Autonomic activation and pain in response to low-grade mental stress in fibromyalgia and shoulder/neck pain patients

Comparing autonomic nervous system function in patients with functional somatic syndromes, stress-related syndromes and healthy controls

BACKGROUND

The goal of this study was to examine autonomic nervous system function by measuring heart rate (HR), heart rate variability (HRV), skin conductance levels (SCL), and peripheral skin temperature (ST) in response to and during recovery from psychosocial stressors in patients with functional somatic syndromes (FSS; fibromyalgia and/or chronic fatigue syndrome), stress-related syndromes (SRS; overstrain or burn-out), and healthy controls (HC).

METHODS

Patients with FSS (n = 26), patients with SRS (n = 59), and HC (n = 30) went through a standardized psychosocial stress test consisting of a resting phase (120 s), the STROOP color word task (120 s), a mental arithmetic task (120 s) and a stress talk (120 s), each followed by a 120 s recovery period. HR, HRV, SCL, and ST were monitored continuously.

RESULTS

Average HR and SCL were higher, and HRV was lower, in both patient groups compared to HC during rest (0.50 < Cohen's d < 0.97). A larger SC response to psychosocial stress was found in FSS compared to HC (d = 0.71). However, HR increased less during psychosocial stress and showed a smaller reduction during recovery in both patient groups compared to HC (0.68 < d < 0.98). HRV was lower in both patient groups compared to HC during recovery (0.91 < d < 0.98). There were no differences in ST levels or responses between groups.

CONCLUSIONS

Our results indicate a dominance of the sympathetic nervous system in both patient groups compared to controls, suggesting that autonomic nervous system dysfunction is a transdiagnostic feature for stress-related and functional somatic syndromes.

Effects of Stress Exposure to Pain Perception in Pre-Clinical Studies: Focus on the Nociceptin/Orphanin FQ-NOP Receptor System

Exposure to physical and psychological stress modulates pain transmission in a dual manner. Stress-induced analgesia (SIA) refers to the reduction in pain sensitivity that can occur in response to acute stress. On the contrary, chronic stress exposure may lead to a phenomenon named stress-induced hyperalgesia (SIH). SIH is a clinically relevant phenomenon since it has been well documented that physical and psychological stress exacerbates pain in patients with several chronic pain syndromes, including migraine. The availability of animal models of SIA and SIH is of high importance for understanding the biological mechanisms leading to these phenomena and for the identification of pharmacological targets useful to alleviate the burden of stress-exacerbated chronic pain. Among these targets, the nociceptin/orphanin FQ (N/OFQ)-N/OFQ peptide (NOP) receptor system has been identified as a key modulator of both pain transmission and stress susceptibility. This review describes first the experimental approaches to induce SIA and SIH in rodents. The second part of the manuscript summarizes the scientific evidence that suggests the N/OFQ-NOP receptor system as a player in the stress-pain interaction and candidates NOP antagonists as useful drugs to mitigate the detrimental effects of stress exposure on pain perception.

Cluster Analysis of Subjective Shoulder Stiffness and Muscle Hardness: Associations with Central Sensitization-Related Symptoms

Background and Objectives: Understanding the relationships between subjective shoulder stiffness, muscle hardness, and various factors is crucial. Our cross-sectional study identified subgroups of shoulder stiffness based on symptoms and muscle hardness and investigated associated factors. Materials and Methods: measures included subjective stiffness, pain, muscle hardness, and factors like physical and psychological conditions, pressure pain threshold, postural alignment, heart rate variability, and electroencephalography in 40 healthy young individuals. Results: Three clusters were identified: Cluster 1 with high stiffness, pain, and muscle hardness; Cluster 2 with low stiffness and pain but high muscle hardness; and Cluster 3 with low levels of all factors. Cluster 1 had significantly higher central sensitization-related symptoms (CSS) scores than Cluster 2. Subjective stiffness is positively correlated with psychological factors. Conclusions: our results suggest that CSS impacts subjective symptom severity among individuals with similar shoulder muscle hardness.

Stress biomarkers in individuals with fibromyalgia syndrome: a systematic review with meta-analysis

ABSTRACT

Evidence suggests an involvement of hypothalamic-pituitary-adrenal (HPA) axis dysregulation in the development and maintenance of fibromyalgia syndrome (FMS). However, studies on the stress response via the HPA-axis in individuals with FMS show conflicting results. To better understand the relationship between FMS and HPA-axis dysregulation, we (1) systematically summarized the current level of evidence on HPA biomarkers in individuals with FMS compared with individuals without and (2) evaluated whether FMS is associated with a specific pattern of HPA dysregulation. The main outcome measures were cortisol, adrenocorticotropic hormone (ACTH), corticotropin-releasing hormone (CRH), epinephrine, and norepinephrine. A systematic search of MEDLINE, EMBASE, and PsychMed yielded 47 studies eligible for meta-analysis, including 1465 individuals with FMS and 1192 FMS-free controls. No main effect of FMS was found on altered levels of blood cortisol, ACTH, CRH, and epinephrine. Compared with controls, salivary and urinary cortisol levels were decreased in individuals with FMS, whereas blood levels of norepinephrine were increased. However, heterogeneity of data was high with significant evidence for publication bias. Overall, the data are compatible with association of FMS with adrenocortical hypofunction in the presence of increased sympathetic tone. However, the data are partially contradictory, so it must be assumed that the data are highly dependent on the respective study designs, patient samples, and analytical methods and do not necessarily demonstrate an abnormal HPA-axis function in FMS.

Corticosterone mediates FKBP51 signaling and inflammation response in the trigeminal ganglion in chronic stress-induced corneal hyperalgesia mice

Stress-induced hyperalgesia is a health-threatening condition that lacks effective therapeutic intervention, impairing the quality of life. Interestingly, a high prevalence of corneal pain symptoms was also found in patients experienced severe stressors. Excessive secretion corticosterone in rodents has been shown to contribute to the development of visceral and mechanical hyperalgesia under stressful conditions. The co-chaperone protein FK506-binding protein 5 (FKBP5) was reported to modulate steroid sensitivity and inhibition of FKBP51 possessed anxiolytic and anti-hyperalgesic in the stressed-mice model. However, whether corticosterone and FKBP5 play a role in chronic stress-induced corneal hyperalgesia remains unknown. The aim of this study was to evaluate the corneal sensitivity after exposure to chronic restraint stress (CRS) and investigate the potential role of corticosterone and FKBP5 mediated proinflammatory cytokines release in trigeminal ganglion (TG) in corneal hyperalgesia under chronic stressful situations. Firstly, mice displayed increased corneal sensitivity without changes in tear production and corneal injury after CRS for 4 hours/day for 14 days. Meanwhile, corticosterone deficiency via adrenalectomy could prevent CRS-induced corneal hyperalgesia, whereas chronic corticosterone feeding increased the corneal sensitivity accompanied by increasing proinflammatory cytokines levels of phospho-NF-κB (p-NF-κB), tumor necrosis factor (TNF)-α and interleukin (IL)-1β in the TG on d14. Notably, we found that FKBP51 was significantly upregulated in the TG in the stressed-mice. Intraperitoneal injection of FKBP51 inhibitor significantly alleviated CRS-induced corneal hyperalgesia, and reversed calcitonin gene related peptide (CGRP) increase and proinflammatory cytokines production in the TG. Moreover, FKBP51 inhibitor could also exert its anti-hyperalgesic effect on corneal pain through intra-TG injection. Our study proves that CRS can induce corneal hyperalgesia in mice and uncovers the role of corticosterone and FKBP51 in modulating corneal sensitivity, providing a novel treatment strategy for stress-induced corneal hyperalgesia. AVAILABILITY OF DATA AND MATERIALS: All data and additional file are available upon request from the corresponding author.

The Biology of Stress Intolerance in Patients with Chronic Pain—State of the Art and Future Directions

Stress has been consistently linked to negative impacts on physical and mental health. More specifically, patients with chronic pain experience stress intolerance, which is an exacerbation or occurrence of symptoms in response to any type of stress. The pathophysiological mechanisms underlying this phenomenon remain unsolved. In this state-of-the-art paper, we summarised the role of the autonomic nervous system (ANS) and hypothalamus-pituitary-adrenal (HPA) axis, the two major stress response systems in stress intolerance. We provided insights into such mechanisms based on evidence from clinical studies in both patients with chronic pain, showing dysregulated stress systems, and healthy controls supported by preclinical studies, highlighting the link between these systems and symptoms of stress intolerance. Furthermore, we explored the possible regulating role for (epi)genetic mechanisms influencing the ANS and HPA axis. The link between stress and chronic pain has become an important area of research as it has the potential to inform the development of interventions to improve the quality of life for individuals living with chronic pain. As stress has become a prevalent concern in modern society, understanding the connection between stress, HPA axis, ANS, and chronic health conditions such as chronic pain is crucial to improve public health and well-being.

Stress-induced hyperalgesia instead of analgesia in patients with chronic musculoskeletal pain

Many individuals with chronic musculoskeletal pain (CMP) show impairments in their pain-modulatory capacity. Although stress plays an important role in chronic pain, it is not known if stress-induced analgesia (SIA) is affected in patients with CMP. We investigated SIA in 22 patients with CMP and 18 pain-free participants. Pain thresholds, pain tolerance and suprathreshold pain ratings were examined before and after a cognitive stressor that typically induces pain reduction (SIA). Whereas the controls displayed a significant increase in pain threshold in response to the stressor, the patients with CMP showed no analgesia. In addition, increased pain intensity ratings after the stressor indicated hyperalgesia (SIH) in the patients with CMP compared to controls. An exploratory analysis showed no significant association of SIA or SIH with spatial pain extent. We did not observe significant changes in pain tolerance or pain unpleasantness ratings after the stressor in patients with CMP or controls. Our data suggest that altered stress-induced pain modulation is an important mechanism involved in CMP. Future studies need to clarify the psychobiological mechanisms of these stress-induced alterations in pain processing and determine the role of contributing factors such as early childhood trauma, catastrophizing, comorbidity with mental disorders and genetic predisposition.

Amplified Vasodilatation within the Referred Pain Zone of Trigger Points Is Characteristic of Gluteal Syndrome-A Type of Nociplastic Pain Mimicking Sciatica

Gluteal syndrome (GS) mimicking sciatica is a new disease that has been recently recognized and included in the International Classification of Diseases, 11th Revision. The present study examines nociplastic pain involvement in GS and sciatica patients using a new Skorupska protocol (SP) test that provokes amplified vasodilatation in the area of expected muscle-referred pain. A positive test is confirmed if there is (i) a development of autonomic referred pain (AURP) and (ii) an increase in the delta of average temperature (Δ₸°) > 0.3 °C at the end of the stimulation and during the observation SP phases. Chronic GS (n = 20) and sciatica (n = 30) patients were examined. The SP test confirmed muscle-referred pain for (i) all GS patients with 90.6% positive thermograms (Δ₸° 0.6 ± 0.8 °C; maximum AURP 8.9 ± 13.6% (both p < 0.05)) and (ii) those sciatica (n = 8) patients who reported pain sensation during the test with 20.6% positive thermograms (Δ₸° 0.7 ± 0.7 °C; maximum AURP 15.1 ± 17.8% (both p < 0.05)). The remaining sciatica (n = 22) patients did not report pain during the test and presented a Δ₸° decrease and the AURP size below 1%. Conclusion: Amplified vasodilatation suggesting nociplastic pain involvement was confirmed for all GS and sciatica patients who reported painful sensations in the zone typical for gluteus minimus referred pain during the test.

Blunted Pain Modulation Response to Induced Stress in Women with Fibromyalgia with and without Posttraumatic Stress Disorder Comorbidity: New Evidence of Hypo-Reactivity to Stress in Fibromyalgia?

There is evidence regarding the presence of alterations in both the stress response and the endogenous pain modulation systems of people with fibromyalgia (FM). However, research on pain modulation under induced stress on FM patients is scarce and contradictory. The present study analyzes stress-induced changes in pain and intolerance thresholds among FM patients, examining the possible existence of differences linked to PTSD comorbidity and gaining insights into the role of cardiovascular reactivity. Eighteen women diagnosed with FM and comorbid PTSD (FM + PTSD), 18 women diagnosed with FM and no PTSD (FM-PTSD), and 38 healthy women (HC) were exposed to the Social Stress Test task. Pressure pain thresholds and intolerance thresholds were measured before and during stress induction, and after a recovery period, while systolic blood pressure and heart rate were simultaneously recorded. Overall, while pain thresholds decreased during stress and recovery for HC, no significant changes were observed for women with FM. The intolerance threshold decreased for HC during stress, but was maintained at basal level during recovery. FM-PTSD women exhibited a delayed response, with a drop at recovery. For FM + PTSD, tolerance levels remained unchanged. In addition, cardiovascular reactivity did not seem to explain these results. This performance of the pain modulation system seems to follow the same pattern of hypoactive responsiveness under stressors that has previously been observed in FM patients on the autonomic and neuroendocrine axes. Such a hypoactive pattern may involve a non-adaptive response that may contribute to the development and maintenance of chronic pain.

Childhood Adversity and Pain Facilitation

OBJECTIVE

This study investigated whether childhood adversity would be associated with hypersensitivity on two measures of central pain facilitation: area of secondary allodynia and temporal summation of second pain (TSSP), and whether pain facilitation would be explained by adult posttraumatic stress disorder (PTSD) symptoms.

METHOD

Participants endorsing high (n = 31) and low (n = 31) childhood adversity underwent capsaicin-induced secondary allodynia and TSSP testing. The tests were conducted a week apart with test order counterbalanced.

RESULTS

Larger areas of secondary allodynia were observed in the high adversity group compared with the low adversity group (F(1,60) = 4.81, p = .032). This group difference was largely (62%) explained by greater PTSD symptoms in the high adversity group. Although no overall difference was found in TSSP slopes (p = .886), this was attributed to an order by group interaction (F(1,58) = 5.07, p = .028) and low power. Subsequent analyses revealed positive TSSP slopes in the high adversity group when TSSP testing was performed first, and this order effect was associated with blunted sympathetic responses to TSSP on the first visit. The two facilitation measures were unrelated (p = .631).

CONCLUSIONS

Larger areas of secondary allodynia were observed in the high adversity group, which was explained largely by PTSD symptoms. This suggests that adversity-related changes in pain facilitation may underlie the association between childhood adversity and generalized widespread pain. Although TSSP was affected by previous testing, adversity-related pain facilitation was observed when TSSP testing occurred first. Finally, adversity was not associated with a consistent pattern of hypersensitivity across the two measures of central pain facilitation.

Hypothalamic-pituitary-adrenal axis feedback sensitivity in different states of back pain

Pain normally signals a threat to bodily integrity and causes emotional distress. Acute pain serves a protective function, yet, when pain turns chronic, the protective function is lost. A chain of psychophysiological alterations including changes in the stress regulation system, apparent in dysfunctional activity and responsivity of the hypothalamic-pituitary-adrenal (HPA) axis, might be an important factor in this context. Moreover, maladaptive responses may be complicated by affective comorbid symptoms such as anxiety and depression, and alter nociceptive processing. However, the relationship among pain chronicity, stress regulation, and contributing components of comorbid symptomatology as well as somatosensory profiles has rarely been examined. In the present study, we obtained diurnal cortisol profiles at baseline and feedback regulation (following a dexamethasone suppression test (DST)) in subacute (SABP) and chronic (CBP) back pain patients and healthy control individuals (HC). We also assessed anxiety, depression and chronic stress levels and used quantitative sensory testing (QST) to detect sensory abnormalities. We found a hyper-suppression of cortisol following DST and thus enhanced negative stress feedback sensitivity in SABP compared to both CBP and HC. In SABP, DST-related cortisol levels were negatively associated with pain intensity, mediated by cold pain thresholds and anxiety. These data support a stress model of pain chronicity and suggest that stress responses might be indicators of individual vulnerability in the transition period of subacute pain.

Genetic Association and Expression Analyses of the Phosphatidylinositol-4-Phosphate 5-Kinase (PIP5K1C) Gene in Alcohol Use Disorder-Relevance for Pain Signaling and Alcohol Use

BACKGROUND

The gene encoding phosphatidylinositol-4-phosphate 5-kinase (PIP5K1C) has been recently implicated in pain regulation. Interestingly, a recent cross-tissue and cross-phenotypic epigenetic analysis identified the same gene in alcohol use disorder (AUD). Given the high comorbidity between AUD and chronic pain, we hypothesized that genetic variation in PIP5K1C might contribute to susceptibility to AUD.

METHODS

We conducted a case-control association study of genetic variants in PIP5K1C. Association analyses of 16 common PIP5K1C single nucleotide polymorphisms (SNPs) were conducted in cases and controls of African (427 cases and 137 controls) and European ancestry (488 cases and 324 controls) using standard methods. In addition, given the prominent role of the opioid system in pain signaling, we investigated the effects of acute alcohol exposure on PIP5K1C expression in humanized transgenic mice for the μ-opioid receptor that included the OPRM1 A118G polymorphism, a widely used mouse model to study analgesic response to opioids in pain. PIP5K1C expression was measured in the thalamus and basolateral amygdala (BLA) in mice after short-term administration (single 2 g/kg dose) of alcohol or saline using immunohistochemistry and analyzed by 2-way analysis of variance.

RESULTS

In the case-control association study using an NIAAA discovery sample, 8 SNPs in PIP5K1C were significantly associated with AUD in the African ancestry (AA) group (p < 0.05 after correction; rs4807493, rs10405681, rs2074957, rs10432303, rs8109485, rs1476592, rs10419980, and rs4432372). However, a replication analysis using an independent sample (N = 3,801) found no significant associations after correction for multiple testing. In the humanized transgenic mouse model with the OPRM1 polymorphism, PIP5K1C expression was significantly different between alcohol and saline-treated mice, regardless of genotype, in both the thalamus (p < 0.05) and BLA (p < 0.01).

CONCLUSIONS

Our discovery sample shows that genetic variants in PIP5K1C are associated with AUD in the AA group, and acute alcohol exposure leads to up-regulation of PIP5K1C, potentially explaining a mechanism underlying the increased risk for chronic pain conditions in individuals with AUD.

Systematic review of quantitative imaging biomarkers for neck and shoulder musculoskeletal disorders

Background

This study systematically summarizes quantitative imaging biomarker research in non-traumatic neck and shoulder musculoskeletal disorders (MSDs). There were two research questions: 1) Are there quantitative imaging biomarkers associated with the presence of neck and shoulder MSDs?, 2) Are there quantitative imaging biomarkers associated with the severity of neck and shoulder MSDs?

Methods

PubMed and SCOPUS were used for the literature search. One hundred and twenty-five studies met primary inclusion criteria. Data were extracted from 49 sufficient quality studies.

Results

Most of the 125 studies were cross-sectional and utilized convenience samples of patients as both cases and controls. Only half controlled for potential confounders via exclusion or in the analysis. Approximately one-third reported response rates. In sufficient quality articles, 82% demonstrated at least one statistically significant association between the MSD(s) and biomarker(s) studied. The literature synthesis suggested that neck muscle size may be decreased in neck pain, and trapezius myalgia and neck/shoulder pain may be associated with reduced vascularity in the trapezius and reduced trapezius oxygen saturation at rest and in response to upper extremity tasks. Reduced vascularity in the supraspinatus tendon may also be a feature in rotator cuff tears. Five of eight studies showed an association between a quantitative imaging marker and MSD severity.

Conclusions

Although research on quantitative imaging biomarkers is still in a nascent stage, some MSD biomarkers were identified. There are limitations in the articles examined, including possible selection bias and inattention to potentially confounding factors. Recommendations for future studies are provided.

Electronic supplementary material

The online version of this article (doi:10.1186/s12891-017-1694-y) contains supplementary material, which is available to authorized users.

Lesions of the central amygdala and ventromedial medulla reduce bladder hypersensitivity produced by acute but not chronic foot shock

Both acute and chronic stress has been shown to exacerbate symptoms of chronic visceral pain conditions such as interstitial cystitis. Studies using animal models support these findings in that both acute and chronic exposure to foot shock-induced stress (FS) augment nociceptive reflex responses to urinary bladder distension (UBD). Only a few studies have examined the neural substrates mediating these phenomena and it is not clear whether acute and chronic stress engage the same or different substrates to produce bladder hypersensitivity. The present studies examined the role of two important central nervous system structures - the amygdala (AMG) and the ventromedial medulla (VMM) - in mediating/modulating hypersensitivity evoked by acute versus chronic FS using responses to graded UBD in adult, female Sprague-Dawley rats. Bladder hypersensitivity produced by acute FS was significantly reduced by either bilateral central AMG or VMM lesions using measures generated by graded UBD, but these lesions had no significant effects using the same measures on bladder hyperalgesia produced by chronic FS. Our findings provide evidence that neural substrates underlying bladder hypersensitivity produced by chronic stress differ from those produced by acute stress. These findings suggest that while the AMG and VMM participate in pain processing during periods of limited exposure to stress, prolonged stress may recruit a new set of neural substrates not initially activated by acute exposure to stress.

Fibromyalgia onset has a high impact on work ability in Australians

BACKGROUND

Although the disabling effects of fibromyalgia (FM) are well recognised, there are no published data regarding the impact of FM on work ability in Australians. The impact of the development of FM symptoms on ability to work in Australians was explored in a pilot survey project.

METHOD

Members of the Fibromyalgia Support Network of Western Australia were invited to undertake an anonymous online survey. Information was gathered regarding demographics, symptom onset, the timing of diagnosis, employment status and changes in the ability to work.

RESULTS

Two hundred and eighty-seven responses were analysed. Of the respondents, 90.6% were female, with a mean age of 51.1 ± 10.6 years and had experienced symptoms between 2 and 20 years; 52.8% were diagnosed less than 5 years previously. Of the participants, 54.2% were working full time and 21.5% working part time at symptom onset; however, only 15.6% were currently working full time, with 44.8% not currently working at all. Because of FM, 24.3% stopped and 32.6% reduced paid work directly within 5 years of symptom development, with 15.3% ceasing and an additional 17.4% reducing work because of symptoms before diagnosis. Due to FM symptoms, 35.1% currently received financial support because they were unable to work. While 24.3% reported FM medication increased their ability to work, 20.8% reported it reduced their ability to work.

CONCLUSION

A community pilot survey of Australians with FM indicates a high impact on work ability. This occurs from symptom onset and often before diagnosis. Early diagnosis and intervention may provide a window of opportunity to prevent work disability in FM.

Sympathetic Dysfunction in Patients With Chronic Low Back Pain and Failed Back Surgery Syndrome

BACKGROUND

Chronic low back pain (CLBP) is defined as pain that persists longer than 12 weeks and is often attributed to degenerative or traumatic conditions of the spine. Failed back surgery syndrome is a condition in which chronic pain persists after spinal surgery. Electrodiagnostic studies can be used to confirm the diagnosis of lumbosacral radiculopathy, but other diagnostic methods are often needed to assess sympathetic nervous system dysfunction.

OBJECTIVES

The aim of this study was to investigate the affection of sympathetic skin response (SSR) in cases of chronic low back pain (LBP) and failed back surgery syndrome (FBSS) and to assess the association of SSR abnormalities with perceived functional disability and pain among these patients.

METHODOLOGY

Twenty patients with CLBP and 10 patients with failed FBSS who fulfilled the inclusion criteria were recruited to the present study. All cases had back, leg, or back and leg pain of at least 3-month duration or following spinal surgery. The control group consists of 10 healthy participants matched in age and sex. Electrophysiologic nerve conduction studies and SSR recording were applied on the symptomatic and normal side in study cases and on both sides in the control group. Pain intensity was analyzed by the visual analogue scale (VAS) and perceived functional disability was assessed with the Oswestry disability index (ODI).

CONCLUSIONS

It was concluded that the sympathetic nervous system is affected in CLBP and FBSS patients with abnormalities in SSR and that the dysfunction of sympathetic nervous system may contribute to the intensity and chronicity of pain in these groups of patients. Moreover, a strong association was found between SSR and functional disabilities in these patients.

Dysfunctional stress responses in chronic pain

Many dysfunctional and chronic pain conditions overlap. This review describes the different modes of chronic deregulation of the adaptive response to stress which may be a common factor for these conditions. Several types of dysfunction can be identified within the hypothalamo-pituitary-adrenal axis: basal hypercortisolism, hyper-reactivity, basal hypocortisolism and hypo-reactivity. Neuroactive steroid synthesis is another component of the adaptive response to stress. Dehydroepiandrosterone (DHEA) and its sulfated form DHEA-S, and progesterone and its derivatives are synthetized in cutaneous, nervous, and adipose cells. They are neuroactive factors that act locally. They may have a role in the localization of the symptoms and their levels can vary both in the central nervous system and in the periphery. Persistent changes in neuroactive steroid levels or precursors can induce localized neurodegeneration. The autonomic nervous system is another component of the stress response. Its dysfunction in chronic stress responses can be expressed by decreased basal parasympathethic activity, increased basal sympathetic activity or sympathetic hyporeactivity to a stressful stimulus. The immune and genetic systems also participate. The helper-T cells Th1 secrete pro-inflammatory cytokines such as IL-1-β, IL-2, IL-6, IL-8, IL-12, IFN-γ, and TNF-α, whereas Th2 secrete anti-inflammatory cytokines: IL-4, IL-10, IGF-10, IL-13. Chronic deregulation of the Th1/Th2 balance can occur in favor of anti- or pro-inflammatory direction, locally or systemically. Individual vulnerability to stress can be due to environmental factors but can also be genetically influenced. Genetic polymorphisms and epigenetics are the main keys to understanding the influence of genetics on the response of individuals to constraints.

Fibromyalgia: A Critical and Comprehensive Review

Fibromyalgia is a disorder that is part of a spectrum of syndromes that lack precise classification. It is often considered as part of the global overview of functional somatic syndromes that are otherwise medically unexplained or part of a somatization disorder. Patients with fibromyalgia share symptoms with other functional somatic problems, including issues of myalgias, arthralgias, fatigue and sleep disturbances. Indeed, there is often diagnostic and classification overlap for the case definitions of a variety of somatization disorders. Fibromyalgia, however, is a critically important syndrome for physicians and scientists to be aware of. Patients should be taken very seriously and provided optimal care. Although inflammatory, infectious, and autoimmune disorders have all been ascribed to be etiological events in the development of fibromyalgia, there is very little data to support such a thesis. Many of these disorders are associated with depression and anxiety and may even be part of what has been sometimes called affected spectrum disorders. There is no evidence that physical trauma, i.e., automobile accidents, is associated with the development or exacerbation of fibromyalgia. Treatment should be placed on education, patient support, physical therapy, nutrition, and exercise, including the use of drugs that are approved for the treatment of fibromyalgia. Treatment should not include opiates and patients should not become poly pharmacies in which the treatment itself can lead to significant morbidities. Patients with fibromyalgia are living and not dying of this disorder and positive outlooks and family support are key elements in the management of patients.

Fibromyalgia syndrome pathology and environmental influences on afflictions with medically unexplained symptoms

Fibromyalgia syndrome (FMS) is a clinical disorder predominant in females with unknown etiology and medically unexplained symptoms (MUS), similar to other afflictions, including irritable bowel syndrome (IBS), chronic fatigue syndrome (CFS), post-traumatic stress disorder (PTSD), Gulf War illness (GFI), and others. External environmental stimuli drive behavior and impact physiologic homeostasis (internal environment) via autonomic functioning. These environments directly impact the individual affective state (mind), which feeds back to regulate physiology (body). FMS has emerged as a complex disorder with pathologies identified among neurotransmitter and enzyme levels, immune/cytokine functionality, cortical volumes, cutaneous innervation, as well as an increased frequency among people with a history of traumatic and/or emotionally negative events, and specific personality trait profiles. Yet, quantitative physical evidence of pathology or disease etiology among FMS has been limited (as with other afflictions with MUS). Previously, our group published findings of increased peptidergic sensory innervation associated with the arterio-venous shunts (AVS) in the glabrous hand skin of FMS patients, which provides a plausible mechanism for the wide-spread FMS symptomology. This review focuses on FMS as a model affliction with MUS to discuss the implications of the recently discovered peripheral innervation alterations, explore the role of peripheral innervation to central sensitization syndromes (CSS), and examine possible estrogen-related mechanisms through which external and internal environmental factors may contribute to FMS etiology and possibly other afflictions with MUS.

Role of sympathetic nervous system in rat model of chronic visceral pain

BACKGROUND

Changes in central pain modulation have been implicated in generalized pain syndromes such as irritable bowel syndrome (IBS). We have previously demonstrated that reduced descending inhibition unveils a role of sympathoneuronal outflow in decreasing peripheral sensory thresholds, resulting in stress-induced hyperalgesia. We investigated whether sympathetic nervous system (SNS) exacerbation of pain sensation when central pain inhibition is reduced is relevant to chronic pain disorders using a rat colon irritation (CI) model of chronic visceral hypersensitivity with hallmarks of IBS.

METHODS

Rats were treated to a series of colorectal balloon distensions (CRD) as neonates resulting in visceral and somatic hypersensitivity and altered stool function that persists into adulthood. The visceral sensitivity was assessed by recording electromyographic (EMG) responses to CRD. Somatic sensitivity was assessed by paw withdrawal thresholds to radiant heat. The effects on the hypersensitivity of (i) inhibiting sympathoneuronal outflow with pharmacological and surgical interventions and (ii) enhancing the outflow with water avoidance stress (WAS) were tested.

KEY RESULTS

The alpha2-adrenergic agonist, clonidine, and the alpha1-adrenergic antagonist, prazosin, reduced the visceral hypersensitivity and WAS enhanced the pain. Chemical sympathectomy with guanethidine and surgical sympathectomy resulted in a loss of the chronic visceral hypersensitivity.

CONCLUSIONS & INFERENCES

The results support a role of the SNS in driving the chronic visceral and somatic hypersensitivity seen in CI rats. The findings further suggest that treatments that decrease sympathetic outflow or block activation of adrenergic receptors on sensory nerves could be beneficial in the treatment of generalized pain syndromes.

Physiological parameters as a tool in the diagnosis of fibromyalgia syndrome in females: A preliminary study

AIMS

Although fibromyalgia (FM) syndrome is associated with many symptoms, there is as yet no specific finding or laboratory test diagnostic of this syndrome. The physical examination and laboratory tests may be helpful in figuring out this syndrome.

MATERIALS AND METHODS

The heart rate, respiration rate, body temperature (TEMP), height, body weight, hemoglobin level, erythrocyte sedimentation rate, white blood cell count, platelet count (PLT), rheumatoid factor and C-reactive protein levels and electrocardiograms (ECG) of FM patients were compared with those of control individuals. In addition, the predictive value of these tests was evaluated via receiver operating characteristic (ROC) analysis.

KEY FINDINGS

The results showed that the TEMP and the PLT were higher in the FM group compared with the control group. Also, ST heights in ECGs which corresponds to a period of ventricle systolic depolarization, showed evidence of a difference between the FM and the control groups. There was no difference observed in terms of the other parameters. According to the ROC analysis, PLT, TEMP and ST height have predictive capacities in FM.

SIGNIFICANCE

Changes in hormonal factors, peripheral blood circulation, autonomous system activity disorders, inflammatory incidents, etc., may explain the increased TEMP in the FM patients. The high PLT level may signify a thromboproliferation or a possible compensation caused by a PLT functional disorder. ST depression in FM patients may interrelate with coronary pathology. Elucidating the pathophysiology underlying the increases in TEMP and PLT and the decreases in ST height may help to explain the etiology of FM.

Neurobiology of stress-induced hyperalgesia

The intensity and severity of perceived pain does not correlate consistently with the degree of peripheral or central nervous system tissue damage or with the intensity of primary afferent or spinal nociceptive neurone activity. In this respect, the modulation of pain by emotion and context is now widely recognized. In particular, stress, fear and anxiety exert potent, but complex, modulatory influences on pain. Stress can either suppress pain (stress-induced analgesia) or exacerbate it (stress-induced hyperalgesia; SIH) depending on the nature, duration and intensity of the stressor. Herein, we review the methods and models used to study the phenomenon of SIH in rodents and humans and then present a detailed discussion of our current understanding of neural substrates and neurobiological mechanisms. The review provides perspectives and challenges for the current and future treatment of pain and the co-morbidity of pain with stress-related psychiatric disorders including anxiety and depression.

Excessive peptidergic sensory innervation of cutaneous arteriole-venule shunts (AVS) in the palmar glabrous skin of fibromyalgia patients: implications for widespread deep tissue pain and fatigue

OBJECTIVE

To determine if peripheral neuropathology exists among the innervation of cutaneous arterioles and arteriole-venule shunts (AVS) in fibromyalgia (FM) patients.

SETTING

Cutaneous arterioles and AVS receive a convergence of vasoconstrictive sympathetic innervation, and vasodilatory small-fiber sensory innervation. Given our previous findings of peripheral pathologies in chronic pain conditions, we hypothesized that this vascular location may be a potential site of pathology and/or serotonergic and norepinephrine reuptake inhibitors (SNRI) drug action.

SUBJECTS

Twenty-four female FM patients and nine female healthy control subjects were enrolled for study, with 14 additional female control subjects included from previous studies. AVS were identified in hypothenar skin biopsies from 18/24 FM patient and 14/23 control subjects.

METHODS

Multimolecular immunocytochemistry to assess different types of cutaneous innervation in 3 mm skin biopsies from glabrous hypothenar and trapezius regions.

RESULTS

AVS had significantly increased innervation among FM patients. The excessive innervation consisted of a greater proportion of vasodilatory sensory fibers, compared with vasoconstrictive sympathetic fibers. In contrast, sensory and sympathetic innervation to arterioles remained normal. Importantly, the sensory fibers express α2C receptors, indicating that the sympathetic innervation exerts an inhibitory modulation of sensory activity.

CONCLUSIONS

The excessive sensory innervation to the glabrous skin AVS is a likely source of severe pain and tenderness in the hands of FM patients. Importantly, glabrous AVS regulate blood flow to the skin in humans for thermoregulation and to other tissues such as skeletal muscle during periods of increased metabolic demand. Therefore, blood flow dysregulation as a result of excessive innervation to AVS would likely contribute to the widespread deep pain and fatigue of FM. SNRI compounds may provide partial therapeutic benefit by enhancing the impact of sympathetically mediated inhibitory modulation of the excess sensory innervation.

Trapezius activity of fibromyalgia patients is enhanced in stressful situations, but is similar to healthy controls in a quiet naturalistic setting: a case-control study

Background

Muscle activity and pain development of fibromyalgia (FM) patients in response to mental stress show inconsistent results, when compared to healthy controls (HCs). A possible reason for the inconsistent results is the large variation in stress exposures in different studies. This study compares muscle responses of FM patients and HCs for different modes and levels of imposed stress, to elucidate features in stress exposures that distinguish stress responses of FM patients from HCs.

Methods

Upper trapezius (clavicular and acromial fibers), deltoid, and biceps surface electromyographic (sEMG) activity was recorded in FM patients (n=26) and HCs (n=25). Heart rate (HR) was recorded and used as indicator of autonomic activation. Tests included inspiratory breath holding (sympathetic activation procedure), mental stress tests (color-word test and backward counting; 28 min), instructed rest prior to stress test (30 min TV watching), and controlled arm movement. sEMG and HR was also recorded during an unrestrained evening stay at a patient hotel. The 5-min period with lowest trapezius muscle activity was determined. Pain (shoulder/neck, low back pain) and perceived tension were scored on VAS scales at the start and the end of the stress test and at bedtime.

Results

Trapezius sEMG responses of FM patients were significantly higher than HCs during sympathetic activation, mental stress, and instructed rest, but similar during arm movement and unrestrained evening activity. HR of FM patients and HCs was similar during mental stress and in the evening, including the 5-min period with lowest trapezius activity. Muscle activity of FM patients during the stress test (with shoulder/neck pain development) and the evening stay (no pain development) was similar.

Conclusions

FM patients show elevated muscle activity (in particular trapezius activity) in situations with imposed stress, including sympathetic activation, and putative anticipatory stress. Muscle activity and HR were similar to HCs in instructed arm movement and in a situation approaching low-stress daily living. Pain development of FM patients during the stress test may be due to activation of several stress-associated physiological systems, and not obviously caused by muscle activity in isolation.

Effect of experimental stress in 2 different pain conditions affecting the facial muscles

Chronic facial muscle pain is a common feature in both fibromyalgia (FM) and myofascial (MF) pain conditions. In this controlled study, a possible difference in the mode of deregulation of the physiological response to a stressing stimulus was explored by applying an acute mental stress to FM and MF patients and to controls. The effects of the stress test were observed on pain, sympathetic variables, and both tonic and reflex electromyographic activities of masseteric and temporal muscles. The statistical analyses were performed through a generalized linear model including mixed effects. Painful reaction to the stressor was stronger (P < .001) and longer (P = .011) in FM than in MF independently of a higher pain level at baseline. The stress-induced autonomic changes only seen in FM patients did not reach significance. The electromyographic responses to the stress test were strongest for controls and weakest for FM. The stress test had no effect on reflex activity (area under the curve [AUC]) or latency, although AUC was high in FM and latencies were low in both pain groups. It is suggested that FM is characterized by a lower ability to adapt to acute stress than MF.

PERSPECTIVE

This study showed that an acute psychosocial stress triggered several changes in 2 pain conditions including an increase in pain of larger amplitude in FM than in MF pain. Similar stress-induced changes should be explored as possible mechanisms for differentiation between dysfunctional pain conditions.

Alcohol dependence as a chronic pain disorder

Dysregulation of pain neurocircuitry and neurochemistry has been increasingly recognized as playing a critical role in a diverse spectrum of diseases including migraine, fibromyalgia, depression, and PTSD. Evidence presented here supports the hypothesis that alcohol dependence is among the pathologies arising from aberrant neurobiological substrates of pain. In this review, we explore the possible influence of alcohol analgesia and hyperalgesia in promoting alcohol misuse and dependence. We examine evidence that neuroanatomical sites involved in the negative emotional states of alcohol dependence also play an important role in pain transmission and may be functionally altered under chronic pain conditions. We also consider possible genetic links between pain transmission and alcohol dependence. We propose an allostatic load model in which episodes of alcohol intoxication and withdrawal, traumatic stressors, and injury are each capable of dysregulating an overlapping set of neural substrates to engender sensory and affective pain states that are integral to alcohol dependence and comorbid conditions such as anxiety, depression, and chronic pain.

Effect of muscle load tasks with maximal isometric contractions on oxygenation of the trapezius muscle and sympathetic nervous activity in females with chronic neck and shoulder pain

Background

Sympathetic nervous activity contributes to the maintenance of muscle oxygenation. However, patients with chronic pain may suffer from autonomic dysfunction. Furthermore, insufficient muscle oxygenation is observed among workers with chronic neck and shoulder pain. The aim of our study was to investigate how muscle load tasks affect sympathetic nervous activity and changes in oxygenation of the trapezius muscles in subjects with chronic neck and shoulder pain.

Methods

Thirty females were assigned to two groups: a pain group consisting of subjects with chronic neck and shoulder pain and a control group consisting of asymptomatic subjects. The participants performed three sets of isometric exercise in an upright position; they contracted their trapezius muscles with maximum effort and let the muscles relax (Relax). Autonomic nervous activity and oxygenation of the trapezius muscles were measured by heart rate variability (HRV) and Near-Infrared Spectroscopy.

Results

Oxyhemoglobin and total hemoglobin of the trapezius muscles in the pain group were lower during the Relax period compared with the control group. In addition, the low frequency / high frequency (LF/HF) ratio of HRV significantly increased during isometric exercise in the control group, whereas there were no significant changes in the pain group.

Conclusions

Subjects with neck and shoulder pain showed lower oxygenation and blood flow of the trapezius muscles responding to isometric exercise, compared with asymptomatic subjects. Subjects with neck and shoulder pain also showed no significant changes in the LF/HF ratio of HRV responding to isometric exercise, which would imply a reduction in sympathetic nervous activity.

The effect of a mental stressor on conditioned pain modulation in healthy subjects

Background and purpose

In animal studies, enhanced sensitivity to painful stimuli succeeding chronic stress has been reported, while acute stress is reported to induce analgesia. Human studies on the effect of mental stress on pain are more equivocal. A disturbed stress-response resulting in an increased sensitivity to painful stimuli has also been discussed as a potential mechanism for e.g., the fibromyalgia syndrome. Endogenous analgesia may be studied in humans by measuring the analgesic effect of heterotopic noxious conditioning stimulation. In neurophysiological animal studies this phenomenon was originally denoted “diffuse noxious inhibitory controls” (DNIC), but for human studies it has been suggested to use the term conditioned pain modulation (CPM).

The clinical relevance of aberrances in CPM is not clear. Inhibitory CPM is reported as being reduced in several medically unexplained syndromes with musculoskeletal pain aggravated by mental stress. However, whether the reported reduced CPM effects are causally related to clinical pain is unknown.

In the present study the effect of a mental stressor on CPM is studied.

Methods

With tourniquet-induced pain as the conditioning stimulus we estimated the CPM effect in twenty healthy subjects. Heat pain threshold (HPT), supra-threshold heat pain level (SHPL) and pressure pain threshold (PPT) were used as test stimuli. Measurements were performed at baseline, after a stressful task and after a non-stressful task presented in a blinded cross-over design. We used repeated-measures ANOVAs in the analysis with simple contrasts for post hoc analysis.

Results

With a ANOVA repeated measures model we found a significant task effect (F = 18.5, p ≤ 0.001), indicating that CPM was successfully induced. In our ANOVA model, we found a significant effect of stress in the contrast analysis (F = 5.2, p = 0.037), indicating that CPM was affected by the stressful task. The effects on PPT could not be analyzed due to a significant carry-over effect (for PPT only).

Conclusions

In the present blinded crossover study, we found a significant small to medium inhibitory effect of mental stress upon the CPM of thermal pain.

Implications

Our results suggest that previously reported reduced inhibitory CPM in several medically unexplained syndromes with musculoskeletal pain aggravated by mental stress possibly can be related to confounding or clinically relevant stress level differences. However, the result might be modality-specific. Further studies in patients are obviously needed, and the impact of mental stress on CPM should be investigated also with other stressors.

Comparison of the cortisol awakening response in women with shoulder and neck pain and women with fibromyalgia

Shoulder and neck pain (SNP) and fibromyalgia syndrome (FMS), two musculoskeletal conditions of unknown pathogenesis, share some common features in terms of altered neuroendocrine responses, pain and stress perception. However, the pain distribution in SNP is localized, whereas in FMS is more widespread. Because regional musculoskeletal pain may represent an intermediate stage along a continuum towards widespread musculoskeletal pain we compared the cortisol awakening response (CAR) in women with SNP with the CAR in FMS patients and healthy controls (HC) in a controlled hospital-hotel setting. The aim of the study was to investigate whether SNP is related to a deviant regulation of the hypothalamic-pituitary-adrenal (HPA) axis. Eighteen women with SNP, 29 female FMS patients, and 27 female HC participated in the study. Cortisol samples were collected upon awakening, 30 and 60 min later. Questionnaires measuring pain levels, sleeping problems, perceived stress, and psychological characteristics were administered to the participants. Compared with HC, women with SNP had a tendency towards higher cortisol levels, whereas FMS had lower cortisol levels. Adjustment for potential confounders did not influence the results. Women with SNP and FMS patients reported more health complaints, pain, and perceived stress than the HC, but women with SNP were less affected than the FMS patients. Women with SNP showed a tendency towards an elevated HPA axis activity compared with HC. The current findings may indicate that the hypercortisolism in regional musculoskeletal pain represent an intermediate stage towards the development of a hypocortisolism in widespread musculoskeletal pain.

Catecholamines and heart rate in female fibromyalgia patients

BACKGROUND

Fibromyalgia syndrome is a disease of unknown pathogenesis characterised by widespread chronic musculoskeletal pain. Fibromyalgia has been associated with dysregulation of the stress systems, but results are inconsistent.

PURPOSE

To investigate autonomic nervous system activity (urinary noradrenaline, adrenaline, dopamine, and heart rate) of fibromyalgia patients and healthy controls.

METHODS

Urinary catecholamines and heart rate were assessed for a 24-hour period in a controlled hospital setting (including relaxation, a test with prolonged mental stress, and sleep), and during daily activity in 29 female fibromyalgia patients and 29 age-matched female healthy controls.

RESULTS

With repeated measures ANOVAs, catecholamine levels were lower in patients than controls (P=.035 for noradrenaline; P=.005 for adrenaline; P=.001 for dopamine). One-way ANOVAs for the single periods showed that patients compared to controls had significantly lower adrenaline levels during the night (P=.010) and the second day (P=.010), significantly lower dopamine levels during the first day (P=.008), the night (P=.001), and the second day (P=.004). However, single time point noradrenaline levels were not significantly different between the groups. Overall, heart rate was significantly higher in patients than controls (P=.014). Specifically, significant differences emerged during relaxation (P=.016) and sleep (P=.011), but not during stress provocation or daily activities.

CONCLUSIONS

The results indicate an altered regulation of the autonomic nervous system in fibromyalgia patients, with attenuated activity of both the sympathetic (adrenal medulla component) and the parasympathetic branch.

Prior exposure to glucocorticoids potentiates lipopolysaccharide induced mechanical allodynia and spinal neuroinflammation

While stress and stress-induced glucocorticoids are classically considered immunosuppressive, they can also enhance proinflammatory responses to subsequent challenges. Corticosterone (CORT) primes rat immune cells, exacerbating pro-inflammatory responses to subsequent immune challenges. Stress can also sensitize pain. One possibility is that stress primes spinal immune cells, predominantly glia, which are key mediators in pain enhancement through their release of proinflammatory cytokines. Therefore, we aimed to identify whether prior CORT sensitizes spinal cord glia such that a potentiated pro-inflammatory response occurs to later intrathecal (IT) lipopolysaccharide (LPS), thereby enhancing pain. Rats received subcutaneous CORT/vehicle 24 h before IT LPS/vehicle. Hind paw pain thresholds were measured before CORT/vehicle, before and up to 48 h after IT LPS/vehicle. In separate rats treated as above, lumbar spinal cord tissue was collected and processed for proinflammatory mediators. CORT alone had no effect on pain responses, nor on any pro-inflammatory cytokines measured. LPS induced allodynia (decreased pain threshold) lasting <4 h and elevated spinal IL-1β and IL-6 protein. Prior CORT potentiated allodynia, lasting >24 h following LPS and potentiated spinal IL-1 and IL-6 protein. Coadministration of IL-1 receptor antagonist with LPS IT completely blocked the allodynia irrespective of whether the system was primed by CORT or not. At 24 h, TLR2, TLR4, MD2, and CD14 mRNAs were significantly elevated within the spinal cord in the CORT+LPS group compared to all other groups. Prior CORT before a direct spinal immune challenge is able to potentiate pain responses and pro-inflammatory cytokine production.

Comparative effects of acupressure at local and distal acupuncture points on pain conditions and autonomic function in females with chronic neck pain

Acupressure on local and distal acupuncture points might result in sedation and relaxation, thereby reducing chronic neck pain. The aim was to investigate the effect of acupressure at local (LP) and distal acupuncture points (DP) in females with chronic neck pain. Thirty-three females were assigned to three groups: the control group did not receive any stimuli, the LP group received acupressure at local acupuncture points, GB 21, SI 14 and SI 15, and the DP group received acupressure at distal acupuncture points, LI 4, LI 10 and LI 11. Verbal rating scale (VRS), Neck Disability Index (NDI), State-Trait Anxiety Inventory (STAI), muscle hardness (MH), salivary alpha-amylase (sAA) activity, heart rate (HR), heart rate variability (HRV) values and satisfaction due to acupressure were assessed. VRS, NDI, STAI and MH values decreased after acupressure in the LP and the DP group. HR decreased and the power of high frequency (HF) component of HRV increased after acupressure in only the LP group. Although acupressure on not only the LP but also the DP significantly improved pain conditions, acupressure on only the LP affected the autonomic nervous system while acupuncture points per se have different physical effects according to location.

The long-term costs of traumatic stress: intertwined physical and psychological consequences

The gradual emergence of symptoms following exposure to traumatic events has presented a major conceptual challenge to psychiatry. The mechanism that causes the progressive escalation of symptoms with the passage of time leading to delayed onset post-traumatic stress disorder (PTSD) involves the process of sensitization and kindling. The development of traumatic memories at the time of stress exposure represents a major vulnerability through repeated environmental triggering of the increasing dysregulation of an individual's neurobiology. An increasing body of evidence demonstrates how the increased allostatic load associated with PTSD is associated with a significant body of physical morbidity in the form of chronic musculoskeletal pain, hypertension, hyperlipidaemia, obesity and cardiovascular disease. This increasing body of literature suggests that the effects of traumatic stress need to be considered as a major environmental challenge that places individual's physical and psychological health equally at risk. This broader perspective has important implications for developing treatments that address the underlying dysregulation of cortical arousal and neurohormonal abnormalities following exposure to traumatic stress.

The effects of nabilone on sleep in fibromyalgia: results of a randomized controlled trial

BACKGROUND

Sleep disorders affect many patients with chronic pain conditions. Cannabis has been reported by several patient populations to help sleep. We evaluated the safety and efficacy of nabilone, a synthetic cannabinoid, on sleep disturbance in fibromyalgia (FM), a disease characterized by widespread chronic pain and insomnia.

METHODS

We conducted a randomized, double-blind, active-control, equivalency crossover trial to compare nabilone (0.5-1.0 mg before bedtime) to amitriptyline (10-20 mg before bedtime) in patients with FM with chronic insomnia. Subjects received each drug for 2 wk with a 2-wk washout period. The primary outcome was sleep quality, measured by the Insomnia Severity Index and the Leeds Sleep Evaluation Questionnaire. Secondary outcomes included pain, mood, quality of life, and adverse events (AEs).

RESULTS

Thirty-one subjects were enrolled and 29 completed the trial (26 women, mean age 49.5 yr). Although sleep was improved by both amitriptyline and nabilone, nabilone was superior to amitriptyline (Insomnia Severity Index difference = 3.2; 95% confidence interval = 1.2-5.3). Nabilone was marginally better on the restfulness (Leeds Sleep Evaluation Questionnaire difference = 0.5 [0.0-1.0]) but not on wakefulness (difference = 0.3 [-0.2 to 0.8]). No effects on pain, mood, or quality of life were observed. AEs were mostly mild to moderate and were more frequent with nabilone. The most common AEs for nabilone were dizziness, nausea, and dry mouth.

CONCLUSIONS

Nabilone is effective in improving sleep in patients with FM and is well tolerated. Low-dose nabilone given once daily at bedtime may be considered as an alternative to amitriptyline. Longer trials are needed to determine the duration of effect and to characterize long-term safety.

Physiological responses to low-force work and psychosocial stress in women with chronic trapezius myalgia

Background

Repetitive and stressful work tasks have been linked to the development of pain in the trapezius muscle, although the underlying mechanisms still remain unclear. In earlier studies, it has been hypothesized that chronic muscle pain conditions are associated with imbalance in the autonomic nervous system, predominantly expressed as an increased sympathetic activity. This study investigates whether women with chronic trapezius myalgia show higher muscle activity and increased sympathetic tone at baseline and during repetitive low-force work and psychosocial stress, compared with pain-free controls.

Methods

Eighteen women with chronic trapezius myalgia (MYA) and 30 healthy female controls (CON) were studied during baseline rest, 100 min of repetitive low-force work, 20 min of psychosocial stress (Trier Social Stress Test, TSST), and 80 min recovery. The subjects rated their pain intensity, stress and energy level every 20 min throughout the experiment. Muscle activity was measured by surface electromyography in the trapezius muscle (EMGtrap) and deltoid muscle (EMGdelt). Autonomic reactivity was measured through heart rate (HR), skin conductance (SCL), blood pressure (MAP) and respiration rate (Resp).

Results

At baseline, EMGtrap, stress ratings, and HR were higher in MYA than in CON. Energy ratings, EMGdelt, SCL, MAP and Resp were, however, similar in the two groups. Significant main group effects were found for pain intensity, stress ratings and EMGtrap. Deltoid muscle activity and autonomic responses were almost identical in MYA and CON during work, stress and recovery. In MYA only, pain intensity and stress ratings increased towards the end of the repetitive work.

Conclusion

We found increased muscle activity during uninstructed rest in the painful muscle of a group of women with trapezius myalgia. The present study could not confirm the hypothesis that chronic trapezius myalgia is associated with increased sympathetic activity. The suggestion of autonomic imbalance in patients with chronic local or regional musculoskeletal pain needs to be further investigated.

Pain as a stressor: effects of prior nociceptive stimulation on escape responding of rats to thermal stimulation

In our previous studies, psychological stress was shown to enhance operant escape responding of male and female rats. The stressors that produced hyperalgesia were physical restraint and social defeat. Nociceptive input also elicits stress reactions, generating the prediction that pain would facilitate pain under certain circumstances. For example, the usual method of evaluating stress in laboratory animals is to test for effects after termination of the stressor. Accordingly, operant escape performance of male and female rats was evaluated during two successive trials involving nociceptive thermal stimulation. The intent was to determine whether nociceptive sensitivity differed on first trials and during pain-induced stress on second trials. Compared to a first trial of 44.5 degrees C stimulation, escape responding increased during a second trial of 44.5 degrees C stimulation (preceded by an escape trial of 10 degrees C). Similarly, escape from cold (10 degrees C) was enhanced when preceded by escapable 44.5 degrees C stimulation. Thus, prior nociceptive stimulation enhanced escape from aversive thermal stimulation. Facilitation of pain by a preceding pain experience is consistent with stress-induced hyperalgesia and contrasts with other models of pain inhibition by concurrent nociceptive stimulation.

Pain induced by a single simulated office-work session: time course and association with muscle blood flux and muscle activity

The present study aimed to assess the development of pain during computer work with high precision demand and time pressure, and the association between pain and muscle blood fluxes and muscle activity. Twenty-eight healthy subjects (range 22-44 years) performed a 90-min standardized task of correcting a text on a word-processor. Monetary reward was given according to productivity in order to induce time pressure. Pain intensity, general tension, and eye strain were reported on visual analogue scales before, during and after the computer session. Intramuscular trapezius blood fluxes were recorded by laser-Doppler flowmetry (LDF) and analyzed as % of baseline level. Muscle activity was measured from the upper trapezius and forearm extensors by surface electromyography (EMG), analyzed as % of a maximal calibration contraction, %EMG(max). Pain, tension, and eye strain increased considerably during the computer session with different time course for pain and tension. The LDF of the active side of trapezius was elevated for 30 min followed by a falling trend. There was an initial short-lasting increase in the inactive trapezius. The upper trapezius EMG was low (<3 % of EMG(max)) but increased during the work, similar in both the active and passive side. There was a significant time and blood flux interaction effect on pain in the shoulders/neck, but no association with EMG. In conclusion, considerable neck/shoulder pain may develop in healthy pain-free subjects during 90 min of office-work and seems to be related to the regulation of trapezius muscle blood flow.

Prolonged gabapentin analgesia in an experimental mouse model of fibromyalgia

In a new mouse model for generalized pain syndrome, including fibromyalgia, which used intermittent cold stress (ICS), bilateral allodynia in the hindpaw was observed that lasted more than 12 days; thermal hyperalgesia lasted 15 days. During constant cold stress (CCS), mice showed only a transient allodynia. A female prevalence in ICS-induced allodynia was observed in gonadectomized but not in gonad intact mice. Systemic gabapentin showed complete anti-allodynic effects in the ICS model at the one-tenth dose for injury-induced neuropathic pain model, and central gabapentin showed long-lasting analgesia for 4 days in ICS, but not the injury model. These results suggest that the ICS model is useful for the study of generalized pain syndrome.