[Etiology and pathophysiology of fibromyalgia syndrome and chronic widespread pain]

A mouse model of chronic primary pain that integrates clinically relevant genetic vulnerability, stress, and minor injury

Chronic primary pain conditions (CPPCs) affect over 100 million Americans, predominantly women. They remain ineffectively treated, in large part because of a lack of valid animal models with translational relevance. Here, we characterized a CPPC mouse model that integrated clinically relevant genetic (catechol-O-methyltransferase; COMT knockdown) and environmental (stress and injury) factors. Compared with wild-type mice, Comt+/- mice undergoing repeated swim stress and molar extraction surgery intervention exhibited pronounced multisite body pain and depressive-like behavior lasting >3 months. Comt+/- mice undergoing the intervention also exhibited enhanced activity of primary afferent nociceptors innervating hindpaw and low back sites and increased plasma concentrations of norepinephrine and pro-inflammatory cytokines interleukin-6 (IL-6) and IL-17A. The pain and depressive-like behavior were of greater magnitude and longer duration (≥12 months) in females versus males. Furthermore, increases in anxiety-like behavior and IL-6 were female-specific. The effect of COMT genotype × stress interactions on pain, IL-6, and IL-17A was validated in a cohort of 549 patients with CPPCs, demonstrating clinical relevance. Last, we assessed the predictive validity of the model for analgesic screening and found that it successfully predicted the lack of efficacy of minocycline and the CB2 agonist GW842166X, which were effective in spared nerve injury and complete Freund's adjuvant models, respectively, but failed in clinical trials. Yet, pain in the CPPC model was alleviated by the beta-3 adrenergic antagonist SR59230A. Thus, the CPPC mouse model reliably recapitulates clinically and biologically relevant features of CPPCs and may be implemented to test underlying mechanisms and find new therapeutics.

Pharmacological treatments of fibromyalgia in adults; overview of phase IV clinical trials

Background: Fibromyalgia is a chronic neurological condition characterized by widespread pain. The effectiveness of current pharmacological treatments is limited. However, several medications have been approved for phase IV trials in order to evaluate them.

Aim: To identify and provide details of drugs that have been tested in completed phase IV clinical trials for fibromyalgia management in adults, including the primary endpoints and treatment outcomes. This article was submitted to Neuropharmacology, a section of the journal Frontiers in Pharmacology.

Method: Publicly available and relevant phase IV trials registered at ClinicalTrials.gov were analyzed. The uses of the trialed drugs for fibromyalgia were reviewed.

Results: As of 8 August 2022, a total of 1,263 phase IV clinical trials were identified, of which 121 were related to fibromyalgia. From these, 10 clinical trials met the inclusion criteria for the current study. The drugs used in phase IV trials are milnacipran, duloxetine, pregabalin, a combination of tramadol and acetaminophen, and armodafinil. The effectiveness of the current pharmacological treatments is apparently limited.

Conclusion: Due to its complexity and association with other functional pain syndromes, treatment options for fibromyalgia only are limited and they are designed to alleviate the symptoms rather than to alter the pathological pathway of the condition itself. Pain management specialists have numerous pharmacologic options available for the management of fibromyalgia.

Functional pain disorders - more than nociplastic pain

BACKGROUND

Nociplastic pain has been recently introduced as a third mechanistic descriptor of pain arising primarily from alterations of neural processing, in contrast to pain due to tissue damage leading to nociceptor activation (nociceptive) or due to lesion or disease of the somatosensory nervous system (neuropathic). It is characterized by hyperalgesia and allodynia, inconsistency and reversibility, as well as dynamic cross-system interactions with biological and psychobehavioral factors. Along with this renewed understanding, functional pain disorders, also classified as chronic primary pain, are being reframed as biopsychosocial conditions that benefit from multimodal treatment.

OBJECTIVE

To summarize the current understanding of nociplastic pain and functional pain disorders, with a focus on conditions that are common in neurology practice.

METHODS

This was a narrative literature review.

RESULTS

Chronic back pain, fibromyalgia syndrome and complex regional pain syndrome are best understood within a biopsychosocial framework of pain perception that considers structural factors (predispositions and sequelae) and psychobehavioral mechanisms. Although pain is often the primary complaint, it should not be the only focus of treatment, as accompanying symptoms such as sleep or mood problems can significantly impact quality of life and offer useful leverage points for multimodal treatment. Analgesic pharmacotherapy is rarely helpful on its own, and should always be imbedded in a multidisciplinary setting.

Effects of Monopolar Dielectric Radiofrequency Signals on the Symptoms of Fibromyalgia: A Single-Blind Randomized Controlled Trial

Monopolar dielectric radiofrequency (MDR) is a non-invasive treatment for pain based on the local application of electromagnetic signals. The study’s goal was to analyze the effects of MDR on the symptoms of fibromyalgia. For this aim, a randomized controlled trial was conducted on 66 female participants (aged 47 ± 17.7) diagnosed with fibromyalgia. Participants were randomly allocated to either an experimental group (n = 23), which received eight 20-minute sessions of MDR; a sham group, which received the same number of sessions of a sham MDR therapy (n = 22); or a control group (n = 21), which received usual care. The outcome variables included pain measured by the visual analogue scale (VAS), score on the hospital anxiety and depression scale (HADS) and quality of life measured by the combined index of fibromyalgia severity (ICAF). A large effect size was observed for the local pain (R² = 0.46), total ICAF (R² = 0.42) and ICAF physical factor scores (R² = 0.38). Significant mean differences were found for the local pain (p = 0.025) and ICAF physical factor (p = 0.031) scores of the experimental group in comparison with the sham group. No statistically significant differences between groups were found in HADS. In conclusion, MDR is more effective than either sham treatment or usual care in the short-term improvement of pain and the physical wellbeing of participants with fibromyalgia.

Motivational Non-directive Resonance Breathing as a Treatment for Chronic Widespread Pain

Chronic widespread pain (CWP) is one of the most difficult pain conditions to treat due to an unknown etiology and a lack of innovative treatment design and effectiveness. Based upon preliminary findings within the fields of motivational psychology, integrative neuroscience, diaphragmatic breathing, and vagal nerve stimulation, we propose a new treatment intervention, motivational non-directive (ND) resonance breathing, as a means of reducing pain and suffering in patients with CWP. Motivational ND resonance breathing provides patients with a noninvasive means of potentially modulating five psychophysiological mechanisms imperative for endogenously treating pain and increasing overall quality of life.

Sustained stimulation of β2- and β3-adrenergic receptors leads to persistent functional pain and neuroinflammation

Functional pain syndromes, such as fibromyalgia and temporomandibular disorder, are associated with enhanced catecholamine tone and decreased levels of catechol-O-methyltransferase (COMT; an enzyme that metabolizes catecholamines). Consistent with clinical syndromes, our lab has shown that sustained 14-day delivery of the COMT inhibitor OR486 in rodents results in pain at multiple body sites and pain-related volitional behaviors. The onset of COMT-dependent functional pain is mediated by peripheral β2- and β3-adrenergic receptors (β2- and β3ARs) through the release of the pro-inflammatory cytokines tumor necrosis factor α (TNFα), interleukin-1β (IL-1β), and interleukin-6 (IL-6). Here, we first sought to investigate the role of β2- and β3ARs and downstream mediators in the maintenance of persistent functional pain. We then aimed to characterize the resulting persistent inflammation in neural tissues (neuroinflammation), characterized by activated glial cells and phosphorylation of the mitogen-activated protein kinases (MAPKs) p38 and extracellular signal-regulated kinase (ERK). Separate groups of rats were implanted with subcutaneous osmotic mini-pumps to deliver OR486 (15 mg/kg/day) or vehicle for 14 days. The β2AR antagonist ICI118551 and β3AR antagonist SR59230A were co-administrated subcutaneously with OR486 or vehicle either on day 0 or day 7. The TNFα inhibitor Etanercept, the p38 inhibitor SB203580, or the ERK inhibitor U0126 were delivered intrathecally following OR486 cessation on day 14. Behavioral responses, pro-inflammatory cytokine levels, glial cell activation, and MAPK phosphorylation were measured over the course of 35 days. Our results demonstrate that systemic delivery of OR486 leads to mechanical hypersensitivity that persists for at least 3 weeks after OR486 cessation. Corresponding increases in spinal TNFα, IL-1β, and IL-6 levels, microglia and astrocyte activation, and neuronal p38 and ERK phosphorylation were observed on days 14-35. Persistent functional pain was alleviated by systemic delivery of ICI118551 and SR59230A beginning on day 0, but not day 7, and by spinal delivery of Etanercept or SB203580 beginning on day 14. These results suggest that peripheral β2- and β3ARs drive persistent COMT-dependent functional pain via increased activation of immune cells and production of pro-inflammatory cytokines, which promote neuroinflammation and nociceptor activation. Thus, therapies that resolve neuroinflammation may prove useful in the management of functional pain syndromes.

Genetic and epigenetic epidemiology of chronic widespread pain

The etiology underlying chronic widespread pain (CWP) remains largely unknown. An integrative biopsychosocial model seems to yield the most promising explanations for the pathogenesis of the condition, with genetic factors also contributing to disease development and maintenance. Here, we conducted a search of studies investigating the genetic and epigenetic epidemiology of CWP through electronic databases including Web of Science, Medline, PubMed, EMBASE, and Google Scholar. Combinations of keywords including CWP, chronic pain, musculoskeletal pain, genetics, epigenetics, gene, twins, single-nucleotide polymorphism, genotype, and alleles were used. In the end, a total of 15 publications were considered relevant to be included in this review: eight were twin studies on CWP, six were molecular genetic studies on CWP, and one was an epigenetic study on CWP. The findings suggest genetic and unique environmental factors to contribute to CWP. Various candidates such as serotonin-related pathway genes were found to be associated with CWP and somatoform symptoms. However, studies show some limitations and need replication. The presented results for CWP could serve as a template for genetic studies on other chronic pain conditions. Ultimately, a more in-depth understanding of disease mechanisms will help with the development of more effective treatment, inform nosology, and reduce the stigma still lingering on this diagnosis.

Somatosensory function in patients with secondary adrenal insufficiency treated with two different doses of hydrocortisone-Results from a randomized controlled trial

Background

Low cortisol levels are associated with several functional pain syndromes. In patients with secondary adrenal insufficiency (SAI), the lack in endogenous cortisol production is substituted by the administration of oral hydrocortisone (HC). Our previous study showed that a lower dose of HC led to an increase in reported subjective pain symptoms. Whether different doses of HC substitution alter somatosensory functioning in SAI patients has not been established yet.

Methods

In this randomized double blind cross-over trial, forty-six patients with SAI participated. Patients randomly received either first a lower dose (0.2–0.3 mg HC/kg body weight/day) for 10 weeks followed by a higher dose (0.4–0.6 mg HC/kg body weight/day) for another 10 weeks, or vice versa. After each treatment period, blood samples were drawn and somatosensory functioning was assessed by determining the mechanical detection threshold (MDT), mechanical pain threshold (MPT), mechanical pain sensitivity (MPS) and the pain pressure threshold (PPT), according to the Quantitative Sensory Testing (QST) battery by the German Network on Neuropathic Pain.

Results

The administration of the higher dose of HC resulted in significantly higher levels of cortisol (mean [SD] 748 [245] nmol/L) than the lower dose (537 [250] nmol/L, P<0.001). No differences were found in MDT, MPT, MPS and PPT z-scores between the two doses of HC. Furthermore, the number of patients showing sensory abnormalities did not differ between the two different doses.

Conclusions

The results suggest that the dose of HC has no impact on somatosensory functioning in response to mechanical stimuli in patients with SAI, despite previously found altered subjective pain reports.

Alterations in opioid inhibition cause widespread nociception but do not affect anxiety-like behavior in oral cancer mice

Widespread pain and anxiety are commonly reported in cancer patients. We hypothesize that cancer is accompanied by attenuation of endogenous opioid-mediated inhibition, which subsequently causes widespread pain and anxiety. To test this hypothesis we used a mouse model of oral squamous cell carcinoma (SCC) in the tongue. We found that mice with tongue SCC exhibited widespread nociceptive behaviors in addition to behaviors associated with local nociception that we reported previously. Tongue SCC mice exhibited a pattern of reduced opioid receptor expression in the spinal cord; intrathecal administration of respective mu (MOR), delta (DOR), and kappa (KOR) opioid receptor agonists reduced widespread nociception in mice, except for the fail flick assay following administration of the MOR agonist. We infer from these findings that opioid receptors contribute to widespread nociception in oral cancer mice. Despite significant nociception, mice with tongue SCC did not differ from sham mice in anxiety-like behaviors as measured by the open field assay and elevated maze. No significant differences in c-Fos staining were found in anxiety-associated brain regions in cancer relative to control mice. No correlation was found between nociceptive and anxiety-like behaviors. Moreover, opioid receptor agonists did not yield a statistically significant effect on behaviors measured in the open field and elevated maze in cancer mice. Lastly, we used an acute cancer pain model (injection of cancer supernatant into the mouse tongue) to test whether adaptation to chronic pain is responsible for the absence of greater anxiety-like behavior in cancer mice. No changes in anxiety-like behavior were observed in mice with acute cancer pain.

Circulating Omentin-1 and Chronic Painful Temporomandibular Disorders

AIMS

To investigate the relationship between omentin-1 levels and painful temporomandibular disorders (TMD).

METHODS

In a case-control design, chronic painful TMD cases (n = 90) and TMD-free controls (n = 54) were selected from participants in the multisite OPPERA study (Orofacial Pain: Prospective Evaluation and Risk Assessment). Painful TMD case status was determined by examination using established Research Diagnostic Criteria for TMD (RDC/TMD). Levels of omentin-1 in stored blood plasma samples were measured by using an enzyme linked immunosorbent assay. Binary logistic regression was used to calculate the odds ratios (ORs) and 95% confidence limits (CLs) for the association between omentin-1 and painful TMD. Models were adjusted for study site, age, sex, and body mass index.

RESULTS

The unadjusted association between omentin-1 and chronic painful TMD was statistically nonsignificant (P = .072). Following adjustment for covariates, odds of TMD pain decreased 36% per standard deviation increase in circulating omentin-1 (adjusted OR = 0.64; 95% CL: 0.43, 0.96; P = .031).

CONCLUSION

Circulating levels of omentin-1 were significantly lower in painful TMD cases than controls, suggesting that TMD pain is mediated by inflammatory pathways.

Programmed symptoms: disparate effects united by purpose

Central sensitivity syndromes (CSS) share features of similar multiple symptoms, virtually unknown mechanisms and lack of effective treatments. The CSS nomenclature was chosen over alternatives because it focused on a putative physiological mechanism of central sensitization common to disorders such as fibromyalgia, irritable bowel syndrome, vulvodynia and temporomandibular disorder. Increasing evidence from multiple biological systems suggests a further development. In this new model central sensitization is part of a ensemble that includes also the symptoms of widespread pain, fatigue, unrefreshing sleep and dyscognition. The main feature is an intrinsic program that produces this ensemble to guide behavior to restore normal function in conditions that threaten survival. The well known “illness response” is a classic example that is triggered in response to the specific threat of viral infection. The major leap for this model in the context of CSS is that the symptom complex is not a reactive result of pathology, but a purposeful feeling state enlisted to combat pathology. Once triggered, this state is produced by potential mechanisms that likely include contributions of the peripheral and central immune systems, as well as stress response systems such as the autonomic system and the hypothalamic–pituitary–adrenal (HPA) axis. These act in concert to alter behavior in a beneficial direction. This concept explains similar symptoms for many triggering conditions, the poorly understood pathology, and the resistance to treatment.

Palmitoylethanolamide in Fibromyalgia: Results from Prospective and Retrospective Observational Studies

Introduction

Fibromyalgia syndrome (FM) is characterized by persistent pain which is often refractory to common analgesic therapies and is particularly disabling. The objective of this study was to evaluate the therapeutic efficacy of duloxetine (DLX) + pregabalin (PGB) in patients suffering from FM and the possible added benefit of the lipid signaling molecule, palmitoylethanolamide (PEA). PEA is well-documented to exert anti-inflammatory, analgesic, and pain-relieving effects at both the preclinical and clinical level.

Methods

A total of 80 patients were recruited in two steps. The first was a retrospective observational study comprising 45 patients. This patient group received DLX + PGB for 6 months. The second step was a prospective observational study with 35 patients. Patients in this cohort began treatment with DLX + PGB at the same dosage as for the retrospective study plus micronized PEA (PEA-m^®; Epitech Group, Italy) and ultramicronized PEA (PEA-um^®; Epitech Group, Italy) for 3 months. Positive tender points (TPs), pain evoked, and pain intensity were evaluated at baseline and after 3 and 6 months in both studies. Statistical analyses were employed for comparison of data within the two studies and between them.

Results

The retrospective observational study (DLX + PGB), after 3 months of treatment showed a decrease of positive TPs, pain evoked, and pain intensity. After 6 months of treatment, these parameters had further improvement. In the prospective observational study (DLX + PGB + PEA), PEA introduction after 3 months of therapeutic regimen with DLX + PGB provided a significant improvement in pain symptoms, with a further reduction in the number of TPs and significant reduction in pain, compared to combined DLX + PGB only (p < 0.0001 for TPs and Visual Analog Scale comparisons). None of the patients experienced adverse side effects.

Conclusion

Our study confirms the efficacy of DLX + PGB and demonstrates as well the added benefit and safety of PEA in the treatment of pain in patients affected by FM.

Electronic supplementary material

The online version of this article (doi:10.1007/s40122-015-0038-6) contains supplementary material, which is available to authorized users.

Fibromyalgia: epidemiology and risk factors, a population-based case-control study in Lebanon

AIM

To investigate the epidemiology of fibromyalgia (FM) and assess its risk factors.

METHODS

Using data from the 2009 Community Oriented Program for Control of Rheumatic Diseases (COPCORD) study conducted in Lebanon, a population-based case control study was performed. The sample included 34 FM patients, frequency matched with 136 controls free from any musculoskeletal complaints and randomly sampled from the population. The controls were frequency matched with cases by age and gender.

RESULTS

The 34 female FM cases were prevalent cases which existed for a long period of time and all those who consulted a doctor were previously misdiagnosed. Family history of joint problems (OR = 4.93, 95% CI: 1.56-15.58) and working status (OR = 2.69, 95% CI: 1.04-6.93) were significant risk factors for FM, after adjusting for body mass index, distress level, smoking status and residence location.

CONCLUSION

This was the first study to address the epidemiology of FM in Lebanon and the region. The chronic nature of FM that is characterized by frequent bouts of intense disabling pain and symptoms constitutes a significant health and economic burden. Clustering of cases in coastal areas was partially explained by other factors such as body mass index, distress level, smoking and work status. The high burden of FM found in our study calls for further investigation of potential risk factors of this condition.

Multisystem dysregulation in painful temporomandibular disorders

Multiple physiological and psychological regulatory domains may contribute to the pathophysiology of pain in temporomandibular disorder (TMD) and other bodily pain conditions. The purpose of this study was to evaluate the relationship between multisystem dysregulation and the presence of TMD pain, as well as the presence of different numbers of comorbid pain conditions in TMD. Secondary data analysis was conducted in 131 non-TMD (without comorbid pain) controls, 14 TMD subjects without comorbid pain, 78 TMD subjects with 1 comorbid pain, and 67 TMD subjects with multiple comorbid pain conditions who participated in a TMD genetic study. Twenty markers from sensory, autonomic, inflammatory, and psychological domains were evaluated. The results revealed that 1) overall dysregulation in multiple system domains (OR [odds ratio] = 1.6, 95% confidence interval [CI] = 1.4-1.8), particularly in the sensory (OR = 1.9, 95% CI = 1.3-2.9) and the psychological (OR = 2.1, 95% CI = 2.1-2.7) domains, were associated with increased likelihood of being a painful TMD case; and 2) dysregulations in individual system domains were selectively associated with the increased odds of being a TMD case with different levels of comorbid persistent pain conditions. These outcomes indicate that heterogeneous multisystem dysregulations may exist in painful TMD subgroups, and multidimensional physiological and psychological assessments can provide important information regarding pathophysiology, diagnosis, and management of pain in TMD patients.

PERSPECTIVE

The concurrent assessment of multiple physiological and psychological systems is critical to our understanding of the pathophysiological processes that contribute to painful TMD and associated comorbid conditions, which will ultimately guide and inform appropriate treatment strategies that address the multisystem dysregulation associated with complex and common persistent pain conditions.

Interaction of the dopaminergic and serotonergic systems significantly influences the risk for multisomatoform disorder: a controlled pilot study

The etiology of multisomatoform disorder (MSD) is largely unknown, but an influence of genetic factors is likely. Since pain is a major component of MSD and dopamine as well as serotonin are involved in pain pathways, genes of the dopaminergic and serotonergic system are promising candidate genes and we assumed that polymorphisms could be associated with MSD. One hundred forty-nine patients with MSD and 149 age- and gender-matched healthy controls participated in this study. DNA from all participants was genotyped for 22 single nucleotide polymorphisms (SNPs) within genes of the dopaminergic and serotonergic system by polymerase chain reaction, a restriction enzyme analysis, and pyrosequencing. The distribution of SNP alleles, genotypes, and haplotypes was compared between patients and controls. Neither an allelic nor a genotypic association was found for any individual SNP, but testing for a haplotypic association revealed that a haplotype of the serotonergic genes HT(1B) and HT(1D) indicated a lower risk. However, this statistically insignificant protective effect became highly significant on the background of two DAT1 haplotypes. Interestingly, if these two DAT1 haplotypes are analyzed without considering the serotonergic genes as confounders, they are significantly associated with an enhanced risk. Taking into account observations from recent publications, this apparent contradiction might be explained with the complex interaction of the dopaminergic and serotonergic systems. To conclude, our results reveal an involvement of polymorphisms in dopaminergic and serotonergic genes in the etiology of MSD in patients of German descent, but their exact role in MSD requires further investigation.

The role of antidepressants in the management of fibromyalgia syndrome: a systematic review and meta-analysis

BACKGROUND

The role of antidepressants in the management of fibromyalgia syndrome (FMS) still needs to be determined.

OBJECTIVE

The objective of this study was to provide a quantitative analysis (meta-analysis) of the efficacy and harms of antidepressants in the management of adult FMS patients.

DATA SOURCES

The data sources used were the databases MEDLINE, SCOPUS and the Cochrane Central Register of Controlled Trials (until December 30, 2010), the reference lists of included articles, and the websites of the US National Institutes of Health (NIH) and the Pharmaceutical Research and Manufacturers of America (PhRMA).

STUDY SELECTION

Studies with a randomized controlled trial (RCT) design comparing any types of antidepressants with pharmacological placebo or head-to-head comparisons of different types of antidepressants in FMS patients were included. RCTs in which antidepressants were combined with any other defined treatment or antidepressants were tested against anything but drug placebo were excluded. Patients diagnosed with FMS according to predefined criteria of any age were included. To be included, studies had to assess at least one key domain of FMS (pain, sleep, fatigue, health-related quality of life [HRQOL]) as outcomes of efficacy and report total treatment discontinuation rates and/or dropout rates due to adverse events as outcomes for harms.

DATA EXTRACTION

Data were extracted according to protocols of previous systematic reviews on antidepressants in FMS. Methodology quality was assessed by the van Tulder score.

DATA SYNTHESIS

Standardized mean differences (SMD) were calculated for continuous outcomes by means and standard deviations and relative risks (RR) for 30% pain reduction and total dropout rate for comparisons of antidepressants with placebo. Examination of the combined results was performed by a random effects model. We used Cohen's categories to evaluate the magnitude of the effect size, calculated by SMD. Heterogeneity was tested by the I2 statistic. Thirty-five studies were included in the meta-analysis. The SMDs of serotonin noradrenaline (norepinephrine) reuptake inhibitors (SNRIs) on pain, sleep, fatigue, depression and HRQOL were significant. Based on Cohen's categories, the effect size on pain was small and the ones on sleep, fatigue, depression and HRQOL were not substantial. 1481/3528 (42.0%) patients with SNRIs and 737/2304 (32.0%) patients with placebo reported a 30% pain reduction (number needed to treat [NNT] 10.0; 95% CI 8.00, 13.4; I2 = 4%). The RR of dropouts due to adverse events was 1.83 (95% CI 1.53, 2.18; I2 = 33%). The SMDs of selective serotonin reuptake inhibitors (SSRIs) on pain, sleep, depression and HRQOL were significant. Based on Cohen's categories, the effect sizes on pain, depression and HRQOL were small and the one on sleep not substantial. 72/198 (36.4%) patients with SSRIs and 40/194 (20.6%) patients with placebo reported a 30% pain reduction (NNT 6.3; 95% CI 4.1, 14.1). The RR of dropouts due to adverse events was 1.60 (95% CI 0.84, 3.04; I2 = 0%). The SMDs of tricyclic antidepressants (TCAs) on pain, sleep, fatigue and HRQOL were significant. Based on Cohen's categories, the effect sizes on pain and sleep were moderate and the ones on fatigue and HRQOL were small. 140/290 (48.3%) patients with TCAs and 70/252 (27.8%) patients with placebo reported a 30% pain reduction (NNT 4.9; 95% CI 3.5, 8.0). The RR of dropouts due to adverse events was 0.84 (95% CI 0.46, 1.52; I2 = 0%).

CONCLUSIONS

The TCA amitriptyline and the SNRIs duloxetine and milnacipran are first-line options for the treatment of FMS patients. Physicians and patients should be realistic about the potential benefits of antidepressants in FMS. A small number of patients experience a substantial symptom relief with no or minor adverse effects. However, a remarkable number of patients dropout of therapy because of intolerable adverse effects or experience only a small relief of symptoms, which does not outweigh the adverse effects.

Cytokine biomarkers and chronic pain: association of genes, transcription, and circulating proteins with temporomandibular disorders and widespread palpation tenderness

For reasons unknown, temporomandibular disorder (TMD) can manifest as localized pain or in conjunction with widespread pain. We evaluated relationships between cytokines and TMD without or with widespread palpation tenderness (TMD-WPT or TMD+WPT, respectively) at protein, transcription factory activity, and gene levels. Additionally, we evaluated the relationship between cytokines and intermediate phenotypes characteristic of TMD and WPT. In a case-control study of 344 females, blood samples were analyzed for levels of 22 cytokines and activity of 48 transcription factors. Intermediate phenotypes were measured by quantitative sensory testing and questionnaires asking about pain, health, and psychological status. Single nucleotide polymorphisms (SNPs) coding cytokines and transcription factors were genotyped. TMD-WPT cases had elevated protein levels of proinflammatory cytokine monocyte chemotactic protein (MCP-1) and antiinflammatory cytokine interleukin (IL)-1ra, whereas TMD+WPT cases had elevated levels of proinflammatory cytokine IL-8. MCP-1, IL-1ra, and IL-8 were differentially associated with experimental pain, self-rated pain, self-rated health, and psychological phenotypes. TMD-WPT and TMD+WPT cases had inhibited transcription activity of the antiinflammatory cytokine transforming growth factor β1 (TGFβ1). Interactions were observed between TGFβ1 and IL-8 SNPs: an additional copy of the TGFβ1 rs2241719 minor T allele was associated with twice the odds of TMD+WPT among individuals homozygous for the IL-8 rs4073 major A allele, and half the odds of TMD+WPT among individuals heterozygous for rs4073. These results demonstrate how pro- and antiinflammatory cytokines contribute to the pathophysiology of TMD and WPT in genetically susceptible people. Furthermore, they identify MCP-1, IL-1ra, IL-8, and TGFβ1 as potential diagnostic markers and therapeutic targets for pain in patients with TMD.

[CNS processing of pain in functional somatic syndromes]

Functional pain syndromes usually are characterized by a local or generalized increase in pain sensitivity, spontaneous ongoing pain, and a variety of other common symptoms. Classification or definition of a syndrome is usually somewhat arbitrarily based on the predominantly affected body region or a main symptom, resulting in significant overlap between conditions. Support for the involvement of the central nervous system (CNS) comes from the frequent comorbidity of affective disorders and symptomatology, disturbances in cognitive function, changes in neuroendocrine function, and dysregulation of the autonomic nervous system, although only subgroups of patients are affected. Findings of neuroimaging studies in functional pain syndromes typically reveal plausible correlates for the patients' subjective complaints and indicate a central augmentation in pain processing but also in other sensory systems including a postulated interoceptive system. The pathophysiology of this augmentation is not clear, and the importance of peripheral input remains unresolved, as well as the contribution of spinal and supraspinal mechanisms. Affective and cognitive factors clearly influence pain processing in these syndromes, but do not fully explain the observed augmentation. For FMS, chronic low back pain, and irritable bowel syndrome a dysfunction of the descending inhibitory systems is supported by these findings. However, longitudinal studies are needed to confirm the causality of the reported associations and to establish a primary role of the CNS in these syndromes. Current techniques like VBM and H-MRS have revealed potential yet highly variable structural abnormalities of the CNS in several of the syndromes, but clinical relevance and conclusions from these studies remain far from clear. New theoretical concepts should drive prospective and interdisciplinary research based on well-defined hypotheses to use the full potential of the current neuroimaging techniques.

Increased basal mechanical pain sensitivity but decreased perceptual wind-up in a human model of relative hypocortisolism

Clinical data have accumulated showing that relative hypocortisolism, which may be regarded as a neuroendocrinological correlate of chronic stress, may be a characteristic of some functional pain syndromes. However, it has not been clarified yet whether deregulations of the hypothalamus-pituitary-adrenal (HPA) axis may directly alter pain perception and thus be causally involved in the pathophysiology of these disorders. To test this hypothesis, we performed a randomized placebo-controlled crossover trial in N=20 healthy drug-free volunteers (median age 24yrs) and analyzed the effects of metyrapone-induced hypocortisolism on quantitatively assessed basal mechanical pain sensitivity (1.5-13m/s impact stimuli), perceptual wind-up (9m/s impact stimuli at 1Hz) and temporal summation of pain elicited by inter-digital web pinching (IWP; 10N pressure stimuli for 2min). Experimentally induced hypocortisolism significantly decreased pain detection thresholds and augmented temporal summation of IWP-induced pain (p<.05). The latter effect was dependent on the relative reduction in cortisol levels, and seemed to rely on a potentiated sensitization and not merely on the observed changes in basal pain sensitivity. Perceptual wind-up by contrast was reduced when cortisol synthesis was blocked (p<.05). This result is reminiscent of findings from animal studies showing a reversal of NMDA receptor activation by glucocorticoid receptor antagonists in neuropathic pain models. Our results speak in favor of a potential causal role of HPA axis alterations in pain chronicity.

Critical role of nociceptor plasticity in chronic pain

The transition from acute to chronic pain states might be the most important challenge in research to improve clinical treatment of debilitating pain. We describe a recently identified mechanism of neuronal plasticity in primary afferent nociceptive nerve fibers (nociceptors) by which an acute inflammatory insult or environmental stressor can trigger long-lasting hypersensitivity of nociceptors to inflammatory cytokines. This phenomenon, "hyperalgesic priming," depends on the epsilon isoform of protein kinase C (PKCepsilon) and a switch in intracellular signaling pathways that mediate cytokine-induced nociceptor hyperexcitability. We discuss the impact of this discovery on our understanding of, and ultimately our ability to treat, a variety of enigmatic and debilitating pain conditions, including those associated with repetitive injury, and generalized pain conditions, such as fibromyalgia.

[Fibromyalgia--the new guideline]

To date, the long-term course of fibromyalgia (FM) generally shows little improvement and many patients have problems managing their private, social and professional lives, if at all. Health workers in various specialties, and even in the same specialty, have differing concepts on etiology, diagnosis and treatment of FM. In its work spanning 2 years, an interdisciplinary working group made up from 10 scientific associations reviewed the literature and developed an S3-level consensus guideline. Various etiopathogenetic concepts converge from the perspective of a biopsychosocial model. A stepwise treatment approach with patient education, endurance training, multi-modal therapy and promotion of significant resources is recommended. Of the psychotherapeutic methods, cognitive behavioural training has proved the most relevant. Only a handful of drug therapies have undergone controlled trials, most however only over a period of a few weeks.

Treatment of fibromyalgia syndrome with gabapentin and pregabalin--a meta-analysis of randomized controlled trials

The efficacy of gabapentin (GPT) and pregabalin (PGB) in the treatment of fibromyalgia syndrome (FMS) was assessed. We screened MEDLINE, PsycINFO, SCOPUS, www.clinicaltrials.org, the Cochrane Library (through October 2008), and the reference sections of original studies on GPT/PGB in FMS. Randomized controlled trials (RCTs) on the treatment of FMS with GPT and PGB were analyzed. Six out of 127 RCTs studying 2422 subjects on treatment with GPT (one study) or PGB (five studies) and 1056 subjects on placebo with a median treatment duration of 11 weeks were included into the systematic review. Five studies were suitable for meta-analysis. Effects were summarized using standardized mean differences (SMD). There was strong evidence for a reduction of pain (SMD -0.28, 95% CI -0.36, -0.20; p<0.001), improved sleep (SMD -0.39, 95% CI -0.48, -0.39; p<0.001), and improved health-related quality of life (HRQOL) (SMD -0.30, 95% CI -0.46, -0.15; p<0.001), but not for depressed mood (SMD -0.12, 95% CI -0.30, 0.06; p=0.18). There was strong evidence for a non-substantial reduction of fatigue (SMD -0.16, 95% CI -0.23, -0.09, p<0.001) and of anxiety (SMD -0.18, 95% CI -0.27, -0.10; p<0.001). The external validity of the studies was limited because patients with severe somatic and mental disorders were excluded.

Fibromyalgia syndrome: classification, diagnosis, and treatment

BACKGROUND

This S3 guideline takes positions on currently contentious issues in the classification and treatment of fibromyalgia syndrome (FMS).

METHODS

A panel of experts from 10 specialist societies and patients belonging to 2 patient self-help organizations reviewed a total of approximately 8000 publications. Recommendations were developed according to the suggested procedure for S3 guidelines and were then reviewed and approved by the boards of the participating specialist societies. The steering committee ensured that the literature review and the recommendations were kept up to date.

RESULTS

Because this disorder is defined by its symptoms and signs, rather than by any consistently identifiable bodily lesion, the term "fibromyalgia syndrome" is a more appropriate designation for it than "fibromyalgia." FMS is defined by the criteria of the American College of Rheumatology and is classified as a functional somatic syndrome. FMS is diagnosed from the typical constellation of symptoms and by the exclusion of inflammatory and metabolic diseases that could cause the same symptoms. A stepwise treatment approach in which the patient and the physician decide jointly on the treatment options is recommended. The most strongly recommended forms of treatment are aerobic exercise, amitriptyline, cognitive behavioral therapy, and spa therapy.

CONCLUSIONS

The guideline recommendations are intended to promote more effective treatment of this disorder.

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.