A deeper look at pain variability and its relationship with the placebo response: results from a randomized, double-blind, placebo-controlled clinical trial of naproxen in osteoarthritis of the knee

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

Introduction

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

Objectives

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

Methods

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

Results

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

Conclusion

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

The Contribution of Sleep Quality and Psychological Factors to the Experience of Within-Day Pain Fluctuations Among Individuals With Temporomandibular Disorders

We assessed the impact of day-to-day sleep quality and psychological variables (catastrophizing, negative affect, and positive affect) to within-day pain fluctuations in 42 females with painful temporomandibular disorders (TMD) using electronic diaries. More specifically, we examined the contribution of these variables to the likelihood of experiencing pain exacerbations defined as 1) an increase of 20 points (or more) in pain intensity on a 0 to 100 visual analog scale from morning to evening, and/or 2) a transition from mild-to-moderate pain over the course of the day; and pain decreases defined as 3) a decrease of 20 points (or more) in pain intensity (visual analog scale) from morning to evening, and/or 4) a reduction from moderate-to-mild pain over the day. The results indicated significantly main effects of sleep on both pain exacerbation outcomes (both P's < .05), indicating that nights with better sleep quality were less likely to be followed by clinically meaningful pain exacerbations on the next day. The results also indicated that days characterized by higher levels of catastrophizing were associated with a greater likelihood of pain exacerbations on the same day (both P's < .05). Daily catastrophizing was the only variable significantly associated with within-day pain decrease indices (both P's < .05). None of the other variables were associated with these outcomes (all P's > .05). These results underscore the importance of addressing patients' sleep quality and psychological states in the management of painful TMD. PERSPECTIVE: These findings highlight the significance of sleep quality and pain catastrophizing in the experience of within-day pain fluctuations among individuals with TMD. Addressing these components through tailored interventions may help to alleviate the impact of pain fluctuations and enhance the overall well-being of TMD patients.

Placebo treatment affects brain systems related to affective and cognitive processes, but not nociceptive pain

Drug treatments for pain often do not outperform placebo, and a better understanding of placebo mechanisms is needed to improve treatment development and clinical practice. In a large-scale fMRI study (N = 392) with pre-registered analyses, we tested whether placebo analgesic treatment modulates nociceptive processes, and whether its effects generalize from conditioned to unconditioned pain modalities. Placebo treatment caused robust analgesia in conditioned thermal pain that generalized to unconditioned mechanical pain. However, placebo did not decrease pain-related fMRI activity in brain measures linked to nociceptive pain, including the Neurologic Pain Signature (NPS) and spinothalamic pathway regions, with strong support for null effects in Bayes Factor analyses. In addition, surprisingly, placebo increased activity in some spinothalamic regions for unconditioned mechanical pain. In contrast, placebo reduced activity in a neuromarker associated with higher-level contributions to pain, the Stimulus Intensity Independent Pain Signature (SIIPS), and affected activity in brain regions related to motivation and value, in both pain modalities. Individual differences in behavioral analgesia were correlated with neural changes in both modalities. Our results indicate that cognitive and affective processes primarily drive placebo analgesia, and show the potential of neuromarkers for separating treatment influences on nociception from influences on evaluative processes.

The efficacy and safety of a fixed-dose combination of apocynin and paeonol, APPA, in symptomatic knee OA: A double-blind, randomized, placebo-controlled, clinical trial

OBJECTIVE

Apocynin (AP) and paeonol (PA) are low molecular weight phenolic compounds with a broad array of anti-inflammatory and immunoregulatory effects. This study assessed of a fixed-dose combination of APPA in people with symptomatic knee osteoarthritis (OA).

METHODS

A multi-center, randomized, placebo-controlled, double-blind phase 2a trial enrolled participants with radiographic knee OA (Kellgren-Lawrence, KL, grades 2-3) and pain ≥40/100 on WOMAC pain subscale, and evaluated the efficacy and safety of oral APPA over a 28-day period. APPA 800 mg or matching placebo was administered twice daily in a 1:1 ratio. Post-hoc analyses explored the response to APPA in sub-groups with more severe pain and structural severity.

RESULTS

The two groups were comparable at baseline; 152 subjects were enrolled and 148 completed the trial. There was no statistically significant difference between groups with respect to the primary outcome, WOMAC pain (mean difference between groups was -0.89, 95% CI: -5.62, 3.84, p = 0.71), nor WOMAC function or WOMAC total. However, predefined subgroup analyses of subjects with symptoms compatible with nociplastic/neuropathic pain features showed a statistically significant effect of APPA compared to placebo. Adverse events (mainly gastrointestinal) were mild to moderate.

CONCLUSION

Treatment with APPA 800 mg twice daily for 28 days in subjects with symptomatic knee OA was not associated with significant symptom improvement compared to placebo. The treatment was well-tolerated and safe. While the study was not powered for such analysis, pre-planned subgroup analyses showed a significant effect of APPA in subjects with nociplastic pain/severe OA, indicating that further research in the effects of APPA in appropriate patients is warranted.

Pain perception as hierarchical Bayesian inference: A test case for the theory of constructed emotion

An intriguing perspective about human emotion, the theory of constructed emotion considers emotions as generative models according to the Bayesian brain hypothesis. This theory brings fresh insight to existing findings, but its complexity renders it challenging to test experimentally. We argue that laboratory studies of pain could support the theory because although some may not consider pain to be a genuine emotion, the theory must at minimum be able to explain pain perception and its dysfunction in pathology. We review emerging evidence that bear on this question. We cover behavioral and neural laboratory findings, computational models, placebo hyperalgesia, and chronic pain. We conclude that there is substantial evidence for a predictive processing account of painful experience, paving the way for a better understanding of neuronal and computational mechanisms of other emotions.

Does Active Inference Provide a Comprehensive Theory of Placebo Analgesia?

Placebo interventions generate mismatches between expected pain and sensory signals from which pain states are inferred. Because we lack direct access to bodily states, we can only infer whether nociceptive activity indicates tissue damage or results from noise in sensory channels. Predictive processing models propose to make optimal inferences using prior knowledge given noisy sensory data. However, these models do not provide a satisfactory explanation of how pain relief expectations are translated into physiological manifestations of placebo responses. Furthermore, they do not account for individual differences in the ability to endogenously regulate nociceptive activity in predicting placebo analgesia. The brain not only passively integrates prior pain expectations with nociceptive activity to infer pain states (perceptual inference) but also initiates various types of actions to ensure that sensory data are consistent with prior pain expectations (active inference). We argue that depending on whether the brain interprets conflicting sensory data (prediction errors) as a signal to learn from or noise to be attenuated, the brain initiates opposing types of action to facilitate learning from sensory data or, conversely, to enhance the biasing influence of prior pain expectations on pain perception. Furthermore, we discuss the role of stress, anxiety, and unpredictability of pain in influencing the weighting of prior pain expectations and sensory data and how they relate to the individual ability to regulate nociceptive activity (endogenous pain modulation). Finally, we provide suggestions for future studies to test the implications of the active inference model of placebo analgesia.

How should uncertainty about upcoming painful procedures be communicated? An experimental study into highly uncertain pain predictions

OBJECTIVE

Uncertainty is unavoidable in the context of painful medical procedures. It is important to investigate the impact of different ways of communicating uncertainty on upcoming pain.

METHODS

In our exploratory study, healthy participants (n = 30) were repeatedly presented with three highly uncertain pain predictions communicated by a hypothetical doctor. A direct statement of high uncertainty ("I don't know") was compared to more indirect predictions (social prediction: "It varies widely among people"; range prediction: "… not painful at all to very highly painful"), followed by individually calibrated electrical stimuli of non-, moderately, or very highly painful intensity.

RESULTS

The direct expression of uncertainty led to the most intense pain sensation (for moderately painful stimuli only), lowest and most certain pain expectations, lowest trust in the hypothetical doctor, and lowest feeling of being well-informed, especially as compared to the social prediction. No differential effects on anxiety were observed.

CONCLUSIONS

Expressing high uncertainty indirectly, with reference to the common experiences of others, may be beneficial for optimizing pain experiences and enhancing patients' trust in a medical professional.

PRACTICE IMPLICATIONS

Our findings inform on how high uncertainty about upcoming pain may impact patient and health outcomes, pointing to some advantages of indirect communication.

Pain Assessment in Oral Medicine through Its Different Dimensions: A Comprehensive Review

Orofacial pain is a complex experience made up of different features and involving various aspects of life. It has demonstrated a connection, especially when chronic, with conditions such as anxiety, depression, and sleep disorders, through paths that still have not been completely clarified. A deep understanding of orofacial pain and its impact on an individual's life is critical for planning accurate diagnostic and therapeutic approaches. This review seeks to provide a comprehensive overview of the components constituting the pain experience, its implications in an individual's life, the different tools for multidimensional pain assessment, and the specific applications for each tool. A comprehensive review was performed using the PubMed, Scopus, and Web of Science electronic databases. Ninety-five studies, including observational studies, clinical trials, case-control studies, and case reports, were included and analyzed in this review. Orofacial pain assessment exploits several methods, ranging from clinical evaluation to rating scales, questionnaires, and daily diaries. The choice of the correct instrument requires an evaluation of the type of pain experienced, of the patient's characteristics and abilities to complete particular tasks, and finally, of the assessment tool features.

Placebo effects in osteoarthritis: implications for treatment and drug development

Osteoarthritis (OA) is the most common form of arthritis worldwide, affecting ~500 million people, yet there are no effective treatments to halt its progression. Without any structure-modifying agents, management of OA focuses on ameliorating pain and improving function. Treatment approaches typically have modest efficacy, and many patients have contraindications to recommended pharmacological treatments. Drug development for OA is hindered by the gradual and progressive nature of the disease and the targeting of established disease in clinical trials. Additionally, new medications for OA cannot receive regulatory approval without demonstrating improvements in both structure (pathological features of OA) and symptoms (reduced pain and/or improved function). In clinical trials, people with OA show high 'placebo responses', which hamper the ability to identify new effective treatments. Placebo responses refer to the individual variability in response to placebos given in the context of clinical trials and other settings. Placebo effects refer specifically to short-lasting improvements in symptoms that occur because of physiological changes. To mitigate the effects of the placebo phenomenon, we must first understand what it is, how it manifests, how to identify placebo responders in OA trials and how these insights can be used to improve clinical trials in OA. Leveraging placebo responses and effects in clinical practice might provide additional avenues to augment symptom management of OA.

Nocebo Hyperalgesia in Patients With Fibromyalgia and Healthy Controls: An Experimental Investigation of Conditioning and Extinction Processes at Baseline and 1-Month Follow-up

Nocebo effects are adverse treatment outcomes that are not ascribed to active treatment components. Potentially, their magnitude might be higher in patients with chronic pain compared to healthy controls since patients likely experience treatment failure more frequently. The current study investigated group differences in the induction and extinction of nocebo effects on pressure pain at baseline (N = 69) and 1-month follow-up (N = 56) in female patients with fibromyalgia and matched healthy controls. Nocebo effects were first experimentally induced via classical conditioning combined with instructions on the pain-increasing function of a sham transcutaneous electrical nerve stimulation device, then decreased via extinction. One month later, the same procedures were repeated to explore their stability. Results suggest that nocebo effects were induced in the healthy control group during baseline and follow-up. In the patient group, nocebo effects were only induced during follow-up, without clear group differences. Extinction was only observed during baseline in the healthy control group. Further comparisons of nocebo effects and extinction indicated no significant changes across sessions, possibly suggesting their overall magnitudes were stable over time and across groups. In conclusion, contrary to our expectations, patients with fibromyalgia did not have stronger nocebo hyperalgesia; instead, they might be less responsive to nocebo manipulations than healthy controls. PERSPECTIVE: The current study is the first to investigate group differences in experimentally manipulated nocebo hyperalgesia between chronic pain and healthy populations at baseline and 1-month follow-up. Since nocebo effects are common in clinical settings, their investigation in different populations is essential to explain and minimize their adverse effects during treatment.

Yoga and massage are associated with small experimental placebo effects in chronic orofacial pain

BACKGROUND

Complementary and Integrative Health Approaches (CIHA), including but not limited to, natural products and Mind and Body Practices (MBPs), are promising non-pharmacological adjuvants to the arsenal of pain management therapeutics. We aim to establish possible relationships between use of CIHA and the capacity of descending pain modulatory system in the form of occurrence and magnitude of placebo effects in a laboratory setting.

METHODS

This cross-sectional study investigated the relationship between self-reported use of CIHA, pain disability, and experimentally induced placebo hypoalgesia in chronic pain participants suffering from Temporomandibular Disorders (TMD). In the 361 enrolled TMD participants, placebo hypoalgesia was measured using a well-established paradigm with verbal suggestions and conditioning cues paired with distinct heat painful stimulations. Pain disability was measured with the Graded Chronic Pain Scale, and use of CIHA were recorded with a checklist as part of the medical history.

RESULTS

Use of physically oriented MBPs (e.g., yoga and massage) was associated with reduced placebo effects (F1,2110.44  = 23.15, p < 0.001, Cohen's d = 0.171). Further, linear regressions indicated that greater number of physically oriented MBPs predicted smaller placebo effects (β = -0.17, p = 0.002), and less likelihood of being a placebo responder (OR = 0.70, p = 0.004). Use of psychologically oriented MBPs and natural product were not associated with placebo effects magnitude and responsiveness.

CONCLUSIONS

Our findings suggest that use of physically oriented CIHA was associated with experimental placebo effects possibly through an optimized capability to recognize distinct somatosensorial stimulations. Future research is needed to understand the mechanisms underlying placebo-induced pain modulation in CIHA users.

SIGNIFICANCE

Chronic pain participants who use physically oriented mind-body practices, such as yoga and massage, demonstrated attenuated experimentally induced placebo hypoalgesia in comparison with those who do not use them. This finding disentangled the relationship between use of complementary and integrative approaches and placebo effects, providing the potential therapeutic perspective of endogenous pain modulation in chronic pain management.

Correlations between within-subject variability of pain intensity reports and rubber hand illusion proprioceptive drift

INTRODUCTION

Consistent with the Bayesian brain hypothesis, the within-subject variability of pain intensity reports as captured with the Focused Analgesia Selection Test (FAST) might be a surrogate measure of the certainty in ascending noxious signals. The outcomes of a non-pain-related task, the rubber hand illusion, were hypothesized to reflect the same construct. This study aimed to explore whether within-subject differences in variability of pain intensity reports and the outcomes of the rubber hand illusion might be related.

METHODS

Nonclinical participants underwent the classic rubber hand illusion under synchronous (experimental) and asynchronous (control) conditions. Two outcomes were assessed: proprioceptive drift and feeling of ownership. Thereafter, participants underwent the FAST to assess the within-subject variability of pain reports in response to heat stimuli. Intraclass correlation (ICC) and the correlation coefficient (R2) were the main outcomes. Spearman's correlations were used to assess associations between the outcomes of the 2 tasks.

RESULTS

Thirty-six volunteers completed the study. Both FAST outcomes-ICC (Spearman's r = 0.355, p = 0.033) and R2 (Spearman's r = 0.349, p = 0.037)-were positively correlated with proprioceptive drift in the synchronous but not asynchronous conditions (p > 0.05). The subjective feeling of ownership and FAST outcomes did not correlate (p > 0.05).

CONCLUSIONS

The associations between the 2 tasks' outcomes imply that both tasks at least partly assess similar constructs. Current knowledge suggests that this construct represents the person's certainty in perceiving ascending sensory signals, or, in Bayesian terminology, the certainty of the likelihood.

Predicting Treatment Responses in Patients With Osteoarthritis: Results From Two Phase III Tanezumab Randomized Clinical Trials

Prediction of treatment responses is essential to move forward translational science. Our question was to identify patient-based variables that predicted responses to treatments. We conducted secondary analyses on pooled data from two randomized phase III clinical trials (NCT02697773 and NCT02709486) conducted in participants with moderate to severe osteoarthritis randomized to subcutaneous placebo (n = 514) or tanezumab 2.5 mg (n = 514). We used gradient boosted regression trees to identify variables that predicted Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) Pain subscale scores at Week 16 and marginal plots to determine the directional relationship between each variable category and responses to placebo or tanezumab within the models. We also used Virtual Twins models to identify potential subgroups of response to the active treatment vs. placebo. We found that responses to placebo were predicted by baseline WOMAC Physical Function, baseline WOMAC Pain, the radiographic classification of the index joint, and the standard deviation of diary pain scores at baseline. In contrast, baseline WOMAC Pain along with failure of prior medications, duration of disease, and standard deviation of diary pain scores at baseline were predictive of tanezumab responses as expressed by the WOMAC Pain scores at Week 16. Those who responded to tanezumab vs. placebo were identified based on the radiographic classification of the index joint and either age or smoking status. These secondary-data analyses identified distinct and common patient-based variables to predict response to placebo or tanezumab. These findings will inform the design of future clinical trials, helping to move forward clinical pharmacology and translational science.

Optimizing and Accelerating the Development of Precision Pain Treatments for Chronic Pain: IMMPACT Review and Recommendations

Large variability in the individual response to even the most-efficacious pain treatments is observed clinically, which has led to calls for a more personalized, tailored approach to treating patients with pain (ie, "precision pain medicine"). Precision pain medicine, currently an aspirational goal, would consist of empirically based algorithms that determine the optimal treatments, or treatment combinations, for specific patients (ie, targeting the right treatment, in the right dose, to the right patient, at the right time). Answering this question of "what works for whom" will certainly improve the clinical care of patients with pain. It may also support the success of novel drug development in pain, making it easier to identify novel treatments that work for certain patients and more accurately identify the magnitude of the treatment effect for those subgroups. Significant preliminary work has been done in this area, and analgesic trials are beginning to utilize precision pain medicine approaches such as stratified allocation on the basis of prespecified patient phenotypes using assessment methodologies such as quantitative sensory testing. Current major challenges within the field include: 1) identifying optimal measurement approaches to assessing patient characteristics that are most robustly and consistently predictive of inter-patient variation in specific analgesic treatment outcomes, 2) designing clinical trials that can identify treatment-by-phenotype interactions, and 3) selecting the most promising therapeutics to be tested in this way. This review surveys the current state of precision pain medicine, with a focus on drug treatments (which have been most-studied in a precision pain medicine context). It further presents a set of evidence-based recommendations for accelerating the application of precision pain methods in chronic pain research. PERSPECTIVE: Given the considerable variability in treatment outcomes for chronic pain, progress in precision pain treatment is critical for the field. An array of phenotypes and mechanisms contribute to chronic pain; this review summarizes current knowledge regarding which treatments are most effective for patients with specific biopsychosocial characteristics.

Exercise and education vs intra-articular saline for knee osteoarthritis: a 1-year follow-up of a randomized trial

OBJECTIVE

To assess the longer-term effect of the Good Life with osteoarthritis in Denmark (GLAD) exercise and education program relative to open-label placebo (OLP) on changes from baseline in core outcomes in individuals with knee osteoarthritis (OA).

METHODS

In this 1-year follow-up of an open-label, randomized trial, patients with symptomatic and radiographically confirmed knee OA were monitored after being randomized to either the 8-week GLAD program or OLP given as 4 intra-articular saline injections over 8 weeks. The primary outcome was the change from baseline in the Knee injury and Osteoarthritis Outcome Score questionnaire (KOOS) pain subscale after 1 year in the intention-to-treat population. Key secondary outcomes were the KOOS function and quality of life subscales, and Patients' Global Assessment of disease impact.

RESULTS

206 adults were randomly assigned: 102 to GLAD and 104 to OLP, of which only 137 (63/74 GLAD/OLP) provided data at 1 year. At one year the mean changes in KOOS pain were 8.4 for GLAD and 7.0 for OLP (Difference: 1.5 points; 95% CI -2.6 to 5.5). There were no between-group differences in any of the secondary outcomes.

CONCLUSIONS

In this 1-year follow-up of individuals with knee OA, the 8-week GLAD program and OLP both provided minor longer-term benefits with no group difference. These results require confirmation given the significant loss to follow-up.

TRIAL REGISTRATION NUMBER

NCT03843931.

Who are likely to benefit from the Good Life with osteoArthritis in Denmark (GLAD) exercise and education program? An effect modifier analysis of a randomised controlled trial

OBJECTIVE

To identify contextual factors that modify the treatment effect of the 'Good Life with osteoArthritis in Denmark' (GLAD) exercise and education programme compared to open-label placebo (OLP) on knee pain in individuals with knee osteoarthritis (OA).

METHODS

Secondary effect modifier analysis of a randomised controlled trial. 206 participants with symptomatic and radiographic knee OA were randomised to either the 8-week GLAD programme (n = 102) or OLP given as 4 intra-articular saline injections over 8 weeks (n = 104). The primary outcome was change from baseline to week 9 in the Knee injury and Osteoarthritis Outcome Score questionnaire (KOOS) pain subscale (range 0 (worst) to 100 (best)). Subgroups were created based on baseline information: BMI, swollen study knee, bilateral radiographic knee OA, sports participation as a young adult, sex, median age, a priori treatment preference, regular use of analgesics (NSAIDs or paracetamol), radiographic disease severity, and presence of constant or intermittent pain.

RESULTS

Participants who reported use of analgesics at baseline seem to benefit from the GLAD programme over OLP (subgroup contrast: 10.3 KOOS pain points (95% CI 3.0 to 17.6)). Participants with constant pain at baseline also seem to benefit from GLAD over OLP (subgroup contrast: 10.0 points (95% CI 2.8 to 17.2)).

CONCLUSIONS

These results imply that patients who take analgesics or report constant knee pain, GLAD seems to yield clinically relevant benefits on knee pain when compared to OLP. The results support a stratified recommendation of GLAD as management of knee OA.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT03843931. EudraCT number 2019-000809-71.

Relations between short-term memory and the within-subject variability of experimental pain intensity reports: Results from healthy and Fibromyalgia patients

While factors contributing to between-subjects differences in pain have been studied extensively, factors contributing to the within-subjects variability of pain reports are yet unexplored. The aim of this investigation was to assess possible associations between short-term memory and the within-subjects variability of pain reports in healthy and chronic pain patients. Healthy participants were recruited at the University of Haifa, Israel, and Fibromyalgia patients were recruited at a rheumatology department in a central hospital in Lisbon, Portugal. Following consent, both cohorts underwent the same procedures, including the digit-span test, assessing short-term memory, and the FAST procedure, assessing within-subject variability of pain intensity reports in response to experimental pain. One-hundred twenty-one healthy volunteers and 29 Fibromyalgia patients completed the study. While a significant correlation was found between the within-subjects variability and the total score of the short-term memory task (Spearman's r = 0.394, P = 0.046) in the Fibromyalgia group, a marginal correlation emerged in the healthy cohort (r = 0.174, P = 0.056). A possible interpretation of these results is that in the patients' group, at least some of the within-subjects variability of pain intensity reports might be due to error measurement derived by poorer short-term memory, rather than true fluctuations in perception.

Characterizing 16-Week Responder Profiles Using Group-Based Trajectory Modeling in Over 4300 Clinical Trial Participants Receiving Pharmaceutical Treatment for Moderate to Severe Osteoarthritis

INTRODUCTION

We sought to identify and characterize distinct responder profiles among osteoarthritis (OA) subjects treated with tanezumab, nonsteroidal anti-inflammatory drugs (NSAIDs), or placebo.

METHODS

Subject-level data were derived from three randomized, double-blind, placebo- or NSAID-controlled trials of tanezumab in subjects with moderate-to-severe OA. Subjects received subcutaneous tanezumab (2.5 mg, n = 1527; 5 mg, n = 1279) every 8 weeks, oral NSAIDs (n = 994) daily, or placebo (n = 513). Group-based trajectory modeling (GBTM, an application of finite mixture statistical modeling that uses response trajectory to identify and summarize complex patterns in longitudinal data) was used to identify subgroups of subjects following similar patterns of response in each treatment arm, based on daily pain intensity scores from baseline through Week 16. We then examined whether subject-related variables were associated with any of the subgroups using multinomial logistic regression.

RESULTS

A three-subgroup/four-inflection point trajectory model was selected based on clinical and statistical considerations. The subgroups were high responders (substantial pain improvement and a large majority of members achieved ≥ 30% improvement before Week 16), medium responders (gradual pain improvement and a majority of members achieved ≥ 30% improvement by Week 16), and non-responders (little to no pain improvement over 16 weeks). Across all treatments, fluctuation in pain intensity in the week prior to treatment was consistently associated with treatment response. Other variables were positively (age, body mass index, days of rescue medication use) or negatively (severity of disease based on Kellgren-Lawrence grading) associated with response but effects were small and/or varied across treatments.

CONCLUSIONS

Across all treatments, GBTM identified three subgroups of subjects that were characterized by extent of treatment response (high, medium, and non-responders). Similar analyses (e.g., grouping of subjects based on response trajectory and identification of subgroup-related variables) in other studies of OA could inform clinical trial design and/or treatment approaches. (NCT02697773; NCT02709486; NCT02528188).

Anxiety sensitivity and Pain Experience: a prospective investigation among World Trade Center Responders

Chronic pain is a significant public health problem and is exacerbated by stress. The World Trade Center (WTC) Disaster represents a unique stressor, and responders to the WTC disaster are at increased risk for pain and other health complaints. Therefore, there is a significant need to identify vulnerability factors for exacerbated pain experience among this high-risk population. Anxiety sensitivity (AS), defined as fear of anxiety-related sensations, is one such vulnerability factor associated with pain intensity and disability. Yet, no work has tested the predictive effects of AS on pain, limiting conclusions regarding the predictive utility and direction of associations. Therefore, the current study examined the prospective associations of AS, pain intensity, and pain interference among 452 (M_age = 55.22, SD = 8.73, 89.4% male) responders to the WTC disaster completing a 2-week daily diary study. Using multi-level modeling, AS total score was positively associated with both pain intensity and pain interference, and that AS cognitive concerns, but not social or physical concerns, were associated with increased pain. These results highlight the importance of AS as a predictor of pain complaints among WTC responders and provide initial empirical evidence to support AS as a clinical target for treating pain complaints among WTC responders.

Intraindividual pain variability and phenotypes of pain in sickle cell disease: a secondary analysis from the Pain in Sickle Cell Epidemiology Study

ABSTRACT

Mean pain intensity alone is insufficient to describe pain phenotypes in sickle cell disease (SCD). The objective of this study was to determine impact of day-to-day intraindividual pain variability on patient outcomes in SCD. We calculated metrics of pain variability and pain intensity for 139 participants with <10% missing data in the first 28 days of the Pain in Sickle Cell Epidemiology Study. We performed Spearman rank correlations between measures of intraindividual pain variability and outcomes. We then used k-means clustering to identify phenotypes of pain in SCD. We found that pain variability was inversely correlated with health-related quality of life, except in those with daily or near-daily pain. Pain variability was positively correlated with affective coping, catastrophizing, somatic symptom burden, sickle cell stress, health care utilization, and opioid use. We found 3 subgroups or clusters of pain phenotypes in SCD. Cluster 1 included individuals with the lowest mean pain, lowest temporal instability and dependency, lowest proportion of days with pain and opioid use, and highest physical function. Cluster 2 included individuals with the highest mean pain, highest temporal dependency, highest proportion of days with pain and opioid use, and lowest physical function. Cluster 3 included individuals with high levels of mean pain, highest temporal instability, but with lower temporal dependency, proportion of days with pain and opioid use, and physical function compared with cluster 2. We conclude that intraindividual pain variability is associated with patient outcomes and psychological characteristics in SCD and is useful in delineating phenotypes of pain in SCD.

On the Relationship Between Pain Variability and Relief in Randomized Clinical Trials

Previous research reports suggest greater baseline variability is associated with greater pain relief in those who receive a placebo. However, studies that evidence this association do not control for confounding effects from regression to the mean and natural history. In this report, we analyzed data from two randomized clinical trials (Placebo I and Placebo II, total N = 139) while adjusting for the effects of natural history and regression to the mean via a no treatment group. Results agree between the two placebo groups in each study: both placebo groups showed negligible semi-partial correlations between baseline variability and adjusted response [r_sp (CI_95%) = 0.22 (0.03, 0.42) and 0 (−0.07, 0.07) for Placebo I and II, respectively]. The no treatment group in Placebo I showed a negative correlation [−0.22 (−0.43, −0.02)], but the no treatment and drug groups in Placebo II's correlations were negligible [−0.02 (−0.08, 0.02) and 0.00 (−0.10, 0.12) for the no treatment and drug groups, respectively]. When modeled as a linear covariate, baseline pain variability accounted for <1% of the variance in post-intervention pain across both studies. Even after adjusting for baseline pain and natural history, the inability of baseline pain variability to account for substantial variance in pain response highlights that previous results concerning pain variability and treatment response may be inconsistent. Indeed, the relationship appears to be neither consistently specific nor sensitive to improvements in the placebo group. More work is needed to understand and establish the prognostic value of baseline pain variability—especially its placebo specificity and generalizability across patient populations.

Impact of variability in baseline pain on the placebo response in randomized, placebo-controlled, crossover trials in peripheral neuropathic pain

ABSTRACT

Large placebo responses often negatively affect randomized controlled trials within the pain area. Understanding different possible factors that influence the placebo response is therefore important. In this retrospective analysis, we hypothesized that a large variability in baseline pain score would predict a greater placebo response and analyzed the impact of the coefficient of variation, SD, and difference between the highest and lowest numeric rating scale (NRS) score at baseline on the placebo response. A total of 160 observations on placebo response from 3 controlled clinical trials with a crossover design were included in this study. In general, the placebo response was low with a mean reduction in pain intensity of 0.5 points (range -5 to 7) measured on a 0 to 10 point NRS, and only 15% were placebo responders as defined by more than 30% reduction in NRS pain score from baseline to the end of the placebo treatment period. We found no significant impact of baseline pain coefficient of variation, SD, or the difference between lowest and highest baseline pain score on the placebo response. Placebo response in one trial did not predict placebo response in another trial. A large placebo response was not associated with a large treatment response. In conclusion, in this retrospective data analysis, there was no impact of baseline pain variability on the placebo response in controlled clinical trials with a crossover design in patients with peripheral neuropathic pain.

An Ecological Momentary Assessment Study of Pain Intensity Variability: Ascertaining Extent, Predictors, and Associations With Quality of Life, Interference and Health Care Utilization Among Individuals Living With Chronic Low Back Pain

This ecological momentary assessment (EMA) study examined the extent of pain intensity variability among 140 individuals with chronic low back pain and explored predictors of such variability and psychosocial and health care utilization outcomes. Individuals completed momentary pain intensity reports (0-10 numeric rating scale) several times daily for two periods of seven consecutive days, one month apart. Participants also completed online questionnaires at baseline which tapped into pain characteristics, pain-related catastrophization, kinesiophobia, activity patterns, and depression and anxiety symptoms. Questionnaires assessing quality of life and health care utilization were administered online one month after completion of the last EMA report. Data were analyzed using linear hierarchical location-scale models. Results showed that pain intensity fluctuated over the course of a week as shown by an average standard deviation of 1.2. The extent of variability in pain intensity scores was heterogeneous across participants but stable over assessment periods. Patients' baseline characteristics along with psychosocial and health care utilization outcomes were not significantly associated with pain intensity variability. We conclude that pain intensity variability differs across patients yet correlates remain elusive. There is an important gap in our knowledge of what affects this variability. Future EMA studies should replicate and extend current findings. PERSPECTIVE: This study provides evidence indicating that there is substantial variability in momentary reports of pain intensity among individuals living with chronic low back pain. However, risk and protective factors for greater lability of pain are elusive as is evidence that greater pain intensity variability results in differential health care utilization.

Efficacy of platelet-rich plasma and plasma for symptomatic treatment of knee osteoarthritis: a double-blinded placebo-controlled randomized clinical trial

Background

Platelet-rich plasma (PRP) has a still conflicting efficacy for knee osteoarthritis (KOA) and might be a minimally invasive and safe treatment alternative. The potential benefit of only plasma (non-enriched) has never been investigated. Our aim was to evaluate the efficacy of intra-articular platelet-rich plasma (PRP) and plasma to improve pain and function in participants with KOA over 24 weeks.

Methods

Randomized, double-blind, placebo-controlled trial with 3 groups (n = 62): PRP (n = 20), plasma (n = 21) and saline (n = 21). Two ultrasound-guided knee injections were performed with a 2-week interval. The primary outcome was visual analog scale 0-10 cm (VAS) for overall pain at week 24, with intermediate assessments at weeks 6 and 12. Main secondary outcomes were: KOOS, OMERACT-OARSI criteria and TUGT.

Results

At baseline, 92% of participants were female, with a mean age of 65 years, mean BMI of 28.0 Kg/m²and mean VAS pain of 6.2 cm. Change in pain from baseline at week 24 were -2.9 (SD 2.5), -2.4 (SD 2.5) and -3.5 cm (SD 3.3) for PRP, plasma and saline, respectively (p intergroup = 0.499). There were no differences between the three groups at weeks 6 and 12. Similarly, there were no differences between groups regarding secondary outcomes. The PRP group showed higher frequency of adverse events (65% versus 24% and 33% for plasma and saline, respectively, p = 0.02), mostly mild transitory increase in pain.

Conclusions

PRP and plasma were not superior to placebo for pain and function improvement in KOA over 24 weeks. The PRP group had a higher frequency of mild transitory increase in pain.

Trial registration

ClinicalTrials.gov, NCT03138317, 03/05/2017.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04706-7.

Placebo Response Reduction and Accurate Pain Reporting Training Reduces Placebo Responses in a Clinical Trial on Chronic Low Back Pain: Results From a Comparison to the Literature

OBJECTIVE

A literature review was conducted to compare placebo responses in a recent trial-which implemented an accurate pain reporting (APR) and placebo response reduction (PRR) training program-with placebo responses in similar previous trials in chronic lower back pain (CLBP) that did not use such training.

METHODS

A literature search was performed to find parallel design, randomized, controlled trials of pharmacological treatments administered orally or through intravenous injection for CLBP. Studies were assessed for the proportion of placebo responders, defined as the proportion of patients in the placebo group with ≥30% reduction in pain intensity. A χ analysis was performed on the proportion of responders from the SPRINT trial and from other similar studies.

RESULTS

Of 844 studies identified in the initial screening process, 16 studies were included for comparison. The percentage of placebo responders was statistically significantly lower in the SPRINT study (19.1%) compared with other CLBP trials (38.0%) (P=0.003). Our results show that the placebo response was lower in the SPRINT trial than other comparable studies on CLBP.

DISCUSSION

These findings are consistent with results from other studies showing that neutralizing subject and study staff expectations of therapeutic benefit can decrease the placebo response in clinical trials. The results of this study suggest training participants and staff to improve pain reporting accuracy, neutralize expectations, and decrease external cues that may bias participants' pain ratings in clinical trials may effectively decrease the placebo response leading to increased assay sensitivity.

Advances in the treatment of neuropathic pain

PURPOSE OF REVIEW

Neuropathic pain remains difficult to treat. This review provides an update regarding recent advances in therapeutic management, particularly with regards to newer drugs, neurostimulation techniques and original study designs.

RECENT FINDINGS

Although the mainstay of neuropathic pain management is still represented by drug therapy, particularly antidepressants and antiepileptics, the place of nonpharmacological therapy including in particular brain neuromodulation techniques has substantially increased in recent years. Newer study designs are also increasingly implemented, based on in depth phenotypic profiling to achieve more individualized therapy, or on screening strategies to decrease placebo effect and contribute to increase assay sensitivity. These approaches are now considered the most promising to decrease therapeutic failures in neuropathic pain.

SUMMARY

Neuropathic pain management should not be restricted to pharmacotherapy but now encompasses multiple approaches including particularly neuromodulation techniques. Multimodal assessment can also help identify predictors of the response in clinical trials in order to ensure appropriate management.

What can be done to control the placebo response in clinical trials? A narrative review

The desire to reduce high placebo response rates in clinical trials is a popular concept. However, few studies have rigorously examined the effectiveness of methods to control for placebo responses that are relevant to randomized controlled trials. The primary objective of this review was to evaluate the effect of experimental placebo manipulations in randomized controlled trials (RCTs). We critically reviewed studies designed to manipulate placebo responses including positive expectations regarding the effectiveness of the placebo treatment, manipulating the time spent with subjects, and training study staff and subjects to accurately report symptom severity. These efforts have generally resulted in reduced placebo response and improved discrimination between drug and placebo. Interventions that neutralize staff and subject expectations and improve the ability of subjects to accurately report symptom severity have shown the most promise. Reduction of the placebo response has the potential to accelerate the development of new therapeutics.

Research design considerations for randomized controlled trials of spinal cord stimulation for pain: Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials/Institute of Neuromodulation/International Neuromodulation Society recommendations

ABSTRACT

Spinal cord stimulation (SCS) is an interventional nonpharmacologic treatment used for chronic pain and other indications. Methods for evaluating the safety and efficacy of SCS have evolved from uncontrolled and retrospective studies to prospective randomized controlled trials (RCTs). Although randomization overcomes certain types of bias, additional challenges to the validity of RCTs of SCS include blinding, choice of control groups, nonspecific effects of treatment variables (eg, paresthesia, device programming and recharging, psychological support, and rehabilitative techniques), and safety considerations. To address these challenges, 3 professional societies (Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials, Institute of Neuromodulation, and International Neuromodulation Society) convened a meeting to develop consensus recommendations on the design, conduct, analysis, and interpretation of RCTs of SCS for chronic pain. This article summarizes the results of this meeting. Highlights of our recommendations include disclosing all funding source and potential conflicts; incorporating mechanistic objectives when possible; avoiding noninferiority designs without internal demonstration of assay sensitivity; achieving and documenting double-blinding whenever possible; documenting investigator and site experience; keeping all information provided to patients balanced with respect to expectation of benefit; disclosing all information provided to patients, including verbal scripts; using placebo/sham controls when possible; capturing a complete set of outcome assessments; accounting for ancillary pharmacologic and nonpharmacologic treatments in a clear manner; providing a complete description of intended and actual programming interactions; making a prospective ascertainment of SCS-specific safety outcomes; training patients and researchers on appropriate expectations, outcome assessments, and other key aspects of study performance; and providing transparent and complete reporting of results according to applicable reporting guidelines.

A combination of pain indices based on momentary assessments can predict placebo response in patients with fibromyalgia syndrome

ABSTRACT

Many factors are known to affect assay sensitivity; however, limited attention has been devoted to understanding whether characteristics of patients' baseline pain impact assay sensitivity. In this study, we tested whether a combination of 3 baseline pain indices based on ecological momentary assessments (EMA) could detect patients with enhanced responses to placebo. The analysis was conducted with secondary data from 2 clinical trials in fibromyalgia patients (N = 2084). For each patient, pain intensity, pain variability (individual SD), and pain consistency (first-order autocorrelation) were computed from baseline EMA. A latent profile analysis identified 3 subgroups of patients based on these indices. Group 1 (n = 857, 41.3%) showed the lowest pain intensity levels, coupled with the highest consistency and greatest variability of pain. Group 3 (n = 110, 5.3%) showed the opposite pattern, and group 2 (n = 1109, 53.4%) showed intermediate levels on all pain indices. It was then tested whether the subgroups moderated treatment effects (changes in pain for active treatment vs placebo) using repeated-measures analysis of variance. Treatment effects varied significantly between subgroups. Patients in group 3 demonstrated greater reduction in pain in response to placebo then those in groups 1 and 2. Further analysis showed that the removal of patients in class 3 would significantly enhance the observed treatment effect by 8% to 15%. In conclusion, profiles of pain characteristics derived from baseline EMA may be useful for detecting patient subgroups with enhanced placebo responses that can diminish assay sensitivity in pain 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.

A 3-way Cross-over Study of Pregabalin, Placebo, and the Histamine 3 Receptor Inverse Agonist AZD5213 in Combination With Pregabalin in Patients With Painful Diabetic Neuropathy and Good Pain-reporting Ability

OBJECTIVES

In this study, patients with painful diabetic neuropathy were trained using an experimental pain paradigm in an attempt to enroll a subset of patients who are "pain connoisseurs" and therefore more able to discriminate between active and placebo treatments.

METHODS

AZD5213, a novel histamine H3 receptor inverse agonist+pregabalin, pregabalin, and placebo were then tested in a 3-period cross-over.

RESULTS

The study did not provide any evidence of clinical efficacy for AZD5213 when combined with pregabalin in the treatment of painful diabetic neuropathy.

DISCUSSION

The training of study patients in pain reporting and subsequent enrichment with good pain reporters also did not enable the robust detection of the efficacy of pregabalin relative to placebo in a small sample size. Further work is required before recommending the use of "connoisseur" patients in future neuropathic pain studies.

A novel diclofenac gel (AMZ001) applied once or twice daily in subjects with painful knee osteoarthritis: A randomized, placebo-controlled clinical trial

PURPOSE

Osteoarthritis Research Society International (OARSI) Expert Consensus Guidelines recommend topical non-steroidal anti-inflammatory drugs as first-line medications for osteoarthritis (OA) knee pain, but several voluminous daily applications are required to achieve efficacy. There is a need to develop new and improved topical analgesics with a faster onset, longer duration of action, and the requirement to apply less gel. This trial investigated the safety and efficacy of a new 3.06% diclofenac gel (AMZ001) in subjects with knee OA.

METHODS

In total, 444 subjects (AMZ001 twice daily (BID) [n = 121], AMZ001 once daily (QD) + placebo QD [n = 121], placebo BID [n = 121], or Voltaren 1% 4-times daily [n = 81]) were enrolled. All except Voltaren 1% (single-blinded) were applied topically in a double-blind manner for a total of 4-weeks. The primary endpoint was the change from baseline to week 4 in the WOMAC pain sub-score in the target knee. Secondary and exploratory endpoints included additional efficacy measures (WOMAC total score, WOMAC function and stiffness sub-scores, WOMAC pain weight-bearing and non-weight-bearing sub-scores, ICOAP, chair-stand test, OMERACT-OARSI responder rate, PGA, WPAI, EQ-5D, rescue medication use, satisfaction questionnaire) and safety.

RESULTS

Treatment with AMZ001 QD was effective at reducing WOMAC pain sub-scores vs placebo (estimated treatment difference [ETD]: -4.61 [95% confidence interval (CI): -9.09, -0.12]; p = 0.0440); however, BID application was not (ETD: -3.76 [95% CI: -8.21, 0.68]; p = 0.0969). For several secondary endpoints, changes from baseline to week 4 conferred nominally statistically significant improvements in favor of AMZ001 vs placebo, including PGA score (AMZ001 BID vs placebo, ETD: -0.61 [95% CI: -1.11, -0.11]; p = 0.0162; AMZ001 QD vs placebo, ETD: -0.63 [95% CI: -1.13, -0.13]; p = 0.0134), WPAI overall work impairment score (AMZ001 QD vs placebo, ETD: -10.44 [95% CI: -20.84, -0.04]; p = 0.0492), and EQ-5D VAS score (AMZ001 BID vs placebo, ETD: 4.70 [95% CI: 0.55, 8.85]; p = 0.0264). Post-hoc analysis excluding 11-14 subjects per group with pain scores that decreased between screening and baseline suggests a consistent effect of both AMZ001 QD (ETD: -5.84 [95% CI: -10.71, -0.97]; p = 0.0189) and BID (ETD: -5.35 [95% CI: -10.16, -0.54]; p = 0.0292) in reducing WOMAC pain sub-scores vs placebo. In general, treatment satisfaction was high, as measured by the satisfaction questionnaire. The frequency and incidence of adverse events (AEs) was greatest in the placebo group. Most AEs (>99%) were of mild or moderate severity. There were no serious AEs. There were no notable effects of any treatment on vital signs, ECGs, physical examination findings, or other laboratory assessments.

CONCLUSIONS

Treatment with AMZ001 BID for 4 weeks improved WOMAC pain sub-scores; however, only QD application conferred nominally statistically significant improvements vs placebo. AMZ001 was generally well tolerated.

The relation between the placebo response, observed treatment effect, and failure to meet primary endpoint: A systematic review of clinical trials of preventative pharmacological migraine treatments

OBJECTIVE

To evaluate the association between the degree of response to placebo in migraine studies and the observed difference between drug and placebo across studies of preventative treatments for migraine.

METHODS

A systematic review was performed using MEDLINE and the Cochrane Central Register of Controlled Clinical Trials from January 1988 to June 2019. Randomized, double-blind, parallel-group, placebo-controlled trials on oral or injection preventative treatments for migraine were included. Single- and multi-variable linear regression analyses were performed on the placebo-subtracted response rate (i.e. placebo responders subtracted from active responders), and the proportion of placebo responders. Fisher's exact tests were performed on the level of placebo response and the success in meeting the study's primary endpoint.

RESULTS

After adjusting for route of administration and number of randomized subjects, there was a statistically significant association between the proportion of patients who were placebo responders and the placebo-subtracted response rate (b = -0.27, p = 0.02). There was a statistically significant difference in trial success rate (60%) between studies with ≤20% placebo responders and studies with > 30% placebo responders (p = 0.03).

CONCLUSION

Considering the detrimental impact that high placebo response can have on clinical trials, it is imperative to find effective solutions to decrease the placebo response and increase assay sensitivity.

Improving Study Conduct and Data Quality in Clinical Trials of Chronic Pain Treatments: IMMPACT Recommendations

The estimated probability of progressing from phase 3 analgesic clinical trials to regulatory approval is approximately 57%, suggesting that a considerable number of treatments with phase 2 trial results deemed sufficiently successful to progress to phase 3 do not yield positive phase 3 results. Deficiencies in the quality of clinical trial conduct could account for some of this failure. An Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials meeting was convened to identify potential areas for improvement in trial conduct in order to improve assay sensitivity (ie, ability of trials to detect a true treatment effect). We present recommendations based on presentations and discussions at the meeting, literature reviews, and iterative revisions of this article. The recommendations relate to the following areas: 1) study design (ie, to promote feasibility), 2) site selection and staff training, 3) participant selection and training, 4) treatment adherence, 5) data collection, and 6) data and study monitoring. Implementation of these recommendations may improve the quality of clinical trial data and thus the validity and assay sensitivity of clinical trials. Future research regarding the effects of these strategies will help identify the most efficient use of resources for conducting high quality clinical trials. PERSPECTIVE: Every effort should be made to optimize the quality of clinical trial data. This manuscript discusses considerations to improve conduct of pain clinical trials based on research in multiple medical fields and the expert consensus of pain researchers and stakeholders from academia, regulatory agencies, and industry.

En Pointe: Dancers Report Their Pain Less Variably Than Do Controls

The subjective nature of pain and the lack of a gold standard for objective measurement hinders effective assessment, diagnosis, and treatment. Some individuals, such as professional dancers, are better in assessing and reporting bodily sensations. This observational study aimed to assess whether dancers report their pain less variably, than other people do. After consenting, subjects completed the focused analgesia selection test (FAST), which assesses subjects' variability of pain reports. FAST outcomes, ICC and R² reflect the magnitude of variability of pain reports observed. In addition, subjects underwent a taste task, which similarly assesses variability of tastes (salty and sweet) intensity reports and completed the Multidimensional Assessment of Interoceptive Awareness questionnaire. Thirty-three professional dancers and 33 healthy aged-matched controls were recruited. The dancers exhibited less variability of pain reports then controls (P = .013), but not in case of tastes-reports. Years of practice was positively correlated with pain reporting variability (r = .447, P = .009, and r = .380, P = .029; for FAST ICC and R², respectively). Multidimensional Assessment of Interoceptive Awareness subscores correlated with pain reporting variability: R² and ICC with emotional awareness (r = .260, P = .040, and r = .274, P = .030, respectively), and R² with trusting [r = .254, P = .044]). PERSPECTIVE: The difference between dancers and controls in the magnitude of variability of pain reports is probably due to the dancers' extensive training, which focuses on attention to body signals. Our results suggest that training can improve subjective pain reports, which are essential for quality clinical care.

Placebos in chronic pain: evidence, theory, ethics, and use in clinical practice

Despite their ubiquitous presence, placebos and placebo effects retain an ambiguous and unsettling presence in biomedicine. Specifically focused on chronic pain, this review examines the effect of placebo treatment under three distinct frameworks: double blind, deception, and open label honestly prescribed. These specific conditions do not necessarily differentially modify placebo outcomes. Psychological, clinical, and neurological theories of placebo effects are scrutinized. In chronic pain, conscious expectation does not reliably predict placebo effects. A supportive patient-physician relationship may enhance placebo effects. This review highlights "predictive coding" and "bayesian brain" as emerging models derived from computational neurobiology that offer a unified framework to explain the heterogeneous evidence on placebos. These models invert the dogma of the brain as a stimulus driven organ to one in which perception relies heavily on learnt, top down, cortical predictions to infer the source of incoming sensory data. In predictive coding/bayesian brain, both chronic pain (significantly modulated by central sensitization) and its alleviation with placebo treatment are explicated as centrally encoded, mostly non-conscious, bayesian biases. The review then evaluates seven ways in which placebos are used in clinical practice and research and their bioethical implications. In this way, it shows that placebo effects are evidence based, clinically relevant, and potentially ethical tools for relieving chronic pain.

The Protective Effect of New Carnosine-Hyaluronic Acid Conjugate on the Inflammation and Cartilage Degradation in the Experimental Model of Osteoarthritis

Osteoarthritis (OA) is a disease that currently has no cure. There are numerous studies showing that carnosine and hyaluronic acid (HA) have a positive pharmacological action during joint inflammation. For this reason, the goal of this research was to discover the protective effect of a new carnosine conjugate with hyaluronic acid (FidHycarn) on the inflammatory response and on the cartilage degradation in an in vivo experimental model of OA. This model was induced by a single intra-articular (i.ar.) injection of 25 µL of normal saline with 1 mg of monosodium iodoacetate solution (MIA) in the knee joint of rats. MIA injection caused histological alterations and degradation of the cartilage, as well as behavioral changes. Oral treatment with FidHycarn ameliorated the macroscopic signs, improved thermal hyperalgesia and the weight distribution of the hind paw, and decreased histological and radiographic alterations. The oxidative damage was analyzed by evaluating the levels of nitrotyrosine and inducible nitric oxide synthase (iNOS) that were significantly reduced in FidHycarn rats. Moreover, the levels of pro-inflammatory cytokines and chemokines were also significantly reduced by FidHycarn. Therefore, for the first time, the effectiveness of oral administration of FidHycarn has been demonstrated in an osteoarthritis model. In conclusion, the new FidHycarn could represent an interesting therapeutic strategy to combat osteoarthritis.

WITHDRAWN: Size Does Matter, But It Isn't Everything: The Challenge of Modest Treatment Effects in Chronic Pain Clinical Trials

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No Relationships Between the Within-Subjects' Variability of Pain Intensity Reports and Variability of Other Bodily Sensations Reports

Purpose

The subjective nature of pain assessment and its large variance negatively affect patient–health care provider communication and reduce the assay sensitivity of pain clinical trials. Given the lack of an objective gold standard measure, identifying the source (true or error) of the within-subject variability of pain reports is a challenge. By assessing the within-subjects variability of pain and taste reports, alongside with interoceptive measures, the current study is aimed to investigate if the ability to reliably report bodily sensations is a cross-modal characteristic.

Patients and Methods

This prospective study enrolled healthy volunteers from local universities. After consenting, subjects underwent the Focus Analgesia Selection Task (FAST), to assess within-subjects variability of pain reports in response to experimental noxious stimuli; a taste task, which similarly assesses within-subjects variability of tastes (salty and sweet) intensity reports; and the heartbeat perception task, an interoceptive task aimed to assess how accurate subjects are in monitoring and reporting their own heartbeat. In addition, all subjects completed the Multidimensional Assessment of Interoceptive Awareness (MAIA), the Perceived Stress Scale (PSS), and Hospital Anxiety and Depression Scale (HADS). Spearman’s correlations were used to assess relations between all measures.

Results

Sixty healthy volunteers were recruited. Variability of intensity reports of different modalities were independent of each other (P > 0.05 for all correlations). The only correlation found was within modality, between variability of intensity reports of salt and sweet tastes (Spearman’s r = 0.477, P < 0.001). No correlations were found between any of the task results and questionnaire results.

Conclusion

Within-subjects variability of pain reports do not relate to variability of reports of other modalities or to interoceptive awareness. Further research is ongoing to investigate the clinical relevance of within-subjects’ variability of pain reports.