BACKGROUND: Endometriosis is a chronic gynaecological disorder that affects 2–10% of women of reproductive age. The aetiology of endometriosis is largely under-explored, yet abnormalities in the immune system have been suggested to explain the origin of ectopic endometrial tissues, and an association between endometriosis and autoimmune diseases has been proposed. Evaluation of current evidence investigating the association between endometriosis and autoimmune diseases from population-based studies will facilitate our understanding of the causes and consequences of endometriosis and provide a reference for better healthcare practices population-wide.OBJECTIVE AND RATIONALE: The aim of this study was to systematically review the literature on population-based studies investigating an association between endometriosis and autoimmune diseases and to conduct a meta-analysis of combinable results to investigate the extent and robustness of evidence.SEARCH METHODS: Four electronic databases were searched (MEDLINE, Embase, Web of Science, and CINAHL) from each database inception date until 7 April 2018. Search terms included a combination of database-specific controlled vocabulary terms and free-text terms relating to ‘endometriosis’ and ‘autoimmune diseases’. Study inclusion criteria focused on peer-reviewed published articles that reported an association between endometriosis and autoimmune diseases, excluding case reports/series, review papers, meta-analyses, organizational guidelines, editorial letters, expert opinions, and conference abstracts. Quality assessment of included studies was performed based on GRADE criteria. Key information of eligible studies was abstracted into a standard form. Meta-analysis was performed for autoimmune diseases with combinable study results from at least three studies investigating an association with endometriosis. For cross-sectional studies and case–control studies, raw data from each study were documented to calculate a Mantel–Haenszel odds ratio with 95% CIs. For cohort studies, an inverse variance probability weighted model was used to pool study results to calculate a rate ratio (a hazard ratio or a standardized incidence rate) with 95% CIs.OUTCOMES: A total of 26 published population-based cross-sectional, case–control, and cohort studies that investigated the association between endometriosis and autoimmune diseases met all eligible criteria and were included in the review. The studies quantified an association between endometriosis and several autoimmune diseases, including systemic lupus erythematosus (SLE), Sjögren’s syndrome (SS), rheumatoid arthritis (RA), autoimmune thyroid disorder, coeliac disease (CLD), multiple sclerosis (MS), inflammatory bowel disease (IBD), and Addison’s disease. However, the quality of the evidence was generally poor due to the high risk of bias in the majority of the chosen study designs and statistical analyses. Only 5 of the 26 studies could provide high-quality evidence, and among these, 4 supported a statistically significant association between endometriosis and at least 1 autoimmune disease: SLE, SS, RA, CLD, MS, or IBD.WIDER IMPLICATIONS: The observed associations between endometriosis and autoimmune diseases suggest that clinicians need to be aware of the potential coexistence of endometriosis and autoimmune diseases when either is diagnosed. Scientists interested in research studies on endometriosis or autoimmune diseases should consider the likelihood of comorbidity when studying these two types of health conditions. Well-designed large prospective cohort studies with confounding control and mediation quantification, as well as genetic and biological studies, are needed to generate further insights into whether endometriosis is a risk factor for, or a consequence of, autoimmune diseases, and whether these two types of disorders share pathophysiological mechanisms even if they arise independently. Such insights may offer opportunities for the development of novel non-hormonal medications such as immuno-modulators or repurposing of existing immunomodulatory therapies for endometriosis.

Endometriosis is estimated to affect 1 in 10 women during the reproductive years. There is often delay in making the diagnosis, mainly due to the non-specific nature of the associated symptoms and the need to verify the disease surgically. A biomarker that is simple to measure could help clinicians to diagnose (or at least exclude) endometriosis; it might also allow the effects of treatment to be monitored. If effective, such a marker or panel of markers could prevent unnecessary diagnostic procedures and/or recognize treatment failure at an early stage. We used QUADAS (Quality Assessment of Diagnostic Accuracy Studies) criteria to perform a systematic review of the literature over the last 25 years to assess critically the clinical value of all proposed biomarkers for endometriosis in serum, plasma and urine. We identified over 100 putative biomarkers in publications that met the selection criteria. We were unable to identify a single biomarker or panel of biomarkers that have unequivocally been shown to be clinically useful. Peripheral biomarkers show promise as diagnostic aids, but further research is necessary before they can be recommended in routine clinical care. Panels of markers may allow increased sensitivity and specificity of any diagnostic test.

To assess patient response rates to medical therapies used to treat endometriosis-associated pain. A systematic review with the use of Medline and Embase. Not applicable. Women receiving medical therapy to treat endometriosis. None. The proportions of patients who: experienced no reduction in endometriosis-associated pain symptoms; had pain symptoms remaining at the end of the treatment period; had pain recurrence after treatment cessation; experienced an increase or no change in disease score during the study; were satisfied with treatment; and discontinued therapy owing to adverse events or lack of efficacy. The change in pain symptom severity experienced during and after treatment, as measured on the visual analog scale, was also assessed. In total, 58 articles describing 125 treatment arms met the inclusion criteria. Data for the response of endometriosis-associated pain symptoms to treatment were presented in only 29 articles. The median proportions of women with no reduction in pain were 11%-19%; at the end of treatment, 5%-59% had pain remaining; and after follow-up, 17%-34% had experienced recurrence of pain symptoms after treatment cessation. After median study durations of 2-24 months, the median discontinuation rates due to adverse events or lack of efficacy were 5%-16%. Few studies of medical therapies for endometriosis report outcomes that are relevant to patients, and many women gain only limited or intermittent benefit from treatment.

Endometriosis is usually diagnosed by an invasive procedure such as a laparoscopy. Great interest therefore lies in the potential to identify biomarkers which may be surrogates of disease presence or activity, especially relating to the effects of therapy. We have reviewed the existing literature on endometrial differences in women with endometriosis, and assess their potential use as disease biomarkers. We used QUADAS (Quality Assessment of Diagnostic Accuracy Studies) criteria to conduct a systematic review of published papers over the past 25 years on the subject of endometrial differences in endometriosis. We searched for all studies assessing differences between eutopic endometrium of women with and without endometriosis. We identified 182 relevant articles that are summarized in the review. These studies assess over 200 potential biomarkers, including hormones and their receptors (n = 29), cytokines (n = 25), factors identified using proteomics (n = 8) and histological analysis (n = 10) of endometrial tissue. Sensitivity and specificity were reported or could be calculated for only 32 articles, and ranged from 0 to 100%. Of the nine highest quality studies, six identified putative biomarkers related to nerve fibre growth or cell cycle control, highlighting these areas as promising candidates for future biomarker research. This systematic review identified several reports of endometrial differences which have the potential to be biomarkers of endometriosis. However, larger studies in well-defined populations are clearly required to determine their true usefulness.

To standardize the recording of surgical phenotypic information on endometriosis and related sample collections obtained at laparoscopy, allowing large-scale collaborative research into the condition. An international collaboration involving 34 clinical/academic centers and three industry collaborators from 16 countries. Two workshops were conducted in 2013, bringing together 54 clinical, academic, and industry leaders in endometriosis research and management worldwide. None. A postsurgical scoring sheet containing general and gynecological patient and procedural information, extent of disease, the location and type of endometriotic lesion, and any other findings was developed during several rounds of review. Comments and any systematic surgical data collection tools used in the reviewers' centers were incorporated. The development of a standard recommended (SSF) and minimum required (MSF) form to collect data on the surgical phenotype of endometriosis. SSF and MSF include detailed descriptions of lesions, modes of procedures and sample collection, comorbidities, and potential residual disease at the end of surgery, along with previously published instruments such as the revised American Society for Reproductive Medicine and Endometriosis Fertility Index classification tools for comparison and validation. This is the first multicenter, international collaboration between academic centers and industry addressing standardization of phenotypic data collection for a specific disease. The Endometriosis Phenome and Biobanking Harmonisation Project SSF and MSF are essential tools to increase our understanding of the pathogenesis of endometriosis by allowing large-scale collaborative research into the condition.