While concrete causes of endometriosis are unknown, multiple theories abound. The disease occurs when endometrial cells, which normally form inside the uterus and are shed during menstruation, appear in areas outside the uterus. Referred to as endometriosis implants, these cells can grow in numerous areas of the body. Although pelvic pain, infertility, and higher risk of cancer have all been pinpointed as effects of this condition, researchers have only narrowed down hypotheses about its causes. The most common beliefs are that it can be caused by metaplasia, retrograde menstruation, genetic predisposition, lymphatic or vascular distribution, immune dysfunction, or environmental influences.
The popular retrograde menstruation theory proposes a sort of backward flow during menstruation as one of the principle causes of endometriosis. This internally redirects the menstrual flow, which could deposit endometriosis implants in locations outside the uterus. This theory is similar to the lymphatic or vascular distribution theory, in which blood vessels or the lymphatic system carries the endometrial cells, and deposits them in locations far from the uterus.
The metaplasia hypothesis posits that, rather than originating in the uterus, endometrial cells may actually transmute from normal cells when triggered by an unknown stimulus. This theory may tie into both the environmental influence and immune deficiency theories, in which outside factors or defective immune activity could lead to cellular mutations. These could either cause normal cells to transform, or prompt the growth of new endometriosis implants in foreign locations. Some researchers have also identified a hereditary tendency for endometriosis, hinting at a genetic source but still providing no obvious information on specific DNA patterns or gene expressions as the causes of endometriosis.
The symptoms are as varied as the possible causes of endometriosis. While many women experience no symptoms at all, others may suffer from pelvic pain, diarrhea, constipation, menstrual cycle irregularities, lower back pain, and blood in the urine. Depending on the location of the endometrial cells, the location of the pain can also vary. Since endometriosis can occur anywhere from the ovaries to the stomach, intestines, lungs, and even the eyes, more severe symptoms could include coughing, bleeding, or respiratory problems, if the endometrial cells interfere with normal cellular function.
As the causes of endometriosis are unknown, treatments are often focused on the symptoms rather than the source. Painkillers and anti-inflammatory drugs can be prescribed for pain. Estrogen-regulating treatments are also used in an attempt to stem endometrial development caused by abnormal hormone function. These treatments can include oral contraceptives, progestin, and synthetic androgens. In more severe cases, surgical treatment may be required to excise the endometriosis implants.