What causes endometriosis?
The cause of endometriosis is unknown. Some experts believe that pieces of endometrium travel back through the fallopian tubes and pass out into the pelvic cavity (space inside the pelvis that holds the reproductive organs). Tiny pieces of tissue may lodge on surfaces of the reproductive organs. During menstruation, the tissue bleeds, just like the endometrium inside the uterus. Blood from the misplaced tissue gets trapped. Surrounding tissue may become swollen and inflamed. Over time, scar tissue and cysts can form.
The retrograde menstruation theory (transtubal migration theory) suggests that during menstruation some of the menstrual tissue backs up through the fallopian tubes, implants in the abdomen, and grows. Some experts believe that all women experience some menstrual tissue backup and that an immune system problem or a hormonal problem allows this tissue to grow in the women who develop endometriosis. Another theory suggests that endometrial tissue is distributed from the uterus to other parts of the body through the lymph system or through the blood system. A genetic theory suggests that it may be carried in the genes in certain families or that some families may have predisposing factors to endometriosis.
Surgical transplantation has also been cited in many cases where endometriosis is found in abdominal scars, although it has also been found in such scars when accidental implantation seems unlikely. Another theory suggests that remnants of tissue from when the woman was an embryo may later develop into endometriosis, or that some adult tissues retain the ability they had in the embryo stage to transform reproductive tissue in certain circumstances.
Endometriosis may result from something called "retrograde menstrual flow", in which some of the tissue that a woman sheds during her period flows into her pelvis. While most women who get their periods have some retrograde menstrual flow, not all of these women have endometriosis. Researchers are trying to uncover what other factors might cause the tissue to grow in some women, but not in others. As endometriosis does occur in rare cases in men and also seems not to be cured by hysterectomies this seems like a very far fetched idea.
Another theory about the cause of endometriosis is that it is hereditary. This disease could be inherited, or it could result from genetic errors, making some women more likely than others to develop the condition. If researchers can find a specific gene or genes related to endometriosis in some women, genetic testing might allow health care providers to detect endometriosis much earlier, or even prevent it from happening at all.
Researchers are exploring other possible causes as well. Estrogen, a hormone involved in the female reproductive cycle, appears to promote the growth of endometriosis. Research is ongoing into looking at endometriosis as a disease of the endocrine system. Another view is that, in some women, their immune system does not remove the menstrual fluid in the pelvic cavity properly, or the chemicals made by areas of endometriosis may irritate or promote growth of more areas. Other researchers are studying the role of the immune system in either stimulating, reacting to endometriosis or that endometriosis might be an autoimmune disease. Other research focuses on determining whether environmental agents, such as exposure to man-made chemicals, cause endometriosis. Additional research is trying to understand what, if any, factors influence the course of the disease.
Dr. Deborah Metzger has been working on the idea that endometriosis is actually an allergic response. She has found that their patients appear to have a large number of allergies, including allergies to their own hormones such as progesterone, LH, estrogen, and also to Candida (yeast). In theory, for patients who have allergies to hormones, the standard treatment of taking estrogen or progesterone in the form of "the Pill" can actually cause the endometriosis to become worse, depending on which particular allergy they have and the pill they are taking. By treating these allergies, sometimes combined with surgical removal, they have found that this seems to provide relief.
Another important area of NICHD research is the search for endometriosis markers. These markers are substances made by or in response to endometriosis that health care providers can measure in the blood or urine. If markers are found, health care providers could diagnose endometriosis by testing a woman's blood or urine, which might reduce the need for surgery.