What Causes Endometriosis?

People with endometriosis spend a lot of time thinking about diagnosis, symptoms and treatment but not much time considering preventative measures. This is partly because we don’t know for certain what causes endometriosis. “If anyone definitively finds the answer for this, they might win a Nobel Prize for Medicine," says Nicholas Fogelson, an expert excision surgeon. While there are currently no clear-cut answers, Fogelson guides us through some of the many theories. 

Immune system impairment causing menstrual blood buildup

“The old theory is that there is bleeding out the fallopian tubes during menstruation that seeds the pelvis with endometrial glands, which go on to invade the pelvic wall and set up endometriosis,” Fogelson explains.

“The assumption is that all women have this, and so the ones that get endometriosis have some kind of immune defect that is keeping the body from cleaning up these cells and preventing endometriosis. This theory has fallen out of favor and is now generally considered to be wrong. At the very least, it is incomplete, as there are many states of endometriosis that do not fit this theory at all. For example, why is it that we can find endo in premenarchal girls? Also, we can sometimes find endo in unborn fetuses. Clearly, in neither of these cases was it retrograde menstruation that caused it.”

Endometrial cells laid down outside the womb as a mistake during prenatal development

“The most modern theory that is now fairly accepted is that endometriosis is laid down in the pelvis and other areas as a result of a mistake of embryogenesis,” Fogelson says. It's also called the embryonic rest theory. “Basically, endometrial cells are put down outside of the uterus, and once the woman hits menarche, they start to bleed just like the cells in the uterus, which over time leads to the pain, scarring and fibrosis that characterize endometriosis.” 

This theory provides hope for people with endometriosis — if endometrial cells were only planted there once during embryogenesis, it’s possible that excision surgery could provide long-term relief.

Environmental exposure

“Research shows a correlation between endocrine (hormone) disruptor molecules and endometriosis. We find many of these endocrine disruptors in common things we are exposed to, such as PET bottles (plasticizers), as well as many toxins that are put into the environment in various industrial processes,” Fogelson explains. 

“Some theorize the increase in endometriosis over time is related to this type of pollution. What is unclear is if these molecules are causing endometriosis, actually transforming normal cells into endometrial cells, or if they just have an estrogen-like effect that causes a woman who already has endometriosis to be more symptomatic and thus more likely to be diagnosed.”

Which one sounds the most likely?

Although these theories might sound convincing, Fogelson believes there’s no one theory to explain the cause of endometriosis in all women. 

“Some women have terrible symptoms but little disease,” he says. “Some women have terrible scarring and physical disease with little symptoms. Some women only have infertility. Some women only have pain but seem to have preserved fertility. Some women have dramatic improvement with surgery that is long-lasting, and others seem to have recurrent symptoms after surgery, with or without physical recurrence of the actual disease.” 

What does this mean for endometriosis patients?

According to Fogelson, it could mean that we are using an umbrella term to describe many different diseases, much in the same way that cancer does not adequately describe each individual type of cancer. 

“We know this as well because many researchers have isolated the genes that are causing the disease, and they are not all the same,” he says. “If endometriosis were only one disease, one would expect all of these genes to code for more or less the same thing, but that’s not what we find.” 

This might be positive news. The hope is that in the future, researchers will be able to genetically subtype women in order to understand the best way to treat them. “I expect major advances in the next five to 20 years,” Fogelson says. 

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