One size does not fit all: towards optimising the therapeutic potential of endogenous pain modulatory systems

Harnessing the therapeutic effects of nature for chronic Pain: A role for immersive virtual reality? A narrative review

BACKGROUND AND OBJECTIVE

There is a growing interest in the relationship between nature and pain relief. Evidence from environmental psychology, neuroscience and physiology-based studies point towards analgesic effects of nature being mediated through various cognitive, affective and/or autonomic factors. Being able to harness these therapeutic effects using immersive virtual reality (VR) could help to optimize and improve accessibility of nature-based environments as part of chronic pain management plans. In this narrative review, we present evidence supporting a new theoretical framework for nature-based analgesia and suggest ways for applying this through immersive VR.

DATABASES AND DATA TREATMENT

We provide an overview of the evidence on (1) the therapeutic effects of nature on pain, (2) environmental psychology theory that underpins the health benefits of nature, (3) key mechanistic evidence from nature neuroimaging and physiology-based studies, (4) previous studies that have used VR-based nature in pain research and (5) how to design effective VR interventions that can be used to integrate nature into immersive 360 environments.

RESULTS

We have demonstrated how environmental psychology, neuroscience and physiology-based research can be used to form a novel theoretical framework for nature-based analgesia. Using this framework, we identify how key aspects of nature can act as analgesic and how this can be harnessed using immersive VR.

CONCLUSIONS

Through developing this theoretical framework, we have provided a foundation on which to guide future experimental and clinical studies as well as helping to improve the accessibility of nature for chronic pain patients through immersive VR technologies.

SIGNIFICANCE

This review article summarizes key multidisciplinary evidence to help understand how nature exerts beneficial effects on pain processing. The use of this theoretical framework alongside advances in immersive VR technologies provides a springboard for future research and can be used to help develop new nature-based therapeutics using VR.

Descending facilitation from rostral ventromedial medulla mu opioid receptor-expressing neurons is necessary for maintenance of sensory and affective dimensions of chronic neuropathic pain

ABSTRACT

Pharmacological ablation of rostral ventromedial medulla (RVM) mu opioid receptor-expressing cells before peripheral nerve injury prevents the development of neuropathic pain. However, whether these neurons are required for the expression of established neuropathic pain is not known. Male Oprm1Cre heterozygous (MOR Cre ) or wild-type (MOR WT ) mice received AAV8-hSyn-DIO-hM4D(Gi)-mCherry in the RVM. After partial sciatic nerve ligation (PSNL), we evaluated pain behaviors and descending control of nociception in response to acute or sustained chemogenetic inhibition of RVM-MOR cells expressing hM4D(Gi). A single systemic administration of hM4D(Gi) agonist clozapine-N-oxide (CNO) reversibly inhibited hind paw tactile allodynia and produced conditioned place preference only in MOR Cre mice with PSNL. Intrathecal CNO also reversibly inhibited PSNL-induced hind paw allodynia, suggesting that the spinal projections from these RVM-MOR cells are critical for manifestation of pain behaviors. Consistent with enhanced descending facilitation from RVM-MOR cells, MOR Cre -hM4D(Gi) mice with PSNL showed diminished descending control of nociception that was restored by systemic CNO. Sustained CNO in drinking water before PSNL prevented expression of chronic pain without affecting acute surgical pain; however, relief of chronic pain required sustained CNO treatment. Thus, in male mice, activity of spinally projecting RVM-MOR cells is required (1) for expression and manifestation of both sensory and affective dimensions of established neuropathic pain and (2) to promote descending facilitation that overcomes apparently intact descending inhibition to maintain chronic pain. Enhanced descending facilitation likely regulates the output signal from the spinal cord to the brain to shape the pain experience and may provide a mechanism for nonopioid management of pain.

Application of the grading system for "nociplastic pain" in chronic primary and chronic secondary pain conditions: a field study

ABSTRACT

The concept "nociplastic pain" has been developed for patients with features of nociceptive system sensitization that are not explained as nociceptive or neuropathic. Here, we tested how well the recently published grading system differentiates between chronic primary and secondary pain conditions. We recruited patients with fibromyalgia (FMS, n = 41), complex regional pain syndrome (CRPS, n = 11), osteoarthritis (OA, n = 21), or peripheral nerve injury (PNI, n = 8). We used clinical history, pain drawings, quantitative sensory testing (QST), and questionnaires to classify their pains as possibly or probably "nociplastic." All patients with chronic primary pain exhibited widespread/regional pain not explainable by either nociceptive or neuropathic mechanisms. Widespread pain occurred in 12 patients with OA but was identified as nociceptive in 11 of 12. Regional pain occurred in 4 patients with PNI but was identified as neuropathic in 3 of 4. At this step, the grading system had 100% sensitivity and 93% specificity. Clinical evidence for pain hypersensitivity by QST, and history of hypersensitivity and mental comorbidities did not differentiate between chronic primary pain (QST: 36/52 = 69%, history: 43/52 = 83%) and secondary pain conditions (QST: 20/29 = 69%, history: 24/29 83%). Based on these data, specificity remained excellent (93%), but sensitivity dropped substantially (60%) due to lacking evidence for pain hypersensitivity in many patients with FMS. This low sensitivity suggests that the published grading system is not suitable for screening purposes. We suggest structural and content modifications to improve sensitivity, including placement of patient history before clinical examination and addition of a high tender point count as evidence for widespread pain hypersensitivity.

Quantitative Sensory Testing - From bench to bedside

The methodology of Quantitative Sensory Testing (QST) comprises standardized testing procedures, which provide information of the integrity of the somatosensory nervous system. Over the years, different protocols have been established, which utilize similar but distinct testing procedures. They pursue the same overall objective to identify loss or gain of function of the respective sensory parameter to better understand the degree of abnormal nervous function and thereby improve patient care in the long-term. Laboratory-based QST protocols, which apply highly standardized testing procedures in pre-defined order and body regions, are considered as the gold standard in sensory testing. However, those protocols often require specifically trained personal, high equipment investment, and are time consuming. Thus, in recent years several attempts have been made to simplify testing protocols as well as reduce high costs of testing equipment such as thermal probe systems. These attempts have culminated in an array of sensory bedside testing protocols subserving the need for protocols that are easy to implement in and provide a standardized assessment within clinical trials. While laboratory and bedside QST that focus on static responses of single stimuli, protocols for testing dynamic QST focus on the functional response to pain also exist. Conditioned pain modulation (CPM) is often applied, which offers the ability to study endogenous inhibition of pain. All of these mentioned methodologies are considered as psychophysical measures and thus rely heavily on the cooperation of the patient or participant. In this chapter we provide an overview of QST along three main lines: (i) laboratory QST, (ii) bedside QST and (iii) dynamic QST. In addition, we discuss advantages and pitfalls of each modality. While we discuss along these lines, it should be noted that methodologies are overlapping: some bedside tests are similar or identical to lab-QST, many lab-QST protocols include a dynamic component, and assessment of dynamic QST requires to start with static assessments.

A myriad of methods to determine temporal summation of pain in people with musculoskeletal pain and healthy participants: a scoping review

Temporal summation of pain (TSP) is a human proxy for wind-up of dorsal horn neurons as assessed in animals. The common paradigm for eliciting TSP is evoked by repetitive nociceptive stimuli of equal intensity. Various stimulation and assessment protocols have been used. This scoping review aims to provide insight into key elements of TSP stimulation and assessment: modality, instruments, test location, familiarization, train characteristics, and calculations. PubMed, Embase, and Ebsco/CINAHL were searched for studies that measured TSP in adults with musculoskeletal conditions and healthy people. Four hundred six studies were included. Mechanical stimuli were the most commonly used modality (250 studies), followed by thermal stimuli (125 studies). Forty-six different instruments were used. Disregarding studies on widespread musculoskeletal pain and healthy participants, 40 studies evaluated TSP at painful sites, 77 in remote areas, and 66 in both locations. Of the 13 tested locations in patients, the hand (74 studies), lower leg (64 studies), and forearm (59 studies) were most commonly tested. A single practice round was the most common familiarization method (46 studies). Repeated stimuli were applied using 31 different frequencies (0.03-200 Hz) and sustained stimulations ranging from 5 to 1080 seconds were used. Twenty-two different train lengths, 63 different calculations (37 absolute, 19 relative, and 7 alternatives using data directly), and 14 different outcome measures (eg, self-reported pain rating scales and reflex thresholds) were used. Temporal summation of pain protocols vary excessively, hindering the comparison and pooling of results. None of the studies provided substantiation for their protocol choice.

Gastrointestinal pain: A systematic review of temporal summation of pain paradigms and outcomes

BACKGROUND AND OBJECTIVE

Since targeted treatment for gastrointestinal pain is elusive, identifying the mechanistic underpinning of this pain type is important. Facilitation of spinal neuronal responses underpins certain pain types, and the psychophysical temporal summation of pain (TSP) paradigm provides a proxy measure of spinal facilitatory processes. Our aim was to systematically review whether facilitated TSP is a feature of gastrointestinal pain in patients with, or pain-free people experiencing experimentally induced, gastrointestinal pain.

DATABASES AND DATA TREATMENT

EMBASE, MEDLINE, PsychInfo, CINAHL, and Web of Science were systematically searched, from inception to July 2023, for human studies reporting TSP paradigm outcomes in the context of gastrointestinal pain. The Appraisal tool for Cross-Sectional studies was used for quality assessment and applied independently by two researchers.

RESULTS

Fifteen papers consisting of cross-sectional (n = 6), case-control (n = 8), and retrospective cohort (n = 1) studies, were included. Thirteen studies investigated TSP in people with gastrointestinal pain with (n = 5) or without (n = 8) defined pathology. Two studies evoked TSP by repetitive gut stimulation in people undergoing abdominal medical procedures. Preliminary evidence showed that facilitated TSP correlated with the presence of functional gastrointestinal pain in women, and those with a history of trauma. No effect was observed in people with inflammatory bowel disease, although it was often unclear if they experienced pain.

CONCLUSIONS

It is not possible to conclude whether facilitated TSP is a feature of gastrointestinal pain. We recommend that subgroup findings are corroborated and that TSP paradigms are standardized in order that direct comparisons between studies may be made.

SIGNIFICANCE STATEMENT

Evidence indicated that pain facilitatory processes, as evidenced by a facilitated TSP outcome, contribute to functional gastrointestinal pain in women and those with a history of trauma. However, heterogeneity of study populations and paradigms precluded statistical synthesis and findings would need be corroborated. Studies exploring facilitatory processes in people with inflammatory bowel diseases did not report significant results, but pain is not a given in these conditions and, conversely, may be driven by peripheral inflammation during active disease. This should be taken in consideration in future explorations.

REGISTRATION REVIEW

PROSPERO CRD42022341845.

Does practice make perfect? Functional connectivity of the salience network and somatosensory network predicts response to mind-body treatments for fibromyalgia

Background

Mind-body treatments can improve coping mechanisms to deal with pain, improve the quality of life of patients with fibromyalgia syndrome (FMS), and reduce perceived pain in some cases. However, responses to these treatments are highly variable, the mechanisms underpinning them remain unclear, and reliable predictors of treatment response are lacking. We employed resting-state blood oxygen level-dependent (rsBOLD) functional magnetic resonance imaging (fMRI) to examine changes in brain functional connectivity (FC) following mind-body treatment that may relate to and predict pain relief.

Methods

We recruited patients with FMS who underwent either mindfulness-based stress reduction (MBSR; n = 18) or a psychoeducational program (FibroQoL; n = 22) and a treatment-as-usual FMS group (TAU; n = 18). We collected rsBOLD data, alongside subjective pain, anxiety, depression, and catastrophizing measures prior to and following treatments. We examined behavioral changes and FC changes in the salience network (SN) and sensorimotor network (SMN) and performed regression analyses to identify predictors for treatment response.

Results

The MBSR and FibroQoL groups experienced significant reductions in pain catastrophizing. After treatment, the FC of the sensorimotor cortex with the rest of the SMN became significantly reduced in the MBSR group compared to the TAU group. The FC between the SN and the SMN at baseline was negatively correlated with pain reductions following MBSR but positively correlated with pain reductions in the FibroQoL group. These results yielded large to very large effect sizes. Following MBSR, only for those patients with lower baseline SMN-SN FC, minutes of mindfulness practice were positively associated with clinical improvement (small to medium effect size).

Conclusions

Different mind-body treatments are underpinned by discrete brain networks. Measures of the functional interplay between SN and SMN have the potential as predictors of mind-body treatment response in patients with FMS.

Pain Science in Practice (Part 7): How Is Descending Modulation of Pain Measured?

SYNOPSIS: Understanding the descending pain modulatory system allows for a neuroscientific explanation of naturally occurring pain relief. Evidence from basic science and clinical studies on the effectiveness of drugs in certain patient groups led to pharmacological manipulation of the descending pain modulatory system for analgesia. Understanding mechanisms and theories helps clinicians make sense of chronic musculoskeletal pain. This editorial explains how test paradigms, including conditioned pain modulation, offset analgesia, and stress-induced analgesia work, provide an overview of a placebo analgesia circuitry, and discusses how evoking activity in the descending pain modulatory system using specific paradigms can give new insights into how specific treatments work to reduce pain. J Orthop Sports Phys Ther 2024;54(2):1-6. doi:10.2519/jospt.2024.12113.

Mindfulness-Based Intervention Effect on the Psychophysiological Marker of Self-Regulation in Women With Endometriosis-Related Chronic Pain

Endometriosis is a gynecological disease that involves a broad biopsychosocial compromise with the potential to create a negative vicious cycle. Despite the complexity of factors influencing women's improvement, most interventions investigated target just the peripheral nociceptive sources of endometriosis-related pain. An alternative is intervening in self-regulation, which can potentially influence multiple domains of the illness experience. The present study examines the effect of a brief Mindfulness-Based Intervention (bMBI) on attention and autonomic nervous system regulation in women with endometriosis-related pain. Also, explore the interaction between these self-regulation domains and the affective pain dimension. An exploratory analysis of the secondary outcomes of a pilot randomized controlled trial was performed. The vagally-mediated Heart Rate Variability (vmHRV) at rest, cognitive stress, and recovery was employed to measure autonomic regulation. The Flanker and Stroop tasks were used to estimate the attention domains. Results showed that bMBI (n = 26) significantly improved Flanker accuracy and Flanker and Stroop reaction time compared to the control group (n = 28). bMBI significantly increased vmHRV at rest and recovery after cognitive stress. Attention mediated the bMBI effect on affective pain improvement. Results suggest that bMBI improves self-regulation domains with the potential to develop a broad biopsychosocial benefit in the endometriosis context. PERSPECTIVE: This article demonstrates the positive impact of a brief Mindfulness-Based Intervention on attention and parasympathetic regulation in women suffering from endometriosis-related pain. This mindfulness-induced self-regulation improvement can benefit affective pain and potentially multiple psychophysiological processes relevant to endometriosis.

Concurrent validity of dynamic bedside quantitative sensory testing paradigms in breast cancer survivors with persistent pain

BACKGROUND

Studies on the concurrent validity of clinically applicable testing protocols for conditioned pain modulation (CPM) and temporal summation of pain (TSP) in breast cancer survivors (BCS) with persistent pain are lacking.

OBJECTIVES

This study investigated the concurrent validity of two bedside protocols for CPM and TSP in comparison to a respective reference protocol. The participants' preferences for bedside CPM and TSP protocols were assessed.

METHODS

Thirty BCS experiencing persistent pain were included in this study. Each participant underwent a reference test along with two bedside alternatives for assessing both TSP and CPM. For CPM, a cold pressor test (CPT) and blood pressure cuff (BPC) were used as conditioning stimulus. The test stimulus was elicited in parallel by pressure pain threshold after 45 and 90 s of conditioning at the lower limb. The CPM reference test consisted of parallel heat stimuli at the forearms using a two-thermode system. TSP was elicited using a von Frey monofilament (256 mN) and an algometer (98 kPa) at the affected site and opposite lower limb. The TSP reference test consisted of heat stimuli at the affected site and opposite lower limb. Participants' testing preference was examined using a purpose-designed questionnaire. Spearman's rank test examined the correlation between protocols.

RESULTS

The two bedside CPM protocols were strongly correlated (r = 0.787-0.939, p < 0.005). A strong correlation was found between the BPC protocol and reference test using the relative effect magnitude (r = 0.541-0.555, p < 0.005). The bedside TSP protocols were moderately correlated with each other only at the lower limb using absolute change scores (r = 0.455, p = 0.012). No significant correlation was found between the bedside and reference TSP protocols.

CONCLUSION

The significantly moderate to very strong correlations between the bedside protocols validate their interchangeability. Researchers and clinicians should be able to choose which bedside protocol they utilize; however, participants favored the use of a BPC and algometer for the evaluation of CPM and TSP, respectively.

Setting the clinical context to non-motor symptoms reflected by Park-pain, Park-sleep, and Park-autonomic subtypes of Parkinson's disease

Non-motor symptoms (NMS) of Parkinson's disease (PD) are well described in both clinical practice and the literature, enabling their management and enhancing our understanding of PD. NMS can dominate the clinical pictures and NMS subtypes have recently been proposed, initially based on clinical observations, and later confirmed in data driven analyses of large datasets and in biomarker-based studies. In this chapter, we provide an update on what is known about three common subtypes of NMS in PD. The pain (Park-pain), sleep dysfunction (Park-sleep), and autonomic dysfunction (Park-autonomic), providing an overview of their individual classification, clinical manifestation, pathophysiology, diagnosis, and potential treatments.

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.