Efforts to redefine endometriosis prevalence in low‐risk patients

Endometriosis has significant implications for patient health and well-being, particularly when it comes to pelvic pain and infertility. However, the true epidemiology of the disease has remained elusive. Many of the foundational studies characterise surgically confirmed endometriosis in highly selected patient populations. It has been hypothesised that the prevalence of endometriosis is approximately 10% in women of reproductive age, and may reach rates of 30–50% in symptomatic women (Vigan o et al., Best Pract Res Clin Obstet Gynaecol 2004;18(2):177– 200). However, other investigators have sought to determine the prevalence in unselected populations, finding rates of around 1.5% (Ballard et al., BJOG 2008;115(11):1382–91). In this edition of BJOG, Eisenberg et al. report on a large population-based database study that sought to describe the ‘real world’ disease burden. They found a point prevalence of endometriosis of 1% in women age 15–55 and 2% in the highest-prevalence age group. Interestingly, a small but significant increase in incidence was noted over time, although it is unclear if this relates to a true increase in the incidence of the disease or simply to an increased awareness of the disease and thus an increase in its diagnosis. While the overall 10-fold decrease in the prevalence of endometriosis found in this study is striking, it is important to take some precautions when translating this into clinical practice. The identification of endometriosis was based solely upon International Classification of Disease (ICD) coding from primary care physicians, gynaecologists, or other specialists. Some had records of ultrasound scans being performed prior to the diagnostic code being given, but, as one might expect in a low-risk population, very few had any record of a surgical procedure before the diagnosis. Further, the diagnosis could not be validated in all cases. The possibility of differential coding bias can be illustrated with the high prevalence in the infertile population, where providers may be more likely to take detailed histories geared towards identification of endometriosis. These findings must be placed into context, given that the apparent incidence of endometriosis varies by diagnostic method, with surgical visualisation greatly increasing the rates (Buck Louis et al., Fertil Steril 2011;96(2):360–5). Thus, one must think about the meaning of clinically diagnosed endometriosis versus surgically diagnosed endometriosis and what patient populations may have been included in those groups historically. There are studies that show that symptoms such as dysmenorrhoea and a history of infertility greatly increase the odds of finding surgically confirmed endometriosis (Peterson et al., Am J Obstet Gynecol 2013;208(6):451.e1–11), but these findings are often studied in cohorts with much higher rates of endometriosis than that reported by Eisenberg et al. Further, this study does not take into account cases of asymptomatic endometriosis, as they would have no record or knowledge of the diagnosis. Beyond the issue of reliable detection, the clinical questions remain: does the clinical identification in the low-risk population lead to interventions that promote overall better quality of life and maybe even prevent progression of disease? These questions are not answered here but must be considered as we determine how best to identify patients in the community setting with endometriosis and determine effective interventions.