Pain-related Catastrophizing in Healthy Women Is Associated With Greater Temporal Summation of and Reduced Habituation to Thermal Pain

Reinforced pain catastrophizing during menstrual phase among women with primary dysmenorrhea is mediated by cerebral blood flow in the medial prefrontal cortex

Pain catastrophizing is a prominent psychological factor that is strongly correlated with pain. Although the complex properties of pain catastrophizing vary across different pain phases, the contribution of chronic pain to its progression from a general trait to a higher state remains unclear. This study aimed to examine the neural mechanisms and degree to which pain catastrophizing is reinforced in the context of primary dysmenorrhea (PDM), one of the most prevalent gynaecological complaints experienced by women of reproductive age. Altogether, 29 women with moderate-to-severe PDM were included in this study. Arterial spin labelling was used to quantify the cerebral blood flow (CBF) in each participant in both the pain-free and painful phases. The pain catastrophizing scale (PCS) was completed in two phases, and the Short-Form McGill Pain Questionnaire was completed in the painful phase. Compared with pain catastrophizing in the pain-free phase (PCSpf), pain catastrophizing in the painful phase (PCSp) is higher and positively correlated with the composite factor of menstrual pain. CBF analysis indicated that the PCSp is positively associated with CBF in the frontal cortex, hippocampus and amygdala. The reinforcement of pain catastrophizing correlates with CBF in the prefrontal cortex. Specifically, the medial prefrontal cortex, which correlates with pain state, plays a crucial role in mediating the reinforcing effect of pain in the PCSp. These results promote the mechanical comprehension of pain catastrophizing management in individuals with chronic pain.

Understanding inter-individual variability of experimental pain habituation and conditioned pain modulation in healthy individuals

Although reduced experimental pain habituation is proposed as a proxy of diminished endogenous pain modulatory capacity in chronic pain, prior studies show contradictory findings. Even across healthy participants, pain habituation varies substantially, which may relate to another measure of endogenous pain modulation, i.e., conditioned pain modulation (CPM). Hence, this study investigated the relationship between pain habituation and CPM. Pain habituation was assessed in 45 healthy participants between two blocks of 15-20 contact-heat stimuli applied to the hand. Habituation of subjective pain ratings and objective neurophysiological readouts (contact-heat evoked potential (CHEP) and palmar sympathetic skin response (SSR)) was investigated. CPM was assessed by comparing heat pain thresholds before and after hand immersion in a noxious cold (9 °C) and lukewarm water bath (32 °C, to control for repeated measures effects). Pain habituation showed a large variability, with subjective but not objective pain habituation correlating with cold-induced CPM effects (r = 0.50; p = 0.025). This correlation was not observed for 'true' CPM effects (corrected for repeated measures effects) nor for CPM effects induced by a lukewarm water bath. These findings suggest that the observed variability in subjective pain habituation may be influenced by both descending endogenous pain modulation and peripheral adaptation processes associated with repeated measures. Objective pain habituation readouts, i.e., CHEPs and SSRs, capture different, complementary aspects of endogenous pain modulation.

Is predictability of the conditioning stimulus (CS) a critical factor in conditioned pain modulation (CPM)?

INTRODUCTION

Conditioned pain modulation (CPM) allows to investigate endogenous pain modulation and its clinical outcomes. Although co-activation of emotions has been shown to affect CPM, the impact of 'threat,' which may accompany CPM stimulation itself, has been mostly neglected. A critical factor for the threat level of the conditioning stimulus (CS) may be its predictability.

METHODS

38 healthy participants (18 female) took part in a CPM study with pressure stimulation on the leg (blood-pressure cuff) serving as CS and heat stimulation on the forearm (contact thermode; CHEPS) serving as test stimulus (TS). While CS varied in intensity and -as operationalisation of threat- in temporary predictability, TS was kept constant. CPM effects were studied by EEG parameters (N2P2) and pain ratings.

RESULTS

We found a significant CPM effect when considering N2P2, with low CS predictability augmenting CPM inhibition; in contrast, a surprisingly facilitatory CPM effect occurred in pain ratings (in the high CS predictability condition). The threat manipulation was only partially successful because CS intensity increased the threat ratings but not -as intended- CS predictability. Correlations between subjective and psychophysiological CPM responses were low.

DISCUSSION

The differing CPM effects in subjective and psychophysiological responses, with both inhibitory and facilitatory effects, is puzzling but has already been observed earlier. The consideration of the CPM stimulation as major threat that is emotionally active is theoretically clearly justifiable but the operationalisation by means of different levels of CS predictability as in the present study might not have been ideal. Thus, further attempts of experimental verification are warranted.

Comparable Conditioned Pain Modulation and Painful-Exercise-Induced Hypoalgesia in Healthy Young Adults: A Randomized Crossover Trial

Conditioned pain modulation and exercise-induced hypoalgesia reflect inhibitory pain controls emanating from the brain. The aim of this study was to compare the extent of pain inhibition from exercise-induced hypoalgesia (isometric wall squat), conditioned pain modulation (cold-water immersion), and their combination (wall squat followed by cold water in fixed order) in healthy pain-free adults. Sixty-one participants (median age 21 years) completed 3 sessions (wall-squat, cold-water, and combined) in random order. Sessions were separated by at least a week. In each session, pressure-pain thresholds, single-pinprick-pain ratings, and pinprick-temporal summation of pain (the fifth minus the first) were obtained at quadriceps, forearms, and forehead, before and after wall squat and/or cold water. Each intervention inhibited pain to pressure (partial η2 = .26) and single pinprick (partial η2 = .16) to a similar extent; however, pressure-pain inhibition was negligible in the forehead. After adjusting for age and sex, single-pinprick-pain inhibition in the forehead induced by wall squat was associated with that induced by cold water (adjusted R2 = .15; P = .007), and stronger pain inhibition was predicted by a higher thigh-pain rating to wall squat (adjusted R2 = .10; P = .027). Neither intervention affected pinprick-temporal summation of pain. Together, the findings suggest that pain-inhibitory effects of exercise-induced hypoalgesia and conditioned pain modulation may overlap when exercise is at least moderately painful (6/10 intensity). Pressure pain in body regions remote from the exercised or conditioned sites may be weakly modulated. PERSPECTIVE: The current findings suggest that pain-inhibitory effects induced by painful wall squat and by cold-water immersion may overlap. The magnitude of pain inhibition in the forehead remote from the exercised thigh or the conditioned foot appears smaller, which could be examined further in future research.

Increased Pain Variability in Patients With Chronic Pain: A Role for Pain Catastrophizing

Pain is an inherently negative perceptual and affective experience that acts as a warning system to protect the body from injury and illness. Pain unfolds over time and is influenced by myriad factors, making it highly dynamic. Despite this, statistical measures often treat any intraindividual variability in pain ratings as noise or error. This is consequential, especially for research on chronic pain, because pain variability is associated with greater pain severity and depression. Yet, differences in pain variability between patients with chronic pain and controls in response to acute pain has not been fully examined-and it is unknown if dispositional factors such as pain catastrophizing (negative cognitive-affective response to potential or actual pain in which attention cannot be diverted away from pain) relate to pain variability. In the current study, we recruited chronic-pain patients (N = 30) and pain-free controls (N = 22) to complete a 30-second thermal pain task where they continually rated a painful thermal stimulus. To quantify pain variability and capture potential dynamics, we used both a traditional intraindividual standard deviation (iSD) metric of variability and a novel derivatives approach. For both metrics, patients with chronic pain had higher variability in their pain ratings over time, and pain catastrophizing significantly mediated this relationship. This suggests patients with chronic pain experience pain stimuli differently over time, and pain catastrophizing may account for this differential experience. PERSPECTIVE: The present study demonstrates (using multiple variability metrics) that chronic pain patients show more variability when rating experimental pain stimuli, and that pain catastrophizing helps explain this differential experience. These results provide preliminary evidence that short-term pain variability could have utility as a clinical marker in pain assessment and treatment.

Gastrointestinal pain: A systematic review of temporal summation of pain paradigms and outcomes

BACKGROUND AND OBJECTIVE

Since targeted treatment for gastrointestinal pain is elusive, identifying the mechanistic underpinning of this pain type is important. Facilitation of spinal neuronal responses underpins certain pain types, and the psychophysical temporal summation of pain (TSP) paradigm provides a proxy measure of spinal facilitatory processes. Our aim was to systematically review whether facilitated TSP is a feature of gastrointestinal pain in patients with, or pain-free people experiencing experimentally induced, gastrointestinal pain.

DATABASES AND DATA TREATMENT

EMBASE, MEDLINE, PsychInfo, CINAHL, and Web of Science were systematically searched, from inception to July 2023, for human studies reporting TSP paradigm outcomes in the context of gastrointestinal pain. The Appraisal tool for Cross-Sectional studies was used for quality assessment and applied independently by two researchers.

RESULTS

Fifteen papers consisting of cross-sectional (n = 6), case-control (n = 8), and retrospective cohort (n = 1) studies, were included. Thirteen studies investigated TSP in people with gastrointestinal pain with (n = 5) or without (n = 8) defined pathology. Two studies evoked TSP by repetitive gut stimulation in people undergoing abdominal medical procedures. Preliminary evidence showed that facilitated TSP correlated with the presence of functional gastrointestinal pain in women, and those with a history of trauma. No effect was observed in people with inflammatory bowel disease, although it was often unclear if they experienced pain.

CONCLUSIONS

It is not possible to conclude whether facilitated TSP is a feature of gastrointestinal pain. We recommend that subgroup findings are corroborated and that TSP paradigms are standardized in order that direct comparisons between studies may be made.

SIGNIFICANCE STATEMENT

Evidence indicated that pain facilitatory processes, as evidenced by a facilitated TSP outcome, contribute to functional gastrointestinal pain in women and those with a history of trauma. However, heterogeneity of study populations and paradigms precluded statistical synthesis and findings would need be corroborated. Studies exploring facilitatory processes in people with inflammatory bowel diseases did not report significant results, but pain is not a given in these conditions and, conversely, may be driven by peripheral inflammation during active disease. This should be taken in consideration in future explorations.

REGISTRATION REVIEW

PROSPERO CRD42022341845.

Habituation to pain: self-report, electroencephalography, and functional magnetic resonance imaging in healthy individuals. A scoping review and future recommendations

ABSTRACT

Habituation to pain is a fundamental learning process and important adaption. Yet, a comprehensive review of the current state of the field is lacking. Through a systematic search, 63 studies were included. Results address habituation to pain in healthy individuals based on self-report, electroencephalography, or functional magnetic resonance imaging. Our findings indicate a large variety in methods, experimental settings, and contexts, making habituation a ubiquitous phenomenon. Habituation to pain based on self-report studies shows a large influence of expectations, as well as the presence of individual differences. Furthermore, widespread neural effects, with sometimes opposing effects in self-report measures, are noted. Electroencephalography studies showed habituation of the N2-P2 amplitude, whereas functional magnetic resonance imaging studies showed decreasing activity during painful repeated stimulation in several identified brain areas (cingulate cortex and somatosensory cortices). Important considerations for the use of terminology, methodology, statistics, and individual differences are discussed. This review will aid our understanding of habituation to pain in healthy individuals and may lead the way to improving methods and designs for personalized treatment approaches in chronic pain patients.

Pain Catastrophizing: Controversies, Misconceptions and Future Directions

Recent reports have pointed to problems with the term "pain catastrophizing." Critiques of the term pain catastrophizing have come from several sources including individuals with chronic pain, advocates for individuals with chronic pain, and pain scholars. Reports indicate that the term has been used to dismiss the medical basis of pain complaints, to question the authenticity of pain complaints, and to blame individuals with pain for their pain condition. In this paper, we advance the position that the problems prompting calls to rename the construct of pain catastrophizing have little to do with the term, and as such, changing the term will do little to solve these problems. We argue that continued calls for changing or deleting the term pain catastrophizing will only divert attention away from some fundamental flaws in how individuals with pain conditions are assessed and treated. Some of these fundamental flaws have their roots in the inadequate training of health and allied health professionals in evidence-based models of pain, in the use of psychological assessment and intervention tools for the clinical management of pain, and in gender equity and antiracism. Critiques that pain scholars have leveled against the defining, operational, and conceptual bases of pain catastrophizing are also addressed. Arguments for reconceptualizing pain catastrophizing as a worry-related construct are discussed. Recommendations are made for remediation of the problems that have contributed to calls to rename the term pain catastrophizing. PERSPECTIVE: The issues prompting calls to rename the construct of pain catastrophizing have their roots in fundamental flaws in how individuals with pain are assessed and treated. Efforts to address these problems will require more than a simple change in terminology.

Psychological factors are associated with pain extent in patients with carpal tunnel syndrome

INTRODUCTION

Widespread pain may be related to psychosocial aspects in several musculoskeletal conditions, but the literature on carpal tunnel syndrome (CTS) is scarce.

OBJECTIVE

To determine the relationship between pain extent and psychological factors (catastrophizing, kinesiophobia, anxiety symptoms, and depression) in people with CTS.

METHODS

A cross-sectional study was conducted. The independent variables were: pain intensity, disability (QuickDASH), duration of symptoms, anxiety and depressive symptoms, catastrophizing, and kinesiophobia. The main outcome was: pain extent (% of total area and categories "pain within the median nerve-innervated territory" versus "extra-median nerve pain"). Correlation analysis was performed using Spearman's correlation coefficient. A linear regression model and binary logistic regression (both with forward selection) were performed to determine the main predictors of pain extent.

RESULTS

Forty-eight participants were included. A moderate positive correlation was found between catastrophizing (r = 0.455; p = 0.024) and disability (r = 0.448; p = 0.024) with total pain extent area. Regression models indicated that catastrophizing explained 22% of the variance in the pain extent (β = 0.003; 95% CI: 0.002-0.005), while kinesiophobia was the variable that best explained the distribution of pain in the extra-median territory (R2 Nagelkerke = 0.182). Null or weak correlations were found for the rest of the associations.

CONCLUSION

Catastrophizing and kinesiophobia were the main indicators of pain extent in people with CTS. Clinicians are advised to use specific questionnaires to check for the presence of catastrophizing or kinesiophobia in people with CTS and wider pain extension.

Quantitative Sensory Testing to Characterize Sensory Changes in Hidradenitis Suppurativa Skin Lesions

Importance

Pain is the most impactful symptom in patients with hidradenitis suppurativa (HS). Characterization of sensory profiles may improve understanding of pain mechanisms in HS and facilitate identification of effective pain management strategies.

Objective

To characterize somatosensory profiles in patients with HS at clinically affected and nonaffected sites compared with pain-free reference data.

Design, Setting, and Participants

This cross-sectional study was conducted at the Emory University Dermatology Clinic. It was hypothesized (1) that patients with HS would demonstrate hypersensitivity to pain in HS lesions and (2) that some patients would have sensory profiles consistent with complex pain mechanisms. Therefore, adults with dermatologist-diagnosed HS and at least 1 painful HS lesion at the time of testing were enrolled between September 10, 2020, and March 21, 2022. Patients with other diagnoses contributing to pain or neuropathy were excluded. Data analysis was conducted between March and April 2022.

Exposure

Quantitative sensory testing was performed on HS lesions and control skin according to a standardized protocol.

Main Outcomes and Measures

Quantitative sensory testing outcomes included innocuous thermal and mechanical sensitivity (cold, warmth, and light touch detection thresholds), noxious thermal and mechanical sensitivity (cold, heat, pinprick, and deep pressure pain thresholds and suprathreshold pinprick sensitivity), temporal summation of pinprick, paradoxical thermal sensations, and dynamic mechanical allodynia (pain upon light stroking of the skin). Sensitivity in HS lesions was compared with sensitivity in a control location (the hand) and in pain-free controls using t tests.

Results

This study included 20 participants with a median age of 35.5 (IQR, 30.0-46.5) years, the majority of whom were women (15 [75%]). In terms of race and ethnicity, 2 participants (10%) self-identified as Asian, 11 (55%) as Black, 6 (30%) as White, and 1 (5%) as more than 1 race or ethnicity. Compared with site-specific reference values from healthy, pain-free control participants, HS lesions were insensitive to innocuous cold and warmth, noxious heat, and light touch (t = -5.69, -10.20, -3.84, and 4.46, respectively; all P < .001). In contrast, HS lesions also demonstrated significant hypersensitivity to deep pressure pain (t = 8.36; P < .001) and cutaneous pinprick (t = 2.07; P = .046). Hypersensitivity to deep pressure pain was also observed in the control site (t = 5.85; P < .001). A subset of patients with HS displayed changes in pain processing that are often seen in neuropathic and nociplastic pain conditions, including hypersensitivity to repetitive pinprick (5 [26%]), paradoxical thermal sensations (3 [15%]), and pain upon light stroking of the skin (10 [50%]).

Conclusions and Relevance

The findings of this cross-sectional study suggest that HS involves local changes in the skin or its free nerve endings, possibly leading to peripheral neuropathy and alterations in the transduction of innocuous and noxious thermal and mechanical stimuli. For some patients, central nervous system changes in somatosensory processing may also occur, but confirmatory evidence is needed. Better understanding of neuropathic and nociplastic mechanisms in HS pain could lead to individually tailored treatments.

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

Background and Objectives

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

Research Design and Methods

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

Results

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

Discussion and Implications

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

Catastrophizing is associated with pain-related disability in temporomandibular disorders

This study aimed to evaluate the association of pain-related disability with biopsychosocial factors in temporomandibular disorders (TMD) patients. The study was carried out at the Orofacial Pain Outpatient Clinic of the State University of Feira de Santana, Bahia, from September 2018 to March 2020. The sociodemographic aspects, TMD subtypes, presence of pain-induced disability, pressure pain threshold, perceived stress, anxiety, depression, and catastrophizing were evaluated in 61 patients. The studied variables were compared between patients with and without pain-induced disability. Crude and adjusted logistic regression were performed to obtain estimates of odds ratios (OR) and 95% confidence intervals. With the exception of catastrophizing, there was no association between the biopsychosocial factors and pain-induced disability. The presence of catastrophizing increased the chance of having chronic pain-induced disability by 4.02 times. The results of this study indicate a strong association between pain catastrophizing and disability in individuals with chronic painful TMD.

Multimodal phenotyping and correlates of pain following hematopoietic cell transplant in children with sickle cell disease

INTRODUCTION

There is limited understanding of pain, patient-reported outcomes (PROs) of health-related quality of life (HRQoL), psychological factors, and experimental pain sensitivity before and following hematopoietic cell transplant (HCT) in children with sickle cell disease (SCD).

METHODS

Individuals aged 8 years and older, English speaking, and scheduled for a HCT were invited to participate in an observational study where they completed assessments of pain, PROs, psychological factors, and qualitative interviews before and around 3 months, 6 months, 1 year, and 2 years post-HCT. An optional substudy of experimental pain sensitivity before and around 6 month, 1 year, and 2 years post-HCT was also offered.

RESULTS

Data from eight participants (median age 13.5 years, 25% female) with sickle cell anemia (SCA) or similarly severe genotype, and successful donor-derived erythropoiesis post-HCT are reported. We found that collection of pain, PROs, psychological factors, and qualitative data were feasible in the context of HCT. We found moderate to large differences in pain and some PROs between baseline to 1 year and baseline to 2 year post-HCT based on effect sizes, but only some differences were statistically significant. We found moderate to large differences in pressure pain threshold and moderate differences in cold pain threshold between baseline to 1 year and baseline to 2 year post-HCT based on effect sizes, but these differences were not statistically significant. Qualitative data indicated an improvement in pain and HRQoL post-HCT.

CONCLUSION

This study provides a framework for the conduct of multimodal pain assessments before and after HCT, which is feasible but faced with unique barriers.

High Blood Glucose and Excess Body fat Enhance Pain Sensitivity and Weaken Pain Inhibition in Healthy Adults: A Single-blind Cross-over Randomized Controlled Trial

To investigate links between blood glucose, body fat mass and pain, the effects of acute hyperglycaemia on pain sensitivity and pain inhibition were examined in healthy adults with normal (n = 24) or excess body fat (n = 20) determined by dual-energy X-ray absorptiometry. Effects of hyperglycaemia on heart rate variability and reactive hyperaemia were also explored. For the overall sample, ingesting 75-g glucose enhanced pain sensitivity during 1-minute cold-water immersion of both feet (conditioning stimulus) and weakened the pain inhibitory effect of cold water on pressure pain thresholds (test stimulus). Exploratory subgroup analyses not adjusted for multiple comparisons suggested that this effect was limited to people with excess fat mass. In addition, acute hyperglycaemia suppressed resting heart rate variability only in people with excess fat mass. Furthermore, regardless of blood glucose levels, people with excess fat mass had weaker pain inhibition for pinprick after cold water and reported more pain during 5-minutes of static blood flow occlusion. Neither high blood glucose nor excess body fat affected pinprick-temporal summation of pain or reactive hyperaemia. Together, these findings suggest that hyperglycaemia and excess fat mass interfere with pain processing and autonomic function. PERSPECTIVE: Ingesting 75-g glucose (equivalent to approximately 2 standard cans of soft drink) interfered with pain-processing and autonomic function, particularly in people with excess body fat mass. As both hyperglycaemia and overweight are risk factors for diabetes, whether these are sources of pain in people with diabetes should be further explored.

Is transcranial direct current stimulation beneficial for treating pain, depression, and anxiety symptoms in patients with chronic pain? A systematic review and meta-analysis

Background

Chronic pain is often accompanied by emotional dysfunction. Transcranial direct current stimulation (tDCS) has been used for reducing pain, depressive and anxiety symptoms in chronic pain patients, but its therapeutic effect remains unknown.

Objectives

To ascertain the treatment effect of tDCS on pain, depression, and anxiety symptoms of patients suffering from chronic pain, and potential factors that modulate the effectiveness of tDCS.

Methods

Literature search was performed on PubMed, Embase, Web of Science, and Cochrane Library from inception to July 2022. Randomized controlled trials that reported the effects of tDCS on pain and depression and anxiety symptoms in patients with chronic pain were included.

Results

Twenty-two studies were included in this review. Overall pooled results indicated that the use of tDCS can effectively alleviate short-term pain intensity [standard mean difference (SMD): -0.43, 95% confidence interval (CI): -0.75 to -0.12, P = 0.007] and depressive symptoms (SMD: -0.31, 95% CI, -0.47 to -0.14, P < 0.001), middle-term depressive symptoms (SMD: -0.35, 95% CI: -0.58 to -0.11, P = 0.004), long-term depressive symptoms (ES: -0.38, 95% CI: -0.64 to -0.13, P = 0.003) and anxiety symptoms (SMD: -0.26, 95% CI: -0.51 to -0.02, P = 0.03) compared with the control group.

Conclusion

tDCS may be an effective short-term treatment for the improvement of pain intensity and concomitant depression and anxiety symptoms in chronic pain patients. Stimulation site, stimulation frequency, and type of chronic pain were significant influence factors for the therapeutic effect of tDCS.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=297693, identifier: CRD42022297693.

Indicators of central sensitization in chronic neuropathic pain after spinal cord injury

BACKGROUND

Central sensitization is considered a key mechanism underlying neuropathic pain (NP) after spinal cord injury (SCI).

METHODS

Two novel proxies for central sensitization were investigated in thoracic SCI subjects with (SCI-NP) and without NP (SCI-nonNP) compared to healthy controls (HC). Specifically, temporal summation of pain (TSP) was investigated by examining pain ratings during a 2-min tonic heat application to the volar forearm. Additionally, palmar heat-induced sympathetic skin responses (SSR) were recorded in order to reveal changes in pain-autonomic interaction above the lesion level. Pain extent was assessed as the percentage of the body area and the number of body regions being affected by NP.

RESULTS

Enhanced TSP was observed in SCI-NP (+66%) compared to SCI-nonNP (-75%, p = 0.009) and HC (-59%, p = 0.021). In contrast, no group differences were found (p = 0.685) for SSR habituation. However, pain extent in SCI-NP was positively correlated with deficient SSR habituation (body area: r = 0.561, p = 0.024; body regions: r = 0.564, p = 0.023).

CONCLUSIONS

These results support the value of TSP and heat-induced SSRs as proxies for central sensitization in widespread neuropathic pain syndromes after SCI. Measures of pain-autonomic interaction emerged as a promising tool for the objective investigation of sensitized neuronal states in chronic pain conditions.

SIGNIFICANCE

We present two surrogate readouts for central sensitization in neuropathic pain following SCI. On the one hand, temporal summation of tonic heat pain is enhanced in subjects with neuropathic pain. On the other hand, pain-autonomic interaction reveals potential advanced measures in chronic pain, as subjects with a high extent of neuropathic pain showed diminished habituation of pain-induced sympathetic measures. A possible implication for clinical practice is constituted by an improved assessment of neuronal hyperexcitability potentially enabling mechanism-based treatment.

Exploration of the trait-activation model of pain catastrophizing in Native Americans: results from the Oklahoma Study of Native American pain risk (OK-SNAP)

OBJECTIVES

Native Americans (NAs) have the highest prevalence of chronic pain of any racial/ethnic group. This issue has received little attention from the scientific community. One factor that may contribute to racial pain disparities is pain catastrophizing. Pain catastrophizing is a construct related to negative pain outcomes in persons with/without chronic pain. It has been suggested that the relationship between trait catastrophizing and pain is mediated by situation-specific (state) catastrophizing. The present study has 2 aims: (1) to investigate whether state pain catastrophizing mediates the relationship between trait catastrophizing and experimental pain (e.g., cold, ischemic, heat and electric tolerance), and (2) to investigate whether this relationship is stronger for NAs.

METHODS

145 non-Hispanic Whites (NHWs) and 137 NAs completed the study. Bootstrapped indirect effects were calculated for 4 unmoderated and 8 moderated mediation models (4 models with path a moderated and 4 with path b).

RESULTS

Consistent with trait-activation theory, significant indirect effects indicated a tendency for trait catastrophizing to be associated with greater state catastrophizing which in turn is associated with reduced pain tolerance during tonic cold (a × b=-0.158) and ischemia stimuli (a × b=-0.126), but not during phasic electric and heat stimuli. Moderation was only noted for the prediction of cold tolerance (path a). Contrary to expectations, the indirect path was stronger for NHWs (a × b for NHW=-.142).

CONCLUSIONS

Together, these findings suggest that state catastrophizing mediates the relationship between trait catastrophizing and some measures of pain tolerance but this indirect effect was non-significant for NAs.

The Effect of Induced Optimism on Situational Pain Catastrophizing

Background

There is broad evidence that optimism is associated with less pain, while pain catastrophizing leads to increased pain. The aim of this study was to examine whether experimentally induced optimism can reduce situational pain catastrophizing and whether this relation is moderated by dispositional optimism and/or dispositional pain catastrophizing.

Methods

Situational pain catastrophizing during two thermal stimulations was measured in 40 healthy participants with the Situational Catastrophizing Questionnaire (SCQ). Between the two stimulations, the Best Possible Self (BPS) imagery and writing task was performed to induce situational optimism in the experimental group while the control group wrote about their typical day. Questionnaires were administered to assess dispositional optimism [Life Orientation Test-Revised (LOT-R)] and dispositional pain catastrophizing [Pain Catastrophizing Scale (PCS)].

Results

There was a significant interaction between the optimism induction and trait pain catastrophizing: the association of trait pain catastrophizing with state pain catastrophizing was weakened after the optimism induction. No overall effect of induced optimism on situational pain catastrophizing and no significant moderating influence of trait optimism were found.

Conclusion

The state optimism induction apparently counteracted the manifestation of dispositional pain catastrophizing as situational pain catastrophizing. This implies that high trait pain catastrophizers may have especially benefitted from the optimism induction, which is in line with resilience models stressing the buffering role of optimism.

Temporal Summation in Fibromyalgia Patients: Comparing Phasic and Tonic Paradigms

Introduction

Fibromyalgia (FM) is associated with dysfunctional pain modulation mechanisms, including central sensitization. Experimental pain measurements, such as temporal summation (TS), could serve as markers of central sensitization and have been previously studied in these patients, with conflicting results. Our objective in this study was to explore the relationships between two different protocols of TS (phasic and tonic) and test the associations between these measures and other clinical variables.

Materials and Methods

In this cross-sectional analysis of a randomized clinical trial, patients were instructed to determine their pain-60 test temperature, then received one train of 15 repetitive heat stimuli and rated their pain after the 1st and 15th stimuli: TSPS-phasic was calculated as the difference between those. We also administered a tonic heat test stimulus at the same temperature continuously for 30 s and asked them to rate their pain levels after 10 s and 30 s, calculating TSPS-tonic as the difference between them. We also collected baseline demographic data and behavioral questionnaires assessing pain, depression, fatigue, anxiety, sleepiness, and quality of life. We performed univariable analyses of the relationship between TSPS-phasic and TSPS-tonic, and between each of those measures and the demographic and clinical variables collected at baseline. We then built multivariable linear regression models to find predictors for TSPS-phasic and TSPS-tonic, while including potential confounders and avoiding collinearity.

Results

Fifty-two FM patients were analyzed. 28.85% developed summation during the TSPS-phasic protocol while 21.15% developed summation during the TSPS-tonic protocol. There were no variables associated TSPS phasic or tonic in the univariable analyses and both measures were not correlated. On the multivariate model for the TSPS-phasic protocol, we found a weak association with pain variables. BPI-pain subscale was associated with more temporal summation in the phasic protocol (ß = 0.38, p = 0.029), while VAS for pain was associated with less summation in the TSPS-tonic protocol (ß = −0.5, p = 0.009).

Conclusion

Our results suggest that, using heat stimuli with pain-60 temperatures, a TSPS-phasic protocol and a TSPS-tonic protocol are not correlated and could index different neural responses in FM subjects. Further studies with larger sample sizes would be needed to elucidate whether such responses could help differentiating subjects with FM into specific phenotypes.

Are Mind-Body Exercise Beneficial for Treating Pain, Function, and Quality of Life in Middle-Aged and Old People With Chronic Pain? A Systematic Review and Meta-Analysis

Background

Aging is a significant risk factor in chronic pain development with extensive disability and greater health care costs. Mind-body exercise (MBE) has been scientifically proven to affect the pain intensity and physical health.

Objectives

To assess the effects of MBE modes (Tai Chi, yoga, and qigong) for treating chronic pain among middle-aged and old people, compared with nonactive and active treatment, as well as function, quality of life, and adverse events.

Methods

We searched PubMed, Embase, Web of Science, Cochrane Library, China National Knowledge Infrastructure (CNKI), Wanfang Database, and Chinese Scientific Journals Full-Text Database (VIP) till March 2022. No restrictions were chartered within the year and language of publication. We included randomized controlled trials of MBE treatment in middle-aged and elderly people with chronic pain. The overall certainty of evidence was evaluated by using the GRADE approach.

Results

A total of 17 studies (n = 1,332) were included in this review. There was low-certainty evidence indicating that MBE had a moderate effect on reducing pain compared with the nonactive and active control group (standard mean difference (SMD): -0.64, 95% confidence interval (CI): -0.86 to -0.42, P < 0.001). Very-low-certainty evidence showed that the pooled SMD for the functional improvement was -0.75 (95% CI: -1.13 to -0.37, P < 0.001). Low-certainty evidence presented that no influence was observed in physical component summary (SMD: 0.23, 95% CI: -0.16 to 0.62, P = 0.24) and mental component summary (SMD: -0.01, 95% CI -0.39 to 0.36, P = 0.95).

Conclusion

Our results indicated that MBE was an effective treatment for reducing symptoms of middle-aged and elderly people with chronic pain compared with nonactive and active control groups. TC and qigong had obvious benefits for knee osteoarthritis in self-reported function, but the efficacy of chronic low back pain was uncertain. No significant benefit of MBE on quality of life in older adults with chronic pain was found. More high-quality RCTs should be conducted to explore the efficacy and mechanism of MBE on chronic pain in middle-aged and elderly people from various dimensions, such as affective and cognitive dimensions.

Systematic Review Registration

https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=316591, identifier CRD42022316591.

Attentional interference by pain in a dishabituation procedure: an experimental investigation

ABSTRACT

The ability to habituate to pain may be adaptive, and it may enable us to pursue valuable goals despite the pain. In this study, we experimentally investigated this idea using the primary task paradigm in which participants had to identify the color of a circle (blue or yellow) as quickly as possible while ignoring painful or tactile distractors that are presented on some of the trials. In the first experiment, we were interested whether the attentional interference effect because of the presentation of the distractors and its habituation would differ between painful and tactile distractor stimuli. In the second experiment, we investigated dishabituation (ie, the phenomenon that the introduction of a different stimulus results in an increase of the decremented response to the original stimulus). We expected habituation of the attentional interference to occur both in the tactile and the painful distractor condition, but to be less complete in the painful condition. Moreover, we hypothesized that the dishabituation would be stronger for the painful than for the tactile distractors. We did find evidence for an interference effect because of the presence of distractors. We also found habituation of attentional interference. However, the interference and its habituation were no different for tactile and painful distractors. Moreover, we did not find evidence for dishabituation. These are the first studies of their kind. Implications and guidelines for future research are formulated.

Using quantitative sensory testing to predict attrition in an interdisciplinary pain management program: a pilot study

Aim: To determine the extent to which quantitative sensory testing (QST) predicted attrition in an interdisciplinary pain program (IPP). Patients & methods: Participants (n = 53) enrolled in an IPP completed pretreatment assessments of QST and the PROMIS-29 quality of life survey. Results & conclusion: Compared with completers, non-completers (24.5%) reported significantly higher pain intensity (7.1, 95% CI [5.8, 8.4] versus 5.4, 95% CI [4.8, 6.1]) and cold hyperalgesia (14.6°C, 95% CI [8.8, 20.4] versus 7.5°C, 95% CI [4.8, 6.1]), with both variables also predicting attrition. This finding highlights a potentially novel and clinically significant use of QST. Higher overall pain intensity and the presence of remote cold hyperalgesia may identify patients at risk for dropping out of an IPP.

The effect of hypertonic saline evoked muscle pain on neurophysiological changes and exercise performance in the contralateral limb

Non-local muscle pain may impair endurance performance through neurophysiological mechanisms, but these are relatively unknown. This study examined the effects of muscle pain on neuromuscular and neurophysiological responses in the contralateral limb. On separate visits, nine participants completed an isometric time to task failure (TTF) using the right knee extensors after intramuscular injection of isotonic saline (CTRL) or hypertonic saline (HYP) into the left vastus lateralis. Measures of neuromuscular fatigue were taken before, during and after the TTF using transcranial magnetic stimulation (TMS) and peripheral nerve stimulation. Mean pain intensity was greater in the left leg in HYP (3.3 ± 1.9) compared to CTRL (0.4 ± 0.7; P < 0.001) which was combined with a reduced TTF by 9.8% in HYP (4.54 ± 0.56 min) compared to CTRL (5.07 ± 0.77 min; P = 0.005). Maximum voluntary force was not different between conditions (all P > 0.05). Voluntary activation was lower in HYP compared to CTRL (P = 0.022). No difference was identified between conditions for doublet amplitude (P > 0.05). Furthermore, no difference in MEP·M_max⁻¹ or the TMS silent period between conditions was observed (all P > 0.05). Non-local pain impairs endurance performance of the contralateral limb. This impairment in performance is likely due to the faster attainment of the sensory tolerance limit from a greater amount of sensory feedback originating from the non-exercising, but painful, left leg.

Pain sensitivity is associated with general attitudes towards pain: Development and validation of a new instrument for pain research and clinical application

BACKGROUND

With regard to attitudes towards pain, many questionnaires have been developed. Although undoubtedly useful, they were specifically designed for the use in chronic pain and are less suitable for the assessment in the general population. The purpose of the present paper was to develop a measure for the assessment of general attitudes towards pain applicable in the general population, regardless of clinical condition, and to test its psychometric properties.

METHODS

We developed the General Attitudes Towards Pain Inventory and conducted two studies in order to provide psychometric data: In a general population sample (N = 362, study one), participants were asked to complete a questionnaire battery. To assess test-retest reliability, participants were contacted again after four weeks (retest sample: N = 101). For the evaluation of criterion validity (study two), a sample with sadomasochistic sexual preference (N = 68) was additionally recruited.

RESULTS

Statistical analyses revealed, overall, acceptable internal consistencies and test-retest reliabilities. A ten-factor model showed acceptable fit and was superior to alternative models. The inventory demonstrated convergent and divergent validity. In this context, we found pain sensitivity to be associated with pain attitudes. Finally, compared to the general population sample, individuals with sadomasochistic sexual preference showed significantly higher scores on fascination-pleasure and challenge subscales.

CONCLUSIONS

In the present paper, we introduce a new and comprehensive instrument for pain research and provide evidence for its reliability and validity. In addition, we present new insights into how interindividual differences in pain sensitivity relate to pain attitudes.

The effect of elevated muscle pain on neuromuscular fatigue during exercise

PURPOSE

Muscle pain can impair exercise performance but the mechanisms for this are unknown. This study examined the effects of muscle pain on neuromuscular fatigue during an endurance task.

METHODS

On separate visits, twelve participants completed an isometric time-to-task failure (TTF) exercise of the right knee extensors at ~ 20% of maximum force following an intramuscular injection of isotonic saline (CTRL) or hypertonic saline (HYP) into the vastus lateralis. Measures of neuromuscular fatigue were taken before, during and after the TTF using transcranial magnetic stimulation (TMS) and peripheral nerve stimulation.

RESULTS

The mean pain intensity was 57 ± 10 in HYP compared to 38 ± 18 in CTRL (P < 0.001). TTF was reduced in HYP (4.36 ± 0.88 min) compared to CTRL (5.20 ± 0.39 min) (P = 0.003). Maximum voluntary force was 12% lower at minute 1 (P = 0.003) and 11% lower at minute 2 in HYP (P = 0.013) compared to CTRL. Voluntary activation was 4% lower at minute 1 in HYP compared to CTRL (P = 0.006) but not at any other time point (all P > 0.05). The TMS silent period was 9% longer at 100 s during the TTF in HYP compared to CTRL (P = 0.026).

CONCLUSION

Muscle pain reduces exercise performance through the excacerbation of neuromuscular fatigue that is central in origin. This appears to be from inhibitory feedback from group III/IV nociceptors which acts to reduce central motor output.

Analysis of the Effect of Wearing Extensible and Non-Extensible Lumbar Belts on Biomechanical Factors of the Sit-to-Stand Movement and Pain-Related Psychological Factors Affecting Office Workers with Low Back Pain

This study aimed to investigate the effects of wearing extensible and non-extensible lumbar belt (LB) on biomechanical factors of the sit-to-stand (STD) movement and pain-related psychological factors affecting office workers with low back pain. Among 30 office workers, 15 with low back pain (LBP) were assigned to the experimental group and 15 healthy adults were assigned to the control group. The participants performed STD movement in random order of three different conditions: without LB (Condition 1), with extensible LB (Condition 2), and with non-extensible LB (Condition 3). Biomechanical variables of STD movement in each condition were measured using a three-dimensional motion analysis system and force plate. Pain-related psychological factors were measured only in the experimental group. Among the biomechanical factors of STD movement, an interaction effect was found in the maximum anterior pelvic tilt angle and total-phase range of motion of the trunk (p < 0.05). Pain intensity, pain-related anxiety, and pain catastrophizing were decreased in the conditions with lumbar belts (Conditions 2 and 3) compared to the condition without LB (Condition 1) (p < 0.05). Extensible and non-extensible lumbar belts engender biomechanically beneficial effects during STD movement in both office workers with LBP and healthy office workers. Further, pain intensity, pain-related anxiety, and pain catastrophizing were decreased in office workers with LBP. Therefore, both types of extensible lumbar belts may be helpful in the daily life of patients with LBP and office workers.

"Big girls don't cry": the effect of the experimenter's sex and pain catastrophising on pain

OBJECTIVES

The expression of pain in males and females involves complex socio-psychological mechanisms. Males may report lower pain to a female experimenter to appear strong, whereas females may report higher pain to a male experimenter to appear weak and to seek protection. However, evidence to support these stereotypes is inconclusive. Individuals who catastrophise about pain rate higher pain than those who do not. How pain catastrophising interacts with the effect of the experimenter's sex on pain reports is yet to be explored. Thus, the aim of this study was to determine whether pain catastrophising moderated the effect of the experimenter's sex on pain reports in healthy males and females.

METHODS

Participants (n=60, 30 males) were assigned to one of four experimental conditions: males tested by male experimenters, males tested by female experimenters, females tested by male experimenters, and females tested by female experimenters. Participants completed the Pain Catastrophising Scale, and then sensitivity to heat and to blunt (pressure-pain threshold) and sharp stimuli was assessed on both forearms, and to high frequency electrical stimulation (HFS) administered to one forearm.

RESULTS

Females reported lower pressure-pain thresholds than males irrespective of the experimenters' sex. Females reported lower sharpness ratings to male than female experimenters only when the test stimuli were moderately or intensely sharp. Higher pain catastrophising scores were associated with higher sharpness ratings in females but not males. Additionally, higher pain catastrophising scores were associated with greater temporal summation of pain to HFS, and with lower pressure-pain thresholds in females who were tested by male experimenters.

CONCLUSIONS

These findings indicate that the experimenters' sex and the participant's pain catastrophising score influence pain reports, particularly in females. Awareness of these psychosocial factors is important in order to interpret pain responses in a meaningful way, especially when females are tested by male experimenters. A greater awareness of sex/gender role biases and their potential interaction with pain catastrophising may help researchers and clinicians to interpret pain reports in meaningful ways. In turn, this may help to improve delivery of treatments for patients with chronic pain.

Knee orthopedics as a template for the temporomandibular joint

Although the knee joint and temporomandibular joint (TMJ) experience similar incidence of cartilage ailments, the knee orthopedics field has greater funding and more effective end-stage treatment options. Translational research has resulted in the development of tissue-engineered products for knee cartilage repair, but the same is not true for TMJ cartilages. Here, we examine the anatomy and pathology of the joints, compare current treatments and products for cartilage afflictions, and explore ways to accelerate the TMJ field. We examine disparities, such as a 6-fold higher article count and 2,000-fold higher total joint replacement frequency in the knee compared to the TMJ, despite similarities in osteoarthritis incidence. Using knee orthopedics as a template, basic and translational research will drive the development and implementation of clinical products for the TMJ. With more funding opportunities, training programs, and federal guidance, millions of people afflicted with TMJ disorders could benefit from novel, life-changing therapeutics.

Psycho-sensory relationships in chronic pain

BACKGROUND

Psychological variables contribute to pain- and injury-related outcomes. We examined the hypothesis that anatomical spread and intensity of persistent pain relate to anxiety-related variables: generalised anxiety, fear of pain and pain catastrophising.

METHODS

An online survey was used to gather data from 413 women with persistent pain (low back pain, n = 139; fibromyalgia syndrome, n = 95; neck pain, n = 55; whiplash, n = 41; rheumatoid arthritis, n = 37; migraine, n = 46). The spread and intensity of pain were assessed using the McGill pain chart and a Numerical Rating Scale. A Bayesian Structural Equation Model assessed if the intensity and spread of pain increased with anxiety-related variables. Men were also surveyed (n = 80), but the sample size was only sufficient for analysing if their data were consistent with the model for women.

RESULTS

Across subgroups of women, one standard deviation increase in catastrophising, generalised anxiety and fear corresponded to 27%, 7% and -1% additional pain areas and a 1.1, 0 and -0.1 change in pain intensity (on 0-10 scale), respectively. Overall, our clinical significance criterion - a 30% shift in pain variable in relation to one standard deviation increase in psychological variable - was not met. However, in subgroups it was met for pain spread (low back pain, neck pain and migraine) and pain intensity (migraine and neck pain) in relation to pain catastrophising. The model generally had low goodness-of-fit to men.

CONCLUSION

These data support a meaningful relationship between some anxiety-related variables and pain in women for some conditions. Since the model did not consistently fit the men, we may conclude that the relationships are moderated by sex. Clinician attention to psychological variables as potential contributing factors can be justified; however, research is needed to understand the relationship and whether psychological treatment can reduce pain.

Pain Catastrophizing Mediates and Moderates the Link Between Acute Pain and Working Memory

The bidirectional relationship between pain and working memory (WM) deficits is well-documented but poorly understood. Pain catastrophizing-exaggerated, negative cognitive and emotional responses toward pain-may contribute to WM deficits by occupying finite, shared cognitive resources. The present study assessed the role of pain catastrophizing as both a state-level process and trait-level disposition in the link between acute pain and WM. Healthy, young adults were randomized to an experimentally-induced ischemic pain or control task, during which they completed verbal and non-verbal WM tests. Participants also completed measures of state- and trait-level pain catastrophizing. Simple mediation analyses indicated that participants in the pain group (vs. control) engaged in more state-level catastrophizing about pain, which led to worse verbal and non-verbal WM. Moderated mediation analyses indicated that the indirect (mediation) effect of state-level pain catastrophizing was moderated by trait-level pain catastrophizing for both verbal and non-verbal WM. Participants in the pain group who reported a greater trait-level tendency to catastrophize about pain experienced greater state-level catastrophizing about pain during the ischemic task, which led to worse verbal and non-verbal WM performance. These results provide evidence for pain catastrophizing as an important mechanism and moderating factor of WM deficits in acute pain. Future research should replicate these results in chronic pain samples, investigate other potential mechanisms (e.g., sleep disturbances), and determine if interventions that target pain catastrophizing directly can ameliorate cognitive deficits in people with pain. PERSPECTIVE: This article presents a laboratory study examining the relationships among pain, pain catastrophizing, and working memory in healthy participants. The results shed new light on these relationships and raise the possibility that interventions that reduce catastrophizing may lead to improved cognitive function among people with pain.

The Resurrection of Interdisciplinary Pain Rehabilitation: Outcomes Across a Veterans Affairs Collaborative

OBJECTIVE

Despite empirical support for interdisciplinary pain rehabilitation programs improving functioning and quality of life, access to this treatment approach has decreased dramatically over the last 20 years within the United States but has grown significantly in the Department of Veterans Affairs (VA). Between 2009 and 2019, VA pain rehabilitation programs accredited by the Commission on Accreditation of Rehabilitation Facilities increased 10-fold in the VA, expanding from two to 20. The aim of this collaborative observational evaluation was to examine patient outcomes across a subset of six programs at five sites.

METHODS

Outcomes were assessed using agreed-upon measures of patient-reported pain intensity, pain interference across various domains, pain catastrophizing, and sleep.

RESULTS

A total of 931 patients enrolled in the selected VA interdisciplinary pain programs, with 84.1% of participants completing the full course of treatment. Overall, all programs showed significant improvements from pretreatment to posttreatment in nearly all patient-reported outcomes. The effect sizes ranged from medium to large. Notably, the results demonstrate that positive outcomes were typical despite differences in structure and resources across programs.

CONCLUSIONS

The adverse impacts of opioid use have highlighted the importance of chronic pain treatment approaches that emphasize team-based care focused on functional improvements. This study represents the first and largest analysis of outcomes across chronic pain rehabilitation programs and demonstrates the need for increased access to similar comprehensive approaches to pain management across the health care system. Further, it suggests that a variety of structures may be effective, encouraging flexibility in adopting this interdisciplinary approach.

Development and Validation of a Predictive Model of Pain Modulation Profile to Guide Chronic Pain Treatment: A Study Protocol

Introduction: Quantitative sensory testing is frequently used in research to assess endogenous pain modulation mechanisms, such as Temporal Summation (TS) and Conditioned Pain Modulation (CPM), reflecting excitatory and inhibitory mechanisms, respectively. Numerous studies found that a dysregulation of these mechanisms is associated with chronic pain conditions. In turn, such a patient's “profile” (increased TS and/or weakened CPM) could be used to recommend different pharmacological treatments. However, the procedure to evaluate these mechanisms is time-consuming and requires expensive equipment that is not available in the clinical setting. In this study, we aim to identify psychological, physiological and socio-demographic markers that could serve as proxies to allow healthcare professionals to identify these pain phenotypes in clinic, and consequently optimize pharmacological treatments.

Method: We aim to recruit a healthy participant cohort (n = 360) and a chronic pain patient cohort (n = 108). Independent variables will include psychological questionnaires, pain measurements, physiological measures and sociodemographic characteristics. Dependent variables will include TS and CPM, which will be measured using quantitative sensory testing in a single session. We will evaluate one prediction model and two validation models (for healthy and chronic pain participants) using multiple regression analysis between TS/CPM and our independent variables. The significance thresholds will be set at p = 0.05, respectively.

Perspectives: This study will allow us to develop a predictive model to compute the pain modulation profile of individual patients based on their biopsychosocial characteristics. The development of the predictive model is the first step toward the overarching goal of providing clinicians with a set of quick and cheap tests, easily applicable in clinical practice to orient pharmacological treatments.

An Experimental Analogue Study on the "Dose-Response Relationship" of Different Therapeutic Instructions for Pain Exposures: The More, The Better?

Objective

Novel suggestions derived from the inhibitory learning model on how to optimize exposure therapy have been debated with enthusiasm in the last few years, particularly with respect to the focus on expectancy violations. However, little is known about how this new approach directly compares to the traditional habituation rationale of exposure therapy. In the present study, we examined these two competing therapeutic instructions among healthy female participants in an experimental heat pain paradigm.

Design and Methods

Participants (N= 116) received a therapeutic instruction derived from either a habituation-based approach or the inhibitory learning model (expectation violation). Participants were repeatedly exposed to painful thermal stimulations until a predefined exposure goal was reached.

Results

The expectation violation instruction led to faster goal attainment and higher response rates than the habituation instruction. Both instructions led to increased pain tolerance in the short and long term (one-week follow-up).

Conclusion

Our results suggest that exposure treatments using an expectation violation instruction are especially time-effective. Although the findings from this analogue design cannot be directly generalized to populations with clinically relevant levels of chronic pain, they do point to some important theoretical and clinical implications for the treatment of pain.

Disentangling trait versus state characteristics of the Pain Catastrophizing Scale and the PHQ-8 Depression Scale

BACKGROUND

Research on the role of trait versus state characteristics of a variety of measures among persons experiencing pain has been a focus for the past few decades. Studying the trait versus state nature of the Pain Catastrophizing Scale (PCS) and the Patient Health Questionnaire (PHQ-8) depression scale would be highly informative given both are commonly measured in pain populations and neither scale has been studied for trait/state contributions.

METHODS

The PHQ-8 and PCS were obtained on persons undergoing knee arthroplasty at baseline, 2-, 6- and 12-month post-surgery (N = 402). The multi-trait generalization of the latent trait-state model was used to partition trait and state variability in PCS and PHQ-8 item responses simultaneously. A set of variables were used to predict trait catastrophizing and trait depression.

RESULTS

For total scores, the latent traits and latent states explain 63.2% (trait = 43.2%; state = 20.0%) and 50.2% (trait = 29.4%; state = 20.8%) of the variability in PCS and PHQ-8, respectively. Patients with a high number of bodily pain sites, high levels of anxiety, young patients and African-American patients had high levels of trait catastrophizing and trait depression. The PCS and the PHQ-8 consist of both enduring trait and dynamic state characteristics, with trait characteristics dominating for both measures.

CONCLUSION

Clinicians and researchers using these scales should not assume the obtained measurements solely reflect either trait- or state-based characteristics.

SIGNIFICANCE

Clinicians and researchers using the PCS or PHQ-8 scales are measuring both state and trait characteristics and not just trait- or state-based characteristics.

The association between daily physical exercise and pain among women with fibromyalgia: the moderating role of pain catastrophizing

Daily physical exercise is associated with more self-reported pain intensity in women with fibromyalgia pain, particularly among those with higher levels of pain catastrophizing.

Introduction:

Fibromyalgia (FM) is a condition marked by widespread chronic pain and an array of somatic and psychological symptoms. The primary objective of this study was to explore daily associations between physical activity and pain intensity among a sample of women with FM and the potential moderation of this association by pain catastrophizing.

Methods:

Women with FM (N = 107) completed questionnaires assessing pain, FM symptoms, and psychological measures and were then asked to report their levels of daily pain catastrophizing, physical activity, and pain intensity once per day for a period of 1 week using daily electronic diary-based tracking. In addition, objective measures of physical activity were collected using an activity tracker (Fitbit Flex), which measured step counts. Daily self-report physical activity was used as the independent variable and pain intensity (Brief Pain Inventory) was the outcome, whereas daily pain catastrophizing was tested in the model as the potential moderator.

Results:

Moderation analyses demonstrated associations between physical activity and pain intensity, which were moderated by patient's level of catastrophizing (B = 0.003, SE = 0.001, P < 0.05), with patients scoring higher in daily catastrophizing showing a relatively stronger link between higher day-to-day physical activity and increased daily FM pain. Significant associations were observed between pain catastrophizing, pain intensity, and Fitbit Flex step count (P < 0.05).

Conclusions:

Our findings suggest that increases in daily physical activity is associated with more self-reported pain intensity in women with FM pain, particularly among those with higher levels of pain catastrophizing.

The Effect of Pain Catastrophizing on Endogenous Inhibition of Pain and Spinal Nociception in Native Americans: Results From the Oklahoma Study of Native American Pain Risk

BACKGROUND

Conditioned pain modulation (CPM) is a task that involves measuring pain in response to a test stimulus before and during a painful conditioning stimulus (CS). The CS pain typically inhibits pain elicited by the test stimulus; thus, this task is used to assess endogenous pain inhibition. Moreover, less efficient CPM-related inhibition is associated with chronic pain risk. Pain catastrophizing is a cognitive-emotional process associated with negative pain sequelae, and some studies have found that catastrophizing reduces CPM efficiency.

PURPOSE

The current study examined the relationship between catastrophizing (dispositional and situation specific) and CPM-related inhibition of pain and the nociceptive flexion reflex (NFR; a marker of spinal nociception) to determine whether the catastrophizing-CPM relationship might contribute to the higher risk of chronic pain in Native Americans (NAs).

METHODS

CPM of pain and NFR was assessed in 124 NAs and 129 non-Hispanic Whites. Dispositional catastrophizing was assessed at the beginning of the test day, whereas situation-specific catastrophizing was assessed in response to the CS, as well as painful electric stimuli.

RESULTS

Situation-specific, but not dispositional, catastrophizing led to less NFR inhibition but more pain inhibition. These effects were not moderated by race, but mediation analyses found that: (a) the NA race was associated with greater situation-specific catastrophizing, which led to less NFR inhibition and more pain inhibition, and (b) situation-specific catastrophizing was associated with greater CS pain, which led to more pain inhibition.

CONCLUSIONS

Catastrophizing may contribute to NA pain risk by disrupting descending inhibition.

Ethnic Differences in Experimental Pain Responses Following a Paired Verbal Suggestion With Saline Infusion: A Quasiexperimental Study

BACKGROUND

Ethnic differences in placebo and nocebo responses are an important, yet underresearched, patient factor that might contribute to treatment disparities.

PURPOSE

The purpose of this study was to examine ethnic differences in pain trajectories following a verbal suggestion paired with a masked, inert substance (i.e., saline).

METHODS

Using a quasiexperimental design, we examined differences between 21 non-Hispanic Black (NHB) participants and 20 non-Hispanic White (NHW) participants in capsaicin-related pain rating trajectories following a nondirectional verbal suggestion + saline infusion. All participants were told that the substance would "either increase pain sensation, decrease it, or leave it unchanged." A spline mixed model was used to quantify the interaction of ethnicity and time on ratings.

RESULTS

There was a significant Ethnicity × Time interaction effect (β = -0.28, p = .002); NHB individuals reported significantly greater increases in pain following, but not before, the verbal suggestion + saline infusion. Sensitivity analyses showed no change in primary results based on differences in education level, general pain sensitivity, or condition order.

CONCLUSIONS

The present results showed ethnic differences in pain response trajectories following a verbal suggestion + saline infusion and suggest that future research rigorously examining possible ethnic differences in placebo/nocebo responses is warranted.

Sex Differences in Interleukin-6 Responses Over Time Following Laboratory Pain Testing Among Patients With Knee Osteoarthritis

Epidemiological studies suggest that women are not only at a higher risk for developing knee osteoarthritis (KOA), but also report greater symptom severity compared to men. One potential underlying mechanism of these sex differences may be exaggerated inflammatory responses to pain among women compared to men. The present study examined sex differences in interleukin-6 (IL-6) response over time following experimental pain testing. We hypothesized that women, when compared to men, would show greater IL-6 reactivity when exposed to acute pain in a human laboratory setting. Eighty-four participants (36 men and 48 women) with KOA scheduled for total knee arthroplasty underwent a quantitative sensory testing (QST) battery. A total of seven IL-6 measurements were taken, twice at baseline, once immediately after QST, and every 30 minutes up to 2 hours after QST. Consistent with our hypothesis, women, when compared to men, showed accelerated increases in IL-6 levels following laboratory-evoked pain, even after controlling for body mass index, marital status, clinical pain, evoked pain sensitivity, and situational pain catastrophizing. Given that KOA is a chronic condition, and individuals with KOA frequently experience pain, these sex differences in IL-6 reactivity may contribute to the maintenance and/or exacerbation of KOA symptoms. PERSPECTIVES: The present study demonstrates that women, when compared to men, exhibit greater IL-6 reactivity after exposure to laboratory-evoked pain. Such sex differences may explain the mechanisms underlying women's higher chronic pain risk and pain perception, as well as provide further insight in developing personalized pain interventions.

Reference values of conditioned pain modulation

Background and aims Endogenous pain modulation can be studied in humans by conditioned pain modulation (CPM): pain induced by a test stimulus is attenuated by a distantly applied noxious conditioning stimulus. The detection of impaired CPM in individual patients is of potential importance to understand the pathophysiology and predict outcomes. However, it requires the availability of reference values. Methods We determined reference values of CPM in 146 pain-free subjects. Pressure and electrical stimulation were the test stimuli. For electrical stimuli, we recorded both pain threshold and threshold for the nociceptive withdrawal reflex. Cold pressor test was the conditioning stimulus. The 5th, 10th and 25th percentiles for the three tests were computed by quantile regression analyses. Results The average thresholds increased after the conditioning stimulus for all three tests. However, a subset of subjects displayed a decrease in thresholds during the conditioning stimulus. This produced negative values for most of the computed percentiles. Conclusions This study determined percentile reference values of CPM that can be used to better phenotype patients for clinical and research purposes. The negative value of percentiles suggests that a slightly negative CPM effect can be observed in pain-free volunteers. Implications Pain facilitation rather than inhibition during the conditioning stimulus occurs in some pain-free volunteers and may not necessarily represent an abnormal finding.

Cross-cultural Adaptation and Psychometric Properties of the Greek Version of the Central Sensitization Inventory

OBJECTIVES

Recent studies support the opinion that central sensitization (CS) plays an important role in the pathophysiology of many chronic pain conditions. CS refers to hyperexcitability of the central nervous system, which can result in pain hypersensitivity and other somatosensory symptoms. Recognition of CS-related symptomology is crucial in chronic pain evaluation and rehabilitation. The Central Sensitization Inventory (CSI) was created to evaluate symptoms that have been found to be associated with CS. The aim of the current study was the cross-cultural adaptation of the CSI into Greek (CSI-Gr).

METHODS

To evaluate discriminate validity, 200 patients with chronic pain and 50 healthy control subjects participated. The sample was divided into 4 diagnostic groups (fibromyalgia, single pain complaints, multiple pain complaints, and a control group) and into 5 CSI severity subgroups, from subclinical to extreme. Convergent validity was determined by evaluation of the relationship between the CSI-Gr and the Pain Catastrophizing Scale (PCS). Additionally, 30 patients completed the CSI a second time for the purpose of a test/retest analysis.

RESULTS

The results showed high internal consistency (Cronbach's alpha = 0.994) and test-retest reliability (intraclass correlation coefficient = 0.993). The standard error of measurement was 2.1. The CSI-Gr correlated moderately with the PCS (r = 0.68). Statistically significant differences were found among the 3 comparison groups, with patients who had fibromyalgia reporting the highest CSI severity and healthy control subjects reporting the lowest severity.

CONCLUSIONS

As determined in the present study, the CSI-Gr was found to be a reliable and valid tool for recognition of CS-related symptomology.

Sleep, Experimental Pain and Clinical Pain in Patients with Chronic Musculoskeletal Pain and Healthy Controls

Purpose

Everyday variations in night sleep in healthy pain-free subjects are at most weakly associated with pain, whereas strong alterations (eg, sleep deprivation, insomnia) lead to hyperalgesic pain changes. Since it remains unclear how substantial sleep alterations need to be in order to affect the pain system and lead to a coupling of both functions, the present study aimed at providing sufficient variance for co-variance analyses by examining a sample consisting of both healthy subjects and chronic pain patients.

Methods

A sample of 20 chronic musculoskeletal pain patients and 20 healthy controls was examined. This sample was assumed to show high inter-individual variability in sleep and pain, as pain patients frequently report sleep disturbances, whereas healthy subjects were required to be pain-free and normal sleepers. Sleep of two non-consecutive nights was measured using portable polysomnography and questionnaires. Experimental pain parameters (pressure pain thresholds (PPT), temporal summation of pain (TSP), conditioned pain modulation (CPM)) and situational pain catastrophizing (SCQ) were assessed in laboratory sessions before and after sleep. Pain patients’ clinical pain was assessed via questionnaire.

Results

As expected, both groups differed in several sleep parameters (reduced total sleep time and sleep efficiency, more time awake after sleep onset, lower subjective sleep quality in the patients) and in a few pain parameters (lower PPTs in the patients). In contrast, no differences were found in TSP, CPM, and SCQ. Contrary to our expectations, regression analyses indicated no prediction of overnight pain changes by sleep parameters.

Conclusion

Since sleep parameters were hardly apt to predict overnight pain changes, this leaves the association of both systems mainly unproven when using between-subject variance for verification.

The moderating role of pain catastrophizing on the relationship between partner support and pain intensity: a daily diary study in patients with knee osteoarthritis

The objective of this study was to examine the day-to-day associations between partner support, pain catastrophizing and pain intensity in individuals with end-stage knee osteoarthritis. In this microlongitudinal cohort study, participants (N = 124) with end-stage knee osteoarthritis completed baseline measures of trait pain catastrophizing and negative affect. Participants also provided daily diary assessments of partner support, pain catastrophizing and pain intensity for a period of 7 days using a personal digital assistant. Multilevel analyses revealed that day-to-day fluctuations in pain catastrophizing were associated with pain intensity. Data from multilevel analyses indicated that the main effect of partner support was not significantly associated with pain intensity. Results also indicated the interactions between partner support and both trait and state pain catastrophizing were significant, suggesting that both trait and state pain catastrophizing moderated the relationship between daily partner support and pain intensity. That is, on days when participants experienced low levels of partner support, high catastrophizers reported higher levels of pain intensity than low catastrophizers. In the presence of higher levels of partner support, pain intensity did not differ between high and low catastrophizers. These results are consistent with the Communal Coping Model of pain catastrophizing, and highlight the interpersonal context within which pain catastrophizing impacts pain outcomes. These findings also suggest that future interventions designed to specifically target the dynamic between pain catastrophizing and partner support may improve pain outcomes in individuals with end-stage knee OA.

Peripheral nerve injuries, pain, and neuroplasticity

INTRODUCTION

Peripheral nerve injuries (PNIs) cause both structural and functional brain changes that may be associated with significant sensorimotor abnormalities and pain.

PURPOSE OF THE STUDY

The aim of this narrative review is to provide hand therapists an overview of PNI-induced neuroplasticity and to explain how the brain changes following PNI, repair, and during rehabilitation.

METHODS

Toward this goal, we review key aspects of neuroplasticity and neuroimaging and discuss sensory testing techniques used to study neuroplasticity in PNI patients.

RESULTS

We describe the specific brain changes that occur during the repair and recovery process of both traumatic (eg, transection) and nontraumatic (eg, compression) nerve injuries. We also explain how these changes contribute to common symptoms including hypoesthesia, hyperalgesia, cold sensitivity, and chronic neurogenic pain. In addition, we describe how maladaptive neuroplasticity as well as psychological and personality characteristics impacts treatment outcome.

DISCUSSION AND CONCLUSION

Greater understanding of the brain's contribution to symptoms in recovering PNI patients could help guide rehabilitation strategies and inform the development of novel techniques to counteract these maladaptive brain changes and ultimately improve outcomes.

Sedentary behaviour facilitates conditioned pain modulation in middle-aged and older adults with persistent musculoskeletal pain: a cross-sectional investigation

INTRODUCTION

Higher physical activity (PA) and lower sedentary behaviour (SB) levels have demonstrated beneficial effects on temporal summation (TS) and conditioned pain modulation (CPM) in healthy adults. This cross-sectional study investigated the relationships between PA and SB and TS/CPM responses in individuals with chronic musculoskeletal pain.

METHODS

Sixty-seven middle-aged and older adults with chronic musculoskeletal pain were recruited from the community. Questionnaires measuring demographics, pain, and psychological measures were completed. Physical activity/SB levels were measured using the International Physical Activity Questionnaire-short form and Sedentary Behaviour Questionnaire, respectively. Semmes monofilament was used to assess mechanical TS (MTS) at the most symptomatic (MTS-S) and a reference region (MTS-R); change in the pain scores (baseline-10th application) was used for analysis. Conditioned pain modulation procedure involved suprathreshold pressure pain threshold (PPT-pain4) administered before and after (CPM30sec, CPM60sec, and CPM90sec) conditioning stimulus (2 minutes; ∼12°C cold bath immersion). For analysis, PPT-pain4 (%) change scores were used.

RESULTS

PPT-pain4 (%) change scores at CPM30sec and CPM60sec demonstrated significant weak positive correlations with SB levels and weak negative correlations with PA measures. After adjusting for confounding variables, a significant positive association was found between SB (h/d) and PPT-pain4 (%) change scores at CPM30sec and CPM60sec. No significant associations between MTS and PA/SB measures.

CONCLUSION

Sedentariness is associated with higher pain inhibitory capacity in people with chronic musculoskeletal pain. The observed relationship may be characteristic of a protective (sedentary) behaviour to enhance pain modulatory mechanism. Prospective longitudinal studies using objective PA/SB measures are required to validate the observed relationship in a larger sample size.

Sensitivity to Physical Activity Predicts Daily Activity Among Pain-Free Older Adults

Objective

Prior research indicates that older adults with knee osteoarthritis have increased sensitivity to physical activity (SPA) and respond to physical activities of stable intensity with increases in pain. Whether SPA is present in healthy older adults without chronic pain and predicts functional outcomes remains relatively unexplored. The purpose of this study was to determine the degree of SPA in healthy older adults in response to a standardized walking task, and whether SPA was associated with temporal summation of pain, pain-related fear of movement, and functional outcomes.

Methods

Fifty-two older adults without chronic pain completed self-reported measures of activity-related pain and physical function, completed the Six-Minute Walk Test (6MWT), underwent quantitative sensory testing to measure temporal summation of heat pain, and wore an accelerometer for one week to measure physical activity behavior. Subjects rated overall bodily discomfort (0-100 scale) prior to and during each minute of the 6MWT. An SPA index was created by subtracting the initial bodily discomfort ratings from the peak ratings.

Results

Repeated-measures analysis of variance indicated that bodily discomfort significantly increased across the walking task, with approximately 60% of the sample experiencing SPA. Hierarchical regressions indicated that greater SPA was associated with fewer average steps per day and greater activity-related pain. Additionally, analyses revealed that temporal summation of pain and pain-related fear of movement significantly predicted the degree of SPA on the walking task.

Conclusions

These findings shed light on potential mechanisms underlying SPA in older adults and suggest that SPA might be a risk factor for reduced physical activity.

Dysfunctional Coping Mechanisms Contribute to Dry Eye Symptoms

Dysfunctional coping behaviors, such as catastrophizing, have been implicated in pain severity and chronicity across several pain disorders. However, the impact of dysfunctional coping has not been examined under the context of dry eye (DE). This study evaluates relationships between catastrophizing and measures of DE, including pain severity and pain-related daily interference. The population consisted of patients seen at Miami Veterans Affairs eye clinic between April 2016 and October 2017. Patients filled out standardized questionnaires assessing symptoms of DE and eye pain, non-ocular pain, mental health, coping behaviors (Pain Catastrophizing Scale, PCS), and pain-related daily interference as a perceived impact on quality of life (Multidimensional Pain Inventory, Interference Subscale, MPI-Interference), and all patients underwent an ocular surface examination. In total, 194 patients participated, with a mean age of 58.8 ± 9.6 years, the majority being male, non-Hispanic, and black. PCS (catastrophizing) was correlated with DE symptom severity, including Dry-Eye Questionnaire 5 (DEQ5; r = 0.41, p < 0.0005), Ocular Surface Disease Index (OSDI; r = 0.40, p < 0.0005), and neuropathic-like eye pain (Neuropathic Pain Symptom Inventory-Eye (NPSI-Eye; r = 0.48, p < 0.0005). Most tear metrics, on the other hand, did not correlate with PCS. Linear regressions showed that PCS, non-ocular pain intensity, and number of pain conditions were significant predictors of DEQ5 (overall DE symptoms), while PCS and non-ocular pain intensity were predictors of NPSI-Eye scores, as were insomnia scores and analgesic use. In a separate analysis, PCS and DE symptoms (OSDI) associated with pain-related interference (MPI-Interference) along with non-ocular pain intensity, post-traumatic stress disorder (PTSD), number of pain conditions, and non-Hispanic ethnicity. These findings suggest that catastrophizing is not significantly related to signs of DE, but is strongly associated to pain-related symptoms of DE and daily interference due to pain.

Pain and Distraction According to Sensory Modalities: Current Findings and Future Directions

BACKGROUND

This review discusses the findings in the literature on pain and distraction tasks according to their sensory modality. Distraction tasks have been shown to reduce (experimentally induced) acute pain and chronic pain. This can be influenced by nature and by the sensory modalities used in the distraction tasks. Yet the effect on reducing pain according to the sensory modality of the distraction task has received little attention.

METHODS

A bibliographic search was performed in different databases. The studies will be systematized according to the sensory modality in which the distraction task was applied.

RESULTS

The analyzed studies with auditory distractors showed a reduction of acute pain in adults. However, these are not effective at healthy children and in adults with chronic pain. Visual distractors showed promising results in acute pain in adults and children. Similarly, tactile and mixed distractors decreased acute pain in adults.

CONCLUSION

Distraction tasks by diverse sensory modalities have a positive effect on decreasing the perception of acute pain in adults. Future studies are necessary given the paucity of research on this topic, particularly with tactile distractors (there is only one study). Finally, the most rigorous methodology and the use of ecological contexts are encouraged in future research.

Non-invasive Motor Cortex Neuromodulation Reduces Secondary Hyperalgesia and Enhances Activation of the Descending Pain Modulatory Network

Central sensitization is a driving mechanism in many chronic pain patients, and manifests as hyperalgesia and allodynia beyond any apparent injury. Recent studies have demonstrated analgesic effects of motor cortex (M1) stimulation in several chronic pain disorders, yet its neural mechanisms remain uncertain. We evaluated whether anodal M1 transcranial direct current stimulation (tDCS) would mitigate central sensitization as measured by indices of secondary hyperalgesia. We used a capsaicin-heat pain model to elicit secondary mechanical hyperalgesia in 27 healthy subjects. In an assessor and subject-blind randomized, sham-controlled, crossover trial, anodal M1 tDCS decreased the intensity of pinprick hyperalgesia more than cathodal or sham tDCS. To elucidate the mechanism driving analgesia, subjects underwent fMRI of painful mechanical stimuli prior to and following induction of the pain model, after receiving M1 tDCS. We hypothesized that anodal M1 tDCS would enhance engagement of a descending pain modulatory (DPM) network in response to mechanical stimuli. Anodal tDCS normalized the effects of central sensitization on neurophysiological responses to mechanical pain in the medial prefrontal cortex, pregenual anterior cingulate cortex, and periaqueductal gray, important regions in the DPM network. Taken together, these results provide support for the hypothesis that anodal M1-tDCS reduces central sensitization-induced hyperalgesia through the DPM network in humans.