A novel paradigm to evaluate conditioned pain modulation in fibromyalgia

Association between myofascial trigger point therapy and conditioned pain modulation

INTRODUCTION

Myofascial trigger point therapy (MTrP) is a widely used therapeutic approach, although the underlying mechanisms remain unclear. Mechanisms discussed include peripheral involvement of muscles as well as central pain modulating processes such as the conditioned pain modulation (CPM). The aim of this study was to investigate whether the analgesic response of MTrP and the analgesic response of CPM correlate in asymptomatic participants in order to identify shared underlying mechanisms of MTrP and CPM.

METHOD

Both, CPM and MTrP protocols consisted of heat-based test stimuli (heat pain thresholds before and after the intervention) and pressure-based (conditioning) stimuli. Asymptomatic participants (n = 94) were randomly assigned to receive either mild, intense or no pressure stimuli (between-group design) to both the fingernail and the MTrP of the infraspinatus muscle (within-group design). Pressure stimuli at both locations (fingernail, MTrP) were applied with a pressure algometer for 120 s and continuously adjusted to maintain a constant pain intensity of mild or intense pain. All thermal stimuli were applied on the lower leg with a thermal stimulator.

RESULTS

A significant correlation was shown between the analgesic effect of CPM and MTrP therapy for mild (r = 0.53, p = 0.002) and intensive stimuli (r = 0.73, p < 0.001). 17.3% of the variance of the MTrP effect were explained by CPM after mild stimulation, and 47.1% after intense stimulation. Pain-related characteristics did not explain the variance within the analgesic response using a regression analysis.

CONCLUSIONS

Between the analgesic responses following MTrP and CPM paradigms, a moderate to strong correlation was observed, suggesting shared underlying mechanisms.

Inflammation and autoimmunity are interrelated in patients with sickle cell disease at a steady-state condition: implications for vaso-occlusive crisis, pain, and sensory sensitivity

This study aimed to comprehensively analyze inflammatory and autoimmune characteristics of patients with sickle cell disease (SCD) at a steady-state condition (StSt) compared to healthy controls (HCs) to explore the pathogenesis of StSt and its impact on patients' well-being. The study cohort consisted of 40 StSt participants and 23 HCs enrolled between July 2021 and April 2023. StSt participants showed elevated white blood cell (WBC) counts and altered hematological measurements when compared to HCs. A multiplex immunoassay was used to profile 80 inflammatory cytokines/chemokines/growth factors in plasma samples from these SCD participants and HCs. Significantly higher plasma levels of 35 analytes were observed in SCD participants, with HGF, IL-18, IP-10, and MCP-2 being among the most significantly affected analytes. Additionally, autoantibody profiles were also altered, with elevated levels of anti-SSA/Ro60, anti-Ribosomal P, anti-Myeloperoxidase (MPO), and anti-PM/Scl-100 observed in SCD participants. Flow cytometric analysis revealed higher rates of red blood cell (RBC)/reticulocyte-leukocyte aggregation in SCD participants, predominantly involving monocytes. Notably, correlation analysis identified associations between inflammatory mediator levels, autoantibodies, RBC/reticulocyte-leukocyte aggregation, clinical lab test results, and pain crisis/sensitivity, shedding light on the intricate interactions between these factors. The findings underscore the potential significance of specific biomarkers and therapeutic targets that may hold promise for future investigations and clinical interventions tailored to the unique challenges posed by SCD. In addition, the correlations between vaso-occlusive crisis (VOC)/pain/sensory sensitivity and inflammation/immune dysregulation offer valuable insights into the pathogenesis of SCD and may lead to more targeted and effective therapeutic strategies.

Clinical Trial Registration

ClinicalTrials.gov, Identifier: NCT05045820.

Differential clinical characteristics across traditional Chinese medicine (TCM) Syndromes in patients with sickle cell disease

Background

Pain is a common, debilitating, and poorly understood complication of sickle cell disease (SCD). The need for clinical pain management of SCD is largely unmet and relies on opioids as the main therapeutic option, which leads to a decreased quality of life (QoL). According to the literature, acupuncture has shown certain therapeutic effects for pain management in SCD. However, these clinical studies lack the guidance of Traditional Chinese Medicine (TCM) Syndrome Differentiation principles for treatment.

Aim

To characterize differences in clinical presentation amongst TCM diagnosed Syndromes in SCD patients.

Method

Fifty-two patients with SCD and 28 age- and sex-matched healthy controls (HCs) were enrolled in an ongoing trial of acupuncture. Each participant completed a series of questionnaires on pain, physical function, fatigue, sleep, anxiety, depression and QoL and underwent cold- and pressure-based quantitative sensory testing at baseline. Data on prescription opioid use over the 12 months prior to study enrollment was used to calculate mean daily morphine milligram equivalents (MME). Differences among the three TCM Syndromes were analyzed by one-way ANOVA followed by Tukey post hoc testing. Two-sample t-tests were used to compare SCD and HC groups.

Results

TCM diagnosis criteria classified SCD patients into one of three TCM Syndromes: (a) Equal; (b) Deficiency; and (c) Stagnation. The Stagnation group exhibited higher pain interference, physical dysfunction, nociplastic pain, fatigue, anxiety, depression, MME consumption and lower sleep quality and QoL compared to the Equal group. Few differences were observed between HCs and the Equal SCD group across outcomes. Deficiency and Stagnation groups were differentiated with observed- and patient-reported clinical manifestations.

Conclusion

These findings suggest that TCM diagnosed Syndromes in SCD can be differentially characterized using validated objective and patient-reported outcomes. Because characteristics of pain and co-morbidities in each SCD patient are unique, targeting specific TCM "Syndromes" may facilitate treatment effectiveness with a Syndrome-based personalized treatment plan that conforms to TCM principles. These findings lay the foundation for the development of tailored acupuncture interventions based on TCM Syndromes for managing pain in SCD. Larger samples are required to further refine and validate TCM diagnostic criteria for SCD.

Role of non-invasive objective markers for the rehabilitative diagnosis of central sensitization in patients with fibromyalgia: A systematic review

BACKGROUND

Central sensitization cannot be demonstrated directly in humans. Therefore, studies used different proxy markers (signs, symptoms and tools) to identify factors assumed to relate to central sensitization in humans, that is, Human Assumed Central Sensitization (HACS). The aims of this systematic review were to identify non-invasive objective markers of HACS and the instruments to assess these markers in patients with fibromyalgia (FM).

METHODS

A systematic review was conducted with the following inclusion criteria: (1) adults, (2) diagnosed with FM, and (3) markers and instruments for HACS had to be non-invasive. Data were subsequently extracted, and studies were assessed for risk of bias using the quality assessment tools developed by the National Institute of Health.

RESULTS

78 studies (n= 5234 participants) were included and the findings were categorized in markers identified to assess peripheral and central manifestations of HACS. The identified markers for peripheral manifestations of HACS, with at least moderate evidence, were pain after-sensation decline rates, mechanical pain thresholds, pressure pain threshold, sound 'pressure' pain threshold, cutaneous silent period, slowly repeated evoked pain sensitization and nociceptive flexion reflex threshold. The identified markers for central manifestations of HACS were efficacy of conditioned pain modulation with pressure pain conditioning and brain perfusion analysis. Instruments to assess these markers are: pin-prick stimulators, cuff-algometry, repetitive pressure stimulation using a pressure algometer, sound, electrodes and neuroimaging techniques.

CONCLUSIONS

This review provides an overview of non-invasive markers and instruments for the assessment of HACS in patients with FM. Implementing these findings into clinical settings may help to identify HACS in patients with FM.

Differential clinical characteristics across traditional Chinese medicine (TCM) syndromes in patients with sickle cell disease

Background

Pain is a common, debilitating, and poorly understood complication of sickle cell disease (SCD). The need for clinical pain management of SCD is largely unmet and relies on opioids as the main therapeutic option, which leads to a decreased quality of life (QoL). According to the literature, acupuncture has shown certain therapeutic effects for pain management in SCD. However, these clinical studies lack the guidance of Traditional Chinese Medicine (TCM) Syndrome Differentiation principles for treatment.

Aim

To characterize differences in clinical presentation amongst TCM-diagnosed syndromes in SCD patients.

Method

52 patients with SCD and 28 age- and sex-matched healthy controls (HCs) were enrolled in an ongoing trial of acupuncture. Each participant completed a series of questionnaires on pain, physical function, fatigue, sleep, anxiety, depression, and QoL and underwent cold- and pressure-based quantitative sensory testing at baseline. Data on prescription opioid use over the 12 months prior to study enrollment was used to calculate mean daily morphine milligram equivalents (MME). Differences among the three TCM syndromes were analyzed by one-way ANOVA followed by Tukey post hoc testing. Two-sample t-tests were used to compare SCD and HC groups.

Results

TCM diagnosis criteria classified SCD patients into one of three TCM syndromes: a) Equal; b) Deficiency; and c) Stagnation. The Stagnation group exhibited higher pain interference, physical dysfunction, nociplastic pain, fatigue, anxiety, depression, MME consumption, and lower sleep quality and QoL compared to the Equal group. Few differences were observed between HCs and the Equal SCD group across outcomes. Deficiency and Stagnation groups were differentiated with observed- and patient-reported clinical manifestations.

Conclusion

These findings suggest that TCM-diagnosed syndromes in SCD can be differentially characterized using validated objective and patient-reported outcomes. Because characteristics of pain and co-morbidities in each SCD patient are unique, targeting specific TCM "syndromes" may facilitate treatment effectiveness with a syndrome-based personalized treatment plan that conforms to TCM principles. These findings lay the foundation for the development of tailored acupuncture interventions based on TCM syndromes for managing pain in SCD. Larger samples are required to further refine and validate TCM diagnostic criteria for SCD.

Inflammation and autoimmunity are interrelated in patients with sickle cell disease at a steady-state condition: implications for vaso-occlusive crisis, pain, and sensory sensitivity

This study aimed to comprehensively analyze inflammatory and autoimmune characteristics of patients with sickle cell disease (SCD) at a steady-state condition (StSt) compared to healthy controls (HCs) to explore the pathogenesis of StSt and its impact on patients' well-being. The study cohort consisted of 40 StSt participants and 23 HCs enrolled between July 2021 and April 2023. StSt participants showed elevated white blood cell (WBC) counts and altered hematological measurements when compared to HCs. A multiplex immunoassay was used to profile 80 inflammatory cytokines/chemokines/growth factors in plasma samples from these SCD participants and HCs. Significantly higher plasma levels of 37 analytes were observed in SCD participants, with HGF, IL-18, IP-10, and MCP-2 being among the most significantly affected analytes. Additionally, autoantibody profiles were also altered, with elevated levels of anti-SSA/Ro60, anti-Ribosomal P, anti-Myeloperoxidase (MPO), and anti-PM/Scl-100 observed in SCD participants. Flow cytometric analysis revealed higher rates of red blood cell (RBC)/reticulocyte-leukocyte aggregation in SCD participants, predominantly involving monocytes. Notably, correlation analysis identified associations between inflammatory mediator levels, autoantibodies, RBC/reticulocyte-leukocyte aggregation, clinical lab test results, and pain crisis/sensitivity, shedding light on the intricate interactions between these factors. The findings underscore the potential significance of specific biomarkers and therapeutic targets that may hold promise for future investigations and clinical interventions tailored to the unique challenges posed by SCD. In addition, the correlations between vaso-occlusive crisis (VOC)/pain/sensory sensitivity and inflammation/immune dysregulation offer valuable insights into the pathogenesis of SCD and may lead to more targeted and effective therapeutic strategies.

Hyper-connectivity between the left motor cortex and prefrontal cortex is associated with the severity of dysfunction of the descending pain modulatory system in fibromyalgia

INTRODUCTION

The association between descending pain modulatory system (DPMS) dysfunction and fibromyalgia has been previously described, but more studies are required on its relationship with aberrant functional connectivity (FC) between the motor and prefrontal cortices.

OBJECTIVES

The objective of this cross-sectional observational study was to compare the intra- and interhemispheric FC between the bilateral motor and prefrontal cortices in women with fibromyalgia, comparing responders and nonresponders to the conditioned pain modulation (CPM) test.

METHODS

A cross-sectional sample of 37 women (23 responders and 14 nonresponders to the CPM test) with fibromyalgia diagnosed according to the American College of Rheumatology criteria underwent a standardized clinical assessment and an FC analysis using functional near-infrared spectroscopy. DPMS function was inferred through responses to the CPM test, which were induced by hand immersion in cold water (0-1°C). A multivariate analysis of covariance for main effects between responders and nonresponders was conducted using the diagnosis of multiple psychiatric disorders and the use of opioid and nonopioid analgesics as covariates. In addition, we analyzed the interaction between the CPM test response and the presence of multiple psychiatric diagnoses.

RESULTS

Nonresponders showed increased FC between the left motor cortex (lMC) and the left prefrontal cortex (lPFC) (t = -2.476, p = 0.01) and right prefrontal cortex (rPFC) (t = -2.363, p = 0.02), even when both were considered as covariates in the regression analysis (lMC-lPFC: β = -0.127, t = -2.425, p = 0.021; lMC-rPFC: β = -0.122, t = -2.222, p = 0.033). Regarding main effects, a significant difference was only observed for lMC-lPFC (p = 0.035). A significant interaction was observed between the psychiatric disorders and nonresponse to the CPM test in lMC-lPFC (β = -0.222, t = -2.275, p = 0.03) and lMC-rPFC (β = -0.211, t = -2.2, p = 0.035). Additionally, a significant interaction was observed between the CPM test and FC in these two region-of-interest combinations, despite the psychiatric diagnoses (lMC-lPFC: β = -0.516, t = -2.447, p = 0.02; lMC-rPFC: β = -0.582, t = -2.805, p = 0.008).

CONCLUSIONS

Higher FC between the lMC and the bilateral PFC may be a neural marker of DPMS dysfunction in women with fibromyalgia, although its interplay with psychiatric diagnoses also seems to influence this association.

Central pain modulatory mechanisms of attentional analgesia are preserved in fibromyalgia

ABSTRACT

Fibromyalgia is a prevalent pain condition that is associated with cognitive impairments including in attention, memory, and executive processing. It has been proposed that fibromyalgia may be caused by altered central pain processing characterised by a loss of endogenous pain modulation. We tested whether attentional analgesia, where cognitive engagement diminishes pain percept, was attenuated in patients with fibromyalgia (n = 20) compared with matched healthy controls (n = 20). An individually calibrated, attentional analgesia paradigm with a 2 × 2 factorial design was used with brain and brainstem-focussed functional magnetic resonance imaging. Patients with fibromyalgia had both lower heat pain thresholds and speeds in a visual attention task. When this was taken into account for both attentional task and thermal stimulation, both groups exhibited an equivalent degree of attentional analgesia. Functional magnetic resonance imaging analysis showed similar patterns of activation in the main effects of pain and attention in the brain and brainstem (with the sole exceptions of increased activation in the control group in the frontopolar cortex and the ipsilateral locus coeruleus). The attentional analgesic effect correlated with activity in the periaqueductal gray and rostral ventromedial medulla. These findings indicate that patients with fibromyalgia can engage the descending pain modulatory system if the attentional task and noxious stimulus intensity are appropriately titrated.

Development and Validation of a Predictive Model of Pain Modulation Profile to Guide Chronic Pain Treatment: A Study Protocol

Introduction: Quantitative sensory testing is frequently used in research to assess endogenous pain modulation mechanisms, such as Temporal Summation (TS) and Conditioned Pain Modulation (CPM), reflecting excitatory and inhibitory mechanisms, respectively. Numerous studies found that a dysregulation of these mechanisms is associated with chronic pain conditions. In turn, such a patient's “profile” (increased TS and/or weakened CPM) could be used to recommend different pharmacological treatments. However, the procedure to evaluate these mechanisms is time-consuming and requires expensive equipment that is not available in the clinical setting. In this study, we aim to identify psychological, physiological and socio-demographic markers that could serve as proxies to allow healthcare professionals to identify these pain phenotypes in clinic, and consequently optimize pharmacological treatments.

Method: We aim to recruit a healthy participant cohort (n = 360) and a chronic pain patient cohort (n = 108). Independent variables will include psychological questionnaires, pain measurements, physiological measures and sociodemographic characteristics. Dependent variables will include TS and CPM, which will be measured using quantitative sensory testing in a single session. We will evaluate one prediction model and two validation models (for healthy and chronic pain participants) using multiple regression analysis between TS/CPM and our independent variables. The significance thresholds will be set at p = 0.05, respectively.

Perspectives: This study will allow us to develop a predictive model to compute the pain modulation profile of individual patients based on their biopsychosocial characteristics. The development of the predictive model is the first step toward the overarching goal of providing clinicians with a set of quick and cheap tests, easily applicable in clinical practice to orient pharmacological treatments.

Quantitative Sensory Testing of Spinal Cord and Dorsal Root Ganglion Stimulation in Chronic Pain Patients

BACKGROUND/OBJECTIVES

The physiological mechanisms underlying the pain-modulatory effects of clinical neurostimulation therapies, such as spinal cord stimulation (SCS) and dorsal root ganglion stimulation (DRGS), are only partially understood. In this pilot prospective study, we used patient-reported outcomes (PROs) and quantitative sensory testing (QST) to investigate the physiological effects and possible mechanisms of action of SCS and DRGS therapies.

MATERIALS AND METHODS

We tested 16 chronic pain patients selected for SCS and DRGS therapy, before and after treatment. PROs included pain intensity, pain-related symptoms (e.g., pain interference, pain coping, sleep interference) and disability, and general health status. QST included assessments of vibration detection theshold (VDT), pressure pain threshold (PPT) and tolerance (PPToL), temporal summation (TS), and conditioned pain modulation (CPM), at the most painful site.

RESULTS

Following treatment, all participants reported significant improvements in PROs (e.g., reduced pain intensity [p < 0.001], pain-related functional impairment [or pain interference] and disability [p = 0.001 for both]; better pain coping [p = 0.03], sleep [p = 0.002]), and overall health [p = 0.005]). QST showed a significant treatment-induced increase in PPT (p = 0.002) and PPToL (p = 0.011), and a significant reduction in TS (p = 0.033) at the most painful site, but showed no effects on VDT and CPM. We detected possible associations between a few QST measures and a few PROs. Notably, higher TS was associated with increased pain interference scores at pre-treatment (r = 0.772, p = 0.009), and a reduction in TS was associated with the reduction in pain interference (r = 0.669, p = 0.034) and pain disability (r = 0.690, p = 0.027) scores with treatment.

CONCLUSIONS

Our preliminary findings suggest significant clinical and therapeutic benefits associated with SCS and DRGS therapies, and the possible ability of these therapies to modulate pain processing within the central nervous system. Replication of our pilot findings in future, larger studies is necessary to characterize the physiological mechanisms of SCS and DRGS therapies.

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.

A novel clinical applicable bed-side tool for assessing conditioning pain modulation: proof-of-concept

Background and aims

In recent years, focus on assessing descending pain modulation or conditioning pain modulation (CPM) has emerged in patients with chronic pain. This requires reliable and simple to use bed-side tools to be applied in the clinic. The aim of the present pilot study was to develop and provide proof-of-concept of a simple clinically applicable bed-side tool for assessing CPM.

Methods

A group of 26 healthy volunteers participated in the experiment. Pressure pain thresholds (PPT) were assessed as test stimuli from the lower leg before, during and 5 min after delivering the conditioning tonic painful pressure stimulation. The tonic stimulus was delivered for 2 min by a custom-made spring-loaded finger pressure device applying a fixed pressure (2.2 kg) to the index finger nail. The pain intensity provoked by the tonic stimulus was continuously recorded on a 0–10 cm Visual Analog Scale (VAS).

Results

The median tonic pain stimulus intensity was 6.7 cm (interquartile range: 4.6–8.4 cm) on the 10 cm VAS. The mean PPT increased significantly (P = 0.034) by 55 ± 126 kPa from 518 ± 173 kPa before to 573 ± 228 kPa during conditioning stimulation. When analyzing the individual CPM responses (increases in PPT), a distribution of positive and negative CPM responders was observed with 69% of the individuals classified as positive CPM responders (increased PPTs = anti-nociceptive) and the rest as negative CPM responders (no or decreased PPTs = Pro-nociceptive). This particular responder distribution explains the large variation in the averaged CPM responses observed in many CPM studies. The strongest positive CPM response was an increase of 418 kPa and the strongest negative CPM response was a decrease of 140 kPa.

Conclusions

The present newly developed conditioning pain stimulator provides a simple, applicable tool for routine CPM assessment in clinical practice. Further, reporting averaged CPM effects should be replaced by categorizing volunteers/patients into anti-nociceptive and pro-nociceptive CPM groups.

Implications

The finger pressure device provided moderate-to-high pain intensities and was useful for inducing conditioning stimuli. Therefore, the finger pressure device could be a useful bed-side method for measuring CPM in clinical settings with limited time available. Future bed-side studies involving patient populations are warranted to determine the usefulness of the method.

The Multidisciplinary Approach to The Study of Chronic Pelvic Pain (MAPP) Research Network*: Design and implementation of the Symptom Patterns Study (SPS)

AIMS

The Multidisciplinary Approach to the Study of Chronic Pelvic Pain (MAPP) Research Network initiated a second observational cohort study-the Symptom Patterns Study (SPS)-to further investigate the underlying pathophysiology of Urologic Chronic Pelvic Pain Syndrome (UCPPS) and to discover factors associated with longitudinal symptom changes and responses to treatments.

METHODS

This multisite cohort study of males and females with UCPPS features a run-in period of four weekly web-based symptom assessments before a baseline visit, followed by quarterly assessments up to 36 months. Controls were also recruited and assessed at baseline and 6 months. Extensive clinical data assessing urological symptoms, nonurological pain, chronic overlapping pain syndromes, and psychosocial factors were collected. Diverse biospecimens for biomarker and microbiome studies, quantitative sensory testing (QST) data under multiple stimuli, and structural and functional neuroimaging scans were obtained under a standardized protocol.

RESULTS

Recruitment was initiated (July 2015) and completed (February 2019) at six discovery sites. A total of 620 males and females with UCPPS and 73 Controls were enrolled, including 83 UCPPS participants who re-enrolled from the first MAPP Network cohort study (2009-2012). Baseline neuroimaging scans, QST measures, and biospecimens were obtained on 578 UCPPS participants. The longitudinal follow-up of the cohort is ongoing.

CONCLUSIONS

This comprehensive characterization of a large UCPPS cohort with extended follow-up greatly expands upon earlier MAPP Network studies and provides unprecedented opportunities to increase our understanding of UCPPS pathophysiology, factors associated with symptom change, clinically relevant patient phenotypes, and novel targets for future interventions.

Quantitative Sensory Testing in pain assesment and treatment. Brief review and algorithmic management proposal

Quantitative Sensory Testing (QST) is used to globally analyze the nociceptive system in order to obtain a more objective understanding of pain perception. In recent years, QST has become a common tool in many pain clinics and anesthesiology departments worldwide. In 2013, the Neuropathic Pain Special Interest Group of the IASP put forward the first recommendations for conducting QST in clinical practice and research. However, the wide variety of QST methodologies and standards in the literature make it difficult to generalize the used of this tool in clinical practice. In this study, we present the basic concepts of QST, the type of tests and devices used, how they are applied, and the role of QST in anesthesiology and pain management.

A Subgroup of Chronic Low Back Pain Patients With Central Sensitization

BACKGROUND

Our knowledge of central sensitization (CS) in chronic low back pain (CLBP) is limited. 2011 fibromyalgia criteria and severity scales (2011 FM survey) have been used to determine FM positive as a surrogate of CS. The major features of CS including widespread hyperalgesia and dysfunction of the descending inhibitory pathways can be identified by pressure pain threshold (PPT) and conditioned pain modulation (CPM) tests. The purpose of the study was to examine neurophysiological characteristics and psychosocial symptoms in a subgroup of FM-positive CLBP compared with FM-negative CLBP patients.

METHODS

A total of 46 participants with CLBP and 22 pain-free controls completed outcome measures of the 2011 FM survey, PPT and CPM tests, and psychosocial questionnaires. Differences between FM-positive and FM-negative CLBP participants on these measures and correlations were analyzed.

RESULTS

The 2011 FM survey identified 22 (48%) participants with CLBP as FM positive. FM-positive CLBP participants showed lower PPT values of the thumbnail (P=0.011) and lower back (P=0.003), lower CPM values of the thumbnail (P=0.002), and more severe pain catastrophizing, anxiety, and depression symptoms (P<0.05) than FM-negative CLBP participants. The 2011 FM scores were significantly correlated with the PPT and CPM values of the thumbnail and with psychosocial symptoms (P<0.001).

DISCUSSION

Our findings suggest a subgroup of CLBP patients exhibiting with signs and symptoms of CS. Associations between subjective and objective CS measures indicate that the 2011 FM survey can be utilized to identify the presence of CS in CLBP in clinical practice.

Association Between the 2011 Fibromyalgia Survey Criteria and Multisite Pain Sensitivity in Knee Osteoarthritis

OBJECTIVES

The present study evaluated the relationship between the 2011 American College of Rheumatology fibromyalgia (FM) survey criteria and quantitative sensory testing (QST).

MATERIALS AND METHODS

Patients with knee osteoarthritis scheduled to undergo knee arthroplasty completed the FM survey criteria and self-report measures assessing clinical symptoms. Patients also underwent a battery of QST procedures at the surgical knee and remote body sites, including pressure algometry, conditioned pain modulation, and temporal summation. All assessments were completed before surgery. FM survey criteria were used to calculate a continuous FM score indicating FM severity.

RESULTS

A total of 129 patients were analyzed. Of these, 52.7% were female, 93.8% were Caucasian, and 3.8% met the FM survey criteria for FM classification. Mean age for females (63.6 y) and males (64.7 y) was similar. Females and males differed significantly in nearly every outcome, including FM severity, clinical pain, anxiety, depression, and pressure pain sensitivity. In females, FM scores significantly correlated with pressure pain sensitivity, but not conditioned pain modulation or temporal summation, such that increased sensitivity was associated with greater FM severity at all body sites examined. In addition, as FM scores increased, the association between pain sensitivity at the surgical knee and pain sensitivity at remote body sites also increased. No relationship between FM score and QST was observed in males.

DISCUSSION

We demonstrated an association between diffuse hyperalgesia as measured by QST and FM severity in females with knee osteoarthritis. These results suggest that the FM survey criteria may represent a marker of pain centralization in females with potential utility in clinical decision making.

Resting Functional Connectivity of the Periaqueductal Gray Is Associated With Normal Inhibition and Pathological Facilitation in Conditioned Pain Modulation

Conditioned pain modulation (CPM), a psychophysical paradigm that is commonly used to infer the integrity of endogenous pain-altering systems by observation of the effect of one noxious stimulus on another, has previously identified deficient endogenous analgesia in fibromyalgia (FM) and other chronic pain conditions. The mechanisms underlying this deficiency, be they insufficient inhibition and/or active facilitation, are largely unknown. The present cross-sectional study used a combination of behavioral CPM testing, voxel-based morphometry, and resting state functional connectivity to identify neural correlates of CPM in healthy controls (HC; n = 14) and FM patients (n = 15), and to probe for differences that could explain the pain-facilitative CPM that was observed in our patient sample. Voxel-based morphometry identified a cluster encompassing the periaqueductal gray (PAG) that contained significantly less gray matter volume in FM patients. Higher resting connectivity between this cluster and cortical pain processing regions was associated with more efficient inhibitory CPM in both groups, whereas PAG connectivity with the dorsal pons was associated with greater CPM inhibition only in HC. Greater PAG connectivity to the caudal pons/rostral medulla, which was pain-inhibitory in HC, was associated with pain facilitation in FM patients.

PERSPECTIVE

These findings indicate that variation in the strength of the PAG resting functional connectivity can explain some of the normal variability in CPM. In addition, pain-facilitative CPM observed in FM patients likely involves attenuation of pain inhibitory as well as amplification of pain facilitative processes in the central nervous system.

Cortical mapping of painful electrical stimulation by quantitative electroencephalography: unraveling the time-frequency-channel domain

The goal of this study was to capture the electroencephalographic signature of experimentally induced pain and pain-modulating mechanisms after painful peripheral electrical stimulation to determine one or a selected group of electrodes at a specific time point with a specific frequency range. In the first experiment, ten healthy participants were exposed to stimulation of the right median nerve while registering brain activity using 32-channel electroencephalography. Electrical stimulations were organized in four blocks of 20 stimuli with four intensities – 100%, 120%, 140%, and 160% – of the electrical pain threshold. In the second experiment, 15 healthy participants received electrical stimulation on the dominant median nerve before and during the application of a second painful stimulus. Raw data were converted into the time–frequency domain by applying a continuous wavelet transform. Separated domain information was extracted by calculating Parafac models. The results demonstrated that it is possible to capture a reproducible cortical neural response after painful electrical stimulation, more specifically at 250 milliseconds poststimulus, at the midline electrodes Cz and FCz with predominant δ-oscillations. The signature of the top-down nociceptive inhibitory mechanisms is δ-activity at 235 ms poststimulus at the prefrontal electrodes. This study presents a methodology to overcome the a priori determination of the regions of interest to analyze the brain response after painful electrical stimulation.