Pain amplification-A perspective on the how, why, when, and where of central sensitization

A description of the development of an innovative multi-component long COVID treatment program based on central sensitization with preliminary patient satisfaction data

OBJECTIVE

Estimates of the prevalence of Long COVID in the United States or worldwide are imprecise, but millions of people are thought to be affected. No effective treatment exists for the often devastating symptoms of Long COVID. Central Sensitization has been postulated as a causal/explanatory mechanism for developing Long COVID. No treatment to date has targeted Central Sensitization. The present cross-sectional study describes the first 140 patients treated in a multi-component treatment program that targets Central Sensitization to reduce symptom burden, improve functioning, and lower the psychological distress observed in these patients.

METHODS

140 patients diagnosed with Long COVID after an extensive medical evaluation were assessed for function, depression, and pain catastrophizing using questionnaires and patient satisfaction measures after completion of a 16-h Cognitive Behavioral Therapy treatment program focused on Central Sensitization.

RESULTS

Upon admission, patients diagnosed with Long COVID were significantly impaired in their ability to function due to their symptoms. Further, 70% of the patients were depressed. Pain catastrophizing was observed in up to 20% of patients.

CONCLUSION

Patient satisfaction measures were high for the sample at the end of the treatment program suggesting that a multicomponent treatment program targeting Central Sensitization is acceptable to patients. Further research is needed to explore the effectiveness and durability of this treatment approach.

Temporomandibular Joint Disorder: An integrated study of the pathophysiology, neural mechanisms, and therapeutic strategies

OBJECTIVE

The study aims to investigate Temporomandibular Joint Disorder (TMJD) through a interdisciplinary lens, integrating insights from neuroscience, dentistry, and psychology to dissect its complex pathophysiology and neural mechanisms. It focuses on exploring the neurobiological underpinnings of TMJD, emphasizing the role of pain perception, modulation, and the impact of neurophysiological changes on the disorder.

DESIGN

This is a comprehensive narrative review of the literature.

RESULTS

Research findings pinpoint altered pain perception and modulation processes as central neural mechanisms contributing to TMJD, highlighting the importance of personalized treatment approaches due to the disorder's complexity and patient variability. The study recognizes advances in neuroscience offering new treatment avenues, such as neuromodulation and biofeedback, which provide non-invasive and personalized options. However, it also addresses the challenges in TMJD research, such as the multifaceted nature of the disorder and the need for more comprehensive, interdisciplinary strategies in research and clinical practice.

CONCLUSIONS

TMJD is a multifaceted disorder requiring an interdisciplinary approach for effective management. The study stresses the crucial role of neuroscience in understanding and treating TMJD, facilitating the development of innovative treatment strategies. It emphasizes the need for further research, advocating an integrated approach that combines neuroscience, dentistry, and psychology to address TMJD's complexities comprehensively and improve patient care, thereby enhancing the quality of life for affected individuals.

Combining Transcranial Direct Current Stimulation With Non-Invasive Interventions for Chronic Primary Pain: A Systematic Review and Meta-Analysis

BACKGROUND

A growing number of studies has combined transcranial direct current stimulation (tDCS) with other non-invasive non-pharmacological therapies (NINPT) to enhance effects in pain reduction. However, the efficacy of these combined approaches in treating chronic primary pain (CPP) warrants thorough investigation.

OBJECTIVE

This study aims to evaluate the efficacy of tDCS in conjunction with other NINPT in alleviating pain severity among CPP patients.

METHODS

We conducted a systematic search for randomized controlled trials (RCTs) comparing the efficacy of tDCS combined with NINPT against control treatments in adult CPP patients. The search spanned multiple databases, including PubMed, EMBASE, LILACS, Scopus, Web of Science, and CENTRAL.

RESULTS

Our systematic review included 11 RCTs with a total of 449 participants. In our meta-analysis, which comprised 228 participants receiving active-tDCS and 221 receiving sham-tDCS, we found a significant reduction in pain intensity (Standard Mean Difference = -0.73; 95% Confidence Interval (CI) = -1.18 to -0.27; P = .002) with the use of active-tDCS combined with NINPT.

CONCLUSION

These findings substantiate the therapeutic potential of combining tDCS with other NINPT, highlighting it as an effective treatment modality for reducing pain intensity in CPP patients.

How should we define and assess painful sensitivity in the hand? An international e-Delphi study

BACKGROUND

Painful sensitivity in the hand is commonly seen with neuropathic pain, interfering with daily activities including rehabilitation. However, there are currently several terms used to describe the problem and a lack of guidance on what assessments should be used.

PURPOSE

To gather expert opinion a) identifying current and common terminology used in hand therapy, b) developing a consensus definition of hypersensitivity, and c) developing consensus guidance on how to best assess allodynia.

STUDY DESIGN

International e-Delphi survey study.

METHODS

We conducted an e-Delphi consensus study drawing on international experts in hand rehabilitation. We planned up to four rounds of consensus-seeking, defining consensus as 75% or more of participants agreeing with a definition or recommendation. Experts were identified from 21 countries, with the nomination of other experts encouraged for 'snowball sampling'. The first round included clinical vignettes describing 'painful sensitivity of the hand' and asked participants to describe how they would assess each case. Definitions for hypersensitivity, tactile hyperesthesia, and allodynia were also requested.

RESULTS

We invited 68 participants: 44 more were added through nominations. Sixty-three agreed to participate and were sent the round one survey; 54 participants from 19 countries completed this survey and were invited to participate in all subsequent rounds. No two definitions of hypersensitivity were the same, while 87% of the definitions for allodynia and 78% for tactile hyperesthesia were concordant with a published taxonomy. Over 700 assessment items were proposed in round one: ultimately 38 items representing eight distinct constructs reached a consensus for assessing allodynia.

CONCLUSIONS

Therapists definitions were consistent with an existing taxonomy for allodynia. Although hypersensitivity conceptualizations varied regarding the qualities of stimulus and response, a working definition was reached. Recommended assessments were relatively consistent internationally, holistic, and reflected a potential link between allodynia and central sensitization.

EEG-Based Cortical Alterations in Individuals With Chronic Knee Pain Secondary to Osteoarthritis: A Cross-sectional Investigation

Chronic painful knee osteoarthritis (OA) is a disabling physical health condition. Alterations in brain responses to arthritic changes in the knee may explain persistent pain. This study investigated source localized, resting-state electroencephalography activity and functional connectivity in people with knee OA, compared to healthy controls. Adults aged 44 to 85 years with knee OA (n = 37) and healthy control (n = 39) were recruited. Resting-state electroencephalography was collected for 10 minutes and decomposed into infraslow frequency (ISF) to gamma frequency bands. Standard low-resolution electromagnetic brain tomography statistical nonparametric maps were conducted, current densities of regions of interest were compared between groups and correlation analyses were performed between electroencephalography (EEG) measures and clinical pain and functional outcomes in the knee OA group. Standard low-resolution electromagnetic brain tomography nonparametric maps revealed higher (P = .006) gamma band activity over the right insula (RIns) in the knee OA group. A significant (P < .0001) reduction in ISF band activity at the pregenual anterior cingulate cortex, whereas higher theta, alpha, beta, and gamma band activity at the dorsal anterior cingulate cortex, pregenual anterior cingulate cortex, the somatosensory cortex, and RIns in the knee OA group were identified. ISF activity of the dorsal anterior cingulate cortex was positively correlated with pain measures and psychological distress scores. Theta and alpha activity of RIns were negatively correlated with pain interference. In conclusion, aberrations in infraslow and faster frequency EEG oscillations at sensory discriminative, motivational-affective, and descending inhibitory cortical regions were demonstrated in people with chronic painful knee OA. Moreover, EEG oscillations were correlated with pain and functional outcome measures. PERSPECTIVE: This study confirms alterations in the rsEEG oscillations and its relationship with pain experience in people with knee OA. The study provides potential cortical targets and the EEG frequency bands for neuromodulatory interventions for managing chronic pain experience in knee OA.

How should we treat painful sensitivity in the hand? An international e-Delphi study

BACKGROUND

Evidence synthesis suggests allodynia resulting from neuropathic pain has few interventions with clear effectiveness. As research continues to build this needed evidence base, expert consensus recommendations can address the conflicting approaches within current hand therapy practice.

PURPOSE

This study aimed to develop consensus recommendations for the clinical management of allodynia from an international panel of hand therapists.

STUDY DESIGN

This was an international e-Delphi survey study.

METHODS

We recruited international hand rehabilitation experts to participate in an e-Delphi survey. Consensus was defined as 75% or more of participants agreeing with a recommendation, and at least 3 rounds of consensus building were anticipated. Experts were identified from 21 countries, and clinical vignettes describing a spectrum of patients with painful sensitivity in the hand were provided to elicit treatment recommendations. Initial recommendations were summarized, and consensus sought for clinical practice recommendations.

RESULTS

Sixty-eight participants were invited, with 44 more added through peer nominations. Fifty-four participants from 19 countries completed the initial survey and were invited to participate in all subsequent rounds. Over 900 treatment suggestions were provided from the initial vignettes across domains, including sensory, physical, and functional interventions, education, and cortical representation techniques: 46 ultimately reached consensus. However, important discrepancies in justification (eg, why allodynia should be covered) and implementation of techniques (eg, desensitization, sensory reeducation) were identified as the consensus exercise progressed.

CONCLUSIONS

Experts recommend individually tailored programs to treat allodynia using a variety of physical/movement, sensory-based, and "top-down" approaches; this is highly aligned with contemporary theories, such as the Neuromatrix Model of Pain. However, consensus was not reached on the justification and implementation of some of these approaches, reflecting the lack of a taxonomy and supporting evidence for tactile stimulation approaches in the current literature. Trials directly comparing the effectiveness of these approaches are needed.

Could Vulnerability to Motion Sickness and Chronic Pain Coexist within a Sensorimotor Phenotype? Insights from over 500 Pre-Pain Motion Sickness Reports

BACKGROUND

The sensorimotor incongruence theory proposes that certain instances of pain result from conflicts in the brain's sensorimotor networks. Indeed, injuries may cause abnormalities in afferent and cortical signaling resulting in such conflicts. Motion sickness also occurs in instances of incongruent sensorimotor data. It is possible that a sensory processing phenotype exists that predisposes people to both conditions.

AIM

The aim of this study was to investigate whether participants with chronic pain recall greater susceptibility to motion sickness before chronic pain onset.

METHOD

Data were collected via an online LimeSurvey. A self-report tendency toward motion sickness was measured using the Motion Sickness Susceptibility Questionnaire. Group differences were analysed using analysis of covariance methods.

RESULTS

530 patients (low back pain, n = 198; neck pain, n = 59; whiplash-associated disorder, n = 72; fibromyalgia syndrome, n = 114; Migraine, n = 41) and 165 pain-free controls were surveyed. ANCOVA analysis, using sex and anxiety as covariates, suggested that childhood motion sickness susceptibility scores differed by group (F = 2.55 (6, 615), p = 0.019, (ηp2) = 0.024). Planned comparisons, with corrected p-values, suggested that childhood motion sickness was not statistically greater for low back pain, rheumatoid arthritis, migraine, neck pain or whiplash-associated disorder (ps > 0.05), although scores were on average 27%, 42%, 47%, 48% and 58% higher, respectively. Childhood susceptibility was statistically higher in people with FMS (p = 0.018), with scores on average 83% higher than controls. ANCOVA analysis, using sex and anxiety as covariates, suggested that adult motion sickness susceptibility scores did not differ by group (F = 1.86 (6, 613), p = 0.086), although average scores were, on average, at least 33% higher in persistent pain groups.

CONCLUSIONS

According to retrospective reporting, greater susceptibility to motion sickness appears to pre-date persistent pain in some conditions. This supports the possibility that motion sickness and chronic pain may, in some cases, have overlapping mechanisms related to the handling of incongruent sensorimotor data.

Polygenic Contributions to Chronic Overlapping Pain Conditions in a Large Electronic Health Record Sample

Chronic overlapping pain conditions (COPCs) are believed to share common etiological mechanisms involving central sensitization. Genetic and environmental factors putatively combine to influence susceptibility to central sensitization and COPCs. This study employed a genome-wide polygenic risk score approach to evaluate genetic influences on 8 common COPCs. COPCs were identified by International Classification of Disease codes in Vanderbilt's deidentified clinical biorepository (BioVU), with each COPC condition empirically weighted for the level of central sensitization based on prior work. A centralized pain score (CPS) was calculated for 55,340 individuals by summing the weighted number of COPCs. Overall, 12,502 individuals (22.6%) were diagnosed with at least 1 COPC, with females exhibiting nearly twice the mean CPS as males. To assess the genetic influence on centralized pain in COPCs, 6 pain polygenic risk scores (PRSs) were developed using UK Biobank data to predict 6 pain criteria (no pain, neck/shoulder, abdomen, hip, knee, low back pain). These PRSs were then deployed in the BioVU cohort to test for association with CPS. In regression models adjusted for age, sex, and BMI, all pain PRSs except hip pain were significantly associated with CPS. Our findings support a shared polygenic influence across COPCs potentially involving central sensitization mechanisms. PERSPECTIVE: This study used a polygenic risk score approach to investigate genetic influences on chronic overlapping pain conditions. Significant findings in this study provide evidence supporting previous hypotheses that a shared polygenic influence involving central sensitization may underly chronic overlapping pain conditions and can guide future biomarker and risk assessment research.

Electrical Stimulation of the Auricular Branch Vagus Nerve Using Random and Alternating Frequencies Triggers a Rapid Onset and Pronounced Antihyperalgesia via Peripheral Annexin A1-Formyl Peptide Receptor 2/ALX Pathway in a Mouse Model of Persistent Inflammatory Pain

This study evaluated the antihyperalgesic and anti-inflammatory effects of percutaneous vagus nerve electrical stimulation (pVNS) by comparing the effects of alternating and random frequencies in an animal model of persistent inflammatory hyperalgesia. The model was induced by Freund's complete adjuvant (CFA) intraplantar (i.pl.) injection. Mice were treated with different protocols of time (10, 20, or 30 min), ear laterality (right, left or both), and frequency (alternating or random). Mechanical hyperalgesia was evaluated, and some groups received i.pl. WRW4 (FPR2/ALX antagonist) to determine the involvement. Edema, paw surface temperature, and spontaneous locomotor activity were evaluated. Interleukin-1β, IL-6, IL-10, and IL4 levels were verified by enzyme-linked immunosorbent assay. AnxA1, FPR2/ALX, neutrophil, M1 and M2 phenotype macrophage, and apoptotic cells markers were identified using western blotting. The antihyperalgesic effect pVNS with alternating and random frequency effect is depending on the type of frequency, time, and ear treated. The pVNS random frequency in the left ear for 10 min had a longer lasting antihyperalgesic effect, superior to classical stimulation using alternating frequency and the FPR2/ALX receptor was involved in this effect. There was a reduction in the levels of pro-inflammatory cytokines and an increase in the immunocontent of AnxA1 and CD86 in mice paw. pVNS with a random frequency in the left ear for 10 min showed to be optimal for inducing an antihyperalgesic effect. Thus, the random frequency was more effective than the alternating frequency. Therefore, pVNS may be an important adjunctive treatment for persistent inflammatory pain.

Emotion regulation and the salience network: a hypothetical integrative model of fibromyalgia

Fibromyalgia is characterized by widespread pain, fatigue, sleep disturbances and other symptoms, and has a substantial socioeconomic impact. Current biomedical and psychosocial treatments are unsatisfactory for many patients, and treatment progress has been hindered by the lack of a clear understanding of the pathogenesis of fibromyalgia. We present here a model of fibromyalgia that integrates current psychosocial and neurophysiological observations. We propose that an imbalance in emotion regulation, reflected by an overactive 'threat' system and underactive 'soothing' system, might keep the 'salience network' (also known as the midcingulo-insular network) in continuous alert mode, and this hyperactivation, in conjunction with other mechanisms, contributes to fibromyalgia. This proposed integrative model, which we term the Fibromyalgia: Imbalance of Threat and Soothing Systems (FITSS) model, should be viewed as a working hypothesis with limited supporting evidence available. We hope, however, that this model will shed new light on existing psychosocial and biological observations, and inspire future research to address the many gaps in our knowledge about fibromyalgia, ultimately stimulating the development of novel therapeutic interventions.

Classical analgesic drugs modulate nociceptive-like escape behavior in Drosophila melanogaster larvae

Introduction: Nociceptive stimulus triggers escape responses in Drosophila melanogaster larvae, characterized by 360° rolling behavior along its own body axis. Therefore, it is possible to study analgesic drugs based on this stereotypical nociceptive-like escape behavior. Here, we aimed to develop an analgesic predictive validity test of thermal nociception through D. melanogaster larvae.

Materials and methods: We evaluated the effect of classical analgesics (morphine, dipyrone, acetylsalicylic acid (ASA) and dexamethasone (DXM)) in the rolling behavior latency of D. melanogaster larvae exposed to thermal-acute noxious stimulus and nociceptive sensitization paradigm. Drugs were injected into hemocoel (100 nL) before nociceptive measurement.

Results and discussion: Rolling behavior latency was increased by morphine (2, 4, 8 and 16 ng) in dose-dependent manner. Naloxone (4 ng) fully reversed maximum effect of morphine. Dipyrone (32, 64 and 128 ng) and DXM (8 and 16 ng) elicited dose-dependent antinociceptive effects. Exposure of larvae to 97% of maximal infrared intensity induced nociceptive sensitization, i.e., latency changed from 12 to 7.5 seconds. ASA (25, 50 and 100 ng) and DXM (4, 8 and 16 ng) were administered 150 min after nociceptive sensitization and displayed reverse sensitization in rapid onset (30 min after injection). DXM (16 ng), injected prior to nociceptive sensitization, displayed a delay in the onset of action (150 min after injection). Locomotor behaviors were not affected by analgesic substances.

Conclusion: Our findings open perspectives for evaluation and discovery of antinociceptive drugs using D. melanogaster larvae model.

Graphical abstract

Central Sensitization in Migraine: A Narrative Review

Central sensitization (CS) is an increase in the responsiveness of nociceptive neurons in the central nervous system to their normal afferent input. As a result, even minor irritation can induce severe pain, leading to the chronicity and severity of various diseases, such as neurological disorders. CS is associated with migraine, which is a major neurological disorder that inflicts a high disability in daily life. Specifically, CS is thought to be involved in the pathogenesis of cutaneous allodynia as well as chronification of migraine. In this article, we reviewed the association between CS and migraine, including pathophysiological aspects and evidence from clinical studies. We suggest that appropriate screening and management of CS in migraine could further improve the quality of life of migraine patients.

Pain is Not a "thing": How That Error Affects Language and Logic in Pain Medicine

Effectiveness in academic and clinical communication depends upon agreement on what words and concepts denote and on the consequent ability to argue logically and accurately. In the pain medicine literature there are many examples of imprecision and confusion in this respect, including misnomers and fallacies in reasoning. This article firstly critically examines some of these misnomers. Identified themes include pain being conceptualised as a "thing," conflation between nociception and pain, and confusion between stimulus and response and between the perspectives of the experiencer and the observer of "pain." Secondly, fallacies in reasoning are identified that contribute to imprecision and confusion. These include reification of pain, attributing to the brain functions that belong to whole organisms, and the illusory truth effect. Thirdly, these themes are identified also in constructs that are shown to be based more on speculation than on fact. Taken together, these observations reveal a need to review and, where necessary, modify terminology and concepts used in Pain Medicine. PERSPECTIVE: This article examines a number of words and constructs commonly found in the pain literature from the perspective of accuracy in terms of their consistency of usage, concordance with fact, degree of speculation and logical argument. A common major theme is the error of considering pain as a "thing" that has agentive properties. A need to clarify much of the language used in Pain Medicine is identified.

Central sensitization in opioid use disorder: a novel application of the American College of Rheumatology Fibromyalgia Survey Criteria

Central sensitization may be an underlying mechanism linking chronic pain and opioid use disorder associated with opioid use disorder onset, maintenance, escalation, treatment delay, and relapse.

Introduction:

Central sensitization (CS) involves dysfunctional central nervous system pain modulation resulting in heightened pain perception. Central sensitization is not commonly assessed among patients with opioid use disorder (OUD), despite the fact that pain has been implicated in the development, maintenance, and relapse of OUD and chronic opioid use may produce opioid-induced hyperalgesia. Central sensitization is a plausibly important mechanism underlying the complex relationship between OUD and chronic pain. However, this premise is largely untested.

Methods:

Participants with OUD (n = 141) were recruited from an academic addiction treatment center in Columbus, Ohio. An established surrogate measure of CS, the American College of Rheumatology 2011 Fibromyalgia Survey Criteria, was administered using electronic survey. Participants also responded to questions about pain interference (Brief Pain Inventory), quality of life (RAND-36), and items regarding pain beliefs and expectations of pain and addiction treatment. Descriptive analyses, Spearman rho correlations, and Mann–Whitney U tests were performed.

Results:

Hypothesized relationships were confirmed between degree of CS, pain interference, and health-related quality of life. Degree of CS was also positively correlated with greater endorsement of pain as a reason for the onset, maintenance, and escalation of OUD; treatment delay; and OUD relapse. Participants with the American College of Rheumatology 2011 Fibromyalgia Survey Criteria ≥13 had significantly greater endorsement of pain as a reason for delaying OUD treatment, continuing and increasing opioid use, and precipitating OUD relapse.

Conclusions:

This study provides early evidence CS may underlie previously observed connections between clinically salient features of chronic pain and OUD, potentially informing future mechanistic research and precision treatment.

Temporal Grading Index of Functional Network Topology Predicts Pain Perception of Patients With Chronic Back Pain

Chronic back pain (CBP) is a maladaptive health problem affecting the brain function and behavior of the patient. Accumulating evidence has shown that CBP may alter the organization of functional brain networks; however, whether the severity of CBP is associated with changes in dynamics of functional network topology remains unclear. Here, we generated dynamic functional networks based on resting-state functional magnetic resonance imaging (rs-fMRI) of 34 patients with CBP and 34 age-matched healthy controls (HC) in the OpenPain database via a sliding window approach, and extracted nodal degree, clustering coefficient (CC), and participation coefficient (PC) of all windows as features to characterize changes of network topology at temporal scale. A novel feature, named temporal grading index (TGI), was proposed to quantify the temporal deviation of each network property of a patient with CBP to the normal oscillation of the HCs. The TGI of the three features achieved outstanding performance in predicting pain intensity on three commonly used regression models (i.e., SVR, Lasso, and elastic net) through a 5-fold cross-validation strategy, with the minimum mean square error of 0.25 ± 0.05; and the TGI was not related to depression symptoms of the patients. Furthermore, compared to the HCs, brain regions that contributed most to prediction showed significantly higher CC and lower PC across time windows in the CBP cohort. These results highlighted spatiotemporal changes in functional network topology in patients with CBP, which might serve as a valuable biomarker for assessing the sensation of pain in the brain and may facilitate the development of CBP management/therapy approaches.

Genetic and epigenetic mechanisms influencing acute to chronic postsurgical pain transitions in pediatrics: Preclinical to clinical evidence

Background

Chronic postsurgical pain (CPSP) in children remains an important problem with no effective preventive or therapeutic strategies. Recently, genomic underpinnings explaining additional interindividual risk beyond psychological factors have been proposed.

Aims

We present a comprehensive review of current preclinical and clinical evidence for genetic and epigenetic mechanisms relevant to pediatric CPSP.

Methods

Narrative review.

Results

Animal models are relevant to translational research for unraveling genomic mechanisms. For example, Cacng2, p2rx7, and bdnf mutant mice show altered mechanical hypersensitivity to injury, and variants of the same genes have been associated with CPSP susceptibility in humans; similarly, differential DNA methylation (H1SP) and miRNAs (miR-96/7a) have shown translational implications. Animal studies also suggest that crosstalk between neurons and immune cells may be involved in nociceptive priming observed in neonates. In children, differential DNA methylation in regulatory genomic regions enriching GABAergic, dopaminergic, and immune pathways, as well as polygenic risk scores for enhanced prediction of CPSP, have been described. Genome-wide studies in pediatric CPSP are scarce, but pathways identified by adult gene association studies point to potential common mechanisms.

Conclusions

Bench-to-bedside genomics research in pediatric CPSP is currently limited. Reverse translational approaches, use of other -omics, and inclusion of pediatric/CPSP endophenotypes in large-scale biobanks may be potential solutions. Time of developmental vulnerability and longitudinal genomic changes after surgery warrant further investigation. Emergence of promising precision pain management strategies based on gene editing and epigenetic programing emphasize need for further research in pediatric CPSP-related genomics.

Advances in targeting central sensitization and brain plasticity in chronic pain

Maladaptation in sensory neural plasticity of nociceptive pathways is associated with various types of chronic pain through central sensitization and remodeling of brain connectivity. Within this context, extensive research has been conducted to evaluate the mechanisms and efficacy of certain non-pharmacological pain treatment modalities. These include neurostimulation, virtual reality, cognitive therapy and rehabilitation. Here, we summarize the involved mechanisms and review novel findings in relation to nociceptive desensitization and modulation of plasticity for the management of intractable chronic pain and prevention of acute-to-chronic pain transition.

Pain descriptors and determinants of pain sensitivity in knee osteoarthritis: a community-based cross-sectional study

Objectives

To explore pain characteristics in individuals with knee osteoarthritis (KOA), to compare pain sensitivity across individuals with KOA, chronic back pain (CBP) and pain-free individuals (NP), and to examine the relationship between clinical and pain characteristics with pain sensitivity in KOA.

Methods

Cross-sectional, community-based online survey. Two datasets were combined comprising Dutch individuals of ≥ 40 years of age, experiencing chronic knee pain (KOA, N = 445), chronic back pain (CBP, N = 504), or no pain (NP, N = 256). Demographic and clinical characteristics, global health, physical activity/exercise, and pain characteristics including intensity, spreading, duration, quality (SF-MPQ), and sensitivity (PSQ) were assessed. Differences between (sub)groups were examined using analyses of variance or Chi-square tests. Regression analyses were performed to examine determinants of pain sensitivity in the KOA group.

Results

Quality of pain was most commonly described as aching, tender, and tiring-exhausting. Overall, the KOA group had higher levels of pain sensitivity compared to NP group, but lower levels than the CBP group. Univariately, pain intensity, its variability and spreading, global health, exercise, and having comorbidities were weakly related to pain sensitivity (standardized betas: 0.12-0.27). Symptom duration was not related to pain sensitivity. Older age, higher levels of continuous pain, lower levels of global health, and exercise uniquely contributed, albeit modest, to pain sensitivity (P&lt;0.05).

Conclusion

Continuous pain such as aching and tenderness in combination with decreased physical activity may be indicative for a subgroup of individuals at risk for pain sensitivity and, ultimately, poor treatment outcomes.

Outcomes of a Comprehensive Pain Rehabilitation Program for Patients With Fibromyalgia

OBJECTIVE

To analyze opioid intake interference with psychological, well-being, and functional outcomes and medication tapering in patients with fibromyalgia admitted to the Mayo Clinic Pain Rehabilitation Program (MCPRP) in Florida.

PATIENTS AND METHODS

A retrospective study on MCPRP outcomes was conducted. We reviewed the health records of 150 patients with fibromyalgia who participated in the program from May 1, 2014, to May 1, 2015. All patients were asked to fill out a survey at admission to and dismissal from the program. Surveys contained questions from the numeric pain score, Multidimensional Pain Inventory (perceived life control and interference of pain subscales), Center for Epidemiological Studies-Depression Scale, Pain Catastrophizing Scale, 36-Item Short-Form Health Status Survey (general health perceptions subscale), and Pain Self-Efficacy Questionnaire. A medical record review identified categories and number of medications at program admission and dismissal. Patients were divided in 2 groups: those whose concomitant medication did not include opioids at admission (no opioids group) and those whose concomitant medication included opioids at admission (opioids group).

RESULTS

By dismissal from the MCPRP, patients with fibromyalgia in the no opioids group had a significant (P<.05) improvement in all the self-reported scores. Medication, including opioids, were effectively tapered at a substantially higher percentage in the opioids group.

CONCLUSION

Benefit of the comprehensive pain rehabilitation program in patients with fibromyalgia was indicated by clinical improvements in pain severity, physical and emotional health, and functional capacity while successfully tapering medication. Opioid intake at admission may modify the program outcomes.

Adaptive body awareness predicts fewer central sensitization-related symptoms and explains relationship between central sensitization-related symptoms and pain intensity: A cross-sectional study among individuals with chronic pain

BACKGROUND

Central sensitization (CS), defined as the amplification of neural signaling within the CNS that elicits pain hypersensitivity, is thought be a characteristic of several chronic pain conditions. Maladaptive body awareness is thought to contribute and maintain CS. Less is known about the relationship between CS and adaptive body awareness.

PURPOSE

This cross-sectional study investigated relationships among self-reported adaptive body awareness (Multidimensional Interoceptive Awareness Scale-2; MAIA-2), CS-related symptoms (Central Sensitization Inventory; CSI), and pain intensity and further delineate potential direct and indirect links among these constructs.

METHODS

Online surveys were administered to 280 individuals with chronic pain reporting elevated CSI scores. Strategic sampling targeted respondents to reflect the 2010 census. Pearson's correlations characterized overall relationship between variables. Multiple regression analyses investigated potential direct links. A path analysis assessed mediational effects of CS-related symptoms on the relationship between adaptive body awareness and pain intensity.

RESULTS

CSI demonstrated strong, inverse correlations with some MAIA-2 subscales, but positive correlations with others. Higher CSI scores predicted greater pain intensity (b = 0.049, p ≤ 0.001). Two MAIA-2 subscales, Not-Distracting (b = -0.56, p ≤ 0.001) and Not-Worrying (b = -1.17, p ≤ 0.001) were unique predictors of lower CSI. Not-Distracting (b = -0.05, p = 0.003) and Not-Worrying (b = -0.06, p = 0.007) uniquely predicted lower pain intensity. CSI completely mediated the relationship between adaptive body awareness and pain intensity [point estimate = -0.04; 95% bootstrap confident intervals (CI) = -0.05 to -0.02].

CONCLUSIONS

Findings also support future research to explore causal relationships of variables. Findings suggest that frequency of attention to bodily sensations is distinct from cognitive-affective appraisal of bodily sensation, and the two distinct higher order processes may have divergent influences on perceived pain and CS-related symptoms. Results also support future research to explore causal relationships of variables.

Opioid Use in Fibromyalgia Continues Despite Guidelines That Do Not Support Its Efficacy or Risk

BACKGROUND/OBJECTIVE

The aim of this cross-sectional study is to determine the prevalence of opioid use in a large sample of fibromyalgia (FM) patients and examine the factors associated with opioid prescription/use despite multiple clinical guidelines that do not recommend opioid use in this population.

METHODS

Data were collected from a convenience sample of 698 patients admitted from August 2017 to May 2019 into an intensive 2-day Fibromyalgia Treatment Program at a tertiary medical center in the United States after FM diagnosis. Patients were administered the Fibromyalgia Impact Questionnaire-Revised, the Center for Epidemiologic Study of Depression Scale, and the Pain Catastrophizing Scale upon admission to the program. Demographic information and opioid use were self-reported. Logistic regression analysis was utilized to determine associations between patient-related variables and opioid use in this prospective study.

RESULTS

Of 698 patients, 27.1% (n = 189) were taking opioids at intake. Extended duration of symptoms (>3 years), increased age, higher degree of functional impairment, and increased pain catastrophizing were significantly associated with opioid use.

CONCLUSIONS

Opioids are not recommended for the treatment of FM under current guidelines. Greater burden of illness appeared to be associated with the prescription and use of opioids in this population. These findings suggest that some providers may not be aware of current recommendations that have been found to be effective in the management of FM that are contained in guidelines. Alternative approaches to the management of FM that do not involve opioids are reviewed in an effort to improve care.

Interoception and Emotion: A Potential Mechanism for Intervention With Manual Treatment

Interoception is considered a perception pathway as important as the exteroceptive pathways for determining responses to maintain homeostasis. There is evidence about the influence of the interoception on emotional responses as these expressions are considered to be a combination of physical, environmental and individual beliefs. A large percentage of afferent fibers in the body are related to free nerve endings which, when stimulated, reach the insular cortex that participates in the process of emotions. The viscera afferent fibers represent 5% to 15% of all these inputs. Evidence emerges that demonstrates the importance of visceral health as part of the treatment of patients with emotional imbalances. It can be postulated that manual treatment applied to visceral fasciae can assist in interoceptive balance and have a positive impact on emotions. Therefore, the objective of the present study is to discuss the concepts of interoception, central sensitization, emotional health and visceral manual treatment.

S-ketamine in patient-controlled analgesia reduces opioid consumption in a dose-dependent manner after major lumbar fusion surgery: A randomized, double-blind, placebo-controlled clinical trial

Background

Spinal fusion surgery causes severe pain. Strong opioids, commonly used as postoperative analgesics, may have unwanted side effects. S-ketamine may be an effective analgesic adjuvant in opioid patient-controlled analgesia (PCA). However, the optimal adjunct S-ketamine dose to reduce postoperative opioid consumption is still unknown.

Methods

We randomized 107 patients at two tertiary hospitals in a double-blinded, placebo-controlled clinical trial of adults undergoing major lumbar spinal fusion surgery. Patients were randomly allocated to four groups in order to compare the effects of three different doses of adjunct S-ketamine (0.25, 0.5, and 0.75 mg ml-1) or placebo on postoperative analgesia in oxycodone PCA. Study drugs were administered for 24 hours postoperative after which oxycodone-PCA was continued for further 48 hours. Our primary outcome was cumulative oxycodone consumption at 24 hours after surgery.

Results

Of the 100 patients analyzed, patients receiving 0.75 mg ml^-1 S-ketamine in oxycodone PCA needed 25% less oxycodone at 24 h postoperatively (61.2 mg) compared with patients receiving 0.5 mg ml^-1 (74.7 mg) or 0.25 mg ml^-1 (74.1 mg) S-ketamine in oxycodone or oxycodone alone (81.9 mg) (mean difference: -20.6 mg; 95% confidence interval [CI]: -41 to -0.20; P = 0.048). A beneficial effect in mean change of pain intensity at rest was seen in the group receiving 0.75 mg ml^-1 S-ketamine in oxycodone PCA compared with patients receiving lower ketamine doses or oxycodone alone (standardized effect size: 0.17, 95% CI: 0.013–0.32, P = 0.033). The occurrence of adverse events was similar among the groups.

Conclusions

Oxycodone PCA containing S-ketamine as an adjunct at a ratio of 1: 0.75 decreased cumulative oxycodone consumption at 24 h after major lumbar spinal fusion surgery without additional adverse effects.

Flipping the Pain Care Model: A Sociopsychobiological Approach to High-Value Chronic Pain Care

OBJECTIVE

Much of the pain care in the United States is costly and associated with limited benefits and significant harms, representing a crisis of value. We explore the current factors that lead to low-value pain care within the United States and provide an alternate model for pain care, as well as an implementation example for this model that is expected to produce high-value pain care.

METHODS

From the perspective of aiming for high-value care (defined as care that maximizes clinical benefit while minimizing harm and cost), we describe the current evidence practice gap (EPG) for pain care in the United States, which has developed as current clinical care diverges from existing evidence. A discussion of the biomedical, biopsychosocial, and sociopsychobiological (SPB) models of pain care is used to elucidate the origins of the current EPG and the unconscious factors that perpetuate pain care systems despite poor results.

RESULTS

An interprofessional pain team within the Veterans Health Administration is described as an example of a pain care system that has been designed to deliver high-value pain care and close the EPG by implementing the SPB model.

CONCLUSIONS

Adopting and implementing a sociopsychobiological model may be an effective approach to address the current evidence practice gap and deliver high-value pain care in the United States. The Phoenix VA Health Care System's Chronic Pain Wellness Center may serve as a template for providing high-value, evidence-based pain care for patients with high-impact chronic pain who also have medical, mental health, and opioid use disorder comorbidities.

Temporal summation of mechanical pain prospectively predicts movement-evoked pain severity in adults with chronic low back pain

BACKGROUND

Biopsychosocial factors above and beyond pathoanatomical changes likely contribute to the severity of chronic low back pain. A pro-nociceptive endogenous pain modulatory balance (↓inhibition and ↑facilitation) may be an important contributor to chronic low back pain severity and physical function; however, additional research is needed to address this possibility. The objective of this study was to determine whether quantitative sensory tests of endogenous pain inhibition and facilitation prospectively predict movement-evoked pain and cLBP severity self-reported on a validated questionnaire.

METHODS

One hundred thirty-four individuals with chronic low back pain were enrolled in this two-session study. During the first study session, temporal summation of mechanical pain and conditioned pain modulation were assessed at the lumbar spine to determine endogenous pain facilitation and inhibition, respectively. One week later, participants returned for a second study session whereby they reported their pain severity and pain interference using the Brief Pain Inventory-Short Form. Movement-evoked pain and physical function capacity were assessed upon completion of the balance, walking, and transition from sit to stand tests of the Short Physical Performance Battery.

RESULTS

Temporal summation of mechanical pain, but not conditioned pain modulation, significantly and prospectively predicted greater movement-evoked pain and poorer physical function on the Short Physical Performance Battery. Neither temporal summation nor conditioned pain modulation were significantly related to self-reported pain severity or pain interference on the Brief Pain Inventory-Short Form.

CONCLUSIONS

Findings suggest that a pro-nociceptive pain modulatory balance characterized by enhanced pain facilitation may be an important driver of movement-evoked pain severity and poor physical function in individuals with chronic low back pain.

Capsaicin: Plants of the Genus Capsicum and Positive Effect of Oriental Spice on Skin Health

BACKGROUND

Capsaicin, the main pungent ingredient in hot chili peppers, causes excitation of small sensory neurons. It also provides the basic pungent flavor in Capsicum fruits.

SUMMARY

Capsaicin plays a vital role as an agonist for the TRPV1 (transient receptor potential cation channel, subfamily V, member 1) receptor. TRPV1 is essential for the reduction of oxidative stress, pain sensations, and inflammation. Therefore, it has many pros related to health issue. Activation and positive impact of TRPV1 via capsaicin has been studied in various dermatological conditions and in other skin-related issues. Past studies documented that capsaicin plays a vital role in the prevention of atopic dermatitis as well as psoriasis. Moreover, TRPV1 is also very important for skin health because it acts as a capsaicin receptor. It is found in nociceptive nerve fibers and nonneural structures. It prompts the release of a compound that is involved in communicating pain between the spinal cord nerves and other parts of the body. Key Messages: Here, we summarize the growing evidence for the beneficial role of capsaicin and TRPV1 and how they help in the relief of skin diseases such as inflammation, permeation, dysfunction, atopic dermatitis, and psoriasis and in pain amplification syndrome.

Correlation Between Central Sensitization and Remote Muscle Performance in Individuals With Chronic Low Back Pain

OBJECTIVE

The purpose of this study was to examine associations between the degree of central sensitization (CS) and remote muscle performance in people with chronic low back pain (CLBP).

METHODS

The 2011 fibromyalgia (FM) criteria and severity scales (2011 FM survey) were used as a surrogate measure of CS to divide the participants into 2 groups: FM-positive CLBP and FM-negative CLBP. Measures related to central sensitization included the 2011 FM survey and pressure pain threshold of the thumbnail. Measures related to muscle performance included neck flexor muscle strength and endurance and plantar flexor muscle strength. Between-groups and correlation analyses were performed.

RESULTS

Sixty people with CLBP were enrolled (30 FM-positive, 30 FM-negative). There was no significant difference between the subgroups in age, sex, or pain duration (P > .05). The FM-positive CLBP group showed poorer neck flexor muscle endurance (P = .01) and plantar flexor muscle strength (P = .002) than the FM-negative CLBP group, whereas neck flexor muscle strength was not different between the groups (P = .175). Scores for FM and values for pressure pain thresholds of the thumbnail were associated with neck flexor muscle strength (respectively, r = -0.320, P = .013, and r = 0.467, P < .001), endurance (r = -0.242, P < .001, and r = 0.335, P = .009), and plantar flexor muscle strength (r = -0.469, P < .001, and r = 0.500, P < .001).

CONCLUSION

We found associations between the degree of CS and remote muscle strength and endurance, suggesting that poor remote muscle performance is possibly a clinical sign of CS in people with CLBP.

Identification of a Quorum Sensing-Dependent Communication Pathway Mediating Bacteria-Gut-Brain Cross Talk

Despite recently established contributions of the intestinal microbiome to human health and disease, our understanding of bacteria-host communication pathways with regard to the gut-brain axis remains limited. Here we provide evidence that intestinal neurons are able to "sense" bacteria independently of the host immune system. Using supernatants from cultures of the opportunistic pathogen Staphylococcus aureus (S. aureus) we demonstrate the release of mediators with neuromodulatory properties at high population density. These mediators induced a biphasic response in extrinsic sensory afferent nerves, increased membrane permeability in cultured sensory neurons, and altered intestinal motility and secretion. Genetic manipulation of S. aureus revealed two key quorum sensing-regulated classes of pore forming toxins that mediate excitation and inhibition of extrinsic sensory nerves, respectively. As such, bacterial mediators have the potential to directly modulate gut-brain communication to influence intestinal symptoms and reflex function in vivo, contributing to homeostatic, behavioral, and sensory consequences of infection.

A retrospective observational study comparing somatosensory amplification in fibromyalgia, chronic pain, psychiatric disorders and healthy subjects

OBJECTIVES

Somatosensory amplification (SA) has been described as an important feature of somatoform disorders, and an "amplifying somatic style" has been reported as a negative connotation of body perception. As widespread pain (WSP) in fibromyalgia (FM) is due to a central sensitization (CS) rather than organic alterations, there has been discussion as to whether FM is equivalent to or distinct from somatization disorder (SD). Assuming SD and FM are two distinct entities, an increase in somatic amplification should be expected only in subjects who have SD, regardless of the type of pain they experience. Purpose of the study was to explore the magnitude of SA in FM, and whether this depends on the association with SD.

METHODS

FM (n=159) other forms of chronic pain (OCP, n=582), psychiatric (Psy, n=53) and healthy (H, n=55) subjects were investigated using the Somatosensory Amplification Scale (SSAS), Illness Behavior Questionnaire, (IBQ), Italian Pain Questionnaire (IPQ), and Cold Pressor Test (CPT) in a retrospective observational study.

RESULTS

FM subjects displayed higher SSAS scores than the other groups. High SSAS score was associated with FM (OR=8.39; 95%CI: 5.43-12.46) but not OCP. Although FM has the highest prevalence of SD (x²=14.07; p=.007), high SSAS scores were associated with SD in OCP but not in FM.

CONCLUSIONS

Unlike in OCP, in FM high SSAS scores were independent of the presence of SD. From a biopsychosocial perspective, SSAS may be a factor associated with the onset of FM.

Measures of central sensitization and their measurement properties in musculoskeletal trauma: A systematic review

BACKGROUND AND OBJECTIVE

Chronic pain following musculoskeletal trauma is common, which may partially be attributed to the early presence of central sensitization (CS). Multiple measures are suggested to assess clinical features of CS, yet no systematic review has evaluated the measurement properties of these measures in a musculoskeletal trauma population.

DATABASES AND DATA TREATMENT

This systematic review, which followed a published and PROSPERO registered protocol (CRD42018091531), aimed to establish the scope of CS measures used within a musculoskeletal trauma population and evaluate their measurement properties. Searches were conducted in two stages by two independent reviewers. The Consensus-based Standards for the selection of Health Measurement Instruments (COSMIN) checklist was used to evaluate risk of bias and overall quality was assessed using the modified Grading of Recommendations Assessment, Development and Evaluation.

RESULTS

From 86 studies, 30 different CS outcome measures were identified. Nine studies evaluated measurement properties of nine outcome measures; eight evaluated reliability and one evaluated construct validity. Measures included seven quantitative sensory testing methods (pressure, cold and electrical pain thresholds; warm, cold and vibration detection thresholds; vibration perception thresholds), pain drawings and a pinwheel. Risk of bias was assessed as doubtful/inadequate for all but one study, overall quality of evidence was low/very low for all measures. Reliability of measures ranged from poor to excellent.

CONCLUSIONS

Many measures are used to evaluate CS but with limited established measurement properties in musculoskeletal trauma. High quality research to establish measurement properties of CS outcome measures is required.

Central mechanisms of pain in orofacial pain patients: Implications for management

BACKGROUND

Central sensitization (CS) is a form of neuroplasticity characterized by changes in the neural sensitivity, responsiveness, and/or output that are not contingent on peripheral input nor activity-dependent. CS is characterized by activation of unmyelinated C-fibers resulting in a cascade of events at molecular and cellular levels which eventuate into generation of synaptic currents at rest. CS, therefore, contributes to heightened generalized pain sensitivity, further complicates the process of reaching a diagnosis, and increases the possibility of treatment failure. BODY: Trigeminal nerve is the main sensory supplier of the anterior part of the head, including the intraoral structures. Primary afferent nociceptors of the trigeminal nerve and low threshold mechanoreceptors synapse with wide dynamic range (WDR) neurons in the pons. This multifaceted network of nerve interactions which is further complicated by the modulatory circuits that can suppress or heighten the activity of WDR neurons is one of the main contributors to CS. The importance of CS in orofacial pain disorders is emphasized in the context of chronic pain development. As for all chronic pain conditions, it is crucial to consider the biopsychosocial aspects of chronic orofacial pain in managing this diverse group of conditions. This review highlights current understanding of the biopsychosocial model and central mechanisms contributing to the pathogenesis of chronic orofacial pain.

Central Nervous System Targets: Inhibitory Interneurons in the Spinal Cord

Pain is a percept of critical importance to our daily survival. In most cases, it serves both an adaptive function by helping us respond appropriately in a potentially hostile environment and also a protective role by alerting us to tissue damage. Normally, it is evoked by the activation of peripheral nociceptive nerve endings and the subsequent relay of information to distinct cortical and sub-cortical regions, but under pathological conditions that result in chronic pain, it can become spontaneous. Given that one in three chronic pain patients do not respond to the treatments currently available, the need for more effective analgesics is evident. Two principal obstacles to the development of novel analgesic therapies are our limited understanding of how neuronal circuits that comprise these pain pathways transmit and modulate sensory information under normal circumstances and how these circuits change under pathological conditions leading to chronic pain states. In this review, we focus on the role of inhibitory interneurons in setting pain thresholds and, in particular, how disinhibition in the spinal dorsal horn can lead to aberrant sensory processing associated with chronic pain states.

Kynurenine and Tetrahydrobiopterin Pathways Crosstalk in Pain Hypersensitivity

Despite the identification of molecular mechanisms associated with pain persistence, no significant therapeutic improvements have been made. Advances in the understanding of the molecular mechanisms that induce pain hypersensitivity will allow the development of novel, effective, and safe therapies for chronic pain. Various pro-inflammatory cytokines are known to be increased during chronic pain, leading to sustained inflammation in the peripheral and central nervous systems. The pro-inflammatory environment activates additional metabolic routes, including the kynurenine (KYN) and tetrahydrobiopterin (BH4) pathways, which generate bioactive soluble metabolites with the potential to modulate neuropathic and inflammatory pain sensitivity. Inflammation-induced upregulation of indoleamine 2,3-dioxygenase 1 (IDO1) and guanosine triphosphate cyclohydrolase I (GTPCH), both rate-limiting enzymes of KYN and BH4 biosynthesis, respectively, have been identified in experimental chronic pain models as well in biological samples from patients affected by chronic pain. Inflammatory inducible KYN and BH4 pathways upregulation is characterized by increase in pronociceptive compounds, such as quinolinic acid (QUIN) and BH4, in addition to inflammatory mediators such as interferon gamma (IFN-γ) and tumor necrosis factor alpha (TNF-α). As expected, the pharmacologic and genetic experimental manipulation of both pathways confers analgesia. Many metabolic intermediates of these two pathways such as BH4, are known to sustain pain, while others, like xanthurenic acid (XA; a KYN pathway metabolite) have been recently shown to be an inhibitor of BH4 synthesis, opening a new avenue to treat chronic pain. This review will focus on the KYN/BH4 crosstalk in chronic pain and the potential modulation of these metabolic pathways that could induce analgesia without dependence or abuse liability.

Quantitative assessment of nonpelvic pressure pain sensitivity in urologic chronic pelvic pain syndrome: a MAPP Research Network study

Experimental pain sensitivity was assessed in individuals with urologic chronic pelvic pain syndrome (UCPPS) as part of the Multidisciplinary Approach to the Study of Chronic Pelvic Pain (MAPP) Research Network. A series of computer-controlled pressure stimuli were delivered to the thumbnail bed, an asymptomatic site distant from the area of UCPPS pain that is considered to be indicative of overall body pain threshold. Stimuli were rated according to a standardized magnitude estimation protocol. Pain sensitivity in participants with UCPPS was compared with healthy controls and a mixed pain group composed of individuals with other chronic overlapping pain conditions, including fibromyalgia, chronic fatigue, and irritable bowel syndromes. Data from 6 participating MAPP testing sites were pooled for analysis. Participants with UCPPS (n = 153) exhibited an intermediate pain sensitivity phenotype: they were less sensitive relative to the mixed pain group (n = 35) but significantly more sensitive than healthy controls (n = 100). Increased pain sensitivity in patients with UCPPS was associated with both higher levels of clinical pain severity and more painful body areas outside the pelvic region. Exploratory analyses in participants with UCPPS revealed that pain sensitivity increased during periods of urologic symptom flare and that less pressure pain sensitivity at baseline was associated with a greater likelihood of subsequent genitourinary pain improvement 1 year later. The finding that individuals with UCPPS demonstrate nonpelvic pain hypersensitivity that is related to clinical symptoms suggests that central nervous system mechanisms of pain amplification contribute to UCPPS.

Top down or bottom up? An observational investigation of improvement in fibromyalgia symptoms following hip and knee replacement

OBJECTIVES

Many patients with osteoarthritis have comorbid symptoms of FM, but it is unknown how these symptoms respond to surgical procedures that address nociceptive input in the periphery, such as total joint replacement. Here we explore differences in clinical characteristics between patients whose FM symptoms do and do not improve following total hip or knee replacement.

METHODS

Participants were 150 patients undergoing knee or hip replacement who had a minimum FM survey score of 4 or greater prior to surgery. The top tertile of patients experiencing the most improvement in FM symptoms at month 6 were categorized as 'Improve' (n = 48) while the bottom two tertiles were categorized as 'Worsen/Same' (n = 102). Baseline symptom characteristics were compared between groups, as well as improvement in overall pain severity, surgical pain severity and physical function at 6 months.

RESULTS

The Worsen/Same group had higher levels of fatigue, depression and surgical site pain at baseline (all P < 0.05). Additionally, they improved less on overall pain severity and physical functioning 6 months after surgery (both P < 0.05).

CONCLUSION

Most patients derive significant benefit in improvement of comorbid FM symptoms following total joint replacement, but a substantial proportion do not. Understanding the neurobiological basis for these different trajectories may help inform clinical judgment and improve patient care.

Comparison of patients with migraine and tension-type headache in terms of somatosensory amplification and health anxiety

INTRODUCTION

Although it is known that anxiety and depressive disorders frequently accompany migraine and TTH, the role of somatic amplification (SSA) and health anxiety in these diseases is not adequately known.

OBJECTIVE

The aim of this study is to compare SSA and health anxiety in patients with migraine or TTH, and healthy controls and to investigate the relationships between SSA, health anxiety, headache characteristics, anxiety and depressive symptoms.

METHODS

Fifty-four migraine, 50 TTH patients from the outpatient unit of the neurology department and 53 healthy volunteers were recruited for the study. The somatosensory amplification scale (SSAS), health anxiety inventory, Beck depression (BDI) and anxiety inventory (BAI) were administered to all participants.

RESULTS

The SSAS scores were significantly higher in migraineurs compared with the healthy controls. The health anxiety scores were significantly higher in both migraine and TTH groups. The BDI and BAI scores were also significantly higher in migraine and TTH groups compared with the controls. A significant positive correlation was found between headache frequency and BAI scores, the visual analogue scale scores and SSAS and BDI scores in migraineurs. The SSAS scores were also significantly correlated with the BDI and BAI scores in both of the headache groups. A similar correlation was determined with the health anxiety scores.

CONCLUSIONS

While patients with migraine and TTH evalute, taking into account the SSA and health anxiety may contribute to the prognosis and treatment of these diseases.

The Landscape of Chronic Pain: Broader Perspectives

Chronic pain is a global health concern. This special issue on matters related to chronic pain aims to draw on research and scholarly discourse from an eclectic mix of areas and perspectives. The purpose of this non-systematic topical review is to précis an assortment of contemporary topics related to chronic pain and its management to nurture debate about research, practice and health care policy. The review discusses the phenomenon of pain, the struggle that patients have trying to legitimize their pain to others, the utility of the acute-chronic dichotomy, and the burden of chronic pain on society. The review describes the introduction of chronic primary pain in the World Health Organization's International Classification of Disease, 11th Revision and discusses the importance of biopsychosocial approaches to manage pain, the consequences of overprescribing and shifts in service delivery in primary care settings. The second half of the review explores pain perception as a multisensory perceptual inference discussing how contexts, predictions and expectations contribute to the malleability of somatosensations including pain, and how this knowledge can inform the development of therapies and strategies to alleviate pain. Finally, the review explores chronic pain through an evolutionary lens by comparing modern urban lifestyles with genetic heritage that encodes physiology adapted to live in the Paleolithic era. I speculate that modern urban lifestyles may be painogenic in nature, worsening chronic pain in individuals and burdening society at the population level.

Deep Dyspareunia: Review of Pathophysiology and Proposed Future Research Priorities

INTRODUCTION

Dyspareunia has been traditionally divided into superficial (introital) dyspareunia and deep dyspareunia (pain with deep penetration). While deep dyspareunia can coexist with a variety of conditions, recent work in endometriosis has demonstrated that coexistence does not necessarily imply causation. Therefore, a reconsideration of the literature is required to clarify the pathophysiology of deep dyspareunia.

AIMS

To review the pathophysiology of deep dyspareunia, and to propose future research priorities.

METHODS

A narrative review after appraisal of published frameworks and literature search with the terms (dyspareunia AND endometriosis), (dyspareunia AND deep), (dyspareunia AND (pathophysiology OR etiology)).

MAIN OUTCOME VARIABLE

Deep dyspareunia (present/absent or along a pain severity scale).

RESULTS

The narrative review demonstrates potential etiologies for deep dyspareunia, including gynecologic-, urologic-, gastrointestinal-, nervous system-, psychological-, and musculoskeletal system-related disorders. These etiologies can be classified according to anatomic mechanism, such as contact with a tender pouch of Douglas, uterus-cervix, bladder, or pelvic floor, with deep penetration. Etiologies of deep dyspareunia can also be stratified into 4 categories, as previously proposed for endometriosis specifically, to personalize management: type I (primarily gynecologic), type II (nongynecologic comorbid conditions), type III (central sensitization and genito-pelvic pain/penetration disorder), and type IV (mixed). We also identified gaps in the literature, such as lack of a validated patient-reported questionnaire or an objective measurement tool for deep dyspareunia and clinical trials not powered for sexual outcomes.

CONCLUSION

We propose the following research priorities for deep dyspareunia: deep dyspareunia measurement tools, inclusion of the population avoiding intercourse due to deep dyspareunia, nongynecologic conditions in the generation of deep dyspareunia, exploration of sociocultural factors, clinical trials with adequate power for deep dyspareunia outcomes, partner variables, female sexual response, pathways between psychological factors and deep dyspareunia, and personalized approaches to deep dyspareunia. Orr N, Wahl K, Joannou A, et al. Deep Dyspareunia: Review of Pathophysiology and Proposed Future Research Priorities. Sex Med Rev 2020;8:3-17.

Preliminary evidence that hydroxyurea is associated with attenuated peripheral sensitization in adults with sickle cell disease

Introduction:

Hydroxyurea (HU) is a drug that targets the underlying pathophysiology of sickle cell disease (SCD); however, it continues to be an underutilized treatment for adults. Previous research suggests that HU treatment can result in fewer hospital contacts for acute vaso-occlusive pain crises (VOC). Hydroxyurea's impact on non-VOC pain, however, is not well established.

Objectives:

This study examined whether HU moderated patterns of static and dynamic pain processing and clinical pain in SCD individuals.

Methods:

Fifty-eight patients with SCD (N taking HU = 17) underwent quantitative sensory testing (QST) and completed twice daily symptom diaries for 12 weeks. Quantitative sensory testing established thermal threshold and tolerance, mechanical thresholds, and thermal and mechanical temporal summation of pain.

Results:

Groups did not differ in age, sex, or opioid use. After controlling for morphine use, QST results showed that participants taking HU had higher heat and mechanical pain thresholds (static QST measures) but not thermal and mechanical temporal summation (dynamic QST measures). Participants taking HU also reported lower VOC pain compared with SCD participants not taking HU; however, HU did not moderate non-VOC clinical pain ratings.

Conclusion:

Findings cautiously suggest that HU acts on pain hypersensitivity and VOC pain, rather than inhibiting pain facilitation and non-VOC pain. These differences may reflect HU's influence on peripheral rather than central sensitization. Future research is warranted to replicate these findings in a larger sample and determine whether early HU administration can prevent peripheral sensitization in SCD individuals.

Chronic pain syndromes: overlapping phenotypes with common mechanisms

The common chronic pain syndromes of fibromyalgia, regional pain syndrome, and complex regional pain syndrome have been made to appear separate because they have been historically described by different groups and with different criteria, but they are really phenotypically accented expressions of the same processes triggered by emotional distress and filtered or modified by genetics, psychology, and local physical factors.

Sensory sensitivity and symptom severity represent unique dimensions of chronic pain: a MAPP Research Network study

Chronic overlapping pain conditions (COPCs) are characterized by aberrant central nervous system processing of pain. This "centralized pain" phenotype has been described using a large and diverse set of symptom domains, including the spatial distribution of pain, pain intensity, fatigue, mood imbalances, cognitive dysfunction, altered somatic sensations, and hypersensitivity to external stimuli. Here, we used 3 cohorts, including patients with urologic chronic pelvic pain syndrome, a mixed pain cohort with other COPCs, and healthy individuals (total n = 1039) from the Multidisciplinary Approach to the Study of Chronic Pelvic Pain (MAPP) Research Network to explore the factor structure of symptoms of centralized pain. Using exploratory and confirmatory factor analysis, we identified 2 general factors in all 3 cohorts, one characterized by a broad increased sensitivity to internal somatic sensations,environmental stimuli, and diffuse pain, termed Generalized Sensory Sensitivity, and one characterized by constitutional symptoms-Sleep, Pain, Affect, Cognition, Energy (SPACE). Longitudinal analyses in the urologic chronic pelvic pain syndrome cohort found the same 2-factor structure at month 6 and 1 year, suggesting that the 2-factor structure is reproducible over time. In secondary analyses, we found that Generalized Sensory Sensitivity particularly is associated with the presence of comorbid COPCs, whereas SPACE shows modest associations with measures of disability and urinary symptoms. These factors may represent an important and distinct continuum of symptoms that are indicative of the centralized pain phenotype at high levels. Future research of COPCs should accommodate the measurement of each factor.

Applications of sensory and physiological measurement in oral-facial dental pain

Dentists regularly employ a variety of self‐report and sensory techniques to aid in the diagnosis and treatment of tooth‐related disease. Many of these techniques leverage principles borrowed from psychophysics, the quantitative measurement of the relationship between stimuli and evoked sensations, which falls under the larger umbrella of quantitative sensory testing (QST). However, most clinicians fail to meet the bar for what could be considered quantitative sensory testing, and instead focus on qualitative and dichotomous “yes/no” aspects of sensory experience. With our current subjective measurements for pain assessments, diagnosis and treatment of dental pain in young children and individuals (any age) with severe cognitive impairment rely extensively on third‐party observations. Consequently, the limitation of inadequate pain diagnosis can lead to poor pain management. In this review, it discusses mechanisms that underlie acute and chronic dental pain. It details the measurement of somatosensory responses and pulpal blood flow as objective measures of tooth health and pain. It proposes that bridging these varied methodologies will significantly improve diagnosis and treatment of orofacial pain and pathology. It concludes that improving the precision of sensory measurements could yield important improvements in diagnostic challenges in pulpal pathology for noncommunicative and cognitively impaired individuals.