Endometriosis and uterine fibroids are two of the most frequently diagnosed reproductive health issues, affecting millions of women of childbearing age globally. Endometriosis affects about 10% of reproductive-aged women, while uterine fibroids are present in up to 80% of women by age 50. The frequent presence of both conditions in the same patient often leads to the assumption of a direct cause-and-effect relationship. This article explores the current understanding of the relationship between these two conditions.
Understanding Endometriosis and Uterine Fibroids
Endometriosis is a condition where tissue similar to the endometrium, the lining inside the uterus, grows in locations outside of the uterus. This ectopic tissue may be found on the ovaries, fallopian tubes, the tissue lining the pelvis, and, in rare instances, even beyond the pelvic region. Unlike the menstrual lining, this displaced tissue has no way to exit the body, leading to irritation, inflammation, the formation of scar tissue, and adhesions.
Uterine fibroids, medically known as leiomyomas, are non-cancerous growths that develop from the muscle layer of the uterus. These benign tumors can vary greatly in size, from tiny “seedlings” to large masses that can distort the shape and size of the uterus. Fibroids are classified based on their location within the uterine wall, such as submucosal (just beneath the lining), intramural (within the wall), or subserosal (on the outer surface).
The Co-occurrence: Is There a Causal Link?
Current medical research does not support the idea that endometriosis directly causes uterine fibroids, or vice versa. Instead, the relationship is characterized by a high rate of co-occurrence, meaning they frequently appear in the same patient at the same time. Epidemiological data shows a substantial association between the two conditions.
Women with endometriosis have a significantly higher odds of also having uterine fibroids compared to women without endometriosis. This strong statistical association is not the same as direct causation. The co-occurrence rate is high enough that some retrospective studies have found endometriosis in up to 87.1% of patients undergoing surgery for uterine fibroids.
This frequent overlap suggests a shared susceptibility rather than one condition being the direct trigger for the other. Both diseases are independently associated with issues like subfertility, supporting the idea that they are two distinct conditions that share common underlying risk factors.
Shared Biological Pathways and Risk Factors
The reason these two conditions are so often found together lies in the common biological pathways that fuel their development and growth.
Hormone Dependence
Both endometriosis and uterine fibroids are hormone-dependent conditions, meaning their growth is largely driven by the presence of certain reproductive hormones. Specifically, both are highly responsive to elevated or prolonged exposure to estrogen, often described as a hyperestrogenic state, which provides the fuel for their proliferation.
Chronic Inflammation
A second factor is the role of chronic inflammation within the pelvic environment. Endometriosis is inherently an inflammatory condition due to the presence of misplaced tissue that bleeds and causes irritation, which promotes a state of chronic inflammation. This persistent inflammatory state, involving immune system dysfunction, may also contribute to the growth of fibroids in the myometrium.
Genetic Predisposition
Genetic predisposition also plays a role in the co-occurrence of these conditions. Research using genetic correlation analyses has provided evidence that the genetic factors contributing to the risk of endometriosis overlap with those contributing to uterine fibroids. A woman whose mother or sister has fibroids, for instance, has a risk of developing them that is approximately three times higher than the general population. This shared genetic background predisposes some individuals to develop one or both conditions.
Managing Both Conditions Simultaneously
The co-existence of endometriosis and uterine fibroids complicates diagnosis and treatment because the symptoms often overlap, including heavy menstrual bleeding, chronic pelvic pain, and issues with fertility. Effective management requires a comprehensive strategy that addresses the specific symptoms caused by each condition. For instance, pain is often more directly linked to endometriosis, while bulk-related symptoms such as pressure on the bladder are typically caused by larger fibroids.
Medical Management
Medical management often involves hormonal suppression therapies aimed at reducing the overall exposure to estrogen, which can help slow the growth of both ectopic endometrial tissue and fibroids. Options such as continuous hormonal contraceptives or gonadotropin-releasing hormone (GnRH) agonists and antagonists can reduce both heavy bleeding and pain symptoms. Newer combination therapies, like oral GnRH receptor antagonists with add-back hormones, allow for long-term treatment by mitigating the side effects of low estrogen.
Surgical Intervention
When surgical intervention is necessary, the approach must be tailored to address both conditions simultaneously. If a patient undergoes a hysterectomy for symptomatic fibroids, any existing endometriosis lesions outside the uterus must also be excised to ensure symptom relief. Similarly, myomectomy to remove fibroids must be accompanied by a thorough search and excision of endometrial lesions to avoid continued pain and potential reoperation. An individualized plan developed by a specialist is necessary.