Increased cutaneous miR-let-7d expression correlates with small nerve fiber pathology in patients with fibromyalgia syndrome

Common miRNAs of Osteoporosis and Fibromyalgia: A Review

A significant clinical association between osteoporosis (OP) and fibromyalgia (FM) has been shown in the literature. Given the need for specific biomarkers to improve OP and FM management, common miRNAs might provide promising tracks for future prevention and treatment. The aim of this review is to identify miRNAs described in OP and FM, and dysregulated in the same direction in both pathologies. The PubMed database was searched until June 2023, with a clear mention of OP, FM, and miRNA expression. Clinical trials, case-control, and cross-sectional studies were included. Gray literature was not searched. Out of the 184 miRNAs found in our research, 23 are shared by OP and FM: 7 common miRNAs are dysregulated in the same direction for both pathologies (3 up-, 4 downregulated). The majority of these common miRNAs are involved in the Wnt pathway and the cholinergic system and a possible link has been highlighted. Further studies are needed to explore this relationship. Moreover, the harmonization of technical methods is necessary to confirm miRNAs shared between OP and FM.

MicroRNA-Related Polymorphism and Their Association with Fibromyalgia

MicroRNAs are tissue-specific expressed short RNAs that serve post-transcriptional gene regulation. A specific microRNA can bind to mRNAs of different genes and thereby suppress their protein production. In the context of the complex phenotype of fibromyalgia, we used the Axiom miRNA Target Site Genotyping Array to search genome-wide for DNA variations in microRNA genes, their regulatory regions, and in the 3'UTR of protein-coding genes. To identify disease-relevant DNA polymorphisms, a cohort of 176 female fibromyalgia patients was studied in comparison to a cohort of 162 healthy women. The association between 48,329 markers and fibromyalgia was investigated using logistic regression adjusted for population stratification. Results show that 29 markers had p-values < 1 × 10^-3, and the strongest association was observed for rs758459 (p-value of 0.0001), located in the Neurogenin 1 gene which is targeted by hsa-miR-130a-3p. Furthermore, variant rs2295963 is predicted to affect binding of hsa-miR-1-3p. Both microRNAs were previously reported to be differentially expressed in fibromyalgia patients. Despite its limited statistical power, this study reports two microRNA-related polymorphisms which may play a functional role in the pathogenesis of fibromyalgia. For a better understanding of the disease pattern, further functional analyses on the biological significance of microRNAs and microRNA-related polymorphisms are required.

Clinical criteria and diagnostic assessment of fibromyalgia: position statement of the Italian Society of Neurology-Neuropathic Pain Study Group

BACKGROUND

The role of central and/or peripheral nervous system dysfunction is basically fundamental in fibromyalgia.

AIM

The aim of this position statement on behalf of the Neuropathic Pain Study Group of the Italian Society of Neurology is to give practical guidelines for the clinical and instrumental assessment of fibromyalgia (FM) in the neurological clinical practice, taking into consideration recent studies.

METHODS

Criteria for study selection and consideration were original studies, case-controls design, use of standardized methodologies for clinical practice, and FM diagnosis with ACR criteria (2010, 2011, 2016).

RESULTS

ACR criteria were revised. For diagnostic procedure of small-fiber pathology, 47 studies were totally considered. Recent diagnostic criteria should be applied (ACR, 2016). A rheumatologic visit seems mandatory. The involvement of small fibers should request at least 2 among HRV + SSR and/or laser-evoked responses and/or skin biopsy and/or corneal confocal microscopy, eventually followed by monitoring of metabolic and/or immunological/ and or/paraneoplastic basis, to be repeated at 1-year follow-up.

CONCLUSIONS

The correct diagnostic approach to FM could promote the exclusion of the known causes of small-fiber impairment. The research toward common genetic factors would be useful to promote a more specific therapeutic approach.

A Comprehensive Review of the Genetic and Epigenetic Contributions to the Development of Fibromyalgia

This narrative review summarizes the current knowledge of the genetic and epigenetic contributions to the development of fibromyalgia (FM). Although there is no single gene that results in the development of FM, this study reveals that certain polymorphisms in genes involved in the catecholaminergic pathway, the serotonergic pathway, pain processing, oxidative stress, and inflammation may influence susceptibility to FM and the severity of its symptoms. Furthermore, epigenetic changes at the DNA level may lead to the development of FM. Likewise, microRNAs may impact the expression of certain proteins that lead to the worsening of FM-associated symptoms.

Integrated omics analysis reveals the epigenetic mechanism of visceral hypersensitivity in IBS-D

Background and objective: IBS-D is a common functional bowel disease with complex etiology and without biomarker. The pathological and physiological basis of IBS-D focuses on visceral hypersensitivity. However, its epigenetic mechanism remains elusive. Our study aimed to integrate the relationship between differentially expressed miRNAs, mRNAs and proteins in IBS-D patients in order to reveal epigenetic mechanism of visceral hypersensitivity from transcription and protein levels and provide the molecular basis for discovering biomarkers of IBS-D.

Methods: The intestinal biopsies from IBS-D patients and healthy volunteers were obtained for high-throughput sequencing of miRNAs and mRNAs. The differential miRNAs were selected and verified by q-PCR experiment followed by target mRNA prediction. Biological functions were respectively analyzed for target mRNAs, differential mRNAs and the previously identified differential proteins in order to explore the characteristic involved visceral hypersensitivity. At last, interaction analysis of miRNAs, mRNAs and proteins was performed for the epigenetic regulation mechanism from transcription and protein levels.

Results: Thirty-three miRNAs were found to be differentially expressed in IBS-D and five of them were further confirmed, including upregulated hsa-miR-641, hsa-miR-1843, hsa-let-7d-3p and downregulated hsa-miR-219a-5p, hsa-miR-19b-1-5p. In addition, 3,812 differential mRNAs were identified. Thirty intersecting molecules were found from the analysis on the target mRNAs of miRNAs and mRNAs. Fourteen intersecting molecules were obtained from the analysis on the target mRNAs and proteins, and thirty-six intersecting molecules were identified from analysis on the proteins and different mRNAs. According to the integrated analysis of miRNA-mRNA-protein, we noticed two new molecules COPS2 regulated by hsa-miR-19b-1-5p and MARCKS regulated by hsa-miR-641. Meanwhile some critical signaling pathways in IBS-D were found such as MAPK, GABAergic synapse, Glutamatergic synapse, and Adherens junction.

Conclusion: The expressions of hsa-miR-641, hsa-miR-1843, hsa-let-7d-3p, hsa-miR-219a-5p, and hsa-miR-19b-1-5p in the intestinal tissues of IBS-D patients were significantly different. Moreover, they could regulate a variety of molecules and signaling pathways, which were involved in the multifaceted and multilevel mechanism of visceral hypersensitivity of IBS-D.

The temporal expression of circulating microRNAs after acute experimental pain in humans

BACKGROUND

MicroRNAs (miRNAs) can modulate several biological systems, including the pain system. This study aimed to evaluate the temporal expression of circulating miRNAs in the plasma of healthy volunteers as a marker for epigenetic changes before and after an acute, experimental, pain provocation by intramuscular hypertonic saline injection.

METHODS

Twenty volunteers were randomly allocated into two groups and received either hypertonic (pain) or isotonic (control) saline injection in the first dorsal interosseous muscle of their dominant hand. Pain intensity was continuously recorded for 20 minutes after injection on a VAS scale from 0 to 100 (0 indicates no pain and 100 the worst imaginable pain). Blood samples were taken at baseline, 30 minutes, 3 hours, and 24 hours post-injection, and plasma was separated. MiRNA extracts were used for RNA sequencing with the Illumina NextSeq platform. MiRNA transcripts were compared between the pain and the no-pain, control group at every time point. Significant differences were considered when folds were >2 and the False Discovery Rate was p < 0.05.

RESULTS

After 30 minutes, 4 miRNAs were significantly altered in the pain group compared to controls, which increased to 24 after 3 hours and to 42 after 24 hours from baseline (p < 0.0001). Two miRNAs were consistently upregulated throughout the experiment. Enrichment analysis showed significant miRNAs involved in brain perception of pain, brain signalling and response to stimuli.

CONCLUSIONS

This exploratory study is the first to report on the temporal expression of circulating miRNAs after an acute, human experimental muscle pain model.

SIGNIFICANCE

This exploratory study evaluated the temporal profile of circulating miRNAs in the plasma of healthy subjects after acute experimental pain. Several miRNAs were altered in subjects at the times of follow-up after the acute pain model when compared to controls. MiRNAs previously associated with pain processes were altered in the pain group. Our results, by showing the fast and prolonged modifications of miRNA elicited by the acute experimental pain model, add new perspectives to the topic of epigenetics and pain.

Understanding the Needs and Priorities of People Living with Persistent Pain and Long-Term Musculoskeletal Conditions during the COVID-19 Pandemic—A Public Involvement Project

Background: Critiques of public involvement (PI) are associated with failing to be inclusive of under-represented groups, and this leads to research that fails to include a diversity of perspectives. Aim: The aim of this PI project was to understand the experiences and priorities of people from three seldom-heard groups whose musculoskeletal pain may have been exacerbated or treatment delayed due to COVID-19. Engaging representatives to report diverse experiences was important, given the goal of developing further research into personalised and integrated care and addressing population health concerns about access and self-management for people with musculoskeletal pain. Methods: The project was approved via Sheffield Hallam University Ethics but was exempt from further HRA approval. A literature review was conducted, followed by informal individual and group discussions involving professionals and people with lived experience of (a) fibromyalgia pain, (b) those waiting for elective surgery and (c) experts associated with the care home sector. Findings from the literature review were combined with the insights from the public involvement. Resulting narratives were developed to highlight the challenges associated with persistent pain and informed the creation of consensus statements on the priorities for service improvement and future research. The consensus statements were shared and refined with input from an expert steering group. Results: The narratives describe pain as a uniformly difficult experience to share with professionals; it is described as exhausting, frustrating and socially limiting. Pain leads to exclusion from routine daily activities and often resigns people to feeling and being unwell. In all cases, there are concerns about accessing and improving services and critical issues associated with optimising physical activity, functional wellbeing and managing polypharmacy. Exercise and/or mobilisation are important and commonly used self-management strategies, but opportunity and advice about safe methods are variable. Services should focus on personalised care, including self-management support and medication management, so that people’s views and needs are heard and validated by health professionals. Conclusions: More research is needed to explore the most effective pain management strategies, and public involvement is important to shape the most relevant research questions. Health and care systems evaluation is also needed to address the scale of the population health need. The pandemic appears to have highlighted pre-existing shortcomings in holistic pain management.

Expression and Biological Functions of miRNAs in Chronic Pain: A Review on Human Studies

Chronic pain is a major public health problem and an economic burden worldwide. However, its underlying pathological mechanisms remain unclear. MicroRNAs (miRNAs) are a class of small noncoding RNAs that post-transcriptionally regulate gene expression and serve key roles in physiological and pathological processes. This review aims to synthesize the human studies examining miRNA expression in the pathogenesis of chronic primary pain and chronic secondary pain. Additionally, to understand the potential pathophysiological impact of miRNAs in these conditions, an in silico analysis was performed to reveal the target genes and pathways involved in primary and secondary pain and their differential regulation in the different types of chronic pain. The findings, methodological issues and challenges of miRNA research in the pathophysiology of chronic pain are discussed. The available evidence suggests the potential role of miRNA in disease pathogenesis and possibly the pain process, eventually enabling this role to be exploited for pain monitoring and management.

A Systematic Review and Meta-Analysis of the Prevalence of Small Fibre Impairment in Patients with Fibromyalgia

Converging evidence shows that patients with fibromyalgia syndrome have signs of small fibre impairment, possibly leading to pain and autonomic symptoms, with a frequency that has not yet been systematically evaluated. To fill this gap, our review aims to define the frequency of somatic and autonomic small fibre damage in patients with fibromyalgia syndrome, as assessed by objective small fibre-related testing. We found 360 articles on somatic and autonomic small fibre assessment in patients with fibromyalgia. Out of the 88 articles assessed for eligibility, 20 were included in the meta-analysis, involving 903 patients with fibromyalgia. The estimated prevalence of somatic small fibre impairment, as assessed with skin biopsy, corneal confocal microscopy, and microneurography, was 49% (95% confidence interval (CI): 39–60%, I² = 89%), whereas the estimated prevalence of autonomic small fibre impairment, as assessed with heart rate variability, sympathetic skin response, skin conductance, and tilt testing, was 45% (95% CI: 25–65%, I² = 91%). Our study shows that a considerable proportion of patients with fibromyalgia have somatic and autonomic small fibre impairment, as assessed by extensive small fibre-related testing. Nevertheless, the heterogeneity and inconsistencies across studies challenge the exact role of small fibre impairment in fibromyalgia symptoms.

The puzzle of fibromyalgia between central sensitization syndrome and small fiber neuropathy: a narrative review on neurophysiological and morphological evidence

Fibromyalgia (FM) is a condition characterized by chronic widespread pain whose pathogenesis is still not fully defined. Evidence based on structural and functional neuroimaging methods, electrophysiological, and morphological - skin biopsy - features demonstrated a central and peripheral nervous system involvement. A dysfunction in nociceptive inputs processing at the central level was highlighted as the primary cause of FM, but other data coming from different laboratories contributed to emphasize again the peripheral origin of FM. In fact, small fibers neuropathy (SFN) was observed in a large number of patients submitted to skin biopsy. The complex interaction between central and peripheral factors is opening a new scenario about the management of this neurological disorder. Whether proximal SFN is an initiating event leading to FM or is the consequence of stress-related insular hyper excitability remains unclear. Mild sufferance of peripheral afferents could function as a trigger for an exaggerated response of the so-called "salience matrix" in predisposed individuals. On the other side, the intriguing hypothesis rising from animal models could indicate that the cortical hyper function could cause peripheral small afferent damage. The research should go on the genetic origin of such peripheral and central abnormalities, the acquired facilitating factors, and the presence of different phenotypes in order to search for efficacious treatments, which are still lacking.

Implications of Nerve Fiber Density on the Diagnosis and Treatment of Juvenile Fibromyalgia

Juvenile fibromyalgia (JFM) is a condition that presents as chronic widespread musculoskeletal pain and affects children and adolescents. JFM remains a challenging diagnosis, as it is both based on subjective criteria and the pathogenesis is poorly understood. Small fiber neuropathy (SFN) is a distinct condition, which is characterized by pathology of small A-delta and C fibers, and can present similarly to JFM. Small fiber pathology is characterized by reduced intraepidermal nerve fiber density (IENFD) on skin biopsy. Recent studies have found that as many as half of patients with JFM can demonstrate decreased IENFD, in pattern similar to SFN. This phenomenon has been referred to as small fiber pathology. The meaning of these findings was disputed; however, the current consensus remains that fibromyalgia and SFN are distinct conditions. Additionally, among patients with fibromyalgia, there are two phenotypes: those with small fiber pathology and those without. The purpose of this review was to characterize the role assessment of IENFD plays in the clinical context. We conducted a narrative review of pertinent articles pertaining to JFM, SFN and small fiber pathology in fibromyalgia. We concluded that assessment of IENFD should be completed if SFN is suspected either when a patient first presents or in patients who were previously diagnosed with fibromyalgia and SFN is later suspected. Distinguishing between JFM and SFN is important because recommended therapies differ between the two conditions. However, there is no evidence to support the use of skin biopsy to distinguish between the two discussed fibromyalgia phenotypes. More studies are needed to elucidate whether IENFD varies with morbidity and if both fibromyalgia phenotypes vary in their response to different therapeutic regimens.

Relevance of Religiosity for Coping Strategies and Disability in Patients with Fibromyalgia Syndrome

Coping strategies are essential for the outcome of chronic pain. This study evaluated religiosity in a cohort of patients with fibromyalgia syndrome (FMS), its effect on pain and other symptoms, on coping and FMS-related disability. A total of 102 FMS patients were recruited who filled in questionnaires, a subgroup of 42 patients participated in a face-to-face interview, and data were evaluated by correlation and regression analyses. Few patients were traditionally religious, but the majority believed in a higher existence and described their spirituality as "transcendence conviction". The coping strategy "praying-hoping" and the ASP dimension "religious orientation" (r = 0.5, P < 0.05) showed a significant relationship independent of the grade of religiosity (P < 0.05). A high grade of belief in a higher existence was negatively associated with the choice of ignoring as coping strategy (r = - 0.4, P < 0.05). Mood and affect-related variables had the highest impact on disability (b = 0.5, P < 0.05). In this cohort, the grade of religiosity played a role in the choice of coping strategies, but had no effects on health and mood outcome.

The plasma microRNA levels and their relationship with the general health and functional status in female patients with fibromyalgia syndrome

Objectives: The aim of this study was to identify the plasma level of micro-ribonucleic acid (microRNA) expressions and the relationship between plasma microRNA levels with the general health and functional status in female patients with fibromyalgia syndrome (FMS).

Patients and methods: Thirty-five female patients (mean age: 42.0±11.8 years; range, 21 to 62 years) diagnosed as FMS and 35 sex-and age-matched healthy controls (mean age: 43.7±8.8 years; range, 21 to 56 years) were enrolled in the study. MicroRNA measurements of the participants in plasma were carried out by using the quantitative polymerase chain reaction (qPCR). A total of 11 plasma levels of microRNA expressions were examined in both groups. The general health and functional status of the patients and controls were assessed by the Fibromyalgia Impact Questionnaire (FIQ) and the Short Form-36 (SF-36) scale.

Results: No significant difference was observed between the plasma levels of microRNA expressions in patients with FMS and healthy controls. The plasma level of miR-320a expression was found to be negatively correlated with the total FIQ score in female patients with FMS (p=0.05, r=-0.34). Negative correlations were also detected between the plasma level of miR-320a and miR-320b expressions and the subscale score of SF-36 physical function in female patients with FMS (p=0.01, r=-0.43 and p=0.01, r=-0.43, respectively). A strong positive correlation was found between miR-142-3p and the subscale score of SF-36 mental symptom score in female patients with FMS (p<0.001, r=1.00).

Conclusion: The expression levels of microRNAs in plasma between female patients with FMS and controls were not significantly different. Only plasma levels of miR-320a, miR-320b, and miR-142-3p expressions were associated with the general health, functional status, and mental symptom score in female patients with FMS.

Preoperative serum circulating microRNAs as potential biomarkers for chronic postoperative pain after total knee replacement

Background

Chronic postoperative pain affects approximately 20% of patients with knee osteoarthritis after total knee replacement. Circulating microRNAs can be found in serum and might act as biomarkers in a variety of diseases. The current study aimed to investigate the preoperative expression of circulating microRNAs as potential predictive biomarkers for the development of chronic postoperative pain in the year following total knee replacement.

Methods

Serum samples, collected preoperatively from 136 knee osteoarthritis patients, were analyzed for 21 circulatory microRNAs. Pain intensity was assessed using a visual analog scale before and one year after total knee replacement. Patients were divided into a low-pain relief group (pain relief percentage <30%) and a high-pain relief group (pain relief percentage >30%) based on their pain relief one year after total knee replacement, and differences in microRNAs expression were analyzed between the two groups.

Results

We found that three microRNAs were preoperatively dysregulated in serum in the low-pain relief group compared with the high-pain relief group. MicroRNAs hsa-miR-146a-5p, -145-5p, and -130 b-3p exhibited fold changes of 1.50, 1.55, and 1.61, respectively, between the groups (all P values < 0.05). Hsa-miR-146a-5p and preoperative pain intensity correlated positively with postoperative pain relief (respectively, R = 0.300, P = 0.006; R = 0.500, P < 0.001).

Discussion

This study showed that patients with a low postoperative pain relief present a dysregulation of circulating microRNAs. Altered circulatory microRNAs expression correlated with postoperative pain relief, indicating that microRNAs can serve as predictive biomarkers of pain outcome after surgery and hence may foster new strategies for preventing chronic postoperative pain after total knee replacement (TKR).

High-dose spironolactone lacks effectiveness in treatment of fibromyalgia (RCT)

BACKGROUND

Spironolactone (SPL) is a reversible mineralocorticoid receptor (MR) and androgen receptor (AR) antagonist which attracts pharmacotherapeutic interest not only because of its beneficial effects in heart failure but also because of the pathogenetic roles of MR and AR activities in neuropsychiatric diseases. Recently, beneficial and rapid-onset effects of SPL have been documented in a case series of women with fibromyalgia syndrome (FMS). To reaffirm this observation, we performed a double-blind placebo-controlled randomized clinical trial (RCT).

METHODS

A total of 69 patients were screened, 56 patients were eligible and randomized to SPL or placebo (each n = 28). Forty-three patients completed the clinical trial to the last visit (n = 21 and n = 22). After a run-in phase of 50 and 100 mg/day, 200 mg/day SPL or placebo were applied between days 7 and 28. Primary outcome was the change in the FIQ-G score (Fibromyalgia Impact Questionnaire, German version). Secondary outcome parameters were the changes in pain (numeric rating scale, NRS), mood (ADS), quality of life (SF-36) and change in FIQ scores 14 days after the end of the medication.

RESULTS

SPL of 200 mg/day did not change significantly either the primary or the secondary end points. SPL evoked a transient rise in serum potassium and a transient fall in GFR maximal after 2 weeks, but without clinical relevance.

CONCLUSIONS

SPL at 200 mg/day does not improve symptoms in women with FMS, but was considered not to cause harm.

SIGNIFICANCE

The mineralocorticoid receptor and androgen receptor antagonist spironolactone is repeatedly tested for its therapeutic effectivity against neuropsychiatric disorders. The present RCT demonstrated that 200 mg spironolactone does not change the symptoms of the fibromyalgia syndrome (FMS) in adult women. Between 2 and 4 weeks, spironolactone evokes a transient decrease in GFR and increase in serum potassium. Spironolactone cannot be recommended for the treatment of FMS.

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.

Small-fibre pathology has no impact on somatosensory system function in patients with fibromyalgia

We aimed to investigate whether small-fibre pathology, a common skin biopsy finding in patients with fibromyalgia, implies clinically important abnormalities of somatosensory system function and verify whether it is associated with voltage-gated sodium channel variants. In 57 consecutively enrolled patients with fibromyalgia, we used skin biopsy to distinguish patients with and without small-fibre pathology. In all patients, we assessed somatosensory system function using quantitative sensory testing (QST) and laser-evoked potentials and investigated voltage-gated sodium channel genotyping. We then compared these variables in patients with and without small-fibre pathology. We found that clinical measures, QST, and laser-evoked potential variables did not differ between patients with and without small-fibre pathology. In most patients with small-fibre pathology, QST and laser-evoked potential variables fell within normative ranges commonly used in clinical practice. Of the 57 patients, one patient without small-fibre pathology and 2 patients with small-fibre pathology had rare variants of voltage-gated sodium channels, namely SCN11A, SCN9A, and SCN1A variants. The SCN9A variant, found in a patient with small-fibre pathology, was an already profiled gain-of-function mutation, previously reported in small-fibre neuropathy. Our findings suggest that small-fibre pathology has a negligible impact on somatosensory system function in fibromyalgia. The genetic analysis suggests that patients with rare small-fibre neuropathy due to voltage-gated sodium channel variants may be misdiagnosed as patients with fibromyalgia.

Intraepidermal Nerve Fiber Density as Measured by Skin Punch Biopsy as a Marker for Small Fiber Neuropathy: Application in Patients with Fibromyalgia

Small fiber neuropathy (SFN) is a type of peripheral neuropathy that occurs from damage to the small A-delta and C nerve fibers that results in the clinical condition known as SFN. This pathology may be the result of metabolic, toxic, immune-mediated, and/or genetic factors. Small fiber symptoms can be variable and inconsistent and therefore require an objective biomarker confirmation. Small fiber dysfunction is not typically captured by diagnostic tests for large-fiber neuropathy (nerve conduction and electromyographic study). Therefore, skin biopsies stained with PGP 9.5 are the universally recommended objective test for SFN, with quantitative sensory tests, autonomic function testing, and corneal confocal imaging as secondary or adjunctive choices. Fibromyalgia (FM) is a heterogenous syndrome that has many symptoms that overlap with those found in SFN. A growing body of research has shown approximately 40-60% of patients carrying a diagnosis of FM have evidence of SFN on skin punch biopsy. There is currently no clearly defined phenotype in FM at this time to suggest whom may or may not have SFN, though research suggests it may correlate with severe cases. The skin punch biopsy provides an objective tool for use in quantifying small fiber pathology in FM. Skin punch biopsy may also be repeated for surveillance of the disease as well as measuring response to treatments. Evaluation of SFN in FM allows for better classification of FM and guidance for patient care as well as validation for their symptoms, leading to better use of resources and outcomes.

Juvenile primary Fibromyalgia Syndrome: epidemiology, etiology, pathogenesis, clinical manifestations and diagnosis

Juvenile primary fibromyalgia syndrome (JPFS) is a chronic, musculoskeletal pain syndrome affecting children and adolescents, most commonly adolescent girls. The syndrome has a multifactorial etiology, with altered central pain processing playing an important role. The hallmark symptom is severe, widespread musculoskeletal pain. Other symptoms include sleep and mood disturbances, headaches, stiffness, and subjective joint swelling. Physical examination can reveal multiple tender points. The diagnosis is clinical, with defined criteria. Early diagnosis and intervention are important. In this part of the review, we discuss the epidemiology, etiology, pathogenesis, clinical manifestations and diagnosis of JPFS. Part two will focus on treatment and prognosis.

MiR103a-3p and miR107 are related to adaptive coping in a cluster of fibromyalgia patients

BACKGROUND

MicroRNA (miRNA) mainly inhibit post-transcriptional gene expression of specific targets and may modulate disease severity.

OBJECTIVE

We aimed to identify miRNA signatures distinguishing patient clusters with fibromyalgia syndrome (FMS).

SUBJECTS AND METHODS

We previously determined four FMS patient clusters labelled "maladaptive", "adaptive", "vulnerable", and "resilient". Here, we cluster-wise assessed relative gene expression of miR103a-3p, miR107, miR130a-3p, and miR125a-5p in white blood cell (WBC) RNA of 31 FMS patients and 16 healthy controls. Sum scores of pain-, stress-, and resilience-related questionnaires were correlated with miRNA relative gene expression. A cluster-specific speculative model of a miRNA-mediated regulatory cycle was proposed, and its potential targets verified by the online tool "target scan human".

RESULTS

One-way ANOVA revealed lower gene expression of miR103a-3p, miR107, and miR130a-3p in FMS patients compared to controls (p < 0.05). Follow-up post-hoc tests indicated the highest peak of gene expression of miR103a-3p for the adaptive cluster (p < 0.05), i.e. in patients with low disability in all symptom categories. Gene expression of miR103a-3p correlated with FMS related disability and miR107 with the score "physical abuse" of the trauma questionnaire (p < 0.05). Target scan identified sucrose non-fermentable serine/threonine protein kinase, nuclear factor kappa-b, cyclin dependent kinase, and toll-like receptor 4 as genetic targets of the miR103a/107 miRNA family.

CONCLUSION

We show an association between upregulated gene expression of miR103a, tendentially of miR107, and adaptive coping in FMS patients. Validation of this pair of miRNA may enable to identify a somatic resilience factor in FMS.

The cornucopia of central disinhibition pain - An evaluation of past and novel concepts

Central disinhibition (CD), as applied to pain, decreases thresholds of endogenous systems. This provokes onset of spontaneous or evoked pain in an individual beyond the ability of the nervous system to inhibit pain resulting from a disease or tissue damage. The original CD concept as proposed by Craig entails a shift from the lateral pain pathway (i.e. discriminative pain processing) towards the medial pain pathway (i.e. emotional pain processing), within an otherwise neurophysiological intact environment. In this review, the original CD concept as proposed by Craig is extended by the primary "nociceptive pathway damage - CD" concept and the secondary "central pathway set point - CD". Thereby, the original concept may be transferred into anatomical and psychological non-functional conditions. We provide examples for either primary or secondary CD concepts within different clinical etiologies as well as present surrogate models, which directly mimic the underlying pathophysiology (A-fiber block) or modulate the CD pathway excitability (thermal grill). The thermal grill has especially shown promising advancements, which may be useful to examine CD pathway activation in the future. Therefore, within this topical review, a systematic review on the thermal grill illusion is intended to stimulate future research. Finally, the authors review different mechanism-based treatment approaches to combat CD pain.

Electrodiagnostic Abnormalities Associated with Fibromyalgia

PURPOSE

Increasing evidence suggests that fibromyalgia most likely represents a neurological dysfunction. We previously hypothesized that at least some fibromyalgia cases may be caused by irritation of nerve root fibers and sensory neurons due to moderately increased cerebrospinal pressure. Because of the rostro-caudal hydrostatic pressure gradient, neurogenic abnormalities are expected to be most pronounced in sacral nerve roots. The purpose was to review electrodiagnostic tests of patients with fibromyalgia.

METHODS

A retrospective review of electrodiagnostic test results, including the lumbar and sacral nerve root myotomes of patients diagnosed with fibromyalgia according to the 1990 criteria of the American College of Rheumatology was done.

RESULTS

All 17 patients were female. Sural nerve responses could not be elicited in 12% and S1-Hoffmann reflex latencies were increased in 41%. In 12% of the patients, fibular motor nerve distal latency and conduction velocity were outside normal limits. Needle-EMG revealed neurogenic motor unit potentials in 0% of L2, 6% of L3, 29% of L4, 71% of L5, 47% of S1, 94% of S2, and 76% of S3-S4 myotomes. S3-S4 nerve-supplied anal reflexes were delayed in 94%.

CONCLUSION

This is the first time that electrodiagnostic data of both lumbar and sacral nerve root myotomes in fibromyalgia patients are presented. All patients showed neurogenic abnormalities that were more pronounced in the sacral than in the lumbar myotomes with a rather patchy distribution pattern. We propose that, in addition to skin punch biopsies to assess small fiber neuropathy, assessment of the anal reflex may be a useful part of the diagnostic pathway in patients with fibromyalgia.

Activation of Transposable Elements in Immune Cells of Fibromyalgia Patients

Advancements in nucleic acid sequencing technology combined with an unprecedented availability of metadata have revealed that 45% of the human genome constituted by transposable elements (TEs) is not only transcriptionally active but also physiologically necessary. Dysregulation of TEs, including human retroviral endogenous sequences (HERVs) has been shown to associate with several neurologic and autoimmune diseases, including Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS). However, no study has yet addressed whether abnormal expression of these sequences correlates with fibromyalgia (FM), a disease frequently comorbid with ME/CFS. The work presented here shows, for the first time, that, in fact, HERVs of the H, K and W types are overexpressed in immune cells of FM patients with or without comorbid ME/CFS. Patients with increased HERV expression (N = 14) presented increased levels of interferon (INF-β and INF-γ) but unchanged levels of TNF-α. The findings reported in this study could explain the flu-like symptoms FM patients present with in clinical practice, in the absence of concomitant infections. Future work aimed at identifying specific genomic loci differentially affected in FM and/or ME/CFS is warranted.

Assessing diagnostic value of microRNAs from peripheral blood mononuclear cells and extracellular vesicles in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a debilitating multisystemic disease of unknown etiology, affecting thousands of individuals worldwide. Its diagnosis still relies on ruling out medical problems leading to unexplained fatigue due to a complete lack of disease-specific biomarkers. Our group and others have explored the potential value of microRNA profiles (miRNomes) as diagnostic tools for this disease. However, heterogeneity of participants, low numbers, the variety of samples assayed, and other pre-analytical variables, have hampered the identification of  disease-associated miRNomes. In this study, our team has evaluated, for the first time, ME/CFS miRNomes in peripheral blood mononuclear cells (PBMCs) and extracellular vesicles (EVs) from severely ill patients recruited at the monographic UK ME biobank to assess, using standard operating procedures (SOPs), blood fractions with optimal diagnostic power for a rapid translation of a miR-based diagnostic method into the clinic. Our results show that routine creatine kinase (CK) blood values, plasma EVs physical characteristics (including counts, size and zeta-potential), and a limited number of differentially expressed PBMC and EV miRNAs appear significantly associated with severe ME/CFS (p < 0.05). Gene enrichment analysis points to epigenetic and neuroimmune dysregulated pathways, in agreement with previous reports. Population validation by a cost-effective approach limited to these few potentially discriminating variables is granted.

Small fiber neuropathy in unexpected clinical settings: a review

Small fiber neuropathy (SFN) is being recognized with increasing frequency in neuromuscular practice due to improved diagnostic techniques. Although there are some common etiologies, up to one-third of cases are considered idiopathic. In recent years, several disorders have unexpectedly been reported in association with SFN, on clinical grounds and complementary investigations, including quantitative sensory testing, intraepidermal nerve fiber density and confocal corneal microscopy. Knowledge of these disorders is important in clinical practice as increased awareness enables prompt diagnosis of SFN in these settings and early optimal therapeutic management of affected patients. Furthermore, these new developments may lead to a better understanding of the pathophysiologic mechanisms underlying SFN in these different disorders as well as, in some cases, an expanded spectrum of affected organs and systems. This article reviews these reported associations, their possible pathophysiologic bases, and the potential resulting management implications.

Reduced association between dendritic cells and corneal sub-basal nerve fibers in patients with fibromyalgia syndrome

In our study, we aimed at investigating corneal langerhans cells (LC) in patients with fibromyalgia syndrome (FMS) and small fiber neuropathy (SFN) as potential contributors to corneal small fiber pathology. We enrolled women with FMS (n = 134) and SFN (n = 41) who underwent neurological examination, neurophysiology, prostaglandin analysis in tear fluid, and corneal confocal microscopy (CCM). Data were compared with those of 60 age-matched female controls. After screening for dry eye disease, corneal LC were counted and sub-classified as dendritic (dLC) and non-dendritic (ndLC) cells with or without nerve fiber association. We further analyzed corneal nerve fiber density (CNFD), length (CNFL), and branch density (CNBD). Neurological examination indicated deficits of small fiber function in patients with SFN. Nerve conduction studies were normal in all participants. Dry eye disease was more prevalent in FMS (17%) and SFN (28%) patients than in controls (5%). Tear fluid prostaglandin levels did not differ between FMS patients and controls. While corneal LC density in FMS and SFN patients was not different from controls, there were fewer dLC in association with nerve fibers in FMS and SFN patients than in controls (P < .01 each). Compared to controls, CNFL was lower in FMS and SFN patients (P < .05 each), CNFD was lower only in FMS patients (P < .05), and CNBD was lower only in SFN patients (P < .001). There was no difference in any CCM parameter between patients with and without dry eyes. Our data indicate changes in corneal innervation and LC distribution in FMS and SFN, potentially based on altered LC signaling.

MicroRNA And Circular RNA Expression In Affected Skin Of Patients With Postherpetic Neuralgia

Mechanisms of postherpetic neuralgia (PHN) are still not clear. Transcripts such as microRNA (miRNA) and circular RNA (circRNA) in the affected skin may take part in the initiation and development of this neuropathic pain; however, their expression profiles in skins of PHN patients have not been reported. The PHN affected skin and the mirror skin were collected and subjected to miRNA and circRNA microarray, and expression profiles were comparatively analyzed. There were 317 differently expressed miRNAs in PHN affected skin compared with mirror skin (fold change ≥2.0), and 13 of them showed fold change >10 in the PHN skin. Only one circRNA, hsa_circRNA_405463 showed fold change >2 in PHN skin, however, 31 circRNAs with fold change ≥1.5. To evaluate functions of differential miRNAs, their target mRNAs were predicted and bioinformatics analyses including gene ontology, Kyoto Encyclopedia of Genes and Genomes pathway were conducted. Target mRNAs significantly (P<0.05) enriched in 85 pathways, such as FoxO, AMPK, MAPK and pathway. These data reported for the first time that miRNA and circRNA differentially expressed in the PHN skin and these transcripts with abnormal expression could be potential targets to treat PHN.

From Mechanism to Cure: Renewing the Goal to Eliminate the Disease of Pain

Objective

Persistent pain causes untold misery worldwide and is a leading cause of disability. Despite its astonishing prevalence, pain is undertreated, at least in part because existing therapeutics are ineffective or cause intolerable side effects. In this review, we cover new findings about the neurobiology of pain and argue that all but the most transient forms of pain needed to avoid tissue damage should be approached as a disease where a cure can be the goal of all treatment plans, even if attaining this goal is not yet always possible.

Design

We reviewed the literature to highlight recent advances in the area of the neurobiology of pain.

Results

We discuss barriers that are currently hindering the achievement of this goal, as well as the development of new therapeutic strategies. We also discuss innovations in the field that are creating new opportunities to treat and even reverse persistent pain, some of which are in late-phase clinical trials.

Conclusion

We conclude that the confluence of new basic science discoveries and development of new technologies are creating a path toward pain therapeutics that should offer significant hope of a cure for patients and practitioners alike. Classification of Evidence. Our review points to new areas of inquiry for the pain field to advance the goal of developing new therapeutics to treat chronic pain.

Differences in the miRNA signatures of chronic musculoskeletal pain patients from neuropathic or nociceptive origins

BACKGROUND

The quality of life for millions of people worldwide is affected by chronic pain. In addition to the effect of chronic pain on well-being, chronic pain has also been associated with poor health conditions and increased mortality. Due to its multifactorial origin, the classification of pain types remains challenging. MicroRNAs (miRNA) are small molecules that regulate gene expression. They are released into the bloodstream in a stable manner under normal and pathological conditions and have been described as potential biomarkers. In the present study, we aimed to investigate whether pain may induce an aberrant, specific dysregulation of miRNA expression, depending on the origin of the pain.

METHODS AND FINDINGS

To do so, we measured the expression changes of 184 circulating miRNAs (c-miRNAs) in the plasma samples of patients with different origins of chronic musculoskeletal pain. After statistical analyses, we identified seven c-miRNA candidates that were differentially expressed depending on the nociceptive or neuropathic origin of the pain. We then developed a two c-miRNA signature (hsa-miR-320a and hsa-miR-98-5p) that was able to correctly classify the pain type of 70% of the patients from the validation set.

CONCLUSIONS

In conclusion, circulating miRNAs are promising biomarkers to identify and characterize the chronic pain type and to further improve its clinical management.

Pain-associated Mediators and Axon Pathfinders in Fibromyalgia Skin Cells

Objective.

To investigate whether the expression of cytokine, nociception-associated ion channel, and axon guidance genes in patients with skin cell fibromyalgia syndrome (FMS) differs from healthy controls, potentially contributing to pain and small-fiber degeneration in FMS.

Methods.

We prospectively recruited 128 patients and 26 healthy controls. All study participants underwent neurological examination, and a skin punch biopsy was obtained from the lateral calf and thigh. Skin samples were processed to histologically determine intraepidermal nerve fiber density (IENFD) and for primary fibroblast and keratinocyte cell cultures. Gene expression of selected pro- and antiinflammatory cytokines, nociception-associated ion channels, and axon guidance cues was assessed with quantitative real-time PCR.

Results.

In fibroblasts, transforming growth factor–ß1 (TGF-ß1) gene expression was higher in patients with FMS compared to controls (calf and thigh: p < 0.001). Also, expression was higher in patients than in controls for these variables: hyperpolarization-activated cyclic nucleotide-gated ion channel 2 (calf: p < 0.01), ephrin-A4 (EFNA4; calf: p < 0.05, thigh: p < 0.001), and ephrin receptor-A4 (EPHA4; thigh: p < 0.05). In keratinocytes, interleukin 10 gene expression was higher in patients with FMS than in controls (thigh: p < 0.05). While no intergroup difference was found for nociception-associated ion channels, EFNA4 and EPHA4 (calf: p < 0.01 each) expression was higher in patients with FMS than in controls. Axon guide expression did not correlate with IENFD.

Conclusion.

In FMS, skin cells may contribute to cutaneous nociception by differentially expressing membrane-bound and soluble pain mediators and axon pathfinders.

Diagnosis and management of sensory polyneuropathy

Sensory polyneuropathies, which are caused by dysfunction of peripheral sensory nerve fibers, are a heterogeneous group of disorders that range from the common diabetic neuropathy to the rare sensory neuronopathies. The presenting symptoms, acuity, time course, severity, and subsequent morbidity vary and depend on the type of fiber that is affected and the underlying cause. Damage to small thinly myelinated and unmyelinated nerve fibers results in neuropathic pain, whereas damage to large myelinated sensory afferents results in proprioceptive deficits and ataxia. The causes of these disorders are diverse and include metabolic, toxic, infectious, inflammatory, autoimmune, and genetic conditions. Idiopathic sensory polyneuropathies are common although they should be considered a diagnosis of exclusion. The diagnostic evaluation involves electrophysiologic testing including nerve conduction studies, histopathologic analysis of nerve tissue, serum studies, and sometimes autonomic testing and cerebrospinal fluid analysis. The treatment of these diseases depends on the underlying cause and may include immunotherapy, mitigation of risk factors, symptomatic treatment, and gene therapy, such as the recently developed RNA interference and antisense oligonucleotide therapies for transthyretin familial amyloid polyneuropathy. Many of these disorders have no directed treatment, in which case management remains symptomatic and supportive. More research is needed into the underlying pathophysiology of nerve damage in these polyneuropathies to guide advances in treatment.

Inflammation in the pathophysiology of neuropathic pain

Peripheral nerve injuries and diseases often lead to pain persisting beyond the resolution of damage, indicating an active disease-promoting process, which may result in chronic pain. This is regarded as a maladaptive mechanism resulting from neuroinflammation that originally serves to promote regeneration and healing. Knowledge on these physiological and pathophysiological processes has accumulated over the last few decades and has started to yield potential therapeutic targets. Key players are macrophages, T-lymphocytes, cytokines, and chemokines. In the spinal cord and brain, microglia and astrocytes are involved. Recently, data have been emerging on the regulation of these players. MicroRNAs and other noncoding RNAs have been discussed as potential master switches that may link nerve injury, pain, and inflammation. Clinical disorders most intensely studied in the context of neuroinflammation and pain are the complex regional pain syndrome, polyneuropathies, postherpetic neuralgia, and the fibromyalgia syndrome, in which recently a neuropathic component has been described. Research from several groups has shown an important role of both proinflammatory and anti-inflammatory cytokines in neuropathic and other chronic pain states in humans. There is ample evidence of an analgesic action of anti-inflammatory cytokines in animal models. The interplay of anti-inflammatory cytokines and the nociceptive system provides possibilities and challenges concerning treatment strategies based on this concept.

Impact of Polypharmacy on Candidate Biomarker miRNomes for the Diagnosis of Fibromyalgia and Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Striking Back on Treatments

Fibromyalgia (FM) and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) are diseases of unknown etiology presenting complex and often overlapping symptomatology. Despite promising advances on the study of miRNomes of these diseases, no validated molecular diagnostic biomarker yet exists. Since FM and ME/CFS patient treatments commonly include polypharmacy, it is of concern that biomarker miRNAs are masked by drug interactions. Aiming at discriminating between drug-effects and true disease-associated differential miRNA expression, we evaluated the potential impact of commonly prescribed drugs on disease miRNomes, as reported by the literature. By using the web search tools SM2miR, Pharmaco-miR, and repoDB, we found a list of commonly prescribed drugs that impact FM and ME/CFS miRNomes and therefore could be interfering in the process of biomarker discovery. On another end, disease-associated miRNomes may incline a patient’s response to treatment and toxicity. Here, we explored treatments for diseases in general that could be affected by FM and ME/CFS miRNomes, finding a long list of them, including treatments for lymphoma, a type of cancer affecting ME/CFS patients at a higher rate than healthy population. We conclude that FM and ME/CFS miRNomes could help refine pharmacogenomic/pharmacoepigenomic analysis to elevate future personalized medicine and precision medicine programs in the clinic.

MiR-134-5p attenuates neuropathic pain progression through targeting Twist1

Neuropathic pain is a kind of chronic pain because of dysfunctions of somatosensory nerve system. Recently, many studies have demonstrated that microRNAs (miRs) play crucial roles in neuropathic pain development. This study was designed to investigate the effects of miR-134-5p on the process of neuropathic pain progression in a rat model established by chronic sciatic nerve injury (CCI). First, we observed that miR-134-5p was significantly decreased in CCI rat models. Overexpression of miR-134-5p strongly alleviated neuropathic pain behaviors including mechanical and thermal hyperalgesia. Meanwhile, inflammatory cytokine expression, such as IL-6, IL-1β and TNF-α in CCI rats were greatly repressed by upregulation of miR-134-5p. Twist1 has been widely regarded as a poor prognosis biomarker in diverse diseases. Here, by using bioinformatic analysis, 3'-untranslated region (UTR) of Twist1 was predicted to be a downstream target of miR-134-5p in our study. Here, we found that overexpression of miR-134-5p was able to suppress Twist1 dramatically. Furthermore, it was exhibited that Twist1 was increased in CCI rats time-dependently and Twist1 was inhibited in vivo. Subsequently, downregulation of Twist1 in CCI rats could depress neuropathic pain progression via inhibiting neuroinflammation. In conclusion, our current study indicated that miR-134-5p may inhibit neuropathic pain development through targeting Twist1. Our findings suggested that miR-134-5p might provide a novel therapeutic target for neuropathic pain.

MiRNA expression profiles in healthy OSAHS and OSAHS with arterial hypertension: potential diagnostic and early warning markers

Background

Obstructive sleep apnea-hypopnea syndrome (OSAHS) is prone to being complicated with various cardiovascular, cerebrovascular and metabolic conditions. OSAHS, due to its multifactorial nature, entails individualized and comprehensive treatment. So far, no well-established diagnostic criteria for the disease are available. In recent years, miRNA has been shown to be a sensitive biomarker suggestive of the progression and prognosis of many diseases. In this study, we examined some serum miRNAs in healthy OSAHS (OSAHS patients without complication) and OSAHS with arterial hypertension, with an attempt to understand the potential effects on the disease, improve the diagnosis of OSAHS and find OSAHS-related diagnostic markers.

Methods

Against various diagnostic criteria, participants were divided into three groups: healthy OSAHS, OSAHS with arterial hypertension and healthy controls. Their serum miRNA profiles were assessed by microarray technology, and then differentially expressed miRNAs were verified by quantitative real-time PCR (qRT-PCR). The receiver operating characteristic (ROC) curves of miRNAs were constructed and the areas under the curve (AUC) were calculated. Meanwhile, the miRNAs were subjected to logistic regression analysis. The target genes were bioinformatically assessed, their functions and signaling pathways further determined and eventually an miRNA-gene network was established.

Results

Analysis with the miRNA array exhibited that, compared with the control group, 12 differentially expressed miRNAs were found in healthy OSAHS, and 33 were found in OSAHS with arterial hypertension. The expression of miR-126-3p, let-7d-5p, miR-7641 and miR-1233-5p, miR-320b, miR-145-5p, miR-107, miR-26a-5p were validated by using qRT-PCR. Bioinformatics analysis predicted that the potential target genes of these miRNAs might be involved in metabolism, and the regulation of endothelial cells and nervous system. Moreover, the ROC analysis showed that the using miR-145-5p and let-7d-5p in combination can identify the healthy OSAHS, presence of miR-126-3p, miR-26a-5p and miR-107 was well indicative of OSAHS with arterial hypertension.

Conclusions

A cluster of dysregulation miRNAs have been found to be involved in the development of OSAHS patients. Moreover, these miRNAs might be used to be potential diagnostic and early warning markers.

A systematic review and meta-analysis of the prevalence of small fiber pathology in fibromyalgia: Implications for a new paradigm in fibromyalgia etiopathogenesis

OBJECTIVES

Fibromyalgia is a condition which exhibits chronic widespread pain with neuropathic pain features and has a major impact on health-related quality of life. The pathophysiology remains unclear, however, there is increasing evidence for involvement of the peripheral nervous system with a high prevalence of small fiber pathology (SFP). The aim of this systematic literature review is to establish the prevalence of SFP in fibromyalgia.

METHODS

An electronic literature search was performed using MEDLINE, EMBASE, PubMed, Web of Science, CINAHL and the Cochrane Library databases. Published full-text, English language articles that provide SFP prevalence data in studies of fibromyalgia of patients over 18years old were included. All articles were screened by two independent reviewers using a priori criteria. Methodological quality and risk of bias were evaluated using the critical appraisal tool by Munn et al. Overall and subgroup pooled prevalence were calculated by random-effects meta-analysis with 95% CI.

RESULTS

Database searches found 935 studies; 45 articles were screened of which 8 full text articles satisfied the inclusion criteria, providing data from 222 participants. The meta-analysis demonstrated the pooled prevalence of SFP in fibromyalgia is 49% (95% CI: 38-60%) with a moderate degree of heterogeneity, (I²= 68%). The prevalence estimate attained by a skin biopsy was 45% (95% CI: 32-59%, I²= 70%) and for corneal confocal microscopy it was 59% (95% CI: 40-78%, I²= 51%).

CONCLUSION

There is a high prevalence of SFP in fibromyalgia. This study provides compelling evidence of a distinct phenotype involving SFP in fibromyalgia. Identifying SFP will aid in determining its relationship to pain and potentially facilitate the development of future interventions and pharmacotherapy.

The role of miR-190a-5p contributes to diabetic neuropathic pain via targeting SLC17A6

Introduction

MicroRNAs play a key role in neuropathic pain. In a previous study, miR-190a-5p was significantly downregulated in diabetic neuropathic pain (DNP). However, the role and pathological mechanism of miR-190a-5p in DNP still remain unclear.

Materials and methods

DNP model was established. The paw withdrawal thresholds were measured to assess the mechanical nociceptive response. Dual-luciferase reporter assay was used to confirm the target gene of microRNA. The expressions of microRNA, gene, and protein were detected by the quantitative real-time polymerase chain reaction or Western blot. The levels of IL-1β and IL-6 were detected with the enzyme-linked immuno sorbent assay.

Results

Compared with the control sample, the expression of miR-190a-5p was decreased and SLC17A6 was increased in the spinal tissue from those developing DNP. The bioinformatics and luciferase reporter assay demonstrated that SLC17A6 is a direct target of miR-190a-5p. Up-regulation of miR-190a-5p and inhibition of SLC17A6 could significantly weaken the painful behavior and reduce IL-1β and IL-6 level in DNP.

Conclusion

miR-190a-5p is involved in DNP via targeting SLC17A6, and miR-190a-5p and SLC17A6 may be the therapeutic targets of this disease.

Pain Processing and Vegetative Dysfunction in Fibromyalgia: A Study by Sympathetic Skin Response and Laser Evoked Potentials

BACKGROUND

A dysfunction of pain processing at central and peripheral levels was reported in fibromyalgia (FM). We aimed to correlate laser evoked potentials (LEPs), Sympathetic Skin Response (SSR), and clinical features in FM patients.

METHODS

Fifty FM patients and 30 age-matched controls underwent LEPs and SSR by the right hand and foot. The clinical evaluation included FM disability (FIQ) and severity scores (WPI), anxiety (SAS) and depression (SDS) scales, and questionnaires for neuropathic pain (DN4).

RESULTS

The LEP P2 latency and amplitude and the SSR latency were increased in FM group. This latter feature was more evident in anxious patients. The LEPs habituation was reduced in FM patients and correlated to pain severity scores. In a significant number of patients (32%) with higher DN4 and FIQ scores, SSR or LEP responses were absent.

CONCLUSIONS

LEPs and SSR might contribute to clarifying the peripheral and central nervous system involvement in FM patients.

Drugging the pain epigenome

More than 20% of adults worldwide experience different types of chronic pain, which are frequently associated with several comorbidities and a decrease in quality of life. Several approved painkillers are available, but current analgesics are often hampered by insufficient efficacy and/or severe adverse effects. Consequently, novel strategies for safe, highly efficacious treatments are highly desirable, particularly for chronic pain. Epigenetic mechanisms such as DNA methylation, histone modifications and microRNAs (miRNAs) strongly affect the regulation of gene expression, potentially for long periods over years or even generations, and have been associated with pathophysiological pain. Several studies, mostly in animals, revealed that inhibitors of DNA methylation, activators and inhibitors of histone modification and modulators of miRNAs reverse a number of pathological changes in the pain epigenome, which are associated with altered expression of pain-relevant genes. This epigenetic modulation might then reduce the nociceptive response and provide novel therapeutic options for analgesic therapy of chronic pain states. However, a number of challenges, such as nonspecific effects and poor delivery to target cells and tissues, hinder the rapid development of such analgesics. In this Review, we critically summarize data on epigenetics and pain, focusing on challenges in clinical development as well as possible new approaches to the drug modulation of the pain epigenome.

Reduced intraepidermal nerve fiber density after a sustained increase in insular glutamate: a proof-of-concept study examining the pathogenesis of small fiber pathology in fibromyalgia

Sustained insular administration of a glutamate uptake inhibitor produced a decrease in peripheral nerve fibers and a persistent increase in pain behaviors in rat.

Introduction:

Neuroimaging reveals increased glutamate within the insula of patients with fibromyalgia (FM), suggesting a link between FM symptoms and increased central excitatory neurotransmission. Many patients with FM also present with decreased intraepidermal nerve fiber density (IENFD), consistent with small fiber pathology. It remains unknown, however, whether either of these mechanistic findings represent a cause or a consequence of the other. This study tests the hypothesis that an excitatory imbalance within the insula leads to small fiber pathology.

Objectives:

This is a proof-of-concept study to examine whether a chronic, bilateral increase in insular glutamate can be a causal factor in the development of small fiber neuropathy in FM.

Methods:

The glutamate transport inhibitor l-trans-Pyrrolidine-2,4-dicarboxylic acid (PDC), which increases endogenous levels of glutamate, was dissolved in Ringer solution and bilaterally delivered into the insula of rats for 6 weeks. Naive rats that did not undergo any surgery or treatment and rats administered Ringer vehicle solution into the insula served as controls. Multimodal nociceptive sensitivity was assessed weekly. Hind paw tissue biopsies were collected for IENFD assessment, at the end of the experiment.

Results:

Compared with controls, increasing endogenous glutamate in the insula with PDC caused sustained decreases in mechanical paw withdrawal threshold and thermal paw withdrawal latency, increased aversion to noxious mechanical stimulation, and a decrease in IENFD. Cold reactivity was not altered by PDC administration.

Conclusion:

Bilateral insular PDC administration produced a persistent increase in multimodal pain behaviors and a decrease in peripheral nerve fibers in rat. These preclinical findings offer preliminary support that insular hyperactivity may be a casual factor in the development of small fiber pathology in FM.