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|What Causes Endometriosis?
Doctors still don't really know what causes the disease, but there a few different theories. These are:
Also called retrograde menstrual flow and transtubal migration theory.
When we have a menstrual flow, the lining of the womb breaks down and is expelled through the vagina (see menstrual cycle for a full explanation). Occasionally some of this blood and tissue, instead of flowing down and out of the vagina, flows in the opposite direction. It flows back up the womb and into one or both fallopian tubes where it can leak into the pelvis and surrounding organs. The tissue sticks (implants) to these organs where it continues to act as it would in the womb. It builds up early in the menstrual cycle and breaks down and bleeds when a period is due. In mild cases the blood is reabsorbed and causes no symptoms of endometriosis. In severe cases bloody cysts can form which irritate the organs. Or due to it's sticky nature the implants can cause organs to glue together, leading to pelvic pain and other physical problems. Occasionally it is even found in remote locations such as the lungs or even the nose.
But retrograde menstrual flow cannot be the sole cause of endometriosis - it is estimated that nearly 90 percent of women experience some reverse flow - and yet only a small proportion develop endometriosis. It appears that other factors must be at play. Researchers think that a hormone imbalance may be one culprit. Excessive hormones may act like a growth-promoter, stimulating the migrant tissue to implant on organs and develop. Alternatively it may be caused by the lack of a healthy immune response which should normally check its growth.
Or in some cases, it may be that a physical obstruction is present in the vagina which prevents the natural expelling of blood. One study found a significant number of younger women with endometriosis had lesions in the vagina or cervix (cervical stenosis and vaginal atresia) which prevented the natural outflow of blood. In other women, scar tissue on the cervix as a result of treatment for cervical cancer or cervical dysplasia (CIN, the precancer stage) can also increase the risk.
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Researchers are also looking into the possible role of the hormone estrogen. This essential hormone is a key player in the reproductive cycle and it appears to promote the growth of endometriosis. This is borne out by a few rare cases of endometriosis appearing in men who were given estrogen therapy. Also, with few exceptions, the disease only arises after menarche (when estrogen levels rise) and declines after menopause (when levels decline). The aim of some treatments for endometriosis is to reduce the amount of estrogen the patient's body produces. More often than not this requires taking regular oral medications to induce an artificial state of menopause or pregnancy - this fools the body into thinking high levels of estrogen are not required and the woman stops having periods. This sort of therapy is only usually successful with mild cases of the disease. In more severe cases, the surgical removal of implants is usually necessary.
See also: effects of estrogen in women.
Immune System Response
When a woman experiences reversed flow menstruation, some of the endometrial tissue and blood is transported through the fallopian tubes and lands in the abdomen. In healthy women, the blood is simply reabsorbed and the endometrial tissue dies (undergo a process called apoptosis) and is then removed by the immune system (macrophages, otherwise known as white-blood cells surround and digest the endometrial cells). In about 10 percent of cases, the woman's immune system does not respond as it should. Instead the endometrial cells are allowed to survive and implant. Typically they stick to the lining of the abdomen, the ovaries and spaces between the rectum and bladder. Once they implant, they divide, multiply and grow. It appears that a faulty immune response may be genetic (passed from mother to daughter - the condition tends to run in families and having a mother or sister with endometriosis increases your risk 7 times), or it can be acquired as a result of exposure to certain pollutants. In particular, exposure to dioxin found in herbicides and pesticides has been linked to endometriosis. The chemical may be ingested through unwashed fruit and vegetables or inhaled when spraying the garden.
Other Autoimmune Conditions
Endometriosis has been associated with allergies, eczema, headaches, fibromyalgia, chronic fatigue syndrome (CFS), chronic yeast infections and hypothyroidism. These are all conditions affected by a failing autoimmune system, suggesting a further link between the two. In a survey of members, the Endometriosis Association found that those with endometriosis had a higher incidence rate of autoimmune related conditions such as rheumatoid arthritis, CFS, hypothyroidism, lupus, multiple sclerosis and Sjogren syndrome compared to the general U.S. population. Yet, other studies have found no such connection.
Left Over Embryo Cells
Another possible explanation is to do with remnants of stem cells found on the pelvic organs. Stem (also called primitive) cells are those we possess since being an embryo. They are highly versatile and can grow into different types of tissue (when we were an embryo some grew into arms, some into legs, eyes, hair and so on). According to this hypothesis, remnants of these cells are still found in adult bodies, lining our organs. In a process called coelomic metaplasia some of these cells spontaneously develop into endometrial cells. It would certainly explain unsuual cases where endometriosis is found in distant sites like the lungs, nose, thighs and knees. A slightly alternative theory is that stem cells found in the bone marrow may spontaneously differentiate into endometrial cells in different parts of the body and start to grow in those locations.
Lymphatic Or Blood Vessel Connection
Yet another possible explanation for how endometrial implants can be found in distant parts of the body (such as the brain) may be that the cells some how find their way into our lymphatic system or blood supply. Once in either system they can be transported and dumped in any area of the body, where they then implant and grow.
As A Result Of Surgery
Inadvertent direct transplantation of endometrial tissue is the most likely explanation for endometriosis found in abdominal scars. For example, endometrial cells may be transported inadvertently from the womb to the abdominal opening during a cesarean section. The cells remain and grow around the resulting scar.
Bottom Line: While scientists generally agree that reverse menstruation in combination with other mitigating factors (such as faulty immune response, estrogen overdrive or physical blockage) is the most likely cause of endometriosis - it is still all theoretical. It may turn out that some, none or all of these factors play a role in the disease. In fact most researchers now believe that there is no one single cause of endometriosis that can explain every individual case.
Next read: Endometriosis diagnosis - how the condition is evaluated.
Can endometriosis lead to cancer?: Endometrial cancer connection?
Can endometriosis cause a miscarriage?: Infertility and miscarriages.