An Elephant Among Us: The Role of Dopamine in the Pathophysiology of Fibromyalgia

Nociplastic pain mechanisms and toll-like receptors as promising targets for its management

ABSTRACT

Nociplastic pain, characterized by abnormal pain processing without an identifiable organic cause, affects a significant portion of the global population. Unfortunately, current pharmacological treatments for this condition often prove ineffective, prompting the need to explore new potential targets for inducing analgesic effects in patients with nociplastic pain. In this context, toll-like receptors (TLRs), known for their role in the immune response to infections, represent promising opportunities for pharmacological intervention because they play a relevant role in both the development and maintenance of pain. Although TLRs have been extensively studied in neuropathic and inflammatory pain, their specific contributions to nociplastic pain remain less clear, demanding further investigation. This review consolidates current evidence on the connection between TLRs and nociplastic pain, with a specific focus on prevalent conditions like fibromyalgia, stress-induced pain, sleep deprivation-related pain, and irritable bowel syndrome. In addition, we explore the association between nociplastic pain and psychiatric comorbidities, proposing that modulating TLRs can potentially alleviate both pain syndromes and related psychiatric disorders. Finally, we discuss the potential sex differences in TLR signaling, considering the higher prevalence of nociplastic pain among women. Altogether, this review aims to shed light on nociplastic pain, its underlying mechanisms, and its intriguing relationship with TLR signaling pathways, ultimately framing the potential therapeutic role of TLRs in addressing this challenging condition.

REAC Neurobiological Modulation as a Precision Medicine Treatment for Fibromyalgia

Fibromyalgia syndrome (FS) is a disorder characterized by widespread musculoskeletal pain and psychopathological symptoms, often associated with central pain modulation failure and dysfunctional adaptive responses to environmental stress. The Radio Electric Asymmetric Conveyer (REAC) technology is a neuromodulation technology. The aim of this study was to evaluate the effects of some REAC treatments on psychomotor responses and quality of life in 37 patients with FS. Tests were conducted before and after a single session of Neuro Postural Optimization and after a cycle of 18 sessions of Neuro Psycho Physical Optimization (NPPO), using evaluation of the functional dysmetria (FD) phenomenon, Sitting and Standing (SS), Time Up and Go (TUG) tests for motor evaluation, Fibromyalgia Impact Questionnaire (FIQ) for quality of life. The data were statistically analyzed, and the results showed a statistically significant improvement in motor response and quality of life parameters, including pain, as well as reduced FD measures in all participants. The study concludes that the neurobiological balance established by the REAC therapeutic protocols NPO and NPPO improved the dysfunctional adaptive state caused by environmental and exposomal stress in FS patients, leading to an improvement in psychomotor responses and quality of life. The findings suggest that REAC treatments could be an effective approach for FS patients, reducing the excessive use of analgesic drugs and improving daily activities.

Pharmacological Interaction of Quercetin Derivatives of Tilia americana and Clinical Drugs in Experimental Fibromyalgia

Fibromyalgia (FM) is a pain syndrome characterized by chronic widespread pain and CNS comorbidities. Tilia americana var. mexicana is a medicinal species used to treat anxiety, insomnia, and acute or chronic pain. However, its spectrum of analgesic efficacy for dysfunctional pain is unknown. To investigate a possible therapeutic alternative for FM-type pain, an aqueous Tilia extract (TE) and its flavonoid fraction (FF) containing rutin and isoquercitrin were evaluated alone and/or combined with clinical drugs (tramadol—TRA and pramipexol—PRA) using the reserpine-induced FM model in rats. Chromatographic analysis allowed the characterization of flavonoids, while a histological analysis confirmed their presence in the brain. TE (10–100 mg/kg, i.p.) and FF (10–300 mg/kg, i.p.) produced significant and dose-dependent antihyperalgesic and antiallodynic effects equivalent to TRA (3–10 mg/kg, i.p.) or PRA (0.01–1 mg/kg, s.c.). Nevertheless, the combination of FF + TRA or FF + PRA resulted in an antagonistic interaction by possible competitive action on the serotonin transporter or µ-opioid and D₂ receptors, respectively, according to the in silico analysis. Flavonoids were identified in cerebral regions because of their self-epifluorescence. In conclusion, Tilia possesses potential properties to relieve FM-type pain. However, the consumption of this plant or flavonoids such as quercetin derivatives in combination with analgesic drugs might reduce their individual benefits.

Gentle Touch Therapy, Pain Relief and Neuroplasticity at Baseline in Fibromyalgia Syndrome: A Randomized, Multicenter Trial with Six-Month Follow-Up

Background: Fibromyalgia (FM) is considered a stress-related disorder characterized mainly by chronic widespread pain. Its pathogenesis is unknown, but cumulative evidence points at dysfunctional transmitter systems and inflammatory biomarkers that may underlie the major symptoms of the condition. This study aimed to evaluate pain scores (primary outcome), quality of life, inflammatory biomarkers and neurotransmitter systems in women with FM (secondary outcomes) subjected to gentle touch therapy (GTT) or placebo. Methods: A total of 64 female patients with FM were randomly assigned to two groups, namely GTT (n = 32) or Placebo (n = 32). Clinical assessments were conducted at baseline and post-intervention with six-month follow-up. We measured serum catecholamines (dopamine), indolamines and intermediary metabolites (serotonin or 5-hydroxyindolacetic acid (5-HIAA)), as well as tetrahydrobiopterin (BH4), which is a cofactor for the synthesis of neurotransmitters and inflammatory biomarkers in women with FM. A group of healthy individuals with no intervention (control group) was used to compare biochemical measurements. Intervention effects were analyzed using repeated measures (RM) two-way ANOVA followed by Bonferroni post hoc test and mixed ANCOVA model with intention to treat. Results: Compared to placebo, the GTT group presented lower pain scores and brain-derived neurotrophic factor (BDNF) levels without altering the quality of life of women with FM. Changes in BDNF had a mediating role in pain. Higher baseline serum BDNF and 5-HIAA or those with a history of anxiety disorder showed a higher reduction in pain scores across time. However, women with higher serum dopamine levels at baseline showed a lower effect of the intervention across the observation period revealed by an ANCOVA mixed model. Conclusions: In conclusion, lower pain scores were observed in the GTT group compared to the placebo group without altering the quality of life in women with FM. Reductions in BDNF levels could be a mechanism of FM pain status improvement. In this sense, the present study encourages the use of these GTT techniques as an integrative and complementary treatment of FM.

The risk of fibromyalgia in patients with iron deficiency anemia: a nationwide population-based cohort study

Since iron is essential for neurotransmitter synthesis, decreased iron stores might lead to reduced production of biogenic amines which phenomenon was shown in Fibromyalgia (FM) patients. The aims are to investigate the association of iron deficiency anemia (IDA) and FM and to find the effects of different interventions. We conducted a study using the Taiwan National Health Insurance Research Database. The IDA cohort consisted of 13,381 patients with newly diagnosed IDA between 2000 and 2008. Each patient with IDA was frequency-matched with one people without IDA, by sex, age and index year. The Cox proportional hazards regression analysis was conducted to estimate the association between IDA and FM risk. The event was the occurrence of FM. The overall incidence density rate of FM in the IDA cohort was higher than in the non-IDA cohort with a multivariable Cox proportional hazards model measured adjusted hazard ratio [HR], 1.19; 95% confidence interval [CI], 1.13-1.25). When using non-IDA group as reference, we compared with different therapies for IDA. The adjusted HRs of FM were 1.38 (95% CI = 1.30-1.47), 1.10 (95% CI = 1.03-1.16), 1.18 (95% CI = 0.98-1.43) and 0.73 (95% CI = 0.58-0.90) for IDA patient without therapy, iron supplement alone, blood transfusion alone and both iron supplement and blood transfusion respectively. Our results suggest IDA is associated with an increased risk of FM. All patients should have iron supplementation both to correct anemia and replenish body stores.

Sleep and pain management: a review

There is a complex interplay between sleep disturbance and patients in pain. There is an increasing appreciation of the direct effects of analgesic drugs and sleep quality. This review provides an overview of the effects of different analgesic drugs and their effects on phases of sleep. The effects of different pain conditions and their direct effects on sleep physiology are also discussed. A structured search of the scientific literature using MEDLINE and PubMed databases. Original human and animal studies were included. A multi-search term strategy was employed. An appreciation of the physiological effects of these drugs will allow a more considered prescription of them to better manage sleep disturbance.

Involvement of the 14-3-3 Gene Family in Autism Spectrum Disorder and Schizophrenia: Genetics, Transcriptomics and Functional Analyses

The 14-3-3 protein family are molecular chaperones involved in several biological functions and neurological diseases. We previously pinpointed YWHAZ (encoding 14-3-3ζ) as a candidate gene for autism spectrum disorder (ASD) through a whole-exome sequencing study, which identified a frameshift variant within the gene (c.659-660insT, p.L220Ffs*18). Here, we explored the contribution of the seven human 14-3-3 family members in ASD and other psychiatric disorders by investigating the: (i) functional impact of the 14-3-3ζ mutation p.L220Ffs*18 by assessing solubility, target binding and dimerization; (ii) contribution of common risk variants in 14-3-3 genes to ASD and additional psychiatric disorders; (iii) burden of rare variants in ASD and schizophrenia; and iv) 14-3-3 gene expression using ASD and schizophrenia transcriptomic data. We found that the mutant 14-3-3ζ protein had decreased solubility and lost its ability to form heterodimers and bind to its target tyrosine hydroxylase. Gene-based analyses using publicly available datasets revealed that common variants in YWHAE contribute to schizophrenia (p = 6.6 × 10-7), whereas ultra-rare variants were found enriched in ASD across the 14-3-3 genes (p = 0.017) and in schizophrenia for YWHAZ (meta-p = 0.017). Furthermore, expression of 14-3-3 genes was altered in post-mortem brains of ASD and schizophrenia patients. Our study supports a role for the 14-3-3 family in ASD and schizophrenia.

Impaired psychomotor ability and attention in patients with persistent pain: a cross-sectional comparative study

Background and aims

Patients with pain have shown cognitive impairment across various domains. Although the pain qualities vary among patients, research has overlooked how cognitive performance is affected by the duration and persistence of pain. The current study sought to fill this gap by examining how qualitatively different pain states relate to the following cognitive functions: sustained attention, cognitive control, and psychomotor ability.

Patients and methods

Patients with musculoskeletal pain in primary care were divided into three pain groups: acute pain (duration <3 months), regularly recurrent pain (duration >3 months), and persistent pain (duration >3 months). These groups were then compared with healthy controls. The MapCog Spectra Test, the Color Word Test, and the Grooved Pegboard Test were used to measure sustained attention, cognitive control, and psychomotor ability, respectively.

Results

Patients with persistent pain showed significantly worse sustained attention and psychomotor ability compared with healthy controls. The acute pain group showed a significant decrease in psychomotor ability, and the regularly recurrent pain group showed a significant decrease in sustained attention. These results remained unchanged when age, education, and medication were taken into account.

Conclusion

Persistent musculoskeletal pain seems to impair performance on a wider range of cognitive tasks than acute or regularly recurrent pain, using pain-free individuals as a benchmark. However, there is some evidence of impairment in psychomotor ability among patients with acute pain and some impairment in sustained attention among patients with regularly recurrent pain.

Implications

Caregivers may need to adjust communication methods when delivering information to cognitively impaired patients.

Potential drug therapies for the treatment of fibromyalgia

INTRODUCTION

Fibromyalgia (FM) is a common, complex chronic widespread pain condition is characterized by fatigue, sleep disturbance and cognitive dysfunction. Treatment of FM is difficult, requiring both pharmacological and non-pharmacological approaches, with an empiric approach to drug therapy focused toward individual symptoms, particularly pain. The effectiveness of current medications is limited with many patients discontinuing use.

AREAS COVERED

A systemic database search has identified 26 molecular entities as potential emerging drug therapies. Advances in the understanding of the pathophysiology of FM provides clues to targets for new medications. Investigation of bioamine modulation and α2δ ligands and novel targets such as dopamine receptors, NMDA receptors, cannabinoid receptors, melatonin receptors and potassium channels has identified potential drug therapies.

EXPERT OPINION

Modest improvement of health status in patients with FM has been observed with drugs targeting a diverse range of molecular mechanisms. No single drug, however, offered substantial efficacy against all the symptoms characteristic of FM. Identification of new and improved therapies for FM needs to address the heterogeneity of the condition, which suggests existence of patient subgroups, the relationship of central and peripheral aspects of the pathophysiology and a requirement of combination therapy with drugs targeting multiple molecular mechanisms.

An update on pharmacotherapy for the treatment of fibromyalgia

INTRODUCTION

Fibromyalgia is a syndrome characterized by chronic generalized pain in addition to different symptoms such as fatigue, sleep disturbances, stiffness, cognitive impairment, and psychological distress. Multidisciplinary treatment combining pharmacological and nonpharmacological therapies is advised.

AREAS COVERED

Publications describing randomized controlled trials and long-term extension studies evaluating drug treatment for fibromyalgia were searched in PubMed and Scopus and included in this review.

EXPERT OPINION

Different drugs are recommended for the treatment of fibromyalgia by different published guidelines, although only three of them have been approved for this indication by the US FDA, and none have been approved by the European Medicines Agency. According to the available evidence, pregabalin, duloxetine and milnacipran should be the drugs of choice for the treatment of this disease, followed by amitriptyline and cyclobenzaprine. Other drugs with at least one positive clinical trial include some selective serotonin reuptake inhibitors, moclobemide, pirlindole, gabapentin, tramadol, tropisetron, sodium oxybate and nabilone. None of the currently available drugs are fully effective against the whole spectrum of fibromyalgia symptoms, namely pain, fatigue, sleep disturbances and depression, among the most relevant symptoms. Combination therapy is an option that needs to be more thoroughly investigated in clinical trials.

High prevalence of restless legs syndrome among women with multi-site pain: a population-based study in Dalarna, Sweden

BACKGROUND

The chronic pain (CP) and chronic multi-site pain (CMP) condition is a highly prevalent health problem. Several studies have reported a high (31-64%) prevalence of co-morbid restless legs syndrome (RLS) in patients with fibromyalgia, one specifically defined form of chronic widespread pain. The current study explored the association between CMP and RLS.

METHOD

The study included 4040 respondents to a postal questionnaire sent to 10,000 women in the age range of 18-64 years and randomly selected from the general population. Complete questionnaire data on type (acute/chronic), degree (mild to severe) and spreading (0-5 body zones) of pain, as well as RLS symptoms (validated questionnaire), were obtained from 3060 subjects. Information on lifestyle, anthropometrics, co-morbidities and medication was collected.

RESULTS

RLS prevalence increased from 9.6% in subjects with no report of pain to 23,9%, 26.4%, 39.2%, 44.9% and 54.8% in those reporting one, two, three, four and five pain areas, respectively (p < 0.001). Further, RLS prevalence increased from 9.6% (no pain) to 27.9%, 37.9% and 42.4% in subjects with mild, moderate and severe chronic pain (p < 0.001). Multi-site pain, pain localized in the leg, extended pain duration and co-morbid psychiatric disorder were all independently associated with a RLS diagnosis in a multiple regression analysis.

CONCLUSION

The prevalence of RLS increased progressively with pain severity and even more sharply with the degree of pain spreading in women recruited from the general population. Both acute and chronic pain was associated with RLS-related symptoms.

Fibromyalgia

Fibromyalgia is a chronic pain condition present in 2-4% of the population. Fibromyalgia consists of widespread pain with similarities to neuropathic pain in clinical findings, pathophysiology, and neuropharmacology. Pain is the predominant symptom and allodynia and hyperalgesia are common signs. Extreme fatigue, impaired cognition and nonrestorative sleep difficulties coexist in addition to other somatic symptoms. Research including neuroimaging investigations shows abnormalities in neurotransmitters and an abnormal response to pain. Altered pain processing peripherally and centrally contribute to central sensitization and a dampened effect of the diffuse noxious inhibitory control (DNIC). Successful management incorporates education of the patient in self-management skills, cognitive behavioral therapy (CBT), exercise, and drug therapy. Tricyclic antidepressants, serotonin-norepinephrine reuptake inhibitors (SNRIs) (duloxetine and milnacipran), α2-δ ligands (gabapentin and pregabalin) are effective in reducing pain by≥30%. Some success has been shown with dopamine agonists (pramipexole), tramadol, other opioids and cannabinoids (nabilone). Further evidence-based trials using complementary treatments are needed. Fibromyalgia is complex and requires a multidisciplinary approach to treatment. Patient self-management is key.

Association of HTR2A polymorphisms with chronic widespread pain and the extent of musculoskeletal pain: results from two population-based cohorts

OBJECTIVE

The aim of the current study was to investigate whether genetic variation in genes across the serotoninergic system is associated with chronic widespread pain (CWP) and the number of pain sites reported.

METHODS

A discovery cohort, with pain data at 3 time points, was used to investigate genetic associations with 2 phenotypes: 1) CWP (at ≥ 2 time points; n = 164) compared with pain-free controls (at 3 time points; n = 172), and 2) the maximum number of pain sites reported at any 1 of the 3 time points (range of sites 0-29; n = 989). A cohort of 2,285 men for whom a DNA sample and pain data were available (including 203 CWP cases and 929 controls) was used for validation. Pairwise tagging (r(2) > 0.8) single-nucleotide polymorphisms (SNPs) were genotyped. Logistic and zero-inflated negative binomial regression analyses were used to test for SNP associations with CWP and the number of pain sites, respectively.

RESULTS

SNPs in HTR2A were associated with both pain phenotypes in the discovery cohort, and a number of these SNP associations were replicated in the validation cohort, some of which were attenuated after adjustment for depression. There was an increased likelihood of having CWP in subjects with 1 or 2 copies of the T allele of rs12584920 (odds ratio [OR] 1.64, 95% confidence interval [95% CI] 1.01-2.60 [P = 0.03] in the discovery cohort, and OR 1.46, 95% CI 1.07-2.00 [P = 0.018] in the validation cohort). A similar association was observed between rs17289394 and the maximum number of pain sites reported in both cohorts. Results from a meta-analysis of the data from the 2 cohorts further strengthened these findings.

CONCLUSION

The findings of this study support the role of HTR2A in the genetic predisposition to musculoskeletal pain.

The role of antipsychotics in the management of fibromyalgia

Fibromyalgia is a syndrome characterized by chronic generalized pain associated with different somatic symptoms, such as sleep disturbances, fatigue, stiffness, balance problems, hypersensitivity to physical and psychological environmental stimuli, depression and anxiety. It has been estimated to affect roughly the 2-4% of the general population in most countries studied, and it has been shown to be much more prevalent in women than in men. Although its pathophysiology is not yet fully understood, it is known that both genetic and environmental factors are involved in its development. Fibromyalgia shares a high degree of co-morbidity with other conditions, including chronic headache, temporomandibular disorder, irritable bowel syndrome, major depression, anxiety disorders and chronic fatigue syndrome. Therefore, this is a syndrome difficult to treat for which multimodal treatments including physical exercise, psychological therapies and pharmacological treatment are recommended. Although different kinds of drugs have been studied for the treatment of fibromyalgia, the most widely used drugs that have the higher degree of evidence for efficacy include the α(2)δ ligands pregabalin and gabapentin, and the tricyclic antidepressants (TCAs) and serotonin noradrenaline (norepinephrine) reuptake inhibitors (SNRIs). However, there is a need to look for newer additional therapeutic pharmacological options for the treatment of this complex and disabling disease. First- and second-generation antipsychotics have shown analgesic properties both in an experimental setting and in humans, although most of the available evidence for the treatment of human pain concerns older antipsychotics and involves clinical trials performed several decades ago. In addition, several second-generation antipsychotics, risperidone, olanzapine and quetiapine, have shown efficacy in the treatment of some anxiety disorders. Some second-generation antipsychotics, mainly quetiapine, aripiprazole and amisulpride, have demonstrated antidepressant activity, with quetiapine approved for the treatment of bipolar depression and refractory major depression, and aripiprazole approved as an adjunctive treatment for major depressive disorder. Finally, several old and new antipsychotics, including promethazine, levopromazine, olanzapine, quetiapine and ziprasidone, have been shown to improve sleep parameters in healthy subjects. Each of these properties suggests that antipsychotics could represent a new potential alternative for the treatment of fibromyalgia syndrome. To date, most of the published studies on the use of antipsychotics in the treatment of fibromyalgia syndrome have been uncontrolled, either case reports or case series, dealing with olanzapine, quetiapine, ziprasidone, levopromazine and amisulpride. The studies on olanzapine and quetiapine have suggested therapeutic efficacy although, in the case of olanzapine, hampered by tolerability problems. A double-blind controlled trial, published in 1980, showed that chlorpromazine increased slow-wave sleep and improved pain and mood disturbances. More recently, four double-blind controlled studies have explored the efficacy of quetiapine, either alone or as an add-on treatment, in fibromyalgia management. None of these trials has yet been published, although two of them have been presented as congress communications, both of them suggesting that quetiapine could be a potential alternative treatment for fibromyalgia. In summary, the current available evidence suggests that at least some antipsychotics, specifically quetiapine, could be useful for the treatment of fibromyalgia and that further studies on the efficacy of these compounds are worth pursuing.

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.

From bad to worse: striatal coding of the relative value of painful decisions

The majority of decision-related research has focused on how the brain computes decisions over outcomes that are positive in expectation. However, much less is known about how the brain integrates information when all possible outcomes in a decision are negative. To study decision-making over negative outcomes, we used fMRI along with a task in which participants had to accept or reject 50/50 lotteries that could result in more or fewer electric shocks compared to a reference amount. We hypothesized that behaviorally, participants would treat fewer shocks from the reference amount as a gain, and more shocks from the reference amount as a loss. Furthermore, we hypothesized that this would be reflected by a greater BOLD response to the prospect of fewer shocks in regions typically associated with gain, including the ventral striatum and orbitofrontal cortex. The behavioral data suggest that participants in our study viewed all outcomes as losses, despite our attempt to induce a status quo. We find that the ventral striatum showed an increase in BOLD response to better potential gambles (i.e., fewer expected shocks). This lends evidence to the idea that the ventral striatum is not solely responsible for reward processing but that it might also signal the relative value of an expected outcome or action, regardless of whether the outcome is entirely appetitive or aversive. We also find a greater response to worse gambles in regions previously associated with aversive valuation, suggesting an opposing but simultaneous valuation signal to that conveyed by the striatum.

Do fall predictors in middle aged and older adults predict fall status in persons 50+ with fibromyalgia? An exploratory study

We explored potential predictors of fall status in 70 community-dwelling persons > or =50 years of age with fibromyalgia (FM). Over 40% of the sample reported one or more falls in the year prior to the study. A logistic regression model using 10 variables known to predict falls in middle aged and older persons predicted 45% of the variance in fall status. Three variables offered significant independent contributions to the overall model predicting fall status: perception of postural instability, balance performance, and executive function processing speed. The results support prior work in both nonclinical and clinical populations of middle aged and older adults indicating that falls are associated with multiple risk factors. Prospective designs with larger samples are needed to (a) validate and extend these findings, and (b) identify risk factors related to fall status that are unique to persons with FM.