pain catastrophizing and CPM (r=0.437, P=0.006; r=0.421, P=0.007; respectively), but not with disc/blood cytokine levels, bacterial infection or MRI measures. CPM (P=0.001) and gender (P=0.029) were associated with average pain intensity (adjusted R2=0.443).

CONCLUSIONS

This exploratory study suggests that pain catastrophizing, CPM and gender, seem to contribute to pain intensity in patients with painful lumbar radiculopathy. The role of mechanical compression and inflammation in determining the intensity of painful radiculopathy remains obscure.

The descending pain modulation system predicts short term efficacy of multimodal pain therapy - an observational prospective cohort study

OBJECTIVES

Treating chronic pain patients with multimodal pain therapy (MMPT) alters perception, awareness, and processing of pain at multiple therapeutic levels. Several clinical observations suggest that the effects of therapy may go beyond the possible sum of each level of therapy and may be due to a central descending inhibitory effect measurable by conditioned pain modulation (CPM). Thus, we investigated whether CPM is able to identify a group of patients that benefit particularly from MMPT.

METHODS

This was an observational prospective cohort study. Patients were hospitalized on a special pain medicine ward with specially trained staff for 10 days. The patients were questioned and had investigations before and shortly after MMPT and were followed-up on 3 months post discharge. Before and after treatment, subjects were investigated via CPM and quantitative sensory testing (QST) as well as completing questionnaires. The study was registered in the German Clinical Trials Register (DRKS00006850).

RESULTS

During the study period of 24 months, 224 chronic pain patients were recruited. 51 percent of patients completed the study period. There was an improvement in overall groups regarding all domains assessed, lasting beyond the end of the intervention. Patients with a sufficient CPM effect, defined as a reduction in pain during the conditioning stimulus, at baseline did show a more pronounced reduction in mean pain ratings than those without. This was not the case 3 months after therapy. Furthermore, sufficient CPM was identified as a predictor for pain reduction using a linear regression model.

CONCLUSION

In conclusion, this study shows that while a heterogeneous group of patients with chronic pain disorders does sustainably benefit from MMPT in general, patients with a sufficient CPM effect do show a more pronounced decrease in pain ratings directly after therapy in comparison to those without.

Association between temporal summation and conditioned pain modulation in chronic low back pain: baseline results from 2 clinical trials

Introduction

Temporal summation (TS) and conditioned pain modulation (CPM) represent different aspects of central pain processing. Their relationship and differential performance within distinct body locations are not well understood.

Objectives

To examine the association between TS and CPM in chronic low back pain and the influence of testing location on this relationship.

Methods

We analyzed baseline data from 2 clinical trials on participants with chronic low back pain (n = 264; 47.3% female; mean age = 41 years, SD = 12; mean pain = 5.3/10, SD = 1.4). Measures used included questionnaires assessing pain and negative affect, phasic thermal TS at the hand (thenar) and the lower back (lumbar), followed by CPM that included a thermal testing stimulus (Heat-6, the temperature where pain rating is 6/10) and a cold-pressor conditioning stimulus. Nonparametric, proportional odds logistic regression was used to model thenar, and separately, lumbar TS, using CPM, Heat-6, negative affect, and demographics.

Results

Our models revealed a small association (βs = 0.17, P = 0.01) between reduced CPM and heightened TS at both testing sites, regardless of demographics or negative affect.

Conclusion

Results suggest a modest association between TS and CPM, irrespective of anatomical testing location, demographics, and negative affect. These findings will help improve the methodology and interpretation of TS and CPM measurement in clinical pain populations.

Relative contributions of the nervous system, spinal tissue and psychosocial health to non-specific low back pain: Multivariate meta-analysis

BACKGROUND AND OBJECTIVES

Nervous system, psychosocial and spinal tissue biomarkers are associated with non-specific low back pain (nsLBP), though relative contributions are unclear.

DATABASES AND DATA TREATMENT

MEDLINE, EMBASE, CINAHL, PsycINFO and SPORTDiscus were searched up to 25 March 2020. Related reviews and reference lists were also screened. Observational studies examining structural and functional nervous system biomarkers (e.g. quantitative sensory tests, structural and functional brain measures), psychosocial factors (e.g. mental health, catastrophizing) and structural spinal imaging biomarkers (e.g. intervertebral disc degeneration, paraspinal muscle size) between nsLBP and pain-free controls were included. For multivariate meta-analysis, two of three domains were required in each study. Random-effects pairwise and multivariate meta-analyses were performed. GRADE approach assessed evidence certainty. Newcastle-Ottawa scale assessed risk of bias. Main outcomes were the effect size difference of domains between nsLBP and pain-free controls.

RESULTS

Of 4519 unique records identified, 33 studies (LBP = 1552, referents = 1322) were meta-analysed. Psychosocial state (Hedges' g [95%CI]: 0.90 [0.69-1.10], p < 0.001) in nsLBP showed larger effect sizes than nervous system (0.31 [0.13-0.49], p < 0.001; difference: 0.61 [0.36-0.86], p < 0.001) and spine imaging biomarkers (0.55 [0.37-0.73], p < 0.001; difference: 0.36 [0.04-0.67], p = 0.027). The relationship between domains changes depending on if pain duration is acute or chronic.

CONCLUSIONS

Psychosocial effect sizes in nsLBP are greater than that for spinal imaging and nervous system biomarkers. Limitations include cross-sectional design of studies included and inference of causality. Future research should investigate the clinical relevance of these effect size differences in relation to pain intensity and disability.

STUDY REGISTRATION

PROSPERO-CRD42020159188.

SIGNIFICANCE

Spinal imaging (e.g. intervertebral disc degeneration), psychosocial (e.g. depression) and nervous system (e.g. quantitative sensory tests, structural and functional brain measures) biomarkers contribute to non-specific low back pain. However, psychosocial factors may be more compromised than nervous system and spinal imaging biomarkers. This relationship depends on if the pain is acute or chronic. These findings underscore that the 'non-specific' label in back pain should be reconsidered, and more specific multidimensional categories evaluated to guide patient management.

Heritability of musculoskeletal pain and pain sensitivity phenotypes: two generations of the Raine Study

ABSTRACT

There is a need to better understand biological factors that increase the risk of persistent musculoskeletal pain and heightened pain sensitivity. Knowing the heritability (how genes account for differences in people's traits) can enhance the understanding of genetic versus environmental influences of pain and pain sensitivity. However, there are gaps in current knowledge, including the need for intergenerational studies to broaden our understanding of the genetic basis of pain. Data from Gen1 and Gen2 of the Raine Study were used to investigate the heritability of musculoskeletal pain, and pressure and cold pain sensitivity. Participants included parents (Gen 1, n=1092) and their offspring (Gen 2, n=688) who underwent a battery of testing and questionnaires including pressure and cold pain threshold testing and assessments of physical activity, sleep, musculoskeletal pain, mental health and adiposity. Heritability estimates were derived using the Sequential Oliogenic Linkage Analysis Routines (SOLAR) software. Heritability estimates for musculoskeletal pain and pressure pain sensitivity were significant, accounting for between 0.190 and 0.289 of the variation in the phenotype. In contrast, heritability of cold pain sensitivity was not significant. This is the largest intergenerational study to date to comprehensively investigate the heritability of both musculoskeletal pain and pain sensitivity, using robust statistical analysis. This study provides support for the heritability of musculoskeletal pain and pain sensitivity to pressure, suggesting the need for further convergence of genetic and environmental factors in models for the development and/or maintenance of these pain disorders.