The Role and Importance of Small Fiber Neuropathy in Fibromyalgia Pain

Pain mechanisms for the practicing rheumatologist

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

Relationship between dysphonia and anxiety in fibromyalgia syndrome

BACKGROUND

Our aim in conducting this study is to determine the relationship dysphonia and anxiety in patients with fibromyalgia syndrome (FS).

METHODS

Between April 2021 and June 2021, 25 FS diagnosed patients (22 females, 3 males; mean age: 45.36 ± 7.68 years; range 27-65 years), and, for the control group, 25 healthy volunteers (20 females, 5 males; mean age: 42.60 ± 9.98 years; range 29-62 years) with similar demographic features were included in the study. Visual Analog Scale (VAS), Beck Anxiety Questionary (BAQ), and voice analyses were evaluated for all the participants. Acoustic parameters (AP), such as F₀ (Hz), jitter (%), shimmer (%), and Maximum Phonation Time (MPT), were measured for dysphonia. The correlation between MPT and BAQ was evaluated.

RESULTS

The demographic characteristics of the groups did not differ statistically significantly (p > 0.05). VAS and BAQ scores were statistically significantly higher in the FS group than healthy individuals. In the assessment of sound, there was no significant difference between F0 and jitteriness between the two groups. While shimmer scores were significantly higher in the FS group, MPT scores were statistically significantly higher in healthy individuals.

CONCLUSIONS

In our study, we observed that FS patients had statistically significantly higher BAQ, VAS scores compared to the control group. The shimmer of voice was increased and MPT values were decreased statistically significantly in FS patients. This says that there may be weakness in the laryngeal muscles affecting the vocal cord and thus voice quality. In addition to this, increased anxiety in FS patients may be associated with dysphonia. There is need for more controlled studies with increased number of patients to investigate the dysphonia in FS patients.

Cardiovascular risk assessment using ASCVD risk score in fibromyalgia: a single-centre, retrospective study using "traditional" case control methodology and "novel" machine learning

BACKGROUND

In autoimmune inflammatory rheumatological diseases, routine cardiovascular risk assessment is becoming more important. As an increased cardiovascular disease (CVD) risk is recognized in patients with fibromyalgia (FM), a combination of traditional CVD risk assessment tool with Machine Learning (ML) predictive model could help to identify non-traditional CVD risk factors.

METHODS

This study was a retrospective case-control study conducted at a quaternary care center in India. Female patients diagnosed with FM as per 2016 modified American College of Rheumatology 2010/2011 diagnostic criteria were enrolled; healthy age and gender-matched controls were obtained from Non-communicable disease Initiatives and Research at AMrita (NIRAM) study database. Firstly, FM cases and healthy controls were age-stratified into three categories of 18-39 years, 40-59 years, and ≥ 60 years. A 10 year and lifetime CVD risk was calculated in both cases and controls using the ASCVD calculator. Pearson chi-square test and Fisher's exact were used to compare the ASCVD risk scores of FM patients and controls across the age categories. Secondly, ML predictive models of CVD risk in FM patients were developed. A random forest algorithm was used to develop the predictive models with ASCVD 10 years and lifetime risk as target measures. Model predictive accuracy of the ML models was assessed by accuracy, f1-score, and Area Under 'receiver operating Curve' (AUC). From the final predictive models, we assessed risk factors that had the highest weightage for CVD risk in FM.

RESULTS

A total of 139 FM cases and 1820 controls were enrolled in the study. FM patients in the age group 40-59 years had increased lifetime CVD risk compared to the control group (OR = 1.56, p = 0.043). However, CVD risk was not associated with FM disease severity and disease duration as per the conventional statistical analysis. ML model for 10-year ASCVD risk had an accuracy of 95% with an f1-score of 0.67 and AUC of 0.825. ML model for the lifetime ASCVD risk had an accuracy of 72% with an f1-score of 0.79 and AUC of 0.713. In addition to the traditional risk factors for CVD, FM disease severity parameters were important contributors in the ML predictive models.

CONCLUSION

FM patients of the 40-59 years age group had increased lifetime CVD risk in our study. Although FM disease severity was not associated with high CVD risk as per the conventional statistical analysis of the data, it was among the highest contributor to ML predictive model for CVD risk in FM patients. This also highlights that ML can potentially help to bridge the gap of non-linear risk factor identification.

Pain in Women: A Perspective Review on a Relevant Clinical Issue that Deserves Prioritization

Introduction

Gender equity and gender medicine are opportunities not to be missed, and this Expert Group Opinion Paper on pain in women aims to review the treatment of pain conditions mainly affecting women, as well as the fundamental aspects of the different clinical response to drug treatment between the genders, and what can be done for gender-specific rehabilitation.

Methods

Perspective review.

Results

Genotypic and phenotypic differences in pain between the sexes are conditioned by anatomical, physiological, neural, hormonal, psychological, social, and cultural factors, such as the response to pharmacological treatment to control pain. The examination of these factors shows that women are affected by pain diseases more frequently and severely than men and that they report pain more frequently and with a lower pain threshold than men. Some forms of pain are inherently related to gender differences, such as pain related to the genitourinary system. However, other forms of chronic pain are seen more frequently in women than men, such as migraine, rheumatological, and musculoskeletal pain, in particular fibromyalgia.

Discussion

Research is needed into the pathophysiological basis for gender differences in the generation of acute pain and maintenance of chronic pain, including the factors that put women at higher risk for developing chronic pain. In addition, different specialties need to collaborate to develop gender-related diagnostic and therapeutic guidelines, and healthcare professionals need to upskill themselves in the appropriate management of pain using existing diagnostic tools and therapeutic options.

Pain Mechanisms in Patients with Rheumatic Diseases

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

Large Fibre Neuropathy: Part of Fibromyalgia or Coexisting Entity?

Zielsetzung Ziel dieser Studie ist es, die Inzidenz von Large Fibre Neuropathy (LFN) bei Fibromyalgie (FM) -Patienten mit peripheren Neuropathie-Beschwerden zu untersuchen und den Einfluss von LFN und FM auf Schmerzen, Lebensqualität, Schlafqualität, Behinderung, und depressive Symptome.

Methoden Zwischen Juni 2018 und Februar 2019 wurden insgesamt 104 Patienten (67 Frauen, 37 Männer; Durchschnittsalter: 52,21±9,53 Jahre; Spanne 31–74 Jahre) mit der Diagnose FM in die Studie eingeschlossen. Die Patienten wurden in 2 Gruppen eingeteilt: Gruppe 1, einschließlich Patienten mit Polyneuropathie (PNP) (n=48) und Gruppe 2, einschließlich Nicht-PNP-Patienten (n=54). Gruppe 1 wurde auch weiter in 2 Untergruppen als sensorische PNP (n=28) und sensomotorische PNP (n=20) unterteilt. Alle Patienten wurden anhand der Visual Analog Scale (VAS), des Fibromyalgia Impact Questionnaire (FIQ), des Short Form-36 (SF-36), des Pittsburgh Sleep Quality Index (PSQI) und des Beck Depression Inventory (BDI) bewertet.

Ergebnisse Es gab keinen statistisch signifikanten Unterschied in den demografischen Merkmalen zwischen den Gruppen (p>0,05). Es gab einen statistisch signifikanten Unterschied in den VAS-, SF-36-, BDI-, FIQ- und PSQI-Werten zwischen Gruppe 1 und Gruppe 2 (p<0,05). Es gab keinen statistisch signifikanten Unterschied in den VAS-, SF-36-, BDI-, FIQ- und PSQI-Werten zwischen den sensorischen und sensomotorischen PNP-Gruppen (p>0,05).

Schlussfolgerungen Unsere Studienergebnisse zeigen, dass FM mit LFN die Schmerzen, die Lebensqualität, die Schlafqualität, die Behinderung und die depressiven Symptome negativ beeinflusst, gegenüber denjenigen ohne LFN, was auf die Bedeutung des Neuropathiemanagements bei FM-Patienten hinweist.

Neuroimmunology: What Role for Autoimmunity, Neuroinflammation, and Small Fiber Neuropathy in Fibromyalgia, Chronic Fatigue Syndrome, and Adverse Events after Human Papillomavirus Vaccination?

Fibromyalgia is a disorder characterized by chronic widespread pain and non-pain symptoms, such as fatigue, dysautonomia, and cognitive and sleep disturbances. Its pathogenesis and treatment continue to be the subject of debate. We highlight the role of three mechanisms-autoimmunity, neuroinflammation, and small fiber neuropathy-in the pathogenesis of the disease. These mechanisms are shown to be closely interlinked (also on a molecular level), and the review considers the implementation of this relationship in the search for therapeutic options. We also pay attention to chronic fatigue syndrome, which overlaps with fibromyalgia, and propose a concept of "autoimmune hypothalamopathy" for its pathogenesis. Finally, we analyze the molecular mechanisms underlying the neuroinflammatory background in the development of adverse events following HPV vaccination and suggesting neuroinflammation, which could exacerbate the development of symptoms following HPV vaccination (though this is hotly debated), as a model for fibromyalgia pathogenesis.

Small Fiber Polyneuropathy Is Prevalent in Patients Experiencing Complex Chronic Pelvic Pain

OBJECTIVE

To demonstrate the prevalence of small fiber polyneuropathy (SFPN) in patients with refractory chronic pelvic pain (CPP).

DESIGN

Retrospective study of prospective database.

SUBJECTS

Participants were complex CPP patients recruited from subspecity referral clinics defined as those who were refractory to initial treatment and/or exhibited comorbid pain syndromes at initial presentation.

METHODS

Comprehensive treatment history for CPP was obtained, and participants referred as above; 3-mm punch biopsies were obtained of the lower extremity and sent to diagnostic reference labs to evaluate for SFPN. The reported lab sensitivity and specificity for SFPN are 78-92% and 65-90%, respectively.

RESULTS

Twenty-five of 39 patients (64%) were positive for SFPN. Comorbid conditions noted in our population included gastroesophageal reflux disease (46%), migraine (38%), irritable bowel syndrome (33%), lower back pain (33%), fibromyalgia (38%), endometriosis (15%), interstitial cystitis (18%), vulvodynia (5%), and other chronic pain syndromes (36%).

CONCLUSIONS

The prevalence of SFPN in our specialty referral patients with complex CPP is remarkably high vs published general population prevalence data (53/100,000). Identification of SFPN in this complex population shifts the focus from undefined syndromes to symptom complexes with linked potentially treatable mechanisms (e.g., SFPN, central sensitization). Most CPP patients with SFPN are undiagnosed. Considering the diagnosis may expand treatment options beyond conventional or so-called adjuvant analgesics. Treatment may expand to therapies such as IV lidocaine, IVIG, or other immunomodulatory options. In addition, the value to the patient of receiving a diagnosis for a multisystem or refractory pain syndrome, often attributed to negative psychologic factors, cannot be underestimated. Identifying SFPN should be contemplated in CPP patients who present with multisystem pain or who have not responded to initial evaluation and management.

The relationship between regional pain with or without neuropathic symptoms and chronic widespread pain

Neuropathic pain was relatively rare and predicted a small number of chronic widespread pain cases. Using these estimates, treatments targeting neuropathic pain would at best prevent 6% of chronic widespread pain cases.

This study was performed to test whether the risk of developing chronic widespread pain (CWP) in those with regional pain was augmented in those with symptoms of neuropathic pain (NP). Persons free of CWP completed the Douleur Neuropathique 4 (scores ≥3 indicating NP); demographics; Hospital Anxiety and Depression scale; Pittsburgh Sleep Quality Index; and pain medications. Participants were classified as having no pain, regional pain with no symptoms of NP (), or regional pain with symptoms of NP (NP). At the 12-month follow-up, participants with CWP were identified. Logistic regression estimated the odds ratio, with 95% confidence intervals, of CWP in the and NP groups compared with no pain, and NP compared with . Partial population attributable risks estimated the proportion of CWP attributable to baseline or NP exposure. One thousand one hundred sixty-two participants completed the baseline DN4 and provided pain data at follow-up: 523 (45.0%) had no baseline pain, 562 (48.4%) , and 77 (6.6%) NP. One hundred fifty-three (13.2%) had CWP at 12 months: 19 (3.6%) no pain, 108 (19.2%) , and 26 (33.8%) NP. (2.9 [1.9-4.3]) and NP (2.1 [1.1-4.0]) predicted CWP after adjusting for demographics, Hospital Anxiety and Depression scale, Pittsburgh Sleep Quality Index, and medications. The partial population attributable risk was 41.3% (25.2-54.0) for and 6.0% (0.1-11.6) for NP. The NP group were not more likely to develop CWP when compared directly with (1.5 [0.8-2.8]). Neuropathic pain was relatively rare and predicted a small number of new-onset CWP cases. Using these estimates, treatments targeting NP would at best prevent 6% of CWP cases.

Small fiber polyneuropathy as a potential therapeutic target in interstitial cystitis/bladder pain syndrome

INTRODUCTION AND HYPOTHESIS

Interstitial cystitis/bladder pain syndrome (IC/BPS) and fibromyalgia (FM) are frequently co-occurring medical diagnoses in patients referred to the urology clinic for secondary and tertiary treatment options.

METHODS

Abundant literature has shown that many patients with FM have small fiber polyneuropathy (SFPN) that can be confirmed via skin punch biopsy and immunological staining to measure nerve density.

RESULTS AND CONCLUSIONS

This finding of SFPN provides a therapeutic target for FM and in this article we hypothesize and provide rationale for the idea that this same phenomenon (SFPN) might explain, in some IC/BPS patients, the finding of widespread pain and likewise provide a therapeutic target for these patients.

Fascial preadipocytes: another missing piece of the puzzle to understand fibromyalgia?

Fibromyalgia (FM) syndrome is a chronic condition causing pain, affecting approximately 0.5%-6% of the developed countries' population, and on average, 2% of the worldwide population. Despite the large amount of scientific literature available, the FM etiology is still uncertain. The diagnosis is based on the clinical presentation and the severity of the symptomatology. Several studies pointed out pathological alterations within the central nervous system, suggesting that FM could originate from a central sensitization of the pain processing centers. Research supports the thesis of a peripheral neuropathic component, with the finding of axonal damages. The fibromyalgia patient has many myofascial system abnormalities, such as pain and fatigue, impairing the symptomatic profile. This paper revises the myopathic compensations, highlighting the possible role of the fascia in generating symptoms, being aware of the new information about the fascia's activity in stimulating inflammation and fat cell production.

Pulsed electromagnetic field therapy in the treatment of pain and other symptoms in fibromyalgia: A randomized controlled study

Low-energy pulsed electromagnetic field (PEMF) therapy has been suggested as a promising therapy to increase microcirculation, which is of great concern in patients with fibromyalgia. This study evaluated the effectiveness of PEMF therapy on the treatment of fibromyalgia. A group of 108 women with fibromyalgia were allocated to a 12-week treatment period with an active Bio-Electro-Magnetic-Energy-Regulation (BEMER) device and a similar treatment period with an inactive device. Each patient received active and sham treatments in a random order. Pain and stiffness were assessed on a visual analog scale (VAS, scale 0-100 mm), and functional status was assessed by the Fibromyalgia Impact Questionnaire (FIQ). Mean VAS pain scores before the active and sham treatment periods were 66 (SD 22) and 63 (SD 22), respectively. After treatment periods, mean VAS pain scores had decreased significantly in active treatment, -12, 95% CI [-18, -6], and in sham treatment, -11, 95% CI [-17, -5]. Similarly, the decrease in stiffness and FIQ index after both treatments was statistically significant. However, per-protocol analysis showed no differences between active and sham treatments at any of the outcomes. This study demonstrated that low-energy PEMF therapy was not efficient in reducing pain and stiffness or in improving functioning in women with fibromyalgia. Bioelectromagnetics. 39:405-413, 2018. © 2018 Wiley Periodicals, Inc.

Evidence of peripheral large nerve involvement in fibromyalgia: a retrospective review of EMG and nerve conduction findings in 55 FM subjects

OBJECTIVE

Whereas small fiber neuropathy (SFN) is now a recognized part of fibromyalgia (FM), surprisingly little attention has been paid to any findings of large fiber neuropathy (LFN) in this disorder. Since 90% to 95% of FM subjects seen in our outpatient facility routinely undergo EMG and nerve conduction studies (NCS) we elected to retrospectively review the EMG/NCS results garnered from a large cohort of unselected subjects in order to describe the electrodiagnostic features of LFN in FM.

METHODS

Records from 100 consecutive, unselected clinic patients meeting the 1990 ACR criteria for FM, who had undergone EMG/NCS, were reviewed. The same electromyographer tested all subjects. After exclusion of FM patients with any other clinically relevant condition that might influence EMG results (e.g., familial neural degenerative conditions, diabetes mellitus, Vitamin B-12 deficiency, etc.) fifty-five FM subjects remained: 29 subjects with "FM Only," and 26 subjects with FM+Rheumatoid Arthritis ("FM+RA"). All subjects had also undergone ankle area skin biopsy for determination of epidermal nerve fiber density (ENFD). Fourteen other subjects, without FM or RA, examined by the same electromyographer, were used as an EMG/NCS comparison group.

RESULTS

Ninety percent of the "FM Only" subjects demonstrated a demyelinating and/or axonal, sensorimotor polyneuropathy, and 63% had findings of SFN (ENFD ≤7 fibers/mm), suggesting a mixed fiber neuropathy in most. Furthermore, 61% of the "FM Only" subjects showed EMG findings suggestive of non-myotomal lower extremity axonal motor denervation, most likely due to a polyneuropathy, and 41% satisfied published criteria for "possible" chronic inflammatory demyelinating polyneuropathy (CIDP). There was surprisingly little difference in the EMG/NCS findings between the "FM Only" and the "FM+RA" groups. With the exception of carpal tunnel syndrome, our EMG/NCS comparison group showed few to none of these findings.

CONCLUSION

Our review of the EMG/NCS results, gleaned from the largest FM cohort yet studied with these modalities, shows that electrodiagnostic features of polyneuropathy, muscle denervation, and CIDP are common in FM. Furthermore these electrodiagnostic findings are often seen coincident with SFN, and are not significantly influenced by the presence of RA. These results, particularly when taken as a whole, suggest that EMG/NCS may be clinically useful in detecting LFN in FM and help in better understanding the etiopathogenesis of this painful disorder.

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.

Diagnostic confounders of chronic widespread pain: not always fibromyalgia

Although chronic widespread pain is the defining feature of fibromyalgia, a myriad of other conditions may present with similar pain complaint leading to misdiagnosis. Conditions that may mimic fibromyalgia may be categorized as musculoskeletal, neurological, endocrine/metabolic, psychiatric/psychological, and medication related. In this review, we examine these various conditions that should be considered in a differential diagnosis and provide direction that will help the clinician differentiate these conditions from fibromyalgia.

Introduction:

Chronic widespread pain (CWP) is the defining feature of fibromyalgia (FM), a worldwide prevalent condition. Chronic widespread pain is, however, not pathognomonic of FM, and other conditions may present similarly with CWP, requiring consideration of a differential diagnosis.

Objectives:

To conduct a literature search to identify medical conditions that may mimic FM and have highlighted features that may differentiate these various conditions from FM.

Methods:

A comprehensive literature search from 1990 through September 2016 was conducted to identify conditions characterized by CWP.

Results:

Conditions that may mimic FM may be categorized as musculoskeletal, neurological, endocrine/metabolic, psychiatric/psychological, and medication related. Characteristics pertaining to the most commonly identified confounding diagnoses within each category are discussed; clues to enable clinical differentiation from FM are presented; and steps towards a diagnostic algorithm for mimicking conditions are presented.

Conclusion:

Although the most likely reason for a complaint of CWP is FM, this pain complaint can be a harbinger of illness other than FM, prompting consideration of a differential diagnosis. This review should sensitize physicians to a broad spectrum of conditions that can mimic FM.

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.

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.

Clinical Endocannabinoid Deficiency Reconsidered: Current Research Supports the Theory in Migraine, Fibromyalgia, Irritable Bowel, and Other Treatment-Resistant Syndromes

Medicine continues to struggle in its approaches to numerous common subjective pain syndromes that lack objective signs and remain treatment resistant. Foremost among these are migraine, fibromyalgia, and irritable bowel syndrome, disorders that may overlap in their affected populations and whose sufferers have all endured the stigma of a psychosomatic label, as well as the failure of endless pharmacotherapeutic interventions with substandard benefit. The commonality in symptomatology in these conditions displaying hyperalgesia and central sensitization with possible common underlying pathophysiology suggests that a clinical endocannabinoid deficiency might characterize their origin. Its base hypothesis is that all humans have an underlying endocannabinoid tone that is a reflection of levels of the endocannabinoids, anandamide (arachidonylethanolamide), and 2-arachidonoylglycerol, their production, metabolism, and the relative abundance and state of cannabinoid receptors. Its theory is that in certain conditions, whether congenital or acquired, endocannabinoid tone becomes deficient and productive of pathophysiological syndromes. When first proposed in 2001 and subsequently, this theory was based on genetic overlap and comorbidity, patterns of symptomatology that could be mediated by the endocannabinoid system (ECS), and the fact that exogenous cannabinoid treatment frequently provided symptomatic benefit. However, objective proof and formal clinical trial data were lacking. Currently, however, statistically significant differences in cerebrospinal fluid anandamide levels have been documented in migraineurs, and advanced imaging studies have demonstrated ECS hypofunction in post-traumatic stress disorder. Additional studies have provided a firmer foundation for the theory, while clinical data have also produced evidence for decreased pain, improved sleep, and other benefits to cannabinoid treatment and adjunctive lifestyle approaches affecting the ECS.