The long-term reliability of static and dynamic quantitative sensory testing in healthy individuals

Impact of adverse childhood experiences on sensory thresholds in adults living with multimorbidity and chronic pain (the ACE-MAP study): protocol for an observational feasibility study

INTRODUCTION

Exposure to adverse childhood experiences (ACEs) is associated with a range of poor long-term health outcomes, including multimorbidity and chronic pain. Epidemiological evidence underpins much of this relationship; however, psychophysical testing methods, such as quantitative sensory testing (QST), may provide valuable insights into potential mechanisms. Previous studies have shown inconsistent links between ACEs and QST, but the QST profiles of people with multimorbidity have not been reported. We hypothesise that exposure to ACEs is associated with lowered QST thresholds (ie, experience of pain with milder stimuli) and that this association is stronger in adults with multimorbidity and/or chronic pain. The ACE-MAP study is a cross-sectional feasibility study with the primary aim of assessing the feasibility and acceptability of the proposed study procedures. The secondary aim is to generate preliminary data to understand the impact of ACEs on QST thresholds.

METHODS AND ANALYSIS

We plan to recruit 40 participants, with 10 in each of the following groups: (1) chronic pain with multimorbidity; (2) chronic pain without multimorbidity; (3) multimorbidity without chronic pain; and (4) controls. Participants will complete a series of questionnaires (including on ACEs, chronic pain and long-term conditions) and will then take part in QST assessments. The primary study outcomes will include measures of feasibility and acceptability of the proposed study design. The secondary study outcomes will include exploratory analysis on the relationship between ACEs and QST thresholds.

ETHICS AND DISSEMINATION

The study was approved by the Scotland B Research Ethics Committee (reference: 24/SS/0031). Results from the study will be presented at scientific conferences, published in a peer-reviewed journal and shared with patients and members of the public through other media streams.

TRIAL REGISTRATION NUMBER

ISRCTN10049430.

Acute and long-term effect of specific and non-specific exercises in patients with chronic neck pain: A protocol for a randomized controlled trial

Exercise therapy is the most common approach for people with chronic neck pain (CNP). Although well-established, it remains unknown which type of exercise is the best for treating this condition. Moreover, pain processing can play a role in the persistence of pain and in the response to interventions. Thus, the aim of this randomized controlled trial is to compare the acute and long-term effects of two exercise protocols (specific and non-specific) on pain and pain processing in individuals with CNP. One hundred and ten participants aged between 18 and 65 years who have had non-specific neck pain for more than 3 months will be recruited. They will be randomized and allocated into two groups (specific exercises and non-specific exercises) and both groups will perform an exercise programme twice a week for 8 weeks. Both programmes are divided into two progressive and individualized phases. The primary outcomes are change in pain intensity after 8 weeks of exercise and exercise-induced hypoalgesia, and secondary outcomes are pressure pain threshold, temporal summation of pain, conditioned pain modulation, the Neck Disability Index, the Baecke Physical Activity Questionnaire, and the Global Perception of Change Scale. Outcomes will be assessed at baseline, after 8 weeks of intervention, and at 6-month follow-up.

Assessing pain in persons with opioid use disorder: Approaches, techniques and special considerations

Pain and opioid use disorder (OUD) are inextricably linked, as the former can be a risk factor for the development of the latter, and over a third of persons with OUD suffer concomitant chronic pain. Assessing pain among people with OUD is challenging, because ongoing opioid use brings changes in pain responses and most pain assessment tools have not been validated for this population. In this narrative review, we discuss the fundamentals of pain assessment for populations with OUD. First, we describe the biological, psychological and social aspects of the pain experience among people with OUD, as well as how opioid-related phenomena may contribute to the pain experience in this population. We then review methods to assess pain, including (1) traditional self-reported methods, such visual analogue scales and structured questionnaires; (2) behavioural observations and physiological indicators; (3) and laboratory-based approaches, such as quantitative sensory testing. These methods are considered from a perspective that encompasses both pain and OUD. Finally, we discuss strategies for improving pain assessment in persons with OUD and implications for future research, including educational strategies for multidisciplinary teams. We highlight the substantial gaps that persist in this literature, particularly regarding the applicability of current pain assessment methods to persons with OUD, as well as the generalizability of the existing results from adjacent populations on chronic opioid therapy but without OUD. As research linking pain and OUD evolves, considering the needs of diverse populations with complex psychosocial backgrounds, clinicians will be better equipped to reduce these gaps.

Selective nociceptive modulation using a novel prototype of transcutaneous kilohertz high-frequency alternating current stimulation: a crossover double-blind randomized sham-controlled trial

BACKGROUND

Kilohertz high-frequency alternating current (KHFAC) stimulation has demonstrated to induce rapid and reversible nerve blocks without causing nerve damage. Previous studies have explored frequency-dependent effects using a transcutaneous approach in humans from 5 to 20 kHz. Nevertheless, its application in humans is limited by the lack of stimulators approved for frequencies above 20 kHz. Therefore, this study aimed to assess the effects and safety of transcutaneous KHFAC stimulation using a novel prototype stimulator, comparing interventions at 30, 40, and 50 kHz to sham stimulation on experimental pain, sensory, motor, and neurophysiological outcomes.

METHODS

A randomized, double-blind, sham-controlled crossover study involving 34 healthy participants was conducted. Four interventions (30, 40, 50 kHz, and sham) were administered, and stimulation was applied for 20 min to the median nerve of the non-dominant hand. A prototype stimulator capable of delivering frequencies between 1 and 50 kHz, with a maximum peak-to-peak output current intensity of 400 mA was designed. The intensity applied during the stimulation was below motor threshold, evoking a 'strong but comfortable' tingling sensation. Primary outcomes included heat pain threshold (HPT), pressure pain threshold (PPT), and adverse effects. The secondary outcomes included static two-point discrimination sensitivity, isometric pinch strength, and median sensory nerve action potential (SNAP).

RESULTS

Compared with the sham stimulation, all the active interventions exhibited a significantly greater increase in the PPT during and immediately after the stimulation, while only a significant increase was observed at 40 kHz (4.1 N/cm2; 95%CI 0.3 to 7.9) at 15 min post-intervention. Compared to sham stimulation, the 40 kHz intervention had a significantly greater effect on the HPT at all time points, with the greatest difference (1.4 °C; 0.6 to 2.1) occurring immediately post-intervention. Adverse effects during active interventions included petechiae, erythema, and itching, which resolved at 24 h post-intervention. For secondary outcomes, only a significant reduction in the median SNAP velocity was observed in the sham stimulation group compared to the 50 kHz group.

CONCLUSIONS

Active KHFAC stimulation, particularly at 40 kHz, delivered through a novel stimulator, effectively increased the PPT and HPT without affecting tactile or motor outcomes, inducing mild skin-related adverse effects. These findings have potential implications for people with pain-related pathologies.

TRIAL REGISTRATION

NCT05230836.

Effects of therapeutic exercise on pain processing in people with chronic non-specific neck pain - A systematic review and meta-analysis

BACKGROUND

Emerging evidence suggests that individuals with chronic non-specific neck pain may experience altered sensory processing, potentially contributing to the modest response to therapeutic exercise treatments.

OBJECTIVE

This systematic review aims to explore the effect of therapeutic exercise on pain processing among patients with chronic non-specific neck pain.

METHODS

A systematic search was conducted in multiple databases (PubMed, EMBASE, CINAHL, PEDro, SportDiscus, and Cochrane CENTRAL) from inception to June 2023. Inclusion criteria included randomized controlled trials (RCT) comparing therapeutic exercise to non-exercise treatments or no treatment. The screening and data extraction was conducted by two reviewers. The methodological quality was evaluated using the PEDro scale and the certainty of evidence using GRADE. The primary outcomes assessed were pressure pain threshold (PPT), temporal summation, and conditioned pain modulation.

RESULTS

Thirteen trials included a total of 948 participants, with 586 in the exercise therapy group and 362 in the non-exercise group. The therapeutic exercise was not superior to non-exercise treatments for both local and PPT in the immediate (MD = 0.13, 95%CI = -0.18 to 0.43), and short-term follow-up (MD = 0.17, 95%CI = -0.27 to 0.61). In the medium term, therapeutic exercise demonstrated a small effect size in increasing local PPT (Kg/cm2) (MD = 0.64, 95%CI = 0.08 to 1.19) compared to non-exercise interventions. The certainty of evidence for these outcomes was very low.

CONCLUSIONS

There is very low certainty of evidence that therapeutic exercise is not superior than non-exercise treatment on pain processing in patients with chronic non-specific neck pain.

Test-retest and interrater reliability of experimental within-subject variability of pain reports as assessed by the focused analgesia selection test

Introduction

Within-subject variability (WSV) of pain intensity reports has been shown to predict the placebo response. The focused analgesia selection test (FAST), which allows to experimentally assess WSV of pain reports, has been used as a screening tool to identify participants who are likely to have a strong placebo response in drug-development clinical trials. Yet, the reliability of FAST has not been reported.

Objectives

To assess test-retest and interrater reliability of the FAST outcomes. To mimic pharma-sponsored clinical trials, we enlisted inexperienced assessors who underwent limited training.

Methods

Healthy volunteers performed the FAST twice within a week and were randomly assigned to either the test-retest group or the interrater group. T-tests, partial Pearson correlations, intraclass correlations (ICC), and Bland-Altman plots were generated to assess FAST outcomes' reliability.

Results

Sixty-three participants completed the study and were assigned to the test-retest (N = 33) or interrater (N = 30) arms. No statistically significant differences in the FAST outcomes were detected between the 2 sessions, except for the FAST covariance (FAST CoV) in the interrater assessment (P = 0.009). Test-retest reliabilities of the FAST-main outcomes were r = 0.461, ICC = 0.385 for the FAST R 2 and r = 0.605, ICC = 0.539 for the FAST ICC and in the interrater cohort, they were FAST R 2: r = 0.321, ICC = 0.337 and FAST ICC: r = 0.355, ICC = 0.330.

Conclusion

Using inexperienced assessors, the FAST outcomes test-retest ranged from moderate to strong, whereas the interrater reliability ranged from weak to poor. These results highlight the importance of adequately training study staff members before using this tool in multicentre clinical trials.

Does pain tolerance mediate the effect of physical activity on chronic pain in the general population? The Tromsø Study

ABSTRACT

Knowledge is needed regarding mechanisms acting between physical activity (PA) and chronic pain. We investigated whether cold pain tolerance mediates an effect of leisure-time physical activity on the risk of chronic pain 7 to 8 years later using consecutive surveys of the population-based Tromsø Study. We included participants with information on baseline leisure-time PA (LTPA) and the level of cold pressor-assessed cold pain tolerance, who reported chronic pain status at follow-up as any of the following: chronic pain for ≥3 months, widespread chronic pain, moderate-to-severe chronic pain, or widespread moderate-to-severe chronic pain. We included 6834 participants (52% women; mean age, 55 years) in counterfactual mediation analyses. Prevalence decreased with severity, for example, 60% for chronic pain vs 5% for widespread moderate-to-severe chronic pain. People with one level higher LTPA rating (light to moderate or moderate to vigorous) at baseline had lower relative risk (RR) of 4 chronic pain states 7 to 8 years later. Total RR effect of a 1-level LTPA increase was 0.95 (0.91-1.00), that is, -5% decreased risk. Total effect RR for widespread chronic pain was 0.84 (0.73-0.97). Indirect effect for moderate-to-severe chronic pain was statistically significant at RR 0.993 (0.988-0.999); total effect RR was 0.91 (0.83-0.98). Statistically significantly mediated RR for widespread moderate-to-severe chronic pain was 0.988 (0.977-0.999); total effect RR was 0.77 (0.64-0.94). This shows small mediation of the effect of LTPA through pain tolerance on 2 moderate-to-severe chronic pain types. This suggests pain tolerance to be one possible mechanism through which PA modifies the risk of moderate-to-severe chronic pain types with and without widespread pain.

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

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

Mechanical and thermal thresholds before and after application of a conditioning stimulus in healthy Göttingen Minipigs

Minipigs are widely used in biomedical research for translational studies. However, information about pain elicited by experimental procedures is lacking. Non-invasive methods as quantitative sensory testing and conditioned pain modulation are particularly attractive. Our overarching aim was to explore and refine these methods for assessing post-operative pain in minipigs after myocardial infarction. As first step, we aimed at defining mechanical and thermal thresholds in healthy adults Göttingen Minipigs, evaluating their reliability, and testing their modifications after the application of a conditioning stimulus. Thresholds were assessed at different body sites before and after a painful conditioning stimulus (CS) (cuffed tourniquet) and sham CS (uncuffed tourniquet) in eleven animals. Thresholds' reliability was assessed using interclass correlation coefficient (ICC). The effect of the CS was assessed calculating absolute change, percentage change of the thresholds and standard error of measurement. Baseline mechanical thresholds (Newton) were: left hindlimb 81 [73; 81]; left forearm 81 [72.1; 81]; right forearm 81 [76; 81]; left chest 80.5 [68; 81]; right chest 81 [76.5; 81]; left neck 81 [70.3; 81]; right neck 74.8 [62.3; 80.5]. Reliability of mechanical thresholds was good at right chest (ICC = 0.835) and moderate at left chest (ICC = 0.591), left hindlimb (ICC = 0.606) and left neck (ICC = 0.518). Thermal thresholds showed poor reliability in all the tested sites. A modulatory effect was present at right chest, but it was seen when both a painful CS and a sham CS was applied. Minipigs tendentially showed a pro-nociceptive profile (i.e. conditioning pain facilitation). The measured thresholds are a reference for future trials in this species. Mechanical thresholds showed to be more reliable and, therefore, more useful, than thermal ones. The pain facilitation might be explained by the phenomenon of stress induced hyperalgesia, but this finding needs to be further investigated with a stricter paradigm.

Reliability and minimal detectable change of dynamic temporal summation and conditioned pain modulation using a single experimental paradigm

BACKGROUND

Quantitative sensory tests (QST) are frequently used to explore alterations in somatosensory systems. Static and dynamic QST like pain threshold and temporal summation (TS) and conditioned pain modulation (CPM) are commonly used to evaluate excitatory and inhibitory mechanisms involved in pain processing. The aim of the present study was to document the reliability and the minimal detectable change (MDC) of these dynamic QST measurements using a standardized experimental paradigm.

MATERIAL AND METHODS

Forty-six (46) pain-free participants took part in 2 identical sessions to collect TS and CPM outcomes. Mechanical (pressure pain threshold [PPT]) and thermal (constant 2-minute heat pain stimulation [HPS]) nociceptive stimuli were applied as test stimuli, before and after a cold-water bath (conditioning stimulus). TS was interpreted as the change in pain perception scores during HPS. CPM were determined by calculating the difference in pain perception between pre- and post- water bath for both PPT and HPS. Relative and absolute reliability were analyzed with intra-class correlation coefficient (ICC2, k), standard error of the measurements (SEMeas) and MDC.

RESULTS

Results revealed a good to excellent relative reliability for static QST (ICC ≥ 0.73). For TS, a poor to moderate relative reliability depending on the calculation methods (ICC = 0.25 ≤ ICC ≤ 0.59), and a poor relative reliability for CPM (ICC = 0.16 ≤ ICC ≤ 0.37), both when measured with mechanical stimulation (PPT) and thermal stimulation (HPS). Absolute reliability varied from 0.73 to 7.74 for static QST, 11 to 22 points for TS and corresponded to 11.42 points and 1.56 points for thermal and mechanical-induced CPM, respectively. MDC analyses revealed that a change of 1.58 to 21.46 point for static QST, 31 to 52 points for TS and 4 to 31 points for CPM is necessary to be interpreted as a real change.

CONCLUSION

Our approach seems well-suited to clinical use. Although our method shows equivalent relative and absolute reliability compared to other protocols, we found that the reliability of endogenous pain modulation mechanisms is vulnerable, probably due to its dynamic nature.

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

BACKGROUND

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

METHODS AND ANALYSIS

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

ETHICS AND DISSEMINATION

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

Test-Retest Reliability of Pain Sensitivity Measures in Individuals with Shoulder Pain

Background

Central sensitization (CS) has been proposed as a possible contributor to persistent shoulder pain. Measures of sensitivity, such as quantitative sensory tests (QSTs) and sensitivity to movements evoked pain (SMEP), have been increasingly used to investigate CS in a wide range of painful conditions. However, there is a lack of data on whether QST and SMEP are reliable among individuals with shoulder pain. Therefore, the present study aimed to investigate the intra-rater test-retest reliability of QST and SMEP in individuals with chronic shoulder pain.

Materials and Methods

Forty-seven individuals with chronic shoulder pain were enrolled in the study. The QST measures, including pressure pain threshold (PPT) and mechanical temporal summation (MTS), were tested, and SMEP was measured with a lifting task. Relative and absolute reliability were analyzed using intraclass correlation coefficients (ICC 3,1) and standard error of the measurement (SEM), respectively.

Results

The results showed that the ICC coefficients for all sensitivity measures were moderate to good, ranging from 0.63 to 0.86. The SEM% for the QST measures at all sites ranged from 21.4% to 36%, with TS at the forearm demonstrating a high SEM% (greater than 30%). The SMEP measure also showed a high SEM% (46%).

Conclusion

The results showed that the sensitivity measures had moderate to good reliability among individuals with shoulder pain. Acceptable limits of accuracy of measurements were demonstrated for TS and PPT measures, while SMEP demonstrated high error, highlighting the need for further refinement of this measure among these populations.

The effects of neck exercise in comparison to passive or no intervention on quantitative sensory testing measurements in adults with chronic neck pain: A systematic review

BACKGROUND

Previous systematic reviews have identified the benefits of exercise for chronic neck pain on subjective reports of pain, but not with objective measures such as quantitative sensory testing (QST). A systematic review was conducted to identify the effects of neck specific exercise on QST measures in adults with chronic neck pain to synthesise existing literature and provide clinical recommendations.

METHODS

The study protocol was registered prospectively with PROSPERO (PROSPERO CRD42021297383). For both randomised and non-randomised trials, the following databases and trial registries were searched: AMED, CINAHL, Embase, Google Scholar, Medline, PEDro, PubMed, Scopus, SPORTDiscus, Science Citation Index and Social Science Citation Index from Web of Science Core Collection, clinicaltrials.gov, GreyOpen, and ISRCTN registry. These searches were conducted from inception to February 2022 and were updated until September 2023. Reference lists of eligible studies were screened. Study selection was performed independently by two reviewers, with data extraction and quality appraisal completed by one reviewer and independently ratified by a second reviewer. Due to high heterogeneity, narrative synthesis was performed with results grouped by exercise type.

FINDINGS

Three trials were included. Risk of bias was rated as moderate and the certainty of evidence as low or moderate for all studies. All exercise groups demonstrated statistically significant improvement at an intermediate-term follow-up, with progressive resistance training combined with graded physical training demonstrating the highest certainty of evidence. Fixed resistance training demonstrated statistically significant improvement in QST measures at a short-term assessment.

INTERPRETATION

Fixed resistance training is effective for short-term changes in pain sensitivity based on low-quality evidence, whilst moderate-quality evidence supports progressive resistance training combined with graded physical training for intermediate-term changes in pain sensitivity.

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.

Longitudinal Changes and Associations Between Quantitative Sensory Testing and Psychological Factors in Whiplash-Associated Disorders: A Systematic Review and Meta-Analyses-Based Data Synthesis

Whiplash-associated disorders (WAD) represent a multifactorial condition often accompanied by altered nociceptive processing and psychological factors. This systematic review on acute and chronic WAD aimed to investigate the relationship between quantitative sensory testing (QST) and psychological factors and quantify whether their trajectories over time follow a similar pattern to disability levels. Eight databases were searched until October 2022. When 2 prospective studies examined the same QST or psychological variable, data synthesis was performed with random-effects meta-analysis by pooling within-group standardized mean differences from baseline to 3-, 6-, and 12-month follow-ups. From 5,754 studies, 49 comprising 3,825 WAD participants were eligible for the review and 14 for the data synthesis. Altered nociceptive processing in acute and chronic WAD, alongside worse scores on psychological factors, were identified. However, correlations between QST and psychological factors were heterogeneous and inconsistent. Furthermore, disability levels, some QST measures, and psychological factors followed general positive improvement over time, although there were differences in magnitude and temporal changes. These results may indicate that altered psychological factors and increased local pain sensitivity could play an important role in both acute and chronic WAD, although this does not exclude the potential influence of factors not explored in this review. PERSPECTIVE: Acute WAD show improvements in levels of disability and psychological factors before significant improvements in nociceptive processing are evident. Facilitated nociceptive processing might not be as important as psychological factors in chronic WAD-related disability, which indicates that chronic and acute WAD should not be considered the same entity although there are similarities. Nonetheless, pressure pain thresholds in the neck might be the most appropriate measure to monitor WAD progression.

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

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

The interrater and test-retest reliability of 3 modalities of quantitative sensory testing in healthy adults and people with chronic low back pain or rheumatoid arthritis

Introduction

Quantitative Sensory Testing (QST) modalities used to assess central pain mechanisms require different protocols in people with different musculoskeletal conditions.

Objectives

We aimed to explore the possible effects of musculoskeletal diagnosis and test site on QST interrater and test-retest reliability.

Methods

The study included participants with rheumatoid arthritis (RA, n = 18; QST conducted on lower leg) and low back pain (LBP, n = 25; QST conducted on forearm), plus 45 healthy control participants (n = 20 QST on lower leg and n = 25 QST on forearm). Test-retest reliability was assessed from QST conducted 1 to 3 weeks apart. Quantitative sensory testing modalities used were pressure pain detection threshold (PPT) at a site distant to tissue pathology, temporal summation (TS), and conditioned pain modulation (CPM). Temporal summation was calculated as difference or ratio of single and repeated punctate stimuli and unconditioned thresholds for CPM used single or mean of multiple PPTs. Intraclass correlation coefficients (ICCs) were compared between different subgroups.

Results

High to very high reliability was found for all assessments of PPT and TS across anatomical sites (lower leg and forearm) and participants (healthy, RA, and LBP) (ICC ≥ 0.77 for PPT and ICC ≥ 0.76 for TS). Reliability was higher when TS was calculated as a difference rather than a ratio. Conditioned pain modulation showed no to moderate reliability (ICC = 0.01-0.64) that was similar between leg or forearm, and between healthy people and those with RA or LBP.

Conclusion

PPT and TS are transferable tools to quantify pain sensitivity at different testing sites in different musculoskeletal diagnoses. Low apparent reliability of CPM protocols might indicate minute-to-minute dynamic pain modulation.

Intra- and inter-session reliability of electrical detection and pain thresholds of cutaneous and muscle primary afferents in the lower back of healthy individuals

To advance evidence-based practice and targeted treatments of low back pain (LBP), a better pathophysiological understanding and reliable outcome measures are required. The processing of nociceptive information from deeper somatic structures (e.g., muscle, fascia) might play an essential role in the pathophysiology of LBP. In this study, we measured the intra- and inter-session reliability of electrical detection and pain thresholds of cutaneous and muscle primary afferents of the lower back. Twenty healthy participants attended two study visits separated by 27.7 ± 1.7 days. To determine the location-specific electrical detection threshold (EDT) and pain threshold (EPT), needle electrodes were inserted in the epidermal layer over, and in the lumbar erector spinae muscle. Additionally, established quantitative sensory testing (QST) parameters were assessed. Reliability was determined by differences between measurements, intraclass correlation coefficients (ICC2,1), Bland-Altman plots, and standard error of measurement (SEM). Correspondence between QST parameters and electrical thresholds was assessed using Pearson's correlation. Except for cutaneous EPT, no significant (p ≤ 0.05) intra- and inter-session differences were observed. Excellent intra-session reliability was shown for cutaneous and intramuscular electrical stimulations and all QST parameters (ICC: 0.76-0.93). Inter-session reliabilities were good (ICC: 0.74-0.75) except for electrical stimulations (ICC: 0.08-0.36). Limits of agreement and SEM were higher for inter-session than intra-session. A medium to strong relationship was found between electrical and mechanical/pressure pain thresholds. In conclusion, cutaneous and intramuscular electrical stimulation will potentially close an important diagnostic gap regarding the selective examination of deep tissue afferents and provide location-specific information for the excitability of non-nociceptive and nociceptive afferents.

A systematic review of the psychometric properties of pressure pain detection threshold in evaluating mechanical pain threshold in people with hand or wrist injuries

PURPOSE

The aim of this study was to conduct a systematic review of the psychometric properties of Pressure Pain Detection Threshold (PPDT) measures in people with hand or wrist injuries.

STUDY DESIGN AND METHODS

MEDLINE, Embase, and CINAHL databases were searched to identify eligible studies evaluating psychometric properties of PPDT in samples composed of at least 50% of people with hand or wrist injury. The Consensus-based Standards for the Measurement of Health Instruments' risk of bias checklist was used to critically appraise the included studies, and qualitative synthesis was performed by pooling the results of all studies that presented the same measurement property using Grading of Recommendations, Assessment, Development, and Evaluation.

RESULTS

From 415 studies, 11 relevant studies were identified. Of the 11 studies, four hand or wrist injuries were represented; carpal tunnel syndrome, distal radius fractures, osteoarthritis, and complex regional pain syndrome. Intra-rater reliability was considered sufficient (intraclass correlation coefficient 0.64-0.94), with small reported standard error of the mean values (5.3-39.2 kPa). Results of validity and responsiveness could not be synthesized due to heterogeneity. Risk of bias for reliability and measurement error was assessed as very good or adequate, whereas validity and responsiveness were doubtful or inadequate. Overall quality of evidence was low or very low for all measurement properties.

CONCLUSIONS

Inconsistent results and low quality evidence provide little confidence in the overall measurement properties of PPDT in a hand or wrist injury population. No criterion standard for pain further highlights complexities around pain measurement such that the results obtained from PPDT measures in clinical practice cannot be compared to a gold standard measure.

Temporal stability and responsiveness of a conditioned pain modulation test

OBJECTIVES

Conditioned pain modulation is a commonly used quantitative sensory test, measuring endogenous pain control. The temporal stability of the test is questioned, and there is a lack of agreement on the effect of different pain conditions on the conditioned pain modulation response. Thus, an investigation of the temporal stability of a conditioned pain modulation test among patients suffering from persistent or recurrent neck pain is warranted. Further, an investigation into the difference between patients experiencing a clinically important improvement in pain and those not experiencing such an improvement will aid the understanding between changes in pain and the stability of the conditioned pain modulation test.

METHODS

This study is based on a randomized controlled trial investigating the effect of home stretching exercises and spinal manipulative therapy vs. home stretching exercises alone. As no difference was found between the interventions, all participants were studied as a prospective cohort in this study, investigating the temporal stability of a conditioned pain modulation test. The cohort was also divided into responders with a minimally clinically important improvement in pain and those not experiencing such an improvement.

RESULTS

Stable measurements of conditioned pain modulation were observed for all independent variables, with a mean change in individual CPM responses of 0.22 from baseline to one week with a standard deviation of 1.34, and -0.15 from the first to the second week with a standard deviation of 1.23. An Intraclass Correlation Coefficient (ICC3 - single, fixed rater) for CPM across the three time points yielded a coefficient of 0.54 (p<0.001).

CONCLUSIONS

Patients with persistent or recurrent neck pain had stable CPM responses over a 2 week course of treatment irrespective of clinical response.

Modulation of Pain Sensitivity by a Hyperventilatory Breathing Exercise and Cold Exposure Training

Background

Evidence indicates that healthy individuals who follow a training program comprised hyperventilatory breathing exercises and cold exposure can voluntarily activate their sympathetic nervous system and attenuate their systemic inflammatory response during experimental endotoxemia (intravenous administration of bacterial endotoxin). Furthermore, trained participants reported less endotoxemia-induced flu-like symptoms. However, it remained to be determined whether the effects on symptoms are due to the mitigated inflammatory response or involve direct analgesic effects of (elements of) the training program.

Methods

In the present study, we used Nijmegen-Aalborg Screening Quantitative sensory testing (NASQ) to objectively map pain sensitivity using non-invasive stimuli to address this question. First, NASQ parameters were evaluated in 20 healthy volunteers before, during, and after the conduct of the hyperventilatory breathing exercise. Second, NASQ measurements were performed before and after 48 healthy volunteers followed different modalities of the training program: breathing exercise training, cold exposure training, the combination of both, or no training. Lastly, NASQ measurements were performed in these 48 subjects during experimental endotoxemia.

Results

Electrical pain detection thresholds increased during the breathing exercise (p = 0.001) as well as four hours afterwards (p = 0.03). Furthermore, cold exposure training resulted in lower VAS scores during hand immersion in ice water (p < 0.001). Systemic inflammation induced by administration of endotoxin nullified the decreased pain perception during the ice water test in subjects trained in cold exposure.

Conclusion

A hyperventilatory breathing exercise decreases pain perception induced by an electrical stimulus. Furthermore, cold exposure training may decrease pain perception induced by hand immersion in ice water.

Preliminary Evidence for the Sequentially Mediated Effect of Racism-Related Stress on Pain Sensitivity Through Sleep Disturbance and Corticolimbic Opioid Receptor Function

Sleep disturbance predicts worse pain outcomes. Because sleep disturbance inequitably impacts Black adults - with racism as the upstream cause - understanding how racism-related stress impacts pain through sleep might help minimize racialized pain inequities. This preliminary study examined sequential mediation of the effect of racism-related stress on experimental pain through sleep disturbance and corticolimbic μOR function in pain-free non-Hispanic Black (NHB) and White (NHW) adults. Participants completed questionnaires, actigraphy, positron emission tomography, and sensory testing. We reproduced findings showing greater sleep disturbance and pain sensitivity among NHB participants; greater sleep disturbance (r = .35) and lower pain tolerance (r=-.37) were significantly associated with greater racism-related stress. In a sequential mediation model, the total effect of racism-related stress on pain tolerance (β=-.38, P = .005) weakened after adding sleep disturbance and ventromedial prefrontal cortex (vmPFC) μOR binding potential (BPND) as mediators (β = -.18, P = .16). The indirect effect was statistically significant [point estimate = -.003, (-.007, -.0003). Findings showed a potential sequentially mediated effect of racism-related stress on pain sensitivity through sleep disturbance and vmPFC μOR BPND. As policy efforts are enacted to eliminate the upstream cause of systemic racism, these results cautiously suggest that sleep interventions within racism-based trauma informed therapy might help prevent downstream effects on pain. PERSPECTIVE: This preliminary study identified the effect of racism-related stress on pain through sleep disturbance and mu-opioid receptor binding potential in the ventromedial prefrontal cortex. Findings cautiously support the application of sleep interventions within racism-based trauma-informed therapy to prevent pain inequities as policy changes function to eliminate all levels of racism.

Somatosensory Outcomes Following Re-Surgery in Persistent Severe Pain After Groin Hernia Repair: A Prospective Observational Study

Purpose

After groin hernia repair (globally more than 20 million/year) 2-4% will develop persistent severe pain (PSPG). Pain management is challenging and may require multimodal interventions, including re-surgery. Quantitative somatosensory testing (QST) is an investigational psychophysiological tool with the potential to uncover the pathophysiological mechanisms behind the pain, ie, revealing neuropathic or inflammatory components. The primary objective was to examine and describe the underlying pathophysiological changes in the groin areas by QST before and after re-surgery with mesh removal and selective neurectomy.

Patients and Methods

Sixty patients with PSPG scheduled for re-surgery and with an inflammatory "component" indicated by blunt pressure algometry were examined in median (95% CI) 7.9 (5.8-11.5) months before and 4.0 (3.5-4.6) months after re-surgery. The QST-analyses included standardized assessments of cutaneous mechanical/thermal detection and pain thresholds. Suprathreshold heat stimuli were applied. Deep tissue sensitivity was tested by pressure algometry. Testing sites were the groin areas and the lower arm. Before/after QST data were z-transformed.

Results

Re-surgery resulted in median changes in rest, average, and maximal pain intensity scores of -2.0, -2.5, and -2.0 NRS (0/10) units, respectively (P = 0.0001), and proportional increases in various standardized functional scores (P = 0.0001). Compared with the control sites, the cutaneous somatosensory detection thresholds of the painful groin were increased before re-surgery and increased further after re-surgery (median difference: 1.28 z-values; P = 0.001), indicating a successive post-surgical loss of nerve fiber function ("deafferentation"). Pressure algometry thresholds increased after re-surgery (median difference: 0.30 z-values; P = 0.001).

Conclusion

In this subset of patients with PSPG who underwent re-surgery, the procedure was associated with improved pain and functional outcomes. While the increase in somatosensory detection thresholds mirrors the surgery-induced cutaneous deafferentation, the increase in pressure algometry thresholds mirrors the removal of the deep "pain generator". The QST-analyses are useful adjuncts in mechanism-based somatosensory research.

Factors Associated with Low Inter-Session Reliability of Conditioned Pain Modulation in Older People with or Without Chronic Musculoskeletal Pain

Purpose

Conditioned pain modulation (CPM) is a measurement of the descending pain pathways that inhibit or facilitate afferent noxious stimuli. The reliability of CPM in older individuals with or without chronic musculoskeletal pain has not been sufficiently reported. This study aimed to examine the inter-session reliability of CPM in these cohorts and the factors in CPM reliability.

Patients and Methods

Individuals aged 65 or older were recruited in Narita, Japan. The measurements were performed on separate days 2 weeks apart (sessions 1 and 2). Each participant's hand was immersed in cold water, and we measured pressure pain threshold (PPT) before and after the immersion. The ratio before and after PPT measurements was presented as CPM index. The autonomic activities (heart rate variability, heart rate, and blood pressure) were simultaneously measured. An absolute reliability of CPM index was analyzed by the adjusted two-way analysis of variance (ANOVA) and the Bland Altman plot, and relative reliability was analyzed by intraclass correlation coefficient (ICC). Spearman's rho correlation and the adjusted multivariate regression analysis were utilized for examining the CPM reliability factors.

Results

Thirty-two participants were divided into two groups: chronic pain (n=19) and non-chronic pain (n=13) groups. The mean difference between session 1 and 2 in CPM index showed a systematic error in the chronic pain group at 17.3 (confidence interval, CI: 15.0 to 19.7), but none in the non-chronic pain group at 3.7 (CI: -0.02 to 7.4). The adjusted two-way ANOVA for CPM index did not identify any differences. ICC was not significant at p=-0.247 in the non-chronic and 0.167 in chronic pain. Multivariate regression analysis revealed total power and low/high frequencies as significant factors for CPM index.

Conclusion

This study identified low inter-session reliability in older adults with chronic musculoskeletal pain and autonomic nervous system activities as factors in CPM reliability.

Assessment of visceral pain with special reference to chronic pancreatitis

A thorough pain assessment is of utmost importance when managing pain in clinical practice as it is the foundation for defining pain in need of treatment, either interventional or pharmacological. Pain characteristics can also guide interventional strategies and help evaluate the effect of treatment. In research settings, standardized pain assessment is crucial to improve comparability across studies and facilitate meta-analysis. Due to the importance of thorough visceral pain assessment, this manuscript describes the key elements of pain evaluation focusing on chronic pancreatitis. Most studies in pain assessment have focused on somatic pain, and although chronic pain often shares characteristics between etiologies, some differences must be addressed when assessing visceral pain. Especially differences between somatic and visceral pain are apparent, where visceral pain is diffuse and difficult to localize, with referred pain aspects and often autonomic symptoms dominating the clinical picture. These aspects need to be incorporated into the pain assessment instrument. The manuscript will discuss the different ways of assessing pain, including unidimensional measurement scales, multidimensional questionnaires, and quantitative sensory testing. The advantages and challenges linked to the different methods will be evaluated.

Algometry for the assessment of central sensitisation to pain in fibromyalgia patients: a systematic review

INTRODUCTION

The pathophysiology of fibromyalgia (FM) is related to central sensitisation (CS) to pain. Algometry allows assessing CS based on dynamic evoked pain. However, current algometrýs protocols require optimising, unifying and updating.

OBJECTIVES

1) identify the dynamic pain measures used most frequently to effectively assess CS processes in FM, and 2) consider the future of the algometry assessing CS in these patients.

METHODS

Cochrane Collaboration guidelines and PRISMA statements were followed. The protocol was registered in PROSPERO database (ID: CRD42021270135). The selected articles were evaluated using the Cochrane risk of bias (ROB) assessment tool. The PubMed, Scopus, and Web of Science databases were searched.

RESULTS

Thirty-four studies were selected, including measures such as temporal summation of pain (TSP), aftersensations (AS), spatial summation of pain (SSP), the noxious flexion reflex (NFR) threshold, conditioned pain modulation (CPM), cutaneous silent period (CuSP), and slowly repeated evoked pain (SREP); and evoked pain combined with neuroimaging. Each measure offered various advantages and limitations. According to ROB, 28 studies were of low quality, 3 of moderate quality, and 3 of high quality.

CONCLUSIONS

Several pain indicators have been demonstrated to successfully examine CS involvement in FM in the last years. Algometry, especially when it involves diverse body sites and tissues, might provide further insight into (1) the evaluation of psychological factors known to influence pain experience, (2) new dynamic pain indicators, and (3) the simultaneous use of certain neuroimaging techniques. Further research clarifying the mechanisms underlying some of these measures, and homogenisation and optimisation of the algometrýs protocols, are needed. KEY MESSAGESAlgometry allows for assessing Central Sensitisation by applying dynamic evoked pain.The future of algometry could relapse in its combination with neuroimaging.Recently-emerged pain indicators should be considered for algometrýs new protocols.

Abdominal examination using pressure pain threshold algometer reflecting clinical characteristics of complementary and alternative medicine in Korea: A systematic review and a brief proposal

BACKGROUND

A review was conducted to determine a pressure algometry measurement during abdominal examination that reflects clinical settings of traditional Korean medicine.

METHODS

After reviewing the previous studies, we have proposed a reference index, common posture and method for performing pressure algometry during abdominal examination. Keyword search using eight databases was performed. To identify the characteristics of pressure algometry during abdominal examination, keywords (e.g., abdomen, abdominal examination) were searched in national Korean databases, including Korean studies Information System (KISS), Research Information Sharing Service (RISS), and Oriental Medicine Advanced Searching Integrated System (OASIS). To examine the methods of measuring pressure pain threshold (PPT) with validity and reliability, combination keywords (e.g., PPT, pressure algometry, pressure pain, validity, reliability) were searched in Pubmed, Cochrane library, Google scholar, Ovid Embase, and China Knowledge Resource Integrated Database (CNKI).

RESULTS

A total of 652 articles were identified, and 22 relevant articles were included. The following main indices are proposed as a standardized pressure algometry method during abdominal examination: unit of measurements, measuring tools, target locations, pressure area, pressure rate, posture of patients, and evaluators. Based on the results of the review combined with clinical practice, useful indices for pressure algometer during abdominal examination were derived (target location: CV 12, unit of measurement: MPa, pressure area: 4 cm2, pressure rate: 0.098 MPa/s, posture of patient: supine position, number, and intervals of measurement: three consecutive measurements at intervals of 30 seconds, 5 minutes rest prior to commencement). Postures and method sequence of pressure algometry during abdominal examination are also proposed.

CONCLUSIONS

Using standardized indices, postures and method for abdominal examination in clinical settings will help make objective assessments.

Somatosensory abnormalities after infection with SARS-CoV-2 - A prospective case-control study in children and adolescents

Background

Long-term neurological complaints after SARS-CoV-2 infection occur in 4-66% of children and adolescents. Controlled studies on the integrity of the peripheral nerve system are scarce. Therefore, we examined the somatosensory function in children and adolescents after SARS-CoV-2 infection in a case-control study compared with age-matched individuals.

Materials and Methods

Eighty-one subjects after SARS-CoV-2 infection (n = 44 female, 11.4 ± 3.5 years, n = 75 SARS-CoV-2 seropositive, n = 6 PCR positive during infection and SARS-CoV-2 seronegative at the time point of study inclusion, n = 47 asymptomatic infection) were compared to 38 controls without SARS-CoV-2 infection (26 female, 10.3 ± 3.4 years, n = 15 with other infection within last 6 months). After standardised interviews and neurological examinations, large fibre (tactile and vibration detection thresholds) and small fibre (cold and warm detection thresholds, paradoxical heat sensation) functions were assessed on both feet following a validated protocol. After z-transformation of all values, all participants were compared to published reference values regarding the number of abnormal results. Additionally, the mean for all sensory parameters values of both study groups were compared to an ideal healthy population (with z-value 0 ± 1), as well as with each other, as previously described. Statistical analyses: t-test, Chi-squared test, and binominal test.

Findings

None of the controls, but 27 of the 81 patients (33%, p < 0.001) reported persistent complaints 2.7 ± 1.9 (0.8-8.5) months after SARS-CoV-2 infection, most often reduced exercise capacity (16%), fatigue (13%), pain (9%), or paraesthesia (6%). Reflex deficits or paresis were missing, but somatosensory profiles showed significantly increased detection thresholds for thermal (especially warm) and vibration stimuli compared to controls. Approximately 36% of the patients after SARS-CoV-2, but none of the controls revealed an abnormal sensory loss in at least one parameter (p < 0.01). Sensory loss was characterised in 26% by large and 12% by small fibre dysfunction, the latter appearing more frequently in children with prior symptomatic SARS-CoV-2 infection. Myalgia/paraesthesia was indicative of somatosensory dysfunction. In all eight re-examined children, the nerve function recovered after 2-4 months.

Interpretation

This study provides evidence that in a subgroup of children and adolescents previously infected with SARS-CoV-2, regardless of their complaints, the function of large or small nerve fibres is presumably reversibly impaired.

Test-Retest Reliability of an Adaptive Thermal Pain Calibration Procedure in Healthy Volunteers

Quantitative sensory testing (QST) allows researchers to evaluate associations between noxious stimuli and acute pain in clinical populations and healthy participants. Despite its widespread use, our understanding of QST’s reliability is limited, as reliability studies have used small samples and restricted time windows. We examined the reliability of pain ratings in response to noxious thermal stimulation in 171 healthy volunteers (n = 99 female, n = 72 male) who completed QST on multiple visits ranging from 1 day to 952 days between visits. On each visit, participants underwent an adaptive pain calibration in which they experienced 24 heat trials and rated pain intensity after stimulus offset on a 0 to 10 Visual Analog Scale. We used linear regression to determine pain threshold, pain tolerance, and the correlation between temperature and pain for each session and examined the reliability of these measures. Threshold and tolerance were moderately reliable (Intra-class correlation = .66 and .67, respectively; P < .001), whereas temperature-pain correlations had low reliability (Intra-class correlation = .23). In addition, pain tolerance was significantly more reliable in female participants than male participants, and we observed similar trends for other pain sensitive measures. Our findings indicate that threshold and tolerance are largely consistent across visits, whereas sensitivity to changes in temperature vary over time and may be influenced by contextual factors.

Intra-rater and inter-rater reliability of pressure pain threshold assessment in stroke patients

BACKGROUND

As pain is a common symptom following a stroke, pressure pain threshold (PPT) assessment can be used to evaluate pain status or pain sensitivity of patients. However, the reliability of PPT test in stroke patients is still unknown.

AIM

To examine the intra- and inter-rater reliability of PPT measurements in poststroke survivors and explore their factors.

DESIGN

An observational study.

SETTING

The setting of the study is a rehabilitation hospital.

POPULATION

The population of the study was represented by a total of 54 patients after stroke.

METHODS

The study included 16 measured points on the affected and unaffected sides. PPT was assessed by two raters in turn. Intra- and inter-rater reliability was evaluated by intraclass correlation coefficients (ICC).

RESULTS

All intra-rater (ICC=0.84-0.97) and inter-rater (ICC=0.83-0.95) reliability for PPT assessment were good or excellent in stroke patients. Of the 16 points, 12 showed higher intra-rater ICC values than inter-rater, whereas no evident difference was observed between the affected and unaffected sides. Furthermore, patients who were male, ischemic, or with higher motor function generally performed higher ICC values than those who were female (24 out of 32 results), hemorrhagic (28 out of 32 results), or mobility dysfunction (26 out of 32 results), respectively.

CONCLUSIONS

PPT assessment with good or excellent reliability can be used in stroke patients. Neither of the two sides (affected or unaffected) affects PPT reliability, and intra-rater reliability is better than inter-rater reliability. In addition, gender, stroke type, and motor function can affect the reliability of measuring mechanical pain threshold in poststroke survivors.

CLINICAL REHABILITATION IMPACT

The pressure algometer can be used as a reliable and portable tool to assess the mechanical pain tolerance and sensory function in stroke patients in clinics.

Clinical identification of the stimulus intensity to measure temporal summation of second pain

Temporal summation of second pain (TSSP) has been suggested as a psychophysical index for central sensitization, one of the critical mechanisms in the chronification of pain. However, there is no gold standard for protocols to measure TSSP. The purpose was to establish the stimulus intensity for measuring TSSP. Female patients with chronic myofascial temporomandibular disorders pain (n = 16) and healthy female volunteers with no pain (n = 15) participated. Pain thresholds (PT °C) were measured, and repetitive heat stimuli at three stimulus intensities (PT °C, PT + 1 °C, PT + 2 °C) were applied. TSSP parameters were quantified as TSSP magnitude (TSm) and TSSP frequency (TSf). In healthy female volunteers, pain ratings significantly decreased at PT °C (p < 0.050), besides TSm and TSf at PT + 2 °C were significantly higher than those at PT °C (p < 0.025). In chronic pain patients, pain ratings significantly increased at PT + 1 °C and PT + 2 °C (p < 0.050). At PT + 2 °C, TSm and TSf in chronic pain patients were significantly higher than those in healthy volunteers (p < 0.050). It could be helpful to measure TSSP with the stimulus intensity adjusted individually to the patient’s pain thresholds + 2 °C for assessing central sensitization.

Reliability of conditioned pain modulation in healthy individuals and chronic pain patients: a systematic review and meta-analysis

OBJECTIVES

Conditioned pain modulation (CPM) is a psychophysical parameter that is used to reflect the efficacy of endogenous pain inhibition. CPM reliability is important for research and potential clinical applications. The aim of this systematic review and meta-analysis was to evaluate the reliability of CPM tests in healthy individuals and chronic pain patients.

METHODS

We searched three databases for peer-reviewed studies published from inception to October 2020: EMBASE, Web of Science and NCBI. Risk of bias and the quality of the included studies were assessed. A meta-analysis with a random effects model was conducted to estimate intraclass correlation coefficients (ICCs).

RESULTS

Meta-analysis was performed on 25 papers that examined healthy participants (k=21) or chronic pain patients (k=4). The highest CPM intra-session reliability was with pressure as test stimulus (TS) and ischemic pressure (IP) or cold pressor test (CPT) as conditioning stimulus (CS) in healthy individuals (ICC 0.64, 95% CI 0.45-0.77), and pressure as TS with CPT as CS in patients (ICC 0.77, 95% CI 0.70-0.82). The highest inter-session ICC was with IP as TS and IP or CPT as CS (ICC 0.51, 95% CI 0.42-0.59) in healthy subjects. The only data available in patients for inter-session reliability were with pressure as TS and CPT as CS (ICC 0.44, 95% CI 0.11-0.69). Quality ranged from very good to excellent using the QACMRR checklist. The majority of the studies (24 out of 25) scored inadequate in Kappa coefficient reporting item of the COSMIN-ROB checklist.

CONCLUSIONS

Pressure and CPT were the TS and CS most consistently associated with good to excellent intra-session reliability in healthy volunteers and chronic pain patients. The inter-session reliability was fair or less for all modalities, both in healthy volunteers and chronic pain patients.

Absolute and relative reliability of a comprehensive quantitative sensory testing protocol in women treated for breast cancer

OBJECTIVE

Quantitative sensory testing (QST) are non-invasive psychophysical assessment techniques to evaluate functioning of the somatosensory nervous system. Despite the importance of reliability for correct use of QST results in research and clinical practice, the relative and absolute intra-and inter-rater reliability of a comprehensive QST protocol to evaluate the functioning of both peripheral and central somatosensory nervous system in a breast cancer population, has not yet been investigated.

SETTING

University Hospitals, Leuven, Belgium.

SUBJECTS

Thirty women at least six months after unilateral breast cancer surgery.

METHODS

The protocol included nine static and dynamic QST methods (mechanical detection-pain thresholds, pressure pain thresholds, thermal detection-pain thresholds for heat and cold, temporal summation and conditioned pain modulation (CPM)) performed in the surgical area and more distant regions. Absolute and relative intra (60-minutes interval) and inter-rater (one-week interval) reliability was evaluated using intraclass correlation coefficients, standard error of measurement and Bland-Altman plots.

RESULTS

A moderate to excellent relative intra- and inter-rater reliability was found for the evaluation of mechanical thresholds, pressure pain thresholds and temporal summation. Reliability of the CPM paradigm was considered weak. Systematic bias between raters was noticed for detection of mechanical and cold stimuli at the non-affected trunk and CPM.

CONCLUSIONS

Except for the evaluation of CPM, the QST protocol was found suitable for identifying differences between subjects (relative reliability) and individual follow-up after breast cancer surgery (limited systematic bias) during a one-week timeframe. Additional research is required to determine measurement properties that influence CPM test stability in order to establish a more reliable CPM test paradigm.

Sensory processing and detection thresholds of burn-injured patients: A comparison to normative data

OBJECTIVE

Emerging evidence suggests that individual levels of sensory sensitivity may impact treatment outcomes for people recovering from burn injuries. For example, individuals with higher levels of sensory sensitivity were less adherent with compression garment wear, often used for scar management. The purpose of this study was to characterise sensory patterns for a sample of burn-injured patients as a cohort, using normative data as the reference. As different patterns of sensory processing can have implications clinically, understanding this at the cohort level may provide valuable insight for therapy.

METHOD

This was a secondary analysis of data collected during a cross-sectional study. Adults (N = 117) attending the Professor Stuart Pegg Adult Burns Unit outpatient clinic completed the Adolescent/Adult Sensory Profile and the following quantitative sensory tests: two-point discrimination; mechanical detection threshold; and pressure pain threshold.

RESULTS

Compared to matched normative data, burn-injured patients reported higher levels of sensory sensitive and avoiding patterns, and experienced lower detection thresholds for touch and pain.

CONCLUSIONS

Higher reports of sensory sensitivity and sensory avoiding, and lower thresholds for touch and pain, have been correlated with tactile defensiveness. Tactile defensiveness has been associated with social withdrawal and isolation, all of which could contribute to decreased engagement in therapy. The ways in which these sensory characteristics impact on burn-related treatments, such as compression garment adherence, warrant further investigation.

Bedside clinical tests to assess sensitization in office workers with chronic neck pain

OBJECTIVE

This study aimed to assess pain sensitization in individual office workers with chronic neck pain through simple bedside quantitative sensory tests (QST) and to associate the findings with pain intensity and pain catastrophizing.

METHODS

One hundred-and-four office workers with chronic neck pain were assessed using pressure pain threshold (PPT) considering pain sensitive if PPTs were lower than 155 kPa in the upper trapezius and 245 kPa in the tibialis anterior. Pain sensitive to temporal summation of pain (TSP) was considered if there was a difference of two points in the visual analogue scale (VAS) comparing the first and last stimulus. Pain sensitive was considered to conditioned pain modulation (CPM) if the CPM-effect was less than -7.5%. Pain intensity and catastrophizing were measured using VAS and with the Pain Catastrophizing Scale.

RESULTS

There was at least one pain sensitive QST finding in 66 office workers (63.5%). TSP findings were the most common (48.1%), followed by PPT's (31.7%) and CPM (20.2%). Based on the QST findings, office workers were divided based on the number of individual QST findings, and higher pain intensity and pain catastrophizing scores were found in office workers with one (N = 38, P < 0.05) or two (N = 28, P < 0.05) compared with office workers with no QST findings (N = 38).

CONCLUSION

This study demonstrated that most office workers with chronic neck pain exhibit either widespread pressure hyperalgesia, facilitated TSP or impaired CPM, indicating pain sensitization within the central nervous system. This was associated with increased clinical pain and pain catastrophizing rumination scores.

Changes in Pain Sensitivity and Conditioned Pain Modulation During Recovery From Whiplash-associated Disorders

OBJECTIVE

The objective of this study was to investigate the pain-sensory profile of patients with whiplash-associated disorders (WADs) prior and post 2 weeks of standardized rehabilitation and after a 6-month follow-up.

MATERIALS AND METHODS

Twenty-two WAD participants (grade II; 14 women) and 22 sex-matched and age-matched healthy pain-free controls were enrolled. Pressure pain thresholds (PPTs) were assessed at local and distal muscles. Conditioned pain modulation (CPM) of PPTs was assessed using cuff pressure around the upper arm. Referred area of pain following supra-threshold pressure stimulation of the infraspinatus muscle was recorded on a body chart. Psychometric variables (pain intensity, area of perceived pain, pain catastrophizing, kinesiophobia, sleep problems, and depression level) were assessed. WAD group additionally completed the Neck Disability Index.

RESULTS

The WAD group demonstrated lower local PPTs compared with controls at all time points (P<0.05) and lower distal PPTs at baseline and at 2 weeks when compared with 6 months (within-group) (P<0.05). The WAD group had a reduced CPM response and larger induced referred pain areas compared with controls (P<0.05), while no within-group changes were observed at any time point. The WAD group reported higher pain intensity and perceived area of pain compared with controls at all time points (P<0.05) and a mean Neck Disability Index score of 41% at baseline, 16% at 2 weeks, and 4% at 6 months. Furthermore, the WAD group reported improvements in all other psychometric variables (P<0.05), although only pain catastrophizing levels were comparable to controls at 2 weeks.

DISCUSSION

PPTs but not CPM improved in the WAD group and were comparable to controls following 2 weeks following standardized rehabilitation, indicating that normalization of CPM may not be required to recover from WAD.

Pain perception in chronic knee osteoarthritis with varying levels of pain inhibitory control: an exploratory study

Background and aims Pain is a disabling symptom in knee osteoarthritis (KOA) and its underlying mechanism remains poorly understood. Dysfunction of descending pain modulatory pathways and reduced pain inhibition enhance pain facilitation in many chronic pain syndromes but do not fully explain pain levels in chronic musculoskeletal conditions. The objective of this study is to explore the association of clinical variables with pain intensity perception in KOA individuals with varying levels of Conditioned Pain Modulation (CPM) response. Methods This is a cross-sectional, exploratory analysis using baseline data of a randomized clinical trial investigating the effects of a non-invasive brain stimulation treatment on the perception of pain and functional limitations due to KOA. Sixty-three subjects with KOA were included in this study. Data on pain perception, mood perception, self-reported depression, physical function, quality of life, and quantitative sensory testing was collected. Multiple linear regression analysis was performed to explore the association between the clinical variables with pain perception for individuals with different levels of CPM response. Results For KOA patients with limited CPM response, perception of limitations at work/other activities due to emotional problems and stress scores were statistically significantly associated with pain scores, F(2, 37) = 7.02, p < 0.01. R-squared = 0.275. For KOA patients with normal CPM response, general health perception scores were statistically significantly associated with pain scores, F(1, 21) = 5.60, p < 0.05. R-squared = 0.2104. Limitations of this study include methodology details, small sample size and study design characteristics. Conclusions Pain intensity perception is associated differently with clinical variables according to the individual CPM response. Mechanistic models to explain pain perception in these two subgroups of KOA subjects are discussed.

Heightened pain facilitation rather than impaired pain inhibition distinguishes those with moderate/severe disability in work-related neck pain

ABSTRACT

To better understand the mechanisms underpinning work-related neck pain, this cross-sectional and single-blinded study compared somatosensory profiles among sonographers with varied neck disability levels. Based on K-mean cluster analysis of scores on the neck disability index (NDI), participants were classified into no (NDI ≤ 8%, n = 31, reference group), mild (NDI = 10%-20%, n = 43), or moderate/severe (NDI ≥ 22%, n = 18) disability groups. Data were collected on bodily pain distribution and severity and psychological measures including depression, anxiety, pain-catastrophizing, and fear-avoidance beliefs using validated scales. Participants attended 1 session of quantitative sensory testing performed according to a standardized protocol, including local and remote thermal and mechanical pain thresholds, temporal summation of pain (TSP), conditioned pain modulation, and an exercise-induced analgesia paradigm. Compared with participants with no and mild disability, those with moderate/severe disability showed more widespread pain, cold and mechanical hyperalgesia at a remote nonpainful site, and significantly higher TSP. Participants with mild disability demonstrated significantly higher TSP than those with no disability. These group differences were attenuated after adjusting for depression or anxiety, indicating these psychological factors may mediate the somatosensory changes associated with neck disability. Group differences were not found for conditioned pain modulation or exercise-induced analgesia. These findings suggest that heightened pain facilitation, rather than impaired pain inhibition may underpin nociplastic pain in participants with moderate/severe disability, and it may be associated with depression and anxiety. Clinicians should be aware that individuals with work-related neck pain presenting with moderate/severe disability display distinct somatosensory features and tailor management strategies accordingly.

The Relationship Between Clinical and Quantitative Measures of Pain Sensitization in Knee Osteoarthritis

OBJECTIVES

Pain sensitization in knee osteoarthritis (OA) is associated with greater symptom severity and poorer clinical outcomes. Measures that identify pain sensitization and are accessible to use in clinical practice have been suggested to enable more targeted treatments. This merits further investigation. This study examines the relationship between quantitative sensory testing (QST) and clinical measures of pain sensitization in people with knee OA.

METHODS

A secondary analysis of data from 134 participants with knee OA was performed. Clinical measures included: manual tender point count (MTPC), the Central Sensitization Inventory (CSI) to capture centrally mediated comorbidities, number of painful sites on a body chart, and neuropathic pain-like symptoms assessed using the modified PainDetect Questionnaire. Relationships between clinical measures and QST measures of pressure pain thresholds (PPTs), temporal summation, and conditioned pain modulation were investigated using correlation and multivariable regression analyses.

RESULTS

Fair to moderate correlations, ranging from -0.331 to -0.577 (P<0.05), were identified between MTPC, the CSI, number of painful sites, and PPTs. Fair correlations, ranging from 0.28 to 0.30 (P<0.01), were identified between MTPC, the CSI, number of painful sites, and conditioned pain modulation. Correlations between the clinical and self-reported measures and temporal summation were weak and inconsistent (0.09 to 0.25). In adjusted regression models, MTPC was the only clinical measure consistently associated with QST and accounted for 11% to 12% of the variance in PPTs.

DISCUSSION

MTPC demonstrated the strongest associations with QST measures and may be the most promising proxy measure to detect pain sensitization clinically.

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.

Noninvasive motor cortex stimulation effects on quantitative sensory testing in healthy and chronic pain subjects: a systematic review and meta-analysis

ABSTRACT

One of the potential mechanisms of motor cortex stimulation by noninvasive brain stimulation (NIBS) effects on pain is through the restoration of the defective endogenous inhibitory pain pathways. However, there are still limited data on quantitative sensory testing (QST), including conditioned pain modulation (CPM), supporting this mechanism. This systematic review and meta-analysis aimed to evaluate the effects of noninvasive motor cortex stimulation on pain perception as indexed by changes in QST outcomes. Database searches were conducted until July 2019 to include randomized controlled trials that performed sham-controlled NIBS on the motor cortex in either the healthy and/or pain population and assessed the QST and CPM. Quality of studies was assessed through the Cochrane tool. We calculated the Hedge's effect sizes of QST and CPM outcomes and their 95% confidence intervals (95% CIs) and performed random-effects meta-analyses. Thirty-eight studies were included (1178 participants). We found significant increases of pain threshold in healthy subjects (ES = 0.16, 95% CI = 0.02-0.31, I2 = 22.2%) and pain populations (ES = 0.48, 95% CI = 0.15-0.80, I2 = 68.8%), and homogeneous higher CPM effect (pain ratings reduction) in healthy subjects (ES = -0.39, 95% CI = -0.64 to -0.14, I2 = 17%) and pain populations (ES = -0.35, 95% CI = -0.60 to -0.11, I2 = 0%) in the active NIBS group compared with sham. These results support the idea of top-down modulation of endogenous pain pathways by motor cortex stimulation as one of the main mechanisms of pain reduction assessed by QST, which could be a useful predictive and prognostic biomarker for chronic pain personalized treatment with NIBS.

Methods to discriminate between mechanism-based categories of pain experienced in the musculoskeletal system: a systematic review

ABSTRACT

Mechanism-based classification of pain has been advocated widely to aid tailoring of interventions for individuals experiencing persistent musculoskeletal pain. Three pain mechanism categories (PMCs) are defined by the International Association for the Study of Pain: nociceptive, neuropathic, and nociplastic pain. Discrimination between them remains challenging. This study aimed to build on a framework developed to converge the diverse literature of PMCs to systematically review methods purported to discriminate between them; synthesise and thematically analyse these methods to identify the convergence and divergence of opinion; and report validation, psychometric properties, and strengths/weaknesses of these methods. The search strategy identified articles discussing methods to discriminate between mechanism-based categories of pain experienced in the musculoskeletal system. Studies that assessed the validity of methods to discriminate between categories were assessed for quality. Extraction and thematic analysis were undertaken on 184 articles. Data synthesis identified 200 methods in 5 themes: clinical examination, quantitative sensory testing, imaging, diagnostic and laboratory testing, and pain-type questionnaires. Few methods have been validated for discrimination between PMCs. There was general convergence but some disagreement regarding findings that discriminate between PMCs. A combination of features and methods, rather than a single method, was generally recommended to discriminate between PMCs. Two major limitations were identified: an overlap of findings of methods between categories due to mixed presentations and many methods considered discrimination between 2 PMCs but not others. The results of this review provide a foundation to refine methods to differentiate mechanisms for musculoskeletal pain.

Slowly repeated evoked pain (SREP) as a central sensitization marker in episodic migraine patients

Migraine headache is a pain condition characterized by severe and recurrent unilateral head pain. Among other mechanisms, central pain sensitization processes seem to be involved in the disorder. An experimental protocol based on slowly repeated evoked pain (SREP) has been shown to indicate pain sensitization in fibromyalgia patients and differentiate these patients from healthy individuals and rheumatoid arthritis patients. This study examined SREP sensitization in migraine patients and explored its potential usefulness as a central sensitization marker. The SREP protocol was administered to 40 episodic migraine (EM) patients not currently experiencing a headache and 40 healthy controls. SREP consisted of a series of 9 suprathreshold painful pressure stimuli of 5 s duration and a 30 s interstimulus interval. SREP sensitization was indexed by the increase in pain ratings across the stimuli. Pain threshold, pain tolerance and temporal summation of pain were also assessed. SREP sensitization was observed in EM, but not in healthy individuals (p < .001). SREP differentiated between EM and healthy individuals with up to 75% diagnostic accuracy. Pain threshold, pain tolerance and temporal summation of pain did not show significant discriminative ability. An SREP index value of 0.5 was the most sensitive cut-off for detecting central pain sensitization when prioritizing diagnostic sensitivity (0.88). Results provide evidence for SREP as a possible central sensitization marker with potential clinical utility in migraine patients. Inclusion of SREP in Quantitative Sensory Testing protocols may enhance the assessment of altered pain modulation in different pain conditions.

Early Detection of Diabetic Peripheral Neuropathy: A Focus on Small Nerve Fibres

Diabetic peripheral neuropathy (DPN) is the most common complication of both type 1 and 2 diabetes. As a result, neuropathic pain, diabetic foot ulcers and lower-limb amputations impact drastically on quality of life, contributing to the individual, societal, financial and healthcare burden of diabetes. DPN is diagnosed at a late, often pre-ulcerative stage due to a lack of early systematic screening and the endorsement of monofilament testing which identifies advanced neuropathy only. Compared to the success of the diabetic eye and kidney screening programmes there is clearly an unmet need for an objective reliable biomarker for the detection of early DPN. This article critically appraises research and clinical methods for the diagnosis or screening of early DPN. In brief, functional measures are subjective and are difficult to implement due to technical complexity. Moreover, skin biopsy is invasive, expensive and lacks diagnostic laboratory capacity. Indeed, point-of-care nerve conduction tests are convenient and easy to implement however questions are raised regarding their suitability for use in screening due to the lack of small nerve fibre evaluation. Corneal confocal microscopy (CCM) is a rapid, non-invasive, and reproducible technique to quantify small nerve fibre damage and repair which can be conducted alongside retinopathy screening. CCM identifies early sub-clinical DPN, predicts the development and allows staging of DPN severity. Automated quantification of CCM with AI has enabled enhanced unbiased quantification of small nerve fibres and potentially early diagnosis of DPN. Improved screening tools will prevent and reduce the burden of foot ulceration and amputations with the primary aim of reducing the prevalence of this common microvascular complication.

The Effect of Stress on Repeated Painful Stimuli with and Without Painful Conditioning

OBJECTIVES

Stress and pain have been interrelated in clinical widespread pain conditions. Studies indicate that acute experimental stress in healthy volunteers has a negative effect on the descending inhibitory pain control system and thus the ability to inhibit one painful stimulus with another (conditioned pain modulation [CPM]) although without effect on general pain sensitivity. CPM effects can be assessed immediately after the stress induction, whereas some physiological stress responses (e.g., cortisol release) are delayed and longer lasting. It is unclear whether CPM may relate to stress-induced increases in cortisol.

DESIGN

Twenty-five healthy men had CPM effects measured over a period of 10 minutes. Pain detection thresholds (PDTs) were assessed by repeated test stimuli with cuff algometry on one leg, with and without painful cuff pressure conditioning on the contralateral leg. CPM effects, assessed as the increase in PDT during conditioning stimulation compared with without, were measured before and after experimental stress and a control condition (Montreal Imaging Stress Task [MIST]). Saliva cortisol levels and self-perceived stress were collected.

RESULTS

Participants reported the MIST to be more stressful compared with the MIST control, but cortisol levels did not change significantly from baseline. In all sessions, PDT increased during conditioning (P = 0.001), although the MIST compared with the MIST control had no significant effect on PDT or CPM effects. A negative correlation between changes in cortisol and conditioned PDT was found when applying the MIST (P < 0.03).

CONCLUSIONS

No significant effect of stress was found on CPM compared with a matched control condition. Individual changes in experimental stress and in conditioned pain sensitivity may be linked with cortisol.

Molecular and cellular correlates of human nerve regeneration: ADCYAP1/PACAP enhance nerve outgrowth

We only have a rudimentary understanding of the molecular and cellular determinants of nerve regeneration and neuropathic pain in humans. This cohort study uses the most common entrapment neuropathy (carpal tunnel syndrome) as a human model system to prospectively evaluate the cellular and molecular correlates of neural regeneration and its relationship with clinical recovery. In 60 patients undergoing carpal tunnel surgery [36 female, mean age 62.5 (standard deviation 12.2) years], we used quantitative sensory testing and nerve conduction studies to evaluate the function of large and small fibres before and 6 months after surgery. Clinical recovery was assessed with the global rating of change scale and Boston Carpal Tunnel Questionnaire. Twenty healthy participants provided normative data [14 female, mean age 58.0 (standard deviation 12.9) years]. At 6 months post-surgery, we noted significant recovery of median nerve neurophysiological parameters (P < 0.0001) and improvements in quantitative sensory testing measures of both small and large nerve fibre function (P < 0.002). Serial biopsies revealed a partial recovery of intraepidermal nerve fibre density [fibres/mm epidermis pre: 4.20 (2.83), post: 5.35 (3.34), P = 0.001], whose extent correlated with symptom improvement (r = 0.389, P = 0.001). In myelinated afferents, nodal length increased postoperatively [pre: 2.03 (0.82), post: 3.03 (1.23), P < 0.0001] suggesting that this is an adaptive phenomenon. Transcriptional profiling of the skin revealed 31 differentially expressed genes following decompression, with ADCYAP1 (encoding pituitary adenylate cyclase activating peptide, PACAP) being the most strongly upregulated (log2 fold-change 1.87, P = 0.0001) and its expression was associated with recovery of intraepidermal nerve fibres. We found that human induced pluripotent stem cell-derived sensory neurons expressed the receptor for PACAP and that this peptide could significantly enhance axon outgrowth in a dose-dependent manner in vitro [neurite length PACAP 1065.0 µm (285.5), vehicle 570.9 μm (181.8), P = 0.003]. In conclusion, carpal tunnel release is associated with significant cutaneous reinnervation, which correlates with the degree of functional improvement and is associated with a transcriptional programme relating to morphogenesis and inflammatory processes. The most highly dysregulated gene ADCYAP1 (encoding PACAP) was associated with reinnervation and, given that this peptide signals through G-protein coupled receptors, this signalling pathway provides an interesting therapeutic target for human sensory nerve regeneration.

Addition of Slowly Repeated Evoked Pain Responses to Clinical Symptoms Enhances Fibromyalgia Diagnostic Accuracy

OBJECTIVE

Fibromyalgia is a chronic pain syndrome characterized by central sensitization. A novel protocol based on slowly repeated evoked pain (SREP) appears to be a useful marker of pain sensitization in fibromyalgia patients. Whether SREP enhances diagnostic accuracy beyond key clinical symptoms that characterize fibromyalgia has not been examined.

METHODS

Fifty fibromyalgia patients, 30 rheumatoid arthritis patients, and 50 healthy individuals were evaluated to assess clinical pain, as well as fatigue, insomnia, pain catastrophizing, and negative mood. The SREP protocol consisted of a series of nine low-intensity painful pressure stimuli of five seconds' duration with 30-second interstimulus intervals. SREP sensitization was indexed by increases in pain intensity ratings across stimuli.

RESULTS

SREP sensitization was observed in fibromyalgia but not in rheumatoid arthritis or healthy individuals. As expected, fibromyalgia patients exhibited a more negative psychosocial profile than did rheumatoid arthritis patients and healthy individuals. SREP was positively associated with clinical pain, fatigue, insomnia, and catastrophizing, but not with negative mood. SREP discriminated fibromyalgia cases from rheumatoid arthritis and healthy individuals even when current clinical pain was included in the analysis. Combining fatigue, insomnia, and SREP led to near perfect diagnostic accuracy (99%) in differentiating fibromyalgia from healthy individuals and 86.3% accuracy in discriminating fibromyalgia from rheumatoid arthritis.

CONCLUSIONS

These results provide further evidence of SREP as a marker of pain sensitization in fibromyalgia and suggest that it captures aspects of fibromyalgia not fully captured by clinical features. Combining SREP with assessment of clinical features could potentially improve fibromyalgia diagnosis.

Spatial aspects of pain modulation are not disrupted in adolescents with migraine

OBJECTIVE

To compare spatial pain modulation capabilities between adolescents with and without migraine.

BACKGROUND

Conditioned pain modulation (CPM) responses at the leg are similar in adolescents with versus without migraine. However, the anatomical region of testing may affect spatial pain modulation capabilities as differences in nociceptive processing between patients with migraine and healthy controls are found in local areas that are near the site of clinical pain but not in nonlocal areas. This study aimed to examine spatial pain modulation capabilities tested by the CPM paradigm using test stimulus applied to a local body area.

METHODS

Nineteen adolescents with migraine (age 14.9 ± 2.3, mean ± SD; 16 female) and 20 healthy adolescents (age 13.8 ± 2.5, mean ± SD; 16 female) completed this case-control study at Cincinnati Children's Hospital Medical Center. Pressure pain thresholds (PPT) were assessed at the trapezius before and during immersion of the foot in a cold water bath (8°C).

RESULTS

In the migraine group (146.0 ± 79.1, mean ± SD), compared to healthy controls (248.0 ± 145.5, mean ± SD), significantly lower PPT (kilopascal) values were found (estimate = 124.28, 95% CI: 58.98, 189.59, p < 0.001; effect size: d = 1.40). No differences between the groups were found for pain intensity and unpleasantness ratings of cold-water immersion nor the CPM response.

CONCLUSIONS

This study found altered ascending nociceptive processing of mechanical stimuli at the neck in adolescents with migraine. However, endogenous pain modulatory mechanisms were functional and not altered. In light of other studies, impairments in inhibitory control may not be involved in migraine pathophysiology in pediatric patients regardless of stimulus location.