Cerebrospinal fluid corticotropin-releasing factor concentration is associated with pain but not fatigue symptoms in patients with fibromyalgia

Fibromyalgia: A Review of the Pathophysiological Mechanisms and Multidisciplinary Treatment Strategies

Fibromyalgia is a syndrome characterized by chronic widespread musculoskeletal pain, which may or may not be associated with muscle or joint stiffness, accompanied by other symptoms such as fatigue, sleep disturbances, anxiety, and depression. It is a highly prevalent condition globally, being considered the third most common musculoskeletal disorder, following lower back pain and osteoarthritis. It is more prevalent in women than in men, and although it can occur at any age, it is more common between the ages of thirty and thirty-five. Although the pathophysiology and etiopathogenesis remain largely unknown, three underlying processes in fibromyalgia have been investigated. These include central sensitization, associated with an increase in the release of both excitatory and inhibitory neurotransmitters; peripheral sensitization, involving alterations in peripheral nociceptor signaling; and inflammatory and immune mechanisms that develop concurrently with the aforementioned processes. Furthermore, it has been determined that genetic, endocrine, psychological, and sleep disorders may influence the development of this pathology. The accurate diagnosis of fibromyalgia remains challenging as it lacks specific diagnostic biomarkers, which are still under investigation. Nonetheless, diagnostic approaches to the condition have evolved based on the use of scales and questionnaires for pain identification. The complexity associated with this pathology makes it difficult to establish a single effective treatment. Therefore, treatment is multidisciplinary, involving both pharmacological and non-pharmacological interventions aimed at alleviating symptoms. The non-pharmacological treatments outlined in this review are primarily related to physiotherapy interventions. The effectiveness of physical exercise, both on land and in water, as well as the application of electrotherapy combined with transcranial therapy and manual therapy has been highlighted. All of these interventions aim to improve the quality of life of patients highly affected by fibromyalgia.

Proteomics in Patients with Fibromyalgia Syndrome: A Systematic Review of Observational Studies

PURPOSE OF REVIEW

Fibromyalgia syndrome (FMS) is a disease of unknown pathophysiology, with the diagnosis being based on a set of clinical criteria. Proteomic analysis can provide significant biological information for the pathophysiology of the disease but may also reveal biomarkers for diagnosis or therapeutic targets. The present systematic review aims to synthesize the evidence regarding the proteome of adult patients with FMS using data from observational studies.

RECENT FINDINGS

An extensive literature search was conducted in MEDLINE/PubMed, CENTRAL, and clinicaltrials.gov from inception until November 2022. The study protocol was published in OSF. Two independent reviewers evaluated the studies and extracted data. The quality of studies was assessed using the modified Newcastle-Ottawa scale adjusted for proteomic research. Ten studies fulfilled the protocol criteria, identifying 3328 proteins, 145 of which were differentially expressed among patients with FMS against controls. The proteins were identified in plasma, serum, cerebrospinal fluid, and saliva samples. The control groups included healthy individuals and patients with pain (inflammatory and non-inflammatory). The most important proteins identified involved transferrin, α-, β-, and γ-fibrinogen chains, profilin-1, transaldolase, PGAM1, apolipoprotein-C3, complement C4A and C1QC, immunoglobin parts, and acute phase reactants. Weak correlations were observed between proteins and pain sensation, or quality of life scales, apart from the association of transferrin and a2-macroglobulin with moderate-to-severe pain sensation. The quality of included studies was moderate-to-good. FMS appears to be related to protein dysregulation in the complement and coagulation cascades and the metabolism of iron. Several proteins may be dysregulated due to the excessive oxidative stress response.

CRF regulates pain sensation by enhancement of corticoaccumbal excitatory synaptic transmission

Both peripheral and central corticotropin-releasing factor (CRF) systems have been implicated in regulating pain sensation. However, compared with the peripheral, the mechanisms underlying central CRF system in pain modulation have not yet been elucidated, especially at the neural circuit level. The corticoaccumbal circuit, a structure rich in CRF receptors and CRF-positive neurons, plays an important role in behavioral responses to stressors including nociceptive stimuli. The present study was designed to investigate whether and how CRF signaling in this circuit regulated pain sensation under physiological and pathological pain conditions. Our studies employed the viral tracing and circuit-, and cell-specific electrophysiological methods to label the CRF-containing circuit from the medial prefrontal cortex to the nucleus accumbens shell (mPFCCRF-NAcS) and record its neuronal propriety. Combining optogenetic and chemogenetic manipulation, neuropharmacological methods, and behavioral tests, we were able to precisely manipulate this circuit and depict its role in regulation of pain sensation. The current study found that the CRF signaling in the NAc shell (NAcS), but not NAc core, was necessary and sufficient for the regulation of pain sensation under physiological and pathological pain conditions. This process was involved in the CRF-mediated enhancement of excitatory synaptic transmission in the NAcS. Furthermore, we demonstrated that the mPFCCRF neurons monosynaptically connected with the NAcS neurons. Chronic pain increased the protein level of CRF in NAcS, and then maintained the persistent NAcS neuronal hyperactivity through enhancement of this monosynaptic excitatory connection, and thus sustained chronic pain behavior. These findings reveal a novel cell- and circuit-based mechanistic link between chronic pain and the mPFCCRF → NAcS circuit and provide a potential new therapeutic target for chronic pain.

Pain mechanisms for the practicing rheumatologist

Pain in rheumatic diseases transcends the traditional nociceptive paradigm, incorporating complex interactions between nociceptive, neuropathic, and nociplastic mechanisms, as well as significant psychosocial factors. Advances in understanding chronic pain highlight the role of peripheral and central sensitization, and the emergence of nociplastic pain-a result of altered central nervous system processing. This modern perspective acknowledges the influence of mood disorders, environmental stressors, and cognitive patterns like catastrophizing, revealing the intricate interplay between biological, psychological, and social determinants of pain. Research emphasizes the brain's pivotal role in pain perception, underscoring the importance of comprehensive approaches that integrate medical, psychological, and social interventions to address the multifaceted nature of chronic pain in rheumatic diseases effectively.

The role of the vagus nerve in fibromyalgia syndrome

Fibromyalgia (FM) syndrome is a common illness characterized by chronic widespread pain, sleep problems, fatigue, and cognitive difficulties. Dysfunctional neurotransmitter systems that influence the body's endogenous stress response systems are thought to underlie many of the major FM-related symptoms. A model of FM pathogenesis suggests biological and psychosocial variables interact to influence the genetic predisposition, but the precise mechanisms remain unclear. The Polyvagal Theory provides a theoretical framework from which to investigate potential biological mechanisms. The vagus nerve (VN) has anti-inflammatory properties via its afferent and efferent fibers. A low vagal tone (as assessed by low heart rate variability), has been observed in painful and inflammatory diseases, including FM, while the ventral branch of the VN is linked to emotional expression and social engagement. These anti-inflammatory and psychological (limbic system) properties of the VN may possess therapeutic potential in treating FM. This review paper summarizes the scientific literature regarding the potential role of the VN in transducing and/or therapeutically managing FM signs and symptoms.

Functional and Anatomical Characterization of Corticotropin-Releasing Factor Receptor Subtypes of the Rat Spinal Cord Involved in Somatic Pain Relief

Corticotropin-releasing factor (CRF) orchestrates our body’s response to stressful stimuli. Pain is often stressful and counterbalanced by activation of CRF receptors along the nociceptive pathway, although the involvement of the CRF receptor subtypes 1 and/or 2 (CRF-R1 and CRF-R2, respectively) in CRF-induced analgesia remains controversial. Thus, the aim of the present study was to examine CRF-R1 and CRF-R2 expression within the spinal cord of rats with Freund’s complete adjuvant-induced unilateral inflammation of the hind paw using reverse transcriptase polymerase chain reaction, Western blot, radioligand binding, and immunofluorescence confocal analysis. Moreover, the antinociceptive effects of intrathecal (i.t.) CRF were measured by paw pressure algesiometer and their possible antagonism by selective antagonists for CRF-R1 and/or CRF-R2 as well as for opioid receptors. Our results demonstrated a preference for the expression of CRF-R2 over CRF-R1 mRNA, protein, binding sites and immunoreactivity in the dorsal horn of the rat spinal cord. Consistently, CRF as well as CRF-R2 agonists elicited potent dose-dependent antinociceptive effects which were antagonized by the i.t. CRF-R2 selective antagonist K41498, but not by the CRF-R1 selective antagonist NBI35965. In addition, i.t. applied opioid antagonist naloxone dose-dependently abolished the i.t. CRF- as well as CRF-R2 agonist-elicited inhibition of somatic pain. Importantly, double immunofluorescence confocal microscopy of the spinal dorsal horn showed CRF-R2 on enkephalin (ENK)-containing inhibitory interneurons in close opposition of incoming mu-opioid receptor-immunoreactive nociceptive neurons. CRF-R2 was, however, not seen on pre- or on postsynaptic sensory neurons of the spinal cord. Taken together, these findings suggest that i.t. CRF or CRF-R2 agonists inhibit somatic inflammatory pain predominantly through CRF-R2 receptors located on spinal enkephalinergic inhibitory interneurons which finally results in endogenous opioid-mediated pain inhibition.

Fibromyalgia: Pathogenesis, Mechanisms, Diagnosis and Treatment Options Update

Fibromyalgia is a syndrome characterized by chronic and widespread musculoskeletal pain, often accompanied by other symptoms, such as fatigue, intestinal disorders and alterations in sleep and mood. It is estimated that two to eight percent of the world population is affected by fibromyalgia. From a medical point of view, this pathology still presents inexplicable aspects. It is known that fibromyalgia is caused by a central sensitization phenomenon characterized by the dysfunction of neuro-circuits, which involves the perception, transmission and processing of afferent nociceptive stimuli, with the prevalent manifestation of pain at the level of the locomotor system. In recent years, the pathogenesis of fibromyalgia has also been linked to other factors, such as inflammatory, immune, endocrine, genetic and psychosocial factors. A rheumatologist typically makes a diagnosis of fibromyalgia when the patient describes a history of pain spreading in all quadrants of the body for at least three months and when pain is caused by digital pressure in at least 11 out of 18 allogenic points, called tender points. Fibromyalgia does not involve organic damage, and several diagnostic approaches have been developed in recent years, including the analysis of genetic, epigenetic and serological biomarkers. Symptoms often begin after physical or emotional trauma, but in many cases, there appears to be no obvious trigger. Women are more prone to developing the disease than men. Unfortunately, the conventional medical therapies that target this pathology produce limited benefits. They remain largely pharmacological in nature and tend to treat the symptomatic aspects of various disorders reported by the patient. The statistics, however, highlight the fact that 90% of people with fibromyalgia also turn to complementary medicine to manage their symptoms.

Pain Mechanisms in Patients with Rheumatic Diseases

Patients with rheumatic diseases often have mixed pain states, with varying degrees of nociceptive, neuropathic, and nociplastic mechanisms, which exist on a continuum. When individuals with any chronic pain have a nociplastic component to their symptoms, they are less likely to respond to treatments (eg, injections, surgery, biologics, and opioids) that work better for acute or purely nociceptive pain.

Low-Dose Dextromethorphan for the Treatment of Fibromyalgia Pain: Results from a Longitudinal, Single-Blind, Placebo-Controlled Pilot Trial

Objective

Fibromyalgia (FM) is a debilitating chronic pain condition with few treatment options. Central sensitization and neuroinflammation have been forwarded as models of FM pathophysiology, both of which indicate dextromethorphan (DXM) as a potential treatment. DXM is an NMDA-receptor antagonist and microglial modulator with anti-neuroinflammatory properties at low doses. It is available for clinical use but has not been tested as a treatment for FM at low dosages. This study evaluated the effectiveness of DXM in treating FM-associated symptoms.

Methods

In a single-blind, placebo-controlled trial, 14 women meeting the 2010 American College of Rheumatology criteria for FM received a placebo for five weeks, followed by 20 mg DXM for ten weeks, while providing daily symptom reports on a 0–100 scale. Pain and physical activity were the primary and secondary outcomes, respectively. Daily symptom ratings during the last four weeks of placebo were contrasted with ratings during the last four weeks of the active treatment using generalized estimating equations (GEE).

Results

DXM was well tolerated, and treatment adherence was high. Baseline pain was reduced by at least 20% in six participants. Self-reported daily pain and physical activity in the entire cohort were not significantly different between the placebo and DXM conditions, and the primary hypotheses were not supported. Exploratory analyses using the entire placebo and DXM data showed that pain was significantly lower in the DXM condition than in the placebo condition (b=−9.933, p=0.013).

Discussion

A strong clinical effect of DXM was not observed at the 20mg/day dosage.

The Search for Biomarkers in Fibromyalgia

Fibromyalgia is the most common of the central sensitivity syndromes affecting 2–5% of the adult population in the United States. This pain amplification syndrome has enormous societal impact as measured by work absenteeism, decreased work productivity, disability and injury compensation and over-utilization of healthcare resources. Multiple studies have shown that early diagnosis of this condition can improve patient outlook and redirect valuable healthcare resources towards more appropriate targeted therapy. Efforts have been made towards improving diagnostic accuracy through updated criteria. The search for biomarkers for diagnosis and verification of Fibromyalgia is an ongoing process. Inadequacies with current diagnostic criteria for this condition have fueled these efforts for identification of a reproducible marker that can verify this disease in a highly sensitive, specific and reproducible manner. This review focuses on areas of research for biomarkers in fibromyalgia and suggests that future efforts might benefit from approaches that utilize arrays of biomarkers to identify this disorder that presents with a diverse clinical phenotype.

Exercise modifies glutamate and other metabolic biomarkers in cerebrospinal fluid from Gulf War Illness and Myalgic encephalomyelitis / Chronic Fatigue Syndrome

Myalgic encephalomyelitis / Chronic Fatigue Syndrome (ME/CFS) and Gulf War Illness (GWI) share many symptoms of fatigue, pain, and cognitive dysfunction that are not relieved by rest. Patterns of serum metabolites in ME/CFS and GWI are different from control groups and suggest potential dysfunction of energy and lipid metabolism. The metabolomics of cerebrospinal fluid was contrasted between ME/CFS, GWI and sedentary controls in 2 sets of subjects who had lumbar punctures after either (a) rest or (b) submaximal exercise stress tests. Postexercise GWI and control subjects were subdivided according to acquired transient postexertional postural tachycardia. Banked cerebrospinal fluid specimens were assayed using Biocrates AbsoluteIDQ® p180 kits for quantitative targeted metabolomics studies of amino acids, amines, acylcarnitines, sphingolipids, lysophospholipids, alkyl and ether phosphocholines. Glutamate was significantly higher in the subgroup of postexercise GWI subjects who did not develop postural tachycardia after exercise compared to nonexercise and other postexercise groups. The only difference between nonexercise groups was higher lysoPC a C28:0 in GWI than ME/CFS suggesting this biochemical or phospholipase activities may have potential as a biomarker to distinguish between the 2 diseases. Exercise effects were suggested by elevation of short chain acylcarnitine C5-OH (C3-DC-M) in postexercise controls compared to nonexercise ME/CFS. Limitations include small subgroup sample sizes and absence of postexercise ME/CFS specimens. Mechanisms of glutamate neuroexcitotoxicity may contribute to neuropathology and “neuroinflammation” in the GWI subset who did not develop postural tachycardia after exercise. Dysfunctional lipid metabolism may distinguish the predominantly female ME/CFS group from predominantly male GWI subjects.

The role of lifetime stressors in adult fibromyalgia: systematic review and meta-analysis of case-control studies

BACKGROUND

Fibromyalgia is a chronic condition characterised by widespread musculoskeletal pain. Although accumulating evidence suggests that exposure to stressful events increases the risk for this complex disorder, this is the first meta-analysis to compare the impact of a full range of lifetime stressors (e.g. physical trauma through to emotional neglect) on adult fibromyalgia.

METHODS

This review was performed in accordance with PRISMA guidelines. Random-effects models examined associations between different stressor exposures and fibromyalgia status with meta-regression investigating the effects of publication year and study quality on effect sizes.

RESULTS

Nineteen studies were included in the meta-analysis. Significant associations with fibromyalgia status were observed for all six exposure types examined: odds ratios (OR) were highest for physical abuse (OR 3.23, 95% confidence interval 1.99-5.23) and total abuse (3.06, 1.71-5.46); intermediate for sexual abuse (2.65, 1.85-3.79) and smaller for medical trauma (1.80, 1.19-2.71), other lifetime stressors (1.70, 1.31-2.20), and emotional abuse (1.52, 1.27-1.81). Results were not significantly changed when childhood, as opposed to adult, exposures were used in studies that reported both. Meta-regression analyses demonstrated no effect of publication year or study quality on effect sizes.

CONCLUSIONS

This study confirmed a significant association between stressor exposure and adult fibromyalgia with the strongest associations observed for physical abuse. Limitations related to current available literature were identified; we provide several suggestions for how these can be addressed in future studies. Stressors are likely to be one of many risk factors for fibromyalgia which we argue is best approached from a biopsychosocial perspective.

(Neuro)Inflammatory Component May Be a Common Factor in Chronic Widespread Pain and Restless Legs Syndrome

Purpose of Review

Recent studies have linked fibromyalgia (nociplastic pain) and depression to neuroinflammation. Restless legs syndrome (RLS) is highly prevalent in CWP (chronic widespread pain) and FMS (fibromyalgia syndrome) as well as in depression. This review focuses on evidence in the relationship between CWP and RLS and possible common pathophysiological mechanisms.

Recent Findings

CWP is chronic pain spread over various locations of the body and is a cardinal sign of fibromyalgia. Poor sleep quality is a common symptom in fibromyalgia as well as high levels of fatigue, poor cognition, and other associated features which include depression, headache, and abdominal pain. Evidence for a bilateral relationship between pain and sleep deficit is robust. The latest research focus is not only on insomnia symptoms in chronic pain but also on other types of sleep disorders such as RLS which is characterized by complaints of an “urge to move” frequently associated with dysesthesias. These sensations can also have painful characteristics. Thus, there is a possible overlap between these two entities. The high prevalence of RLS (33–54%) in CWP has been shown in several studies. The pathophysiological mechanisms behind CWP and RLS are still not completely known, but there is a rising amount of evidence on proinflammatory and neuroinflammatory processes in CWP. In RLS, there are links to dopaminergic dysfunction and more generally to monoaminergic dysfunctional circuits, BID (brain iron deficiency), altered glutamatergic neurotransmission, and genetic traits. Depression is a common comorbidity as well in CWP as RLS, and proinflammatory mechanisms have also been demonstrated in this condition.

Summary

The association between CWP and RLS is shown to be high and the pathogenesis of both conditions is still not completely understood. Recent research is focusing on proinflammatory and neuroinflammatory processes, not uniquely emerging in fibromyalgia/CWP, but inflammatory features have been found in depression as well as in sleep deficit. Proinflammatory/neuroinflammatory processes may be an underlying, common factor in both CWP and RLS that future research should investigate further.

T Cell Subpopulations in the Physiopathology of Fibromyalgia: Evidence and Perspectives

Fibromyalgia is one of the most important “rheumatic” disorders, after osteoarthritis. The etiology of the disease is still not clear. At the moment, the most defined pathological mechanism is the alteration of central pain pathways, and emotional conditions can trigger or worsen symptoms. Increasing evidence supports the role of mast cells in maintaining pain conditions such as musculoskeletal pain and central sensitization. Importantly, mast cells can mediate microglia activation through the production of proinflammatory cytokines such as IL-1β, IL-6, and TNFα. In addition, levels of chemokines and proinflammatory cytokines are enhanced in serum and could contribute to inflammation at systemic level. Despite the well-characterized relationship between the nervous system and inflammation, the mechanism that links the different pathological features of fibromyalgia, including stress-related manifestations, central sensitization, and dysregulation of the innate and adaptive immune responses is largely unknown. This review aims to provide an overview of the current understanding of the role of adaptive immune cells, in particular T cells, in the physiopathology of fibromyalgia. It also aims at linking the latest advances emerging from basic science to envisage new perspectives to explain the role of T cells in interconnecting the psychological, neurological, and inflammatory symptoms of fibromyalgia.

CSF levels of apolipoprotein C1 and autotaxin found to associate with neuropathic pain and fibromyalgia

Objective

Neuropathic pain and fibromyalgia are two common and poorly understood chronic pain conditions that lack satisfactory treatments, cause substantial suffering and societal costs. Today, there are no biological markers on which to base chronic pain diagnoses, treatment choices or to understand the pathophysiology of pain for the individual patient. This study aimed to investigate cerebrospinal fluid (CSF) protein profiles potentially associated with fibromyalgia and neuropathic pain.

Methods

CSF samples were collected from 25 patients with neuropathic pain (two independent sets, n=14 patients for discovery, and n=11 for verification), 40 patients with fibromyalgia and 134 controls without neurological disease from two different populations. CSF protein profiling of 55 proteins was performed using antibody suspension bead array technology.

Results

We found increased levels of apolipoprotein C1 (APOC1) in CSF of neuropathic pain patients compared to controls and there was a trend for increased levels also in fibromyalgia patients. In addition, levels of ectonucleotide pyrophosphatase family member 2 (ENPP2, also referred to as autotaxin) were increased in the CSF of fibromyalgia patients compared to all other groups including patients with neuropathic pain.

Conclusion

The increased levels of APOC1 and ENPP2 found in neuropathic pain and fibromyalgia patients may shed light on the underlying mechanisms of these conditions. Further investigation is required to elucidate their role in maintaining pain and other main symptoms of these disorders.

Mast Cells, Neuroinflammation and Pain in Fibromyalgia Syndrome

Fibromyalgia Syndrome (FMS) is a disorder of chronic, generalized muscular pain, accompanied by sleep disturbances, fatigue and cognitive dysfunction. There is no definitive pathogenesis except for altered central pain pathways. We previously reported increased serum levels of the neuropeptides substance P (SP) and its structural analogue hemokinin-1 (HK-1) together with the pro-inflammatory cytokines IL-6 and TNF in FMS patients as compared to sedentary controls. We hypothesize that thalamic mast cells contribute to inflammation and pain, by releasing neuro-sensitizing molecules that include histamine, IL-1β, IL-6 and TNF, as well as calcitonin-gene related peptide (CGRP), HK-1 and SP. These molecules could either stimulate thalamic nociceptive neurons directly, or via stimulation of microglia in the diencephalon. As a result, inhibiting mast cell stimulation could be used as a novel approach for reducing pain and the symptoms of FMS.

Effects of an Extract of Salmon Milt on Symptoms and Serum TNF and Substance P in Patients With Fibromyalgia Syndrome

PURPOSE

The aim of this study was to evaluate the effects of a dietary supplement containing primarily an extract of salmon's milt (semen) on symptoms and blood levels of proinflammatory molecules in patients with fibromyalgia syndrome (FMS), a chronic, painful musculoskeletal disease without a distinct pathogenesis or treatment. We recently reported increased serum levels of the proinflammatory molecules substance P (SP) and tumor necrosis factor (TNF) in patients with FMS as compared to those in normal controls.

METHODS

This prospective, open-label study was conducted in patients with FMS (n = 87; 80 women, 7 men; age range, 18-80 years) selected from 2 clinical centers in Spain. Patients were administered the supplement and were evaluated at weeks 1 (before treatment), 4, 8, and 12 (end of treatment) for clinical parameters of functioning, fatigue, and pain, as well as overall impression. Patients were directed to take 1 capsule per day in the morning for the first 4 weeks, followed by 1 capsule in the morning and 1 capsule in the evening for the remaining 8 weeks. Differences in symptom scores in patients with FMS between weeks 1 and weeks 4, 8, and 12 were evaluated using ANOVA. Blood was obtained and serum separated in patients with FMS at 1 and 12 weeks and in a separate population of healthy controls (n = 20; 15 women, 5 men; age range, 25-65 years). Serum levels of SP and TNF were measured in patients with FMS at 1 and 12 weeks and in healthy controls by ELISA. TNF and SP levels in patients with FMS were compared between weeks 1 and 12, as well as between patients with FMS and untreated controls, using the Mann-Whitney U test.

FINDINGS

Clinical parameters of functioning, fatigue, and pain, as well as overall impression, were improved significantly at 4 weeks as compared to 1 week and remained unchanged for the duration of the study (all, P < 0.0001). Serum TNF and SP levels were significantly elevated at 1 week in patients with FMS compared to controls and were decreased significantly at 12 weeks as compared to 1 week (all, P < 0.0001).

IMPLICATIONS

Our findings indicate that this dietary supplement may significantly improve symptoms in patients with FMS. This is the first time to our knowledge that any molecule has been reported to be associated with a reduction in serum SP level. Consequently, the supplement or its hypothesized main active ingredient, spermine, may be developed as a novel treatment approach to FMS or other neuroinflammatory conditions. ClinicalTrials.gov identifier: NCT03911882.

Possible Molecular Mediators Involved and Mechanistic Insight into Fibromyalgia and Associated Co-morbidities

Fibromyalgia is a chronic complex syndrome of non-articulate origin characterized by musculoskeletal pain, painful tender points, sleep problems and co-morbidities including depression, migraine. The etiopathogenesis of fibromyalgia is complex, variable and remains inconclusive. The etiological factors that have been defined include stress, genetic predisposition and environmental components. As per the reports of the American College of Rheumatology (ACR) the prevalence of fibromyalgia varies from 2 to 22% among the general population with poor diagnostic features primarily pain. Fibromyalgia encompasses a spectrum of co-morbid conditions with multifarious pathogenesis. The highly prevalent manifestations of fibromyalgia include heterogeneous pain and aches. Biochemical and neurobiological elements of fibromyalgia include neurotransmitters, hypothalamic pituitary adrenal axis (HPA axis), inflammatory cytokines, monoaminergic pathway, opioid peptides, sex hormones, nerve growth factor (NGF) and local free radical insult. An imbalance in the serotonergic system is the major underlying etiological factor that has been explored most widely. Owing to complex interplay of diverse pathophysiological pathways, overlapping co-morbidities such as depression have been clinically observed. Therapeutic management of fibromyalgia involves both non pharmacological and pharmacological measures. The current review presents various dysregulations and their association with symptoms of fibromyalgia along with their underlying neurobiological aspects.

Cortisol and Subjective Stress Responses to Acute Psychosocial Stress in Fibromyalgia Patients and Control Participants

OBJECTIVE

Hypothalamic-pituitary-adrenal axis dysfunction may play a role in fibromyalgia (FM) pathogenesis but it remains understudied in this disorder. Furthermore, early childhood adversities (ECA) are common in FM, but whether they moderate stress reactivity is unknown. Hence, we investigated cortisol and subjective responses to acute psychosocial stress in FM and controls, while adjusting for ECA.

METHODS

Twenty-seven female FM patients and 24 age-matched female controls were recruited in a tertiary care center and through advertisements, respectively. The Childhood Trauma Questionnaire was used to measure ECA history. Salivary cortisol levels and subjective stress ratings were measured at multiple time points before and after the Trier Social Stress Test (TSST) was administered.

RESULTS

Significant main effects of group [F(1,43) = 7.04, p = .011, lower in FM] and ECA [F(1,43) = 5.18, p = .028, higher in participants with ECA] were found for cortisol responses. When excluding controls with ECA (n = 5), a significant group-by-time interaction was found [F(6,39) = 2.60, p = .032], driven by a blunted response to the stressor in FM compared with controls (p = .037). For subjective stress responses, a significant main effect of group [F(1,45) = 10.69, p = .002, higher in FM] and a trend toward a group-by-time interaction effect [F(6,45) = 2.05, p = .078, higher in FM 30 minutes before and 30 and 75 minutes after the TSST, and impaired recovery (difference immediately after - 30 minutes after the TSST) in FM] were found.

CONCLUSIONS

Blunted cortisol responsivity to the TSST was observed in FM patients compared with controls without ECA. FM patients had higher subjective stress levels compared with controls, particularly at baseline and during recovery from the TSST. In FM patients, ECA history was not associated with cortisol or subjective stress levels or with responsivity to the TSST. Future research should investigate the mechanisms underlying hypothalamic-pituitary-adrenal axis dysregulation in FM.

Stress-Induced Chronic Visceral Pain of Gastrointestinal Origin

Visceral pain is generally poorly localized and characterized by hypersensitivity to a stimulus such as organ distension. In concert with chronic visceral pain, there is a high comorbidity with stress-related psychiatric disorders including anxiety and depression. The mechanisms linking visceral pain with these overlapping comorbidities remain to be elucidated. Evidence suggests that long term stress facilitates pain perception and sensitizes pain pathways, leading to a feed-forward cycle promoting chronic visceral pain disorders such as irritable bowel syndrome (IBS). Early life stress (ELS) is a risk-factor for the development of IBS, however the mechanisms responsible for the persistent effects of ELS on visceral perception in adulthood remain incompletely understood. In rodent models, stress in adult animals induced by restraint and water avoidance has been employed to investigate the mechanisms of stress-induce pain. ELS models such as maternal separation, limited nesting, or odor-shock conditioning, which attempt to model early childhood experiences such as neglect, poverty, or an abusive caregiver, can produce chronic, sexually dimorphic increases in visceral sensitivity in adulthood. Chronic visceral pain is a classic example of gene × environment interaction which results from maladaptive changes in neuronal circuitry leading to neuroplasticity and aberrant neuronal activity-induced signaling. One potential mechanism underlying the persistent effects of stress on visceral sensitivity could be epigenetic modulation of gene expression. While there are relatively few studies examining epigenetically mediated mechanisms involved in visceral nociception, stress-induced visceral pain has been linked to alterations in DNA methylation and histone acetylation patterns within the brain, leading to increased expression of pro-nociceptive neurotransmitters. This review will discuss the potential neuronal pathways and mechanisms responsible for stress-induced exacerbation of chronic visceral pain. Additionally, we will review the importance of specific experimental models of adult stress and ELS in enhancing our understanding of the basic molecular mechanisms of pain processing.

Emerging pharmacological strategies for the treatment of fibromyalgia

Fibromyalgia (FM) has been described as a chronic clinical condition related to multisensory hypersensitivity presenting with a complex of symptoms dominated by chronic widespread pain associated with the existence of a range of co-morbidities, such as fatigue, sleep disturbance, cognitive impairment, anxiety and depression. Current treatments include drugs that target serotonin and noradrenaline levels within the central nervous system, e.g., tricyclic antidepressants, serotonin noradrenaline reuptake inhibitors, and voltage-gated calcium channel subunit ligands, e.g., gabapentin and pregabalin. Investigation of a range of novel targets, such as melatoninergic, cannabinoid, dopamine, NMDA, angiotensin, orexin and opioid receptors, and ion channels, in addition revisiting bioamine modulation and subunits has provided efficacy outcomes that improve the health status of patients with FM. Nevertheless, modest and limited efficacy is often observed reflecting the heterogeneity of FM with existence of subpopulations of patients, the contribution of peripheral and central components to the pathophysiology, and the extensive range of accompanying co-morbidities. The complexity and multidimensional nature of FM is emphasized by the diversity of pharmacological targets gaining interest. Clues to underlying mechanisms which offer themselves as novel and potential targets for new medications are being provided by advances in the understanding of the pathophysiology of FM.

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.

Neurobiology of fibromyalgia and chronic widespread pain

Fibromyalgia is the current term for chronic widespread musculoskeletal pain for which no alternative cause can be identified. The underlying mechanisms, in both human and animal studies, for the continued pain in individuals with fibromyalgia will be explored in this review. There is a substantial amount of support for alterations of central nervous system nociceptive processing in people with fibromyalgia, and that psychological factors such as stress can enhance the pain experience. Emerging evidence has begun exploring other potential mechanisms including a peripheral nervous system component to the generation of pain and the role of systemic inflammation. We will explore the data and neurobiology related to the role of the CNS in nociceptive processing, followed by a short review of studies examining potential peripheral nervous system changes and cytokine involvement. We will not only explore the data from human subjects with fibromyalgia but will relate this to findings from animal models of fibromyalgia. We conclude that fibromyalgia and related disorders are heterogenous conditions with a complicated pathobiology with patients falling along a continuum with one end a purely peripherally driven painful condition and the other end of the continuum is when pain is purely centrally driven.

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.

Neuropeptides CRH, SP, HK-1, and Inflammatory Cytokines IL-6 and TNF Are Increased in Serum of Patients with Fibromyalgia Syndrome, Implicating Mast Cells

Fibromyalgia syndrome (FMS) is a chronic, idiopathic condition of widespread musculoskeletal pain affecting more women than men. Even though clinical studies have provided evidence of altered central pain pathways, the lack of definitive pathogenesis or reliable objective markers has hampered development of effective treatments. Here we report that the neuropeptides corticotropin-releasing hormone (CRH), substance P (SP), and SP-structurally-related hemokinin-1 (HK-1) were significantly (P = 0.026, P < 0.0001, and P = 0.002, respectively) elevated (0.82 ± 0.57 ng/ml, 0.39 ± 0.18 ng/ml, and 7.98 ± 3.12 ng/ml, respectively) in the serum of patients with FMS compared with healthy controls (0.49 ± 0.26 ng/ml, 0.12 ± 0.1 ng/ml, and 5.71 ± 1.08 ng/ml, respectively). Moreover, SP and HK-1 levels were positively correlated (Pearson r = 0.45, P = 0.002) in FMS. The serum concentrations of the inflammatory cytokines interleukin (IL)-6 and tumor necrosis factor (TNF) were also significantly (P = 0.029 and P = 0.006, respectively) higher (2.97 ± 2.35 pg/ml and 0.92 ± 0.31 pg/ml, respectively) in the FMS group compared with healthy subjects (1.79 ± 0.62 pg/ml and 0.69 ± 0.16 pg/ml, respectively). In contrast, serum IL-31 and IL-33 levels were significantly lower (P = 0.0001 and P = 0.044, respectively) in the FMS patients (849.5 ± 1005 pg/ml and 923.2 ± 1284 pg/ml, respectively) in comparison with healthy controls (1281 ± 806.4 pg/ml and 3149 ± 4073 pg/ml, respectively). FMS serum levels of neurotensin were not different from controls. We had previously shown that CRH and SP stimulate IL-6 and TNF release from mast cells (MCs). Our current results indicate that neuropeptides could stimulate MCs to secrete inflammatory cytokines that contribute importantly to the symptoms of FMS. Treatment directed at preventing the secretion or antagonizing these elevated neuroimmune markers, both centrally and peripherally, may prove to be useful in the management of FMS.

Intrathecal urocortin I in the spinal cord as a murine model of stress hormone-induced musculoskeletal and tactile hyperalgesia

Stress is antinociceptive in some models of pain, but enhances musculoskeletal nociceptive responses in mice and muscle pain in patients with fibromyalgia syndrome. To test the hypothesis that urocortins are stress hormones that are sufficient to enhance tactile and musculoskeletal hyperalgesia, von Frey fibre sensitivity and grip force after injection of corticotropin-releasing factor (CRF), urocortin I and urocortin II were measured in mice. Urocortin I (a CRF1 and CRF2 receptor ligand) produced hyperalgesia in both assays when injected intrathecally (i.t.) but not intracerebroventricularly, and only at a large dose when injected peripherally, suggesting a spinal action. Morphine inhibited urocortin I-induced changes in nociceptive responses in a dose-related fashion, confirming that changes in behaviour reflect hyperalgesia rather than weakness. No tolerance developed to the effect of urocortin I (i.t.) when injected repeatedly, consistent with a potential to enhance pain chronically. Tactile hyperalgesia was inhibited by NBI-35965, a CRF1 receptor antagonist, but not astressin 2B, a CRF2 receptor antagonist. However, while urocortin I-induced decreases in grip force were not observed when co-administered i.t. with either NBI-35965 or astressin 2B, they were even more sensitive to inhibition by astressin, a non-selective CRF receptor antagonist. Together these data indicate that urocortin I acts at CRF receptors in the mouse spinal cord to elicit a reproducible and persistent tactile (von Frey) and musculoskeletal (grip force) hyperalgesia. Urocortin I-induced hyperalgesia may serve as a screen for drugs that alleviate painful conditions that are exacerbated by stress.

Fibromyalgia syndrome in need of effective treatments

Fibromyalgia syndrome (FMS) is a chronic, idiopathic condition of widespread musculoskeletal pain, affecting primarily women. It is clinically characterized by chronic, nonarticular pain and a heightened response to pressure along with sleep disturbances, fatigue, bowel and bladder abnormalities, and cognitive dysfunction. The diagnostic criteria have changed repeatedly, and there is neither a definitive pathogenesis nor reliable diagnostic or prognostic biomarkers. Clinical and laboratory studies have provided evidence of altered central pain pathways. Recent evidence suggests the involvement of neuroinflammation with stress peptides triggering the release of neurosenzitizing mediators. The management of FMS requires a multidimensional approach including patient education, behavioral therapy, exercise, and pain management. Here we review recent data on the pathogenesis and propose new directions for research and treatment.

Knockdown of steroid receptors in the central nucleus of the amygdala induces heightened pain behaviors in the rat

Previously we demonstrated that exposure of the central nucleus of the amygdala (CeA) to elevated corticosterone (CORT) induces nociceptive behaviors that are reversed by glucocorticoid and/or mineralocorticoid (GR/MR) receptor antagonism. Here we test the hypothesis that in a cholesterol (CHOL)-implanted control rat, selective knockdown of GR/MR in the CeA would, via a corticotropin-releasing factor (CRF)-mediated mechanism, replicate the nociceptive behaviors produced by elevated amygdala CORT. Micropellets of CHOL or CORT were stereotaxically placed on the dorsal margin of the CeA. Cannulae were implanted into the CeA for the delivery of vehicle or oligodeoxynucleotide (ODN) of either antisense (ASO) or random sequences (RSO) targeting GR or MR. Visceromotor behavioral response quantified visceral sensitivity in response to colonic distension, while von Frey filaments assessed somatic sensitivity. Receptor expression was determined with qRT-PCR. In CHOL implanted controls, knockdown of GR in the CeA increased both colonic and somatic sensitivity, whereas selective knockdown of MR in the CeA induced colonic hypersensitivity without affecting somatic sensitivity. CRF expression in the CeA was increased in CHOL-implanted rats treated with GR or MR ASO and resembled the augmented CRF expression seen in the CORT-implanted rats. This is the first study to demonstrate that decreasing either GR or MR within the CeA is sufficient to induce visceral hypersensitivity whereas somatic hypersensitivity developed after only GR knockdown. The loss of either GR or MR was associated with an increased CRF expression, and may represent a common mechanism for the development of CeA-mediated nociceptive behaviors.

Beyond pain in fibromyalgia: insights into the symptom of fatigue

Fatigue is a disabling, multifaceted symptom that is highly prevalent and stubbornly persistent. Although fatigue is a frequent complaint among patients with fibromyalgia, it has not received the same attention as pain. Reasons for this include lack of standardized nomenclature to communicate about fatigue, lack of evidence-based guidelines for fatigue assessment, and a deficiency in effective treatment strategies. Fatigue does not occur in isolation; rather, it is present concurrently in varying severity with other fibromyalgia symptoms such as chronic widespread pain, unrefreshing sleep, anxiety, depression, cognitive difficulties, and so on. Survey-based and preliminary mechanistic studies indicate that multiple symptoms feed into fatigue and it may be associated with a variety of physiological mechanisms. Therefore, fatigue assessment in clinical and research settings must consider this multi-dimensionality. While no clinical trial to date has specifically targeted fatigue, randomized controlled trials, systematic reviews, and meta-analyses indicate that treatment modalities studied in the context of other fibromyalgia symptoms could also improve fatigue. The Outcome Measures in Rheumatology (OMERACT) Fibromyalgia Working Group and the Patient Reported Outcomes Measurement Information System (PROMIS) have been instrumental in propelling the study of fatigue in fibromyalgia to the forefront. The ongoing efforts by PROMIS to develop a brief fibromyalgia-specific fatigue measure for use in clinical and research settings will help define fatigue, allow for better assessment, and advance our understanding of fatigue.

Stress-induced pain: a target for the development of novel therapeutics

Although current therapeutics provide relief from acute pain, drugs used for treatment of chronic pain are typically less efficacious and limited by adverse side effects, including tolerance, addiction, and gastrointestinal upset. Thus, there is a significant need for novel therapies for the treatment of chronic pain. In concert with chronic pain, persistent stress facilitates pain perception and sensitizes pain pathways, leading to a feed-forward cycle promoting chronic pain disorders. Stress exacerbation of chronic pain suggests that centrally acting drugs targeting the pain- and stress-responsive brain regions represent a valid target for the development of novel therapeutics. This review provides an overview of how stress modulates spinal and central pain pathways, identifies key neurotransmitters and receptors within these pathways, and highlights their potential as novel targets for therapeutics to treat chronic pain.

Childhood stressors in the development of fatigue syndromes: a review of the past 20 years of research

BACKGROUND

Chronic fatigue syndrome (CFS) and fibromyalgia (FM) are both highly prevalent conditions associated with extreme disability and with the development of co-morbid psychiatric disorders, such as depression and anxiety. Childhood stressors have been shown to induce persistent changes in the function of biological systems potentially relevant to the pathogenesis of both CFS and FM, such as the inflammatory system and the hypothalamic-pituitary-adrenal (HPA) axis. In this review, we examined whether multiple forms of childhood stressors are contributing factors to the development of these disorders, and of the associated psychiatric symptoms.

METHOD

Using PubMed, we identified 31 papers relevant to this narrative review. We included cohort studies and case-control studies, without any exclusion in terms of age and gender. No study characteristics or publication date restrictions were imposed.

RESULTS

Most studies across the literature consistently show that there is a strong association between experiences of childhood stressors and the presence of CFS and FM, with rates of CFS/FM being two- to three-fold higher in exposed than in unexposed subjects. We also found evidence for an increased risk for the development of additional symptoms, such as depression, anxiety and pain, in individuals with CFS and FM with a previous history of childhood stressors, compared with individuals with CFS/FM and no such history.

CONCLUSIONS

Our review confirms that exposure to childhood stressors is associated with the subsequent development of fatigue syndromes such as CFS and FM, and related symptoms. Further studies are needed to identify the mechanisms underlying these associations.

Physiologic changes associated with violence and abuse exposure: an examination of related medical conditions

Although the extant evidence is replete with data supporting linkages between exposure to violence or abuse and the subsequent development of medical illnesses, the underlying mechanisms of these relationships are poorly defined and understood. Physiologic changes occurring in violence- or abuse-exposed individuals point to potentially common biological pathways connecting traumatic exposures with medical outcomes. Herein, the evidence describing the long-term physiologic changes in abuse- and violence-exposed populations and associated medical illnesses are reviewed. Current data support that (a) specific neurobiochemical changes are associated with exposure to violence and abuse; (b) several biological pathways have the potential to lead to the development of future illness; and (c) common physiologic mechanisms may moderate the severity, phenomenology, or clinical course of medical illnesses in individuals with histories of exposure to violence or abuse. Importantly, additional work is needed to advance our emerging understanding of the biological mechanisms connecting exposure to violence and abuse and negative health outcomes.

Fibromyalgia and depression

Fibromyalgia and depression might represent two manifestations of affective spectrum disorder. They share similar pathophysiology and are largely targeted by the same drugs with dual action on serotoninergic and noradrenergic systems. Here, we review evidence for genetic and environmental factors that predispose, precipitate, and perpetuate fibromyalgia and depression and include laboratory findings on the role of depression in fibromyalgia. Further, we comment on several aspects of fibromyalgia which support the development of reactive depression, substantially more so than in other chronic pain syndromes. However, while sharing many features with depression, fibromyalgia is associated with somatic comorbidities and absolutely defined by fluctuating spontaneous widespread pain. Fibromyalgia may, therefore, be more appropriately grouped together with other functional pain disorders, while psychologically distressed subgroups grouped additionally or solely with affective spectrum disorders.

A preliminary investigation of the effects of cognitive behavioral therapy for panic disorder on gastrointestinal distress in patients with comorbid panic disorder and irritable bowel syndrome

BACKGROUND

High comorbidity between panic disorder with/without agoraphobia (PD/A) and irritable bowel syndrome (IBS) has been identified in the literature. These findings have resulted in the recent development of neurobiological models to explain their overlapping symptoms and related origins. This study was a preliminary investigation of the influence of cognitive behavioral therapy (CBT) for PD/A on PD/A patients with and without comorbid IBS.

METHODS

All patients completed a thorough intake assessment, brief waitlist period, and a 12-week CBT group for PD/A.

RESULTS

The results demonstrated significant reductions in the symptoms of anxiety, depression, and overall impairment in both patient groups (ts>2.3; Ps<.05). In addition, PD/A patients with comorbid IBS also experienced reductions in the disability and distress associated with their gastrointestinal symptoms of IBS (ts>1.9; Ps<.07).

CONCLUSIONS

Although additional research still is needed, these preliminary findings suggest that CBT for PD/A can be used to simultaneously treat comorbid symptoms of PD/A and IBS. Implications for the neurobiological models for these comorbid conditions were discussed.

Early life adversity as a risk factor for fibromyalgia in later life

The impact of early life events is increasingly becoming apparent, as studies investigate how early childhood can shape long-term physiology and behaviour. Fibromyalgia (FM), which is characterised by increased pain sensitivity and a number of affective co-morbidities, has an unclear etiology. This paper discusses risk factors from early life that may increase the occurrence or severity of FM in later life: pain experience during neonatal life causes long-lasting changes in nociceptive circuitry and increases pain sensitivity in the older organism; premature birth and related stressor exposure cause lasting changes in stress responsivity; maternal deprivation affects anxiety-like behaviours that may be partially mediated by epigenetic modulation of the genome—all these adult phenotypes are strikingly similar to symptoms displayed by FM sufferers. In addition, childhood trauma and exposure to substances of abuse may cause lasting changes in developing neurotransmitter and endocrine circuits that are linked to anxiety and stress responses.

Dysfunctional neurotransmitter systems in fibromyalgia, their role in central stress circuitry and pharmacological actions on these systems

Fibromyalgia is considered a stress-related disorder, and hypo- as well as hyperactive stress systems (sympathetic nervous system and hypothalamic-pituitary-adrenal axis) have been found. Some observations raise doubts on the view that alterations in these stress systems are solely responsible for fibromyalgia symptoms. Cumulative evidence points at dysfunctional transmitter systems that may underlie the major symptoms of the condition. In addition, all transmitter systems found to be altered in fibromyalgia influence the body's stress systems. Since both transmitter and stress systems change during chronic stress, it is conceivable that both systems change in parallel, interact, and contribute to the phenotype of fibromyalgia. As we outline in this paper, subgroups of patients might exhibit varying degrees and types of transmitter dysfunction, explaining differences in symptomatoloy and contributing to the heterogeneity of fibromyalgia. The finding that not all fibromyalgia patients respond to the same medications, targeting dysfunctional transmitter systems, further supports this hypothesis.

Functional somatic syndromes, anxiety disorders and the upper airway: a matter of paradigms

The relationship between the functional somatic syndromes, anxiety disorders and the upper airway (particularly, sleep disordered breathing) remains ambiguous. This ambiguity, despite a growing body of research supporting a relationship, may result from the absence of a paradigm to explain how upper airway dysfunction can promote disorders commonly associated with one's mental health. This review models the functional somatic syndromes and anxiety disorders as consequences of chronically increased hypothalamic-pituitary-adrenal axis activity. It then examines the literature supporting a relationship between these disorders and upper airway dysfunction during wakefulness and sleep. Finally, building upon an existing paradigm of neural sensitization, sleep disordered breathing is linked to functional somatic syndromes and anxiety disorders through chronic activation of the hypothalamic-pituitary-adrenal axis.

The role of corticosteroids and stress in chronic pain conditions

The relationship between corticosteroids (endogenous and exogenous) and stress is well known, as is the use of steroids as concomitant treatment in pain management during acute inflammation. In the past, steroids have not been considered the first line of treatment in pain management. In this review, we examine new scientific and clinical evidence that demonstrates the direct role that steroids play in the generation and clinical management of chronic pain. We will discuss the new findings demonstrating the fact that steroids and related mediators produce paradoxical effects on pain such as analgesia, hyperalgesia, and even placebo analgesia. In addition, we will examine the physiologic effect of stress, high allostatic load, and idiopathic disease states such as chronic fatigue syndrome, fibromyalgia, irritable bowel syndrome, and burnout. The recently observed positive relationship between glutaminergic activity in the insula and clinical pain will be examined in the context of understanding the central role of steroids in chronic pain. The complex role of the hypothalamic-pituitary-adrenal axis in pain will be discussed as well as other heterogeneous forms of chronic pain that involve many components of the central nervous system. Components of the hypothalamic-pituitary-adrenal axis have paradoxical effects on certain types of pain that are dependent on dose and on site (whether peripheral or central) and mode of application. Recent studies on glia have shown that they prolong a state of neuronal hypersensitization in the dorsal root ganglia by releasing growth factors and other substances that act on the immune system. We will discuss the implication of these new findings directly linking pain to steroids, stress, and key higher brain regions in the context of future therapeutic targets.