Recognising endometriosis as a syndrome would refocus treatment away from surgical eradication of lesions towards multidisciplinary care for complex symptoms such as chronic pain.

Endometriosis is a condition of global importance affecting an estimated 176 million women worldwide with health and socioeconomic costs to the UK of around £12.5 billion per annum.^1,2  It is defined by the presence of endometrial-like tissue (‘lesions’) outside the uterus. Symptoms of endometriosis include chronic pelvic pain, painful periods and painful sex, but the association between symptoms and visible endometriotic lesions is poorly understood.

Women with disease that appears ‘severe’ can have minimal symptoms and women with ‘minimal’ evidence of endometriosis can have severe, life impacting symptoms.³ This varied clinical picture, combined with the requirement for laparoscopic visualisation of lesions to make a diagnosis of the condition, has contributed to an average delay of 7-8 years between the onset of symptoms and confirmed diagnosis.^4,5

Current treatment options for endometriosis are largely inadequate. Medical treatments mostly reduce circulating oestrogen concentrations and, hence, may induce menopausal-like symptoms and lead to bone demineralisation. Surgical treatments aim to excise or ablate all visible disease, but persistence/recurrence rates of endometriotic lesions after surgery are as high as 20% after 2 years and 40%–50% after 5 years.^1,3 Women with endometriosis are at higher risk of infertility, ovarian, endometrial, and breast cancers, melanoma, asthma, and autoimmune and cardiovascular disease.⁶ The cause and natural history of endometriosis is unknown: genetic, hormonal, anatomical, and immunological factors are all implicated in the formation, development, and survival of endometriotic lesions.¹

Currently, endometriosis is considered a “disease” with the diagnosis based solely on the basis of lesion(s) being visualised outside the uterus.⁷ We believe that this disease model and basing the diagnosis exclusively on visible lesions is unhelpful for patients, clinicians and scientists. We propose that endometriosis is instead considered a “syndrome”, diagnosed only when a patient has both visible lesions and characteristic symptoms.

Our opinion is based on the fundamental and substantial gaps in our understanding of the causes, pathophysiology, symptoms and natural history of endometriosis. There is simply not enough known about endometriosis to call it a “disease”. Diseases should have clearly defined and identifiable symptoms, consistent physiological and anatomical characteristics, known pathophysiological processes, and an established biological cause.⁸ Many diseases do not meet all these criteria, but endometriosis fails to meet any. The lesions are not consistently related to symptoms, the anatomical characteristics vary, the cause and pathophysiology are unknown and the response to treatment is unpredictable.^9,10 

Endometriosis is only considered clinically significant when it causes symptoms, but symptoms are not even included in the diagnostic criteria.⁷ Persistent pelvic pain is recognised as the cardinal symptom,¹¹ but most women with pelvic pain do not have endometriotic lesions and many women with lesions are asymptomatic.^12,13 Limiting diagnosis to lesions has focused treatment on eradicating lesions, potentially exposing women with endometriosis to risk, such as reduced ovarian reserve as a result of ovarian surgery.^10-14

The diagnosis of endometriosis syndrome would require both confirmation of the presence of lesions and characteristic symptoms. A syndrome (from the Greek “running together”) describes a group of signs and symptoms that consistently occur together but where the underlying pathological process is not necessarily understood. For example, “Polycystic Ovary Syndrome (PCOS)” includes a defined ovarian phenotype that is only clinically significant in combination with specific symptoms or hormonal measures.¹⁵ Treatments for a disease generally target the cause whilst the management of a syndrome generally targets symptoms.⁸ Basing the diagnosis, prognosis, and evaluation of treatments for endometriosis exclusively on lesions ignores the fact that preventing and managing symptoms are the leading patient priorities for research, treatment and prognosis.¹⁶ 

Including symptoms in the diagnostic criteria would benefit patients by focusing research on the wide spectrum of associated symptoms and the development of treatments to reduce or resolve symptoms. Syndromes often require multidisciplinary care. Recognising endometriosis as a syndrome would refocus treatment away from surgical eradication of lesions towards multidisciplinary care for complex symptoms such as chronic pain.¹⁷

Patients only benefit from being diagnosed with a disease if this improves understanding of their symptoms, reduces their risk of future health-related events or informs specific treatments.⁸ The existing diagnostic criteria put asymptomatic women at risk of over-diagnosis, in the same way that women with isolated polycystic ovaries should not be diagnosed with PCOS. Potential harms of over-diagnosis include stigmatisation and worry, harms from over-treatment and, in some countries, considerable financial burden from consultations, surgery and medical therapies.¹⁸

Clinicians often associated endometriosis with pelvic pain and infertility, but non-gynaecological symptoms such as fatigue and irritable bowel symptoms are common and have a major impact on quality of life. Including symptoms in the diagnosis would stimulate a more holistic management approach.¹⁶ Delayed diagnosis is particularly concerning for women with endometriosis.¹⁶ Recognising that symptoms are not confined to pelvic pain or infertility may increase awareness and lead to quicker investigation and diagnosis. However, we recognise that the lack of surgical services to identify endometriosis lesions may continue to cause delays in diagnosis.⁹

As knowledge advances, syndromes may become diseases. For example, “Acquired Immune Deficiency Syndrome” became a disease (“HIV”) when the cause was identified. The leading priorities in endometriosis include better understanding of the underlying pathophysiological processes and more effective strategies to help women manage their symptoms.¹⁶ Our aim is not to downplay the severity or importance of endometriosis, but rather to focus diagnosis and treatment on patient priority areas and to promote multi-specialty care and discovery. Patients clearly recognise that gaps in knowledge at all levels from cause through to treatments limits their access to effective care.¹⁶ Reclassifying endometriosis as a syndrome is one step further towards addressing these gaps.

Martha Hickey, Professor of Obstetrics and Gynaecology, Department of Obstetrics and Gynaecology, University of Melbourne and The Royal Women’s Hospital, Victoria, Australia. 

Stacey Missmer, Professor of Obstetrics, Gynaecology, and Reproductive Biology at Michigan State University, Grand Rapids, Michigan, USA and Harvard T.H. Chan School of Public Health, Boston, Massachusetts, USA. 

Andrew W. Horne, Professor of Gynaecology and Reproductive Sciences, Honorary Consultant Gynaecologist, MRC Centre for Reproductive Health, University of Edinburgh, UK.

Competing interests: MH is an editor for the Cochrane Menstrual Disorder and Fertility Group and an NHMRC Practitioner Fellow. AH has received research support from the MRC, NIHR, Wellbeing of Women, Roche Diagnostics, Astra Zeneca and Ferring, and has served as a consultant for AbbVie, Roche Diagnostics, Ferring and Nordic Pharma. SM has received research support from the NIH, DoD, Endometriosis Foundation of America, Marriott Daughters’ Foundation and the J. Willard and Alice S. Marriott Foundation, and has served as a consultant for AbbVie and Roche Diagnostics related to endometriosis.

Report of patient involvement: Women with endometriosis and patients undergoing treatment for endometriosis were consulted in the development of this proposal and have commented on the draft and final manuscript. Within our article, we use the terms ‘women’ and ‘women’s health’. However, we acknowledge that it is necessary for all assigned female at birth, including those whose gender identity does not align with the sex they were assigned at birth, to access evidence-based care in order to maintain their gynaecological health and reproductive wellbeing. 

This piece was peer reviewed

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