Patient phenotyping in clinical trials of chronic pain treatments: IMMPACT recommendations. Pain. 2016;157:1851-1871. [PMID: 27152687 DOI: 10.1097/j.pain.0000000000000602]

Stratification of patients based on the Neuropathic Pain Symptom Inventory: development and validation of a new algorithm

ABSTRACT

The personalization of neuropathic pain treatment could be improved by identifying specific sensory phenotypes (ie, specific combinations of symptoms and signs) predictive of the response to different classes of drugs. A simple and reliable phenotyping method is required for such a strategy. We investigated the utility of an algorithm for stratifying patients into clusters corresponding to specific combinations of neuropathic symptoms assessed with the Neuropathic Pain Symptom Inventory (NPSI). Consistent with previous results, we first confirmed, in a cohort of 628 patients, the existence of a structure consisting of 3 clusters of patients characterized by higher NPSI scores for: pinpointed pain (cluster 1), evoked pain (cluster 2), or deep pain (cluster 3). From these analyses, we derived a specific algorithm for assigning each patient to one of these 3 clusters. We then assessed the clinical relevance of this algorithm for predicting treatment response, through post hoc analyses of 2 previous controlled trials of the effects of subcutaneous injections of botulinum toxin A. Each of the 97 patients with neuropathic pain included in these studies was individually allocated to one cluster, by applying the algorithm to their baseline NPSI responses. We found significant effects of botulinum toxin A relative to placebo in clusters 2 and 3, but not in cluster 1, suggesting that this approach was, indeed, relevant. Finally, we developed and performed a preliminary validation of a web-based version of the NPSI and algorithm for the stratification of patients in both research and daily practice.

A psychophysical study comparing massage to conditioned pain modulation: A single blind randomized controlled trial in healthy participants

INTRODUCTION

Pain-inducing massage results in greater pain inhibition than pain free massage, suggesting a mechanism dependent on conditioned pain modulation (CPM). The purpose of this study was to test the hypothesis that pain inducing massage produces similar magnitude of reduction in pain sensitivity as a cold pressor task and that baseline conditioned pain modulation efficiency predicts pain inducing massage related hypoalgesia.

METHODS

Sixty healthy participants were randomly assigned to receive either pain inducing massage to the neck, cold pressor task to the hand, or pain free massage to the neck. Participants also underwent pre and immediate post-intervention quantitative sensory testing. A repeated measures ANCOVA determined between group differences in pain sensitivity changes.

RESULTS

Pain inducing massage used as a conditioning stimulus resulted in comparable experimental pain sensitivity changes as a cold pressor task (p > 0.05). Pain intensity during the intervention demonstrated a weak correlation (r = 0.20, p = 0.12) with changes in pain sensitivity at a remote site. Individuals with an efficient CPM at baseline who received the pain inducing massage displayed greater increases in pressure pain threshold compared to individuals with a less efficient CPM indicating the potential benefit of treatment stratification by mechanism.

CONCLUSION

Although pain inducing massage resulted in less self-reported pain than a cold pressor task, both resulted in similar magnitude of the CPM response, suggesting shared underlying mechanisms. Understanding mechanisms of interventions can move us closer to mechanistic based treatments for pain which is consistent with a personalized medicine approach to care.

Assessment of Pain Modulatory and Somatosensory Profiles in Chronic Tension-Type Headache Patients

Objective

The aim of this study was to thoroughly phenotype a group of chronic tension-type headache (CTTH) patients.

Methods

Fifteen CTTH patients diagnosed according to the International Classification of Headache Disorders–3 and 15 healthy controls were included in this study. Furthermore, 70 healthy controls were included to establish normative values. Quantitative sensory testing (QST), including temporal summation of pain (TSP), conditioned pain modulation (CPM), and psychological and sleep variables, was assessed in a single session. TSP and CPM were then combined to build pain modulation profiles (PMP) for each individual.

Results

No difference was found between groups for PMP, TSP, and CPM. However, 10 CTTH patients showed a pronociceptive PMP, with 8 related to a deficient CPM and 2 to both a deficient CPM and increased TSP. Increased cold detection thresholds were the most common sensory disturbance found in CTTH patients. Significant differences were seen between groups for pain catastrophizing, depression, and sleep quality although not all patient’s scores were above the clinically meaningful cutoffs.

Conclusions

In summary, CTTH patients presented with different PMP. These PMP may be related to increased TSP, deficient CPM, alterations in thermal detection that may be related to autonomic dysregulation, or a combination of all three. Overall, this suggests that due to their heterogeneous pathophysiology, CTTH patients should be managed according to their underlying pathophysiology and not with a one-size-fits-all approach.

Exploring pain phenotypes in workers with chronic low back pain: Application of IMMPACT recommendations

Background: Chronic low back pain (CLBP) is a major cause of disability globally. Stratified care has been proposed as a means to improve prognosis and treatment but is generally based on limited aspects of pain, including biopsychosocial drivers.

Aims: Following Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) recommendations, the present study explored pain phenotypes with a sample of workers with CLBP, a population for which no pain phenotypes have been derived to date.

Methods: A cross-sectional design was used with a sample of 154 workers with CLBP attending a rehabilitation clinic, recruited in person and from social media. Latent class analysis was used to identify subgroups of patients with different pain profiles based on ten pain indicators (pain variability, pain intensity, pain quality, somatization, sleep quality, depression, fatigue, pain catastrophizing, neuropathic pain, and central sensitization).

Results: The majority of the sample (85%) were recruited through social media. Both the two-class and three-class solutions were found to be satisfactory in distinguishing phenotypes of workers with CLBP. Three variables proved particularly important in distinguishing between the pain phenotypes—pain quality, fatigue, and central sensitization—with higher scores on these indicators associated with pain phenotypes with higher pain burden. Increased chronic pain self-efficacy, work-related support, and perceived work abilities were protective risk factors for being in a higher pain burden class.

Conclusions: The present study is the first to explore IMMPACT recommendations for pain phenotyping with workers with CLBP. Future prospective research will be needed to validate the proposed pain phenotypes.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Pain Management in Chronic Pancreatitis: Summary of Clinical Practice, Current Challenges and Potential Contribution of the M-ANNHEIM Classification

Abdominal pain, diarrhea with weight loss, and endocrine insufficiency represent the dominant symptoms of chronic pancreatitis (CP). High intensity of pain and constant pain have been shown to reduce quality of life in CP and may result in disability and increased health resource utilization. Various basic challenges and unanswered questions still exist regarding the treatment of pain in CP. Recently, limited evidence has been gained that early surgery for painful disease might be associated with better treatment results. Thus, timing of pancreatic surgery in painful disease represents a major issue that needs to be clarified in future studies. In this context, surveillance of patients is necessary in clinical practice. It appears that a generally accepted classification of the disease represents a major requirement for inter-institutional comparison of data with future progress in clinical research. Among recently proposed classification systems, the M-ANNHEIM classification system of CP with its recently presented M-ANNHEIM Surgery Score might be a useful tool to picture the course of the disease and to monitor treatment results. Future research is required to clarify the possible role of this system in the management of pain in CP. In the present article, we provide an overview of current status, challenges, and unanswered questions in the treatment of pain in CP, and we demonstrate the potential benefits of the M-ANNHEIM classification system in the management of painful CP.

Qualitative Sensory Testing in Outcome Prediction of Transforaminal Epidural Steroid Injection for Chronic Painful Unilateral Lumbosacral Radiculopathy: Prospective Observational Study

BACKGROUND

Transforaminal epidural steroid injection (TFESI) is widely practiced for the treatment of radicular pain. As its effectiveness is still subject to debate, a better patient selection for TFESI is necessary. We aimed to evaluate the potential of bedside-suitable qualitative sensory testing (QualST) to determine the early effectiveness of TFESI for the treatment of chronic lumbosacral radiculopathy (LSR)-related pain.

METHODS

Thirty-six patients with chronic painful unilateral LSR were evaluated in a prospective observational study using five standardized sensory tests (10 g monofilament, 200 to 400 mN brush, Lindblom rollers with controlled 25 and 40°C temperature, and 40 g neurological pin). Quality of sensory perceptions on the painful leg was compared to the non-painful leg and rated as normal sensitivity, hyposensitivity, or hypersensitivity. Pain and related characteristics were evaluated before TFESI, 1 week after and 4 weeks after intervention.

RESULTS

Seven sensory phenotypes were distinguished according to individual sets of sensory disturbances acquired with five sensory tests. Patients were grouped into four groups of allied phenotypes (normal sensitivity, hyposensitivity to 1 to 3 modalities, hyposensitivity to 4 to 5 modalities, and hypersensitivity). The whole study group showed significant improvement in most parameters of outcome measurements. Statistical analysis revealed some significant differences between sensory groups in patient-reported treatment effect scales after 4 weeks. We also detected significant differences between sensory groups in repeated measures after 1 and 4 weeks in some pain intensity characteristics and patient-reported treatment effect scales.

CONCLUSION

QualST might be clinically applicable for detecting patient subgroups that could differ in the early treatment results of radicular pain by TFESI.

Age differences in cognitive-affective processes in adults with chronic pain

BACKGROUND

Chronic pain is associated with significant physical and psychological impairments across the adult lifespan. However, there is a relative gap in knowledge on individual differences that predict pain-related functioning. The current study highlights one important source of individual variation: age.

METHODS

We used cross-sectional data from a large treatment-seeking cohort of 2,905 adults (M age = 46.6 [13.1]; 71.8% women) presenting to a tertiary pain centre in the United Kingdom to determine age differences in cognitive-affective processes (catastrophizing, acceptance, self-efficacy), including their differential patterns and effects on disability and depression.

RESULTS

Older adults (ages 65-75) were found to experience higher pain acceptance and pain self-efficacy compared to both middle-aged (ages 40-64) and young adult (ages 18-39) age groups. Older adults also experienced lower levels of catasophizing compared to middle-age adults. Testing age as a moderator, we found that the relationships of pain self-efficacy and acceptance with depression as well as the relationship between pain self-efficacy and disability were comparatively weakest among older adults and strongest among young adults. Similarly, the relationship between pain catastrophizing and depression was relatively stronger for young and middle-aged adults compared to older adults.

CONCLUSIONS

Age-related differences in psychological mechanisms that influence pain-related functioning present unique challenges and opportunities for scientists and clinicians to improve our understanding and treatment of pain across the lifespan. Additional work is needed to refine our knowledge of age-related differences in cognitive-affective, biopsychosocial dimensions of chronic pain and to develop and test the efficacy of age-tailored interventions.

SIGNIFICANCE

Our cross-sectional analysis of 2,905 treatment-seeking adults with chronic pain presenting to a tertiary care center in the United Kingdom revealed distinct age differences in cognitive-affective linked to disability and depression. This study contributes to the limited knowledge on age-related variance in psychological mechanisms underlying adjustment to chronic pain. Promising avenues for future research include refining our understanding of age-related differences in cognitive-affective, biopsychosocial dimensions of chronic pain and elucidating the most salient treatment targets among different age groups.

Optimizing management of low back pain through the pain and disability drivers management model: A feasibility trial

INTRODUCTION

Self-reported levels of disability in individuals with low back pain (LBP) have not improved in the last decade. A broader perspective and a more comprehensive management framework may improve disability outcomes. We recently developed and validated the Low Back Pain and Disability Drivers Management (PDDM) model, which aims to identify the domains driving pain and disability to guide clinical decisions. The objectives of this study were to determine the applicability of the PDDM model to a LBP population and the feasibility of conducting a pragmatic trial, as well as to explore clinicians' perceived acceptability of the PDDM model's use in clinical settings.

METHODS

This study was an one-arm prospective feasibility trial. Participants included physiotherapists working with a population suffering from LBP and their patients aged 18 years or older presenting with a primary complaint of LBP that sought a new referral and deemed fit for rehabilitation from private and public clinical settings. Clinicians participated in a one-day workshop on the integration of the PDDM model into their clinical practice, and were asked to report various LBP-related outcomes via self-reported questionnaires (i.e., impact of pain on physical function, nervous system dysfunctions, cognitive-emotional factors, work disabilities) at baseline and at six-week follow-up. Physiotherapists' acceptability of the use of the PDDM model and appreciation of the training were assessed via semi-structured phone interviews. Analyses focused on a description of the model's applicability to a LBP population, feasibility outcomes and acceptability measures.

RESULTS

Applicablity of the PDDM model was confirmed since it successfully established the profile of patients according to the elements of each categories, and each of the 5 domains of the model was represented among the study sample. Trial was deemed feasible contingent upon few modifications as our predefined success criteria for the feasibility outcomes were met but feasibility issues pertaining to data collection were highlighted. Twenty-four (24) clinicians and 61 patients were recruited within the study's timeframe. Patient's attrition rate (29%) and clinicians' compliance to the study protocol were adequate. Clinicians' perceived acceptability of the use of the model in clinical settings and their appreciation of the training and online resources were both positive. Recommendations to improve the model's integration in clinical practice, content of the workshop and feasibility of data collection methods were identified for future studies. A positive effect for all patients' reported outcome measures were also observed. All outcome measures except for the PainDetect questionnaire showed a statistically significant reduction post-intervention (p<0.05).

CONCLUSION

These findings provide preliminary evidence of the potential of the PDDM model to optimize LBP management as well as conducting a future larger-scale pragmatic trial to determine its effectiveness.

TRIAL REGISTRATION

Clinicaltrial.gov: NCT03949179.

Psychometric properties of Short Form-36 Health Survey, EuroQol 5-dimensions, and Hospital Anxiety and Depression Scale in patients with chronic pain

Supplemental Digital Content is Available in the Text.

This large-sample item response theory-based evaluation assessed the measurement properties of SF-36, EQ-5D, and hospital anxiety and depression scale for chronic pain patients in clinical settings.

Recent research has highlighted a need for the psychometric evaluation of instruments targeting core domains of the pain experience in chronic pain populations. In this study, the measurement properties of Short Form-36 Health Survey (SF-36),EuroQol 5-dimensions (EQ-5D) and Hospital Anxiety and Depression Scale (HADS) were analyzed within the item response-theory framework based on data from 35,908 patients. To assess the structural validity of these instruments, the empirical representations of several conceptually substantiated latent structures were compared in a cross-validation procedure. The most structurally sound representations were selected from each questionnaire and their internal consistency reliability computed as a summary of their precision. Finally, questionnaire scores were correlated with each other to evaluate their convergent and discriminant validity. Our results supported that SF-36 is an acceptable measure of 2 independent constructs of physical and mental health. By contrast, although the approach to summarize the health-related quality of life construct of EQ-5D as a unidimensional score was valid, its low reliability rendered practical model implementation of doubtful utility. Finally, rather than being separated into 2 subscales of anxiety and depression, HADS was a valid and reliable measure of overall emotional distress. In support of convergent and discriminant validity, correlations between questionnaires showed that theoretically similar traits were highly associated, whereas unrelated traits were not. Our models can be applied to score SF-36 and HADS in chronic pain patients, but we recommend against using the EQ-5D model due to its low reliability. These results are useful for researchers and clinicians involved in chronic pain populations because questionnaires' properties determine their discriminating ability in patient status assessment.

Clinical outcome assessment in clinical trials of chronic pain treatments

Clinical outcome assessments (COAs) measure outcomes that are meaningful to patients in clinical trials and are critical for determining whether a treatment is effective. The objectives of this study are to (1) describe the different types of COAs and provide an overview of key considerations for evaluating COAs, (2) review COAs and other outcome measures for chronic pain treatments that are recommended by the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) or other expert groups, and (3) review advances in understanding pain-related COAs that are relevant to clinical trials. The authors reviewed relevant articles, chapters, and guidance documents from the European Medicines Agency and U.S. Food and Drug Administration. Since the original core set of outcome measures were recommended by IMMPACT 14 years ago, several new advancements and publications relevant to the measurement or interpretation of COAs for chronic pain trials have emerged, presenting new research opportunities. Despite progress in the quality of measurement of several outcome domains for clinical trials of chronic pain, there remain some measurement challenges that require further methodological investigation.

Essential statistical principles of clinical trials of pain treatments

This article presents an overview of fundamental statistical principles of clinical trials of pain treatments. Statistical considerations relevant to phase 2 proof of concept and phase 3 confirmatory randomized trials investigating efficacy and safety are discussed, including (1) research design; (2) endpoints and analyses; (3) sample size determination and statistical power; (4) missing data and trial estimands; (5) data monitoring and interim analyses; and (6) interpretation of results. Although clinical trials of pharmacologic treatments are emphasized, the key issues raised by these trials are also directly applicable to clinical trials of other types of treatments, including biologics, devices, nonpharmacologic therapies (eg, physical therapy and cognitive-behavior therapy), and complementary and integrative health interventions.

The ACTTION Guide to Clinical Trials of Pain Treatments, part II: mitigating bias, maximizing value

Summaries of the articles included in part II of the ACTTION Guide to Clinical Trials of Pain Treatments are followed by brief overviews of methodologic considerations involving precision pain medicine, pragmatic clinical trials, real world evidence, and patient engagement in clinical trials.

Design and conduct of confirmatory chronic pain clinical trials

The purpose of this article is to provide readers with a basis for understanding the emerging science of clinical trials and to provide a set of practical, evidence-based suggestions for designing and executing confirmatory clinical trials in a manner that minimizes measurement error. The most important step in creating a mindset of quality clinical research is to abandon the antiquated concept that clinical trials are a method for capturing data from clinical practice and shifting to a concept of the clinical trial as a measurement system, consisting of an interconnected set of processes, each of which must be in calibration for the trial to generate an accurate and reliable estimate of the efficacy (and safety) of a given treatment. The status quo of inaccurate, unreliable, and protracted clinical trials is unacceptable and unsustainable. This article gathers aspects of study design and conduct under a single broad umbrella of techniques available to improve the accuracy and reliability of confirmatory clinical trials across traditional domain boundaries.

Electroacupuncture for Treating Chronic Low-Back Pain: Preliminary Research Results

This report, prepared by a lead researcher, describes 2 independent, but similarly designed, clinical trials that were conducted to investigate the effectiveness, mechanisms, and predictors of electroacupuncture (EA) for treating chronic low-back pain (CLBP). Both trials recruited adults (ages 21-65) who had CLBP with an intensity ≥4/10 and a duration ≥6 months. Verum EA or sham EA was administered twice per week for 6-8 weeks. The common outcome between the 2 studies was the patients' responses to the Roland Morris Disability Questionnaire. Using least absolute shrinkage and selection operator (LASSO), the authors were able to predict clinical outcome in the second study by using a prediction model based on data from the first study. This work demonstrated the feasibility of predicting clinical outcomes when using acupuncture for treating CLBP.

Hopes and fears before opioid tapering: a quantitative and qualitative study of patients with chronic pain and long-term opioids

Background

It is clear that the risks of opioids in chronic pain outweigh the benefits, creating a drive for clinicians to support patients taper and stop long-term opioids. However, it is not known how patients who have been taking these medicines for months or years feel about reducing them. Using quantitative and qualitative data, this study describes the psychological complexity of these patients and examines their hopes and fears before opioid reduction.

Methods

Sixty patients attending the opioid clinic completed psychological and pain questionnaires, providing quantitative data, just before they commenced opioid tapering. They scored the severity of opioid side effects and completed a free text framework to express their beliefs about stopping or continuing opioids. A phenomenological approach was used to identify common qualitative themes.

Results

Most patients were taking opioid doses above the UK recommended maximum dose and reported severe pain with high pain interference. Over 80% of patients described significant depression and 60% significant anxiety. Negative themes around stopping opioids were more common than positive ones, with 63% patients fearing increased pain. A quarter of patients referred to addiction and 16% feared withdrawal. Five patients hoped for a better quality of life; seven feared a worse one. Opioid side effects were common and severe.

Conclusion

Patients with chronic pain taking long-term opioids demonstrate high psychological distress and low self-efficacy. Their concerns around opioid tapering relate to pain, quality of life and withdrawal. Identifying and addressing patients' individual concerns should increase the likelihood of successful opioid tapering.

II. Indices of Pain Intensity Derived From Ecological Momentary Assessments and Their Relationships With Patient Functioning: An Individual Patient Data Meta-analysis

Pain intensity is a complex and dynamic experience. A focus on assessing patients' average pain levels may miss important aspects of pain that impact functioning in daily life. In this second of 3 articles investigating alternative indices of pain intensity derived from Ecological Momentary Assessments (EMA), we examine the indices' associations with physical and psychosocial functioning. EMA data from 10 studies (2,660 patients) were reanalyzed to construct indices of Average Pain, Maximum Pain, Minimum Pain, Pain Variability, Time in High Pain, Time in Low Pain, Pain after Wake-up. Three sets of individual patient data meta-analyses examined 1) the test-retest reliability of the pain indices, 2) their convergent validity in relation to physical functioning, fatigue, depression, mental health, and social functioning, and 3) the incremental validity of alternative indices above Average Pain. Reliabilities approaching or exceeding a level of .7 were observed for all indices, and most correlated significantly with all functioning domains, with small to medium effect sizes. Controlling for Average Pain, Maximum Pain and Pain Variability uniquely predicted all functioning measures, and Time in High Pain predicted physical and social functioning. We suggest that alternative pain indices can provide new perspectives for understanding functioning in chronic pain. PERSPECTIVE: Alternative summary measures of pain intensity derived from EMA have the potential to help better understand patients' pain experience. Utilizing EMA for the assessment of Maximum Pain, Pain Variability, and Time in High Pain may provide an enhanced window into the relationships between pain and patients' physical and psychosocial functioning.

An exploration of psychological symptom-based phenotyping of adult cochlear implant users with and without tinnitus using a machine learning approach

The identification of phenotypes within populations with troublesome tinnitus is an important step towards individualizing tinnitus treatments to achieve optimal outcomes. However, previous application of clustering algorithms has called into question the existence of distinct tinnitus-related phenotypes. In this study, we attempted to characterize patients' symptom-based phenotypes as subpopulations in a Gaussian mixture model (GMM), and subsequently performed a comparison with tinnitus reporting. We were able to effectively evaluate the statistical models using cross-validation to establish the number of phenotypes in the cohort, or a lack thereof. We examined a cohort of adult cochlear implant (CI) users, a patient group for which a relation between psychological symptoms (anxiety, depression, or insomnia) and trouble tinnitus has previously been shown. Accordingly, individual item scores on the Hospital Anxiety and Depression Scale (HADS; 14 items) and the Insomnia Severity Index (ISI; 7 items) were selected as features for training the GMM. The resulting model indicated four symptom-based subpopulations, some primarily linked to one major symptom (e.g., anxiety), and others linked to varying severity across all three symptoms. The presence of tinnitus was self-reported and tinnitus-related handicap was characterized using the Tinnitus Handicap Inventory. Specific symptom profiles were found to be significantly associated with CI users' tinnitus characteristics. GMMs are a promising machine learning tool for identifying psychological symptom-based phenotypes, which may be relevant to determining appropriate tinnitus treatment.

Patient and Disease Characteristics Associate With Sensory Testing Results in Chronic Pancreatitis

BACKGROUND

Abdominal pain is the most common symptom in chronic pancreatitis (CP) and has an extensive impact on patients' lives. Quantitative sensory testing (QST) provides information on sensitivity to pain and mechanisms that can help quantify pain and guide treatment. The aims of this study were (1) to explore sensitivity to pain in patients with CP using QST and (2) to associate patient and disease characteristics with QST results.

METHODS

Ninety-one patients with painful CP and 28 healthy control participants completed a QST paradigm using static tests (muscle pressure stimulation and electrical skin stimulations) to unravel segmental and widespread hyperalgesia as a consequence of visceral pain. A dynamic conditioned pain modulation (CPM) paradigm was used as a proxy of pain modulation from the brainstem to inhibit incoming nociceptive barrage, and questionnaires were used to gather information on pain experience and quality of life.

RESULTS

Patients had impaired CPM compared with controls (18.0±29.3% vs. 30.9±29.3%, P=0.04) and were hypersensitive to pressure stimulation, specifically in the pancreatic (Th10) dermatome (P<0.001). The capacity of CPM was associated with clinical pain intensity (P=0.01) and (in the univariate analysis only) the use of opioids was associated with hyperalgesia to pressure stimulation (P<0.05).

CONCLUSIONS

Sensitivity to pain in CP patients can be characterized by a simple bedside QST. Severe clinical pain in CP was associated with reduced CPM function and should be targeted in management.

Internet-Based Multimodal Pain Program With Telephone Support for Adults With Chronic Temporomandibular Disorder Pain: Randomized Controlled Pilot Trial

BACKGROUND

Chronic pain from temporomandibular disorders remains an undertreated condition with debate regarding the most effective treatment modalities.

OBJECTIVE

The aim of the study was to investigate the treatment effect of an internet-based multimodal pain program on chronic temporomandibular disorder pain and evaluate the feasibility of a larger randomized controlled trial.

METHODS

An unblinded randomized controlled pilot trial was conducted with 43 participants (34 females, 9 males; median age 27, IQR 23-37 years) with chronic temporomandibular pain. Participants were recruited within the Public Dental Health Service and randomized to intervention (n=20) or active control (n=23). The intervention comprised a dentist-assisted internet-based multimodal pain program with 7 modules based on cognitive behavior therapy and self-management principles. The control group received conventional occlusal splint therapy. Primary outcomes included characteristic pain intensity, pain-related disability, and jaw functional limitation. Secondary outcomes were depression, anxiety, catastrophizing, and stress. Outcomes were self-assessed through questionnaires sent by mail at 3 and 6 months after treatment start. Feasibility evaluation included testing the study protocol and estimation of recruitment and attrition rates in the current research setting.

RESULTS

Only 49% of participants (21/43) provided data at the 6-month follow-up (internet-based multimodal pain program: n=7; control: n=14). Of the 20 participants randomized to the internet-based multimodal pain program, 14 started treatment and 8 completed all 7 modules of the program. Between-group analysis showed no significant difference for any outcome measure at 3- or 6-month follow-up-characteristic pain intensity (3 months: P=.58; 6 months: P=.41), pain-related disability (3 months: P=.51; 6 months: P=.12), jaw functional limitation (3 months: P=.45; 6 months: P=.90), degree of depression (3 months: P=.64; 6 months: P=.65), anxiety (3 months: P=.93; 6 months: P=.31), stress (3 months: P=.66; 6 months: P=.74), or catastrophizing (3 months: P=.86; 6 months: P=.85). Within-group analysis in the internet-based multimodal pain program group showed a significant reduction in jaw functional limitation score at the 6-month follow-up compared to baseline (Friedman: χ2=10.2, P=.04; Wilcoxon: z=-2.3, P=.02). In the occlusal splint group, jaw function limitation was also reduced at the 6-month follow-up (Friedman: χ2=20.0, P=.045; Wilcoxon: z=-2.3, P=.02), and there was a reduction in characteristic pain intensity at the 3- and 6-month follow-up (Friedman: χ2=25.1, P=.01; Wilcoxon 3 months: z=-3.0, P=.003; Wilcoxon 6 months: z=-3.3, P=.001).

CONCLUSIONS

This study was not able to demonstrate a difference in treatment outcome between an internet-based multimodal pain program and occlusal splint therapy in patients with chronic temporomandibular pain. However, the findings suggested that the internet-based multimodal pain program improves jaw function. The results also confirmed the treatment effect of occlusal splint therapy for chronic temporomandibular pain. Furthermore, because of the high attrition rate, this pilot study showed that a randomized controlled trial with this design is not feasible.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04363762; https://clinicaltrials.gov/show/NCT04363762.

Trajectories in severe persistent pain after groin hernia repair: a retrospective analysis

Objectives

Severe persistent post-surgical pain (PPSP) remains a significant healthcare problem. In the third most common surgical procedure in the U.K., groin hernia repair, including 85,000 surgeries, estimated 1,500–3,000 patients will annually develop severe PPSP. While the trajectory of PPSP is generally considered a continuation of the acute post-surgery pain, recent data suggest the condition may develop with a delayed onset. This study evaluated pain-trajectories in a consecutive cohort referred from groin hernia repair-surgeons to a tertiary PPSP-center. Potential explanatory variables based on individual psychometric, sensory, and surgical profiles were analyzed.

Methods

Patients completed graphs on pain trajectories and questionnaires on neuropathic pain, pain-related functional assessments, and psychometrics. Surgical records and quantitative sensory testing profiles were obtained. Pain trajectories were normalized, and pre- and post-surgical segments were analyzed by a normalized area-under-the-curve (AUC) technique. Principal component analysis (PCA) was applied to the explanatory variables. Significant PCA-components were further examined using multiple logistic regression models.

Results

In 95 patients, the AUC identified groups of post-surgical pain trajectories (p<0.0001): group I (n=48), acute high-intensity pain progressing to PPSP; group II (n=28), delayed onset of PPSP; group III (n=7), repeat-surgery gradually inducing PPSP. Data from groups IV (n=3) and V (n=9) were not included in the statistical analysis due to small sample size and data heterogeneity, respectively. The PCA/logistic analyses indicated that neuropathic pain scores, composite pain scores, and pain-related functional assessments were explanatory variables for groups I and II.

Conclusions

Pain trajectories in PPSP after groin hernia repair are heterogeneous but can be classified into meaningful groups. Examination of pain trajectories, mirroring the transition from acute to severe persistent post-surgical pain, has the potential of uncovering clinically relevant pathophysiological mechanisms.

COMT Genotype and Efficacy of Propranolol for TMD Pain: A Randomized Trial

Propranolol is a nonselective β-adrenergic receptor antagonist that is efficacious in reducing facial pain. There is evidence that its analgesic efficacy might be modified by variants of the catechol-O-methyltransferase (COMT) gene. We tested the hypothesis in a subset of 143 non-Hispanic Whites from a randomized controlled trial of patients with painful temporomandibular disorder (TMD). Patients were genotyped for rs4680, a single nucleotide polymorphism of COMT, and randomly allocated to either propranolol 60 mg twice daily or placebo. During the 9-wk follow-up period, patients recorded daily ratings of facial pain intensity and duration; the product was computed as an index of facial pain. Postbaseline change in the index at week 9 (the primary endpoint) was analyzed as a continuous variable and dichotomized at thresholds of ≥30% and ≥50% reduction. Mixed models for repeated measures tested for the genotype × treatment group interaction and estimated means, odds ratios (ORs), and 95% confidence limits (95% CLs) of efficacy within COMT genotypes assuming an additive genetic model. In secondary analysis, the cumulative response curves were plotted for dichotomized reductions ranging from ≥20% to ≥70%, and genotype differences in area under the curve percentages (%AUC) were calculated to signify efficacy. Mean index reduction did not differ significantly (P = 0.277) according to genotype, whereas the dichotomized ≥30% reduction revealed greater efficacy among G:G homozygotes (OR = 10.9, 95%CL = 2.4, 50.7) than among A:A homozygotes (OR = 0.8, 95%CL = 0.2, 3.2) with statistically significant interaction (P = 0.035). Cumulative response curves confirmed greater (P = 0.003) efficacy for G:G homozygotes (%AUC difference = 43.7, 95%CL = 15.4, 72.1) than for A:A homozygotes (%AUC difference = 6.5, 95%CL = -30.2, 43.2). The observed antagonistic effect of the A allele on propranolol’s efficacy was opposite the synergistic effect hypothesized a priori. This unexpected result highlights the need for better knowledge of COMT’s role in pain pathogenesis if the gene is to be used for precision-medicine treatment of TMD (ClinicalTrials.gov NCT02437383).

Trajectories of Pain Intensity Over 1 Year in Adults With Disabling Subacute or Chronic Neck Pain

Supplemental Digital Content is available in the text.

Objectives:

The objectives of this study were to describe the 1-year trajectories of disabling subacute or persistent neck pain and to investigate whether baseline age, sex, pain characteristics, and depressive symptoms are associated with such trajectories.

Study Design and Setting:

Participants (n=617) included in a randomized controlled trial provided weekly pain intensity ratings by responding to text messages over 1 year. We used latent class mixed model analyses to identify clusters of individual trajectories. Thereafter, we used logistic regression to determine the association between baseline age, sex, pain characteristics, depressive symptoms and treatment, and trajectories of neck pain.

Results:

Six different clusters of trajectories were identified. Most participants (73%) followed a trajectory of decreasing pain throughout follow-up. The remaining experienced unfavorable trajectories: persistent pain of high intensity (22%) and slightly (3%) or highly (2%) fluctuating levels of pain reaching high levels of pain intensity. Pain intensity at baseline: odds ratio (OR): 3.76 (95% confidence interval [CI]: 2.49-5.68), depressive symptoms: OR: 3.46 (95% CI: 2.01-5.95), younger age: OR: 2.29 (95% CI: 1.48-3.54), female sex: OR: 1.51 (95% CI: 1.01-2.26), and sudden onset of pain: OR: 1.74 (95% CI: 1.13-2.69) were associated with unfavorable trajectories.

Conclusions:

Most individuals with disabling subacute or chronic neck pain show improvement in pain intensity over a year. However, a quarter present unfavorable trajectories. High pain intensity at baseline, depressive symptoms, younger age, female sex, and sudden onset of pain are factors associated with unfavorable trajectories.

Reliability and Validity of the Boston Bedside Quantitative Sensory Testing Battery for Neuropathic Pain

OBJECTIVE

Recent studies suggest that sensory phenotyping may provide critical information for the diagnosis and management of patients with chronic neuropathic pain (NP). However, many formal quantitative sensory testing (QST) paradigms require expensive equipment, a dedicated location, and substantial time commitments on the part of patient and examiner, highlighting the need for a convenient and portable "bedside" QST battery. We developed and tested a bedside QST battery in a sample of patients with chronic NP.

METHODS

Participants (N = 51) attended two in-person visits over approximately two weeks, during which they underwent QST using both laboratory-based equipment and simple, easily accessible bedside tools. Participants also completed questionnaires about their daily pain and NP symptoms.

RESULTS

Test-retest reliability estimates were highly statistically significant and did not differ between bedside (mean r = 0.60) and laboratory-based (mean r = 0.72) QST. Bedside QST variables and corresponding laboratory-based QST variables were highly correlated, suggesting adequate criterion validity for the bedside tests.

CONCLUSIONS

Results from the present study may have important implications for the sensory phenotyping and subsequent management of patients with chronic NP. Implementation of a protocol that uses inexpensive, portable, and convenient tools may allow for the application of QST in variety of clinical settings and advance NP research.

High individual pain variability in people living with HIV: A graphical analysis

BACKGROUND

People living with HIV (PLWH) frequently experience pain. Following calls to analyse individual-level data in addition to group-level data in pain studies, we compared individual and group-level changes in pain prevalence, intensity and number of pain sites over 48 weeks in a large cohort of PLWH. This is the largest ever cohort study of pain in PLWH, and is the first to report pain at the level of the individual.

METHODS

Participants included all participants with complete pain records from a randomized clinical trial (RCT) for the treatment of HIV (n = 787/1053). At weeks 0, 12, 24, 36 and 48 we assessed participants' pain in the last week; presence of pain, and if present, the intensity and locations of the pain. We used standard averaging methods to describe data at the group level, and unique graphical reporting methods to analyse data at the level of the individual.

RESULTS

Group-level data demonstrated a trend for pain prevalence to decline over time (19% week 0, 12% week 48). Worst pain intensity remained stable (median between 4/10 and 5/10), as did the number (median = 1) and common sites of pain across the 48 weeks. In contrast, individual-level data demonstrated high intra-individual variability with regards to the presence of pain, and the intensity and location of the pain.

CONCLUSIONS

While our group-level data were similar to previous longitudinal studies, an apparent reduction in pain over 48 weeks, the individual-level data showed large variability within individuals in that same time frame.

SIGNIFICANCE

This graphical analysis highlights the high variability in pain (pain prevalence, intensity and body sites) across time in people living with HIV, and how presenting averaged data hides this important variability. Our data support the reporting of individual-level data in human experimental and observational studies.

Subgroups of Pediatric Patients With Functional Abdominal Pain: Replication, Parental Characteristics, and Health Service Use

OBJECTIVES

Prior work in a cohort of youth with functional abdominal pain (FAP) identified patient subgroups (High Pain Dysfunctional, High Pain Adaptive, Low Pain Adaptive) that predicted differences in the course of FAP from childhood into young adulthood. We aimed to replicate these subgroups in a new sample of adolescents with FAP using the original classification algorithm and to extend subgroup characteristics to include parental characteristics and health service use.

METHODS

Adolescents (n=278; ages 11 to 17 y, 66% females) presenting to a gastroenterology clinic for abdominal pain, and their parents (92% mothers) completed self-report measures; adolescents also completed a 7-day pain diary.

RESULTS

The replicated patient subgroups exhibited distress and impairment similar to subgroups in the original sample. Moreover, in novel findings, the High Pain Dysfunctional subgroup differed from other subgroups by the predominance of mother-daughter dyads jointly characterized by high levels of anxiety, depressive symptoms, pain behavior, and pain catastrophizing. The High Pain Dysfunctional subgroup used more health care services than Low Pain Adaptive but did not differ from High Pain Adaptive.

DISCUSSION

Findings replicate and extend the original FAP classification and suggest that the subgroups have unique patient and parent features that may reflect distinct illness mechanisms requiring different treatments.

Low-Dose Naltrexone for the Treatment of Fibromyalgia: Investigation of Dose–Response Relationships

Objective

This study explores dose–response relationships when treating fibromyalgia with low-dose naltrexone.

Design

A single-blinded clinical trial was carried out using the “up-and-down” method.

Subjects

Subjects included women with a diagnosis of fibromyalgia aged 18–60 years who had been referred to treatment at a public pain clinic at a Danish university hospital.

Methods

The test doses were in the range 0.75–6 mg, and the dosing interval was 0.75 mg. The method was sequential and allowed predicting the dose effective in 50% (ED50) and 95% (ED95) of the subjects when the dose had shifted direction 10 times, and six pairs of “up-and-down” data were available.

Results

A total of 27 subjects were included in the study; two subjects were withdrawn. After inclusion of 25 evaluable subjects, the dose estimates were calculated as 3.88 mg for ED50 and 5.40 mg for ED95. As a secondary outcome, the effects on 10 common fibromyalgia symptoms were evaluated. A high interindividual variation was observed both in the symptom presentation at baseline and in which symptoms were reduced by low-dose naltrexone.

Conclusions

This study is the first to explore dose–response relationships in the treatment of fibromyalgia with low-dose naltrexone. Future placebo-controlled randomized clinical trials are needed, and according to our findings, 4.5 mg, which has previously been used, seems to be a relevant test dose. We recommend that future studies include additional nonpain fibromyalgia symptoms as outcome measures.

Latent Class Trajectory Modeling of 2-Component Disease Activity Score in 28 Joints Identifies Multiple Rheumatoid Arthritis Phenotypes of Response to Biologic Disease-Modifying Antirheumatic Drugs

OBJECTIVE

To determine whether using a reweighted disease activity score that better reflects joint synovitis, i.e., the 2-component Disease Activity Score in 28 joints (DAS28) (based on swollen joint count and C-reactive protein level), produces more clinically relevant treatment outcome trajectories compared to the standard 4-component DAS28.

METHODS

Latent class mixed modeling of response to biologic treatment was applied to 2,991 rheumatoid arthritis (RA) patients in whom treatment with a biologic disease-modifying antirheumatic drug was being initiated within the Biologics in Rheumatoid Arthritis Genetics and Genomics Study Syndicate cohort, using both 4-component and 2-component DAS28 scores as outcome measures. Patient groups with similar trajectories were compared in terms of pretreatment baseline characteristics (including disability and comorbidities) and follow-up characteristics (including antidrug antibody events, adherence to treatments, and blood drug levels). We compared the trajectories obtained using the 4- and 2-component scores to determine which characteristics were better captured by each.

RESULTS

Using the 4-component DAS28, we identified 3 trajectory groups, which is consistent with previous findings. We showed that the 4-component DAS28 captures information relating to depression. Using the 2-component DAS28, 7 trajectory groups were identified; among them, distinct groups of nonresponders had a higher incidence of respiratory comorbidities and a higher proportion of antidrug antibody events. We also identified a group of patients for whom the 2-component DAS28 scores remained relatively low; this group included a high percentage of patients who were nonadherent to treatment. This highlights the utility of both the 4- and 2-component DAS28 for monitoring different components of disease activity.

CONCLUSION

Here we show that the 2-component modified DAS28 defines important biologic and clinical phenotypes associated with treatment outcome in RA and characterizes important underlying response mechanisms to biologic drugs.

Daytime and Nighttime Sleep Characteristics and Pain Among Adults With Stable Heart Failure

BACKGROUND

Pain and sleep disturbance are common among patients with heart failure (HF) and are associated with symptom burden, disability, and poor quality of life. Little is known about the associations between specific sleep characteristics and pain in people with HF.

OBJECTIVE

The aim of this study was to describe the relationships between nocturnal sleep characteristics, use of sleep medication, and daytime sleep characteristics and pain among people with HF.

METHODS

We conducted a cross-sectional study of stable participants with HF. We administered the SF36 Bodily Pain Scale, Pittsburgh Sleep Quality Index, and Sleep Habits Questionnaire and obtained 3 days of wrist actigraphy and 1 night of home unattended polysomnography. We conducted bivariate analyses and generalized linear models.

RESULTS

The sample included 173 participants (mean [SD] age, 60 [16.1] years; 65.3% [n = 113] male). Insomnia symptoms (P = .0010), sleep duration (P = .0010), poor sleep quality (P = .0153), use of sleep medications (P = .0170), napping (P = .0029), and daytime sleepiness (P = .0094) were associated with increased pain. Patients with the longest sleep duration, who also had insomnia, had more pain (P = .0004), fatigue (P = .0028), daytime sleepiness (P = .0136), and poorer sleep quality (P < .0001) and took more sleep medications (P = .0029) than did those without insomnia.

CONCLUSIONS

Pain is associated with self-reported poor sleep quality, napping, daytime sleepiness, and use of sleep medication. The relationship between pain and sleep characteristics differs based on the presence of insomnia and sleep duration. Studies are needed to evaluate the causal relationships between sleep and pain and test interventions for these cooccurring symptoms.

Discovery and validation of biomarkers to aid the development of safe and effective pain therapeutics: challenges and opportunities

Pain medication plays an important role in the treatment of acute and chronic pain conditions, but some drugs, opioids in particular, have been overprescribed or prescribed without adequate safeguards, leading to an alarming rise in medication-related overdose deaths. The NIH Helping to End Addiction Long-term (HEAL) Initiative is a trans-agency effort to provide scientific solutions to stem the opioid crisis. One component of the initiative is to support biomarker discovery and rigorous validation in collaboration with industry leaders to accelerate high-quality clinical research into neurotherapeutics and pain. The use of objective biomarkers and clinical trial end points throughout the drug discovery and development process is crucial to help define pathophysiological subsets of pain, evaluate target engagement of new drugs and predict the analgesic efficacy of new drugs. In 2018, the NIH-led Discovery and Validation of Biomarkers to Develop Non-Addictive Therapeutics for Pain workshop convened scientific leaders from academia, industry, government and patient advocacy groups to discuss progress, challenges, gaps and ideas to facilitate the development of biomarkers and end points for pain. The outcomes of this workshop are outlined in this Consensus Statement.

Reconnecting the Brain With the Rest of the Body in Musculoskeletal Pain Research

A challenge in understanding chronic musculoskeletal pain is that research is often siloed between neuroscience, physical therapy/rehabilitation, orthopedics, and rheumatology which focus respectively on 1) neurally mediated effects on pain processes, 2) behavior and muscle activity, 3) tissue structure, and 4) inflammatory processes. Although these disciplines individually study important aspects of pain, there is a need for more cross-disciplinary research that can bridge between them. Identifying the gaps in knowledge is important to understand the whole body, especially at the interfaces between the silos-between brain function and behavior, between behavior and tissue structure, between musculoskeletal and immune systems, and between peripheral tissues and the nervous system. Research on "mind and body" practices can bridge across these silos and encourage a "whole person" approach to better understand musculoskeletal pain by bringing together the brain and the rest of the body. PERSPECTIVE: Research on chronic musculoskeletal pain is limited by significant knowledge gaps. To be fully integrated, musculoskeletal pain research will need to bridge across tissues, anatomical areas, and body systems. Research on mind and body approaches encourages a "whole person" approach to better understand musculoskeletal pain.

Individual differences of maladaptive brain changes in migraine and their relationship with differential effectiveness of treatments

Migraine is a difficult disorder to identify with regard to its pathophysiological mechanisms, and its treatment has been primarily difficult owing to interindividual differences. Substantial rates of nonresponsiveness to medications are common, making migraine treatment complicated. In this review, we systematically analyzed recent studies concerning neuroimaging findings regarding the neurophysiology of migraine. We linked the current imaging research with anecdotal evidence from interindividual factors such as duration and pain intensity of migraine, age, gender, hormonal interplay, and genetics. These factors suggested the use of nonpharmacological therapies such as transcranial magnetic stimulation, transcranial direct current stimulation, and placebo therapy for the treatment of migraine. Finally, we discussed how interindividual differences are related to such nondrug treatments.

A Step Towards a Better Understanding of Pain Phenotypes: Latent Class Analysis in Chronic Pain Patients Receiving Multimodal Inpatient Treatment

Purpose

The number of non-responders to treatment among patients with chronic pain (CP) is high, although intensive multimodal treatment is broadly accessible. One reason is the large variability in manifestations of CP. To facilitate the development of tailored treatment approaches, phenotypes of CP must be identified. In this study, we aim to identify subgroups in patients with CP based on several aspects of self-reported health.

Patients and Methods

A latent class analysis (LCA) was carried out in retrospective data from 411 patients with CP of different origins. All patients experienced severe physical and psychosocial consequences and were therefore undergoing multimodal inpatient pain treatment. Self-reported measures of pain (visual analogue scales for pain intensity, frequency, and impairment; Pain Perception Scale), emotional distress (Patient Health Questionnaire, PHQ-9; Generalized Anxiety Disorder Scale, GAD-7) and physical health (Short Form Health Survey; SF-8) were collected immediately after admission and before discharge. Instruments assessed at admission were used as input to the LCA. Resulting classes were compared in terms of patient characteristics and treatment outcome.

Results

A model with four latent classes demonstrated the best model fit and interpretability. Classes 1 to 4 included patients with high (54.7%), extreme (17.0%), moderate (15.6%), and low (12.7%) pain burden, respectively. Patients in class 4 showed high levels of emotional distress, whereas emotional distress in the other classes corresponded to the levels of pain burden. While pain as well as physical and mental health improved in class 1, only the levels of depression and anxiety improved in patients in the other groups during multimodal treatment.

Conclusion

The specific needs of these subgroups should be taken into account when developing individualized treatment programs. However, the retrospective design limits the significance of the results and replication in prospective studies is desirable.

The OPTIMIZE study: protocol of a pragmatic sequential multiple assessment randomized trial of nonpharmacologic treatment for chronic, nonspecific low back pain

BACKGROUND

Low back pain is a prevalent condition that causes a substantial health burden. Despite intensive and expensive clinical efforts, its prevalence is growing. Nonpharmacologic treatments are effective at improving pain-related outcomes; however, treatment effect sizes are often modest. Physical therapy (PT) and cognitive behavioral therapy (CBT) have the most consistent evidence of effectiveness. Growing evidence also supports mindfulness-based approaches. Discussions with providers and patients highlight the importance of discussing and trying options to find the treatment that works for them and determining what to do when initial treatment is not successful. Herein, we present the protocol for a study that will evaluate evidence-based, protocol-driven treatments using PT, CBT, or mindfulness to examine comparative effectiveness and optimal sequencing for patients with chronic low back pain.

METHODS

The Optimized Multidisciplinary Treatment Programs for Nonspecific Chronic Low Back Pain (OPTIMIZE) Study will be a multisite, comparative effectiveness trial using a sequential multiple assessment randomized trial design enrolling 945 individuals with chronic low back pain. The co-primary outcomes will be disability (measured using the Oswestry Disability Index) and pain intensity (measured using the Numerical Pain Rating Scale). After baseline assessment, participants will be randomly assigned to PT or CBT. At week 10, participants who have not experienced at least 50% improvement in disability will be randomized to cross-over phase-1 treatments (e.g., PT to CBT) or to Mindfulness-Oriented Recovery Enhancement (MORE). Treatment will consist of 8 weekly sessions. Long-term outcome assessments will be performed at weeks 26 and 52.

DISCUSSION

Results of this study may inform referring providers and patients about the most effective nonoperative treatment and/or sequence of nonoperative treatments to treat chronic low back pain.

TRIAL REGISTRATION

This study was prospectively registered on March 1, 2019, with Clinicaltrials.gov under the registration number NCT03859713 (https://clinicaltrials.gov/ct2/show/NCT03859713).

S100B single nucleotide polymorphisms exhibit sex-specific associations with chronic pain in sickle cell disease in a largely African-American cohort

BACKGROUND

Pain in sickle cell disease (SCD) is severe and multifaceted resulting in significant differences in its frequency and intensity among individuals. In this study, we examined the influence of S100B gene single nucleotide polymorphisms (SNP) on acute and chronic pain variability in SCD.

METHODS

Composite pain index (CPI) scores captured chronic pain. Painful crisis related emergency care utilization recorded acute pain incidence. Genotyping was performed using MassARRAY iPLEX platform.

RESULTS

Regression analysis revealed associations of increased CPI with rs9722 A allele in additive (p = 0.005) and dominant (p = 0.005) models. Rs1051169 G allele on the other hand was associated with decreased CPI in additive (p = 0.001), and dominant (p = 0.005) models. Sex-specific analysis found that these associations were significant in females but not males in this cohort. Linkage analysis identified two haploblocks. Block 1 (rs9983698-rs9722) haplotype T-A was associated with increased CPI (p = 0.002) while block 2 (rs1051169-rs11911834) haplotype G-G was associated with decreased CPI (p = 0.001). Both haplotypic associations were only significant in females. No association of S100B SNPs with utilization reached statistical significance.

CONCLUSIONS

S100B SNPs and haplotypes are associated with chronic pain in female, but not male, patients with SCD, implicating a potential role of S100B polymorphism in SCD pain heterogeneity in a sex-dependent manner.

Moderators of Internet-Delivered Cognitive-Behavioral Therapy for Adolescents With Chronic Pain: Who Benefits From Treatment at Long-Term Follow-Up?

Cognitive behavioral therapy (CBT) is effective for pediatric chronic pain, but little is understood about which youth are most likely to benefit. The current study aimed to identify individual characteristics for which CBT yielded the greatest (and least) clinical benefit among adolescents with chronic pain participating in a multicenter randomized controlled trial of Internet-delivered CBT (WebMAP2). A total of 273 adolescents ages 11 to 17 with chronic pain (M age = 14.7; 75.1% female) were randomly assigned to Internet-delivered CBT or Internet-delivered pain education and evaluated at pretreatment, post-treatment, and 2 longer term follow-up periods (6 and 12 months). Multilevel growth models tested several adolescent- and parent-level moderators of change in pain-related disability including 1) adolescent age, sex, pain characteristics, distress, and sleep quality and 2) parent education level, distress, and protective parenting behavior. Younger adolescents (ages 11-14; vs older adolescents ages 15-17) and those whose parents experienced lower levels (vs higher levels) of emotional distress responded better to Internet CBT treatment, showing greater improvements in disability up to 12 months post-treatment. This study expands knowledge on who benefits most from Internet-delivered psychological treatment for youth with chronic pain in the context of a large multicenter randomized controlled trial, suggesting several avenues for maximizing treatment efficacy and durability in this population. PERSPECTIVE: This study identified adolescent- and parent-level predictors of treatment response to Internet-based CBT for pediatric chronic pain up to 12 months later. Younger adolescents and those whose parents had lower levels of distress may particularly benefit from this intervention. Older adolescents and those whose parents exhibit higher distress may require alternative treatment approaches.

Validity of the cold pressor test and pain sensitivity questionnaire via online self-administration

To determine the feasibility of complex home-based phenotyping, 1,876 research participants from the customer base of 23andMe completed an online version of a Pain Sensitivity Questionnaire (PSQ) as well as a cold pressor test (CPT) which is used in clinical assessments of pain. Overall our online version of the PSQ performed similarly to the original pen-and-paper version. Construct validity of the PSQ total was demonstrated by internal consistency and consistent discrimination between more and less painful items. Criterion validity was demonstrated by correlation with pain sensitivity as measured by the CPT. Within the same cohort we performed a cold pressor test using a layperson description and household equipment. Comparison with published reports from controlled studies revealed similar distributions of cold pain tolerance times (i.e., time elapsed before removing the hand from the water). Of those who elected to participate in the CPT, a large majority of participants did not report issues with the test procedure or noncompliance with the instructions (97%). We confirmed a large sex difference in CPT thresholds in line with published data, such that women removed their hands from the water at a median of 54.2 seconds, with men lasting for a median time of 82.7 seconds (Kruskal-Wallis statistic, p < 0.0001), but other factors like age or current pain treatment were at most weakly associated, and inconsistently between men and women. We introduce a new paradigm for performing pain testing, called testing@home, that, in the case of cold nociception, showed comparable results to studies conducted under controlled conditions and supervision of a health care professional.

Challenges of neuropathic pain: focus on diabetic neuropathy

Neuropathic pain is a frequent condition caused by a lesion or disease of the central or peripheral somatosensory nervous system. A frequent cause of peripheral neuropathic pain is diabetic neuropathy. Its complex pathophysiology is not yet fully elucidated, which contributes to underassessment and undertreatment. A mechanism-based treatment of painful diabetic neuropathy is challenging but phenotype-based stratification might be a way to develop individualized therapeutic concepts. Our goal is to review current knowledge of the pathophysiology of peripheral neuropathic pain, particularly painful diabetic neuropathy. We discuss state-of-the-art clinical assessment, validity of diagnostic and screening tools, and recommendations for the management of diabetic neuropathic pain including approaches towards personalized pain management. We also propose a research agenda for translational research including patient stratification for clinical trials and improved preclinical models in relation to current knowledge of underlying mechanisms.

The addition of blood flow restriction to resistance exercise in individuals with knee pain: a systematic review and meta-analysis

BACKGROUND

Blood flow restriction (BFR) is an effective clinical intervention used to increase strength in healthy individuals. However, its effects on pain and function in individuals with knee pain are unknown.

OBJECTIVE

To determine the effectiveness of adding BFR to resistance exercise for pain relief and improvement of function in patients with knee pain.

METHODS

Systematic review with meta-analysis of randomized clinical trials. Medline, Central, Embase, PEDro, Lilacs, CINAHL, SPORTDiscus, and Web of Science databases were searched from inception to May 2019. Randomized clinical trials that compared resistance exercise with or without BFR to treat knee pain and function in individuals older than 18 years of age with knee pain were included.

RESULTS

Eight randomized clinical trials met the eligibility criteria and for the quantitative synthesis, five studies were included. The pooled standardized mean difference (SMD) estimate showed that resistance exercises with BFR was not more effective than resistance exercises for reducing pain (SMD: -0.37cm, 95% CI=-0.93, 0.19) and improving knee function (SMD=-0.23 points, 95% CI=-0.71, 0.26) in patients with knee pain.

CONCLUSION

In the short term, there is low quality of evidence that resistance exercise with BFR does not provide significant differences in pain relief and knee function compared to resistance exercises in patients with knee pain. PROSPERO registration number: CRD42018102839.

Chemotherapy-induced peripheral neuropathy: where are we now?

Chemotherapy-induced peripheral neuropathy (CIPN) is a major challenge, with increasing impact as oncological treatments, using potentially neurotoxic chemotherapy, improve cancer cure and survival. Acute CIPN occurs during chemotherapy, sometimes requiring dose reduction or cessation, impacting on survival. Around 30% of patients will still have CIPN a year, or more, after finishing chemotherapy. Accurate assessment is essential to improve knowledge around prevalence and incidence of CIPN. Consensus is needed to standardize assessment and diagnosis, with use of well-validated tools, such as the EORTC-CIPN 20. Detailed phenotyping of the clinical syndrome moves toward a precision medicine approach, to individualize treatment. Understanding significant risk factors and pre-existing vulnerability may be used to improve strategies for CIPN prevention, or to use targeted treatment for established CIPN. No preventive therapies have shown significant clinical efficacy, although there are promising novel agents such as histone deacetylase 6 (HDAC6) inhibitors, currently in early phase clinical trials for cancer treatment. Drug repurposing, eg, metformin, may offer an alternative therapeutic avenue. Established treatment for painful CIPN is limited. Following recommendations for general neuropathic pain is logical, but evidence for agents such as gabapentinoids and amitriptyline is weak. The only agent currently recommended by the American Society of Clinical Oncology is duloxetine. Mechanisms are complex with changes in ion channels (sodium, potassium, and calcium), transient receptor potential channels, mitochondrial dysfunction, and immune cell interactions. Improved understanding is essential to advance CIPN management. On a positive note, there are many potential sites for modulation, with novel analgesic approaches.

Factors associated with persistent pain after childbirth: a narrative review

A systematic literature search was performed to identify studies that reported risk factors for persistent pain after childbirth. Many studies have sought to identify risk factors for post-delivery pain in different populations, using different methodologies and different outcome variables. Studies of several different but interrelated post-partum pain syndromes have been conducted. Factors strongly and specifically associated with persistent incisional scar pain after Caesarean delivery include a coexisting persistent pain problem in another part of the body and severe acute postoperative pain. For persistent vaginal and perineal pain, operative vaginal delivery and the magnitude of perineal trauma have been consistently linked. History of pregnancy-related and pre-pregnancy back pain and heavier body weight are robust risk factors for persistent back pain after pregnancy. Unfortunately, limitations, particularly small samples and lack of a priori sample size calculation designed to detect specific effect sizes for risk of persistent pain outcomes, preclude definitive conclusions about many other predictors and the strength of outcome associations. In future studies, assessments of specific phenotypes using a rigorous analysis with appropriate predetermined sample sizes and validated instruments are needed to allow elucidation of stronger and reliable associations. Interventional studies targeting the most robustly associated, modifiable risk factors, such as acute post-partum pain, may lead to solutions for the prevention and treatment of these common problems that impact a large population.

Regulatory mechanisms and therapeutic potential of microglial inhibitors in neuropathic pain and morphine tolerance

Microglia are important cells involved in the regulation of neuropathic pain (NPP) and morphine tolerance. Information on their plasticity and polarity has been elucidated after determining their physiological structure, but there is still much to learn about the role of this type of cell in NPP and morphine tolerance. Microglia mediate multiple functions in health and disease by controlling damage in the central nervous system (CNS) and endogenous immune responses to disease. Microglial activation can result in altered opioid system activity, and NPP is characterized by resistance to morphine. Here we investigate the regulatory mechanisms of microglia and review the potential of microglial inhibitors for modulating NPP and morphine tolerance. Targeted inhibition of glial activation is a clinically promising approach to the treatment of NPP and the prevention of morphine tolerance. Finally, we suggest directions for future research on microglial inhibitors.