Intensity dependence of auditory-evoked cortical potentials in fibromyalgia patients: a test of the generalized hypervigilance hypothesis

Deciphering nociplastic pain: clinical features, risk factors and potential mechanisms

Nociplastic pain is a mechanistic term used to describe pain that arises or is sustained by altered nociception, despite the absence of tissue damage. Although nociplastic pain has distinct pathophysiology from nociceptive and neuropathic pain, these pain mechanisms often coincide within individuals, which contributes to the intractability of chronic pain. Key symptoms of nociplastic pain include pain in multiple body regions, fatigue, sleep disturbances, cognitive dysfunction, depression and anxiety. Individuals with nociplastic pain are often diffusely tender - indicative of hyperalgesia and/or allodynia - and are often more sensitive than others to non-painful sensory stimuli such as lights, odours and noises. This Review summarizes the risk factors, clinical presentation and treatment of nociplastic pain, and describes how alterations in brain function and structure, immune processing and peripheral factors might contribute to the nociplastic pain phenotype. This article concludes with a discussion of two proposed subtypes of nociplastic pain that reflect distinct neurobiological features and treatment responsivity.

Attentional deficits in fibromyalgia: an ERP study with the oddball dual task and emotional stroop task

The present study investigated the neural correlates of attentional deficits in fibromyalgia through an Oddball Dual Task and an Emotional Stroop Task, both performed during EEG recordings. Thirty female participants were recruited, being divided into two groups: a group of patients with fibromyalgia (FM, n = 15, Mage = 51.87, SDage = 7.12) and a healthy control group (HC, n = 15, Mage = 46.13, SDage = 8.41). In the Emotional Stroop Task, the behavioural results showed that patients with FM had less hits and longer times reactions than healthy controls. These results were consistent with those obtained with our Event-related Potential (ERP) methodology, which evidenced that patients with FM had higher frontal latencies in the P200 time-window compared to healthy controls. Regarding the Oddball Dual Task, we found that patients with FM had lower P300 amplitudes than healthy participants. Moreover, we found that rare stimuli elicited higher P300 amplitudes than frequent stimuli for healthy controls, but this comparison was non-significant for patients with FM. Taken together, our results suggest that fibromyalgia may be associated to a reduced processing speed, along to reduced neural resources to process stimuli, mainly in distinguishing relevant (rare) and irrelevant (frequent) stimuli according to the goals of the task. Altogether, our results seem to support the hypothesis of generalized attentional deficits in FM.

Feasibility, reliability, and validity of ambulatory cognitive tests in fibromyalgia and matched controls

OBJECTIVE

This observational study examined the feasibility, reliability, and validity of repeated ambulatory cognitive tests in fibromyalgia (FM).

METHOD

Adults with FM (n = 50) and matched controls (n = 50) completed lab-based neuropsychological tests (NIH Toolbox) followed by eight days of smartphone-based ambulatory testing of processing speed (symbol search) and working memory (dot memory) five times daily. Feasibility was assessed based on response rates. Reliability was evaluated using overall average between-person reliabilities for the full assessment period and by determining the number of assessment days necessary to attain reliabilities of >.80 and >.90. To assess convergent validity, correlations were calculated between ambulatory test scores and NIH Toolbox scores. Test performance was contrasted between the FM and non-FM groups to examine known-groups validity.

RESULTS

Average rates of response to the ambulatory cognitive tests were 89.5% in FM and 90.0% in non-FM. Overall average between-person reliabilities were ≥.96. In FM, between-person reliability exceeded .90 after two days for symbol search and three days for dot memory. Symbol search scores correlated with NIH Toolbox processing speed scores in both groups, though there were no significant group differences in symbol search performance. Dot memory scores correlated with NIH Toolbox working memory scores in both groups. FM participants exhibited worse dot memory performance than did non-FM participants.

CONCLUSIONS

Repeated ambulatory tests of processing speed and working memory demonstrate feasibility and reliability in FM, though evidence for construct validity is mixed. The findings demonstrate promise for future research and clinical applications of this approach to assessing cognition in FM.

Neural indices of multimodal sensory and autonomic hyperexcitability in fibromyalgia

Fibromyalgia (FM) is characterized by chronic widespread musculoskeletal pain and psychological distress. Research suggests people with FM experience increased somatosensory sensitization which generalizes to other sensory modalities and may indicate neural hyperexcitability. However, the available evidence is limited, and studies including measures of neural responsivity across sensory domains and both central and peripheral aspects of the neuraxis are lacking. Thirty-nine participants (51.5 ± 13.6 years of age) with no history of neurological disorders, psychosis, visual, auditory, or learning deficits, were recruited for this study. People with FM (N = 19) and control participants (CNT, N = 20) did not differ on demographic variables and cognitive capacity. Participants completed a task that combined innocuous auditory stimuli with electrocutaneous stimulation (ECS), delivered at individually-selected levels that were uncomfortable but not painful. Event-related potentials (ERPs) and electrodermal activity were analyzed to examine the central and sympathetic indices of neural responsivity. FM participants reported greater sensitivity to ECS and auditory stimulation, as well as higher levels of depression, anxiety, ADHD, and an array of pain-related experiences than CNT. In response to ECS, the P50 deflection was greater in FM than CNT participants, reflecting early somatosensory hyperexcitability. The P50 amplitude was positively correlated with the FM profile factor obtained with a principal component analysis. The N100 to innocuous tones and sympathetic reactivity to ECS were greater in FM participants, except in the subgroup treated with gabapentinoids, which aligns with previous evidence of symptomatic improvement with GABA-mimetic medications. These results support the principal tenet of generalized neural hyperexcitability in FM and provide preliminary mechanistic insight into the impact of GABA-mimetic pharmacological therapy on ameliorating the neural excitation dominance.

Neurophysiological and Psychosocial Mechanisms of Fibromyalgia: A Comprehensive Review and Call for An Integrative Model

Research into the neurobiological and psychosocial mechanisms involved in fibromyalgia has progressed remarkably in recent years. Despite this, current accounts of fibromyalgia fail to capture the complex, dynamic, and mutual crosstalk between neurophysiological and psychosocial domains. We conducted a comprehensive review of the existing literature in order to: a) synthesize current knowledge on fibromyalgia; b) explore and highlight multi-level links and pathways between different systems; and c) build bridges connecting disparate perspectives. An extensive panel of international experts in neurophysiological and psychosocial aspects of fibromyalgia discussed the collected evidence and progressively refined and conceptualized its interpretation. This work constitutes an essential step towards the development of a model capable of integrating the main factors implicated in fibromyalgia into a single, unified construct which appears indispensable to foster the understanding, assessment, and intervention for fibromyalgia.

Relationship of loudness-dependent auditory evoked potentials with change-related cortical responses

Previous studies have suggested that change-related cortical responses are phenomena similar to the onset response and could be applied to the loudness dependence of auditory evoked potential (LDAEP) paradigm. In the present study, we examined the relationship between LDAEP and the change-related response using electroencephalography findings in 50 healthy subjects. There were five conditions (55, 65, 75, 85, and 95 dB) for LDAEP and five similar conditions (abrupt sound pressure increase from 70 to 75, 80, 85, 90, and 95 dB) for the change-related response. Both the onset and abrupt sound pressure increase evoked a triphasic response with peaks at approximately 50 (P50), 100 (N100), and 200 (P200) ms. We calculated the peak-to-peak amplitudes for P50/N100 and N100/P200. Medians and slopes for P50/N100 and N100/P200 amplitudes were calculated and compared between the two measures. Results revealed a significant correlation for both the slope and median for P50/N100 (r = 0.36, 0.37, p = 1.0 × 10⁻², 7.9 × 10⁻³), N100/P200 (r = 0.40, 0.34, p = 4.0 × 10⁻³, 1.6 × 10⁻²), and P50/N100/P200 (r = 0.36, 0.35, p = 1.0 × 10⁻², 1.3 × 10⁻²). These results suggested that the change-related response and LDAEP shared generation mechanisms at least partially.

Neurofeedback Therapy for Sensory Over-Responsiveness-A Feasibility Study

Background: Difficulty in modulating multisensory input, specifically the sensory over-responsive (SOR) type, is linked to pain hypersensitivity and anxiety, impacting daily function and quality of life in children and adults. Reduced cortical activity recorded under resting state has been reported, suggestive of neuromodulation as a potential therapeutic modality. This feasibility study aimed to explore neurofeedback intervention in SOR. Methods: Healthy women with SOR (n = 10) underwent an experimental feasibility study comprising four measurement time points (T1—baseline; T2—preintervention; T3—postintervention; T4—follow-up). Outcome measures included resting-state EEG recording, in addition to behavioral assessments of life satisfaction, attaining functional goals, pain sensitivity, and anxiety. Intervention targeted the upregulation of alpha oscillatory power over ten sessions. Results: No changes were detected in all measures between T1 and T2. Exploring the changes in brain activity between T2 and T4 revealed power enhancement in delta, theta, beta, and gamma oscillatory bands, detected in the frontal region (p = 0.03−<0.001; Cohen’s d = 0.637−1.126) but not in alpha oscillations. Furthermore, a large effect was found in enhancing life satisfaction and goal attainment (Cohen’s d = 1.18; 1.04, respectively), and reduced pain sensitivity and anxiety trait (Cohen’s d = 0.70). Conclusion: This is the first study demonstrating the feasibility of neurofeedback intervention in SOR.

Neural correlates of the attentional bias towards pain-related faces in fibromyalgia patients: An ERP study using a dot-probe task

BACKGROUND

One of the major cognitive deficits in fibromyalgia has been linked to the hypervigilance phenomenon. It is mainly reflected as a negative bias for allocating attentional resources towards both threatening and pain-related information. Although the interest in its study has recently grown, the neural temporal dynamics of the attentional bias in fibromyalgia still remains an open question.

METHOD

Fifty participants (25 fibromyalgia patients and 25 healthy control subjects) performed a dot-probe task. Two types of facial expressions (pain-related and neutral) were employed as signal stimuli. Then, as a target stimulus, a single dot replaced the location of one of these two faces. Event-related potentials (ERP) in response to facial expressions and target stimulation (i.e., dot) were recorded. Reaction time (RT) and accuracy measures in the experimental task were collected as behavioural outcomes.

RESULTS

Temporal dynamics of brain electrical activity were analysed on two ERP components (P2 and N2a) sensitive to the facial expressions meaning. Pain-related faces elicited higher frontal P2 amplitudes than neutral faces for the whole sample. Interestingly, an interaction effect between group and facial expressions was also found showing that pain-related faces elicited enhanced P2 amplitudes (at fronto-central regions, in this case) compared to neutral faces only when the group of patients was considered. Furthermore, higher P2 amplitudes were observed in response to pain-related faces in patients with fibromyalgia compared to healthy control participants. Additionally, a shorter latency of P2 (at centro-parietal regions) was also detected for pain-related facial expressions compared to neutral faces. Regarding the amplitude of N2a, it was lower for patients as compared to the control group. Non-relevant effects of the target stimulation on the ERPs were found. However, patients with fibromyalgia exhibited slower RT to locate the single dot for incongruent trials as compared to congruent and neutral trials.

CONCLUSIONS

Data suggest the presence of an attentional bias in fibromyalgia that it would be followed by a deficit in the allocation of attentional resources to further process pain-related information. Altogether the current results suggest that attentional biases in fibromyalgia might be explained by automatic attentional mechanisms, which seem to be accompanied by an alteration of more strategic or controlled attentional components.

Auditory change-related cortical response is associated with hypervigilance to pain in healthy volunteers

Background

Patients with chronic pain exhibit hypervigilance (heightened responsiveness to stimuli) to innocuous auditory stimuli as well as noxious stimuli. “Generalized hypervigilance” suggests that individuals who show heightened responsiveness to one sensory system also show hypervigilance to other modalities. However, research exploring the existence of generalized hypervigilance in healthy subjects is limited.

Methods

We investigated whether hypervigilance to pain is associated with auditory stimuli in healthy subjects using the pain vigilance and awareness questionnaire (PVAQ) and auditory change‐related cortical responses (ACRs). ACRs are thought to reflect a change detection system, based on preceding sensory memory. We recorded ACRs under conditions that varied in terms of the accumulation of sensory memory as follows: short‐ACR, with short preceding continuous stimuli and long‐ACR, with long preceding continuous stimuli. In addition, the attention to pain (PVAQ‐AP) and attention to changes in pain (PVAQ‐ACP) subscales were evaluated.

Results

Amplitudes of long‐ACR showed significant positive correlations with PVAQ‐ACP, whereas those of short‐ACR did not show any significant correlations.

Conclusions

Generalized hypervigilance may be observed even in healthy subjects. ACR may be a useful index to evaluate the hypervigilance state in the human brain.

Fibromyalgia Patients Are Not Only Hypersensitive to Painful Stimuli But Also to Acoustic Stimuli

Fibromyalgia is a chronic widespread pain syndrome associated with hypersensitivity to nociceptive stimuli. This increased sensitivity of FM patients has been associated with central sensitization of dorsal horn neurons. Increasing evidence, however, suggests that the mechanisms of FM hypersensitivity not only affect pain but include light, smell, and sound. We hypothesized that supraspinal augmentation of sensory input including sound represent a hallmark of FM. We tested 23 FM patients and 28 healthy controls (HC) for sensory augmentation of nociceptive and non-nociceptive sensations: For assessment of nociceptive augmentation we used sensitivity adjusted mechanical and heat ramp & hold stimuli and for assessment of sound augmentation, we applied wideband noise stimuli using a random-staircase design. Quantitative sensory testing demonstrated increased heat and mechanical pain sensitivity in FM participants (P < .001). The sound pressures needed to report mild, moderate, and intense sound levels were significantly lower in FM compared to HC (P < .001), consistent with auditory augmentation. FM patients are not only augmenting noxious sensations but also sound, suggesting that FM augmentation mechanisms are not only operant in the spinal cord but also in the brain. Whether the central nervous system mechanisms for auditory and nociceptive augmentation are similar, needs to be determined in future studies. PERSPECTIVE: This study presents QST evidence that the hypersensitivity of FM patients is not limited to painful stimuli but also to innocuous stimuli like sound. Our results suggest that abnormal brain mechanisms may be responsible for the increased sensitivity of FM patients.

Effects of intensity, attention and medication on auditory-evoked potentials in patients with fibromyalgia

Fibromyalgia (FM) has been associated to an increased processing of somatosensory stimuli, but its generalization to other sensory modalities is under discussion. To clarify this, we studied auditory event-related potentials (AEPs) to stimuli of different intensity in patients with FM and healthy controls (HCs), considering the effects of attention mechanisms and medication. We performed two experiments: In study 1 (n = 50 FM, 60 HCs), the stimuli were presented randomly within the sequence; in study 2 (n = 28 FM, 30 HCs), they were presented in blocks of the same intensity. We analyzed intensity and group effects on N1-P2 amplitude and, only for the FM group, the effect of medication and the correlation between AEPs and clinical variables. Contrary to the expectation, the patients showed a trend of reduced AEPs to the loudest tones (study 1) or no significant differences with the HCs (study 2). Medication with central effects significantly reduced AEPs, while no significant relationships between the N1-P2 amplitude/intensity function and patients’ symptoms were observed. The findings do not provide evidence of augmented auditory processing in FM. Nevertheless, given the observed effect of medication, the role of sensory amplification as an underlying pathophysiological mechanism in fibromyalgia cannot be discarded.

Bildgebende Untersuchungen des neuronalen Schmerznetzwerks

Der vorliegende Artikel soll eine Übersicht über bildgebende Untersuchungen im Bereich chronischer Schmerzsyndrome bieten. Auf die einleitenden Worte zur allgemeinen Phänomenologie des Schmerzes folgt ein umfassender Einblick in die gegenwärtige Anwendung funktioneller und struktureller Bildgebungstechniken am Beispiel ausgewählter Schmerzsyndrome (Chronischer Rückenschmerz, Fibromyalgiesyndrom (FMS), Phantomschmerz und Komplexes regionales Schmerzsyndrom (CRPS)). In diesem Zusammenhang werden Gemeinsamkeiten und Besonderheiten der spezifischen neurologischen Korrelate verschiedener chronischer Schmerzerkrankungen diskutiert.

Effects of COMT Genotypes on Working Memory Performance in Fibromyalgia Patients

Growing research has reported the presence of a clear impairment of working memory functioning in fibromyalgia. Although different genetic factors involving dopamine availability (i.e, the COMT gene) have been associated with the more severe presentation of key symptoms in fibromyalgia, scientific evidence regarding the influence of COMT genotypes on cognitive impairment in these patients is still lacking. To this end, 167 participants took part in the present investigation. Working memory performance was assessed by the application of the SST (Spatial Span Test) and LNST (Letter and Number Sequence Test) belonging to the Weschler Memory Scale III. Significant working memory impairment was shown by the fibromyalgia patients. Remarkably, our results suggest that performance according to different working memory measures might be influenced by different genotypes of the COMT gene. Specifically, fibromyalgia patients carrying the Val/Val genotype exhibited significantly worse outcomes for the span of SST backward, SST backward score, SST total score and the Working Memory Index (WMI) than the Val/Val healthy carriers. Furthermore, the Val/Val patients performed worse on the SST backward and SST score than heterozygotes. Our findings are the first to show a link between the COMT gene and working memory dysfunction in fibromyalgia, supporting the idea that higher COMT enzyme activity would contribute to more severe working memory impairment in fibromyalgia.

Aberrant Salience? Brain Hyperactivation in Response to Pain Onset and Offset in Fibromyalgia

OBJECTIVE

While much brain research on fibromyalgia (FM) focuses on the study of hyperresponsiveness to painful stimuli, some studies suggest that the increased pain-related brain activity often reported in FM studies may be partially explained by stronger responses to salient aspects of the stimulation rather than, or in addition to, the stimulation's painfulness. Therefore, this study was undertaken to test our hypothesis that FM patients would demonstrate elevated brain responses to both pain onset and offset-2 salient sensory events of opposing valences.

METHODS

Thirty-eight FM patients (mean ± SD age 46.1 ± 13.4 years; 33 women) and 15 healthy controls (mean ± SD age 45.5 ± 12.4; 10 women) received a moderately painful pressure stimulus to the leg during blood oxygen level-dependent (BOLD) functional magnetic resonance imaging. Stimulus onset and offset transients were analyzed using a general linear model as stick functions.

RESULTS

During pain onset, higher BOLD signal response was observed in FM patients compared to healthy controls in dorsolateral and ventrolateral prefrontal cortices (DLPFC and VLPFC, respectively), orbitofrontal cortex (OFC), frontal pole, and precentral gyrus (PrCG). During pain offset, higher and more widespread BOLD signal response was demonstrated in FM patients compared to controls in frontal regions significantly hyperactivated in response to onset. In FM patients, some of these responses were positively correlated with pain unpleasantness ratings (VLPFC, onset; r = 0.35, P = 0.03), pain catastrophizing scores (DLPFC, offset; r = 0.33, P = 0.04), or negatively correlated with stimulus intensity (OFC, offset; r = -0.35, P = 0.03) (PrCG, offset; r = -0.39, P = 0.02).

CONCLUSION

Our results suggest that the increased sensitivity exhibited by FM patients in response to the onset and offset of painful stimuli may reflect a more generalized hypersensitivity to salient sensory events, and that brain hyperactivation may be a mechanism potentially involved in the generalized hypervigilance to salient stimuli in FM.

The Role of Environmental Distractions in the Experience of Fibrofog in Real-World Settings

Objective

Perceived cognitive dysfunction in people with fibromyalgia (FM), “fibrofog,” is commonly reported and has been demonstrated in neurocognitive testing. Distractibility and inattention have been implicated as potential contributors to fibrofog, but the role of environmental distractions has not been explored. In this study, ambulatory assessment methods were used to examine whether FM is related to more environmental distractions and to examine the impact of distractions on subjective and objective cognitive functioning.

Methods

Fifty people with FM and 50 age‐, sex‐, and education‐matched controls without FM completed 8 consecutive days of ambulatory assessments. Five times per day, participants reported perceived cognitive functioning and environmental distractions and completed validated tests of processing speed and working memory.

Results

The FM group reported distractions in a higher proportion of the ambulatory cognitive testing sessions (40.5%) compared with the group without FM (29.8%; P < 0.001) and more often reported multiple simultaneous distractions. For both groups, sound was the most common distraction. The group with FM reported more distractions caused by light, and the group without FM reported more social distractions. Group differences in subjective and objective cognitive functioning were not augmented during distraction relative to during periods of no distraction. There were no group differences in within‐person changes in cognitive functioning as a function of distraction.

Conclusion

The group with FM reported more distractions than the group without FM; both groups reported poorer processing speed when distracted, and the effects of distraction on test performance did not differ significantly by group. Findings suggest that sensitivity to environmental distractions may play a role in the experience of cognitive dysfunction in FM.

The LURN Research Network Neuroimaging and Sensory Testing (NIST) Study: Design, protocols, and operations

The Neuroimaging and Sensory Testing (NIST) Study of the Symptoms of Lower Urinary Tract Dysfunction Research Network (LURN) is a cross-sectional, case-control study designed to investigate whether disrupted brain connectivity and sensory processing are associated with abnormal lower urinary tract symptoms (LUTS) in patients with overactive bladder syndrome (OAB). The NIST Study tests the hypotheses that patients with urinary urgency will demonstrate: (1) abnormal functional and structural connectivity of brain regions involved in urinary sensation on magnetic resonance imaging (MRI), and (2) hypersensitivity to painful (pressure) and non-painful (auditory) sensory stimuli on quantitative sensory testing (QST), compared to controls. Male and female adults (18 years or older) who present at one of the six participating LURN clinical centers for clinical care of their LUTS, with symptoms of urinary urgency with or without urgency urinary incontinence, are eligible to participate. The NIST Study is the largest MRI and QST study of its kind, yielding a neuroimaging and sensory testing dataset unprecedented in OAB research. Advanced multi-modal techniques are used to understand brain functional and structural connectivity, including gray matter volume, and sensory function. Unlike previous MRI studies which involved invasive catheterization and repeated cycles of non-physiologic bladder filling and emptying via a catheter, we use a water ingestion protocol to mimic more physiological bladder filling through natural diuresis. Furthermore, these data will be used in concert with other phenotyping data to improve our understanding of clinically meaningful subtypes of patients with LUTS in order to improve patient care and management outcomes.

Altered theta oscillations in resting EEG of fibromyalgia syndrome patients

Background

Fibromyalgia syndrome (FM) is a chronic pain disorder characterized by widespread pain, sleep disturbance, fatigue and cognitive/affective symptoms. Functional imaging studies have revealed that FM and other chronic pain syndromes can affect resting brain activity. This study utilized electroencephalographic (EEG) recordings to investigate the relative power of ongoing oscillatory activity in the resting brain.

Methods

A 64‐channel EEG was recorded at rest in 19 female FM patients and 18 healthy, age‐matched, control subjects. The Manual Tender Point Scale (MTPS) examination was performed to quantify tonic pain and tenderness on the day of testing along with measures of mood, arousal and fatigue. Oscillations in delta, theta, alpha, beta and gamma frequency bands were analysed using Standardised Low‐Resolution Brain Electromagnetic Tomography to evaluate sources of spectral activity throughout the whole brain.

Results

FM patients exhibited greater pain, tiredness and tension on the day of testing relative to healthy control participants and augmented theta activity in prefrontal and anterior cingulate cortices. No significant differences were seen in other frequency bands. Augmented frontal theta activity in FM patients significantly correlated with measures of tenderness and mean tiredness scores.

Conclusions

The findings indicate that alterations to resting‐state oscillatory activity may relate to ongoing tonic pain and fatigue in FM, and manifest in brain regions relevant for cognitive‐attentional aspects of pain processing and endogenous pain inhibition. Enhanced low‐frequency oscillations were previously seen in FM and other chronic pain syndromes, and may relate to pathophysiological mechanisms for ongoing pain such as thalamocortical dysrhythmia.

Significance

Increased prefrontal theta activity may contribute to persistent pain in fibromyalgia or represent the outcome of prolonged symptoms. The findings point to the potential for therapeutic interventions aimed at normalizing neural oscillations, while further research utilizing quantitative analysis of resting EEG could benefit our understanding of fibromyalgia pathophysiology.

Pharmacologic attenuation of cross-modal sensory augmentation within the chronic pain insula

Supplemental Digital Content is Available in the Text.

Sensitivity to visual stimuli is increased in patients with fibromyalgia and improved with administration of pregabalin.

Pain can be elicited through all mammalian sensory pathways yet cross-modal sensory integration, and its relationship to clinical pain, is largely unexplored. Centralized chronic pain conditions such as fibromyalgia are often associated with symptoms of multisensory hypersensitivity. In this study, female patients with fibromyalgia demonstrated cross-modal hypersensitivity to visual and pressure stimuli compared with age- and sex-matched healthy controls. Functional magnetic resonance imaging revealed that insular activity evoked by an aversive level of visual stimulation was associated with the intensity of fibromyalgia pain. Moreover, attenuation of this insular activity by the analgesic pregabalin was accompanied by concomitant reductions in clinical pain. A multivariate classification method using support vector machines (SVM) applied to visual-evoked brain activity distinguished patients with fibromyalgia from healthy controls with 82% accuracy. A separate SVM classification of treatment effects on visual-evoked activity reliably identified when patients were administered pregabalin as compared with placebo. Both SVM analyses identified significant weights within the insular cortex during aversive visual stimulation. These data suggest that abnormal integration of multisensory and pain pathways within the insula may represent a pathophysiological mechanism in some chronic pain conditions and that insular response to aversive visual stimulation may have utility as a marker for analgesic drug development.

Generalized hypervigilance in fibromyalgia: Normal interoceptive accuracy, but reduced self-regulatory capacity

OBJECTIVE

The factors underlying the aetiology of fibromyalgia (FM) are largely unknown. According to the generalized hypervigilance hypothesis (GHH), FM patients show excessive attention towards pain stimuli and other sensory events, thereby increasing pain perception and dysfunctional behaviour. We tested this notion by assessing interoceptive accuracy (IA) in FM patients and matched healthy controls. We also tested the hypothesis that FM is characterized by reduced self-regulatory capacity as indexed by heart rate variability (HRV).

METHODS

47 FM patients (M_age=45.5, 39 females) and 45 healthy controls (M_age=44.9, 37 females) completed several self-report scales (Body Vigilance Scale, Depression Anxiety Stress Scales, Pain Catastrophizing Scale). To derive HRV, heart rate was monitored under resting conditions; for the assessment of IA participants performed a heartbeat tracking task in which they were asked to silently count their heartbeats.

RESULTS

FM patients reported higher body vigilance than healthy controls, but there were no group differences in IA. FM patients had lower HRV compared with healthy controls. HRV did not predictor IA.

CONCLUSION

In conclusion, our findings do not support the hypothesis of generalized hypervigilance in FM patients. Patients reported a heightened focus on bodily sensations, which was not reflected in IA. It may be that hypervigilance is not a general and stable characteristic but is rather context dependent and modality-specific.

A possible neural mechanism for photosensitivity in chronic pain

Patients with functional pain disorders often complain of generalized sensory hypersensitivity, finding sounds, smells, or even everyday light aversive. The neural basis for this aversion is unknown, but it cannot be attributed to a general increase in cortical sensory processing. Here, we quantified the threshold for aversion to light in patients with fibromyalgia, a pain disorder thought to reflect dysregulation of pain-modulating systems in the brain. These individuals expressed discomfort at light levels substantially lower than that of healthy control subjects. Complementary studies in lightly anesthetized rat demonstrated that a subset of identified pain-modulating neurons in the rostral ventromedial medulla unexpectedly responds to light. Approximately half of the pain-facilitating "ON-cells" and pain-inhibiting "OFF-cells" sampled exhibited a change in firing with light exposure, shifting the system to a pronociceptive state with the activation of ON-cells and suppression of OFF-cell firing. The change in neuronal firing did not require a trigeminal or posterior thalamic relay, but it was blocked by the inactivation of the olivary pretectal nucleus. Light exposure also resulted in a measurable but modest decrease in the threshold for heat-evoked paw withdrawal, as would be expected with engagement of this pain-modulating circuitry. These data demonstrate integration of information about light intensity with somatic input at the level of single pain-modulating neurons in the brain stem of the rat under basal conditions. Taken together, our findings in rodents and humans provide a novel mechanism for abnormal photosensitivity and suggest that light has the potential to engage pain-modulating systems such that normally innocuous inputs are perceived as aversive or even painful.

Towards a neurophysiological signature for fibromyalgia

Patients with fibromyalgia (FM) show characteristically enhanced unpleasantness to painful and nonpainful sensations accompanied by altered neural responses. The diagnostic potential of such neural alterations, including their sensitivity and specificity to FM (vs healthy controls) is unknown. We identify a brain signature that characterizes FM central pathophysiology at the neural systems level. We included 37 patients with FM and 35 matched healthy controls, and analyzed functional magnetic resonance imaging responses to (1) painful pressure and (2) nonpainful multisensory (visual-auditory-tactile) stimulation. We used machine-learning techniques to identify a brain-based FM signature. When exposed to the same painful stimuli, patients with FM showed greater neurologic pain signature (NPS; Wager et al., 2013. An fMRI-based neurologic signature of physical pain. N Engl J Med 2013;368:1388-97) responses. In addition, a new pain-related classifier ("FM-pain") revealed augmented responses in sensory integration (insula/operculum) and self-referential (eg, medial prefrontal) regions in FM and reduced responses in the lateral frontal cortex. A "multisensory" classifier trained on nonpainful sensory stimulation revealed augmented responses in the insula/operculum, posterior cingulate, and medial prefrontal regions and reduced responses in the primary/secondary sensory cortices, basal ganglia, and cerebellum. Combined activity in the NPS, FM pain, and multisensory patterns classified patients vs controls with 92% sensitivity and 94% specificity in out-of-sample individuals. Enhanced NPS responses partly mediated mechanical hypersensitivity and correlated with depression and disability (Puncorrected < 0.05); FM-pain and multisensory responses correlated with clinical pain (Puncorrected < 0.05). The study provides initial characterization of individual patients with FM based on pathophysiological, symptom-related brain features. If replicated, these brain features may constitute objective neural targets for therapeutic interventions. The results establish a framework for assessing therapeutic mechanisms and predicting treatment response at the individual level.

The Association of Sensory Responsiveness with Somatic Symptoms and Illness Anxiety

BACKGROUND

Somatoform Disorders or Somatic Symptom and Related Disorders are a major public health problem.The pathophysiology underlying these disorders is not yet understood.

PURPOSE

The aim of this study was to explore if sensory responsiveness could contribute to a better understanding of pathophysiological mechanisms underlying two key symptoms of Somatoform Disorders, namely somatic symptoms and illness anxiety.

METHODS

We measured vibrotactile perception thresholds with the HVLab Perception Meter and examined their association with somatic symptoms, illness anxiety and trait anxiety. A sample of 205 volunteers participated in the study.

RESULTS

Sensory responsiveness was neither associated with somatic symptoms (β = -0.01; 95% confidence interval (CI), -0.37, 0.39) nor trait anxiety (β = -0.07; 95% CI, -0.30, 0.07). However, lower vibrotactile perception thresholds were associated with increased scores of the overall illness anxiety scale (β = -0.65; 95% CI, -1.21, -0.14) and its constituent subscale disease conviction (β = -2.07; 95% CI, -3.94, -0.43).

CONCLUSIONS

Our results suggest that increased sensory responsiveness is associated with illness anxiety and hence should be examined further as potential target within the etiopathology of somatoform disorders.

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.

Vitamin D in Fibromyalgia: A Causative or Confounding Biological Interplay?

Fibromyalgia (FM) is a chronic syndrome with an increasing prevalence, characterized by widespread musculoskeletal pain in combination with a variety of cognitive symptoms and fatigue. A plethora of scientific evidence that has accumulated during the last decades, resulted in a significant improvement of the understanding of the pathophysiology of the disease. However, current therapeutic approaches in patients with FM remains a multidimensional approach including patient education, behavioral therapy, exercise, pain management, and relief of chronic symptoms, rather than the use drug therapies, based on the mechanisms of disease development. Vitamin D, a fat-soluble vitamin derived mainly from skin synthesis through ultraviolet radiation, has been recognized to manifest a plethora of extraskeletal actions, apart from its fundamental role in skeletal and calcium homeostasis, including modulation of cell growth, neuromuscular actions, and potential anti-inflammatory properties. Recent findings indicate that hypovitaminosis D to be highly prevalent in patients with FM. Supplementation studies are limited so far, indicating potential beneficial effects on pain and severity of the disease, however specific recommendations are lacking. This review aims to summarize and critically appraise data regarding the pathophysiological interplay between vitamin D and FM, available results from observational and supplementation studies so far, with a clinical discourse on current knowledge gaps and future research agenda.

A Brain Signature to Differentiate Acute and Chronic Pain in Rats

The transition from acute pain to chronic pain entails considerable changes of patients at multiple levels of the nervous system and in psychological states. An accurate differentiation between acute and chronic pain is essential in pain management as it may help optimize analgesic treatments according to the pain state of patients. Given that acute and chronic pain could modulate brain states in different ways and that brain states could greatly shape the neural processing of external inputs, we hypothesized that acute and chronic pain would show differential effects on cortical responses to non-nociceptive sensory information. Here by analyzing auditory-evoked potentials (AEPs) to pure tones in rats with acute or chronic pain, we found opposite influences of acute and chronic pain on cortical responses to auditory inputs. In particular, compared to no-pain controls, the N100 wave of rat AEPs was significantly enhanced in rats with acute pain but significantly reduced in rats with chronic pain, indicating that acute pain facilitated cortical processing of auditory information while chronic pain exerted an inhibitory effect. These findings could be justified by the fact that individuals suffering from acute or chronic pain would have different vigilance states, i.e., the vigilance level to external sensory stimuli would be increased with acute pain, but decreased with chronic pain. Therefore, this auditory response holds promise of being a brain signature to differentiate acute and chronic pain. Instead of investigating the pain system per se, the study of pain-induced influences on cortical processing of non-nocicpetive sensory information might represent a potential strategy to monitor the progress of pain chronification in clinical applications.

Altered functional magnetic resonance imaging responses to nonpainful sensory stimulation in fibromyalgia patients

OBJECTIVE

Fibromyalgia (FM) is a disorder characterized by chronic pain and enhanced responses to acute noxious events. However, the sensory systems affected in FM may extend beyond pain itself, as FM patients show reduced tolerance to non-nociceptive sensory stimulation. Characterizing the neural substrates of multisensory hypersensitivity in FM may thus provide important clues about the underlying pathophysiology of the disorder. The aim of this study was to characterize brain responses to non-nociceptive sensory stimulation in FM patients and their relationship to subjective sensory sensitivity and clinical pain severity.

METHODS

Functional magnetic resonance imaging (MRI) was used to assess brain response to auditory, visual, and tactile motor stimulation in 35 women with FM and 25 matched controls. Correlation and mediation analyses were performed to establish the relationship between brain responses and 3 types of outcomes: subjective hypersensitivity to daily sensory stimulation, spontaneous pain, and functional disability.

RESULTS

Patients reported increased subjective sensitivity (increased unpleasantness) in response to multisensory stimulation in daily life. Functional MRI revealed that patients showed reduced task-evoked activation in primary/secondary visual and auditory areas and augmented responses in the insula and anterior lingual gyrus. Reduced responses in visual and auditory areas were correlated with subjective sensory hypersensitivity and clinical severity measures.

CONCLUSION

FM patients showed strong attenuation of brain responses to nonpainful events in early sensory cortices, accompanied by an amplified response at later stages of sensory integration in the insula. These abnormalities are associated with core FM symptoms, suggesting that they may be part of the pathophysiology of the disease.

Impaired pre-attentive auditory processing in fibromyalgia: A mismatch negativity (MMN) study

OBJECTIVE

Fibromyalgia (FM) patients often show deficits in cognitive functions such as attention and working memory. We assumed that pre-attentive information processing, a crucial element in human perception and cognition, would be altered in FM patients. Thus, the objective of this study was to determine whether FM patients exhibit alterations in pre-attentive processing as assessed by auditory mismatch negativity (MMN).

METHODS

Auditory evoked magnetic fields were recorded in FM patients (n=18) and healthy control subjects (n=21) during a duration-deviant auditory oddball paradigm. The magnetic mismatch negativity (MMNm) was obtained by subtracting responses to standard tones from responses to deviant tones. Pressure pain thresholds over the thenar and trapezius muscles were determined using an algometer.

RESULTS

MMNm peak amplitudes in right hemispheres were attenuated, and the directional asymmetry coefficient of the MMNm amplitude was lower in FM patients, indicating a more leftward asymmetry than in healthy control subjects. Smaller right MMNm amplitude was associated with lower pressure pain thresholds of thenar muscles in FM patients.

CONCLUSIONS

Our results suggested that pre-attentive processing of auditory information is impaired in FM patients.

SIGNIFICANCE

This study provided neurophysiological evidence of impaired pre-attentive sensory change detection in FM.

Profiles in fibromyalgia: algometry, auditory evoked potentials and clinical characterization of different subtypes

The heterogeneity found in fibromyalgia (FM) patients has led to the investigation of disease subgroups, mainly based on clinical features. The aim of this study was to test the hypothesis that clinical FM subgroups are associated with different underlying pathophysiological mechanisms. Sixty-three FM patients were classified in type I or type II, according to the Fibromyalgia Impact Questionnaire (FIQ), and in mild/moderate versus severe FM, according to the severity of three cardinal symptoms considered in the American College of Rheumatology (ACR) 2010 criteria (unrefreshed sleep, cognitive problems and fatigue). To validate the subgroups obtained by these two classifications, we calculated the area under the receiver operating characteristic curves for various clinical variables and for two potential biomarkers of FM: Response to experimental pressure pain (algometry) and the amplitude/intensity slopes of the auditory evoked potentials (AEPs) obtained to stimuli of increasing intensity. The variables that best discriminated type I versus type II were those related to depression, while the indices of clinical or experimental pain (threshold or tolerance) did not significantly differ between them. The variables that best discriminated the mild/moderate versus severe subgroups were those related to the algometry. The AEPs did not allow discrimination among the generated subsets. The FIQ-based classification allows the identification of subgroups that differ in psychological distress, while the index based on the ACR 2010 criteria seems to be useful to characterize the severity of FM mainly based on hyperalgesia. The incorporation of potential biomarkers to generate or validate classification criteria is crucial to advance in the knowledge of FM and in the understanding of pathophysiological pathways.

Behavioral and neuronal investigations of hypervigilance in patients with fibromyalgia syndrome

Painful stimuli are of utmost behavioral relevance and thereby affect attentional resources. In health, variable effects of pain on attention have been observed, indicating alerting as well as distracting effects of pain. In the human brain, these effects are closely related to modulations of neuronal gamma oscillations. As hypervigilance as an abnormal increase of attention to external stimuli has been implicated in chronic pain states, we assumed both attentional performance and pain-induced gamma oscillations to be altered in patients with fibromyalgia syndrome (FMS). We recorded electroencephalography from healthy subjects (n = 22) and patients with FMS (n = 19) during an attention demanding visual reaction time task. In 50% of the trials we applied painful laser stimuli. The results of self-assessment questionnaires confirm that patients with FMS consider themselves hypervigilant towards pain as compared to healthy controls. However, the experimental findings indicate that the effects of painful stimuli on attentional performance and neuronal gamma oscillations do not differ between patients and healthy subjects. We further found a significant correlation between the pain-induced modulation of visual gamma oscillations and the pain-induced modulation of reaction times. This relationship did not differ between groups either. These findings confirm a close relationship between gamma oscillations and the variable attentional effects of pain, which appear to be comparable in health and disease. Thus, our results do not provide evidence for a behavioral or neuronal manifestation of hypervigilance in patients with FMS.

Neurobiology underlying fibromyalgia symptoms

Fibromyalgia is characterized by chronic widespread pain, clinical symptoms that include cognitive and sleep disturbances, and other abnormalities such as increased sensitivity to painful stimuli, increased sensitivity to multiple sensory modalities, and altered pain modulatory mechanisms. Here we relate experimental findings of fibromyalgia symptoms to anatomical and functional brain changes. Neuroimaging studies show augmented sensory processing in pain-related areas, which, together with gray matter decreases and neurochemical abnormalities in areas related to pain modulation, supports the psychophysical evidence of altered pain perception and inhibition. Gray matter decreases in areas related to emotional decision making and working memory suggest that cognitive disturbances could be related to brain alterations. Altered levels of neurotransmitters involved in sleep regulation link disordered sleep to neurochemical abnormalities. Thus, current evidence supports the view that at least some fibromyalgia symptoms are associated with brain dysfunctions or alterations, giving the long-held “it is all in your head” view of the disorder a new meaning.

Association between wind-up ratio and central serotonergic function in healthy subjects and depressed patients

Temporal summation of C-fiber evoked responses generates an increase in action potential discharge in second-order neurons and in perceived pain intensity (wind-up). This may be related to the central serotonergic system which modulates and partly inhibits sensory input. Aim of the study was to investigate the relationship between wind-up and serotonergic activity using loudness dependence of auditory evoked potentials (LDAEP). 18 healthy subjects were compared to 18 patients with major depression, a disease with a putative serotonin deficit. They were examined with quantitative sensory testing (QST) using the protocol of the German Research Network on Neuropathic Pain (DFNS), including the wind-up ratio (WUR), LDAEP, and psychometric measurements. We found a slight positive correlation between WUR and LDAEP both in healthy controls and depressed patients combined (r=0.340, p=0.043), indicating that WUR may be modulated by serotonergic activity. It can be concluded that inhibitory control to noxious stimuli is partly associated with the central serotonergic function as indicated by LDAEP.

Multisensory hypersensitivity in women with fibromyalgia: implications for well being and intervention

OBJECTIVE

To document sensory sensitivities to nonnoxious sensory stimuli in daily life for participants with fibromyalgia (FM).

DESIGN

Descriptive study of a convenience sample using a self-report survey of sensory processing.

SETTING

Participants were recruited from the general community. The procedure took place in a research room at the University of Wisconsin-Madison.

PARTICIPANTS

Women with FM (n=27) were compared with women with rheumatoid arthritis (RA) (n=28) and healthy pain-free women (controls) (n=28) (N=83).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURE

A self-report measure of sensory sensitivity to stimuli encountered in daily life. Items ask participants if they are sensitive to sensations that do not seem to bother other people or avoid common activities or environments because of sensory stimuli.

RESULTS

The FM group reported significantly increased sensory sensitivities to both somatic (tactile) and nonsomatic (eg, auditory and olfactory) sensory stimuli compared with the RA and control groups. The RA and control groups did not differ in reported hypersensitivities.

CONCLUSIONS

Women with fibromyalgia reported increased sensitivities to stimuli in the environment and could experience more stress related to sensory conditions in daily life.

Differential effects of painful and non-painful stimulation on tactile processing in fibromyalgia syndrome and subjects with masochistic behaviour

BACKGROUND

In healthy subjects repeated tactile stimulation in a conditioning test stimulation paradigm yields attenuation of primary (S1) and secondary (S2) somatosensory cortical activation, whereas a preceding painful stimulus results in facilitation.

METHODOLOGY/PRINCIPAL FINDINGS

Since previous data suggest that cognitive processes might affect somatosensory processing in S1, the present study aims at investigating to what extent cortical reactivity is altered by the subjective estimation of pain. To this end, the effect of painful and tactile stimulation on processing of subsequently applied tactile stimuli was investigated in patients with fibromyalgia syndrome (FMS) and in subjects with masochistic behaviour (MB) by means of a 122-channel whole-head magnetoencephalography (MEG) system. Ten patients fulfilling the criteria for the diagnosis of FMS, 10 subjects with MB and 20 control subjects matched with respect to age, gender and handedness participated in the present study. Tactile or brief painful cutaneous laser stimuli were applied as conditioning stimulus (CS) followed by a tactile test stimulus (TS) 500 ms later. While in FMS patients significant attenuation following conditioning tactile stimulation was evident, no facilitation following painful stimulation was found. By contrast, in subjects with MB no attenuation but significant facilitation occurred. Attenuation as well as facilitation applied to cortical responses occurring at about 70 ms but not to early S1 or S2 responses. Additionally, in FMS patients the amount of attenuation was inversely correlated with catastrophizing tendency.

CONCLUSION

The present results imply altered cortical reactivity of the primary somatosensory cortex in FMS patients and MB possibly reflecting differences of individual pain experience.

Generalized hypervigilance in fibromyalgia patients: an experimental analysis with the emotional Stroop paradigm

OBJECTIVE

In recent years, a good deal of serious research has been carried out on the hypothesized presence of generalized hypervigilance to sensory stimulation in fibromyalgia (FM). However, there are no studies which, following an operationalization of generalized hypervigilance as a propensity to attend to any task-irrelevant stimuli presented, make use of interference paradigms as the most appropriate experimental models for its analysis. The purpose of this study was to test the hypothesis of generalized hypervigilance in FM using the emotional modification of the Stroop task and to explore the possible mediating role of anxiety.

METHODS

To this end, 25 women diagnosed with fibromyalgia and 25 matched controls were shown 32 stimulus words equally distributed in four categories: fibromyalgia symptoms, arousing-negative (A-), arousing-positive (A+), and neutral (N). These words had been selected on the basis of the results of an independent study. In addition to the emotional Stroop task, measures of trait and state anxiety were included.

RESULTS

The results showed the possible presence of a generalized hypervigilance response in fibromyalgia patients based on significant slowness in the color-naming. This effect was mediated by the degree of perceived unpleasantness of the A-stimuli. However, the expected mediation effect of anxiety was not found.

CONCLUSIONS

These results suggest the presence of a generalized hypervigilance response in FM patients that is not mediated by anxiety. Implications for the correct functioning of controlled self-regulatory processes in fibromyalgia and similar pathologies are discussed.

Treatment options and patient perspectives in the management of fibromyalgia: future trends

Fibromyalgia (FM) is a common, complex, and difficult to treat chronic widespread pain disorder, which usually requires a multidisciplinary approach using both pharmacological and non-pharmacological (education and exercise) interventions. It is a condition of heightened generalized sensitization to sensory input presenting as a complex of symptoms including pain, sleep dysfunction, and fatigue, where the pathophysiology could include dysfunction of the central nervous system pain modulatory systems, dysfunction of the neuroendocrine system, and dysautonomia. A cyclic model of the pathophysiological processes is compatible with the interrelationship of primary symptoms and the array of postulated triggers associated with FM. Many of the molecular targets of current and emerging drugs used to treat FM have been focused to the management of discrete symptoms rather than the condition. Recently, drugs (eg, pregabalin, duloxetine, milnacipran, sodium oxybate) have been identified that demonstrate a multidimensional efficacy in this condition. Although the complexity of FM suggests that monotherapy, non-pharmacological or pharmacological, will not adequately address the condition, the outcomes from recent clinical trials are providing important clues for treatment guidelines, improved diagnosis, and condition-focused therapies.

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

OBJECTIVE

To write a systematic review on the etiology and pathophysiology of the fibromyalgia syndrome (FMS) and of chronic widespread pain (CWP).

METHODS

An interdisciplinary level-3 guideline (i.e. systematic literature search and assessment, logic analysis, formal consensus procedure) for the diagnosis and therapy of FMS was created in cooperation with 10 medical and psychological societies and 2 patient self-help organizations. A literature search was performed covering all available review articles on the etiology and pathophysiology of FMS and CWP using the Cochrane Collaboration Reviews (1993-12/2006), Medline (1980-2006), PsychInfo (1966-12/2006), and Scopus (1980-12/2006). For the assignment of evidence classes the system of the Oxford Centre for Evidence-Based Medicine was applied. Consensus was achieved by a multi-step nominal group procedure.

RESULTS

FMS aggregates in families (evidence level 2c). Physical and psychological stress at the workplace are risk factors for the development of CWP and FMS. Affective disorders are risk factors for the development and maintenance of FMS. Operant learning mechanisms and sensitization are risk factors for the chronification of FMS (evidence levels 2b). Several factors are associated with the pathophysiology of FMS, but the causal relationship is unclear. This includes alterations of central pain pathways, hyporeactivity of the hypothalamus-pituitary-adrenal axis, increased systemic pro-inflammatory and reduced anti-inflammatory cytokine profiles and disturbances in the dopaminergic and serotonergic systems.

CONCLUSIONS

FMS is the common final product of various etiological factors and pathophysiological mechanisms.