Nocebo vs. placebo: the challenges of trial design in analgesia research

The Nocebo Effect: A Bias in Clinical Practice-An Ethical Approach

BACKGROUND

The nocebo effect is often disregarded in medical practice and is certainly much less known than the placebo effect, although, in reality, both can influence therapeutic decision making and the quality of life of patients. However, the nocebo effect raises a number of issues not only of a practical nature related to clinical activity but also ethical dilemmas related to the observance of the patient's autonomy, nonmaleficence, or informed consent and the information on which it is based.

AREAS OF UNCERTAINTY

The ethical dilemmas raised by the nocebo effect revolve around how informed consent can be achieved, the accuracy and volume of information that is transmitted to the patient, and how to report negative side effects of therapeutic treatment.

DATA SOURCES

In September 2023, a narrative analysis of the literature was conducted using a combination of keywords such as nocebo, placebo, ethics, therapeutic relationship from PubMed, Scopus, Google Scholar, and so on, as well as from official documents developed at an international level (World Health Organization), for a period of 10 years (2012-2021).

RESULTS

Analyzing the articles that remarked upon the significant impact of ethics in nocebo research or in the therapeutic relationship, we can state that the existence of several relevant issues of interest have been detected regarding the ethical use of nocebo and its impact in research or in clinics and thus the need for proper knowledge and management of the impact of nocebo effects. The ethical paradox of obtaining informed consent with the 2 goals, first, the need for complete information and second, the preservation of the autonomy of the patient, respectively, that of "primum non-nocere" and of avoiding unnecessary harm by revealing probable adverse effects is a point of interest for numerous studies. The potential for a nocebo effect is present when we inform patients about the risks and benefits of treatment, there being a clear link between the moral and ethical duty to inform patients and the need to avoid situations that increase the nocebo impact on how the disease or the adverse effects of the treatment are perceived. Adapting information about the side effects of medicines should focus on ensuring a balance between transparency and caution, especially in patients with a high potential for nocebo effect.

CONCLUSIONS

The nocebo effect had for a long time been unknown or denied, although it can interfere with the results of the treatment used. As the nocebo phenomenon becomes increasingly known in medical practice, the clinical and ethical implications are identified by medical staff, and nocebo's adverse responses are no longer ignored.

The Roles of Endogenous Opioids in Placebo and Nocebo Effects: From Pain to Performance to Prozac

Placebo and nocebo effects have been well documented for nearly two centuries. However, research has only relatively recently begun to explicate the neurobiological underpinnings of these phenomena. Similarly, research on the broader social implications of placebo/nocebo effects, especially within healthcare delivery settings, is in a nascent stage. Biological and psychosocial outcomes of placebo/nocebo effects are of equal relevance. A common pathway for such outcomes is the endogenous opioid system. This chapter describes the history of placebo/nocebo in medicine; delineates the current state of the literature related to placebo/nocebo in relation to pain modulation; summarizes research findings related to human performance in sports and exercise; discusses the implications of placebo/nocebo effects among diverse patient populations; and describes placebo/nocebo influences in research related to psychopharmacology, including the relevance of endogenous opioids to new lines of research on antidepressant pharmacotherapies.

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.

Blinding and sham control methods in trials of physical, psychological, and self-management interventions for pain (article I): a systematic review and description of methods

ABSTRACT

Blinding is challenging in randomised controlled trials of physical, psychological, and self-management therapies for pain, mainly because of their complex and participatory nature. To develop standards for the design, implementation, and reporting of control interventions in efficacy and mechanistic trials, a systematic overview of currently used sham interventions and other blinding methods was required. Twelve databases were searched for placebo or sham-controlled randomised clinical trials of physical, psychological, and self-management treatments in a clinical pain population. Screening and data extraction were performed in duplicate, and trial features, description of control methods, and their similarity to the active intervention under investigation were extracted (protocol registration ID: CRD42020206590). The review included 198 unique control interventions, published between 2008 and December 2021. Most trials studied people with chronic pain, and more than half were manual therapy trials. The described control interventions ranged from clearly modelled based on the active treatment to largely dissimilar control interventions. Similarity between control and active interventions was more frequent for certain aspects (eg, duration and frequency of treatments) than others (eg, physical treatment procedures and patient sensory experiences). We also provide an overview of additional, potentially useful methods to enhance blinding, as well as the reporting of processes involved in developing control interventions. A comprehensive picture of prevalent blinding methods is provided, including a detailed assessment of the resemblance between active and control interventions. These findings can inform future developments of control interventions in efficacy and mechanistic trials and best-practice recommendations.

Consideration in Randomized Placebo-Controlled Trial on Neck Pain to Avoid the Placebo Effect in Analgesic Action

Background: In neck pain treatment, many therapies are focused on etiology, while it is well-known that placebo analgesia is also present in these therapies. The specific efficacy for etiology may be underestimated by ignoring their actual placebo effect. In this study, a logistic regression analysis is used to explore the risk factors causing different placebo responses in patients with neck pain among two RCTs. The probability of the placebo effect is predicted based on these risk factors.

Methods: Trial A and Trial B were similarly designed, randomized, double-/single-blind, placebo-controlled trials in patients treating neck pain with Qishe pill or Shi-style manipulation. Both studies set a placebo pill twice a day or traction for every other day as control. For further analyses on the placebo effect in neck pain management, logistic regression was used to assess subgroup-placebo interactions. The odds ratio assessed a significant influence on the placebo effect.

Results: In this pooled analysis, the total number of patients recruited for these two studies was 284, of which 162 patients received placebo treatment (placebo drug or traction for every other day). No statistically significant differences are found at baseline between the participants with placebo effect and non-placebo effect in the gender, age, and disease duration except in VAS and NDI at the initial time. There are numerically more patients with placebo effect in the shorter disease duration subgroup (< 4 months [76%]), higher initial VAS subgroup (>60 mm [90%]), and worse initial NDI subgroup (>24 [72%]) compared with the gender and age subgroup. An ROC curve is established to assess the model-data fit, which shows an area under the curve of 0.755 and a 95% confidence interval of 0.677–0.830. Participants who show placebo effect after 2 weeks have significantly lower VAS scores after 4 weeks, while there is no significant difference in NDI improvement between the two groups after 4 weeks.

Conclusion: Neck pain patients with shorter disease duration are more likely to overscore their pain severity, because of their less experience in pain perception, tolerance, and analgesia expectation.

Myths and Truths about Placebo Effect in Rehabilitation for Musculoskeletal Pain

This commentary provides the authors' point of view about the biopsychosocial perspective of placebo effect on musculoskeletal pain in the rehabilitation field.

Analgesic effect of perineural local anesthetics, steroids, and conventional medical management for trauma and compression-related peripheral neuropathic pain: a retrospective cohort study

INTRODUCTION

Trauma and compression are common causes of peripheral neuropathic pain (NP) refractory to conventional medical management (CMM). The role of perineural interventions in relieving this type of pain is unclear.

OBJECTIVES

The objectives of this retrospective study were to determine the analgesic benefits of adding a combination of perineural local anesthetic and steroids (LA-S) to CMM compared with CMM alone in patients who had moderate-to-severe refractory NP after trauma to the ankle and the foot.

METHODS

Health care records of 60 patients in exposed (3 injections of perineural LA-S at weekly intervals with CMM) and 60 in unexposed (CMM) cohorts were reviewed. Data on patient characteristics, pain, and mental and physical function were extracted at baseline and at the postintervention follow-up. Data were analyzed to evaluate analgesic benefit from the study interventions and the impact of baseline characteristics.

RESULTS

Perineural LA-S with CMM cohort had lower pain numerical rating scale scores at 1 to 3 months after the intervention as compared to the CMM alone cohort (5.50 [interquartile range 4.00-7.00] and 7.00 [interquartile range 5.00-8.00], respectively; P < 0.01). However, multivariable analysis did not show an independent beneficial analgesic effect with the addition of perineural LA-S to CMM compared with CMM alone. A greater severity of preintervention catastrophizing (each unit increase in pain catastrophizing score increased pain score at follow-up by 0.04, 95% confidence interval: 0.01-0.07) was associated with reduction in the analgesic benefit.

CONCLUSION

Perineural local anesthetic and steroid injections do not confer an analgesic benefit for trauma- or compression-related peripheral NP.

Changes in patient functioning and disability: results from a phase 3, double-blind, randomized, placebo-controlled clinical trial evaluating galcanezumab for chronic migraine prevention (REGAIN)

PURPOSE

To evaluate secondary outcomes including changes in functioning and disability associated with galcanezumab, a humanized monoclonal antibody to calcitonin gene-related peptide, in patients with chronic migraine.

METHODS

Patients randomly received galcanezumab (120 mg n = 278, 240 mg n = 277) or placebo (n = 558) during 3 months of double-blind treatment, followed by a 9-month open-label extension. The Migraine-Specific Quality-of-Life Questionnaire v2.1 (MSQv2.1) measured the impact of migraine on patient functioning. The Migraine Disability Assessment (MIDAS) quantified headache-related disability. Changes from baseline were analyzed with mixed model repeated measures or analysis of covariance.

RESULTS

Total MSQ score at baseline was 44.88 ± 18.02 (mean ± SD), indicating significant functional impairment. At Month 3, least squares (LS) mean change ± SE in total MSQ for galcanezumab-treated patients were 20.51 ± 1.49 (120 mg) and 20.49 ± 1.49 (240 mg), both statistically significantly greater vs placebo-treated patients (14.55 ± 1.21; both P < 0.001). Total MIDAS score at baseline was 67.24 ± 57.31 (mean ± SD). At Month 3, LS mean change ± SE from baseline in total MIDAS for galcanezumab-treated patients was statistically significantly greater than placebo for 120 mg group (placebo: - 11.53 ± 3.38 vs 120 mg: - 20.27 ± 4.07; P < 0.05) but not for 240 mg group (- 17.02 ± 4.05). At Month 12, within-group mean changes from baseline for total MSQ (28.56 ± 1.19 previous placebo; 29.53 ± 1.51 previous 120 mg; 25.83 ± 1.49 previous 240 mg) and MIDAS scores (- 28.47 ± 2.95 previous placebo; - 31.47 ± 3.69 previous 120 mg; - 31.13 ± 3.62 previous 240 mg) were statistically significant (P < 0.001) for the open-label treatment population regardless of previous double-blind treatment assignment.

CONCLUSIONS

Galcanezumab-treated patients with chronic migraine reported statistically significant improvements in functioning and disability, representing a clinically significant change.

TRIAL REGISTRATION

ClinicalTrials.gov registry: NCT02614261. Registered 25 November 2015.

Optimizing Aggregated N-Of-1 Trial Designs for Predictive Biomarker Validation: Statistical Methods and Theoretical Findings

Background and Significance: Parallel-group randomized controlled trials (PG-RCTs) are the gold standard for detecting differences in mean improvement across treatment conditions. However, PG-RCTs provide limited information about individuals, making them poorly optimized for quantifying the relationship of a biomarker measured at baseline with treatment response. In N-of-1 trials, an individual subject moves between treatment conditions to determine their specific response to each treatment. Aggregated N-of-1 trials analyze a cohort of such participants, and can be designed to optimize both statistical power and clinical or logistical constraints, such as allowing all participants to begin with an open-label stabilization phase to facilitate the enrollment of more acutely symptomatic participants. Here, we describe a set of statistical simulation studies comparing the power of four different trial designs to detect a relationship between a predictive biomarker measured at baseline and subjects' specific response to the PTSD pharmacotherapeutic agent prazosin.

Methods: Data was simulated from 4 trial designs: (1) open-label; (2) open-label + blinded discontinuation; (3) traditional crossover; and (4) open label + blinded discontinuation + brief crossover (the N-of-1 design). Designs were matched in length and assessments. The primary outcome, analyzed with a linear mixed effects model, was whether a statistically significant association between biomarker value and response to prazosin was detected with 5% Type I error. Simulations were repeated 1,000 times to determine power and bias, with varied parameters.

Results: Trial designs 2 & 4 had substantially higher power with fewer subjects than open label design. Trial design 4 also had higher power than trial design 2. Trial design 4 had slightly lower power than the traditional crossover design, although power declined much more rapidly as carryover was introduced.

Conclusions: These results suggest that an aggregated N-of-1 trial design beginning with an open label titration phase may provide superior power over open label or open label and blinded discontinuation designs, and similar power to a traditional crossover design, in detecting an association between a predictive biomarker and the clinical response to the PTSD pharmacotherapeutic prazosin. This is achieved while allowing all participants to spend the first 8 weeks of the trial on open-label active treatment.

Testing a positive-affect induction to reduce verbally induced nocebo hyperalgesia in an experimental pain paradigm

There is an ethical obligation to notify individuals about potential pain associated with diagnoses, treatments, and procedures; however, supplying this information risks inducing nocebo hyperalgesia. Currently, there are few empirically derived strategies for reducing nocebo hyperalgesia. Because nocebo effects are linked to negative affectivity, we tested the hypothesis that a positive-affect induction can disrupt nocebo hyperalgesia from verbal suggestion. Healthy volunteers (N = 147) were randomly assigned to conditions in a 2 (affect induction: positive vs neutral) by 2 (verbal suggestion: no suggestion vs suggestion of pain increase) between-subjects design. Participants were induced to experience positive or neutral affect by watching movie clips for 15 minutes. Next, participants had an inert cream applied to their nondominant hand, and suggestion was manipulated by telling only half the participants the cream could increase the pain of the upcoming cold pressor test. Subsequently, all participants underwent the cold pressor test (8 ± 0.04°C), wherein they submerged the nondominant hand and rated pain intensity on numerical rating scales every 20 seconds up to 2 minutes. In the neutral-affect conditions, there was evidence for the nocebo hyperalgesia effect: participants given the suggestion of pain displayed greater pain than participants not receiving this suggestion, P's < 0.05. Demonstrating a blockage effect, nocebo hyperalgesia did not occur in the positive-affect conditions, P's > 0.5. This is the first study to show that positive affect may disrupt nocebo hyperalgesia thereby pointing to a novel strategy for decreasing nocebo effects without compromising the communication of medical information to patients in clinical settings.

Can insights from placebo and nocebo mechanisms studies improve the randomized controlled trial?

Background and aims The randomized controlled trial (RCT) is currently facing several challenges, one of these being that the placebo response appears to be increasing in RCTs, thereby making it difficult to demonstrate an effect of potentially new treatments over placebo. This problem has primarily been approached by predicting the magnitude of the placebo response via stable factors, such as demographic variables, and/or by developing complex designs aimed at reducing the placebo response in the hope that it will improve the test of the active treatment. Yet, the success of this approach has so far been limited. Methods A new approach toward improving the RCT is put forward based on placebo and nocebo mechanism studies, i.e. studies that investigate the mechanisms underlying placebo analgesia and nocebo hyperalgesia. In a series of meta-analyses the magnitude of placebo and nocebo effects were determined. Experimental studies across nociplastic and neuropathic pain conditions and across pharmacological and acupuncture treatments investigated psychological and neurobiological mechanisms underlying these effects. The obtained results were used to make approximations of expectations to see if that could predict the placebo response in RCTs and function as a new way of tapping into the placebo component of treatment effects. Results The magnitude of placebo and nocebo effects is large and highly variable. Placebo effects exist across chronic pain conditions with varying degrees of known etiology as well as across pharmacological and non-pharmacological treatments. Patients' perception of the treatment, the verbal suggestions given for pain relief, and the patients' expectations toward pain relief contribute to the magnitude of the placebo effect and to pain relief following placebo interventions. Also, unintentional unblinding and patients' perception of a treatment markedly influence the treatment outcome. By making approximations of expectations toward treatment effects it was possible to predict the magnitude of the placebo response in RCTs. Conclusions and implications The new approach of tapping into or directly asking patients about their perception and expectations toward a treatment, along with the account of the natural history of pain, has the potential to improve the information that can be obtained from RCTs. Thus, by interfacing insights from placebo and nocebo mechanism studies, it may be possible to enhance the information that can be obtained from RCTs and to account for a large part of the variability in the placebo component of the overall treatment effect. This approach has the potential to improve the scientific evaluation of treatments, as well as to illustrate how the effect of treatments can be optimized in clinical practice, which is the crux of evidence-based medicine.

Context matters: the psychoneurobiological determinants of placebo, nocebo and context-related effects in physiotherapy

Background

Placebo and nocebo effects embody psychoneurobiological phenomena where behavioural, neurophysiological, perceptive and cognitive changes occur during the therapeutic encounter in the healthcare context. Placebo effects are produced by a positive healthcare context; while nocebo effects are consequences of negative healthcare context. Historically, placebo, nocebo and context-related effects were considered as confounding elements for clinicians and researchers. In the last two decades this attitude started to change, and the understanding of the value of these effects has increased. Despite the growing interest, the knowledge and the awareness of using the healthcare context to trigger placebo and nocebo effects is currently limited and heterogeneous among physiotherapists, reducing their translational value in the physiotherapy field.

Objectives

To introduce the placebo, nocebo and context-related effects by: (1) presenting their psychological models; (2) describing their neurophysiological mechanisms; (3) underlining their impact for the physiotherapy profession; and (4) tracing lines for future researches.

Conclusion

Several psychological mechanisms are involved in placebo, nocebo and context-related effects; including expectation, learning processes (classical conditioning and observational learning), reinforced expectations, mindset and personality traits. The neurophysiological mechanisms mainly include the endogenous opioid, the endocannabinoid and the dopaminergic systems. Neuroimaging studies have identified different brain regions involved such as the dorsolateral prefrontal cortex, the rostral anterior cingulate cortex, the periaqueductal gray and the dorsal horn of spine. From a clinical perspective, the manipulation of the healthcare context with the best evidence-based therapy represents an opportunity to trigger placebo effects and to avoid nocebo effects respecting the ethical code of conduct. From a managerial perspective, stakeholders, organizations and governments should encourage the assessment of the healthcare context aimed to improve the quality of physiotherapy services. From an educational perspective, placebo and nocebo effects are professional topics that should be integrated in the university program of health and medical professions. From a research perspective, the control of placebo, nocebo and context-related effects offers to the scientific community the chance to better measure the impact of physiotherapy on different outcomes and in different conditions through primary studies.

Prior Therapeutic Experiences, Not Expectation Ratings, Predict Placebo Effects: An Experimental Study in Chronic Pain and Healthy Participants

INTRODUCTION

Many clinical trials fail because of placebo responses. Prior therapeutic experiences and patients' expectations may affect the capacity to respond to placebos in chronic disorders.

OBJECTIVE

The scope of this study in 763 chronic orofacial pain and healthy study participants was to compare the magnitude and prevalence of placebo effects and determine the putative role of prior therapeutic experiences vs. expectations.

METHODS

We tested placebo propensity in a laboratory setting by using 2 distinct levels of individually tailored painful stimulations (high pain and low pain) to reinforce expectations and provide a hypoalgesic experience (conditioning phase). Afterwards, both levels of pain were surreptitiously set at a moderate pain level to test for placebo effects (testing phase). Pain and expectation ratings were assessed as primary outcomes using visual analog scales.

RESULTS

In both chronic pain and healthy participants, placebo effects were similar in magnitude, with the larger prevalence of responders in the healthy participants. Although chronic pain participants reported higher pain relief expectations, expectations did not account for the occurrence of placebo effects. Rather, prior experience via conditioning strength mediated placebo effects in both pain and healthy participants.

CONCLUSIONS

These findings indicate that participants with chronic pain conditions display robust placebo effects that are not mediated by expectations but are instead directly linked to prior therapeutic experiences. This confirms the importance of assessing the therapeutic history while raising questions about the utility of expectation ratings. Future research is needed to enhance prediction of responses to placebos, which will ultimately improve clinical trial designs.

Pain, placebo, and test of treatment efficacy: a narrative review

Over the past decade, the mechanisms underlying placebo effects have begun to be identified. At the same time, the placebo response appears to have increased in pharmacological trials and marked placebo effects are found in neurostimulation and surgical trials, thereby posing the question whether non-pharmacological interventions should be placebo-controlled to a greater extent. In this narrative review we discuss how the knowledge of placebo mechanisms may help to improve placebo control in pharmacological and non-pharmacological trials. We review the psychological, neurobiological, and genetic mechanisms underlying placebo analgesia and outline the current problems and potential solutions to the challenges with placebo control in trials on pharmacological, neurostimulation, and surgical interventions. We particularly focus on how patients' perception of the therapeutic intervention, and their expectations towards treatment efficacy may help develop more precise placebo controls and blinding procedures and account for the contribution of placebo factors to the efficacy of active treatments. Finally, we discuss how systematic investigations into placebo mechanisms across various pain conditions and types of treatment are needed in order to 'personalise' the placebo control to the specific pathophysiology and interventions, which may ultimately lead to identification of more effective treatment for pain patients. In conclusion this review shows that it is important to understand how patients' perception and expectations influence the efficacy of active and placebo treatments in order to improve the test of new treatments. Importantly, this applies not only to assessment of drug efficacy but also to non-pharmacological trials on surgeries and stimulation procedures.

Prolonged Perioperative Use of Pregabalin and Ketamine to Prevent Persistent Pain after Cardiac Surgery

Editor’s Perspective

What We Already Know about This Topic

What This Article Tells Us That Is New

Background

Persistent postsurgical pain is common and affects quality of life. The hypothesis was that use of pregabalin and ketamine would prevent persistent pain after cardiac surgery.

Methods

This randomized, double-blind, placebo-controlled trial was undertaken at two cardiac surgery centers in the United Kingdom. Adults without chronic pain and undergoing any elective cardiac surgery patients via sternotomy were randomly assigned to receive either usual care, pregabalin (150 mg preoperatively and twice daily for 14 postoperative days) alone, or pregabalin in combination with a 48-h postoperative infusion of intravenous ketamine at 0.1 mg · kg−1 · h−1. The primary endpoints were prevalence of clinically significant pain at 3 and 6 months after surgery, defined as a pain score on the numeric rating scale of 4 or higher (out of 10) after a functional assessment of three maximal coughs. The secondary outcomes included acute pain, opioid use, and safety measures, as well as long-term neuropathic pain, analgesic requirement, and quality of life.

Results

In total, 150 patients were randomized, with 17 withdrawals from treatment and 2 losses to follow-up but with data analyzed for all participants on an intention-to-treat basis. The prevalence of pain was lower at 3 postoperative months for pregabalin alone (6% [3 of 50]) and in combination with ketamine (2% [1 of 50]) compared to the control group (34% [17 of 50]; odds ratio = 0.126 [0.022 to 0.5], P = 0.0008; and 0.041 [0.0009 to 0.28], P &lt; 0.0001, respectively) and at 6 months for pregabalin alone (6% [3 of 50]) and in combination with ketamine 0% (0 of 5) compared to the control group (28% [14 of 50]; odds ratio = 0.167 [0.029 to 0.7], P = 0.006; and 0.000 [0 to 0.24], P &lt; 0.0001). Diplopia was more common in both active arms.

Conclusions

Preoperative administration of 150 mg of pregabalin and postoperative continuation twice daily for 14 days significantly lowered the prevalence of persistent pain after cardiac surgery.

How May Placebo Mechanisms Influence Orofacial Neuropathic Pain?

The conceptualization of placebo has changed from inactive pills to a detailed understanding of how patients' perception of receiving a treatment influences pain processing and overall treatment outcome. Large placebo effects were recently demonstrated in chronic neuropathic pain, thereby opening the question of whether placebo effects also apply to orofacial neuropathic pain. In this article, we review the new definitions, magnitude, and social, psychological, neurobiologic, and genetic mechanisms of placebo effects in pain, especially neuropathic pain, to illustrate that placebo effects are not simply response bias but psychoneurobiological phenomena that can be measured at many levels of the neuroaxis. We use this knowledge to carefully illustrate how patients' perceptions of the treatment, the relationship with the health care provider, and the expectations and emotions toward a treatment can influence test and treatment outcome and potentially skew the results if they are not taken into consideration. Orofacial neuropathic pain is a new research area, and we review the status on definition, diagnosis, mechanisms, and pharmacologic treatment of neuropathic pain after trigeminal nerve injury, as this condition may be especially influenced by placebo factors. Finally, we have a detailed discussion of how knowledge of placebo mechanisms may help improve the understanding, diagnosis, and treatment of orofacial neuropathic pain, and we illustrate pitfalls and opportunities of applying this knowledge to the test of dental treatments.

The impact of contextual factors on nursing outcomes and the role of placebo/nocebo effects: a discussion paper

INTRODUCTION

Placebo and nocebo effects represent one of the most fascinating topics in the health care field.

OBJECTIVES

the aims of this discussion paper were (1) to briefly introduce the placebo and nocebo effects, (2) to elucidate the contextual factors able to trigger placebo and nocebo effects in the nursing field, and (3) to debate the impact of contextual factors on nursing education, practice, organisation, and research.

METHODS

a narrative review was conducted based on the available evidence.

RESULTS

Placebo responses (from Latin "I shall please") are a beneficial outcome(s) triggered by a positive context. The opposite are the nocebo effects (from Latin "I shall harm"), which indicates an undesirable outcome(s) caused by a negative context. Both are complex and distinct psychoneurobiological phenomena in which behavioural and neurophysiological changes arise subsequent to an interaction between the patient and the health care context.

CONCLUSION

Placebo and nocebo concepts have been recently introduced in the nursing discipline, generating a wide debate on ethical issues; however, the impact on nursing education, clinical practice, nursing administration, and research regarding contextual factors triggering nocebo and placebo effects has not been debated to date.

Sensory-specific predictive models in the human anterior insula

Expectations affect the subjective experience of pain by increasing sensitivity to noxious events, an effect underlain by brain regions such as the insula. However, it has been debated whether these neural processes operate on pain-specific information or on more general signals encoding expectation of unpleasant events. To dissociate these possibilities, two independent studies ( Sharvit et al., 2018, Pain; Fazeli and Büchel, 2018, J. Neurosci) implemented a cross-modal expectancy paradigm, testing whether responses to pain could also be modulated by the expectation of similarly unpleasant, but painless, events. Despite their differences, the two studies report remarkably convergent (and in some cases complementary) findings. First, the middle-anterior insula response to noxious stimuli is modulated only by expectancy of pain but not of painless adverse events, suggesting coding of pain-specific information. Second, sub-portions of the middle-anterior insula mediate different aspects of pain predictive coding, related to expectancy and prediction error. Third, complementary expectancy effects are also observed for other negative experiences (i.e., disgust), suggesting that the insular cortex holds prospective models of a wide range of events concerning their sensory-specific features. Taken together, these studies have strong theoretical implications on the functional properties of the insular cortex.

A novel neurocognitive approach for placebo analgesia in neurocognitive disorders

Neural correlates of placebo analgesia (PA) in patients with neurocognitive disorders have not yet been elucidated. The present study aimed to evaluate how and to what extent executive (dys)functions of the medial prefrontal cortex (MPFC) may be related to PA. To this end, twenty-three subjects complaining of different cognitive deficits (from mild cognitive impairment likely due to Alzheimer's disease to mild AD) were recruited. PA was investigated by a well-known experimental venipuncture pain paradigm (open versus hidden [O-H] application of lidocaine). Patients also underwent a comprehensive neuropsychological evaluation and a functional magnetic resonance imaging (fMRI) GO/No-GO task for eliciting selective activation of the MPFC. Selected neuropsychological variables were correlated to the OH-PA paradigm. The association between the fMRI response on the "No-GO" versus "GO" contrast and PA was investigated over the whole-brain by regression analysis. We showed the existence of a relationship between a lower PA and MPFC dysfunctions through the neuropsychological and fMRI assessment. A separate voxel-based morphometry (VBM) analysis controlled for possible influence of grey matter (GM) volume reduction on both fMRI results and PA. fMRI results were not directly affected by, and therefore independent of, disease-specific GM atrophy, which was indeed located more anteriorly within the rostral anterior cingulate and inversely correlated with PA. Our findings shed new light on the underestimated contribution of executive (dys)functions mediated by the MPFC (response-inhibition, self-monitoring and set-shifting abilities) in PA pathogenesis, with a special purely (i.e. independently from brain structural alterations) functional role played by the MCC. Results are discussed in terms of possible clinical relevance in the management of patients with neurocognitive disorders.

The Placebo Effect in Pain Therapies

Pharmacological strategies for pain management have primarily focused on dampening ascending neurotransmission and on opioid receptor-mediated therapies. Little is known about the contribution of endogenous descending modulatory systems to clinical pain outcomes and why some patients are mildly affected while others suffer debilitating pain-induced dysfunctions. Placebo effects that arise from patients' positive expectancies and the underlying endogenous modulatory mechanisms may in part account for the variability in pain experience and severity, adherence to treatment, distinct coping strategies, and chronicity. Expectancy-induced analgesia and placebo effects in general have emerged as useful models to assess individual endogenous pain modulatory systems. Different systems and mechanisms trigger placebo effects that highly impact pain processing, clinical outcomes, and sense of well-being. This review illustrates critical elements of placebo mechanisms that inform the methodology of clinical trials, the discovery of new therapeutic targets, and the advancement of personalized pain management.

Unique aspects of clinical trials of invasive therapies for chronic pain

Nearly all who review the literature conclude that the role of invasive procedures to treat chronic pain is poorly characterized because of the lack of “definitive” studies. The overt nature of invasive treatments, along with the risks, technical skills, and costs involved create challenges to study them. However, these challenges do not completely preclude evaluating invasive procedure effectiveness and safety using well-designed methods. This article reviews the challenges of studying outcomes of invasive therapies to treat pain and discuss possible solutions. Although the following discussion can apply to most invasive therapies to treat chronic pain, it is beyond the scope of the article to individually cover every invasive therapy used. Therefore, most of the examples focus on injection therapies to treat spine pain, spinal cord stimulation, and intrathecal drug therapies.

Can knowledge of Placebo and Nocebo Mechanisms Help Improve Randomized Clinical Trials?

Over the last decade, there has been a substantial increase in negative results from randomized controlled trials (RCTs), which may be due to an increasing placebo response among other factors. Currently, identification and exclusion of placebo responders from trials are attempted to overcome this problem, but so far the success of these approaches has been limited. At the same time, the placebo-mechanism literature has highlighted how contextual factors, such as patients' expectations, interfere with the effect of drug administration, leading to a certain degree of uncertainty in RCTs. In this chapter, we review the current challenges of RCTs including the uncertainties of the active arm, the placebo arm, the additivity assumption, and the double-blind procedure. We use the placebo-mechanism literature to debate the strengths and weaknesses of attempts to identify and exclude placebo responders from trials. Finally, we illustrate how insights from the placebo-mechanism literature may point to new ways of improving RCTs.

Side effects can enhance treatment response through expectancy effects: an experimental analgesic randomized controlled trial

In randomized controlled trials, medication side effects may lead to beliefs that one is receiving the active intervention and enhance active treatment responses, thereby increasing drug-placebo differences. We tested these hypotheses with an experimental double-blind randomized controlled trial of a nonsteroidal anti-inflammatory drug with and without the addition of atropine to induce side effects. One hundred healthy volunteers were told they would be randomized to either combined analgesics that might produce dry mouth or inert placebos. In reality, they were randomized double blind, double-dummy to 1 of the 4 conditions: (1) 100 mg diclofenac + 1.2 mg atropine, (2) placebo + 1.2 mg atropine, (3) 100 mg diclofenac + placebo, or (4) placebo + placebo, and tested with heat-induced pain. Groups did not differ significantly in demographics, temperature producing moderate pain, state anxiety, or depression. Analgesia was observed in all groups; there was a significant interaction between diclofenac and atropine, without main effects. Diclofenac alone was not better than double-placebo. The addition of atropine increased pain relief more than 3-fold among participants given diclofenac (d = 0.77), but did not enhance the response to placebo (d = 0.09). A chain of mediation analysis demonstrated that the addition of atropine increased dry mouth symptoms, which increased beliefs that one had received the active medication, which, in turn, increased analgesia. In addition to this indirect effect of atropine on analgesia (via dry mouth and beliefs), analyses suggest that among those who received diclofenac, atropine directly increased analgesia. This possible synergistic effect between diclofenac and atropine might warrant future research.

Clinical relevance of contextual factors as triggers of placebo and nocebo effects in musculoskeletal pain

Placebo and nocebo effects are embodied psycho-neurobiological responses capable of modulating pain and producing changes at different neurobiological, body at perceptual and cognitive levels. These modifications are triggered by different contextual factors (CFs) presented in the therapeutic encounter between patient and healthcare providers, such as healing rituals and signs. The CFs directly impact on the quality of the therapeutic outcome: a positive context, that is a context characterized by the presence of positive CFs, can reduce pain by producing placebo effects, while a negative context, characterized by the presence of negative CFs, can aggravate pain by creating nocebo effects. Despite the increasing interest about this topic; the detailed study of CFs as triggers of placebo and nocebo effects is still lacked in the management of musculoskeletal pain.

Increasing evidence suggest a relevant role of CFs in musculoskeletal pain management. CFs are a complex sets of internal, external or relational elements encompassing: patient’s expectation, history, baseline characteristics; clinician’s behavior, belief, verbal suggestions and therapeutic touch; positive therapeutic encounter, patient-centered approach and social learning; overt therapy, posology of intervention, modality of treatment administration; marketing features of treatment and health care setting. Different explanatory models such as classical conditioning and expectancy can explain how CFs trigger placebo and nocebo effects. CFs act through specific neural networks and neurotransmitters that were described as mediators of placebo and nocebo effects.

Available findings suggest a relevant clinical role and impact of CFs. They should be integrated in the clinical reasoning to increase the number of treatment solutions, boosts their efficacy and improve the quality of the decision-making. From a clinical perspective, the mindful manipulation of CFs represents a useful opportunity to enrich a well-established therapy in therapeutic setting within the ethical border. From a translational perspective, there is a strong need of research studies on CFs close to routine and real-world clinical practice in order to underline the uncertainty of therapy action and help clinicians to implement knowledge in daily practice.

Midazolam as an active placebo in 3 fentanyl-validated nociceptive pain models

The use of inactive placebos in early translational trials of potentially analgesic compounds is discouraged because of the side-effect profiles of centrally acting analgesics. Therefore, benzodiazepines are used, although their use has not been validated in this context. Whether benzodiazepines confound the results of acute pain tests is unknown. Midazolam (0.06 mg/kg) as an active placebo was investigated in 3 nociceptive models that included contact heat, electrical pain, and pressure pain thresholds in 24 healthy volunteers. Fentanyl (1 μg/kg) served as an internal validator in this randomized, placebo (saline) controlled, 3-way cross-over trial. The primary outcome parameter (contact heat pain) was analyzed using a one-way, repeated measures analysis of variance and Tukey's post test. Midazolam did not reduce pain ([numeric rating scale], 0-100) in a statistically significant manner compared with placebo for the contact heat (mean difference -1.7, 95% confidence interval -10.6 to 7.3; P = 0.89) or electrical pain (4.3, -5.1 to 13.7; P = 0.51) test, nor did it raise the pressure pain thresholds (-28 kPa, -122; 64 kPa, P = 0.73). The width of the confidence intervals suggested that there were no clinically meaningful analgesic effects compared with the placebo. In contrast, the analgesic efficacy of fentanyl was effectively demonstrated in all 3 models (P < 0.01 vs midazolam and placebo). The findings of this study show that midazolam can be used as an active placebo in analgesic drug trials. Furthermore, the proposed models were simple to implement and very effective in detecting analgesia. The test battery can be used in translational trials for new compounds and comes with an active placebo and an optional active comparator.

Are placebo and drug-specific effects additive? Questioning basic assumptions of double-blinded randomized clinical trials and presenting novel study designs

Double-blinded randomized clinical trials (RCTs) assume that pharmacological interventions have drug-specific and unspecific components. Traditional RCTs postulate an additivity of these two components. In this review, we provide evidence from both clinical trials and experimental studies that questions this 'additive model'. Given that the evaluation of drug treatments in RCTs is based on the assumption of additivity, its violation has far-reaching consequences. Therefore, we discuss an interactive model that, in contrast to the additive model, considers interactions between placebo and drug-specific effects. Moreover, we discuss implications for future clinical trials and present novel study designs enabling researchers to consider the complex interplay of drug-specific and unspecific effects.

Placebo, nocebo, and neuropathic pain

Over the last decade, the apparent increase in placebo responses in randomized controlled trials (RCTs) of neuropathic pain have complicated and potentially limited development and availability of new effective pain medication. Placebo analgesia and nocebo hyperalgesia effects are well described in nociceptive and idiopathic pain conditions, but less is known about the magnitude and mechanisms of placebo and nocebo effects in neuropathic pain. In neuropathic pain, placebo treatments have primarily been used as control conditions for active agents under investigation in RCTs and these placebo responses are typically not controlled for the natural history of pain and other confounding factors. Recently, mechanistic studies that control for the natural history of pain have investigated placebo and nocebo effects in neuropathic pain in their own right. Large placebo analgesia but no nocebo hyperalgesic effects have been found, and the underlying mechanisms are beginning to be elucidated. Here we review placebo and nocebo effects and the underlying mechanisms in neuropathic pain and compare them with those of nociceptive and idiopathic pain. This allows for a novel discussion on how knowledge of psychological, neurobiological, and genetic factors underlying well-controlled placebo effects may help improve the information that can be obtained from and potentially restore the utility of RCTs.

Better than treated as usual: Transcranial magnetic stimulation augmentation in selective serotonin reuptake inhibitor-refractory obsessive-compulsive disorder, mini-review and pilot open-label trial

OBJECTIVE

1 Hz repetitive transcranial magnetic stimulation (rTMS) over the supplementary motor area has been shown to be effective in a subset of obsessive-compulsive disorder (OCD) subjects, yet these results are still to be confirmed. This preliminary study compares the efficacy of augmentation with 1 Hz rTMS over the supplementary motor area and the usual augmentation treatment (TAU; treated as usual) with antipsychotics in a sample of selective serotonin reuptake inhibitor (SSRI)-refractory OCD patients.

METHOD

Fifty SSRI-refractory OCD patients consecutively admitted were studied: 25 were treated with a three-week trial of 1Hz, bilateral rTMS over the supplementary motor area and 25 with antipsychotic drugs. Yale-Brown Obsessive-Compulsive Scale (Y-BOCS; primary outcome measure), Hamilton Depression and Hamilton Anxiety scales were administered at first, second and third week of treatment.

RESULTS

Y-BOCS showed a statistically significant time effect from the baseline to the third week, with a 68% of responders (Y-BOCS score reduction of ⩾ 25%), in comparison with 24.0% in the TAU group. In the rTMS group, 17.6% of patients achieved remission.

CONCLUSIONS

1 Hz rTMS over the supplementary motor area appeared to be effective in approximately 2/3 of SSRI-refractory OCD subjects, whereas in the TAU group only 1/4 of subjects were responders. The supplementary motor area might be a new target area to be further explored with neuromodulation for OCD treatment.

Enhance placebo, avoid nocebo: How contextual factors affect physiotherapy outcomes

INTRODUCTION

Placebo and nocebo represent complex and distinct psychoneurobiological phenomena in which behavioural and neurophysiological modifications occur together with the application of a treatment. Despite a better understanding of this topic in the medical field, little is known about their role in physiotherapy.

PURPOSE

The aim of this review is: a) to elucidate the neurobiology behind placebo and nocebo effects, b) to describe the role of the contextual factors as modulators of the clinical outcomes in rehabilitation and c) to provide clinical and research guidelines on their uses.

IMPLICATIONS

The physiotherapist's features, the patient's features, the patient-physiotherapist relationship, the characteristics of the treatment and the overall healthcare setting are all contextual factors influencing clinical outcomes. Since every physiotherapy treatment determines a specific and a contextual effect, physiotherapists should manage the contextual factors as a boosting element of any manual therapy to improve placebo effects and avoid detrimental nocebo effects.

The topical 5% lidocaine medicated plaster in localized neuropathic pain: a reappraisal of the clinical evidence

Topical 5% lidocaine medicated plasters represent a well-established first-line option for the treatment of peripheral localized neuropathic pain (LNP). This review provides an updated overview of the clinical evidence (randomized, controlled, and open-label clinical studies, real-life daily clinical practice, and case series). The 5% lidocaine medicated plaster effectively provides pain relief in postherpetic neuralgia, and data from a large open-label controlled study indicate that the 5% lidocaine medicated plaster is as effective as systemic pregabalin in postherpetic neuralgia and painful diabetic polyneuropathy but with an improved tolerability profile. Additionally, improved analgesia and fewer side effects were experienced by patients treated synchronously with the 5% lidocaine medicated plaster, further demonstrating the value of multimodal analgesia in LNP. The 5% lidocaine medicated plaster provides continued benefit after long-term (≤7 years) use and is also effective in various other LNP conditions. Minor application-site reactions are the most common adverse events associated with the 5% lidocaine medicated plaster; there is minimal risk of systemic adverse events and drug–drug interactions. Although further well-controlled studies are warranted, the 5% lidocaine medicated plaster is efficacious and safe in LNP and may have particular clinical benefit in elderly and/or medically compromised patients because of the low incidence of adverse events.

When should placebo surgery as a control in clinical trials be carried out?

Placebo surgery – often maligned as ‘sham surgery’ – is a tough sell to patients and to many clinicians. But could surgical research benefit from increased use of placebo control groups?

Accounting for Behavior in Treatment Effects: New Applications for Blind Trials

The double-blind randomized controlled trial (DBRCT) is the gold standard of medical research. We show that DBRCTs fail to fully account for the efficacy of treatment if there are interactions between treatment and behavior, for example, if a treatment is more effective when patients change their exercise or diet. Since behavioral or placebo effects depend on patients' beliefs that they are receiving treatment, clinical trials with a single probability of treatment are poorly suited to estimate the additional treatment benefit that arises from such interactions. Here, we propose methods to identify interaction effects, and use those methods in a meta-analysis of data from blinded anti-depressant trials in which participant-level data was available. Out of six eligible studies, which included three for the selective serotonin re-uptake inhibitor paroxetine, and three for the tricyclic imipramine, three studies had a high (>65%) probability of treatment. We found strong evidence that treatment probability affected the behavior of trial participants, specifically the decision to drop out of a trial. In the case of paroxetine, but not imipramine, there was an interaction between treatment and behavioral changes that enhanced the effectiveness of the drug. These data show that standard blind trials can fail to account for the full value added when there are interactions between a treatment and behavior. We therefore suggest that a new trial design, two-by-two blind trials, will better account for treatment efficacy when interaction effects may be important.