Peripheral, Central, and Cross Sensitization in Endometriosis-Associated Pain and Comorbid Pain Syndromes

Pain from Internal Organs and Headache: The Challenge of Comorbidity

Headache and visceral pain are common clinical painful conditions, which often co-exist in the same patients. Numbers relative to their co-occurrence suggest possible common pathophysiological mechanisms. The aim of the present narrative review is to describe the most frequent headache and visceral pain associations and to discuss the possible underlying mechanisms of the associations and their diagnostic and therapeutic implications based on the most recent evidence from the international literature. The conditions addressed are as follows: visceral pain from the cardiovascular, gastrointestinal, and urogenital areas and primary headache conditions such as migraine and tension-type headache. The most frequent comorbidities involve the following: cardiac ischemic pain and migraine (possible shared mechanism of endothelial dysfunction, oxidative stress, and genetic and hormonal factors), functional gastrointestinal disorders, particularly IBS and both migraine and tension-type headache, primary or secondary dysmenorrhea and migraine, and painful bladder syndrome and headache (possible shared mechanisms of peripheral and central sensitization processes). The data also show that the various visceral pain-headache associations are characterized by more than a simple sum of symptoms from each condition but often involve complex interactions with the frequent enhancement of symptoms from both, which is crucial for diagnostic and treatment purposes.

Association of Uterine Tissue Innervation and Peripheral Nerve Density with Adenomyosis Related Pain. A Systematic Review

Adenomyosis is associated with dysmenorrhea and chronic pelvic pain; however, the triggering mechanisms of painful stimuli and the role of uterine nerve fibers in the manifestation of pain remain poorly understood. The objective of this study was to systematically review the role of uterine nerve fibers' presence and density in the occurrence of pain in patients with adenomyosis. An electronic search was performed using the Embase, PubMed/Medline, and Cochrane databases. We included all studies from inception to November 2023. A total of ten studies that compared uterine biopsies samples of women with and without adenomyosis were included. The biomarker antiprotein gene product 9.5 was decreased or absent in the endometrium of most included women with adenomyosis. None of the included studies observed a difference in neurofilament (NF) staining between the adenomyosis and non-adenomyosis groups. Studies that assessed nerve growth factor (NGF) staining were heterogeneous in design. One study reported no difference in immunohistochemistry staining in any endometrial layer between the adenomyosis and non-adenomyosis groups, while another reported increased staining in the adenomyosis functional endometrial layer, and a third study reported overexpression of NGF, synaptophysin (SYN), and microtubule-associated protein 2 mRNA in focal adenomyosis alone. Preliminary data from poor-quality studies suggest an increase in the uterine density of nerve fibers in patients with adenomyosis. Well-designed studies are essential to assess the cause-and-effect relationship between uterine nerve fibers and pain in patients with adenomyosis.

Study on the Mechanisms of Glrα3 in Pain Sensitization of Endometriosis

Endometriosis, often associated with chronic pelvic pain, can lead to anxiety and depression. This study investigates the role and mechanism of Glycine receptor alpha 3 (Glrα3) in the central sensitization of pain in endometriosis, aiming to identify new therapeutic targets. Using a Glrα3 knockout mouse model of endometriosis, we employed behavioral tests, qPCR, immunofluorescence, Nissl staining, MRI, and Western blot to assess the involvement of Glrα3 in central pain sensitization. Our results indicate that endometriosis-induced hyperalgesia and anxiety-depressive-like behaviors are linked to increased Glrα3 expression. Chronic pain in endometriosis leads to gray matter changes in the sensory and insular cortices, with Glrα3 playing a significant role. The inhibition of Glrα3 alleviates pain, reduces neuronal abnormalities, and decreases glial cell activation. The absence of Glrα3 effectively regulates the central sensitization of pain in endometriosis by inhibiting glial cell activation and maintaining neuronal stability. This study offers new therapeutic avenues for the clinical treatment of endometriosis-related pain.

Holistic Approaches in Endometriosis - as an Effective Method of Supporting Traditional Treatment: A Systematic Search and Narrative Review

Endometriosis is one of the gynecological diseases where women suffer from pain, quality of life decreased. The aim of this review was to describe the most common non-medical methods used in the treatment of symptoms associated with endometriosis and to determine their effectiveness. The review was performed in PubMed, Embase and Web of Science databases. Randomized controlled trials, case studies, observational studies, retrospective studies, prospective studies, pilot studies, trails, publications in English or Polish were searched based on the Participant-Intervention-Comparator-Outcomes-Study design (PICOS) format. The criteria used to select studies were: women with endometriosis, no cancer, included any physiotherapeutic or non-medical intervention. 3706 articles were found, however only 26 met the inclusion criteria and were included in the review. Quality of the studies was assessed by Risk of Bias 2 tool and ROBINS-1 tool. The most holistic approach used in the treatment of symptoms of endometriosis include physical therapy, manual therapy, electrophysical agents acupuncture, diet and psychological interventions. Most research has focused on relieving pain and increasing quality of life. Non-medical methods showed reduction of symptoms of endometriosis. Physical activity, manual therapy, electrophysical agents, acupuncture, diet and cognitive behavioral therapy showed no negative side effects and reduced pain, what improved the quality of life and reduced the perceived stress.

Virtual Mindfulness-Based Therapy for the Management of Endometriosis Chronic Pelvic Pain: A Novel Delivery Platform to Increase Access to Care

OBJECTIVES

This study assessed the effectiveness of a virtual mindfulness-based stress reduction (MBSR) program to improve quality of life and pain in people with endometriosis.

METHODS

This was a multiple-method, before and after study design. Fifteen patients with a clinical or surgical diagnosis of endometriosis were recruited from a Canadian outpatient gynaecology clinic. Participants completed the Endometriosis Health Profile, a validated survey tool, and a pain medication use questionnaire before and after a virtual 8-week MBSR program run by an experienced social worker. A focus group was held upon completion of the program to assess participants' experiences using mindfulness for management of endometriosis symptoms. Quantitative data was analyzed with paired-samples t tests. Qualitative data was thematically analyzed.

RESULTS

A total of 67% of people enrolled completed the MBSR course (10/15). Following the MBSR program, participants had a statistically significant decrease in 4 components of the Endometriosis Health Profile: control and powerlessness (P = 0.012), emotional well-being (P = 0.048), social support (P = 0.030), and self-image (P = 0.014). There was no change in pain scores or medication use. Participants felt the program's benefits came from a sense of community, education about their condition, and application of mindfulness tools when approaching pain. Participants felt more comfortable with the virtual format over in-person sessions.

CONCLUSIONS

A virtual MBSR course can improve quality of life domains in people with endometriosis. The virtual format was effective and preferred by participants. Virtual MBSR programs may increase access to this type of care.

Efficacy and factors of myofascial release therapy combined with electrical and magnetic stimulation in the treatment of chronic pelvic pain syndrome

The objective of this study was to evaluate the efficacy and factors of myofascial release therapy combined with electrical and magnetic stimulation in the treatment of chronic pelvic pain syndrome (CPPS). A total of 79 female patients diagnosed with CPPS from January 2021 to December 2022 were prospectively analyzed. Every patient received 3 weeks of treatment which included myofascial release therapy combined with electrical and magnetic stimulation. The visual analog score (VAS) of pelvic floor muscle (PFM) trigger points (TrPs) and the changes in pelvic floor surface electromyography before and after treatment were compared. Multiple linear regression was used to analyze the influencing factors of each outcome index. There were significant differences in VASs of muscle TrPs before and after treatment (P < 0.05). For the surface electromyography of PFMs, the differences in pre-baseline rest, post-baseline rest, isometric contractions for muscle endurance evaluation, and coefficient of variation were statistically significant (P < 0.05). Linear regression analysis showed that disease course (X 1), dyspareunia (X 5), and urinary incontinence (X 6) were influencing factors for the decline of pre-baseline rest (r5 = 1.067, R 2 = 0.089), post-baseline rest (r1 = 0.055, r5 = 0.99, R 2 = 0.119), VASs of ischial spine (r5 = 0.916, R 2 = 0.102), obturator internus (r5 = 0.796, r6 = -0.703, R 2 = 0.245), and pubococcygeus (r5 = 0.885, R 2 = 0.149) after treatment in the CPPS group. This study confirmed that individualized myofascial release therapy combined with electrical and magnetic stimulation has significant efficacy for patients with CPPS. At the same time, it is more effective for CPPS patients with longer course of disease, dyspareunia, and without urinary incontinence.

Inflammation, lipid dysregulation, and transient receptor potential cation channel subfamily V member 4 signaling perpetuate chronic vulvar pain

ABSTRACT

Localized provoked vulvodynia is characterized by chronic vulvar pain that disrupts every aspect of the patient's life. Pain is localized to the vulvar vestibule, a specialized ring of tissue immediately surrounding the vaginal opening involved in immune defense. In this article, we show inflammation is the critical first step necessary for the generation of pain signals in the vulva. Inflammatory stimuli alone or combined with the transient receptor potential cation channel subfamily V member 4 (TRPV4) agonist 4α-phorbol 12,13-didecanoate stimulate calcium flux into vulvar fibroblast cells. Activity is blocked by the TRPV4 antagonist HC067047, denoting specificity to TRPV4. Using lipidomics, we found pro-resolving lipids in the vulvar vestibule were dysregulated, characterized by a reduction in pro-resolving mediators and heightened production of inflammatory mediators. We demonstrate specialized pro-resolving mediators represent a potential new therapy for vulvar pain, acting on 2 key parts of the disease mechanism by limiting inflammation and acutely inhibiting TRPV4 signaling.

Advanced Insights into Human Uterine Innervation: Implications for Endometriosis and Pelvic Pain

(1) Background: Understanding uterine innervation, an essential aspect of female reproductive biology, has often been overlooked. Nevertheless, the complex architecture of uterine innervation plays a significant role in conditions such as endometriosis. Recently, advances in histological techniques have provided unprecedented details about uterine innervation, highlighting its intricate structure, distribution, and density. The intricate nature of uterine innervation and its influence on pathologies such as endometriosis has garnered increasing attention. (2) Objectives: This review aims to compile, analyze, and summarize the existing research on uterine innervation, and investigate its implications for the pathogenesis of endometriosis and associated pain. (3) Methods: A systematic review was conducted in line with PRISMA guidelines. Using the PubMed database, we searched relevant keywords such as "uterine innervation", "endometriosis", and "pain association". (4) Results: The initial literature search yielded a total of 3300 potential studies. Of these, 45 studies met our inclusion criteria and were included in the final review. The analyzed studies consistently demonstrated that the majority of studies focused on macroscopic dissection of uterine innervation for surgical purposes. Fewer studies focused on micro-innervation for uterine innervation. For endometriosis, few studies focused on neural pain pathways whereas many studies underlined an increase in nerve fiber density within ectopic endometrial tissue. This heightened innervation is suggested as a key contributor to the chronic pain experienced by endometriosis patients. (5) Conclusions: The understanding of uterine innervation, and its alterations in endometriosis, offer promising avenues for research and potential treatment.

Does Sexual Function and Quality of Life Improve after Medical Therapy in Women with Endometriosis? A Single-Institution Retrospective Analysis

BACKGROUND

Endometriosis is a gynecological condition affecting up to 10% of women of reproductive age and characterized by chronic pain. Pain is the major cause of the impairment of quality of life in all aspects of these patients. Previous studies have shown that endometriosis treatment, hormonal or surgical, has proven effective not only in controlling the disease but also in improving symptoms, and we can assume also effective in improving quality of life.

METHODS

This study evaluates quality of life and sexual function in patients with endometriosis at the time of diagnosis and after 6 months of medical therapy, to assess the impact of treatment on these aspects. We evaluated retrospectively patients with a diagnosis of endometriosis between 2018 and 2020. All patients underwent gynecological examination and transvaginal ultrasound and filled in three questionnaires. The same evaluation was provided after taking medical hormonal therapy.

RESULTS

The improvement of dysmenorrhea, chronic pelvic pain, and dyspareunia after medical treatment were statistically significant. Instead, items concerning arousal, lubrication, and sexual satisfaction showed a statistically significant worsening after therapy.

CONCLUSIONS

We can state that hormone therapy alone is not sufficient to achieve an improvement in the patient's quality of life and sexual function. Emerging evidence suggests that most of these patients showed a central sensibilization phenomenon characterized by an amplification of the response to a peripheral and/or neuropathic nociceptive trigger, which is expressed by hyperalgesia and allodynia. For this reason, in these patients, it is better to adopt a multimodal and multidisciplinary approach, including other professional figures, that acts on pain and also intervenes in all those conditions that contribute to worsening quality of life.

Evaluation of a scoring system for the detection of central sensitization among women with chronic pelvic pain

BACKGROUND

Central sensitization is frequently associated with chronic pelvic pain and requires specific management. The pain is described as hypersensitivity to an innocuous stimulus that is both widespread and persistent. However, no study has evaluated if central sensitization can be measured objectively with neurophysiological tests in the pelvic and perineal area to prove this concept in women with chronic pelvic pain.

OBJECTIVE

This study aimed to evaluate nociceptive thresholds (primary objective) and spatial and temporal diffusion of pain among women with chronic pelvic pain and high or low scores of central sensitization.

STUDY DESIGN

This prospective, assessor-blinded, comparative study compared a cohort of women with chronic pelvic pain and a high (>5/10; n=29) vs low (<5/10; n=24) score of sensitization according to the Convergences PP criteria. Participants underwent a noninvasive bladder sensory test, a rectal barostat test, and a muscular (algometer) and a vulvar (vulvagesiometer) sensory test. Poststimulation pain (minutes), quality of life (Medical Outcomes Study 36-Item Short Form Survey), and psychological state, comprising anxiety (State-Trait Anxiety Inventory), depression (Beck Depression Inventory Short Form), and catastrophizing (Pain Catastrophizing Scale), were assessed.

RESULTS

The participants mostly suffered from endometriosis (35.8%), irritable bowel syndrome (35.8%), bladder pain syndrome (32.1%), and vestibulodynia (28.3%). Baseline characteristics were similar. Women with a high sensitization score had more painful diseases diagnosed (2.7±1.3 vs 1.6±0.8; P=.002) and suffered for longer (11±8 vs 6±5 years; P=.028) than participants with a low score. The bladder maximum capacity was equivalent between participants (399±168 vs 465±164 mL; P=.18). However, the pain felt at each cystometric threshold was significantly increased in women with a high sensitization score. No difference was identified for the rectal pain pressure step (29.3±5.5 vs 30.7±6.5 mm Hg; P=.38). Rectal compliance was decreased in women with a high sensitization score with a considerable increase in pain felt. The average of pain pressure thresholds at the 5 vulvar sites tested was decreased in these participants (162.5±90.5 vs 358.7±196.5 g; P=.0003). Similar results were found for the average of the pain pressure thresholds at 6 muscles tested (1.34±0.41 vs 2.63±1.52 kg/m2; P=.0002). A longer period was needed for patients with high sensitization score to obtain a VAS <3 out of 10 after the stimulation of the bladder (4.52±5.26 vs 1.27±2.96 minutes; P=.01), the rectum (3.75±3.81 vs 1.19±1.23 minutes; P=.009), and the muscles (1.46±1.69 vs 0.64±0.40 minutes; P=.002). The psychological state was equivalent between groups. No association was found between the sensory thresholds and the psychological state results. The physical component of the quality of life score was reduced in women with high sensitization score (P=.0005), with no difference in the mental component.

CONCLUSION

Using neurophysiological tests, this study showed that there are objective elements to assess for the presence of central sensitization, independently of psychological factors.

Endometriosis-Related Chronic Pelvic Pain

Endometriosis, which is the presence of endometrial stroma and glands outside the uterus, is one of the most frequently diagnosed gynecologic diseases in reproductive women. Patients with endometriosis suffer from various pain symptoms such as dysmenorrhea, dyspareunia, and chronic pelvic pain. The pathophysiology for chronic pain in patients with endometriosis has not been fully understood. Altered inflammatory responses have been shown to contribute to pain symptoms. Increased secretion of cytokines, angiogenic factors, and nerve growth factors has been suggested to increase pain. Also, altered distribution of nerve fibers may also contribute to chronic pain. Aside from local contributing factors, sensitization of the nervous system is also important in understanding persistent pain in endometriosis. Peripheral sensitization as well as central sensitization have been identified in patients with endometriosis. These sensitizations of the nervous system can also explain increased incidence of comorbidities related to pain such as irritable bowel disease, bladder pain syndrome, and vulvodynia in patients with endometriosis. In conclusion, there are various possible mechanisms behind pain in patients with endometriosis, and understanding these mechanisms can help clinicians understand the nature of the pain symptoms and decide on treatments for endometriosis-related pain symptoms.

Endometriosis and menopause-management strategies based on clinical scenarios

Endometriosis is largely considered a premenopausal disease with symptoms often improving during menopausal transition. However, 2%-4% of postmenopausal women are affected by endometriosis symptoms. At the same time, many peri- and postmenopausal women experience menopausal symptoms and inquire about treatment. Because of the estrogen-dependent nature of endometriosis, treatment with menopausal hormone therapy requires careful assessment of the patient but should nevertheless be considered. Recurrence of endometriosis symptoms and risk for malignant transformation are potential risks to weigh when prescribing menopausal hormonal therapy. Choice of treatment should be guided by the presence and severity of current endometriosis symptoms, nature of menopausal symptoms, risk assessment of potential contraindications for treatment in patient history, and preferences of the woman after an informative discussion. Recurrence of endometriosis symptoms in a postmenopausal patient should always prompt rigorous evaluation, both in the presence and absence of hormonal treatment. Many recommendations on the topic are based on expert opinion and new studies are urgently needed to obtain evidence for optimal patient care.

Endometriosis and the Temporomandibular Joint-Preliminary Observations

(1) Background: The complete picture of the disease is not fully recognized and extends far beyond the pelvis. The disease's impacts lead to systemic inflammation, in turn resulting in sensitization to pain. The aim of this study was to check whether statistical correlations exist in women with endometriosis with regard to their experience of pain: headache, pelvic pain, temporomandibular joint pain, along with teeth clenching and the treatment of the disease. We constructed contingency tables, followed by Pearson's chi-square test and Cramer's V coefficient values. (2) Methods: A survey was conducted among 128 women aged 33.43 ± 5.79 with a diagnosis of endometriosis (disease duration 6.40 ± 5.88 years). (3) Results: There was a correlation between the occurrence of pain on the right and left sides of the pelvis and pain on the right and left sides of the temporomandibular joint, p-value = 0.0397, V = 0.2350, and between the presence of pelvic pain and the treatment of endometriosis, p-value = 0.0104, V = 0.3709, and between the presence of pain outside the pelvis and the treatment of endometriosis, p-value = 0.0311, V = 0.4549. There was a highly significant correlation between teeth clenching and temporomandibular joint pain, p-value = 0.0005, V = 0.3695. (4) Conclusions: The study revealed a correlation between pelvic endometriosis symptoms and symptoms in the temporomandibular joint.

Endometriosis-associated chronic pelvic pain

Endometriosis is a heterogeneous disease where neurogenic sensitization can lead to chronic pain within and beyond the pelvis. Coincident pain and comorbidities merit specific attention. We discuss the causes, comorbidities, and management of endometriosis-associated chronic pelvic pain, advocating for a multidisciplinary approach to develop more effective treatments.

Serological autoimmune profile of systemic lupus erythematosus in deep and non-deep endometriosis patients

OBJECTIVE

Several studies have reported a high prevalence of autoimmune diseases such as systemic lupus erythematosus (SLE) in endometriosis patients. The aim of this study was to evaluate the SLE autoimmune antibody profile in patients with deep (DE) and non-deep endometriosis (Non-DE).

MATERIALS AND METHODS

Four groups of premenopausal patients were evaluated: patients with DE (n = 50); patients with ovarian endometriomas (Non-DE; n = 50); healthy patients without endometriosis (C group; n = 45); and SLE patients without endometriosis (SLE group; N = 46). Blood samples were obtained and the standard SLE autoimmune profile was evaluated in all patients. Pain symptoms related to endometriosis and clinical SLE manifestations were also recorded.

RESULTS

The DE group presented a statistically significant higher proportion of patients with antinuclear antibodies (ANA) (20%) compared to the Non-DE group (4%) and C group (2.2%). Levels of complement were more frequently lower among DE and Non-DE patients although differences did not reach statistical significance. Similarly, anti-dsDNA antibodies and anticoagulant lupus were positive in more patients of the DE group but did not reach statistical significance. The DE group complained of more arthralgia and asthenia compared to the Non-DE and C groups.

CONCLUSIONS

The results of this study showed higher positivity of ANA and greater arthralgia and asthenia in patients with DE compared with Non-DE patients and healthy controls, suggesting that they may have a higher susceptibility to autoimmune diseases and present more generalized pain.

The Unmet Needs for Studying Chronic Pelvic/Visceral Pain Using Animal Models

The different definitions of chronic pelvic/visceral pain used by international societies have changed over the years. These differences have a great impact on the way researchers study chronic pelvic/visceral pain. Recently, the role of systemic changes, including the role of the central nervous system, in the perpetuation and chronification of pelvic/visceral pain has gained weight. Consequently, researchers are using animal models that resemble those systemic changes rather than using models that are organ- or tissue-specific. In this review, we discuss the advantages and disadvantages of using bladder-centric and systemic models, enumerating some of the central nervous system changes and pain-related behaviors occurring in each model. We also present some drawbacks when using animal models and pain-related behavior tests and raise questions about possible, yet to be demonstrated, investigator-related bias. We also suggest new approaches to study chronic pelvic/visceral pain by refining existing animal models or using new ones.