Cold pain hypersensitivity predicts trajectories of pain and disability after low back surgery: a prospective cohort study

Multi-omics profiles of chronic low back pain and fibromyalgia-Study protocol

BACKGROUND

Chronic low back pain (CLBP) and fibromyalgia (FM) are leading causes of suffering, disability, and social costs. Current pharmacological treatments do not target molecular mechanisms driving CLBP and FM, and no validated biomarkers are available, hampering the development of effective therapeutics. Omics research has the potential to substantially advance our ability to develop mechanism-specific therapeutics by identifying pathways involved in the pathophysiology of CLBP and FM, and facilitate the development of diagnostic, predictive, and prognostic biomarkers. We will conduct a blood and urine multi-omics study in comprehensively phenotyped and clinically characterized patients with CLBP and FM. Our aims are to identify molecular pathways potentially involved in the pathophysiology of CLBP and FM that would shift the focus of research to the development of target-specific therapeutics, and identify candidate diagnostic, predictive, and prognostic biomarkers.

METHODS

We are conducting a prospective cohort study of adults ≥18 years of age with CLBP (n=100) and FM (n=100), and pain-free controls (n=200). Phenotyping measures include demographics, medication use, pain-related clinical characteristics, physical function, neuropathic components (quantitative sensory tests and DN4 questionnaire), pain facilitation (temporal summation), and psychosocial function as moderator. Blood and urine samples are collected to analyze metabolomics, lipidomics and proteomics. We will integrate the overall omics data to identify common mechanisms and pathways, and associate multi-omics profiles to pain-related clinical characteristics, physical function, indicators of neuropathic pain, and pain facilitation, with psychosocial variables as moderators.

DISCUSSION

Our study addresses the need for a better understanding of the molecular mechanisms underlying chronic low back pain and fibromyalgia. Using a multi-omics approach, we hope to identify converging evidence for potential targets of future therapeutic developments, as well as promising candidate biomarkers for further investigation by biomarker validation studies. We believe that accurate patient phenotyping will be essential for the discovery process, as both conditions are characterized by high heterogeneity and complexity, likely rendering molecular mechanisms phenotype specific.

Trajectories of cold but not mechanical sensitivity correspond with disability trajectories after whiplash injury

ABSTRACT

Developmental trajectories for neck disability after whiplash injury have been identified. Their relationship to cold and mechanical sensitivity trajectories is not known. We aimed to (1) identify recovery trajectories of cold and mechanical sensitivity, (2) explore their codevelopment with disability trajectories, (3) identify predictors of sensitivity trajectories, and (4) explore codevelopment of cold and mechanical sensitivity trajectories. Participants (n = 233) were assessed at <1, 3, 6, and 12 months after whiplash injury. Outcomes were cold pain detection threshold (CPT at neck), pressure pain detection thresholds (PPT, neck C5, and tibialis anterior), and the Neck Disability Index. We used group-based trajectory models to identify postinjury recovery trajectories and multinominal logistic regression to explore associations between baseline characteristics and trajectory membership. We identified the following trajectory groups: CPT (low [50.0%], moderate [29.7%], and high [20.4%] sensitivity); PPT C5 (low [10.8%] and high [89.2%] sensitivity); and PPT tibialis anterior (low [23.9%], moderate [39.0%], and high [37.1%] sensitivity); all were stable over the 12 months. There was good correspondence between disability and cold sensitivity trajectory groups but not for mechanical sensitivity; cold and mechanical sensitivity trajectories were not well associated. Higher baseline pain predicted membership of the high cold sensitivity trajectory (RR 1.27, 95% CI 1.01-1.59) and hyperarousal symptoms predicted membership of the moderate cold sensitivity trajectory (RR 1.17, 95% CI 1.01-1.36). We found no associations between baseline characteristics and mechanical sensitivity. There is an interplay between cold allodynia, pain, and hyperarousal symptoms in development of ongoing disability after whiplash injury. Different mechanisms likely underlie cold and mechanical sensitivity.

Changes in spatial bodily pain distribution one year after benign hysterectomy with emphasis on prevalence and risk factors for de novo and persistent pelvic pain- a prospective longitudinal multicenter study

BACKGROUND

The objectives were to determine the prevalence of de novo and persistent pelvic pain after benign hysterectomy and to assess risk factors.

METHODS

A Swedish prospective multicenter study of 440 women undergoing benign hysterectomy was conducted between October 2011 and March 2017. Measures of pain, the spatial extent of bodily pain, and pain sensitivity were assessed using a self-reporting questionnaire, Margolis's patient pain drawing, and quantitative sensory testing of pain thresholds for pressure, heat, and cold, respectively. Quality of life was evaluated by EQ-5D-3L and SF-36. Psychological distress was assessed by the Hospital Anxiety and Depression Scaleand the Stress-Coping Inventory. Logistic regression models were used to assess risk factors, and the outcome was presented as an adjusted odds ratio (aOR) and 95% confidence interval (CI).

RESULTS

Preoperatively, 18.0% of the women reported no bodily pain, 41.5% had pelvic pain, either as the only location (7.0%) or along with pain in other locations (34.5%), and 40.5% had non-pelvic pain only. Postoperatively, 6.2% developed de novo pelvic pain and 16.4% had persistent pelvic pain. De novo pelvic pain developed exclusively in women who preoperatively had non-pelvic pain only. Risk factors for de novo pelvic pain were a long hospital stay (aOR 1.50 (95%CI) 1.02-2.21)), high preoperative pain intensity (aOR 1.25 (95%CI 1.01-1.62)) and a high number of pain areas (aOR 1.15 (95%CI 1.05-1.27)), along with anxiety (aOR 10.61 (95%CI 1.84-61.03)) and low EQ-5D-3L health index (aOR 0.02 (95%CI 0.00-0.31)). Risk factors for persistent pelvic pain were lower age (aOR 0.89 (95%CI 0.81-0.97)), higher number of pain areas (aOR 1.08 (95%CI 1.02-1.14)), and a higher frequency of preoperative pain (aOR 12.75 (95%CI 2.24-72.66)).

CONCLUSION

Although hysterectomy appeared to be reasonably effective in curing pelvic pain, a non-negligible proportion of women developed de novo pelvic pain or had persistent pelvic pain. De novo pelvic pain seemed to affect only those who preoperatively had widespread bodily pain. Women at risk for de novo and persistent pelvic pain after hysterectomy could be identified preoperatively.

TRIAL REGISTRATIONS

The study was retrospectively registered in ClinicalTrial.gov (NCT01526668) on 01/27//2012.

Lessons learnt in evidence-based perioperative pain medicine: changing the focus from the medication and procedure to the patient

Over time, the focus of evidence-based acute pain medicine has shifted, from a focus on drugs and interventions (characterized by numbers needed to treat), to an appreciation of procedure-specific factors (characterized by guidelines and meta-analyses), and now anesthesiologists face the challenge to integrate our current approach with the concept of precision medicine. Psychometric and biopsychosocial markers can potentially guide clinicians on who may need more aggressive perioperative pain management, or who would respond particularly well to a given analgesic intervention. The challenge will be to identify an easily assessable set of parameters that will guide perioperative physicians in tailoring the analgesic strategy to procedure and patient.

Multi-Omics Profiles of Chronic Low Back Pain and Fibromyalgia - Study Protocol

Background

Chronic low back pain (CLBP) and fibromyalgia (FM) are leading causes of suffering, disability, and social costs. Current pharmacological treatments do not target molecular mechanisms driving CLBP and FM, and no validated biomarkers are available, hampering the development of effective therapeutics. Omics research has the potential to substantially advance our ability to develop mechanism-specific therapeutics by identifying pathways involved in the pathophysiology of CLBP and FM, and facilitate the development of diagnostic, predictive, and prognostic biomarkers. We will conduct a blood and urine multi-omics study in comprehensively phenotyped and clinically characterized patients with CLBP and FM. Our aims are to identify molecular pathways potentially involved in the pathophysiology of CLBP and FM that would shift the focus of research to the development of target-specific therapeutics, and identify candidate diagnostic, predictive, and prognostic biomarkers.

Methods

We are conducting a prospective cohort study of adults ≥18 years of age with CLBP (n=100) and FM (n=100), and pain-free controls (n=200). Phenotyping measures include demographics, medication use, pain-related clinical characteristics, physical function, neuropathiccomponents (quantitative sensory tests and DN4 questionnaire), pain facilitation (temporal summation), and psychosocial function as moderator. Blood and urine samples are collected to analyze metabolomics, lipidomics and proteomics. We will integrate the overall omics data to identify common mechanisms and pathways, and associate multi-omics profiles to pain-related clinical characteristics, physical function, indicators of neuropathic pain, and pain facilitation, with psychosocial variables as moderators.

Discussion

Our study addresses the need for a better understanding of the molecular mechanisms underlying chronic low back pain and fibromyalgia. Using a multi-omics approach, we hope to identify converging evidence for potential targets of future therapeutic developments, as well as promising candidate biomarkers for further investigation by biomarker validation studies. We believe that accurate patient phenotyping will be essential for the discovery process, as both conditions are characterized by high heterogeneity and complexity, likely rendering molecular mechanisms phenotype specific.

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.

Personalized medicine: Somatosensory phenotyping in musculoskeletal pain conditions

BACKGROUND

Current clinical phenotyping of musculoskeletal pain provides very limited evidence- based support to personalized medicine. This paper discusses the potential of somatosensory phenotyping to contribute to personalized medicine for prognosis and prediction of treatment effects.

METHODS

Highlight of definitions and regulatory requirements for phenotypes and biomarkers. Appraisal of the literature on somatosensory phenotyping in musculoskeletal pain.

RESULTS

Somatosensory phenotyping can identify clinical conditions and manifestations that may affect treatment decisions. However, studies have shown inconsistent associations of phenotyping measures with clinical outcomes, and the strength of association is mostly weak. Most somatosensory measures have been developed for research, are too demanding to find large acceptance in clinical settings, and have uncertain clinical usefulness.

CONCLUSIONS

Current somatosensory measures will unlikely be validated as strong prognostic or predictive biomarkers. However, they still have the potential to support personalized medicine. Including somatosensory measures in biomarker signatures, that is, a set of measures that are collectively associated with outcomes, is potentially more useful than aiming to the identification of single biomarkers. Furthermore, somatosensory phenotyping may be introduced as part of patient's evaluation to contribute to better-informed and personalized treatment decisions. To this purpose, a change in the way research currently approaches somatosensory phenotyping is warranted. A pathway is proposed that involves: (1) the identification of clinically applicable measures that are specific to clinical conditions; (2) the association of somatosensory phenotypes with outcomes; (3) multi-site replication; and (4) the determination of clinical benefits in randomized controlled trials.

SIGNIFICANCE

Somatosensory phenotyping has the potential to support personalized medicine. However, current measures do not seem to meet the criteria for being strong prognostic or predictive biomarkers, most of them are too demanding to find large acceptance in clinical settings, and their clinical usefulness has not been proven. The value of somatosensory phenotyping can be more realistically determined by re-orienting research to the development of simplified testing protocols, applicable to large-scale clinical practice, and tested for clinical usefulness in randomized controlled trials.

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.

Association Between Experimental Pain Thresholds and Trajectories of Postoperative Recovery Measures After Benign Hysterectomy

Purpose

Quantitative sensory testing (QST) can be applied to quantify the sensitivity to different painful stimuli. This study aims to evaluate the association between preoperative pressure and thermal pain thresholds and trajectories of measurements of postoperative recovery (patient-reported daily maximum and average pain intensity, sum score of symptoms, and analgesic consumption) after benign hysterectomy.

Patients and Methods

A prospective, longitudinal single-blinded, observational multicenter study was conducted in five hospitals in the southeast of Sweden between 2011 and 2017. A total of 406 women scheduled for abdominal or vaginal hysterectomy for benign conditions were enrolled in the study. QST measuring pressure (PPT), heat (HPT), and cold pain thresholds (CPT) were performed preoperatively. The cut-off levels for dichotomizing the pain thresholds (low/high) were set at the 25-percentile for PPT and HPT and the 75-percentile for CPT. The Swedish Postoperative Symptom Questionnaire was used to measure postoperative pain and other symptoms of discomfort (symptom sum score) on 13 occasions for six weeks postoperatively. Daily analgesic consumption of opioids and non-opioids was registered.

Results

A CPT above the 75-percentile was associated with high postoperative maximum pain intensity (p = 0.04), high symptom sum score (p = 0.03) and greater consumption of non-opioids (p = 0.03). A HPT below the 25-percentile was only associated with greater consumption of non-opioids (p = 0.02). PPT was not associated with any of the outcome measures.

Conclusion

CPT seemed to be predictive for postoperative pain and symptoms of discomfort after benign hysterectomy. Preoperative QST may be used to individualize the management of postoperative recovery for low pain threshold individuals.

Prediction of pain responses to subsequent cold pressor test via baseline heart rate variability in healthy adults

BACKGROUND

Baseline heart rate variability (HRV) that reflects parasympathetic nervous system (PNS) activity may serve as an objective, physiological index of pain assessment, but more research is warranted to examine the link between HRV and laboratory pain responses. This study examined whether baseline HRV would predict pain responses to subsequent cold pressor test (CPT) in healthy adults.

METHODS

One hundred twenty-three participants completed resting HRV assessment and CPT consisting of immersing their right hand into a cold-water bath for a maximum of 2 minutes. Pain threshold and pain rating were assessed during CPT. Completion status of CPT, defined as completing CPT or terminating CPT before 2 minutes, was recorded as an additional laboratory pain measure. Pearson's correlation analysis was performed to examine the link between HRV and pain responses, whereas regression analysis was performed to test the prediction of pain responses via baseline HRV.

RESULTS

HF-HRV_log , which reflects PNS activity, was significantly associated with the CPT completion status (r = 0.23, p = 0.01), but not significantly associated with pain threshold (r = 0.17, p = 0.06) nor pain rating (r = -0.11, p = 0.24). HF- HRV_log was found to be a significant predictor of the CPT completion status (B = 0.53, p = 0.013).

CONCLUSIONS

Baseline HF- HRV_log may serve as an objective, physiological index to predict laboratory pain responses, and completion status of laboratory pain tests, such as CPT, may be used as a laboratory pain measure to capture important individual differences in pain processing.

Development and validation of a multivariable prediction model for early prediction of chronic postsurgical pain in adults: a prospective cohort study

BACKGROUND

Early identification of patients at risk of developing chronic postsurgical pain (CPSP) is an essential step in reducing pain chronification in postsurgical patients. We aimed to develop and validate a prognostic model for the early prediction of CPSP including pain characteristics indicating altered pain processing within 2 weeks after surgery.

METHODS

A prospective cohort study was conducted in adult patients undergoing orthopaedic, vascular, trauma, or general surgery between 2018 and 2019. Multivariable logistic regression models for CPSP were developed using data from the University Medical Centre (UMC) Utrecht and validated in data from the Erasmus UMC Rotterdam, The Netherlands.

RESULTS

In the development (n=344) and the validation (n=150) cohorts, 28.8% and 21.3% of patients reported CPSP. The best performing model (area under the curve=0.82; 95% confidence interval [CI], 0.76-0.87) included preoperative treatment with opioids (odds ratio [OR]=4.04; 95% CI, 2.13-7.70), bone surgery (OR=2.01; 95% CI, 1.10-3.67), numerical rating scale pain score on postoperative day 14 (OR=1.57; 95% CI, 1.34-1.83), and the presence of painful cold within the painful area 2 weeks after surgery (OR=4.85; 95% CI, 1.85-12.68). Predictive performance was confirmed by external validation.

CONCLUSIONS

As only four easily obtainable predictors are necessary for reliable CPSP prediction, the models are useful for the clinician to be alerted to further assess and treat individual patients at risk. Identification of the presence of painful cold within 2 weeks after surgery as a strong predictor supports altered pain processing as an important contributor to CPSP development.

Development of a bedside tool-kit for assessing sensitization in patients with chronic osteoarthritis knee pain or chronic knee pain after total knee replacement

ABSTRACT

Different pathophysiological mechanisms contribute to the pain development in osteoarthritis (OA). Sensitization mechanisms play an important role in the amplification and chronification of pain and may predict the therapeutic outcome. Stratification of patients according to their pain mechanisms could help to target pain therapy. This study aimed at developing an easy-to-use, bedside tool-kit to assess sensitization in patients with chronic painful knee OA or chronic pain after total knee replacement (TKR). In total, 100 patients were examined at the most affected knee and extrasegmentally by the use of 4 standardized quantitative sensory testing parameters reflecting sensitization (mechanical pain threshold, mechanical pain sensitivity, dynamic mechanical allodynia, and pressure pain threshold), a bedside testing battery of equivalent parameters including also temporal summation and conditioned pain modulation, and pain questionnaires. Machine learning techniques were applied to identify an appropriate set of bedside screening tools. Approximately half of the patients showed signs of sensitization (46%). Based on machine learning techniques, a composition of tests consisting of 3 modalities was developed. The most adequate bedside tools to detect sensitization were pressure pain sensitivity (pain intensity at 4 mL pressure using a 10-mL blunted syringe), mechanical pinprick pain sensitivity (pain intensity of a 0.7 mm nylon filament) over the most affected knee, and extrasegmental pressure pain sensitivity (pain threshold). This pilot study presents a first attempt to develop an easy-to-use bedside test to probe sensitization in patients with chronic OA knee pain or chronic pain after TKR. This tool may be used to optimize individualized, mechanism-based pain therapy.

The Definition, Assessment, and Prevalence of (Human Assumed) Central Sensitisation in Patients with Chronic Low Back Pain: A Systematic Review

Central sensitisation is assumed to be one of the underlying mechanisms for chronic low back pain. Because central sensitisation is not directly assessable in humans, the term 'human assumed central sensitisation' (HACS) is suggested. The objectives were to investigate what definitions for HACS have been used, to evaluate the methods to assess HACS, to assess the validity of those methods, and to estimate the prevalence of HACS. Database search resulted in 34 included studies. Forty different definition references were used to define HACS. This review uncovered twenty quantitative methods to assess HACS, including four questionnaires and sixteen quantitative sensory testing measures. The prevalence of HACS in patients with chronic low back pain was estimated in three studies. The current systematic review highlights that multiple definitions, assessment methods, and prevalence estimates are stated in the literature regarding HACS in patients with chronic low back pain. Most of the assessment methods of HACS are not validated but have been tested for reliability and repeatability. Given the lack of a gold standard to assess HACS, an initial grading system is proposed to standardize clinical and research assessments of HACS in patients with a chronic low back.

The association of sensory phenotype and concomitant mood, sleep and functional impairment with the outcome of carpal tunnel surgery

BACKGROUND

Up to 25% of people who have had carpal tunnel release surgery (CTR) fail to report improvement; however, evidence for prognostic indicators in this surgical cohort is limited. To identify candidate prognostic factors, this study investigated the association of quantitative sensory testing (QST) derived sensory phenotype and attendant impairment with patient-reported surgical outcome.

METHODS

With ethical approval and informed consent, this prospective observational longitudinal study recruited patients from two London hospitals. Multimodal phenotyping measures including quantitative sensory testing (QST), pain parameters, insomnia, pain-related worry, mood and function, were evaluated prior to; and at 3- and 6-months post-surgery. Pain in median nerve distribution with electrophysiologically confirmed conduction delay and DN4 score ≥ 4 was defined as neuropathic. Primary outcome was patient-rated change at 6 months, dichotomised as poor outcome; "worse" or "no change" and good outcome; "slightly better", "much better" or "completely cured".

RESULTS

Seventy-six patients participated. Prior to surgery, substantial heterogeneity in established categories of somatosensory function was observed with 21% of participants categorised as having a healthy sensory phenotype; 29% with thermal hyperalgesia; 32% mechanical hyperalgesia and 18% sensory loss. Seventy six percent of participants were classified as having neuropathic pain, 33% with high levels of pain related worry and 64% with clinical insomnia. Observed differences in pain, sleep impairment, psychological factors and function, between sensory phenotypic groups, was not significant. At 3- and 6-months post-surgery there was significant improvement in all phenotyping measures with a moderate to large effect size. Thermal and mechanical measures of somatosensation improved (p < 0.001), as did functional ability (p < 0.001). Symptom severity diminished (p < 0.001), as did pain-related worry (p < 0.001), anxiety (p = 0.02) and insomnia (p < 0.001). Patient-rated surgical outcome was good in 92% of the cohort, poor in 8%. Baseline sensory phenotype category was not associated with surgical outcome however pain-related worry, anxiety and functional interference were significantly associated with outcome (p ≤ 0.05).

CONCLUSION

In patients undergoing carpal tunnel surgery, pain-related worry, anxiety and pain functional interference are candidate prognostic outcome factors and require further elucidation.

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

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

Thermal Pain Thresholds Are Significantly Associated with Plasma Proteins of the Immune System in Chronic Widespread Pain-An Exploratory Pilot Study Using Multivariate and Network Analyses

Chronic widespread pain (CWP), including fibromyalgia (FM), is characterized by generalized musculoskeletal pain. An important clinical feature is widespread increased pain sensitivity such as lowered pain thresholds for different stimuli such as heat (HPT) and cold (CPT). There is a growing interest in investigating the activated neurobiological mechanisms in CWP. This explorative proteomic study investigates the multivariate correlation pattern between plasma and muscle proteins and thermal pain thresholds in CWP and in healthy controls (CON). In addition, we analysed whether the important proteins and their networks for CPT and HPT differed between CWP and CON. We used a proteomic approach and analysed plasma and muscle proteins from women with CWP (n = 15) and CON (n = 23). The associations between the proteins and CPT/HPT were analysed using orthogonal partial least square (OPLS). The protein-protein association networks for the important proteins for the two thermal pain thresholds were analysed using STRING database. CWP had lowered pain thresholds for thermal stimulus. These levels were generally not related to the included clinical variables except in CWP for HPT. Highly interacting proteins mainly from plasma showed strong significant associations with CPT and HPT both in CWP and in CON. Marked differences in the important proteins for the two thermal pain thresholds were noted between CWP and CON; more complex patterns emerged in CWP. The important proteins were part of the immune system (acute phase proteins, complement factors, and immunoglobulin factors) or known to interact with the immune system. As expected, CWP had lowered pain thresholds for thermal stimulus. Although different proteins were important in the two groups, there were similarities. For example, proteins related to the host defence/immunity such as acute phase proteins, complement factors, immunoglobulin factors, and cytokines/chemokines (although not in CON for CPT) were important habitual/tonic factors for thermal pain thresholds. The fact that peripheral proteins contribute to thermal pain thresholds does not exclude that central factors also contribute and that complex interactions between peripheral and central factors determine the registered pain thresholds in CWP.

Human cells and networks of pain: Transforming pain target identification and therapeutic development

Chronic pain is a disabling disease with limited treatment options. While animal models have revealed important aspects of pain neurobiology, therapeutic translation of this knowledge requires our understanding of these cells and networks of pain in humans. We propose a multi-institutional collaboration to rigorously and ethically address this challenge.

Prolonged time of after-sensation after experimental pain stimuli despite efficient conditioned pain modulation in patients with chronic neuropathic pain after traumatic nerve injuries in upper extremity

Prolonged time of after-sensation after experimental pain stimuli despite efficient conditioned pain modulation was observed in patients with neuropathic pain after traumatic nerve injuries

As yet, there is limited research that can identify factors that differentiate between painful and nonpainful neuropathies after traumatic nerve injury. The aim of this study was to compare subjects with pain and without pain, all after operative nerve repair in the upper extremities.