Prediction of chronic post-operative pain: Pre-operative DNIC testing identifies patients at risk

The Link between Endogenous Pain Modulation Changes and Clinical Improvement in Fibromyalgia Syndrome: A Meta-Regression Analysis

Conditioned pain modulation (CPM) and temporal summation (TS) tests can measure the ability to inhibit pain in fibromyalgia syndrome (FMS) patients and its level of pain sensitization, respectively. However, their clinical validity is still unclear. We studied the association between changes in the CPM and TS tests and the clinical improvement of FMS patients who received therapeutic intervention. We systematically searched for FMS randomized clinical trials with data on therapeutic interventions comparing clinical improvement (pain intensity and symptom severity reduction), CPM, and TS changes relative to control interventions. To study the relationship between TS/CPM and clinical measures, we performed a meta-regression analysis to calculate odds ratios. We included nine studies (484 participants). We found no significant changes in TS or CPM by studying all the interventions together. Our findings show that this lack of difference is likely because pharmacological and non-pharmacological interventions resulted in contrary effects. Non-pharmacological interventions, such as non-invasive neuromodulation, showed the largest effects normalizing CPM/TS. Meta-regression was significantly associated with pain reduction and symptom severity improvement with normalization of TS and CPM. We demonstrate an association between clinical improvement and TS/CPM normalization in FMS patients. Thus, the TS and CPM tests could be surrogate biomarkers in FMS management. Recovering defective endogenous pain modulation mechanisms by targeted non-pharmacological interventions may help establish long-term clinical recovery in FMS patients.

Effect of Transcutaneous Auricular Vagus Nerve Stimulation on Conditioned Pain Modulation in Trigeminal Neuralgia Patients

INTRODUCTION

Conditioned pain modulation (CPM) is a quantitative estimation of the capacity for endogenous pain modulation. Reduced CPM enables chronic painful event development or exacerbates pre-existing pain symptoms. Emerging reports indicate that patients with trigeminal neuralgia (TN) have dysregulated endogenous pain modulation. Transauricular vagus nerve stimulation (taVNS) is known to alleviate both acute and chronic pain symptoms. Its role in modulation or management of TN remains unknown. Here, we evaluated the taVNS efficacy in modulating CPM among TN patients. Conclusions from this investigation may facilitate establishment of novel non-invasive adjunctive approaches to treating TN patients.

METHODS

All research work was conducted at the First Affiliated Hospital of the University of Science and Technology of China (Anhui Provincial Hospital). In all, we recruited 62 study participants, 31 TN patients and 31 healthy volunteers, for a 2-day experimental test. At the beginning of the experiment (Day 1), all subjects received 30 min of active taVNS. On Day 2, they received sham taVNS with the same duration and intensity. Meanwhile, technicians documented participant pressure pain thresholds (PPT) and CPM values at baseline, and at 15 and 30 min post-active or sham taVNS.

RESULTS

A 30-min active taVNS exposure substantially elevated the PPT and CPM effect (P < 0.05) among TN patients, and we also observed a notable rise in the PPT and CPM effect (P < 0.05) among healthy controls. Additionally, there were no serious adverse events from the administered treatment.

CONCLUSION

Exposure to 30 min of active taVNS strongly augmented the CPM effect and elevated the PPT among TN patients and healthy controls. These effects were not observed with sham stimulation. Despite the limitations inherent to survey studies, such as duration and compliance biases, we consider that taVNS is a promising, safe, and cost-effective therapy. In future investigations, we recommend assessment of long-term taVNS application and its effects on CPM and clinical pain.

TRIAL REGISTRATION

ChiCTR2300078673 ( www.Chictr.org.cn ).

Preoperative pain sensitivity and its correlation with postoperative acute and chronic pain: a systematic review and meta-analysis

BACKGROUND

Preoperative pain sensitivity (PPS) can be associated with postsurgical pain. However, estimates of this association are scarce. Confirming this correlation is essential to identifying patients at high risk for severe postoperative pain and for developing analgesic strategy. This systematic review and meta-analysis summarises PPS and assessed its correlation with postoperative pain.

METHODS

PubMed, Scopus, Cochrane Library, and PsycINFO were searched up to October 1, 2023, for studies reporting the association between PPS and postsurgical pain. Two authors abstracted estimates of the effect of each method independently. A random-effects model was used to combine data. Subgroup analyses were performed to investigate the effect of pain types and surgical procedures on outcomes.

RESULTS

A total of 70 prospective observational studies were included. A meta-analysis of 50 studies was performed. Postoperative pain was negatively associated with pressure pain threshold (PPT; r=-0.15, 95% confidence interval [CI] -0.23 to -0.07]) and electrical pain threshold (EPT; r=-0.28, 95% CI -0.42 to -0.14), but positively correlated with temporal summation of pain (TSP; r=0.21, 95% CI 0.12-0.30) and Pain Sensitivity Questionnaire (PSQ; r=0.25, 95% CI 0.13-0.37). Subgroup analysis showed that only TSP was associated with acute and chronic postoperative pain, whereas PPT, EPT, and PSQ were only associated with acute pain. A multilevel (three-level) meta-analysis showed that PSQ was not associated with postoperative pain.

CONCLUSIONS

Lower PPT and EPT, and higher TSP are associated with acute postoperative pain while only TSP is associated with chronic postoperative pain. Patients with abnormal preoperative pain sensitivity should be identified by clinicians to adopt early interventions for effective analgesia.

SYSTEMATIC REVIEW PROTOCOL

PROSPERO (CRD42023465727).

Age-related differences in functional connectivity associated with pain modulation

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

Biobehavioral Predictors of Pain Intensity, Pain Interference, and Chronic Pain Episodes: A Prospective Cohort Study of African-American Adults

Racial disparities in pain experiences are well-established, with African-American (AA) adults reporting higher rates of daily pain, increased pain severity, and greater pain-related interference compared to non-Hispanic Whites. However, the biobehavioral factors that predict the transition to chronic pain among AA adults are not well understood. This prospective cohort study provided a unique opportunity to evaluate predictors of chronic pain onset among 130 AA adults (81 women), ages 18 to 44, who did not report chronic pain at their baseline assessment and subsequently completed follow-up assessments at 6- and 12-months. Outcome measures included pain intensity, pain-related interference, and chronic pain status. Comprehensive assessments of sociodemographic and biobehavioral factors were used to evaluate demographics, socioeconomic status, stress exposure, psychosocial factors, prolonged hypothalamic-pituitary-adrenal secretion, and quantitative sensory testing responses. At baseline, 30 adults (23.1%) reported a history of prior chronic pain. Over the 12-month follow-up period, 13 adults (10.0%) developed a new chronic pain episode, and 18 adults (13.8%) developed a recurrent chronic pain episode. Whereas socioeconomic status measures (ie, annual income, education) predicted changes in pain intensity over the follow-up period, quantitative sensory testing measures (ie, pain threshold, temporal summation of pain) predicted changes in pain interference. A history of chronic pain and higher depressive symptoms at baseline independently predicted the onset of a new chronic pain episode. The present findings highlight distinct subsets of biobehavioral factors that are differentially associated with trajectories of pain intensity, pain-related interference, and onset of chronic pain episodes in AA adults. PERSPECTIVE: This prospective study sought to advance understanding of biobehavioral factors that predicted pain outcomes over a 12-month follow-up period among AA adults without chronic pain at their initial assessment. Findings revealed distinct subsets of factors that were differentially associated with pain intensity, pain-related interference, and onset of chronic pain episodes.

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

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

Posttraumatic headache: pain related evoked potentials (PREP) and conditioned pain modulation (CPM) to assess the pain modulatory function

Posttraumatic headache (PTH) is common following traumatic brain injury and impacts quality of life. We investigated descending pain modulation as one possible mechanism for PTH and correlated it to clinical measures. Pain-related evoked potentials (PREP) were recorded in 26 PTH-patients and 20 controls after electrical stimulation at the right hand and forehead with concentric surface electrodes. Conditioned pain modulation (CPM) was assessed using painful cutaneous electric stimulation (PCES) on the right hand as test stimulus and immersion of the left hand into 10 °C-cold water bath as conditioning stimulus based on changes in pain intensity and in amplitudes of PCES-evoked potentials. All participants completed questionnaires assessing depression, anxiety, and pain catastrophising. PTH-patients reported significantly higher pain ratings during PREP-recording in both areas despite similar stimulus intensity at pain threshold. N1P1-amplitudes during PREP and CPM-assessment were lower in patients in both areas, but statistically significant only on the hand. Both, PREP-N1-latencies and CPM-effects (based on the N1P1-amplitudes and pain ratings) were similar in both groups. Patients showed significantly higher ratings for anxiety and depression, which did not correlate with the CPM-effect. Our results indicate generalized hyperalgesia for electrical stimuli in both hand and face in PTH. The lacking correlation between pain ratings and EEG parameters indicates different mechanisms of pain perception and nociception.

Could Relationship-Based Learnt Beliefs and Expectations Contribute to Physiological Vulnerability of Chronic Pain? Making a Case to Consider Attachment in Pain Research

Pain is an interpersonal and inherently social experience. Pain perception and administration of medical treatment all occur in a particular environmental and social context. Early environmental influences and early learning experiences and interactions condition the body's response to different threats (like pain), ultimately shaping the underlying neurophysiology. These early interactions and experiences also determine what situations are perceived as threatening, as well as our belief in our own ability to self-manage, and our belief in others to offer support, during perceived threats. These beliefs intrinsically drive the combination of behaviors that emerge in response to perceived threats, including pain. Such behaviors can be categorized into attachment styles. In this interdisciplinary review, we synthesize and summarize evidence from the neurobiological, psychobiological, psychosocial, and psychobehavioral fields, to describe how these beliefs are embedded in the brain's prediction models to generate a series of expectations/perceptions around the level of safety/threat in different contexts. As such, these beliefs may predict how one experiences and responds to pain, with potentially significant implications for the development and management of chronic pain. Little attention has been directed to the effect of adult attachment style on pain in research studies and in the clinical setting. Using interdisciplinary evidence, we argue why we think this interaction merits further consideration and research. PERSPECTIVE: This review explores the influence of attachment styles on pain perception, suggesting a link between social connections and chronic pain development. It aligns with recent calls to emphasize the social context in pain research and advocates for increased focus on adult attachment styles in research and clinical practice.

Examination of Conditioned Pain Modulation in Myofascial TMD With Consideration of Temporal Summation

Research on myofascial temporomandibular disorder (mTMD) has often focused on potential dysfunction in endogenous pain modulation. However, studies on the specific inhibitory and facilitatory components of endogenous pain modulation using conditioned pain modulation (CPM) and temporal summation of second pain (TSSP) have shown mixed results. This study aimed to 1) examine whether women with mTMD demonstrated efficient CPM compared to controls; 2) explore the association between independent measures of CPM and TSSP in women with mTMD relative to controls; and 3) determine whether resulting modulatory profiles differentially predicted pain intensity among cases. All participants were recruited from dental clinics. Cases were women who met the research diagnostic criteria for mTMD. Controls did not have facial pain on exam and were selected to be sociodemographically similar to cases. CPM and TSSP were assessed via independent psychophysical protocols. CPM was examined in linear mixed models predicting pain thresholds adjusted for age and stratified by TSSP. Mean CPM was estimated at a 2.2 (SD = 2.8) degree increase in pain thresholds (P ≤ .001), similar in cases and controls (P = .67). CPM was less efficient in cases with enhanced TSSP (P = .031), but not in controls. Although the double-pronociceptive profile of both low CPM and high TSSP trended higher among cases than controls, it did not predict higher levels of pain intensity among cases. This study does not support deficient inhibitory endogenous pain modulation in mTMD, but results suggest that inhibitory and facilitatory pain modulation should be examined concomitantly in the study of endogenous pain modulation. PERSPECTIVE: This manuscript presents a novel examination of inhibitory modulation by the level of facilitatory modulation in mTMD. The findings and approach may prove useful for mechanistic researchers studying endogenous pain modulation and clinical researchers seeking to jointly examine conditioned pain modulation and temporal summation in future research on chronic pain.

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

BACKGROUND

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

OBJECTIVE

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

DESIGN

Prospective cohort study.

METHOD

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

RESULTS

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

CONCLUSIONS

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

Pain trajectories and neuropathic pain symptoms following lung cancer surgery: A prospective cohort study

BACKGROUND

Persistent postsurgical pain (PPSP) after lung cancer surgery is common and current definitions are based on evaluations at a single time point after surgery. Pain intensity and symptoms may however fluctuate and change over time, and be impacted by multiple and shifting factors. Studies of postoperative recovery patterns and transition from acute to chronic pain are needed for further investigation of preventive measures and treatments to modify unfavourable recovery paths.

METHODS

In this explorative study, 85 patients undergoing surgery due to either presumptive or confirmed lung cancer reported pain intensities bi-monthly for 12 months. Pain trajectories during recovery were investigated, using group-based trajectory modelling. Associations with possible risk factors for PPSP, including clinical variables and anxiety and depression score (HADS), were also explored.

RESULTS

A trajectory model containing three 12-month pain recovery groups was computed. One group without PPSP fully recovered (50%) within two to three months. Another group with mild-intensity PPSP followed a protracted recovery trajectory (37%), while incomplete recovery was observed in the last group (13%). Acute postoperative pain and younger age were associated with a less favourable recovery trajectory. More neuropathic pain symptoms were observed in patients with incomplete recovery.

CONCLUSIONS

Three clinically relevant recovery trajectories were identified, based on comprehensive pain tracking. Higher acute postoperative pain intensity was associated with an unfavourable pain recovery trajectory.

SIGNIFICANCE STATEMENT

Understanding the transition from acute to chronic postoperative pain and identifying preoperative risk factors is essential for the development of targeted treatments and the implementation of preventive measures. This study (1) identified distinct recovery trajectories based on frequent pain assessment follow-ups for 12 months after surgery and (2) evaluated risk factors for unfavourable postoperative pain recovery paths. Findings suggest that early higher postoperative pain intensity is associated with an unfavourable long-term recovery path.

Sex differences in visceral sensitivity and brain activity in a rat model of comorbid pain: a longitudinal study

ABSTRACT

Temporomandibular disorder (TMD) and irritable bowel syndrome (IBS) are 2 chronic overlapping pain conditions (COPCs) that present with significant comorbidity. Both conditions are more prevalent in women and are exacerbated by stress. While peripheral mechanisms might contribute to pain hypersensitivity for each individual condition, mechanisms underlying the comorbidity are poorly understood, complicating pain management when multiple conditions are involved. In this study, longitudinal behavioral and functional MRI-based brain changes have been identified in an animal model of TMD-like pain (masseter muscle inflammation followed by stress) that induces de novo IBS-like comorbid visceral pain hypersensitivity in rats. In particular, data indicate that increased activity in the insula and regions of the reward and limbic systems are associated with more pronounced and longer-lasting visceral pain behaviors in female rats, while the faster pain resolution in male rats may be due to increased activity in descending pain inhibitory pathways. These findings suggest the critical role of brain mechanisms in chronic pain conditions and that sex may be a risk factor of developing COPCs.

Sex differences in descending control of nociception (DCN) responses after chronic orofacial pain induction in rats and the contribution of kappa opioid receptors

Descending control of nociception (DCN), a measure of efficiency of descending pain inhibition, can be assessed in animals by the combined application of test and conditioning noxious stimuli. Evidence from pre-clinical and clinical studies indicates that this mechanism of pain control may differ between sexes and might be impaired in many chronic pain states. However, little is known about sex differences in DCN efficiency in models of acute and chronic orofacial pain. Herein, we first evaluated DCN responses in male and female rats by the applying formalin into the upper lip or capsaicin into the forepaw as the conditioning stimulus, followed by mechanical stimulation (Randall-Selitto) of the hind paw as the test stimulus. The same protocol (i.e., capsaicin in the forepaw followed by mechanical stimulation of the hind paw) was evaluated in male and female rats on day 3 after intraoral incision and on day 15 and 30 after chronic constriction injury of the infraorbital nerve (CCI-ION). Additionally, we assessed the effect of the kappa opioid receptor (KOR) antagonist Norbinaltorphimine (nor-BNI) on DCN responses of female nerve-injured rats. This study shows that naïve female rats exhibit less efficient DCN compared to males. Postoperative pain did not alter DCN responses in female and male rats, but CCI-ION induced loss of DCN responses in females but not in males. Systemic pretreatment with nor-BNI prevented the loss of DCN induced by CCI-ION in female rats. The results reveal sex differences in DCN responses and female-specific impairment of DCN following chronic orofacial pain. Moreover, the findings suggest that, at least for females, blocking KOR could be a promising therapeutic approach to prevent maladaptive changes in chronic orofacial pain.

The Predictive Value of Cold Pack Test for Pain After Third Molar Surgery

BACKGROUND

Early identification of patients who are prone to postoperative pain may provide individualization of postoperative analgesia strategies.

PURPOSE

The aim of the study was to investigate whether the cold pack test is associated with postoperative pain levels after mandibular third molar surgery.

STUDY DESIGN, SETTING, SAMPLE

This prospective cohort study included healthy male patients admitted to Department of Oral and Maxillofacial Surgery of a tertiary health-care center between June 2022 and December 2022 and scheduled for lower third molar extraction. Those who had used any analgesic within the past 10 days or had a history of intolerance/allergy to analgesics were excluded.

PREDICTOR VARIABLE

The primary predictor variable was pain tolerance, measured using the endurance test score. Subjects were grouped into two categories, low tolerance test score (withdrew the hand from the cold pack in <240 seconds) and high tolerance test score (maintained the hand on the cold pack for 240 seconds).

MAIN OUTCOME VARIABLES

The primary outcome variable was pain measured by the patients from 0 to 10 with the visual analog scale, and the secondary outcome variables were the amount of ibuprofen and paracetamol consumed in the postoperative period. Pain measurements and ibuprofen consumption were recorded at 0-2, 8, 16, 24, 32, 40, 48, 56, 64, 72, 80, 88, and 96 hours (0-2 interval of the first 2 hours immediately after surgery).

COVARIATES

Age, classification and position of mandibular third molar were utilized as covariates.

ANALYSES

The relationship between pain tolerance and postoperative pain was analyzed using the Mann-Whitney U test and the Fisher exact test. Statistical analysis was performed using the SPSS version 28.0 software.

RESULTS

A total of 30 male patients with a mean age of 22.5 ± 4.8 years were included in our study. In the group with low pain tolerance, the pain scores at the first 2 hours, 32, and 48 hours after the operation (4.55 ± 3.59, 2.91 ± 2.59, 2.91 ± 2.43, respectively) were found to be significantly higher than the group with high pain tolerance (2.00 ± 2.67, 0.95 ± 1.68, 0.95 ± 1.39, respectively) (P < .05). In the first 2 hours after the operation, the amount of ibuprofen consumed was also significantly higher in the group with low pain tolerance compared to the other group, and 81.8% of this group felt the need to consume ibuprofen (P < .05).

CONCLUSIONS AND RELEVANCE

The cold pack test, a more practical version of quantitative sensory testing, is useful in identifying male patients at risk of developing greater pain after third molar surgery. It can be helpful to provide effective analgesia in male patients with different pain tolerance thresholds.

Opposing Effects on Descending Control of Nociception by µ and κ Opioid Receptors in the Anterior Cingulate Cortex

BACKGROUND

The efficiency of descending pain modulation, commonly assessed with the conditioned pain modulation procedure, is diminished in patients with chronic pain. The authors hypothesized that the efficiency of pain modulation is controlled by cortical opioid circuits.

METHODS

This study evaluated the effects of µ opioid receptor activation in the anterior cingulate cortex on descending control of nociception, a preclinical correlate of conditioned pain modulation, in male Sprague-Dawley rats with spinal nerve ligation-induced chronic pain or in sham-operated controls. Additionally, the study explored the consequences of respective activation or inhibition of κ opioid receptor in the anterior cingulate cortex of naive rats or animals with neuropathic pain. Descending control of nociception was measured as the hind paw withdrawal response to noxious pressure (test stimulus) in the absence or presence of capsaicin injection in the forepaw (conditioning stimulus).

RESULTS

Descending control of nociception was diminished in the ipsilateral, but not contralateral, hind paw of rats with spinal nerve ligation. Bilateral administration of morphine in the anterior cingulate cortex had no effect in shams but restored diminished descending control of nociception without altering hypersensitivity in rats with neuropathic pain. Bilateral anterior cingulate cortex microinjection of κ opioid receptor antagonists, including nor-binaltorphimine and navacaprant, also re-established descending control of nociception in rats with neuropathic pain without altering hypersensitivity and with no effect in shams. Conversely, bilateral injection of a κ opioid receptor agonist, U69,593, in the anterior cingulate cortex of naive rats inhibited descending control of nociception without altering withdrawal thresholds.

CONCLUSIONS

Anterior cingulate cortex κ opioid receptor activation therefore diminishes descending control of nociception both in naive animals and as an adaptive response to chronic pain, likely by enhancing net descending facilitation. Descending control of nociception can be restored by activation of μ opioid receptors in the anterior cingulate cortex, but also by κ opioid receptor antagonists, providing a nonaddictive alternative to opioid analgesics. Navacaprant is now in advanced clinical trials.

EDITOR’S PERSPECTIVE

Comparison of Quality of Recovery between Modified Thoracoabdominal Nerves Block through Perichondrial Approach versus Oblique Subcostal Transversus Abdominis Plane Block in Patients Undergoing Total Laparoscopic Hysterectomy: A Pilot Randomized Controlled Trial

Modified thoracoabdominal nerves block through a perichondrial approach (M-TAPA) provides a wide analgesic range. Herein, we examined the quality of recovery (QoR) of M-TAPA for total laparoscopic hysterectomy (TLH) compared with oblique subcostal transversus abdominis plane block (OSTAPB) and measured plasma levobupivacaine concentrations (PClevo). Forty female patients undergoing TLH were randomized to each group. Nerve blocks were performed bilaterally with 25 mL of 0.25% levobupivacaine administered per side. The primary outcome was changes in QoR-15 scores on postoperative days (POD) 1 and 2 from the preoperative baseline. The main secondary outcomes were PClevo at 15, 30, 45, 60, and 120 min after performing nerve block. Group differences (M-TAPA-OSTAPB) in mean changes from baseline in QoR-15 scores on POD 1 and 2 were -11.3 (95% confidence interval (CI), -24.9 to 2.4, p = 0.104; standard deviation (SD), 22.8) and -7.0 (95% CI, -20.5 to 6.6, p = 0.307; SD, 18.7), respectively. Changes in PClevo were similar in both groups. The post hoc analysis using Bayesian statistics revealed that posterior probabilities of M-TAPA being clinically more effective than OSTAPB were up to 22.4 and 24.4% for POD 1 and 2, respectively. In conclusion, M-TAPA may not be superior to OSTAPB for TLH.

Temporal Relations Between Pain Catastrophizing and Adverse Health and Mental Health Outcomes After Whiplash Injury

OBJECTIVES

Pain catastrophizing has been shown to be a prognostic indicator for pain severity and the co-occurrence of mental health conditions such as depression and post-traumatic stress disorder after whiplash injury. However, the pattern of available findings is limited in its implications for the possible "antecedent" or "causal" role of pain catastrophizing. The purpose of the present study was to examine the temporal relations between pain catastrophizing, pain severity, depressive symptoms, and post-traumatic stress symptoms (PTSS) in individuals receiving treatment for whiplash injury.

MATERIALS AND METHODS

The sample consisted of 388 individuals enrolled in a multidisciplinary program for whiplash injury. Participants completed self-report measures of pain catastrophizing, pain severity, depressive symptoms, and PTSS at the time of admission, mid-treatment (4 week), and treatment completion (7 week). A cross-lagged panel analysis was used to examine the temporal relations between pain catastrophizing, pain severity, depressive symptoms, and PTSS across all 3 timepoints.

RESULTS

Model fit was acceptable after the inclusion of modification indices. Pain catastrophizing at the time of admission predicted all other variables at 4 weeks. Pain catastrophizing at 4 weeks also predicted all other variables at 7 weeks. In addition, some bidirectional relations were present, particularly for variables assessed at week 4 and week 7.

DISCUSSION

Findings support the view that pain catastrophizing might play a transdiagnostic role in the onset and maintenance of health and mental health conditions. The findings call for greater emphasis on the development of treatment techniques that target pain catastrophizing in intervention programs for whiplash injury.

Sex moderates the association between quantitative sensory testing and acute and chronic pain after total knee/hip arthroplasty

OBJECTIVES

Acute postsurgical pain (APSP) may persist over time and become chronic. Research on predictors for APSP and chronic postsurgical pain (CPSP) has produced inconsistent results. This observational study aimed to analyze psychological and psychophysical variables associated with APSP and CPSP after total knee or hip arthroplasty, and to explore the role of sex.

METHODS

Assessments were conducted before surgery, 48 h, and 3 months postsurgery, including questionnaires (sociodemographic, pain related, and psychological) and quantitative sensory testing (QST). Hierarchical linear regression models analyzed potential predictors of APSP and CPSP, and moderation analyses evaluated the role of sex.

RESULTS

The study included 63 participants undergoing total knee (34, 54%) or hip (29, 46%) arthroplasty. Thirty-one (49.2%) were female and 32 (50.8%) were male. APSP (48 h) was associated with impaired conditioned pain modulation (CPM) (β = 0.301, p = 0.019). CPSP (3 months) was associated with being female (β = 0.282, p = 0.029), longer presurgical pain duration (β = 0.353, p = 0.006), knee arthroplasty (β = -0.312, p = 0.015), higher APSP intensity (β = 373, p = 0.004), and impaired CPM (β = 0.126, p = 0.004). In multivariate analysis, these clinical variables were significant predictors of CPSP, unlike sex, and CPM (adj. R 2 = 0.349). Moderation analyses showed that wind-up ratio (WUR) was a significant predictor of APSP in men (WUR × sex: b = -1.373, p = 0.046) and CPM was a significant predictor of CPSP in women (CPM × sex: b = 1.625, p = 0.016).

CONCLUSIONS

Specific QST parameters could identify patients at risk for high-intensity APSP and CPSP, with sex as a moderator. This has important clinical implications for patient care, paving the way for developing tailored preventive pain management strategies.

Postoperative pain: What can we do?

Chronic postoperative pain (CPOP) is a potentially devastating consequence of a surgical procedure. It leads to increased medical costs, painful, and stress experience to the patients. After a surgical decompression performed in a patient with a non-traumatic compartment syndrome, a muscle biopsy confirmed McArdle disease, and after surgery, severe pain of neuropathic characteristics developed in the arm decompressed. Advanced techniques up to neuromedullary stimulation failed to improve the clinical status, after which repeated treatment with capsaicin patch ameliorated the patient's condition. This case report illustrates the need for a high index of suspicion for metabolic diseases in patients who present compartment syndrome without prior history of trauma and also the challenges in treating neuropathic pain after surgery.

Clinical Diagnosis and Treatment of Chronic Pain

More than 600 million people globally are estimated to be living with chronic pain. It is one of the most common complaints seen in an outpatient setting, with over half of patients complaining of pain during a visit. Failure to properly diagnose and manage chronic pain is associated with substantial morbidity and mortality, especially when opioids are involved. Furthermore, it is a tremendous financial strain on the healthcare system, as over USD 100 billion is spent yearly in the United States on healthcare costs related to pain management and opioids. This exceeds the costs of diabetes, heart disease, and cancer-related care combined. Being able to properly diagnose, manage, and treat chronic pain conditions can substantially lower morbidity, mortality, and healthcare costs in the United States. This review will outline the current definitions, biopsychosocial model, subclassifications, somatosensory assessments, imaging, clinical prediction models, and treatment modalities associated with chronic pain.

Effects of Transcranial Direct Current Stimulation (t-DCS) of the Cerebellum on Pain Perception and Endogenous Pain Modulation: a Randomized, Monocentric, Double-Blind, Sham-Controlled Crossover Study

Accumulating evidence demonstrates a role of the cerebellum in nociception. Some studies suggest that this is mediated via endogenous pain modulation. Here, we used t-DCS to test the effects of modulation of cerebellar function on nociception and endogenous pain modulation. Anodal, cathodal, and sham cerebellar t-DCS were investigated in a cross-over design in 21 healthy subjects. The nociceptive flexor (RIII) reflex, conditioning pain modulation (CPM), and offset analgesia (OA) paradigms were used to assess endogenous pain modulation. Somatosensory evoked potentials (SEPs) and pain ratings were used to assess supraspinal nociception and pain perception, respectively. No significant t-DCS effects were detected when including all t-DCS types and time points (baseline, 0, 30, 60 min post t-DCS) in the analysis. Exploratory analysis revealed an increased RIII reflex size immediately after cathodal t-DCS (compared to sham, P = 0.046, η2p = 0.184), in parallel with a trend for a decrease in electrical pain thresholds (P = 0.094, η2p = 0.134), and increased N120 SEP amplitudes 30 min after cathodal compared to anodal t-DCS (P = 0.007, η2p = 0.374). OA was increased after anodal compared to sham stimulation (P = 0.023, η2p = 0.232). Exploratory results suggested that cathodal (inhibitory) cerebellar t-DCS increased pain perception and reduced endogenous pain inhibition while anodal (excitatory) t-DCS increased endogenous pain inhibition. Results are principally compatible with activation of endogenous pain inhibition by cerebellar excitation. However, maybe due to limited t-DCS skull penetration, effects were small and unlikely to be clinically significant.

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.

Longitudinal changes in human supraspinal processing after RIII-feedback training to improve descending pain inhibition

The human body has the ability to influence its sensation of pain by modifying the transfer of nociceptive information at the spinal level. This modulation, known as descending pain inhibition, is known to originate supraspinally and can be activated by a variety of ways including positive mental imagery. However, its exact mechanisms remain unknown. We investigated, using a longitudinal fMRI design, the brain activity leading up and in response to painful electrical stimulation when applying positive mental imagery before and after undergoing a previously established RIII-feedback paradigm. Time course analysis of the time preceding painful stimulation shows increased haemodynamic activity during the application of the strategy in the PFC, ACC, insula, thalamus, and hypothalamus. Time course analysis of the reaction to painful stimulation shows decreased reaction post-training in brainstem and thalamus, as well as the insula and dorsolateral PFC. Our work suggests that feedback training increases activity in areas involved in pain inhibition, while simultaneously decreasing the reaction to painful stimuli in brain areas related to pain processing, which points to an activation of decreased spinal nociception. We further suggest that the insula and the thalamus may play a more important role in pain modulation than previously assumed.

Can Ultrasound-Guided Continuous Paravertebral Block Reduce the Incidence of Chronic Postsurgical Pain in Patients with Thoracoscopic Lung Cancer Surgery? A Randomized Controlled Trial

Background

Thoracoscopic lung cancer surgery is accompanied by severe pain. Both continuous paravertebral block (CPVB) and continuous wound infiltration (CWI) are widely used for perioperative analgesia in thoracoscopic surgery. However, the effects of these different methods on chronic postsurgical pain (CPSP) are still unknown. Patients and Methods. This prospective randomized controlled trial assessed the eligibility of 113 patients. Ninety-seven patients who met the inclusion criteria were randomly divided into a CPVB group and a CWI group, and 80 patients were analyzed in the final study. The primary outcome measures were the incidence and intensity of chronic postsurgical pain (CPSP) at 3, 6, and 9 months after surgery. The secondary outcome measures were the numerical rating scale (NRS) score of rest and activity at 12, 18, and 24 hours and on the 2nd, 3rd, and 7th days postoperatively; the Barthel Activities of Daily Living (ADL) score of activity levels on the 1st, 2nd, 3rd, and 7th days postoperatively; and the long-term quality of the life score at 3, 6, and 9 months postoperatively.

Results

The incidence of chronic postsurgical pain in the CWI group was significantly higher than that in the CPVB group at 3, 6, and 9 months after surgery (all P < 0.05). The intensity of chronic postsurgical pain was significantly decreased in the CPVB group at 3, 6, and 9 months after surgery (P < 0.05). NRS-R and NRS-A scores were significantly decreased in the CPVB group within the first week after thoracoscopic surgery (P < 0.001). ADL scores were increased in the CPVB group within 3 days postoperatively. However, there were no differences in the ADL score on the 7th postoperative day or the long-term quality of the life score at 3, 6, and 9 months postoperatively.

Conclusion

Continuous ultrasound-guided paravertebral block reduced the intensity of acute pain within 7 days postoperatively and reduced the incidence of chronic pain at 3, 6, and 9 months after surgery, but there was no significant advantage in long-term quality of life. This trial is registered with ChiCTR2000038505.

Preoperatively assessed offset analgesia predicts acute postoperative pain following orthognathic surgery

OBJECTIVES

High intensity and longer duration of acute postoperative pain are generally associated with a higher risk of developing chronic postoperative pain. Therefore, it is important to identify the preoperative predictors for acute postoperative pain. Preoperative evaluation of offset analgesia (OA) and the Pain Catastrophising Scale (PCS) may be potential predictors for acute postoperative pain. This study aimed to investigate the relationship between preoperative OA, PCS, and acute postoperative pain following orthognathic surgery.

METHODS

Thirty patients (19 females) scheduled to undergo orthognathic surgery were included in this study. OA and PCS were evaluated preoperatively, and the patients reported their postoperative pain intensity using the visual analogue scale [0-100 mm] until it reached zero (number of days with pain). OA was induced on the dominant forearm via three consecutive painful heat pulses delivered for 5 s (T1=46 °C), 5 s (T2=47 °C), and 20 s (T3=46 °C). Subsequently, the associations between OA, PCS, and the number of days with pain were analysed.

RESULTS

The median duration of postoperative pain was 10.3 days. Multiple linear regression analysis showed a significant (p=0.0019) predictive value of OA (p=0.008) for the number of days with pain. The PCS-magnification component was positively correlated with the number of days with pain (R=0.369, p=0.045), with no predictive values of PCS-total and PCS-subscale scores observed.

CONCLUSIONS

Preoperative evaluation of OA may be a new individualised, predictive tool for the number of days with acute postoperative pain following orthognathic surgery; hence, a possible biomarker for the patient's vulnerability to developing chronic postoperative pain.

ETHICAL COMMITTEE NUMBER

The study was approved by the Ethics Committee of Meikai University (A1624, A2113).

TRIAL REGISTRY NUMBER

This study was registered in the University Hospital Medical Information Network Clinical Trials Registry (UMIN-CTR) Clinical Trial (Unique ID: UMIN000026719, UMIN000046957).

Chronic pain after posterolateral and axillary approaches to lung surgery: a monocentric observational study

PURPOSE

Post-thoracotomy pain syndrome (PTPS) and chronic postsurgical neuropathic pain (CPNP) were evaluated 4 months after thoracic surgery whether the approach was a posterolateral (PL) incision or the less invasive axillary (AX) one.

METHODS

Patients, 79 in each group, undergoing a thoracotomy between July 2014 and November 2015 were analyzed 4 months after surgery in this prospective monocentric cohort study.

RESULTS

More PL patients suffered PTPS (60.8% vs. 40.5%; p = 0.017) but CPNP was equally present (45.8% and 46.9% in the PL and AX groups). Patients with PTPS have more limited daily activities (p < 0.001) but a similar psychological disability (i.e., catastrophism). Patients with CPNP have an even greater limitation of daily activities (p = 0.007) and more catastrophism (p = 0.0002). Intensity of pain during mobilization of the homolateral shoulder at postoperative day 6 (OR = 1.40, CI 95% [1.13-1.75], p = 0.002); age (OR = 0.97 [0.94-1.00], p = 0.022), and presence of pain before surgery (OR = 2.22 [1.00-4.92], p = 0.049) are related to the occurrence of PTPS; while, height of hypoesthesia area on the breast line measured 6 days after surgery is the only factor related to that of CPNP (OR = 1.14 [1.01-1.30], p = 0.036).

CONCLUSION

Minimally invasive surgery was associated with less frequent PTPS, but with equal risk of CPNP. Pain before surgery and its postoperative intensity are associated with PTPS. This must lead to a more aggressive care of pain patients before surgery and of a better management of postoperative pain. CPNP can be forecasted according to the early postoperative height of hypoesthesia area on the breast line.

Descending Control of Nociception Poorly Predicts the Development of Persistent Postsurgical Pain-like Behavior in Consomic Dahl S Rat Strains

BACKGROUND

Chronic postsurgical pain is a poorly recognized outcome of surgery where patients experience pain long after healing from the surgical insult. Descending control of nociception, a phenomenon whereby application of a strong nociceptive stimulus to one part of the body of animals inhibits pain in remote body regions, offers one strategy to identify a propensity to develop chronic postsurgical pain-like behavior. Here, consomic rat panel was used to test the hypothesis that pain persistence is mechanistically linked to ineffective descending control of nociception.

METHODS

Male and female Brown Norway, Dahl S, and eight consomic strains (SS-xBN) were used to determine the presence of chronic postsurgical pain-like behaviors by using paw-withdrawal threshold evaluation (von Frey method) in the area adjacent to a hind paw plantar incision. Descending control of nociception was assessed by measuring hind paw-withdrawal thresholds (Randall-Selitto method) after capsaicin (125 µg) injection into a forepaw. Consomic rats were developed by introgressing individual Brown Norway chromosomes on the Dahl S rat genetic background, as Dahl S rats lack preoperative descending control of nociception.

RESULTS

Substitution of several chromosomes from the "pain-resistant" Brown Norway to the "pain-prone" Dahl S/Medical College of Wisconsin reduced mechanical nociceptive sensitivity and increased endogenous pain modulation capacity by differing degrees. Statistical modeling of these data revealed that descending control of nociception is a poor general predictor of the propensity to develop chronic postsurgical pain-like behavior (poor fit for model 1). However, a significant strain-by-descending control of nociception interaction was revealed (model 3, -2*log likelihood; 550.668, -2ll change; 18.093, P = 0.034) with SS-13BN and SS-15BN strains showing a negative descending control of nociception relationship with chronic postsurgical pain-like behavior.

CONCLUSIONS

Descending control of nociception poorly predicted which rat strains developed chronic postsurgical pain-like behavior despite controlling for genetic, environmental, and sex differences. Two consomic strains that mimic clinical chronic postsurgical pain criteria and display a strong negative correlation with descending control of nociception were identified, offering novel candidates for future experiments exploring mechanisms that lead to chronic postsurgical pain.

EDITOR’S PERSPECTIVE

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

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

Pain-free default mode network connectivity contributes to tonic experimental pain intensity beyond the role of negative mood and other pain-related factors

BACKGROUND

Alterations in the default mode network (DMN) connectivity across pain stages suggest a possible DMN involvement in the transition to persistent pain.

AIM

This study examined whether pain-free DMN connectivity at lower alpha oscillations (8-10 Hz) accounts for a unique variation in experimental peak pain intensity beyond the contribution of factors known to influence pain intensity.

METHODS

Pain-free DMN connectivity was measured with electroencephalography prior to 1 h of capsaicin-evoked pain using a topical capsaicin patch on the right forearm. Pain intensity was assessed on a (0-10) numerical rating scale and the association between peak pain intensity and baseline measurements was examined using hierarchical multiple regression in 52 healthy volunteers (26 women). The baseline measurements consisted of catastrophizing (helplessness, rumination, magnification), vigilance, depression, negative and positive affect, sex, age, sleep, fatigue, thermal and mechanical pain thresholds and DMN connectivity (medial prefrontal cortex [mPFC]-posterior cingulate cortex [PCC], mPFC-right angular gyrus [rAG], mPFC-left Angular gyrus [lAG], rAG-mPFC and rAG-PCC).

RESULTS

Pain-free DMN connectivity increased the explained variance in peak pain intensity beyond the contribution of other factors (ΔR2  = 0.10, p = 0.003), with the final model explaining 66% of the variation (R2  = 0.66, ANOVA: p < 0.001). In this model, negative affect (β = 0.51, p < 0.001), helplessness (β = 0.49, p = 0.007), pain-free mPFC-lAG connectivity (β = 0.36, p = 0.003) and depression (β = -0.39, p = 0.009) correlated significantly with peak pain intensity. Interestingly, negative affect and depression, albeit both being negative mood indices, showed opposing relationships with peak pain intensity.

CONCLUSIONS

This work suggests that pain-free mPFC-lAG connectivity (at lower alpha) may contribute to individual variations in pain-related vulnerability.

SIGNIFICANCE

These findings could potentially lead the way for investigations in which DMN connectivity is used in identifying individuals more likely to develop chronic pain.

Predicting chronic postsurgical pain: current evidence and a novel program to develop predictive biomarker signatures

ABSTRACT

Chronic pain affects more than 50 million Americans. Treatments remain inadequate, in large part, because the pathophysiological mechanisms underlying the development of chronic pain remain poorly understood. Pain biomarkers could potentially identify and measure biological pathways and phenotypical expressions that are altered by pain, provide insight into biological treatment targets, and help identify at-risk patients who might benefit from early intervention. Biomarkers are used to diagnose, track, and treat other diseases, but no validated clinical biomarkers exist yet for chronic pain. To address this problem, the National Institutes of Health Common Fund launched the Acute to Chronic Pain Signatures (A2CPS) program to evaluate candidate biomarkers, develop them into biosignatures, and discover novel biomarkers for chronification of pain after surgery. This article discusses candidate biomarkers identified by A2CPS for evaluation, including genomic, proteomic, metabolomic, lipidomic, neuroimaging, psychophysical, psychological, and behavioral measures. Acute to Chronic Pain Signatures will provide the most comprehensive investigation of biomarkers for the transition to chronic postsurgical pain undertaken to date. Data and analytic resources generatedby A2CPS will be shared with the scientific community in hopes that other investigators will extract valuable insights beyond A2CPS's initial findings. This article will review the identified biomarkers and rationale for including them, the current state of the science on biomarkers of the transition from acute to chronic pain, gaps in the literature, and how A2CPS will address these gaps.

Multimodal hypersensitivity derived from quantitative sensory testing predicts pelvic pain outcome: an observational cohort study

ABSTRACT

Multimodal hypersensitivity (MMH)-greater sensitivity across multiple sensory modalities (eg, light, sound, temperature, pressure)-is associated with the development of chronic pain. However, previous MMH studies are restricted given their reliance on self-reported questionnaires, narrow use of multimodal sensory testing, or limited follow-up. We conducted multimodal sensory testing on an observational cohort of 200 reproductive-aged women, including those at elevated risk for chronic pelvic pain conditions and pain-free controls. Multimodal sensory testing included visual, auditory, and bodily pressure, pelvic pressure, thermal, and bladder pain testing. Self-reported pelvic pain was examined over 4 years. A principal component analysis of sensory testing measures resulted in 3 orthogonal factors that explained 43% of the variance: MMH, pressure pain stimulus response, and bladder hypersensitivity. The MMH and bladder hypersensitivity factors correlated with baseline self-reported menstrual pain, genitourinary symptoms, depression, anxiety, and health. Over time, MMH increasingly predicted pelvic pain and was the only component to predict outcome 4 years later, even when adjusted for baseline pelvic pain. Multimodal hypersensitivity was a better predictor of pelvic pain outcome than a questionnaire-based assessment of generalized sensory sensitivity. These results suggest that MMHs overarching neural mechanisms convey more substantial long-term risk for pelvic pain than variation in individual sensory modalities. Further research on the modifiability of MMH could inform future treatment developments in chronic pain.

Pain sensitivity after Roux-en-Y gastric bypass - associations with chronic abdominal pain and psychosocial aspects

OBJECTIVES

The aims of this study were to investigate modifications in pain sensitivity after RYGB and to explore associations between pain sensitivity and weight loss, chronic abdominal pain, total body pain, anxiety, depression, and pain catastrophizing.

METHODS

In total, 163 patients with obesity were examined with a cold pressor test for pain sensitivity before and two years after RYGB. Two aspects of pain sensitivity were registered: Pain intensity (numeric rating scale, range 0-10) and pain tolerance (seconds). Associations between pain sensitivity and the explanatory variables were assessed with linear regression.

RESULTS

Two years after RYGB the pain intensity increased (mean ± SD 0.64 ± 1.9 score units, p<0.001). Pain tolerance decreased (7.2 ± 32.4 s, p=0.005). A larger reduction in body mass index was associated with increased pain intensity, β=-0.090 (95 % CI -0.15 to -0.031, p=0.003), and decreased pain tolerance β=1.1 (95 % CI 0.95 to 2.2, p=0.03). Before surgery, participants with chronic abdominal pain reported 1.2 ± 0.5 higher pain intensity (p=0.02) and had 19.2 ± 9.3 s lower pain tolerance (p=0.04) than those without abdominal pain. No differences in pain sensitivity were observed between participants who did or did not develop chronic abdominal pain after RYGB. Pain sensitivity was associated with symptoms of anxiety but not with pain catastrophizing, depression or bodily pain.

CONCLUSIONS

The pain sensitivity increased after RYGB and was associated with larger weight loss and anxiety symptoms. Changes in pain sensitivity were not associated with development of chronic abdominal pain after RYGB in our study.

Chronic post-thoracotomy pain after lung cancer surgery: a prospective study of preoperative risk factors

OBJECTIVES

The objective of this longitudinal cohort study was to investigate if preoperative pain mechanisms, anxiety, and depression increase risk of developing chronic post-thoracotomy pain (CPTP) after lung cancer surgery.

METHODS

Patients with suspected or confirmed lung cancer undergoing surgery by either video-assisted thoracoscopic surgery or anterior thoracotomy were recruited consecutively. Preoperative assessments were conducted by: quantitative sensory testing (QST) (brush, pinprick, cuff pressure pain detection threshold, cuff pressure tolerance pain threshold, temporal summation and conditioned pain modulation), neuropathic pain symptom inventory (NPSI), and the Hospital Anxiety and Depression Scale (HADS). Clinical parameters in relation to surgery were also collected. Presence of CPTP was determined after six months and defined as pain of any intensity in relation to the operation area on a numeric rating scale form 0 (no pain) to 10 (worst pain imaginable).

RESULTS

A total of 121 patients (60.2 %) completed follow-up and 56 patients (46.3 %) reported CPTP. Development of CPTP was associated with higher preoperative HADS score (p=0.025), higher preoperative NPSI score (p=0.009) and acute postoperative pain (p=0.042). No differences were observed in relation to preoperative QST assessment by cuff algometry and HADS anxiety and depression sub-scores.

CONCLUSIONS

High preoperative HADS score preoperative pain, acute postoperative pain intensity, and preoperative neuropathic symptoms were was associated with CPTP after lung cancer surgery. No differences in values of preoperative QST assessments were found. Preoperative assessment and identification of patients at higher risk of postoperative pain will offer opportunity for further exploration and development of preventive measures and individualised pain management depending on patient risk profile.

The mechanisms and management of persistent postsurgical pain

An estimated 10%-50% of patients undergoing a surgical intervention will develop persistent postsurgical pain (PPP) lasting more than 3 months despite adequate acute pain management and the availability of minimally invasive procedures. The link between early and late pain outcomes for surgical procedures remains unclear-some patients improve while others develop persistent pain. The elective nature of a surgical procedure offers a unique opportunity for prophylactic or early intervention to prevent the development of PPP and improve our understanding of its associated risk factors, such as pre-operative anxiety and the duration of severe acute postoperative pain. Current perioperative pain management strategies often include opioids, but long-term consumption can lead to tolerance, addiction, opioid-induced hyperalgesia, and death. Pre-clinical models provide the opportunity to dissect mechanisms underpinning the transition from acute to chronic, or persistent, postsurgical pain. This review highlights putative mechanisms of PPP, including sensitisation of peripheral sensory neurons, neuroplasticity in the central nervous system and nociceptive signalling along the neuro-immune axis.

Indifference or hypersensitivity? Solving the riddle of the pain profile in individuals with autism

ABSTRACT

Excitatory-inhibitory (E/I) imbalance is a mechanism that underlies autism spectrum disorder, but it is not systematically tested for pain processing. We hypothesized that the pain modulation profile (PMP) in autistic individuals is characterized by less efficient inhibitory processes together with a facilitative state, indicative of a pronociceptive PMP. Fifty-two adults diagnosed with autism and 52 healthy subjects, age matched and sex matched, underwent quantitative sensory testing to assess the function of the (1) pain facilitatory responses to phasic, repetitive, and tonic heat pain stimuli and (2) pain inhibitory processes of habituation and conditioned pain modulation. Anxiety, pain catastrophizing, sensory, and pain sensitivity were self-reported. The autistic group reported significantly higher pain ratings of suprathreshold single ( P = 0.001), repetitive (46°C- P = 0.018; 49°C- P = 0.003; 52°C- P < 0.001), and tonic ( P = 0.013) heat stimuli that were cross correlated ( r = 0.48-0.83; P < 0.001) and associated with sensitivity to daily life pain situations ( r = 0.39-0.45; P < 0.005) but not with psychological distress levels. Hypersensitivity to experimental pain was attributed to greater autism severity and sensory hypersensitivity to daily stimuli. Subjects with autism efficiently inhibited phasic but not tonic heat stimuli during conditioned pain modulation. In conclusion, in line with the E/I imbalance mechanism, autism is associated with a pronociceptive PMP expressed by hypersensitivity to daily stimuli and experimental pain and less-efficient inhibition of tonic pain. The latter is an experimental pain model resembling clinical pain. These results challenge the widely held belief that individuals with autism are indifferent to pain and should raise caregivers' awareness of pain sensitivity in autism.

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

Background

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

Methods

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

Results

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

Conclusion

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

Outcomes of a QST Protocol in Healthy Subjects and Chronic Pain Patients: A Controlled Clinical Trial

Chronic pain is an important cause of disability with a high burden to society. Quantitative sensory testing (QST) is a noninvasive multimodal method used to discriminate the function of nerve fibers. The aim of this study is to propose a new, reproducible, and less time-consuming thermal QST protocol to help characterize and monitor pain. Additionally, this study also compared QST outcomes between healthy and chronic pain subjects. Forty healthy young/adult medical students and fifty adult/elderly chronic pain patients were evaluated in individual sessions including pain history, followed by QST assessments divided into three proposed tests: pain threshold, suprathreshold, and tonic pain. In the chronic pain group, a significantly higher pain threshold (hypoesthesia) and a higher pain sensibility (hyperalgesia) were demonstrated at threshold temperature when compared to healthy participants. The sensitivity to the suprathreshold and tonic stimulus did not prove to be significantly different between both groups. The main results demonstrated that the heat threshold QST tests can be helpful in evaluating hypoesthesia and that the sensitivity threshold temperature test can demonstrate hyperalgesia in individuals with chronic pain. In conclusion, this study demonstrates the importance of using tools such as QST as a complement to detect changes in several pain dimensions.

Gonadal hormone-dependent nociceptor sensitization maintains nociplastic pain state in female mice

ABSTRACT

Nociplastic pain conditions develop predominantly in women. We recently established a murine nociplastic pain model by applying postinjury thermal (40°C) stimulation to an injured (capsaicin-injected) area, triggering a transition to a nociplastic pain state manifesting as persistent mechanical hypersensitivity outside of the previously injured area. The nociplastic pain state was centrally maintained by spinal microglia in males but peripherally by ongoing afferent activity at the previously injured area in females. Here, we investigated whether gonadal hormones are critical for the development of this peripherally maintained nociplastic pain state in females. Although the transition to a nociplastic pain state still occurred in ovariectomized females, the pain state was maintained neither by ongoing afferent activity at the previously injured area nor by spinal microglia. Estradiol reconstitution a week before the injury plus postinjury stimulation, but not after the transition had already occurred, restored the development of peripherally maintained nociplastic mechanical hypersensitivity in ovariectomized females. G protein-coupled estrogen receptor antagonism during the transition phase mimicked ovariectomy in gonad-intact females, whereas the receptor antagonism after the transition gradually alleviated the nociplastic mechanical hypersensitivity. At the previously injured area, afferents responsive to allyl isothiocyanate (AITC), a TRPA1 agonist, contributed to the maintenance of nociplastic mechanical hypersensitivity in gonad-intact females. In ex vivo skin-nerve preparations, only AITC-responsive afferents from the nociplastic pain model in gonad-intact females showed ongoing activities greater than control. These results suggest that gonadal hormones are critical for peripherally maintained nociplastic pain state in females by sensitizing AITC-responsive afferents to be persistently active.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Predicting pain after standard pain therapy for knee osteoarthritis - the first steps towards personalized mechanistic-based pain medicine in osteoarthritis

OBJECTIVES

The prevalence of osteoarthritis (OA) is rising, and pain is the hallmark symptom of OA. Pain in OA is complicated and can be influenced by multiple joint-related factors and factors related to, e.g., physiological, epigenetic, and pain sensory profiles. Increasing evidence suggests that a subset of patients with OA are pain sensitive. This can be assessed using quantitative sensory testing (QST). Common treatments of OA are total knee arthroplasty (TKA) and administration of 3-weeks of non-steroidal anti-inflammatory drugs (NSAIDs), which provide pain relief to many patients with OA. However, approx. 20% of patients experience chronic postoperative pain after TKA, whereas NSAIDs provide an average pain relief of approx. 25%. The current topical review focuses on the emerging evidence linking pretreatment QST to the treatment response of TKA and NSAID treatments.

CONTENT

MEDLINE was systematically searched for all studies from 2000 to 2022 on pretreatment QST, TKA, and NSAIDs. Pre-clinical studies, reviews, and meta-analyses were excluded.

SUMMARY

Currently, 14 studies on TKA and four studies on NSAIDs have been published with the aim to attempt prediction of the treatment response. The QST methodologies in the studies are inconsistent, but 11/14 (79%) studies on TKA and 4/4 (100%) studies on NSAIDs report statistically significant associations between pretreatment QST and chronic postoperative pain after TKA or analgesic effect after NSAID treatment. The strength of the associations remains low-to-moderate. The most consistent pretreatment QST predictors are pressure pain thresholds, temporal summation of pain, and conditioned pain modulation.

OUTLOOK

The use of QST as predictors of standard OA treatment is interesting, but the predictive strength remains low-to-moderate. A transition of QST from a research-based setting and into the clinic is not advised until the predictive strength has been improved and the methodology has been standardized.

Response profile in a rat model of exercise-induced hypoalgesia is associated with duloxetine, pregabalin and diclofenac effect on constriction-induced neuropathy

BACKGROUND

Exercise is a known trigger of the inhibitory pain modulation system and its analgesic effect is termed exercise-induced hypoalgesia (EIH). Previous studies have demonstrated that rats with deficient analgesic response following exercise develop more significant hypersensitivity following nerve injury compared to rats with substantial analgesic response following exercise.

OBJECTIVES

A rat model of EIH as an indicator of the pain inhibitory system's efficiency was used to explore the association between EIH profiles and the effect of pharmacotherapy on rat's neuropathic pain.

METHODS

EIH profiles were assessed by evaluating paw responses to mechanical stimuli before and after exercise on a rotating rod. Rats with a reduction of ≤33% in responses were classified as low EIH and those with ≥67% as high EIH. Low and high EIH rats underwent sciatic nerve chronic constriction injury (CCI). Paw responses to mechanical stimuli were measured at baseline, following CCI, and after treatment with diclofenac, duloxetine or pregabalin. In a different group of low and high EIH rats, EIH was measured before and following treatment with the same medications.

RESULTS

Low EIH rats developed more significant hypersensitivity following CCI. Duloxetine and pregabalin successfully reduced hypersensitivity, although significantly more so in low EIH rats. Diclofenac had limited effects, and only on low EIH rats. Four days of duloxetine administration transformed low EIH rats' profiles to high EIH.

CONCLUSIONS

The findings of this study suggest that EIH profiles in rats can not only predict the development of hypersensitivity following injury but may also support targeted pharmacological treatment.

SIGNIFICANCE

Exercise is a known trigger of the inhibitory pain modulation. Rats with deficient analgesic response following exercise develop more significant hypersensitivity following nerve injury. Pain modulation profiles in rats can also support targeted pharmacological treatment; rats with deficient analgesic response following exercise benefit more from treatment with duloxetine and gabapentin. Treatment with duloxetine can improve pain modulation profile.

Chronic pain domains and their relationship to personality, abilities, and brain networks

Chronic pain is a multidimensional pathological state. Recent evidence suggests that specific brain properties and patients' psychological and physical traits are distorted in chronic pain patients. However, the relationship between these alterations and pain dimensions remains poorly understood. Here, we first evaluated multiple dimensions of chronic pain by assessing a broad battery of pain-related questionnaire scores (23 outcomes) of 107 chronic low back pain patients and identified 3 distinct chronic pain domains: magnitude, affect & disability, and quality. Second, we investigated the pain domains relationship with measures of personality, social interaction, psychological traits, and ability traits (77 biopsychosocial & ability [biopsy&ab] outcomes). Pain magnitude (out-of-sample [OOS] ) is associated with emotional control, attention, and working memory, with higher pain scores showing lower capacity to regulate and adapt behaviorally. Pain affect & disability (OOS associated with anxiety, catastrophizing and social relationships dysfunction. Pain quality did not relate significantly to biopsy&ab variables. Third, we mapped these 3 pain domains to brain functional connectivity. Pain magnitude mainly associated with the sensorimotor and the cingulo-opercular networks (OOS ). Pain affect & disability related to frontoparietal and default mode networks (OOS . Pain quality integrated sensorimotor, auditory, and cingulo-opercular networks (OOS ). Mediation analysis could link functional connectivity and biopsy&ab models to respective pain domains. Our results provide a global overview of the complexity of chronic pain, showing how underlying distinct domains of the experience map to different biopsy&ab correlates and underlie unique brain network signatures.

Neural mechanisms underlying the conditioned pain modulation response: a narrative review of neuroimaging studies

ABSTRACT

Processing spatially distributed nociceptive information is critical for survival. The conditioned pain modulation (CPM) response has become a common psychophysical test to examine pain modulation capabilities related to spatial filtering of nociceptive information. Neuroimaging studies have been conducted to elucidate the neural mechanisms underlying the CPM response in health and chronic pain states, yet their findings have not been critically reviewed and synthesized before. This narrative review presents a simplified overview of MRI methodology in relation to CPM assessments and summarizes the findings of neuroimaging studies on the CPM response. The summary includes functional MRI studies assessing CPM responses during scanning as well as functional and structural MRI studies correlating indices with CPM responses assessed outside of the scanner. The findings are discussed in relation to the suggested mechanisms for the CPM response. A better understanding of neural mechanisms underlying spatial processing of nociceptive information could advance both pain research and clinical use of the CPM response as a marker or a treatment target.

Applying the Rapid OPPERA Algorithm to Predict Persistent Pain Outcomes Among a Cohort of Women Undergoing Breast Cancer Surgery

Persistent postmastectomy pain after breast surgery is variable in duration and severity across patients, due in part to interindividual variability in pain processing. The Rapid OPPERA Algorithm (ROPA) empirically identified 3 clusters of patients with different risk of chronic pain based on 4 key psychophysical and psychosocial characteristics. We aimed to test this type of group-based clustering within in a perioperative cohort undergoing breast surgery to investigate differences in postsurgical pain outcomes. Women (N = 228) scheduled for breast cancer surgery were prospectively enrolled in a longitudinal observational study. Pressure pain threshold (PPT), anxiety, depression, and somatization were assessed preoperatively. At 2-weeks, 3, 6, and 12-months after surgery, patients reported surgical area pain severity, impact of pain on cognitive/emotional and physical functioning, and pain catastrophizing. The ROPA clustering, which used patients' preoperative anxiety, depression, somatization, and PPT scores, assigned patients to 3 groups: Adaptive (low psychosocial scores, high PPT), Pain Sensitive (moderate psychosocial scores, low PPT), and Global Symptoms (high psychosocial scores, moderate PPT). The Global Symptoms cluster, compared to other clusters, reported significantly worse persistent pain outcomes following surgery. Findings suggest that patient characteristic-based clustering algorithms, like ROPA, may generalize across diverse diagnoses and clinical settings, indicating the importance of "person type" in understanding pain variability. PERSPECTIVE: This article presents the practical translation of a previously developed patient clustering solution, based within a chronic pain cohort, to a perioperative cohort of women undergoing breast cancer surgery. Such preoperative characterization could potentially help clinicians apply personalized interventions based on predictions concerning postsurgical pain.

Characterization of the Dahl salt-sensitive rat as a rodent model of inherited, widespread, persistent pain

Animal models are essential for studying the pathophysiology of chronic pain disorders and as screening tools for new therapies. However, most models available do not reproduce key characteristics of clinical persistent pain. This has limited their ability to accurately predict which new medicines will be clinically effective. Here, we characterize the Dahl salt-sensitive (SS) rat strain as the first rodent model of inherited widespread hyperalgesia. We show that this strain exhibits physiological phenotypes known to contribute to chronic pain, such as neuroinflammation, defective endogenous pain modulation, dysfunctional hypothalamic-pituitary-adrenal axis, increased oxidative stress and immune cell activation. When compared with Sprague Dawley and Brown Norway rats, SS rats have lower nociceptive thresholds due to increased inflammatory mediator concentrations, lower corticosterone levels, and high oxidative stress. Treatment with dexamethasone, the reactive oxygen species scavenger tempol, or the glial inhibitor minocycline attenuated the pain sensitivity in SS rats without affecting the other strains while indomethacin and gabapentin provided less robust pain relief. Moreover, SS rats presented impaired diffuse noxious inhibitory controls and an exacerbated response to the proalgesic mediator PGE₂, features of generalized pain conditions. These data establish this strain as a novel model of spontaneous, widespread hyperalgesia that can be used to identify biomarkers for chronic pain diagnosis and treatment.

Brain Connectivity Predicts Chronic Pain in Acute Mild Traumatic Brain Injury

OBJECTIVES

Previous studies have established the role of the cortico-mesolimbic and descending pain modulation systems in chronic pain prediction. Mild traumatic brain injury (mTBI) is an acute pain model where chronic pain is prevalent and complicated for prediction. In this study, we set out to study whether functional connectivity (FC) of the nucleus accumbens (NAc) and the periaqueductal gray matter (PAG) is predictive of pain chronification in early-acute mTBI.

METHODS

To estimate FC, resting-state functional magnetic resonance imaging (fMRI) of 105 participants with mTBI following a motor vehicle collision was acquired within 72 hours post-accident. Participants were classified according to pain ratings provided at 12-months post-collision into chronic pain (head/neck pain ≥30/100, n = 44) and recovery (n = 61) groups, and their FC maps were compared.

RESULTS

The chronic pain group exhibited reduced negative FC between NAc and a region within the primary motor cortex corresponding with the expected representation of the area of injury. A complementary pattern was also demonstrated between PAG and the primary somatosensory cortex. PAG and NAc also shared increased FC to the rostral anterior cingulate cortex (rACC) within the recovery group. Brain connectivity further shows high classification accuracy (area under the curve [AUC] = .86) for future chronic pain, when combined with an acute pain intensity report.

INTERPRETATION

FC features obtained shortly after mTBI predict its transition to long-term chronic pain, and may reflect an underlying interaction of injury-related primary sensorimotor cortical areas with the mesolimbic and pain modulation systems. Our findings indicate a potential predictive biomarker and highlight targets for future early preventive interventions. ANN NEUROL 2022;92:819-833.

Autonomic nervous system markers of music-elicited analgesia in people with fibromyalgia: A double-blind randomized pilot study

Purpose

To investigate the feasibility of using music listening by adults with fibromyalgia (FM) as a potential tool for reducing pain sensitivity.

Patients and methods

We report results from a double-blind two-arm parallel randomized pilot study (NCT04059042) in nine participants with FM. Pain tolerance and threshold were measured objectively using quantitative sensory tests; autonomic nervous system (ANS) reactivity was measured with an electrocardiogram. Participants were randomized to listen to instrumental Western Classical music or a nature sound control to test whether music listening elicits greater analgesic effects over simple auditory distraction. Participants also completed separate control testing with no sound that was counterbalanced between participants.

Results

Participants were randomized 1:1 to music or nature sounds (four Music and five Nature). Although the groups were not different on FM scores, the Music group had marginally worse temporal pain summation (p = 0.06), and the Nature group had higher anxiety scores (p < 0.05). Outcome measures showed a significant difference between groups in the magnitude of change in temporal summation between sessions (p < 0.05), revealing that the Nature group had greater pain reduction during audio compared to silence mode, while the Music group had no difference between the sessions. No significant effects were observed for either mechanical pain tolerance or ANS testing. Within the Music group, there was a trend of vagal response increase from baseline to music listening, but it did not reach statistical significance; this pattern was not observed in the Nature group.

Conclusion

Auditory listening significantly altered pain responses. There may be a greater vagal response to music vs. nature sounds; however, results could be due to group differences in pain and anxiety. This line of study will help in determining whether music could be prophylactic for people with FM when acute pain is expected.

Identifying Patients at High Risk of Chronic Pain After Video-Assisted Thoracoscopic Surgery Using Thermal Quantitative Sensory Testing

OBJECTIVE

To examine whether perioperative thermal quantitative sensory testing could be used to identify patients at high risk of chronic pain after video-assisted thoracoscopic surgery (VATS).

DESIGN

A single-center, prospective, observational study.

SETTING

At the Peking University People's Hospital.

PARTICIPANTS

A total of 111 patients scheduled to undergo VATS were enrolled.

INTERVENTIONS

Quantitative sensory testing was conducted at the anterior intercostal incision prior to surgery and after chest tube removal.

MEASUREMENTS AND MAIN RESULTS

The patient's chronic pain was assessed at 3 months after surgery using a questionnaire. The incidence of chronic pain was 35 out of 107 evaluable patients (32.7%). Among the 35 patients with chronic pain, 26 had features characteristic of neuropathic pain (74.3%). Compared to the patients without chronic pain, subjects with chronic pain had a significantly greater perioperative change in cold pain threshold (CPT; p = 0.032), but not cold detection threshold, warm detection threshold, and hot pain threshold . In the multivariate regression, perioperative CPT change was associated with chronic pain after VATS (odds ratio = 1.043, p = 0.026).

CONCLUSIONS

Chronic pain after VATS is typically neuropathic. The change in perioperative CPT at the incision site may help to identify patients at higher risk of chronic pain after VATS.