What is Endometriosis?

An estimated 176 million worldwide people born female have endometriosis (Endo). This number is thought to be incresing as awareness increases, this may be because we know more about the condition and more people are being diagnosed correctly. At present it is often thought of as a disease that primarily affects women of reproductive age but there is increasing literature that points to endometriosis affecting girls before menarche and women after menopause. The pathogenesis of endo is still unclear (1), and treatment is inadequate, often ending in putting a woman in chemical menopause using chemotherapy drugs or hysterectomy. Neither of which cure the condition and individuals often require ongoing care. Surgical and medical therapies that are available to women with Endo can be effective, however there is a recurrence of symptoms at a rate of 20-50%, but this varies greatly between studies (2). The symptoms present in Endo are dysmenorrhea (pain during menstruation), dyspareunia (painful intercourse), dyschezia (difficult or painful defecation), dysuria (painful urination), cyclic and acyclic pelvic pain, menstrual disorders and infertility, as well as persistent pelvic pain (PPP, also known as chronic pelvic pain, (3) however these symptoms are heterogeneous and may overlap with many other conditions making diagnosis a hard and slow process (4).

Endo affects patients with different severity, and manifests as three phenotypes;

(i) superficial Endo, that is characterised by peritoneal lesions that are usually found in the pelvic region;

(ii) ovarian endometrioma, that is characterised by chocolate coloured fluid-filled cysts, the fluid originating from repeated haemorrhages of the endometriotic foci in the cyst during menses, and; (iii)

Deep Infiltrating Endo (DIE) that is characterised by undifferentiated glandular and/or stromal cells surrounded by fibrotic tissue. These phenotypes are not exclusive of each other and it is often the case that all three are found within the same patient (5).


On top of the confusing "typing" there is the complication that the pain felt by a woman is not necessarily comparable to the severity or phenotype of the patient, making Endo a complicated and complex condition to treat. Furthermore it suggests that pain felt by patients may have an association with psychosocial factors (6). The inability to successfully identify the aetiology of Endo and its associated pain is the obstruction that prevents the design and provision of effective treatment for patients with Endo (7).


Without effective treatment and intervention Endo will affect all aspects of a patient’s life, with growing evidence showing that it can be present both before menarche, as well as after menopause. Indeed, a study found endometrial tissue outside of the uterus in post-mortem foetuses (8).

Endo is a hormone dependent disease, where stem cells are dysfunctional due to progesterone resistance which causes disruption to endometrial homeostasis (9). This then disrupts the bi-directional communication between stem-cell signalling pathways are affected by local inflammation which forms an inflammation-hormonal loop that is dysregulated (10). This shows that endometriosis is also an inflammatory disease and needs to be treated as such (11).

The current standard of care is to treat Endo with combined oral contraceptives, progestins, or short-term treatment with gonadotropin- releasing hormone (GnRH) agonists. This approach is not taking the inflammatory side of Endo into account and patients with the disease are not being treated efficiently or effectively (6). Many studies have found that there is no strong data that suggests hormone therapy to treat Endo-related pain works sufficiently, and many patients who are on hormone therapy report higher intensity and frequency of pain when compared to patients that are not (12).

Endo has a variety of co-morbidities and up to 20% of women with Endo also suffer with irritable bowel syndrome (IBS), interstitial cystitis (IC) and migraines (8).

  • It has been suggested that to receive appropriate care there is a need for accredited centres of excellence whose main goal is to reduce diagnosis time (currently on average 7.5 years), cost of Endo on the UK economy (currently £8.2bn a year), and time from being diagnosed with Endo to being referred to individualised specialist care (13). However, as of 2018 there are only 63 British Society for Gynaecological Endoscopy (BSGE) accredited Endometriosis Centres in the UK (14).

  • The socioeconomic burden of the disease in the UK is estimated to be in excess of £8.2 billion per year (15).

  • More than 75% of women have reported being absent from work due to endometriosis, on average 5.3 days out of the month, as well as 40% of women becoming unemployed due to the disease (4).

  • 46% of patients with endometriosis need to have appointments with upward of five doctors to gain a correct diagnosis (Bach et al., 2016). Despite prevalence rates of endometriosis being so high, there is very little research and funding to undertake large high-quality studies into the care and lived experiences of patients with endometriosis.

  • In 2016, the National Health and Medical Research Council allocated £669,025 to endometriosis research, with diabetes being allocated £51.2 million (17), despite endometriosis having very similar prevalence rates to diabetes. 82% of women are unable to carry out day to day activities due to symptoms associated with endo.

There is a severe lack of high-quality studies, or published evidence regarding Endo and the pain associated with the disease. There is also the problem of measuring pain as severity, generality and importance of pain is subjective and varies from patient to patient (18).

1.          Bersinger NA, Mckinnon B, Kuhn A, Santi A, Mueller MD. Pain symptoms and peritoneal fluid cytokine and marker concentrations in women with and without endometriosis. J Endometr. 2009;1(3):137–49.

2.          Selçuk I, Bozdağ G. Recurrence of endometriosis; risk factors, mechanisms and biomarkers; review of the literature. J Turkish Ger Gynecol Assoc [Internet]. 2013;14(2):98–103. Available from: http://www.ncbi.nlm.nih.gov/pubmed/24592083

3.          Chiantera V, Abesadze E, Mechsner S. How to understand the complexity of endometriosis- related pain. J Endometr Pelvic Pain Disord. 2017;9(1):30–8.

4.          Bernuit D, Ebert AD, Halis G, Strothmann A, Gerlinger C, Geppert K, et al. Female perspectives on endometriosis: Findings from the uterine bleeding and pain women’s research study. J Endometr. 2011;3(2):73–85.

5.          Andres MP, Borrelli GM, Abrão MS. Endometriosis classification according to pain symptoms: can the ASRM classification be improved? Best Pract Res Clin Obstet Gynaecol. 2018;51:111–8.

6.          Aerts L, Grangier L, Streuli I, Dällenbach P, Marci R, Wenger JM, et al. Psychosocial impact of endometriosis: From co-morbidity to intervention. Best Pract Res Clin Obstet Gynaecol. 2018;50:2–10.

7.          Ray KL, Mitchell BL, Santanam N. Power over pain : a brief review of current and novel interventions for endometriosis-associated pain. J Endometr Pelvic Pain Disord. 2014;6(10):163–73.

8.          Hogg S, Vyas S. Endometriosis update. Obstet Gynaecol Reprod Med [Internet]. 2018;28(3):61–9. Available from: https://doi.org/10.1016/j.ogrm.2017.12.003

9.          Riccio L da GC, Santulli P, Marcellin L, Abrão MS, Batteux F, Chapron C. Immunology of endometriosis. Best Pract Res Clin Obstet Gynaecol. 2018;50:39–49.

10.        Wang Y, Nicholes K, Shih I-M. The Origin and Pathogenesis of Endometriosis. Annu Rev Pathol Mech Dis. 2020;15(1):71–95.

11.        Laux-Biehlmann A, D’hooghe T, Zollner TM. Menstruation pulls the trigger for inflammation and pain in endometriosis. Trends Pharmacol Sci [Internet]. 2015;36(5):270–6. Available from: http://dx.doi.org/10.1016/j.tips.2015.03.004

12.        Brandes I, Neuser M, Kopf A, Chiantera V, Sehouli J, Mechsner S. Endometriosis-associated pain in patients with and without hormone therapy. J Endometr Pelvic Pain Dissorders. 2017;9(3):200–5.

13.        D’Hooghe T, Hummelshoj L. Multi-disciplinary centres/networks of excellence for endometriosis management and research: A proposal. Hum Reprod. 2006;21(11):2743–8.

14.        BSGE. BSGE British Society for Gynaecological Endoscopy [Internet]. Data for BSGE Accredited Endometriosis Centres. 2018. p. 1. Available from: https://www.bsge.org.uk/data-for-bsge-accredited-endometriosis-centres/

15.        Horne AW, Daniels J, Hummelshoj L, Cox E, Cooper KG. Surgical removal of superficial peritoneal endometriosis for managing women with chronic pelvic pain: time for a rethink? BJOG An Int J Obstet Gynaecol. 2019;126(12):1414–6.

16.        Bach AM, Risoer MB, Forman A, Seibaek L. Practices and Attitudes Concerning Endometriosis Among Nurses Specializing in Gynecology. Glob Qual Nurs Res. 2016;

17.        NHMRC. all-grants-2000-2016 [Internet]. 2017. Available from: https://www.nhmrc.gov.au/funding/data-research/research-funding-data

18.        Gerlinger C, Schumacher U, Wentzeck R, Uhl-Hochgraber K, Solomayer EF, Schmitz H, et al. How can we measure endometriosis-associated pelvic pain? J Endometr. 2012;4(7):109–16.


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